Thermal image analysis of electrothermal debonding of ceramic brackets: an in vitro study.
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This study used modern thermal imaging techniques to investigate the temperature rise induced at the pulpal well during thermal debonding of ceramic brackets. Ceramic brackets were debonded from vertically sectioned premolar teeth using an electrothermal debonding unit. Ten teeth were debonded at the end of a single 3-second heating cycle. For a further group of 10 teeth, the bracket and heating element were left in contact with the tooth during the 3-second heating cycle and the 6-second cooling cycle. The average pulpal wall temperature increase for the teeth debonded at the end of the 3-second heating cycle was 16.8 degrees C. When the heating element and bracket remained in contact with the tooth during the 6-second cooling cycle an average temperature increase of 45.6 degrees C was recorded. (+info)
Super pulse CO2 laser for bracket bonding and debonding.
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A super pulse and a normal pulse CO2 laser were used to carry out enamel etching and bracket debonding in vitro and in vivo. The shear bond strength of the orthodontic brackets attached to laser-etched and conventional chemically-etched extracted premolars was measured. The pulp cavity temperature was also measured using the same laser irradiation conditions as the shear test. Both super pulse and normal pulse CO2 laser etching resulted in a lower shear bond strength (super pulse: 6.9 +/- 3.4 kg, normal pulse: 9.7 +/- 5.2 kg) than that of chemical etching (15.3 +/- 2.8 kg). Furthermore, the super pulse CO2 laser was able to create debonding at 2 watts within a period of less than 4 seconds (2.9 +/- 0.9 seconds). The super pulse, when irradiating the ceramic brackets from above, during debonding showed a 1.4 degrees C temperature increase in the dental pulp at 2 watts and an increase of 2.1 degrees C at 3 watts. While etching, directly irradiating the enamel surface at 3 watts, the dental pulp showed a temperature increase of 3.5 degrees C. These temperature increases were within the physiologically acceptable limits of the pulp. These results indicate that, in orthodontic treatments, super pulse CO2 laser debonding is more useful than laser etching. (+info)
Distortion of metallic orthodontic brackets after clinical use and debond by two methods.
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The objective of this paper was to compare distortion of the tie wings and bases of metallic orthodontic brackets following clinical use and after debond by either of two methods, and took the form of a prospective random control trial. Five-hundred-and-seven brackets were debonded using either bracket removing pliers or a lift off debonding instrument (LODI). By a system of random allocation contralateral opposing quadrants were debonded with a 0.019 x 0.025-inch archwire either in place or removed. After debond brackets were tested for slot closure by the fit of rectangular test wires from 0.016 x 0.022 to 0.021 x 0.025 inch in size. The LODI produced few slot closures sufficient to affect the fit of all but the largest test wire. Bracket removing pliers used after removal of the archwire produced significantly greater numbers of distorted brackets in response to testing with all but the largest wire. With the 0.021 x 0.025 inch wire in place the presence or absence of the archwire at the time of debond made no difference to the number of slot closures. Ten per cent of the brackets debonded using bracket removing pliers had distorted bases, no base damage was produced by the LODI. The use of bracket removing pliers at debond caused significantly more slot closures than use of the LODI. When bracket removing pliers are used the archwire should be left in place at the time of debond since this reduces the number of distortions. (+info)
Factors affecting the shear bond strength of orthodontic brackets to porcelain.
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The aim of this investigation was to establish a regime for orthodontic bonding to feldspathic porcelain, which ensures adequate bond strength (6-8 MPa) with minimal damage on debond and consisted of an ex vivo investigation measuring the effects of porcelain surface preparation and thermocycling on shear bond strength of orthodontic brackets. One-hundred-and-twenty feldspathic porcelain bonded crown surfaces were divided into 12 equally-sized groups to assess the effects of: (1) glaze removal, (2) application of hydrofluoric acid, phosphoric acid, or omission of acid treatment, and (3) silane priming upon the bond strength of premolar brackets bonded with Right-on (TM) composite resin adhesive. Specimens were subjected to thermocycling and then to shear debonding forces on an Instron machine. Removal of the porcelain glaze, or use of hydrofluoric acid, prior to bonding were found to be unnecessary to secure the target bond strength. Hydrofluoric acid application was associated with increased porcelain surface damage. Thermocycling caused a significant reduction in shear bond strength to porcelain (P < 0*001). The best regime for orthodontic bonding to feldspathic porcelain was to apply phosphoric acid for 60 seconds, and prime with silane prior to bonding. Usually the porcelain surfaces could be repolished. Refereed Paper (+info)
An evaluation of the stresses generated in a bonded orthodontic attachment by three different load cases using the Finite Element Method of stress analysis.
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The objective of the investigation was to develop a clinically valid three-dimensional computer model of the orthodontic bracket-cement-tooth continuum, and determine the magnitude and distribution of stresses generated by three different load cases. A three-dimensional finite element model of the bracket-cement-tooth system was constructed consisting of 15,324 nodes and 2,971 finite elements. The stresses induced in the bracket-tooth interface by a masticatory load, a peel force and a twisting couple were recorded. The maximum principal stresses resulting from occlusal and 'twisting' forces are distributed toward the lute periphery. Peel forces, applied to the bracket tie wing, are concentrated beneath the bracket stem. Twisting forces result in the highest enamel stresses. The quality of orthodontic attachment can be explained by the magnitude and distribution of major principal stresses within the cement and impregnated bracket base. Shear and shear/peel forces are most likely to induce crack propagation within the adhesive layer. However, when a twisting action is used to remove orthodontic brackets, enamel failure is most likely. A clearer insight into the complexity of the bracket-cement-tooth system has been provided by numerical and finite element investigations. Further investigations, evaluating the influence of bracket base designs and orthodontic cement physical and geometric properties are indicated. Refereed Scientific Paper (+info)
The force levels required to mechanically debond ceramic brackets: an in vitro comparative study.
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The in vitro force levels generated by four differing methods of mechanical debonding techniques for ceramic brackets, using debonding pliers, were measured. The forces generated using wide (method W) and narrow blades (method N) were compared with those generated using a diagonally opposite corner application of the wide blades (method C) and incisal-gingival application of a pair of pointed blades (method P). Chemically retained ceramic brackets (Transcend) were bonded to bovine teeth using a filled, two-paste, chemically cured composite (Concise). After 24 hours storage at 37 degrees C in water, each specimen was subjected to one of the four mechanical debonding methods in a custom-built jig, simulating the clinical application of conventional debonding pliers. A one-way ANOVA with a Tukey's honestly significant difference test revealed statistically significant differences in debonding strengths between the four methods at the 0.05 level of significance. The mean debonding strength generated by method C was 40 and 25 per cent lower than that for methods W and N, respectively. Scoring of the adhesive remnant index (ARI) revealed that the predominant bond failure site was at the bracket/adhesive interface for all groups. Macroscopically, no enamel damage or bracket fractures were observed. (+info)
An ex vivo assessment of resin-modified glass ionomer bonding systems in relation to ceramic bracket debond.
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This ex vivo study assessed three new resin-modified glass ionomer cements (Fuji ORTHO LC, Vitremer, and Dyract-Cem) in relation to ceramic bracket removal. It was hypothesized that the use of these cements would facilitate bracket removal and eliminate debond complications Eighty extracted premolar teeth were divided into four groups of 20 teeth and bonded with Intrigue brackets using each of the resin-modified cements (groups 1, 2, and 3), the control group 4 was bonded with Concise chemically-cured adhesive. The teeth were debonded by applying a shear load using an Instron universal testing machine. The mean force to debond was calculated for each group and each tooth was examined under the stereomicroscope to record the site of bond failure and the Adhesive Remnant Index (ARI). The results showed that the resin-modified cements were very effective at eliminating ceramic bracket debond problems. Bracket fracture was eliminated compared with a 40 per cent fracture rate with the control and the ARI scores were all reduced. The elimination of debond problems appears to be related to the significantly reduced (P < 0.001 using ANOVA and Tukey tests) mean and maximal debond forces compared with the control. (+info)
Tensile bond strength of a light-cured glass ionomer cement when used for bracket bonding under different conditions: an in vitro study.
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The purpose of this study was to investigate the tensile bond strength of a new light-cured resin reinforced glass ionomer cement (Fuji Ortho LC), following the bonding of stainless steel brackets to 40 extracted human premolar teeth under four different enamel surface conditions: (1) non-etched, moistened with water; (2) etched, moistened with water; (3) etched, moistened with human saliva; and (4) etched, moistened with human plasma. The etched surface produced a higher bond strength than the non-etched surface when contaminated with distilled water. Contamination with human saliva resulted in a further increase in bond strength whilst plasma contamination produced an even higher strength. However, one-way analysis of variance showed no statistically significant difference between the various groups. After debonding, enamel and bracket base surfaces were examined for residual adhesive. The location of the adhesive also indicated improved bonding to etched enamel. This investigation shows that regardless of enamel surface pretreatment or environment, Fuji Ortho LC provides an adequate strength for bonding of orthodontic brackets. (+info)