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Radiographic analysis of bone gain from guided bone regeneration utilizing tenting screws

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Radiographic analysis of bone gain from guided bone regeneration utilizing tenting screws

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RADIOGRAPHIC ANALYSIS OF BONE GAIN FROM
GUIDED BONE REGENERATION UTILIZING TENTING SCREWS

by

Na Eun (Sarah) Chung

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
in Biomedical Implants and Tissue Engineering

December 2021
Copyright 2021 Na Eun (Sarah) Chung
ii
Table of Contents

List of Tables …………………………………………………………………………………….iii
List of Figures ………………………………………………………………………………..…..iv
Abstract …………………………………………………………………………………………...v
Introduction ……………………………………………………………………………………….1
Material and methods ……………………………………………………………………………..7
Study Protocol ……………………………………………………………………………..7
Study population …………………………………………………………………………...8
Surgical protocol …………………………………………………………………………..8
CBCT Evaluation ………………………………………………………………………….9
Statistical Analysis ……………………………………………………………………….10
Results …………………………………………………………………………………………...12
Discussion ……………………………………………………………………………………….17
Conclusion ………………………………………………………………………………………21
References ……………………………………………………………………………………….22
Tables …………………………………………………………………………………………....27
Figures ...…………………………………………………………………………………………29

iii
List of Tables

Table 1: Demographic of the sample population...……………………………………………....27
Table 2: Mean bone gain in mesial, distal, apical and coronal directions……………………….28

iv
List of Figures

Figure 1: Superimposition of CBCT files ...……………………………………………………..29
Figure 2: Schematic of measurement of bone gain in the coronal, apical, mesial and distal
direction in 1mm increments ...………………………………………………………………….30
Figure 3: Example of measurement taken for a tenting screw in the mesial direction ...………..31
Figure 4: Mean bone Gain in the mesial direction ……………………………………………....32
Figure 5: Mean bone gain in the distal direction ...……………………………………………...33
Figure 6: Mean bone gain in the apical direction ...……………………………………………..34
Figure 7: Mean bone gain in the coronal direction ...…………………………………………....35

v
Abstract
Objectives: Guided bone regeneration (GBR) is one of many surgical techniques used to
augment the edentulous ridge. This study utilizes a novel approach to measuring bone gain
around a single tenting screw. This retrospective study’s aim is to identify how horizontal and
vertical bone gain are affected by the tenting screws relation to each other.

Materials and Methods: This retrospective study includes subjects who underwent GBR
treatment with the use of tenting screws at the private office of one of the authors (B.L.).
Inclusion criteria consisted of: 1) the availability of pre- and post-therapy diagnostic quality cone
beam computed tomography (CBCT) scans, 2) the alveolar ridge augmentation technique
utilized mineralized particulate allograft with resorbable barrier membrane and tenting screws.
Exclusion criteria consisted of: 1) non-diagnostic CBCTs, 2) alveolar bone augmentation
techniques not utilizing the combination of mineralized particulate allograft with resorbable
barrier membranes and tenting screws. The pre- and post-therapy CBCTs were imported in
Amira software and subsequently superimposed. A cross-section of the center of the tenting
screw was obtained and measurements were taken of the bony ridge pre- and post-operatively in
1mm increments in the mesial, distal, apical and coronal direction.

Results: The total number of patients that met the inclusion and exclusion criteria was
nine. All nine patients were female. The average age of the patients was 61.3 + 6 years old. The
average time between pre- and post-therapy CBCT was 12.1 + 9.2 months. Out of those subjects,
a total of 23 tenting screws were included in the study.

vi
Conclusions: In this study, space maintenance in GBR is achieved by titanium tenting
screws and resorbable barrier membranes, which prevents resorption of the mineralized
particulate allograft. Bone gain was limited beyond 3mm away from the center of the tenting
screw in the apical and coronal direction. Within the limitations of this study, these research
findings can show the optimum distance between tenting to maximize bone gain. More research
including randomized controlled trials are necessary to elucidate further patterns of bone gain
around tenting screws.

1
Introduction

Although the prevalence of tooth loss has steadily declined over the years, it still affects
numerous people in the United States. 10.13% of the American adult population of 50 to 64
years have no remaining teeth according to an NHANES survey 1999-2004 (NIH, 2018) The
adequate treatment of edentulism is a fundamental property of any dental specialty. Dental
implants are one of the primary therapies provided for our patients in recent years, as its success
rate can be up to 94.6% (Moraschini et al., 2015). One of the most complicated aspects of
treatment of edentulism is the effects of tooth loss on the surrounding bone.

After tooth loss, the edentulous ridge decreases in size vertically and horizontally, with
the change being especially pronounced in the buccal aspect of the ridge (Araujo & Lindhe,
2005). Within 6 months after tooth extraction, the ridge undergoes a mean horizontal reduction
of 3.8mm and a mean vertical reduction of 1.2mm (Tan et al., 2012). Within 2 to 3 years, the
bone undergoes a shrinkage of 40-60% (Ashman, 2000). Dental implants need adequate bone
quantity to have a stable foundation. Therefore, the loss of bone necessitates more complicated
therapy and increased number of surgeries for optimal implant restoration. This then results in
complex treatment options necessitating bone augmentation procedures to accommodate a
successful dental implant surgery and appropriate position and angulation.

Guided bone regeneration (GBR) is one of many surgical techniques used to augment the
edentulous ridge. Autogenous, allograft, xenograft particulate or block graft material is placed on
a bony foundation. A barrier membrane is then placed over the graft area to selectively permit
2
bone-forming cells to establish themselves, but exclude epithelial cells and fibroblasts (Fiorellini
& Nevins, 2003). This practice stems from Nyman and Karring’s biological principle of healing,
in which they found that the cells that first populate a wound area determine the type of tissue
that ultimately occupies that space (Karring et al., 1980). Therefore, the barrier membranes are
used as an agent that prevents undesired cells such as epithelial and connective tissue cells from
occupying the targeted wound space, but at the same time allows for desired cells such as
osteoblasts to contribute to the prioritized tissue in the original wound space. In this surgical
technique, complementary titanium screws buttress the resorbable collagen membrane and
particulate bone graft complex to allow space maintenance for bone maturation over a period of
6-9 months (Le et al., 2010). The end result of applying these principles is the provision of more
bone in an edentulous space for optimal implant therapy. This GBR procedure can be executed
with various types of membranes, bone grafts and bone graft substitutes.

Two of the most popular available membranes are expanded polytetrafluoroethylene (e-
PTFE) and resorbable collagen membrane. E-PTFE is a synthetic polymer with porous structure
that forms a non-resorbable membrane; there are several advantages to this membrane material.
Its composition is not only biocompatible but also provides resistance to enzymatic degradation
by host tissues and microbes at the wound site (Zitzmann et al., 1997). Additionally, titanium-
reinforced e-PTFE membranes have increased mechanical stability which allows for shaping of
the membranes to the defect site. The drawbacks to e-PTFE, however, is that if this material is
exposed to the oral cavity prematurely, the porous surface of the material is rapidly colonized by
oral microbes and leads to infections and impaired bone regeneration at the wound site (Simion
et al., 1994). This non-resorbable membrane also needs to be removed before endosteal implant
3
placement can be performed. Another rigid membrane is the titanium mesh membrane which
possesses stiffness and strength that can resist the collapse of the soft tissue complex during
healing period after GBR is performed. However, the presence of pores in the titanium mesh
may contribute to soft tissue infiltration and can be present under the titanium at the time of
uncovery (Xie et al., 2020). Rigid-type membranes are useful in that they are strong and stiff
enough to provide spatial support for osteogenesis, which is crucial in maintaining the grafted
volume (Louis et al., 2008)

The alternative to rigid membranes is the resorbable collagen membrane. This material
does not necessitate an additional membrane removal surgery, as it resorbs over time. It has
been shown to epithelialize spontaneously in case of mucosal dehiscence (Friedmann et al.,
2001). However, its use is limited as it has poor resistance to collapse and has a fast resorption
time. A chemical process called cross-linking has been found to elongate biodegradation time of
the collagen membrane and has also decreased soft tissue infiltration, which improved GBR
therapy efficacy (Rothamel et al., 2005).

Bone grafting materials can be divided into four categories: autograft, allograft, xenograft
and alloplast. Autograft is the patient’s own tissue and is currently the gold standard for bone
grafting materials due to its osteogenic, osteoinductive and osteoconductive properties
(Burchardt, 1983). Autologous bone grafts can be acquired from numerous extraoral and
intraoral locations such as the iliac crest, tibia, mandibular ramus and mandibular symphysis
(Dimitriou et al., 2011; Ferraz et al., 2014; Hirota et al., 2019). These autografts can be
technically challenging from a surgical standpoint, and, as with any additional surgery, increase
4
the rates of morbidity and complications for the procedure as a whole (Cricchio & Lundgren,
2003). Therefore, synthetically produced alloplast, xenograft from other species and allografts
from other individuals within the same species have been utilized in bone grafting procedures.

Of these materials, allografts have shown particular success in bone regeneration therapy.
This is especially helpful in regenerating large edentulous defects in which harvesting enough
autogenous bone can be a great challenge. The use of allograft bone blocks in conjunction with
collagen membranes in rehabilitating a severely atrophic alveolar ridges has been proved to be
efficacious (Le et al., 2008). Implants that were placed in those sites had 98.8% survival rate
with mean follow-up period of 48+22 months (Nissan et al., 2012). GBR facilitated by “tent-
poles” has shown successful long-term outcome in the reconstruction of severely resorbed
mandibles, with all patients progressing to a functional denture with mean follow-up time of 4.9
years (Marx et al., 2002). This idea was first experimented by Marx who used 4x15 mm standard
sized parallelly placed implants to serve as “tent-poles” to keep the reflected soft-tissue matrix
from collapsing down on itself. Nowadays, titanium screws are commercially available in
various diameters and lengths for clinicians to utilize. Research done by Simon et al has shown
that the advantageous features of allografts, such as reduced healing period, low risk of
complications and high predictability are boasted by the tenting screw facilitated GBR (Simon et
al., 2010).

The application of tenting screws to bone grafting material is a basic and low impact
surgical procedure. Typically, a small osteotomy is prepared to ease the tenting screw into the
cortical plate. Then, the screw can engage into the buccal cortical plate only, or for further
5
stability, it can also engage into the palatal/ lingual cortex depending on size of screw and depth
of placement. In the latter, additional palatal/ lingual augmentation with bone graft material can
also be performed (Chasioti et al., 2013). Decortication of the bone through using a high-speed
surgical handpiece is also performed during placement of tenting screws. This releases growth
factors which promote cell proliferation and angiogenesis that leads to increased bone maturation
(Frost, 1983). With the benefits of tenting screws, optimizing their placement would be of value
to clinical practice. In current literature, there are no studies demonstrating the most efficient
standardized distance between tenting screws. Currently, the placement of tenting screws in
practice is determined by operator preference.

The combination of all these materials and techniques is used to provide optimal bone
gain for prosthetic restoration via implant therapy. This bone gain occurs in three dimensions and
depends on the original bony defect.

To date, there are several articles that evaluate the quantity of bone gain after performing
GBR via tenting screws, some of which will be discussed in this paragraph. All of these studies
evaluate the bone gain from tenting screws as a cross section in the grafted ridge starting at the
crest at either 3 or 5mm increments. Guillen took clinical and radiographic measurements after
GBR therapy utilizing of differently sized tenting screws. For the standard screws, clinical
measurements showed ridge width augmentation of 1.05mm, 2.45 mm and 2.70mm at the crest
of the ridge, 5mm and 10mm respectively. Similarly, for the standard screws, CBCT
measurements showed ridge width augmentation of 0.74mm, 3.88mm and 4.72mm (Guillen et
al., 2020). In a prospective study by Daga, bone height is measured after GBR facilitated by
6
tenting screws and the mean bone gain was 2.87 + 0.79 mm (Daga et al., 2018). By evaluating
the ridge radiographically, Neto showed that the use of tenting screws exhibited a positive effect
on GBR with a greater final ridge width at the level 3mm below the crest, which was 3.98 + 2.53
mm (Cesar Neto et al., 2020).

This retrospective study aims to identify how horizontal and vertical bone gain are
affected by the position and distance between tenting screws by utilizing a comprehensive 3D
technology to provide more detailed and accurate measurements of bone growth in relation to
tenting screws. This study aims to provide the foundation for future guidelines of how far tenting
screws should be placed in relation to each other to maximize bone gain in GBR.

7
Materials and Methods

Study Protocol:

The protocol of this retrospective study was reviewed and approved by the Institutional
Review Board of the University of Southern California. Informed consent was exempted because
the dataset of the study was anonymous. This study was conducted by a resident in the Advanced
Periodontology Department (N.E.C.) based on the cone-beam computer tomography (CBCT)
scans of nine consecutive patients presenting with large alveolar ridge defect. These patients
were selected from the patient pool of a private clinic of one of the authors (B.L.). Each patient
had been treated with guided bone regeneration using tenting screws by B.L. between 2012-
2015. The records identified fourteen patients meeting the inclusion and exclusion criteria
described below. Out of these fourteen patients, the records of nine patients (twenty-two tenting
screws) could be used for three-dimensional CBCT analysis.

Inclusion Criteria:

Inclusion criteria consisted of: 1) the availability of pre- and post-therapy diagnostic
quality CBCT scans, and 2) GBR technique using mineralized particulate allograft with
resorbable barrier membrane and tenting screws.

8
Exclusion Criteria:

Exclusion criteria consisted of: 1) non-diagnostic CBCT radiographs 2) alveolar bone
augmentation techniques not utilizing the combination of mineralized particulate allograft with
resorbable barrier membranes and tenting screws, and 3) smokers, diabetic patients, and any
medically compromised patients were excluded from the study.

Study Population:

The patients who presented to B.L.’s private clinic were either partially or fully
edentulous and were seeking dental implant therapy. Before the bone augmentation, all grafted
sites were deemed inadequate for placement of endosteal dental implants with the length of said
implants being at least 10 mm.

Surgical Protocol:

Patients were given a pre-operative chlorhexidine rinse for 2 minutes, which was then
expectorated. Intravenous anesthesia was provided for surgical treatment and 2% lidocaine with
1:100,000 epinephrine was given as blocks initially and then as infiltrations throughout the
surgical procedure. A crestal incision with vertical releases were made in all cases, identifying
available keratinized tissue and including it in the flap design. To achieve tension-free closure,
tissue releases were performed before screw or graft placement. In the anterior maxilla,
subperiosteal releases were performed all the way to the nasal spine to obtain adequate release.
9
Between 5-7 mm of the titanium screw threads were left exposed (1.5mm, KLS Martin,
Jacksonville, FL) over the alveolar ridge. A high-speed handpiece was utilized to create bleeding
points on the bony ridge. Ridge augmentation was performed using human mineralized allograft
(cancellous particles, 250 to 1,000 um, Puros; Zimmer Dental, Carlsbad, CA) mixed with
patient’s blood placed around titanium screws to tent out the soft tissue. A resorbable membrane
(OSSIX PLUS; OraPharma, Warminster, PA) was placed over the grafted sites. Interrupted
sutures were placed with 4-0 resorbable chromic gut sutures and passive primary closure was
achieved.

Post-operatively, the removable prosthesis was adjusted to prevent compression on the
grafted site. All patients were placed on post-operative antibiotic treatment consisting of
penicillin 500 mg x 7 days (for penicillin-allergic patients, clindamycin 300 mg x 7 days) and a
chlorhexidine mouth rinse for 1 week. After 4 to 5 months, the grafted sites were uncovered and
the screws were removed, and at this time, the ridges were clinically evaluated with additional
post-therapy CBCT scans which were used to evaluate all grafted segments. No autogenous
bone was used in this study.

CBCT Evaluation:

Pre- and post-therapy CBCT scan dicom files were imported to Amira® software
(AMIRA; Materialise Inc, Leuven, Belgium). Pre-therapy CBCT rendered volume was marked
in orange and post-therapy CBCT rendered volume was marked in blue to distinguish between
the two scans (Figure 1A). Pre- and post-therapy CBCT images were cropped in relation to the
10
area of interest (Figure 1B). They were aligned manually to close proximity, followed by
software registration of superimposition of pre- and post-therapy scans (Figure 1C).
Superimposition of both scans was performed to allow measurements in the same cross-sectional
locations (Figure 1D).

A customized cross-section of the tenting screw for each scan was manually obtained in
the software via marking the head and tip of the screw, then creating a line between these two
points. The computer software then created a reference for this line and a cross-sectional plane of
this line could then be generated. Using this generated cross-sectional plane, perpendicular
measurements were taken of the bony ridge pre- and post-operatively in 1mm increments in the
apical, coronal, mesial and distal directions (Figure 2). Bone gain was then calculated as a
difference of the pre- and post-therapy ridge width, with the center of the tenting screw being the
focal point. Quantitative analysis of the CBCT images were performed by a single calibrated
examiner (N.E.C.) which limited user variability. An example of the measurements in the mesial
direction is illustrated in Figure 3.

Statistical Analysis:

Descriptive statistics were calculated for all variables of interest: bone gain at different
directions and various distance from the center of the tenting screw. Continuous measures were
summarized using means and standard deviations. Linear mixed models were run to assess the
relationship between bone gain and distance with patient treated as a random effect. Separate
11
models were run for mesial, distal, apical and coronal as well as an interaction model to compare
the 4 groups.

A type III test of fixed effects was performed for each direction category comparing
values of bone growth at different distances from tenting screw relative to bone growth values
from each distance within that same direction category. This allowed for statistical analysis of
significant difference in bone growth between the distances from the tenting screw in one set
direction. Additionally, a type III test of fixed effects was also performed for all measurements
of bone growth at each distance in relation to the bone growth values at that same distance in a
different direction category - coronal, mesial, distal, apical. This allowed for statistical analysis
of significant differences in bone growth between different dimensions at a set distance from the
tenting screw. Significance for all calculated values was considered at P < .05 (95% CI). All
analyses were carried out using SAS Version 9.4 (SAS Institute, Cary, NC, USA).

12
Results

The final sample data was composed of 9 patients and 23 sites, all of which were all
located in the maxilla. All nine patients were female. The overall mean age was 61.3 + 6 years
ranging from age 52 to 72. The average time between pre- and post-therapy CBCT was 12.1 +
9.2 months ranging from 4 to 64 months (Table 1). All patients were non-smokers and all
patients were classified as ASA type I. All 9 patients were treated to correct alveolar ridge
defects by one experienced oral surgeon (B.L.). These procedures were performed in a private
practice setting during the years 2012 – 2019. No complications were reported during the healing
period.

Bone gain was measured as a difference of the pre- and post-therapy ridge width with the
center of a tenting screw being the focal point (Table 2). Measurements were taken in 1mm
increments from the center of the screw to 5mm away from the screw, in the mesial, distal, apical
and coronal directions. For the mesial measurements, the mean bone gain was 5.44 + 1.58 mm,
5.52 + 1.42 mm, 5.04 + 1.10 mm, 4.73 + 0.99 mm, 4.87 + 1.15 mm and 4.55 + 1.17 mm at the
center, 1mm mark, 2mm mark, 3mm mark, 4mm mark and 5mm mark, respectively. For the
distal measurements, the mean bone gain was 5.44 + 1.58 mm, 5.05 + 1.22 mm, 5.24 + 1.42 mm,
4.77 + 1.66 mm, 4.34 + 1.34 mm and 4.11 + 1.34 mm at the center, 1mm mark, 2mm mark, 3mm
mark, 4mm mark and 5mm mark, respectively. For the apical measurements, the mean bone gain
was 5.44 + 1.58 mm, 5.34 + 1.17 mm, 4.93 + 1.31 mm, 4.50 + 2.44 mm, 3.44 + 1.6 mm, and
2.76 + 1.48 mm at the center, 1mm mark, 2mm mark, 3mm mark, 4mm mark and 5mm mark,
respectively. For the coronal measurements, the mean bone gain was 5.44 + 1.58 mm, 5.35 +
13
1.34 mm, 4.66 + 1.18 mm, 3.68 + 1.45 mm, 3.4 + 1.38 mm and 2.83 + 1.46 mm at the center,
1mm mark, 2mm mark, 3mm mark, 4mm mark and 5mm mark, respectively. Figures 1, 2, 3 and
4 below represent these values graphically.

As mentioned in the previous section, a type III test of fixed effects run for each direction
category – mesial, distal, apical and coronal – to see whether there was significant difference in
bone gain between the distances from the center of the tenting screw in one given direction.

Within the mesial direction, bone gain between the different distances from the center of
the tenting screw was compared using the type III test of fixed effects as described above
p=0.02). No significant difference in bone gain existed between the distances of the center, 1mm,
and 2mm increments. Significant decrease in bone gain was found at the increment of 3mm in
relation to the center and 1mm increments. Significant decrease in bone gain was recorded at the
4mm increment in relation to the 1mm increment. Finally, significant decrease in bone gain was
noted for the 5mm increment in relation to the center and 1mm increments.

In the distal direction, the same type III test of fixed effects was performed, with the
model being significant (p=0.004). No significant difference in bone gain was present between
the distances of the center, 1mm, 2mm and 3mm increments. Significant decrease in bone gain
was noted at the increment of 4mm in relation to the center, 1mm and 2mm. Bone gain at the
increment 5mm also had significant decline in bone gain in relation to the center, 1mm and 2mm.

14
In the apical direction, the type III test of fixed effects revealed the following and the
model was significant (p<0.0001). No significant difference in bone gain was present between
the distances of the center, 1mm and 2mm increments. Significant decline in bone gain was seen
in increments 3mm, 4mm and 5mm increments in relation to the center. Marginal decrease in
bone gain was seen in increment 3mm in relation to the 1mm increment, while significant
decrease was seen in the 4mm and 5mm increments in relation to the 1mm increment. Bone
decline follows a more gradual pattern in the apical direction. Bone gain observed in the 4mm
and 5mm is significantly less than that of 2mm and 3mm.

In the coronal direction, the same test was run and the model was significant (p<0.0001).
Bone gain at the 2mm, 3mm, 4mm, and 5mm increments were significantly less than that of the
center. Bone gain at the 2mm, 3mm, 4mm and 5mm increments were significantly less than that
of the 1mm increment. Bone gain at the 3mm, 4mm and 5mm increments were significantly less
than that of the 2mm increment. Lastly, bone gain at the 5mm increment was less than that of the
3mm increment.

Furthermore, to ascertain a statistical analysis of significant differences in bone gain
between different directions at a set distance from the center of the tenting screw, another type
III test of fixed effects was performed for all measurements of bone gain at each distance in
relation to the bone gain values at the same distance in a different direction category – mesial,
distal, apical and coronal. For the center of the tenting screw, 1mm increment and 2 mm
increment, the statistical model found no significant differences in bone gain between all
direction categories. Significantly greater bone gain was recorded at the 3mm increment between
15
the apical, mesial, and distal dimension in relation to the coronal direction. No significant
difference was found between the apical, mesial and distal direction at the 3mm increment.
Analysis of bone gain at the 4mm increment showed no significant difference between the mesial
and distal direction relative to each other, as well as between the apical and coronal direction
relative to each other. However, both the mesial and distal direction showed significantly greater
bone gain at the 4mm increment in relation to the apical and coronal direction. Similarly, at the
5mm increment, there was no significant difference in bone gain between the mesial and distal
direction relative to each other and the apical and coronal direction relative to each other.
Significantly greater bone gain was found when analyzing the mesial and distal direction in
relation to the apical and coronal direction at the 5mm increment.

16
Discussion

Guided bone regeneration facilitated by tenting screws is a widely used technique that
was developed to improve multi-dimensional bone graft stability during post-operative healing.
The technique has changed over time and requires further research for optimization. Previously,
widely popularized GBR techniques used various materials such as non-resorbable titanium-
reinforced membranes and autogenous bone block grafts. However, the use of non-resorbable
titanium-reinforced membranes is no longer considered standard therapy due to the high risk of
mucosal dehiscence and infectious complications (Chiapasco & Zaniboni, 2009). Additionally,
although bone block grafts boast excellent mechanical properties, clinical handling and precise
adaptation of the graft to the bony defect can prove to be a surgical challenge (Zecha et al.,
2011).

Due to these complications, new techniques have been developed to facilitate a more
predictable surgical outcome. The technique described in this study uses a particulate allograft,
and was demonstrated previously to decrease patient morbidity and decrease surgical time, as
extra-oral and intra-oral autogenous bone sources are not needed (Le et al., 2008). Further
evaluation of this technique has focused on analyzing its associated bone gain in relation to
tenting screws in order to more accurately identify ideal distribution of tenting screws maximize
bone gain. This is especially pertinent as several studies show that survival rates of dental
implants placed simultaneously with or after GBR are similar to survival rates of implants placed
in native bone (Cesar Neto et al., 2020; Donos et al., 2008; Hämmerle et al., 2002).

17
Previous studies have attempted to quantify bone growth using this surgical technique by
examining bone gain in increments relative to the alveolar crest pre- and post-therapy. Up to
date, there has been only one study that performed both clinical and radiographic analysis in the
same sample (de Freitas et al., 2013). The systematic review states that radiographic evaluation
of bone width enables a more comprehensive assessment of the alveolar width at different
heights (Naenni et al., 2019). This is especially relevant for the current study, as bone gain was
measured through a line drawn through the tenting screw in 1mm increments in four directions –
mesial, distal, apical and coronal. One study evaluates bone gain from GBR via tenting screws
radiographically such as the present study but takes measurements in the cross-section of bone,
1mm, 3mm, 5mm and 7mm below the crestal bone (Cesar Neto et al., 2020). From which the
authors conclude that regeneration procedures were more effective mainly at the first 3mm
below the crest of the edentulous ridge with the use of tenting screws.

Combined, these studies provided a general picture of bone gain overall, but did not
accurately paint the pattern of bone gain or create a basis for exact operative standards when
placing tenting screws to facilitate bone gain. This study provides a novel measurement protocol
using CBCT radiographs to better quantify the pattern of bone gain relative to a tenting screw.

The results of the present study conveys that bone gain around tenting screws are
predictable in the mesial, distal and apical directions within 3mm of the center of the screw. This
bone growth is theorized by the authors to be due to the mechanical support given to the
membrane by the tenting screw, which leads to increased stability of the allograft particles
underneath.
18

The results of this study also suggest a predictable bone gain pattern in distances greater
than 3mm from the tenting screw. In the mesial and distal direction, bone gain was found to be
significantly less at 4mm and 5mm increments from the tenting screw as compared to the values
within 3mm. However, at 4mm and 5mm increments from the center of the tenting screw, mesial
and distal bone gain was significantly greater than the same increments in the apical and coronal
directions. This suggests that the bone gain was also limited in the apical direction and coronal
direction, more so than in the mesial and distal direction. Occurrence of crestal resorption post-
GBR was a phenomenon also observed in another study (Cesar Neto et al., 2020).

In regards to the greater limitations of coronal bone gain, it was previously shown that the
compressive forces of the sutures on the graft causes displacement of grafting particles and limits
growth (Mir-Mari et al., 2016). This is resonated in another study that evaluated the positive
effect of tenting screws in GBR – in at least 10 cases, vertical crestal resorption of a certain
extent was detected (Cesar Neto et al., 2020). It is likely that the bone gain in the apical direction
was limited due to short extension of the flap creating limitations in available apical space for
bone growth. When the flap is not released deep enough, there is tension at the most apical
region, preventing placement of the bone graft material. Knowing this information, the position
and angulation of the tenting screws can be methodically placed to maximize bone gain in the
apical and coronal region to maintain the volume horizontally and vertically.

Currently, there are no standardized guidelines on how far apart the tenting screws must
be placed from one another. This present study’s data showed that bone growth was maximized
19
within the first 3mm increments from the tenting screw. Therefore, from the results of the
present study while also considering limits, it can be speculated that the tenting screws can be
spaced 6mm apart from each other to maximize possible bone gain. However, for future studies,
the location and anatomy of the recipient site should be considered, as bone gain may differ
depending on the region. For example, there may be more bone gain in the maxillary anterior
area, especially if the patient presents with a prominent nasal spine but bone level may taper
towards the posterior. A more limiting example can be when a tenting screw is placed too
apically, the bone gain is limited by the flap extension and is dependent on the depth of the flap.
These points should be considered when creating a guideline for the tenting screw distribution to
gain the most bone in GBR.

For the current study, only completely edentulous maxillary anterior areas were sampled
but it will be interesting to see whether the bone gain distribution will differ for tooth-bound sites
vs. completely edentulous, anterior vs. posterior and mandible vs. maxilla. Some limitations of
the present study include its retrospective design, lack of a control group and absence of
randomization. Also, the follow-up protocol was not standardized, as it would have been in a
randomized controlled trial. However, some strengths of the study comprise of the fact that one
experienced operator performed all surgeries and CBCT superimposition and measurement
method was performed by one calibrated examiner. CBCT radiographs also allowed for detailed
measurements in a three-dimensional space. Future randomized control trials can potentially
incorporate placement of the tenting screws in varying distance.

20
GBR with tenting screws has many clinical applications – not only is it utilized to
augment the bony ridge prior to endosteal implant placement, it has recently been used to address
mucosal recession on the labial aspects of implants in the esthetic zone. This method of
augmentation around implants with bone loss has shown long-term success of over 2 years in the
retrospective study (Le et al., 2016). Tenting screws have also been used in conjunction with
ridge preservation following tooth extraction for implant site preparation (Reddy et al., 2016).
The results from the present study can greatly aid clinicians in planning for bone augmentation in
various applications.

21
Conclusion

Within the limitations of this study, GBR facilitated by tenting screws was assessed to be
a predictable technique in treatment of atrophic bony ridges. Bone gain was limited beyond 3mm
away from the center of the tenting screw in the apical and coronal direction. Randomized
controlled clinical trials will be necessary to compare the efficacy of GBR using tenting screws.

22
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27
Tables
Table 1: Demographic of the sample population (N = 9)
Age (year)
Mean + SD
Range

61.3 + 6
52 - 72
Sex
Female
Male

n = 9 (100%)
n = 0 (0%)
Race
Caucasian
Hispanic
Asian

n = 4
n = 1
n = 4
Average follow-up time (months)
Mean + SD
Range

12.1 + 9.2
4 - 34

28
Table 2: Mean bone gain in mesial, distal, apical and coronal directions
Mean Bone Gain + SD (mm)
Distance Mesial Distal Apical Coronal
Center 5.44 + 1.58 5.44 + 1.58 5.44 + 1.58 5.44 + 1.58
1mm 5.52 + 1.42 5.05 + 1.22 5.34 + 1.17 5.35 + 1.34
2mm 5.04 + 1.10 5.24 + 1.42 4.93 + 1.31 4.66 + 1.18*
3mm 4.73 + 0.99* 4.77 + 1.66 4.50 + 2.44* 3.68 + 1.45*
4mm 4.87 + 1.15* 4.34 + 1.34* 3.44 + 1.6* 3.4 + 1.38*
5mm 4.55 + 1.17* 4.11 + 1.34* 2.76 + 1.48* 2.83 + 1.46*
* Significantly different between the distances within the same direction category. P < 0.05

29
Figures
Figure 1

Figure 1. Superimposition of CBCT files A) Pre- and post-therapy CBCT rendered volumes B)
CBCT rendered volumes cropped to region of interest C) Manual superimposition of the pre- and
post-therapy CBCT rendered volumes D) Registered superimposition of the pre- and post-
therapy CBCT rendered volumes via Amira software function

30
Figure 2

Figure 2. Schematic of measurement of bone gain in the coronal, apical, mesial and distal
direction in 1mm increments

31
Figure 3

Figure 3. Example of measurement taken for a tenting screw in the mesial direction. A) Center of
tenting screw, B) 1mm mesial, C) 2mm mesial, D) 3mm mesial, E) 4mm mesial, and F) 5mm
mesial.

32
Figure 4

Figure 4: Mean bone Gain in the mesial direction

0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
center 1mm 2mm 3mm 4mm 5mm
Average Bone Gain (mm)
Distance from Tenting Screw
Bone Gain in the Mesial Direction
33
Figure 5

Figure 5: Mean bone gain in the distal direction

0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
center 1mm 2mm 3mm 4mm 5mm
Average Bone Gain (mm)
Distance from Tenting Screw
Bone Gain in the Distal Direction
34
Figure 6

Figure 6: Mean bone gain in the apical direction

0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
center 1mm 2mm 3mm 4mm 5mm
Average Bone Gain (mm)
Distance from Tenting Screw
Bone Gain in the Apical Direction
35
Figure 7

Figure 7: Mean bone gain in the coronal direction

0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
center 1mm 2mm 3mm 4mm 5mm
Average Bone Gain (mm)
Distance from Tenting Screw
Bone Gain in the Coronal Direction

Abstract (if available)

Abstract Objectives: Guided bone regeneration (GBR) is one of many surgical techniques used to augment the edentulous ridge. This study utilizes a novel approach to measuring bone gain around a single tenting screw. This retrospective study’s aim is to identify how horizontal and vertical bone gain are affected by the tenting screws relation to each other. ❧ Materials and Methods: This retrospective study includes subjects who underwent GBR treatment with the use of tenting screws at the private office of one of the authors (B.L.). Inclusion criteria consisted of: 1) the availability of pre- and post-therapy diagnostic quality cone beam computed tomography (CBCT) scans, 2) the alveolar ridge augmentation technique utilized mineralized particulate allograft with resorbable barrier membrane and tenting screws. Exclusion criteria consisted of: 1) non-diagnostic CBCTs, 2) alveolar bone augmentation techniques not utilizing the combination of mineralized particulate allograft with resorbable barrier membranes and tenting screws. The pre- and post-therapy CBCTs were imported in Amira software and subsequently superimposed. A cross-section of the center of the tenting screw was obtained and measurements were taken of the bony ridge pre- and post-operatively in 1mm increments in the mesial, distal, apical and coronal direction. ❧ Results: The total number of patients that met the inclusion and exclusion criteria was nine. All nine patients were female. The average age of the patients was 61.3 ± 6 years old. The average time between pre- and post-therapy CBCT was 12.1 ± 9.2 months. Out of those subjects, a total of 23 tenting screws were included in the study. ❧ Conclusions: In this study, space maintenance in GBR is achieved by titanium tenting screws and resorbable barrier membranes, which prevents resorption of the mineralized particulate allograft. Bone gain was limited beyond 3mm away from the center of the tenting screw in the apical and coronal direction. Within the limitations of this study, these research findings can show the optimum distance between tenting to maximize bone gain. More research including randomized controlled trials are necessary to elucidate further patterns of bone gain around tenting screws.

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Asset Metadata

Creator Chung, Na Eun (Sarah) (author)

Core Title Radiographic analysis of bone gain from guided bone regeneration utilizing tenting screws

School School of Dentistry

Degree Master of Science

Degree Program Biomedical Implants and Tissue Engineering

Publication Date 11/11/2021

Defense Date 11/10/2021

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

Tag Amira,bone augmentation,bone graft,cbct,cone beam computed tomography,dental implants,GBR,guided bone regeneration,implants,OAI-PMH Harvest,radiographic analysis,ridge augmentation,tenting screw,tenting screws

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Bakhshalian, Neema (committee chair), Chen, Casey (committee member), Kar, Kian (committee member)

Creator Email naeunchu@usc.edu,naeunsarahchung@icloud.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC17138464

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