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.
Longitudinal changes in tooth/single-implant relationship and bone topography: An 8-year retrospective analysis
It has been established that the bone peak at the surface of a natural tooth is the dominant factor for determining the fullness of the interproximal papilla between a tooth and an adjacent implant. Furthermore the changes over time in the vertical discrepancy between tooth and implant due to alveolar growth and vertical tooth drift or indeed due to marginal bone loss at the surface of the implant, results in loss of bone height at the surface of the tooth and eventually a loss of papilla height, compromising esthetics.
Purpose: This study was established to determine any longitudinal changes in the bone topography adjacent to Astra Tech ST (Single-Tooth) implants.
Materials and Methods: Only 4.5 mm diameter tapered implants (TiOblast", MicroThread") placed in the upper jaw between 15 and 25 and in function for at least 5 years were included in the study. Baseline radiographs were required from time of crown cementation and then at 5 years follow-up. If 8-year radiographs were available these were also included. All implants were placed using a submerged protocol and allowed to heal for 6 months prior to abutment connection using the ST-Abutment system. At exposure all implants were temporized and definitive crowns inserted one month later. Standardized radiographs were taken using individually fabricated film holders to ensure the film was perpendicular to the x-ray beam. Linear measurements were recorded on digitized images of each radiograph, using the implant diameter and micro-threaded conical collar length to calibrate each radiograph. The most coronal bone contact at the mesial and distal of each implant (CBC) was evaluated with respect to the base of the bevel at the shoulder of the implant, which was used as the reference, 0.3 mm below the microgap. In addition the level of the bone peak at the adjacent teeth was measured from the cementenamel junction (TBP).
The tooth-implant vertical discrepancy (TIVD) was measured from the cementenamel junction to the reference line and the horizontal gap (TIHG) was measure from implant surface to tooth surface at the level of the reference line. Apical position was measured in relation to the thread level on the implant.
Measurement error was evaluated using 10 randomly selected images which were re-assessed after a 2 week period. Differences for CBC, and TBP were only 0.01 mm while TIHG was 0.02 mm and TIVD was 0.04 mm. The differences equated to less than half a thread. Results are expressed as mean values, mm (+/- SD).
Results: A total of 33 implants were included in the study, 10 of which were in central incisor positions, 9 lateral incisors, and 11 first bicuspids and 3 second bicuspids. The mean change in CBC to 5 years was -0.1(1.1), and for TBP was 0.0 (0.4). 8-year values were -0.1 (1.3) and -0.1 (0.5) respectively. The mean TIVD was 4.1 mm and mean TIHG was 2.1 mm. When assessing the tooth apexl relation to the threads of the implants it was apparent that the vertical change at 5 years measured 0.37 mm for incisors and 0.19 mm for premolars. At 8 years these values were 0.53 mm and 0.15 mm respectively. Statistical analysis revealed no significant influence of any variable on the outcome data. Change in vertical position of adjacent teeth at 5 and 8 years was statistically significant, p < 0.05. This correlated to a greater presence of infraocclusion in the incisor positions, p = .025.
Discussion and Conclusion: Consistent with previous studies the Astra Tech ST implant demonstrates minimal changes in marginal bone levels, only -0.1 mm over 8 years. Indeed 48% of implants revealed no marginal bone loss, with only 13% demonstrating bone loss > 1.0 mm. Similarly bone loss at adjacent teeth over 8 years was also minimal and it could be confirmed that both vertical and horizontal relationships between tooth and implant exerted no influence over outcome. This finding bodes well for long-term esthetic stability for interdental papillae and gingival zenith for teeth adjacent to Astra Tech ST implants. However ongoing tooth eruption may result in infraocclusion and a discrepancy of gingival zenith for single-tooth implant restorations.
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