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Objectives: An alcohol-free tissue conditioner based on a n-butyl methacrylate/i-butyl methacrylate copolymer has recently been developed. The purpose of the present study was to compare some key properties of the new tissue conditioner with those of poly(ethyl methacrylate)-based conventional materials containing ethyl alcohol. The effect of a coating, which consisted of poly(ethyl methacrylate) and methyl methacrylate, was also evaluated. Methods: The new alcohol-free tissue conditioner (Fictioner) and three tissue conditioners containing ethyl alcohol (FITT, Hydro-Cast, SR-Ivoseal) were evaluated. The coated alcohol-free material was also used. Gelation characteristics, dynamic viscoelastic properties and compatibility with dental stones were measured using a displacement rheometer, dynamic viscoelastometer and profilometer, respectively. In addition, weight changes during immersion in water were determined. Results: The working time and gelation time of the alcohol-free tissue conditioner were similar to those of the conventional materials. This alcohol-free material had significantly lower shear storage modulus and shear loss modulus, and higher loss tangent (P

Summary Objective The purpose of this study was to investigate the effect of two-step adhesive systems on secondary caries inhibition around fluoride-releasing materials in vitro. Methods Two self-etching primer systems, Clearfil SE Bond (SE) and UniFil Bond (UB), and two one-bottle systems with a total-etch wet-bonding technique, Single Bond (SB) and One-Step (OS), were used prior to placement of resin composites either with (Reactmer) or without (Z100) fluoride release. Class V cavities prepared in extracted human premolars were restored with various combinations of materials: Reactmer/SE, Reactmer/UB, Reactmer/SB, Reactmer/OS, Z100/SE, Z100/UB, Z100/SB and Z100/OS. After storage for 14 days, the restored teeth were incubated in bacterial medium containing sucrose with Streptoccus mutans for 2 weeks. Water sorption and desorption of the adhesives and fluoride release from the resins either coated with adhesive or uncoated were also determined. Results The one-bottle groups showed higher water sorption and desorption than the self-etching primer groups. Although fluoride release from the Reactmer specimens was suppressed by the adhesive coating, the one-bottle groups allowed significantly higher fluoride release than the self-etching primer groups. On microradiographs, the radio-opaque layers adjacent to the Reactmer restorations were thick and clear, while the layers adjacent to the Z100 restorations were thin and unclear. For the Reactmer restorations, the radio-opaque layers associated with the one-bottle groups were significantly thicker than for the self-etching primer groups. Conclusions These results indicated that the use of one-bottle wet-bonding systems for bonding of fluoride-releasing resin composites to dentine may contribute to inhibit secondary caries compared to self-etching primer systems.

Objective: the aims of this study were to determine the appropriate composition and purity limits of aluminium alloy radiopacity standards for dental biomaterials, taking into account the current status in representative laboratories worldwide, and to formalise the calculation procedure for processing radiopacity data. Methods: a series of aluminium step-wedges were obtained from academic and industrial research laboratories. These were analysed by energy dispersive X-ray procedures. The set of step-wedges were independently characterised for radiopacity at two University dental schools. Results: the percentage of aluminium together with the percentages of minor alloying elements (magnesium, manganese, iron and silicon) have been determined as mass percentages. For each centre, the optical density versus step-height for all wedges was judged to fall on a common curve, with the main exception of one step-wedge that was found to contain 4% copper, by mass. A suitable calculation procedure was described explicitly. Conclusion: of the examined representative step-wedges, all but the aluminium–4% copper material were satisfactory and gave results comparable with wedges of high purity. Limits should therefore be revised for composition of aluminium radiopacity step-wedges or test blocks to a more realistic level of purity. Alloys with more than 0.05% copper or 1.0% iron should be excluded and the aluminium content should be at least 98% by mass. In the calculations deployed for deriving radiopacity as `equivalent aluminium thicknesses', an appropriate linear regression procedure should be employed and considerable care taken in the evaluation of materials of low or borderline radiopacity, relative to specification limits. The method described is principally suitable for materials with radiopacity greater than 1 mm. For materials with radiopacity less than 1 mm aluminium, thicker specimens (2 mm) should be used.

A new denture soft lining material based on a polyvinylsiloxane system, similar to that used in addition-curing silicone impression materials, has recently been developed. The purpose of the work reported here was to compare certain key properties of the new material with those of other commercially available materials. Setting characteristics, resistance to penetration, elastic properties, water absorption, peel strength and contact angle with water were determined for five materials including the new product. In addition, the change in properties following water storage were determined. In many respects the properties of the new material were noted to be similar to those of a heat-cured silicone product. It is initially elastic and of "medium" softness as defined by ISO 10139-2. It was the only product which did not lose weight on storage in water and over 90 days of storage it gave only a small change in compliance as measured by surface penetration. Bond strength of the new material to an acrylic denture base appears only moderate. However, failure was cohesive within the soft material with no peeling, suggesting that peeling is unlikely to occur in practice. The affinity between the surface of the material and water, as determined by contact angle, is significantly better than for other silicone products. The properties of the polyvinylsiloxane denture soft lining material are in many respects similar to those of other silicone soft lining materials. However, the efficacy of the adhesive which prevents peeling combined with a convenient packaging, proportioning and mixing system suggests that the material may offer some advantages which warrant its clinical evaluation.

This critical review of the published literature on dental materials for the year 1996 has been compiled by the Dental Materials Panel of the UK. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, resin-bonded bridges and ceramo-metallic restorations, ceramics, denture base resins and soft lining materials, impression materials, implants materials, orthodontic materials, biomechanics and image processing, resin composites and casting investment materials and waxes). Three hundred and thirteen articles have been reviewed.

This critical review of the published literature on dental materials for the year 1995 has been compiled by the Dental Materials Panel of the United Kingdom. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, resin composites, dentine bonding, dental amalgam, endodontic materials, casting alloys, investment materials, resin-bonded bridges and ceramo-metallic restorations, all ceramic restorations, denture base and soft lining materials, impression materials, dental implants, orthodontic materials and biomechanics). Three hundred and thirty articles published in 68 titles have been reviewed.

Objective: To compare the durability of a minimal composite sealant restoration (MCR) with that of a glass ionomer sealant restoration (GSR). Methods: Under local anaesthesia, a MCR and a GSR were placed in the mouths of selected patients; allocation of restoration type was made randomly. All restorations were placed by one operator using standard procedures and were then assessed clinically at baseline and thereafter every 6 months. Results: Fifty-eight patients, with a total of 66 pairs of restorations, were reviewed for up to 27 months. Assessment criteria were based upon the amount of sealant lost, the state of the pit restoration and the occurrence of caries. There were no cases of recurrent caries, and a total of only four pit restorations failed, three (4.5%) GSRs and one (1.5%) MCR. Three MCRs and seven GSRs required further additions of sealant. Survival analysis was carried out using the loss of more than a third of the sealant as the failed status. At this level, the MCRs had a significantly greater Median Survival Time (MST) (24.7 months) than the GSRs (20.7 months) (p < 0.05). Only seven (10.6%) of the MCRs lost more than a third of their sealant as compared with 17 (25.8%) of the GSRs. Conclusions: There was no significant difference in the durability of the MCR compared with the GSR in the treatment of occlusal caries. However, there was significantly better retention of the fissure sealant over the composite restoration than over the glass ionomer.

The viscoelastic properties of a new light-activated temporary denture soft lining material have been monitored in vitro using a force/distance probe. Its baseline behaviour was characteristic of an elastic material and its compliance considerably less than that of both a short-term and a long-term soft lining material which were used as controls. Sample thickness had no appreciable effect on this compliance. These results suggest that the new product is likely to be perceived as being significantly harder by a patient. Twenty-four weeks' immersion in distilled water had no significant effect on either the compliance or elasticity of the test material and would suggest an improved durability when compared to other conventional short-term resilient denture lining materials, albeit at the expense of compliance.

The shear bond strengths of three dental adhesives to dentine and a NiCrBe alloy were determined. Forty human third permanent molar teeth were ground to expose superficial dentine, to 20 of which P50 composite was bonded, using All-Bond 2 (n = 10) or Scotchbond 2 (n = 10). Alloy discs were bonded to the remaining 20 specimens, using either All-Bond 2 (n = 10) or Panavia Ex (n = 10). All specimens were stored at 37 °C, 100% RH, for 24 h. Testing was carried out using a shear jig at a cross-head speed of 1 mm min−1, following which a 0.5 mm increment was removed to expose middle dentine for further bond tests (n = 10 for each adhesive). Removal of a further 0.5 mm increment exposed ‘deep’ dentine for final dentine bond strength tests. Results were then aggregated for each substrate/adhesive combination (n = 30). Alloy/alloy bond strengths were determined after bonding alloy discs together using Panavia Ex (n = 30) or All-Bond 2 (n = 30). Results were analysed using ANOVA and Weibull analysis. All-Bond 2 produced significantly greater and more reliable bond strengths to dentine than did either Scotchbond 2 or Panavia Ex. The bond strength of Scotchbond 2 and Panavia Ex to dentine was dependent upon the dentine depth whereas the bond strength of All-Bond 2 to dentine was independent of dentine depth. Alloy/alloy bond strengths were significantly greater when using Panavia Ex compared with All-Bond 2.

The effects of sample thickness on the in vitro bond strength of two light-activated glass polyalkenoate cements to dentine have been investigated. The buccal and/or lingual surfaces of non-carious human third molar teeth were used for bonding. The tensile bond strengths to dentine of samples of the cements of 0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm were measured 10 min after bonding. For one of the materials bond strength and reliability were found to decrease as the sample thickness increased. The bond strength to dentine of the second material was also affected by changes in the thickness of the cement but as the bond strengths were all very low for this material, any differences are probably of little clinical relevance.

The viscoelastic properties of a widely used temporary soft lining material have been monitored in vivo and in vitro using a force distance probe. Over a period of 8 weeks' clinical use, Coe Soft demonstrated a significant and continued reduction in compliance with time, the reduction being particularly rapid over the first week. These changes were not associated with a reduction in measured lining thickness for which significant changes were not found. In vitro immersion in water, saline or artificial saliva was characterized by a rapid and significant reduction in compliance values over the first week. Further continued reductions in compliance values were only observed in artificial saliva over 8 weeks, and on prolonged immersion in distilled water over 96 weeks. All reductions in compliance were significantly less than those seen clinically.

Age-related changes in the viscoelasticity of an acrylic-based (Palasiv 62) and silicone (Molloplast-B) permanent soft lining material were evaluated in parallel clinical and laboratory longitudinal studies using a force/distance probe. Changes in the viscoelastic properties of Palasiv 62 in clinical use were characterized by a significant and continued reduction in both initial and delayed compliance. That is, the material became harder whilst still retaining the underlying pattern of viscoelasticity seen at baseline. Laboratory immersion in distilled water resulted in significant reductions in compliance values. These reductions were cumulatively similar to those seen clinically but did not occur as rapidly. There was evidence of small, continued reductions in the measured thickness of clinical linings of Palasiv 62. The clinical and laboratory compliance of Molloplast-B remained stable over time. Ageing did not affect the essential elasticity of this material.

Direct composite inlays may sometimes be difficult to remove from the cavity following primary polymerization. The aim of this work was to find the lowest cavity convergence angle (taper) which would allow reliable inlay removal. Cavity finish and cavity size were also taken into account. Standardized mesio-occlusal-distal cavities of 6 degrees taper were cut into 10 teeth of varying mesiodistal width and finished with either 12-bladed tungsten carbide or 25 microns diamond burs. After separating medium had been applied. Coltene Brilliant Dentin composite resin was packed into the cavity and light cured. The force required to remove the inlay was measured with an Instron Universal Testing Machine. The cavities were then refinished with the alternative finish and the experiment repeated. The same sequence was used for cavities of 12 degrees and finally 18 degrees convergence angle which were cut consecutively in the same 10 teeth. Force levels related to cavity convergence angle, cavity finish and tooth size were tested by ANOVA and regression analysis. The forces required to remove some of the inlays from the 6 degrees, and to a lesser extent 12 degrees angled cavities, proved unacceptably high, while an 18 degrees convergence angle resulted in statistically significant lower forces which were unlikely to damage tooth or inlay. Cavity finish and tooth size did not influence inlay withdrawal force.

The tensile bond strength to dentine of four dentine bonding agents has been measured at various depths within dentine and the results analysed using Weibull analysis. There were significant differences in the bond strength values among the four products particularly with near-surface dentine. Despite the differences in chemical composition among the materials the trend of decreasing bond strength with increasing depth of dentine was common to them all. This suggests that the underlying mechanism of adhesion may be common to all four products despite their differing chemical compositions.

Self-aspirating dental local anaesthetic syringe systems rely on deformation of rubber diaphragms contained in the anaesthetic cartridges to produce the aspirating force. A test has been developed which can examine the performance of these rubber diaphragms under functional conditions. This method could be useful in the production of standards for dental local anaesthetic cartridges. The test has been used to determine the influence of storage conditions on the performance of dental local anaesthetic cartridges. The results show that, with the cartridges investigated, storage at 37°C increased the amount of distortion per unit force of the aspirating diaphragms in comparison with storage at room temperature. However recovery of the diaphragms was unaffected. Storage at the higher temperature decreased the amount of force required to initiate movement of the cartridge rubber bung during injection. Soaking cartridges in alcohol did not affect the distortion of the aspirating diaphragms or the force needed to move the bung during injection, but did increase the degree of recovery of the diaphragm in the bung of self-aspirating cartridges.

To compare the ability of re-usable and partly disposable dental cartridge syringes to aspirate in vitro.A laboratory investigation comparing two re-usable (Astra and Rotor) and one partly disposable (Ultra Safety-plus) dental cartridge syringes. Forces needed to move the cartridge plunger and forces required to produce aspiration of Bonney's Blue dye were measured using an Instron testing machine.There were significant differences in the forces needed to produce aspiration in the different systems (F = 194, p0.001). The Astra system needed the least force to produce aspiration. The forces required to aspirate in the Rotor and Ultra Safety-plus systems did not differ. Each system aspirated effectively in vitro at the initial aspiration manoeuvre. The forces available for subsequent aspiration attempts varied with the speed of cartridge plunger movement. The volume of local anaesthetic cartridge used did not affect the force needed to produce aspiration in the Ultra Safety-plus syringe. The method of testing free-flow of solution through the needle affected the force generated at subsequent plunger movements.The re-usable and partly disposable syringes investigated aspirated effectively at the initial aspiration manoeuvre. The force available to produce aspiration at subsequent attempts varies with the speed of injection. The method of testing free-flow of solution through the needle in a loaded syringe affects the force available at the first aspiration manoeuvre.

Objectives. The aim of this study was to investigate the quantities of total and free fluoride ions released from four resin-based composites containing fluoride (Heliomolar (HE), UniFil S (UF), Beautifil (BE) and Reactmer paste (RP)) and one glass ionomer cement (Ketac-Fil Plus Aplicap (KF)). Methods. Five disk specimens of each material were prepared and the fluoride release was measured at 1, 2, 4, 7, 14, 21 and 28 days. The amounts of total and free fluoride ions released from materials were measured by using an ion-selective electrode (ISE) and ion chromatography (IC). Data were statistically analyzed using a t-test at a significant level of 0.05. Results. For HE, fluoride release is undetectable using the ISE but was detected by the IC method. There were no significant differences in the free and total fluoride ions released from UF and BE (p>0.05). For RP, the free fluoride ions were significantly lower than the total fluoride ions after 4 days (p

The purpose of the study was to evaluate the effect of the mixing method on the compressive strength and porosity of dental glass ionomer cements.Five glass ionomer cements were chosen for use in the study. Two were hand mixed and three were encapsulated. The latter were mixed either by shaking or rotating. Following mixing by rotation some samples were centrifuged before use. The 24h compressive strength was determined for each cement/mixing regime combination and fracture surfaces were examined using SEM.The mixing method had a significant effect on compressive strength (P0.05). For the luting/lining cement, hand mixing produced a significantly greater compressive strength (P0.05). For the restorative cement, there were only small differences between specimens mixed by different methods and hand mixing gave a significantly lower compressive strength than mixing by rotation followed by centrifuging (P0.05). Porosity was incorporated in all samples and low values of compressive strength were associated with larger pores.The strength of glass ionomer cements is affected by incorporated porosity and this is dependent on the method of mixing. For some cements hand mixing is favoured in order to reduce porosity and increase strength but this is not generally applicable to all cements.

Objectives: To determine at 5 year follow-up the failure rate, wear rates and other aspects of clinical performance of direct composite inlays compared with conventional composite restorations placed incrementally. Methods: 100 matched pairs of restorations were originally entered into the trial. Each pair consisted of a direct composite inlay and a conventional composite restoration made from the same material. At 5 years it was possible to recall 65 pairs, of which 54 were complete. Clinical assessments were made using USPHS criteria (indirect measurements of occlusal wear were made using Ivoclar standard dies) and annual bite wing radiographs. Results: There was a trend to more failure of inlays than conventional composites (17.4 c.f. 7.5%) but this was not significant. The clinical performance of both types of restoration was similar and compared favourably with the results of studies of other materials. Secondary decay was diagnosed in only one restoration. Between 3 and 5 years there was some deterioration in cavo-marginal discoloration, marginal adaptation (occlusally) and surface roughness (occlusally). There was no apparent deterioration in colour match, proximal contact, shim stock contacts and Gingival Index. Wear rates of both types of restoration showed no significant difference and were essentially linear with a mean of 33–34 μm per year. Conclusions: Both inlays and conventional composite restorations complied with ADA specification minimum requirements for posterior composite restorations. In this study the direct inlay technique gave no clinical advantage over conventional, incremental placement.

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.

To investigate the daily fluoride release of two glass ionomers (Ketac-Fil and ChemFil Superior) and two compomers (Compoglass and Dyract Restorative) over 6 months.A pilot study evaluated the time taken for sample solutions to equilibrate to establish an appropriate time period for sample solution storage between fluoride ion measurements. In the main study storage water replacement and fluoride ion determination was made daily using a specific ion electrode, TISAB buffer and standard solutions for calibration.Equilibration of fluoride concentration in aqueous solution occurred in under 48 h for all materials. Total fluoride released (microgram mm-2) after 6 months by Ketac-Fil (30.6, s.d. 4.9) was significantly greater than ChemFil Superior (12.7, s.d. 2.5), Compoglass (10.4, s.d. 1.0) and Dyract Restorative (7.7, s.d. 1.7) (P0.05). Daily fluoride release at 24 h and 10 days was significantly higher for the glass ionomers than the compomers (P0.05). After 40 days the daily fluoride release (microgram mm-2) from ChemFil Superior (0.05, s.d. 0.01) was not significantly different from Compoglass (0.04, s.d. 0.01) and Dyract Restorative (0.03, s.d. 0.00) (P0.05). Daily fluoride release from Ketac-Fil remains significantly higher than the compomers at 3 and 6 months (P0.05).Specimens stored in water equilibrate rapidly, suggesting the rate at which storage water is changed may alter the relative fluoride release rates of materials. This important fact is often overlooked. Fluoride release from the glass ionomers is initially higher than for the compomers. Fluoride release from glass ionomers falls rapidly to approach levels released by compomers. Compomers produce no initial burst of fluoride and levels of release remain relatively constant.

Objectives: One of the reasons for using composite inlays is that restorations can be tempered. Composites tempered with heat and light have, at least initially, an enhanced degree of cure which, it is claimed, improves their physical properties, including wear resistance. The aim of this study was to compare the wear rates of a selection of composites in their regular and tempered conditions. Methods: Two hybrid composites (Brilliant Dentin, Coltene; Occlusin, ICI) and a microfilled material (Heliomolar, Ivoclar-Vivadent) were chosen to provide a variety of filler particle and resin systems. Regular composites were cured normally with light while tempered composites were given an additional 8 min secondary cure at 120 °C in the Coltene DI500 heat and light oven. Specimens of an amalgam (Dispersalloy, Johnson & Johnson) and a heat/pressure cured composite (Isosit, Ivoclar-Vivadent) were used for comparison. The specimens were stored for either 7 days or 1 year to determine if prolonged water storage affected wear rate. Wear testing was carried out in a two-body wear machine using a steatite abrader as an enamel substitute. ANOVA was used to test the effects on wear rate of tempering, storage time and type of material. Results: Significant differences were found in wear rate between materials (p < 0.001), but not for tempering or prolonged storage time. Conclusion: These findings agree with clinical studies which have shown that tempering has little or no influence on the occlusal wear of composite inlays.

Objectiw: The main purpose of this paper is to present a new method of predicting clinical performance using mechanical loading in a ball mill. Methods: A series of four experiments (two involving a hybrid composite and one each on orthodontic brackets and bands) is described in which the ball mill was used to subject specimens to mechanical fatigue. Results: A reproducibility study using composite beam specimens showed no significant difference between the Mean Survival Time (MST) in all the three experimental runs (P = 0.42). When subjected to thermal cycling, the MST of the cycled group was 155.0 min compared to 247.0 min for the control group (P < 0.01). The MST of untreated and sandblasted brackets was 7.9 h and 14 h respectively (P < 0.01). There is also a significant difference (P < 0.001) in the MST of sandblasted bands when compared to the untreated bands. Conclusions: The ball mill proved to be a convenient and reproducible means of producing mechanical fatigue and may be useful in predicting the clinical performance of dental materials.

Objectives: Previously, we have reported that dental composite incorporating the new monomer methacryloy-loxydodecylpyridinium bromide (MDPB) showed no release of antibacterial components after being cured but still exhibited antibacterial activity against Streptococcus mutans on its surface. In this study, in order to elucidate the mechanism of the antibacterial effect of immobilized MDPB, the bactericidal activity of MDPB polymer in water-soluble and -insoluble form was investigated, and the effect of MDPB polymer on bacterial attachment was estimated. Methods: Solutions of homo-polymer of MDPB and co-polymer of MDPB with acrylamide were prepared and the viability of seven major oral streptococci was determined after incubation with each polymer solution. For the estimation of bactericidal activity of insolubilized MDPB polymer, bacteria were kept in contact with cured unfilled Bis-GMA-based resin discs with or without MDPB, and the recovery of viable cells was measured. Attachment of streptococci to cured resin discs with or without MDPB was also compared using radiolabelled bacteria. Results: Water-soluble homo-polymer of MDPB and co-polymer with acrylamide showed bactericidal activity against oral streptococci. However, cured resin incorporating MDPB, which is in water-insoluble form, had little bactericidal activity. Attachment of streptococci, including species which are early colonizers in dental plaque formation, to the cured resin containing MDPB was significantly less than to the control without MDPB. Conclusions: These results indicate that the bactericidal activity of MDPB polymer is reduced after immobilization, but MDPB on the surface of a resin-based material still shows a bacteriostatic effect and antiadhesion property against oral streptococci.

The slow rate of the setting reaction of glass ionomer cements (GICs) is one of the problems associated with their clinical use. The manufacturers of these materials suggest that increasing the mixing time will increase the rate of reaction and it was the purpose of this study to investigate the limits of this relationship. The method used to monitor the setting reaction with Differential Thermal Analysis (DTA). The results obtained using DTA were compared with those obtained using the ISO penetrometer method as defined in the ISO standard for water-based cements, ISO 9917 : 1991E. It was shown that increasing the mixing time of cements did not significantly reduce the setting time ( P > 0.05). Under the conditions of the study it was only possible to measure a working time for the Chemfil II (and then only if it was mixed for less than 12 s). Storing the capsules at 4°C did enable a working time to be measured using the DTA for all the materials, however these storage conditions also produced a significant increase in the setting time which would be undesirable to the clinician. The penetrometer method underestimated the duration of the setting reaction by up to 32% compared with the DTA method. However it was a quick and reproducible method of measuring setting time and as such may still be an appropriate method for use in the ISO standards.

This review of the published literature on Dental Materials during 1992 has been compiled by the members of the Dental Materials Panel of the United Kingdom. Please note that the views expressed in this review are those of the individual authors and not of the Dental Materials Panel. The contribution of each author has been clearly identified with each topic. Therefore, if there is anything in the review you disagree with or dislike, or possibly even like, then put pen to paper and write to the editor, who will be happy to pass these comments to the appropriate contributor for reply. Both the original letter and the author’s response will be published together in a later issue of the Journal, but only if the views expressed add to the scientific argument. As this will be my last review as editor I would like to thank all the contributors, as without their cooperation

A new method of measuring both working time and setting time of elastomeric impression materials has been developed. A Displacement Rheometer was used to monitor the development of elasticity in setting elastomers. The results obtained with the Displacement Rheometer were compared to the results of the ISO test as well as those of the Controlled Stress Rheometer. Working time using the ISO method was calculated according to the standard method described in the specification, while for both the Controlled Stress Rheometer and the Displacement Rheometer working times were the times when initial elastic recovery was observed at 23 degrees C. With the Displacement Rheometer the setting time is the time when the mixed material reaches optimal elastic recovery at 37 degrees C. Statistical analysis with ANOVA showed that for five of the test materials there were no differences between the three methods. For three of the materials the working time determined by the ISO method was significantly longer than that determined by the other two methods. The advantages and disadvantages of each method are discussed and the Displacement Rheometer is recommended as a supplement to the standard specification method.

Denture soft lining materials are widely used in prosthetic dentistry. Their success has been attributed to their softness and resilience, properties described by their viscoelasticity. Though these properties have been extensively investigated in laboratory studies, clinical studies have been limited. The viscoelastic properties of the temporary soft lining material Coe Soft and the permanent soft lining materials Palasiv 62 and Molloplast-B have been studied using a force/distance probe whereby penetration was measured against time under constant stress. Derived values of an initial and time-dependent compliance has allowed a quantitative in vivo and in vitro assessment of freshly prepared samples of each test material and comparison between materials. The baseline behaviour of each test material in response to the test regimen was similar for both clinical and laboratory specimens. Three types of behaviour could be identified: (i) constant strain in which penetration was clearly less than specimen thickness--elastic behaviour (Molloplast-B); (ii) constant strain in which the penetration was equal or nearly equal to specimen thickness--apparent elastic behaviour (Coe Soft); (iii) strain which increased with time of load application--viscoelastic behaviour (Palasiv 62). The mean and range of baseline clinical thickness for Coe Soft was approximately half that seen for the permanent soft lining materials. There was a much smaller range in the baseline compliance of all materials than might have been anticipated from a knowledge of their relative softness.

The setting reaction of two light-activated glass polyalkenoate cements has been investigated using differential thermal analysis and surface hardness measurements. One material was found to have two distinct phases to its setting reaction. Light activation resulted in a rapid initial set with a large exotherm. A slower setting reaction was detectable when the cement was allowed to set in the absence of light. The surface hardness of this cement increased for some time after the cessation of light activation, indicating continuation of the chemical setting reaction within the material. The ultimate hardness of the cement was significantly higher than its hardness at the termination of light activation. Light activation of the second material increased the rate of set of the cement but no evidence of a dual setting reaction was observed. This material remained very soft and flexible for over 1 h after light activation. A 30 s exposure with a visible light source produced some immediate hardening up to 1.5-2.0 mm below the surface for both materials.

Adhesion of tooth-coloured restorative materials to the instruments used to place them is a clinical problem. This paper examines the low-stick properties and the durability of a 5 micron coating of titanium nitride on stainless steel when used with two composites (a hybrid and a microfilled) and a glass polyalkenoate (ionomer) cement. Titanium nitride-coated dies were compared to polished stainless steel for adhesion to the unset restorative material before and after a period of wear, and also for properties of surface hardness, contact angle with unfilled resin and frictional coefficient. The results demonstrated that, while the coated instruments were significantly harder and showed a lower coefficient of friction and a higher contact angle with resin, they were slightly 'stickier' than highly polished stainless steel, and this difference persisted even after wear. However, the material is very hard, resistant to damage, and appears to have little potential to discolour the restorative materials with which it is used. It is concluded that a titanium nitride coating confers no additional advantage as regards low-stick properties, over clean, polished stainless steel used for dental instruments.

This paper describes monitoring the wear of restorations borne by partial dentures over a 12 month period using a novel photogrammetric technique and modified United States Public Health Service (USPHS) criteria. The performance of Class II restorations of Dispersalloy was compared with that of similar restorations of either KetacFil or Occlusin. The photogrammetric technique highlighted differences in performance not detected by the modified USPHS criteria. It is concluded that the photogrammetric technique should prove valuable in the in vivo assessment of the performance of restorative materials but that further refinement of the method is required particularly with regard to the orientation of replicas for sequential measurements.

A preliminary scanning electron microscope (SEM) study was carried out to investigate how the adaptation of two calcium hydroxide bases (one chemically cured, one light cured) was affected by the polymerization contraction of a supervening light-cured composite resin restoration. Occlusal cavities were prepared in 40 sound extracted human premolars, divided into two equal groups. In the first group a chemically cured calcium hydroxide (Dycal, De Trey Dentsply, Konstanz, FRG) was placed as a base. In the second group a new light-cured calcium hydroxide product (Prisma VLC Dycal, De Trey Dentsply) was used. The restorations were completed with an acid-etched, incrementally placed composite resin. The specimens were sectioned vertically and debrided. A replica was made of each half-tooth. The interfaces between composite resin/base and base/dentine were viewed and photographed in the SEM. The marginal adaptation at these two interfaces was classified into three categories according to the extent of the gaps that were observed. Prisma VLC Dycal base was found to be pulled away from the dentine floor of the cavity as a result of an apparent adhesion to the composite resin during polymerization contraction. Dycal was better adapted to the cavity floor than Prisma VLC Dycal. Disorganization of the resin-bonded Prisma VLC Dycal was minimal even after acid etching the enamel, sectioning and ultrasonic debridement. Dycal appeared to be more friable, and occasionally exhibited marked disorganization as a result of these procedures.

The suitability of a test for standard specification testing depends inter alia on the ability to repeat the tests in a reproducible manner at a number of test centres. This work involved the investigation of three tests currently proposed as standard specification tests for dental materials. It was found that one test (compressive strength of cements) is inappropriate for inclusion in standards due to an unacceptable variation in test results between test centres. The treatment of results suggested in standards should place less emphasis on the mean value of a relatively small number of test specimens and the use of a simple form of probability theory in which, say, 80 per cent of specimens are required to achieve a certain pass level. In some standards there may be a need to increase the numbers of test specimens significantly in order to achieve a more meaningful and reliable result. The use of Weibull statistics can be adopted as a means of identifying tests which are suitable for inclusion in standard specifications, although it is doubtful that a test at this level of sophistication is required or desirable for inclusion in the standards themselves.

This review of the published literature on dental materials during 1988 has been compiled by the members of the Dental Materials Panel of the United Kingdom. The editor would like to extend his grateful thanks to all the contributors who continue year after year to provide their views and critical assessment of what in their opinion have been the main contributions to their area of research. The field of dental materials is still growing apace and these regular reviews allow the reader to keep abreast of the main advances, a task which proves more and more difficult even within a particular speciality. Although the format of the review is well established this is by no means written in tablets of stone. Hence the editor would like to invite the readers to provide comments or criticisms of the review. Is the review sufficiently comprehensive? Is there too much or too little? Are there any topics which are not included and should be? Any suggestions from the readers of the Journal of Dentistry would be very helpful, as we are continually seeking to improve the review. Whatever your views, we would like to hear from you.