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Purpose To investigate the risk of debonding of resin-bonded fixed dental prosthesis frameworks and the effects on the periodontal tissue in patients with reduced alveolar bone levels. Materials & methods The abutment teeth were the upper central incisor and the canine. Resin-bonded fixed dental prosthesis framework fabricated using zirconia was set to models with five different alveolar bone levels. A 200-N load (the maximum clenching force of the anterior teeth) was applied to the center of the pontic to analyze the internal stress on the framework, adhesive cement, and periodontal tissue using finite element analysis. Results The mean maximum principal stress generated in the framework was 25.33 and 29.35 MPa in the models with the normal and the lowest alveolar bone level, respectively. Regarding shear stress on the adhesive cement, stress concentration was observed on the connector side in all models, and it increased on the cervical side of the central incisor as the alveolar bone level decreased. In addition, the mean maximum and minimum principal strains generated on the periodontal ligament of the central incisor and canine tended to increase as alveolar bone loss progressed. Furthermore, the mean maximum principal stress on the cortical bone was the greatest in the model with the most significant bone loss at 5.10 MPa. Conclusions This study suggested that the risk of debonding and periodontal tissue damage might be higher when resin-bonded fixed dental prosthesis frameworks were used in patients with reduced alveolar bone levels compared to those in a healthy state. This article is protected by copyright. All rights reserved.

Recently, metal-free restoration has become the standard in prosthetic treatment. However, it is still unclear which combination is most effective in preventing root fracture and secondary caries. The purpose of this study was to evaluate the influence of different post systems, crown materials, crown thickness and luting agents on the stress distribution around the crown margins, cervical dentin and the tip of the post.Ninety-six mandibular first premolar models were developed and analyzed using finite element analysis (FEA). Two designs of crowns, six kinds of crown materials, four types of post and core systems and two kinds of luting agents were included and evaluated for the stress distribution within the abutment teeth. The Von Mises stress magnitudes were compared among all models.The stress at the tip of the post decreased as the young's modulus of luting agent decreased; The stress concentrated more at the cervical area (dentin and crown), as the physical properties of the crown material increased.Crowns fabricated using polyetheretherketone (PEEK) can reduce the stress concentration at the cervical area, so it may be possible to reduce the amount of tooth reduction during abutment tooth preparation. The stress distribution around the post tip is affected by the post and core systems and luting agent, regardless of crown materials and thickness. When inserting a post of the higher Young's modulus such as zirconia post, methyl methacrylate luting cement can reduce the stress concentration at the tip of the post.

This study aims to elucidate the relationships between the flexural strength and surface topography of composite resin blocks, utilized for the CAD/CAM system, after milling in various step-over amounts. The rectangular specimens were milled from CAD/CAM blocks with step-over amount 0.01, 0.02, 0.05, 0.1, and 0.2 mm; further, a three-point bending test was conducted to reveal the flexural strength. The surface morphology after milling was assessed by a 3D laser microscope. The surface roughness significantly decreased by reducing the step-over amount. Although there was significant association between the surface roughness and flexural strength by the Pearson correlation, the 95% confidence intervals of the flexural strength were between the mirror-polished and sand-blasted groups. These results suggest that a precise step-over amount enables us to obtain a smooth surface. Furthermore, the flexural strength of the rough surface milled by a large step-over amount caused no damage to the composite resin for CAD/CAM crown.

Purpose To investigate stress and strain concentrations on resin-bonded fixed dental prostheses (RBFDPs) frameworks of different design using finite element analysis. Methods A human dry skull was scanned and models were produced using three-dimensional printer. After abutment preparation, three frameworks, including a three-unit RBFDP, and two-unit cantilevered RBFDPs using #21 and #23 for the abutment tooth, were fabricated. Scanned data were subtracted to define boundary of each structure. Occlusal force (200N) was loaded at 45° to long axis of the pontic. The distributions of shear stress and principal strain in the RBFDP models were measured to evaluate the risk for framework-debonding from the abutment teeth and the impact on periodontal tissue. Results The percentage voxels with shear stress >11MPa in adhesive cement layer of three-unit RBFDP using #21 and #23 were 4.16% and 2.25%, respectively; in two-unit cantilevered RBFDPs, it was 19.25% using #21, and 23.4% using #23. The maximum principal strain on periodontal ligaments in two-unit cantilevered RBFDPs using #21 was the largest, and smallest in the three-unit RBFDP. The maximum principal strain in framework was largest in the two-unit cantilevered RBFDP using #23, and smallest in the three-unit RBFDP. Conclusions The risk for framework-debonding in three-unit RBFDPs was substantially lower than that in two-unit RBFDPs. In difficult cases with indication for three-unit RBFDPs, two-unit cantilever design using the canine would be more advantageous for preservation of periodontal tissue, while for risk of framework-debonding, the design using the central incisor would be more advantageous.

Purpose This study introduces a newly developed zirconia complete denture (ZrD) that incorporates a ceria-stabilized zirconia/alumina nano-composite framework fabricated with computer-aided design/computer-aided manufacture (CAD/CAM). Materials and methods Twenty-nine edentulous patients received either a maxillary ZrD (n = 10) or a maxillary conventional complete denture (CD) (n = 19). Patient satisfaction was evaluated before and 12 months after prosthesis placement using the McGill Denture Satisfaction Instrument. Results During follow-up periods of up to 2 years, no denture fractures were found in the ZrD or CD group. All aspects of patient satisfaction improved, and no significant group differences were found. Conclusion Within the limitations of this study, it can be concluded that maxillary complete dentures with nano-zirconia frameworks might be an alternative prosthetic treatment option.

Bacterial adhesion to dental materials is a major cause of caries and periodontitis, necessitating the development of compounds such as yttria-stabilized zirconia (YSZ) and silver nanoparticles (AgNPs), which are widely employed in medicine due to their high antimicrobial activity and low cytotoxicity. The main goal of this study is the synthesis of the broad antimicrobial activity of AgNP-coated YSZ with facile methods. The bactericidal AgNPs were immobilized on the surface of YSZ and tested for bactericidal activity against Staphylococcus aureus, Streptococcus mutans, Escherichia coli, and Aggregatibacter actinomycetemcomitans based on ISO 22196:2007. The loading of AgNPs was optimized by culturing mouse fibroblast cells on AgNP-coated YSZ with cell viability test based on ISO 10993-5. In addition, the silver release profile of AgNP-coated YSZ in artificial saliva was determined using an accelerated aging test. Antibacterial activity, and cell viability test revealed optimum performance with no cytotoxicity at a level of 32 μg/cm2. Accelerated aging test showed that the AgNP-coated surface was extremely stable, exhibiting a total silver leaching level of only 1% and confirming the effectiveness of this coating method for retaining AgNPs while exerting an antibacterial effect against oral pathogens. This finding also implies that the bactericidal action of AgNP-coated YSZ is not mediated by the released Ag ions, but rather corresponds to contact killing. Abbreviations: Yttria-stabilized zirconia, YSZ; silver nanoparticles, AgNPs; field emission scanning electron microscopy, FE-SEM; X-ray photoelectron spectroscopy, XPS; grazing incidence X-ray diffraction, GIXRD; ultraviolet-visible, UV-vis; inductively coupled plasma atomic emission spectrometry, ICP-AES.

The purpose of this study was to evaluate the surface strain of zirconia fixed partial denture frameworks and their abutment roots when restored with two types of post and core materials. Artificial mandibular first premolars and second molars were used as the abutment teeth. Posts and cores were of two types: resin composite with glass fiber posts (RC) and cast platinum gold alloy (MC). The cores and 4-unit zirconia frameworks were bonded to the specimens. Static loading was applied to the occlusal surfaces, and the surface strain of the frameworks and roots (distal premolar and mesial molar) was measured by strain gauge method. Premolar root showed a significantly higher magnitude of principal strain than molar root. RC showed a significantly higher magnitude of principal strain than MC. The results suggest that MC restrain the surface strain compared to RC when the missing teeth are replaced by a 4-unit zirconia framework.

Titania (TiO2) has attracted much attention recently for reducing bacterial diseases by the generation of reactive oxygen species (ROS) under UV irradiation. However, demand for higher photocatalytic activity due to higher recombination of electron and hole remains. The aims of this study were to make titania with higher antibacterial property and show the mechanisms of the bactericidal effect. In this study, we hydrothermally synthesized TiO2 nanosheets (NS) with highly-oriented structures. Samples were divided into five groups, depending on the fluorine/titanium ratio in the raw material, namely NS1.0, NS1.2, NS1.5, NS1.8, and NS2.0. Facet ratio and nanosheet size increased with an increase of fluorine/titanium ratio. The photocatalytic activity of TiO2 nanosheet was assessed by the generation of ROS. Hydroxyl radicals and superoxides were generated efficiently by ultraviolet light irradiation on NS1.5 and NS1.0, respectively. Antibacterial activity against Streptococcus mutans was assessed in the presence and absence of UV irradiation, NS1.0 showed superior antibacterial properties compared to commercially available TiO2 nanoparticles, under both conditions, due to the oxidation of intracellular components and cell membrane. These results together suggested TiO2 nanosheet induced bacterial cell death by oxidation, and TiO2 facet engineering resulted in enhancement of both photocatalytic and antibacterial activities of TiO2.

The purpose of this study was to evaluate the design of resin-bonded fixed partial dentures (RBFPDs) with zirconia frameworks. The abutment teeth were the upper central incisor and the canine. Three types of frameworks were fabricated as follows: 0.5-mm- and 0.8-mm-thick zirconia frameworks with grooves and holes (0.5ZrG, 0.8ZrG) and 0.5-mm-thick zirconia frameworks without grooves and holes (0.5Zr). The control group was designed as a 0.8-mm-thick metal framework with grooves and holes (0.8MG). Static loading was applied and the surface strain of the retainers was measured with strain gages. The magnitude of the principal strain of the 0.5ZrG framework was significantly lower than that of the 0.8MG and the 0.5Zr frameworks. This result suggests that the zirconia and retention form had a significant effect on decreasing the framework deformation, indicating that the RBFPDs that use a 0.5-mm thick zirconia framework are effective for replacing a single anterior missing tooth.