Fracture toughness comparison of six resin composites.

OBJECTIVES: This study investigated the Mode I and II fracture toughness values of resin composites used for the restorations of anterior teeth by the Brazilian disk test method. METHODS: The Brazilian disk test was performed on six commercially available dental resin composites, Venus (hybrid resin composite), Durafill (micro-filled resin composite), Gradia (micro-filled/hybrid resin composite), Point4 (hybrid resin composite), Supreme (nano-particle resin composite) and Filtek Z250 (resin composite with zirconia particles). Five resin composite disks of 25 mm in diameter and 2mm in thickness with chevron notches were prepared for each fracture mode per material. The specimens were stored in distilled water for 24h at 37 degrees C, and then tested by a Zwick testing machine under compression mode with a constant crosshead speed of 0.25 mm/min at room temperature. The stress intensity factors under combined Modes I and II fracture toughness were calculated by the formula presented by Atkinson et al. The fracture patterns of two specimens randomly selected from each test group were examined using a scanning electron microscope. A one-way analysis of variance (ANOVA) was performed for the statistical evaluations followed by the post-hoc Tukey's Student Range (HSD) test. RESULTS: The highest mean Mode I and II fracture toughness values were found in Filtek Z250 and Filtek Supreme and they were significantly higher than other materials (comparisons significant at the 0.05 level). The intermediate group consisted of Point4, Venus and Gradia ANTERIOR, whereas Durafill, statistically, had the lowest mean value for fracture toughness. SIGNIFICANCE: Fracture toughness values of hybrid and nano-particle resin composites are significantly higher than those of micro-filled resin composites. This suggests that the latter should be used for non-stress bearing areas.

An advanced approach for computer modeling and prototyping of the human tooth.

This paper presents a systematic and practical method for constructing accurate computer and physical models that can be employed for the study of human tooth mechanics. The proposed method starts with a histological section preparation of a human tooth. Through tracing outlines of the tooth on the sections, discrete points are obtained and are employed to construct B-spline curves that represent the exterior contours and dentino-enamel junction (DEJ) of the tooth using a least square curve fitting technique. The surface skinning technique is then employed to quilt the B-spline curves to create a smooth boundary and DEJ of the tooth using B-spline surfaces. These surfaces are respectively imported into SolidWorks via its application protocol interface to create solid models. The solid models are then imported into Pro/MECHANICA Structure for finite element analysis (FEA). The major advantage of the proposed method is that it first generates smooth solid models, instead of finite element models in discretized form. As a result, a more advanced p-FEA can be employed for structural analysis, which usually provides superior results to traditional h-FEA. In addition, the solid model constructed is smooth and can be fabricated with various scales using the solid freeform fabrication technology. This method is especially useful in supporting bioengineering applications, where the shape of the object is usually complicated. A human maxillary second molar is presented to illustrate and demonstrate the proposed method. Note that both the solid and p-FEA models of the molar are presented. However, comparison between p- and h-FEA models is out of the scope of the paper.