The material most commonly used for the fabrication of complete dentures is poly (methyl methacrylate) (PMMA). This material is not ideal in every respect and it is the combination of virtues rather than one single desirable property that accounts for its popularity and usage. Despite its popularity in satisfying aesthetic demands it is still far from ideal in fulfilling the mechanical requirements of a prosthesis. The fracture of dentures may be due to the mechanical properties of the acrylic resin or may be due to a multiplicity of factors leading to failure of the denture base material. Generally, there are three routes which have been investigated to improve the impact properties of PMMA: the search for, or development of, an alternative material to PMMA; the chemical modification of PMMA such as by the addition of a rubber graft copolymer; and the reinforcement of PMMA with other materials such as carbon fibres, glass fibres and ultra-high modulus polyethylene. The following review of attempts to improve the mechanical properties of denture base material takes account of papers published during the last 30 years.

Denture cleanliness is essential to prevent malodour, poor aesthetics and the accumulation of plaque/calculus with its deleterious effects on the mucosa. There are a large number of solutions, pastes and powders available for cleaning dentures with a variety of claims for their relative efficacies. Denture cleansers in common use can broadly be divided into those having mechanical or chemical effects. Surveys show that some denture wearers experience difficulty in cleaning their dentures satisfactorily and many wear dirty dentures. Replacement dentures are sometimes necessary due to general deterioration of the denture base material because of the misuse or abuse of a range of approved denture cleaning methods or do-it-yourself cleaning methods such as the use of household bleach. Current popular cleaning methods used among complete and partial denture wearers are discussed and advice is given on recommended methods of cleaning dentures. The results of a survey conducted to assess patients' knowledge of cleaning procedures and methods and materials used are also presented. Respondents used a variety of combinations of cleaning methods. The findings of this survey that a large number of people do not know how to clean their dentures satisfactorily are in agreement with those of previous surveys. Recommendations are given on suitable methods of cleaning both metal and acrylic resin dentures.

A range of materials, often marketed as high strength resins is available. These materials are often expensive options to conventional heat-cured acrylic resin. The aim of this study was to investigate transverse and impact strength of five "high strength" acrylic resin denture base materials. A conventional heat-cured acrylic resin was used as a control. Specimens were prepared as specified in the International Standard Organization (ISO 1567: 1988) and British standards for the Testing of Denture Base Resins (BS 2487: 1989) and the British Standard Specification for Orthodontic resins (BS 6747: 1987) for transverse bend and impact testing. The impact strength was measured using a Zwick pendulum impact tester and the transverse bend strength measured using a Lloyds Instruments testing machine. The results showed that Metrocryl Hi, Luctitone 199 and N.D.S. Hi all had an impact strength which was significantly higher than the control. For the modulus of rupture, there was a significant difference between Sledgehammer and the other groups. There was no significant difference between the other groups and the control. For the modulus of elasticity, Sledgehammer produced the highest value followed by the control. The remaining four materials had a modulus of elasticity less than the control.

Abfraction lesions are angular, wedge-shaped defects found at the cervical region of teeth and are caused by mechanical overloading initiated by cuspal flexure. Clinically, these lesions are more prevalent on the labial aspect of maxillary incisors. The aim of this study was to provide a biomechanical explanation for this clinical variation. Two-dimensional plane strain finite element models of an maxillary incisor, canine and first premolar were developed and the cervical stress profiles were examined along a horizontal plane 1.1 mm above the amelo-cemental junction. The local X (horizontal) stress on the labial/buccal side was 176.4 MPa for the incisor, 57.8 MPa for the premolar, and 3.4 MPa for the canine. Similarly, the maximum labial/buccal principal stress was 181.4 MPa for the incisor, 25.2 MPa for the premolar, and 66.8 MPa for the canine. The labial/buccal stress profile in the cervical region of an maxillary incisor was always greater than that found in an maxillary canine or premolar tooth. These findings provide a biomechanical explanation for the clinical variation seen in the prevalence of cervical abfraction lesions.