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Biomedical subjects

R J Smales

Publications and source records attributed to R J Smales.

At least 19 recordsLinked to original sources
PubMed1992

The influence of examination frequency and changing dentist on dental treatment provision in an Australian defence force population.

During the early 1980s, a number of studies into dental treatment provision in the General Dental Service were conducted in Scotland. These studies indicated that the frequency with which an individual attended the dentist for treatment, or changed their dentist, influenced the amount of dental treatment that they received. The present study was designed to test these findings in an independent population, in this case, 100 members of the Royal Australian Air Force. While the frequency of attending the dentist did not have any significant effect on restoration longevity or the number of restorations a subject received, it did influence the cost of such treatment, indicating that frequent attenders received more expensive treatments rather than more treatment. Changing dentist did not display any significant influence on any of the parameters used in the present study.

Adult↗
PubMed1992

Clinical evaluation of four anterior composite resins over five years.

Four hundred and thirty nine chemical-cured composite resin restorations were placed in the anterior teeth of 86 patients treated in a private dental practice. Four anterior resins were used, and placement was performed with acid etching and appropriate enamel bonding resins. Assessments were made of the handling characteristics, condition of the gingiva, surface staining, marginal staining, color deterioration, and of the longevity of the four materials. Clinical deterioration rates and failures of the different types of composites were evaluated over periods of up to five years. Although all the assessed clinical factors deteriorated with time, there were very few unsatisfactory rating scores. Most of the composite restorations performed well over the study. Eight per cent of the restorations failed during the study. Class IV preparations showed the highest restoration failure rates.

Acrylic Resins↗
PubMed1992

Predictions of restoration deterioration.

This study evaluated the application of a mixture model involving a Weibull distribution function to predict the median times for restorations of three dental restorative materials to achieve unsatisfactory rating scores for six clinical factors. The accuracy of the method was assessed graphically against the known actuarial long-term deterioration observations of 1813 amalgam, 1774 anterior resin composite and 474 glass polyalkenoate (ionomer) cement restorations, assessed over periods of up to 20, 18 and 14 years, respectively. Of the six clinical factors investigated (which included marginal fracture), only four had sufficient long-term unsatisfactory rating score data to enable their median times to be predicted. These predicted times were: for amalgam restorations, surface roughness 32.5 years and surface tarnishing 16.0 years; for resin composites, marginal staining 25.4 years and colour mismatch 14.2 years; and for glass polyalkenoate (ionomer) cements, marginal staining 17.6 years and colour mismatch 3.6 years. The known and predictive unsatisfactory rating score results were generally in close agreement. However, it was not possible to predict median times for unsatisfactory rating scores associated with very slowly deteriorating restoration factors. The actual replacement rates of the amalgam restorations were too low to obtain their median survival time. However, for the faster failing resin composites this time was 7.9 +/- 0.5 years, and for the glass polyalkenoate (ionomer) cements 2.2 +/- 0.2 years. The relationship of restoration deterioration to restoration replacement and dental health requires further analysis.

Actuarial Analysis↗
PubMed1992

Restoration longevity in an Australian Defence Force population.

Replacement of restorations comprises a considerable portion of the work of most dentists. Consequently, factors that affect restoration longevity can influence the pattern of dental practice in a given community. Based on the results of research into treatment provision in the General Dental Service in Scotland, it was considered possible that factors such as the frequency with which patients were examined, and the frequency with which they changed dentists, might influence restoration longevity in other populations. Therefore, the present study was initiated to investigate the effects of these two factors in a population of 100 long-term members of the Royal Australian Air Force. No statistically significant relationship could be found between examination frequency, or frequent changes in dental practitioner, and restoration longevity. It is proposed that the large differences found in restoration longevity between this study and the Scottish study upon which it was based, may be due in part to the differing modes of remuneration of the dentists in the two studies.

Adult↗
PubMed1992

Comparative elasticity tests for elastomeric (non putty) impression materials.

This study was conducted to evaluate the methods used for measuring the elastic recovery of various elastomeric impression materials. One brand from each chemical group was selected to allow relative ranking of the results from each deforming test mode. For compression tests, the polysulphide and silicone specimens made in metal moulds gave significantly less set than those made in acrylic moulds; this was not so for the polysiloxane and polyether specimens. For polysulphide and polyether materials, the set in compression was greater using the BSI balanced beam method than for an optical method without inertia or load effects; this was not so for silicone or polysiloxane materials. The elastic recovery of the materials did not alter significantly after ten minutes of strain release, except in tensile tests, where the elastic recovery continued to change for twenty minutes. The rank ordering of the deformation set showed a relative correlation for the compression test, a new tensile test method, and bend and torsion testing methods. Thus only one method is needed to determine set per cent.

Dental Impression Materials↗
PubMed1992

Some parameters for testing deformation of elastomeric impression materials.

Because of conflicting published data, the temperature rise in four elastomeric materials was measured with a thermistor during setting in the oral cavity and in metal and plastic moulds of varying shapes and volumes for 'elastic set' specimens. The clinical temperature rise was 2-3 degrees C higher in the molar region than anteriorly, except for the polysiloxane. The temperature range attained in the set materials varied from 29 degrees C to nearly 35 degrees C for clinical and in vitro specimens. The average time taken by a group of operators to remove this type of impression from the mouth was five seconds. In a custom tray with light and heavy viscosity materials, the syringe material layer was only 0-0.15 mm thick and, essentially, the heavy viscosity material provided the elastic components for the impression.

Dental Impression Materials↗
PubMed1992

Clinical evaluation of light-cured anterior resin composites over periods of up to 4 years.

Seven hundred light-cured anterior restorations were placed in the permanent teeth of 161 patients by one researcher and evaluated over 4 years. One microfilled and two hybrid resins were assessed for their handling and for gingivitis adjacent to them, surface staining, marginal staining, and color mismatch. Restorative failures were related to the material, patient age, tooth site, and class of preparation. The different handling properties of the three resins did not affect their clinical behavior. There were only 10 unsatisfactory instances from 1626 restoration observations for the four clinical parameters assessed, and no clinically significant differences were found between the three materials, apart from the initial lighter shade mismatches of the microfilled resin. There was no obvious clinical deterioration recorded for most of the restoration observations, although all restorations deteriorated slightly over the study. There were no significant failure differences between the three resins, but significantly more failures occurred in elderly patients, restored (Class V) premolar teeth, and Class IV and V preparations. Of the 43 restoration failures, 81% were from Class V preparations, which reflected undue reliance on a dentin-bonding resin system for restoration retention in premolar cervical abrasion-erosion lesions.

Adolescent↗
PubMed1992

Effect of rubber dam isolation on restoration deterioration.

The consequence of using either rubber dam or cotton roll isolation on the subsequent clinical deterioration of 546 polished amalgam and 148 anterior enamel-bonded resin composite restorations was evaluated over periods of up to 15 and 10 years, respectively. Double-blind assessments for several clinical factors or parameters of the restorations were made using both direct and indirect observation methods. The transformed rating scores obtained were evaluated using a mixed model analysis of variance. With very few exceptions, all restoration placements were of high quality, and there were relatively few unsatisfactory rating scores given for any of the clinical factors assessed over the study. The low mean deterioration scores for most of the clinical factors assessed were also fairly similar, irrespective of the isolation method used. Therefore, although a statistically significant difference was found between the two isolation methods for marginal fracture of the composites, the clinical relevance of this difference is questionable.

Adolescent↗
PubMed1991

Prediction of amalgam restoration longevity.

The purpose of the present study was to assess predictions of longevity for amalgam restorations using a fitted Weibull distribution against base estimates using actuarial methods. The 1345 restorations involved were from 100 members of the Royal Australian Air Force whose dental conditions had been monitored regularly over a minimum period of 10 years. Based on maximum likelihood estimates of the parameters of a Weibull distribution, Weibull curves could be determined and were found to be very close to actuarial survival curves established from the same data set. However, Weibull estimates based on survival experience of less than 5-6 years failed to predict long-term survival. Using the 6 year actuarial survival data, the predicted and observed survival curves disagreed by less than 10 per cent for every time period. Twenty-five per cent of restorations had failed for the 6 year data, compared to 22 per cent in these first 6 years for the full 17 year data set.

Dental Amalgam↗
PubMed1991

Survival predictions of amalgam restorations.

The purpose of this study was to evaluate survival predictions made for four different amalgam alloy restorations, using a mixture model involving the standard Weibull function. The amalgam alloys were placed by students and staff in patients attending a dental hospital, and 1680 restorations were examined over periods of up to 18 years. Based on maximum likelihood estimations of the parameters of the mixture model distribution, predictive survival distributions were generated and found to match closely the actuarial survival estimates established from the same data. The 13-year restoration survivals of one low-copper alloy could be predicted accurately from the 6-year survival results. However, another low-copper alloy and two high-copper alloys with much lower restoration failure rates required 18 years of data for accurate long-term survival predictions.

Actuarial Analysis↗
PubMed1991

Survival predictions of four types of dental restorative materials.

The present study assessed the survival predictions made for four different types of dental restorative materials, using a mixture model involving the standard Weibull distribution function. A large number of amalgam, anterior resin, glass polyalkenoate (ionomer) cement, and pit and fissure sealant restorations were examined over varying periods of up to 18 years. The materials had been placed by numerous staff and students at a teaching hospital. Based on maximum likelihood estimations of the parameters of the mixture model distribution, survival curves were generated and found to agree closely with the actuarial survival curves estimated from the same data. As the years of data used to fit the mixture model curves decreased, then the fitted curves started to exhibit obvious divergences from the actuarial curves at 12-13 years for amalgams, 3-4 years for anterior resins and sealants, and 1-2 years for glass polyalkenoate (ionomer) cements. At least 5 per cent of restorations needed to have failed over any period to allow close agreement of the two curves, with the slower failing materials requiring longer observation periods.

Composite Resins↗
PubMed1991

Valiant-PhD and Lojic N amalgam alloys: four-year clinical results.

From 1984 to 1986, 97 similar pairs of Valiant-PhD and Lojic N amalgam restorations were placed at random by one dentist in Class II cavities prepared in 105 molar and 89 premolar permanent teeth of 73 patients treated in a private practice. Assessments were made of the different handling properties of the two alloys and of the effects of polishing, or otherwise, on the clinical behaviour of the restorations. Valiant-PhD alloy had more 'body' for condensing and was easier to carve and polish than was Lojic N alloy. After periods of up to four years, there was only one restoration failure (from bulk fracture) for each alloy although both materials deteriorated over time. Both the polished and the unpolished restorations showed similar deterioration for marginal fracture and staining, and for surface tarnish, and their initially-different surface textures became more similar during the study. Statistically, Lojic N restorations showed significantly more surface tarnish, but less marginal fracture than did Valiant-PhD restorations, and the tarnishing did not appear to be related to the effects of corrosion.

Adult↗
PubMed1991

Large database management in clinical dental research.

Previously the management and analysis of large databases for longitudinal clinical dental research has been severely restricted by the costs of custom-made software and access to suitable computing equipment. However, the recent availability of powerful personal computers and the use of the Scientific Information Retrieval Database Management System (SIR/DBMS) in association with BMDP Statistical Software has now created an enormously powerful tool for extensive and fast data manipulation requiring relatively few commands and the capability to easily perform detailed statistical analyses.

Computer Graphics↗
PubMed1991

Comparison of dental needs with the treatments actually received.

The main purpose of the study was to determine the types, causes, dental needs, and follow-up treatments of the chief complaints of a socioeconomically disadvantaged population of patients attending a public dental hospital. Around half of the 301 patients examined were 45 years of age and older, and the vast majority were of caucasian origin. The most common dental complaints in 259 patients were toothache, broken teeth, lost fillings, and painful, broken or loose dentures. The most frequent causes of the chief complaints were judged to be dental caries, and inadequate restorations and removable prostheses. On examination, most of the patients also had one or more other unsatisfactory restorations or removable prostheses, especially in the 35 years and over age group. Deep periodontal pockets were also found most often in this age group. After four to six months, of the 259 patients with chief complaints, 113 had had their complaints treated and 45 had not, 47 patients were given a different form of treatment from that proposed, while 31 treatments were uncompleted, and 23 patients could not be followed up.

Adult↗
PubMed1991

Effects of enamel-bonding, type of restoration, patient age and operator on the longevity of an anterior composite resin.

This study examined the survival of an anterior composite resin placed with or without enamel acid-etching using a low viscosity enamel bonding resin, for periods of approximately 16 years. The 950 conventional composite resin restorations were placed by numerous students and dentists for patients attending a dental hospital. Restorative failures were assessed using the life table method and specifically evaluated the placement method, type of restoration, patient age, and the dentist. There were no significant statistical differences between the two placement methods, or the two university and hospital dentist groups. However, there were significantly more failures with the Class IV restorations and in the oldest patient group. The enamel acid-etching and an enamel bonding resin did not display an advantage over unetched cavity preparations. The median survival for both methods of composite resin placement was 8-9 years.

Acid Etching, Dental↗
PubMed1990

Clinical evaluation of occlusal glass ionomer, resin, and amalgam restorations.

The purpose of the study was to evaluate four materials (a glass ionomer (polyalkenoate) silver cermet, two composite resin restoratives and a high copper content dental amalgam) placed in either conventional Class I cavities or in modified odontotomy-enameloplasty-sealant (OES) fissure preparations. One experienced operator inserted 438 occlusal. Class I restorations in the posterior permanent teeth of 124 patients in a private dental practice. Restorations were assessed for bulk loss of material, surface voids and cracking, restoration margin fractures and staining, and surface staining and roughness, by using colour transparencies taken at baseline and at recalls for up to 3 years. The glass ionomer cermet was the most difficult material to handle and also gave the least satisfactory clinical result. Loss of material and surface voids were common in the cermet restorations with surface cracking or crazing being seen in 11.4 per cent of the restorations, especially in the larger, conventional Class I preparations. One posterior resin was more viscous and difficult to handle than the other resin and exhibited more surface voids. The amalgam alloy was used in Class I preparations only and showed more restoration margin fractures and surface staining than did the other three materials. However, there were no unsatisfactory clinical assessments given for either restoration margin fracture and staining, or surface staining and roughness for any of the materials. Patient acceptance of the modified OES fissure preparation was extremely good.

Adult↗
PubMed1990

Clinical behaviour of high-copper amalgams with time, site, size and class of cavity preparation.

In this study 767 amalgam restorations placed in the posterior permanent teeth of 122 patients were evaluated at 6-monthly intervals up to 2 years. Six commercially available high-copper alloy amalgams were assessed for surface roughness, surface tarnish, marginal staining and marginal fracture and the results were related to product, restoration age, restoration cavity class type, restoration size (normal or large Class II preparations) and tooth type (premolar or permanent molar). Dispersalloy (Johnson and Johnson, East Windsor, USA) gave restorations which were overall superior for the clinical characteristics examined. Large restorations on the occlusal surfaces of molar teeth showed more signs of deterioration over the study than did other restoration types. However, all restorations remained clinically satisfactory throughout the study.

Analysis of Variance↗