Dental materials journal最新文献

The purpose of this study was to investigate the wear behavior of pure titanium when opposed to six different crown restorative materials. Abrader specimens were prepared by casting pure titanium and these were paired with substrates including pure titanium, resin composite, lithium disilicate, zirconia, silver-palladium-copper (Ag-Pd-Cu) alloy, and bovine enamel. The wear volume of each abrader and substrate specimen was measured using the two-body wear test, and factors affecting wear behavior, such as microstructures and hardness, were evaluated. Results indicated that titanium-to-titanium abrasion caused significant wear in both the abrader and the substrate. In contrast, no significant wear was observed for the zirconia and Ag-Pd-Cu alloy against titanium. SEM images showed linear wear marks in most specimens other than zirconia and resin composite, microcracks in enamel, and filler fall in resin composite. A strong correlation between the wear volume and Vickers hardness was found for ceramics, resin composites, and enamel. However, due to the small slope of the approximate straight line in this correlation suggests that the wear behavior of materials when abraded by titanium is only partially influenced by the microstructure and hardness of the material.

The purpose of this study is to investigate the effects of surface treatment methods using polyetheretherketone (PEEK) (with or without a functional monomer-containing primer following treatment with alumina blasting or concentrated sulfuric acid) on the shear bond strength (SBS) of resin luting material after artificial aging. The PEEK specimens were classified into five groups according to their treatment methods: untreated, alumina blasting (AB), concentrated sulfuric acid (SA), alumina blasting+primer (ABP), and concentrated SA+primer (SAP). The SBS score of each group was determined experimentally using a universal testing machine. The SBS tests revealed that the initial bond strengths of ABP and SAP were significantly higher than those of AB and SA. In addition, both SBS after 20,000 thermal cycles remained high (>15 MPa). These results suggest that the ABP and SAP groups are the best predictive methods for evaluating SBS with PEEK and resin cement.

This study investigated the thermal stability and top-to-bottom hardness ratio of six bulk-fill composites (STARK^® Bulk Fill Composite, Filtek™ One Bulk Fill Restorative, SDR^® Plus Bulk Fill Flowable, Tetric^® N-Ceram Bulk Fill, X-tra fil, and Beautifil-Bulk Restorative) following acidic softening. Discs-shaped specimens were fabricated and photo-cured for 20 s. Vickers hardness was sequentially measured, immediately after irradiation (VH₀), after 24 h of dry storage (VH_dry) and after 24 h of acidic storage (VH_acidic) at 37°C. Network integrity was assessed by comparing the relative hardness decrease (VH_RD) after acidic softening with the initial maximum rate temperature (IRT) of mass loss. Compared to VH₀, VH_dry significantly increased, whereas VH_acidic significantly decreased. The VH_RD of top surface ranged from 16.62% for FBF to 62.84% for SDR. IRT primarily reflects resin composition and residue is a filler-based value. Relative network integrity estimated by IRT revealed a negative correlation with VH_RD. Consequently, acidic erosion hardness development can be indirectly employed to assess network integrity in bulk-fill composites.

This study investigated the effect of vacuum plasma treatment on the shear bond strength (SBS) of three-dimensional (3D)-printed resin and resin cement. Specimens were categorized based on airborne-particle abrasion (APA), plasma, and bonding agent treatments. Long-term adhesive stability was examined by comparing their SBSs before and after thermocycling. The group with the bonding agent applied after plasma treatment and before thermocycling exhibited the highest SBS of 23.9±2.2 MPa. No significant SBS difference was observed among the remaining groups, except for that subjected only to plasma treatment after thermocycling. The wettability of distilled water improved in the groups treated with plasma, whereas that of the bonding agent decreased in the group treated only with APA. Surface analysis revealed a roughened surface on the plasma-treated 3D-printed resin. Therefore, vacuum-plasma treatment before thermocycling can enhance the SBS of 3D-printed resin without compromising its properties.

Dentin cavity wall pretreatments to improve the bond strength of direct and computer-aided design/computer-aided manufacturing (CAD/CAM) restorations using resin composite were examined. Experiment 1 divided 18 standardized MOD cavities into three conditions: no pretreatment (Group N, control); chemical pretreatment with EDTA solution (Group C); and mechanical pretreatment with glycine air-powder polishing (Group M). Specimens were restored using direct resin composites. Micro-tensile bond strength (μ-TBS) was measured after cyclic loading. The μ-TBS was significantly higher for Groups C and M than for Group N. Group M showed the best bonding reliability. In Experiment 2, cavity preparation, dentin pretreatment, cyclic loading, and μ-TBS testing were performed using the same methods applied in Experiment 1. Specimens were restored using CAD/CAM resin composite inlays. The μ-TBS was significantly higher for Groups C and M than for Group N. No significant difference in bonding reliability was apparent among all groups.

Dental titanium implants and their surface modifications markedly improve implant biocompatibility. However, studies evaluating the mechanical biocompatibility of implants are scarce. In particular, the analysis of mechanical biocompatibility deficiencies leading to stress shield-induced bone resorption. Recently, we focused on using PEEK as a dental material. This study explored the hypothesis that PEEK implants improve the stress shielding of titanium. In this study, artificial bone surfaces were examined to measure strains on the artificial bone surface under compressive loading with the implants in place. Additionally, 3D image analysis of the fracture state inside the bone tissue was performed using micro-CT (µCT). This hypothesis was supported by µCT imaging analysis of bone tissue changes under stress, which revealed that PEEK implants transfer greater loads than titanium implants. µCT imaging and statistical analysis showed that bone porosity had little effect on stress shielding.

The objective of this study was to investigate the effects of repetitive removal/insertion and a load equivalent to the occlusal force on the retentive force of rest plate-I bar (RPI) clasps fabricated by selective laser melting (SLM) on powder bed fusion. RPI clasp fabricated by SLM and casting were evaluated to the retentive force by repetitive removal/insertion (SLM-RI and Cast-RI), and the retentive force of RPI clasp by SLM was also evaluated by repetitive removal/insertion under load (SLM-L). SLM-RI group was kept superior retentive force during repetitive removal/insertion than Cast-RI group. SLM-L group showed the decrease of retentive force, and all specimens fractured during less than 7,000 repetitive removal/insertion. In SLM-L, the fracture of RPI clasp occurred at minor connector due to stress concentration. In conclusion, the RPI clasp by SLM demonstrated the superior retentive force and fitting for repetitive removal/insertion, yet improvements were necessary to withstand a load equivalent to occlusal force.

The purpose of this study was to construct an artificial intelligence object detection model to detect the articular disk from temporomandibular joint (TMJ) magnetic resonance (MR) images using YOLO series. The study included two experiments using datasets from different MR imaging machines. A total of 536 MR images were retrospectively examined. The performance of YOLOv5 and YOLOv8 in detecting the TMJ articular disk in both normal and displaced conditions was evaluated. The impact of image-processing techniques, such as histogram equalization (HE) and contrast-limited adaptive HE (CLAHE) on model performance, was also examined. The results showed that the YOLO series could detect the articular disk regardless of displacement, with superior performance on images of normal disk position. The results suggest the applicability of object detection models in improving the diagnosis of TMJ disorders.

Enamel microcracks are often apparent in the teeth of elderly individuals. However, accurate clinical diagnosis of enamel microcracks is very difficult. The purpose of this study was to examine the utility of inspections for enamel microcracks using a near-infrared light transillumination device with fluorescence staining. Human upper incisors with typical enamel microcracks were selected. Grayscale pictures of each tooth specimen were then taken by digital camera under visible light as control. Every tooth specimen was stained using indocyanine green solutions, then examined, and photographed under visible light. All digital images were compared with the background enamel surface and measured using image analysis software. Inspection using near-infrared light transillumination with indocyanine green solution was effective for detecting the presence of enamel microcracks. This method offers a non-invasive method of chair-side diagnosis and appears effective for detecting the presence of enamel microcracks.

This study investigates the moments generated when applying third-order bends to lingual brackets with different slot shapes and wires made of different materials. Three types of lingual brackets with different slot shapes: 0.018×0.018-inch square slot self-ligation bracket (AL-bracket); 0.018×0.025-inch slot self-ligation bracket (CL-bracket); 0.018×0.025-inch slot self-ligation bracket (ST-bracket). Wires of three different materials were measured. The torque value generated during torque application was measured using a torque gauge. The AL-bracket had a significantly larger torque moment than the CL- and ST-brackets at the same angles. The CL-bracket had the smallest torque moment of the three for the square wire; however, the CL-bracket revealed a larger torque moment than the ST-bracket for the rectangular wire. The torque moment of Ti-Ni wires was observed the smallest. In lingual orthodontic treatment, the results suggested the shape of the lingual bracket slot and the wire material should be considered when adjusting and applying third-order bends.