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Biomedical subjects

D H Retief

Publications and source records attributed to D H Retief.

At least 55 records · Page 3Linked to original sources
PubMed1990

Effects of etchant concentration and duration on the retention of orthodontic brackets: an in vivo study.

Etching of enamel before the bonding of orthodontic attachments is usually done with a solution of 37% H3PO4 for 60 seconds. The purpose of this study was to evaluate the effects of etchant concentration and duration on the clinical retention of bonded orthodontic attachments. Two randomly selected groups of orthodontic patients participated in the study. In both groups, teeth in contralateral quadrants, excluding the molar teeth, were bonded. In the first group, 158 teeth were etched with a solution of 37% H3PO4 for 60 seconds, and 155 teeth were etched with 37% H3PO4 for 15 seconds. In the second group, 196 teeth were etched with 37% H3PO4 and 196 teeth with 15% H3PO4, both for 60 seconds. Conventional edgewise mechanotherapy was used in both groups of patients. After 24 months of treatment, in the first group, 8 brackets were dislodged when etched with 37% H3PO4 for 60 seconds and 9 when etched with 37% H3PO4 for 15 seconds. In the second group, 6 brackets were dislodged when etched with 37% H3PO4 for 60 seconds and 13 were dislodged when etched with 15% H3PO4 for 60 seconds. Reducing the etching time of 37% H3PO4 from 60 seconds to 15 seconds or reducing the acid concentration from 37% to 15% H3PO4 applied for 60 seconds had no significantly different effect on the retention of bonded orthodontic attachments. The results suggest that the reduction of etchant concentration and the duration of etching in orthodontic bonding should be considered.

Acid Etching, Dental↗
PubMed1990

Shear bond strength of light-cured glass ionomer to enamel and dentin.

The shear bond strengths of a light-cured glass-ionomer cement to enamel and dentin were determined with use of extracted human maxillary permanent canines and molars. Bonding sites on the ground, etched enamel and ground dentin surfaces were demarcated by the punching of a hole, 3 mm in diameter, in an adhesive tape. The mixed glass-ionomer cement was transferred to the demarcated site, cured by exposure to visible light for 30 s, and the cement surface treated with Scotchprep Dentin Primer followed by Scotchbond 2 Light Cure Dental Adhesive. The embedded teeth were positioned in an assembly apparatus, and Silux composite was bonded to the glass-ionomer-cement surfaces. The specimens were disassembled after 15 min and subjected to a shear load (in an Instron machine) immediately after disassembly; after storage in water at 37 degrees C for 24 h, without and with temperature cycling; and after storage in water for four weeks, without and with temperature cycling. The shear bond strength of the glass-ionomer cement to etched enamel was in the order of 12 MN.m-2, and to dentin it was 9 MN.m-2. Temperature cycling and duration of storage had no adverse effect on the shear bond strength. The enamel and dentin aspects of fractured test specimens were examined, and the percentage of the bonding area that failed in the cement was estimated. Most of the test specimens failed partly at the enamel and dentin interfaces and within the glass-ionomer cement.

Analysis of Variance↗
PubMed1990

Shear bond strengths to dentin and fluoride release from fluoride-containing liners.

The purpose of this study was to determine the shear bond strengths of five commercially available fluoride-containing restorative systems to dentin and to evaluate the fluoride release from them. The five systems evaluated were: (A) Vitrabond/Silux; (B) Zionomer Powder Liquid/Perfection; (C) Zionomer Paste Paste/Perfection; (D) TimeLine/Prisma-Fil; and (E) GC Dental Cement/Fuji II. Eighteen test specimens were prepared on the dentin surfaces of extracted human permanent first and second molars ground on 600 grit SiC paper with each system. The bonded cylinders were removed from the assembly apparatus 15 minutes after cure, stored in physiological saline at 37 degrees C for 24 hours and subjected to a shear load at 0.5 mm/min. Five cylindrical specimens were prepared for each system, the discs were suspended in 25 microL glass distilled water and the fluoride release (microgram F/mm2) determined at daily intervals for 15 days and then after 30 and 90 days. The data were analyzed by a one-way analysis of variance and Duncan's multiple range test. The following shear bond strengths (Mean +/- SD) were recorded (MPa): A: 8.86 +/- 1.49; B: 4.24 +/- 1.23; C: 4.41 +/- 1.39; D: 3.85 +/- 1.60; E: 4.81 +/- 1.21. With all the systems, the fluoride release dropped sharply during the first 7 days and then remained constant. The shear bond strength and the fluoride release from Vitrabond/Silux were significantly greater than that of the other systems.

Acrylic Resins↗
PubMed1990

Shear bond strengths of the tenure dentin bonding systems.

A third generation dentinal bonding system, Tenure Solution dentin bonding system, has recently become commercially available. The original system has been modified twice. The objectives of this in vitro study were to determine the shear bond strengths of the three systems to dentin 15 minutes after specimen preparation, after 24 hours storage in physiological saline at 37 degrees C with and without temperature cycling, and after 4 weeks storage with and without temperature cycling. The shear bond strengths decreased with duration of storage but of each storage interval temperature cycling had no adverse effect on shear bond strength.

Benzoates↗
PubMed1990

Extracted human versus bovine teeth in laboratory studies.

The purpose of this study was to determine the shear bond strengths and microleakage of Scotchbond 2/Silux to dentin and to evaluate resin penetration into the dentinal tubules of human and bovine teeth. The shear bond strengths (SBS) were determined on occlusal dentin of 25 human permanent molars (H) and on facial dentin of 25 bovine permanent mandibular incisors (B). The test specimens were stored in physiological saline at 37 degrees C for 24 hours prior to the application of a shear load in an Instron machine at a speed of 0.5 mm/min. Microleakage (ML) of Class V restorations placed on the facial surfaces of the roots of 15 human canines (H) and 15 bovine incisors (B) was determined quantitatively. The restored teeth were thermocycled x500 in 2% methylene blue solution, the dye extracted in 50% HNO3 and the dye concentrations determined spectrophotometrically. The resin penetration into the dentinal tubules was evaluated in the SEM. The following results were obtained: SBS (MPa): H, 6.2 +/- 2.9; B, 4.4 +/- 1.2; ML (microgram dye): H, 4.7 +/- 3.2; B, 15.9 +/- 10.5. The data were analyzed by t-test. The shear bond strength of Scotchbond 2/Silux to human dentin was significantly greater (P = 0.0096) and the microleakage significantly less (P = 0.0004) than to bovine dentin despite the fact that the restorative system penetrated more densely into bovine dentin. The use of bovine teeth instead of human teeth in these types of tests is not indicated.

Age Factors↗
PubMed1990

Laboratory study of the Herculite XR system.

The shear bond strengths of the Herculite XR system to dentin were determined the quantitative microleakage of Class V restorations in dentin evaluated; the fluoride release from the XR-Ionomer determined, and fractured test specimens depicting various failure patterns examined in the scanning electron microscope. The shear bond strength of the XR-Ionomer to dentin was 6.6 +/- 1.7 MPa and the Herculite XR 15.4 +/- 3.7 MPa. Sixteen of the 20 Herculite XR test specimens fractured in dentin. The quantitative microleakage of Class V Herculite XR restorations in dentin was 2.22 +/- 1.94 micrograms dye which was significantly reduced to 0.91 +/- 0.63 micrograms when the XR-Ionomer was placed in the floors of the preparations. The fluoride release from the XR-Ionomer dropped sharply during the first 6 days after which it reached a plateau at approximately 0.5 microgramsF.mm-2.

Composite Resins↗
PubMed1990

Marginal leakage and marginal gap dimensions of three dentinal bonding systems.

Standardized cylindrical Class V preparations, 3 mm in diameter and 1.5 mm deep, were made on the roots of 60 extracted human maxillary permanent canines. The teeth were restored with Scotchbond 2/Silux (S); Gluma/Lumifor (G); and Tenure/Perfection (T), respectively. The root apices were sealed with Copalite/amalgam and two coats of nail varnish applied to the teeth except for 1 mm around the restorations. For the qualitative microleakage evaluation the teeth were thermocycled x500 in 0.5% basic fuchsin between 8 degrees C and 50 degrees C and for the quantitative microleakage evaluation in 2% methylene blue solution. The marginal gap dimensions were measured on cylindrical restorations placed on the facial surfaces of ground root surfaces of 30 teeth. Epoxy replicas were made of the restorations, coated with gold/palladium and examined with the SEM. The maximum marginal gap dimensions were measured. The data were analyzed by ANOVA, Duncan's and their nonparametric analogues. In the qualitative microleakage evaluation the total microleakage was: S: 16; G: 50; T: 18. The quantitative microleakage (micrograms) was: S: 3.1 +/- 2.9; G: 16.1 +/- 5.3; T: 4.4 +/- 4.1. The maximum marginal gap dimensions (microns) were: S: 4.1 +/- 3.6; G: 9.3 +/- 3.4; T: 16.4 +/- 7.0.

Analysis of Variance↗
PubMed1989

Effects of phosphoric acid concentration and etch duration on the shear bond strength of an orthodontic bonding resin to enamel. An in vitro study.

The purpose of this in vitro study was to determine the effects of phosphoric acid (H3PO4) concentration and duration of etching on the shear bond strength of an orthodontic bonding resin to enamel. Nine bonding procedures, each involving 18 extracted human maxillary permanent canines, were used. Ground enamel surfaces were etched with a 37% H3PO4 solution, a 15% H3PO4 gel, or a 5% H3PO4 solution for 60, 30, and 15 seconds, respectively. Cylinders of an orthodontic bonding resin, Concise, were prepared in a special device. The test specimens were disassembled 15 minutes after preparation and stored in distilled water at 37 degrees C for 24 hours. A shear load was applied to the bonded cylinders at a crosshead speed of 0.02 in.min-1 in an Instron testing machine, and the shear bond strengths were calculated and expressed in MN.m-2. A two-factor analysis of the data showed that the H3PO4 concentration had no significant effect on the shear bond strength, but the duration of etching affected shear bond strength significantly. The enamel aspects of the fractured test specimens were examined microscopically and the percent failure within the bonding resin at the bonding sites estimated. The correlation between shear bond strength and percentage failure within the bonding resin was not significant. The effects of the nine etching procedures on ground and unground enamel surfaces were studied by scanning electron microscopy. The etching procedures produced well-defined etching patterns on both ground and unground enamel surfaces.

Acid Etching, Dental↗
PubMed1989

In vivo study on the prevention of postradiation caries.

Postradiation caries is usually prevented by the application of topical fluorides (F) at high concentrations. The aim of this study was to develop an optimal preventive program for postradiation caries by evaluating the effects of F concentration and application procedures in subjects with radiation-related xerostomia. Six ground enamel slabs were mounted on each side of the lower denture of each of 7 xerostomia patients. Four procedures were used: no F exposure (control), neutral F gel applied every 2nd day or weekly, and a daily rinse with a F mouthwash for a period of 6 weeks. The enamel slabs were analyzed at weekly intervals by scanning optical monitoring, longitudinal microradiography, and scanning electron microscopy. In addition, hardness measurements were performed on the slabs. F analyses of the enamel slabs were done prior to their insertion in the appliances and after 6 weeks of intraoral exposure. In the control experiments severe demineralization of enamel occurred within 6 weeks. Application of F gel or the use of the F mouthrinse resulted in a significant inhibition of the demineralization process. Of the procedures evaluated, F gel applied every 2nd day was the most effective in preventing the onset of postradiation caries.

Aged↗
PubMed1989

The effect of storage media and duration of storage of extracted teeth on the shear bond strength of Scotchbond 2/Silux to dentin.

The objective was to determine the effect of storage media and the duration of storage of extracted teeth on the shear bond strength (SBS) of Scotchbond 2/Silux to dentin. Extracted human mandibular and maxillary first permanent molars were stored in buffered formalin (A), 1% chloramine (B), 70% ethanol (C), physiological saline (D), or 0.05% thymol (E). Fifteen test specimens were prepared on teeth stored in each medium two days after extraction (Procedures A1 to E1) or after six months storage (Procedures A2 to E2). The teeth were embedded in brass tooth cups and the occlusal surfaces ground wet on 180 and then 600 grit SiC immediately prior to the preparation of a test specimen. The Scotchprep Primer and the Scotchbond 2 Adhesive were applied to the dentin surfaces as directed by the manufacturer. Cylinders of Silux Composite were bonded to the treated dentin surfaces in a special device. The specimens were removed 15 minutes after cure and stored in distilled water at 37 degrees C for 24 hours. A shear load was applied to the bonded cylinders in an Instron machine at a crosshead speed of 0.02 inch.min-1. The SBS were calculated and expressed in MN.m-2. The data were analyzed by ANOVA and Duncan's multiple range test at the 5% level of significance.2+e mean SBS + SD

Bisphenol A-Glycidyl Methacrylate↗
PubMed1989

Effect of adhesive thickness on the shear bond strength of Scotchbond 2/Silux to dentin.

Seventy-five extracted human permanent molars were embedded in brass cups with cold-cure acrylic. Immediately prior to the preparation of a test specimen, the occlusal surface was ground wet on 180 followed by 600 grit SiC to expose dentin. The Scotchprep Dentin Primer was applied to the dried dentin surface with a brush for 60 seconds, and dried with compressed air for 15 seconds. The tooth was mounted in a special device containing a split Teflon mold with a circular hole, 3.5 mm in diameter and 5 mm deep, and A:0.5 microL (50 microns), B:1.0 microL (100 microns), C:2.5 microL (250 microns), D:5 microL (500 microns) or E:10 microL (1000 microns) Scotchbond 2 pipetted into the teflon mold. The adhesive was cured by visible light for 30 seconds. Three increments of Silux were transferred to the Teflon mold, compressed firmly, and each cured for 30 seconds. The test specimens were disassembled 15 minutes after cure and stored in distilled water at 37 degrees C for 24 hours. A shear load was applied via a knife-edge rod in an Instron machine. The shear bond strength was expressed in MPa. The data were analyzed by ANOVA and Duncan's multiple range test. The mean (+/- SD) of the shear bond strengths were: A: 8.8 (3.5), B: 7.9 (2.7), C: 6.8 (2.5), D: 8.1 (4.2), E: 5.3 (2.4). Adhesive thickness from 50 microns to 500 microns (A, B, C and D) had no significantly different effect on shear bond strength. An adhesive thickness of 1000 microns resulted in a significant reduction in shear bond strength.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1989

Adhesion to enamel and dentin.

The physical and chemical properties of restorative materials and procedures that influence the extent of microleakage at the tooth/restoration interface are discussed. Adhesion to enamel is achieved and microleakage at the enamel/restoration interface has been controlled by acid etching enamel surfaces with orthophosphoric acid. The acid concentration and the duration of etching are reviewed. Adhesion to dentin and microleakage at the restoration/dentin (cementum) interface are more difficult. The development of dentin bonding agents and the tremendous advances made with these restorative systems are reviewed. Particular attention is directed towards the Gluma/Lumifor dentin bonding restorative system and the development of an experimental conditioning solution for both enamel and dentin.

Acid Etching, Dental↗
PubMed1988

A model to investigate xerostomia-related dental caries.

The aim of this study was to develop an in vivo model in which onset, progression, and prevention of xerostomia-related dental caries can be studied. The progress of the caries process was investigated on ground and polished human enamel blocks placed in the lower denture of 7 edentulous subjects suffering from xerostomia. During a period of 6 weeks the samples were analyzed at weekly intervals by means of scanning optical monitoring, scanning longitudinal microradiography, scanning electron microscopy, and hardness measurements. Although the indentation length increased significantly within 2 weeks, no demineralization could be yet observed with scanning optical monitoring, longitudinal microradiography, and electron microscopy in most samples. Starting from the 3rd week a progressive demineralization could be observed by all methods. The mineral loss (hydroxyapatite) in the 3rd week was 0.0126 kg.m-2 (median) which increased to 0.0761 kg.m-2 after 6 weeks. Scanning electron microscopy showed a destruction which resembled that of natural xerostomia-related dental caries. From this study it may be concluded that the in vivo model developed is suitable for studying onset, progression, and prevention of xerostomia-related dental caries.

Aged↗