(1/1061) 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)
(2/1061) 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)
(3/1061) Pathological evaluation of the effects of intentional disocclusion and overloading occlusion in odontogenesis disorders in N-methylnitrosourea-treated hamsters.
This study compares the effects of disocclusion and overloading occlusion on dental lesions. Ten-day-old Syrian hamsters were divided into 4 groups: group I, untreated animals; group II, animals whose hemilateral incisors were disoccluded; group III, N-methylnitrosourea (MNU)-treated animals; and group IV, MNU-treated animals whose hemilateral incisors were disoccluded. The ipsilateral maxillary and mandibular incisors were repetitively cut with diamond discs. The hamster is easier to anesthetize. Animals received a 0.2% solution of MNU (10 mg/kg body weight) intragastrically twice a week for 16 wk. All the cut mandibular incisors and the MNU-treated uncut mandibular incisors showed lack of iron deposition on the enamel surface. The eruption rate was significantly higher in the cut disoccluded incisors of groups II and IV (p < 0.05) and significantly lower in the uncut overloaded incisors of groups II and IV (p < 0.05). In the cut mandibular incisors of group IV, the degree of the disturbance of odontogenesis and the atypical proliferation of odontogenic epithelium were more prominent (p < 0.02), and the dental lesions occurred earlier. Histologically, the disturbed Hertwig's epithelial sheath and the Hertwig's epithelial sheath-like transformed U-shaped part and enamel organ seemed to lead to disturbances of amelogenesis and detinogenesis as well as to atypical proliferation of odontogenic epithelium nests. Thus, this method of disocclusion of the incisors of rodents may represent a useful model for the investigation of the effects of various agents on tooth formation over a short experimental period. (+info)
(4/1061) Super pulse CO2 laser for bracket bonding and debonding.
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)
(5/1061) An immunocytochemical study of amelogenin proteins in the developing tooth enamel of the gar-pike, Lepisosteus oculatus (Holostei, Actinopterygii).
Previous studies have demonstrated the morphological similarity of the enamel-like layer found in the teeth of the coelacanth, lungfish and gar-pike to the enamel of tetrapods. In order to clarify the phylogenetic continuity between both structures, tooth germs of the gar-pike were immunocytochemically studied using an anti-bovine amelogenin polyclonal antibody. Intense immunoreaction was shown over the enamel-like matrix layer. Certain cell organelles associated with the secretory pathway of the ameloblasts were recognized as immunoreactive. These results indicate that the enamel-like layer of the gar-pike is a tissue homologous with the mammalian enamel because both possess a common, amelogenin-like substance. (+info)
(6/1061) Aspects of cell proliferation kinetics of the inner dental epithelium during mouse molar and incisor morphogenesis: a reappraisal of the role of the enamel knot area.
First lower E-14 and E-16 mouse molars and E-13 lower incisors were cultured in vitro and either sequentially or continuously labelled with BrdU (5-bromo-2'-deoxyuridine). The behaviour of the non-cycling inner dental epithelial cells emerging from the enamel knot area of the molars was analysed by 3D (three dimensional) reconstructions of serial sections. These cells, as well as slow cycling cells underwent a coordinated temporo-spatial patterning leading to their patchy segregation at the tips of the forming cusps. In incisors (in vitro and in vivo), non-cycling cells were also present in the inner dental epithelium of the enamel knot area. However, these cells were not redistributed during incisor morphogenesis. These non-dividing inner dental epithelium cells of the enamel knot area which are either redistributed or not according to the tooth type specific morphogenesis might represent the organizers of morphogenetic units (OMU), the cusps. (+info)
(7/1061) A laboratory investigation to compare enamel preparation by sandblasting or acid etching prior to bracket bonding.
A laboratory investigation to compare the mean shear debonding force and mode of bond failure of metallic brackets bonded to sandblasted and acid-etched enamel is described. The buccal surfaces of 30 extracted human premolars were sandblasted for 5 seconds with 50 mu alumina and the buccal surfaces of a further 30 human premolars were etched with 37 per cent phosphoric acid for 15 seconds. Following storage for 24 hours at 37 degrees C in distilled water, shear debonding force was measured using an Instron Universal Testing Machine with a cross-head speed of 10 mm/minute. Mean shear debonding force was significantly lower for brackets bonded to sandblasted enamel compared to acid etched enamel (P < 0.001). Weibull analysis showed that at a given stress the probability of failure was significantly greater for brackets bonded to sandblasted enamel. Brackets bonded to etched enamel showed a mixed mode of bond failure whereas following sandblasting, failure was adhesive at the enamel/composite interface (P < 0.01). (+info)
(8/1061) Biodosimetry results obtained by various cytogenetic methods and electron spin resonance spectrometry among inhabitants of a radionuclide contaminated area around the siberian chemical plant (Tomsk-7).
On April 6, 1993, near the town of Tomsk (Russia) there was an accident at the Siberian Chemical Plant (SCP) which resulted in extensive contamination of an area of 250 km(2) to the north of SCP with long-lived radionuclides such as (239)Pu, (137)Cs and (90)Sr. Cytogenetic methods and electron spin resonance (ESR) spectrometry of tooth enamel were used to estimate the radiation doses received by the population. The ESR signal intensity and the chromosomal aberration frequency in lymphocytes of the tooth donors showed a good correlation. The data showed that 15% of the inhabitants of the Samus settlement received a radiation dose >90 cGy. The exceptions were results of an examination of fishermen, where ESR gave high values (80-210 cGy) but both the chromosome assay and the cytokinesis block micronucleus method gave lower ones (8-52 cGy). A large increase in chromosome damage was observed in people born between 1961 and 1969. It was found that during these years several serious accidents at the Siberian Chemical Plant had occurred causing radiation pollution of the area. The number of cells with chromosome aberrations was significantly less among the people arriving in Samus after 1980. We found good correlations between the level of carotene consumption and a decrease in frequency of both micronuclei in binucleated lymphocytes (r = 0.68, P < 0.01) and chromatid aberrations (r = 0.61, P < 0.01) among the inhabitants. We also examined the inhabitants of Samus for opisthorchis infection, which was present in 30% of the population. The Samus inhabitants affected by Opisthorchis felineus showed significantly increased levels of micronuclei in binucleated lymphocytes and chromatid aberrations as compared with the controls. (+info)