Variation in the total lengths of abutment/implant assemblies generated with a function of applied tightening torque in external and internal implant-abutment connection

Abstract

Aim: Settling (embedment relaxation), which is the main cause for screw loosening, is developed by microroughness between implant and abutment metal surface. The objective of this study was to evaluate and compare the relationship between the level of applied torque and the settling of abutments into implants in external and internal implant-abutment connection. Material and methods: Five different implant-abutment connections were used (Ext, External butt joint+two-piece abutment; Int-H2, Internal hexagon+two-piece abutment; Int-H1, Internal hexagon+one-piece abutment; Int-O2, Internal octagon+two-piece abutment; Int-O1, Internal octagon+one-piece abutment). All abutments of each group were assembled and tightened with corresponding implants by a digital torque gauge. The total lengths of implant-abutment samples were measured at each torque (5, 10, 30Ncm and repeated 30Ncm with 10-min interval) by an electronic digital micrometer. The settling values were calculated by changes between the total lengths of implant-abutment samples. Results: All groups developed settling with repeated tightening. The Int-H2 group showed markedly higher settling for all instances of tightening torque and the Ext group was the lowest. Statistically significant differences were found in settling values between the groups and statistically significant increases were observed within each group at different tightening torques (P<0.05). After the second tightening of 30Ncm, repeated tightening showed almost constant settling values. Conclusions: Results from the present study suggested that to minimize the settling effect, abutment screws should be retightened at least twice at 30Ncm torque at a 10-min interval in all laboratory and clinical procedures.ⓒ 2010 John Wiley & Sons A/S.