The Study Of Wear Resistance, Hardness And Color Stability Of Artificial Denture Teeth

Artificial denture teeth was the important component of conventional removable partial or complete dentures. Previously, acrylic resin teeth were commonly used as artificial teeth for removable dentures in clinic. However, resin teeth had the disadvantage of being more subject to wear than ceramic resin denture teeth. Because of excessive wear and Bruxism, the outer surface or enamel layer of artificial denture teeth was often removed. This had led to the exposure of the sub-enamel layer. And also, would result in loss of masticatory efficiency, alteration of the functional path of masticatory movement, and fatigue of masticatory muscles. Furthermore, resin denture teeth could become discoloured over a period of time in the oral environment. Consequently, the wear resistance of artificial teeth was important in the function of complete dentures. And also, the colour stability was crucial for maintaining their dental esthetics.Nowadays, there were no consensus on the selection of various artificial denture teeth. Previous in vitro studies focused on the outermost layer and did not relate to the study of the sub-enamel layer. So, the study evaluated the wear resistance, hardness and color stability of5groups of commercially available artificial teeth, to provide theoretical foundations and directions in clinic selection.Purpose:The purpose of this study was to examine the3-body wear resistance of5resin denture teeth with different layers. The Vickers microhardness of the outer surfaces and sub-enamel layer was measured, and the correlations between wear resistance and hardness was examined. And to investigate the effect of immersion method on the color change of acrylic resin denture teeth.Method:5groups of commercially available artificial teeth:Heraeus Kulzer, Kaijing (Huge dental), Vitalife (Vita), Excellence IPN (Dentsply), Endura (Shofu). The maxillary incisors and first molars were selected to prepare the samples for the observation of the microstructure with stereomicroscope and the analysis of the composition with EDX. The three-body wear test was performed in a chewing simulator, vertical substance and volume loss were analyzed using an optical3-dimensional (3-D)surface profilometer, as well as scanning electron microscopy. The Vickers microhardness of the outer surfaces and sub-enamel layer was measured, and the correlations between wear resistance and hardness was examined. Color measurements on each tooth were made before and after their immersions in solutions, the colourimetric were analysed to evaluated the color stability of denture teeth.Results:1Regarding layer structure, all the5artificial teeth consisted of a3-layer structure, Microfillers were observed in the enamel layer of the composite resin artificial, but did not indicate any type of filler in the four types of resin denture teeth.2The wear resistance among the5types of teeth was different. Composite resin teeth demonstrated significantly lower wear values than conventional and cross-linked acrylic resin teeth. The wear values of conventional acrylic resin teeth was higher than cross-linked acrylic resin teeth. The substance loss of the enamel was less than sub-enamel, but there was no statistical differences were found except the composite teeth.3The Vickers microhardness among the5types of teeth was different. Composite resin teeth demonstrated significantly higher values than conventional and cross-linked acrylic resin teeth. The Vickers microhardness of the enamel was higher than the sub-enamel, but there was no statistical differences were found except the composite teeth. Hardness appeared to correlate with wear resistance, the correlation coefficient of the enamel between the volume loss and hardness was-0.787, and the sub-enamel was-0.430. The correlation coefficient of the enamel between the height loss and hardness was-0.808,and the sub-enamel was-0.481.4The results showed significant changes in color after artificial aging in all the groups after4weeks immersions in the four solutions. The degree of discolouration of denture teeth was time dependent. Immersion in distilled water for4weeks did not cause any discolouration to the denture teeth. Red wine was more chromogenic than coffee and cola. After4weeks immersion, the discolouration of group A and D was apparent, and there was slight change in the other3groups.Conclusion:The composite denture teeth with microfillers showed improved wear resistance compared to other acrylic resin denture teeth. Cross-linked acrylic resin teeth showed slightly improved in wear resistance compared to conventional acrylic resin denture teeth. A positive correlation between wear resistance and hardness could be found in this study. The degree of discolouration of acrylic and compostite teeth after their immersion in red wine, coffee and cola was time dependent. Red wine was more chromogenic than coffee, cola and distilled water. The color stability of composite denture and cross-linked resin teeth was greater than the conventional acrylic resin denture teeth.