Biomedical subjects

A C Shortall

Publications and source records attributed to A C Shortall.

At least 37 records · Page 2Linked to original sources

PubMed1997

Clinical performance of porcelain laminate veneers. A retrospective evaluation over a period of 6.5 years.

Three-hundred and seventy-two porcelain laminate veneers were fitted to defective and discoloured teeth in 102 patients. Ninety per cent of the restorations were fitted to unprepared teeth. Restorations were reviewed up to 78 months after cementation. Survival probabilities were calculated using the Kaplan-Meier method. Results showed higher rates of failure and problem development in veneers fitted over existing restorations and in those fitted by inexperienced operators. A considerable number of veneers suffered minor problems that were successfully repaired.

Adolescent↗

PubMed1996

Light-activated restorative materials: a method of determining effective radiation times.

The aim of this investigation was to develop a test method that allows an operator to determine the appropriate radiation time for any light-activated material, irrespective of the characteristics of the light-activation unit or material to be cured. A computer-based radiometer was used to monitor the radiation energy transmitted through a number of light-activated materials during irradiation, and a method was devised to determine the predicted radiation time for any given material/shade/light unit combination based upon the change in transmission against time that occurred as the material polymerized. Additional test samples were cured for the predicted radiation times and upper and lower surface microhardness measurements were taken to verify the validity of the test method. Predicted times varied from 16 to 44 s for 2 mm thick samples of the materials/shade/light-activation units used. This method may allow operators to determine appropriate radiation times for any new light-activated restorative they decide to use with their own light-activation unit.

Amplifiers, Electronic↗

PubMed1996

Effect of light intensity on polymerisation of three composite resins.

The polymerisation ability of twelve light activation units, a mixture of new and old, was assessed by micro-hardness evaluation of samples of three composite resins cured with the lights. Light intensity was assessed using a commercially available band held dental radiometer. Intensity values were representative of the range of intensities that may be found in clinical practice. When a 2 mm thick sample of a microfilled composite was cured for 40s less than half of the light units evaluated produced an acceptable lower surface polymerisation. All but one of the light units tested produced a satisfactory lower surface cure with the monomodal and the hybrid composites. For the products tested material composition was an important factor in regard to the ability to cure a 2 mm thick increment of material with a 40s irradiation time. A significant correlation was found between lower surface hardness and light intensity. Standardising the area of the light sensing device of the hand held radiometer with respect to the diameter of the specimen to be cured improved the correlation between light intensity and lower surface micro-hardness.

Composite Resins↗

PubMed1995

Light curing unit effectiveness assessed by dental radiometers.

OBJECTIVES: The purpose of this investigation was to assess the effectiveness of five commercially available hand-held dental radiometers and a computer-based experimental radiometer. METHODS: Light intensity of five visible light activation units was determined using the dental radiometers. The influence of curing light intensity on depth of cure of a hybrid composite material was determined using a digital penetrometer. RESULTS: The radiometers evaluated varied with respect to sensor aperture diameter, scale readings (analogue or digital) and the units of measurement (arbitrary or mW cm2). The experimental computer-based radiometer allowed continuous recording of intensity against time; thus the light output could be monitored over the entire irradiation period. CONCLUSIONS: When light intensity readings were normalized with regard to a standardized light sensing device aperture of 4 mm diameter, a linear relationship was found between depth of cure and the logarithm of the intensity of the light. The results of this investigation support the use of dental radiometers for periodically monitoring visible light activation units.

Composite Resins↗

PubMed1995

Depth of cure of radiation-activated composite restoratives--influence of shade and opacity.

Inadequate depth of cure may reduce the longevity of visible light-activated composite restorations. Radiation-activated composites, originally marketed for the restoration of anterior teeth, have been developed and refined for restoring occlusal and proximal cavities in posterior teeth. Clinical factors such as the accessibility of the light source, the direction of the light, intervening tooth tissue and cavity depth may limit depth of cure. Unfortunately, a hard top surface is no indication of adequate polymerization at the base of the cavity. The current investigation used a penetrometer to evaluate the depth of cure of a range of recently introduced 'universal' composite materials and assess the influence of shade and opacity on depth of cure. Depth of cure of the enamel opacity is always greater than that of the same shade of dentine for each manufacturer's product range.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1993

Operating variables affecting the working time of a dual-cure composite luting cement.

Dual-cure composite resin luting cements are increasingly being used for the cementation of porcelain veneers, composite and ceramic inlays, onlays and crowns. This investigation assessed the effect of a dual-cure adhesive (Bondlite) on the working time of a dual-cure composite resin luting cement (Porcelite Dual-Cure). An oscillating rheometer was used to measure the working time of the composite resin luting cement with and without prior application of dual-cure adhesive. The results demonstrated that use of the dual-cure adhesive significantly reduced the working time of the manufacturer's dual-cure composite resin luting cement.

Analysis of Variance↗

PubMed1992

In vitro microleakage of Class V composite resin restorations with and without light-cured glass-ionomer (poly alkenoate) cement lining.

The restoration of Class V cavities with composite resin when the cervical cavity margin extends onto the root surface poses a special problem with regard to marginal seal. The use of glass-ionomer (poly alkenoate) cement (GIC) linings has not overcome this problem completely. The efficacy of a new light-cured GIC lining was tested in vitro, as was the use of a modern dentine-bonding agent. The light-cured GIC lining afforded a reliable marginal seal but the efficacy of the dentine-bonding agent related to the time of finishing of the composite restoration.

Adolescent↗

PubMed1991

Microleakage around direct composite inlays.

The purpose of this study was to compare the microleakage around direct composite inlays bonded with a dual cure luting composite into Class V type inlay cavities in extracted molar teeth. Bonding methods which included two cavity cleansing regimes and three bonding treatments were used. Either pumice and rinse or rinse only cavity cleansing was used to remove the separator agent (agar/alcohol) from the cavity surface prior to inlay bonding. Restorations were thermocycled between 5 degrees C and 55 degrees C (with intermediate baths at 36 degrees C) before (240 cycles) and during (12 cycles) silver staining. Microleakage around the sectioned restorations was quantified using digital imaging microscopy at x 40 magnification. Data analysis indicated that failure to include pumice slurry application as part of the cavity cleansing regime prior to bonding lead to a marked increase in microleakage at the enamel/restoration interface following one of the three bonding treatments.

Air↗

PubMed1989

Marginal seal of injection-molded ceramic crowns cemented with three adhesive systems.

This in vitro investigation evaluated the marginal seal of an injection-molded ceramic crown system used in combination with three adhesive luting systems. One of these systems was a glass-ionomer cement and the other two were based on composite resin materials. One of the latter materials is claimed by the manufacturer to bond to tooth structure and also to porcelain. The final luting material was used in conjunction with a commercially available porcelain bonding system and specific dentin bonding pretreatments. Following thermocycling, the marginal seal of the crowns was tested by use of a chemical marker intrusion technique. The extent of leakage along the sectioned crown/luting agent/tooth structure interfaces was recorded by using digital imaging microscopy. Minimal microleakage was demonstrated with the composite luting cement used in association with specific porcelain and dentin bonding pretreatments.

Adhesives↗

PubMed1988