The effects of chronic absence of active nasal respiration on the growth of the skull: a pilot study.

Oral respiration associated with an obstructed nasal airway is common in orthodontic patients. For several years chronic oral respiration has been implicated as a prime causative factor in the development of "adenoid facies or the "long-face syndrome. The animal experiment reported here begins a series designed to study, as separate variables, the 2 components of chronic oral respiration: (1) chronic absence of active nasal respiration and 2) chronic mouth opening to find out what dentofacial changes can be attributed to chronic absence of active nasal respiration alone. In this pilot study, 5 growing dogs underwent tracheotomy so that significant active nasal respiration was not possible and oral respiration was not essential.

The rotation of maxillary first molars, mandibular first molars, and maxillary first premolars in acceptable occlusions.

The rotation of the maxillary molars is considered important in the orthodontic treatment of malocclusions. In this study, a computer analysis program was developed to examine the rotations of maxillary molars, mandibular molars, and maxillary first premolars in casts of permanent dentitions with acceptable occlusions. Ninety-three sets of untreated 'acceptable occlusion' models from the collection of the Foundation for Orthodontic Research (FOR) were scanned on a flat bed scanner. The images were analysed using custom software. Measurements were made by relating maxillary first permanent molars to the midline, archform, opposite canine, and mandibular first permanent molars. The mandibular first molars and maxillary first premolars were also analysed and their rotations measured. The mean rotations of the maxillary first molars, measured as the angle between a line joining the tips of the buccal cusps and a line tangent to the appropriate archwire form (from Ricketts' Pentamorphic Arches) at the first molars, were 0.59 and -0.72 degree (positive values represent mesio-lingual rotations) for the right and left, respectively. For the mandibular molars, these means were 6.34 and 8.40 degrees, respectively. The mean differences in rotation between buccal cusp tips of maxillary and mandibular first molars in occlusion were 5.75 and 9.12 degrees for the right and left, respectively, with the mandibular being more mesio-lingually rotated. The differences between left and right were significant for all measurements. The present study brings into question the suitability of our present "straight wire" prescriptions in producing similar occlusions. It also suggests that scanning models for computer analysis may be a practical and precise way to measure similar rotations in untreated normal and treated occlusions.

Prosthodontic considerations when using implants for orthodontic anchorage.

STATEMENT OF PROBLEM: The use of implants for orthodontic anchorage can produce superior preprosthetic tooth positions. Their use often requires a crown or prosthesis to be fabricated for use as a connection between the orthodontic devices and the implant. PURPOSE: In this article, factors that affect the design of prostheses required for orthodontic movement and examples of prosthesis designs and materials, based on the authors' experience, are presented.

Deformation of metal brackets: a comparative study.

The purpose of this study was to determine the effect of material and design on the force and stress required to permanently deform metal brackets. Fourteen types of metal brackets were categorized according to raw material composition, slot torque degree, and wing type. Five types of raw materials, three types of slot torque degree, and four types of wing design were tested using an archwire torque test developed by Flores. An analysis of variance (ANOVA) and t-test showed that all three categories had a significant effect on the force and stress needed to permanently deform metal brackets. Of the three, raw material had the greatest effect on the amount of force. Results showed that 17-4PH and 303S had higher yield strengths and regular twin brackets had higher resistance to deformation. Also, as slot torque degree increased, brackets deformed with less force. Result confirmed that brackets requiring the greatest stress to permanently deform were made of steel with the greatest hardness.

The fracture strength of ceramic brackets: a comparative study.

Recent demand for esthetic brackets has led to the development and use of ceramic brackets in orthodontics. The purpose of this study was to compare the fracture strength of different ceramic brackets under different surface conditions and ligation methods using a torsional wire bending force. Five different bracket types (two polycrystalline, two single-crystal, and one metal) were tested using elastic and wire ligation, with half being scratched and the other half remaining unscratched. Results showed a significant difference between bracket types and surface conditions. Non-scratched single-crystal brackets had higher fracture strengths and slightly higher fracture loads than polycrystalline brackets. However, single-crystal brackets were significantly adversely affected by surface damage (scratching), while polycrystalline brackets were not significantly affected by surface damage. The fracture behavior of ceramic brackets followed the Griffith model where fracture strength decreased following surface damage.