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Retrospective analysis of crestal bone changes on dental implant sites after a bone augmentation procedure: graft material comparisons

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Retrospective analysis of crestal bone changes on dental implant sites after a bone augmentation procedure: graft material comparisons

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Content RETROSPECTIVE ANALYSIS OF CRESTAL BONE CHANGES ON DENTAL
IMPLANT SITES AFTER A BONE AUGMENTATION PROCEDURE:
GRAFT MATERIAL COMPARISONS
Daniel Kruk-Leahy, DDS
A Thesis Presented to the
FACULTY OF 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 2024

ii
Dedication
I dedicate this thesis to my parents who have encouraged me to achieve academic excellence and
continuous growth throughout all my years of education.

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Table of Contents
Dedication…………………………………………………………………………………………ii
Abstract……………………………………….……………………………………………..…....iv
Results…………………………………………………………………………………….v
Conclusion………………………………………………………………………………..vi
Chapter One: Introduction…….….………….….….……………………………………………..1
Chapter Two: Material and methods…………………….…..………………………………….. 10
Study Protocol………………………………….……..………………………………….10
Study Population…………………………….……..….….……….……………….…….11
Radiographic Evaluation……………...….……….……….…….……………………….12
Statistical Analysis……………….….….……………….……………………………….14
Chapter Three: Results………………………….….…………………………………………….16
Chapter Four: Discussion……….……………...….…….……..…….…………………………..22
Chapter Five: Conclusion…………...……………………………………………….…………..30
References………………………………………………………………………………………..31

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Abstract
Objectives
To compare crestal bone loss of dental implants placed at sites with different graft materials
at the Herman Ostrow School of Dentistry who underwent bone augmentation procedures in the
Department of Advanced Periodontology. In the present study we evaluated the crestal bone loss
around implants with different restorative designs placed after a bone augmentation procedure via
guided bone regeneration using different biomaterials and/or autogenous block grafts.
Materials and Methods
This retrospective study includes subjects Screening of Axium® records of patients seen
at the Herman Ostrow School of Dentistry who underwent bone augmentation and dental implant
placement in the Department of Advanced Periodontology during the 2015-2022 period.
Inclusion criteria consisted of a) adults over 18 years old, b) bone augmentation with graft
materials and occlusive membranes and c) dental implants successfully placed at sites where bone
was augmented. Exclusion criteria consisted of a) uncontrolled systemic disease i.e. diabetes,
b) implants of which radiographs after placement were not available, and c) implants not
restored during the course of the study period.
The groups compared included dental implant sites with autogenous/allograft bone mix (group
A), sites with autogenous/xenograft bone mix (group B), and sites with autogenous bone alone
(group C).
The two outcomes evaluated were: alveolar crest bone levels at implant placement, at implant
crown impression, at delivery of restorative component, at six months after restorative loading,
one year after restorative loading, and further time points if available. The second outcome

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involved a comparison of sites where the implant’s final restoration was splinted versus nonsplinted. These were assessed by a radiographic comparison of marginal bone loss at peri-implant
alveolar crest sites as well as with the clinical evaluation depicted on the procedure notes
describing the outcome of the dental implants placed at bone augmented sites.
Survival was defined as the presence of a dental implant in the jaw. Success was defined using the
criteria from Karoussis et al. (2004): absence of mobility, absence of persistent patient subjective
complaints (pain, foreign body sensation, dysesthesia), no PPD > 5 mm, no PPD = 5 mm and BOP,
absence of continuous radiolucency around the implant, after the first year of service, annual
vertical bone loss that does not exceed 0.2 mm. An unsuccessful implant therefore was defined as
one that did not fulfill any of the following clinical or radiographic criteria: PPD > 5 mm, PPD =
5 mm with BOP (even at one implant site) or mesial or distal annual bone loss > 0.2 mm after the
first year of service (however, a periapical radiograph after 1 year of service was rarely available).
Results
The total number of patients that met the inclusion and exclusion criteria was 128. The
average age of the patients was 58.34 years old. Out of those subjects, a total of 198 dental implants
were included in the study. The average implant diameter was 3.75mm and the average implant
length was 9.93mm. The groups compared included 58 implant sites with autogenous/allograft
bone mix (group A), 25 implant sites with autogenous/xenograft bone mix (group B), and 115
implant sites with autogenous bone alone (group C). On average, the crestal bone at implant
placement was estimated to be 1.15mm (standard deviation 0.58), the crestal bone at impression
time was estimated to be 1.11mm (standard deviation 0.64). Crestal bone at delivery on average
measured 1.03mm (standard deviation 0.67), while crestal bone measured 12 months after

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delivery, when available, was on average 0.94mm (standard deviation 0.80). Two dental implants
failed before loading, and one after loading, all three from group A. However, the differences were
not statistically significant.
Insufficient data was reported on the clinical parameters of bleeding on probing or probing depths
above 5mm to determine any significant correlation with the bone graft or splinting variables.
About 60% of the implants studied were restored with splinted restorations and 40% of the implant
restorations were not splinted. Overall, the splinted group had a 0.31mm drop in crestal bone level
compared to the 0.09mm in the non-splinted group, this negative slope appeared over time and
was found to be statistically significant.
Conclusion
Within the limitation of the current retrospective study, it was concluded that there was no
significant difference for crestal bone remodeling using different graft materials. As a significant
finding, higher alveolar crestal bone resorption was observed around dental implants where the
definitive restorations where splinted compared to non splinted restorations. Further research is
needed to analyze the correlation of crestal bone loss with splinted restorations including different
restorative contour designs and number of restorations splinted together.

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Chapter One: Introduction
Rehabilitation of edentulous sites in the human dentition with dental implants may often
present clinical challenges due to the insufficient bone volume, anatomical factors and low-density
cancellous bone. While the literature reports various causes of bone loss including periodontal
disease, trauma, and medical conditions such as osteoporosis, it remains important to note that
simple tooth extraction is associated with dimensional changes of the alveolar ridge.
A variety of techniques have been proposed to augment lost or deficient bone. These include
ridge augmentation with bone block grafts, the use of particulate grafts, ridge splitting, distraction
osteogenesis, as well as guided bone regeneration (GBR) with various barrier membranes. These
techniques have all been proposed and compared as means to facilitate bone regeneration. While
block grafts were once the standard of care for alveolar ridge augmentation, a series of studies
advocated for utilizing less invasive techniques with GBR having similarly effective results and
lower morbidity (3).
Guided bone regeneration is one of the most predictable surgical procedures to reconstruct the
atrophic alveolar ridge. This technique can provide the necessary bone dimensions for dental
implant placement and osseointegration. Different grafting materials are used for guided bone
regeneration, including autogenous bone grafts, allografts, alloplasts, xenografts, and a mix of two
or more of these (Table 1). The gold standard for bone regeneration is autologous bone and it is
considered the ideal scaffold due to osteogenic, osteoinductive and osteoconductive proprieties.
Autologous bone grafts present some restrictions given the limited availability of the material from
the donor site, and the potential of additional morbidity for the patient. Heterologous bone

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substitutes, such as bovine or porcine derived bone, may represent a valid alternative because of
their osteoconductive properties. Furthermore, their structural characteristics seem to be similar to
human bone; they do not tend to induce adverse reactions and they show low resorbability. Such
properties appear to be appropriate for the guided bone regeneration procedure.
Table 1. Grafting materials used for guided bone regeneration procedures
The alveolar housing dimensions modified through bone augmentation for dental implant
placement has long been a subject of investigation, as graft stability may represent one of the
prognostic factors for long-term implant success. Several previous clinical studies have
investigated the radiographic changes of graft height and volume in augmented sites using different
grafting materials. Autologous bone grafts have been reported to have larger amount of resorption,
compared ton deproteinized bovine bone that show very slow or no resorption long term. A certain
amount of dimensional reduction of the graft is a physiological consequence of early remodeling
during graft healing, but only minor changes are expected thereafter (1).
The use of autogenous bone grafts with osseointegrated implants was discussed originally by
Brånemark et al, who used the iliac crest as a donor site (1,2). This early Swedish study looked at
completely edentulous cases and proposed the autogenous re-transplantation of bone from the iliac
crest to increase the bulk of the thin cortical bone. Since then, a great deal of research has further
increased the predictability and suitability of autogenous block grafting in daily clinical practice.

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Today the clinician has many factors to consider for autogenous bone grafting, including
harvesting and application. It is difficult to demonstrate the superiority of one surgical procedure
over another (3); the majority of clinical studies show very comparable bone gain and final implant
survival, with no single surgical method deemed a gold standard (4,5). For effective bone
regeneration, five key principles have been discussed in the literature (6,7):
1. Incision design/flap management
2. Site preparation—angiogenesis
3. Space maintenance
4. Graft stability
5. Tension-free primary closure
Following incisions and full-thickness flap elevation, decortication with intramarrow
perforations is advised (8,9). This will allow access to trabecular bone, which is known to be richer
in blood vessels and platelets, improves graft union to host bone, and increases the release of
circulating growth factors important for tissue regeneration. It was previously reported by Buser
et al that decortication allowed migration of cells with angiogenic and osteogenic potential. The
bone marrow also provides a rich source of undifferentiated progenitor cells. Seol et al also
previously showed that cortical perforations increase early bone formation after implant
placement. Wound stabilization and graft fixation are also necessary for predictable bone
augmentation. The initial clot formation that occurs is a rich source of growth factors, cytokines
and many signaling molecules that recruit cells to the wound site (10,11). Moreover, blood clots
serve as the precursor of initial highly vascular granulation tissue that is the site of initial
intramembranous bone formation and remodeling. Various studies have elucidated on the finding

4
that micro-motion of bone grafts and/or implants has consistently been associated with early graft
failure.
Space creation also plays a key role for this protocol for bone augmentation. However,
accomplishing tension-free closure over the recipient site, becomes critical to the success of the
graft incorporation. Therefore, flap management including periosteal release, is critically
important. Furthermore, studies have revealed the importance of excluding the epithelium and
connective tissue from populating the wound, a goal that has been shown to be effectively
accomplished with the utilization of barrier membranes. To reiterate, the concept of primary
wound closure is highly relevant during bone augmentation. Generally speaking, membrane
exposure has been associated with less attachment gain compared with membranes that remain
submerged.
Guided bone regeneration has become a common treatment modality for augmentation of ridge
deficiencies since the year 2000 for the regeneration of localized bone defects and implant site
development. A systematic review by Aghaloo and Moy showed excellent outcomes utilizing this
well-documented surgical technique among various surgical protocols used for localized ridge
augmentation (4).
Bone grafts and bone-graft substitutes
Due to its potential osteogenic, osteoconductive and osteoinductive properties, historically
autogenous bone has been considered the ideal grafting material for bone augmentation procedures
(12). However, morbidity and complications related to the donor site, limited graft availability and

5
unpredictable graft resorption are major limitations related to the use of autogenous grafts (13, 14).
As a means to overcome these shortcomings, bone-graft substitutes have been developed as
adjuncts to, or replacements for autogenous grafts in bone augmentation procedures.
Bone grafts and bone substitutes can be classified into four groups, according to their origin:
autografts, from the same individual; allografts, from another individual within the same species;
xenografts, from another species; and alloplasts, which are synthetically produced. As mentioned,
it has been claimed that grafts and bone-graft substitutes for guided bone regeneration need to
fulfill the following requirements: biocompatibility; osteoconductivity; adequate mechanical
support of the membrane to provide the volume for the regenerated bone; biodegradability; and
replacement with the patient’s own bone. Recent studies have suggested that a slow substitution
may be advantageous for maintenance of the augmented volume (15,16,17).
Originally bone grafting materials were developed to serve as a passive, structural scaffold,
with their main criterion being biocompatibility. However, advancements in regenerative medicine
and tissue engineering have enhanced each of their regenerative capacities, which some studies
claim to confirm with histologic analysis. Today many bone grafting materials have specially
designed surface topographies aimed to further guide new bone formation once implanted in situ.
Data from the United States has shown that allografts are the most utilized bone graft currently
available on the market (Figure 1). Interestingly, only 15% of augmentation procedures utilize
autogenous bone, despite it being the gold standard for bone grafting (18).

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Fig 1. Regarding the proportional use of each class of bone grafting material in the United States in 2019. The largest percentage
of regenerative procedures are performed with allografts (37% mineralized, 16% demineralized), followed by xenografts (22%),
autografts (15%), and synthetic grafts/bone morphogenetic protein (5% each) (18).
Considering the wide range of uses for bone grafting materials, the expectation should be that
no single material can fulfill the task of augmenting bone in every clinical situation. Furthermore,
in many clinical instances, a combination of two or more bone grafting materials is necessary to
lead to better and more predictable outcomes. The ideal graft should (a) contain osteogenic
progenitor cells within the bone grafting scaffold capable of laying new bone matrix, (b)
demonstrate osteoinductive potential by recruiting and inducing mesenchymal cells to differentiate
into mature bone-forming osteoblasts, and (c) provide an osteoconductive scaffold that facilitates
three-dimensional tissue ingrowth (19). Consequently, the gold standard for bone grafting is
autogenous bone because it possesses these three important biologic properties. Despite its potent
ability to enhance new bone formation, limitations including additional surgical time and cost, as
well as limited supply and additional patient morbidity have triggered the constant research for
alternatives.

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A variation of xenografts, which consist of minerals derived from animals, corals or algae, are
commercially available. The most documented bone substitute used in implant dentistry, is a
deproteinized bovine-derived bone mineral. Biocompatibility and osteoconductivity of
deproteinized bovine-derived bone mineral have been demonstrated in several preclinical studies.
However, whether deproteinized bovine-derived bone mineral is bioresorbable still remains
controversial (20). The presence of cells with osteoclastic characteristics was interpreted as a sign
of ongoing resorption of the deproteinized bovine-derived bone mineral bone-graft substitute (21).
A clinical trial including 20 patients concluded that deproteinized bovine-derived bone mineral
particles were not resorbed and remained encapsulated in the bone 11 years after sinus floor
augmentation (22). The clinical consequences of the pattern and rate of resorption of deproteinized
bovine-derived bone mineral in diverse patient situations remain to be investigated.
Recently, several new xenograft bone substitutes have been developed. Preclinical studies and
clinical case series demonstrated that these materials are biocompatible, osteoconductive and can
be used as bone substitutes without interfering with the normal reparative bone process (23, 24,
25). In a clinical study, deproteinized bovine-derived bone mineral blocks and collagen
membranes were applied to 12 patients to treat horizontal bone deficiencies before implant
placement (26). After 9–10 months, in 11 of 12 patients the resulting bone volume was sufficient
to allow implant placement in the ideal prosthetic position. It was therefore concluded that the
procedure was effective for horizontal ridge augmentation. These results are in agreement with a
preclinical study comparing autogenous bone blocks with deproteinized bovine-derived bone
mineral blocks for buccal ridge augmentation, in which a similar increase of ridge augmentation
was measured clinically in both groups (27). In the study, all sites treated with deproteinized

8
bovine-derived bone mineral blocks for horizontal bone ridge augmentation appeared, clinically,
to be appropriate for implant placement. Histologically, however, various studies found that
deproteinized bovine-derived bone mineral blocks were mainly embedded in connective tissue and
only a moderate amount of new bone formation was observed in peripheral parts of the graft (28,
29).
Between the several allografts available fresh-frozen bone, freeze-dried bone and
demineralized freeze-dried bone are the major examples. The main limitation of allografts is
derived from the risk of immunologic reactions and possible disease transmission as a result of
their protein content (30). Clinical studies have reported successful use of freeze-dried bone and
demineralized freeze-dried bone for bone augmentation concomitant to implant placement (31,32).
Bone allografts involve the harvesting of bone from a human cadaver and safely processing and
decontaminating it. They are categorized into two main groups: fresh-frozen bone or FDBA and
demineralized FDBA or DFDBA. While allografts have been the most widely utilized replacement
grafting material in North America, many Asian and European countries do not permit their use.
The main advantage of allografts over other commercially available bone substitute materials are
their incorporation of osteoinductive growth factors. Many studies have demonstrated their
effectiveness in promoting new bone formation across a wide array of defect types (33,34).
Allografts remain the ideal replacement material for a number of regenerative procedures utilized
in dentistry, including extraction socket healing, sinus elevation procedures, GBR procedures, and
other adjunctive grafting procedures in implant dentistry.
The last group of bone grafting materials includes all synthetically fabricated alloplasts. These
grafts generally do not possess the same osteogenic potential as the other classes and are not

9
commonly utilized in implant dentistry. Future research aimed at optimizing their potential with
and without growth factors is certainly an area of ongoing study.
The present retrospective clinical study aims to evaluate the behavior of different bone graft
materials, including autogenous bone grafts, allografts and xenografts in terms of dimensional
changes and bone regeneration in edentulous sites after a bone augmentation procedure via guided
bone regeneration and their correlation to crestal bone loss around dental implants placed under
the conditions of the graduate periodontology program at a university institution.
Hypothesis
• Hypothesis: There are no differences in crestal bone level changes and implant success
utilizing autogenous grafts, allografts and xenografts for bone regeneration procedures.
• Null hypothesis: Guided bone regeneration with allografts and xenografts will provide
different outcomes in volume gain and implant success depending on the graft material utilized.

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Chapter Two: 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 two residents in the
Advanced Periodontology Department at Herman Ostrow School of Dentistry of USC. The study
involved screening of Axium® records of patients seen at the Herman Ostrow School of Dentistry
who underwent bone augmentation with block grafts or guided bone regeneration (GBR) and
dental implant placement in the Department of Advanced Periodontology during the 2015-2022
period.
Inclusion Criteria
The main inclusion criteria for candidates to implant surgery were as follows: patients of
at least 18 years of age, in good general health, and able to undergo surgical and restorative
procedures (ASA-1 and ASA-2 according to the American Society of Anesthesiologists
classification system). Specific criteria for this study were as follows:
a) adults over 18 years old,
b) bone augmentation with graft materials and occlusive membranes and
c) dental implants successfully placed at sites where bone was augmented.
The diagnosis for patient inclusion was based on intraoral radiographs and clinical assessment.
The calibration was based on known implant diameter.

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Exclusion Criteria
The exclusion criteria were as follows: patients with uncontrolled systemic conditions (e.g.,
diabetes), implants of which radiographs after placement were not available, and implants not
restored during the course of the study period.
The three groups to be compared included:
Group A) implant sites where GBR was performed using an autogenous/allograft bone mix,
Group B) implant sites where GBR was performed with autogenous/xenograft bone mix, and
Group C) implant sites where bone augmentation was performed with autogenous bone alone.
The clinical outcomes evaluated were as follows:
Dental implant survival and success assessment at different time points including time of implant
placement, at time of delivery of restorative component, six months after the implant placement,
one year after restorative loading, and beyond the year, when radiographs and data was available.
The evaluation included:
a) radiographic comparison of marginal bone loss at peri-implant alveolar crest sites
b) implant survival and success placed at bone augmented sites

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Survival was defined as the presence of a dental implant in the jaw.
Success was defined using the criteria from Karoussis et al. (2004):
- absence of mobility
- absence of persistent patient subjective complaints (pain, foreign body sensation,
dysesthesia)
- no PPD > 5 mm, no PPD = 5 mm and BOP
- absence of continuous radiolucency around the implant
- after the first year of service, annual vertical bone loss that does not exceed 0.2 mm
An unsuccessful implant was defined as one that demonstrated any of the following clinical or
radiographic criteria: PPD > 5 mm, PPD = 5 mm with BOP, or mesial or distal annual bone loss >
0.2 mm after the first year of service (however, a periapical radiograph after 1 year of service was
rarely available).
Radiographic evaluation:
Bone level changes were evaluated by comparing the measurements at baseline (on the day
of implant placement) with those at follow-up visits specifically at time of implant crown
impression, delivery of restorative component, six months after the implant placement, one year
after restorative loading, and beyond the year (when such radiographs were available). In cases
where both mesial and distal implant surfaces had similar alveolar crest levels at placement,
measurements were obtained with intraoral radiographs that depicted the vertical distance between
the alveolar crest position and the most coronal bone to implant contact, with an average of both
mesial and distal measurements calculated at all time points. (Figure 2).

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In cases where the evaluators could observe (radiographically or expressed in the clinical notes)
that bone profiling and smoothening of one of the alveolar crest surfaces was significant, only the
untouched side was evaluated for that individual implant (Figure 3).
Fig. 2: Screenshots depicting the radiographic evaluation process from calibration, to crestal measurements at
implant placement and at restoration delivery. An average of both mesial and distal measurements were calculated
at all timepoints.
This decision was made on the premise that alveolar crest changes evaluated would be a product
of physiological ridge remodeling rather than clinician manipulation. All the intraoral radiographs
were taken using the parallel technique, full visibility of the implant threads and careful calibration
between the examiners was constantly practiced ensuring reproducibility. When the radiographs
did not meet the criterion, the implant was not taken into consideration. Measurements were
always performed by the same two investigators (D.K. and D.Z.) through the software Axium®
Imaging application, using the known implant diameter for calibration.

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Fig. 3: Screenshots depicting the radiographic evaluation process from calibration, to crestal measurements at
implant placement and at restoration delivery. Note the bone profiling completed at the mesial aspect.
Clinical notes were thoroughly evaluated for every surgical and prosthetic visits. Periodontal
charting and any patient symptoms or concerns reported with either the dental implants or the
restorations were reported in the study’s data collection. Clinical findings including probing
depths, bleeding on probing, clinical implant mobility, pain perception, suppuration, and the
restoration type (splinted vs non-splinted) were taken into consideration throughout the data
collection and production of study final results.
Statistical Analysis
The analysis was carried out using SAS Version 9.4 (SAS Institute, Cary, NC, USA).
Descriptive statistics were run for variables of interest. Continuous variables were reported using
means and standard deviations, whereas categorical variables were reported as counts and
percentages.

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Two analyses were carried out. The first looked at the crestal bone level stability as an
outcome to compare between the 3 graft types. To test whether there was a relationship among
bone graft material, type of restoration (splinted vs non splinted), and alveolar crest bone loss a
linear mixed model was run to account for repeat measures provided by some patients.
The second analysis involved looking at the rate of change over time (6 timepoints) in crest
values between all 3 graft types. This model also used a linear mixed model with patient as a
random effect. All models used a p-value <0.05 to denote statistical significance.

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Chapter Three: Results
The total number of patients that met the inclusion and exclusion criteria was 128, with a
total of 77 females and 51 male subjects. The average age of the patients was 58.34 years old. Out
of those subjects, a total of 198 dental implants were included in the study. The average implant
diameter was 3.75mm and the average implant length was 9.93mm. As depicted in Figure 2a and
2b. the groups compared included 58 implant sites with autogenous/allograft bone mix (group
A), 25 implant sites with autogenous/xenograft bone mix (group B), and 115 implant sites with
autogenous bone alone (group C). A total of 3 dental implants were reported as failures and were
explanted, 2 failed before being loaded and 1 after loading average, all 3 were sites with
autogenous/allograft mix. This finding, however, was not statistically significant. The intra rater
and inter-rater reliability was assessed using an intraclass correlation coefficient (ICC) and its
corresponding 95% confidence interval (CI).
Table 2 a.b. Comparison of graft material variables and mean alveolar crest levels at different time points

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Fig 4. Graft material groups and mean alveolar crest changes throughout the study.
As depicted in Figure 4: For group A (allograft/autogenous mix), amongst the 58 implant
grafted sites, the mean crestal bone at implant placement was 1.14mm (standard deviation 0.51).
The crestal bone level at time of restoration delivery had a mean value of 1.09mm (standard
deviation 0.71). The mean alveolar crest value 12 months and above was calculated to be 1.02mm
(standard deviation 0.70) Figure 4a. When calculating the mean amount of bone level changes, it
was estimated that a total of 0.12mm of alveolar bone remodeled from the time of implant
placement compared to over 12 months later.
Fig 4a. Allograft group A - alveolar crest changes through the main timepoints

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For group B (xenograft/autogenous mix), amongst the 25 implant grafted sites evaluated
in this study, the mean crestal bone at implant placement was 1.19mm (standard deviation 0.87).
The crestal bone level at time of restoration delivery had a mean value of 1.04mm (standard
deviation 0.86). The mean alveolar crest value 12 months and above was calculated to be 0.90mm
(standard deviation 0.72) Figure 4b. When calculating the mean amount of bone level changes, it
was estimated that a total of 0.29mm of alveolar bone remodeled from the time of implant
placement compared more than 12 months later.
Fig 4b. Xenograft group B - alveolar crest changes through the main timepoints
For group C (autogenous only), amongst the 115 implant grafted sites evaluated in this
study, the mean crestal bone at implant placement was 1.15mm (standard deviation 0.53). The
alveolar crest bone level at time of restoration delivery had a mean value of 1.01mm (standard
deviation 0.73). The mean alveolar crest value 12 months and above was calculated to be 0.97mm
(standard deviation 0.69) Figure 4c. When calculating the mean amount of bone level changes, it
was estimated that a total of 0.18mm of alveolar bone remodeled from the time of implant
placement in relation to more than 12 months later.

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Fig 4c. Autogenous group C - alveolar crest changes through the main timepoints
Overall, when all values were added and an average value was obtained crestal bone at
implant placement was estimated to be 1.15mm (standard deviation 0.58), the crestal bone at
impression time was estimated to be 1.11mm (standard deviation 0.64). Crestal bone at delivery
on average measured 1.03mm (standard deviation 0.67), while crestal bone measured 12 months
after delivery, when available, was on average 0.94mm (standard deviation 0.80). When
comparing the mean alveolar bone level changes between all three groups (0.12mm, 0.29mm,
0.18mm) group B showed the highest mean crestal bone loss, followed by group C and finally
group A. These changes between the groups were not statistically significant.

20
Insufficient data was reported on the clinical parameters of bleeding on probing or probing
depths above 5mm to determine any significant correlation with the bone graft or splinting
variables. About 110 (or 60%) of the implants studied were restored with splinted restorations and
88 (or 40%) of the implant restorations were not splinted. For the splinted group, the mean crestal
bone at implant placement was 1.16mm (standard deviation 0.51). The alveolar crest bone level at
time of restoration delivery had a mean value of 0.97mm (standard deviation 0.63). The mean
alveolar crest value 12 months and above was calculated to be 0.85mm (standard deviation 0.58)
(Figure 5).
Fig. 5: Splinted vs non-splinted implant restoration distribution. Table depicts the crestal bone average measures in
relation to the restoration type.

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For the non-splinted group, the mean crestal bone at implant placement was 1.15mm (standard
deviation 0.73). The alveolar crest bone level at time of restoration delivery had a mean value of
1.14mm (standard deviation 0.68). The mean alveolar crest value 12 months and above was
calculated to be 1.06mm (+/-0.63). Overall, the splinted group had a 0.31mm drop in crestal bone
level compared to the 0.09mm in the non-splinted group, this negative slope appeared over time
and was found to be statistically significant (Figure 6).
Fig. 6: Splinted vs non-splinted implant restoration and mean crestal bone loss data.

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Chapter Four: Discussion
The present retrospective study aimed to evaluate the crestal bone loss of implants placed
in different bone graft materials, including autogenous bone grafts, allografts and xenografts. The
importance of crestal bone stability around dental implants for the success and longevity of
treatment cannot be overemphasized. The radiographic bone loss is an important measure of
treatment outcome. It is well accepted by clinicians that stable bone with remodeling of less than
0.2 mm per year is one measure of successful long-term implant treatment, along with no bleeding
on probing and a probing depth of no more than 5 to 7 mm (35). On the other hand, crestal bone
loss may be indicative of a failing implant — peri-implant tissue disease that can lead to a loss of
the implant, leaving the clinician uncertain of the implant’s long-term prognosis.
Crestal bone loss has been classified into different types. For example, early crestal bone loss
is defined as bone resorption around the neck of the dental implant from placement to 1 year after
loading. This definition is most likely based on the implant success criteria suggested by
Albrektsson et al in 1986, which state that 1.5 mm of bone loss within the first year of loading can
be considered a success if later bone loss does not exceed 0.2 mm annually. This concept was
developed after observations of the original Brånemark implants; however, implants in
contemporary dentistry have evolved with various designs and surfaces that result in higher
success and bone stability. Therefore, some recent studies have questioned the accepted success
criteria, stating that it is possible for implants to have lower amounts of bone loss after 1 year of
function. For example, it was reported that implants with micro threads in the neck region and a
conical implant-abutment interface may be expected to have only 0.33 to 0.56 mm of bone loss
within 12 months of loading (36).

23
In the dental literature, early crestal bone loss is sometimes described as “saucer-shaped,”
“crater-like,” or “ditch-like,” as these descriptions indicate the typical pattern of bone loss seen on
radiographs. This type of loss has historically been considered physiologic as well as an
unavoidable result of biologic remodeling and differences in bone density. Occlusal trauma has
been suggested as a factor; however, if occlusal functioning causes constant overload at the implant
neck area, it is unclear why bone loss seems to cease after some time rather than continuing until
complete implant failure. To explain such phenomenon, it has been suggested that bone is less
dense and more sensitive to stresses in the beginning of prosthetic loading, causing overloading
with subsequent resorption; however, in theory, within the first year of loading, bone matures and
gains density, so the occlusal forces that initially cause crestal bone loss are not strong enough to
evoke further bone resorption. And yet, despite constant innovation and development of new
effective techniques and materials, clinicians still face the problem of bone loss.
It becomes important to consider that most dental implant systems consist of 2 components:
the endosteal fixture (the implant), which is placed in a first surgical phase, and the transmucosal
connection (the abutment), which is typically attached once implant osseointegration is successful,
in order to support a prosthetic restoration. When the prosthetic abutment is placed on the
subgingival implant, contact with the peri-implant soft tissue and microbial dissemination into the
implant body becomes nearly unavoidable. Penetration of oral microorganisms through gaps
between these components may be a risk factor for soft tissue inflammation or be responsible for
the failure of peri-implantitis treatment (38). This connective gap is located near the level of the
alveolar bone crest for most implant systems; thus, microbial colonization of the gap may lead to
bone resorption. Location of such gap near the alveolar crest could also be responsible for the 1
mm of bone loss observed during the first year of functional loading of implants (39).

24
Multiple in vitro studies have demonstrated bidirectional fluid and bacterial leakage into and
out of implant- abutment assemblies of common implant systems. Microbial penetration along the
implant-abutment interface of the Brånemark System implant (Nobel Biocare, Sweden) has been
reported; inward as well as outward leakage was shown in the study (39). Clinical studies have
also demonstrated the presence of viable bacteria on the inside of implant assemblies.
Regarding implant dentistry, the hard and soft tissue biological dimensions can. be initially
recorded based upon the timing of the initial load. This difference in record keeping is observed
on comparing two‐stage dental implant cases when tissue dimensions are defined after the initial
submerged healing period, versus non-submerged/single‐stage dental implants, where
measurements are recorded at the time of implant placement (40).
Considering the novelty in technology on dental implant joints, Jokstad et al. noted the
development of internal connections showing improved results regarding esthetic outcomes and
mechanical stability (41). Currently, common examples of internal implant‐abutment connection
designs are the internal hexagonal and the Morse taper connection. A design feature of the Morse
taper implant‐abutment connection is an internal joint design between two conical structures. In
implant dentistry, a conical “male” abutment is tightened into a “female” conical fixture design.
The internally tapered design creates significant friction via the high propensity of parallelism
between the two structures within the joint space. The Morse taper angle determination will be
according to the mechanical properties of each material. For instance, titanium‐based structures
have an ideal relationship between contacting surface angles and coefficient of friction.
In concept at least, the internal Morse taper implant‐abutment design aligns the micro-gap sizes
to be further separated from the marginal bone. In addition, this internally stable design allows for
a narrower abutment platform abutment design that can be then combined with platform switching.

25
In studies, the platform switching abutment design has been shown clinically to reduce marginal
bone loss and provide additional space for soft tissue development and maintenance over longer
follow‐up periods (42).
In our study, we didn’t look into the type of abutment connection as a variable, yet we evaluated
crestal bone loss of different implant platforms placed in a variety of bone graft materials,
including autogenous bone grafts, allografts and xenografts. Bone level changes were evaluated
by comparing the measurements of crestal bone to first bone to implant contact at baseline (on the
day of implant placement) with those at follow-up visits specifically at time of implant crown
impression, delivery of restorative component, six months after the implant placement, one year
after restorative loading, and beyond the year. It was hypothesized that comparable radiographic
and clinical outcome in crestal bone level changes and implant success were expected utilizing
autogenous grafts, allografts and xenografts for guided bone regeneration procedures.
The results of the present study convey that, regardless of the grafting material involved, all
alveolar crest bone levels resulted in some degree of remodeling leading to bone resorption. This
is in agreement with aforementioned information developed after observations of the original
Brånemark implants. As scientific data are lacking on the influence of guided bone regeneration
on the survival and the success rates of implants, a statement on the need for guided bone
regeneration in cases of small bone dehiscences cannot be made. However, augmentation of buccal
bone defects may play an important role as far as the esthetic outcome of the rehabilitation is
concerned.
It has been demonstrated clinically that guided bone regeneration of peri-implant defects, in
conjunction with transmucosal healing, is a successful procedure with a high degree of defect
repair.

26
Biomaterials used in dentistry include diverse bone grafts and barrier membranes. They come
from various sources including that of human origin from the patients own body (autogenous
graft), from a human donor source (allograft), animal sources (xenograft), and synthetic sources
(alloplast). In a multicultural country such as The United States, we have patients in our office that
come from all walks of life. These patients will present to our office with a variety of ethical,
religious, cultural, and philosophical beliefs, and may have a strong objection to a certain
material. Similarly, as dentists, we often have our own treatment and material preferences based
on our own experience and biases. We need to support our material and treatment selection with
strong scientific evidence that supports our treatment recommendations. One can define evidencebased medicine as “the integration of the best research evidence with clinical expertise and patient
values.” We often face a dilemma and a tug-of-war when recommending a material, because the
material that we feel provides the strongest outcome may be a material that a patient will object
to, because of strong and very personal convictions. Patients always have the right to refuse a
material, or refuse treatment despite our recommendations, even when supported by science.
Understanding the biomaterials available to clinicians today will allow a well-informed, and
evidence-based discussion, taking into account individual patient beliefs and concerns. The
trusting and long-standing relationship a clinician may cultivate with their patients develops over
time and can very well be a direct result of continued open communication and dialogue to have
with every treatment recommendation. Patients appreciate it when they are included in the
decision-making process, and when you have taken the time to help them understand all aspects
of treatment. This can also help alleviate any misunderstanding that can lead to future conflict.
Retrospective studies may not be the highest form of evidence and they do present with limitation

27
that are important to acknowledge, yet this study can certainly provide anecdotal evidence one can
use when discussing treatment options as well as material alternative with patients.
Future developments in bone regeneration procedures will have the goal of simplifying the clinical
handling and influencing the biologic processes. New materials should enhance optimal cell
ingrowth and present adequate mechanical properties sufficient to maintain space for bone
regeneration. To simplify clinical handling, no membranes or procedures for mechanical fixation
should be needed. The use of synthetic bone substitutes could decrease the risk of disease
transmission and immunologic reactions potentially inherent to the use of organic based materials.
In turn, this could result in lower morbidity of surgical procedures compared with the harvesting
and transplantation of autogenous tissue. Customized devices for bone regeneration, produced
using three-dimensional imaging and computer-aided manufacturing technologies, could represent
a very efficient new process for treatment.
From a biological standpoint, application of growth and differentiation factors may induce faster
growth of bone into the area to be regenerated, thus reducing the healing time and treatment efforts
of extended bone defect volumes (43). Modifying the biomaterial surface, which can be achieved
by coating with cell-adhesion molecules or nanoparticles, may lead to more desirable tissue
responses (44). The incorporation of antimicrobial solutions might mitigate the influence of
bacterial contamination at the regenerated site (45). Additional efforts of future research should
focus on understanding the regulation of gene expression and the molecular features of the bone
regeneration process. Cell-based tissue engineering and gene-delivery therapy represent new
therapeutic strategies that have the potential to overcome several shortcomings associated with the
existing bone regeneration techniques (46).

28
In our study, splinting was found to have 3.4 times greater crestal bone remodeling in multivariate
analyses adjusted for duration and mean annual number of maintenance visits. This finding is in
contrast to the conclusions of a systematic review that a) there was no difference in MBL between
splinted and non-splinted implant restorations and b) splinting was associated with lower risk for
implant failure (37). On the contrary, our finding was in agreement with another study that also
found greater risk of peri-implant bone loss in splinted implant restorations (38). To explain this
observation, one can offer the possibility that splinted restorations may present a bigger challenge
for oral hygiene access, as well as the possibility that the restorative contours might fill more space
and lead to further bone remodeling. A study by Lin, et al on the influence of vertical platform
discrepancies and splinting, on marginal bone levels, suggests that the crestal bone loss beyond
the initial remodeling could occur when the adjacent implant platforms are at different vertical
levels with a tendency of bone loss towards the platform level of the most apically positioned
implant (38).
It should be noted that our study was not able to assess the accessibility for cleaning the implants
and their restorations.
Further, in this study we measured the crestal bone changes from crest of bone to first bone to
implant contact. With this measurement we evaluate the stability of the entirety of bone and net
outcome of crestal bone changes in grafted sites. The total changes can therefore be influenced by
physiological alveolar bone crest remodeling, remodeling from flap elevation, difference in
implant platform designs, operator manipulation of tissues, amongst other factors.

29
This study has several limitations. Since the study was performed retrospectively via twodimensional radiographs it is impossible to determine whether the angulation of the radiographs
was consistent at all time points. The measurement was not performed from a pre-determined level
such as the implant platform which could lead to a higher skew in the data collection. Additionally,
all three groups evaluated had some percentage of autogenous bone material involved. This
percentage was not standardized, and it would be impossible to retrospectively evaluate such
differences. The influence of the autogenous graft might have played a part in the lack of
differencesthat we observed in this study’s results. Moreover, the data collection involved different
implant systems with different restorative connections, such features can influence the behavior of
bone formation around the dental implants.

30
Chaper Five: Conclusion
In conclusion, we retrospectively evaluated two-dimensional radiographs on alveolar crest
level changes of implant sites grafted with three different configurations of grafting materials
including autogenous bone alone, as well as allograft and xenograft mixes with autogenous
particles. We did not find statistically significant differences in bone remodeling from the time of
implant placement to the time of implant delivery and over 12 months after loading amongst
different groups. Higher alveolar crestal bone loss was observed around dental implants where the
definitive restorations where splinted compared to independent non-splinted restorations. Further,
well-designed, and calibrated studies should be conducted to validate our findings. Future studies
are needed to analyze the correlation of crestal bone loss with splinted restorations including
different restorative contour designs and number of restorations splinted together.

31
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Abstract (if available)

Abstract Objectives: To compare crestal bone loss of dental implants placed at sites with different graft materials at the Herman Ostrow School of Dentistry who underwent bone augmentation procedures in the Department of Advanced Periodontology. In the present study we evaluated the crestal bone loss around implants with different restorative designs placed after a bone augmentation procedure via guided bone regeneration using different biomaterials and/or autogenous block grafts.

Materials and Methods: This retrospective study includes subjects Screening of Axium® records of patients seen at the Herman Ostrow School of Dentistry who underwent bone augmentation and dental implant placement in the Department of Advanced Periodontology during the 2015-2022 period. Inclusion criteria consisted of a) adults over 18 years old, b) bone augmentation with graft materials and occlusive membranes and c) dental implants successfully placed at sites where bone was augmented. Exclusion criteria consisted of a) uncontrolled systemic disease i.e. diabetes, b) implants of which radiographs after placement were not available, and c) implants not restored during the course of the study period. The groups compared included dental implant sites with autogenous/allograft bone mix (group A), sites with autogenous/xenograft bone mix (group B), and sites with autogenous bone alone (group C). The two outcomes evaluated were: alveolar crest bone levels at implant placement, at implant crown impression, at delivery of restorative component, at six months after restorative loading, one year after restorative loading, and further time points if available. The second outcome involved a comparison of sites where the implant’s final restoration was splinted versus non-splinted. These were assessed by a radiographic comparison of marginal bone loss at peri-implant alveolar crest sites as well as with the clinical evaluation depicted on the procedure notes describing the outcome of the dental implants placed at bone augmented sites. Survival was defined as the presence of a dental implant in the jaw. Success was defined using the criteria from Karoussis et al. (2004): absence of mobility, absence of persistent patient subjective complaints (pain, foreign body sensation, dysesthesia), no PPD > 5 mm, no PPD = 5 mm and BOP, absence of continuous radiolucency around the implant, after the first year of service, annual vertical bone loss that does not exceed 0.2 mm. An unsuccessful implant therefore was defined as one that did not fulfill any of the following clinical or radiographic criteria: PPD > 5 mm, PPD = 5 mm with BOP (even at one implant site) or mesial or distal annual bone loss > 0.2 mm after the first year of service (however, a periapical radiograph after 1 year of service was rarely available).

Results: The total number of patients that met the inclusion and exclusion criteria was 128. The average age of the patients was 58.34 years old. Out of those subjects, a total of 198 dental implants were included in the study. The average implant diameter was 3.75mm and the average implant length was 9.93mm. The groups compared included 58 implant sites with autogenous/allograft bone mix (group A), 25 implant sites with autogenous/xenograft bone mix (group B), and 115 implant sites with autogenous bone alone (group C). On average, the crestal bone at implant placement was estimated to be 1.15mm (standard deviation 0.58), the crestal bone at impression time was estimated to be 1.11mm (standard deviation 0.64). Crestal bone at delivery on average measured 1.03mm (standard deviation 0.67), while crestal bone measured 12 months after delivery, when available, was on average 0.94mm (standard deviation 0.80). Two dental implants failed before loading, and one after loading, all three from group A. However, the differences were not statistically significant. Insufficient data was reported on the clinical parameters of bleeding on probing or probing depths above 5mm to determine any significant correlation with the bone graft or splinting variables. About 60% of the implants studied were restored with splinted restorations and 40% of the implant restorations were not splinted. Overall, the splinted group had a 0.31mm drop in crestal bone level compared to the 0.09mm in the non-splinted group, this negative slope appeared over time and was found to be statistically significant.

Conclusion: Within the limitation of the current retrospective study, it was concluded that there was no significant difference for crestal bone remodeling using different graft materials. As a significant finding, higher alveolar crestal bone resorption was observed around dental implants where the definitive restorations where splinted compared to non splinted restorations. Further research is needed to analyze the correlation of crestal bone loss with splinted restorations including different restorative contour designs and number of restorations splinted together.

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Creator Kruk-Leahy, Daniel (author)

Core Title Retrospective analysis of crestal bone changes on dental implant sites after a bone augmentation procedure: graft material comparisons

School School of Dentistry

Degree Master of Science

Degree Program Biomedical Implants and Tissue Engineering

Degree Conferral Date 2024-08

Publication Date 07/01/2024

Defense Date 06/05/2024

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

Tag allografts,autografts,block grafts,dental implants,guided bone regeneration,splinted restorations,xenografts

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Advisor Kar, Kian (committee chair), Chen, Casey (committee member), Paine, Michael (committee member)

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