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Retrospective analysis of early implant placement in non-grafted extraction sites: two-dimensional radiographic evaluation of crestal bone remodeling in four implant systems

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Retrospective analysis of early implant placement in non-grafted extraction sites: two-dimensional radiographic evaluation of crestal bone remodeling in four implant systems

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Content Retrospective analysis of early implant placement in non-grafted extraction sites:
Two-dimensional radiographic evaluation of crestal bone remodeling in four implant systems
By
Leah Andriasian, DDS
A Thesis Presented to the
FACULTY OF THE USC HERMAN OSTROW SCHOOL OF DENTISTRY
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(BIOMEDICAL IMPLANTS AND TISSUE ENGINEERING)
August 2024
Copyright 2024 Leah Andriasian

Table of Contents
List of Tables……………………………………………………………………………………iii
List of Figures……………………………………………………………………………………iv
Abstract…………………………………………………………………………………………..v
Introduction……………………………………………………………………………………….1
Chapter 1: Methods & Materials……………..………………………………………………….7
Chapter 2: Results………………………………………………………………………………..10
Chapter 3: Discussion…………………………………..………………………………………..15
Chapter 4: Conclusion……………………………………………………………………………19
Figures and Tables……………………………………………………………………………….20
References………………………………………………………………………………………31
ii

List of Tables
Table 1: Average Bone Level…………………………………………………………………….24
Table 2: 3i Osseotite Bone Level Change……………………………………………………….25
Table 3: Internal Connection Bone Level Change………………………………………………26
Table 4: Splinted Implant Bone Level Change………………………………………………….27
Table 5: Average Bone Level Change in implants diameter > 4 mm……………………………28
Table 6: Average Bone Level Change External vs. Internal Connection………………………..29
Table 7: Average Bone Level Change Tissue-Level Platforms………………………………….30
iii

List of Figures
Figure 1-1 Implant Connection Distribution……………………………………………………20
Figure 1-2 Implant Distribution…………………………………………………………………21
Figure 1-3: Anterior/Posterior Implant Distribution…………………………………………….22
Figure 1-4: Anterior Implant Distribution……………………………………………………….23
Figure 2: Average Bone Level………………………………………………………………….. 24
Figure 3: 3i Osseotite Bone Level Change………………………………………………………25
Figure 4: Internal Connection Bone Level Change……………………………………………..26
Figure 5: Splinted Implant Bone Level Change…………………………………………………27
Figure 6: Average Bone Level Change in implants diameter > 4 mm…………………………..28
Figure 7: Average Bone Level Change External vs. Internal Connection……………………….29
iv

Abstract
This study seeks to investigate the effect of marginal bone loss around dental implants
from the time of placement, to the time of impression and 6-12 months after crown delivery. The
aim of this retrospective analysis is to assess implant placement at non-grafted extraction sites
with early placement protocol and to evaluate crestal bone remodeling in four implant systems
amongst different restorative platform types, including external hex, internal connection, and
transmucosal platform.
Electronic dental records were obtained from patients who underwent dental implant
placement in USC’s faculty practice from 2012 till December 2023. Implants were placed at sites
with history of simple or surgical extractions without ridge preservation by providers at USC’s
faculty practice. Implant placement was done by one experienced periodontist. The implant
systems represented in the study were Straumann Bone Level NC or RC, Straumann TL,
Dentium, Zimmer Biomet 3i Certain, and Zimmer Biomet 3i Osseotite. Two-dimensional
radiographs were taken at the time implant placement, impression stage and 6 months to 1 year
follow up after implant crown delivery. These radiographs were used to evaluate mesial and
distal crestal bone level changes from the platform of the dental implants to the first bone to
implant contact. The marginal bone loss on mesial and distal were recorded at the time of
implant placement, impression and 6-12 months follow up post-crown delivery.
Charts of 158 patients and 197 implants were included in the study. Among the total of
197 implants placed, 84 (42.63%) were external hex connection, 100 (50.76%) were internal
connection and 13 (6.6%) were tissue-level (TL) platforms. External hex implants exhibited the
v

highest marginal bone loss compared to either the internal platform implants or tissue-level
implants from the time of placement, impression taking and 6-12 months post-crown delivery
(p<0.0001). A strong correlation was found between splinted implants and increased marginal
bone loss on the mesial and distal from the time impression (p=0.05) , and 6-12 months postcrown delivery (p=0.02). A significant difference was seen for splinted implants and average
bone loss at 6-12 months post-crown delivery (p=0.03). No statistically significant correlation
was found between tissue-level implants and marginal bone loss on the mesial, distal, and
average bone loss at the time of implant placement, impression taking, and 6-12 months postcrown delivery.
vi

Introduction
Dental implants have become a widely accepted solution for replacing missing teeth,
offering both functional and esthetic benefits over traditional dentures and bridges (1).
Successful implant placement relies on the conditions of the alveolar ridge, which can be
compromised following tooth extraction. It has been heavily documented that after tooth
extraction there are dimensional changes to the alveolar ridge in both the apicocoronal and
buccolingual dimensions (2,3). Resorption of the alveolar buccal bone is more pronounced than
that of the palatal bone plate (4). It has been determined that the buccal wall is comprised of
bundle bone which loses its function after the tooth is extracted and thus resorbs as a result (3).
The greatest diminution of the alveolar ridge occurs during the first months after tooth
extraction. Changes in soft and hard tissue are also seen during this healing period (5). The
healing process of an extraction socket involves several stages, starting with the formation of a
blood clot. This clot is eventually replaced by woven bone as the socket walls undergo resorption
and gradual remodeling. Eventually, trabecular bone fills the extraction sites, forming a residual
bony ridge that continues to remodel throughout the patient's edentulous life, sustaining ongoing
resorptive changes (6). Given the importance of ridge dimensions, preserving the alveolar crest
after tooth extraction is crucial for maintaining the vertical and horizontal dimensions of the
alveolar ridge (7). Numerous studies have proposed various ridge preservation methods,
including the use of different grafting materials and occlusive membranes (8,9). These
approaches help prevent soft-tissue invagination and the formation of fibrous tissue in the
coronal portion of the alveolus (11, 12). Although autogenous bone is generally considered the
gold standard for bone augmentation, harvesting autogenous bone for minor bone deficiencies
1

may be impractical. Many researchers have evaluated the effectiveness of using allografts or
xenografts for these purposes, as they eliminate the need for an additional surgical site for bone
collection (13-15). A comprehensive systematic review concluded that implants placed in
augmented edentulous sites exhibit a survival rate comparable to those placed in native bone
(16). Soft and hard tissue characteristics of the healing socket affect the decision to place an
implant following tooth extraction. Though these characteristics do not follow rigid time frames
they vary according to the site and specific patient factors. This often necessitates the use of bone
grafts to ensure sufficient bone volume for implant stability (17).
The timing of implant placement post-extraction can significantly impact clinical
outcomes. Immediate placement has the advantage of reducing treatment time and maintaining
alveolar bone height, but poses challenges related to primary stability and soft tissue
management (18). One of the most important requirements of immediate implant placement is to
have a fully intact facial bony wall (>1mm) with a thick gingival phenotype (19). Various CBCT
studies have found that a thick wall phenotype is rarely seen in the anterior maxilla (20, 21, 22).
Braut et al specifically analyzed the facial bone wall thickness at different tooth positions in the
anterior maxilla. They found that only 4.6% of central incisor sites had a thick wall phenotype (>
1 mm), compared to 27.5% of first premolar sites. There appears to be a correlation between the
facial bone wall phenotype and soft tissue biotype (23), although recent studies have shown
conflicting results, likely due to methodological differences (24).
2

Early implant placement, with soft tissue healing in the socket, typically occurs 4-8
weeks after extraction (25). Some advantages to this time frame are that it allows for initial soft
tissue healing, reduces risk of infection and soft tissue complication and facilitates better primary
stability than immediate implant placement. Several biologic events take place during this time
which are in favor for both the clinician and the patient, which simplifies the surgical procedure
and reduces the risk for post-surgical complications. Soft tissue healing will provide an
additional 3-5 mm of keratinized mucosa in the future implant site and the bundle bone will
reorganize which will affect the mid-facial aspect of the socket (26).
Early placement with partial bone healing, typically 12-16 weeks after extraction
provides further bone healing maturation and better opportunity for initial implant stability (24).
This approach is used when a peri-apical bony lesion is present and does not allow implant
placement in the correct position with primary stability in immediate or early implant placement.
Some advantages are that it ensures complete healing of soft tissues and any residual infection
and generally provides good primary stability and predictable outcomes. Early implant
placement has traditionally been the standard approach, offering high survival rates and
predictable outcomes. It is particularly advantageous in cases where immediate or early
placement is contraindicated due to infection or insufficient bone quality (27, 28). All implants
placed in this study were done utilizing the early placement protocol.
Delayed implant placement protocols are more than 6 months post-extraction healing. For
patients, this is not as attractive of a treatment option since the healing time frame is 6 months or
longer. There are certain indications for delayed placement which can be classified into either
patient or site specific reasons (26). One of the patient specific reasons for delayed implant
3

placement includes adolescent patients with trauma related tooth loss or an age too young for
implant therapy. Site specific reasons for delayed implant placement can include periodontal
apical lesions or teeth that will have insufficient bone volume to stabilize the implant with either
immediate or early placement (29).
After dental implants are placed, crestal bone remodeling also takes place. Crestal bone
remodeling around dental implants is a critical factor influencing the success and longevity of
implant-supported prostheses. This process involves changes in the bone at the crest of the
alveolar ridge surrounding the implant and can be affected by numerous factors, including
implant design, surgical technique, loading conditions, and biological factors. Understanding the
pathophysiology and contributing factors to crestal bone remodeling is essential for optimizing
implant outcomes and preventing complications.
There are several factors which can contribute to crestal bone remodeling around dental
implants. This is a dynamic process influenced by the body's physiological responses to the
implant. The initial phase involves bone resorption followed by new bone formation. This
remodeling process is essential for achieving osseointegration, where the bone firmly attaches to
the implant surface. However, factors such as mechanical loading, peri-implant inflammation,
and surgical trauma can disrupt this balance, leading to bone loss. Several factors contribute to
crestal bone remodeling around dental implants. Notably, the presence of a microgap at the
implant-abutment interface can allow bacterial infiltration, leading to inflammation and bone
resorption (30, 31). Peri-implant inflammation, often due to bacterial contamination, can also
lead to bone resorption (32). One way thought to reduce crestal bone loss around dental implants
is to use platform switching. This technique involves using an abutment with a smaller diameter
4

than the implant platform, which has been shown to reduce crestal bone loss by shifting the
inflammatory cell infiltrate away from the bone crest (33, 34). The restorative contours including
the shape of the crown can influence the distribution of mechanical forces on the implant,
affecting bone remodeling (35). Additionally, functional overloading of implants can result in
crestal bone loss due to excessive stress on the peri-implant bone (35). The use of grafted bone
can influence the initial stability and subsequent remodeling of the bone around implants. Studies
have shown varying effects on bone remodeling depending on the graft material and technique
used (36). It was concluded that implants placed in grafted extraction sockets demonstrated
clinical performance comparable to those in non-grafted sites regarding implant survival and
marginal bone loss. However, grafted sites enabled the placement of larger implants and required
fewer augmentation procedures during implant placement compared to naturally healed sites
(37). A randomized control trial by the Avila Ortiz group found that additional GBR was needed
in 48.1% of cases where socket grafting was not done at the time of extraction and 11.5% in
ridge preserved sites. When quantitative analyses were performed it was revealed that alveolar
ridge preservation (ARP) is an effective therapy to reduce the dimensional reduction of the
alveolar ridge that normally takes place after tooth extraction. In congruence with previous
systematic reviews, it was observed that ARP via grafting of sockets does not predictably prevent
resorption in full and that the outcomes vary substantially across the sites receiving the same
therapies. This suggests that the effects of ridge preservation may largely be dependent on sitespecific factors (38).
5

Thus, the aim of this retrospective study is to assess implant placement at non-grafted
extraction sites with early placement protocol and to evaluate crestal bone remodeling in four
implant systems amongst different restorative platform types, including external hex, internal
connection, and transmucosal platforms.
6

Chapter 1: Materials and Methods
Study Design:
This study was conducted using the Herman Ostrow School of Dentistry’s patient
records. The University of Southern California Institutional Review Board (IRB) approved the
use of patient records for this retrospective study (HS-23-00563). Radiographs and chart note
documentation records for 288 implants were acquired from the Herman Ostrow School of
Dentistry Faculty Practice USC Axium Records from 2012 to December 2023.
Study Population:
The study population were patients treated at Herman Ostrow School of Dentistry Faculty
Practice. Patient population consisted of 80 females and 78 males with a range of 22-93 years old
and average age of 61.5 years old.
Inclusion criteria:
The inclusion criteria for the study: (1) Patients over the age of 18 years old. (2) Record
of extraction available at USC. (3) Extraction completed at USC’s Faculty Practice (4) Dental
implant placement done by the same practitioner, K.K.
Exclusion criteria:
The exclusion criteria for the study: (1) Existing healed sites without record of extraction
at USC. (2) Radiographs that were non-diagnostic where the mesial and distal bone levels could
not be discerned. (3) Current smokers. (4) History of previous implant failure. (5) Medically
compromised, uncontrolled ASA II, III, or IV patients.
7

Clinical Records Assessment:
An Axium query search was pulled via the extraction code followed by surgical implant
body placement code. From there, 288 implants were identified and two-dimensional
radiographs, medical history records, clinical chart notes and scanned implant identification were
obtained. Chart notes were reviewed for how extraction was executed, whether or not there was
grafting at the time of extraction, the implant site, implant system and size and if any grafting
was needed prior to or at the time of implant placement
Radiographic Assessment:
The mesial and distal two-dimensional radiographic measurements extended from the
platform of the implant to the first bone to implant contact at the level of the alveolar crest. These
measurements were made from radiographs at the time of implant placement, time of impression
and 6-12 months post-crown delivery. Calibration using the Schick radiographic calibrating
measuring tool was completed using the diameter of the implants documented in the clinical
chart note and uploaded serial number. Calibration of measurements was performed by both
examiners. To achieve intra- and inter-examiner calibration, ten cases were randomly selected,
and the same measurements were taken over the next ten days. Each examiner measured the
same site three times. The data were then compared to ensure consistency. Intra-examiner ICC
for examiner LA was 0.94 and for AB was 0.95 which is considered excellent reproducibility.
Inter-examiner ICC was 0.96 which is considered excellent reproducibility.
8

Statistical Analyses:
Descriptive statistics were calculated for all variables of interest. Continuous measures
were summarized using means and standard deviations whereas categorical measures were
summarized using counts and percentages. The variables were assessed to determine the correct
ranking of values between the two groups of internal and external platforms using a Wilcoxon
Rank Sum test. Changes over time in variables such as mesial bone depth and distal depth were
analyzed using this test. Bone level changes from the platform of the dental implants to the first
bone-to-implant contact at different time intervals—implant placement, impression, and 6-12
months follow-up—were assessed using analysis involving two variables adjusting for the
correlation among observations taken on the same aspect, mesial or distal (in millimeters). All
analyses were carried out using SAS Version 9.4 (SAS Institute, Cary, NC, USA).
9

Chapter 2: Results
Patient and Implant Demographics
Out of the 288 implants evaluated radiographically and from past clinical chart
documentation, only 197 met the study criteria. The 197 implants were placed in 158 patients at
the Herman Ostrow School of Dentistry Faculty Practice from 2012 to December 2023. Patient
population consisted of 80 females and 78 males. The range of the patients age was 22-93 years
old with an average age of 61.5 years old. The following implant connections were included: 100
internal connection, 84 external hex and 13 transmucosal (Figure 1-1). The implant distribution
included: 78 Straumann Bone Level NC or RC, 2 Straumann Bone Level Tapered NC or RC, 13
Straumann TL, 17 Dentium, 3 Zimmer Biomet 3i Certain, and 84 Zimmer Biomet 3i Osseotite
(Figure 1-2). There were a total of 135 posterior implants and 62 anterior implants (Figure 1-3).
Of the 62 anterior implants, 53 were placed in the maxilla and 9 were placed in the mandible
(Figure 1-4). All two-dimensional radiographic measurements were made by two individuals (LA
and AB). No inter or intraexaminer measurement discrepancies were observed. ICC
Averages
The overall crestal bone remodeling on the mesial and distal was a mean of 0.27 mm
(SD=0.50). The overall average bone remodeling at the time of placement was 0.02 mm
(SD=0.09), time of impression 0.15 mm (SD=0.36 mm) and at 6-12 months post-crown delivery
was 0.28 mm (SD=0.50) (Fig. 2, Table 1)
10

Analysis of Bone Changes:
External Hex
At the mesial site the measurement of bone change was 0.30 mm (SD=0.51mm) from
time of placement to impression, 0.24 mm (SD=0.34) from time of impression to 6-12 months
after crown delivery and 0.55 mm (SD=0.62 mm) from time of placement to 6-12 months after
crown delivery. Statistically significant difference in bone change was noted on the mesial from
time of placement to impression (p<0.0001), time of impression to 6-12 months after crown
delivery (p<0.0001), and time of placement to 6-12 months after crown delivery (p<0.0001)
(Figure 3, Table 2).
At the distal site the measurement of bone change was 0.27 mm (SD=0.50mm) from time
of placement to impression, 0.24 mm (SD=0.36) from time of impression to 6-12 months after
crown delivery and 0.52 mm (SD=0.62 mm) from time of placement to 6-12 months after crown
delivery. Statistically significant difference in bone change was noted on the mesial from time of
placement to impression (p<0.0001), time of impression to 6-12 months after crown delivery
(p<0.0001), and time of placement to 6-12 months after crown delivery (p<0.0001) (Figure 3,
Table 2).
The average crestal bone remodeling at the time of placement was 0.03 mm
(SD=0.13mm), time of impression was 0.32 mm (SD=0.50 mm), and at 6-12 months after crown
delivery was 0.56 mm (SD=0.56mm). Statistically significant difference in average bone
remodeling was noted the at time of placement (p=0.03), time of impression (p<0.0001), and
time of placement to 6-12 months after crown delivery (p=0.03) (Figure 3, Table 2).
11

Internal Connection
At the mesial site the measurement of bone change was 0.01 mm (SD=0.05mm) from
time of placement to impression, 0.06 mm (SD=0.22 mm) from time of impression to 6-12
months after crown delivery and 0.07 mm (SD=0.25 mm) from time of placement to 6-12
months after crown delivery. Statistically significant difference in bone change was noted on the
mesial from time of placement to impression (p<0.0001), time of impression to 6-12 months
after crown delivery (p<0.0001), and time of placement to 6-12 months after crown delivery
(p<0.0001) (Fig 4, Table 3).
At the distal site the measurement of bone change was 0.03 mm (SD=0.16mm) from time
of placement to impression, 0.06 mm (SD=0.23mm) from time of impression to 6-12 months
after crown delivery and 0.09 mm (SD=0.30 mm) from time of placement to 6-12 months after
crown delivery. Statistically significant difference in bone change was noted on the distal from
time of placement to impression (p<0.0001), time of impression to 6-12 months after crown
delivery (p<0.0001), and time of placement to 6-12 months after crown delivery (p<0.0001 ) (Fig
4, Table 3).
The average crestal bone remodeling at the time of placement was 0.01 mm
(SD=0.05mm), time of impression was 0.02 mm (SD=0.08 mm), and at 6-12 months after crown
delivery was 0.09 mm (SD=0.26mm). Statistically significant difference in average bone
remodeling was noted the at time of impression (p<0.0001), and time of placement to 6-12
months after crown delivery (p<0.0001) (Fig 4, Table 3).
Splinted
12

At the mesial site, the measurement of bone change was 0.20 mm (SD=0.48mm) from
time of placement to impression, 0.22 mm (SD=0.35mm) from time of impression to 6-12
months after crown delivery and 0.42 mm (SD=0.60 mm) from time of placement to 6-12
months after crown delivery. Statistically significant difference in bone change was noted on the
mesial from time of impression to 6-12 months after crown delivery (p=0.05), and time of
placement to 6-12 months after crown delivery (p=0.02) (Fig 5, Table 4).
At the distal site, the measurement of bone change was 0.18 mm (SD=0.41mm) from
time of placement to impression, 0.22 mm (SD=0.36mm) from time of impression to 6-12
months after crown delivery and 0.40 mm (SD=0.58 mm) from time of placement to 6-12
months after crown delivery. Statistically significant difference in bone change was noted on the
distal from time of impression to 6-12 months after crown delivery (p=0.05), and time of
placement to 6-12 months after crown delivery (p=0.02) (Fig 5, Table 4).
The average crestal bone remodeling at the time of placement was 0.03 mm
(SD=0.15mm), time of impression was 0.22 mm (SD=0.47 mm), and at 6-12 months after crown
delivery was 0.4 mm (SD=0.61mm). No statistically significant difference in average bone
remodeling was noted the at time of placement (p=0.55) or at time of impression (p=0.38). A
statistically significant difference in average bone remodeling was noted time of placement to
6-12 months after crown delivery (p=0.03) (Fig 5, Table 4).
Implant Diameter > 4 mm
The average crestal bone remodeling for implant diameter > 4 mm at the time of
placement was 0.01 mm (SD=0.04mm), time of impression was 0.10 mm (SD=0.23 mm), and at
13

6-12 months after crown delivery was 0.16 mm (SD=0.37mm). No statistically significant
difference in average bone remodeling was noted the at time of placement (p=0.77) or at time of
impression (p=0.08). A statistically significant difference in average bone remodeling was noted
time of placement to 6-12 months after crown delivery (p<0.0001) (Fig 6, Table 5).
External Hex vs Internal Connection
The average external hex implant connection crestal bone remodeling at the time of 6-12
months post-crown delivery was 0.56 mm (SD=0.61mm) which was found to be statistically
significant (p<0.0001) compared to internal connection implant. The average internal implant
connection crestal bone remodeling at the time of 6-12 months post-crown delivery was 0.09 mm
(SD=0.26mm) which was found to be statistically significant (p<0.0001) compared to internal
connection implant (Fig 7, Table 6).
Tissue-Level
The average crestal bone remodeling was 0 mm (SD=0 mm). Statistically significant
changes on the mesial were between 6-12 months and impression (p=0.01) as well as between
placement and 6-12 months (p=0). On the distal, statistically significant changes were seen
between impression and placement as well (p=0.02) and between placement and 6-12 months
(p=0.008). In the average bone change, statistically significant changes were seen at time of
impression (p=0.04) and 6-12 months post crown-delivery (p=0.002).
14

Discussion
This study investigates the impact of different implant connection types and implant
diameters on crestal bone remodeling over three time points in non-grafted extraction sites. The
results indicate that both the type of implant connection and time intervals significantly affect
crestal bone remodeling.
The study observed a mean crestal bone remodeling of 0.27 mm, with minimal
remodeling at the time of placement (0.02 mm), which increased to 0.15 mm at the time of
impression and approached 0.28 mm at 6-12 months post-crown delivery. These findings are
consistent with existing literature, which indicates that the majority of crestal bone remodeling
occurs within the first year after implant placement, often stabilizing thereafter (39). Early bone
remodeling can be attributed to surgical trauma, microgap movement, and initial bone healing
processes (40).
A comparison between external hex and internal connection implants revealed
statistically significant differences in crestal bone remodeling (p<0.0001). External hex implants
showed greater marginal bone loss at all time points, particularly at 6-12 months post-crown
delivery (0.56 mm) compared to internal connection implants (0.09 mm). This finding supports
earlier studies suggesting that internal connection implants reduce bone loss due to better
biomechanical stability and reduced bacterial infiltration at the implant-abutment interface (41).
Internal connections distribute mechanical loads more evenly and minimize micro-movements,
which are crucial in preserving crestal bone. A study by Koo et al. investigated marginal bone
loss according to the implant abutment connection. It was found that the mean marginal bone
15

loss around external connection implants was 0.61 mm until loading whereas the mean marginal
bone loss around internal connection implants was 0.08 mm. These findings are similar to the
values recorded in this study. Internal connection implants have an inherent platform switching
structure which allows the implant abutment junction to be moved away from the adjacent
marginal bone level which can minimize microgaps and prevent bacterial infiltration (42)
Bone remodeling patterns were consistent at both mesial and distal sites across all
implant types. The significant bone changes observed from the time of placement to 6-12 months
post-crown delivery highlight a critical period for peri-implant bone remodeling. The mesial
bone change in external hex implants from time of placement to 6-12 months was 0.55 mm,
while for internal connection implants was only 0.07 mm. Similar patterns were noted at the
distal sites. These results are in line with studies that emphasize the importance of implant design
and its impact on peri-implant bone stability (43, 44).
For splinted implants, no statistically significant difference in bone remodeling was noted
at the time of placement or impression. However a mean of 0.4 mm (SD=0.61 mm) was noted at
6-12 months post crown delivery. These findings are in line with results from Vigolo and
Zaccario who reported that peri-implant marginal bone loss around non-splinted implants was
not statistically significantly different from that observed in splinted implants in a 5 year
prospective study (45).
Implants with diameters greater than 4 mm demonstrated significantly less bone loss,
particularly at 6-12 months post-crown delivery (0.16 mm). This finding corroborates the
literature suggesting that wider implants provide a greater surface area for osseointegration,
16

enhancing primary stability and reducing stress concentration at the crestal bone level (46). The
increased stability of wider implants is particularly beneficial in areas of poor bone quality or
high occlusal loads (47).
The findings of this study have significant clinical implications for implant selection and
placement strategies. Internal connection implants are preferable for reducing crestal bone loss
due to their superior biomechanical properties. Additionally, opting for implants with larger
diameters can further mitigate bone loss, especially in challenging clinical scenarios.
Understanding the timing and extent of bone remodeling can aid clinicians in planning for
optimal implant placement and prosthetic loading protocols (48).
There are several limitations in this study. The first is that since the study was performed
retrospectively via two-dimensional radiographs it is difficult to determine the consistency of the
angulation of the radiographs at the time of implant placement, impression and 6-12 months
post-crown delivery. A major reason why some charts were excluded from the study were due to
inconsistencies in the radiographs at the various time points. A second limitation to this study is
the total number of implants placed. This study was limited only to implants placed by a single
practitioner at the USC Faculty Practice. Future studies can expand the implants placed to the
Advanced Periodontology Clinic at USC Herman Ostrow School of Dentistry. Additionally, this
study evaluated four different implant systems: Straumann Bone Level, Bone Level Tapered,
Tissue-Level, Dentium, Zimmer Biomet 3i Certain, and Zimmer Biomet 3i Osseotite. With the
exception of Zimmer Biomet 3i Osseotite and Straumann Tissue-Level, the remaining systems
are internal connection. Both Straumann Bone Level and Dentium are platform switched as
17

opposed to Zimmer Biomet 3i Certain. The Zimmer Biomet 3i Certain implant has a polished
collar with machined surface on the coronal 3 mm. Straumann Bone Level and Bone Level
Tapered presents with SLA rough surface. Dentium presents with coronal micro thread, SLA
rough surface and a beveled platform. The Zimmer Biomet 3i Osseotite implant has a dual acidetch surface with a polished external hex collar with machined surface on the coronal 3 mm.
Though the main difference between the systems is their connection (internal vs. external), the
implants exhibit different designs, sizes, thread presentation and surface treatments.As such,
there are many variables to take into consideration and future studies should be designed with
implants manufactured specifically for a more controlled research study to eliminate such
variables. This study is limited by its relatively short follow-up period of 6-12 months postcrown delivery. Future research should aim for longer follow-up periods to assess the long-term
stability of crestal bone levels. Additionally, further investigations should consider patientspecific factors such as systemic health, bone density, occlusal forces, and one vs two stage
implant placement which can also influence bone remodeling patterns (48).
18

Conclusion
External hex implants showed the highest marginal bone loss compared to internal
platform and tissue-level implants from placement through to one year post-crown delivery. A
strong correlation was observed between splinted implants and increased marginal bone loss on
the mesial, distal, and average measurements from placement through the one-year follow-up.
Additionally, implant diameters greater than 4 mm were strongly correlated with increased
marginal bone loss at the one-year follow-up, affecting both external and internal implants.
However, no statistically significant correlation was found between tissue-level implants and
marginal bone loss on the mesial, distal, and average measurements from placement through the
one-year follow-up. Within the limitations of this retrospective observation, favorable clinical
outcomes in implant placement and crestal bone maintenance can be expected in non-grafted
extraction sites. The need for bone augmentation at implant sites can be postponed using early
placement protocols. Minor differences in crestal bone remodeling may occur with different
restorative platforms. Risk-benefit considerations should be applied when selecting restorative
platforms.
19

Figures & Tables
Figure 1-1: Implant Connection Distribution. Internal Connection Platform (N=100), External
Connection Platform (N=84), Tissue Level Platform (N=13)
Implant Connection Distribution
Total=197
Internal Connection (N=100)
External Connection (N=84)
Tissue Level (N=13)
42.64% 50.76%
6.60%
20

Figure 1-2: Implant Distribution. Straumann Bone Level (BL) (N=78), Zimvie 3i Osseotite
(N=84), Straumann Tissue Level (TL) (N=13), Dentium (N=17), Straumann BLT (N=2), Zimvie
3i Certain (N=3).
Total = 197 implants
Straumann BL (N=78)
Osseotite (N=84)
Dentium (N=17)
Straumann TL (N=13)
Straumann BLT (N=2)
Certain (N=3)
39.59%
42.64%
8.63%
6.60% 1.02% 1.52%
Implant Type
21

Figure 1-3: Anterior/Posterior Implant Distribution: Posterior implants (N=135) and anterior
implants (N=62).
22
Number of Anterior/Posterior Implants
Anterior Implants
Posterior Implants
N=135 N=62
N=197

Figure 1-4: Anterior Implant Distribution: Maxillary implants (N=53) and mandibular
implants (N=9).
N=62
Maxillary Anterior
Mandibular Anterior
N=62
N=53
N=9
Anterior Implant Distribution
23

Figure 2: Average Bone Level (in millimeters). Average bone level calculated on mesial, distal and
three different time points of all implant type.

Table 1: Average Bone Level (in millimeters). Average bone level calculated on mesial, distal and three
different time points of all implant type. Average bone level on mesial and distal was 0.27 mm
(SD=0.50mm) Average bone level at time of placement 0.02 mm (SD=0.09 mm). Average bone level at
time of impression was 0.15 mm (SD=0.36mm). Average bone level at 6-12 months after crown-delivery
was 0.28 mm (SD=0.50).
Mesial
Distal
Placement
Impression
6 months
0.0
0.2
0.4
0.6
0.8
1.0
Bone (mm)
Mean Bone Levels
Overall Mean Bone Level
Mesial Distal Placement Impression 6-12
months
Mean
(mm)
0.27 0.27 0.02 0.15 0.28
SD
(mm)
0.50 0.50 0.09 0.36 0.50
24

Figure 3: 3i Osseotite Bone Level Change (in millimeters). Bone change was calculated at three
different time points on the mesial, distal and as an average for 3i Osseotite. Time points were between
placement and impression, impression and 6-12 months follow-up and placement and 6-12 months
follow-up. Statistically significant changes were noted at all time points.
Table 2: 3i Osseotite Bone Level Change (in millimeters). Statistically significant differences in bone
change were seen at all time points. The average bone change at time of placement was 0.13 mm
(SD=0.13) (p=0.03*). The average bone change at the time of impression was 0.32 mm (SD=0.50)
(p<0.0001)*. The average bone change at 6-12 months follow-up was 0.56 mm (SD=0.56 mm) (p=0.03*)
impression & placement
6 months & impression
6 months & placement
impression & placement
6 months & impression
6 months & placement
impression & placement
6 months & impression
6 months & placement
0.00
0.25
0.50
0.75
1.00
1.25
1.50
Bone Change (mm)
3i Osseotite Bone Level Change
*
*
Mesial bone level Δ Distal bone level Δ
*
*
*
Average bone level Δ
*
*
*
*
Mesial Bone Change Distal Bone Change Average Bone Change
Osseotite
N=84
Impression
&
placement
6-12
months &
impression
6-12
months &
placement
Impression
&
placement
6-12
months &
impression
6-12
months &
placement
Placement Impression 6-12
months
Significance p<0.0001* p<0.0001* p<0.0001* p<0.0001* p<0.0001* p<0.0001* p=0.03* p<0.0001* p=0.03*
Mean (mm) 0.30 0.24 0.55 0.27 0.24 0.52 0.03 0.32 0.56
SD (mm) 0.51 0.34 0.62 0.50 0.36 0.62 0.13 0.50 0.56
25

Figure 4: Internal Connection Bone Level Change (in millimeters). Bone change was calculated at
three different time points on the mesial, distal and as an average for Internal Connection implant
platforms Time points were between placement and impression, impression and 6-12 months follow-up
and placement and 6-12 months follow-up. Statistically significant changes were noted at all time points.
Table 3: Internal Connection Bone Level Change (in millimeters). Statistically significant differences
in bone change were seen at all time points except at the change between impression and placement. The
average bone change at time of placement was 0.01 mm (SD=0.05) (p=0.09). The average bone change at
the time of impression was 0.02 mm (SD=0.08) (p<0.0001)*. The average bone change at 6-12 months
follow-up was 0.09 mm (SD=0.26 mm) (p<0.0001*)
impression & placement
6 months & impression
6 months & placement
impression & placement
6 months & impression
6 months & placement
impression & placement
6 months & impression
6 months & placement
0.00
0.25
0.50
Bone Change (mm)
Internal Connection Bone Level Change
*
*
*
*
*
*
*
Mesial bone level Δ Distal bone level Δ Average bone level Δ
Mesial Bone Change Distal Bone Change Average Bone Change
Internal
Connection
N=100
Impression
&
placement
6-12
months &
impression
6-12
months &
placement
Impression
&
placement
6-12 months
&
impression
6-12
months &
placement
Placement Impression 6-12
months
Significance p=0.09 p<0.0001* p<0.0001* p=0.0006* p<0.0001* p<0.0001* p=0.09 p<0.0001* p<0.0001*
Mean (mm) 0.01 0.06 0.07 0.03 0.06 0.09 0.01 0.02 0.09
SD (mm) 0.05 0.22 0.25 0.16 0.23 0.30 0.05 0.08 0.26
26

Figure 5: Splinted Implant Bone Level Change (in millimeters). Bone change was calculated at three
different time points on the mesial, distal and as an average for splinted implants. Time points were
between placement and impression, impression and 6-12 months follow-up and placement and 6-12
months follow-up. Statistically significant changes were noted at all time points.
Table 4: Splinted Implant Bone Level Change (in millimeters). Statistically significant differences in
bone change were seen on the mesial and distal between impression and 6-12 months as well as overall
between placement and 6-12 months post-crown delivery. The average bone change at time of placement
was 0.03 mm (SD=0.15) (p=0.55). The average bone change at the time of impression was 0.22 mm
(SD=0.47) (p=0.38). These findings were not statistically significant. The average bone change at 6-12
months follow-up was 0.44 mm (SD=0.61 mm) (p=0.03*) which was statistically significant.
impression & placement
6 months & impression
6 months & placement
impression & placement
6 months & impression
6 months & placement
impression & placement
6 months & impression
6 months & placement
0.00
0.25
0.50
0.75
1.00
1.25
1.50
Bone Change (mm)
Splinted Implant Bone Level Change
*
*
*
* *
Mesial bone level Δ Distal bone level Δ Average bone level Δ
Mesial Bone Change Distal Bone Change Average Bone Change
Splinted
N=38
Impression
& placement
6-12 months
&
impression
6-12
months &
placement
Impression
&
placement
6-12 months
&
impression
6-12
months &
placement
Placement Impression 6-12
months
Significance p=0.35 p=0.05* p=0.02* p=0.33 p=0.05* p=0.02* p=0.55 p=0.38 p=0.03*
Mean (mm) 0.20 0.22 0.42 0.18 0.22 0.40 0.03 0.22 0.44
SD (mm) 0.48 0.35 0.60 0.41 0.36 0.58 0.15 0.47 0.61
27

Figure 6: Average Bone Level Change in implants diameter > 4 (in millimeters). Average bone
change was calculated at three different time points on the mesial, distal and as. Time points were
between placement and impression, impression and 6-12 months follow-up and placement and 6-12
months follow-up. Statistically significant changes were noted only during the 6-12 month follow up.
Table 5: Average Bone Change in Implant > 4 (in millimeters). Average bone level calculated on three
different time points of all implant types with diameter > 4 mm.. Average bone level at time of placement
was 0.01 mm (SD=0.04mm) Average bone level at time of impression 0.08 mm (SD=0.23 mm). Average
bone level at 6-12 months after crown-delivery was 0.16 mm (SD=0.37 mm) which was statistically
significant (p<0.0001).
Placement
Impression
6-12 months
0.0
0.2
0.4
0.6
Bone (mm)
Average Bone Change Implant > 4 mm
*
Average Bone Change
Implant Diameter > 4mm Time of placement Impression 6-12 months
Significance p=0.77 p=0.08 p<0.0001*
Mean (mm) 0.01 0.10 0.16
SD (mm) 0.04 0.23 0.37
28

Figure 7: Average Bone Level Change External vs. Internal Connection. Average bone change was
calculated between external and internal connection. Statistically significant changes in bone level were
noted for both external and internal connection.
Table 6: Average Bone Level Change External vs. Internal Connection. Average bone change was
calculated between external and internal connection. Overall mean bone change for external connection
was 0.56 mm (SD=.61 mm) (p<0.0001). Overall mean bone change for external connection was 0.09 mm
(SD=.26 mm) (p<0.0001) Statistically significant changes in bone level were noted for both external and
internal connection.
External Connection (N=84)
Internal Connection (N=100)
0.0
0.5
1.0
1.5
Bone Change (mm)
Average Bone Change External vs. Internal Connection
29
Average Bone Level Change External vs. Internal Connection
External Connection Internal Connection
Significance p<0.0001* p<0.0001*
Mean (mm) 0.56 0.09
SD (mm) 0.61 0.26

Table 7: Average Bone Level Change Tissue-Level Platforms. Average bone change was calculated for
tissue-level platform on the mesial, distal and overall. Statistically significant changes were seen at
multiple time points.
Mesial Bone Change Distal Bone Change Average Bone Change
Tissue Level
N=13
Impression
&
placement
6-12 months
&
impression
6-12
months &
placement
Impression
&
placement
6-12
months &
impression
6-12
months &
placement
Placement Impression 6-12
months
Significance p=0.08 p=0.01* p=0* p=0.02* p=0.09 p=0.008* p=0.42 p=0.04* p=0.002*
Mean (mm) 0 0 0 0 0 0 0 0 0
SD (mm) 0 0 0 0 0 0 0 0 0
30

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36

Abstract (if available)

Abstract This study seeks to investigate the effect of marginal bone loss around dental implants from the time of placement, to the time of impression and 6-12 months after crown delivery. The aim of this retrospective analysis is to assess implant placement at non-grafted extraction sites with early placement protocol and to evaluate crestal bone remodeling in four implant systems amongst different restorative platform types, including external hex, internal connection, and transmucosal platform.
Electronic dental records were obtained from patients who underwent dental implant placement in USC’s faculty practice from 2012 till December 2023. Implants were placed at sites with history of simple or surgical extractions without ridge preservation by providers at USC’s faculty practice. Implant placement was done by one experienced periodontist. The implant systems represented in the study were Straumann Bone Level NC or RC, Straumann TL, Dentium, Zimmer Biomet 3i Certain, and Zimmer Biomet 3i Osseotite. Two-dimensional radiographs were taken at the time implant placement, impression stage and 6 months to 1 year follow up after implant crown delivery. These radiographs were used to evaluate mesial and distal crestal bone level changes from the platform of the dental implants to the first bone to implant contact. The marginal bone loss on mesial and distal were recorded at the time of implant placement, impression and 6-12 months follow up post-crown delivery. Charts of 158 patients and 197 implants were included in the study. Among the total of 197 implants placed, 84 (42.63%) were external hex connection, 100 (50.76%) were internal connection and 13 (6.6%) were tissue-level (TL) platforms. External hex implants exhibited the highest marginal bone loss compared to either the internal platform implants or tissue-level implants from the time of placement, impression taking and 6-12 months post-crown delivery (p<0.0001). A strong correlation was found between splinted implants and increased marginal bone loss on the mesial and distal from the time impression (p=0.05) , and 6-12 months post-crown delivery (p=0.02). A significant difference was seen for splinted implants and average bone loss at 6-12 months post-crown delivery (p=0.03). No statistically significant correlation was found between tissue-level implants and marginal bone loss on the mesial, distal, and average bone loss at the time of implant placement, impression taking, and 6-12 months post-crown delivery.

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Asset Metadata

Creator Andriasian, Leah (author)

Core Title Retrospective analysis of early implant placement in non-grafted extraction sites: two-dimensional radiographic evaluation of crestal bone remodeling in four implant systems

School School of Dentistry

Degree Master of Science

Degree Program Biomedical Implants and Tissue Engineering

Degree Conferral Date 2024-08

Publication Date 06/25/2024

Defense Date 06/24/2024

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

Tag bone loss,bone remodeling,crestal bone remodeling,dental implant,external hex,implant,internal hex,non-grafted extraction,OAI-PMH Harvest,ridge preservation,Straumann

Format theses (aat)

Language English

Contributor Electronically uploaded by the author (provenance)

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

Creator Email andriasi@usc.edu,leahandriasian@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC1139970NJ

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Legacy Identifier etd-Andriasian-13151

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Internet Media Type application/pdf

Type texts

Source 20240625-usctheses-batch-1174 (batch), University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright.

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA

Repository Email cisadmin@lib.usc.edu