Longitudinal shape changes of the nasal dorsum

This investigation quantifies childhood and adolescent growth changes of the upper and lower nasal dorsum and evaluates various aspects of the persons' morphology that relate to shape changes of the dorsum. A longitudinal sample of 37 French-Canadian girls, each having cephalograms at 6, 10, and 14 years of age, was evaluated. The 6- to 10-year interval was chosen to represent childhood growth; the 10- to 14-year interval represented adolescent growth. The upper dorsum rotates upward and forward (counterclockwise) approximately 10 degrees between 6 to 14 years of age. The lower dorsum shows both downward and backward (clockwise) and upward and forward (counterclockwise) rotation average childhood and adolescent changes in angulation were not significant. The results clearly indicate that changes in the nasal dorsum are most closely related to angulation changes of the lower dorsum, particularly during adolescence. The lower dorsum rotates downward and backward in persons who show greater vertical and less horizontal growth changes. Rotational changes of the lower dorsum are most closely related with vertical changes at pronasale.

Failure mode analysis of ceramic brackets bonded to enamel

The purpose of this study was to evaluate in vitro the failure pattern of ceramic brackets bonded to enamel with a light-cured orthodontic adhesive. Five types of ceramic brackets and 125 incisors were used in the study. The brackets were bonded onto enamel with a light-cured orthodontic adhesive. After 1 week storage and thermal cycling, the samples were debonded by one operator according to the individual technique for each bracket group proposed by each manufacturer. The fracture surfaces were examined under a stereomicroscope to reveal the type of failures. The effect of the debonding procedure on enamel structure was significantly affected by the various bonding mechanisms of the bracket bases. Cohesive enamel fractures were detected from brackets that provided a bonding mechanism of micromechanical retention and chemical adhesion. The brackets that combined mechanical retention and chemical adhesion, presented both cohesive resin fractures and fractures located at the bracket resin or the resin enamel interface. The higher frequency of cohesive bracket fractures was obtained from a monocrystalline bracket.

Scanning electron microscope (SEM) evaluation of clinical failures of single crystal ceramic brackets

The objective of this work was to perform failure analysis on Starfire brackets that failed in clinical use. The failed brackets were examined with a scanning electron microscope (SEM) to obtain micrographs at magnifications of 20, 50, 100, and other magnifications, whenever necessary. With the aid of the micrographs, the fracture origin and the probable defect that initiated the fracture were identified. The percentages of failure origins for each area of the bracket were arch wire slot 36.0%, tie wing slot 22.0%, undetermined 11.0%, saddle 9.0%, impact 9.0%, during removal 7.5%, and parting area 5.5%. By observing the micrographs pertaining to each field failure, the primary causes of failure were internal defects 47.5%, machining interference 42.5%, and undetermined 10.0%.

Current concepts in education and research in orthodontics

The science of dentistry is quickly advancing toward the 21st century. The constant innovations in dental material development, along with the ever-new concepts that are emerging in basic science and clinical research, are helping dentists to design methods of practice that have a more biologic and preventive substrate and a less restorative aim. As a result, all specialties of dentistry are undergoing constant changes in an effort to conform and manage the need of an educated, modern society. This report highlights some current concepts in orthodontic education and clinical research that are shaping the way that the specialty of orthodontics is taught and practiced.

Enamel fluoride uptake from an experimental fluoride-releasing orthodontic adhesive

The purpose of this study was to evaluate quantitatively the fluoride uptake by enamel from an experimental visible light-cured orthodontic adhesive (VP-862) based on YbF3 filler. Sixteen contralateral premolars were extracted from 10 orthodontic patients and were classified in four groups (A, B, C, D) of four buccal surfaces each. Standardized enamel areas located on these surfaces were acid etched and were subjected to the following adhesive treatments: (A) VP-862; (B) Heliosit Orthodontic; (C) Heliobond + VP 862; and (D) Heliobond + Heliosit Orthodontic. Groups B and D were used as a reference. After 9 months in vivo, the teeth were extracted and cross-sectioned, and the enamel-adhesive interfaces were studied by combined wavelength-energy dispersive electron probe microanalysis. According to the results, the cumulative fluoride uptake by enamel from the experimental adhesive was not statistically different from the fluoride detected in the reference groups. No effect of the liquid resin, Heliobond, on the fluoride uptake gradients of enamel could be differentiated.

Bonding of ceramic brackets to enamel: morphologic and structural considerations

The purpose of this study was to evaluate the form and microstructure of three types of ceramic bracket and to assess their interfacial surface shapes and bond strengths with visible light-cured and chemically cured adhesives after thermocycling. One monocrystalline and two polycrystalline structures were identified. The form of the bonding bases implied three types of bonding with the adhesive: a chemical bonding, a combination of mechanical retention and adhesion, and a combination of micromechanical retention and adhesion. All the ceramic bases were covered with a layer of gamma-methacryloxypropyltrimethoxysilane coupling agent. The thickness of the adhesive layer was affected by the design of the bracket bases. The highest bond strength was obtained from the brackets by a combination of micromechanical retention and adhesion, with the site of failure located at the resin/bracket interface. The other types of ceramic brackets had a greater amount of resin left on the enamel and some cases of cohesive bracket fractures.

Bond strength of ceramic brackets under shear stress: an in vitro report

The shear bond strength and the potential enamel damage on debonding of various currently available ceramic and stainless steel brackets were examined in vitro using extracted premolar teeth. The brackets were divided into two groups, one bonded with a new light-cured orthodontic adhesive and the other with a conventional chemically cured system. An Instron Universal testing machine was used to apply the shear stress. Mean, standard deviation, and extreme values were calculated for each group. Statistical analysis showed that the mean shear bond strength of the silane chemical bond provided by some ceramic brackets is significantly higher (p less than 0.05) than the mean of the mechanical bond of other ceramic and stainless steel brackets. There was no statistically significant difference between the mean shear bond strength of the two adhesives used. Mechanical bonds failed primarily within the adhesive itself, whereas chemical bonds failed predominantly at the adhesive-bracket interface. Single-crystal ceramic brackets tend to be more brittle than the polycrystalline ones. Strong chemical bonds can potentially lead to enamel failure on debonding.

Enamel abrasion from ceramic orthodontic brackets under an artificial oral environment

The purpose of this investigation was to examine the potential enamel abrasion on contact with stainless steel and various ceramic orthodontic brackets under a simulated oral environment. Three groups of eight lower premolar ceramic brackets and one group of eight stainless steel brackets were used from four different manufacturers. An upper premolar was brought in contact with the bracket bonded to a lower premolar tooth and subjected to a lateral excursion type of movement by the artificial oral environment. A constant load of approximately 2 lb was used for the masticatory force. The rate of chewing was 1 cycle/sec. The teeth were subjected to 15, 60, and 100 masticatory cycles. The before-and-after occlusal surfaces of the upper premolars were compared by means of a computerized profiling system and the enamel volume loss was calculated. Qualitative changes, such as rate of enamel wear, were examined visually by means of computer graphics and the scanning electron microscope. Abrasion scores (mean +/- SD) in mm3 were 0.015 +/- 0.01 from the metal brackets and 0.135 +/- 0.103, 0.255 +/- 0.242, and 0.581 +/- 0.524 from the three ceramic bracket groups. The abrasion scores were significantly different at p less than 0.05. Ceramic brackets caused significantly greater enamel abrasion than stainless steel brackets. Artificial mouth in vitro testing gave a good indication of clinical performance of orthodontic brackets.

[Enamel wear from ceramic and stainless steel orthodontic brackets]

The purpose of this investigation was to examine the potential enamel wear upon contact with ceramic and stainless steel orthodontic brackets of the same company into an artificial mouth, which is a simulated oral environment. Two groups of ten lower premolars were bonded with ceramic and stainless steel brackets. The same number of upper premolars were used and each upper premolar was brought in contact with the opposing bracket and subjected to a lateral type of movement, like a mastication movement, by the artificial mouth. A constant load of approximately two pounds was used for the masticatory force, the rate of chewing was one cycle per second and the teeth were subjected to 2.5 and 10 masticatory cycles. The before and after occlusal surfaces of the upper premolars were compared using a computerized profiling system and the enamel volume loss was calculated. Qualitative changes, such as rate of enamel wear, were examined visually using SEM and computer graphics. Abrasion scores (mean +/- SD) in mm3 were 0.0142 +/- 0.020 for the metal and 0.2433 +/- 0.150 for the ceramic brackets and were significantly different at p less than 0.05. Ceramic brackets caused significantly greater enamel abrasion than stainless steel brackets.

Enamel surface abrasion from ceramic orthodontic brackets: a special case report

The purpose of this report is to present a dramatic case of enamel abrasion from ceramic orthodontic appliances that was discovered only after appreciation of the initial findings of a study underway at the Department of Orthodontics, University of Minnesota. An artificial oral environment used in this study to simulate mastication also is described. The potential detrimental effects of ceramic appliances on tooth contact are discussed. All aspects of any new material should be investigated before its clinical application to prevent undesired side effects.