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.
Implant-supported single-tooth restorations: A 5-year prospective study
Purpose: This prospective study set out to evaluate the 5-year clinical and radiographic outcome of implant supported single-tooth crowns.
Materials and Methods: Forty-five Astra Tech ST implants (MicroThreaddesign on the implant neck) were inserted into forty healthy patients requiring one or more single-tooth implants. A lack of bone volume necessitating augmentation excluded a patient from the study. However if dehiscences occurred during implant preparation, these implants were included but no efforts were made to cover the dehiscence defects. Smokers were included (n = 12). All implants benefited from a two-stage protocol according to standard surgical techniques. 89% of implants (n = 40) were inserted into the maxilla. At exposure, a prefabricated ST abutment was connected to ensure that the abutment shoulder was 1-2 mm below the mucosal margin and an acrylic temporary crown was fabricated chairside. On completion of the treatment all patients received a ceramometal crown, which was cemented with zinc phosphate cement.
Patients were followed up for 5 years to record the clinical parameters including plaque score, mucositis, and pocket probing depth and radiographic outcome with particular emphasis on monitoring the marginal bone changes. Radiographs were taken at crown insertion (baseline) and annually thereafter. Mea-surements were made by two independent radiographers at x7 magnification to determine the distance between the implant reference point, at the top of the implant and the first point of bone-to-implant contact. Marginal bone data was statistically analyzed at both the patient level and implant level.
Results: Only one implant was known to have failed after 2.5 years of function. However 4 implants were lost to follow-up due to death or patient relocation, however of these two were confirmed to be retained in function without complication by telephone interview. Thus the overall implant survival rate was 97.4%. One abutment screw loosened in two patients, one after one year and the other after 4.5 years. In a third patient the abutment screw loosened twice before the implant eventually failed. This patient was diagnosed as a bruxer.
In the first year of function marginal bone loss measured 0.02 mm and 0.11 mm at the end of the study period. 24.5% implants appeared to demonstrate an improved bone height after 5 years of function compared to baseline. These changes were not significant. Interestingly there was no significant difference between smokers and non-smokers.
Clinical parameters were stable, with low plaque and bleeding scores and the majority of pockets mea-suring <3 mm.
Discussion and Conclusion: In the current study only minimal changes were seen to the marginal bone levels around free-standing Astra Tech ST implants. Implant survival was 97.4% and compares favourably with other studies. There was a 6.5% technical complication rate due to abutment screw loosening (3/45).
Marginal bone changes were minimal and compared very favourably to existing data where a greater initial bone loss is seen after exposure to baseline, typically 1.5 mm. No such bone loss was seen at the Astra Tech ST implant with a marginal bone loss of only 0.06 mm from baseline to the first year recall. This is remarkable when one considers that approximately one third of the implants were associated with a dehiscence type defects, which have been shown to result in interproximal bone loss if left untreated.
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