R. Huggett

The effect of disinfection procedures on flexural properties of denture base acrylic resins.

This study evaluates the effects of long-term disinfection immersion on the flexural properties of denture base resins; it was conducted against a background of increasing awareness of the importance of cross-infection control in dental clinics and laboratories. The transverse bend testing procedure used followed that specified in the International Standard for denture base polymers. The results demonstrate that alcohol-based disinfectants are not suitable for use with denture base materials of non-cross-linked acrylic resin.

Finite element analysis of stress distribution at the tooth-denture base interface of acrylic resin teeth debonding from the denture base

Acrylic resin teeth present a problem when they detach unexpectedly from the denture base resin. Detachment is caused by stress concentrations at the tooth/denture base resin interface. In this study, the finite element method was used to examine the stress distribution at this interface when a single static force that resembled incisal bite force was applied. The results indicated that irrespective of the type of acrylic resin teeth used, maximum tensile stresses were found at the palatal aspect of the interface. It is suggested that boxing the tooth in the acrylic resin will help redistribute stress concentrations favorably.

Dimensional accuracy and stability of acrylic resin denture bases.

Proponents of injection molding systems have claimed a number of benefits over conventional press-pack dough molding systems. The aim of this study was to evaluate a recently developed injection (dry heat) procedure of processing compared with press-pack dough molding utilizing three curing cycles. The dimensional accuracy and stability of acrylic resin bases produced by the two molding procedures were compared. Dimensional changes were assessed over a period of 4 months using an optical comparator. The results demonstrate that baseplates produced by the injection molding procedure exhibit less shrinkage than those produced by the conventional press-pack procedures.

Stress analysis techniques in complete dentures.

The fracture of acrylic resin dentures remains an unresolved problem. It is known that eventual fracture of an appliance occurs due to crack initiation and propagation from areas of high stress concentration. In order to understand and overcome the problem of fracture, it is important to identify the regions of stress concentration. A number of different methods are used in stress analysis. However, the finite element method, a numerical technique, appears to overcome most of the problems associated with the earlier experimental methods. This article reviews the different techniques and their application to examining stresses in dentures.

The effect of cross-linking on sorption properties of a denture-base material

Cross-linking of the polymer of the interstitial matrix of a heat-cured resin denture base is said to provide craze resistance for the denture base. The mechanism of crazing can be related to both water sorption and solvent attack. The present study shows that the addition of ethylene glycol dimethacrylate in concentrations of 0-100% of monomer volume has little effect on water sorption properties but is an efficient method of providing solvent resistance.

Evaluation of analytical techniques for measurement of denture-base acrylic resin glass-transition temperature

The glass-transition temperature of a range of acrylic resin materials used in prosthetic dentistry was determined. The techniques used to make the measurement included: thermal mechanical analysis, dynamic mechanical thermal analysis, and differential scanning calorimetry. It was found that the measuring techniques used yielded very similar results, and as a consequence it was concluded that: familiarity and easy availability of thermal mechanical analysis lead to the recommendation that this technique should be employed as the standard glass-transition evaluation technique for denture-base acrylic resins.

Measurement methods used for the determination of dimensional accuracy and stability of denture base materials

The literature relating to methods of measurement of dimensional accuracy and stability of denture base materials is reviewed. The papers are presented chronologically together with information on the measurement technique used and the reported level of accuracy. Most authors utilized optical measuring apparatus, with the use of calipers being the second most popular method.

Effect of water and artificial saliva on mechanical properties of some denture-base materials

Two artificial saliva samples selected on the basis of being chemically and physically similar to natural saliva were used as saturation media so that we could investigate their effects on mechanical properties of four denture-base materials, and the results were compared with the effect of water on the same materials. Diffusion coefficients in the more viscous saliva were different from those in water but, in general, mechanical properties were similarly affected in all liquids, indicating that the aqueous phase of the artificial medium was a major factor influencing the results.

Factors that affect the rheologic properties of acrylic resin denture base materials

The rheologic characteristics of different formulations of acrylic resin denture base materials are presented in this study. This is of practical significance in selecting resins with optimum rheologic properties for denture base construction. The materials are characterized in respect to their constituents, mean powder particle size and distribution, molecular weight averages and distributions, and glass transition temperature. A comparison of the polymers indicates that smaller particles saturate with monomer more readily, and this results in a higher viscosity. A higher viscosity for higher molecular weight and lower viscosity for lower molecular weight have been observed. Increasing the percentage of copolymerization increases the viscosity. No correlation has been found between the rheologic properties of denture base polymers and the powder glass transition temperature.

The effect of esthetic fibers on the flow properties of an acrylic resin denture base material.

OBJECTIVES This study was conducted to measure the effect of viscose rayon esthetic fibers on the flow properties of an acrylic resin denture base material. METHODS Two testing methods using a needle penetrometer and an oscillating rheometer were employed on weighed proportions (0.1%, 0.2%, 0.8%, and 0.3%) of fiber. RESULTS The results show that the fibers affect the flow properties of the polymer/monomer mix. Increasing the percentage of fibers decreases the flow of the material and reduces the doughing time. With increasing amounts of fiber, a rapid increase in the viscosity occurs with a corresponding adverse effect on flow properties. SIGNIFICANCE It is concluded that these properties are important for the successful handling of acrylic materials since they can influence the accuracy and quality of the molded denture.