The Astra Tech Implant System™ has been documented when used to support a wide range of prosthetic solutions. Good clinical and mechanical results have been obtained for single tooth, fixed partial and complete prostheses as well as for removable overdentures. Please read more about it in this section.
Bone level change at implant-supported fixed partial dentures with and without cantilever extension after 5 years in function
Purpose: This retrospective study set out to analyze the effect of cantilevers on marginal bone levels at implants supporting freestanding fixed partial dentures (FPDs).
Materials and Methods: Fifty-one periodontally compromised patients were restored with a total of 56 FPDs supported by Astra Tech implants. All patients had undergone a comprehensive periodontal program before, during and after implant reconstruction. Of the total series 6 FPDs had less than 5 years follow-up, 3 FPDs were in patients lost to follow-up and a further 3 FPDs failed as a result of implant failure two of which had cantilever units. Thus 50 FPDs were available for radiographic analysis. Of these 24 had cantilever extensions (Group C) and 26 did not (Group NC). All FPDs were screw-retained and a classic healing and two-stage surgical protocol was employed. The two groups were comparable for age, number of remaining teeth, prevalence for smoking, and number of supporting implants which was 2.6 as a mean for the cantilever group and 2.8 for the non-cantilever group. For group c, 16 FPDs were maxillary and 8 were mandibular compared to 12 and 14 respectively for group NC. The mean number of units per FPD was 4 for group c and 3 for group NC.
Cantilevers were on average 9.0 mm long. Three cantilevers were kept clear of the occlusion. Radiographs of each implant were obtained using standardized long cone radiographs in customized film holders. Baseline radiographs taken at prosthesis insertion were compared to those taken at the 5-year follow-up. Bone levels were recorded with respect to the implant-abutment junction. Marginal bone levels were analyzed at the FPD level, the implant level or the surface level (i.e. the distal surface of the most distal implant related to the cantilever or absence thereof.)
Statistics was performed by the use of a bivariate analysis (Mann-Whitney U-test) and a stepwise regression analysis utilized to evaluate influence of confounding factors on the longitudinal peri-implant bone level change.
Results: For the pooled data the mean marginal bone loss (xMBL) measured 0.4 mm. The xMBL for maxillary FPDs measured 0.6 mm compared to 0.2 mm for the mandible, (p < 0.05). The xMBL for implants in group c measured 0.49 mm compared to 0.38 mm in group NC. The bone loss at the most distal surface of the distal implant in both groups measured 0.35 mm and 0.22 mm respectively. 33% of the implants in group c recorded a bone loss of >1.0 mm compared to only 19% in the NC group. None of the above results demonstrated any significant difference.
When stepwise regression analysis was used, the only factors that appeared to influence longitudinal bone changes was smoking and treated jaw.
Discussion and Conclusion: In this retrospective cohort study with a 5-year follow up, the inclusion of a distal cantilever did not appear to negatively influence marginal bone loss data whether considered at the FPD level, the implant level or more importantly at the level of the implant surface facing a cantilever. However data did reveal a tendency towards small increases in marginal bone loss for implants supporting cantilever prostheses. This might be a reflection of the fact that a greater proportion of FPDs in group c were maxillary and as such may not have been a reflection of the presence of a cantilever at all. The only other related influential factors on longitudinal bone levels was smoking and treated jaw. The overall mean peri-implant bone level change over 5-years in function was 0.4 mm, which is by all standards very small. Only 6 technical complications were recorded, equally distributed between the two groups.
In conclusion, the findings in the present study show that inclusion of cantilever extensions in patients with good oral hygiene and well performed occlusion (of the prosthesis) may not jeopardize the long-term prognosis of the Astra Tech implant supported FPDs.
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