In this study, a mean bone thickness of 1.81 mm at PL0 and 1.97 mm at PL2 in the control group and 2.21 mm at PL0 and 2.26 mm at PL2 in the test group was present facial to the implants at the definitive prosthesis connection period. These results suggest that sufficient bone thickness could be acquired with immediate implant placement and delayed provisionalization in both groups . However, in the control group, TW decreased significantly from T0 to T1 at PL0 because of the decrease in BW. The soft tissue thickness (GW) in the control group remained stable following immediate placement, leading to the assumption that mucosal contour loss is mostly related to underlying facial hard tissue resorption. However, in the test group, the decrease in BW was compensated for by the increase in GW gained by CTG, resulting in a significant increase in TW at both PL0 and PL2.
The soft tissue thickness increased significantly with CTG; the mean soft tissue gain was 1.37 mm at PL0 and 1.20 mm at PL2. Previous studies have shown that the thickness of the palatal mucosa of Asians is 2.0 to 3.7 mm, and CTG results in a soft tissue thickness increase of 0.92–1.40 mm as measured with an endodontic needle or ultrasonic device [22,23,24]. The results obtained from this study are also in line with the previous reports.
Numerous reports have described the superiority and inferiority of immediate implant placement. Multiple studies have shown that immediate implant placement can lead to facial mucosal recessions [25, 26]. On the other hand, placing an implant simultaneously as tooth extraction allows a decrease in the number of surgical procedures and treatment time and minimizes bone and soft tissue resorption after tooth extraction and maintains the preoperative mucosal contour [2, 3]. Postoperative bone resorption is suppressed by combining bone augmentation with immediate implant placement . In the present study, GBR was conducted in all patients simultaneously as immediate implant placement using deproteinized bovine bone mineral (DBBM) granules and resorbable membranes to achieve contour augmentation and prevent bone resorption. Although DBBM granules have a low substitution rate and were used to fill the implant-socket gap to help maintain the dimensions of the facial wall, a mean of 0.49 mm of horizontal hard tissue resorption at PL0 was observed. This result is probably due to the resorption of the original facial bundle bone along with tooth extraction. Particularly in the maxillary anterior region, where the initial facial bone thickness is thin, and most of it is composed of bundle bones attached to the natural tooth through the periodontal ligament. It has been reported that facial bone thickness is less than 1.0mm in most cases and even 0.5mm or less in half of the sites . Therefore, bone resorption is likely to occur after tooth extraction within a few weeks [6, 29]. In the present study, the initial bone width facially to the implant was 0.61mm, suggesting that most original facial bones must have been resorbed during 1 year of follow-up. This result could mean that the newly augmented bone functioned as a new facial plate.
A previous study showed that immediate implant placement is contraindicated if there is a dehiscence bone defect facially to the implant . Otherwise, preoperative labial bony defects can be reconstructed by simultaneous bone augmentation even if a dehiscence bone defect is present at implant placement [27, 30, 31]. In the present study, patients who had a labial bony defect mesiodistally greater than the implant diameter or vertically more than 4mm from the implant platform level were excluded.
The influence of the implant–socket gap size or the initial facial bone thickness in the case of immediate implant placement is contentious. Chen et al. and Chappuis et al. have reported that sites with thinner post-extraction facial bone underwent significantly more bone resorption than sites with thicker facial bone [32, 33]. The initial bone width facially to the implant is consistent with past reports that facial bone thickness is less than 1.0mm in most cases . Chen also has reported that if the gap width of the extraction socket is 2 mm or less, the interior of the gap will be filled with new bone . In the present study, the horizontal implant-socket gap size was 1.89mm. This result suggests that implants were placed in an ideal position that could keep the proper size of implant-socket gap. Under this criterion, sufficient bone thickness of approximately 2.0mm could be acquired by immediate implant placement with simultaneous GBR facially to the implant during a 1-year follow-up period.
This study supports a past report that found facial bone resorption cannot be wholly prevented even if bone augmentation is combined with immediate placement [3, 11]. However, concerning horizontal thickness, facial bone resorption is compensated for by soft tissue gain after CTG, and the preoperative mucosal contour is maintained. Thus, when the need to preserve the preoperative mucosal contour is not high, as in patients with defects of contralateral teeth, it is considered possible to acquire an esthetically satisfactory outcome without CTG. However, in cases in which a contralateral tooth is present (such as in patients with a single tooth defect), and mucosal contour symmetry between the peri-implant mucosa and the gingival contour of the contralateral tooth is required, CTG should be performed with immediate implant placement to maintain the preoperative mucosal contour.
In this surgical procedure, immediate implant placement and delayed provisionalization were applied to patients, so a mucoperiosteal flap was raised, and sutures were placed to achieve primary wound closure at the time of implant placement. Immediate placement and provisionalization with a flapless technique have been suggested to decrease the amount of soft tissue recession and the risk of wound failure after implant placement [35, 36]. On the other hand, immediate implant placement with delayed restoration is a well-established procedure, especially when the facial bone to implant has dehiscence [30, 37]. This study also included patients with labial bony defects, so contour augmentation should be performed simultaneously with implant placement. Surgical flaps were elevated to allow for GBR procedures to be performed to standardize surgery in this study.
The following limitations of this study should be taken into consideration. First, vertical bone and soft tissue changes were not evaluated in this study. This was because the vertical height of the soft tissue will be positively changed when the implant prosthesis is connected or the emergence profile or facial contour of the provisional restoration is modified. For this reason, it is challenging to evaluate vertical peri-implant tissue changes with the same criteria preoperatively and after connection of the implant prosthesis. Second, the impact of the implant site (central or lateral incisor) or preoperative facial bone condition (presence or size of labial bony defect around the failing tooth) was not explored. If the influence of these factors is to be clarified, future studies with larger samples must be carried out for a more detailed evaluation. Third, only the evaluation 1 year after prosthesis connection has been performed. It has been reported that immediate placement can cause soft tissue recession after treatment and continue for an extended period, up to 5 years after implant placement [5, 38]. A more extended observation period will be necessary to evaluate the grafted peri-implant tissue’s stability and marginal bone levels over time. Forth, in this study, two surgeons decided whether to perform CTG (discrimination of the patients between test and control groups) based on the clinical status of each patient such as mucosal contour compared to the contralateral tooth or gingival biotype. The baseline patient characteristic and initial tissue thickness in the two groups are described in Table 1; there were no statistically significant differences between the groups. However, this study is not based on the randomized selection, and that is one of the limitations of this study. Finally, an esthetic evaluation such as the pink esthetic score was not performed in this study. CTG is beneficial for preserving preoperative mucosal contour, but it is not easy to correlate with esthetic achievement.
In this study, the use of CTG in immediate implant placement was found to be an effective treatment option in the maxillary anterior zone compensating for bone resorption and preserving the preoperative mucosal contour.
In conclusion, facial hard tissue resorption was found in immediate placement sites with GBR only. However, immediate placement sites with GBR and CTG showed evidence of compensation for bone resorption occurring after implant placement with a 1.37 mm soft tissue gain, thus still capable of preserving the preoperative mucosal contour 1 year after connection of the implant prosthesis.