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One hundred and thirty-three second graders in rural public school were assessed on a number of dental, skeletal, and oral muscle function measures. Correlational analyses were conducted in order to determine whether specific myofunctional variables were associated with dentofacial development. Significant relationships were observed between open mouth posture and a narrow maxillary arch and long facial height. Labial and lingual rest and swallow patterns were also related to poor coordination of lip and tongue movements.

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Case records were evaluated for 30 patients who had undergone serial extraction of deciduous teeth plus first premolars followed by compehensive orthodontic treatment and retention. Diagnostic records were available for the following stages: pre-extraction, start of active treatment, end of active treatment, and a minimum of 10 years postretention. All cases were treated with standard edgewise mechanics and were judged clinically satisfactory by the end of active treatment. Twenty-two of the 30 cases (73%) demonstrated clinically unsatisfactory mandibular anterior alignment postretention. lntercanine width and arch length decreased in 29 of the 30 cases by the postretention stage. There was no difference between the serial extraction sample and a matched sample extracted and treated after full eruption.

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The records of 23 patients who underwent mandibular second premolar enucleation in the early mixed dentition were studied. The patients were selected at random from a group which had mandibular plane angles in excess of 38 degrees to SN and had not worn headgear prior to mechanical orthodontic therapy. Pre- and posttreatment measurements were compared to measurements made in an earlier study by lsaacson et al.¹ and a significant decrease in lower anterior face height was found.

This paper was presented at the Biennial Meeting of the Edward H. Angle Society in September 1989 in Chicago, Illinois.

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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.

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The finite element method has been used to determine the stress distribution generated by the initial placement of a simulated preset bracket-type orthodontic appliance utilizing titanium-nickel alloy archwire.

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The clinician must now consider the alloy along with cross-sectional shape and size when selecting archwires. The purpose of this study is to quantify permanent deformation after long-term deflection of available nickel-titanium archwires. Nine nickel-titanium, one beta-titanium and one stainless steel archwires, .016 inch round, were deflected into orthodontic brackets of simulated archform. One lateral incisor was positioned to yield a deflection of 5 mm in a lingual direction. After wire deactivation, deformation was measured at 1, 14, and 28 days. Two-way ANOVA and Tukey's critical difference tests were used to determine statistical differences. The nickel-titanium wires exhibited better springback characteristics and less permanent deformation than the stainless steel and TMA wires. Several wires increased deformation as deflection time increased. No clinically significant difference was found between presently available nickel-titanium wires in terms of permanent deformation, long- or short-term.

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