The Astra Tech Implant System™ is designed and proven clinically to maintain marginal bone. Outstanding long-term (i.e. > 5 years) clinical results on the maintenance and preservation of the marginal bone is summarized here. Some of the articles even report on marginal bone gain around Astra Tech implants in several patients.
Bone level alterations at implants placed in the posterior segments of the dentition: outcome of submerged/non-submerged healing. A 5-year multicenter, randomized, controlled clinical trial
Purpose: This study set out to evaluate the long-term marginal bone level changes at implants placed using a one-or two-stage surgical protocol.
Materials and Methods: Eighty-four healthy patients were randomly assigned to either a one-stage (group A) or two-stage (group B) surgical protocol for the insertion of 324 Astra Tech (TiOblasf 3.5, 4.0) implants to support Fixed Partial Dentures, FPDs. As an inclusion criteria, patients had to present with an adequate amount of bone to receive implants of at least 9 mm in length without recourse to grafting. In the current cohort 25% of the patients were smokers.
Implants were placed according to manufacturer's protocol. For implants in group A, standard UniAbutments were connected at the same operative procedure as implant placement and were left exposed to the oral cavity during the healing phase. For implants in group B, cover screws were placed and the implants were submerged for a healing period of 3 months in the mandible and 6 months in the maxilla. At this time all submerged implants were exposed in a conventional manner and บทiAbutments were connected.
The restorative treatment followed recommended protocol for the fabrication of screw-retained FPDs. At definitive prosthesis connection, baseline records were taken for plaque score, mucositis, and intraoral radiographs were taken for bone level measurements. The same follow-up data was recorded at yearly visits during the 5 years course of the study.
Results were statistically analyzed.
Results: Four implants in group A and 3 in group B failed to integrate (early failures), 5 of these implants were recorded as having a reduced primary stability. Another 3 implants were lost during the first year (2 fractured and 1 was removed due to advanced bone loss). At the 5-year follow-up, 35 implants were lost to follow-up. Among these, 3 patients (11 implants) had died during the course of the study. In total, 10 bridge screws fractured (5 patients), and 8 veneers had to be replaced (5 patients).
Plaque and mucositis scores were low throughout the study.
Radiographic measurements revealed a mean marginal bone loss of only 0.02 mm for group A implants and 0.17 mm for group B implant after 1 year in function with no significant differences between the groups. After another 4 years in function there was some mean radiographic bone gain in group A (0.07 ± 0.5 mm), and a slight bone reduction in group B (0.02 ± 0.6 mm), but these were not statistically significant from each other. Only 16 implants (4 in group A and 12 in group B) experienced bone loss > 2 mm during the study period.
Discussion and Conclusion: The current study was conducted as a randomized controlled study to determine the influence of one- versus two-stage surgical protocol on the long-term marginal bone response. Clinical and radiographic outcome variables indicate that the use of a one-stage surgical protocol did not impact upon the implant success rate, peri-implant soft tissue health, or the change in marginal bone levels which were very minor. Neither did the treatment modality affect the number of technical complications.
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