Effect of simulated debracketing on enamel damage.

BACKGROUND/PURPOSE: A smooth enamel surface after the removal of a bracket from a tooth is essential for both esthetic demands and the prevention of plaque accumulation. The purpose of this study was to evaluate enamel damage caused by three standardized debracketing techniques. METHODS: We established three standardized test devices based on the principles of the squeezing, shearing, and tensile testing methods, which were simulated using a How Plier (TASK 60-306), a Direct Bond Bracket Remover (TASK 60-335 T), and a Lift-Off Debracketing Instrument (3 M-Unitek 444-761), respectively. Thirty teeth in each group were evaluated after debracketing. An optical stereomicroscope and a CCD camera with a computerized image analysis system were used to ascertain the proportion of remnant adhesive area (RAE) on the enamel surface. Fractography was analyzed using a scanning electron microscope. RESULTS: The squeezing debracketing method exhibited the highest debonding force (54.3 ± 7.0 N) and the least damage to the enamel surface (RAE = 99.5% ± 2.4%). The tensile debracketing method preserved most of the adhesive on the enamel surface (RAE = 98.7% ± 3.3%) and required the least debonding force (6.8 ± 1.2 N). However, the shearing debracketing method exhibited a significantly higher debonding force (32.0 ± 8.2 N) and smaller RAE (77.3% ± 33.5%) compared to the tensile debracketing method (p < 0.05). Three specimens appeared to have vertical fractures on their enamel prisms when using the shearing method. CONCLUSION: With the proposed method, we conclude that the squeezing and tensile methods are acceptable for clinical use when debracketing, whereas the Direct Bond Bracket Remover may cause shearing failure, leading to a risk for enamel damage.

Morphometric analysis of mandibular growth in skeletal Class III malocclusion.

BACKGROUND: The craniofacial growth patterns of untreated individuals with skeletal Class III malocclusion have rarely been systemically investigated. This study used morphometric techniques to investigate the growth characteristics of the mandible in individuals with skeletal Class III malocclusion. METHODS: Lateral cephalometric head films of 294 individuals with untreated skeletal Class III malocclusion (134 males, 160 females) were selected and divided into five triennial age groups (T1-T5) and by gender to identify the morphologic characteristics and sexual dimorphism in changes of mandibular growth. Procrustes, thin-plate spline, and finite element analyses were performed for localization of differences in shape and size changes. Maximum and minimum principal axes were drawn to express the directions of shape changes. RESULTS: From T1 (age 6-8 years) to T4 (age 15-17 years), the distribution of localized size and shape changes of the mandible was very similar between the two genders. From T1 to T2 (age 9-11 years), significant lengthening of the condylar region was noted (23.4-39.7%). From T2 to T3 (age 12-14 years), the greatest size and shape change occurred at the condylar head (27.4-34.9%). From T3 to T4, the greatest size and shape changes occurred in the symphyseal region (23.6-42.1%). From T4 to T5 (age>or=18 years), significant sexual dimorphism was found in the distribution and amount of localized size and shape changes. Females displayed little growth increments during T4. Despite differences in the remodeling process, the whole mandibular configurations of both genders exhibited similarly significant upward and forward deformation from T4 to T5. CONCLUSION: We conclude that thin-plate spline analysis and the finite element morphometric method are efficient for the localization and quantification of size and shape changes that occur during mandibular growth. Plots of maximum and minimum principal directions can provide useful information about the trends of growth changes.

Thin-plate spline analysis of the effects of face mask treatment in children with maxillary retrognathism.

BACKGROUND: Face mask therapy is indicated for growing patients who suffer from maxillary retrognathia. Most previous studies used conventional cephalometric analysis to evaluate the effects of face mask treatment. Cephalometric analysis has been shown to be insufficient for complex craniofacial configurations. The purpose of this study was to investigate changes in the craniofacial structure of children with maxillary retrognathism following face mask treatment by means of thin-plate spline analysis. METHODS: Thirty children with skeletal Class III malocclusions who had been treated with face masks were compared with a group of 30 untreated gender-matched, age-matched, observation period-matched, and craniofacial configuration-matched subjects. Average geometries, scaled to an equivalent size, were generated by means of Procrustes analysis. Thin-plate spline analysis was then performed for localization of the shape changes. RESULTS: Face mask treatment induced a forward displacement of the maxilla, a counterclockwise rotation of the palatal plane, a horizontal compression of the anterior border of the symphysis and the condylar region, and a downward deformation of the menton. The cranial base exhibited a counterclockwise deformation as a whole. CONCLUSION: We conclude that thin-plate spline analysis is a valuable supplement to conventional cephalometric analysis.

Evaluation of the changes in midfacial configuration after face mask therapy in skeletal Class III growing patients by morphometric analysis techniques.

BACKGROUND AND PURPOSE: The prevalence of Angle Class III malocclusion is relatively high in Taiwan. For children who suffer from maxillary retrognathia, face mask therapy is a promising treatment modality. The purpose of this study was to evaluate the changes in midfacial configuration after face mask therapy in skeletal Class III growing patients by morphometric analysis techniques. METHODS: Thirty children who had been treated with face masks were compared with a group of 30 gender-matched, age-matched, observation period-matched, and craniofacial configuration-matched subjects with untreated Class III malocclusions. Average geometries, scaled to an equivalent size, were generated by means of Procrustes analysis. Graphical analysis, utilizing thin-plate spline analysis and strain tensor methods, was performed for localization of differences in shape and size changes. Maximum and minimum principal extensions were drawn to express the directions of shape change. RESULTS: Maxillary protraction-induced changes resulted from a combination of both orthopedic and dental effects. A significant increase in size (7.7% to 9.9%) was noted at the supero-anterior region of the midfacial configuration (rhinion-orbitale-midpalatal point-anterior nasal spine) when subjected to an extraoral traction force; 7.7% to 12.1% of increase in size and 14.4% to 33.4% of change in shape were found at the anterior portion of the maxillary alveolar bone. The directions and amount of principal strain tensors could express the magnitudes and directions of morphological changes within the midfacial complex in an efficient way. CONCLUSIONS: We conclude that morphometric analysis techniques can be used to evaluate the changes in midfacial configuration after face mask therapy and can provide a valuable supplement for conventional cephalometric analysis.