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Biomedical subjects

R Huggett

Publications and source records attributed to R Huggett.

At least 19 recordsLinked to original sources

Cross-infection control in dental laboratories.

The attitudes to cross-infection control of 800 dental laboratories registered with the Dental Laboratories Association have been surveyed. Considering the topicality of the subject material and the need for careful cross-infection control within and beyond the dental surgery, the response rate of 22% (175) was disappointingly low. As a result of the low response rate, the results should be seen as a guide only. Forty-nine percent of respondents had a cross-infection policy and of those with no policy 64% intended to implement one in the future. Thirty percent of laboratories receive known undisinfected work from the dental surgery. Of those items disinfected on arrival at the laboratory, those most frequently disinfected are dental impressions (77%) and dentures (51%). The most popular chemicals used for disinfection are household bleach, chlorhexidine and glutaraldehyde. Forty-four percent of the respondents generally (90% or more of the time) wear gloves when handling dental work received and opened in the laboratory. Seventy-four percent wear protective eye spectacles when trimming or polishing prostheses. Sixty-one percent used no disinfectant in the pumice and 93% did not disinfect the polishing instruments, eg wheels and mops. Forty-six percent had a policy for immunisation of staff against Hepatitis B.

Attitude of Health Personnel↗

Finite element analysis of stress distribution at the tooth-denture base interface of acrylic resin teeth debonding from the denture base.

Acrylic resin teeth present a problem when they detach unexpectedly from the denture base resin. Detachment is caused by stress concentrations at the tooth/denture base resin interface. In this study, the finite element method was used to examine the stress distribution at this interface when a single static force that resembled incisal bite force was applied. The results indicated that irrespective of the type of acrylic resin teeth used, maximum tensile stresses were found at the palatal aspect of the interface. It is suggested that boxing the tooth in the acrylic resin will help redistribute stress concentrations favorably.

Acrylic Resins↗

The effect of variation in powder particle size on the doughing and manipulation times and some mechanical properties of acrylic resin.

In this study, the hypothesis examined is that differences in polymer particle size affect the doughing and manipulation times and the mechanical properties of the cured product. Six batches of polymers were used varying in particle size from <38 micrometers diameter to > 75 micrometers diameter. A penetration test was undertaken to investigate the influence of polymer particle size on the doughing and manipulation times of acrylic resin. It was demonstrated that the particle size in the range examined influenced the doughing and manipulation times, the smaller particle sizes having shorter times. No significant difference was demonstrated in the impact resistance of surface hardness of acrylic resin specimens constructed from polymers of varying particle size and although there were some significant differences in the transverse (flexural) strength these were small in real terms. Further, the molecular weight of the polymerised product was found to be consistently higher than that of the original powder component.

Acrylic Resins↗

Denture fracture--a survey.

The fracture of dentures is an unresolved problem. Despite increasing costs incurred by the nation on the repair of these prostheses, very little has been documented on the type of fracture encountered. This survey was carried out to determine the prevalence of type of fracture by the distribution of questionnaires to three different laboratories. Results obtained showed that 33% of the repairs carried out were due to debonded/detached teeth. Twenty-nine per cent were repairs to midline fractures, more commonly seen in upper complete dentures. The remaining 38% were other types of fractures, the majority of which constituted repairs to upper partial dentures. The latter involved detachment of acrylic resin saddles from the metal in metal based dentures and the fractures of connectors in the all-acrylic resin partial dentures.

Acrylic Resins↗

Factors that affect the rheologic properties of acrylic resin denture base materials.

The rheologic characteristics of different formulations of acrylic resin denture base materials are presented in this study. This is of practical significance in selecting resins with optimum rheologic properties for denture base construction. The materials are characterized in respect to their constituents, mean powder particle size and distribution, molecular weight averages and distributions, and glass transition temperature. A comparison of the polymers indicates that smaller particles saturate with monomer more readily, and this results in a higher viscosity. A higher viscosity for higher molecular weight and lower viscosity for lower molecular weight have been observed. Increasing the percentage of copolymerization increases the viscosity. No correlation has been found between the rheologic properties of denture base polymers and the powder glass transition temperature.

Acrylic Resins↗

The effect of esthetic fibers on the flow properties of an acrylic resin denture base material.

OBJECTIVES: This study was conducted to measure the effect of viscose rayon esthetic fibers on the flow properties of an acrylic resin denture base material. METHODS: Two testing methods using a needle penetrometer and an oscillating rheometer were employed on weighed proportions (0.1%, 0.2%, 0.8%, and 0.3%) of fiber. RESULTS: The results show that the fibers affect the flow properties of the polymer/monomer mix. Increasing the percentage of fibers decreases the flow of the material and reduces the doughing time. With increasing amounts of fiber, a rapid increase in the viscosity occurs with a corresponding adverse effect on flow properties. SIGNIFICANCE: It is concluded that these properties are important for the successful handling of acrylic materials since they can influence the accuracy and quality of the molded denture.

Acrylic Resins↗

Stress analysis techniques in complete dentures.

The fracture of acrylic resin dentures remains an unresolved problem. It is known that eventual fracture of an appliance occurs due to crack initiation and propagation from areas of high stress concentration. In order to understand and overcome the problem of fracture, it is important to identify the regions of stress concentration. A number of different methods are used in stress analysis. However, the finite element method, a numerical technique, appears to overcome most of the problems associated with the earlier experimental methods. This article reviews the different techniques and their application to examining stresses in dentures.

Birefringence↗

Effect of microwave irradiation on the flexural strength and residual monomer levels of an acrylic resin repair material.

The degree of polymerization of an acrylic resin repair material, as established by residual monomer estimation, was compared using three different polymerization methods, i.e. bench-cure, hydroflask-cure and microwave irradiation cure. The repair strength of a conventional heat-polymerized resin was then assessed following repairs using each of these three methods. The lowest level of residual monomer was achieved with the microwave irradiation cure. It was also demonstrated that of the three methods, polymerization using microwave energy resulted in the strongest repair.

Analysis of Variance↗

Measurement of residual monomer in denture base material: studies on variations in methodology using gas-liquid chromatography.

It is known that high levels of residual monomer have a deleterious effect on the properties of denture base polymers and may cause irritation or hypersensitivity of the oral tissues. In the present study variations in determination methodology and their influence on residual monomer levels are evaluated. The results demonstrate that filtration of the sample, sealed storage and incorporation of an appropriate volume of internal standard enhanced the accuracy of the technique.

Chromatography, Gas↗

The effect of impurities on the stress distribution at the tooth/denture base resin interface.

The most common cause of teeth detaching from the denture base is the presence of impurities along the tooth denture-base interface. However detachment after a period of wear of the denture probably occurs due to the presence of stress concentrations along the interface from which cracks may initiate. The presence of the impurity will inevitably lower the stress threshold for cracks to propagate thereby increasing the risk of tooth detachment. Although this is obvious, there is no evidence to show the effect of impurities on the stress distribution at this interface. This pilot study utilised the finite element method to examine stresses at the tooth-denture base interface in the presence of simulated impurities interspersed along different positions on the interface. Within the limitations of the two-dimensional model used, it was concluded that the presence of an impurity at the edge of the palatal aspect of the interface has a significant effect on the stress magnitude. However, the presence of impurities elsewhere along the interface had no significant effect on the stress magnitude. This would have important implications during the processing of dentures.

Acrylic Resins↗

The effect of aesthetic fibres on the strength of acrylic resin denture base material.

Aesthetic fibres are added to denture base polymers to simulate the natural appearance. The aim of this study was to measure the effect of aesthetic fibres on the low strain rate transverse bend strength and the high strain rate impact strength of an acrylic resin denture base material. Varying amounts of 2 and 4 mm Viscose Rayon aesthetic fibres, ranging from 0.1 to 3%, were incorporated into the polymer to evaluate their effect on these strength properties. The results showed that the fibres had minimal physical effect and that bonding of the fibres to the denture base polymer is not uniform or complete.

Analysis of Variance↗

A comparison of the dimensional accuracy of microwave and conventionally polymerized denture base materials.

This study compares the dimensional changes of microwave and conventionally polymerized denture bases and also establishes the degree of monomer conversion using gas-liquid chromatography. Dimensional changes of three denture base materials were assessed using an optical comparator and the results showed no significant differences between the materials employed or the curing method used. Efficient monomer conversion was demonstrated with levels of residual monomer of less than 1% for all materials.

Chromatography, Gas↗

The tooth-denture base bond: stress analysis using the finite element method.

Although acrylic resin teeth are the most popular artificial teeth used for denture construction, a high number fracture away at the tooth-denture base interface. Various causes have been documented for this failure; however, it is logical that eventual fracture occurs due to localised tensile stresses at this interface. Examination of these stresses using the finite element method showed that on load application to the upper incisors, the maximum tensile stresses were concentrated within the body of the tooth and not at the tooth-denture base interface. Stresses encountered at the interface were relatively low and introduction of a crack made no significant difference to their magnitude.

Acrylic Resins↗

A survey of complete denture prosthetics for the elderly, the handicapped and difficult patients.

A survey was carried out to establish information on the facilities and management of the elderly and the handicapped and to evaluate the treatment of the difficult edentulous patient in general dental practice. A postal questionnaire was sent to a total of 1090 dentists in three regions of England and Wales. There was a 50.4% response. Ninety-nine per cent of practitioners were able to treat the ambulant elderly, whereas only 72% offered treatment if the patient was wheelchair dependent. Ninety-six per cent of all respondents undertook domiciliary visits. All practitioners provided prosthetic treatment (complete and partial dentures) for the elderly, whereas fewer felt able to treat the physically and the mentally handicapped. There was less conservative and periodontal treatment provided than prosthetic treatment. A similar pattern was obtained in all three regions. Forty-seven per cent preferred to treat difficult complete denture patients privately, 44% under the NHS and 6% not at all. There were regional variations in the referral patterns of these difficult denture cases. The majority of respondents considered that there should be more opportunities for postgraduate education in prosthetic dentistry.

Aged↗

The effect of disinfection procedures on flexural properties of denture base acrylic resins.

This study evaluates the effects of long-term disinfection immersion on the flexural properties of denture base resins; it was conducted against a background of increasing awareness of the importance of cross-infection control in dental clinics and laboratories. The transverse bend testing procedure used followed that specified in the International Standard for denture base polymers. The results demonstrate that alcohol-based disinfectants are not suitable for use with denture base materials of non-cross-linked acrylic resin.

Acrylic Resins↗