The aim of this study was to evaluate clinical and radiographic results of submerged and non-submerged implants for posterior single-tooth replacements and to assess patient-based outcomes. Twenty patients were included in the study. A split-mouth design was used; implants inserted using a submerged technique were compared to those inserted with a non-submerged technique. Implants were restored with metal–ceramic crowns after 3 months. Reconstructions were examined at baseline, 6, 12, and 24 months. Standardized radiographs were made. Radiographic crestal bone level changes were calculated, as well as soft tissue parameters, including pocket probing depth, bleeding on probing, plaque index, and gingival index. Results were analyzed by two-way repeated measures of variance (ANOVA). To evaluate patient-based outcomes, patients were asked to complete a questionnaire at the 6-month follow-up; the Wilcoxon paired signed rank test was used to compare scores. The data of 18 patients were reviewed. During 24 months, non-submerged implants (0.57 ± 0.21 mm) showed significantly lower bone loss than submerged implants (0.68 ± 0.22 mm) ( P < 0.01). Patient satisfaction with non-submerged implants (median 87.5) was significantly higher than with submerged implants (median 81.5) ( P < 0.01). Non-submerged implants showed comparable clinical results to submerged implants and resulted in higher patient satisfaction due to decreased surgical intervention.
Over the past 35 years, endosseous dental implants have demonstrated predictable results when used to support restorations that replace missing teeth. Currently, probably the most common indication for implant placement is restoration of a missing or failing single tooth. Success rates for single-tooth replacements supported by implants have been very promising in terms of both implant survival and prosthetic outcomes. The results of implant-supported single-tooth replacements are commonly evaluated independently, because there are differences between edentulous and partially edentulous patients that may have an impact on the final result. Single implant restorations are more prone to biomechanical complications because they are subjected to greater functional forces than splinted implants. Furthermore the replacement of one tooth may be a great aesthetic challenge, particularly in the anterior region. In contrast to the majority of patients with edentulous jaws, single-tooth replacements are frequently performed in young patients.
The original Brånemark concept prescribed two-stage surgery with a submerged healing period of 3 months in the mandible and 6 months in the maxilla in order to optimize the process of new bone formation and remodelling following implant installation. The outcome of the submerged technique was verified in several clinical studies, which reported high success rates. However, recent studies have shown that osseointegration can be achieved using single-stage surgery where the implants are left to heal non-submerged. Non-submerged implant placement has gained interest since it reduces the number of surgical interventions, thus reducing the surgical time and patient discomfort; it also results in a healed and healthy peri-implant mucosa at the time of prosthetic rehabilitation. However, the submerged technique is preferable in combination with bone augmentation, because it prevents overloading of the implants and secures an infection-free environment during the healing period. Some studies on the non-submerged technique have implemented exclusion criteria such as bruxism and heavy smoking. Although promising results have been reported for non-submerged implant installation, divergent results have also been presented.
Clinical studies comparing submerged and non-submerged techniques have generally been performed in edentulous and partially edentulous patients. The present study was designed to evaluate clinical and radiographic results of submerged and non-submerged implants for single-tooth replacements in the same patient using a split-mouth technique and to assess patient-based outcomes with the two treatment protocols. The hypothesis was that there would be no difference in results between the two surgical methods concerning implant survival, clinical parameters, and patient satisfaction.
Materials and methods
A split-mouth study was designed to determine any differences in outcome between implants installed using the submerged surgical technique and those installed using the non-submerged technique. The study protocol was reviewed and approved by the clinical research ethics board of the faculty. The CONSORT statement ( www.consort-statement.org ) was used as a guide for reporting the present clinical study.
Twenty patients (nine men and 11 women) ranging in age from 23 to 51 years (mean age 38.4 years) were included in the study. The surgical and prosthetic treatments and follow-up visits were performed between September 2009 and October 2012. All patients received oral and written information about the study and those who agreed to participate gave their written consent.
Inclusion criteria were the following: good general health for implant surgery; no untreated periodontal disease or other mucosal or bone lesions; not being a heavy bruxer or clencher; single-tooth bilateral edentulous sites in the canine, premolar, or molar region with adequate bone width and similar bone height at the implant sites; at least 2 months since tooth extraction; good arch stability (or an occlusal scheme that allowed the establishment of identical occlusal cusp/fossa contacts).
A total of 20 patients were treated according to the study protocol. The surgical procedure was performed under local anaesthesia. Each patient received two implants (IDcam implants; IDI, Paris, France). The main features of the implant include a threaded, tapered shape, with a Morse taper implant–abutment connection, and a concave-shaped apex design (CSO; concave securit osseo-wedging) ( Fig. 1 ). The CSO apex has been designed to act as a bone reservoir for bone grafting (with its concave shape), to limit the risks of damaging the sinus membrane and nerve (with its ‘securit’ round-shaped end), and to increase the apical bone retention surface (with its peripheral and wedging groove). For implant placement, it was considered to provide a minimal 0.5 mm bone thickness around the inserted implants.
Midcrestal incisions and vertical releasing incisions were used and full thickness flaps were reflected. One side was selected at random to be restored with the submerged technique and the other with the non-submerged technique. To perform within-subject comparisons, left–right randomization was done directly after implant placement. One clinician performed the random allocation of implants in each patient and followed-up the patients between implant insertion and the beginning of the prosthetic procedure (abutment connection). For implants allocated to the submerged technique, a cover screw was applied and the flaps were adapted to achieve primary closure. For the non-submerged group, a healing abutment was secured to the implant and the flaps were adapted. During the primary healing period, chemical plaque control was recommended via rinsing with a 0.1% chlorhexidine solution twice daily for 1 week.
Sutures were removed after 7 days. The implants were allowed to osseointegrate for 3 to 4 months. The patients did not use layering provisional restorations during the osseointegration period. At the end of osseointegration period, gingival removal and abutment connection was performed for the submerged implants (second-stage surgery), and healing abutment removal and abutment connection was performed for the non-submerged implants. The abutments were tightened with a torque control device, up to 30 N cm.
Provisional restorations were placed 2 weeks after the second-stage surgery. The patients used the provisional restorations for 2 months; both implants were then restored with metal–ceramic crowns. To avoid unfavourable loading of the implants, the occlusal scheme was designed to have only light centric occlusion, and no lateral guidance was created at the implant crowns. All prosthetic procedures from abutment connection to cementation of the crowns were performed by one experienced prosthodontist who was blinded to the study assignment.
The reconstructions were examined radiographically and clinically at baseline, 6, 12, and 24 months. Probing depth (PD) measurements were recorded at the mesiobuccal, midbuccal, distobuccal, mesiolingual, midlingual, and distolingual surfaces using Williams probes. The PD was assessed as the longest distance between the gingival margin and the base of the gingival sulcus. The full mouth gingival index (GI) and plaque index (PI) were also determined. Bleeding on probing (BOP) was recorded as positive if it occurred within 30 s of probing. Clinical examinations were conducted by a single, experienced dental examiner who was not involved in the treatment procedures and was blinded to the study assignment.
Standardized peri-apical radiographs of the implants were taken and radiographic crestal bone level changes were calculated. Standardized radiographs were performed with an individualized custom-made bite block using a long cone parallel technique. The films were placed parallel to the implant long axis to provide the perpendicular direction of the beam to the film. Radiographs were taken at implant insertion, after 6 months, 12 months, and 24 months from the placement of crowns. For the evaluation of the marginal bone level, the radiographs were digitized. The most coronal edges of the implant platform mesially and distally were chosen as reference points ( Fig. 2 ). The length of the implant was used as an internal reference to calibrate the measurements for distortions. Distal and mesial bone distances from the implant shoulder and marginal bony crest were measured and averaged for each implant. Mean bone loss values were calculated from baseline to the 6-, 12-, and 24-month follow-ups.