Reline materials--handle with care? An investigation into the effect of varying the powder/liquid ratio on some properties of auto-polymerising acrylic resin materials.

The fit of the denture base to the alveolar ridge progressively declines with alveolar ridge resorption. Once a denture becomes ill-fitting there are two main treatment options: to construct a new denture or to restore the fit of the existing denture. A denture may be relined as a laboratory procedure or at the chairside in the dental clinic. The chairside reline technique involves the direct application of auto-polymerising acrylic resin materials to the prepared denture base and the material is allowed to polymerise in the patient's mouth. The reline materials are generally supplied as a powder and a liquid. Clinicians and laboratory dental staff do not always follow manufacturers' recommended guidelines and the tendency can be simply to add varying quantities of powder and liquid until the desired consistency is achieved. This method however may have deleterious effects on the properties of the resultant material. The aim of the study was to investigate the effect of varying the powder/liquid ratio on some properties of three auto-polymerising acrylic resin reline materials. The properties investigated were the flow characteristics in terms of the manipulation and setting time and the hardness. Four powder and liquid ratios were chosen. For all the materials studied, a clinically useful lengthening of the manipulation time can be achieved by increasing the amount of liquid added to the powder. However, this is perhaps offset by the fact that it is associated with a corresponding increase in the setting time and resultant increase in clinical chairside time. There were significant differences in surface hardness when the powder/liquid ratio was altered.