Does abutment preparation affect abutment screw joint stability? An in vitro study.

STATEMENT OF PROBLEM: Whether preparation of an implant abutment decreases the stability of the abutment screw joint is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the abutment preparation in laboratory conditions on the reverse torque value (RTV) of the abutment screw. MATERIAL AND METHODS: Sixty implants, implant analogs, and abutments obtained from 2 different manufacturers were used in the present study and divided into 2 groups (groups B and N) according to the manufacturer. Each group was then divided into 3 subgroups (n=10) according to the remaining wall thickness (control, 0.4 mm, 0.6 mm). All abutments were tightened to analogs with 15 Ncm, and standardized preparation was made with a custom-designed copy-milling system. All abutments were tightened to the implants with 30 Ncm, and then, the abutment screws were removed and RTVs were recorded. Subgroups were analyzed by using 1-way ANOVA (alpha=.05), and the independent-sample t test was used to compare groups. Relationships between categorical variables were analyzed by chi-square tests. One abutment screw from each subgroup was randomly selected and analyzed by using a scanning electron microscope. RESULTS: A statistically significant difference was found between RTVs of different manufacturers (group B=28.2 +/-1.2 Ncm, group N=25.9 +/-1.4 Ncm; P<.005). In group N, there was a significant difference among subgroups, control (26.7 +/-1.4 Ncm), and 0.6-mm wall thickness (24.8 +/-0.8 Ncm) (P<.05). A statistically significant relationship was found between preparation and RTV for the NucleOSS only (P<.05) and between manufacturer and RTV (P<.001). Scanning electron microscopy evaluations identified different screw head and thread designs. CONCLUSIONS: The abutment screw joint stability of the BioHorizons implant was not affected by abutment preparation.