Shear bond strength of brackets rebonded with a fluoride-releasing and -recharging adhesive system.

OBJECTIVE: To ascertain the effects of repeated bonding on the shear bond strength of orthodontic brackets bonded with a fluoride-releasing and -recharging adhesive system with a self-etching primer in comparison with two other types of adhesive system. MATERIALS AND METHODS: A total of 48 premolars were collected and divided equally into three groups of 16. Each group was assigned one of three adhesive systems: Transbond XT, Transbond Plus, or a fluoride-releasing and -recharging adhesive system, Beauty Ortho Bond. Shear bond strength was measured 24 hours after bracket bonding, with the bonding/debonding procedures repeated twice after the first debonding. A universal testing machine was used to determine shear bond strengths, and bracket/adhesive failure modes were evaluated with the adhesive remnant index after each debonding. RESULTS: At every debonding sequence, all of these three adhesive systems had a shear bond strength of 6 MPa, which is a minimum requirement for clinical use. Transbond XT and Transbond Plus had significantly higher mean shear bond strengths than did Beauty Ortho Bond at each debonding. No significant differences in mean bond strength were observed between the three debondings in each adhesive system. Bond failure at the enamel/adhesive interface occurred more frequently in Beauty Ortho Bond than in Transbond XT or Transbond Plus. CONCLUSIONS: The fluoride-releasing and -recharging adhesive system with the self-etching primer (Beauty Ortho Bond) had clinically sufficient shear bond strength in repeated bracket bonding; this finding can help orthodontists to decrease the risk of damage to enamel at debonding.

Comparison of shear bond strengths of orthodontic brackets bonded to deciduous and permanent teeth.

INTRODUCTION: This study was conducted (1) to compare the bond strengths of identical orthodontic brackets bonded to deciduous and permanent teeth with either of 2 primer/adhesive systems and (2) to evaluate the modes of bracket/adhesive failure. METHODS: Thirty-four permanent teeth and 34 deciduous teeth were collected. To these freshly extracted teeth, metal brackets were bonded with 2 primer/adhesive systems. These specimens were divided into 4 groups. In group I, consisting of 17 permanent teeth, the brackets were bonded with an acid-etching adhesive system; in group II, the self-etching adhesive system was used for bonding the brackets to 17 permanent teeth; in group III, consisting of 17 deciduous teeth, the acid-etching adhesive system was used; and in group IV, the self-etching adhesive system was used for bonding the brackets to 17 deciduous teeth. Shear bond strength was measured with a universal testing machine, and the mode of bracket/adhesive failure was determined according to the adhesive remnant index. RESULTS: The shear bond strengths of all 4 groups exceeded what is believed to be clinically sufficient strength of 6 to 8 MPa. Whether deciduous or permanent teeth, there were no significant differences in shear bond strength between the acid-etching and self-etching adhesive systems. The shear bond strengths of the brackets bonded to the deciduous teeth with either adhesive system were lower than those to the permanent teeth. Bond failure occurred at the enamel-adhesive interface more frequently in the self-etching adhesive system than in the acid-etching adhesive system. CONCLUSIONS: Bond strengths of brackets were lower with deciduous teeth but were high enough for clinical purposes.

Congenitally missing mandibular incisors and mandibular symphysis morphology.

OBJECTIVE: To explore the association between congenital absence of permanent mandibular incisors and craniofacial and mandibular symphysis morphology in Japanese orthodontic patients. MATERIALS AND METHODS: A total of 27 girls with one or two congenitally absent mandibular incisors (group M) were selected and divided into group 1M (16 girls with the absence of one incisor) and group 2M (11 girls with the absence of two incisors). In addition, 20 other Japanese girls without hypodontia and with little or no mandibular incisor crowding were enrolled as a control (group C). Using the lateral cephalogram of each subject, 17 angular, 8 linear, and 3 area measurements were made for evaluation of craniofacial and mandibular symphysis morphology. The cephalometric data thus obtained were statistically analyzed and compared between the groups. RESULTS: A significantly greater retroclination of the retained mandibular incisors was found in group 1M than in group C. Groups 1M and M showed a significantly greater retroclination of mandibular alveolar bone than group C. Groups 2M and M exhibited a significantly smaller mandibular symphysis area than group C. CONCLUSION: The retroclination of the mandibular incisors and alveolar bone and the reduced mandibular alveolar bone area should be taken into consideration in planning orthodontic treatment on patients with congenitally missing permanent mandibular incisors.

Shear bond strength differences of types of maxillary deciduous and permanent teeth used as anchor teeth.

OBJECTIVE: To compare the bond strengths of identical orthodontic brackets bonded to maxillary deciduous and permanent teeth, which were used as anchor teeth in sectional edgewise appliance therapy, and to evaluate the modes of bracket/adhesive failure. MATERIALS AND METHODS: A total of 28 human maxillary teeth were divided into four groups by tooth type: permanent first premolars (group I), permanent second premolars (group II), deciduous canines (group III), and deciduous second molars (group IV). Each group consisted of seven teeth. Metal premolar brackets were bonded to these specimens using an acid-etching adhesive system. Shear bond strengths were measured using a universal testing machine, and the bracket/ adhesive failure modes were evaluated with the Adhesive Remnant Index. RESULTS: The shear strengths of the bonds on the deciduous canines and second molars were significantly lower than those on the permanent first and/or second premolars. There were no significant differences in shear bond strength between the permanent first and second premolars, and between the deciduous canines and second molars. The shear bond strengths of all four tooth types were higher than the clinically sufficient range of strengths from 6 to 8 MPa. Bond failure at the enamel-adhesive interface occurred more frequently in the deciduous second molars than in the permanent first premolars. CONCLUSIONS: There were significant differences in shear bond strength among different permanent and deciduous tooth types, but deciduous teeth could be used as anchor teeth in orthodontic treatment with sectional edgewise appliances.

Hypodontia patterns and variations in craniofacial morphology in Japanese orthodontic patients.

OBJECTIVE: The purpose of this study was to explore the association of hypodontia patterns and variations in craniofacial morphology in Japanese orthodontic patients. MATERIALS AND METHODS: A total of 50 girls with hypodontia (the total group) were selected and categorized into anterior, posterior, and anterior-posterior groups according to the location of the congenitally missing teeth. By using the lateral cephalograms of each subject, 28 angular and 37 linear measurements were made. The cephalometric data were statistically analyzed and compared among the groups and with the Japanese cephalometric standards from 36 age-matched female subjects without hypodontia or malocclusion (the control group). RESULTS: Every hypodontia group showed shorter anterior and overall cranial base lengths, shorter maxillary length, greater retroclination and elongation of mandibular incisors, and a larger interincisal angle than the control group. The total and anterior-posterior groups especially exhibited a significantly more prognathic mandible, larger retroclination of maxillary incisors, and a more counterclockwise-rotated occlusal plane. Furthermore, these skeletal and dental deviations were more remarkable in the anterior-posterior group than in either the anterior or the posterior group. Anterior hypodontia exerted as much influence on craniofacial morphology as posterior hypodontia. CONCLUSIONS: When orthodontic treatment is performed on patients with hypodontia, not only the number but also the distribution of missing teeth should be taken into consideration, though there was no significant difference in craniofacial morphology between anterior hypodontia and posterior hypodontia.

Initial shear bond strength of orthodontic brackets bonded to bleached teeth with a self-etching adhesive system.

OBJECTIVES: To examine the initial shear bond strength of orthodontic brackets bonded to bleached teeth with a self-etching adhesive system, as well as the effect of the length of time after bleaching on the initial bond strength. METHOD AND MATERIALS: Ninety premolars were collected and divided equally among a control group (CG) of unbleached teeth with brackets bonded, an immediate group (IG) with teeth bonded soon after bleaching, and a delayed group (DG) consisting of teeth bleached and then immersed in artificial saliva for 7 days before bracket bonding. Subsequently, the teeth of each group were equally assigned to two different primer adhesive systems: the acid-etch-and-rinse adhesive system (35% phosphoric acid gel and Transbond XT primer) and the self-etching adhesive system (Transbond Plus self-etching primer). Initial bond strength was measured 24 hours after bracket bonding. RESULTS: IG registered the lowest mean initial bond strength when the self-etching adhesive system was in use, followed by DG and CG (in that order). As for the acid-etch-and-rinse adhesive system, the mean initial bond strength was significantly lower in IG than in CG and DG. Significant differences in mean initial bond strength were noted between the two adhesive systems in IG and DG. CONCLUSION: In trials using a self-etching adhesive system, the mean initial bond strength that declined immediately after bleaching returned to a clinically acceptable level of 6 MPa after the specimens were immersed in artificial saliva for 7 days but fell short of the level of unbleached teeth.

Effects of moisture conditions of dental enamel surface on bond strength of brackets bonded with moisture-insensitive primer adhesive system.

The purposes of this study were to evaluate the effects of different degrees of water contamination on the shear bond strength of orthodontic brackets bonded to dental enamel with a moisture-insensitive primer (MIP) adhesive system and to compare the modes of bracket/adhesive failure. A total of 68 human premolars were divided into four groups by primers and enamel surface conditions (desiccated, blot dry, and overwet). In group I, the hydrophobic Transbond XT primer adhesive system was used under desiccated conditions for bonding the brackets; in group II, the hydrophilic Transbond MIP adhesive system was used under desiccated conditions; in group III, the hydrophilic Transbond MIP adhesive system was used under blot dry conditions; and in group IV, the hydrophilic Transbond MIP adhesive system was used under overwet conditions. Shear bond strength was measured with a universal testing machine, and the mode of bracket/adhesive failure was determined according to the adhesive remnant index. The mean shear bond strengths were not significantly different among groups I, II, and III, and were higher than the clinically required range of 6 to 8 MPa. The mean shear bond strength achieved in group IV was significantly lower than that achieved in groups I, II, and III, and also lower than the clinically required values. Bond failure occurred at the enamel-adhesive interface more frequently in group IV than in groups I and III. To achieve clinically sufficient bond strengths with the hydrophilic MIP adhesive system, excess water should be blotted from the water-contaminated enamel surface.

A survey of hypodontia in Japanese orthodontic patients.

INTRODUCTION: The purpose of this retrospective study was to assess the prevalence and distribution of hypodontia in the permanent dentition, excluding the third molars, in a sample of Japanese orthodontic patients. METHODS: Orthopantomograms of 3358 Japanese orthodontic patients (1453 boys and 1905 girls) between the ages of 5 and 15 years were examined for evidence of hypodontia. RESULTS: The prevalence of hypodontia was 8.5% (7.5% for boys, 9.3% for girls) with no statistically significant difference between the sexes. The average number of missing teeth per child was 2.4 (2.5 for boys, 2.4 for girls). Most (76.3%) children with hypodontia were missing either 1 or 2 teeth (77.1% for boys, 75.7% for girls). The prevalence of advanced hypodontia was 10.1% (11.0% for boys, 9.7% for girls). The most commonly missing teeth were the mandibular second premolars, followed by the mandibular and maxillary lateral incisors, and the maxillary second premolars; minor differences in the order of prevalence existed among groups of children classified by the number of missing teeth. Symmetrical hypodontia was predominant, and the most commonly symmetrical hypodontia was mandibular second premolar agenesis. No consistent finding was obtained as to which jaw had more missing teeth. The distribution of missing teeth was similar between the right and left sides of the dental arches in each group of children. Anterior tooth agenesis was predominant in children with minor hypodontia, and posterior tooth agenesis increased with hypodontia severity. CONCLUSIONS: The distinct characteristic of hypodontia in the Japanese population compared with other populations was a higher prevalence of both advanced hypodontia and mandibular lateral incisor agenesis in children with minor hypodontia.

Association of advanced hypodontia and craniofacial morphology in Japanese orthodontic patients.

The purpose of this study was to examine the effects of advanced hypodontia on craniofacial morphology in Japanese patients. We defined advanced hypodontia as a congenital absence of four or more permanent teeth, excluding the third molars. Lateral cephalometric radiographs of 20 female orthodontic patients (age range, 8.5 to 19 years; mean age, 13.9 years) were examined. Twenty-eight angular and 37 linear measurements were taken from each cephalogram, and these cephalometric data were statistically analyzed and compared with the Japanese cephalometric standards. The most frequently missing teeth were the mandibular and maxillary second premolars, followed by the maxillary first premolars and the maxillary first molars, in that order. Compared with the Japanese standards, a smaller cranial base length and angle, a shorter maxillary length, a slightly prognathic and upward-rotated mandible, and retroclination of the upper and lower incisors were found in the patients studied. These craniofacial anomalies should be taken into consideration in treatment planning and mechanotherapy.