Anterior teeth root inclination prediction derived from digital models: A comparative study of plaster study casts and CBCT images.

BACKGROUND: To assess the accuracy of digital models generated using commercially available software to predict anterior teeth root inclination characteristics and compare the results to relevant data obtained from CBCT images. MATERIAL AND METHODS: Following sample size calculation and after application of inclusion and exclusion criteria, pre-treatment maxillary and mandibular plaster models and the corresponding CBCT scans of 31 patients attending a private orthodontic clinic were selected. The subjects were 10 males and 21 females with age range 12 to 40 years. Plaster models were scanned using the high resolution mode of an Ortho Insight 3D scanner and CBCT scans were taken using a Kodak 9500 Cone Beam 3D System machine. The teeth on the digital scans were segmented and virtual roots were predicted and constructed by the Ortho Insight 3D software. The long axes of the predicted roots and the actual roots, as segmented from the CBCT images, were computed using best-fit lines. The inter-axis angle was used to assess error in root inclination prediction by the software. Mann-Whitney and Kruskal-Wallis tests were used. Intra-examiner error was evaluated using the Bland-Altman method. RESULTS: The maximum disparity in angle between images derived from digital models and CBCT data was almost 40 degrees (upper left canine). The upper and lower canines produced the worst results, followed by the lower lateral incisors. The upper central incisors showed the best results, although the maximum angle of difference exceeded 20 degrees (with the median around 8 degrees). CONCLUSIONS: Root morphology imaging prediction is not a primary function of this software and this study confirmed its limitation as a sole tool in routine clinical applications. At present these predictions cannot be considered accurate or reliable unless correlated clinically with a radiographic image. Key words:Digital models, CBCT, tooth root inclination prediction software.

Maxillary and mandibular contribution to the establishment of class II malocclusion in an adult Lebanese population.

INTRODUCTION: The main aim of this study was to describe the contribution of the maxilla and the mandible to the establishment of a Class II skeletal malocclusion in an adult Lebanese population. Secondary aims were to detect the presence of sex-based dimorphism and to study the influence of the vertical dimension on the Class II skeletal pattern. MATERIAL AND METHOD: A sample of 90 adults in skeletal Class II was recruited and equally distributed according to sex and vertical typology. The study describes the skeletal and dentoalveolar cephalometric characteristics of the Class II sample, essentially according to Coben's cephalometric analysis. RESULTS: The total effective depth of the cranial base and the anterior cranial base angle (SN-BaH) were both greater in the Class II sample. In females, the effective depth of the maxilla (Ptm-A) was larger than normal while SNB was smaller. The parameters describing the size and shape of the body of the mandible were significantly different from those of normal subjects. The upper incisors were in a retrusive position, while the axis of the lower incisors was located normally. The mandibular molars had a more distal sagittal position. Hyperdivergent subjects had more significant posterior alveolar growth, a more retrusive mandibular position and smaller mandibular dimensions than the other two vertical sub-groups. CONCLUSION: The cranial base contributes to the establishment of a Class II malocclusion, and mandibular retrusion cannot be considered as a characteristic shared by all skeletal Class II subjects. Lessening of the absolute length of the mandibular body is the second most frequent etiological factor noted in the Class II sample studied. Most individuals in skeletal Class II have an associated dental Class II malocclusion, and the vertical dimension has an influence on the Class II skeletal pattern.

Shear bond strength of orthodontic brackets bonded with self-etching primer to intact and pre-conditioned human enamel.

OBJECTIVE: The purpose of this study was to evaluate the shear bond strength of orthodontic bracket when bonded to pre-conditioned and intact enamel using a self-etching primer within 6 hours and after thermal cycling. MATERIAL AND METHODS: One hundred and twenty freshly-extracted human teeth were divided into four groups according to how the buccal surface to be bonded had been pre-conditioned: 1) acid-etched with 37% phosphoric acid, 2) sand-blasted with 50 microns aluminum-oxide, 3) matted with diamond burr, and 4) intact enamel used as control. Orthodontic metal brackets were bonded to the teeth using the same composite resin (Transbond XT) and self-etching primer (Transbond Plus Self-Etching Primer). Brackets were debonded within 6 hours or after thermal cycling for 2500 times (5 degrees C--37 degrees C--55 degrees C). Shear bond strength was measured on a testing machine at a crosshead speed of 3 mm/min. The bracket-failure interface was quantified according to the modified adhesive remnant index score (ARI). Data were analyzed using the two-way ANOVA test, Scheffé confidence interval of differences of means, and the chi-square test (p < 0.05). RESULTS: All the pre-conditioned groups showed significantly higher shear bond strength before and after thermal cycling than the control group. There was no significant correlation between thermal cycling and shear bond strength. The ARI scores revealed that the bond failed primarily on the adhesive-enamel interface in all groups before and after thermal cycling, with the exception of the acid-etched group, whose bonds failed mainly on the adhesive-bracket interface after thermal cycling. CONCLUSION: The authors recommend that the enamel be preconditioned before applying the self-etching primer when greater shear bond strength is desired.