Application of Composite Biomaterials in Dentistry

The use of dental resin composites adapted to computer-aided design/computer-aided manufacturing (CAD/CAM) processes for indirect tooth restoration has increased. A key factor for a successful tooth restoration is the bond between the CAD/CAM composite crown and abutment tooth, achieved using resin-based cement. However, the optimal pairing of the resin cement and CAD/CAM composites remains unclear. This study aimed to identify the optimal combination of a CAD/CAM composite and resin cement for bonding. A commercial methyl methacrylate (MMA)-based resin cement (Super-Bond (SB)) and four other composite-based resin cements (PANAVIA V5; PV, Multilink Automix (MA), ResiCem EX (RC), and RelyX Universal Resin Cement (RX)) were tested experimentally. For the CAD/CAM composites, a commercial polymer-infiltrated ceramic network (PICN)-based composite (VITA ENAMIC (VE)) and two dispersed filler (DF)-based composites (SHOFU BLOCK HC (SH) and CERASMART300 (CE)) were used. Each composite block underwent cutting, polishing, and alumina sandblasting. This was followed by characterization using scanning electron microscopy, inorganic content measurement, surface free energy (SFE) analysis, and shear bond strength (SBS) testing. The results demonstrated that the inorganic content and total SFE of the VE composite were the highest among the examined composites. Furthermore, it bonded highly effectively to all the resin cements. This indicated that PICN-based composites exhibit unique bonding features with resin cements. Additionally, the SBS test results indicated that MMA-based resin cement bonds effectively with both DF- and PICN-based composites. The combination of the PICN-based composite and MMA-based resin cement showed the best bonding performance. Full article

Zirconia is a high-strength ceramic material that expands the design and application possibilities for all-ceramic restorations and dental implants. To enhance the bonding of zirconia restorations to tooth substrates and the osseointegration of implants with the surrounding bone, the surface should be modified by surface treatment. Unfortunately, the effective treatment of sintered zirconia is difficult. Surface treatment for presintered zirconia may be less difficult; thus, the effectiveness of surface treatments of presintered zirconia was investigated herein. The zirconia specimens were randomly divided into eight groups: (1) control (untreated) and seven treated groups subjected to surface treatment (s.ttt.) in the presintered stage, followed by sintering: (2) s.ttt. 1: hydrofluoric acid (HF) gel left during sintering; (3) s.ttt. 2: HF gel washed before sintering; (4) s.ttt. 3: coated with nanosilica; (5) s.ttt. 4: coated with microsilica; (6) s.ttt. 5: coat followed by airborne-particle abrasion; (7) s.ttt. 6: coat followed by partial etching; and (8) s.ttt. 7: coat followed by total etching. The surface microstructure was examined using scanning electron microscopy (SEM) and the crystalline phase was identified using X-ray diffraction (XRD). Biaxial flexural strength was also tested. The results of SEM for s.ttt. 1 and 2 displayed irregular surfaces. S.ttt. 3 showed deeper penetration of the nanosilica into zirconia (27 µm) compared to the microsilica used in s.ttt. 4. S.ttt. 5 and 6 showed irregular coats. S.ttt. 7 showed intergranular pores. The XRD of s.ttt. 1, 2, and 3 revealed tetragonal zirconia as the control group. S.ttt. 4 and 5 showed cristobalite silica and tetragonal zirconia. S.ttt. 6 and 7 contained amorphous silica and tetragonal zirconia, while s.ttt. 7 also showed monoclinic zirconia. The highest flexural strength was for s.ttt. 4 (982.4 MPa), while the lowest was for s.ttt. 7 (386.6 MPa). There was no significant difference in the flexural strength between the control, s.ttt. 1, and 2 (846.3 MPa, 830.0 MPa, and 835 MPa, respectively). Compared to the control group, s.ttt. 3 had a lower flexural strength (634.1 MPa), while s.ttt. 5 and 6 had higher flexural strengths (863.1 MPa and 872.2 MPa, respectively). It can be concluded that the surface modification of presintered zirconia is a promising method as long as no phase transformation or deep subsurface penetration occurs. Full article

This article reports the variation in incident and transmitted light through four different computer-aided-designed/computer-assisted-manufactured (CAD/CAM) resin-based composites (RBC) of thicknesses up to 4 mm after simulating clinically relevant but non-ideal curing conditions. A violet-blue light curing unit (LCU) was used to simulate 39 different curing conditions for each material and thickness, setting an exposure distance of up to 7 mm in the vertical direction and an additional 13 horizontally varying positions that included a central position and up to 3 mm off-center positions in mesial, distal, buccal, and lingual directions. The data clearly indicate that exposure distance has a stronger influence on the measured light characteristics than the directional and offset deviations from the center position. Increasing exposure distance leveled the differences and should be limited to 3 mm. In all materials, the parameters of the transmitted light follow the pattern of variation of the incident light. The attenuation of light while passing RBCs is high and increases exponentially with thickness to 95–96% of the incident light for 4-millimeter-thick samples. Significant differences in light transmission were observed between the materials, which are well related to chemical composition and refractive index differences between filler and organic matrix. Violet light is still measurable after passing through 4-millimeter-thick RBC layers, but its proportion relative to blue light is drastically reduced. Full article