University of Groningen
Immediate dental implant placement in the aesthetic zoneSlagter, Kirsten Willemijn
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Citation for published version (APA):Slagter, K. W. (2016). Immediate dental implant placement in the aesthetic zone. RijksuniversiteitGroningen.
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6Buccal bone measurements at dental
implants the aesthetic region:
a 1 year follow-up cone -beam
computed tomography study.
This chapter is an edited version of the manuscript: KW Slagter, GM Raghoebar, NA Bakker, A Vissink, HJA Meij er.
Buccal bone measurements at dental implants the aesthetic zone: a 1 year follow-up cone beam computed tomography study. Submitted.
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Abstract
Background: Sufficient buccal bone thickness (BBT) is important for optimal aesthetic results of implant
treatment in the aesthetic zone. BBT measurements can be done with cone beam computed
tomography (CBCT), but studies are scarce.
Aim:To assess the mean amount of BBT as a function of time after implant placement and relate
it to immediate and delayed placed implants in the aesthetic zone with a 1 year follow-up
using CBCT-scans.
Materials and Methods: After 1 month and 1 year of definitive crown placement, BBT was measured on CBCTs of
80 patients, part of 2 randomized clinical trials. Patients were divided in 4 study groups
according bony defect (<5 or ≥5 mm) and timing of implant placement (immediate or
delayed). Area of interest was the upper 5mm section of the implant, beginning at the neck
of the implant towards the apical direction and measured in steps of 1 mm along the axis of
the implant).
Results:BBT 1 year after placement of the definitive crown, varied for the immediate placed
implants of study group 1 from 1.52(sd:0.89) to 2.04(sd:0.77) mm (i.e., at the level of the
upper 5 mm of the implant); for study group 2 from 1.08(sd:0.55) to 1.44(sd:0.72) mm and
for study group 3 from 1.00(sd:0.47) to 1.29(sd:0.72) mm. BBT varied from 0.71(sd:0.28)
to 0.92(sd:0.57) mm for the delayed placed implants in study group 4. Mean loss of BBT
between 1 month and 1 year was negigible and independent of the size of the buccal bone
defect (<5 or ≥5 mm) prior to implant insertion and timing of implant insertion.
Conclusion:BBT at dental implants in the aesthetic zone measured on CBCTs, appears to be stable
for immediate and delayed placed implants after placement of the definitive crown,
independent of the size of buccal bone defect prior to implant insertion and timing of
provisionalization.
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Introduction
Single-tooth immediate implant placement in the aesthetic zone is a highly reliable treatment option
for replacing a failing tooth.1-3 Particularly in the aesthetic zone, establishment and maintenance of
healthy peri-implant hard and soft tissues is crucial.4,5 The presence of sufficient bone volume is the most
important prerequisite to achieve primary stability in case of immediate implant placement in an extraction
socket. Peri-implant bone preservation could be considered as one of the key factors in aesthetic
outcome.6 The morphological assessment of bone volume is of great interest to clinicians. In the literature
there is insufficient evidence to set a threshold for minimum buccal bone thickness to ensure the aesthetic
outcome and the long-term stability.6-8 In the aesthetic zone there is data of buccal bone dimensions at
different apical positions when the tooth is still in situ.9 Mean buccal bone thickness (BBT) varied from
0.6 mm to 0.8 mm, measured at different locations at central incisors and lateral incisors.9 The lack of
clinical data regarding bone thickness at buccal aspect of dental implants is probably related to frequently
encountered difficulties in standardization of the measurements. Cone-beam computed tomography
(CBCT) has proven to be a useful tool that has been successfully employed for various dental procedures.10
The choice of an accurate and reliable imaging modality is clinically important in terms of postoperative
monitoring of bone volume stability and to choose an adequate treatment approach.9 The CBCT might be
used for evaluation of implant buccal bone dimension.11-13 The use of 3D image diagnostic and treatment
planning software programs in combination with software programs for tracking and registration of the
exact position of existing dental implants in radiographs can be of help. In view of the aforementioned,
there is need for more studies which measure BBT at single tooth implants in the aesthetic zone on CBCT-
scans. To the best of our knowledge, no clinical trials yet assessed the amount of implant buccal bone
with a reproducible measure method on CBCT-scans at different apical positions along the implant axis.
It is therefore not known how reliable the CBCT-scan is to assess BBT as a function of time after implant
placement in the aesthetic zone.
The aim of the present study was to assess the mean buccal bone thickness (BBT) as a function of time and
relate it to immediate and delayed placed implants in the aesthetic zone in after 1 month and 1 year follow-
up using CBCT-scans.
Material and methods
To measure BBT on a CBCT-scan were 80 patients included with an immediate or delayed placed implant in
the aesthetic region (region 13 to 23) of the maxilla (Figure 1). Patients were part of two randomized clinical
trials. Both trials14,15 were approved by the local Medical Ethic Board (METC 2010.246) and registered in
a trial register (www.isrtcn.com: ISRCTN57251089) as well as that written informed consent was obtained
from all patients. Patients were divided according the bony defect after removal of the failing tooth before
implant placement. Due to sample size calculation, the two trials consisted each out of 20 patients per
study group, with a total of 4 study groups (3 study groups with immediate implant placement and 1 study
group with delayed implant placement).
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Figure 1. Cohort flow diagram.
Enrollment Assessed for eligibility (n=80)
Excluded (n=0) • Not meeting inclusion criteria (n=0) • Declined to participate (n=0) • Other reasons (n=0)
Allocated to intervention (n=40) • Received allocated intervention (n=40) • Did not receive allocated interven tion (give reasons) (n=0)
Lost to follow-up (give reasons) (n=1, patient did not show up at appointments) Discontinued intervention (give reasons) (n=0)
Analysed (n=39) • Excluded form analysis (give reasons) (n=0)
Allocated to intervention (n=40) • Received allocated intervention (n=40) • Did not receive allocated interven tion (give reasons) (n=0)
Lost to follow-up (give reasons) (n=0) Discontinued intervention (give reasons) (n=0)
Analysed (n=40) • Excluded form analysis (give reasons) (n=0)
Randomized (n=80)
Allocation
Follow-Up
Analysis
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A research-nurse not involved in the study blindly allocated by a computerized random number the
patients in:
Study A with patients with a buccal bony defect of <5 mm:
- Group 1 (n=20) : immediate placed implant (NobelActive, Nobel Biocare AB, Goteborg, Sweden) and
immediate provisionalization;
- Group 2 (n=20): immediate placed implant (NobelActive) and delayed provisionalization.
Study B with patients bony defect of ≥5 mm:
- Group 3 (n=20): immediate placed implant (NobelActive) and delayed provisionalization;
- Group 4 (n=20): delayed placed implant (NobelActive) and delayed provisionalization.
For the present study to measure changes in the BBT at the level of implants as a function of time, CBCT
scans were made after one month and 1 year after placement of the definitive crown (iCAT 3D exam
scanner,KaVo Dental GmbH, Biberach, Germany). This scanner was validated for measuring bone thickness
by Fourie et al.16 The method error of this scanner is very small, i.e. 0.05 mm (95 CI 0.03-0.07). The standard
used voxel size was 0.30 and FoV was 100 x100 mm on the CBCT scans. Bone measurements at implants
on the CBCT-scans were done using 3D image diagnostic and treatment planning software (Nobelclinician,
version 2.1 (Nobel Biocare - Guided Surgery Center, Mechelen, Belgium). To allow for reproducible
measurements, a CBCT imaging and software protocol was developed and validated.17
Measuring procedure
Acquired CBCT Digital Imaging and Communications in Medicine (DICOM) datasets were transferred to a
computer. The CBCT images were exported in DICOM multi-file format and imported into a medical image
computing program, Maxilim, version 2.3 (Medicim, Sint-Niklass, Belgium). With Multimodality Image
Registration using Information Theory (MIRIT), which has an accuracy of a subvoxel, the exact position of
the implant could be recognized, determined and implemented in the patients DICOM files.18 The implant
and patient dataset were exactly aligned by the MIRIT method, so that the distance from the central axis
of the implant to the outer contour of the buccal bone could be measured. Area of interest was the upper
5 mm section of the implant, beginning at the neck of the implant towards the apical direction. Exact
dimensions along the implant axis of each implant configuration used in the study was provided by the
manufacturer. Buccal bone measurements (in mm) were performed calculating the distance to the buccal
bone outline minus the radius of the interior contour of the implant. These buccal bone measurements
were done for 5 mm at each millimeter along the axis beginning at the neck of the implant (M0) towards
apical (M1,M2,M3,M4,M5) (Figure 2). Measurements were done (with time interval to prevent recollection)
by two independent operators (HM and KS) in a random order. This after validation of the measurement
procedure17 and an interobserver intraclass correlation coefficient of 0.96 (95%CI 0.93-0.98) and an
intra-observer intraclass correlation coefficient of 0.93 (95%CI 0.88-0.96) for examiner one and an intra-
observer intraclass correlation coefficient of 0.96 (95%CI 0.93-0.97) for examiner two.
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Figure 2a. Measurements were performed at each millimeter along the axis of the implant for 5 mm,
beginning at the neck of the implant.
Figure 2b. Actual measurements beginning at the neck of the implant of the axis of the implant for 5
mm towards apical.
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Statistical analysis
Friedman’s test was used to compare between bone thickness measurements at diff erent levels. In
case of uncertainty of the signifi cance because of the relatively small number of patients analysed and
the large number of outcomes, Bonferroni correction was considered in case of a p-value 0.01<>0.05. A
p-value of 0.05 was considered to indicate statistical signifi cance. All analyses were performed using
SPSS (PASW Statistics 20.0, SPSS Inc.; IBM Corporation, Chicago, IL, USA).
Results
One patient from study group 2 did not show up at appointments and was therefore excluded from
the study, which lead to evaluation of CBCT’s of 79 patients. Baseline charasteristics and treatment
specifi cations are presented in Table 1. The mean and standard deviation values of buccal bone thickness
(BBT) at diff erent levels 1 year after defi nitive crown placement are presented per study and study group
in Table 2.
In study A, with bony defects of <5 mm, the BBT in mm varied at the diff erent apical positions between
1.58(0.55)- 2.12(0.78) in group 1 (immediate placement and immediate provisonalization) and 1.10(0.70)-
1.46(0.82) in group 2 (immediate placement and delayed provisonalization) after 1 month with a
signifi cant diff erence at M1,M2,M3 and M4 (1-4mm apical). After 1 year the BBT in mm varied between
1.52(0.89)- 2.04(0.77) in group 1 and 1.08(0.55)- 1.44(0.72) in group 2 with a signifi cant diff erence at
M1,M2 and M3.
In study B, with bony defects of ≥5 mm, the BBT in mm varied at the diff erent apical positions between
1.11(0.65)-1.29(0.60) in group 3 (immediate placement and delayed provisonalization) and 0.79(0.46)-
0.93 (0.59) in group 4 (immediate placement and delayed provisonalization) after 1 month with a
signifi cant diff erence at M1. After 1 year the BBT in mm varied between 1.00(0.47) – 1.29 (0.72) in group 3
and 0.71(0.28) – 0.92 (0.57) in group 4 with a signifi cant diff erence at M0 (neck) and M1.
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Table 1. Baseline characteristics and treatment specifications per study group.
Variable
Immediate
Group 1 (n=20)
Immediate
Group 2 (n=20)
Immediate
Group 3 (n=20)
Delayed
Group 4 (n=20)
Age Mean ± SD Range
39.4±16.9 19-70
42.3±14.2 23-66
43.7 ±13.9 18-63
48.6 ±16.4 20-72
Gender Male Female
5 15
8 12
11 9
7 13
Implant location
Incisor 1 Incisor 2 Canine
7 8 5
13 6 1
12 5 3
14 6 0
Table 2. Buccal bone measurements and changes after 1 month and 1 year.
Group 1 (n=20)
Group 2 (n=19)
Level of sign.
Group 3 (n=20)
Group 4 (n=20)
Level of sign.
Measurements 1 month
Mean (sd) in mm
Mean (sd) in mm
Mean (sd) in mm
Mean (sd) in mm
M0 (at neck) 1.84 (0.91) 1.27 (0.82) 0.06 1.01 (0.55) 0.79 (0.46) 0.19
M1 2.05 (0.80) 1.39 (0.94) 0.03* 1.29 (0.60) 0.88 (0.57) 0.03*
M2 2.12 (0.78) 1.46 (0.82) 0.02* 1.19 (0.61) 0.93 (0.59) 0.18
M3 2.08 (0.63) 1.39 (0.76) 0.01* 1.26 (0.61) 0.92 (0.62) 0.08
M4 1.89 (0.54) 1.31 (0.75) 0.01* 1.25 (0.67) 0.85 (0.66) 0.06
M5 1.58 (0.55) 1.10 (0.70) 0.07 1.11 (0.65) 0.82 (0.71) 0.18
Measurements 1 year
M0 (at neck) 1.52 (0.89) 1.28 (0.85) 0.41 1.00 (0.47) 0.71 (0.28) 0.07
M1 1.94 (0.79) 1.37 (0.78) 0.04* 1.25 (0.53) 0.81 (0.46) 0.01*
M2 2.04 (0.74) 1.44 (0.72) 0.02* 1.28 (0.67) 0.92 (0.57) 0.08
M3 1.91 (0.64) 1.39 (0.63) 0.02* 1.29 (0.72) 0.90 (0.55) 0.06
M4 1.66 (0.71) 1.24 (0.58) 0.07 1.24 (0.70) 0.85 (0.58) 0.06
M5 1.57 (0.90) 1.08 (0.55) 0.43 1.14 (0.66) 0.77 (0.59) 0.06
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Discussion
A successful aesthetic outcome is suggested to be dependent on establishment of an optimal 3D implant
position within the available bone dimensions and the maintenance of adequate buccal bone over the
buccal implant surface19,20 but the amount of buccal bone is not known. The position of the implant in
relation to the bucco-oral dimension of the alveolar ridge is thought to influence the degree of bone
remodeling following implant placement.21 When there is no buccal bone present due to a bony defect
after extraction, the position and depth of the placed implant could be different compared to an intact
extraction socket or healed site. In the study of El Nahass and Naiem (2015) a mean buccal bone thickness,
in relation to natural incisors still in situ, of 0.57 mm and 0.84 mm was found in the first 4 mm towards
apically. This means that due to the surgical procedure with the slightly palatal placement of the implant
and augmentation of the buccal space in the extraction socket between implant and buccal wall, more
thickness of buccal bone is present at dental implants compared to natural teeth.
The reason behind the 6 measurements (M0-M5) performed after 1 month and 1 year after placement
of the definitive crown is to investigate the buccal bone thickness at different apical positions, clinically
relevant with dental implants in the aesthetic zone. No measurements for BBT at different positions along a
dental implant are known in the literature. Although measured in a different study design, a mean value of
0.16 (0.21) mm BBT is found in an immediate implant group of Raes et al.22 and 2.12 (0.92) mm BBT found
by Degidi et al.23 These numbers are in line for the immediate placed implants in this study. For delayed
placed implants, only a mean amount of 0.20 (0.22)mm is described by Raes et al.22 This number is lower
then the mean amount of BBT in this study.
Loss of buccal bone is inevitable, mainly as a consequence of the disappearance of bundle bone. Therefore
information on the original buccal bone contour prior to removal of the tooth should be provided to
measure the amount of change before and after implant placement. On post-operative CBCTs it is not
known how much of the original contour has been changed after dental implant treatment. It would be
interesting to include preoperative dimensions on CBCT-scans in relation to the actual position of the
placed implant on a post-operative CBCT’scan. More insight would be gained on alterations in BBT due
to the surgical procedure and occurring during the follow-up period. Consequently, implant positioning
in relation to the bucco-oral dimensions of the alveolar ridge, which is thought to influence the degree of
bone remodeling, could then be evaluated.6
Limitations of the study
Some limitations have to be addressed. The interpretation of the buccal bone adjacent to dental implants
on the resolution of the CBCT is insufficient in comparison with light microscopy.11 In the case of very thin
buccal bone, CBCT images seem not always reliable due to background scattering and problems with
standardization of the measurements.22,24,25 The quality and accuracy of a three-dimensional (3D) model
derived from a CBCT is dependent on scanner related factors such as type of scanner, field of view (FoV),
artifacts and voxel size.12 In addition, patient related factors such as patient position and metal artifacts26,
and operator related factors as the segmentation process or interpretation of the CBCT are of influence.27
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Conclusion
Buccal Bone Thickness at dental implants in the aesthetic zone measured on CBCTs, appears to be stable
for immediate and delayed placed implants after placement of the definitive crown, independent of the
size of buccal bone defect prior to implant insertion and timing of provisionalization.
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