Stress distribution in the mini-screw and alveolar bone during orthodontic treatment: a finite element study analysis.

Objective: This study aimed to investigate the reason for high failure rates of mini-screws during orthodontic treatment. We hypothesized that decreasing the length of the mini-screw outside the bone relative to the length inside the bone (outside/inside length ratio) and equalising it to the tooth crown/root ratio would lead to increased stability of the mini-screw against lateral loading when assessed using finite element analysis.

Methods: We analysed stress distribution of mini-screws in the cortical and trabecular bone and von Mises stress levels when a 2-N force was applied to the head of four mini-screws of 6, 8, 10 and 12 mm in length.

Model analysis in "8020" achievers using three-dimensional images.

The purpose of this study was to clarify the effect of aging on the dentition by quantifying the dimensions of the dental arches in elderly persons aged over 80 years with 20 or more remaining teeth (8020 achievers). The study included twenty 8020 achievers (10 males and 10 females, with an average age of 82.3 years and an average of 28.

Tooth inclination in elderly with many remaining teeth observed by 3-D imaging.

Tooth inclination has been discussed many times in terms of esthetics and functionality, but reports related to aging are extremely rare. The purpose of this study was to evaluate tooth inclination in the elderly from the orthodontic point of view. The dental casts of twenty elderly persons with many remaining teeth were digitized with a 3-D laser scanner (VMS-100F,UNISN INC.

Mesio-distal tooth angulation in elderly with many remaining teeth observed by 3-D imaging.

Few studies have investigated the morphologic characteristics of teeth, dental arches and occlusion in elderly persons with many remaining teeth. The purpose of this study was to establish a method of measurement using 3-D imaging to investigate tooth angulation in the elderly from the orthodontic point of view. The dental casts of 20 elderly persons with many remaining teeth were digitized with a 3-D laser scanner (VMS-100F, UNISN INC.