D. C. Jagger

An in vitro investigation into the wear effects of unglazed, glazed, and polished porcelain on human enamel

Abrasive wear tests were performed on unglazed, glazed, and polished porcelain stud specimens using human enamel as the opposing plate specimens. The wear tests were carried out on a wear machine that was specifically designed to simulate the masticatory cycle. The amount of enamel wear produced by both glazed and unglazed porcelain was similar; however, that produced by polished porcelain was substantially less. Investigation of the glazed porcelain surface showed that the glaze was removed in less than 2 hours of wear on the machine.

An in vitro investigation into the wear effects of selected restorative materials on enamel

Abrasive wear testing of five restorative materials was carried out with human enamel as the opposing surface using a wear machine specifically designed to simulate the masticatory cycle. The results showed that enamel demonstrated good abrasion resistance against amalgam and microfine composite and moderate abrasion resistance against gold. Conventional composite produced marked destruction of enamel and the greatest amount of enamel wear was produced by porcelain. The ranking order compared favourably with results from in vivo studies.

Computer-generated study of the correlation between tooth, face, arch forms, and palatal contour.

STATEMENT OF PROBLEM Several factors have been suggested as aids for artificial tooth selection. Numerous methods have been devised for the evaluation of reliable esthetic factors in determining artificial tooth form. There is no universally accepted single esthetic factor that can be used reliably to aid artificial tooth selection. PURPOSE This article describes a new method incorporating a computer program to analyze four esthetic factors: form of the face, arch form, palatal contour, tooth shape, and to determine whether there was correlation between tooth, face, and arch forms and palatal contour. MATERIAL AND METHOD Impressions were made of the maxillary dentition of 50 dentate undergraduate dental students with irreversible hydrocolloid impression material and casts formed. A standardized photographic procedure was used to record portrait slides of each subjects face and of maxillary dental arches and central incisors made from dental casts. A comprehensive computer program was developed to correlate esthetic factors by superimposition. RESULTS Superimposing outline form between face, tooth, and arch showed that for tooth to face form nearly half the comparisons were dissimilar and only 22% corresponded. This is the lowest level of correspondence in this group. Highest correspondence (28%) occurred between arch to face form, followed by arch to tooth form (24%). Arch to tooth showed the lowest level of dissimilarity (32%). For correlation among the four factors across the sample group based on a comparison of classifications in each subject, men tended to dominate tapering classes, whereas women dominated square and ovoid classes. CONCLUSION Correspondence of outline forms through superimposition revealed an insignificant correlation between face, tooth, and arch forms. Although this method applies high technology, it does not improve the accuracy of determining shape and size of teeth in an edentulous patient. The cost and complexity of the method of measurement may also make it impractical for common application.

Two- and three-dimensional accuracy of dental impression materials: Effects of storage time and moisture contamination

Dental impression materials are used to create an inverse replica of the dental hard and soft tissues, and are used in processes such as the fabrication of crowns and bridges. The accuracy and dimensional stability of impression materials are of paramount importance to the accuracy of fit of the resultant prosthesis. Conventional methods for assessing the dimensional stability of impression materials are two-dimensional (2D), and assess shrinkage or expansion between selected fixed points on the impression. In this study, dimensional changes in four impression materials were assessed using an established 2D and an experimental three-dimensional (3D) technique. The former involved measurement of the distance between reference points on the impression; the latter a contact scanning method for producing a computer map of the impression surface showing localised expansion, contraction and warpage. Dimensional changes were assessed as a function of storage times and moisture contamination comparable to that found in clinical situations. It was evident that dimensional changes observed using the 3D technique were not always apparent using the 2D technique, and that the former offers certain advantages in terms of assessing dimensional accuracy and predictability of impression methods. There are, however, drawbacks associated with 3D techniques such as the more time-consuming nature of the data acquisition and difficulty in statistically analysing the data.

Differential adhesion of Streptococcus gordonii to anatase and rutile titanium dioxide surfaces with and without functionalization with chlorhexidine

The majority of dental implants are composed primarily of titanium and have an outer layer of titanium dioxide. Crystalline titanium dioxide most commonly exists in one of the two structures, anatase and rutile, and both of these have been observed on commercially available dental implants. Early implant failure can be associated with postoperative infection due to implant contamination during or immediately after surgery. The impetus of this study was to investigate whether functionalization of anatase and rutile titanium dioxide surfaces with chlorhexidine-reduced subsequent colonization of the surface by Streptococcus gordonii. Exposure to 100 mg x L(-1) chlorhexidine for 60 s resulted in a fivefold reduction in S. gordonii coverage on anatase and a twofold reduction on rutile. This may be related to a preferential adsorption of chlorhexidine to anatase compared with rutile. The reduction in bacterial coverage was not due to desorption of chlorhexidine into solution. More bacteria were observed on anatase than rutile surfaces without chlorhexidine functionalization, indicating that crystal structure may have a significant effect on bacterial colonization. In conclusion, functionalization with chlorhexidine reduced bacterial coverage on titanium dioxide surfaces, and anatase surfaces may be more amenable to such treatment than rutile.

The effect of the addition of surface treated chopped and continuous poly (methyl methacrylate) fibres on some properties of acrylic resin

Poly (methyl methacrylate), the material most commonly used in the construction of dentures, is not without limitations particularly in terms of mechanical strength, such as flexural and fatigue strength. The Dental Practice Board for England statistics show that many dentures fail as a result of fracture. This study investigated the self-reinforcement of acrylic resin through the addition of surface treated poly (methyl methacrylate) fibres in chopped and continuous form. The effect of the addition of fibres on transverse and impact strengths was investigated. The addition of surface treated chopped or continuous fibres to acrylic resin did not improve the transverse or impact strengths. The addition of surface treated poly (methyl methacrylate), in the present form, to acrylic resin cannot be recommended as a method of reinforcement.

A survey of undergraduate education in dental implantology in UK dental schools

The aim of this study was to ascertain knowledge on current teaching of implant dentistry in the undergraduate curriculum of Dental Schools in the UK. Information on the teaching modalities, including year of introduction of implant dentistry into undergraduate curriculum, departments involved in teaching, format of teaching, use of adjunctive teaching aids, and types of implant systems used in undergraduate teaching was collected by means of a questionnaire, which was sent to all undergraduate dental schools in the UK. Based on a 100% response rate, the findings indicate that all dental schools in the UK reported that they included dental implantology in their undergraduate curriculum; however there were marked variations in the content and delivery of the teaching.

An assessment of the ability of dental undergraduates to choose artificial teeth which are appropriate for the age and sex of the denture wearer: a pilot study

One of the main objectives in selecting and arranging artificial teeth is to produce prostheses which defy detection. With an appropriate degree of clinical experience and expertise it should be a relatively straightforward procedure to select a suitable artificial tooth mould. However, for the relatively inexperienced dental undergraduate it can be a challenging process. The aim of this study was to assess the ability of dental undergraduates to select artificial teeth which are appropriate for the age and sex of the denture wearer. One hundred and fifty dental undergraduates aged 18-35 were asked to complete a questionnaire to assess their attitudes towards artificial tooth selection and asked to correctly identify six artificial tooth arrangements according to age and sex. The results showed that a large percentage of dental undergraduates at Bristol experience difficulty in selecting artificial teeth which are appropriate for the age and sex of the denture wearer. There is a need for improved training and guidance on artificial tooth selection and arrangement.

Denture Hygiene Care for Residents in Nursing Homes in North Wales

Many elderly people who reside in nursing homes are dependent on care staff for all aspects of care, including oral health and denture hygiene. The aim of this study was to investigate the provision of one aspect of oral care, denture hygiene, in nursing homes in North Wales. Out of the 20 nursing homes identified for inclusion in the study, 10 nursing homes agreed to participate. The results of the study showed that denture hygiene care for elderly residents was still far from ideal. Perceived barriers to the provision of care include lack of training and a poor understanding of the importance of denture hygiene. In general the carers were keen to have training in oral and denture hygiene. This study has highlighted that one fundamental and important aspect of oral care for elderly residents, denture hygiene, is still a problem. This vulnerable group of individuals are not receiving essential care required to enhance their quality of life.