Prospective clinical study of zirconia posterior fixed partial dentures: 3-year follow-up.

OBJECTIVES: The purpose of this prospective clinical cohort study was to determine the success rate of 3- to 5-unit posterior fixed partial dentures (FPDs) with zirconia frameworks after 3 years of function. METHOD AND MATERIALS: Forty-five patients in need of at least 1 FPD to replace 1 to 3 posterior teeth were included. The frameworks were produced by means of a prototype computer-assisted manufacture system. They were milled with a precisely calculated increase in size out of presintered zirconia blanks and subsequently shrunk to the required size. Fifty-seven FPDs were cemented using either Variolink or Panavia TC cement. Clinical and radiographic examinations were performed at baseline, 12, 24, and 36 months after cementation. Statistical analysis was performed by descriptive statistics and the Kaplan-Meier survival analysis. Comparisons of probing depth, Plaque Index, and bleeding on probing between test (abutment) and control (contralateral) teeth were done with the McNemar test. RESULTS: Thirty-six patients with 46 FPDs were available for examination after 36 months. No fractures occurred, rendering a 100% success rate of the zirconia frameworks. Seven FPDs had to be replaced because of biologic and technical problems. The survival rate, therefore, was 84.8%. Secondary caries was found in 10.9% of the FPDs, and chipping of the veneering ceramic was found in 13.0%. There were no significant differences regarding the probing depth in test and control teeth. CONCLUSION: Zirconia frameworks demonstrated sufficient stability for replacement of posterior teeth. However, the high rates of technical problems should be reduced by further developments of the prototype processing technology.

Experimental zirconia abutments for implant-supported single-tooth restorations in esthetically demanding regions: 4-year results of a prospective clinical study.

PURPOSE: This prospective clinical study evaluated an experimental implant abutment made of densely sintered zirconia with respect to peri-implant hard and soft tissue reaction as well as fracture resistance over time. MATERIALS AND METHODS: Twenty-seven consecutively treated patients with 54 single-tooth implants were included. Zirconia abutment ingots were individually shaped and set on the implants with gold screws. All-ceramic (Empress I) crowns were cemented using a composite cement. At the 1- and 4-year examinations, reconstructions were evaluated for technical problems (fracture of abutment or crown, loosening of abutment screw). Modified Plaque and simplified Gingival Indices were recorded at implants and neighboring teeth, and peri-implant bone levels were radiographically determined. RESULTS: All but 1 of the 27 patients with 53 restorations could be evaluated at 1 year, and 36 restorations in 18 patients were evaluated 4 years after abutment and crown insertion. The median observation period for the reconstructions was 49.2 months. No abutment fractures occurred. Abutment screw loosening was reported for 2 restorations at 8 months and 27 months, respectively. Mean Plaque Index was 0.4 (SD 0.6) at abutments and 0.5 (SD 0.6) at teeth; mean Gingival Index was 0.7 (SD 0.5) at abutments and 0.9 (SD 0.5) at teeth. Mean marginal bone loss measured 1.2 mm (SD 0.5) after 4 years of functional loading. CONCLUSION: Zirconia abutments offered sufficient stability to support implant-supported single-tooth reconstructions in anterior and premolar regions. The soft and hard tissue reaction toward zirconia was favorable.

Effect of rhBMP-2 on guided bone regeneration in humans.

The aim of the present clinical study was to test whether or not the addition of recombinant human bone morphogenetic protein-2 (rhBMP-2) to a xenogenic bone substitute mineral (Bio-Oss) will improve guided bone regeneration therapy regarding bone volume, density and maturation. In 11 partially edentulous patients, 34 Brånemark implants were placed at two different sites in the same jaw (five maxillae, six mandibles) requiring lateral ridge augmentation. The bone defects were randomly assigned to test and control treatments: the test and the control defects were both augmented with the xenogenic bone substitute and a resorbable collagen membrane (Bio-Gide). At the test sites, the xenogenic bone substitute mineral was coated with rhBMP-2 in a lyophilization process. Following implant insertion (baseline), the peri-implant bone defect height was measured from the implant shoulder to the first implant-bone contact. After an average healing period of 6 months (SD 0.17, range 5.7-6.2), the residual defects were again measured and trephine burs were used to take 22 bone biopsies from the augmented regions. The healing period was uneventful except for one implant site that showed a wound dehiscence, which spontaneously closed after 4 weeks. Later at reentry, all implants were stable. At baseline, the mean defect height was 7.0 mm (SD 2.67, range 3-12 mm) at test and 5.8 mm (SD 1.81, range 3-8 mm) at control sites. At reentry, the mean defect height decreased to 0.2 mm (SD 0.35, range 0-1 mm) at test sites (corresponding to 96% vertical defect fill) and to 0.4 mm (SD 0.66, range 0-2 mm) at the control site (vertical defect fill of 91%). Reduction in defect height from baseline to reentry for both test and control sites was statistically significant (Wilcoxon P<0.01). Histomorphometric analysis showed an average area density of 37% (SD 11.2, range 23-51%) newly formed bone at test sites and 30% (SD 8.9, range 18-43%) at control sites. The fraction of mineralized bone identified as mature lamellar bone amounted to 76% (SD 14.4, range 47.8-94%) at test compared to 56% (SD 18.3, range 31.6-91.4%) at control sites (paired t-test P<0.05). At BMP-treated sites 57% (SD 16.2, range 29-81%) and at control sites 30% (SD 22.6, range 0-66%) of the surface of the bone substitute particles were in direct contact with newly formed bone (paired t-test P<0.05). It is concluded that the combination of the xenogenic bone substitute mineral with rhBMP-2 can enhance the maturation process of bone regeneration and can increase the graft to bone contact in humans. rhBMP-2 has the potential to predictably improve and accelerate guided bone regeneration therapy.