Differential expression of circular RNAs in interleukin 6-promoted osteogenic differentiation of human stem cells from apical papilla.

INTRODUCTION: Studies have shown that interleukin 6 (IL-6) can regulate stem cell osteogenic differentiation; however, the exact mechanism is not clear. Circular RNAs (circRNAs) are closed circular non-coding RNAs that are involved in the process of stem cell osteogenic differentiation. Therefore, the purpose of this present study was to investigate the effect of IL-6 treatment on osteogenic differentiation of human apical tooth papillae stem cells (hSCAPs), and to detect the difference in circRNA expression using gene microarray technology. METHODS: After extraction and identification of hSCAPs, alkaline phosphatase (ALP) activity, alizarin red staining, and calcium ion quantitative assay were used to determine the changes of ALP enzyme, mineralized nodules, and matrix calcium levels before and after IL-6 treatment of hSCAPs gene microarray technology was used to analyze the changes in circRNA expression levels before and after IL-6 induction of mineralization. The four selected circRNAs were validated by qRT-PCR. Moreover, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to predict the potential functions and biological signaling pathways of circRNAs. Finally, these data are integrated and analyzed to construct circRNA-microRNA-mRNA networks. RESULTS: Alp and Alizarin red staining confirmed that IL-6 promoted the osteogenic differentiation of hSCAPs. The gene microarray results identified 132 differentially expressed circRNAs, of which 117 were upregulated and 15 were downregulated. Bioinformatic analysis predicted that the circRNA-406620/miR-103a-3p/FAT atypical cadherin 4 (FAT4) pathway might be involved in regulating IL-6 to promote osteogenic differentiation of hSCAPs. CONCLUSION: Differentially expressed circRNAs might be closely involved in regulating IL-6 to promote osteogenic differentiation of hSCAPs.

Effect of platelet concentrates for pain and symptom management in oral lichen planus: an evidence-based systematic review.

BACKGROUND: Platelet Concentrate (PC) injection therapy has shown potential as a local therapy for oral lichen planus (OLP). However, its safety and efficacy have not yet been fully established. Our research compared the efficacy of PC with topical steroid treatment in alleviating pain and symptoms related to OLP. We aims to present evidence-based alternatives that dentists can use to improve patient outcomes while reducing potential side effects. METHODS: We conducted a systematic search of five electronic databases up to April 2023, including Embase, Cochrane Central Register of Controlled Trials, PubMed, OVID Medline, and WanFang, to evaluate PCs' efficacy compared to topical corticosteroid therapy for OLP. The literature quality was assessed using the Cochrane ROB tool. A fixed-effects model was used to determine the Weighted Mean Difference (WMD) and Mean Difference (MD) at a 95% confidence interval (CI) for pain severity and other relevant clinical indicators. RESULTS: The comparison between topical corticosteroid therapy and PCs showed no significant difference for pain relief (WMD = -0.07, CI = 95% -0.34 to 0.19), symptom improvement (MD = -0.21, CI = 95% -0.55 to 0.13), or the severity of included lesions measured by REU scores (MD = -0.25, CI = 95% -0.32 to 0.82). CONCLUSIONS: Locally injected PC have been found efficient in managing oral lichen planus, indicating that they are a promising alternative option to steroid therapy for OLP patients, particularly those who have not responded favorably to steroid therapy. However, further research is needed to establish determining the recurrence rate and long-term adverse effects. TRIAL REGISTRATION: The systematic review protocol has been registered in advance with the PROSPERO database (CRD42023415372).

The bioceramic sealer iRoot SP promotes osteogenic differentiation of human stem cells from apical papilla via miR-141-3p/SPAG9/MAPK signalling pathway.

AIM: The premixed bioceramic sealer iRoot SP that is widely used clinically has been reported to kill bacterial biofilms and promote osteogenic differentiation of human stem cells from the apical papilla (hSCAPs). Although miR-141-3p has been substantiated to be involved in the osteogenic process, the underlying mechanisms remain unclear. The aim of this study was to investigate the role of miR-141-3p in osteogenic differentiation and underlying mechanisms of iRoot SP-treated hSCAPs. METHODOLOGY: hSCAPs were extracted from tissue blocks with enzyme digestion and identified by using immunofluorescence, flow cytometry and alizarin red staining. The mRNA expression level of miR-141-3p in hSCPAs after culture with iRoot SP was examined by quantitative real-time PCR (qRT-PCR) assay. SPAG9 was identified as a downstream target gene of miR-141-3p by dual-luciferase report assay. Alkaline phosphatase (ALP) staining and activity detection, alizarin red staining, calcium concentration assay, qRT-PCR and western blot were used to estimate osteogenic differentiation ability and involved protein expression levels of the osteogenic makers and signalling pathway-related factors in iRoot SP-treated hSCAPs. Data were analysed by one-way anova and post hoc Tukey's test to determine any statistical differences between the experimental groups and the control group. p < .05 was considered statistically significant. RESULTS: Expression of miR-141-3p was reduced in iRoot SP-treated hSCAPs with the increased exposure time up to 7 days, and the western blot and qRT-PCR results revealed that the osteogenic markers osteocalcin (OCN), osterix (OSX), runt-related transcription factor 2 (RUNX2) and dentin sialophosphoprotein (DSPP) were inversely correlated with miR-141-3p. The negative regulatory relationship between miR-141-3p and SPAG9/ mitogen-activated protein kinases (MAPK) signalling axis was validated in this in vitro experiments. CONCLUSIONS: The bioceramic sealer iRoot SP promoted osteogenic differentiation of hSCAPs by inhibiting miR-141-3p following down-regulated SPAG9 expression, and activated MAPK pathway. These findings proposed a novel therapeutic impact of bioceramic sealer iRoot SP inducing bone regeneration in refractory periapical periodontitis.

GCN5 regulates ZBTB16 through acetylation, mediates osteogenic differentiation, and affects orthodontic tooth movement.

In the process of orthodontic tooth movement (OTM), periodontal ligament fibroblasts (PDLFs) must undergo osteogenic differentiation. OTM increased the expression of Zinc finger and BTB domain-containing 16 (ZBTB16), which is implicated in osteogenic differentiation. Our goal was to investigate the mechanism of PDLF osteogenic differentiation mediated by ZBTB16. The OTM rat model was established, and PDLFs were isolated and exposed to mechanical force. Hematoxylin-eosin staining, Alizarin Red staining, immunofluorescence, and immunohistochemistry were carried out. The alkaline phosphatase (ALP) activity was measured. Dual-luciferase reporter gene assay and chromatin immunoprecipitation assay were conducted. In OTM models, ZBTB16 was significantly expressed. Additionally, there was an uneven distribution of PDLFs in the OTM group, as well as an increase in fibroblasts and inflammatory infiltration. ZBTB16 interference hindered PDLF osteogenic differentiation and decreased Wnt and ß-catenin levels. Meanwhile, ZBTB16 activated the Wnt/ß-catenin pathway. ZBTB16 also enhanced the expression of the osteogenic molecules osterix, osteocalcin (OCN), osteopontin (OPN), and bone sialo protein (BSP) at mRNA and protein levels. The interactions between Wnt1 and ZBTB16, as well as GCN5 and ZBTB16, were also verified. The adeno-associated virus-shZBTB16 injection also proved to inhibit osteogenic differentiation and reduce tooth movement distance in in vivo tests. ZBTB16 was up-regulated in OTM. Through acetylation modification of ZBTB16, GCN5 regulated the Wnt/ß-catenin signaling pathway and further mediated PDLF osteogenic differentiation.

Influence of anatomical factors related to maxillary sinus on outcomes of transcrestal sinus floor elevation.

BACKGROUND/PURPOSE: Graft bone maturation and remodeling in the maxillary sinus require adequate angiogenesis and osteoprogenitor cells migration from the surrounding bony walls and Schneiderian membrane. This study aimed to evaluate the influence of anatomical factors related to maxillary sinus on the outcomes of transcrestal sinus floor elevation using cone-beam computed tomography (CBCT). MATERIALS AND METHODS: Forty-five patients (63 elevated sites) were included in this study. CBCT were obtained preoperatively, immediately and 6 months after surgery. The anatomical features of residual bone height, maxillary sinus width, maxillary sinus angle and Schneiderian membrane thickness were measured on preoperative CBCT. Descriptive statistics and correlation analysis were conducted to evaluate the influence of anatomical factors on outcome parameters, including sinus lift height, graft bone resorption and marginal bone loss. RESULTS: The results showed that there was a positive correlation between sinus width and graft bone resorption. A significantly positive correlation between sinus angle and graft bone resorption was also found. CONCLUSION: Our findings indicate that the anatomical factors of maxillary sinus (sinus width and sinus angle) have influence on the linear change of bone grafts after transcrestal sinus floor elevation.

Effects of iRoot SP on osteogenic differentiation of human stem cells from apical papilla.

BACKGROUND: Research shows that nano-bioceramics can modulate the differentiation of dental stem cells. The novel ready-to-use calcium-silicate-based root-canal sealer iRoot SP is widely used in root filling. Accordingly, the aim of this study was to evaluate the effects of iRoot SP on proliferation and osteogenic differentiation in human stem cells from the apical papilla (hSCAPs). METHODS: hSCAPs were isolated and characterized in vitro, then cultured with various concentrations of iRoot SP extract. Cell proliferation was assessed by CCK-8 assay, and scratch-wound-healing assays were performed to evaluate cell-migration capacity. hSCAPs were then cultured in osteogenic medium supplemented with iRoot SP extracts. Alkaline phosphatase (ALP) activity assay was used to evaluate ALP enzyme levels. Alizarin red staining and cetylpyridinium chloride (CPC) assays were performed to assess calcified-nodule formation and matrix-calcium accumulation of hSCAPs. The mRNA and protein expression levels of the osteogenic markers OCN, OSX, Runx2, and DSPP were determined by qRT-PCR and Western blotting. The data were analyzed using one-way ANOVA and LSD-t tests. RESULTS: iRoot SP at low concentrations (2, 0.2, and 0.02 mg/mL) is nontoxic to hSCAPs. iRoot SP at concentrations of 0.02 and 0.2 mg/mL significantly increases cell-migration capacity. In terms of osteogenic differentiation, 0.2 mg/mL iRoot SP promotes intracellular ALP activity and the formation of mineralized nodules. Moreover, the expression of osteogenic markers at the mRNA and protein levels are upregulated by iRoot SP. CONCLUSION: iRoot SP is an effective filling material for periapical bone regeneration.

[Effect of anatomical parameters of maxillary sinus on the outcomes of transcrestal sinus lift].

OBJECTIVE: To investigate the effect of three anatomical parameters (maxillary sinus width, maxillary sinus angle, and residual bone height) on the outcomes of transcrestal sinus lift with simultaneous implant placement. METHODS: A total of 60 maxillary sinuses in 42 patients were included in this study. All patients were treated with transcrestal sinus lift procedure associated with simultaneous implant placement using a composite graft material of autogenous bone and Bio-Oss. For each patient, beam computed tomography (CBCT) scans were performed preoperatively, immediately after surgery, and 6 months after surgery. The parameters were measured on the preoperative and postoperative CBCT images. The correlation of three anatomical parameters with graft resorption was analyzed using Pearson's correlation test. RESULTS: The average residual bone height was (4.46±1.55) mm. The average width of maxillary sinus was (13.86±2.71) mm. The average sinus angle was 78.09°±10.27°. A significant positive correlation was observed between maxillary sinus width and graft resorption (P<0.01). A positive association was also found between sinus angle and graft resorption (P<0.01). CONCLUSIONS: The findings show that graft bone resorption in elevated sinus has a positive correlation with the sinus width and sinus angle.

Lingual Lymph Node Metastasis in cT1-2N0 Tongue Squamous Cell Carcinoma: Is It an Indicator for Elective Neck Dissection.

Objective: Accurate predictors for occult metastasis in cT1-2N0 tongue squamous cell carcinoma (SCC) remains scarce, the main goal in current study was to evaluate whether there is significant association between lingual lymph node (LLN) metastasis and occult lymph node metastasis as well as whether there is prognostic value of LLN metastasis in early stage tongue SCC. Methods: Patients with surgically treated primary cT1-2N0 tongue SCC were prospectively enrolled from January 2010 to December 2018. LLNs were dissected independently for pathologic analysis. The main study endpoints were locoregional control survival (LRC) and disease-specific survival (DSS). The Chi-square test and multivariate regression analysis were used to assess the predictors for occult metastasis. The Kaplan-Meier approach and Cox model were used to analyze the potential prognostic factors. Results: A total of 317 patients were enrolled for analysis. Eighty-eight patients had occult metastasis with a prevalence of 27.8%. LLNs presented in 89 patients, in which 43 patients had LLN metastasis. In the 43 patients with positive LLNs, 20 patients had occult metastasis, in 274 patients with negative LLNs or no LLNs, 68 patients had occult metastasis, the difference was significant (p = 0.012). Further multivariate regression analysis confirmed the independence of LLN metastasis in predicting the occult metastasis. In patients without LLNs, the 5-year LRC rate was 79%, in patients with negative LLNs, the 5-year LRC rate was 78%, in patients with positive LLNs, the 5-year LRC rate was 62%, the difference was significant (p = 0.024). In patients without LLNs, the 5-year DSS rate was 84%, in patients with negative LLNs, the 5-year DSS rate was 74%, in patients with positive LLNs, the 5-year DSS rate was 51%, the difference was significant (p < 0.001), further Cox model confirmed the independence of LLN metastasis in affecting the LRC and DSS. Conclusions: LLN metastasis is significantly associated with occult neck lymph node metastasis, and decrease the LRC and DSS in early stage tongue SCC.

miR-221-3p and miR-222-3p downregulation promoted osteogenic differentiation of bone marrow mesenchyme stem cells through IGF-1/ERK pathway under high glucose condition.

OBJECTIVE: This study aims to investigate the roles of miR-221-3p and miR-222-3p in the regulation of osteogenic differentiation of bone marrow mesenchyme stem cells (BMSCs) under high glucose condition. MATERIALS AND METHODS: The expreesions of miR-221-3p, miR-222-3p and insulin-like growth factor 1 (IGF-1) were detected by qRT-PCR. The protein levels of osteoblast-related proteins (Osterix, Runx-2 and Osteopontin) were detected by western blot. Whether miR-221-3p and miR-222-3p can target IGF-1 was assessed by dual luciferase reporter gene assay. RESULTS: miR-221-3p and miR-222-3p were up-regulated in the mandibles of diabetic rats and BMSCs cultured in high glucose condition. Silencing miR-221-3p or/ and miR-222-3p increased ALP activity and up-regulated osteoblast-related protein levels, and the simultaneous silence the two miRNAs showed stronger effects on ALP activity and osteoblast-related protein levels. Next, we confirmed that miR-221-3p and miR-222-3p both targeted IGF-1 and cooperatively regulated its expression. Besides, miR-221-3p and miR-222-3p regulated ERK activation through IGF-1. Silencing miR-221-3p and miR-222-3p promoted osteogenic differentiation of BMSCs through IGF-1 under high glucose condition. CONCLUSION: miR-221-3p and miR-222-3p inhibited osteogenic differentiation of BMSCs via IGF-1/ERK pathway under high glucose condition.

Improving the Stability of Liposomal Curcumin by Adjusting the Inner Aqueous Chamber pH of Liposomes.

Curcumin (CURC) is a hydrophobic molecule and its water solubility can be greatly improved by liposome encapsulation. However, investigations on the stability of pH-sensitive molecules incorporated into liposomal membranes are limited. In this study, CURC-loaded liposomes with varied internal pH values (pH 2.5, 5.0, or 7.4) were prepared and designated as CURC-LP (pH 2.5), CURC-LP (pH 5.0), and CURC-LP (pH 7.4). Physical properties including particle size, ζ-potential, morphology, entrapment efficiency, and physical stabilities of these CURC-LPs were assessed. In addition, the chemical stability of liposomal CURC to different external physiological environments and internal microenvironmental pH levels were investigated. We found that among these CURC-LPs, CURU-LP (pH 2.5) has the highest entrapment efficiency (73.7%), the best physical stabilities, and the slowest release rate in vitro. Liposomal CURC remains more stable in an acid external environment. In the physiological environment, the chemical stability of liposomal CURC is microenvironmental pH-dependent. In conclusion, we prove that the stability of liposomal CURC is external physiological environment- and internal microenvironmental pH-dependent. These findings suggest that creating an acidic microenvironment in the internal chamber of liposomes is beneficial to the stability of liposomal CURC, as well as for other pH-sensitive molecules.

Use of IL-1 ß, IL-6, TNF-α, and MMP-8 biomarkers to distinguish peri-implant diseases: A systematic review and meta-analysis.

OBJECTIVE: To investigate the use of peri-implant crevicular fluid (PICF) interleukin-1ß (IL-1ß), IL-6, tumor necrosis factor-α (TNF-α), and matrix metalloproteinase-8 (MMP-8) biomarkers in distinguishing between healthy implants (H), peri-implant mucositis (MU), and peri-implantitis (PI). MATERIAL AND METHODS: Electronic using three databases (Pubmed, EMBASE, and Cochrane) and manual searches were conducted for articles published up to March 2018 by two independent calibrated reviewers. Meta-analyses using a random-effects model were conducted for each of the cytokines; IL-1ß, IL-6, and TNF-α, to analyze standardized mean difference (SMD) between H and MU, MU and PI, H and PI with their associated 95% confidence intervals (CI). Qualitative assessment of MMP-8 was provided consequent to the lack of studies that provide valid data for a meta-analysis. RESULTS: Nineteen articles were included in this review. IL-1ß, IL-6, and TNF-α, levels were significantly higher in MU than H groups (SMD: 1.94; 95% CI: 0.87, 3.35; P < .001, SMD: 1.17; 95% CI: 0.16, 3.19; P = .031 and SMD: 3.91; 95% CI: 1.13, 6.70; P = .006, respectively). Similar results were obtained with PI compared to H sites (SMD: 2.21, 95% CI: 1.32, 3.11; P < .001, SMD: 1.72; 95% CI: 0.56, 2.87; P = .004 and SMD: 3.78; 95% CI: 1.67, 5.89; P < .001, respectively). IL-6 was statistically higher in PI than MU sites (SMD = 1.46; 95% CI: 0.36, 2.55; P = .009); while IL-1ß increase was not significant. Despite absence of meta-analysis, MMP-8 show to be a promising biomarker in detection of PI in literature. CONCLUSION: Within the limitations of this study, pro-inflammatory cytokines in PICF, such as IL-1ß and IL-6, can be used as adjunct tools to clinical parameters to differentiate H from MU and PI.

Comparison between wait-and-see policy and elective neck dissection in clinically N0 cutaneous squamous cell carcinoma of head and neck.

To analyze the superiority of wait-and-see policy and elective neck dissection in treating cN0 patients with facial cutaneous cell carcinoma (cSCC).Patients with clinically negative parotid and neck metastasis disease were prospectively enrolled. Three groups were divided based on whether the patient received an operation of superficial parotidectomy or/and elective dissection, and regional control and disease-specific survival rates were compared.The occult parotid and neck metastasis rate was 20% and 16%, respectively. There was neck node metastasis without parotid metastasis in only 1 patient. All the node metastasis occurred in level II. Regional recurrence was noted in 16 (16%) patients, and 6 patients died of the disease. In the group undergoing superficial parotidectomy and elective neck dissection, 2 patients had neck node metastasis, and there was no disease-related death, further survival analysis indicated it had better regional control and disease-specific survival rates compared with the other 2 groups.Superficial parotidectomy and elective neck dissection are suggested for patients with T3-4 facial cutaneous squamous cell carcinoma.

Assessment of quality of life and sociocultural aspects in patients with ameloblastoma after immediate mandibular reconstruction with a fibular free flap.

Our aim was to evaluate the quality of life (QoL) in patients with ameloblastoma who had been treated by immediate mandibular reconstruction with a fibular free flap, and to analyse the association between QoL and their sociocultural and medical characteristics. We assessed the QoL outcomes of 33/45 patients using the University of Washington quality of life (UW-QoL) questionnaire and the 14-item Oral Health Impact Profile (OHIP-14). Thirty-three of the 45 questionnaires were returned (73%). In the UW-QoL the best-scoring domain was "shoulder", whereas the lowest scores were for "chewing" and "activity". In the OHIP-14 the lowest-scoring domain was "handicap", followed by "social disability" and "psychological discomfort". Mandibular reconstruction with a fibular free flap significantly influenced the patients' QoL and oral function. Their sociocultural data showed that most patients had a fairly low level of education.

Comparison between anterolateral thigh perforator free flaps and pectoralis major pedicled flap for reconstruction in oral cancer patients-A quality of life analysis

The aim of this study was to compare the differences between anterolateral thigh perforator free flaps (ALTFF) and pectoralis major myocutaneous flap (PMMF) for reconstruction in oral cancer patients. Method and Patients: who received free flap or PMMF reconstruction after ablation surgeries were eligible for the current study. The patients’ demographic data, medical history, and quality of life scores(Medical Outcomes Study-Short Form-36 (MOS SF-36) and the University of Washington Quality of Life (UW-QOL) questionnaires were collected. Results: 81 of 118 questionnaires were returned (68.64%). There was significant differences between two groups in the gender (P<0.005). Patients reconstructed with ALTFF had better appearance domains and better shoulders domains, in addition to better role emotion domains. Conclusions: Using either PMMF or ALTFF for reconstruction of oral defects after cancer resection significantly influences a patient’s quality of life. Data from this study provide useful information for physicians and patients during their discussion of reconstruction modalities for oral cancers (AU)

Comparison between anterolateral thigh perforator free flaps and pectoralis major pedicled flap for reconstruction in oral cancer patients--a quality of life analysis.

UNLABELLED: The aim of this study was to compare the differences between anterolateral thigh perforator free flaps (ALTFF) and pectoralis major myocutaneous flap (PMMF) for reconstruction in oral cancer patients. Method Patients: who received free flap or PMMF reconstruction after ablation surgeries were eligible for the current study. The patients' demographic data, medical history, and quality of life scores(Medical Outcomes Study-Short Form-36 (MOS SF-36) and the University of Washington Quality of Life (UW-QOL) questionnaires were collected. RESULTS: 81 of 118 questionnaires were returned (68.64%). There was significant differences between two groups in the gender (P<0.005). Patients reconstructed with ALTFF had better appearance domains and better shoulders domains, in addition to better role emotion domains. CONCLUSION: Using either PMMF or ALTFF for reconstruction of oral defects after cancer resection significantly influences a patient's quality of life. Data from this study provide useful information for physicians and patients during their discussion of reconstruction modalities for oral cancers.

Measures of health-related quality of life and socio-cultural aspects in young patients who after mandible primary reconstruction with free fibula flap.

BACKGROUND: The reconstruction of mandibular defects after trauma or tumor resection is one of the most challenging problems facing reconstructive surgeons. Although the primary intended outcome of surgery to treat head-and-neck malignancies is still the disease-free survival of the patient, health-related quality of life (HRQOL) is now seen as an essential secondary outcome. This study aims to evaluate HRQOL outcomes in young patients undergoing primary mandible reconstruction with free fibula flap and to collect information about their socio-cultural situation. METHODS: The HRQOL outcomes of 25 young patients after primary mandible reconstruction with free fibula flap for mandible malignancies were assessed using the Medical Outcomes Study-Short Form-36 (MOS SF-36) and University of Washington Quality of Life (UW-QOL) questionnaires 12 months postoperatively. RESULTS: Using the UW-QOL questionnaire, the best-scoring domain was 'pain', whereas 'chewing' and 'anxiety' were given the lowest scores. Using the MOS SF-36 questionnaire, the best-scoring domain was 'physical functioning', while 'bodily pain' and 'general health' also scored well. CONCLUSIONS: Mandible reconstruction with fibula flap will significantly influence a young patient's HRQOL. Young patients pay more attention to postoperative facial appearance; this should be considered in surgical planning. The socio-cultural data show a fairly low level of education for the majority of patients.

[Finite element contact stress analysis of simulating teeth with wedge shaped defects in the cervical region].

OBJECTIVE: To study the distribution of stress of simulating teeth with wedge shaped defects in the cervical region. METHODS: The models of anisotropic enamel of the mandibular first premolar and the opposite maxillary first premolar crown were created. A defect was introduced into the model of mandibular premolar in the buccal cervical region along the enamelo-dentinal junction (DEJ). The stress distribution in the cervical region of the mandibular premolar was investigated considering lateral condition simulating working micromotions. In this case, the stroke was applied to the maxillary first mandibular in a stepping procedure using nonlinear contact analysis. RESULTS: The stresses were concentrated in the defect of the enamel and dentin at the DEJ in the condition of lateral loading. As the defect length increased in size, the peak maximum principal stress (MPS) value and the magnitude of the stress field along the DEJ both increased. CONCLUSION: Undermined cervical DEJ had a significant effect on the stress distribution in the buccal cervical region.

[Effects of laser welding on bond of porcelain fused cast pure titanium].

OBJECTIVE: To investigate the influence of the laser welding on bond of porcelain fused to cast pure titanium. METHODS: Twenty cast titanium plates were divided into two groups: laser welded group and control group. The low-fusing porcelain was fused to the laser welded cast pure titanium plates at fusion zone. The bond strength of the porcelain to laser welded cast pure titanium was measured by the three-point bending test. The interface of titanium and porcelain was investigated by scanning electron microscopy (SEM) and energy depressive X-ray detector (EDX). The non-welded titanium plates were used as comparison. RESULTS: No significant difference of the bond strength was found between laser-welded samples [(46.85 +/- 0.76) MPa] and the controls [(41.71 +/- 0.55) MPa] (P > 0.05). The SEM displayed the interface presented similar irregularities with a predominance. The titanium diffused to low-fusing porcelain, while silicon and aluminum diffused to titanium basement. CONCLUSIONS: Laser welding does not affect low-fusing porcelain fused to pure titanium.

[Structural characteristics of laser-welded cast pure titanium joints by different gap distance].

OBJECTIVE: To measure the microstructure of laser-welded cast pure titanium by different gap distance. METHODS: Forty specimens were sectioned and welded at four gaps (0.00 mm, 0.25 mm, 0.50 mm and 1.00 mm). Took microhardness test and metallographic examination of welded zone surface. RESULTS: There were no difference in microhardness value and metallographic observation between welded specimens. The width of heat-effected zone was different. The smaller grains and needle-like alphamartensitic structure were found in the heat-affected zone. CONCLUSION: The effects of the joint gap were not significant.