Reinforcement of acrylic polymers with radiopaque cellulose fibres

Abstract

The incorporation of BaS04 containing cotton threads into acrylic matrices was studied, as a means of reinforcing the polymer and producing radiopacity at the same time. Coating the threads with a thin poly(vinyl acetate) film containing BaS04 was defined as the most suitable method, providing strength and wettability to the fibres. A percentage of about 10 p.h.r, fibres can be characterized as satisfactory for both objectives, i.e. radiopacity and reinforcement. |ntroduetionPoly(methyl methacrylate) (PMMA) is a well established material in dental prosthetics because of the combination of properties such as biocompatibility, versatility in preparation and repair as well as excellent appearance. A recognized disadvantage of the acrylics used for the construction of dentures, is their brittleness leading to breaks during service as a result of fatigue failure in the mouth or impact failure out of the mouth.Many attempts have been made to overcome this problem by the introduction of new materials or the modification of existing acrylics. Stafford and Smith [1] investigated polycarbonates and pointed out that this polymer is superior to acrylic resins in deflection, impact strength and thermal expansion. Grant and Greener [2] attempted to reinforce acrylic resins using sapphire whiskers and reported an improvement of physical properties such as flexural strength.The development of new, high-strength and highmodulus reinforcing fibres has, of course, attracted the interest of many scientists. Schreiber I-3, 4] investigated the reinforcing effect of carbon fibres and reported considerable improvement. The same reinforcing medium was also used by Manley et al. [5,6], whereas other researchers studied the effect of carbon fibres on the fatigue resistance and bending properties of denture resins, the modification of ftexural strength and modulus of carbon fibre-acrylic resin composites [8]. Apart from carbon fibres, many other reinforcements have been tested, such as carbon black [9], aramid fibres [10], or combinations of carbon and glass fibres leading to hybrid composites [-11]. On the other hand, the strengthening of acrylic resins has also been attempted by the incorporation of shock absorbers such as small rubber particles [12,13].* Author to whom all correspondence should be addressed.An additional problem of the acrylics as well as other polymers used as prosthetic materials is that they are radiolucent, i.e. transparent to X-rays. There is, therefore, a danger in their use in dentistry, medicine and surgery. Dentures or parts of dentures may be aspirated or swallowed and it is also possible that in case of traumatic injuries to the face (as in road traffic accidents) dentures or fractured portions of dentures may become impacted into the tissues. The radiolucency of the material causes problems in the detection of such foreign bodies, Many attempts were made therefore to modify acrylics and other prosthetic polymers to radiopaque materials, including the dispersion of finely divided inorganic salts, such as bismu...