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Biomedical subjects

V B Dhuru

Publications and source records attributed to V B Dhuru.

16 recordsLinked to original sources
PubMed1995

The fracture toughness of various core materials.

PURPOSE: This study determined the fracture toughness of four core buildup materials. MATERIALS AND METHODS: Single-edge notch, bar-shaped specimens conforming to the American Society for Testing Materials standard E-399 were fabricated for a high copper amalgam alloy, two composite resins, and a glass ionomer buildup material. The specimens were stored in air for 1 week and then tested in three-point bending mode with an Instron Universal Testing Machine (Instron Corporation, Canton, MA). RESULTS: Fracture toughness values obtained were as follows: Fluorocore (composite resin; Caulk, Milford, DE), 1.54 MN.m-1.5; Ti-Core (composite resin and titanium; Essential Dental Systems, New York, NY), 1.34 MN.m-1.5; Valiant Ph.D. (amalgam; Caulk), 1.29 MN.m-1.5; and Coreshade Glass Ionomer Base Cement (Shofu Inc, Kyota, Japan), 0.55 MN.m-1.5. CONCLUSIONS: Glass ionomer materials are probably unsuitable as core buildup materials because of their relatively low fracture toughness. Fluorocore, Ti-Core, and amalgam all had fracture toughness values significantly greater than the glass ionomer (P < .01).

Analysis of Variance↗
PubMed1993

Composite microfiller content and its effect on fracture toughness and diametral tensile strength.

Previous studies have examined the relationship between total filler content in hybrid restorative composites and some of their mechanical properties. This investigation evaluated the effect of varying the amount of microfiller in an experimental hybrid composite on fracture toughness (single edge-notch technique) and diametral tensile strength. The microfiller content in the experimental hybrid composite was varied from 0-44 wt% for seven specimen groups, while the total filler content ranged from 77-84 wt%. It was found that 9 wt% microfiller loading produced the highest mean fracture toughness (1.33 MPa.m(1/2)) and 44 wt% loading produced the lowest mean value (0.80 MPa.m(1/2)). Only the 9 wt% microfiller content group differed significantly in fracture toughness from the other specimen groups. The diametral tensile strength displayed only small differences for the range of microfiller content studied with mean values ranging from 42.1-49.6 MPa. Additional research on the viscoelastic properties of these heavily filled hybrid composites may provide some insight into the differences for the fracture toughness and diametral tensile strength results.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1991

Shear, torsional, and tensile bond strengths of ceramic brackets using three adhesive filler concentrations.

The effect of changes in adhesive filler concentration on the shear, torsional, and tensile bond strength of a chemical, a mechanical, and a chemical/mechanical retained ceramic bracket was evaluated. Two hundred ten bovine teeth were bonded with one of three ceramic brackets using a 30%, 55%, or 80% filled adhesive. The brackets were debonded with a shear, torsional, or tensile force to test the bond strength and the site of bond failure. No significant difference was found in the shear, torsional, or tensile bond strength of each ceramic bracket type in relation to changes in the adhesive filler concentration. However, there was a trend toward increased bond strength with increasing filler concentration. Combining the data according to adhesive type revealed that the 80% filled adhesive displayed a significantly greater shear bond strength than the 30% or 55% filled adhesive and a greater torsional bond strength than the 30% filled adhesive. This supports the hypothesis of increased bond strength with increased adhesive filler concentration. The mechanically retained ceramic bracket showed greater shear bond strength and maximum shear bond strength in torsion than the chemical or chemical/mechanical retained ceramic bracket. The tensile bond strength of the mechanically retained ceramic bracket was similar to that of metal brackets reported in other studies, and the failure site was at the bracket-adhesive interface.

Adhesives↗
PubMed1989

Infection control in North American dental schools.

A questionnaire concerning infection control issues was sent to all North American dental schools in 1987. The results were compared with a similar survey conducted by the same authors in 1982. The purposes of the survey were to identify changes that have occurred in dental school infection control policies in the past six to seven years, and to study strengths and weaknesses of current policies. The results of the survey indicate a much greater emphasis on instrument sterilization and the use of barriers during dental treatment than in 1982. Compliance with the policy is not always satisfactory, however. It also shows some inconsistency and confusion in areas dealing with hepatitis B and HIV carrier patients and dental school personnel. Several respondents included written infection control protocols with the questionnaire. Information gained from the survey and the enclosures were used to develop guidelines to help schools improve and update their infection control policies.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Accuracy of impression materials for complete-arch fixed partial dentures.

The accuracy of 12 impression materials of six different types were studied by using complete-arch FPD impressions. Sixty impressions were made of a Columbia dentoform maxillary model with complete cast crown abutment preparations on the canines and the second molars. A one-piece casting was constructed by connecting the four individual castings made for the four abutment teeth. The master prosthesis was seated on the stone casts produced from the impressions. The marginal adaptation on the four abutments was then evaluated with a travelling microscope. The individual marginal adaptation of the four castings on the abutments was also examined after sectioning the four joints. The following conclusions were drawn. 1. The polyethers produced the most accurate complete-arch replicas. The second most accurate were the vinyl polysiloxanes, followed by the polysulfides and the irreversible-reversible hydrocolloids. The least accurate were the reversible hydrocolloids and the irreversible hydrocolloids. 2. The polyether impression materials exhibited the most consistent accuracy for a master cast to fabricate a complete-arch FPD.

Alginates↗
PubMed1986

The fracture toughness of repaired composite.

The fracture toughness (K'IC) at the interface formed between a composite substrate and more recently placed composite has been measured to determine the strength of the repair. The substrate material was 24 h old at the time of the repair and the fracture toughness of the repair was measured 24 h later. Five composite products were selected for repair by using either that particular product or one of the others. Repairs were made to clean fractured surfaces, and these after contamination with artificial saliva. The fracture toughness factor of any repair was significantly less than that for the respective control. The effect of surface contamination proved highly significant and reduced the fracture toughness. An interaction existed between adherend (substrate) and adhesive (addition) materials. Compatibility between these for matrix and initiation chemistries did not appear to be significant.

Acrylic Resins↗
PubMed1985

Comparison of accuracy of multiunit one-piece castings.

An investigation was conducted to evaluate the accuracy of one-piece castings of FPDs consisting of three, four, and five units with a ceramometal alloy cast in a large circular ring. A three-piece aluminum mold with stainless steel dies simulating the various lengths of the FPDs was used. A total of 18 castings, six castings for each FPD, were fabricated. Marginal discrepancies of the castings on the dies and the length of the castings were compared before and after sectioning the castings at the connectors. The following conclusions were drawn from the study. Seating of the castings improved approximately 50% after sectioning, which indicates that the castings were distorted. The distortion was a three-dimensional phenomenon, with the greatest discrepancy on the mesiogingival surface of the anterior retainer and on the distolingual surface of the posterior retainer. The distortion was least for the three-unit FPDs and greatest for the five-unit FPDs. The lingual-facial diameter of the castings at the gingival axial line angle was significantly larger than the dies in most cases. The mesiodistal diameter of the castings at the gingival axial line angle was smaller than that of the dies but was only significant with the three-unit FPDs. Although the castings were slightly oversized or undersized, the primary reason the castings did not seat was warpage.

Dental Alloys↗
PubMed1983

Infection control in North American dental schools.

Treatment of patients with transmissible infections is a particular concern in an institutional setting. This paper discusses the results of a questionnaire relating to infection control that was sent to all North American dental schools. The purpose of the survey was to aid in the development of a comprehensive protocol at Marquette University for treating patients with transmissible infections and, in particular, hepatitis B carriers. Currently, the dental community is reluctant to treat patients with a history of hepatitis and hepatitis B carriers. The protection offered by the recently available hepatitis B vaccine should contribute greatly to the reduction of transmission of hepatitis B. It is emphasized that the use of this vaccine in dental schools in no way obviates the need for meticulous infection control protocols.

Canada↗
PubMed1979

Axial stiffness of retention pins in human dentin.

Axial deflections of pins, anchored in specimens of human dentin by five different procedures, were measured by a specially constructed apparatus to an accuracy of 0.1 mu. Axial stiffness values calculated from these measurements were found to be significantly different for different methods of anchorage. Cemented pins displayed the lowest axial stiffness when compared with friction-locked and self-threading pins.

Acrylic Resins↗
PubMed1978

Criterion-oriented grading system for preclinical operative dentistry laboratory course.

The object of this study was to evaluate instructor reliabilities when using empirical or traditional and criterion-oriented grading methods. To do so, 52 sample preparations made in plastic teeth by freshman dental students in the preclinical operative dentistry laboratory course were graded by 12 instructors. The preparations included those for amalgam, inlay, and gold foil restorations. The instructors were divided into two groups according to their teaching experience. Intraclass correlation coefficients were calculated by using a one way analysis of variance technique. The criterion method, in general, yielded greater intraclass correlation coefficients. The increase in the intraclass correlation coefficient was found to be significant at the alpha = 0.10 error level for all restorations judged by experienced instructors. The different degrees of increase in correlation may be attributed to the vary ing clinical biases of the instructors and the differences in the types of preparations.

Analysis of Variance↗
PubMedDate not supplied

Fracture toughness of high alumina core dental ceramics: the effect of water and artificial saliva.

The fracture toughnesses of two high alumina core ceramics were determined by using the single edge notched specimen method. Measurements were made in air, water, and artificial saliva. Fracture toughnesses of 1.89 and 1.75 MPa.m1/2 were obtained for Cerestore and Vitadur N samples, respectively, tested in air. Values obtained from Vitadur N samples that were tested in deionized water were significantly lower than those that were measured in air. Values for samples of both ceramics that were tested in artificial saliva were not significantly different from those that were tested in air. The fracture mode was a combination of intergranular and transgranular for Cerestore and predominantly transgranular for Vitadur N.

Air↗