Biomedical subjects

J Chai

Publications and source records attributed to J Chai.

126 records · Page 7Linked to original sources

PubMedDate not supplied

Assessment of shear bond strength between three denture reline materials and a denture base acrylic resin.

PURPOSE: This study reports the effect of five surface treatments on the bond strength established between three denture reline materials and a denture base resin. MATERIALS AND METHODS: Cylindric columns of denture reline materials were bonded to columns of denture base resins that received one of the surface treatments: application of dichloromethane, the monomer of the denture base resin, the recommended bonding agent or the monomer of the denture reline material, polishing with 240-grit silicone carbide paper, and air abrasion. A control group without surface treatment was included for each material. Specimens were immersed in water for 1 day and then thermocycled. The strength at which the bond failed under shear was recorded. RESULTS: None of the surface treatments significantly improved the bond strength of Kooliner. Triad bonding agent and denture base monomer applications most significantly improved the bond strengths of Triad and GC reline, respectively. CONCLUSION: Triad bonding agent and denture base monomer should be used in conjunction with Triad and GC reline, respectively, when relining a denture base resin.

Acrylic Resins↗

PubMedDate not supplied

The mechanical properties of milled and cast titanium for ceramic veneering.

This study compared the mechanical properties of machine-milled pure titanium and cast titanium. The metals were cast or milled to the dimensions of a standard tensile bar pattern. Each group was treated under three different conditions: as-cast (or as-milled), standard heat, and extended heat. Tensile testing found no difference in the mechanical properties of as-cast and as-milled titanium. Heat treatment significantly increased the ultimate tensile strength and the yield strength of cast titanium but had no such effects on milled titanium. There was no significant difference between the two metals in the modulus of elasticity or the percentage of elongation under the three treatment conditions.

Alloys↗

PubMedDate not supplied

A study of the surface hardness and dimensional stability of several intermaxillary registration materials.

This study compared the surface hardness, the effect of time on surface hardness, and the dimensional stability of various intermaxillary relationship registration materials. The Shore hardness values of one zinc oxide-eugenol material, one polyether, and seven poly(vinyl siloxane) materials were obtained at 30 minutes and 24 hours after the start of mixing. The dimensional stability of one polyether and seven poly(vinyl siloxane) materials was measured using a standard mold as described in American Dental Association (ADA) Specification No. 19. All materials exhibited relatively high surface hardness despite some statistical differences among them. Four materials possessed higher surface hardness at 24 hours than at 30 minutes. Although the polyether showed significantly lower dimensional stability than the other materials, all materials satisfied the minimum requirement for Type I elastomeric impression material.

Analysis of Variance↗

PubMedDate not supplied

Marginal fit of machine-milled titanium and cast titanium single crowns.

Eighteen type IV dental stone dies were fabricated from a metal master die that replicated a tooth prepared to receive a metal ceramic crown. They were divided into three groups according to the type of crowns to be made: (a) machine-milled, spark-eroded titanium crowns (Procera); (b) cast titanium crowns; and (c) noble alloy crowns (as the control). The control specimens showed the smallest mean marginal openings at 25 microns and were significantly different from both the machine-milled crowns (54 microns) and the cast titanium crowns (60 microns). The two types of titanium crowns were not significantly different from each other.

Analysis of Variance↗

PubMedDate not supplied

A study of the "thixotropic" property of elastomeric impression materials.

Shear-thinning, the decrease in the apparent viscosity of an impression material under a shear load, is a characteristic of many elastomeric impression materials and improves handling properties. However, it is unknown whether the subsequent viscosity of such material continues to be lower. This study compared the apparent viscosities of five elastomeric impression materials under two conditions. One group of the materials was manually spatulated and injected through an impression syringe before being tested; the other group of materials was manually spatulated only. It was found that the viscosities of these materials were not affected by the shear load applied during syringing.

Dental Impression Materials↗

PubMedDate not supplied

Alternative restorative techniques of the CeraOne single-tooth abutment: a technical note.

The screw-joint stability of single-tooth implant-supported restorations has been shown to be significantly improved with an abutment system (CeraOne) that uses a gold-alloy screw tightened at a prescribed amount of torque. The abutment system requires the cementation of the restoration to the abutment. This negates the possibility of accessing the abutment screw when the removal of the restoration is desired. This article described two alternative restorative techniques to maintain accessibility to the screw joint.

Dental Abutments↗

PubMedDate not supplied

Color stability of low-fusing porcelains for titanium.

The resistance to staining of two low-fusing porcelains (Procera and Duceratin) for use with titanium and one conventional feldspathic porcelain (Vita VMK 68) were examined visually according to a protocol similar to the ADA Specification No. 69. The color deviation was also quantified using a colorimeter. Forty samples of each product were prepared using manufacturer's instructions and the samples divided into two groups of 20. The samples of one group were immersed in methylene blue, and the control group in distilled water. Of the twenty samples from each group, ten were ground to remove the glaze. The color values for each sample were recorded prior to and after immersion in the staining medium. The color deviation value, Delta E, for each sample was calculated. Visually discernible stain was present on the unglazed samples of all three porcelain products immersed in methylene blue. No stain was visually detectable on the glazed samples or the unglazed samples immersed in distilled water for all three porcelain products. The objective evaluation confirmed that the unglazed porcelain products had statistically higher color deviation after immersion in methylene blue.

American Dental Association↗

PubMedDate not supplied

Working times of elastomeric impression materials according to dimensional stability and detail reproduction.

This study was conducted to evaluate the working times of seven elastomeric impression materials according to their detail reproduction and dimensional accuracy. Impressions were made of a standard ADA Specification No. 19 die at 30-second intervals until they were no longer workable. The detail reproduction and dimensional stability of these impressions were evaluated according to the ADA Specification No. 19 criteria and the dimensional stability was analyzed. It was found that the working times of the impression materials according to detail reproduction generally agreed with those estimated according to dimensional stability but not with the manufacturers' suggested working times.

American Dental Association↗

PubMedDate not supplied

Working times of elastomeric impression materials determined by dimensional accuracy.

The working times of five poly(vinyl siloxane) impression materials were estimated by evaluating the dimensional accuracy of stone dies of impressions of a standard model made at successive time intervals. The stainless steel standard model was represented by two abutments having known distances between landmarks in three dimensions. Three dimensions in the x-, y-, and z-axes of the stone dies were measured with a traveling microscope. A time interval was rejected as being within the working time if the percentage change of the resultant dies, in any dimension, was statistically different from those measured from stone dies from previous time intervals. The absolute dimensions of those dies from the rejected time interval also must have exceeded all those from previous time intervals. Results showed that the working times estimated with this method generally were about 30 seconds longer than those recommended by the manufacturers.

Analysis of Variance↗

PubMedDate not supplied

A 5-year prospective multicenter follow-up report on overdentures supported by osseointegrated implants.

This report presents the results of a 5-year prospective multicenter study including nine centers worldwide. A total of 30 patients received 117 Brånemark implants in the maxillae, and 103 patients received 393 implants in the mandibles. According to the protocol, all integrated maxillary implants were to be loaded; however, only two of four mandibular implants were planned for support of the overdentures, leaving the remaining implants covered by mucosa as backup for possible implant failures. Thirty-five patients (26.3%) who were provided with 127 implants (24.9%) were withdrawn from the study. Six patients treated in the maxilla lost all their implants and resumed wearing complete dentures. The cumulative success rates for implants and for overdentures supported by two implants in the edentulous mandible were 94.5% and 100%, respectively. The corresponding cumulative success rates for implants and for overdentures supported by an optimal number of implants in the maxilla were 72.4% and 77.9%, respectively. Significantly better jawbone characteristics at the time of implant surgery were considered to contribute to the better cumulative success rates in the mandibles. Mean marginal bone loss was 0.8 mm (SD 0.8) and 0.5 mm (SD 0.8) for loaded implants during a 5-year period of time in the maxillae and mandibles, respectively. Measurements of the clinical height of the abutment cylinders indicated a mean recession (0.2 mm) of peri-implant mucosa during the follow-up period in the mandibles. Conversely, hyperplasia was observed in the maxillae.

Adult↗

PubMedDate not supplied

Mechanical properties of titanium connectors.

The tensile mechanical properties of welded titanium joints were studied, and intact titanium was used as controls. Welded joints were fabricated with either a stereographic laser-welding technique or a gas tungsten arc welding technique. The effect of heat treatment following a simulated porcelain application was also investigated. Heat-treated laser welds had significantly lower ultimate tensile strengths. Heat treatment had no effect on the modulus of elasticity or elongation, but generally significantly decreased the yield strength of the titanium specimens. The gas tungsten are welding specimens had significantly higher yield strengths and elastic moduli than the other two groups. The elongation of the control specimens was significantly greater than the elongation of the gas tungsten arc welding specimens, which was in turn significantly higher than that of the laser-welded specimens.

Analysis of Variance↗

PubMedDate not supplied

The physical properties of low-fusing porcelains for titanium.

This study compared the firing shrinkages, flexural strengths, and chemical solubilities of two low-fusing porcelains formulated for use with titanium (Procera, Nobel Biocare, Göteborg, Sweden; and Duceratin, Degussa, Plainfield, NJ) to those of a conventional low-fusing feldspathic porcelain (Vita VMK 68, Vident, Baldwin Park, CA). Procera demonstrated the highest mean firing shrinkage and was significantly different from the other two porcelains. There were no significant differences among the porcelains in flexural strength and chemical solubility.

Analysis of Variance↗

PubMedDate not supplied

Prosthodontic treatment, patient response, and the need for maintenance of complete implant-supported overdentures: an appraisal of 5 years of prospective study.

The prosthodontic methods and outcomes of treating 127 patients in nine centres over a period of 5 years is described. The benefits perceived by patients and the changes induced in the denture-bearing tissues and temporomandibular joints are reported. To sustain effective treatment outcomes, the levels of maintenance needed by the overdentures are contrasted for restoration of the edentulous mandibles and maxillae.

Alveolar Bone Loss↗

PubMedDate not supplied

A comparison of the marginal fit of In-Ceram, IPS Empress, and Procera crowns.

The in vitro marginal fit of three all-ceramic crown systems (In-Ceram, Procera, and IPS Empress) was compared. All crown systems were significantly different from each other at P = 0.05. In-Ceram exhibited the greatest marginal discrepancy (161 microns), followed by Procera (83 microns), and IPS Empress (63 microns). There were no significant differences among the various stages of the crown fabrication: core fabrication, porcelain veneering, and glazing. The facial and lingual margins exhibited significantly larger marginal discrepancies than the mesial and distal margins.

Aluminum Oxide↗

PubMedDate not supplied

Flexural strength at the proportional limit of a denture base material relined with four different denture reline materials.

This study evaluated the resistance to plastic deformation under a flexural load (PLf) of a denture base material relined with four different types of denture reline materials. A heat-processed poly(methyl methacrylate) denture base was relined with varying thicknesses of denture reline materials and subjected to a flexural load. The flexural load at the proportional limit (PLf) was recorded. The PLf of the bulk denture base and denture reline materials were also measured for comparison. All relined denture bases showed significantly lower PLf than the bulk denture base. Generally, the PLf of the reline-denture base composite progressively decreased with an increasing proportional thickness of the reline material.

Analysis of Variance↗

PubMedDate not supplied

Effect of water sorption on the resistance to plastic deformation of a denture base material relined with four different denture reline materials.

PURPOSE: The effect of water sorption on the flexural strength at the proportional limit (FSp) of a denture base material relined with four different denture reline materials was studied. MATERIALS AND METHODS: Denture base specimens were relined either after 24 hours or 30 days of water immersion. The relined specimens were tested after another period of 24 hours or 30 days of water immersion. RESULTS: Relined denture specimens generally exhibited lower FSp with an increase in water immersion time and an increase in the thickness of the reline material. CONCLUSIONS: The plasticizing effect of absorbed water molecules explains the general decrease in FSp of immersed relined specimens. The absence of a significant effect that water immersion had on some relined specimens under certain immersion conditions was explained by water sorption into the denture base achieving an equilibrium after a period of water immersion, and the resistance of some reline materials to the effect of water immersion.

Analysis of Variance↗

PubMedDate not supplied

The flexural strengths of denture base acrylic resins after relining with a visible-light-activated material.

PURPOSE: Previous studies disclosed the ability of a light-activated denture reline material to strengthen a particular denture base material. The present study investigated the ability of the reline material to strengthen denture base materials processed by other means. MATERIALS AND METHODS: Four denture base materials were tested for flexural strength at proportional limit (FSpl) with or without being relined. RESULTS: The reline material maintained the FSpl of the microwave-processed and the autopolymerizing denture base materials. It increased the FSpl of the heat-processed and the light-activated denture base materials. CONCLUSION: the light-cured reline material increased the flexural strengths of the heat-processed and the light-activated denture base materials and maintained those of the microwave-processed and the autopolymerizing denture base materials.

Acrylic Resins↗

PubMedDate not supplied

Clinically relevant mechanical properties of elastomeric impression materials.

PURPOSE: This study investigates the modulus of elasticity, yield strength, the strain at yield point, and the tear energy of nine elastomeric impression materials. MATERIALS AND METHODS: The values of the first three variables were computed from a tensile load test of 10 dumbbell-shaped specimens of each impression material. Tear energy was calculated from the results of a standard trousers tear test on 10 specimens of each impression material. RESULTS: A general descending order of modulus of elasticity (rigidity) follows: poly(vinyl siloxane) putty > polyether > polysulfides and the poly(vinyl siloxane) tray and syringeable materials. The descending order of yield strength was: poly(vinyl siloxane) putty > polyether and most poly(vinyl siloxane) tray and syringeable materials > one poly(vinyl siloxane) and the two polysulfides. The general descending order in strain at yield point (strain tolerance) was: two poly(vinyl siloxane) syringeable materials > four poly(vinyl siloxane) materials of various viscosities > polyether and the two polysulfides. Tear energy followed a general descending order of: polysulfides > polyether > poly(vinyl siloxane). CONCLUSION: The difficulty of removing impressions made of the putty or the polyether, and the increased risk of die breakage could be associated with the higher rigidity of these materials. The high strain tolerance of the poly(vinyl siloxane) impression materials allows their removal without distortion from appreciable tissue undercuts. The high tear energy of polysulfides indicates their superiority over other impression materials in their resistance to tear in thin sections.

Analysis of Variance↗