Buccal bone thickness at dental implants in the maxillary anterior region with large bony defects at time of immediate implant placement: A 1‐year cohort study

Abstract Background There is lack of studies regarding preservation and possible changes in BBT at dental implants. Purpose To assess, on cone beam computer tomograms, the presence of bone at the time of tooth extraction in the maxillary esthetic region and the mean buccal bone thickness 1 month and 1 year after final restoration placement in patients with large bony defects. Material and Methods In a cohort study, patients were selected presenting a failing tooth with a large bony defect (test group [n = 20]: large bony defect, immediate placed implant and delayed provisionalization). Results were compared with a group in which patients presented a failing tooth without or with a small bony defect: (control group [n = 20]: without or small bony defect, immediate placed implant and delayed provisionalization). Cone beam computer tomograms were made preoperatively, and 1 month and 1 year after placement of the restoration, and buccal bone thickness was analyzed. Results In both groups approximately 1 mm of buccal bone thickness was present after 1 month and 1 year, without a significant difference between the groups. Conclusion In patients with large bony defects at a failing tooth it was possible to create a bone layer buccally of the implant and this bone layer remained stable during a 1‐year follow‐up; there were no significant differences between thickness of buccal bone at 1 month and 1 year in patients with large buccal bony defects and patients without or with small bony defects.


| INTRODUCTION
Immediate implant placement in the esthetic region is stated to be a favorable treatment modality for replacing failing teeth. [1][2][3] Conversely, there are also studies which conclude to be cautious with immediate implant placement, especially if highly esthetic demands are involved. 4 Particularly in the esthetic zone, preservation and establishment of labial mucosa and underlying buccal bone has been shown to be a key factor in achieving optimal results. 5,6 In the esthetic region, there is data regarding buccal bone thickness (BBT) when the tooth is still in situ. 7,8 Januário and colleagues 7 showed that the buccal bone wall in most cases was less than 1.0 mm thick and even in half of the sites 0.5 mm or less. In the study of El Nahass and Naiem 8 it was reported that usually mean BBT at the central and lateral incisors was less than 1.0 mm. Removal of a maxillary anterior tooth will lead to significant loss of BBT within a few weeks. 9 It has been posed that immediate dental implant placement with augmentation of the space between implant and buccal wall should prevent these dimensional changes, but the results of this preservation technique are contradictory. 3,10,11 It is of interest if the original buccal wall still exists in time or disappears and the augmented bone functions as a new buccal plate at the implant. 12 If a large bony defect results after extraction, hard and soft tissue grafting is often recommended in combination with delayed implant placement. 13,14 However, there are also studies reporting a favorable esthetic outcome when placing implants in fresh extraction sockets with buccal wall dehiscences. 15,16 The morphological assessment of buccal bone volume before placement of dental implants and at dental implants during a followup period is of great interest to clinicians to predict reliability of treatment in the esthetic region. Cone-beam computed tomography (CBCT) has been successfully used for various dental procedures. 17 The CBCT has also been used to assess buccal bone dimensions prior and after implant placement. 18,19 Despite the interest to clinicians, there is lack of studies regarding preservation and possible changes in BBT at dental implants, especially with large bony defects at the time of immediate implant placement. One reason is because in analyzing BBT on CBCT's difficulties are encountered with standardization of measurements. The use of three-dimensional (3D) image diagnostic and treatment planning software programs could be helpful. 20 The purpose of the present cohort study was to assess, on CBCT's, BBT at the time of tooth extraction in the esthetic region in patients with large bony defects and 1 month and 1 year after final restoration placement and compare it with a group without or with small bony defects.

| Patient selection
Forty participants with an implant-supported restoration in the esthetic region of the maxilla were included in the study, originally part of two randomized controlled trials performed at the University Medical Center Groningen in the Netherlands. 21,22 These trials got approval by the Medical Ethic Board (METC 2010.246) and registered (www.isrtcn.com: ISRCTN57251089). All participants gave written informed consent and research was carried out in accordance with the Declaration of Helsinki.
The following group was selected from a study in which patients presented a failing tooth in the maxillary esthetic region with a large bony buccal defect 21 : • test group (n = 20): large bony defect and compared with a group selected from a study in which patients presented a failing tooth in the maxillary esthetic region without or with a small bony buccal defect 22 : • control group (n = 20): without or small bony defect A large bony defect was defined as being ≥2 mm and a small bony defect as <2 mm, after the review of Chen and colleagues 23 and confirmed by the Consensus Statements of Hämmerle and colleagues. 24 In both the test group and the control group, implants were immediately placed implant and delayed provisionalized.

| Clinical soft tissue outcomes and esthetic appearance
To complete insight of the labial aspect of soft tissues at dental implants, the following clinical and esthetic items have been evaluated: • change in midfacial mucosal level in mm at 1 year as compared with the gingival level of the preoperative failing tooth; • esthetic appearance scored with the pink esthetic score (PES) at 1 year (Belser and colleagues). 27

| Statistical analysis
For comparison between test and control group, the Mann-Whitney U test was performed. A P-value of .05 was considered being statistical significance.

| RESULTS
One patient from the control group did not show up at follow-up and was excluded from further analysis. Five pretreatment CBCT's were not available (two in the test group and three in the control group).
This resulted in CBCT's of 34 patients available for the present study.
Median and interquartile ranges, together with means and standard deviations, of bone thickness at M0-M5 at pretreatment, 1 month and 1 year after final restoration placement are depicted per study group in Table 1.
In patients from the test group, the median distance from the outer surface of the buccal bone to the surface of the future implant at all different positions was at pretreatment 0 mm. One year after     16 in which implants were immediately placed in patients with large buccal defects. At start of the restorative phase, after 6 months of healing, at the neck of the implant a mean BBT of 3.0 mm was achieved. It must be noted that in the present study this was much less, being a little bit more than 1 mm.
In the control group without or with small bony defects, there was always bone present before treatment at the buccal side of the future implant position, varying from a median value from outer contour of the bone to the surface of the virtual implant of 1.99-2.28 mm. Consistent with the test group, the next CBCT in the control group was taken after 7 months. In these 7 months, the median BBT diminished significantly with at least 0.5 mm. It could well be that the total original wall has been resorbed in these 7 months.
Between 7 months and 18 months, there was not a significant TABLE 1 Buccal bone measurements pre-extraction, 1 month and 1 year after dental implant surgery in the test group and control group (test group: large bony and immediate placement/delayed provisionalization; control group: without or small bony defect and immediate placement/ delayed provisionalization) expressed as median and mean and significant differences between the groups   It appeared from the present study that buccal bone thickness at dental implants in the esthetic region was hardly subject to change.
This can be called a very favorable outcome, because it means that A limitation of analyzing buccal bone thickness on radiographs is that measuring the thickness of a radio-opaque structure does not automatically mean that this structure is actually bone. It could well be that only limited living bone material is present in the applied bone substitute or even that only a mixture of bone substitute and connective tissues is assumed to be bone.
Clinical soft tissue outcomes, being change in midfacial mucosal level and pocket probing depth, showed limited recession in both groups and normal probing depth values in both groups. Also esthetic appearance, expressed with PES, revealed high scores without a difference between the groups. These good clinical features correspond with the presence of buccal bone at the implants in both groups, giving support to the soft tissues.
A limitation of the present study design is the direct comparison of a group with a large bony defect with a group without or with a small defect. Although the same outcome measures were used and with the same treatment team and observers, it could be that procedures between the groups differ more than just the augmentation.
Next to this only a limited sample size was used; to strengthen the conclusions more patients are needed.
From this CBCT study can be concluded that: • in patients with large bony defects at a failing tooth, it was possible to create a bone layer buccally of the implant and this bone layer remained stable during a 1-year follow-up; • there were no significant differences between thickness of buccal bone at 1 month and 1 year in patients with large buccal bony defects and patients without or with small bony defects.