Evaluation of Alveolar Bone on Dental Implant Treatment using Cone Beam Computed Tomography

Objective: To observe the outcomes of dental implant treatment based on the evaluation of bone conditions using Cone Beam Computed Tomography (CBCT). Material and Methods: A total of 31 dental implants were collected for the present study. Subsequently, mesial and distal bone losses were examined, while buccal and lingual bone thickness were measured at 7 levels. Evaluation and interpretation of CBCT results was performed by 3 independent examiners. Results: The average of mesial bone loss was 1.08 mm and 1.36 mm on distal bone. Every dental implant had lingual/palatal bone on level 1 to 3, only 1 (6.5%) didn’t have bone on level 4, 3 implants (9.7%) had no bone at level 5 and 6, and 22 implants (74.2%) had no bone at level 7/implant platform. There were 8 implants (25.8%) didn’t have buccal bone at level 7, only 1 implant (3.2%) didn’t have buccal bone at level 2,4,5 and 6, and there were 2 implants (6.5%) had no buccal bone on level 3. Dehiscence / fenestration can be seen on 90% of the implant subjects. Conclusion: These bone loss condition could be consequence of several factors such as infection, diagnosis, treatment plan, and operator’s surgery skills. The implants that placed without CBCT could lead to operator miscalculation on bone condition, therefore in moderate to advanced cases, the use of CBCT should be mandatory for treatment plan.


Introduction
The increasing awareness of better dental prostheses makes dental implants the most favorable choice for patients, due to its comfort and its ability to prevent further bone resorption. In a previous analysis through a meta-analytic review on 19 research efforts, it was found that the average survival rates of dental implant treatments after one year was 95.5%, with a confidence level 95% [1].
The high survival rate could not be confirmed as being successful implant treatments, where the implants have no pathologic conditions and work functionally well [2]. It has been reported common parametric used to evaluate dental implant. Specifically, these are implant fixture (mobility, pain, radiolucency, and bone loss around the implant), soft tissue around implant, prostheses, and patient's subjective assessment [3].
Radiographic parametric on mesial and distal bone has been widely used for the successful evaluation of dental implants [4]. Observing a marginal bone loss of 1.5 mm on the first year and 0.2 mm on subsequent years on periapical a radiograph is considered to be normal and acceptable [4,5].
In an earlier study, it was found that 37.9% only of dental implants have buccal bone on the implant platform six months after placement, with a 0.4 mm horizontal resorption [6]. Bone loss around implants could influence both osseointegration and long-term prognosis [7,8].
The radiographic evaluation of dental implants could provide information on the: tissue surrounding the implant; degree of marginal bone loss; and condition of implant mechanic's component [9]. However, while periapical radiographs can visualize interproximal bone and bone level from an apical to a coronal view, only Cone Beam Computed Tomography (CBCT) can visualize the bone's actual three-dimensional condition [10].
The use of CBCT on dental implants could show: bone angulation and form; bone contour; bone thickness at different height levels; and the position along with the anatomical structure surrounding it [11]. Furthermore, CBCT projection can contribute to the early detection of bone loss around dental implant. This in turn can help the improvement of existing implants before further destruction occurs, as well as identify factors for the next implant placement [12].
Dental implant evaluation using CBCT was never been done before in Dental Teaching

Hospital of Universitas Indonesia (Rumah Sakit Khusus Gigi Mulut Fakultas Kedokteran Gigi
Universitas Indonesia) and it could be used to provide an improvement of the standard operational procedures of implant placement. In the present study, we aim at evaluating bone thickness and height around dental implants by means of CBCT.

Study Design
In the present study, we performed a descriptive clinical analysis of dental implants originating from the Periodontics Clinic, Faculty of Dentistry, Universitas Indonesia between 2009 and 2016. The study was performed between June and November 2017.
The patients received Straumann dental implants, either at a bone level or at a tissue level with similar methods and surgical technique. The exclusion criteria were as follows: subjects with aggressive periodontitis; necrotizing ulcerative gingivitis (NUG); necrotizing ulcerative periodontitis (NUP); and diabetes mellitus.
Dental implants' evaluation was performed radiographically using CBCT (3D Aquitomo ® 170, Morita Inc, Japan) with FOV 40x40 mm or 60x60 mm, voxel 80 µm. Evaluation and interpretation of CBCT results was performed by 3 independent examiners in the Oral and Maxillofacial Radiology Clinic, Faculty of Dentistry, Universitas Indonesia.

Data Collection
With the aim of analyzing bone level and bone thickness on mesial, distal, buccal/labial, and lingual/palatal aspects, we evaluated the projection of CBCT by using the One Volume Viewer     Table 1 describes the distribution of subjects enrolled in this study. Analytic validity among 3 examiners was performed with the Dahlberg formula in Table 2. Acceptable difference is maximum 1 mm and the results showed this data can be utilized for additional analysis (0.16 -0.47). Technical error of measurement (TEM) performed by using the non-parametric Wilcoxon analysis demonstrated that the difference between examiner 1 and 2 has the least delta score can be seen on Table 3. Therefore, the data from examiner 1 was utilized. We observed pathologic bone loss on 29.3% of the samples on the mesial aspect; 22.6% of the sample on the distal aspect. This evaluation was based on Albrektsson's criteria of bone loss. Table 4 shown average bone loss on the mesial aspect was 1.08 mm and 1.36 mm on the distal aspect. As Figures 3 and 4 show, the percentage of bone loss on the buccal and lingual area was identified. It was found that at Buccal Level 1 all subjects had bone. Only 1 subject (3.2%) did not have buccal bone on level 2, 4, 5, and 6 found, level 3 had 2 subjects (6.5%), and at level 7 got 8 subjects (25.8%) who doesn't have buccal bones at all.  This is estimated because dental implant patients generally have good oral hygiene so that they do not have any periodontal problems, which causes them to feel that they do not need to carry out routine controls. After an explanation and signing of an informed consent, only 92% of patients understood the possible risks and complications, 24% of patients believed that dental implants would remain in the mouth, 12% did not understand that there was a possibility of gingival recession, periimplantitis, implant fracture, or permanent nerve damage, and 20% were unaware that periodontal disease could affect dental implants [14].

Results
The use of CBCT could aid in the accurate identification of peri-implant damage. Similarly, in a study performed on dogs comparing the accuracy of CBCT with histologic evaluation showed that CBCT could not identify buccal bone thickness smaller than 0.5 mm [15,16]. We observed that the average mesial bone loss was 1.08 mm and distal bone loss was 1.36 mm between one to eight years. The variation of anterior and posterior implants with wide range of time after placement could give a broad outlook of implant's bone modification throughout the time.
Albrektsson criteria was used to determined acceptable bone loss at each year of placement [5] and we found pathologic bone loss of the mesial aspect was 29% and of the distal aspect was 22.6%. These results were similar to previous findings showing that, of 4.591 dental implants after 8-10 years, 15% had more than 1.02 mm bone loss on the mesial/distal area and 5% had more than 2.28 mm bone loss [17]. Other authors get better results in 58 dental implants after 2 years of installation, the loss of bone bones was only 0.32 mm with a standard deviation of ± 0.37 mm [18].
A systematic review on dental implant placements with minimum 10-year-evaluation found a 1.3 mm average bone loss [19].
All subjects had buccal bone at level 1 at the apical dental implant, while there were 1 (3.2%) subject that had no buccal bone at levels 2, 4, 5, and 6. There were 2 dental implants (6.5 %) those who were not covered by bone at level 3 and there were 8 dental implants did not have buccal bones at level level 7 (cervical dental implants). All dental implant samples in this study had lingual / palatal bone level 1 to 3. Bone loss was seen at level 4 as many as 2 dental implants (6.5%), level 5 to 6 as many as 3 dental implants (9.7%), and the highest bone loss was found at level 7 (on platform implants), as many as 23 dental implants (74.2%) did not have lingual / palatal bone. This study found that 90% of dental implants had dehiscence or fenestration.
These results are slightly better than those found previously, which evaluated 168 dental implants in the anterior region with 56% of dental implants at level 7 (on implant platforms), 44% at level 6, 42% at level 5, 36% at level 4, 27% at level 3, 16% at level 2, and 14% at level 1 (at apical implant) with absolutely no buccal bone [13]. After an average of 8.9 years none of the dental implants they evaluated were covered with bone on the entire surface. The buccal bone is about 3.8mm more apical than the shoulder implant, but this thin or missing condition of the buccal bone clinically does not interfere with the aesthetics and stability of the dental implant [20].
Vertical bone changes measured from the implant / abutment interface after 1 year are reduced by 1.12 mm. Horizontal bone changes in the cervical implant decreased by 0.62 mm, in the middle of the implant 0.57 mm, and at the apical reduced by 0.19 mm [21]. A previous study showed that of the 66 dental implants evaluated only 37.9% had buccal bone on the implant platform after 6 months of placement. Vertical buccal resorption occurs as much as 1 mm at 6 months to 1 year and there is a horizontal resorption of 0.4 mm within 6 months of installation.
This present study limitation was the absence of bone thickness's baseline, since the radiograph taken before and immediately after implant placement were either panoramic or periapical. CBCT examination for implant placement was not mandatory before 2016 thus preliminary data not available in this study. This could provide a very important evidence to predict whether the initial placement of the dental implant was too lingual / palatal to cause bone loss occurred at the implant platform as much as 74.2% of the total sample. Operators could face challenge in diagnosing volume, contour and bone angulation due to the fact that all of the implant subjects were placed only by panoramic and bone caliper guidance. Implant treatment plan using a panoramic radiograph is not adequate since the distortion factor could made operator incorrectly predict available bones. This deficiency can have an impact on the selection of larger implants and increase the risk of injuring the adjacent anatomical structures [22].
Operator's skill and experience are also very important in determining the success of dental implant treatment [23,24]. Dental implants that are not installed by a surgeon significantly have a 2.5-5 times greater probability of failure [25]. However, a previous study found there were no statistically significant difference in the success rates of dental implants installed by resident oral surgery from various levels of residency [26].

Conclusion
We found that 90% implant subjects had dehiscence or fenestration at various bone level with concerning result of 74.2% implants did not have lingual/palatal bone at implant platform level.
This could be a result of several factors such as infection, diagnosis, treatment plan, and operator's surgery skills. Only eight of the 14 patients who performed routine dental checkup every 6 months after implant placement could increase the risk of peri-implantitis.
Bone loss on the mesial and distal aspects of dental implants was observed after 1-8 years of placement found the bone loss were averagely 1.08 mm on mesial and 1.36 mm on distal. All the implants were placed without CBCT could lead to operator miscalculation on bone volume, contour, and angulation. Therefore, in moderate to advanced cases, the use of CBCT should be mandatory for treatment plan and could serves as long term evaluation reference. Dental implant evaluation using CBCT can also contribute to early detection of bone loss and help the improvement of existing implants conditions before further destruction occurs.