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Association between the depth of implant cover screw and the marginal bone loss with the use of a removable provisional restoration: a retrospective two-dimensional radiographic evaluation
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Association between the depth of implant cover screw and the marginal bone loss with the use of a removable provisional restoration: a retrospective two-dimensional radiographic evaluation
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i
Association between the depth of implant cover screw and the marginal bone loss with the use of
a removable provisional restoration: A retrospective two-dimensional radiographic evaluation
By
Mylea Wilson Hunter, RDH BS, DDS
A Thesis Presented to the
FACULTY OF THE USC HERMAN OSTROW SCHOOL OF DENTISTRY
UNIVERSITY OF SOUTHERN CALIFONRIA
In Partial Fulfilment of the
Requirements for the Degree
MASTER OF SCIENCE
(BIOMEDICAL IMPLANTS AND TISSUE ENGINEERING)
August 2023
Copyright 2023 Mylea Hunter
ii
Table of Contents
List of Figures…………...……………………………………………….………………….……iii
Abstract……..…………………………………………………………………………………….iv
Introduction………………………………………………………………….…………………….1
Chapter 1: Methods & Materials…………………………………………………………………..4
Chapter 2: Results…………………………………………………………………………………7
Chapter 3: Discussion..………………………………………………………………………..…10
Chapter 4: Conclusion……………………………………………………………………………14
References….…………………………………………………………………………………….15
Figures and Table………………….……………………………………………………..………18
iii
List of Figures
Figure 1. Example of 2D Radiographs of
Straumann Bone Level Implant and calibration
measuring tool……………………………………………………………………………………18
Figure 2. Example of 2D Radiographs of
Zimmer Biomet 3i Certain Implant and calibration
measuring tool……………………………………………………………………………………19
Figure 3. Example of 2D Radiographs of
Astra Tech OsseoSpeed EV Implant and calibration
measuring tool……………………………………………………………………………………20
Figure 4. Mean Mesial Cover Screw Depth……………………………………………………..21
Figure 5. Mean Distal Cover Screw Depth……………………………………………………...22
Figure 6. Mean Mesial Cover Screw Depth at
Implant Placement and at Implant Uncovery for
each group: sub-crestal placement (N=56),
equi-crestal placement (N=6), and supra-crestal
placement (N=5)…………………………………………………………………………………23
Figure 7. Mean Distal Cover Screw Depth at
Implant Placement and at Implant Uncovery for
each group: sub-crestal placement (N=56),
equi-crestal placement (N=6), and supra-crestal
placement (N=5)…………………………………………………………………………………24
Figure 8. Mean Mesial Bone Change from
Placement to Uncovery……………………………………………………………………..……25
Figure 9. Mean Distal Bone Change from
Placement to Uncovery……………………………………………………….………………….26
Figure 10. Pearson Correlation plot graph
of the mesial bone level change……………………………………………………….…………27
Table 1. Difference of Square Means Mesial
and Distal Measurements…………………………………………………………….…………..28
iv
Abstract
This study seeks to investigate the effect of vertical position of the cover screw on the
early marginal bone loss around dental implants. The aim of this retrospective observational
study was to determine if there is a relationship between the vertical position of the cover screw
with the crestal bone remodeling around dental implants when using removable prostheses.
Electronic dental records were obtained from patients who underwent dental implant
placement in a two-stage protocol and were prescribed a removable prosthesis to be worn during
the interim. The implant systems represented in the study were Straumann Bone Level NC or
RC, Astra Tech OsseoSpeed EV, and Zimmer Biomet 3i Certain. Two-dimensional radiographs
that were taken at implant placement and implant uncovery were evaluated and mesial and distal
apicocoronal bone levels were measured from the height of the coverscrew to the crestal of the
bone. The vertical height of the implant cover screws was defined as sub-crestal, equi-crestal, or
supra-crestal.
Charts of 50 patients and 67 implants were included. The statistical analysis showed that
the vertical position of the cover screw (sub-, equi- or supra-crestal) significantly affected the
mesial marginal bone, such that equi-crestal group showed the highest marginal bone loss
compared either the sub-crestal or supra-crestal groups (P=0.0056 and 0.008, respectively). No
statistically significant difference was found between sub-crestal vs. supra-crestal group
(p=0.3645). When evaluating for correlation between sub-crestal implant placement depth and
amount of bone changes on the mesial aspect there was a statistically significant inverse
correlation between placing the implant beyond 1.2mm to obtain less bone loss (p=0.02). The
distal marginal bone levels did not show any significant difference between the groups.
1
Introduction
The placement of dental implants in a two-stage “submerged” surgical approach has
remained an advantageous protocol when bone augmentation is needed in conjunction with
implant placement, if soft tissue deficiencies are present at the time of implant placement or if
the osteotomy site(s) exhibit areas of loose trabecular bone, grafted sites, and sites with lesser
implant stability. Primary stability of the implant occurs at the time of implant placement and
secondary stability of the implant is achieved over time with healing. Factors influencing
primary stability include macro and micro design of the implant threads, implant surfaces,
quality, and quantity of surrounding bone, which will determine the percentage of contacts
between the implant and bone (19). When preparing an osteotomy site for a dental implant
placement Branemark et al. (2) recommended the use of a countersink drill and sub-crestal
implant placement preventing implant exposure during bone remodeling. Several human and
animal studies have evaluated sub-crestal verse equi-crestal placement of dental implants and
described influence of subsequent bone remodeling, resulting in resorption or formation of newly
formed bone over the implant shoulder, to evaluate the changes to the position of the soft tissue
margin (5,15). However, when the patient is prescribed an interim removable prosthesis to wear
from the time of implant placement to the time of implant uncovery the depth of implant
placement may influence crestal bone remodeling given the constant mucosal loading of the
interface with the removable prosthesis and the underlying soft tissue overlying the implant
platform.
According to Siddat et al., the influence of interim prostheses can be categorized in three
therapy phases: phase one prior to implant placement, phase two following implant placement,
not loaded, and phase three after placing the implant in the loading time (17). During phase one,
2
following tooth extraction a fixed or removable interim prosthesis may be prescribed. Interim
prostheses are prescribed to enhance esthetics, provide stabilization, and may act as a guide in
designing the definitive prosthesis (8). Removable prosthetic options include an essix appliance,
resin-based removable prostheses, resin-based removable prostheses with metal clasps, or
removable prostheses with metal framework. The advantage of an essix appliance is limited
trauma upon the surgical site. The disadvantages of an essix appliance include the inability to
capture the surrounding soft tissue contours, lack of patient compliance and compromised
esthetics. The advantages of the resin-based removable prostheses with or without metal clasps
or framework include lower treatment cost, ease of removal and replacement, simple fabrication
and that they can be worn prior to implant placement. The disadvantages of the resin-based
removable prostheses with or without metal clasps or framework include instability during
speaking or chewing, undesirable pressure upon grafted sites and uncontrolled implant loading
(4). Immediate or early (1-2 weeks following placement) soft tissue loading of implant platform
by removable prosthesis decreased rigidity of the bone is observed which may be indicative of
bone resorption. Therefore, care must be taken to control against overload. It is also important to
recognize that sites with limited primary stability or less bone-to-implant contact will go through
a period of even less bone support in the early stages of bone healing due to the initial phase of
bone resorption (18).
Numerous studies have been conducted evaluating the bone remodeling that occurs
following placement of dental implants when loaded with a fixed prosthesis. Our study is
conducted to evaluate the relation of the vertical placement of the implant to bone remodeling
when a removable prosthesis is worn during the interim phase between implant placement and
implant uncovery. To the best of our knowledge, this is the first study to evaluate the effect of
3
coverscrew depth on bone remodeling when a removable prosthesis is worn during the healing
phase between implant placement and implant uncovery.
A retrospective two-dimensional radiographic evaluation was conducted to evaluate the
effect of the vertical position of implant cover screw to the mesial and distal marginal bone
changes between implant placement and implant uncovery/second stage in patients prescribed
removable prostheses. The occluso-gingival height of the implant cover screws was defined as
sub-crestal, equi-crestal, or supra-crestal. Our hypothesis is that if the implant coverscrew is
located slightly sub-crestal at time of implant placement there will be less incidence of marginal
bone level changes when compared to implant cover screws that are placed equi-crestal or supra-
crestal. The null hypothesis was that the apico-coronal position of the cover screw has no effect
on the mesial or distal marginal bone loss around implants in patients wearing removable
prostheses.
4
Chapter 1: Methods and Materials
Study Design:
This study was conducted using the Herman Ostrow School of Dentistry of USC patient records.
The University of Southern California Institutional Review Board (IBR) approved the use of
patient records for this retrospective study (HS-22-00295). Radiographs, and chart note
documentation records for 274 implants were acquired from the Herman Ostrow School of
Dentistry of USC Axium Records from September 2017 to December 2022.
Study Population:
The study population was patients treated by the pre-doctorate or post-doctorate implant
programs under surgical faculty supervision (Periodontists or Oral and Maxillofacial Surgeons).
Inclusion criteria:
The inclusion criteria for the study: (1) All patients were diagnosed with partial or full
edentulism, treatment planned for tooth replacement via dental implant(s) and prescribed a
removable provisional prosthesis via either an interim partial or complete denture or cast-metal
removable partial or complete denture prior to dental implant placement. The purpose of this was
to limit the variability of those not wearing a prosthesis. (2) All implants were placed in a two-
stage protocol with implant cover screws. (3) All implants evaluated were internal connection
systems which included three implant systems: Straumann Bone Level, Astra Tech OsseoSpeed
EV and Zimmer Biomet 3i Certain.
Exclusion Criteria:
The exclusion criteria for the study: (1) Implants placed without interim removable prosthesis
prescription and evidence of delivery in clinical chart notes. (2) Implants placed in one-stage
protocol receiving a healing abutment. (3) Implants that are designed with an external
5
connection. (4) Radiographs that were non-diagnostic where the mesial and distal bone levels
could not be discerned. (5) Medically compromised patients with uncontrolled medical
conditions.
Clinical Records Assessment:
An Axium search query was pulled via the surgical implant body placement code and the interim
removable complete and partial denture codes. From there, 274 implants with removable
prostheses were identified and two-dimensional radiographs, medical history records, clinical
chart notes and scanned implant identification were obtained. From there, chart notes were
reviewed for “adjustments made to the prosthesis at time of implant placement”, implant site,
maxilla vs. mandible, which implant system and size was placed, stability documented, bone
type (9), date of implant placement, date of implant uncovery, if the implant was placed
immediately and if bone augmentation was performed simultaneously with the implant
placement.
Radiographic Assessment:
The mesial and distal radiographic measurements extended from the height of the implant cover
screw to the level of the alveolar crest were calibrated using the Schick radiographic calibrating
measuring tool (see Figure 1) to the diameter of the implants documented in the clinical chart
note and uploaded implant serial number. Each implant that was evaluated radiographically was
placed into one of the three placement groups: “sub-crestal”, “equi-crestal”, or “supra-crestal”.
The values measured were positive integers for the “sub-crestal” group, zero for the “equi-
crestal” group and negative integers for the “supra-crestal” group.
6
Statistical Analyses:
Descriptive statistics were calculated for all variables of interest. Continuous measures
were summarized using means and standard deviations whereas categorical measures were
summarized using counts and percentages. The variables were assessed for normality using a
Shapiro-Wilk test. Changes over time in variables such as mesial depth and distal depth were
analyzed using paired t-tests (p<0.05). Changes between sites “sub-crestal”, “equi-crestal”, and
“supra-crestal” placement over time were assessed using linear mixed models adjusting for the
correlation among observations taken on the same aspect, mesial or distal. Comparisons between
continuous variables such as mesial depth at implant placement (in millimeters) to the difference
between mesial depth at implant placement (in millimeters) vs mesial depth at implant uncovery
(in millimeters) were run using Pearson correlation coefficients. All analyses were carried out
using SAS Version 9.4 (SAS Institute, Cary, NC, USA).
7
Chapter 2: Results
Patients’ and Implant demographics:
Out of the 274 implants evaluated radiographically and from past clinical chart documentation,
only 67 met the study criteria. The 67 implants were placed in 50 patients at the Herman Ostrow
School of Dentistry of USC from September 2017 to November 2022, 23 males and 27 females.
The following implants were included: 49 Straumann Bone Level, 7 Astra Tech OsseoSpeed EV,
and 11 Zimmer Biomet 3i Certain. All two-dimensional radiographic measurements were
measured by one individual (MH) to eliminate any inter-examiner measurement discrepancies.
To evaluate the relation of coverscrew level to amount of bone remodeling at uncovery, the level
of coverscrew to the mesial and distal alveolar ridge of implant was measured based on
radiograph at time of implant placement and uncovery (Fig. 1-3).
Analysis of Mesial Bone Changes:
At the mesial site, the measurement of the level of coverscrew to mesial alveolar ridge was
1.11mm (SD = 0.90mm) at the time of implant placement and 0.84mm (SD = 1.04mm) at the
time of uncovery (Fig. 4). There was a statistical significance between the mesial bone height at
implant placement to mesial bone height at implant uncovery (p = 0.005; paired t-test). Further
analysis was performed to evaluate the amount of bone remodeling at the time of uncovery in
different sub-groups of implant placement levels, including sub-crestal, equi-crestal and supra-
crestal. In the equi-crestal group, the mesial bone level compared to the level of the cover screws
was 0.38 mm (SD = 0.61) at the time of implant placement and -0.73 mm (SD = 1.66) at the time
of uncovery, which showed a greater negative difference of bone level (Fig. 6). There was a
statistically significant difference of bone remodeling at the time of uncovery between sub-
crestal vs. equi-crestal groups (p=0.0056) and equi-crestal vs. supra-crestal groups (p=0.008)
8
(Fig. 6 and Table 1). However, no statistically significant difference was identified between the
sub-crestal vs. the supra-crestal group (p=0.3645) for the bone remodeling at the time of implant
uncovery (Fig. 6 and Table 1). When evaluating for correlation between the depth of sub-crestal
implant placement and amount of bone changes on the mesial aspect, there was a statistically
significant inverse correlation beyond the level of 1.2mm of implant placement sub-crestally
which showed no statistically significant bone changes (p = 0.02; Fig 10).
Analysis of Distal Bone Changes:
A similar analysis was performed on the distal site of implant to evaluate the bone changes
between implant placement and uncovery at the distal aspect. The level of coverscrew to distal
alveolar ridge was 0.98mm (SD = 0.72mm) and 0.73mm (SD = 1.08mm) at the time of implant
placement and uncovery, respectively (Fig. 5). There was a statistical significance between distal
bone height at implant placement to distal bone height at implant uncovery (p = 0.005; paired t-
test). However, in the evaluation of sub-groups (sub-, equi- or supra-crestal implant placements),
no statistically significant difference was detected between the groups (Fig. 7, 9 and Table 1).
The following data were also analyzed:
Maxillary vs mandibular sites: No statistical differences found comparing the difference between
maxillary implant (53) and mandibular implants (14) (p=0.56).
Primary stability: 2 implants did not report the primary stability achieved, 27 implants were
placed with a primary stability of £ 25Ncm, and 38 implants were placed with a primary stability
> 26 Ncm. A t-test showed no statistical differences comparing the difference between levels of
this variable (p=0.64).
No augmentation vs simultaneous augmentation via bone grafting and/or soft tissue grafting: 35
implants were placed with augmentation and 32 implants were placed without augmentation. A t-
9
test showed no statistical differences comparing the difference between levels of this variable
(p=0.74).
10
Chapter 3: Discussion
When placing dental implants, the surgeon may elect to place the implant in a two-stage
protocol with a coverscrew in place due to low bone density or quality, ridge location or in a
previously or simultaneously placed hard or soft tissue graft material to allow for submerged
healing. Consequently, the patient may wear a fixed or removable partial denture to provide them
with provisional tooth replacement during the osseointegration healing period. Our study
included patients who wear removable prostheses that were supported either by surrounding
dentition or soft tissue. We evaluated the marginal bone remodeling and vertical position of the
implant cover screw. Implants were placed in a two-stage protocol in individuals wearing
removable prostheses as tooth replacement from the time of implant placement to the time of
implant uncovery. Our hypothesis was that when individuals are wearing removable prostheses
there will be increased bone remodeling around the implant cover screw when the vertical
position of the implant cover screw is at the level of the crest of the alveolar bone or slightly
supra-crestal to the level of the alveolar bone. On the other hand, we hypothesized that the
implants placed subcrestally with cover screw positions below the crest of the alveolar bone
would present with less evidence of bone remodeling from the time of implant placement to the
time of implant uncovery.
Previous pre-clinical and clinical studies have been performed evaluating two-
dimensional radiographic marginal bone remodeling around the implant platform from the time
of implant placement to the time of prosthetic loading: whether it be immediate loading or
conventional loading (7, 3, 11, 15). Additionally, previous literature has described methods,
guidelines, advantages, and disadvantages for interim tooth replacement via interim removable
prostheses, interim prostheses fixed to adjacent teeth or implants and interim immediately loaded
11
implants (17, 4, 12). However, to the best of our knowledge, no study to date has evaluated the
vertical position of the implant coverscrew radiographically from time of implant placement to
the time of implant uncovery in individuals prescribed interim removable prostheses. In our
study we evaluated implants placed in a two-stage protocol by measuring the height of the
implant cover screw, rather than the implant platform, to the height of the interproximal bone
level in two-dimensional radiographs. We measured the mesial bone heights and the distal bone
level heights at the time of implant placement and implant uncovery by using the measuring tool
on Axium, calibrating the measurements to the reported diameter of the dental implant platform.
We categorized the implant cover screw depths as sub-crestal, equi-crestal, or supra-crestal
depending on the relation to the mesial and distal alveolar crest.
Furthermore, both the mesial and distal bone levels presented with statistically significant
changes from time of implant placement to time of implant uncovery. However, when evaluating
the mesial bone level changes the equi-crestal implant placement group presented with the most
significant bone changes when compared to the sub-crestal and supra-crestal implant placement
groups. One could infer that by placing the implant cover screw at the same level of the alveolar
crest the forces applied to the removable prosthesis are translated to the underlying bone
surrounding the implant cover screw and lead to pressure-induced marginal bone loss (9). On the
other hand, this marginal bone remodeling in equi-crestally placed implants could also signify
biological width adjustments occurring within the first few months of implant placement and
could be related to the implant design and the abutment-implant connection in relation to bone
(6). Alternatively, when the implant cover screw is located 0.5mm to 1.2mm sub-crestal, less
bone remodeling occurs from the time of implant placement to implant uncovery than the bone
remodeling found when the cover screw is placed less than 0.5mm subcrestal. However, when
12
the dental implant is placed beyond 1.2mm sub-crestal, an inverse correlation was found where
there is more marginal bone loss. This observation may indicate that perhaps bone is more likely
to grow over the coverscrew of the implant when placed beyond 1.2mm (5).
This study has several limitations. One is that since the study was performed
retrospectively via two-dimensional radiographs it is impossible to determine whether the
angulation of the radiographs was consistent at the time of implant placement and implant
uncovery. Secondly, many patients did not have a radiograph with the cover screw at time of
uncover only a follow-up radiograph with the healing abutment in place was available at the time
of implant uncovery. Thirdly, although all patients were prescribed removable prostheses to wear
during the time between implant placement and implant uncovery it is impossible to discern
whether all patients where consistent with wearing their prostheses throughout this period. For
some patients, esthetic demand is low, and they may refrain from wearing the prosthesis during
the healing phase from implant placement to implant uncovery. Additionally, we did not analyze
radiographic bony changes amongst the population for whom an interim removable prosthesis
was not prescribed, therefore; we cannot deduce whether the bone changes measured were as a
result from the removable prosthesis or not. Additionally, this study evaluated three different
implant systems: Straumann Bone Level, Astra Tech OsseoSpeed EV and Zimmer Biomet 3i
Certain. Although all three systems are internal connection, they have differences. Both
Straumann Bone Level and Astra Tech OsseoSpeed EV are platform switched as opposed to
Zimmer Biomet 3i Certain. The Zimmer Biomet 3i Certain has a polished collar with machined
surface on coronal 3 mm. Astra Tech OsseoSpeed EV presents with coronal micro thread and
rough surface. Straumann bone level presents with SLA rough surface. Other than these systems
all being internal connection implant devices they all exhibit different designs, sizes, thread
13
presentation, surface treatments, etc. (12, 14, 13). Therefore, there are many variables to take
into consideration. Future studies should be designed with implants manufactured specifically for
a more controlled research study to eliminate such variables.
14
Chapter 4: Conclusion
In conclusion, we retrospectively evaluated two-dimensional radiographs on internal
connection implants placed in a two-stage protocol, measuring the occluso-gingival position of
the implant cover screw and its relation to the alveolar crest on the mesial and distal aspects in
patients prescribed a removable prosthesis. Our calibrated measurements displayed statistically
significant bone remodeling from the time of implant placement to the time of implant uncovery.
The most noteworthy finding was the bone remodeling that took place when the implant cover
screw was placed equi-crestally at the level of the alveolar crest. Within the limitations of this
study, the slight sub-crestal placement of the implant cover screw may be beneficial in patients
prescribed a removable prosthesis. Further, well-designed, and calibrated studies should be
conducted to validate our findings.
15
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↑ Figure 1. Example of 2D Radiographs and calibration measuring tool. Implant Placement
(A and B). Implant Uncovery (C and D). Measurements are taken from the level of coverscrew
to the level of the mesial bone height (A and C) and distal bone height (B and D).
A B
C
D
19
↑ Figure 2. Example of 2D Radiographs of Zimmer Biomet 3i Certain Implant and
calibration measuring tool. Implant Placement (A and B). Implant Uncovery (C and D).
Measurements are taken from the level of coverscrew to the level of the mesial bone height (A
and C) and distal bone height (B and D).
A B
C D
20
↑ Figure 3. Example of 2D Radiographs of Astra Tech OsseoSpeed EV Implant and
calibration measuring tool. Implant Placement (A and B). Implant Uncovery (C and D).
Measurements are taken from the level of coverscrew to the level of the mesial bone height (A
and C) and distal bone height (B and D).
A B
C D
21
↑ Figure 4. Mean Mesial Cover Screw Depth. N=67, the mean mesial coverscrew depth at
implant placement was 1.11mm (SD=0.90mm) and the mean mesial coverscrew depth at implant
uncovery was 0.84mm (SD=1.04mm). p=0.005.
22
↑ Figure 5. Mean Distal Cover Screw Depth. N=67, the mean distal coverscrew depth at
implant placement was 0.98mm (SD=0.84mm) and the mean distal coverscrew depth at implant
uncovery was 0.73mm (SD=1.08mm). p=0.005**.
23
↑ Figure 6. Mean Mesial Cover Screw Depth at Implant Placement and at Implant
Uncovery for each group: sub-crestal placement (N=56), equi-crestal placement (N=6), and
supra-crestal placement (N=5). Sub-crestal Placement depth 1.36mm (SD=0.67) and Uncovery
depth 1.15mm (SD=0.68). Equi-crestal Placement depth 0.38mm (SD=0.61) and Uncovery depth
-0.73mm (SD=1.66). Supra-crestal Placement depth -0.77mm (SD=0.73) and Uncovery depth -
0.68mm (SD=0.60).
24
↑ Figure 7. Mean Distal Cover Screw Depth at Implant Placement and at Implant
Uncovery for each group: sub-crestal placement (N=56), equi-crestal placement (N=6), and
supra-crestal placement (N=5). Sub-crestal Placement depth 0.12mm (SD=0.66) and Uncovery
depth 0.99mm (SD=0.81). Equi-crestal Placement depth 0.12mm (SD=0.3) and Uncovery depth
-0.59mm (SD=1.79). Supra-crestal Placement depth -0.69mm (SD=0.35) and Uncovery depth -
0.64mm (SD=0.52).
25
↑Figure 8. Mean Mesial Bone Change from Placement to Uncovery. Sub-crestal Placement -
0.21mm (SD=0.6). Equi-crestal Placement -1.1mm (SD=1.63). Supra-crestal Placement 0.1mm
(SD=0.39).
26
↑Figure 9. Mean Distal Bone Change from Placement to Uncovery. Sub-crestal Placement -
0.23mm (SD=0.57). Equi-crestal Placement -0.71mm (SD=1.67). Supra-crestal Placement
0.05mm (SD=0.54). p=0.19.
27
↑ Figure 10. Pearson Correlation plot graph of the mesial bone level change from implant
placement to implant uncovery. Indicates that there is an inverse correlation such that as you
place your implant deeper than 1.2mm you will observe less bone remodeling.
28
Placement Estimate Standard Error DF t Value Pr>ôtô
Mesial Sub-crestal Vs.
Mesial Equi-crestal
0.8895 0.3105 64 2.86 0.0056*
Mesial Sub-crestal Vs.
Mesial Supra-crestal
-0.3081 0.3374 64 -0.91 0.3645
Mesial Equi-crestal Vs.
Mesial Supra-crestal
-1.1977 0.4377 64 -2.74 0.008*
Distal Sub-crestal Vs.
Distal Equi-crestal
0.4817 0.3074 64 1.57 0.1221
Distal Sub-crestal Vs.
Distal Supra-crestal
-0.2776 0.3340 64 -0.83 0.4090
Distal Equi-crestal Vs.
Distal Supra-crestal
-0.7593 0.4334 64 -1.75 0.0845
↑Table 1. Difference of Square Means Mesial and Distal Measurements. For the mesial
aspects there is statistically significant difference found between Sub-crestal Vs. Equi-crestal
groups (p=0.0056) and Equi-crestal Vs. Supra-crestal groups (p=0.008). There was no
statistically significant difference between mesial aspects Sub-crestal Vs. Supra-crestal group
(p=0.3645). There was no statistically significant difference between the distal aspect groups:
Sub-crestal Vs. Equi-crestal groups (p=0.1221), Sub-crestal Vs. Supra-crestal groups (p=0.4090),
and Equi-crestal Vs. Supra-crestal (p=0.0845).
Abstract (if available)
Abstract
This study seeks to investigate the effect of vertical position of the cover screw on the early marginal bone loss around dental implants. The aim of this retrospective observational study was to determine if there is a relationship between the vertical position of the cover screw with the crestal bone remodeling around dental implants when using removable prostheses.
Electronic dental records were obtained from patients who underwent dental implant placement in a two-stage protocol and were prescribed a removable prosthesis to be worn during the interim. The implant systems represented in the study were Straumann Bone Level NC or RC, Astra Tech OsseoSpeed EV, and Zimmer Biomet 3i Certain. Two-dimensional radiographs that were taken at implant placement and implant uncovery were evaluated and mesial and distal apicocoronal bone levels were measured from the height of the coverscrew to the crestal of the bone. The vertical height of the implant cover screws was defined as sub-crestal, equi-crestal, or supra-crestal.
Charts of 50 patients and 67 implants were included. The statistical analysis showed that the vertical position of the cover screw (sub-, equi- or supra-crestal) significantly affected the mesial marginal bone, such that equi-crestal group showed the highest marginal bone loss compared either the sub-crestal or supra-crestal groups (P=0.0056 and 0.008, respectively). No statistically significant difference was found between sub-crestal vs. supra-crestal group (p=0.3645). When evaluating for correlation between sub-crestal implant placement depth and amount of bone changes on the mesial aspect there was a statistically significant inverse correlation between placing the implant beyond 1.2mm to obtain less bone loss (p=0.02). The distal marginal bone levels did not show any significant difference between the groups.
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Asset Metadata
Creator
Hunter, Mylea W.
(author)
Core Title
Association between the depth of implant cover screw and the marginal bone loss with the use of a removable provisional restoration: a retrospective two-dimensional radiographic evaluation
School
School of Dentistry
Degree
Master of Science
Degree Program
Biomedical Implants and Tissue Engineering
Degree Conferral Date
2023-08
Publication Date
07/10/2023
Defense Date
07/07/2023
Publisher
University of Southern California
(original),
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Tag
cover screw,dental implant,marginal bone loss,OAI-PMH Harvest,removable prosthesis
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Language
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Bakhshalian, Neema (
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Tags
cover screw
dental implant
marginal bone loss
removable prosthesis