Biomedical subjects
Publications and source records attributed to B G Smith.
In this second article a range of clinical techniques for producing minor axial tooth movement is described, including the simple, cemented metal anterior bite-plane which has proved to be one of the most useful of the techniques. Methods of monitoring and measuring the relative tooth movements are also described.
In this first of two articles the theory and practice of creating occlusal clearance for restorative procedures without the removal of tooth tissue is discussed. Earlier techniques for producing minor axial tooth movement are reviewed, together with the relevant literature on continuous eruption and occlusal stability. The indications for axial tooth movement and alternative treatment options are also considered.
Wear of the surface of the teeth is a natural consequence of ageing, but various conditions can render it pathological. In this article the authors describe two strategies for obtaining sensitive, personal information from patients who may be reluctant to disclose such details to a stranger.
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Clinically, in modern populations, tooth wear can be differentiated into three main types--attrition, abrasion and erosion, acting either separately or together. Anthropologists generally have not recognized erosion as a factor affecting the teeth of past populations. This study compares the patterns of wear known to be associated with erosion in present-day dental patients with those found in some British, pre-Conquest, skeletons. It is concluded that erosion may have been a major factor causing the extensive tooth wear in some 20 of 151 individuals.
The use of deoxyribonucleic acid (DNA) cytometry to identify a subset of patients with grade 1, stage Ta or T1 transitional cell carcinoma at high risk for death or recurrence was investigated in a retrospective study using paraffin blocks from 88 low grade transitional cell carcinomas of the bladder with an absorptiometric video-based image analysis system. Tumors were evaluated for ploidy (70 diploid, 16 aneuploid and 2 tetraploid) and the presence of cells with greater than 5C DNA. Survival analysis of 62 patients with adequate followup (15 to 20 years) showed that 43 of 62 (69%) suffered recurrences and 13 (21%) died of bladder cancer. The single most important predictors of death and recurrence were stem line aneuploidy and the presence of cells with greater than 5C DNA, respectively.
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Tooth wear seems to be an increasing problem, particularly amongst older patients who are retaining their teeth for longer. Having survived the ravages of caries and periodontal disease, they are then at risk of wearing out their dentition. Diagnosis and a full understanding of the aetiology is crucial to the effective management of unacceptable levels of tooth wear. Monitoring over a long period is helpful in planning life long management. There are specific treatment techniques which are useful in restoring badly worn teeth.
Sandblasted surfaces of a beryllium-free, nickel-chromium alloy were bonded with one of three chemical adhesives. After either immersion in water for up to 6 months or thermal cycling between 5 degrees and 60 degrees C for 500 cycles, the bonded specimens were tested for both shear and tensile strength. The highest values of tensile and shear bond strengths were found with Panavia Ex material, and these values showed no significant changes after thermal cycling. For ABC cement and for Super-Bond C & B material, the strength of the bond was significantly improved with thermal cycling. However, immersion in water for 6 months caused a significant decrease in the strength of the bond of specimens adhered with ABC cement.
The diagnosis of caries and treatment planning decisions have been reported to vary widely between individual dentists. However, opinions differ as to whether, in general, this results in too much or too little treatment. Eighty-six dentists, mainly attending post-graduate meetings, participated in this study. They were asked to make diagnostic and treatment planning decisions on a selection of extracted teeth set in realistic contact with each other. These decisions were compared with the appearance of the proximal surfaces before setting the teeth in contact, and the histological appearance of the teeth that were sectioned after the dentists had made their decisions. Opinions as to whether caries was present and whether it required treatment showed a wide distribution. However, had the decisions been acted upon, between 1-6% of the sound surfaces would have been filled, but 20-68% of teeth with clearly cavitated surfaces or histological evidence of dentine involvement would not have been filled.
Society is becoming more litigious, and dentistry has not been exempt. However, by following correct and prudent professional procedures at all times, dentists may sensibly expect to avoid serious litigation. In the first of an irregular series on dento-legal topics, Bernard Smith reviews the thorny subject of negligence in dentistry, and gives advice on both how to prevent and how to respond to accusations. Other articles in the series will look at particular legal problems in the dental specialties.
Potential academic ability, practical skill and personality characteristics should all be assessed in selecting dental students. Of these, practical skill commonly receives the least attention, largely because valid and reliable predictive tests are not available. The Spatial Relations Test, which might be used for this purpose, was administered to 1391 applicants to a dental school. There was little correlation between the results of the test and GCE 'A' level grades, showing that the test measured different abilities. However, there was a strong relationship between poor scores on the test and the number of students resigning from the course or failing to graduate on time.
Tooth wear attributed to the physical wear of teeth by clenching and grinding (attrition) has been described previously in alcoholic patients. However, the pattern of wear seen in the series of cases reported here is more consistent with chemical damage (erosion) than attrition. A possible mechanism for this process is suggested, and it is further suggested that erosion is likely to play a more important role in the wear of the teeth in chronic alcoholic patients than attrition.
The accuracy of some spatial discriminations, including spatial frequency and orientation, is independent of the contrasts of the stimuli discriminated except when contrasts are near the detection threshold. This fact is surprising because higher contrasts should improve signal-to-noise ratios and performance. Two alternative explanations of this puzzle are examined, using a signal-detection-theory vector model: (1) noise increases with stimulus contrast in such a way that signal-to-noise ratios remain constant; (2) noise is constant, but the difference signal generated by each individual tuned mechanism is independent of contrast because the response function of the mechanism becomes compressive (approximately logarithmic) at a low contrast. The alternative explanations generate different predictions, which have been tested in several experiments. The results reject alternative (1) as a model of suprathreshold discrimination and give mixed support to alternative (2).
The move towards restoring teeth with materials which more closely match the properties of the lost dental tissues is gathering momentum. Of the materials currently available, glass ionomer cements are adhesive to dentine and enamel, leach fluoride, have negligible contraction on setting and are tooth-coloured; but their abrasion resistance is poor. Composite materials can be bonded to enamel and dentine and are made in a range of tooth-coloured shades. Their polymerisation contraction is a problem and, although they are more abrasion resistant than glass ionomer cements, there is still some anxiety about this. Porcelain has good abrasion resistance but does not bond directly to dental tissues and the need to manufacture porcelain restorations in the laboratory adds to their cost and increases the number of clinical appointments necessary. The CEREC machine produces porcelain inlays at the chairside which are used in combination with composite and glass ionomer materials to produce a restoration which optimises the advantageous properties of all three materials. The restoration can be completed in a single appointment.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.