Viscoelastic properties of elastomeric chains: an investigation of pigment and manufacturing effects.

INTRODUCTION: Orthodontic elastomeric chains are commercially available in various colors from many manufacturers. In this study, we investigated the viscoelastic properties of elastomeric chains using dynamic mechanical analysis to perform color and brand comparisons. METHODS: Ten colors of Sunburst chains (GAC International, Bohemia, NY) were selected for the color study. Three colors of Sunburst, Bobbin Alastik (3M Unitek, Monrovia, Calif), and Energy (Rocky Mountain Orthodontics, Denver, Colo) chains were selected for the brand study. Nine specimens of each type were measured and tested. Dynamic mechanical analysis was performed at room temperature at 8 frequencies ranging from 0.125 to 16.0 Hz. Three variables (storage stiffness, loss stiffness, and tan δ) were analyzed by using repeated-measures analysis of variance (ANOVA) and pairwise t tests, comparing all frequencies for each specimen type and all specimen types for each frequency (with Bonferroni corrections). Significance was set at α = 0.05. RESULTS: Significant differences were found among all specimen dimensions, all frequencies, and all 3 dynamic mechanical analysis variables in both the color and brand studies. Comparisons focused on tan δ, which does not depend on specimen dimensions as do storage stiffness and loss stiffness. CONCLUSIONS: Statistically significant differences in tan δ values among colors were relatively small, so the clinical significance is questionable and requires further investigation. Differences in tan δ values among brands were greater and more likely to be clinically significant. Further studies are needed to relate viscoelastic properties to force decay.

The Americleft study: an inter-center study of treatment outcomes for patients with unilateral cleft lip and palate part 4. Nasolabial aesthetics.

OBJECTIVE: To compare the nasolabial aesthetics for individuals with nonsyndromic complete unilateral cleft lip and palate between the ages of 5 and 12 years. DESIGN: Retrospective cross-sectional study. SETTING: Four cleft centers in North America. SUBJECTS: A total of 124 subjects with repaired complete unilateral cleft lip and palate who were treated at the four centers. METHODS: After ethics approval was obtained, 124 preorthodontic frontal and profile patient images were scanned, cropped to show the nose and upper lip, and coded. Using the coded images, four nasolabial features that reflect aesthetics (i.e., nasal symmetry, nasal form, vermilion border, and nasolabial profile) were rated by five examiners using the rating system reported by Asher-McDade et al. (1991) . Intrarater and interrater reliabilities were determined using weighted kappa statistics. Mean ratings, by center, were compared using analysis of variance. RESULTS: Intrarater reliability scores were good to very good and interrater reliability scores were moderate to good. Total nasolabial scores were Center B = 2.98, Center C = 3.02, Center D = 2.80, and Center E = 2.87. No statistically significant differences among centers were detected for both total aesthetic scores and for any of the individual aesthetic components. CONCLUSION: There were no significant differences in nasolabial aesthetics among the centers evaluated. Overall good to fair nasolabial aesthetic results were achieved using the different treatment protocols in the four North American centers.