Effects of multiple firings on metal-ceramic bond strength of Co-Cr alloy fabricated by selective laser melting.

STATEMENT OF PROBLEM: Selective laser melting (SLM) is a new technique for fabricating dental restorations, but the metal-ceramic bond strength of the restorations after multiple firings must be considered because adequate bond strength is a clinical requirement for long-term performance. PURPOSE: The purpose of this study was to investigate the effects of repeated firing on the metal-ceramic bond strength of an SLM Co-Cr alloy. MATERIAL AND METHODS: Thirty-six SLM-fabricated (Group SLM) and conventional lost wax cast (Group Cast) Co-Cr metal bars were prepared. Eighteen bars from each group were molded into dimensions of 25×3×0.5 mm, following International Organization for Standardization (ISO) standard 9693:2012. In the center of each bar, a 1.1-mm thickness of porcelain was fused onto an 8×3-mm rectangular area. In each group, specimens were divided into 3 subgroups based on the number of firing cycles (3, 5, 7) for the veneering process. Metal-ceramic bond strength, fracture mode analysis, and area fraction of adherence porcelain (AFAP) of each subgroup was evaluated with a 3-point bend test and by measuring the Si content of specimens with scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). The results were statistically analyzed first with the Shapiro-Wilk test, where a P value of .364 was considered normally distributed, and then with the Student t test to determine significant differences (α=.05). RESULTS: Student t test results showed no statistical differences between the metal-ceramic bond strength of SLM and that of conventionally cast groups after firing 3, 5, and 7 times (P>.05). However, after SEM/EDS analyses, the SLM group showed significantly more porcelain adherence than that of the control group (P<.05) after 5 or 7 firings. CONCLUSIONS: The SLM group showed superior metal-ceramic bond strength that exceeded ISO 9691:1999 (E) requirements at all firing periods. Also, the bond showed better behavior in terms of AFAP than the conventional cast group, especially after 5 or 7 firings.

Genome-wide DNA methylation profile of human dental pulp stem cells during odontogenic differentiation.

OBJECTIVES: Human dental pulp stem cells (hDPSCs) is essential for dentin formation and regeneration, emerging evidence revealed that epigenetic regulation plays vital roles in odontogenic differentiation of hDPSCs. The purpose of this study was to explore the genome-wide DNA methylation changes during odontogenic differentiation of hDPSCs. DESIGN: hDPSCs were isolated from young healthy premolars and reduced representation bisulfite sequencing (RRBS) was taken to detect the genome-wide DNA methylation profile of hDPSCs during odontogenic differentiation. Genome-wide DNA methylation map, differentially methylated region (DMR) analysis, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were performed. RESULTS: We found a totally different DNA methylation patterns during the odontogenic differentiation of hDPSCs. A total of 9309 differentially methylated genes (DMG) were identified. Bio-information analysis revealed that calcium signaling pathway, pathways in cancer, and HTLV-I infection signaling pathways may play potential roles in odontogenic differentiation of hDPSCs. NOTCH1, WNT7B, and AXIN2 proteins were related with calcium signaling pathway. CONCLUSIONS: This study revealed a comprehensive analysis of global DNA methylation profiles in odontogeinc differentiation of hDPSCs and provided several possible underlying signaling pathways and candidate genes that may regulate the odontogenic differentiation of hDPSCs.

[Research of implant accuracy using a digital registration method].

PURPOSE: The aim of this study was to introduce a new method to evaluate the clinical accuracy of implant position. The results were compared to traditional cone beam CT (CBCT) method. METHODS: A total of 36 implants from 24 patients with sufficient bone volume were enrolled into the study. CBCT method and digital registration method were compared to evaluate the accuracy of implant position. The measurement parameters were defined as deviations between ideal and postsurgical implant position at occlusal point(d1), apical point(d2) and axis(α). The deviations between two methods were analyzed with SPSS 19.0 software package. RESULTS: The deviations between ideal and postsurgical implant position using CBCT were (0.88±0.64) mm for occlusal point, (1.07±0.85) mm for apical point and (4.74±2.35)° for angle. In digital registration method, the deviations were (0.86±0.67) mm for occlusal point, (1.12±0.88) mm for apical point and (4.56±2.66)° for angle. No significant difference(P＞0.05) was found between the two methods. CONCLUSIONS: There was no significant difference between the two methods in evaluating the clinical accuracy of implant position. Digital registration method could be accepted in clinical application.

Promoting lacunar bone regeneration with an injectable hydrogel adaptive to the microenvironment.

Injectable hydrogel is suitable for the repair of lacunar bone deficiency. This study fabricated an injectable, self-adaptive silk fibroin/mesoporous bioglass/sodium alginate (SMS) composite hydrogel system. With controllable and adjustable physical and chemical properties, the SMS hydrogel could be easily optimized adaptively to different clinical applications. The SMS hydrogel effectively showed great injectability and shapeability, allowing defect filling with no gap. Moreover, the SMS hydrogel displayed self-adaptability in mechanical reinforcement and degradation, responsive to the concentration of Ca2+ and inflammatory-like pH value in the microenvironment of bone deficiency, respectively. In vitro biological studies indicated that SMS hydrogel could promote osteogenic differentiation of bone marrow mesenchymal stem cells by activation of the MAPK signaling pathway. The SMS hydrogel also could improve migration and tube formation of human umbilical vein endothelial cells. Investigations of the crosstalk between osteoblasts and macrophages confirmed that SMS hydrogel could regulate macrophage polarization from M1 to M2, which could create a specific favorable environment to induce new bone formation and angiogenesis. Meanwhile, SMS hydrogel was proved to be antibacterial, especially for gram-negative bacteria. Furthermore, in vivo study indicated that SMS could be easily applied for maxillary sinus elevation, inducing sufficient new bone formation. Thus, it is convincing that SMS hydrogel could be potent in a simple, minimally invasive and efficient treatment for the repair of lacunar bone deficiency.

[Accuracy evaluation of static guided implant placement using an intraoral scan method].

PURPOSE: To evaluate the accuracy of static guided implant placement with intraoral scanning technology and to analyze the influencing factors of guided surgery. METHODS: Totally 27 cases were included in this retrospective study. The implant designs were made in 3Shape Implant Studio and then guided implant surgeries were performed with CAD-CAM templates. Postoperative implant positions were detected with an intraoral scanner (3Shape TRIOS) and deviation of implantation was evaluated using established CAD/CAM based evaluation method. SAS 9.4 software package was used for data analysis. RESULTS: The mean deviation of entrance point and apical point was (1.182±0.609) mm and (1.658±0.741) mm, respectively. Angular deviation was (5.712±3.347)°. Implant quadrant, location of the implant site, guidance degree, supporting type and implant size influenced direction deviation, while angular deviation was mainly affected by guidance degree and number of missing teeth. CONCLUSIONS: Accuracy of static guided implant placement can be influenced by many factors. More research is needed to improve the accuracy of static guided implantation.

Synergistic effect between 2-N,6-O-sulfonated chitosan and bone morphogenetic protein-2.

The molecular structure of sulfonated chitosan is similar to heparin, and it has been proved to have some heparin functions. Studies have shown that heparin and bone morphogenetic protein-2 (BMP-2) have synergistic effects, but heparin has limitations in clinical application. In this paper, the synergistic effect of 2-N,6-O-sulfonated chitosan (26SCS) and BMP-2 was studied. The preparation of 26SCS was explored and 26SCS was co-cultured with bone marrow mesenchymal stem cells (BMSCs) to study the effects of 26SCS on the proliferation, adhesion behavior and osteogenic differentiation of BMSCs. The synergistic mechanism of 26SCS and BMP-2 was explored by circular dichroism and isothermal calorimetric titration. The results showed that 26SCS affected the secondary structure of BMP-2 protein, mainly caused the significant change of antiparallel conformation in ß-fold, and then improved the biological activity of BMP-2 and showed a dose-dependent manner. 26SCS was expected to be a synergistic factor of BMP-2.

[Nonradiological methods for implant surgical guide accuracy measurement].

PURPOSE: To evaluate the accuracy of static computer-navigated implantation with surgical guides, based on a non-radiological method. Traditional measurements with a second cone-beam CT (CBCT) were applied to verify the accuracy. METHODS: A total of thirty template-guided implantations were designed and performed on 15 resin models. Two paralleled bone-level implants were planned in the edentulous space of each model, between which the distance was 4 mm. Postoperative implant positions were detected with both CAD/CAM-based measurements applying an intraoral scanner (3Shape TRIOS) and traditional ways via CBCT. Both methods were conducted with a CAD quality-control, reverse engineering software, Geomagic Studio 2013, comparing the positions with the virtual ones. Statistical analysis was processed with SPSS 23.0 software package. RESULTS: Measurements using CBCT (control group) showed a trend toward greater deviations when the results were directly compared(P<0.05). In the CAD/CAM-based evaluation of the 30 samples, the mean deviation of the insertion axis from the planned implant axis was 1.134°. The mean deviations of the implant shoulders in the horizontal direction and at the implant apices were 0.447 mm and 0.557 mm, respectively. No significant difference was observed when measuring distance deviation with the two assessment ways. CONCLUSIONS: Compared with evaluation based on radiology, CAD/CAM based evaluation system is able to evaluate implant accuracy precisely, effectively reduce radiological exposure of patients, being suitable for clinical evaluation.

Delivery vehicle of muscle-derived irisin based on silk/calcium silicate/sodium alginate composite scaffold for bone regeneration.

BACKGROUND: Irisin is a cytokine produced by skeletal muscle and usually plays a pivotal role in inducing fat browning and regulating energy expenditure. In recent years, it was found that irisin might be the molecular entity responsible for muscle-bone connectivity and is useful in osteogenesis induction. MATERIALS AND METHODS: To study its effect on bone regeneration, we developed silk/calcium silicate/sodium alginate (SCS) composite scaffold based on an interpenetrating network hydrogel containing silk fibroin, calcium silicate, sodium alginate. Then we loaded irisin on the SCS before coating it with polyvinyl alcohol (PVA). The SCS/P scaffold was physically characterized and some in vitro and in vivo experiments were carried out to evaluate the scaffold effect on bone regeneration. RESULTS: The SCS/P scaffold was showed a porous sponge structure pursuant to scanning electron microscopy analysis. The release kinetics assay demonstrated that irisin was stably released from the irisin-loaded hybrid system (i/SCS/P system) to 50% within 7 days. Moreover, osteoinductive studies using bone marrow stem cells (BMSCs) in vitro exhibited the i/SCS/P system improved the activity of alkaline phosphatase (ALP) and enhanced the expression levels of a series of osteogenic markers containing Runx-2, ALP, BMP2, Osterix, OCN, and OPN. Alizarin red staining also demonstrated the promotion of osteogenesis induced by i/SCS/P scaffolds. In addition, in vivo studies showed that increased bone regeneration with better mineralization and higher quality was found during the repair of rat calvarial defects through utilizing the i/SCS/P system. CONCLUSION: These data provided strong evidence that the composite i/SCS/P would be a promising substitute for bone tissue engineering.

Novel injectable strontium-hardystonite phosphate cement for cancellous bone filling applications.

Injectable bone cement (IBC) such as those based on methacrylates and hydraulic calcium phosphate and calcium sulfate-based cements have been used extensively for filling bone defects with acceptable clinical outcomes. There is a need however for novel IBC materials that can address some of the inherent limitations of currently available formulations to widen the clinical application of IBC. In this study, we characterized a novel hydraulic IBC formulation consisting of bioactive strontium-doped hardystonite (Sr-HT) ceramic microparticles and sodium dihydrogen phosphate, herein named Sr-HT phosphate cement (SPC). The resultant cement is comprised of two distinct amorphous phases with embedded partially reacted crystalline reactants. The novel SPC formulation possesses a unique combination of physicochemical properties suitable for use as an IBC, and demonstrates in vitro cytocompatibility when seeded with primary human osteoblasts. In vivo injection of SPC into rabbit sinus defects show minor new bone formation at the SPC periphery, similar to those exhibited in sinus defects filled with a clinically available calcium phosphate cement. The current SPC formulation presented in this paper shows promise as a clinically applicable IBC which can be further enhanced with additives.

[Establishment of traumatic occlusion model in Sprague-Dawley rats].

PURPOSE: In this study, different methods were used to observe and obtain the most effective one to establish occlusal trauma model in Sprague-Dawley rats. METHODS: SPF male SD rats weighing 150~200 g and aged 10 to 12 weeks were used in this study. The rats' maxillary molars were bonded with stainless steel wire, resin , casting half crown , casting half combined crowns, half crown using selective laser melting (SLM) technology, half combined crowns using SLM technology through Super-bond and Multi-link bonding under general anesthesia. After bonding, the experimental device expulsion rates were observed daily. The data was analyzed statistically using Fisher's exact test with SAS 8.2 software package. RESULTS: There was no significant difference between the falling rates of using super-bond and using multi-link. Under the situation in which different bonding methods exerted no influence on the falling rates, there was significant difference between different experimental devices (P<0.0001). CONCLUSIONS: The restorations fabricated with SLM technology is valid and feasible to induce occlusal point in building occlusal trama model using SD rats.

An Analysis of the Proximity of Maxillary Posterior Teeth to the Maxillary Sinus Using Cone-beam Computed Tomography.

INTRODUCTION: It is known that the level of the maxillary sinus floor varies with age. Because few studies have investigated whether the position of the posterior roots relative to the maxillary sinus varied with the variation of the sinus floor or not, the present study assessed the position according to age. METHODS: Cone-beam computed tomographic images of 848 patients were reconstructed to evaluate the position of the posterior roots relative to the sinus floor, which were divided into 3 types, and quantify the distances between posterior root apexes and the adjacent border of the sinus floor. Measurements were taken for each root, and data were correlated with age, which was divided into 4 groups (≤20 years, 21-40 years, 41-60 years, and >60 years). RESULTS: A total of 3063 premolars and 3095 molars were evaluated. The mean distances from the root tips to the border of the maxillary sinus floor increased with increasing age. From the first and second premolar roots, the mean distances ranged from 3.6 ± 4.1 mm to 8.9 ± 4.6 mm and from 0.7 ± 3.3 mm to 5.3 ± 3.9 mm, respectively. From the mesiobuccal, distobuccal, and palatinal roots of the first molars, the mean distances were -0.4 ± 2.8 mm to 4.6 ± 4.0 mm, -0.3 ± 2.4 mm to 4.4 ± 3.8 mm, and -0.4 ± 3.5 mm to 3.9 ± 4.1 mm, respectively. From the mesiobuccal, distobuccal, and palatinal roots of the second molars, the mean distances were -0.5 ± 2.2 mm to 3.4 ± 3.5 mm, 0.3 ± 2.2 mm to 3.9 ± 3.7 mm, and 1.1 ± 3.2 mm to 4.6 ± 4.5 mm, respectively. The frequency of type IS decreased with increasing age. It was very low in first premolars (0%-8.13%) and higher in second premolars (0%-25.68%), first molars (0%-44.75%), and second molars (0%-32.89%). Age significantly influenced the mean distances to the sinus floor and the frequencies of type IS (inside). CONCLUSIONS: Cone-beam computed tomographic imaging is an effective method to study the position of the posterior roots to the maxillary sinus floor. Variation in proximity measurements was found by age, with those under the age of 40 showing a greater likelihood of the position of maxillary roots above/inside the sinus floor.

Surface properties and corrosion behavior of Co-Cr alloy fabricated with selective laser melting technique.

We sought to study the corrosion behavior and surface properties of a commercial cobalt-chromium (Co-Cr) alloy which was fabricated with selective laser melting (SLM) technique. For this purpose, specimens were fabricated using different techniques, such as SLM system and casting methods. Surface hardness testing, microstructure observation, surface analysis using X-ray photoelectron spectroscopy (XPS) and electrochemical corrosion test were carried out to evaluate the corrosion properties and surface properties of the specimens. We found that microstructure of SLM specimens was more homogeneous than that of cast specimens. The mean surface hardness values of SLM and cast specimens were 458.3 and 384.8, respectively; SLM specimens showed higher values than cast ones in hardness. Both specimens exhibited no differences in their electrochemical corrosion properties in the artificial saliva through potentiodynamic curves and EIS, and no significant difference via XPS. Therefore, we concluded that within the scope of this study, SLM-fabricated restorations revealed good surface properties, such as proper hardness, homogeneous microstructure, and also showed sufficient corrosion resistance which could meet the needs of dental clinics.

Metal-ceramic bond strength of Co-Cr alloy fabricated by selective laser melting.

OBJECTIVES: This study was to evaluated the metal-ceramic bond strength of a Co-Cr dental alloy prepared using a selective laser melting (SLM) technique. METHODS: Two groups comprised of twenty Co-Cr metal bars each were prepared using either a SLM or traditional lost-wax casting method. Ten bars from each group were moulded into standard ISO 9693:1999 dimensions of 25 mm × 3 mm × 0.5 mm with 1.1 mm of porcelain fused onto an 8 mm × 3 mm rectangular area in the centre of each bar. Metal-ceramic bonding was assessed using a three-point bending test. Fracture mode analysis and area fraction of adherence porcelain (AFAP) were determined by measuring Si content of specimens by SEM/EDS. RESULTS: Student's t-test within the groups demonstrated no significant difference for the mean bond strength between the SLM and traditional cast sample groups. While SEM/EDS analysis indicated a mixed fracture mode on the debonding interface of both the SLM and the cast groups, the SLM group showed significantly more porcelain adherence than the control group (p<0.05). CONCLUSIONS: The SLM metal-ceramic system exhibited a bonding strength that exceeds the requirement of ISO 9691:1999(E) and it even showed a better behaviour in porcelain adherence test comparable to traditional cast methods.

[Clinical application of reverse island flap based on tibial planter digital artery].

OBJECTIVE: To study the therapeutic effect of reverse island flap based on tibial plantar digital artery for soft tissue defect at the distal end of first toe. METHODS: 18 cases with soft tissue defect at the distal end of first toe were treated with reverse island flap based on tibial plantar digital artery. RESULTS: The patients were followed up for 6 to approximately 12 months (mean 9.5 months). All the flaps survived completely with good functional and cosmetic results. CONCLUSIONS: The reversed island flap based on tibial plantar digital artery has a reliable blood supply and is adjacent to the recipient area. It is practical and suitable for soft tissue defect at the distal end of first toe.