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.
A 10-year prospective study of single tooth implants placed in the anterior maxilla
In an effort to achieve a high degree of esthetics and function the single-tooth implant replacement (STIR) has been identified as the treatment of choice, especially when the adjacent teeth are un-restored. The 5-to 10-year survival has been shown to be comparable to that for fixed conventional bridgework, although there are few 10-year follow-up studies on STIR to date. The literature suggests that such studies might demonstrate a higher complication rate. In addition differing protocols for immediate, versus early and delayed placement might yield differing outcomes.
Purpose: The aim of this study was to presents 10-year data from a cohort of STIRs placed in both an early and delayed manner and reflect on both bio-logical and mechanical outcome.
Material and Methods: Twenty healthy patients, mean age 33 years, required replacement of a single missing tooth in the anterior segment. Two groups each with 10 patients were assigned to early placement (Group EP) 4 weeks after extraction and delayed placement (Group DP) 12 weeks after extraction. No socket preservation procedures were undertaken. Implants (Astra Tech ST, 4.5 mm o) were placed with the shoulder bevel leveled with the lingual crest. Any residual buccal defects were protected by a non-resorbable membrane to aid guided bone regeneration. Submerged healing was allowed for 6 months prior to exposure and membrane removal. Implants in group EP were restored using prefabricated abutments while those in the DP group received prepable abutments. All implants were restored with cemented ceramometal crowns. Occlusion was refined to within 40 pm.
Baseline clinical and radiographic assessments were made within 2 weeks of crown cementation and annually thereafter. Examinations included an assessment of implant/crown immobility, presence/ absence of pain, plaque scores, bleeding on probing to a depth of 2 mm, and the recording of any adverse biological or technical events. Radiographs were taken using a standardized paralleling technique with an Eggen film holder. The distances from the implant reference point at the base of the coronal bevel to the first point of bone-to-implant contact as determined at x7 magnification was recorded on the mesial and distal of each implant. Finally patient were asked to score the esthetics and function of the crown at the 3- and 10-year review on a 100 mm VAS scale where 0 = dissatisfied and 100 = very satisfied. Statistical analysis using paired and unpaired t-tests was undertaken to determine the influence of time and protocol respectively on the resultant marginal bone levels.
Results: While some patients were absent from the occasional annual review all patients were seen across the study and only one patient missed the final review although this patient was available for telephone interview to confirm that nothing had changed from the previous review. Thus it was possible to confirm a 100% survival rate for implants and a 90% survival rate for crowns, with 2 crowns having to be replaced during the study. With regard to adverse events, one patient presented with a mucositis at the 10-year review, two crowns required re-cementation, three crowns fractured one of which required replacement and two abutment screws came loose and required re-tightening, one of which resulted in the need for a new crown. Patients scored a mean of 9.4 for function at 3 years which reduced to 8.4 at 10 years and 9.3 at 3 years reducing to 7.6 at 10 years for esthetics.
At the 10-year review the mean marginal bone loss measured 0.64 mm in group EP and 0.86 mm in group DP, there was no significant difference over time or between the groups for any of the clinical or radiographic parameters assessed.
Discussion and Conclusions: Results of the current study corroborate the findings of previous systematic reviews with respect to both implant and crown survival. The maintenance of marginal bone in the current study was superior to that anticipated by established criteria, while technical complications with the crown appeared more consistent with previous studies. However the use of the more robust prepable abutment appeared to resolve the problems of decementation and abutment screw loosening. It can be concluded that the Astra Tech implant is well suited to single-tooth replacement and that patient scores for function and esthetics, while reducing over time, remain high even after 10 years.
Astra Tech
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