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Biomedical subjects

K W Stephen

Publications and source records attributed to K W Stephen.

At least 73 records · Page 4Linked to original sources
PubMed1988

Comparison of solution- and gel-prepared enamel lesions--and in vitro pH-cycling study.

A variety of methods has been employed to produce artificial caries-like enamel lesions. The aim of this paper was to use a pH-cycling regime to compare the de-/remineralization behavior of lesions prepared by two methods. Lesions were produced by use of either an acidified undialyzed gelatin system or a buffered solution. Enamel sections, each containing four lesions, were allocated to four groups (A, B, C, D) and subjected to a daily pH-cycling regime of 16-hour demineralization and eight-hour remineralization. Groups A & B contained gelatin-prepared lesions, whereas Groups C & D contained solution-prepared lesions. To the remineralizing solutions used in Groups B & D, 2 ppm fluoride was added. The mineral content in the lesions was assessed, by means of microradiography/microdensitometry, at baseline and at intervals for six weeks. The lesions in all four groups exhibited net demineralization. In terms of the total mineral lost from the lesion (the delta z parameter), the demineralization rates of the solution-prepared lesions were significantly greater than those of the corresponding gelatin-prepared lesions. All sections in the non-fluoride groups showed subsurface demineralization in initially sound enamel, whereas only one section in the fluoride groups showed an area of mineral loss. Laminations in the mineral content profiles were apparent only in Group D. The results of this study indicate that the method of lesion preparation affects the subsequent behavior of lesions when exposed to de- and remineralizing protocols.

Bicuspid↗
PubMed1987

Comparison of fibre optic transillumination with clinical and radiographic caries diagnosis.

Fibre optic transillumination (FOTI) has been employed during the course of a 3-yr clinical dentifrice trial which initially involved 3003 children. At the initial examination, a subgroup of 813 13-yr-olds, and at the following annual visit, 2247 14-yr-olds, were examined using a 150 W lamp and 0.5 mm diameter probe. Routine clinical and radiographic examinations were performed separately. Compared to the clinical scores for anterior teeth, FOTI detected an additional 64% of interproximal lesions at the first visit while, for the larger number of children at the second visit, the increase in lesion detection level using FOTI was 37%. For the posterior teeth the comparable figure at the second examination was 92%. When FOTI data were compared to radiographic data for more than 52,000 posterior interproximal surfaces, FOTI could only detect 17% of radiographic Grade 2 lesions and 48% Grade 3 lesions. Thus any assumption that FOTI diagnoses may be a substitute for bitewing radiography appears premature.

Adolescent↗
PubMed1987

The effect of baseline lesion mineral loss on in situ remineralization.

The effect of baseline lesion mineral loss on the remineralization of enamel lesions by a sodium fluoride dentifrice was studied in situ by means of an appliance carrying enamel sections. Artificial lesions of various sizes were created, by means of acidified gelatin, and were then mounted on the appliances of five volunteers. Each brushed twice daily for two min with a 1000 ppm F sodium fluoride dentifrice. Measurements of mineral content were made at baseline and at weekly intervals by microradiographic/microdensitometric techniques. Data from all five volunteers showed a linear increase in remineralization rate with increasing lesion size. Thus, in studies which compare the effects of different remineralizing formulations, care must be taken to ensure that initial lesion sizes are matched, or that the results are expressed as a percentage change in mineral content.

Cariostatic Agents↗
PubMed1986

Preventive dentistry in a health centre: effectiveness and cost.

The clinical and economic effects of a programme of preventive dentistry for children in an inner-city health centre are compared with those for traditional restorative care. Reductions in the rate of dental caries are estimated to be 70% for children aged 4-6 after 4 years in the programme (dmft) and 85% for children aged between 7 and 10 years after 4 years (DMFT). The cost-effectiveness analysis on which the economic appraisal is based identifies the issue of differences in the quality of output as critical to choices between the two treatment regimes. The preventive programme was primarily intended for pre-school children; for this younger group, assumptions about the quality of the preventive outcome would have to value it at between 0.8 and 1.2 times the quality of the restorative outcome in order to make up the difference in cost between the two regimes. For 7-10 year olds, the 4-year analysis showed the preventive programme to be more costly than restorative care largely because of low rates of incremental change at these ages. These rates were partly influenced by the design of the study and partly by the eruption status of the permanent dentition across this age-group. There is a need for further study of measures of dental outcome which combine aspects of both the quality and length of life of teeth.

Child↗
PubMed1986

An assessment of visible-light polymerizing sources.

Measurements were made of the spectral distribution of light emitted from five commercially available visible-light polymerization units. All emissions peaked between 400 and 500 nm but the 'functional' irradiance varied by a factor of 20 for the sources investigated. Timer checks revealed errors of up to 20%. Light output was plotted as a function of time and, after 60 s, varied from-15% to +38% of the initial level. The decrease in irradiance with distance from the end of the guide was such that irradiance at 20 mm was between 20% and 40% of that at 2 mm. The light distribution across the face of each light guide was investigated and significant inhomogeneities discovered. An ultraviolet light (UV) hazard assessment was performed and it was concluded that none of the light sources presented a hazard to the operator in normal use.

Chemical Phenomena↗
PubMed1986

Further abrasion resistance and bond strength studies of fissure sealants.

As part of a laboratory evaluation, measurements of abrasion loss and tensile enamel--sealant bond strengths have been made on three visible light cured sealants (two filled, one unfilled), two chemically cured sealants (one filled and one unfilled) and an experimental sealant with alumina filler particles. A UV-cured filled sealant was used as a control. The unfilled sealants had abrasion loss approximately twice that of the filled commercial sealants. The experimental sealant, with filler content above 50%, had an abrasion loss approximately half that of the filled commercial sealants. The chemical cured sealants had bond strengths lower than the UV-cured control, while the bond strengths of the two visible light-cured filled sealants and the experimental sealant were not statistically different from either the unfilled visible light-cured sealant or from the UV-cured filled sealant.

Animals↗
PubMed1986

Laboratory studies of visible-light cured fissure sealants: setting times and depth of polymerization.

Measurements were made, using an acoustic transmission method, of the setting times of three visible-light curing sealants (two filled, one unfilled). Five commercially available visible-light polymerizing sources were tested with each material. Only three of the light sources gave setting times not significantly different from the manufacturers' recommended times for all three materials tested. The variation in microhardness with depth of sealant was measured to study the depth of polymerization of the sealants, all of which were adequate. The filled sealants had microhardness values greater than the unfilled sealant, at all depths studied.

Chemical Phenomena↗