Wear of human enamel against a commercial castable ceramic restorative material

This study determined the effect of castable ceramic, with and without shading porcelain applied, on enamel wear. The wear produced by conventional dental porcelain was used as a control. Cusp tips from extracted human third molars were precision-machined into cones of enamel approximately 1 mm long. Three groups of nine cones each were abraded against rotating disks of (1) castable ceramic with shading porcelain, (2) castable ceramic without shading porcelain, and (3) conventional dental porcelain. Enamel wear was calculated from microscopic measurements of the enamel cones before and after abrading. Mean and standard deviation values were 1.220 +/- 0.218 for castable ceramic with shading porcelain, 0.639 +/- 0.218 for castable ceramic without shading porcelain, and 0.785 +/- 0.311 for glazed conventional dental porcelain (all values are X 10(-3) cm3). Significant differences were found between castable ceramic with and without shading porcelain and between conventional dental porcelain and castable ceramic with shading porcelain (p less than 0.001 ANOVA and 0.05 Scheffe's test). These findings suggest that castable ceramic with shading porcelain should not be used in regions that will function against opposing natural teeth.     

An in vitro evaluation of bond strength of three glass ionomer cements

The purpose of this study was to determine the bond strength of three commercially available glass ionomer cements when used to bond mesh-backed medium twin (0.130 inch) brackets to enamel surface. Three different enamel surface conditions, which included use of pumice, pumice and polyacrylic acid, and pumice followed by acidulated phosphate fluoride, were also tested to determine their effect on the bond strength. In addition, bond strength of one composite resin was compared with those of glass ionomer cements. The teeth were bonded with all the materials according to manufacturers' instructions. Each specimen was embedded in Super-Die with the bonded facial surface exposed. A surveyor was used to align the teeth in the stone uniformly for all specimens. A special bracket holder was used to hold the brackets precisely under the wings during debonding. An Instron universal testing machine was used to measure the force required for bond failure. To stimulate oral conditions, the direction of pull was so designed that it included an element of torsional stress along with tensile force. The findings indicate that a large variation existed between the bond strengths of all materials tested. The bond strength of glass ionomer cements was significantly less than that composite resin. However, the bond strength of at least one glass ionomer cement appears to be adequate for clinical use. The different surface preparation before bonding did not significantly affect the bond strengths of glass ionomer cements. Further investigation is required to test the bond strengths of glass ionomer cements clinically.     

Evaluation of friction between ceramic brackets and orthodontic wires of four alloys

The purpose of this investigation was to determine the frictional resistance offered by ceramic brackets used in combination with wires of different alloys and sizes during in vitro translatory displacement of brackets. Findings with ceramic brackets were also compared with outcomes of treatment with stainless steel brackets. Stainless steel, cobalt-chromium, beta-titanium, and nickel-titanium wires of different cross-sectional sizes were tested in medium-twin monocrystalline ceramic brackets with both 0.018-inch and 0.022-inch slot sizes. The wires were ligated into the brackets with elastomeric modules. Brackets were moved along the wire by means of an Instron universal testing machine, and frictional force was measured by a compression cell and recorded graphically on an xy recorder. Wire friction in the ceramic brackets increased as wire size increased, and rectangular wires produced greater friction than round wires. Beta-titanium and nickel-titanium wires were associated with higher frictional forces than stainless steel or cobalt-chromium wires. These findings follow the same general trends as those found with stainless steel brackets; however, wires in ceramic brackets generated significantly stronger frictional force than did wires in stainless steel brackets.     

Clinical crown lengthening in the esthetic zone

Periodontal surgical procedures consisting of gingival flaps and osseous recontouring are indicated for crown lengthening of several contiguous teeth in the esthetic zone; both in cases where restorations are required and in cases where no restorations are planned, such as in patients with excessive gingival display due to altered passive eruption. Forced tooth eruption via orthodontic extrusion is the technique of choice when clinical crown lengthening is necessary on isolated teeth in the esthetic zone.     

Comparison of clinical and magnetic resonance imaging diagnoses in patients with TMD history

The aim of this study was to evaluate the diagnostic accuracy of a well-defined clinical examination for diagnosing anterior disc displacement with and without reduction. A series of 40 patients with temporomandibular disorder (TMD) history were examined according to well-defined routine criteria. This examination included detailed history-taking, standardized clinical head and neck examination that included measurements of the range of motion, palpation of the temporomandibular joints and muscles of mastication for pain and auscultation of joint sounds. Magnetic resonance images of the joints were used as 'gold standard'. Diagnostic accuracy of the clinical examination was 83% for determining normal disc-condyle relationship, 72% for diagnosing anterior disc displacement with reduction, and 81% for diagnosing anterior disc displacement without reduction. Our results suggest that anterior displacement of the disc can be diagnosed with considerable accuracy using a well-defined clinical examination only. Therefore, we conclude that not all patients with TMD symptoms require magnetic resonance imaging examination before treatment.     

Densitometric evaluation of seven dental film processing solutions

In order to determine the effect of 7 dental film processing solutions on the quality of the radiographic image, an aluminium step-wedge phantom was exposed, using Agfa Dentus M2, speed group D, intra-oral x-ray films. The exposures were done under standardized conditions. Processing was carried out, using each of the 7 processing solutions, namely Agfa, Dürr, EBX, Kolchem, MEMS, Premier and Pro-tech strictly in accordance with the manufacturers' recommendations. After the processed films were subjected to densitometric evaluation, a step-wedge curve was drawn for each processing solution. The data pertaining to the radiographic contrast and relative speed values were calculated from the step-wedge curve and, together with the base plus fog values, were tabulated. Kolchem produced the highest radiographic contrast, followed closely by MEMS and Dürr. The relative film speed was almost identical for Kolchem, MEMS and Dürr. Regarding the base plus fog values, all 7 processing solutions were within the acceptable limit of 0.25.     

A radiologic method for determining the thickness of the hard crown tissues

This study describes a radiologic method that provides a reliable evaluation of the thickness of the hard crown tissues of the tooth scheduled for prosthetic and conservative preparation. The first stage consisted of calculating the discrepancy between the actual dimensions of the specimen under examination and the dimensions of the same specimen as measured and radiographed. Some coefficients of distortion were calculated for the distance(s) more usually involved clinically. Radiographs were made by using the "paralleling" technique. In the second stage, radiographs were made of 83 extracted teeth (22 incisors, 12 canines, and 51 premolars). On the resulting radiographs some prefixed distances were measured. Finally, to gain an anatomic comparison of the values obtained radiologically, 24 of the previously radiographed teeth were sectioned along the sagittal plane at the diameter, and measurements were made and compared with the radiologic data to which the correction coefficients had been applied.     

Diagnostic casts--an additional dimension

The indications and usefulness of diagnostic casts are well documented in the literature. A method is presented that enables increased access to the lingual aspect of the casts by sectioning them in a midsagittal plane. The sectioned portions are held together in maximum intercuspation by acrylic keys. The interdigitated casts can thus be examined from all aspects, thereby deriving maximum benefit from them.     

Assessment of the effectiveness of glove use as a barrier technique in the dental operatory

To assess the effectiveness of routine glove use as a barrier technique in the dental operatory, the relationship between frequency of glove use and hepatitis B infection was examined. Hepatitis B screening results and information on infection control practices of 1,109 dentists who attended the 1985 annual session were compiled and statistically analyzed. The results showed that 18% of the dentists wore gloves routinely, 65% wore gloves intermittently, and 17% never wore gloves. Frequency of glove use was related to hepatitis B infection (P less than .01), with dentists who never wore gloves being infected more than twice as often as dentists who wore gloves routinely. Dentists with less frequent glove use and more years in practice had a higher incidence of hepatitis B infection (P less than .0001).     

A clinical evaluation of one and two-appointment root canal therapy using calcium hydroxide

A clinical study using vital maxillary central incisors was performed to evaluate the incidence of postoperative pain after root canal treatment in one- or two-appointments using a calcium hydroxide-containing root canal sealer. No differences were observed between the two groups.