THESIS ABSTRACTS

Frictional resistance evaluation oforthodontic brackets and archwireswith sliding mechanics using quanti-fied simulation of canine retraction D. V. Smith, P. E. Rossouw, R. Pilliar, and P. Watson Department of Dentistry, University of Toronto, Canada

Canine distalization has been observed to occur through aseries of tipping and uprighting movements that approximatetranslation of the tooth when sliding mechanics are employed.However, canine distalization is impeded by frictional resis-tance that results from the combination of classical frictionbetween the bracket and the archwire at nonbinding angula-tions and a binding phenomenon of the bracket and the arch-wire at binding angulations. By using an experimental canineretraction model capable of tipping and uprighting, quantifi-able analysis of the frictional resistance for various bracketsand archwires with varying parameters can be achieved andwill be more clinically meaningful. The purpose of this studywas to evaluate by quantitative analysis the frictional resis-tance of various bracket/archwire combinations using anexperimental canine retraction model capable of tipping anduprighting to approximate orthodontic tooth movements rep-resenting sliding mechanics. The friction-testing apparatus forthis study was comprised of an Instron testing machine and aload cell, with a servomotor interface for second-order bracketcontrol. This allowed dynamic and progressive bracket tippingand uprighting concurrent with linear bracket traction toexperimentally approximate canine retraction with slidingmechanics while simultaneously acquiring frictional resis-tance data with temporal integration. The average kinetic fric-tion over a tip/countertip cycle was determined for each trialof various bracket/archwire combinations. Multiple ANOVAusing the general linear models procedure demonstrated sig-nificant effects (P < .05) for bracket type, archwire type, arch-wire size, and archwire shape, and pairwise interactions forbracket type/archwire type, bracket type/archwire size,bracket type/archwire shape, archwire type/archwire size,archwire type/archwire shape, and archwire size/archwireshape. The Duncan multiple range test (P < .05) revealed thegeneral trends regarding the frictional performance of thebrackets and the archwires, and a least squares means table (P < .05) illustrated significant interactions of pairwise factorsthat differed from the general trends. This study revealed thesegeneral trends regarding brackets and archwires: for ortho-dontic brackets, ceramic brackets with and without a metal

slot had the greatest friction followed by metal brackets,active self-ligating brackets, variable self-ligating brackets,and passive self-ligating brackets; for orthodontic archwires,stainless steel and twisted stainless steel had greater frictionthan did nickel-titanium; smaller-dimension wires had lessfriction than larger wires, and round wires had less frictionthan rectangular wires. In addition, considering specificbrackets leads to coupling them with specific archwires toreduce the frictional resistance with sliding.

0889-5406/2001/$35.00 + 0 8/3/118931doi:10.1067/mod.2001.118931

The dimensional relationships betweenthe cranial base, body height, and thefacial complex R. Targownik, R. B. Ross, B. Tompson, and D. G. Woodside Department of Dentistry, University of Toronto, Canada

The aims of the study were to investigate the dimensionalrelationships between the cranial base, body height, and thefacial complex and to establish a method of size adjusting lin-ear measurements when comparing groups with overall sizedifferences. Data were obtained from lateral cephalometricradiographs, tracings, and history profiles of 117 orthodonti-cally untreated males (ages 12 and 18+) from the University ofToronto’s Burlington Growth Study. The total cranial baselength (either N-Ba or {S-N + S-Ba}) and body height dis-played the strongest correlations to the linear facial dimensions.At age 12, strong correlations (r > 0.4) existed between {S-N +S-Ba} and mandibular length, upper face height, and bodyheight. N-Ba strongly correlated to maxillary length. At age18+, the correlations to mandibular length and upper faceheight weakened. Body height correlated strongly to mandibu-lar length and upper face height at both ages. Independent t testsdemonstrated that children who were short or had small totalcranial base lengths exhibited smaller linear facial dimensionsthan children who were taller or had longer total cranial baselengths, thereby validating the need for linear size adjustingamong diverse populations. Study-specific equations were gen-erated that predicted adjusted linear facial dimensions based onknown total cranial base length and body height. The evidencesuggested that size adjusting is a statistically valid conceptwhen studying populations that differ in overall body, cranialbase, and face size, when comparisons of absolute measure-ments would otherwise be invalid. This is especially importantwhen comparing groups with craniofacial anomalies.

0889-5406/2001/$35.00 + 0 8/3/118932doi:10.1067/mod.2001.118932

American Journal of Orthodontics and Dentofacial Orthopedics/December 2001 681

REVIEWS AND ABSTRACTS

Book reviews and article abstractsAlex Jacobson, DMD, MS, PhDBirmingham, Ala