Faculty Bibliography

BACKGROUND: Despite technical advancement, treatment of congenital alveolar clefts has remained controversial. Currently, primary alveolar cleft repair (i.e., gingivoperiosteoplasty) has a 41 to 73 percent success rate. However, the remaining patients have persistent alveolar bone defects requiring secondary grafting procedures. Morbidity of secondary procedures includes pain, graft resorption, extrusion or infection, and graft or tooth loss. The authors present a novel rat alveolar defect model designed to facilitate investigation of therapeutics aimed at improving bone formation following primary alveolar cleft repair in humans. METHODS: Sixteen 8-week-old Sprague-Dawley rats underwent creation of a 7 x 4 x 3-mm complete alveolar defect from the maxillary incisors to the zygomatic arch. Four animals were humanely killed at each of the following time points: 0, 4, 8, and 12 weeks. Morphometric analysis of the alveolar defect was determined by means of micro-computed tomography and histology. RESULTS: Micro-computed tomography demonstrated that new bone filled 43 +/- 5.6 percent of the alveolar defect at 4 weeks, 53 +/- 8.3 percent at 8 weeks, and 48 +/- 3.5 percent at 12 weeks. Histologically, at 4 weeks, proliferating fibroblasts and polymorphonuclear cells were scattered throughout the disorganized collagen in the intercalary gap. By 8 weeks, nascent woven bone spicules extended from the edges of the defect. At 12 weeks, the woven spicules had remodeled, with scant additional bone deposition. CONCLUSION: This model creates a critical-size alveolar defect that is similar in size and location to human alveolar defects and is suitable for studying proposed therapeutics.

INTRODUCTION: A tapered dental implant (Laser-Lok [LL] surface treatment) with a 2 mm wide collar, that has been laser micromachined in the lower 1.5 mm to preferentially accomplish bone and connective tissue attachment while inhibiting epithelial downgrowth, was evaluated in a prospective, controlled, multicenter clinical trial. MATERIALS: Data are reported at measurement periods from 1 to 37 months postoperative for 20 pairs of implants in 15 patients. The implants are placed adjacent to machined collar control implants of the same design. Measurement values are reported for bleeding index, plaque index, probing depth, and crestal bone loss. RESULTS: No statistical differences are measured for either bleeding or plaque index. At all measurement periods there are significant differences in the probing depths and the crestal bone loss differences are significant after 7 months (P < 0.001). At 37 months the mean probing depth is 2.30 mm and the mean crestal bone loss is 0.59 mm for LL versus 3.60 and 1.94 mm, respectively, for control implant. Also, comparing results in the mandible versus those in the maxilla demonstrates a bigger difference (control implant - LL) in the mean in crestal bone loss and probing depth in the maxilla. However, this result was not statistically significant. DISCUSSION: The consistent difference in probing depth between LL and control implant demonstrates the formation of a stable soft-tissue seal above the crestal bone. LL limited the crestal bone loss to the 0.59 mm range as opposed to the 1.94 mm crestal bone loss reported for control implant. The LL implant was found to be comparable with the control implant in safety endpoints plaque index and sulcular bleeding index. There is a nonstatistically significant suggestion that the LL crestal bone retention superiority is greater in the maxilla than the mandible.

This study, analytically, through finite element analysis, predicts the minimization of crestal bone stress resulting from implant collar surface treatment. A tapered dental implant design with (LL) and without (control, C) laser microgrooving surface treatment are evaluated. The LL implant has the same tapered body design and thread surface treatment as the C implant, but has a 2-mm wide collar that has been laser micromachined with 8 and 12 microm grooves in the lower 1.5 mm to enhance tissue attachment. In vivo animal and human studies previously demonstrated decreased crestal bone loss with the LL implant. Axial and side loading with two different collar/bone interfaces (nonbonded and bonded, to simulate the C and LL surfaces, respectively) are considered. For 80 N side load, the maximum crestal bone distortional stress around C is 91.9 MPa, while the maximum crestal bone stress around LL, 22.6 MPa, is significantly lower. Finite element analysis suggests that stress overload may be responsible for the loss of crestal bone. Attaching bone to the collar with LL is predicted to diminish this effect, benefiting crestal bone retention.

PURPOSE/OBJECTIVE:Calcium sulfate (CS) is an excellent bone graft material not only because of its osteoconductive, biodegradable, biocompatible, and nontoxic properties, but also because of its angiogenic, barrier membrane, and hemostatic properties. The latter make it unique as a bone graft material. Nevertheless, its clinical use for this purpose is limited by its rapid degradation rate: it usually completely degrades in 4 to 5 weeks, often not enough time for bone to grow into a defect. To overcome this limitation, a CS-based bone graft with a controlled degradation profile was developed. METHODS:A composite of CS and poly (L-lactic acid) (PLLA) (ratio, 96:4) was developed and a degradation profile of the composite generated. Bone response to pure CS and to this composite at time points ranging from 4 to 16 weeks was studied in the rabbit tibial intramedullary canal model. RESULTS:This composite underwent controlled degradation in vitro and in vivo, taking 16 weeks for complete degradation in both cases. It stimulated stronger bone formation in bone defects than did pure CS. CONCLUSION/CONCLUSIONS:A CS/PLLA composite (ratio, 96:4) is an excellent bone graft material.

PURPOSE: The purpose of this study was to examine the crestal bone, connective tissue, and epithelial cell response to a laser microtextured collar compared with a machined collar, in the dog model. MATERIALS: Six mongrel dogs had mandibular premolars and first molars extracted and after healing replaced with BioLok implants 4 x 8 mm. Each dog had 3 control implants placed on one side of the mandible and 3 experimental, laser microtextured, implants placed contralaterally. After 3 months, 1 dog was killed. Bridges were placed on the implants of 4 of the dogs. The sixth dog served as a negative control for the duration of the experiment. Two of the dogs were killed 3 months after loading, of the dogs were killed 6 months after loading as was the negative (unloaded) control. Histology, electron microscopy, and histomorpho-metric analysis was done on histologic sections obtained from block sections of the mandible containing the implants. RESULTS: Initially the experimental implants showed greater bone attachment along the collar. With time the bone heights along the control and experimental collars were equivalent. However, the controls had more soft tissue downgrowth, greater osteoclastic activity, and increased saucerization compared with sites adjacent to experimental implants. There was closer adaptation of the bone to the laser microtextured collars. CONCLUSION: Use of tissue-engineered collars with microgrooving seems to promote bone and soft tissue attachment along the collar and facilitate development of a biological width.