Vohtme 102 Reviews attd abstracts 575 Number 6

and fitted with orthodontic appliances delivering a 40 g initial tipping force to the maxillary molar. The cross-sectional groups were equally divided into 6 sacrifice subgroups (1, 3, 5, 7, 10, and 14 days). Extraoral ccphalometric radiographs were obtained at appliance placement and sacrifice or match- ing times in the longitudinal animals. Tooth movement was determined with respect to palatal implants. Movement in the force group animals was adjusted by subtracting predicted distal molar drift. Analysis of variance was performed to examine differences within groups across time and among groups at each time point. Within group analyses indicated significant differences existed over time in each group (p = 0.0001). Continuous forces generated a classic tooth movement curve: an initial movement, a delay period (day 1 to day 7), and a late movement (day 10 to day 14). Short- term forces were characterized by an initial movement, a relapse period (day 3 to day 5), and a late movement period (day 7 to day 14). The results suggested short-term forces of 1 and 24 hours initiated a cascade of biologic remodeling events, which resulted in tooth movement manifested 7 to 14 days later. In addition, it appears that the minimum effective strain duration at 40 gf necessary to stimulate a conventional tooth movement curve is less than 1 hour. Supported by NIDR grant DE 8659.

Relationship of root resorption to magnitude and direction of tooth movement following orthodontic treatment. Diane Paxton, E. Joanne Low, Roger Boero, Sheldon Baumrind, Robert Boyd, San Francisco: University of California, San Francisco, 1991

The purpose of this study was two-fold: First, to measure the association between incisor root resorption and the mag- nitude and direction of tooth movement; and second to de- termine the association between measurements of tooth length made on cephalometric radiographs and those made on peri- apical radiographs. The sample consisted of 55 randomly selected orthodontic patients, (17 adults and 38 adolescents) receiving standard edgewise orthodontic treatment in the pri- vate office of one orthodontist.

Pretreatment and posttreatment cephalometrie radio- graphs were digitized. Measurements and superimpositions were made with a computerized cephalometrie analysis pro- gram. The variables of root resorption and tooth movement were correlated.

Mean apical root resorption values obtained for this sam- ple were 0.56 mm. (SD = 1.96) for the maxillary incisors and 1.04 mm (SD = 2.34) for the mandibular incisors. Sta- tistically significant correlations were found in all groups stud- ied for levels of root-resorption alad vertical movement of the mandibular incisor apex.

Cephalometric measurements of tooth length and root resorption were compared with measurement of the same teeth made on periapical radiographs. A significant correlatioii (p < 0.01) was found for tooth length; however, root re- sorption only correlated for the mandibular incisors

(p < 0.004). Supported by grant #NIDR-R01DE03598; NIH-DE08713.

Radiographic determination of alveolar bone height changes in adults vs. adolescents during fixed orthodontic treatment. Mark Lowe Ray Rafetto, Roger Boero, Sheldon Baumrind, Robert Boyd, San Francisco: Unirersity of California, San Francisco, and Universio' of the Pacific, 1991

The purpose of this study was to examine retrospectively the radiographic differences in alveolar bone height between four groups of patients after fixed orthodontic treatment. The four groups were: adults treated with nonextraction therapy, adults treated with extraction therapy, adolescents treated with nonextraction therapy, and adolescents treated with extraction therapy. Fifteen adult cases (including seven nonextraction and eight extraction cases) and 31 adolescent cases (including 20 nonextraction and 11 extraction cases) were randomly selected from an expert clinician's orthodontic office. The prctreatment and posttreatment bitewing radiographs from all four quadrants were digitized by two examiners. The mean alveolar bone loss for four posterior sites per quadrant (distal of the canine, mesial and distal of the second premolar, and mesial of the first molar) was calculated for each group. There were no statistically significant hztergroup differences fottttd; however, there were large intraindividual attd hzterindividual variations hz the amount of bone loss. Supported by grant #NIDR-R01DE03598; NIH-DE08713.

Longitudinal study of signs of temporomandibular disorders (TMD) in orthodontically-treated and non-treated groups. R. H. Hirata, M. W. Heft, B. M. Hernandez, G. J. King, Gainesville, Florida: College of Dentistry, UniversiO" of Florida, 1991

This study measured the prevalence and incidence of signs of temporomandibular (TM) disorders in both a group un- dergoing orthodontic treatment in the University of Florida graduate orthodontic program and a control group. A ques- tionnaire pertaining to the patients reports of signs and symp- toms of TM disorder and a clinical examination were admin- istered by a trained dental examiner. Data collection sessions occurred at baseline (before treatment) and at /2-month in- tervals to 24 months. Data were also collected for the control group at the same time intervals. There were 102 patients (43 males, 59 females) mean age 15.3 years. An untreated control group of 41 nonorthodontically treated subjects mean age 16.2 years was used. The incidence of TM signs for the treatment group and control group were not significantly different. Pre- liminary results are in agreement with the contention that orthodontically treated patients are not more likely to develop TM signs while undergoing treatment. Results underscore the changing, inconstant and ephemeral nature of TM signs in many patients over the course of time.