Influence of microgap location and configuration on peri-implant bone morphology in nonsubmerged implants: an experimental study in dogs.

PURPOSE: It is unknown whether different microgap configurations can cause different peri-implant bone reactions. Therefore, this study sought to compare the peri-implant bone morphologies of two implant systems with different implant-abutment connections. MATERIALS AND METHODS: Three months after mandibular tooth extractions in six mongrel dogs, two oxidized screw implants with an external-hex connection were inserted (hexed group) on one side, whereas on the contralateral side two grit-blasted screw implants with an internal Morse-taper connection (Morse group) were placed. On each side, one implant was inserted level with the bone (equicrestal) and the second implant was inserted 1.5 mm below the bony crest (subcrestal). Healing abutments were inserted immediately after implant placement. Three months later, the peri-implant bone levels, the first bone-to-implant contact points, and the width and steepness of the peri-implant bone defects were evaluated histometrically. RESULTS: All 24 implants osseointegrated clinically and histologically. No statistically significant differences between the hexed group and Morse group were detected for either the vertical position for peri-implant bone levels (Morse equicrestal -0.16 mm, hexed equicrestal -0.22 mm, Morse subcrestal 1.50 mm, hexed subcrestal 0.94 mm) or for the first bone-to-implant contact points (Morse equicrestal -2.08 mm, hexed equicrestal -0.98 mm, Morse subcrestal -1.26 mm, hexed subcrestal -0.76 mm). For the parameters width (Morse equicrestal -0.15 mm, hexed equicrestal -0.59 mm, Morse subcrestal 0.28 mm, hexed subcrestal -0.70 mm) and steepness (Morse equicrestal 25.27 degree, hexed equicrestal 57.21 degree, Morse subcrestal 15.35 degree, hexed subcrestal 37.97 degree) of the peri-implant defect, highly significant differences were noted between the Morse group and the hexed group. CONCLUSION: Within the limits of this experiment, it can be concluded that different microgap configurations influence the size and shape of the peri-implant bone defect in nonsubmerged implants placed both at the crest and subcrestally.

The effects of recombinant human growth/differentiation factor-5 (rhGDF-5) on bone regeneration around titanium dental implants in barrier membrane-protected defects: a pilot study in the mandible of beagle dogs.

PURPOSE: This dog study sought to evaluate guided bone regeneration (GBR) in peri-implant defects following implantation of beta-tricalcium phosphate (beta-TCP) with and without osteoinductive recombinant human growth/differentiation factor-5 (rhGDF-5). MATERIALS AND METHODS: In five beagle dogs, all mandibular premolars and the first molar were extracted. After 2 months, six buccolingual critical-size defects were created, and an implant was inserted into the center of each defect. One defect was filled with beta-TCP coated with rhGDF-5 (600 microg/g beta-TCP) and covered with a titanium-reinforced e-PTFE membrane (GDF group). A second defect received the same treatment, but pure uncoated beta-TCP was used (TCP group). A third defect was filled with beta-TCP mixed with autograft and not protected with a membrane (control group). The remaining three defects were filled with other biomaterials. After 2 months, total new bone area, regenerated bone height, and residual amount of beta-TCP were determined histomorphometrically. RESULTS: All implants osseointegrated. One membrane in each group became exposed. Mean new bone area for GDF, TCP, and control sites was 43.9 +/- 18.7 mm2, 32.3 +/- 16.1 mm2, and 13.1 +/- 4.0 mm2, respectively, with a significant difference between GDF and control groups. Mean regenerated bone height was 103.8 +/- 29.7%, 75.4 +/- 36.6%, and 67.2 +/- 19.1% for the GDF, TCP, and control groups, respectively. Mean residual matrix volumes were 25.9 +/- 13.6%, 30.0 +/- 13.0%, and 13.4 +/- 6.5%, respectively. Membrane protection of peri-implant defects filled with beta-TCP resulted in a stronger effect on bone regeneration, although this was not statistically significant. The most pronounced regenerative results were achieved in rhGDF-5/beta-TCP filled membrane-protected defects. CONCLUSION: Delivery of rhGDF-5 on beta-TCP might have the potential to enhance the results of GBR in peri-implant defects.

Influence of microgap location and configuration on the periimplant bone morphology in submerged implants. An experimental study in dogs.

OBJECTIVES: The vertical location of the implant-abutment connection influences the periimplant bone morphology. It is unknown, however, whether different microgap configurations cause different bone reactions. Therefore, in this study the bone morphologies of two different implant systems were compared. MATERIAL AND METHODS: Three months after tooth extraction in eight mongrel dogs, two grit-blasted screw implants with internal Morse taper connection (ANK group) were placed on one side whereas the contralateral side received two oxidized screw implants with external hex (TIU group). One implant on each side was placed level with the bone (equicrestal), the second implant was inserted 1.5 mm below bone level (subcrestal). After 3 months the implants were uncovered. Three months after stage two surgery, histometrical evaluations were performed in order to assess the periimplant bone levels (PBL), the first bone-to-implant contact points (BICP), the width (HBD) and the steepness (SLO) of the bone defect. RESULTS: All implants osseointegrated clinically and histologically. Bone overgrowth of the microgap was seen in ANK implants only. No significant differences between ANK and TIU could be detected in neither vertical position for PBL and BICP. However, a tendency in favor of ANK was visible when the implants were placed subcrestally. In the parameters HBD (ANK equicrestal -0.23 mm; TIU equicrestal -0.51 mm; ANK subcrestal +0.19 mm; TIU subcrestal -0.57 mm) and SLO (ANK equicrestal 35.36 degrees; TIU equicrestal 63.22 degrees; ANK subcrestal 20.40 degrees; TIU subcrestal 44.43 degrees) more pronounced and significant differences were noted. CONCLUSIONS: Within the limits of this study, it is concluded that different microgap designs cause different shapes and sizes of the periimplant ('dish-shaped') bone defect in submerged implants both in equicrestal and subcrestal positions.