Associations of mortality and cardiovascular disease risks with diabetes and albuminuria in urban Indigenous Australians: the DRUID follow-up study.

AIM: To assess the relationships of diabetes and albuminuria with all-cause mortality and cardiovascular disease outcomes in a population without prior cardiovascular disease using data from the Darwin Region Urban Indigenous Diabetes (DRUID) study. METHODS: We conducted a prospective cohort study of 706 participants (aged 15-81 years, 68% women) without prior cardiovascular disease who underwent a 75-g oral glucose tolerance test. Deaths and fatal or non-fatal cardiovascular disease were determined over 7 years, and hazard ratios with 95% CIs and population attributable risks were estimated for baseline glycaemia and albuminuria. RESULTS: Compared with normoglycaemia and after adjustment for age, sex, hypertension, dyslipidaemia and smoking, known diabetes was associated with an adjusted hazard ratio of 4.8 (95% CI 1.5-14.7) for all-cause mortality and 5.6 (95% CI 2.1-15.2) for cardiovascular disease. Compared with normoalbuminuria, the respective adjusted risks for macroalbuminuria were 10.9 (95% CI 3.7-32.1) and 3.9 (95% CI 1.4-10.8). The Adjusted all-cause mortality and cardiovascular disease estimated population attributable risks for diabetes were 27% and 32%, and for albuminuria they were 32% and 21%, respectively. CONCLUSIONS: In our study population, the burden of mortality and cardiovascular disease was largely driven by diabetes and albuminuria. This finding on the influence of diabetes and albuminuria is consistent with reports in other high-risk Indigenous populations and should be better reflected in risk scores and intervention programmes.

How well is the National Cervical Screening Program performing for Indigenous Australian women? Why we don't really know, and what we can and should do about it.

Since its inception in 1991, Australia's organised approach to cervical screening, the National Cervical Screening Program (NCSP), has seen a 50% reduction in both incidence and mortality from cervical cancer in Australia. However, Indigenous Australian women continue to experience a disproportionately higher burden of cervical cancer. No national data on screening participation of Indigenous women currently exist, in large part because pathology forms, the primary source of data for Pap Test Registers (PTR), do not record Indigenous status. While including Indigenous status on pathology forms is the obvious solution for producing essential information about cervical screening of Indigenous women, this will require an appropriate consultative process and it will be many years before reliable data are available. One interim option being explored is the feasibility of linking the PTR to another data source which includes Indigenous status, such as hospital data. However, despite its promise, there remain major impediments to obtaining useful linked data in Australia, and it continues to be unclear whether such an approach is viable for routine reporting. If we are to understand and improve cervical screening participation and outcomes for Indigenous women in the foreseeable future, Australia needs to act now to include Indigenous status in pathology forms and (subsequently) PTRs.

Performance of comorbidity indices in measuring outcomes after acute myocardial infarction in Australian indigenous and non-indigenous patients.

BACKGROUND: Indigenous Australians have higher prevalence of chronic diseases and worse acute care outcomes than other Australians. The extent to which higher chronic disease comorbidity levels are responsible for their worse outcomes is not clear, and the performance of comorbidity indices has not been assessed for this population with very high comorbidity levels. METHODS: Using hospital separations data, the Charlson and Elixhauser comorbidity indices were used to measure chronic disease prevalence in 2035 indigenous and non-indigenous patients hospitalised after their first acute myocardial infarction (AMI) in the Northern Territory of Australia between 1992 and 2004, and to adjust for comorbidity in multivariate analysis of mortality outcomes (in-hospital and long-term deaths from coronary heart disease and all causes). Index performance was assessed by the difference between C statistic, Akaike information criterion statistic and estimate of excess indigenous mortality in models with and without comorbidity adjustment. RESULTS: Comorbidity index scores were higher for indigenous than non-indigenous patients and increased considerably over time, at least partly because of information bias. Indigenous patients' higher risk of in-hospital all-cause death was almost fully explained by their higher comorbidity levels. Their higher risk of long-term coronary heart disease and all-cause death was partially explained by higher comorbidity levels. Charlson and Elixhauser indices performed satisfactorily and similarly in this population. CONCLUSION: Comorbidity indices performed well in a population with very high chronic disease prevalence. After adjusting for comorbidity, short-term outcomes were similar for indigenous and non-indigenous AMI patients, but comorbidity at the time of the acute episode only partly explained the worse long-term outcomes for indigenous patients.

Cancer diagnosis and treatment in the Northern Territory: assessing health service performance for indigenous Australians.

Indigenous Australians with cancer are diagnosed with more advanced disease and have lower survival than other Australians. To investigate reasons for these differences. Retrospective cohort study of 1197 indigenous and nonindigenous people in the Northern Territory diagnosed with cancers of the colon and rectum, lung, breast, cervix and non-Hodgkin lymphoma between 1991 and 2000. Outcome measures were stage at diagnosis and relative risk of cancer death. Indigenous people compared with nonindigenous people had higher relative odds of advanced stage of cancer at diagnosis (relative odds 1.9, 95% CI 1.3-2.7) for four cancers but lower relative odds for lung cancer (relative odds 0.3, 95% CI 0.2-0.5). None of the potentially contributing factors examined could explain this difference. Risk of cancer death (adjusted for cancer type and age and stage at diagnosis) was higher in indigenous than in nonindigenous people (relative risk 1.7, 95% CI 1.4-2.1). This difference, however, was confined to indigenous people with an indigenous first language (relative risk 2.9, 95% CI 2.2-3.8). Adjustment for cancer treatment variables further reduced but did not eliminate this higher risk of death. Although more advanced stage at diagnosis appeared to be a sufficient explanation for poorer cancer outcome in indigenous people whose first language was English, poorer treatment also contributed to, but was still not sufficient to explain, poorer outcome in those who had an indigenous first language. Other factors, possibly including communication difficulties, knowledge of and attitudes to cancer symptoms and treatment and social and cultural 'distance' from mainstream health services, may also be involved.

Cancer in Indigenous Australians: a review.

OBJECTIVES: To summarize for the first time evidence of the impact of cancer on Indigenous Australians. METHODS: Medline search of peer-reviewed scientific journals, and extensive search of reports of government agencies, publications of cancer registries and non-government organizations, and other non-peer-reviewed sources. RESULTS: Indigenous Australians have much higher incidence rates than other Australians of cancers of the lung, liver, and cervix; but much lower rates of cancers of the breast, colon and rectum, prostate, melanoma of skin, and lymphoma. Some of these differences can be explained, in part at least, by differences in risk factor prevalence. Indigenous Australians also have higher mortality and lower survival from cancer as a whole than other Australians. More advanced disease at diagnosis, and possibly poorer treatment, are partly responsible for these differences, but other factors may also be involved. CONCLUSIONS: Less accessible and less effective health programs are as great a problem for cancer control as for other aspects of Indigenous health in Australia. Major improvements in preventive services, screening, primary care, and specialist treatment services are required to reduce cancer incidence and improve cancer outcomes for Australia's Indigenous people.

Reduction of polymerization contraction stress for dental composites by two-step light-activation.

OBJECTIVES: The goal of this study was to assess the reduction of polymerization contraction stress of composites during a two-step light-activation process and to relate this reduction to the process of polymerization shrinkage and specimen thickness. METHODS: Three test procedures were performed to compare two-step light-activation with delay with one-step continuous irradiation of composites: polymerization contraction stress using a closed-loop servohydraulic testing instrument, polymerization shrinkage by a mercury dilatometer, and degree of conversion by FTIR. For the one-step continuous curing method, the samples were light-activated for 60s at 330 mW/cm(2). For the two-step curing method, a 5s light exposure at 60 mW/cm(2) was followed by 2 min without light exposure, and then a second light exposure for 60s at 330 mW/cm(2). The same light parameters were used for measurements of stress, shrinkage, and degree of conversion. Three composites, Heliomolar, Herculite and Z100 were evaluated. The contraction stress experiments were repeated with varying thickness for Herculite using the one-step and two different two-step techniques. RESULTS: Polymerization contraction stress 10 min after light-activation was significantly reduced (P<0.05) by the two-step method: 29.7% for Heliomolar, 26.5% for Herculite, and 19.0% for Z100. Total volumetric shrinkage and degree of conversion were not significantly different for composites cured by the two different techniques. Increasing the thickness of the composite sample reduced the measured contraction stress, especially for one of the two-step curing methods. SIGNIFICANCE: A combination of low initial energy density followed by a lag period before a final high-intensity light irradiation provides a reduction of polymerization contraction stresses in dental composites. The stress reductions cannot be attributed to reductions in degree of conversion or unrestrained volumetric shrinkage.

Assessing the effect of composite formulation on polymerization stress.

BACKGROUND: In this study, the authors measured the magnitude of the polymerization stress of a variety of dental composite materials and explored the effect of a novel monomer, a methacrylated derivative of styrene-allyl alcohol, or MSAA, in reducing polymerization stress. METHODS: Eleven commercially available composites and a series of experimental composites were evaluated in a mechanical testing machine to measure the maximum stress generated during placement in a confined setting. RESULTS: A significant relationship between higher filler volume and increased polymerization stress was found among the commercial materials. Introduction of MSAA produced a 30 percent reduction in polymerization stress in an experimental composite material. CONCLUSIONS: Composites that contain lower levels of inorganic filler particles are less likely to produce high levels of polymerization stress during placement. Modifications to traditional composite chemistry can result in materials that produce lower polymerization stress levels. CLINICAL IMPLICATIONS: The polymerization stress produced by dental composite materials during light-curing is a leading reason for bond failures in adhesive restorations, resulting in postoperative sensitivity, marginal staining and recurrent caries.

The effects of adhesive thickness on polymerization contraction stress of composite.

A layer of an unfilled adhesive resin placed between the tooth and composite restoration has been shown to absorb some of the stress generated in the composite during polymerization and to reduce interfacial leakage. The objectives of this study were to measure the change in polymerization contraction stress of bonded composite as the thickness of the resin adhesive was systematically varied, and to correlate the effects of the adhesive thickness and reduced stress on marginal leakage in class V cavities. The maximum contraction force of composite (Herculite XRV) was measured in a tensilometer as the thickness of the adhesive bonding agent (Scotchbond MP) was varied from 20 to 300 microm. Composite was placed in Class V cavities prepared on the labial surfaces of bovine teeth to which different thicknesses of adhesive had been applied by layering, and a marginal leakage test was performed by means of staining with silver nitrate. Contraction stress decreased significantly as the adhesive thickness was increased. This result was supported by a theoretical examination of the data. In class V cavities, additional adhesive layering in the marginal area reduced the overall degree of microleakage. The contraction stress generated during the placement of a composite restoration contributes significantly to early marginal leakage, and this stress was significantly absorbed and relieved by the application of an increasing thickness of low-stiffness adhesive.

In vitro evaluation of the marginal degradation of dental composites under simulated occlusal loading.

OBJECTIVES: Our objective was to use an in vitro oral wear simulator to compare the susceptibility to marginal breakdown of different classes of dental composites. METHODS: Two microfill composites (Silux Plus, 3M and Heliomolar, Vivadent), two minifills (Z100, 3M and Herculite, Kerr) and two midifills (Fulfil, Caulk and Clearfil, Kuraray) were placed in two increments (40 s cure) into class I cavities (5 x 3.5 x 2 mm3 deep) cut into the facial enamel surfaces of bovine incisors treated with an adhesive (Scotchbond MP, 3M). The restored teeth were aged 1 day in water, mounted in the OHSU oral wear simulator, covered with a slurry of poppy seeds/PMMA beads and subjected to 50 K cycles of wear against an enamel stylus [J.R. Condon, J.L. Ferracane, Evaluation of composite wear with a new multi-mode oral wear simulator, Dent. Mater. 12 (1996) 218-226). The specimens (n = 10) were positioned to produce abrasive wear (load = 20 N] across one margin and attrition wear (load = 70 N) across the second margin. Volume loss of material (mm3 x 1000) was estimated from 10 profilometric tracings perpendicular to the attrition margin, and then differentiated into composite and enamel degradation. Fracture toughness of the composites was measured in bending with the single-edge notch technique. Results were compared with ANOVA and Tukey's test at p < 0.05. RESULTS: Significant wear of the composite was produced at the attrition margin. Enamel degradation at the margin paralleled the composite results. The microfills, and to a lesser extent the minifills, showed more marginal breakdown than the midifill composites. Marginal breakdown shows an excellent inverse correlation with fracture toughness for these composites. SIGNIFICANCE: These results are in general agreement with clinical studies showing greater marginal degradation for microfill composites and suggest that the OHSU oral wear simulator may be a useful adjunct for the study of the marginal degradation of dental composites.

Prevention of hypercalcaemic nephropathy and tissue calcification by glucagon during phosphate infusion.

Patients with serum calcium above 4.5 mmol/litre risk sudden death. Rehydration and frusemide may decrease calcium levels by 0.5-1 mmol/litre but result in a high renal filtered load of calcium which, if above 3.7 mmol/litre, causes calcium phosphate protein complexes to form giving rise to hypercalcaemic nephropathy. Current drugs namely clodronate, calcitonin and plicamycin take days to lower serum calcium and have disadvantages. Intravenous phosphate rapidly lowers serum calcium but when the calcium phosphate product rises above 4.6 mmol/litre the saturation point for the precipitation of calcium hydrogen phosphate is reached and tissue calcification occurs. Intravenous glucagon results in a steep reduction in serum phosphate within minutes and also lowers serum calcium, resulting in a marked fall in the calcium phosphate product to well below the critical level of 4.6 mmol/litre. If, in addition to glucagon, intravenous phosphate is now given, it should have a further calcium-lowering effect by inhibiting bone osteoclasts.

A single issue program in an isolated area: mammography screening in Darwin, NT.

OBJECTIVE: A process evaluation of the Northern Territory (NT) mammography program, NT Breast Screen (NTBS), during its initial 18 months of operation. METHODS: The study was undertaken in Darwin, NT, from December 1994 to May 1996. Clinical outcomes were obtained by reviewing computerised and manual program records to determine waiting times for results, recall rates and cancer detection rates. Client satisfaction was assessed by a questionnaire sent to all women with normal results over a 12-week period. General practitioner satisfaction was assessed by a questionnaire sent to all general practitioners in the region who had one or more clients who had attended the service. RESULTS: During this time, 2,882 screening mammograms were performed; 98 women were recalled for assessment (3.4%). Breast cancer was detected in 10 women (3.5 per 1000 women screened). The program was well accepted by clients and general practitioners. Performance criteria were not met for waiting times for results. CONCLUSIONS: NTBS faced challenges because of its small and dispersed population, a lack of local radiologists with mammographic experience and the conflict with other pressing health issues, particularly in Aboriginal health. Despite these challenges, the program functioned effectively during its initial 18 months. IMPLICATIONS: Mammography screening programs in isolated areas can function effectively. The constraints encountered by NTBS are likely to apply to similar programs. Issues identified requiring further research are the psychological consequences of long waiting times for results, and the prioritisation of mammography for Aboriginal women.

In vitro wear of packable dental composites.

The in vitro abrasion and attrition wear of several packable composites were evaluated on the Oregon Health Sciences University oral wear simulator and compared to two popular commercial composites. In general, the wear of the packable composites was equivalent to that of the nonpackable microfill and minifill composites. The wear of the enamel cusps opposing the composites in the wear machine was also found to be similar to that of enamel opposing the nonpackable composites. Based on these results, one would expect that these new packable composites would not offer improved clinical performance over current nonpackable composites in terms of wear resistance.

In vitro aging of dental composites in water--effect of degree of conversion, filler volume, and filler/matrix coupling.

The purpose of this study was to evaluate the long-term effect of aging in water on the physical properties of experimental composites having systematically controlled differences in degree of conversion (DC), filler volume fraction (Vf), and percentage of silane-treated fillers. Composites were made with a 50% Bis-GMA:50% TEGDMA light-cured resin and a 1-2 microm (average size) strontium glass filler (+ 5 wt% SiO2 microfiller). For composites A-E, the DC was varied from 56-66% by changing the curing time; for D and F-I, the Vf was varied from 28-62 vol%; and for D and J-M, the percent of fillers with a silane coupling agent (gamma-MPS) was varied from 20-100%. Fracture toughness (KIc), flexure strength (FS), elastic modulus (E), and hardness (KHN) were tested after soaking in water at 37 degrees C for 1 day, 6 months, 1 year, and 2 years. The KIc was reduced 20-30% for all composites after 6 months, with minimal changes thereafter. The FS was reduced for several composites at 6 months, but only those with poor cure (A and B) were lower at 2 years than they were initially. The E was not reduced for most composites. Hardness was reduced for most composites after 6 months, but many returned to their original levels at 2 years. Long-term aging in water caused a reduction in the KIc, independent of composition, but had little effect on other properties, suggesting limited degradation of composites in water.

Anaesthesia for aboriginal Australians.

This prospective study was designed to describe problems that arise when Aboriginal people undergo anaesthesia, in order to develop guidelines for anaesthetists who are not accustomed to treating Aboriginal people. Data were collected on 1122 consecutive different individuals undergoing anaesthesia at Royal Darwin Hospital, 24.5% of whom described themselves as Aboriginal. Aboriginal patients were in a poorer physiological state than were non-Aboriginal patients. The prevalence of diabetes mellitus, renal disease and rheumatic heart disease reported in Aboriginal patients was very high. Communication difficulties were more commonly reported in Aboriginal patients; the most common difficulty was apparent shyness or fear, rather than actual language difficulty. The results suggest that the treatment of Aboriginal people involves diagnosis and management of diverse preoperative medical problems, and that better management may be achieved by learning simple cultural strategies and by adding Aboriginal interpreters and health workers to the anaesthetic team.

Reduction of composite contraction stress through non-bonded microfiller particles.

OBJECTIVES: To determine the reduction in composite polymerization stress through the addition of non-bonded microfiller particles. METHODS: Microfillers that were unsilanated, silanated, and treated with a nonfunctional silane were added to dental resin and to a small-particle composite. The contraction stress generated by these materials was measured by polymerizing them between glass plates mounted in a mechanical testing machine. The maximum force was recorded 15 min after photo-initiation. Results were analysed by ANOVA (analysis of variance)/Turkey's test (p < or = 0.05). RESULTS: The addition of non-functional silanated microfillers to dental resin resulted in a significant 50% decrease in polymerization stress. The addition of unsilanated microfillers did not reduce the contraction stress. When added to small-particle composite, the unsilanated microfillers produced a significant 30% reduction in contraction stress compared to the composite containing silanated microfillers. The non-functional silanated microfillers did not reduce the contraction stress in the small-particle composite. SIGNIFICANCE: The polymerization shrinkage of dental composite can impose high levels of stress on the tooth surfaces to which it is bonding. This contraction stress can lead to failure of bond formation with the surrounding tooth structure. Microfiller particles that are not bound to the resin matrix might provide sites for relief of internal stresses, significantly reducing contraction stress in dental composite.

Wear and marginal breakdown of composites with various degrees of cure.

Loss of anatomical form due to wear has been cited as one factor limiting the clinical use of posterior composites. The physical properties and possibly the wear resistance of composite are influenced by the extent to which it is cured. The aim of this study was to vary degree of conversion (DC) in composites to test the hypothesis that resistance to wear and marginal breakdown could be improved by enhanced curing. A light-cured hybrid composite containing a 50% Bis-GMA/50% TEGDMA resin and 62 vol% of strontium glass (1 to 2 microm) with microfill silica was formulated (Bisco). Composite was placed into two 2.5-mm-diameter cylindrical holes in Co-Cr teeth replacing first and second molars in the mandibular dentures of 50 edentulous patients. The composites were light-cured for different time periods (9 s, 12 s, 25 s, 40 s, and 40 s + 10 min at 120 degrees C) and then polished. The microfill Heliomolar was also tested. DC (%) was measured by FTIR and ranged between 55% for 9 s of light-curing and 67% for 40 s of light-curing followed by heat application. Impressions were evaluated at baseline, 6 mo, 1 yr, and 2 yrs. Stone casts were evaluated independently by three observers to determine the % of the total margin exhibiting breakdown. Epoxy replicas were measured with a profilometer for wear. Wear of the hybrid composite at 2 yrs ranged from a high of 144 microm with 9 s of light-curing to a low of 36 microm with 40 s of light-curing followed by heat. Heliomolar exhibited from 11 to 16 microm of wear at 2 yrs. There was a strong negative correlation (r2 = 0.91) between the degree of cure and the abrasive wear of the hybrid composites. Marginal breakdown was negligible for the hybrids, and was reduced for the microfill from 40% to 15% of the margin by heat treatment. This study showed that the resistance to abrasive wear of a dental composite could be improved by enhancement of its degree of conversion.

In vitro wear of composite with varied cure, filler level, and filler treatment.

For the clinical wear of composite filing materials to be reduced, compositional factors such as degree of cure, filler level, and silanation level should be optimized. An oral-wear-stimulating machine was used to explore the effects of these factors on abrasion and attrition wear as well as on opposing enamel wear. The composites were made from Sr glass (1-2 micron avg) and a 50/50 Bis-GMA/TEGDMA resin. Series I (A-D, E) were light-cured (Triad II) for 9, 12, 25, and 40 sec/side to produce degree of cure (DC) as measured by FTIR of 56, 60, 61, and 63%, respectively. E received an additional heat cure (120 degrees C for 10 min) to reach a DC of 66%. Series II (D, F-I) were filled to 62, 53, 48, 37, and 28 vol%, respectively. In series III (D, J-M), the portion of fillers treated with a silane coupler (MPS) was 100, 80, 60, 40, and 20%, respectively. Samples were cycled 50,000 times against an enamel antagonist in a poppy seed/PMMA slurry in the oral wear simulator to produce abrasion (load = 20 N) and attrition (load = 70 N) simultaneously. Wear depth (micron: n = 5) was measured by profilometry. Results for each series were analysed by ANOVA/Turkey's (p < or = 0.05). The wear depths did reflect cure values, though only the abrasion difference for E < A was significant. Greater wear was correlated with lower filler levels (r2 = 0.88; p < 0.05), significantly increasing below 48 vol% (G). Wear increased linearly as the percent of silane-treated fillers was reduced (r2 = 0.99; p < 0.05). Abrasion and attrition did not differ significantly for any composite. Wear of the opposing enamel was largely unchanged by these factors. Compositional factors including degree of cure, filler level, and silanation directly affected the wear resistance of dental composites evaluated in an oral wear simulator.

Factors effecting dental composite wear in vitro.

The wear of posterior dental composite restorations takes place through a complex combination of wear mechanisms. To isolate and measure the contribution of the different tribological phenomena in a controlled manner, an oral wear simulator was employed. Results previously reported demonstrated the simulator's ability to form strong correlations with clinical results for both abrasion and attrition wear. These results were generated with the device configured to mimic masticatory dynamics, specifically employing a human enamel stylus, physiologic load levels, and a foodlike slurry for a third body. In this study the slurry was replaced with water to examine the role of the third body in producing abrasion. The third body was found to reduce wear for most materials. In a separate test the enamel stylus tip was replaced with steatite, a semiporous ceramic with wear characteristics similar to enamel when opposing dental composite. The use of a steatite antagonist increased abrasion for the larger particle filled materials. The adhesive wear mechanism was found to be a contributing factor in dental composite wear.

Premature mortality in aboriginal adults in the Northern Territory, 1979-1991.

OBJECTIVE: To identify important causes of premature mortality among Aboriginal adults in the Northern Territory (NT), 1979-1991. METHODS: All deaths of NT Aboriginal residents aged 15-64 years which occurred in the NT between 1979 and 1991 and which were recorded by the Registry of Births, Deaths and Marriages were included. Standardised mortality ratios (SMRs) were used to compare the number of deaths observed among Aboriginals in the NT to those expected, based on overall Australian rates. Years of potential life lost before age 65 (YPLL65) were estimated for specific causes of death. RESULTS: Aboriginal women (overall SMR, 5.5) and Aboriginal men (SMR, 4.7) experienced a high burden of excess mortality from almost every cause of death. This excess increased over time, especially for Aboriginal women. Among Aboriginal men, the most important causes of premature death were motor vehicle accidents (11% of excess deaths and 17% of YPLL65), ischaemic heart disease (10% of excess deaths and 10% of YPLL65), pneumonia and influenza (8% of excess deaths and 6% of YPLL65), and homicide (7% of excess deaths and 8% of YPLL65). For Aboriginal women, the most important causes included homicide (7% of excess deaths and 11% of YPLL65), chronic obstructive pulmonary disease (10% of excess deaths and 5% of YPLL65), rheumatic heart disease (7% of excess deaths and 8% of YPLL65), and ischaemic heart disease (6% of excess deaths and 5% of YPLL65). CONCLUSIONS: The wide variety of causes of excess mortality will require an equally wide variety of solutions, both medical and non-medical, and a long term commitment will be necessary to achieve reductions in premature mortality among NT Aboriginal adults.

Evaluation of composite wear with a new multi-mode oral wear simulator.

OBJECTIVES: The goals of this study were to develop a machine which simultaneously produces wear through the two main oral wear mechanisms of abrasion and attrition by the action of an enamel antagonist and to compare the results obtained for dental composites using this machine to those obtained from clinical studies and other in vitro studies. METHODS: The accuracy of this new wear tester was determined by examining 11 commercial composite filling materials and 1 amalgam. Specimens were subjected to three-body abrasion and attrition wear for 50,000 cycles. Profilometry was used to quantitate wear of the composites. Linear regression analysis was used to correlate the results to those obtained from clinical studies, as well as from other in vitro wear testers. The area of enamel wear was also determined by image analysis. The SEM was used to evaluate the wear surfaces. RESULTS: The lowest abrasion wear was recorded for the amalgam and for the microfill and smaller-particle composites. Attrition wear was enhanced for the microfill composites and one small-particle hybrid. There was a strong correlation between the results obtained with the new wear tester and those obtained in the clinical trials cited in the literature. Wear of the enamel antagonist was the greatest for the composites with the largest particle sizes. The wear tester showed a reasonable correlation with other wear-producing machines. SIGNIFICANCE: A new wear tester developed to evaluate and discriminate abrasion and attrition wear provided results similar to those reported in the literature for a variety of commercial composites. The new machine is capable of characterizing the behavior of a material in multiple wear modes simultaneously with one simple, realistic test.