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Analysis of clinical outcomes of implants via a guided surgery system: a retrospective radiographic analysis

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Analysis of clinical outcomes of implants via a guided surgery system: a retrospective radiographic analysis

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ANALYSIS OF CLINICAL OUTCOMES OF IMPLANTS VIA A GUIDED SURGERY
SYSTEM: A RETROSPECTIVE RADIOGRAPHIC ANALYSIS

By

Sanchita Mehra DMD, MBS

A Thesis Presented to the
FACULTY OF THE USC HERMAN OSTROW SCHOOL OF DENTISTRY
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
BIOMEDICAL IMPLANTS AND TISSUE ENGINEERING

August 2021

ii

TABLE OF CONTENTS
List of Tables……………………………………………………………………………………..iii
List of Figures…………………………………………………………………………………….iv
Abstract……………………………………………………………………………………………v
Introduction………………………………………………………………………………………..1
Materials & Methods……………………………………………………………………………...8
Results………………………………………………………………………………………...….16
Discussion…………………………………………………………………………………….….21
Conclusions………………………………………………………………………………………30
References………………………………………………………………………………………..31
Tables………………………………………………………………………………………...…..35
Figures……………………………………………………………………………………………40

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List of Tables:
Table 1: Demographics……………………………..……………………………..…………………………………35
Table 2: Implant Systems……………………………..……………………………..……………………………….35
Table 3: Bone Augmentation Cases……………………………..……………………………..…………………….35
Table 4: Bone loss……………………………..……………………………..………………………………………35
Table 5: Implant failure……………………………..……………………………..…………………………………36
Table 6: Bone loss with platform-switching implants and non platform-switching implants……………………….36
Table 7: Excluded implants from data analysis……………………………..……………………………………….36
Table 8: Implant types……………………………..……………………………..…………………………………..36
Table 9: Implant failure comparing platform-switching to non platform-switching………………...………………37
Table 10: Frequency and percentage of fully or partially guided cases with Biomet 3i implants…………………...37
Table 11: Frequency and percentage of fully or partially guided cases with Straumann Bone Level and
Dentsply/Astra EV implants……………………………..……………………………..…………………………….37

Table 12: Total frequency and percentage of fully or partially guided cases with Zimmer Biomet 3i, Straumann
Bone Level and Dentsply/Astra EV implants……………………………..………………………………………….37

Table 13: Multicollinearity analysis of predictors……………………………..…………………………………….38
Table 14: Analysis of effects……………………………..……………………………..……………………………38
Table 15: Odds ratio estimates……………………………..……………………………..………………………….38
Table 16: Analysis of implant failure compared with flap surgery……………………………..……………………38
Table 17: Odds ratio estimates of implant failure compared with flap surgery……………………………………...39

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List of Figures:
Figure 1: Diagnostic wax-up, buccal view……………………………..……………………………..……………..40
Figure 2: Diagnostic wax-up, occlusal view……………………………..……………………………..……………40
Figure 3: Analog impression……………………………..……………………………..……………………………41
Figure 4: Surgical guide……………………………..……………………………..………………………………...41
Figure 5: Zimmer Biomet 3i Certain collar length……………………………..……………………………..……..42
Figure 6: Zimmer Biomet 3i Certain implant diameter……………………………..……………………………….42
Figure 7: Zimmer Biomet 3i Certain implant length……………………………..………………………………….43
Figure 8: Straumann Bone Level collar length……………………………..……………………………..…………43
Figure 9: Straumann Bone Level implant diameter……………………………..……………………….…………..44
Figure 10: Straumann Bone Level implant length……………………………..……………………….……..……..44
Figure 11: Dentsply/Astra EV implant diameter……………………………..……………………….……………..45
Figure 12: Dentsply/Astra EV implant length……………………………..……………………………..………….45
Figure 13: Bone Loss (mesial) ……………………………..……………………………..…………………………46
Figure 14: Bone Loss (distal) ……………………………..……………………………..…………………………..46
Figure 15: Guided surgery planning……………………………..……………………………..……………………47
Figure 16: Flap vs Flapless……………………………..……………………………..……………………………..47
Figure 17: Number of failures in flap versus flapless cases……………………………..……………………...…...48
Figure 18: Percentage of failures in flap versus flapless cases……………………………..………………………..48
Figure 19: Guided versus non-guided case frequency and percentage……………………………..………………..49
Figure 20: Bone augmentation percentage……………………………..……………………………..….…………..50
Figure 21: One-stage versus two-stage……………………………..……………………………..…………………50
Figure 22: Bone-loss with platform-switching implants and non platform-switching implants………………….....51
Figure 23: Excluded implants from data analysis……………………………..……………………………..………51
Figure 24: Frequency and percentage of fully or partially guided cases with Biomet 3i implants……….…………52
Figure 25: Frequency and percentage of fully or partially guided cases with Straumann Bone Level and
Dentsply/Astra EV implants……………………………..……………………………..…………………………….52

Figure 26: Total frequency and percentage of fully or partially guided cases with Zimmer Biomet 3i, Straumann
Bone Level and Dentsply/Astra EV implants……………………………..……………………………..……...……53
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ABSTRACT
Background:
Restorative-driven implant dentistry is a process in which the prosthetic outcome precedes
implant placement planning. Ultimately a digital impression is taken, and a surgical stent can be
fabricated. Several advantages and disadvantages exist when it comes to guided surgery, in
addition to the practicability of using the guide. Therefore, the primary aim of this retrospective
study is to assess the implant success through placement via a guided surgery system, and the
feasibility of using that guide. The secondary aims were to evaluate the crestal bone loss and the
factors that attributed to implant failure.
Methods:
Electronic dental records were examined of 306 implant sites 6 months to 6 years after implant
loading from January 2014 to December 2019 at the undergraduate implant clinic at the Herman
Ostrow School of Dentistry. Implant measurements were completed for 3 different implant
systems placed at the Herman Ostrow School of Dentistry: Zimmer Biomet 3i, Straumann, Astra.
When the guide could be utilized for both the osteotomy and implant placement, it was
categorized as the guided group. When the guide could not be utilized for surgery, it was
categorized as the non-guided group. When the guide could be used for the osteotomy but not
implant placement, it was categorized as the partially guided group. Radiographic bone
measurements were taken at time of implant placement, at time of loading, and the latest survival
date of the implant. Bone loss was compared to the following: flap or no flap, implant system,
one-stage or two-stage, reason for tooth loss, and implant diameter.

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Results:
The frequency of guided verses non-guided surgeries was 233 (76.14%) and 56 (18.30%)
surgeries, respectively. 17 (5.56%) surgeries were unknown. 6 cases, or 60% of implants in the
flap group failed; 4 cases, or 40% of implants in the flapless group failed. 43.4% (96/220) of
flaps had ³1mm bone loss, and 27% (19/70) of flapless had ³1mm bone loss. A logistic
regression model found flap surgery to be significant (p<0.0015), such that flap surgery had 2.98
times higher odds of ³1mm bone loss than flapless surgery (95% CI 1.52-5.83). Implant system
was also significant (p<0.0001), such that non-platform switching implants had 3.92 times higher
odds of ³1mm bone loss than platform-switching (95% CI is 1.97-7.79). One-stage vs two-stage
surgery (p=0.53), reason for tooth loss (0.43), and implant diameter (p=0.29) were not significant
when compared to bone loss. A logistic regression analysis of implant failure compared with flap
surgery did not find any significant difference (p=0.23).
Conclusion:
Within the limitations of this study, we reached the following conclusions based on our
data analysis and observations:
1) In 18.30% of surgeries a guide ultimately could not be used requiring free-hand
surgery.
2) In 54.90% of cases a fully guided surgery could not be performed, and implants were
placed freehand
3) The implant success rate was 96.73% regardless of flap or flapless surgery.
4) Flap surgery was found to have 2.98 times higher odds of ³1mm bone loss than
flapless surgery.
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5) Non platform-switching implants had 3.92 times higher odds of ³1mm bone loss than
platform-switching implants, although 9 platform-switching implants failed, and only
1 non platform-switching implant failed.
6) There was no significant difference of bone loss with one-stage vs two-stage surgery,
reasons for tooth loss, and implant diameter

Although this study was the first to assess the feasibility of guided surgery, future studies
are necessary. Guided surgery can be a useful tool for implant placement, however, there are
limitations and challenges in clinical implementation. Some of these challenges negate the use of
the guide and requires surgical expertise to overcome and correct the shortcomings.

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1. INTRODUCTION

The concept of osseointegration was founded by Per-Ingvar Brånemark in the 1960s.
Initially used in orthopedic prosthetics, it was found that the mechanism could be applied to
titanium implants in the oral cavity, through different means. The process begins by a blood clot
that forms between the implant fixture and bone. Soon after, polymorphonuclear leukocytes,
lymphoid cells, and macrophages infiltrate the site causing haversian bone to calcify. Occlusal
forces stimulate the surrounding bone to further remodel into cortical lining around the implant.
Ultimately, the Haversian bone becomes organized, and forms osteon (Jayesh & Dhinakarsamy,
2015). This process leads to the phenomenon of implant osseointegration. Albrektsson (1981)
defines osseointegration as the “direct contact between living bone and implant.” A study by
Davies (1998) suggests that there are three phase that occur in peri-implant bone healing:
osseoconduction, de novo bone formation, and bone remodeling. The study also suggests that
peri-implant bone healing results in bone growth on the implant surface, a phenomenon known
as contact osteogenesis. This occurs when osteogenic cells are recruited to the implant surfaces,
and blood vessels form between cells and old bone. Bone matrix is then laid down on the implant
surface. Another study found that there is direct contact between Ca atoms and titanium oxide
surfaces without a protein interlayer. A purely inorganic interface is created, as demonstrated by
the role of nanotopography (Karlsson et al., 2014).

Aside from osseointegration, the restorative aspect of implant placement is a crucial part
of implant success. Restorative-driven implant dentistry is a process in which the prosthetic
outcome precedes implant placement planning. Historically, this process began with several
options of radiographs: lateral cephalometric, panoramic, tomographic, and intraoral
2
radiographs. The lateral cephalometric cannot provide an exact implant location, although
helpful for visualizing both maxilla and mandible. The panoramic radiograph also provides
visualization of maxilla and mandible, however, has a high probability of distortion, nonuniform
magnification, and at times, overlapping images. Conventional tomography provides
radiographic slices of the body, and allows the provider to evaluate cortical bone, trabecular
bone, anatomical structures, and the location of the future implant. However, magnification must
be calculated due to the enlargement of the image slices. Computer-assisted tomography was
also previously used, however, images appear less sharp than conventional tomography
(Engelman et al., 1988). Today, the most common radiographic examination in surgical planning
of implant placement is a cone beam computed tomography (CBCT) scan. This three-
dimensional scan identifies anatomical and bone structures in order to ensure proper placement
of the implant, which is a crucial step in guided surgery protocols for implant surgery (Mijiritsky
et al., 2021).

When using analog protocols, a diagnostic wax-up is used in order to provide the patient
with a restorative preview of the definitive prosthesis (Figure 1, 2). This preview can also be
directly used for the definitive restoration. The initial step of the diagnostic wax-up is the analog
impression (Figure 3) which allows the operator to transfer the clinical implant position into the
laboratory (Güth et al., 2013). Ultimately, a digital impression is created, and CAD-CAM
restorations are provided for the patient (Marsango et al., 2014). Surgically, a surgical guide
(Figure 4) can be utilized to facilitate implant placement. The stent can incorporate radiopaque
markers in order to mark the contour of the definitive restoration on the CBCT. A surgical guide
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allows the provider visualization of the planned implant positioning, the final prosthesis position,
emergence profile, and available space for restorative components (Talwar et al., 2010).

When using a digital workflow, a digital model is created by either scanning a traditional
impression and pouring a stone model, or through the use of an intraoral scanner. Then, an
interactive software is utilized in order to combine data from both the CBCT and digital
impression. Once implant placement is determined along with abutment type and prosthetic
configurations, another software is used to fabricate a surgical guide (Mijiritsky et al., 2021).

The same digital workflow is utilized for guided surgery protocols for dental implant
placement. There are several advantages and disadvantages of computer-guided implant
placement. Digitally visualizing vital anatomical structures in correlation to an actual position of
the planned implant is a crucial advantage of a digitally planned implant position. Among the
several factors that determine implant success, accurate implant position is a crucial element that
can be controlled in order to avoid crucial anatomical structures (Nickenig & Eitner, 2007). One
technique that facilitates their placement is computer-guided surgery, which has the ability to
convert a three-dimensional image to provide a virtual implant position. This three-dimensional
image is produced from an implant planning software combined with computerized tomography
to simulate both the surgical and prosthetic aspects of the procedure. Implant location may be
determined based on the quality and volume of bone while avoiding major anatomical structures
such as the sinus or nerves (Vercruyssen, Fortin, et al., 2014). The first step in the process of
digitized computer-guided surgery which is also seen in the present study is transforming
intraoral scans into a Standard Tessellation Language, or STL file. These files are highly
4
accurate and portray surface geometry of three-dimensional objects. Since digital technology
approximates the prosthetic and surgical implant treatment via virtual planning to the computer-
assisted design/computer-assisted manufacturing-based design (CAD/CAM), superimposition of
the CBCT Digital Imaging and Communications in Medicine (DICOM) file is required. The
superimposition combines three reference points: facial skeleton, extraoral soft tissue, and
dentition. Together, these three reference points are referred to as a triad. This process is an
innovative one that takes combines underlying anatomical structures with superficial structures
as well as tooth morphology and providing relatively reproducible accuracy (Joda et al., 2017).

Another potential advantage is the ability of performing surgery without the need for flap
elevation (Behneke et al., 2012). This may reduce post-operative pain, swelling, and morbidity.
It may also minimize surgical time and preserve blood supply in newly grafted sites. Guided
surgery may facilitate the immediate loading protocol as well as maintain transfer accuracy from
the pre-surgical planning period to the surgery itself (Behneke et al., 2012).

Some potential disadvantages exist in performing guided surgery protocols. These
include the inability to make changes of implant positioning should there be a difference in
presurgical assessment and clinical observations at the time of the procedure. Additionally,
flapless procedures when the bone crest cannot be visualized, do not allow for identification and
correction of crestal bone deficiencies. Difficulty in evaluating the alveolar morphology and
angulation may result in perforation of cortical plates. This may lead to placement of implants in
a compromised position which can adversely affect buccal bone thickness and negatively impact
esthetic, functional, and health outcomes of therapy. Also, interference with osseointegration
5
may occur in which the implant surface becomes contaminated and epithelial migration of soft
tissue could result within the osteotomy site (Fürhauser et al., 2015). In terms of implant success,
one study showed that there was no statistically significant difference of flap versus flapless
surgery on implant failure, however, flapless surgery saved 17 minutes of surgical time
(Cannizzaro et al., 2011). A systematic review by Lemos et al. found similar results in which
there was no significant differences between flapless and open-surgical techniques with regards
to implant survival rates, marginal bone levels, or complication rates in 1,873 dental implant
sites (Lemos et al., 2020). Another study by Bashutski et al. found an implant success rate of
92% in the flapless and traditional flap surgeries. Both groups had a decreased level of
keratinized gingiva from baseline to 3 months, however, the flap group faced a greater loss of
keratinized gingiva over time than the flapless group (Bashutski et al., 2013). On the other hand,
flapless surgery results in a greater loss of keratinized tissue, and an inability to manipulate the
soft tissue around the implant (Sclar, 2007).

Several studies evaluate the accuracy of guided surgery. In a 2014 systematic review,
Tahmaseb et al. found that there was a total mean error of 1.12 mm at the entry point of an
implant and 1.39 mm at the apex for guided surgery. They also stated that there was no evidence
that supported the theory that computer-aided surgery was superior to conventional surgery
(Tahmaseb et al., 2014). In terms of the methods of guide fabrication, in 2009 Scneider et al.
reported there was no statistically significant difference in clinical parameters for laboratory
manufactured guides as compared with rapid prototyped guides in terms of deviation level
(Schneider et al., 2009). Another study by Van Assche (2012) found that there was a statistically
significant difference at the coronal and apical entries with no statistically significant difference
6
in the angular deviation between a laboratory fabricated guide versus a computer-aided guide.
One study evaluated tooth-, mucosal-, and bone-supported SLA (stereolithographic) surgical
guides. For SLA guides, multiple-type and single-type surgical guides were evaluated. The
multiple-type guide (SurgiGuide) was for “partially” guided surgeries in which only osteotomy
sites were prepared using removable, surgical, sequential drilling guides. The single-type guides
(Safe SurgiGuide) were “totally” guided in that a guide is used for preparing the osteotomy site
in addition to implant insertion. The study found that mucosal-supported SurgiGuide (multiple)
showed a statistically significantly better accuracy as compared to Safe SurgiGuide (single). It
also showed that tooth and bone-supported fixed Safe Surgiguide (single) had a higher
statistically significant accuracy as compared to non-fixed Safe SurgiGuide (single) and
SurgiGuide. Having fixation in both tooth and bone-supported surgical guides was shown to
improve the accuracy at the coronal, apical, and axial levels (Cassetta et al., 2013). Another
systematic review examined the accuracy of a “dynamic” system versus a “static” system. The
dynamic system refers to a navigational system in which intraoperative feedback is produced
where a handpiece with infrared cameras is recorded or has haptic feedback to aid with live
navigation of implant placement. The static system is when the guide is fabricated in a laboratory
and is fixated. The review found a statistically significant difference of 0.5mm deviation at the
coronal level, and 0.52mm at the apical level favoring the dynamic navigation system (Jung et
al., 2009). On the other hand, another systematic review concluded that sCAIP (static computer-
aided implant placement) was shown to have clinical advantages over conventional implant
placement methods, as long as there is stabilization of the surgical guide (Tattan et al., 2020).
Another study compared the accuracy of mucosa and bone-supported guided surgery to mental
navigation and use of a surgical template in fully edentulous jaws. They discovered that there
7
was a significantly lower difference in deviation at the entry point, apex, and angular deviation
for the guided surgery group as compared to the mental navigation and surgical template groups.
There was no statistically significant difference in the deviations between mucosal and bone-
supported surgical guides, or between the different static systems (Vercruyssen, Cox, et al.,
2014).

The accuracy of guided surgery can also be evaluated based on anatomical factors. Ochi
(2013) concluded that higher bone density results in more superficial placement of implants.
They also found that the thicker the mucosa, the more likely the global deviation of the implant
apex. They did not find a correlation between the alveolar ridge shape to any deviation
parameters. Vasak (2011) discovered that there were significantly smaller deviations of implant
placement in the anterior region as compared to the posterior region. They also found that the
deviations were smaller in the mandible than the maxilla. However, the results were clinically
insignificant.

It is evident that despite the relative consistency of studies in regard to computer-guided
implant surgeries, there is no data on the frequency of the inability to use surgical guides.
Therefore, the primary aim of this retrospective study is to assess the implant success through
placement via a guided surgery system, and the feasibility of using that guide. The secondary
aims were to evaluate the crestal bone loss and the factors that attributed to implant failure.

8
2. Materials & Methods:
Study Design:
The study protocol was approved by the Institutional Review Board at the University of
Southern California. Informed consent for this study was exempt due to the anonymity of the
participants. Subjects were labeled using a code that could be linked to subjects’ personal
identifying information.

Guided surgery protocols have been employed in predoctoral and postdoctoral implant
training at Herman Ostrow School of Dentistry of USC since 2014 as an educational tool for
novice practitioners training in implant surgery under direct, hands on supervision. The aims of
this present retrospective study are to analyze the clinical outcomes of implant surgery using a
guided surgery system. These include implant success, the feasibility of using the guide for
implant osteotomy and implant placement, crestal bone remodeling and its correlation to flap vs
flapless surgery. The study was conducted by one Advanced Periodontology resident at the
University of Southern California.

Study Population:
Electronic dental records were examined 6 months to 6 years after implant loading during
a period from January 2014 to December 2019 at the undergraduate implant clinic at the Herman
Ostrow School of Dentistry.

9
Inclusion Criteria:
Individuals above the age of 18 who had no contraindications for implant surgery as
assessed by clinical guideline for implant surgery at Herman Ostrow School of Dentistry of USC
(HOSD-USC) were included in this study. These included ASA I patients or ASA II patients
with a well-controlled health history. Individuals below age 18 or uncontrolled medical
conditions such as uncontrolled diabetes, immunocompromised medical history, presence of
active intraoral infection and inflammation were contraindicated for implant surgery at HOSD-
USC predoctoral clinic and therefore not included in this study.

Digital prosthetic and surgical planning of guided surgery were performed by expert
prosthodontics and surgical faculty (periodontist or oral surgeon). Surgical providers were novice
trainees (dental students or Prosthodontic residents) operating under direct hands-on supervision
with expert surgical (Periodontist or Oral Surgeon) faculty. The implant position was planned
according to a diagnostic wax up with anticipation of at least 1 mm buccal bone around the
implant. Cases requiring bone augmentation (prior or in combination) to implant placement or
requiring more than 2 mm crestal sinus elevation were not included for guided surgery planning.

When reviewing radiographs for crestal bone measurement, non-diagnostic images in
which separation of implant threads were not visualized, foreshortened images, elongated
images, and radiographs in where less than 3 implant threads could be seen were excluded from
analysis.

10
Surgical Protocol
Surgeries were completed under local anesthesia administered through block and/or local
infiltration. A tissue punch was utilized to mark the circumference of the osteotomy site. If less
than 2mm of soft tissue was present on the buccal and/or lingual of the marked site, then a mid-
crestal incision was placed and a full thickness flap was elevated. The guided surgery protocol of
the specific system was followed according to the surgical plan created by the planning software.

Implants were placed fully guided with the Zimmer Biomet 3i system. For the Straumann
Bone Level and Dentsply/Astra EV systems, most implants were placed either freehand or were
initially positioned through the guide initially and completed to depth freehand, and
subsequently, positions were verified with the surgical guide.

Study Outcome Parameters:
All patient charts were reviewed, and the following information were recorded:
(a) Patient ID
(b) Patient age
(c) Patient sex
(d) Patient ethnicity
(e) Medical history
(f) Smoking history
(g) Reason for tooth loss
(h) Treatment site
(i) Implant system
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(j) Implant size
(k) Guided surgery system
(l) Whether or not implant placement was fully guided
(m) Whether or not guide was used and why
(n) Flap or no flap used during surgical procedure
(o) Type of bone substitute material (if used)
(p) Sinus elevation performed or not
(q) Whether or not soft tissue augmentation was performed
(r) Whether there was a need to correct implant position, depth, or size
(s) Insertion torque
(t) One-stage or two-stage protocol
(u) Pre-operative CBCT date
(v) Surgery date
(w) Radiographic observation at time of placement
(x) Date of implant loading
(y) Radiographic observation at time of loading
(z) Date of last radiographic follow-up
(aa) Observation in latest radiograph
(bb) Latest post-operative periapical radiograph date
(cc) Evident bone loss on radiograph
(dd) Last restorative follow-up
(ee) Last survival date of implant
(ff) Reason for implant failure (if failed)
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(gg) Post-operative CBCT date (if taken)
(hh) Whether restoration was screw-retained or cement-retained
(ii) Restorative complication (if present)
(jj) Surgical provider (i.e. student, resident)

Radiographic Measurements:
Implant measurements were completed for 3 different implant systems placed at the
Herman Ostrow School of Dentistry predoctoral implant clinic: Zimmer Biomet 3i Certain,
Straumann Bone Level, Dentsply/Astra EV. All measurements were calibrated on the Schick
digital radiography software according to known measurements using the following (note: when
possible, implant length and implant collar length were used first and foremost):

a. Zimmer Biomet 3i Certain:
(a) 1mm collar length for a 4.1 diameter implant, 1.25mm collar length for a 5mm
diameter implant (Figure 5)
(b) Implant diameter, i.e., 3.25mm, 4.1mm, 5mm (Figure 6)
(c) Implant length, i.e., 8.5mm, 10mm, 11.5mm, 13mm (Figure 7)

b. Straumann Bone Level:
(a) 1.8mm collar length for all implant diameters (Figure 8)
(b) Implant diameter, i.e., 3.3mm, 4.1mm, 4.8mm (Figure 9)
(c) Implant length, i.e., 6mm, 8mm, 10mm, 12mm (Figure 10)

13
c. Dentsply/Astra EV:
(a) Implant diameter, i.e., 3.6mm, 4.2mm, 4.8mm (Figure 11)
(b) Implant length, i.e., 9mm, 11mm (Figure 12)

Measurements were completed for implants where a minimum of 3 threads were visible
in periapical and interproximal (bitewing) radiographs that were considered diagnostic
(periapical radiographs could not be elongated or foreshortened where the apex could be seen;
interproximal radiographs had to show proximal contacts between dentition). The protocol for
measurement calibration was as follows for each implant system:

Bone Loss Measurements:
(a) Radiographic observation at time of implant placement
Implant measurement was observed in relation to the top of the implant collar. If the
implant was placed subcrestal in relation to the bone, meaning the bone level was above
the top of the implant collar, the bone level was given a positive (+) value with a
measurement to the nearest tenth of a millimeter. If the implant was placed supracrestal
in relation to the bone, meaning the bone level was below the top of the implant collar,
the bone level was given a negative (-) value with a measurement to the nearest tenth of a
millimeter. The amount of bone loss present was measured from the top of the implant
collar to the most apical portion of the bony defect (Figures 13, 14)

(b) Radiographic observation at time of loading
Protocol was the same as described previously.
14

(c) Last radiographic follow up
Protocol was the same as described previously. In addition, if substantial bone loss was
present, it was noted up to which thread bone level had receded to.

Guided Surgery:
Implant positions were planned according to a diagnostic wax-up with the anticipation of
at least 1 mm of buccal bone around the implant. Figure 15 shows an example of the digital
planning of a Straumann implant. The green outline of the tooth represents the location of the
wax-up, and what is shown on the ridge is a replica of the sleeve. The bottom portion of the
image contains a yellow rod which shows the projected trajectory of the implant.

Osteotomies were performed using the surgical guides and guided surgery kit. For
Zimmer Biomet 3i cases, most implants were placed fully guided through the surgical guide. The
Biomet 3i Navigator system mount engages the hex and is attached with the screw to the
implant. For the Straumann Bone Level and Dentsply/Astra EV cases, most implants were
placed either freehand or were initially positioned through the guide and completed to depth
freehand; subsequently, implant positions were verified with the surgical guide. The placement
tool of the Straumann and Dentsply/Astra implants engages the hex with friction and without an
internal screw. The implant could not be placed through the guide since the implant driver was
engaging the mount or internal connection via a friction grip mechanism; often, the implant
would separate from the placement during the process when using the guide for placement.
Additionally, many times, interocclusal space limitations did not allow the use of the guide for
15
placement due to the size of the components. All other cases in which the guide could not be
properly utilized for osteotomy and implant placement were recorded as “non-guided.”

Statistical Analysis:
Descriptive analyses were recorded for all variables of interest in 254 cases. 52 cases in
which non-diagnostic radiographs, failed implants, and implants that were not loaded were
excluded from the analysis. Prior to analysis, the predictors were assessed for multicollinearity.
The predictors that were assessed included the following: flap or no flap, implant system, one-
stage or two-stage, reason for tooth loss, and implant diameter. A logistic regression model was
then run with the outcome and predictors. The outcome evaluated was bone loss.

16
3. Results:
Descriptive Analysis
A total of 306 implants were examined in 247 individuals in this retrospective study
(Table 1). The population consisted of 141 females and 106 males, with a mean age of 56.27 ±
14.23 years (Table 1). 97 Zimmer Biomet 3i implants were placed, 156 Straumann Bone Level
implants were placed, and 53 Dentsply/Astra EV implants were placed (Table 2). Figure 16
exhibits flap versus flapless procedures. 223 surgeries consisted of a flap which accounted for
72.88% of cases. 70 surgeries, or 22.88% of cases were flapless. 1 case only utilized a buccal
flap, or 0.33%. 13 cases, or 4.25% of surgeries were recorded as unknown in that the patient’s
chart did not specify whether the surgery was flap or flapless.

Figure 17 portrays the number of implant failures in flap versus flapless cases. Figure 18
portrays the percentage. There were a total of 10 failures of the 306 implants placed, or 3.27%, 6
cases, or 1.96% of failures in the flap group, and 4 cases, or 1.31% of failures in the flapless
group.

Figure 19 represents the number of cases that were guided versus non-guided, and their
percentages. Non-guided cases were those in which the guide could not be used as planned.
Reasons for this included: guide was too lingual from the ridge, incorrect positioning of implant
preparation with the guide, limited interocclusal space, limited mouth opening, depth needed to
be adjusted to create enough restorative space, transcrestal sinus lift was necessary, improper
angulation/position, dehiscence present/avoidance of dehiscence, fenestration present/avoidance
of fenestration, improper space between guide and implant drill, implant instability so larger
17
implant had to be placed, or implant had to be hand torqued to ensure proper depth placement.
The frequency of fully guided verses non-guided surgeries were 233 and 56 surgeries,
respectively. These accounted for 76.14% and 18.30%. 17 surgeries, or 5.56% of the surgeries
were unspecified whether they were guided or not guided.

Table 3 represents the number of cases that used augmentation at the time of implant
placement, and Figure 20 shows the percentage of the cases that used augmentation. No
augmentation was used in 278 cases; this value was 90.85% of the total. 4 cases (1.31%) used
bone augmentation without the use of a collagen plug, collagen tape, or a resorbable membrane.
13 cases (4.25%) were augmented with the use of a collagen plug, collagen tape, or a resorbable
membrane, without the use of bone. 5 cases (1.63%) utilized the combination of bone with
collagen plug or collagen tape. 3 cases (0.98%) utilized bone in addition to a resorbable
membrane. 3 cases (0.98%) did not specify the type of augmentation that was done.

Figure 21 exhibits the number of cases that were one-stage surgery versus two-stage
surgery. One-stage surgery described surgeries in which a healing abutment was placed at time
of implant surgery. Two-stage surgery described surgeries in which a cover screw was placed at
time of implant surgery, and a second surgery was required to place a healing abutment on the
implant after a minimum of 3 months from the time of implant placement. 210 cases (68.63)
were one-stage, whereas 94 cases (30.72%) were two-stage. 2 cases were not specified
(unknown) in the patient chart and represented 2 cases, or 0.07%. The decision for a two-stage
procedure were based on less than 30 Ncm insertion torque using incremental torquing
placement starting at 25 Ncm.
18
Table 4 evaluates the amount of bone loss (³1mm, <1mm, no bone loss, unknown,
implant failed before bone loss was evident/implant not yet loaded). 38.89% of total cases had
³1mm bone loss. 7.52% of cases showed <1mm of bone loss. 36.60% of cases had no bone loss.
3.92% of cases were unknown due to undiagnostic radiograph follow up. 13.07% of cases had
implants that failed prior to evidence of bone loss was recorded, or the implants were not yet
loaded. 43.4% (96/220) of flaps had ³1mm bone loss, and 27% (19/70) of flapless had ³1mm
bone loss.

There were 10 total implant failures which ranged between <2 months of implant
placement to 2.5 years of follow-up after implant placement (Table 5). 2 implants failed <2
months after placement, 4 implants failed between 2 – 6 months of placement, 2 implants failed
6 months – 1 year after placement, and 2 implants failed 2 – 2.5 years.

Peri-implant bone loss was also assessed based on amount of bone loss with platform-
switching versus non platform-switching implant systems. Straumann and Astra implants were
recorded with the platform-switching cases (209 cases total), and Biomet 3i implants were
recorded with the non platform-switching cases (97 cases total) for a total of 254 cases (Table 6,
Figure 22). Table 7 and Figure 23 show the cases that were excluded from statistical analysis. 52
cases of the total 306 implants from the study were excluded due to non-diagnostic follow-up
radiographs, implant failure, or because the implants were not loaded. Type of implants are
shown in Table 8. Implant failure was noted based on platform-switching versus non platform-
switching implants (Table 9).
19
Table 10 and Figure 24 show the frequency and percentage of the time that the Biomet 3i
system was used as partially guided or fully guided. Of the 97 total implants placed with the
Biomet 3i system (non platform-switching), 72.16% (70 cases) of the time was the surgery fully
guided. 21.65% of the time (21 cases) the surgery was partially guided, meaning that the guide
could not be fully utilized as planned. 6 cases (6.19%) were unspecified if the guide was fully or
partially utilized. Table 11 and Figure 25 show the frequency and percentage of the time that the
Straumann and Dentsply/Astra EV system was partially or fully guided. Of the 209 total
implants placed with those systems, 163 (77.99%) implants were fully guided, 35 (16.75%)
implants were partially guided, and 6 implants (6.19%) were unspecified if the surgery was fully
or partially utilized. Table 12 and Figure 26 show the frequency and percentage of all 3 implant
systems together. In 121 cases (39.54%) the surgery was fully guided. In 168 cases (54.9%) the
surgery was partially guided. In 17 total cases (5.56%) it was unspecified if the surgery was fully
or partially guided.

Prior to analysis, the predictors were assessed for multicollinearity. Multicollinearity was
not found to be a concern (all tolerance values > 0.4) as shown in Table 13.

A logistic regression model found flap surgery to be significant (p<0.0015), such that flap
surgery had 2.98 times higher odds of ³1mm bone loss than flapless surgery (95% CI 1.52-5.83).
Implant system was also significant (p<0.0001), such that non-platform switching implants had
3.92 times higher odds of ³1mm bone loss than platform-switching (95% CI is 1.97-7.79). One-
stage vs two-stage surgery (p=0.54), reason for tooth loss (0.43), and implant diameter (p=0.29)
were not significant. These values are shown in Tables 14 and Table 15.
20

A logistic regression analysis of implant failure compared with flap surgery (Table 16,
17) did not find any significant difference (p=0.23).

21
4. Discussion:

Although guided surgery can be successful in the hands of an expert, there are several
intricacies that need to be considered during the digital planning process. A drilling sequence
with a predetermined angulation may accelerate the surgical process, however, if space
limitations are present, it can make the process more time consuming. In our retrospective chart
review, accuracy of implant positioning was compromised in cases where the radiographic
appearance of bone was different from that of the clinical appearance of the bone. These
situations required modifying implant position, angulation, depth, and size via a free-handed
approach. In some cases, bone augmentation was needed to compensate for defects. In the
population studied, when surrounding bone around digitally planned implants was clearly
identifiable with more than 2mm of bone width surrounding the implant, no surgical
modification for implant repositioning or bone augmentation was needed, although some cases
required depth modifications. In our observation, the cases requiring surgical modification from
the digitally planned position or required unanticipated grafting, were the ones that more than
2mm of surrounding bone could not be clearly established at the time of digital planning. This
may be an important factor that warrants further investigation when considering digital planning
of dental implant surgery.

There is limited literature on the feasibility of utilization of surgical guides as planned.
The frequency of instances in which the guide could not be completely or partially utilized as
planned is not well known. For example, the guide may not fit properly on existing dentition/soft
tissue/bone or may fracture. One study showed that bone-supported guides provide less accuracy
than tooth-supported or mucosa-supported guides (Tatakis et al., 2019). This may be due to the
22
interference of reflected tissue. In addition, the guide may not be positioned properly, or may
move during the surgical procedure. Although the guide may fit, the additional components or
drill may not have adequate space in the patient’s mouth (Tatakis et al., 2019). In our
retrospective analysis we encountered several incidences that the guide could not be used as
planned either completely or partially. In our analysis, we identified that 18.30% of the time, the
surgeons were unable to utilize the surgical guide (and hence the guided surgery system) for
implant placement. In those cases, the procedure was completed use a free-handed technique.
The most common problems with the use of the surgical guide were: lack of interocclusal space
for drill components (specifically when performing molar surgeries, requiring either placement
of the drill component in the guide prior to insertion in the mouth or a free-handed approach and
subsequent verification with the guide), inadequate drilling depth (requiring depth adjustment
with the free-handed approach), separation of the guided sleeve (requiring a free-handed
procedure), and an osteotomy site too far facial causing the need to adjust the osteotomy with the
a free-handed approach. In our experience, the use of the guide was more useful for the
osteotomy process than implant placement. For the Biomet 3i Navigator system, the mount
engages the hex and is attached with the screw to the implant. The placement tool of the
Straumann and Dentsply/Astra implants engages the hex with friction and without an internal
screw; many times, the implant would separate from the placement because of this friction grip
mechanism. Majority of implants utilizing Straumann Bone Level and Denstply/Astra EV
implants were placed without the guide after the osteotomy was prepared with the guide. In our
study, out of 306 implants, 168, or 54.9%, were placed partially guided meaning that the
osteotomy was performed with the guide, but the implants were placed freehand. The two major
23
reasons for freehand placement were either to adjust the depth of the implant for the emergence
profile or due to lack of interocclusal space.

When placing Dentsply/Astra EV and Straumann Bone Level implants, 70.33% implants
could not be placed through the guide since the implant driver was engaging the mount or
internal connection via a friction grip mechanism; often, the implant would separate from the
placement tool during the process when using the guide for placement. Additionally, many times,
interocclusal space limitations did not allow the use of the guide for placement due to the size of
the components. However, for the Biomet 3i system in which the implant driver was engaging
the implant via a screw mechanism, the guide was only able to be fully utilized 72.16% (N=70)
of the time. In 21.65% (N=21) of the cases, the surgery was partially guided, which for the
Biomet 3i system meant that one of the aforementioned circumstances had occurred
approximately 1 out of every 5 cases. In total, fully guided surgery could only be utilized for
39.54% of all implants analyzed in this study.

Implant stability is another important factor to consider when planning a one-stage versus
two-stage approach to the surgery. A lower insertion torque value has been associated with a
higher implant failure rate (Ottoni et al., 2005). Therefore, the present study utilized a two-stage
approach for implants placed with an insertion torque of less than 30 Ncm. About 31% of the
implants were placed with a two-stage approach due to achieving less than 30 Ncm stability
measured with incremental torquing.

24
The role of keratinized mucosa plays a large role in regard to the longevity of implant
health. One study suggests that the absence of keratinized mucosa around implants may increase
the vulnerability of the implant site to plaque accumulation which may enter the peri-implant
sulcus and cause tissue destruction (Warrer et al., 1995). Another study evaluated the influence
of per-implant keratinized mucosa on implant tissue health as well as brushing discomfort
(Perussolo et al., 2018). The study found that the presence of 2 mm or greater of keratinized
mucosa has a protective effect on peri-implant tissues, brushing comfort, and tissue health. Less
than 2 mm of keratinized mucosa leads to plaque accumulation, tissue inflammation, as well as
brushing discomfort (Perussolo et al., 2018). Additionally, a systematic review found that
inadequate mucosal width has been associated with marginal recession and attachment loss (Lin
et al., 2013). Soft tissue augmentation procedures completed to create soft tissue thickness have
also been shown to have greater peri-implant health as well as higher marginal bone levels
(Thoma et al., 2018). In addition to keratinized mucosa, connective tissue thickness is also an
important factor for long-term maintenance of the buccal mucosal level and preservation of
buccal bone (Linkevicius et al., 2009). In the present study, the analysis of keratinized mucosa
and tissue thickness could not be assessed since the surgical protocol required for flap elevation
when less than 2 mm of remaining keratinized tissue on the buccal and/or lingual of the implant
was anticipated. Moreover, many times an edentulous ridge may have a sharper/pointed ridge as
opposed to a flat/square-shape. In some circumstances, a 2 mm width of keratinized tissue may
be available, however, when a tissue punch is created, the tissue punch tends to fall more buccal
of the slope leaving thin (less than 2mm) tissue thickness. Therefore, the keratinized tissue width
may be present, however, connective tissue thickness may not be.

25
The present study follows the trends of previous studies in which mid-crestal incisions
give similar implant success rates when compared with the classic protocol (Scharf & Tarnow,
1993). This study shows comparable efficacy with flap versus flapless surgeries. 6 cases, or 60%
of failures were found in flap surgeries, whereas 4 cases, or 40% of failures were found in
flapless surgeries. In total, there were 10 failures throughout the study, which accounts for a
3.27% failure rate, or 96.73% success rate. This success rate is comparable to previous studies
which compare incision type to the success rate of implant integration (Casino et al., 1997).

Flapless implant surgery is not uncommon in implantology, however, it does come with
some shortcomings. Lack of visibility is a major limitation of flapless surgery, as concavities,
dehiscences, fenestrations and bone quality may not be evaluated clinically. It can potentially
cause damage to anatomical structures such as adjacent tooth roots, the sinus, and important
nerves due to a lack of visualization of submucosal anatomical landmarks and depth estimation.
Although keratinized mucosal width is a controversial topic for implant success, flapless surgery
may remove vital tissue that can improve oral hygiene and act as protection over the implant.
Also, lack of a full thickness periodontal flap can inhibit correcting soft tissue insufficiencies that
may be a crucial part in esthetics and longevity of the implant (Romero-Ruiz et al., 2015).
Therefore, our observation is that the decision to raise a flap or not should not be based on the
success of implant integration but should be decided based on the soft tissue management
parameters and/or the need to modify the ridge for implant placement.

Similar to current literature, in our analysis we observed that implants placed with flap
surgery presented with more radiographic bone loss than those with a flapless surgical method.
26
However, these differences were not meaningful in terms of implant failure. One, study showed
crestal bone loss with flap surgeries and no bone loss with flapless surgeries (Tsoukaki et al.,
2013). They also reported flapless surgeries had better clinical, radiographic, and immunological
outcomes (Tsoukaki et al., 2013). Another study showed no statistical differences of bone
resorption between flap and flapless surgeries. It also reported that surgery approach made no
difference on peri-implant bone loss (Pisoni et al., 2016).

In this study 80% (N=8 out of 10) of implant failures occurred within 1 year of
placement. Only 20% (N=2 out of 10) of failed implants failed after 1 year of placement. This
observation was consistent with recent studies for implant failure timing. Levin (2006) showed
that 94.8% of implants in their study also failed within the first year of placement. Similar results
were also found by Rasmusson (2005), in which there was a 96.9% implant success rate, and all
implants that failed occurred within 1 year of placement. The present study had 90% (N=9 out of
10) implant failures in platform-switching implants. Currently, there is no reported evidence
available in the literature about the correlation of implant failure to platform-switching implants,
so this observation could be a coincidental one.

Generally, the initial bone biological response to an implant is to separate the foreign
body from the tissues (Albrektsson et al., 2016). A study by Cecchinato (2013) states that out of
407 implant sites, 229 implants (56%) had marginal bone loss >0.5 mm at the 1 year follow-up,
and only 11% of sites lost greater than 1 mm of marginal bone. Another study suggests that when
assessing implant survival and success, marginal bone levels should be less than 1-1.5 mm
within 1 year of implant placement, and ongoing annual bone loss should be less than 0.2 mm
27
(Albrektsson et al., 1986). A review completed on Brånemark implants reported that after the
first year of loading, the mean marginal bone loss was 1.5mm, with a range of 0.4-1.6 mm (Adell
et al., 1981). Therefore, in the present study, ³1 mm of bone loss was marked as an observation
point. In addition, 67 out of 209 cases, or 32.06% of platform-switching implants had ³1mm
bone loss, whereas 52 cases, or 53.61% of non platform-switching implants had ³1mm bone
loss. Currently the review of literature and consensus reports support the notion that platform-
switching implants where the restorative abutments are smaller than the diameter of the implant
restorative platform, limit the amount of remodeling/crestal bone loss (Hagiwara, 2009).
Ericsson (1995) describes a biological process responsible for this. The study suggests that 1 mm
of healthy connective tissue always surrounds bone, and that crestal bone remodeling occurs in
order to create space between bone and inflammatory cell tissue in order to institute a biological
seal surrounding the implant and abutment platform. The crestal bone loss/remodeling could also
be related to the presence of microleakage or a microgap at the abutment-to-implant junction
(Hermann et al., 2001), which is present amongst different implant systems with external,
internal, or morse-tapered design (Abrahamsson et al., 1997). Additionally, the depth of implant
placement may influence inflammatory processes at the implant/abutment interface leading to an
increased inflammatory process in the crestal and subcrestal placement compared to supracrestal
placement (Broggini et al., 2006). A study by Piattelli et al. (2003) states that subcrestal implant
placement can cause bacterial colonization at the implant-abutment junction and therefore a low
concentration of oxygen which can heighten production of anaerobic bacteria causing an increase
in bone loss. It has been our observation that implants without a platform-switching feature
exhibit bone remodeling that extends laterally to the implant platform creating a “V” shape
appearance on radiographs. However, platform-switching implants do not generally express bone
28
remodeling extending laterally, and the bone remodeling tends to be internalized creating a
trough between the bone and implant that is apparent upon clinical observation but may not be
expressed clearly in radiographs. Furthermore, platform-switching implants tend to be placed
more subcrestally than non platform-switching implants. This variance in implant depth
combined with internal remodeling of the bone will give an appearance of less crestal bone
remodeling amongst platform-switching implants during radiographic observation.

Our logistical regression analysis found that non-platform implants had 3.92 times higher
odds of ³1mm bone loss than platform implants. Platform-switching implants tend to be placed
more subcrestal, and crestal bone remodeling is more detectable on radiographs. A study by
Vervaeke (2018) showed that at 6-month, 1-year, and 2-year follow-ups, implants placed
subcrestal versus crestal had significantly higher bone levels. Another study retrospectively
examined histology of implants placed equicrestal and subcrestal; similarly, the results showed
that in all implants that were placed subcrestally, preexisting and newly formed bone was seen
over the implant shoulder, with no resorption of crestal bone (Degidi et al., 2011).

It must be recognized that although novel, this study has several limitations. Two-
dimensional radiographs were utilized in the study without positional consistency in subsequent
radiographs for each case. In addition, some cases had to compare interproximal radiographs to
periapical radiographs with differences in parallelism, which could have caused discrepancies in
radiographic calibration values. Furthermore, due to the retrospective nature of the study,
electronic records were limited to patient notes completed by several different providers. This
29
also may have contributed to data inconsistency due to presentation of data in individualized
records where relevant information was not always recorded.

Although several of the results of the descriptive analysis can be confirmed in the
literature, it should be noted that further studies are needed in order to establish concrete
evidence on the feasibility of using surgical guides.

30
5. Conclusion:

Within the limitations of this study, we reached the following conclusions based on our
data analysis and observations:
1) In 18.30% of surgeries a guide ultimately could not be used requiring free-hand
surgery.
2) In 54.90% of cases a fully guided surgery could not be performed, and implants were
placed freehand
3) The implant success rate was 96.73% regardless of flap or flapless surgery.
4) Flap surgery was found to have 2.98 times higher odds of ³1mm bone loss than
flapless surgery.
5) Non platform-switching implants had 3.92 times higher odds of ³1mm bone loss than
platform-switching implants, although 9 platform-switching implants failed, and only
1 non platform-switching implant failed.
6) There was no significant difference of bone loss with one-stage vs two-stage surgery,
reasons for tooth loss, and implant diameter

Although this study was the first to assess the feasibility of guided surgery, future studies
are necessary. Guided surgery can be a useful tool for implant placement, however, there are
limitations and challenges in clinical implementation. Some of these challenges negate the use of
the guide and requires some surgical expertise to overcome and correct the shortcomings.

31
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35
TABLES

Table 1: Demographics
Subjects
Male 106
Female 141

Table 2: Implant Systems
Implant System Implants
Zimmer Biomet 3i 97
Straumann Bone Level 156
Dentsply/Astra EV 53

Table 3: Bone Augmentation Cases
Frequency
No Augmentation 278
Augmentation 25
Unknown 3
Total 306

Table 4: Bone loss
Bone loss Flap Buccal
flap, only
Initially
no,
ultimately
full
thickness
flap
Flapless Unknown Total Percentage
³1mm bone
loss
96 1 0 19 3 119 38.89%
<1mm bone
loss
16 0 0 7 0 23 7.52%
No bone loss 72 0 1 32 7 112 36.60%
Unknown 7 0 0 5 0 12 3.92%
Implant
failure/not
yet loaded
29 0 1 7 3 40 13.07%
Total 220 1 2 70 13 306 100%

36
Table 5: Implant Failure
Time Number of Implants Percentage
<2 months 2 20%
2 – 6 months 4 40%
6 months – 1 year 2 20%
2 – 2.5 years 2 20%
Total 10 100%

Table 6: Bone loss with platform-switching implants and non platform-switching implants
Bone loss Number of implants Percentage
³1mm, platform-switching* 67 32.06%
<1mm, platform-switching* 16 7.66%
³1mm, non platform-switching** 52 53.61%
<1mm , non platform-switching** 7 7.22%
None, platform-switching* 86 41.15%
None, non platform-switching** 26 26.80%
*platform-switching implants include Straumann and Astra implants, percentage calculated from a total of 209 cases
**non platform-switching implants include Biomet 3i implants, percentage calculated from a total of 97 cases

Table 7: Excluded implants from data analysis
Excluded Number of implants Percentage
Non-diagnostic, platform-switching* 10 4.78%
Non-diagnostic, non platform-
switching**
2 2.06%
Implant failed/implant not loaded,
platform-switching*
30 14.35%
Implant failed/implant not loaded,
non platform-switching**
10 10.31%
*platform-switching implants include Straumann and Astra implants, percentage calculated from a total of 209 cases
**non platform-switching implants include Biomet 3i implants, percentage calculated from a total of 97 cases

Table 8: Implant types
Type of implant Number of implants
Platform-switching 209
Non platform-switching 97
Total 306

37
Table 9: Implant failure comparing platform-switching to non platform-switching
Implant Failure Number of implants failed Percentage
Platform-switching 9 90%
Non platform-switching 1 10%
Total 10 100%

Table 10: Frequency and percentage of fully or partially guided cases with Biomet 3i implants
Frequency Percentage
Fully Guided 70 72.16%
Partially Guided 21 21.65%
Unknown 6 6.19%
Total 97 100%

Table 11: Frequency and percentage of fully or partially guided cases with Straumann Bone
Level and Dentsply/Astra EV implants

Frequency Percentage
Fully Guided 51 24.4%
Partially Guided 147 70.33%
Unknown 11 5.26%
Total 209 100%

Table 12: Total frequency and percentage of fully or partially guided cases with Zimmer
Biomet 3i, Straumann Bone Level and Dentsply/Astra EV implants

Frequency Percentage
Fully Guided 121 39.54%
Partially Guided 168 54.90%
Unknown 17 5.56%
Total 306 100%

38
Table 13: Multicollinearity analysis of predictors
Variable DF Parameter
Estimate
Standard
Error
t Value Pr > |t| Tolerance
Intercept 1 0.36701 0.39986 0.92 0.3596
Flap surgery 1 0.24035 0.07326 3.28 0.0012 0.97406
Implant system 1 0.31132 0.07629 4.08 <.0001 0.73393
One-stage 1 0.04231 0.06951 0.61 0.5433 0.96655
Reason for tooth loss 1 0.14233 0.17327 0.82 0.4122 0.99491
Implant diameter 1 -0.08805 0.08579 -1.03 0.3058 0.76682

Table 14: Analysis of effects
Effect DF Wald Chi-Square Pr > Chisq
Flap surgery 1 10.0971 0.0015
Implant system 1 15.1517 <.0001
One-stage 1 0.3688 0.5436
Reason for tooth loss 1 0.6222 0.4302
Implant diameter 1 1.1142 0.2912

Table 15: Odds ratio estimates
Effect Point Estimate 95% Wald Confidence Limits
Flap vs flapless surgery 2.976 (1.519, 5.831)
Platform-switching vs non
platform-switching
3.916 (1.969, 7.787)
One-stage vs two-stage 0.831 (0.458, 1.509)
Reason for tooth loss
(periodontal vs non-periodontal)
1.832 (0.407, 8.251)
Implant diameter 0.671 (0.320, 1.407)

Table 16: Analysis of implant failure compared with flap surgery
Effect DF Wald Chi-square Pr > ChiSq
Flap surgery 1 1.4114 0.2348

39
Table 17: Odds ratio estimates of implant failure compared with flap surgery
Effect Point Estimate 95% Wald Confidence Limits
Flap vs flapless surgery 2.192 (0.601, 8.001)

40
FIGURES

Figure 1: Diagnostic wax-up, buccal view

Figure 2: Diagnostic wax-up, occlusal view

41
Figure 3: Analog impression

Figure 4: Surgical guide

42
Figure 5: Zimmer Biomet 3i Certain collar length

Figure 6: Zimmer Biomet 3i Certain implant diameter

43
Figure 7: Zimmer Biomet 3i Certain implant length

Figure 8: Straumann Bone Level collar length

44
Figure 9: Straumann Bone Level implant diameter

Figure 10: Straumann Bone Level implant length

45
Figure 11: Dentsply/Astra EV implant diameter

Figure 12: Dentsply/Astra EV Implant length

46
Figure 13: Bone Loss (mesial)

Figure 14: Bone Loss (distal)

47
Figure 15: Guided surgery planning

Figure 16: Flap vs Flapless

Flap
72.88% (n=223)
Flapless
22.88% (n=70)
Unknown
4.25% (n=13)
Flap Flapless Unknown
48
Figure 17: Number of Failures in Flap versus Flapless Cases

Figure 18: Percentage of Failures in Flap versus Flapless Cases

6
4
0
1
2
3
4
5
6
7
# failed in flap # failed in flapless
3.27%
1.96%
1.31%
0.00%
0.50%
1.00%
1.50%
2.00%
2.50%
3.00%
3.50%
% all failures % failed in flap % failed in flapless
49
Figure 19: Guided versus Non-Guided Case Frequency and Percentage

233
56
17
76.14%
18.3%
5.56%
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
Guided Non-Guided Unknown
Frequency Percentage
50
Figure 20: Bone Augmentation Percentage

Figure 21: One-stage versus two-stage

90.85%
8.17%
0.98%
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
No Augmentation Augmentation Unknown
210
94
2
68.63%
30.72%
0.07%
0
50
100
150
200
250
one stage two stage Unknown
Frequency Percentage
51
Figure 22: Bone-loss with platform-switching implants and non platform-switching implants

Figure 23: Excluded implants from data analysis

67
16
52
7
86
26
32.06%
7.66%
53.61%
7.22%
41.15%
26.8%
0
10
20
30
40
50
60
70
80
90
100
≥1mm bone loss
platform-switching
(Straumann, Astra)
<1mm bone loss
platform-switching
(Straumann, Astra)
≥1mm non platform-
switching (Biomet 3i)
<1mm non platform-
switching (Biomet 3i)
No bone loss platform-
switching (Straumann,
Astra)
No bone loss non
platform-switching
(Biomet 3i)
# of implants Percentage
10
2
30
10
4.78%
2.06%
14.35%
10.31%
0
5
10
15
20
25
30
35
Unclear/unknown
platform-switching
(Straumann, Astra)
Unclear/unknown non
platform-switching
(Bionet 3i)
Implant failed/implant
not loaded platform-
switching (Straumann,
Astra)
Implant failed/implant
not loaded non
platform-switching
(Biomet 3i)
# of implants Percentage
52
Figure 24: Frequency and percentage of fully or partially guided cases with Biomet 3i
implants

Figure 25: Frequency and percentage of fully or partially guided cases with Straumann Bone
Level and Dentsply/Astra EV implants

70
21
6
72.16%
21.65%
6.19%
0
10
20
30
40
50
60
70
80
Fully Guided Partially Guided Unknown
Frequency Percentage
51
147
11
24.4%
70.33%
5.26%
0
20
40
60
80
100
120
140
160
Fully Guided Partially Guided Unknown
Frequency Percentage
53
Figure 26: Total frequency and percentage of fully or partially guided cases with Zimmer
Biomet 3i, Straumann Bone Level and Dentsply/Astra EV implants

121
168
17
39.54%
54.90%
5.56%
0
20
40
60
80
100
120
140
160
180
Fully Guided Partially Guided Unknown
Frequency Percentage

Abstract (if available)

Abstract Background: Restorative-driven implant dentistry is a process in which the prosthetic outcome precedes implant placement planning. Ultimately a digital impression is taken, and a surgical stent can be fabricated. Several advantages and disadvantages exist when it comes to guided surgery, in addition to the practicability of using the guide. Therefore, the primary aim of this retrospective study is to assess the implant success through placement via a guided surgery system, and the feasibility of using that guide. The secondary aims were to evaluate the crestal bone loss and the factors that attributed to implant failure. ? Methods: Electronic dental records were examined of 306 implant sites 6 months to 6 years after implant loading from January 2014 to December 2019 at the undergraduate implant clinic at the Herman Ostrow School of Dentistry. Implant measurements were completed for 3 different implant systems placed at the Herman Ostrow School of Dentistry: Zimmer Biomet 3i, Straumann, Astra. When the guide could be utilized for both the osteotomy and implant placement, it was categorized as the guided group. When the guide could not be utilized for surgery, it was categorized as the non-guided group. When the guide could be used for the osteotomy but not implant placement, it was categorized as the partially guided group. Radiographic bone measurements were taken at time of implant placement, at time of loading, and the latest survival date of the implant. Bone loss was compared to the following: flap or no flap, implant system, one-stage or two-stage, reason for tooth loss, and implant diameter. ? Results: The frequency of guided verses non-guided surgeries was 233 (76.14%) and 56 (18.30%) surgeries, respectively. 17 (5.56%) surgeries were unknown. 6 cases, or 60% of implants in the flap group failed; 4 cases, or 40% of implants in the flapless group failed. 43.4% (96/220) of flaps had ?1mm bone loss, and 27% (19/70) of flapless had ?1mm bone loss. A logistic regression model found flap surgery to be significant (p<0.0015), such that flap surgery had 2.98 times higher odds of ?1mm bone loss than flapless surgery (95% CI 1.52–5.83). Implant system was also significant (p<0.0001), such that non-platform switching implants had 3.92 times higher odds of ?1mm bone loss than platform-switching (95% CI is 1.97–7.79). One-stage vs two-stage surgery (p=0.53), reason for tooth loss (0.43), and implant diameter (p=0.29) were not significant when compared to bone loss. A logistic regression analysis of implant failure compared with flap surgery did not find any significant difference (p=0.23). ? Conclusion: Within the limitations of this study, we reached the following conclusions based on our data analysis and observations: ? 1) In 18.30% of surgeries a guide ultimately could not be used requiring free-hand surgery. ? 2) In 54.90% of cases a fully guided surgery could not be performed, and implants were placed freehand ? 3) The implant success rate was 96.73% regardless of flap or flapless surgery. ? 4) Flap surgery was found to have 2.98 times higher odds of ?1mm bone loss than flapless surgery. ? 5) Non platform-switching implants had 3.92 times higher odds of ?1mm bone loss than platform-switching implants, although 9 platform-switching implants failed, and only 1 non platform-switching implant failed. ? 6) There was no significant difference of bone loss with one-stage vs two-stage surgery, reasons for tooth loss, and implant diameter ? Although this study was the first to assess the feasibility of guided surgery, future studies are necessary. Guided surgery can be a useful tool for implant placement, however, there are limitations and challenges in clinical implementation. Some of these challenges negate the use of the guide and requires surgical expertise to overcome and correct the shortcomings.

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Creator Mehra, Sanchita (author)

Core Title Analysis of clinical outcomes of implants via a guided surgery system: a retrospective radiographic analysis

School School of Dentistry

Degree Master of Science

Degree Program Biomedical Implants and Tissue Engineering

Degree Conferral Date 2021-08

Publication Date 07/23/2021

Defense Date 05/11/2021

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag analysis,Astra,clinical,feasibility,flap surgery,flapless surgery,free-hand surgery,fully guided,guided,guided surgery,implants,non guided,non platform switching,non platform-switching,non-guided,OAI-PMH Harvest,one stage,one-stage,platform switching,platform-switching,radiograph,radiographic,retrospective,Straumann,Surgery,two stage,two-stage,Zimmer Biomet 3i

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