Artificial teeth

Artificial teeth are essential components of removable partial dentures, contributing significantly to both esthetics and function. Posterior teeth serve to restore masticatory efficiency, maintain interarch relationships, and re-establish the lost facial contour. Anterior teeth, on the other hand, assist in mastication, play a crucial role in improving esthetics, and contribute to phonation.

The diverse combinations of missing teeth and edentulous spaces, when integrated into various removable partial denture designs, necessitate artificial teeth with different structural and functional characteristics.

Artificial teeth for removable partial dentures can be composed of acrylic resin or porcelain. Alternatively, they may be cast in metal as integral components of the denture framework.

Characteristics of acrylic resin and porcelain teeth

Strength
Acrylic resin teeth are considered more advantageous than porcelain teeth in terms of strength, especially when the interarch distance is limited or when extensive reduction is required to adapt the artificial tooth to the clasp of an adjacent abutment. Even when thinned, acrylic teeth do not significantly lose their strength. In contrast, porcelain is inherently weaker in thin sections, and when the retentive elements of porcelain teeth are reduced in size, the mechanical interlocking with the denture base is compromised.

Microleakage
Microleakage refers to the penetration of fluids into the interface between the artificial tooth and the denture base. A chemical bond between the tooth material and the denture base material prevents microleakage. If the bonding procedure is not meticulously performed, leakage may occur at the interface of porcelain teeth. During the polymerization of acrylic resin, methyl methacrylate initially expands once a specific temperature is reached during the curing cycle, and then contracts in a later phase. Due to this dimensional change and the absence of a chemical bond between the acrylic denture base and the porcelain tooth, microcracks may form. These cracks may absorb fluids and food pigments, resulting in discoloration and compromised esthetics.

Stain resistance
Although not a frequent concern, acrylic teeth may absorb stains under certain conditions. In contrast, porcelain teeth exhibit excellent resistance to staining, which is regarded as a significant advantage.

Wear resistance
Artificial teeth in removable partial dentures undergo continuous wear in response to occlusal contacts. Wear in acrylic resin teeth typically appears on the lingual and labial surfaces of anterior teeth and the occlusal surfaces of posterior teeth. This results in a loss of vertical dimension and a deterioration in the esthetic appearance of the anterior region. While acrylic resin teeth have relatively low wear resistance, this may be advantageous when opposed by metal crowns or natural teeth, as the acrylic teeth absorb the occlusal forces, reducing wear on the opposing enamel or metal surfaces.

Porcelain teeth offer excellent resistance to wear. As a result, anterior porcelain teeth are able to retain their esthetic appearance for many years, and the occlusal surfaces of posterior teeth maintain vertical dimension by resisting attrition. However, porcelain teeth may cause wear on opposing enamel or metal restorations.

To reduce the wear of acrylic resin teeth, porcelain teeth can be used in one arch and acrylic in the opposing arch. It has been suggested that when maxillary porcelain teeth occlude with mandibular acrylic teeth, the wear of acrylic teeth is significantly reduced. This is based on the principle that the coefficient of friction between dissimilar materials is lower than that between similar materials. However, this effect is only achieved when the porcelain surface is glazed. Unglazed or roughened porcelain surfaces have increased abrasiveness; therefore, adjustments should be made to acrylic teeth rather than porcelain ones, and final polishing should never be omitted.

Trauma
Due to their inherent hardness, porcelain teeth are believed to exert greater traumatic forces on the residual ridges. An opposing view suggests that because porcelain enhances masticatory efficiency, it may result in less trauma to the residual ridge. Nevertheless, since teeth frequently come into contact even in the absence of food, the opinion that porcelain causes greater trauma is generally more accepted.