A clinical trial comparing the efficacy of a glass polyalkenoate cement (GPC) restoration with an amalgam cement restoration (ACR) in the management of caries in the deciduous molar dentition was undertaken. Two hundred and thirty-eight restorations, that is 119 pairs, were placed in 76 patients with an age range of 5 to 11 years. The durability of these restorations was assessed during a 5-year follow-up period, using modified United States Public Health Service criteria. The glass polyalkenoate cement restorations occupied 16% of the occlusal surface of the tooth compared to 28% for the amalgam restorations, had a lower median survival time (33.4 [SE 2.26] months compared to 41.4 [SE 2.24] months) and underwent greater loss of anatomical form and marginal integrity than the paired amalgam controls.

No abstract

A clinical trial of direct composite inlays versus conventionally (incrementally) placed restorations made from the same material was started in January 1989. Restorations were randomly allocated to matched pairs of cavities. This study reports the 3-year performance of 71 of the 100 pairs of restorations placed over a 2-year period and followed-up every 6 months. Clinical assessments were made using USPHS criteria (indirect measurements of occlusal wear were made using Ivoclar standard dies) and annual bite wing radiographs. Direct inlays showed significantly less occlusal wear than conventional restorations, but the difference was small. The clinical performance of both types of restoration was similar and compared favourably with studies of other materials. No secondary decay was diagnosed. The direct inlays, however, took longer to place and did not reduce postoperative sensitivity or failure rate (8% failure of inlays and 4% of conventional composites over 3 years). Contouring of proximal and occlusal aspects was not facilitated with direct inlays but may be easier with indirect inlays on removable dies.

Most dental materials are designed to have a relatively ‘neutral’ existence in the mouth. It is considered that if they are ‘passive’ and do not react with the oral environment they will be more stable and have a greater durability. At the same time, it is hoped that our materials will be well accepted and will cause neither harm nor injury. This is an entirely negative approach to material tolerance and biocompatibility and hides the possibility that some positive gains can be achieved by using materials which behave in a more dynamic fashion in the environment in which they are placed. An example of materials which have potential for ‘dynamic’ behaviour exists with structures which are partly water‐based or have phases or zones with significant water content and for which the water within the material can react to changes in the ambient conditions. Such materials may even be said to have the potential for ‘smart’ behaviour, i.e. they can react to changes in the environment to bring about advantageous changes in properties, either within the material itself or in the material‐tooth complex. The controlled movement of water or aqueous media through the material may cause changes in dimensions, may be the carrier for various dissolved species, and may influence the potential for the formation of biofilms at the surface. Some of these issues may be closely interrelated. Clearly, materials which do not have the capacity for water transport or storage do not have the potential for this sort of behaviour. Some materials which are normally resistant to the healthy oral environment can undergo controlled degradation at low pH in order to release ions which may prove beneficial or protective. It is doubtful whether such behaviour should be classified as ‘smart’ because the material cannot readily return to its original condition when the stimulus is removed. Other materials, such as certain alloys, having no means of transporting water through their structure, can display smart behaviour by undergoing predictable changes in structure in response to applied mechanical or thermal stimuli. It has been difficult to harness such behaviour to the benefit of patients but progress in this area is slowly being made.

No abstract

The development of adhesive restorative materials has led to more conservative cavity design with greater reliance being placed upon the bond of a material with tooth tissue for retention of the restoration. Glass-ionomer cements may offer particular advantages but have yet to achieve the durability reported for amalgam. This study reports on the results of a 2.5-year prospective clinical trial comparing the durability of two glass-ionomer cements, a conventional material (Ketac Fil) and a metal reinforced cermet (Ketac Silver) in the restoration of Class II lesions in primary molars. Forty-six pairs of restorations were assessed in 37 children. The failure rate of Ketac Fil, 23%, was significantly lower than that of Ketac Silver, 41% (P < 0.05). The median survival time of the Ketac Fil restorations was significantly greater, 25.3 months, than that of the Ketac Silver restorations, 20.3 months (P < 0.05). These values may be an underestimate of the true longevity of both restoration types as many of the restorations survived intact at the censor date. Neither the age of the child nor the tooth restored influenced the durability of the restoration. The deterioration in both marginal integrity and anatomic form of the Ketac Silver restorations was significantly greater than the Ketac Fil restorations (P < 0.05). The durability of Ketac Silver was such that it cannot be recommended for use in restoring carious primary molars.

In this study, we examined the rheological properties of elastomeric impression materials, both before and during setting, to assess the clinical significance of certain key characteristics such as viscosity, pseudoplasticity, and the rate of development of elasticity. The hypothesis to be tested was that monitoring the change in tan delta is the most appropriate means of monitoring the setting characteristics of elastomers. The loss tangent (tan delta) and the dynamic viscosity (eta') for five impression materials (both unmixed pastes and mixed/setting materials) were measured by means of a controlled-stress rheometer in a cone/plate configuration. For unmixed pastes, tests were performed at various frequencies (0.1 to 10 Hz) and torques (from 1 to 50 x 10(-4) Nm), while testing on setting materials was performed at constant frequency (1 Hz) and torque (3 x 10(-3) Nm). Most base and catalyst pastes were pseudoplastic before being mixed. Immediately after being mixed, the polyether (tan delta = 9.85) and polysulfide (tan delta = 9.54) elastomers showed tan delta markedly higher than those of other mixed materials (tan delta = 4.96 to 3.01). The polyvinylsiloxane elastomers showed lower initial tan delta, which rapidly reduced even further with time. This suggests that these materials should be used as soon as possible after being mixed. The polyether elastomer had a comparatively long induction period during which the tan delta remained at a high value. These characteristics are thought to be key factors in controlling clinical efficacy and therefore support the hypothesis that monitoring tan delta is an appropriate method for evaluating the setting characteristics of elastomers. One limitation was that the controlled-stress rheometer was unable to monitor rheological properties through to completion of setting.

SUMMARYThis study investigated the effects of environmental temperature on the fluoride release and recharging ability of glass ionomers. Five disk specimens (15 mm in diameter and 1 mm thick) were made of each of the following materials: a conventional luting glass ionomer, two high viscosity restorative glass ionomers and a restorative resin-modified glass ionomer. The fluoride release of each material was measured at 4°C, 37°C and 55°C. An additional three groups, which were made of the same materials, were stored in distilled and deionized water for 30 days and recharged in 250 ppm fluoride solution at 4°C, 37°C and 55°C for five minutes. The fluoride rerelease was measured daily from two days prior to two days after the recharging process. At all temperatures, the luting glass ionomers showed the greatest fluoride release and recharging ability, followed by the resin-modified glass ionomer, then the high viscosity glass ionomers. For each material, the fluoride release increased with increasing temperature and all glass ionomers showed greater recharging ability at higher temperatures. An increase in environmental temperature increased both the fluoride release and recharging of the glass ionomers. This may be important in developing regimes for improving the delivery of topical fluoride products.