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Relationship between dental and alveolar bony arch form and whole tooth mesiodistal angulation and faciolingual inclination in three-dimensional space
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Relationship between dental and alveolar bony arch form and whole tooth mesiodistal angulation and faciolingual inclination in three-dimensional space
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Relationship Between Dental and Alveolar Bony Arch Form and Whole Tooth Mesiodistal Angulation and Faciolingual Inclination In Three-Dimensional Space By Bita Moalej A Thesis Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE (CRANIOFACIAL BIOLOGY) May 2013 Copyright 2013 Bita Moalej ii Acknowledgements I would like to express my deepest appreciation to my research mentor, Dr. Hongsheng Tong. I would not have been able to complete this project without his patience, expertise, guidance, and dedication. Dr. Tong is an extremely valuable asset to the field of orthodontics and I am honored to have had the chance to be a part of his vision. My sincerest appreciation to my co-resident Dr. Virginia Pham for spending countless hours in the resident’s room by my side digitizing the 76 cases over and over again. I would also like to extend my appreciation to Dr. Reyes Enciso who helped me analyze the final statistics. iii Table of Contents Acknowledgements ii List of Tables v List of Figures vi List of Graphs viii Abstract ix Chapter 1: Introduction 1 I. Orthodontic History and Evolution 1 II. Arch Shape 6 III. Cone Beam Computer Tomography (CBCT) 10 CBCT History 11 CBCT Image Production 14 CBCT Image Resolution 16 CBCT Image Reconstruction 18 CBCT Image Display 18 CBCT Radiation Dosage 18 CBCT Accuracy 19 CBCT Limitations 20 Chapter 2: Research Objective 21 Chapter 3: Materials & Methods 22 I. Case Selection Criteria 22 Photo Screening 22 Radiographic Screening 22 II. Global Head Orientation 23 III. Determination of anterior and posterior alveolar bony 24 height and the corresponding arch length IV. Tooth long axis digitization and determination of each 27 tooth mesiodistal angulation V. Determination of the Dental and the Alveolar Bony Arch 29 Forms VI. Reproducibility of Measurements 33 iv VII. Correlation study between arch ratios and mesiodistal 33 angulation and faciolingual inclination of each tooth VIII. Institutional Review Board Approval 34 Chapter 4: Results 35 I. Inter/Intra Examiner Measurement Reproducibility 35 II. Normality 36 III. Correlation Studies 38 Tip 38 1. Effect of Anterior Dental Arch (w/l) Ratio 39 on Mesiodistal Angulation (no correlations) 2. Effect of Posterior Dental Arch (w/l) Ratio 39 on Mesiodistal Angulation (+L4s) 3. Effect of Anterior Alveolar Bony (h/l) Ratio 39 on Mesiodistal Angulation (-L5s) 4. Effect of Posterior Alveolar Bony (h/l) Ratio 39 on Mesiodistal Angulation (+L4s) Torque: 40 1. Effect of Anterior Dental Arch (w/l) Ratio 41 on Faciolingual Inclination (none) 2. Effect of Posterior Dental Arch (w/l) Ratio 41 on Faciolingual Inclination (none) 3. Effect of Anterior Alveolar Bony (h/l) Ratio 41 on Faciolingual Inclination (-U2, -L1~L5) 4. Effect of Posterior Alveolar Bony (h/l) Ratio 41 on Faciolingual Inclination (+L6 , +L7) Chapter 5: Discussion 42 Chapter 6: Conclusion 52 References 53 v List of Tables Table 1: ICC Maxillary alveolar bony measurements 35 Table 2: ICC Mandibular alveolar bony measurements 35 Table 3: ICC Maxillary Dental arch measurements 35 Table 4: ICC Mandibular Dental arch measurements 35 Table 5: Kolmogorov-Smimov normality testing on upper and lower arch 36 Table 6: Kolmogorov-Smimov normality testing on upper and lower teeth 37 angulation and inclination Table 7: Maxillary Ratio Tip Correlation Values 38 Table 8: Mandibular Ratio Tip Correlation Values 38 Table 9: Maxillary Ratio Torque Correlation Values 40 Table 10: Mandibular Ratio Torque Correlation Values 40 vi List of Figures Figure 1: Standard Edgewise Bracket 2 Figure 2: First, Second, and Third Order Bends 3 Figure 3: Standard Twin Edgewise Bracket 3 Figure 4: FACC and FA Points 5 Figure 5: Square, Ovoid, and Tapered Arch Form 7 Figure 6: Noorozi et al. arch form depiction 8 Figure 7: Superimposition of Square, Ovoid, Tapered Arch Forms 9 Figure 8: CT vs. Conventional Radiograph 12 Figure 9: Evolution of CT 13 Figure 10: CT vs. CBCT: Fan vs. Cone 15 Figure 11: CT vs. CBCT: Base Projections 16 Figure 12: Isotropic vs. Anisotropic Voxels 17 Figure 13: Global Three Dimensional System 24 Figure 14: MxA and MxP Points 25 Figure 15: MdA and MdP Points 26 Figure 16: Maxillary and mandibular anterior and posterior alveolar 26 process height points Figure 17: Digitization of the Center of the Crown 27 Figure 18: Digitization of the Center of the Root 28 Figure 19: Determination of Maxillary Arch Form 29 Figure 20: Determination of Mandibular Arch Form 29 Figure 21: Determination of Maxillary Anterior Dental Arch 30 W/L Ratio Figure 22: Determination of Maxillary Posterior Dental Arch 31 W/L Ratio vii Figure 23: Determination of Maxillary and Mandibular Anterior 32 Alveolar H/L Ratio Figure 24: Determination of Maxillary and Mandibular 33 Posterior Alveolar H/L Ratio viii List of Graphs Graph 1: Lower Teeth Faciolingual Inclination 47 Graph 2: Comparison of Mandibular faciolingual inclination 47 in relation to mandibular alveolar bony (h/l) ratio ix Abstract Introduction: In today’s orthodontic era, treatment consists of the use of the same, non- customized prescription brackets for every individual in a given office. In most instances, neither prescriptions nor treatment goals are modified to reflect an individual’s arch form. However, numerous studies on orthodontic stability have demonstrated the importance in preservation of an individual’s arch form. Purpose: The objective of the current study was to determine whether correlations are present between the mesiodistal angulation and faciolingual inclination of each whole tooth (crown and root) for various arch forms in three-dimensional space in a sample of near normal patients. Methods: After determining a set of inclusion and exclusion criteria, 76 near-normal cases were chosen and digitized utilizing CBCT imaging. Maxillary and mandibular dental and alveolar bony arches were digitized; anterior and posterior dental arch width and length and alveolar bony arch height and length were obtained. Dental arch width/length (w/l) ratios and alveolar bony arch height/length (h/l) ratios for the two arches, both anterior and posterior, were calculated. Correlations between these ratios and the mesiodistal angulation and faciolingual inclination of each whole tooth were studied. Results: Pearson and Spearman correlation coefficient analysis revealed the following results: (1).The mesiodistal angulation and faciolingual inclination of none of the maxillary teeth were affected by our arch ratios except for the upper lateral incisor inclination which demonstrated a negative correlation with the maxillary anterior alveolar bony arch (h/l) ratio. (2).The mandibular anterior and posterior dental arch (w/l) ratio did not affect the angulation or inclination of the mandibular teeth except that the mandibular posterior dental arch (w/l) ratio demonstrated a significantly positive correlation with the mesiodistal angulation of the mandibular first premolar (p <0.00714). (3).A significant negative correlation was demonstrated between the mandibular anterior alveolar bony arch (h/l) ratio and the faciolingual inclination of the mandibular teeth from the central incisors to the x second premolars (p<0.00714). The mandibular posterior alveolar bony arch (h/l) ratio demonstrated a positive correlation with the buccolingual inclination of both the mandibular first and second molars. Conclusion: Within our sample of 76 patients who have near-normal occlusions, the maxillary teeth angulation and inclination are not affected by the dental arch or alveolar bony arch ratios, whereas the vertical tendency shown in alveolar bony arch (h/l) ratio would requires all mandibular teeth to be more upright. 1 Chapter 1: Introduction I. Orthodontic Evolution and History Orthodontics is the branch of dentistry that is focused on the study and treatment of malocclusions resulting from dental alignment irregularities and/or disproportionate jaw relationships. Treatment objectives include attainment of functional occlusion, esthetics, and stability. In order to obtain a functional occlusion, all teeth must have ideal axial inclinations in all three planes of space at the end of active treatment (Ugur and Yukay, 1997). The art and science of aligning teeth dates back to ancient times as archeologists have recently discovered Egyptians mummies with crude metal bands wrapped around individual teeth. However, it was not until the late 18th century that the first practical appliances came into use, most of which were fine tuned in the 1900s (Wahl, 2004). Significant contributions have been made worldwide throughout history in the field of orthodontics among which Drs. Edward Angle and Lawrence Andrews might have made the most impact. Dr. Edward Angle (1855-1930) is regarded by most as the “Father of modern orthodontics.” Through his leadership orthodontics was separated from other branches of dentistry (Asbell, 1990). In addition, Dr. Angle provided practitioners with a guideline for evaluating occlusion that continues to be used today. Prior to Angle, minimal importance was placed on bite relationships and the main orthodontic objectives were to resolve crowding and alignment issues. Angle’s classification system revolved around where the buccal groove of the mandibular first molar contacted the mesiobuccal cusp of the maxillary first molar. According to Angle, the most favorable occlusion pattern occurred when the mesiobuccal cusp of the upper first molar occluded with the buccal groove of the lower first molar (Andrews, 1972). In addition to his contribution on occlusion, Angle also developed the first generation orthodontic appliances 2 which included the E-arch, pin and tube, and ribbon arch, all of which ultimately evolved into the Edgewise appliance. Angle’s standard edgewise appliance was the first orthodontic appliance designed that delivered three dimensional control to the dentition. Furthermore, the appliance provided orthodontists with something they had never experienced before: absolute control over all teeth, individually and collectively at the same time (Figure 1) (Brodie, 1931). The universal application, durability, and three dimensional control of the edgewise bracket when combined confirmed Angle’s claim that it offered the “latest and best in orthodontic mechanisms” at the time (Angle, 1929). Figure 1: Angle’s Standard Edgewise Bracket (Brodie, 1931) The downside of Angle’s universal appliance was the assumption that all teeth follow a general alignment. However, we now understand that each individual tooth in the arch has its own designated position and inclination in relation to its neighboring teeth in three dimensional space. As a result, in order to achieve the most ideal tooth position, Angle’s standard edgewise appliance system called for three dimensional bending of the rectangular arch wire. These bends were referred to as 1 st , 2 nd , and 3 rd order (Figure 2) (Brodie, 1931). First order or in-out bends are those that are made in the horizontal plane and account for a tooth’s buccolingual thickness. 3 Second order or up-down bends are made in the vertical plane. Third degree bends are the torque bends which take care of crown inclination in a faciolingual direction (Brodie, 1931). Figure2: A—first order bends, B—second order bends, C—third order bends Since the advent of Angle’s standard edgewise fixed appliance, many modifications and improvements have been made to the appliance. The bracket was doubled and wings were added to make today’s popular twin edgewise bracket (Figure 3). The most significant of these improvements can be accredited to Dr. Lawrence Andrews. Figure 3: Standard Twin Edgewise Bracket During 1960-1964, Dr. Andrews collected and studied 120 study models of non- orthodontic patients that had optimal tooth alignment and occlusion which he professionally 4 deemed did not require orthodontic treatment. He determined that the angulation and inclination of individual tooth types began to show predictable natures when compared among different individuals. Andrews described six characteristics that were common among his 120 non- orthodontic patient study models (Andrews, 1972). The “six keys” were related to the following concepts: 1. Molar relationship 2. Crown angulation, the mesiodistal “tip” 3. Crown inclination, the faciolingual or buccolingual inclination 4. Rotations 5. Spaces 6. Occlusal plane Using the above categories, Dr. Andrews concluded that the ideal occlusion consisted of the following characteristics: class I molar relationship, consistent tip for same type of teeth among different individuals, consistent torque for same type of teeth among different individuals, no rotations, no spaces, and leveled occlusal plane. Based on these findings, Andrews designed the Straight-Wire Appliance (SWA) or the sophisticated edgewise appliance. The SWA sought to build dimensional and angular features into the appliance in order to decrease the amount of wire bending necessary at each appointment. In a way, the SWA was the first orthodontic appliance that was somewhat customized for each specific tooth and enabled orthodontists to finish cases with minimal bends in the rectangular arch wire (Andrews, 1976). The straight-wire appliance contained brackets customized for its specific tooth type, pre- angulated slots that accomplished mesiodistal tooth tip, and bases with specific inclinations for each tooth type that enabled proper tooth torque to be achieved. In addition, the distance from slot base to bracket base varied for each tooth thus satisfying in/out requirements. Since all 1 st , 2 nd , and 3 rd order bends (in/out, tip, and torque respectively) were built into the bracket prescription, the amount of wire bending was minimized. As a result, achieving better occlusal 5 relationship, functional goals, and overall treatment outcome in addition to shortened treatment time became much more efficient (Andrews, 1976). Since the advent of the straight-wire appliance, orthodontists have continued to build upon the basic principles of Andrews’ “six keys” in order to further customize bracket prescriptions and placement in order to enable the operator to treat patients with less effort, greater efficiency, and higher quality case finishes (McLaughlin and Bennet, 1995). In addition, Andrews stated that in order to take full advantage of the prescription appliance, the long axis of the central developmental lobe of each crown, defined as facial axis of the clinical crown (FACC) and the center point of the FACC which is the center of the clinical crown or FA point must be precisely located. Otherwise, the orthodontist will need to make bends in the arch wire to compensate for the imprecise bracket placement. Though, most orthodontists agree with the statement that it is sometimes very difficult or impractical to locate the FACC and FA points accurately (Figure 4) (Armstrong et al., 2007; Balut et al., 1992; Wheeler, 1974). Figure 4: The FACC drawn through the central developmental lobe of the clinical crown. The FA point is determined as the center of the FACC (Andrews, 1976). 6 Tong et al. built upon Andrews’ classic study in recognizing that the whole tooth, crown and root, should be taken into consideration with regards to proper tooth position. They used CBCT scans of 76 near-normal orthodontic patients to determine standards for the mesiodistal angulation and buccolingual inclination for each tooth (crown and root) in three-dimensional space. They found distinctive trends in the intra-arch relationships from tooth to tooth in the mesiodistal angulations and buccolingual inclinations (Tong et al., 2012b). However, in addition to identifying the proper tip and torque for these near-normal individuals, it is also important to know how the mesiodistal tip and buccolingual inclination of the whole teeth is affected by different dental arch forms when customizing bracket prescriptions, treatment plans, and overall treatment objectives. II. Arch Shape Since Angle’s time, many geometric forms and mathematical functions had been proposed as models of the human dental arch in an effort to define an “ideal” and universal arch form that would be the standard for orthodontic patients (Noroozi et al., 2001). Many authors claimed that there might be a standard form of dental arch and some geometric or mathematical curve; eg, semicircle; ellipse; parabola, hyperbola; catenary curve; polynomial functions; Euclidean distance matrices; Fourier series; and beta function to name a few have all been described in the past as standard ideal forms that should fit the dental arch and ensure accuracy in describing arch forms (Lee et al., 2011). However, as research continued within this topic, investigators such as Raberin et al. and others have demonstrated that a single ideal and universal orthodontic arch form does not exist (Raberin et al., 1993). Furthermore, customization would be necessary in order to achieve stable results (Felton et al., 1987; Noroozi et al., 2001). 7 Today in the field of orthodontics, we recognize that well-aligned dental arches are categorized into three distinct forms: square, ovoid, and tapered (Figure 5). Moreover, it is imperative to take the dental arch form into consideration when treating an orthodontic patient in order to achieve a stable, functional, and esthetic dentition (Little, 1990; McLaughlin and Bennet, 1995; McLaughlin et al., 2011). Failure to maintain the patient’s arch form can further increase the probability of relapse and can also result in an unnatural smile (McLaughlin et al., 2011). As studies on relapse have shown, post orthodontic occlusal stability is strengthened through maintenance of the original mandibular intercanine width and preservation of the original arch form (Little 1990, McLaughlin et al., 2011). Furthermore, Little recommended that the patient’s pre-treatment arch form be used as the guide for the patient’s post treatment arch form (Little, 1990). Figure 5: Square Arch Form (A), Tapered Arch Form (B), Ovoid Arch Form (C) (McLaughlin et al., 2011) As stated earlier, various methods to determine dental arch shape have been described. In his study of the form of the human dental arch shape, Braun demonstrated that a mathematical model, in this case the beta function test, could be used accurately to represent the human dental arch form. The beta function test depended on two independent variables: molar width (distance between second molar distobuccal cups tips in mm) and arch depth (average perpendicular distance from the central incisors to the molar cross-arch dimension in mm) (Braun et al., 1998). Then, the beta function, representing the dental arch shape is given by the following formula: 8 Figure 6: W = cross-arch distance between the second molar distobuccal cusp tip (mm) D = perpendicular distance from the most anterior point between the two central incisors to the molar cross-arch dimension (mm) (Braun et al., 1998). Noorozi et. al built upon Braun’s mathematical technique in order to define ovoid, square, and tapered arch forms. This method relied upon four parameters defined by the depths and widths of the dental arch at the canine and second molar regions: 1. intersecond molar width (Wm): distance between the distobuccal cusp tips of the second molars 2. intercanine width (Wc): distance between the canine cusp tips 3. second molar depth (Dm): distance between the contact of the central incisors and a line that connects the distobuccal cusp tips of the second molars 4. canine depth (Dc): distance between the contact of the central incisors and a line that connects the canine cusp tips The parameters were defined based on the relative ratio of the canine and the second molar cross-arch widths along with their relative arch depths. When the Wc/Wm ratio increases or the Dc/Dm ratio decreases, the arch becomes squarer. However, when Wc/Wm ratio decreases 9 or Dc/Dm ratio increases, the arch gets a more tapered form. Therefore, they stated that the (Wc/Wm) X (Dc/Dm)^-1 ratio may be able to describe the arch form. When this ratio is within the range of mean +/- 1 SD, the arch form is ovoid. However, when this ratio is more than mean + 1 SD the arch form can be considered square. Lastly, the arch form is considered tapered when the ratio is less than mean + 1 SD (Figure7) (Noroozi et al., 2011). Figure 7: Superimposition of 3 template arch forms: square (widest), ovoid, and tapered (narrowest). Triangles represent tooth dimensions; the triangle base represents the mesiodistal tooth width. The base vertex represents the contact points, and the head vertex represents the bracket position (McLaughlin et al., 2011). Lee et al. took their study on the classification of dental arch forms one step further by not only measuring arch width and depth similar to prior reports, but they also measured tooth size, basal arch width, mesiodistal angulations, and buccolingual inclinations of teeth using dental study casts and mathematical models. They used an angulation-and-inclination measuring gauge to measure the angulation and inclination of teeth on dental casts. Their study concluded that arch form type was influenced by the following factors: tooth sizes, arch width, basal arch width and inclination of the posterior teeth. However, they stated that mesiodistal angulation of the teeth did not make a significant difference in relation to arch form (Lee et al., 2011). Moreover, they emphasized that basal arch width and inclination of the posterior teeth both were significantly different between arch form types. They found that maxillary and mandibular tooth 10 inclination gradually decreased as one went from narrow to wide arch forms. This finding placed a great deal of emphasis on the role of the basal bone anatomy on dental arch formation as had been suggested in the past by Ronay et al (Ronay et al., 2008). They also further concluded that mandibular incisor inclination was a significant influencing factor on arch shape as had been previously published by Mutinelli et al (Lee et al., 2011; Mutinelli et al., 2000). All of the aforementioned methods described had measured arch from based on three- dimensional study models. Other researchers have studied dental arch forms using digital scanned models. The scanned data is then processed and viewed using 3-D computer software. In this way because measurements are no longer obtained manually, the resultant data is demonstrated to be more accurate and detailed (Redlich et al., 2008). However, with the introduction of CBCT imaging within the orthodontic field, dental arch form analysis can now be investigated in three dimensions using the whole tooth (crown and root) in addition to bony landmarks. III. Cone Beam Computer Tomography (CBCT) Most of the new bonding techniques available in orthodontics today such as indirect bonding, geodigm, and orthocad use the measurements of the crown tip and torque, while mostly ignoring the root position. Furthermore, since there is difficulty in identifying the FACC and FA points precisely, it would be advantageous to the orthodontist if the roots of the teeth were also included in the bonding and virtual treatment planning set-ups. In the past, Andrews and other pioneers in the orthodontic field used only the long axis of the crown, not the whole tooth, on study models in order to measure crown angulation and inclination. This was considered the most efficient method for tip and torque calculation since roots were not visible clinically and radiographic technology was insufficient. Moreover, the 11 imaging available in most orthodontic practices traditionally has consisted of panoramic x-rays and lateral cephalograms. However, panoramic radiographs have distortions due to the culmination of distortions in the horizontal and vertical dimensions (Xie et al., 1996). In addition, panoramic x-rays do not reflect the three-dimensional mesiodistal tooth angulations since the x-ray beam is not always orthogonal to the target teeth (McKee et al., 2002). Lateral cephalograms have been constantly criticized for errors related to inherent magnification, superimposition, and distortion of structures. Although lateral cephalograms allow visualization of the long axis of the incisors, they do not provide information on crown angulation and inclinations of the posterior teeth (Mitra and Raui, 2011). Thus, both panoramic x-rays and lateral cephalograms suffer from the same inherent limitations of all planar two-dimensional (2D) projections: magnification, distortion, superimposition, and misrepresentation of structures (Scarfe and Farman, 2007; 2008). All of the aforementioned downsides of the panoramic and lateral cephalograms are inherently unavoidable when one is viewing a three dimensional structure on a two-dimensional plane. With the introduction of cone beam computer tomography into the United States in 2001, the orthodontic profession had an opportunity for three-dimensional visualization, treatment planning, and diagnosis of the craniofacial anatomy. Orthodontists were now able to accurately evaluate the mesiodistal angulation and faciolingual inclination of each whole tooth (root and crown) in all three planes of space (Tong et al., 2012a). CBCT History: In 1979, Sir Godfrey Hounsfield and A. M. Cormack won the Nobel Prize in medicine for their invention of the CT. This invention was the first time in radiographic history where non- superimposed, cross-sectional images of the body were evaluated on a 1:1 scale while also 12 isolating desired anatomic landmarks with designated x-ray slices. Furthermore, CT technology allowed the ability to view specific angles of a desired object in comparison with conventional 2D imaging techniques which focused on a single fixed angle (Figure 8). Since its introduction in 1967 by Sir Godfrey Housnfield, CT technology has evolved quite dramatically (Hughes and Neel, 2000; Siemens, 2011). Figure 8: CT image versus a conventional radiograph: In conventional radiography, information on the slice plane P projects into a single line, A-A; whereas in the associated CT image, the full spatial information is preserved (Hughes and Neel, 2000). First generation CT scanners were known as rotate/translate or pencil beam scanners. They were characterized by a single X-ray source and a single detector that undergo both linear translation and rotational motions. The source and detector were translated perpendicular to the X-ray beam which resulted in a single view with each translation. This process was repeated until 180 projections were acquired at 1 degree intervals. The disadvantage of first generation CT scans was the increased scan time (Figure 9) (Hughes and Neel, 2000; Taradaj, 2007). Second generation scanners also contained the rotate/translate design and were known as fan beam. This generation used a fan beam of radiation of approximately 10 degrees and approximately 30 detectors which resulted in scans that were 15 times faster than first generation scanners (Figure 9) (Hughes and Neel, 2000; Taradaj, 2007). 13 Third generation scanners were designed to rotate/ rotate. In comparison to the previous generation of scanners which had to be stopped once each translation was completed, this system was designed in such a way where both the x-ray tube and a large, arc shaped detector rotated. Translational movement was therefore no longer necessary; thus, mechanical problems were vastly reduced (Figure 9) (Hughes and Neel, 2000; Taradaj, 2007). Fourth generation CT scanners were designed to contain both a rotating and a stationary element. In this system, a stationary circular array of the detectors was used while the x-ray tube rotated around the patient (Figure 9) (Hughes and Neel, 2000; Taradaj, 2007). Finally, fifth generation CT scanner contain zero mechanical motion. These scanners used a circular array of X-ray sources, which were electronically switched on and off. In this way, a series of 2D projections of a 3D object was collected instead of a series of 1D projections of a 2D object (Figure 9) (Hughes and Neel, 2000; Taradaj, 2007). Figure 9: Sketches illustrating the evolution of CT scan geometries, each a distinct generation of instrumentation; (a) first generation single pencil beam translate/rotate scanner; (b) second generation multiple pencil beam translate/rotate scanner; (c) third generation rotate/rotate fan beam scanner; (d) fourth generation rotate/stationary inverted fan beam scanner; (e) fifth generation cone beam cylindrical scanner (Hughes and Neel, 2000; Siemens, 2011). Cone-beam computed tomography (CBCT) was introduced into the US market in 2001and its application to scanning the maxillofacial region heralded a true paradigm shift from 14 a 2D to a 3D approach for data acquisition and image reconstruction (Hatcher, 2010; Scarfe and Farman, 2008). CBCT technology was initially introduced into the medical field as a tool for angiography and was later expanded to include radiotherapy guidance and mammography (Scarfe and Farman, 2007; 2008). The cone beam geometry was introduced as a substitute for CT imaging in order to provide not only a cheaper radiation detector but moreover because the system allowed a more rapid acquisition of data set through the use of a larger field of view (FOV). In comparison to traditional CT, advantages of the CBCT include rapid exam time, reduced patient radiation dose, decreased image distortion due to patient movement, and increased image accuracy (Scarfe and Farman, 2007). The main disadvantage of the CBCT is its limitation in image quality relation to noise and contrast resolution due to the large amounts of scattered radiation seen because of a larger FOV (Scarfe and Farman, 2008). CBCT Image Production: There are four components involved in the production of a CBCT image. These four components include: acquisition configuration, image detection, image reconstruction, and image display. The image is acquired through a single partial or full rotational scan from a cone-shaped x-ray beam while simultaneously the detector moves around a fixed fulcrum within the patient’s head. During the scan rotation, each projection image of the field of view is made by sequential, single-image capture of attenuated x-ray beams by the detector. In this way, similar to an orthopantogram, the x-ray beam which is aimed at a detector on the other side of the patient’s head produces a series of 2-D images for a selected FOV. These images are then reconstructed through computer programs to form a set of 3-D images (Scarfe and Farman, 2008; Van Vlijmen et al., 2012). 15 This method of image acquisition varies from traditional medical CT image production which uses instead a fan shaped x-ray beam to image the patient as a series of axial cuts similar to a fan (Mozzo et al., 1998). Once individual image slices of the FOV are acquired, they are then stacked to obtain a 3-D representation. In this way, each slice requires a separate scan and separate 2D reconstruction. In contrast, because CBCT exposure incorporates the entire FOV, only one rotational sequence of the framework is required to obtain sufficient data for image reconstruction (Figure 10-11) (Scarfe and Farman, 2008). Figure 10: Traditional CT vs. CBCT; Traditional CT uses a “Fan” of X-rays and need multiple helical passes around the subject; CBCT uses a “cone of x-rays and only needs a single pass around the subject (Mozzo et al., 1998). 16 Figure 11: X-ray beam projection scheme comparing acquisition geometry of conventional or ‘‘fan’’ beam (right) and ‘‘cone’’ beam (left) imaging geometry and resultant image production. In cone-beam geometry (left), multiple basis projections form the projection data from which orthogonal planar images are secondarily reconstructed. In fan beam geometry, primary reconstruction of data produces axial slices from which secondary reconstruction generates orthogonal images. The amount of scatter generated (sinusoidal lines) and recorded by cone-beam image acquisition is substantially higher, reducing image contrast and increasing image noise (Scarfe and Farman, 2008). CBCT Image Resolution: As stated previously, a 3-D image is composed of a stack of 2-D slices. Furthermore, a 2D image is composed of pixels which represent the smallest sampled unit of a 2-D image while a 3-D image is composed of voxels which is defined as the volume element of a 3D image. A pixel has dimensions along two axes which dictate in-plane spatial resolution while voxel dimensions are made up of the pixel in addition to a third axes which is defined as the thickness of the slice (Grauer et al., 2010). The FOV, acquisition matrix, and the slice thickness determine voxel volume. The pixel size (FOV/matrix) determines the in-plane resolution. Reducing the FOV, increasing the matrix number, or reducing the slice thickness results in an image with reduced voxel volume. A 17 smaller voxel produces images with a higher resolution, but a lower signal-to-noise ratio (SNR), which may cause the image to look grainy (Runge et al., 2009). CBCT resolution and thus detail is governed by the voxels generated from the data set, which in turn is dependent on the pixel size of the detector (0.07mm-.4mm) (Hatcher, 2010; Scarfe and Farman, 2008). Since CBCT data is obtained through one rotation of the source, voxel elements are thus isotropic (all three dimensions of equal length). On the other hand, since traditional fan-beam CT source must rotate several times before creating an image, the third dimension is constructed by the computer based on slice thickness in order to create the voxel. Thus, voxel elements become anistropic (unequal dimensions) (Figure 12) (Hatcher, 2010; Scarfe and Farman, 2008). Figure 12: Comparison of volume data sets obtained isotropically (left) and anisotropically (right). Because CBCT data acquisition depends on the pixel size of the area detector and not on the acquisition of groups of rows with sequential translational motion, the compositional voxels are equal in all three dimensions, rather than columnar with height being different from the width and depth dimensions (Scarfe and Farman, 2007; 2008). 18 CBCT Image Reconstruction: Once the scan is completed, the data is reconstructed to obtain the 3-D data set. Image reconstruction consists of combining individual projection frames, ranging from 100-600, each containing more than one million pixels, with 12 to 16 bits of data assigned to each pixel. A computer program then pieces together the projection images into a 3-D volumetric set of data. Although econstruction times vary based on voxel size, FOV, number of projections, hardware, and software, it should nonetheless take less than 3 minutes to complete scans of standard resolutions (Scarfe and Farman, 2008). CBCT Image Display: The final volumetric data set is a compilation of all available voxels and is presented to the clinician on screen as secondary reconstructed images in three orthogonal planes (axial, sagittal, and coronal), usually at a thickness defaulted to the native resolution. Visualization can be optimized to favor a particular anatomical area of interest based on adjustments of window level and window width (Scarfe and Farman, 2007; 2008). CBCT Radiation Dosage: Although the use of CBCT technology reduces the patient’s exposure to ionizing radiation when compared with traditional CT scans, it does however cause significantly more radiation than the conventional radiographic procedures used routinely in orthodontics. Because radiation dose depends on the field of view, scan time, milliampere setting, peak kilovaltage, voxel sixe, sensor sensitivity, and number of images obtained, there will be radiation dose variations based on the CBCT unit used (Hatcher, 2010; Van Vlijmen et al., 2012). In 2007, The International Commission of Radiological Protection recommended effective doses for panoramic radiograph to range between 14.2 to 24.3 micro Sieverts and from 5.1 to 5.6 μSv for a 19 conventional cephalometric radiograph (ICRP, 2007; Taradaj, 2007). The radiation dose for CBCT ranges from 19 to 1,073 μSv, depending on the CBCT unit and the field of view. 33 For a CBCT exposure of approximately 200 μSv, the associated risk of developing fatal cancer is one in 50,000 according to the European Committee on Radiation Risk (ECRR) estimates and one in 100,000 according to ICRP estimates (Van Vlijmen et al., 2012). CBCT Accuracy: As mentioned earlier, traditional orthodontic panoramic and cephalometric radiographs are highly inaccurate due to beam projection angle, magnification errors, image distortion due to superimposition of neighboring structures, and patient positioning (Honey et al., 2007; Peck et al., 2007). However, the disadvantages of traditional 2-D radiographs have been eliminated through the use of CBCT. Magnification and distortion errors are eliminated with CBCT scans because the x-ray beams are almost parallel to each other, the raw data is obtained in one rotation, and because the voxels are isotropic to one another; as a result, the image has a 1:1 ratio to the original object. Lateral cephalograms constructed from CBCT scans have shown no systemic error in landmark coordinates when traditional cephalograms and CBCT generated cephalograms were compared in homologous patients (Grauer et al., 2010). Panoramic radiographs generated from CBCT scans have also been shown to be of superior quality and diagnostic value in comparison to digital panoramic images (Angelopoulos et al., 2008). Imaging of the TMJ is also shown with more reliability and accuracy when compared with corrected angle linear tomography and TMJ panoramic projections (Honey et al., 2007). Thus, CBCT scans make it possible to reconstruct arbitrarily-cut slices in all three dimensions and to evaluate them qualitatively and quantitatively in the field of orthodontics during treatment planning and visualization of the maxillofacial region (Holberg et al., 2005; Mozzo et al., 1998). 20 CBCT Limitations: The limitations of currently available CBCT technology are related to the following: cone-beam projection geometry, detector sensitivity, and contrast resolution. These limitations lead to the production of images that lack the clarity seen in CT images. Furthermore, the precision of CBCT images is also affected by artifacts defined as any error or distortion in the image independent of the subject being examined, noise, and poor soft tissue contrast (Scarfe and Farman, 2008). Patient movement including head, jaw, and swallowing affect the quality of the entire volume data recorded with CBCT and result in a blurriness of the reconstructed image (Holberg et al., 2005). The polychromatic nature of the x-ray beam results in beam hardening which also causes CBCT image artifacts in two different forms. The first artifact formed through beam hardening is known as the cupping artifact and it arises through distortion of metallic structures. The second form of beam hardening occurs as streaks and dark bands between two dense objects (Scarfe and Farman, 2008). Artifacts related to the scanner appear circular or ring- shaped and are due to imperfections in scanner detection or poor calibration. CBCT image noise is caused by scattered radiation which is produced omnidirectional. The scattered radiation is recorded on the cone-beam area detector. The additional recorded nonlinear x-ray attenuation contributes to the image degradation observed (Scarfe and Farman, 2008). The cumulative effect of the aforementioned can lead to an increase in background noise and a decrease in image contrast which can impair the diagnostic assessment of fine dental structures in the axial slices and the 3D representations (Holberg et al., 2005). 21 Chapter 2: Research Objective The purpose of this study is to determine whether there is a correlation between the mesiodistal angulation and faciolingual inclination of each whole tooth (crown and root) for various arch forms in three-dimensional space. 22 Chapter 3: Materials & Methods I. Case Selection Criteria During the period between April 2004 to October 2009, approximately 1840 CBCT scans were taken as a routine part of the patient’s initial orthodontic examination. Each CBCT scan was taken using a NewTom 3G Volumetric Scanner under the following conditions: 110kV, 15mA, 17-second exposure time, 12-in field of view, and 12-bit gray scale. Patients were positioned supinely with the dentition in full occlusion and Frankfort horizontal plane perpendicular to the floor. From the above scans, “near-normal” cases were selected based on the following criteria: no history of past orthodontic treatment; good health demonstrating normal growth; well aligned arches with normal appearing teeth; no supernumerary teeth; a low decayed, missing, filled tooth index numerical; no large restorations or fixed replacements; and close to normal vertical, transverse, and anteroposterior relationships. Photographic and x-ray screening was used to evaluate these factors. Photo Screening: 1. Complete dentition (did not require the presence of 3 rd molars or 2 nd molar fully erupted) 2. Molar relationship ranging from ½ step Class II to ¼ step Class III 3. Overbite and Overjet between 0-5mm 4. Spacing less than 6mm 5. Crowding less than 4mm (limited to maximum of 3 teeth) 6. Rotations less than 15 degrees (limited to maximum of 3 teeth) 7. No dental crossbite (limited to no more than 1 tooth and a maximum of 2mm) 8. No apparent facial or arch form asymmetry Radiographic Screening: 1. Panoramic showing mostly parallel roots 2. ANB between -1º to 6.5 º 3. FMA between 14 º to 37 º 23 4. Interincisal angle between 110 º to 146 º 5. No obvious skeletal PA and vertical asymmetry After the initial photo and radiograph screening, 125 patients remained. From this group, 26 more patients were removed due to the unacceptable quality of their CBCT images, teeth that were not in full occlusion during the scan, or the volumetric view of occlusion did not meet Angle’s classification. After the cephalometric criteria were applied, 76 patients remained which qualified as the near-normal group. A customized, 3D analysis program was developed by Dolphin Imaging that enabled Tong et al.’s previous study and the current study to digitize each tooth in all three planes of space. II. Global Head Orientation A global three dimensional coordinate system is first generated for the proper orientation of the head and maxillofacial structure. The three planes used in developing this coordinate system are: sagittal, coronal, and transverse with each plane being perpendicular to the other two planes. The sagittal plane divides the head into left and right side. The coronal plane is perpendicular to the sagittal plane at both sides of the maxillary first molar buccal grooves. The transverse plane is defined as the functional occlusal plane that bisects the incisor and molar overbite (Figure 13). 24 Figure 13: Global three dimensional coordinate system III. Determination of anterior and posterior alveolar bony height and the corresponding arch length Once the global coordinate system was set, maxillary and mandibular bony landmarks were digitized in the sagittal plane to determine the anterior and posterior alveolar process height and the corresponding bony arch length for the 76 near-normal patient population. Anterior maxillary ridge point (MxR) is at the tip of the interproximal ridge between the two maxillary central incisors; maxillary anterior alveolar bony point (MxA) is on the anterior palate at the posterior border of the incisive canal; maxillary posterior alveolar bony point (MxP) is at the height of the posterior palatal vault at the intersection of the sagittal plane and the coronal plane (Figure 14-16). Anterior mandibular ridge point (MdR) is the mandibular point that corresponds to the MxR in the maxilla. Mandibular posterior alveolar bony point (MdP) is digitized at the intersection of the transverse, sagittal, and coronal planes when the transverse plane is moved to the level of the mental foramen. The mandibular anterior alveolar bony point (MdA) is digitized 25 when the transverse plane is placed half way between the MdP level and the MdR level along the posterior border of the mandibular anterior alveolar process (Figure 15-16). Figure 14: MxA point on anterior palate at posterior border of the incisive canal and MxP point representing the height of the posterior palatal vault at the intersection of the sagittal plane and the coronal plane. 26 Figure 15: MdA point representing the half-way mark between MdP and MdR along the posterior border of the mandibular anterior alveolar process. MdP point representing the intersection of the transverse, sagittal, and coronal planes at the level of the mental foramen. Figure 16: Maxillary and mandibular anterior and posterior alveolar process height placed on the coordinate system. 27 IV. Tooth long axis digitization and determination of each tooth mesiodistal angulation In the previous study by Tong et al., the same near-normal population was used to digitize individual teeth long axis in order to determine a set of norms for ideal tip and torque. This data was made available and used in the current study in order to study the correlation between arch form and individual tooth angulation and inclination. Briefly, the same global coordinate system described earlier was used in the previous study in order to properly align the head and maxillofacial regions. The crown and root centers of each tooth were then digitized using a different three-perpendicular-plane system specific for each tooth: the anatomic mesiodistal plane, the anatomic faciolingual plane, and the axial plane at each tooth crown or root center level, respectively (Figure 17-18) (Tong et al., 2012b). Figure 17: The maxillary right first molar was rotated until it was orthogonal in all 3 perpendicular planes of its specific coordinate; the crown center was digitized at the intersection of the anatomic mesiodistal, faciolingual, and axial planes (Tong et al., 2012b). 28 Figure 18: The maxillary right first molar root center was digitized after the anatomic axial plane was raised to the root center level. Orthogonal views of the tooth in 3 perpendicular planes were maintained (Tong et al., 2012b). Once the crown and root points were digitized, the dental arch form was placed utilizing four points along the right side facial aspect of the transverse plane for the maxilla and mandible: the mid-incisor, the canine, the second premolar, and the second molar distal. A symmetric arch form was formed through the software program adding the mirror image of the digitized right half to the left half of the arch (Figure 19-20) (Tong et al., 2012b). 29 Figure 19: Determination of the maxillary dental arch form by placing points (shown in yellow) facial to the mid-incisal, right side canine, second premolar, and second molar. Left half of the arch was a mirror image of the right side of the arch. Figure 20: Determination of the mandibular dental arch form by placing points (shown in yellow) facial to the mid-incisal, right canine, second premolar, and second molar. Left half of the arch was a mirror image of the right side of the arch. V. Determination of the Dental and the Alveolar Bony Arch Forms In order to examine the correlation between the dental and alveolar arch forms and each tooth mesiodistal angulation and faciolingual inclination values, we calculated four ratios. These four ratios were: anterior dental arch width/length (A-W/L) ratio, posterior dental arch width/length (P-W/L) ratio, anterior alveolar bony height/length (A-H/L) ratio, and posterior 30 alveolar bony height/length (P-H/L) ratio for the maxilla and mandible respectively. A-W/L and P-W/L ratios were determined utilizing values obtained from Kwon’s previous dental arch digitizations. The A-H/L and P-H/L ratios were calculated utilizing the newly described maxillary and mandibular bony point digitization method described previously (Kwon, 2011). 1. A-W/L ratio: From the maxillary dental arch form digitization, we have obtained the X, Y Coordinates for the maxillary mid-incisal point (UMI x, y ), the right side canine point (URC x, y ), and the right side second molar distal point (UR7D x, y ). A-W/L ratio =Anterior Dental Arch Width/ Anterior Dental Arch Length Maxillary Anterior Dental Arch Width = 2*(URC x - UMI x ) Maxillary Anterior Dental Arch Length= UMI y - URC y *** same formulas were calculated using the mandibular dental arch values*** Figure 21: Determination of maxillary anterior dental arch W/L ratio 2. P-W/L ratio: P-W/L ratio = Posterior Dental Arch Width / Posterior Dental Arch Length Maxillary Posterior Dental Arch Width = 2* (UMI x -UR7D x ) 31 Maxillary Posterior Dental Arch Length =UMI y – UR7D y) *** same formulas were calculated using the mandibular dental arch values*** Figure 22: Determination of maxillary posterior dental arch W/L ratio 3. A-H/L ratio: From digitization of the maxillary and mandibular alveolar bony points, we have obtained the y and z coordinates for the maxillary and mandibular anterior alveolar ridge points (MxR, MdR), anterior points (MxA, MdA), and posterior points (MxP, MdP). These coordinates are used to calculate the anterior and posterior alveolar bony height/ length (H/L) ratios. Maxillary A- H/L ratio = Maxillary Anterior Alveolar Height/ Maxillary Anterior Alveolar Length Maxillary Anterior Alveolar Height = MxA y – MxR y Maxillary Anterior Alveolar Length = MxR z - MxA z 32 Mandibular A-H/L ratio = Mandibular Anterior Alveolar Height/Mandibular Anterior Alveolar Length Mandibular Anterior Alveolar Height = MdA y – MdR y Mandibular Anterior Alveolar Length = MdR z - MdA z Figure 23 Determination of maxillary and mandibular anterior alveolar H/L ratio 4. P-W/L ratio: Maxillary P-H/L ratio = Maxillary Posterior Alveolar Height/ Maxillary Posterior Alveolar Length Maxillary Posterior Alveolar Height = MxP y – MxR y Maxillary Posterior Alveolar Length = MxR z - MxP z Mandibular P-H/L ratio = Mandibular Posterior Alveolar Height/Mandibular Posterior Alveolar Length Mandibular Posterior Alveolar Height = MdR y – MdP y Mandibular Posterior Alveolar Length = MdR z - MdP z 33 Figure 24: Determination of maxillary and mandibular posterior alveolar H/L ratio VI. Reproducibility of Measurements In order to confirm the accuracy of the methodology described above, 10 cases were randomly selected to be digitized twice by two different examiners or the same examiner but at two different time points. Once all of the measurements from the 10 cases were obtained, they were entered into a Microsoft Excel Spreadsheet and analyzed with Statistical Package for Social Sciences (SPSS) version 16.0 software for Windows. Inter- and intra-examiner correlation coefficients (ICC) tests were performed to check the reproducibility of the data. VII. Correlation study between arch ratios and mesiodistal angulation and faciolingual inclination of each tooth A Kolmogorov-Smirnov normality test was used to check for normality in all of our data. Any value with p value greater than 0.05 was considered to be normal and was thus analyzed using Pearson correlation coefficients. For non-normal data, Spearman correlation coefficients were used instead. 34 Due to the large number of comparisons utilized, the Dunn-Bonferroni correction was used to adjust the significance level. The standard significance level of p < 0.05 was divided by the number of independent tests (7) that were performed to yield an adjusted p value of 0.00714. Furthermore, in Kwon’s previous study it was shown that the differences between the left and right side angulation and inclination values were mostly statistically insignificant. Therefore, arch ratios were correlated utilizing those averaged angulation and inclination values of the near normal patients (Kwon, 2011). VIII. Institutional Review Board Approval This study was approved by the University of Southern California Institutional Review Board (IRB). The IRB approval ID number is: HS-11-00323. 35 Chapter 4: Results I. Inter/Intra Examiner Measurement Reproducibility Maxillary Measurements Anterior Height Anterior Length Posterior Height Posterior Length ICC B/B 0.902 0.753 0.934 0.885 ICC V/V 0.893 0.881 0.981 0.995 ICC B/V 0.878 0.833 0.963 0.799 Table 1 Inter/intra-examiner correlation coefficient (ICC) of maxillary alveolar bony measurements (Drs. Bita Moalej (B), Virginia Pham (V)). Mandibular Measurements Anterior Height Anterior Length Posterior Height Posterior Length ICC B/B 0.942 0.935 0.946 0.939 ICC V/V 0.980 0.979 0.991 0.957 ICC B/V 0.959 0.983 0.972 0.970 Table 2 Inter/intra-examiner correlation coefficient (ICC) of mandibular alveolar bony measurements (Drs. Bita Moalej (B), Virginia Pham (V)). Maxillary Measurements Anterior Width Anterior Length Posterior Width Posterior Length ICC D/D 0.954 0.931 0.961 0.931 Table 3 Inter/intra-examiner correlation coefficient (ICC) of maxillary dental arch measurements (Dr. Donald Kwon (D)).*Digitized points obtained from previous research done by Kwon.* Mandibular Measurements Anterior Width Anterior Length Posterior Width Posterior Length ICC D/D 0.958 0.916 0.853 0.928 Table 4 Inter/intra-examiner correlation coefficient (ICC) of the mandibular dental arch measurements (Dr. Donald Kwon (D)).*Digitized points obtained from previous research done by Kwon.* The intraclass correlation coefficient (ICC) is used as a tool to measure both the reproducibility of the methodology used and the agreement between two or more examiners on the same subject. ICC can be interpreted as follows: 0-0.2 indicates poor agreement; 0.3-0.4 indicates fair agreement; 0.5-0.6 indicates moderate agreement; 0.7-0.8 indicates 36 strong agreement; and >0.8 indicates almost perfect agreement (Landis and Kack, 1977; Portney and Watkins, 1993). All of the above ICC values were obtained from 10 cases that were digitized twice by the same or two different examiners at two separate time points. For the alveolar bony measurements, the ICC values range from a low of 0.753 for maxillary anterior alveolar bony length measurements obtained from B/B digitization to a high of 0.983 for mandibular anterior alveolar bony length measurements obtained from B/V digitization (Table 1-2). Although the maxillary anterior alveolar bony length value for B/B had an ICC Of 0.753, it is still deemed as a strong agreement based on the above definition. In regards to the dental arch measurements, the ICC values range from a low of 0.853 for mandibular posterior dental arch width measurements to a high of 0.961 for maxillary posterior dental arch width measurements (Table 3-4). Overall, there is a high degree of consistency and accuracy with the same examiner and between different examiners at different time points. II. Normality Kolmogorov-Smirnov(a) Statistic df Sig. UAarch (w/l) .073 76 .200(*) UParch (w/l) .124 76 .006 UAarch (h/l) .061 76 .200(*) UPArch (h/l) .076 76 .200(*) LAarch (w/l) .081 76 .200(*) LParch (w/l) .138 76 .001 LAArch (h/l) .076 76 .200(*) LPArch (h/l) .049 76 .200(*) Table 5 Results of Kolmogorov-Smimov normality testing on upper and lower arch ratios. Values highlighted in yellow had p value <0.05. * Is a lower bound of true significance. 37 Kolmogorov-Smirnov(a) Kolmogorov-Smirnov(a) Statistic df Sig. Statistic df Sig. U1 Tip .115 65 .032 U1 Torque .058 65 .200(*) U2 Tip .077 65 .200(*) U2 Torque .061 65 .200(*) U3 Tip .062 65 .200(*) U3 Torque .087 65 .200(*) U4 Tip .066 65 .200(*) U4 Torque .102 65 .090 U5 Tip .108 65 .056 U5 Torque .047 65 .200(*) U6 Tip .076 65 .200(*) U6 Torque .046 65 .200(*) U7 Tip .064 65 .200(*) U7 Torque .081 65 .200(*) L1 Tip .074 65 .200(*) L1 Torque .114 65 .034 L2 Tip .086 65 .200(*) L2 Torque .111 65 .045 L3 Tip .104 65 .081 L3 Torque .060 65 .200(*) L4 Tip .079 65 .200(*) L4 Torque .085 65 .200(*) L5 Tip .078 65 .200(*) L5 Torque .103 65 .084 L6 Tip .058 65 .200(*) L6 Torque .062 65 .200(*) L7 Tip .046 65 .200(*) L7 Torque .068 65 .200(*) Table 6 Results of Kolmogorov-Smimov normality testing on upper and lower teeth angulation and inclination values. Values highlighted in yellow had p value <0.05. * Is a lower bound of true significance. The Kolmogorov-Smirnov normality test detected the following non-parametric values with p< 0.05: upper and lower posterior dental arch (w/l) ratios and U1 tip, L1 torque, and L2 torque. These measurements were thus analyzed utilizing Spearman correlation coefficients. 38 III. Correlation Studies: Tip: Table 7 Maxillary Tip X Anterior Dental Arch (w/l) Ratio; Tip X Posterior Dental Arch (w/l) Ratio; Tip X Anterior Alveolar Bony (h/l) Ratio; Tip X Posterior Alveolar Bony (h/l) Ratio *Correlation is significant at the 0.05 level (2-tailed). Table 8 Mandibular Tip X Anterior Dental Arch (w/l) Ratio; Tip X Posterior Dental Arch (w/l) Ratio; Tip X Anterior Alveolar Bony (h/l) Ratio; Tip X Posterior Alveolar Bony (h/l) Ratio *Correlation is significant at the 0.05 level (2-tailed). **Measurements were highlighted in yellow if the p-value < 0.00714(Dunn-Bonferroni adjustment). MAXILLARY Ratio U1 Tip (Spearman) U2 Tip U3 Tip U4 Tip U5 Tip U6 Tip U7 Tip Anterior Dental Arch (w/l) Ratio Pearson Correlation Sig (2 tailed) N -0.126 0.28 76 -0.116 0.318 76 0.01 0.929 76 -0.025 0.831 76 0.006 0.962 76 0.137 0.239 76 .278* 0.025 65 Posterior Dental Arch (w/l) Ratio Spearman Correlation Sig (2 tailed) N -0.026 0.826 76 0.061 0.599 76 0.093 0.423 76 0.158 0.173 76 0.042 0.721 76 0.1 0.391 76 0.184 0.143 65 Anterior Alveolar Bony (h/l) Ratio Pearson Correlation Sig (2 tailed) N 0.055 0.637 76 -0.134 0.25 76 0.12 0.303 76 0.06 0.608 76 -0.127 0.274 76 0.052 0.655 76 -0.015 0.906 65 Posterior Alveolar Bony (h/l) Ratio Pearson Correlation Sig (2 tailed) N 0.003 0.979 76 0.001 0.996 76 0.26* 0.023 76 0.256* 0.026 76 0.078 0.504 76 0.219 0.058 76 0.246* 0.049 65 MANDIBULAR Ratio L1 Tip L2 Tip L3 Tip L4 Tip L5 Tip L6 Tip L7 Tip Anterior Dental Arch (w/l) Ratio Pearson Correlation Sig (2 tailed) N -0.230* 0.045 76 -0.223 0,053 76 -0.158 0.173 76 0.167 0.15 76 0.087 0.457 76 -0.024 0.835 76 -0.138 0.258 69 Posterior Dental Arch (w/l) Ratio Spearman Correlation Sig (2 tailed) N 0.68 0.562 76 0.032 0.781 76 0.083 0.476 76 0.362** 0.001 76 0.199 0.085 76 0.107 0.358 76 -0.075 0.54 69 Anterior Alveolar (h/l) Ratio Pearson Correlation Sig (2 tailed) N -0.048 0.678 76 -0.058 0.617 76 -0.105 0.365 76 -0.104 0.37 76 -0.364** 0.001 76 0.048 0.681 76 0.016 0.899 69 Posterior Alveolar Arch (h/l) Ratio Pearson Correlation Sig (2 tailed) N -0.048 0.682 76 0.075 0.52 76 0.229* 0.047 76 0.341** 0.003 76 0.049 0.672 76 0.03 0.794 76 -0.155 0.203 69 39 1. Effect of Anterior Dental Arch (w/l) Ratio on Mesiodistal Angulation (no correlations) The anterior dental arch (w/l) ratio did not affect the tip of any of the maxillary or mandibular teeth except the upper second molar with which it shared a positive correlation and lower central incisor with which it shared a negative correlation. These correlations were both associated with p value of less than 0.05, but did not meet the adjusted p-value of 0.00714 demanded by the Dunn-Bonferroni correction. 2. Effect of Posterior Dental Arch (w/l) Ratio on Mesiodistal Angulation (+L4s) The posterior dental arch (w/l) ratio did not affect the tip of any of the maxillary teeth. It did however, have a positive correlation with the mesiodistal angulation of the mandibular first premolar (p <0.01). This correlation also met the adjusted Bonferroni p-value of 0.00714. 3. Effect of Anterior Alveolar Bony (h/l) Ratio on Mesiodistal Angulation (-L5s) The anterior alveolar bony (h/l) ratio did not affect the mesiodistal angulation of any of the maxillary teeth. However, an inverse correlation was demonstrated between the mesiodistal angulation of the mandibular second premolar and the anterior alveolar bony height ratio (p<0.01). This correlation met the adjusted Bonferroni p-value of 0.00714. 4. Effect of Posterior Alveolar Bony (h/l) Ratio on Mesiodistal Angulation (+L4s) The maxillary posterior alveolar bony (h/l) ratio demonstrated a positive correlation with the mesiodistal angulation of maxillary canine, first premolar, and second molar. There was also a positive correlation noted between the mandibular posterior alveolar bony (h/l) ratio and the mandibular canine and first premolar. However, the lower first premolar was the only tooth in this group to meet the adjusted Bonferroni p-value. 40 Torque: Table 9 Maxillary Torque X Anterior Dental Arch (w/l) Ratio; Torque X Posterior Dental Arch (w/l) Ratio; Torque X Anterior Alveolar Bony (h/l) Ratio; Torque X Posterior Alveolar Bony (h/l) Ratio *Correlation is significant at the 0.05 level (2-tailed). **Measurements were highlighted in yellow if the p-value < 0.00714 (Dunn- Bonferroni adjustment). Table 10 Mandibular Torque X Anterior Dental Arch (w/l) Ratio; Torque X Posterior Dental Arch (w/l) Ratio; Torque X Anterior Alveolar Bony (h/l) Ratio; Torque X Posterior Alveolar Bony (h/l) Ratio *Correlation is significant at the 0.05 level (2-tailed). **Measurements were highlighted in yellow if the p-value < 0.00714 (Dunn- Bonferroni adjustment). MAXILLARY Ratio U1 Torque U2 Torque U3 Torque U4 Torque U5 Torque U6 Torque U7 Torque Anterior Dental Arch (w/l) Ratio Pearson Correlation Sig (2 tailed) N -0.155 0.182 76 -0.081 0.485 76 -0.128 0.271 76 -0.115 0.322 76 -0.046 0.694 76 -0.025 0.833 76 -0.18 0.15 65 Posterior Dental Arch (w/l) Ratio Spearman Correlation Sig (2 tailed) N 0.022 0.852 76 0.034 0.771 76 -0.028 0.81 76 0.132 0.257 76 0.288* 0.048 76 0.053 0.647 76 0.161 0.2 76 Anterior Alveolar Bony (h/l) Ratio Pearson Correlation Sig (2 tailed) N -0.222 0.054 76 -0.328** 0.004 76 -0.290* 0.011 76 -0.251* 0.029 76 -0.129 0.266 76 -0.002 0.989 76 -0.006 0.965 65 Posterior Alveolar Bony (h/l) Ratio Pearson Correlation Sig (2 tailed) N -0.074 0.523 76 0.048 0.678 76 0.05 0.669 76 0.048 0.682 76 0.08 0.493 76 0.075 0.522 76 -0.061 0.632 65 MANDIBULAR Ratio L1 Torque (Spearman) L2 Torque (Spearman) L3 Torque L4 Torque L5 Torque L6 Torque L7 Torque Anterior Dental Arch (w/l) Ratio Pearson Correlation Sig (2 tailed) N -0.274* 0.017 76 -0.068 0.56 76 0.051 0.664 76 -0.025 0.831 76 -0.03 0.795 76 -0.061 0.599 76 0.025 0.84 69 Posterior Dental Arch (w/l) Ratio Spearman Correlation Sig (2 tailed) N -0.149 0.198 76 -0.094 0.419 76 0.067 0.567 76 0.004 0.972 76 -0.007 0.949 76 0.141 0.225 76 0.181 0.136 69 Anterior Alveolar Bony (h/l) Ratio Pearson Correlation Sig (2 tailed) N -0.371** 0.001 76 -0.563** 0 76 -0.427** 0 76 -0.392** 0 76 -0.376** 0.001 76 -0.284* 0.01 76 -0.124 0.309 69 Posterior Alveolar Bony (h/l) Ratio Pearson Correlation Sig (2 tailed) N 0.237* 0.039 76 0.12 0.304 76 0.173 0.136 76 0.265* 0.021 76 0.158 0.172 76 0.340** 0.003 76 0.389** 0.001 69 41 1. Effect of Anterior Dental Arch (w/l) Ratio on Faciolingual Inclination (no correlations) The anterior dental arch (w/l) ratio did not affect the torque of any of the maxillary or mandibular teeth except the mandibular central incisor with which it demonstrated a negative correlation. Its significance did not meet the adjusted Bonferroni p-value. 2. Effect of Posterior Dental Arch (w/l) Ratio on Faciolingual Inclination (no correlations) The posterior arch (w/l) ratio affected the torque of only the maxillary second premolar through a positive correlation with a p-value of 0.048. It did not meet the adjusted Bonferroni p- value. 3. Effect of Anterior Alveolar Bony (h/l) Ratio on Faciolingual Inclination (-U2, -L1~L5) The maxillary anterior alveolar bony (h/l) ratio affected the torques of the maxillary teeth. A negative correlation was observed with the faciolingual inclination of the maxillary lateral incisor, canine, and first premolar. Only the lateral incisor satisfied the adjusted Bonferroni p value. The mandibular anterior alveolar bony (h/l) ratio significantly and negatively affected the faciolingual inclination of almost all of the mandibular teeth from the lower incisors to the lower second premolars with p values meeting the Bonferroni adjustment (p<0.00714). The lower first molar (p< 0.05) failed to meet the Bonferroni adjustment. 4. Effect of Posterior Alveolar Bony (h/l) Ratio on Faciolingual Inclination (+L6 , +L7) The maxillary posterior alveolar bony (h/l) ratio of the maxillary arch did not influence the torque of any of the maxillary teeth. The mandibular posterior alveolar bony (h/l) ratio however positively affected the torque of the mandibular first and second molars with p values satisfying the adjusted Bonferroni values (p<0.007144). The lower central incisors and lower first premolars (p<0.01) failed to meet the Bonferroni adjustment standard. 42 Chapter 5: Discussion The purpose of the current study was to evaluate whether there is relationship between arch form and the mesiodistal angulation and faciolingual inclination of each whole tooth (crown and root) in three-dimensional space. We hope that today’s orthodontists can incorporate our findings into their everyday practices in order to achieve optimal customized tooth positioning and to aid in minimizing the probability of orthodontic relapse. Andrews developed the straight wire appliance based on his findings of 120 dental casts of non-orthodontic patients with occlusion that he deemed were optimal. The SWA with its built- in prescriptions replaced older generations of orthodontic appliances and greatly diminished the need for wire bending at every step in treatment (Busato, 2009). However, final tooth positioning with Andrews’ appliance was based on bracket placement which relied heavily on the identification of the FACC and FA points. These two points were and continue to be extremely difficult for the orthodontist to locate clinically. Moreover, even if the FACC and FA point are correctly located and the brackets are placed as required, due to variations in tooth shape and size, correct occlusion may not be guaranteed. Using whole tooth long axis for tooth angulation and inclination may be superior to using crown angulation and inclination that are based on FACC and FA points, but the roots are not visible on study models. Panoramic imaging can be used to locate the roots; however, distortion is a limiting factor since it is a 2D view of a 3D object and the view angle is often not orthogonal. Achieving a stable dental arch form is also of importance when treating an orthodontic patient. Previous studies have demonstrated that the chances of orthodontic relapse increase if the clinician fails to take the patient’s natural arch form into consideration during treatment (McLaughlin and Bennet, 1995; McLaughlin et al., 2011). It is suggested that teeth may have to 43 align in a particular arch form for the final treatment result to stay stable. In addition to affecting teeth alignment, there remains the question of whether arch form will affect each tooth mesiodistal angulation and faciolingual inclination. Therefore, in addition to determining the ideal values for the inclination and angulation of the teeth, it is also of clinical significance orthodontically to determine how the mesiodistal angulation and buccolingual inclination of each whole tooth is affected by different dental arch forms when customizing bracket prescriptions, treatment plans, and overall treatment objectives. Traditionally, the imaging available in most orthodontic practices has consisted of panoramic x-rays and lateral cephalograms which entail the same limitations that any 2D image of a 3D object would have: magnification errors, distortion issues, superimposition, and misrepresentations of structures (Scarfe and Farman, 2008). Studies on dental arch forms in the past have consisted of either the use of mathematical models or study casts (Braun et al., 1998; Lee et al., 2011; Noroozi et al., 2001; Raberin et al., 1993). Through the use of CBCT imaging in the current study, we were not only able to eliminate the errors seen with traditional imaging methods, but we were also able to perform dental arch form analysis in three dimensions utilizing bony landmarks and to correlate the dental arch form with the mesiodistal angulation and faciolingual inclination of each whole tooth (crown and root). It is our belief that through the use of CBCT imaging and through the establishment of a specific set of guidelines for our methodology, we have been able to diminish the amount of human error in such studies. However, as mentioned earlier, 3D imaging also has its own limitations. Of importance is patient cooperation. The NewTom three-dimensional imaging available to the present study consists of one of the longest scan times of approximately 17 seconds. Any movement of the patient (head, jaw, swallowing) during scan acquisition results in a blurry reconstructed image. 44 Therefore, in order to obtain an accurate image of high quality, any patient movement no matter how minor must be eliminated. Since every point (center of crown and root, center of alveolar ridge and apex) used in this study was digitized manually, the methodology is not without human error; however, efforts were taken to minimize these errors. Every point was digitized using the mesiodistal, buccolingual, and transverse planes. By making sure the plotted point was in the center of the desired landmark in each of the three planes, errors in the digitization procedure were minimized. Moreover, the calibration phase was used to further determine the reliability and reproducibility of our digitization procedure. In order to ensure that our procedure could be repeated at various time points by the same examiner or different examiners, 10 cases were randomly selected to be digitized by the principal investigator (BM) twice at different time points. The same 10 cases were then digitized by a co-investigator (VP) at different time points as well (Table 1-4). Although the majority of the measurements had ICC values of around 0.9 for both the maxilla and mandible, the maxillary alveolar bony arch anterior length measurement displayed varying degrees of consistency with its ICC values ranging from 0.753-0.881. The inconsistency seen amongst this measurement is most likely due to human error amongst the two examiners. Nonetheless, overall there was a high degree of reliability and reproducibility not only with one individual but between two individuals at different time points as well. Since the ICC depicts the accuracy of our methodology, we can assume that the digitized points used to determine our arch measurements are consistent. 45 Overall, looking at our data we can observe that several teeth had correlations with p- value <0.05 and some teeth had correlations consisting of p-value < 0.01. Because our values were obtained through the use of multiple comparisons, for the sake of our discussion we will focus only on the correlations that met the adjusted Bonferroni p-value of <0.05/7= 0.00714. When looking at our data, we can determine that the mesiodistal angulation or faciolingual inclination of none of the maxillary teeth is affected by any of the ratios we examined, with the exception of upper lateral torque being affected negatively by maxillary anterior alveolar bony (h/l) ratio. While the significance of this single exception may warrant further investigation, the lack of relationship between both angular measurements of the majority of the maxillary teeth and three-dimensional maxillary arch form may be strongly indicated. These results may be the basis for us to apply our standard maxillary teeth mesiodistal angulation and faciolingual inclination to patients regardless of the maxillary arch form. This would thus simplify the process of setting up maxillary teeth angulation and inclination with confidence. Besides the maxillary laterals having a negative relation with maxillary anterior alveolar bony (h/l) ratio, there are a few other relationships that are found to be statistically significant: the lower first premolars mesiodistal angulation is positively affected by the mandibular posterior dental arch (w/l) ratio and the mandibular posterior alveolar bony (h/l) ratio; the lower second premolar mesiodistal angulation is negatively affected by the mandibular anterior alveolar bony (h/l) ratio. These relationships are spotty and their true significance may need to be validated by further studies. The most significant finding of our study was that the torque of the lower central incisor through the second premolar was affected through an inverse relationship with the mandibular 46 anterior alveolar bony (h/l) ratio and the lower first and second molar torque was affected through a positive relationship with the mandibular posterior alveolar bony (h/l) ratio. As the mandibular anterior alveolar height increased or the alveolar bony arch length became smaller, the mandibular teeth from central incisor to the second premolars demonstrated a decrease in labial crown inclination or more upright from the normal labial crown inclination (Figure 25) (Tong et al., 2012b), whereas as the mandibular posterior alveolar height increased or the alveolar bony arch length became smaller, the mandibular molars demonstrated an increase in labial crown inclination, or more upright from the normal lingual crown inclination (Figure 25) (Tong et al., 2012b). Thus, patients who have tall but short mandibular bony arch forms in terms of height and length respectively, or who may be slightly vertical, may have more upright mandibular teeth faciolingually (Figure 26). Yet, the torque of the maxillary teeth does not seem to be affected at all. This may be explained by the possibility that patients with different alveolar bony (h/l) ratios may have different interdental torque between the maxillary and mandibular teeth. However, equilibrium can still be maintained in these patients who tend to have different facial musculature function around the teeth. Also, it is worth noticing that all patients used in this study are deemed near normal and those in this sample who had higher mandibular alveolar bony (h/l) ratios were only slightly more vertical. Whether such relationships can be extended to patients who have abnormal facial types, for example those who have long lower facial height syndrome, remains to be investigated. 47 Graph 1: Lower Teeth faciolingual inclination (Tong et al., 2012b) Graph 2: Comparison of mandibular faciolingual inclination in relation to mandibular alveolar bony (h/l) ratio. Our data indicated the most significant relationships are between the mandibular (h/l) alveolar bony ratio and the torque of the mandibular teeth. As has been suggested in previous literature, it is the mandibular arch that determines maxillary arch form and alignment (Little, 48 1990). In this way, the mandibular arch serves as a template around which the maxillary arch develops and functions. Thus, we can see that the trend observed in our data is in congruence with previously reported research. Several limitations of significance can be noted when evaluating our data. First, our sample size consisted of 76 patients with near-normal occlusion. Ideally, we would have liked to have a bigger sample size which consisted of patients with optimal occlusion. However, due to ethical reasons regarding unnecessary patient exposure to radiation, we had to use the patient pool that was available to us. Thus, our patient pool consisted of pre-treatment orthodontic records of those individuals which fit the criteria closest to having ideal occlusion. Also, various ethnicities were grouped together since our sample size consisted of only 76 individuals. Subsequently, our preliminary results should be used with caution when applied across different ethnicities. Limitations can also be depicted within our digitization protocol. Our arch forms ratios were correlated with data gathered in the previous study by Kwon. The custom program that they used in their digitization procedures was meant to be used in analysis of near-normal subjects. Moreover, specifically of interest to this study is that the arch form mirroring technique enabled by the Dolphin program cannot be applied to asymmetric arch forms. Consequently, the data and subsequent results obtained in this project must be used with caution when being applied to individuals with severe malocclusion and arch forms varying a great deal from the standard norm. This project is the first to utilize the ideal tip and torque data obtained from Kwon’s previous study to determine correlation between arch form and tooth position (Kwon, 2011). 49 CBCT imaging allowed us to develop a reliable and reproducible protocol for measuring tooth angulation and inclination, alveolar ridge inclination, and the location of specific bony landmarks within the maxilla and mandible. The use of CBCT imaging allowed for the first time to view the dental arch form in three dimensions through utilizing bony landmarks for each individual rather than study models or mathematical analysis. The combination of the aforementioned principles enabled us to develop more accurate relationships than previously studied. As previously mentioned, since the sample of patients available to us was limited, we were not able to divide the patient pool into multiple comparison groups. In the future, if the patient sample size were to be increased, we could broaden the scope of this project to determine comparisons between different ethnicities, arch form, and tooth tip and torque. Other areas of comparison between arch form and tooth tip and torque could include age, gender, and skeletal and dental class II or class III patients. By expanding the current patient sample to different inclusion and exclusion criteria, we would thus be able to obtain more accurate and relevant clinical data that could be implemented in routine orthodontic practice. Although as we stated earlier, it is quite difficult to expand the patient sample when there are many concerns regarding increased patient radiation exposure. Many individuals argue that CBCT imaging can only be justified if the information it provides can lead to improved treatment outcomes. Therefore, we can only justify the use of CBCT imaging for the purposes of sample size expansion on this project if the information obtained through this project can be implemented into everyday orthodontic practice. For the time being, it seems that we have to make with what we have until an improved version of CBCT using the same amount of radiation or less than current 2D imaging techniques becomes available. 50 The clinical implications of this study is the importance it has in recognizing and realizing that dental arch forms and especially lower teeth torque may be unique to each individual. The straight wire appliance was one of the greatest contributions to the field of orthodontics allowing for more efficient and higher quality results. However, orthodontists cannot treat individuals to the one size fits all mentality. It is important for the orthodontist to realize and understand that treatment must be customized to meet each individual’s unique arch form. Through this project, we now understand that while maxillary teeth tip and torque can be treated to ideal regardless of the maxillary arch form, in which case we could let esthetics take priority in the maxillary arch treatment, treatment of an individual with a tall and short mandibular bony arch may require more upright lower teeth faciolingually. Nature may have set a biological limitation for the mandibular teeth in relation to the mandibular alveolar bone. The current research was just the tip of the iceberg for the vast number of possibilities there are to expand on the past and current research projects done by Tong et al. through the use of CBCT imaging. It is our hope that through the establishment of norms for tooth angulation and inclination in specific arch forms, specific goals can be set for treatment even before the appliances are placed. Virtual set-ups can be used to place teeth in their optimal buccolingual and mesiodistal dimensions based on that particular patient’s arch form. A straight wire with brackets attached can then be placed with modifications being only made to the bracket base. In this way, bracket prescriptions become negligible as will the need to bend the arch wire to maintain the patient’s original arch form. Consequently, by incorporating the findings of this project into routine practice, the patient’s original arch form can be maintained and more importantly orthodontic relapse may be minimized. By utilizing the technology and advancements available 51 in our field, we can customize individual patient treatment which in turn will enable us to provide efficient, optimal, and most importantly stable results. 52 Chapter 6: Conclusion 1. We have developed a method to determine the relationship between the tip and torque of an individual’s teeth in comparison with their arch form utilizing 3-D imaging. The validity of our digitization and formula calculation were confirmed with strong agreement of ICC averages over 0.9. 2. Mesiodistal angulation and faciolingual inclination of none of the maxillary teeth is affected by any of the arch ratios, with the exception of upper lateral torque which is affected negatively by maxillary anterior alveolar bony (h/l) ratio. 3. As the mandibular anterior alveolar bone height increased or the alveolar bony arch length decreased, the mandibular teeth from central incisor to the second premolars became more upright from a facially inclined position; as the mandibular posterior alveolar bone height increased or the alveolar bony arch length decreased, the mandibular molars became more upright from a lingually inclined position. 4. Arch form has a more significant impact on the mandibular teeth in comparison to the maxillary teeth and more on the faciolingual inclination (torque) of the dentition rather than the mesiodistal angulation (tip); and alveolar bony (h/l) ratios affect the tip and torque of the teeth more than the dental arch (w/l) ratios. 53 References Andrews, L.F. (1972). The six keys to normal occlusion. Am J Orthod Dentofacial Orthop 62, 296-309. Andrews, L. (1976). The Straight-Wire Appliance: Origin, Controversy, Commentary. Journal of Clinical Orthodontics 10, 99-114. 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Portney, L.G., and Watkins, M.P. (1993). Foundations of clinical research: applications to practice (Connecticut: Appleton & Lange Press). Raberin, M., Laumon, B., Martin, J., and Brunner, F. (1993). Dimensions and form of dental arches in subjects with normal occlusions. Am J Orthod Dentofacial Orthop 104, 67-72. Redlich, M., Weinstock, T., Abed, Y., Schneor, R., Holdstein, Y., and Fischer, A. (2008). A new system for scanning, measuring and analyzing dental casts based on a 3D holographic sensor. Orthodontics and Craniofacial Research 11, 90-95. Ronay, V., Miner, R.M., Will, L.A., and Arai, K. (2008). Mandibular arch form: the relationship between dental and basal anatomy. Am J Orthod Dentofacial Orthop 134, 430- 438. Ross, V.A., Isaacson, R.J., Germane, N., and Rubenstein, L.K. (1990). Influence of vertical growth pattern on faciolingual inclinations and treatment mechanics. Am J Orthod Dentofacial Orthop 98, 422-429. 56 Runge, V., Nitz, W., and Schmeets, S. (2009). The Physics of Clinical MR Taught Through Images (New York: Thieme Medical Publisher). Scarfe, W., and Farman, A. (2007). Cone beam computed tomography: A paradigm shift for clinical dentistry. Australian Dental Practice 2, 92-100. Scarfe, W., and Farman, A. (2008). What is Cone-Beam CT and How Does it Work? Dental Clinics of North America 52, 707-730. Siemens, A.G. (2011). Computed Tomography: Its history and technology 1, 1-36. Taradaj, J. (2007). Biophysical principles of X-ray computed tomography. (Poland: Silesian University School of Medicine). Tong, H., Enciso, R., Elslande, D.V., Major, P., et al. (2012a). A new method to measure mesiodistal angulation and faciolingual inclination of each whole tooth with volumetric cone-beam computed tomography images. American Journal of Orthodontics & Dentofacial Orthopedics 142, 133-143. Tong, H., Kwon, D., Shi, J., Sakai, N., et al. (2012b). 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Effect of head positioning in panoramic radiography on vertical measurements: an in vitro study. Dentomaxillofac Radiol 25, 61-66.
Abstract (if available)
Abstract
Introduction: In today’s orthodontic era, treatment consists of the use of the same, non-customized prescription brackets for every individual in a given office. In most instances, neither prescriptions nor treatment goals are modified to reflect an individual’s arch form. However, numerous studies on orthodontic stability have demonstrated the importance in preservation of an individual’s arch form. Purpose: The objective of the current study was to determine whether correlations are present between the mesiodistal angulation and faciolingual inclination of each whole tooth (crown and root) for various arch forms in three-dimensional space in a sample of near normal patients. Methods: After determining a set of inclusion and exclusion criteria, 76 near-normal cases were chosen and digitized utilizing CBCT imaging. Maxillary and mandibular dental and alveolar bony arches were digitized
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Moalej, Bita
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Relationship between dental and alveolar bony arch form and whole tooth mesiodistal angulation and faciolingual inclination in three-dimensional space
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School of Dentistry
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Master of Science
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Craniofacial Biology
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03/22/2013
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02/27/2013
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arch form,OAI-PMH Harvest,tip,torque
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Sameshima, Glenn T. (
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