Sang-on Cho

Screw loosening for standard and wide diameter implants in partially edentulous cases: 3- to 7-year longitudinal data.

Screw loosening is considered to be a common problem with both screw - retained and cemented implant restorations. A wider abutment platform, as well as using a torque driver to tighten specifically designed screws may help prevent this loosening. However, there has been no clinical study evaluating either of these. To longitudinally compare the frequency of screw loosening in standard diameter, (3.75 and 4.0 mm) implant supported prostheses to that of wide diameter, (5.0 and 6.0 mm) implant supported prostheses that were hand tightened, and to evaluate whether using a torque driver would minimize or prevent this problem, if screw loosening occurred. A total of 213 dental implants in 106 patients were included in this prospective longitudinal study. Of the implants 68 were wide diameter and 145 were standard diameter implants. Wide diameter implants showed 5.8% screw loosening, while standard diameter implants showed 14.5% screw loosening after insertion with only hand torquing. When these loose screws were tightened with a torque driver, there was no more loosening of screws. Within the limitations of this study, the wide diameter implants tested showed less screw loosening than the standard diameter implants when hand torqued. Additionally, within the scope of our study, using a torque driver to tighten the screws with the recommended force prevented this loosening from reoccurring in all cases.

New Bone Formation in the Maxillary Sinus Using Only Absorbable Gelatin Sponge

PURPOSE The purpose of the present study was to evaluate the predictability of new bone formation in the maxillary sinus using only absorbable gelatin as the graft material. PATIENTS AND METHODS Seven patients (9 sinus augmentations) were consecutively treated with sinus floor elevation by the lateral window approach. The lateral bony window was created using a piezoelectric device and the schneiderian membrane was elevated to make a new compartment. After 18 resorbable blast media surfaced dental implants were simultaneously placed, absorbable gelatin sponges were loosely inserted to support the sinus membrane over the implant apex and the bony portion of lateral window was repositioned to seal the lateral window. RESULTS After uncovering the implants an average of 6 months after placement, new bone consolidation in the maxillary sinus was observed on radiographs without bone graft. Two implants were removed due to failed osseointegration on uncovering. Failures were caused by insufficient initial stability. CONCLUSION This study suggests that placement of a dental implant in the maxillary sinus with a gelatin sponge can be a predictable procedure for sinus augmentation.

Survival Rate of Immediately vs Delayed Loaded Implants: Analysis of the Current Literature

Immediate loading of oral implants has been reported as a beneficial treatment protocol in implant dentistry that increases the comfort of the patient. However, documentation in the literature is poor regarding the clinical outcome and the peri-implant bone response of immediately loaded implants compared with the conventional loading protocol placed in different bone qualities. The aim of this report was to present the role of bone quality in the survival rate of implants using conventional or immediate loading according to the literature. A literature search analysis was performed to demonstrate the survival rate of immediately loaded implants, as well as data from the histologic and histomorphometric evaluation in comparison with conventional loaded implants. This analysis showed high survival rates of immediately loaded implants along with osseointegration, with high percentages of bone-to-implant contacts based on histologic evaluation from human and animal studies of immediately and conventionally loaded implants. This study may provide histologic and clinical evidence of the immediate loading protocol for different bone qualities.

Effect of Interimplant Distance (2 and 3 mm) on the Height of Interimplant Bone Crest: A Histomorphometric Evaluation

BACKGROUND Implants restored according to a platform-switching concept (implant abutment interface with a reduced diameter relative to the implant platform diameter) present less crestal bone loss than implants restored with a standard protocol. When implants are placed adjacent to one another, this bone loss may combine through overlapping, thereby causing loss of the interproximal height of bone and papilla. The present study compares the effects of two interimplant distances (2 and 3 mm) on bone maintenance when bone-level implants with platform-switching are used. METHODS This study evaluates marginal bone level preservation and soft tissue quality around a bone-level implant after 2 months of healing in minipig mandibles. The primary objective is to evaluate histologically and histomorphometrically the affect that an implant design with a horizontally displaced implant-abutment junction has on the height of the crest of bone, between adjacent implants separated by two different distances. RESULTS Results show that the interproximal bone loss measured from the edge of the implant platform to the bone crest was not different for interimplant distances of 2 or 3 mm. The horizontal position of the bone relative to the microgap on platform level (horizontal component of crestal bone loss) was 0.31 ± 0.3 mm for the 2-mm interimplant distance and 0.57 ± 0.51 mm above the platform 8 weeks after implantation for the 3-mm interimplant distance. CONCLUSIONS This study shows that interimplant bone levels can be maintained at similar levels for 2- and 3-mm distances. The horizontally displaced implant-abutment junction provided for a more coronal position of the first point of bone-implant contact. The study reveals a smaller horizontal component at the crest of bone than has been reported for non-horizontally displaced implant-abutment junctions.

A two-stage full-arch ridge expansion technique: review of the literature and clinical guidelines.

Ridge expansion techniques have been acknowledged to offer several advantages in the correction of ridge deformities. The expanded defect heals in a similar manner to an extraction socket. In selected cases patients can wear their dentures after surgery. Secondary surgical sites are not a prerequisite, and simultaneous implant placement can be achieved during ridge expansion. The limitation of this technique lies in its inability to create bone vertically. Therefore, it is not indicated for the correction of vertical defects. The application of the split ridge expansion technique has been reported in the literature as it pertains to partially edentulous deficient ridges. The purpose of this article was to present the application of the split ridge expansion technique in the fully edentulous maxilla and discuss the distinction between the immediate or one-stage approach and the delayed or two-stage approach. Histologic results are discussed. Two case reports demonstrate the results that can be obtained with this technique.

Effect of Maxillary Sinus Membrane Perforation on Vital Bone Formation and Implant Survival: A Retrospective Study

BACKGROUND The maxillary sinus augmentation procedure (SAP) using the lateral window technique has been documented to be a highly predictable procedure. However, the most common intraoperative complication has been reported to be maxillary sinus membrane perforation (MSMP). The present study evaluates the percentage of vital bone and implant survival in sinuses that had perforations repaired during surgery versus a non-perforated sinus group. METHODS Data were obtained retrospectively from an Institutional Review Board-approved anonymous database at New York University, Kriser Dental Center, Department of Periodontology and Implant Dentistry, New York, New York, from 23 patients who had undergone SAP with a total of 40 treated sinuses. Sinuses were grafted with mineralized cancellous bone allograft, anorganic bovine bone matrix, or biphasic calcium phospate. Perforation complications occurred in 15 sinuses with 25 non-perforated sinuses. All perforations were repaired during surgery with absorbable collagen membrane barriers. Histologic cores were taken from all treated sinuses 26 to 32 weeks after surgery. The implant success rate of 79 placed implants was recorded. RESULTS The average percentage of vital bone was 26.3% ± 6.3% in the perforated (repaired) sinuses versus 19.1% ± 6.3% in the non-perforated sinuses. The differences were statistically significant (SS). The implant success rate was 100% (35 of 35) compared to 95.5% (43 of 45) in the perforated/repaired vs. non-perforated sinuses, respectively. There was no SS difference in implant failure rates. CONCLUSIONS The augmented sinuses in this study that exhibited MSMPs that occurred during the SAP (which were treated during surgery) show SS greater vital bone percentages compared with the non-perforated sinus group. There were no SS differences in implant survival in the perforated versus non-perforated groups. In this study, sinus MSMPs, when properly repaired during surgery, do not appear to be an adverse complication in terms of vital bone production or implant survival.

Unexpected return of sensation following 4.5 years of paresthesia: case report.

Neural damage leads to a transient or persistent alteration, depending on the severity or type of injury sustained. During the last decade, many investigators reported on paresthesia related to dental implants. In this case report, the patient had presented repeatedly with swelling and suppuration, showing typical signs of peri-implantitis. In addition, the implant was placed in proximity to the mental foramen and possibly had traumatized the mental nerve because the patient had had an altered sensation on his left side for the past 4.5 years. After removal of the implant, a significant diminishing of the paresthesia had occurred, described by the patient as a 40% improvement. Further improvement occurred at 6 and 9 months. In this case report, the findings differ from the current literature in that the return of sensation occurred following a prolonged state of paresthesia. This report documents 2 unique findings. First, an area of persistent paresthesia significantly improved 50 months after the initial injury, upon the removal of the offending implant. Second, the placement of another implant in the same vicinity did not result in recurrent paresthesia.

Radiological and micro‐computed tomography analysis of the bone at dental implants inserted 2, 3 and 4 mm apart in a minipig model with platform switching incorporated

BACKGROUND The purpose of this study was to assess the effect of inter-implant distance on interproximal bone utilizing platform switching. Analysis of interproximal bone usually depends on traditional two-dimensional radiographic assessment. Although there has been increased reliability of current techniques, there has been an inability to track bone level changes over time and in three dimensions. Micro-CT has provided three-dimensional imaging that can be used in conjunction with traditional two-dimensional radiographic techniques. METHODS This study was performed on 24 female minipigs. Twelve animals received three implants with an inter-implant distance of 3 mm on one side of the mandible and another three implants on the contra-lateral side, where the implants were placed 2 mm apart creating a split mouth design. Twelve other animals received three implants with an inter-implant distance of 3 mm on one side of the mandible and another three implants on the contra-lateral side, where the implants were placed 4 mm apart creating a split mouth design too. The quantitative evaluation was performed comparatively on radiographs taken at t 0 (immediately after implantation) and at t 8 weeks (after termination). The samples were scanned by micro-computed tomography (μCT) to quantify the first bone to implant contact (fBIC) and bone volume/total volume (BV/TV). Mixed model regressions using the nonparametric Brunner-Langer method were used to determine the effect of inter-implant distance on the measured outcomes. RESULTS The change in bone level was determined using radiography and its mean was 0.05 mm for an inter-implant distance of 3 and 0.00 mm for a 2 mm distance (P = 0.7268). The mean of this outcome was 0.18 mm for the 3 mm and for 4 mm inter-implant distance (P = 0.9500). Micro-computed tomography showed that the fBIC was always located above the reference, 0.27 and 0.20 mm for the comparison of 2-3 mm (P = 0.4622) and 0.49 and 0.34 mm for the inter-implant distance of 3 and 4 mm (P = 0.1699). BV/TV inside the defined parallelepipedic masks reached 82.38% for the 2 mm inter-implant distance and 85.00% for 3 mm, P = 0.8432. For the comparison of the 3-4 mm inter-implant distance, the means were 84.69% and 84.38%, respectively, P = 0.8401. Non-inferiority tests for the smaller inter-implant distances for both comparisons showed similar differences and similar tolerance ranges. CONCLUSION The effect of a smaller interproximal distances between implants on bone level, fBIC and BV/TV assessed by two convergent investigation methods, radiology and μCT, was similar to that of larger distances. Implants can potentially be placed 2 mm apart instead of 3 mm and 3 mm apart instead of 4 mm when platform switching is utilized. Further research with a conventional platform is warranted.

Maxillary Sinus Grafting With Biphasic Bone Ceramic or Autogenous Bone: Clinical, Histologic, and Histomorphometric Results From a Randomized Controlled Clinical Trial.

Purpose:The present, randomized, controlled clinical trial compared the histologic and histomorphometric results from maxillary sinus augmentation with either biphasic calcium phosphate (BCP) (60% hydroxyapatite and 40% &bgr;-tricalcium phosphate) or autogenous bone (AB) as bone-grafting materials. Material and Methods:Ten patients received bilateral sinus elevation surgery with intraoral AB chips (control group) on one side and BCP (test group) on the contralateral side. After a healing period of 6 to 8 months, implant sites were created and trephine cores were harvested for histological and histomorphometric analysis of the grafted areas. Results:The histological examination of biopsies showed BCP particles interconnected by bridges of a vital newly formed bone. Histomorphometry demonstrated that the amount of newly formed bone in the control group (36.8%) was significantly greater than that in the BCP (28.2%) group (P = 0.0032). BCP and AB cores revealed an average of residual graft particles of 32.9% and 4.8%, respectively. The average percentage of soft tissue components was 38.9% in the BCP cores and 58.4% in the AB cores. Conclusions:Based on our findings, the amount of vital bone formation was significantly higher for AB than that for BCP. However, BCP seemed to be a biocompatible and osteoconductive material that can be used with success as a bone substitute in maxillary sinus procedures.

The use of a xenogeneic collagen matrix at the time of implant placement to increase the volume of buccal soft tissue.

The purpose of this study was to evaluate the efficacy of Mucograft (MG; a porcine-derived purified collagen membrane) to increase the thickness and height of the buccal soft tissue when placed at the time of implant placement in patients with thin or deficient keratinized tissue (KT). The primary endpoint of the study was the change in thickness and height of the buccal KT. Secondary endpoints included stability of the midbuccal soft tissue level; clinician rating of color, texture, and contour of treatment site; probing pocket depths (PPDs); assessment of satisfaction outcome; and patient assessment of pain/discomfort. Thirty-two patients were enrolled and 31 patients completed the study. There were no statistically significant (SS) differences between the MG and control groups for height measures. There was no SS difference for KT thickness (P = .117) between the groups at the final measurement (3 months postsurgery). However, there was an SS difference (P = .009) in favor of the MG group when comparing the difference in presurgical KT thickness to that 3 months postsurgery. Thus, MG was successful (compared to the control) in increasing the buccal KT. There were no SS differences between the groups for any of the other endpoints, including color, texture, contour, and pain assessment at any visit or successful outcome between the treatment group and the control. More cases and longer follow-up of implants placed with MG are needed to verify the results of this randomized prospective study.