In vitro comparison of the retention capacity of new aesthetic brackets.
Tensile bond strength and bond failure location were evaluated in vitro for two types of aesthetic brackets (non-silanated ceramic, polycarbonate) and one stainless steel bracket, using bovine teeth as the substrate and diacrylate resin as the adhesive. The results show that metallic bracket had the highest bond strength (13.21 N) followed by the new plastic bracket (12.01 N), which does not require the use of a primer. The non-silanated ceramic bracket produced the lowest bond strength (8.88 N). Bond failures occurred mainly between bracket and cement, although a small percentage occurred between the enamel-cement interface with the metal and plastic brackets and within the cement for the plastic bracket. With the ceramic bracket all the failures occurred at the bracket-cement interface. This suggests that the problems of enamel lesions produced by this type of bracket may have been eliminated. The results also show that the enamel/adhesive bond is stronger than the adhesive/bracket bond in this in vitro study. (+info)
The crystal growth technique--a laboratory evaluation of bond strengths.
An ex vivo study was carried out to determine differences in the bond strengths achieved with brackets placed using a crystal growth technique compared with a conventional acid-etch technique. A solution of 37 per cent phosphoric acid was used for acid-etching and a commercially available polyacrylic acid gel, Crystal-lok for crystal growth. A heavily-filled composite resin was used for all samples to bond brackets to healthy premolar teeth extracted for orthodontic purposes. Polycrystalline ceramic and stainless steel brackets were used and tested to both tensile and shear failure using an Instron Universal Testing machine. The tensile and shear bond strengths were recorded in kgF. In view of difficulties experienced with previous authors using different units to describe their findings, the data were subsequently converted to a range of units in order to facilitate direct comparison. The crystal growth technique produced significantly lower bond strengths than the acid-etch technique for ceramic and stainless steel brackets, both in tensile and shear mode. The tensile bond strength for stainless steel brackets with crystal growth was 2.2 kg compared with 6.01 kg for acid-etch, whilst with ceramic brackets the tensile bond strengths were 3.9 kg for crystal growth and 5.55 kg for acid-etch. The mean shear bond strength for stainless steel brackets with crystal growth was 12.61 kg compared with 21.55 kg for acid-etch, whilst with ceramic brackets the shear bond strengths were 7.93 kg with crystal growth compared with 16.55 kg for acid-tech. These bond strengths were below those previously suggested as clinically acceptable. (+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 ex vivo investigation into the bond strength of orthodontic brackets and adhesive systems.
The aim of this study was to compare the shear bond strength of Adhesive Precoated Brackets (APC) with that of two types of uncoated bracket bases, Straight-Wire and Dyna-Lock. Two types of orthodontic adhesives were used, Transbond XT and Right-On. Three different curing times were evaluated with the APC brackets in order to find the best. Adhesive remnants on the enamel surface following debond were evaluated using the Adhesive Remnant Index (Artun and Bergland, 1984). Bond strengths ranged from 11.00 to 22.08 MPa. For both types of brackets Transbond produced a significant increase in bond strength compared to Right-On. The Dyna-Lock/Right-On combination produced the poorest results. APC brackets cured for 40 s had similar bond strengths to uncoated brackets fixed by means of Transbond. Overall, 79 per cent of specimens had less than half the tooth surface covered with adhesive following debond. Significantly more adhesive remained on tooth surfaces following debond of the Straight-Wire/Right-On group than any other bracket/adhesive combination. Bond strengths were higher with light-cured Transbond than with chemically-cured Right-On. When Transbond is used in association with APC brackets a 40-second cure time is recommended. (+info)
Determination of bisphenol A and related aromatic compounds released from bis-GMA-based composites and sealants by high performance liquid chromatography.
Most of the composites and sealants used in dentistry are based on bisphenol A diglycidylether methacrylate (Bis-GMA). Reports revealed that in situ polymerization is not complete and that free monomers can be detected by different analytic methods. Concerns about the estrogenicity of bisphenol A (BPA) and other aromatic components leached from commercial products have been expressed. We studied biphenolic components eluted from seven composites and one sealant before and after in vitro polymerization using HPLC and gas chromatography/mass spectrometry and we investigated how pH modifications affect the leaching of these components. We found BPA (maximal amount 1.8 microg/mg dental material), its dimethacrylate derivative (Bis-DMA, 1.15 microg/mg), bisphenol A diglycidylether (6. 1 microg/mg), Bis-GMA (2.0 microg/mg), and ethoxylate and propoxylate of bisphenol A in media in which samples of different commercial products were maintained under controlled pH and temperature conditions. Our results confirm the leaching of estrogenic monomers into the environment by Bis-GMA-based composites and sealants in concentrations at which biologic effects have been demonstrated in in vivo experimental models. The main issue with implications for patient care and dentist responsibility is to further determine the clinical relevance of this estrogenic exposure. (+info)
Effects of composite thickness on the shear bond strength to dentin.
The manufacturers of some condensable posterior composites claim that their products can be placed in bulk and light-cured in 5-mm-thick increments. This study compared the shear bond strengths of three composite resins when bonded to dentin in 2- and 5-mm-thick increments. Overall the bond strengths were adversely affected by the composite thickness (p < 0.0001). The shear bond strength of each composite tested was much lower when polymerized in a 5-mm increment than in a 2-mm increment of composite (p < or = 0.0005). The two condensable composites tested had a lower bond strength than the conventional composite when polymerized in a 5-mm bulk increment (p < or = 0.01). (+info)
Cytotoxicity of dental resin monomers in the presence of S9 mix enzymes.
The purpose of the this study was to evaluate the cytotoxicity of dental resin monomers in the presence of a rat liver S9 mix containing cytochrome P 450 enzymes. JTC-12 cells derived from a monkey kidney were seeded on a 96-well multi-well-plate at 9 x 10(3) cells per well. After cultivation, the S9 mix was added to the wells as an S9 mix group (+S9), and PBS- was added to the other wells as a none-S9 mix group (-S9), then 7 different concentrations of various monomers were added to each well. All the specimens were cultured for another 24 hrs. The cell survival ratios (CSR) were calculated by using a neutral red cytotoxicity assay. CSR for 50 micrograms/mL of Bis-GMA/S9 mix was 92.6% while for none-S9 mix it was 6.6%. The values of CSR for UDMA, Bis-MPEPP, EGDMA, TEGDMA, DMAEM, 4-META and HEMA exhibited a reduction in cytotoxicity in the presence of the S9 mix. There were significant differences between +S9 and -S9 for respective monomers (p < 0.05). However, there were no significant differences between +S9 and -S9 for MMA (p < 0.05). (+info)
Analysis of major components contained in Bis-GMA monomer.
The major components contained in commercial Bis-GMA monomer were isolated by thin layer chromatography (TLC) and identified by NMR and high resolution mass spectroscopy. In addition to the two major components already known (Bis-GMA and Iso-bis-GMA), an unknown hydrophilic third major component was isolated and identified as 2,2-[4-(2-hydroxy-3- methacryloyloxy-1-propoxy)-4'-(2,3-dihydroxy-1-propoxy)]dipheny lpropane. This compound was designated as BIS-GMA-H, because it has a structure of Bis-GMA with one of which methacrylic ester bond hydrolyzed. (+info)