Effect of tightening torque on the marginal adaptation of cement-retained implant-supported fixed dental prostheses

Abstract

Background:The final position of the abutment changes with the amount of tightening torque. This could eventually lead to loss of passivity and marginal misfit of prostheses. The aim of this study was to evaluate the effect of three different tightening torques on the marginal adaptation of 3-unit cement-retained implant-supported fixed dental prostheses (FDPs).Materials and Methods:Two implants (Straumann) were inserted in an acrylic block so that one of the implants was placed vertically and the other at a 15° vertical angle. A straight abutment and a 15° angulated abutment were connected to the vertically and obliquely installed implants, respectively, so that the two abutments were parallel. Then, 10 cement-retained FDPs were waxed and cast. Abutments were tightened with 10, 20, and 35 Ncm torques, respectively. Following each tightening torque, FDPs were luted on respective abutments with temporary cement. The marginal adaptation of the retainers was evaluated using stereomicroscope. FDPs were then removed from the abutments and were sectioned at the connector sites. The retainers were luted again on their respective abutments. Luting procedures and marginal adaptation measurement were repeated. Data were analyzed by ANOVA and least significant difference tests (α = 0.05). After cutting the FDP connectors, the independent samples t-test was used to compare misfit values (α = 0.05).Results:Following 10, 20, and 35 Ncm tightening torques, the marginal discrepancy of the retainers of FDPs significantly increased (P < 0.05). There was no significant difference between the marginal discrepancies of these two retainers (P > 0.05). The marginal gap values of angulated abutment retainers (ANRs) were significantly higher than those of the straight abutment after cutting the connectors (P = 0.026).Conclusion:Within the limitations of this study, the marginal misfit of cement-retained FDPs increased continuously when the tightening torque increased. After cutting the connectors, the marginal misfit of the ANRs was higher than those of the straight abutment retainers.

Abutment misfit in implant-supported prostheses manufactured by casting technique: An integrative review

“…[ 5 ] considered misfit values at 100 μm. The lowest values reported as clinically usual were at 70[ 33 ] and 50 μm. [ 34 ] Oyagüe et al .…”

“…However, the other articles examined in this study suggest that the magnitude of the marginal misfit is not a reliable indicator in the prognosis of the stresses generation, once the stress distribution is more related to other factors such as screw tightening. [ 29 33 36 ]…”

“…In most studies, the marginal discrepancy considered clinically usual was around 100 μm; however, Ghanbarzadeh et al . [ 33 ] and Siadat et al . [ 34 ] considered lower values of 70 and 50 μm, respectively.…”

“…[ 34 ] reported a clinically discrepancy at 50 μm although the laboratory tests have revealed slightly higher values. Three studies revealed results that are suitable for this standard, obtaining a misfit mean values of 45,[ 33 ] 45.1,[ 35 ] and 50 μm. [ 28 ]…”

Marginal adaptation of fixed prosthodontics

“…Ghanbarzadeh et al [28] observed that, following 10, 20, and 35 Ncm binding torques, the marginal variance of the retainers of FDPs significantly increased (p < 0.05). There was no significant difference between the marginal discrepancies of these two fasteners (p > 0.05).…”