Pull-out strength of monocortical screws at 6 weeks postinsertion

82 Reviews and abstracts

The effect of argon laser irradiation on reducing enamel decalcification during orthodontic treatment: an in vitro and in vivo study Thomas S. Shipley West Virginia University, Morgantown, WVa

Objective: To evaluate the effect of argon laser in reducing enamel decalcification during orthodontic treatment. Methods: The in vitro portion of this study used 39 extracted human third molars. The teeth were sectioned into buccal and lingual halves. The enamel surfaces were pumiced, etched with self-etching primer, and divided into 5 groups with various levels of exposure to argon laser irradiation (40, 80, 120, or 240 J/cm2) or no laser exposure (control group). The teeth were exposed to a demineralization solution (pH ⫽ 4.46) for 48 hours in the first experiment and for 72 hours in the second experiment. Lesion depth, lesion area, and lesion fluorescence were measured by using confocal microscopy. Results were analyzed by using ANOVA and TukeyKramer analyses. For the in vivo study, 21 patients who received comprehensive orthodontic treatment were included. Orthodontic brackets were bonded to the maxillary and mandibular teeth with a split-arch bonding technique: half of the teeth were bonded with conventional visible light and the other half with 40 J/cm2 of argon laser irradiation to the mesial and distal portions of the orthodontic brackets. All teeth were pumiced and etched with self-etching primer before bonding. Results were analyzed by using ANOVA, chi-square, and Tukey-Kramer analyses. Results: The in vitro results show that, as the intensity of argon laser exposure increased, lesion depth and area decreased. For samples placed in a demineralizing solution for 48 hours and exposed to 120 J/cm2 or 240 J/cm2, the lesion depths were reduced 30.9% and 42.4%, respectively, compared with the control group. Lesion areas were reduced by 44.3% and 44.9%, respectively (P ⫽ .01). No other significant differences were found. In the in vivo study, enamel surfaces exposed to 40 J/cm2 of argon laser irradiation had a mean decalcification score of 1.84, compared with 2.01 in the control group (P ⫽ .05). Conclusions: These results suggest that exposing enamel surfaces to argon laser irradiation provides protection against enamel decalcification. Am J Orthod Dentofacial Orthop 2006;129:82 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.05.018

Diagnostic value of plaster models in contemporary orthodontics Chad Callahan University of Alabama at Birmingham, Birmingham, Ala

Introduction: Advances in digital technology have allowed for photographic images that can be immediately

American Journal of Orthodontics and Dentofacial Orthopedics January 2006

evaluated in the clinical setting. Clinical photography can currently be relied on to be of predictable diagnostic value, and unsatisfactory images can be immediately replaced. Objective: The purpose of this study was to evaluate how information obtained from traditional plaster models contributed to the diagnosis and treatment planning of orthodontic patients who were originally evaluated with digital photographs and radiographs alone. Methods: A sample of 20 orthodontic patients from the Department of Orthodontics at the University of Alabama at Birmingham was selected, based Angle molar classification, comprised of 11 Class I, 7 Class II, and 2 Class III patients to attempt to provide an average range of malocclusions as reported in the literature. Four orthodontists, given digital photographs, a panoramic radiograph, and a traced lateral cephalometric radiograph for each patient, were asked to complete a diagnostic questionnaire and formulate a preliminary treatment plan for each record set. The orthodontists were then shown plaster models for each patient, and the questionnaire and treatment plan were revised for a final treatment plan if the orthodontists considered this to be appropriate. Any changes that the orthodontists deemed necessary for the diagnosis and formulation of the final treatment plan were recorded. A binomial probability and a chi-square analysis were used with a P ⫽ .05 level of significance. Results: The results indicated 83 changes of the 1600 diagnostic values among 20 diagnostic categories recorded. The 5 categories that were statistically significant included the anteroposterior relationship of the molars, the anteroposterior relationship of the canines, the amount of overbite, the amount of overjet, and the depth of the curve of Spee in the mandible. There were no clinically significant changes in treatment recommended by the orthodontists from preliminary to final treatment plans after examining the study casts. Conclusions: Plaster models might not be needed for planning the treatment of every orthodontic patient. Am J Orthod Dentofacial Orthop 2006;129:82 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.05.020

Pull-out strength of monocortical screws at 6 weeks postinsertion J. A. Struckhoff, S. S. Huja, F. M. Beck, and A. S. Litsky Ohio State University, Columbus, Ohio

Screws (mini-implants) are increasingly used in orthodontics to provide anchorage for tooth movements. The objective of this study was to determine the biomechanical stability of these screws. We hypothesized that pull-out strengths of screws at 6 weeks (T6) postinsertion (1) vary by location, (2) are directly related to cortical bone thickness, and (3) are different at T6 than at insertion (T0). The T0 time point had been examined in a previous related study. Six skeletally mature male dogs received a total of 88 screws (Synthes USA, Monument, Colo; 2 ⫻ 6 or 2 ⫻ 8 mm) at

American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 1

predetermined sites in the anterior, middle, posterior, and palatal regions of the jaws. The monocortical screws were not loaded. Seventeen screws became loose or were lost over the healing period. Of the 71 surviving screws, 48 were randomized for mechanical testing and 23 for histology. The harvested bone blocks were prepared for mechanical testing and aligned in a custom-made fixture to record the maximum pull-out force (Bionix 858, MTS, Eden Prairie, Minn). Statistical analyses were conducted with ANOVA and the Tukey-Kramer method. Of the 17 failed screws, 11 were in mandibular anterior sites, 4 in maxillary anterior sites, 1 in a mandibular posterior site, and 1 in the palate. Mean peak pull-out strengths for the various sites ranged from 153.5 ⫾ 37.6 N to 389.3 ⫾ 32.5 N (mean ⫾ SEM) with significantly (P ⬍ .05) higher strengths in the mandibular posterior sites versus the maxillary anterior and palatal sites. Pull-out strength was related to cortical bone thickness (r ⫽ 0.59, P ⬍ .0001). Mean pull-out strengths at T0 and T6 showed no significant (P ⬍ .05) differences between the 2 time periods. The results give the clinical orthodontist an estimate of the holding power of these screws for each millimeter of cortical bone purchase. After correction for load orientation, a clinician can expect a static holding power of approximately 122 N (95% CI, 93-150 N) for 1 mm of cortical bone purchase and about 174 N (95% CI, 147-205 N) for 2 mm of cortical bone purchase. Histological analyses of screws placed in the maxillae and mandibles of dogs might give further insight to the early healing response, adaptation physiology, bone contact, and potential reasons for success and failure of the screws. Am J Orthod Dentofacial Orthop 2006;129:82-83 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.08.009

Dimensional accuracy of orthodontic models obtained from three impression materials under varying conditions N. M. Downey, W. A. Brantley, W. M. Johnston, and H. W. Fields Ohio State University, Columbus, Ohio

Accurate impressions are required for pour up and digitization into models for diagnostic purposes and custom-

Reviews and abstracts 83

molded orthodontic alignment appliances, such as the Invisalign System (Align Technology, Santa Clara, Calif). Accuracies of a traditional irreversible hydrocolloid (Jeltrate), a more dimensionally stable alginate (Kromopan), and a polyvinylsiloxane impression material (Precision Penta) were compared. Impressions were obtained of 3 aluminum dies with undercuts of 0°, 10°, and 20°. There were 2 times for pouring up stone models (immediately and after 3 days) and 3 repours. Impressions were separated from dies with a mechanical testing machine that provided a reproducible technique. Five specimens were collected for each impression material and condition. Impressions not poured up immediately were wrapped in a damp paper towel, placed in a plastic bag, and stored in a freezer (–17°C), on a table (20°C), or in a heated hood (60°C) for 72 hours and then poured up into models. All models were examined for voids or failures, and the impression materials and conditions were compared by using the chi-square test. For quantitative comparisons of accuracy, 8 points were determined on the dies with a measuring microscope, and pooled results from 12 measured lines between these points were compared with the master model by using a generalized linear model ANOVA. Three clinically relevant line lengths were also compared with the master model by using repeated-measures ANOVA. The testing machine required twice the time to remove impressions from the die than removal by hand. For pooled results from the 12 measured lines, significant differences (P ⱕ .001) were found between impression materials and for amount of undercut, storage temperature, and number of pours. No significant difference (P ⬎ .05) was found for time of pour. Significant interactions (P ⬍ .01) existed between most experimental variables. When the 3 clinically relevant line lengths were analyzed, significant interactions (P ⬍ .05) were also found between most experimental conditions. For these comparisons, only stone models (269 of 540) without tears and failures were used. Although all 3 impression materials, when properly manipulated, can produce clinically acceptable results under normal conditions, the addition of silicone might be contraindicated for patients with extremely tapered teeth. Three-day low-temperature storage of the traditional alginate was problematic, as was the more dimensionally stable alginate for the 20° undercut and the third pour. Am J Orthod Dentofacial Orthop 2006;129:83 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2005.08.011