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Biomedical subjects

R Grajower

Publications and source records attributed to R Grajower.

At least 19 recordsLinked to original sources
PubMed1989

Improving the fit of crowns with die spacers.

This investigation studied the dependence of seating crowns on the thickness of layers of spacers applied to dies. Extracted molars were prepared to designated taper angles. Artificial stone dies were prepared in polyether impressions of tooth preparations and covered with one to five layers of new or old spacer material in a predetermined manner. Wax patterns were invested to obtain a uniform and low expansion. Crowns were cast, luted to the teeth, invested in acrylic resin, ground parallel to the axes of the teeth, and inspected microscopically. The average thickness of layers of new and old spacer material was determined. The application of spacers up to the shoulder margins of dies decreased the elevation of the casting above the margin of the tooth preparation until an average minimum elevation above the shoulder of the preparation was obtained. A further increase in the spacer thickness did not affect the elevation, but increased the cement thickness at the axial walls. The average minimum elevation results mainly from individual protrusions on the casting surface. The optimum thickness of the spacer results in the minimum elevation at the margin together with a low cement thickness at the axial walls. Leaving the cervical part of the axial walls near the margin uncovered with spacer negates the effect of a thick spacer on the remaining die surface almost completely and is therefore contraindicated.

Cementation↗
PubMed1989

Linings and caries in retrieved permanent teeth with amalgam restorations.

Possible correlations between the presence or position of cavity linings and the incidence of caries were studied in a sample of 57 extracted permanent teeth with amalgam fillings. Linings could be detected if their thickness was greater than approximately 20 microns, and if they were observed on 74% of the teeth. On 53% of the teeth caries were found adjacent to the restorations, and on 11% not adjacent to the restorations. The incidence of adjacent caries on the teeth with lined cavities was not lower than on the unlined ones. In 36% of the teeth with linings, evidence was found for washout of linings which had been present at the cavosurface margin. These teeth showed a significantly higher incidence of adjacent caries than the unlined ones. Carious sites associated with washout of linings were found in 31% of the lined specimens.

Dental Amalgam↗
PubMed1989

Clinical, radiographic, SEM evaluation and assessment of microleakage of Class II composite restorations.

The influence of incremental or bulk filling techniques, and reapplication of unfilled resin (impregnation) to the margins with an enamel bonding agent, on marginal adaptation was evaluated in Class II composite restorations by clinical, radiographic, scanning electron microscope (SEM) and dye penetration techniques. Cavities were prepared in 80 extracted permanent posterior teeth. All cavity walls were treated with polyacrylic acid for 10 seconds. The enamel was etched for 1 minute, rinsed, dried, and lined with Scotchbond. Forty cavities were filled by increments of P30 and 40 cavities in bulk. The margins of the restorations of 20 teeth in each group were re-etched for 30 seconds and Concise Enamel Bond reapplied. The clinical scores were excellent for all restorations. Radiographic examination showed twice as many bubbles in the incrementally filled restoration than in the group filled in bulk. In 53 teeth, a radiolucent area between the dentin and the restorative material was found. After sectioning, this area was found to correspond to a hard material. The SEM revealed excellent margins in the groups of teeth that were impregnated with an unfilled resin, whereas 13 teeth without impregnation showed defective margins. The dye penetration, as a test for marginal leakage, was minimal at the occlusal surface of all teeth. At the cervical surface, 10.5% of the impregnated teeth showed severe dye penetration compared to 18% of the nonimpregnated teeth. No correlation was found between dye penetration at the cervical surface and the thickness of the residual enamel in this area.(ABSTRACT TRUNCATED AT 250 WORDS)

Composite Resins↗
PubMed1988

The amalgam margin angle, marginal breakdown and adjacent caries in occlusal enamel, a pilot study on extracted teeth.

The object of this study was to determine for amalgam restorations the relationship between marginal breakdown and (i) over- or undercarving; (ii) the amalgam margin angle (AMA); and (iii) the incidence of carious occlusal enamel adjacent to the restoration. Fifty-two extracted human teeth with occlusal amalgam fillings from the Chicago (C) area and forty-three teeth from the Jerusalem (J) area, were examined with a probe. Employing common clinical criteria, it was found that replacement of the fillings was indicated due to extensive marginal defects, in 45% of the C teeth, and 41% of the J teeth. The occlusal amalgam margins and the incidence of caries adjacent to these margins were studied on facio-lingual sections. The incidence and the average AMA values for six margin types were measured on random sections and were found to be: all margins (100%, 67 degrees); intact flush margins (31%, 69 degrees); fractured flush margins (21%, 56 degrees); undercarved margins which fractured (22%, 74 degrees), or did not fracture (9%, 80 degrees) near the cavity margin; margins with amalgam deficiencies (12%, 62 degrees); and margins with separation between enamel and amalgam by remnants of linings (5%). Marginal breakdown was found in 42% of the margins and was associated mainly with flush carving at low AMAs, and with broken flashes resulting from undercarving. Occlusal carious enamel was detected on 19% of the J teeth and none of the C teeth. Sixty-three per cent of these lesions were associated with fractured undercarved margins.

Chicago↗
PubMed1985

Effect of manipulative variables on the accuracy of crown wax patterns.

An instrument was developed to carve wax patterns in a reproducible manner. The methods of wax application to the die and wax removal during carving were similar to routine laboratory procedures. The wax patterns were invested in stone with the dies on which they were prepared, and sectioned to allow the determination of their adaptation on sectioned samples. Shrinkage of wax patterns on dies was found to create a marginal gap at shoulders and bevels. Further shrinkage observed after removal from the die was attributed to relaxation of elastic stresses in the wax. Carving of bevels improved adaptation to the die for samples with large gaps at the shoulder. This improved adaptation can be attributed to plastic deformation in the wax bevel. Remodeling of pattern margins was found to improve adaptation to the die, especially if carried out after the pattern was removed and replaced on the die. Remodeling the margin should involve heating with a spatula of a narrow band of wax around the margin up to the axial die wall over the entire shoulder width.

Chemical Phenomena↗
PubMed1985

Fit of crown wax patterns after removal from the die.

The effects of loading the wax pattern before investment was determined. Various loads were placed on the pattern after its margin was remodeled. The patterns were replaced on the die with a load of 50 gm before investment. For loads of 0, 250, and 1000 gm, the average elevation of the pattern on the die was found to be greater by 29, 56, and 19 micron, respectively, than before removal from the die. Repetitive loading showed that the plastic deformation in wax was less in the second than in the first cycle for a specific load. This decrease in plastic deformation may explain the improved adaptation of the pattern after a load of 1000 gm.

Crowns↗
PubMed1985

The effective minimum cement thickness of zinc phosphate cement for luted non-precious crowns.

Non-precious metal crowns were prepared for natural teeth which were ground to a taper angle of 5 degrees. The movement of the crowns on teeth during repeated try-on seating was measured with a micrometer. Increasing the applied load from 2 to 10 kg resulted in an average crown movement of 63 micron. For most samples this movement continued when try-on was repeated. Casting irregularities were found to create furrows on some regions of the axial tooth surface during try-on seating. The diameter of the ADA specification consistency disk for zinc phosphate cement was found to depend strongly on the P:L ratio and the ambient temperature. The castings were cemented with zinc phosphate cement of controlled consistency. Cementation with a load of 10 kg gave rise to an average crown elevation of 54 micron and a range of measurements between -8 and 113 micron. The effective minimum cement thickness corresponding to this average was calculated to be 4.7 micron. Small negative values of elevation were attributed to deepening of tooth furrows during cementation. An analysis is given of data from the literature, relevant to the cement flow and irregularities in cement thickness.

Cementation↗
PubMed1984

Dycal: physical properties and resistance to amalgam condensation.

Simulated clinical experiments showed that the hand condensation of amalgam on single or multiple layers of Dycal in Class II cavities does not cause significant fracture or displacement of the liner. Cyclic loading experiments demonstrated that the plastic deformation of Dycal decreases and its stiffness increases with each additional load cycle. This indicates that minor displacement of Dycal during amalgam condensation occurs mainly during the first thrusts with the condenser, and that its mechanical properties are improved by repeated condensation with heavy pressure. Cyclic loading tests may be of considerable value in the evaluation of the performance of liners during amalgam condensation.

Calcium Hydroxide↗
PubMed1984

The transverse strength of acrylic resin strips and of repaired acrylic samples.

A method was developed for measuring the transverse strength of repaired acrylic samples at a single butt joint. The strength was determined for samples prepared from two types of heat polymerizing resins and two types of repair resins. The temperature elevation during curing of the repair resins was determined. Cross-linking of the resins was evaluated by immersion of samples in solvents. The appearance of the bead microstructure after various treatments was considered to indicate relaxation at the sample surface. Repaired samples of the heat polymerizing resin which exhibited relaxation after immersion in monomer, had a lower strength than samples prepared from the resin for which relaxation was not observed, although both resins were cross-linked to a similar extent. The application of pressure during curing increased the strength of the samples repaired with the rapid curing, cross-linked, repair resin. The strength of the samples repaired with the uncross-linked, slow curing, repair resin was affected by pressure only if the insertion of the repair resin between the sample parts was delayed after mixing. Variations in the powder to liquid ratio of the uncross-linked repair resin did not affect the sample strength. Wetting of the sample parts with monomer before repair, and variations in the curing temperature did not affect the sample strength for the investigated resin combinations.

Acrylic Resins↗
PubMed1984

Observations on a calcium hydroxide lining in retrieved deciduous teeth, with proximal amalgam fillings.

The integrity and thickness of Dycal linings were determined on exfoliated deciduous teeth in which proximal fillings had been placed in vivo. The teeth remained in the oral cavity for more than 18 months after placement of the restorations. The average lining thickness was found to be 114 microns. One-third of the samples showed evidence for the presence of Dycal at the gingival floor, up to the proximal tooth wall. Wash-out of the lining was observed for most teeth in which Dycal had been present near the proximal tooth wall. Incipient caries formation, associated with wash-out of the lining, was noted in a few samples. Contact between amalgam and dentine was frequently observed at the line angle, pulpal floor and axial wall.

Calcium Hydroxide↗
PubMed1983

Marginal adaptation of glass-ionomer cements.

The effect of thermocycling on the marginal adaptation of two glass-ionomer cements was determined by means of scanning electron microscopy. Small gaps in the cement as well as at the enamel-cement interface were observed after curing, but these phenomena were not enhanced by thermocycling. Localized areas of surface deterioration were observed for both cements after thermocycling.

Dental Bonding↗
PubMed1983

A mathematical treatise on the fit of crown castings.

A mathematical analysis was given to calculate the marginal cement thickness, Dm, of a cemented crown casting as a function of the minimum cement film thickness, F; the width, W, of the base of the tapered region; the width, W', at the bevel (if present) of the tooth preparation; the taper angle, theta; the marginal angle, beta; and the compensatory expansion, X, of the metal investment system: Dm = [F/sin theta - 0.5(X - 1) (W cot theta - W' cot beta)] sin beta. The elevation of the cemented casting, delta H, above the tooth preparation may also be obtained from this equation by substituting beta = 90 degrees, in which case Dm = delta H. The effect of the preparation of a chamfer margin or bevel on the marginal film thickness may be calculated from this equation. An additional analysis showed that the minimum marginal cement thickness, Dm = F, can be obtained for a shoulder preparation and X values of common metal-investment systems by applying a spacer of appropriate thickness on the entire occlusal and axial walls of the die. This renders the preparation of bevels superfluous. The thickness of the spacer should allow for the cement film thickness, roughness of the tooth and casting surfaces, dimensional inaccuracies of the die, and distortions of the wax pattern. If the spacer is thicker than required, a minimum value of Dm is still obtained for preparations without bevels. If the horizontal part of the die shoulder is covered as well with the spacer, a greater spacer thickness is required to obtain a minimum value of Dm than if the spacer extends to the end of the axial walls. In this case the spacer thickness should be greater on the occlusal die wall than on other regions of the die for values of X smaller than 1. The spacer should also be thicker in the occlusal region if restriction of the investment setting expansion by the wax pattern occurs mainly in this region.

Cementation↗