Development of calcium phosphate cement for rapid crystallization to apatite.
The purpose of this study was to develop an alpha-tricalcium phosphate (alpha-TCP) cement which transforms to hydroxyapatite (HAP) in a relatively short period. We used calcium and phosphate solutions as the liquid phase for the alpha-TCP cement. The alpha-TCP powder was first mixed with CaCl2 solution, and then mixed with NaH2PO4 or Na2HPO3 solution for a total powder/liquid ratio of 1.8. The setting time became shorter with the increase in the concentration of calcium and phosphate solutions, reaching 5 min, whereas the setting time was longer than 30 min when distilled water was used as the liquid phase. X-ray diffraction analysis revealed that the cement was mostly transformed to HAP within 24 h when kept in an incubator. We concluded that alpha-TCP should be mixed with calcium and phosphate solutions since this results in a moderate setting time and fast transformation to HAP even if the method of mixing becomes a little complex. (+info)
Thermal image analysis of electrothermal debonding of ceramic brackets: an in vitro study.
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)
An evaluation of the stresses generated in a bonded orthodontic attachment by three different load cases using the Finite Element Method of stress analysis.
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)
Influence of composite inlay/onlay thickness on hardening of dual-cured resin cements.
This investigation evaluated the effect of resin composite inlay/onlay thickness on the hardness of a group of eight dual-cure resin-based cements. Fourteen disc specimens measuring 6 mm in diameter and 2.5 mm thick were prepared from each of eight dual-cure cements: Adherence, Choice, Duolink, Enforce, Lute-It, Nexus, Resinomer and Variolink. Two specimens from each material were directly light-cured while the remainder of the specimens were light-cured through resin composite spacers varying in thickness from 1 mm to 6 mm. Curing through the spacers always resulted in a decrease in the Knoop hardness number. For some cements, hardness values were reduced by 50% or more when the resin composite spacer thickness was 4 mm or greater even when measurements were made one week after dual-curing. Low hardness values indicate the presence of a weak chemical-curing mechanism that may compromise cement quality in areas of the cavity not readily accessible to the curing light. (+info)
Porcelain esthetics for the 21st century.
BACKGROUND: Dental procedures play a vital role in the modern dental practice. Considerable research has addressed improvements in the properties of dental porcelains. CLINICAL IMPLICATIONS: This article examines the trends in the scientific advances in dental porcelains. It highlights properties of the new low-fusing porcelains and describes indications for their use. New luting cements also are addressed. (+info)
The force levels required to mechanically debond ceramic brackets: an in vitro comparative study.
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)
The influence of bracket base design on the strength of the bracket-cement interface.
The objectives of the study were to isolate the bracket-cement interface, and to determine the influence of bracket base morphology and orthodontic bonding agent chosen on strength of adhesion. The bracket bases evaluated included 60, 80, and 100 single mesh bases, a double mesh base, and the Dynalock, and Mini Twin bases. The strength of interface provided by each of these bases with Concise, Transbond, Right On, and non-encapsulated Fuji Ortho LC cements, was measured in tension and recorded in Mega Pascals. The single-mesh bases performed well with either Concise or Right On (11*88-22*72 MPa) and, other than the 80-mesh bracket, relatively poorly with Transbond (2*18-5*15 MPa). With Fuji Ortho LC, the single mesh bases performed well (6*05-12*19 MPa). The double mesh base performed well with Right On (13*75 MPa), and reasonably well with Concise, Transbond, and Fuji Ortho LC (6*00-9*20 MPa). The Dynalock and Mini Twin Bases performed fairly well with all cements (8*87-17*16 MPa). It was concluded that the orthodontic bonding agent selected would appear to largely determine the bond strength achieved with a particular bracket base design. A definite trend was difficult to identify in this study, and it appeared that certain combinations of bracket base and bonding agent performed optimally. Particular base designs may allow improved adhesive penetration or improved penetration of curing light. Alternatively, the dimension and distribution of resin/cement tags prescribed by one base could promote a stress distribution that is better resisted by a particular adhesive. (+info)
The use of a cyanoacrylate adhesive for bonding orthodontic brackets: an ex-vivo study.
The purpose of this study was to evaluate the performance of a cyanoacrylate orthodontic adhesive with regard to tensile bond strength and bond failure location in comparison with a conventional no-mix orthodontic composite adhesive using stainless steel and ceramic brackets. One-hundred-and-twenty caries-free extracted premolar teeth were used in this study. There were 30 specimens for each tooth, adhesive, and bracket combination, and of these half were tested at 24 hours and half at 3 months. Hence, there were 15 samples in each test group. Bond strengths were assessed using an Instron Universal Testing Machine after storage for 24 hours and for 3 months at 37 degrees C in distilled water. Analysis of variance showed the mean bond strength of specimens bonded with cyanoacrylate was significantly lower than for those bonded with Right-on (P < 0.001). Weibull analysis showed that at a given stress the probability of failure significantly increased after 3 months for brackets bonded with cyanoacrylate. A Chi-square test of the ARI scores revealed no significant difference among the groups tested. This study showed that cyanoacrylate adhesives are unsuitable for use as a bonding agent in routine orthodontic practice. (+info)