Photoelastic analysis of stress distribution in mandibular second molar roots caused by several uprighting mechanics

Mandibular molar uprighting is indicated when mesial inclination of the second molars occurs because of missing first molars. There are many methodologies to perform such movement. In this study, we aimed to analyze and compare the stress distributions in different molar uprighting techniques.

Four photoelastic models were designed to evaluate different mandibular second molar uprighting techniques: a miniscrew positioned in the retromolar region, a beta-titanium alloy cantilever spring, a beta-titanium alloy wire with a T-loop spring, and an 0.018-in stainless steel archwire with an open-coil spring between the second premolar and the second molar.

On the miniscrew test specimen, the greatest concentration of strains was observed in the cervical zone of the distal root. The cantilever spring had many strains in the cervical zone of the mesial root. On the T-loop spring test specimen, mainly the observed strains were in the apical zone of the mesial root. The open-coil spring specimen showed fringes in the cervical zone and the apical zone of the mesial root without formation of large sequences of strains.

The miniscrew mechanical action had the least and the cantilever spring mechanical action had the greatest strain means on the roots of mandibular second molars.