The frictional coefficients and associated wear resistance of novel low-shrink resin-based composites.

OBJECTIVES: Frictional forces play a major role in the oral wear process of dental resin-based composites (RBCs) and it would be of interest to consider how the energy from friction is dissipated at the material surface. Consequently, the micromechanical wear properties of conventional methacrylate compared with novel oxirane RBCs were assessed. METHOD: The frictional coefficient (mu), volume loss and Vickers hardness number (VHN) of oxirane (EXL596 and H1) and methacrylate RBCs (Z100 and Filtek Z250) were evaluated. Archard's wear equation was implemented to obtain the wear coefficient (K) and expressed as a 'fraction of friction' (K/micro) to indicate the dissipation of frictional energy that resulted in wear. Scanning electron microscopy (SEM) was used to qualitatively asses the wear facets of each RBC following 50000-cycles. RESULTS: The mean frictional coefficients observed between the oxirane and methacrylate RBCs were not significantly different (P > 0.05). However, the volume loss of EXL596 and H1 (5.9 +/- 0.4 and 4.7 +/- 0.3 x 10(-2) mm(3)) was significantly increased compared with Z100 and Filtek Z250 (1.7 +/- 0.2 and 2.3 +/- 0.3 x 10(-2) mm(3)). The VHN of EXL596 and H1 was either significantly greater (P = 0.021) or similar (P = 0.089) to Filtek Z250, respectively. An increase in K/micro was reported for EXL596 and H1 (34.7 +/- 4.1 and 22.8+ /- 2.4 x 10(-4)) compared with Z100 and Filtek Z250 (8.50 +/- 0.7 x 10(-4) and 8.62 +/- 1.0 x 10(-4)) (P < 0.05). SEM images of the oxirane RBCs exhibited increased surface fatigue and delamination of the surface layers compared with the methacrylate RBC specimens following 50,000-cycles. CONCLUSION: The significant decrease in wear resistance of the oxirane compared with methacrylate RBCs was unexpected since frictional coefficients and/or surface hardness were statistically similar. The decreased wear resistance of EXL596 and H1 compared with Z100 and Filtek Z250 was further explained by the increase in K/micro from wear theory and the associated increase in surface fatigue identified from SEM. The simplistic testing procedure combined with SEM utilized in the current investigation provided a greater insight into the wear mechanism by considering the effect of frictional energy at the specimen surface which may benefit the development of improved wear resistance for experimental RBC materials.

The influence of short and medium-term water immersion on the hydrolytic stability of novel low-shrink dental composites.

OBJECTIVES: Differences in mechanical and physical properties exhibited by novel low-shrink resin-based composite (RBC) formulations compared with conventional methacrylate RBCs may contribute to the clinical success of the candidate material. The aim of the current study was to investigate the effect of water uptake characteristics and water solubility on the mechanical properties of two methacrylate (Z100 and Filtek Z250), an experimental oxirane (OXI) and silorane (SIL) RBC following short- and medium-term immersion. METHODS: The water sorption/solubility and associated diffusion coefficients of each material (n=5) were measured using gravimetric analysis following short- (0.1, 0.5, 1, 4, 24 and 48 h) and medium-term (1, 4, 12 and 26w) immersion. The bi-axial flexure strength, associated Weibull moduli (n=20) and fracture analysis using scanning electron microscopy (SEM) of each material for similar immersion periods was also investigated. RESULTS: Following 0.5h and each subsequent short- and medium-term immersion period the water sorption of Z100 and Filtek Z250 was decreased compared with OXI. A significant decrease in bi-axial flexure strength and associated increase in filler particle exfoliation identified through SEM was identified for OXI compared with Z100, Filtek Z250 and SIL following 26w immersion. SIL exhibited the significantly lowest water sorption, solubility and associated diffusion coefficient following each immersion period. SIGNIFICANCE: The increase in water sorption, solubility and the associated diffusion coefficient of the experimental oxirane RBC, OXI was manifested as a significant decrease in bi-axial flexure strength and attributed to the decrease in synergy between the filler particles and resin matrix. The decreased water sorption, solubility and associated diffusion coefficient of the experimental silorane RBC, SIL may potentially improve hydrolytic stability of RBC restorations demonstrated by the non-significant decrease in bi-axial flexure strength following medium-term immersion.

Direct restorative materials use in Australia in 2002.

BACKGROUND: This study aimed to determine the reasons for dentists' choice of materials, in particular amalgam and resin composite, in Australia. METHOD: A questionnaire was developed to elicit this information. The names and addresses of 1000 dentists in Australia were selected at random. The questionnaire was mailed to these dentists with an explanatory letter and reply-paid envelope. RESULTS: A total of 560 replies were received. Regarding choice of material, 99 per cent of respondents cited clinical indication as an influencing factor, although patients' aesthetic demands (99 per cent of respondents), patients' wish (96 per cent), patients' financial situation (82 per cent), and lecturers' suggestions (72 per cent) were also reported to influence respondents' choice of materials. Twelve per cent of respondents used composite 'always', 29 per cent 'often', 32 per cent 'sometimes', 23 per cent 'seldom' and 4 per cent 'never' in extensive load-bearing cavities in molar teeth. For composite restorations in posterior teeth, 84 per cent 'always', 'often' or 'sometimes' used the total etch technique, 84 per cent used a thick glass-ionomer layer and 36 per cent never used rubber dam. Fifty-nine per cent of respondents reported a decreased use of amalgam over the previous five years. Sixty-eight per cent of respondents agreed with the statement 'discontinuation of amalgam restricts a dentist's ability to adequately treat patients'. Seventy-five per cent considered that the growth in the use of composites increased the total cost of oral health care. CONCLUSIONS: Of the respondents from Australia 73 per cent place large composite restorations in molar teeth and their choice of material is influenced greatly by clinical indications, and patients' aesthetic demands.

Amalgam and composite use in UK general dental practice in 2001.

OBJECTIVE: This study determined the reasons for dentists' choice of materials, in particular amalgam and resin composite, in Great Britain. METHOD: A questionnaire was developed to elicit this information. The names and addresses of 1,000 UK-based dentists were selected at random. The questionnaire was mailed to these dentists with an explanatory letter and reply-paid envelope. RESULTS: Six hundred and fifty four replies were received. Regarding choice of material, 100% of respondents cited clinical indication as the most influential factor, although patients' aesthetic demands (99%), patients' choice (95%) and patients' financial situation (92%) were also reported to influence respondents' choice. Thirty-five per cent of respondents used composite 'sometimes', 15% 'often', and 1% 'always' in extensive load-bearing cavities in molar teeth. For composite restorations in posterior teeth, 92% 'always', 'often' or 'sometimes' used the total etch technique and 53% never used rubber dam. Seventy per cent of respondents agreed with the statement 'discontinuation of amalgam restricts a dentist's ability to adequately treat patients'. Eighty-one per cent considered that the growth in the use of composites increased the total cost of oral healthcare. CONCLUSIONS: Forty nine per cent of the respondents from England and Wales seldom or never place large composite restorations in molar teeth. Their choice of material is influenced greatly by clinical indications, and patients' aesthetic demands.

Current trends in restorative dentistry in the UK: a Delphi approach.

OBJECTIVES: The purpose of the study was to obtain insight into current trends in restorative dentistry in the UK by means of a Delphi technique. METHODS: A panel of nine experts was convened to define areas where changes were thought to occur in contemporary restorative dentistry. The defining statements obtained were circulated amongst the Panel to reach consensus on the content and wording, and then formatted into a questionnaire which was distributed amongst 407 clinical academic staff in Restorative Dentistry in UK dental schools. Good agreement with a statement was defined as a score of > or =70%, statements that received such scores were taken as indicating possible trends. RESULTS: The Expert Panel reached consensus on the wording of 21 defining statements, which were formatted into a 23-item questionnaire. The questionnaire achieved a useable response rate of 70%, and the academic respondents reached good agreement on 15 (65%) of the statements. CONCLUSIONS: The 15 statements which received scores of 70% or greater were considered to be possible indicators of trends in aspects of the clinical practice of restorative dentistry in the UK.

A practice-based, randomized, controlled clinical trial of a new resin composite restorative: one-year results.

This study evaluated the performance of a low-shrinking resin composite compared with an amalgam for restoration of Class I and II cavities of moderate size in posterior teeth in a general practice setting. Fifty-two pairs of test and control restorations were placed in 49 patients. Clinical evaluations and assessments of replica models were carried out at baseline, six months and one year. Patients recorded their level of satisfaction with the restorations by means of visual analog scales. Apart from one control restoration that failed due to a fractured cusp, all of the restorations reviewed at six months and one year were intact with no unacceptable scores for any of the evaluation criteria. It was concluded that the resin composite evaluated, when used in conjunction with the recommended adhesive system, may be an appropriate alternative to amalgam in the restoration of posterior teeth over one year in clinical service.

Ease of use versus clinical effectiveness of restorative materials.

"Ease of use," as applied to dental materials and techniques, means different things to different people. Factors that may contribute to ease of use include a minimum number of application stages, easy application and shaping ability, quickness of use, lack of stick, and moisture sensitivity. Ease of use may also imply that a material or technique does not cause stress for the dentist and patient, is cost effective, is easy to learn, and should provide the operators with a sense of satisfaction with their work. Similarly, "clinical effectiveness" of the treatments prescribed for patients is not always capable of being accurately defined. Suggested factors that may contribute to clinical effectiveness include a lack of patient complaints with respect to longevity and/or cost, no secondary caries, and preservation of the remaining tooth structure during functional loading. Ease of use and clinical effectiveness are not necessarily related, but they must be combined for a technique to be successful. The achievement of this demands a partnership between clinicians, manufacturers, and patients.

Efficacy of preformed metal crowns vs. amalgam restorations in primary molars: a systematic review.

BACKGROUND: The authors evaluated the treatment efficacy of preformed metal crowns, or PMCs, vs. amalgam restorations in primary molars by means of a literature review and meta-analysis. TYPES OF STUDIES REVIEWED: From a literature search, the authors selected clinical studies that evaluated treatment with PMCs vs. amalgam control restorations in primary molars and provided data against which treatment outcomes could be compared. RESULTS: Ten studies with durations ranging from 1.6 to 10 years fulfilled the selection criteria. Their failure rates, based on need for subsequent treatment or retention of the restoration at final evaluation, ranged from 1.9 to 30.3 percent for PMCs and 11.6 to 88.7 percent for amalgam restorations. Overall, PMCs demonstrated greater longevity and reduced retreatment need compared with amalgam control restorations. The odds ratio for all studies fell within the boundary favoring treatment with PMCs. CLINICAL IMPLICATIONS: Analysis of the literature, though mainly retrospective studies, demonstrated evidence of a more favorable outcome for PMCs than for amalgam restorations in primary molars requiring multisurface restorations.

Zooarchaeological and taphonomic analysis of the Die Kelders Cave 1 layers 10 and 11 Middle Stone Age larger mammal fauna.

Middle Stone Age (MSA) and Middle Paleolithic (MP) faunal assemblages have gained widespread attention due to their relevance to the debate over the modernity of hominid behavior during the MSA/MP. A recent critique of the scavenging argument for MSA/MP behavior drew on a summary presentation of the skeletal abundance and surface modification data from Die Kelders Cave 1 Layer 10 (Marean, 1998). This paper provides a more complete presentation of those data, adds the smaller Layer 11 sample, and provides a detailed analysis of the taphonomic history of both samples.Bone fragment density is higher in Layer 10 than in Layer 11. Bone densities vary horizontally as well, with Layer 10 showing greater deposition in the exposed areas of the cave. An analysis of long bone breakage patterns indicates that non-nutritive breakage on the Layers 10 and 11 samples was present but not intense. Size 1 mammals were predominantly accumulated by owls and/or other large raptors, not hominids, in Layer 10. Hominids were the predominant accumulator of Sizes 2-4 mammals in Layers 10 and 11 as indicated by the frequency of hammer-stone percussion marks and carnivore toothmarks. After discard by hominids, a significant portion of these remains were discovered and scavenged by carnivores. Overall, the larger mammal fauna of Layer 10 is dominated by Sizes 3 and 4 bovids, mostly young and adult eland, and thus hominids were focusing on the high-ranked prey items. Shaft portions of long bones, the portions with the most flesh, have the highest frequencies of cutmarks. A comparison of the Layers 10 and 11 cutmark frequencies to Selvaggio's (1998) scavenging model shows that the frequencies are significantly outside the range of variation documented in Selavaggio's scavenging sample.

Clinical testing of restorative materials: some historical landmarks.

OBJECTIVES: The aim of the study was to review the historical background of the methodologies currently in use for clinical investigations of contemporary tooth coloured dental restorative materials and techniques, and to attempt to identify the likely general direction of such research projects in the future. DATA SOURCES: Published articles obtained as a result of a wide ranging literature search of both dental and medical journals. STUDY SELECTION: Historical and contemporary accounts of clinical trial management, upon which an overview of the key events important in the evolution of clinical methods of evaluation of dental restorative materials, and a prediction of possible future trends in this area, could be based. CONCLUSIONS: Publication of dental restoratives clinical research has not kept up with that in medicine, where editors of leading journals require that clinical trials be run in accordance with the Consolidated Standards of Reporting Trials (CONSORT) guidelines. The current trend towards evidence based treatment in dentistry can be expected to initiate more statistically powerful clinical studies of dental restoratives, and the merit of involving general dentists in practice based research can also be anticipated to become increasingly recognised in the future.

Glass-ionomer restoratives: a systematic review of a secondary caries treatment effect.

It is generally accepted that glass ionomers inhibit secondary caries in vivo, and data from in vitro studies support this effect. The aim of this review was a systematic assessment, from the literature, of clinical evidence for the ability of glass-ionomer restoratives to inhibit secondary caries at the restoration margin. Inclusion and exclusion criteria for selection of the review papers were established prior to commencement of the literature search. Papers which conformed to these criteria, and reported on secondary caries as an outcome, were selected (N = 52). Primary and secondary lists of systematic criteria for use in the assessment of the papers were drawn up. The primary list of 14 criteria was applied to each paper. No paper fulfilled all these criteria, necessitating the use of the secondary measures: (i) a prospective study and (ii) use of an appropriate control. This yielded 28 papers. Tabulation of these papers by occurrence of secondary caries in the glass-ionomer or control groups demonstrated an even distribution between positive and negative outcomes. Valid evidence is considered to be best obtained from randomized, controlled studies of sufficient sample size. No conclusive evidence for or against a treatment effect of inhibition of secondary caries by the glass-ionomer restoratives was obtained from the systematic review. There is a need for appraisal of the methods currently adopted for the clinical evaluation of glass-ionomer restorative materials, and for further development of the methodology to support future systematic reviews.

Impression materials and techniques for crown and bridgework: a survey of undergraduate teaching in the UK.

The aim of this study was to document the teaching of impression materials and techniques for crown and bridgework in the undergraduate curriculum in UK dental schools. A questionnaire sent to each school during the 1993/1994 academic year elicited fourteen replies (100% response). Addition-cured silicones were found to predominate; 71% of schools taught and used clinically a one-stage, full arch impression technique involving stock trays, and 57% of schools a full-arch custom tray technique. Routine disinfection of impressions was taught and practised in 43% of schools. The results demonstrated variation between UK dental schools in their teaching of impression materials and techniques for crown and bridgework in the undergraduate curriculum.

Effect of a resin-modified glass ionomer liner on volumetric polymerization shrinkage of various composites.

OBJECTIVE: The aim of this study was to evaluate the volumetric polymerization shrinkage of a selection of composite resins alone, and in contact with a resin-modified glass ionomer (RMGI) liner. METHODS: Volumetric polymerization shrinkage was measured for five different composite resins by means of the Watts and Cash deflecting disk method. Shrinkage measurements were determined for 300 s for each composite alone, and when placed over pre-cured RMGI liner. Each sample was placed within a brass ring fixed to a glass microscope slide. A linear vertical displacement transducer (LVDT) was brought into contact with a flexible glass coverslip placed over the composite sample. On curing, the contraction of the setting composite sample caused distortion of the coverslip, the resulting deflection being recorded via the LVDT by means of data-logging software. All RMGI samples were prepared at 85% relative humidity (RH) and 35 degrees C. In all cases the composite was light-cured at ambient RH and 35 degrees C. RESULTS: Analysis of the data demonstrated statistically significantly less shrinkage for each composite when cured in contact with the set RMGI liner than when cured alone, at p < 0.001. SIGNIFICANCE: Use of an RMGI liner was found to significantly reduce volumetric polymerization contraction for all the light-curing composite resin restorative materials tested.