Cytokine co-stimulation effect on odontogenic differentiation of stem cells.

OBJECTIVE: The study aims to evaluate the effect of bone morphogenetic protein-2 (BMP-2) and transforming growth factor-beta 1 (TGF-ß1) co-stimulation on odontogenic differentiation of human dental pulp stem cells (hDPSCs). MATERIALS AND METHODS: The viability/proliferation of hDPSCs treated with BMP-2 (group B), TGF-ß1 (group T), or BMP-2/TGF-ß1 (group BT) were evaluated. The experiments on odontogenic differentiation were done for 14 days. The following subgroups were added to investigate the effect of co-stimulation with different timing: subgroup B1, TGF-ß1 co-stimulation in the first week; subgroup B2, TGF-ß1 co-stimulation in the second week; subgroup T1, BMP-2 co-stimulation in the first week; and subgroup T2, BMP-2 co-stimulation in the second week. The mineralization was assessed using alizarin red staining. The expression of following genes was assessed using quantitative real-time polymerase chain reaction: dentin sialophosphoprotein (DSPP), dentin matrix protein-1 (DMP1), osteopontin (OPN), and alkaline phosphatase. RESULTS: All groups showed viability similar to the control group (P > .05). The greater mineralization was detected in B groups on day 14. The expressions of DSPP, DMP-1, and OPN increased on day 14 (P < .05). In the combination groups, the higher expressions of DSPP and DMP-1 were observed in subgroups B1 and B2 than groups B and T (P < .05). CONCLUSIONS: BMP-2 was the key in odontogenic differentiation of hDPSCs, which was further enhanced by co-stimulation with TGF-ß1. Continuous stimulation with TGFß-1 did not improve the differentiation of hDPSCs. CLINICAL RELEVANCE: Combined use of the BMP-2 and TGFß-1 at the specific sequence can provide a tissue engineering approach for the future guided dentin regeneration.

Effect of thickness of monolithic zirconia ceramic on final color.

STATEMENT OF PROBLEM: Achieving excellent esthetics with monolithic zirconia restorations is challenging, and the impact of monolithic zirconia thickness on the final color is unclear. PURPOSE: The purpose of this in vitro study was to assess the effect of thickness of monolithic zirconia ceramic on its final color and to define the minimum thickness needed to gain an acceptable final color. MATERIAL AND METHODS: Sixty monolithic zirconia disk specimens with a 10-mm diameter and 3 different thicknesses (0.7, 0.9, and 1.1 mm) were fabricated from 2 zirconia brands. The specimens were divided into 6 groups of 10 based on the thickness and brand. All the specimens were colored with an A2 shade liquid. The specimens were placed on an A4 shade substrate, and their CIELab values were measured with a spectrophotometer. ΔE values were calculated to determine color differences between the specimens and the A2 VITA classical shade tab. The ΔE values were compared with an acceptability threshold (ΔE=3.3). Two-way ANOVA, the Bonferroni test, and 1-sample t test were used to analyze data (α=.05). RESULTS: Mean ΔE values ranged between 2.4 and 4.1. The zirconia thickness affected the ΔE (P<.001); however, the zirconia brand did not affect the ΔE (P=.059). The mean ΔE values for the zirconia thickness of 0.7 mm for both brands were more than the threshold (P<.05). CONCLUSIONS: The thickness of monolithic zirconia ceramic affected its final color. The minimum thickness of a monolithic zirconia ceramic should be 0.9 mm to gain the acceptable final color.

The Effect of Composite Thickness on the Stress Distribution Pattern of Restored Premolar Teeth with Cusp Reduction.

PURPOSE: Different thicknesses of restorative material can alter the stress distribution pattern in remaining tooth structure. The assumption is that a thicker composite restoration will induce a higher fracture resistance. Therefore, the present study evaluated the effect of composite thickness on stress distribution in a restored premolar with cusp reduction. MATERIALS AND METHODS: A 3D solid model of a maxillary second premolar was prepared and meshed. MOD cavities were designed with different cusp reduction thicknesses (0, 0.5, 1, 1.5, 2.5 mm). Cavities were restored with Valux Plus composite. They were loaded with 200 N force on the occlusal surface in the direction of the long axis. Von Mises stresses were evaluated with Abaqus software. RESULTS: Stress increased from occlusal to gingival and was maximum in the cervical region. The stressed area in the palatal cusp was more than that of the buccal cusp. Increasing the thickness of composite altered the shear stress to compressive stress in the occlusal area of the teeth. CONCLUSION: The model with 2.5 mm cusp reduction exhibited the most even stress distribution.

Effect of Er,Cr:YSGG laser treatment on microshear bond strength of zirconia to resin cement before and after sintering.

PURPOSE: To evaluate the effect of Er,Cr:YSGG laser treatment on microshear bond strength of zirconia to resin cement before and after sintering. MATERIALS AND METHODS: Ninety pre-sintered yttrium-stabilized tetragonal zirconia specimens (4 × 3 × 2 mm) were divided into 6 groups (n = 15). In group C, sintered zirconia was not treated (control group). In groups AS2 and AS3, sintered zirconia blocks were irradiated by Er,Cr:YSGG using a power of 2 and 3 W, respectively. Groups PS2 and PS3 consisted of pre-sintered blocks conditioned by Er,Cr:YSGG at 2 and 3 W, respectively. In group AA, sintered zirconia was air abraded with 50-µm alumina powder. One block was made using the same preparations as mentioned above and was morphologically assessed by SEM. Microcylinders of Panavia F 2.0 were placed on the treated surface of the groups. Samples were incubated at 37°C and 98% humidity for 48 h and then subjected to microshear bond strength testing. The mode of failure was evaluated. Data were analyzed by one-way ANOVA and Tukey's HSD test (p < 0.05). RESULTS: There was a statistically significant difference between group AA and the others (p < 0.0001). A significant difference was also noted between groups AS3 and C (p = 0.031). Complete surface roughness was seen in group AA and the bond failure was mostly cohesive, while in laser-treated groups, the surfaces roughness was much lower vs other groups, and the mode of failure was mostly adhesive. CONCLUSION: Laser treatment of pre-sintered Y-TZP cannot be recommended for improving the bond. Although sandblasting of sintered Y-TZP yielded better results than the rest of the groups, 3 W power after sintering can also be effective in enhancing the bonding strength of resin cement to zirconia.

Effects of Growth Factors on Cellular Activities of Dental Stem Cells: A Systematic Review and Meta-analysis (Part I)

INTRODUCTION: To evaluate the biological interaction between dental stem cells (DSCs) and different growth factors in the field of regenerative endodontics. METHODS: A systematic search was conducted in the electronic databases up to October 2021. This study followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Ex vivo studies evaluating the biological interactions of DSCs and growth factors were included. The meta-analysis was performed according to the type of growth factor. The outcomes were cell viability/proliferation and mineralization. Standardized mean differences (SMDs) were estimated using the random-effect maximum-likelihood method (P<.05). Additional analysis was performed to find any potential source of heterogeneity. RESULTS: Twenty articles were included in the systematic review; meta-analysis was performed for fibroblast growth factor-2 (FGF-2) and Transforming growth factor-ß1 (TGF-ß1) (n=5). Results showed that use of FGF-2 significantly increased cell proliferation on day 1-(SMD=3.56,P=0.00), 3-(SMD=9.04,P=0.00), 5-(SMD=8.37,P=0.01), and 7 (SMD=8.51,P=0.00) than the control group. TGF-ß1 increased alkaline phosphatase (ALP) activity more than control only on day 3 (SMD=3.68,P=0.02). TGF-ß1 had no significant effect on cell proliferation on days 1 and 3 (P>0.05) and on ALP activity on days 5 and 7 (P>0.05). Meta-regression analysis showed that different covariates (i.e., cell type, passage number, and growth factors' concentration) could significantly influence the effect sizes at different follow-ups (P<0.05). CONCLUSION: Specific growth factors might enhance the proliferation and mineralization of DSCs; however, the obtained evidence was weak. Due to the high heterogeneity among the included studies, other growth factors' inhibitory/stimulatory effects on DSCs could not be evaluated.

Effects of 3 different light-curing units on the physico-mechanical properties of bleach-shade resin composites.

Objectives: This study investigated the microhardness, flexural strength, and color stability of bleach-shade resin composites cured with 3 different light-curing units. Materials and Methods: In this in vitro experimental study, 270 samples were fabricated of bleach and A2 shades of 3 commercial resin composites (Point 4, G-aenial Anterior, and Estelite Sigma Quick). Samples (n = 5 for each trial) were cured with Bluephase N, Woodpecker LED.D, and Optilux 501 units and underwent Vickers microhardness and flexural strength tests. The samples were tested after 24 hours of storage in distilled water. Color was assessed using a spectrophotometer immediately after preparation and 24 hours after curing. Data were analyzed using 3-way analysis of variance and the Tukey test (p ≤ 0.001). Results: Samples cured with Optilux exhibited the highest and those cured with LED.D exhibited the lowest microhardness (p = 0.023). The bleach shade of Point 4 composite cured with Optilux displayed the highest flexural strength, while the same composite and shade cured with Sigma Quick exhibited the lowest (p ≤ 0.001). The color change after 24 hours was greatest for the bleach shade of G-aenial cured with Bluephase N and least for the A2 shade of Sigma Quick cured with Optilux (p ≤ 0.001). Conclusions: Light curing with polywave light-emitting diode (LED) yielded results between or statistically similar to those of quartz-tungsten-halogen and monowave LED in the microhardness and flexural strength of both A2 and bleach shades of resin composites. However, the brands of light-curing devices showed significant differences in color stability.

Extract of Propolis on Resin-Modified Glass Ionomer Cement: Effect on Mechanical and Antimicrobial Properties and Dentin Bonding Strength.

This study assessed the effect of addition of aqueous extract of propolis in different concentrations on the mechanical and antimicrobial properties of resin-modified glass ionomer cement (RMGIC). In this in vitro study, powder of Fuji II LC RMGIC was mixed with 25% and 50% aqueous extracts of propolis. Samples (n = 15 for shear bond strength, n = 5 for flexural strength, and n = 20 for the antibacterial activity test) were fabricated using this mixture. The buccal and lingual surfaces of 23 premolars were ground to expose dentin. Tygon tubes were filled with cement, bonded to dentin, and subjected to bond or the flexural strength test in a universal testing machine. Antibacterial activity was assessed using the disc diffusion and well-plate techniques against S. mutans. Data were analyzed using one-way ANOVA and Tukey's test. The three groups showed significant differences (p < 0.001). The 50% propolis group had the lowest flexural and shear bond strength. The control group had the highest flexural and shear bond strength. No growth inhibition zone was noted around any of the discs. It can be concluded that addition of propolis to RMGIC did not confer any antibacterial activity against S. mutans and decreased the flexural and shear bond strength of RMGIC.

Shade reproduction and the ability of lithium disilicate ceramics to mask dark substrates.

OBJECTIVES: This study aimed to evaluate the ability of lithium disilicate ceramics to reproduce the A2 shade and to mask A4 substrates. MATERIALS AND METHODS: Twenty-four discs (8 mm in diameter, shade A2) of high translucency (groups 1-3) and low translucency (groups 4-6) of IPS e.max ceramic with different thicknesses (0.5, 0.75, and 1 mm) were fabricated as monolithic structures. In addition, discs of medium opacity (group 7-8) with different core/veneer combinations (0.3 mm/0.7 mm and 0.5 mm/0.5 mm) were fabricated as bilayer structures. Specimens were superimposed on an A4 substrate (complex). The color changes of the complex were measured using a spectrophotometer on a black background, and the ΔE values of the complex were compared with either the A4 substrate or the A2 shade tab. One-way analysis of variance, the Tukey honest significant difference test, and the Fisher test were used to analyze the data (p < 0.05). RESULTS: Significant between-group differences were found for comparisons to both the A4 substrate and the A2 shade (p < 0.05). When compared with the A4 substrate, the ΔE values in all groups were in the non-acceptable range. When compared with the A2 shade, the ΔE values in all groups, except groups 2 and 3, were in the clinically acceptable range. CONCLUSIONS: All translucencies and thicknesses masked the underlying dark substrate. However, the low-translucency IPS e.max Press better reproduced the A2 shade.

Bioactivity of endodontic biomaterials on dental pulp stem cells through dentin.

OBJECTIVES: This study investigated the indirect effect of calcium-enriched mixture (CEM) cement and mineral trioxide aggregate (MTA), as 2 calcium silicate-based hydraulic cements, on human dental pulp stem cells (hDPSCs) through different dentin thicknesses. MATERIALS AND METHODS: Two-chamber setups were designed to simulate indirect pulp capping (IPC). Human molars were sectioned to obtain 0.1-, 0.3-, and 0.5-mm-thick dentin discs, which were placed between the 2 chambers to simulate an IPC procedure. Then, MTA and CEM were applied on one side of the discs, while hDPSCs were cultured on the other side. After 2 weeks of incubation, the cells were removed, and cell proliferation, morphology, and attachment to the discs were evaluated under scanning electron microscopy (SEM). Energy-dispersive X-ray (EDXA) spectroscopy was performed for elemental analysis. Alkaline phosphatase (ALP) activity was assessed quantitatively. The data were analyzed using the Kruskal-Wallis and Mann-Whitney tests. RESULTS: SEM micrographs revealed elongated cells, collagen fibers, and calcified nucleations in all samples. EDXA verified that the calcified nucleations consisted of calcium phosphate. The largest calcifications were seen in the 0.1-mm-thick dentin subgroups. There was no significant difference in ALP activity across the CEM subgroups; however, ALP activity was significantly lower in the 0.1-mm-thick dentin subgroup than in the other MTA subgroups (p < 0.05). CONCLUSIONS: The employed capping biomaterials exerted biological activity on hDPSCs, as shown by cell proliferation, morphology, and attachment and calcific precipitations, through 0.1- to 0.5-mm-thick layers of dentin. In IPC, the bioactivity of these endodontic biomaterials is probably beneficial.

Perceived barriers to the provision of preventive care among Iranian dentists.

PURPOSE: The aim of this study was to examine the perceived barriers to preventive dental practice among Iranian dentists. MATERIALS AND METHODS: A questionnaire survey was performed among the dentists who participated in two annual dental meetings (conducted in December 2004 and in July 2005) in Tehran, Iran. The dentists who attended the meeting completed the self-administered questionnaire anonymously. The questionnaire included 12 statements with answer alternatives rated on a 5-point scale to which the dentists were asked to indicate how much each of the 12 items, later classified as three barriers (practice-, dentist- and patient-related), impedes them from practising preventive care. The sum of the scores of the four items in each barrier served as an indicator of each dentist's perception of the strength of each barrier. The background data included dentists' personal and professional characteristics. In total, 1033 dentists completed the questionnaire, of whom 980 (64% men) were eligible. Statistical evaluation was performed using analysis of variance, t test and Pearson's correlation coefficient. RESULTS: Of the respondents, 29% to 66% rated the items of the practice-related barrier as very strong impediments. Corresponding figures for the dentist- and the patient-related barriers were 20% to 54% and 70% to 77%, respectively. The highest mean of the score sum was for the patient-related barrier (11.9) and the lowest mean was for the dentist-related barrier (7.9). For both practice- and dentist-related barriers, male dentists reported significantly higher scores than the female dentists (P < 0.001). CONCLUSIONS: The perceived barriers to the provision of preventive care should be meticulously explored and tackled to enhance oral health in Iran.

Comparing the effect of dry and wet brushing on dental plaque removal in children.

AIMS: This study was aimed to assess the efficacy of wet and dry brushing on cleaning outcome of tooth surfaces. METHODS: Forty-three children aged 10-12 years were randomly selected and instructed for this brushing project. Each case served as self-control. Each patient was requested to brush through one of the wet/dry techniques for 1 week and other technique on the 2nd week. Samples had a washout step using pumice prophylaxis prior to each brushing week. Tooth Cleanliness Index was used to measure the plaque removal level. Two uniform Oral-B toothbrushes were used one for each week through the Modified Stillman technique. Mann-Whitney test was employed along with the Wilcoxon signed-rank test to analyze the data. RESULTS: The level of brushing efficacy was slightly higher in males with no statistically significant difference between sexes. Remaining plaque measured was higher in wet group with significant difference (7.3 ± 1.7 for dry brushing and 7.6 ± 2.6 for wet brushing) (P < 0.05). CONCLUSIONS: Dry and wet brushing did not show a significant difference in their capacity to remove plaque indicating that dry brushing could be considered as an acceptable brushing technique.

Risk-based approach in preventive practice among Iranian dentists.

PURPOSE: To study risk-based preventive practice among Iranian dentists. MATERIALS AND METHODS: A questionnaire survey was conducted at two annual dental meetings in 2004 and 2005 in Tehran. Using a five-point Likert scale, respondents indicated their level of agreement with taking preventive measures including oral hygiene, use of fluoride, diet and dental check-up for a high- and a low-risk (HR and LR, respectively) hypothetical patient case. Respondent's smoking and activity in smoking cessation were enquired about as well. Of 1033 responding dentists, 980 (64% men) were eligible for this study. Statistical evaluation was by the chi-square test and logistic regression. RESULTS: The top four of the eight measures were instructions on tooth brushing and flossing, advice related to fluoridated toothpaste, and regular dental check-ups, with the choice 'fully agree' being more prevalent for the HR (74%-58%) than for the LR case (59%-41%). For the HR case, 45% of the respondents fully agreed with applying chair-side tooth cleaning, 41% with advice on diet modification, and 38% with advice on home-use of sodium fluoride mouthwash. Of all respondents, 76% were nonsmokers and 56% reported that they always recommend their smoking patients to quit. Female gender and activity in professional reading were associated with higher levels of agreement for applying preventive measures to the HR case. Non-smoking was the strongest explanatory factor (OR = 3.6, 95% CI = 2.6-5.1) of dentist's higher involvement in smoking cessation. CONCLUSION: Risk-based preventive dental care should be emphasised and applied in order to maximise efficient use of resources.

Double Antibiotic Paste for Management of External Inflammatory Root Resorption.

External inflammatory root resorption (EIRR) is one of the common complications following dental trauma which when remained untreated, may lead to tooth loss. Successful treatment outcomes depend on elimination of bacteria from root canal system and apical sealing. This case presents the endodontic management of an EIRR that was nonresponsive to calcium hydroxide (CH) therapy. An 11-year-old boy was referred for management of a traumatized maxillary central incisor. Tooth #8 was symptom-free, nonresponsive to vitality pulp tests and had an immature root with sever EIRR. Using chemomechanical debridement and CH dressing, the treatment was initiated. The tooth was remained asymptomatic; however, after five weeks the size of periradicular lesion increased and intracanal exudate was present, signifying a resistant endodontic infection. In second appointment, double antibiotic paste (DAP; ciprofloxacin/metronidazole) was applied to the canal. Eight weeks later, the tooth continued to be asymptomatic and the size of the lesion decreased. Finally, the root canal was entirely obturated with calcium-enriched mixture (CEM). At 18-month follow-up, the tooth was asymptomatic/functional, EIRR did not further progress and tooth discoloration was not observed. Based on the results, DAP has the potential to be used to manage the CH-resistant endodontic infection. Furthermore, CEM root filling/sealing seems to be an applicable choice in EIRR management.

Treatment Outcomes of 4 Vital Pulp Therapies in Mature Molars.

INTRODUCTION: Vital pulp therapy (VPT) is a biological approach to minimally invasive endodontics. This randomized clinical trial aimed to evaluate and compare clinical and radiographic success of 4 VPTs (indirect pulp capping [IPC], direct pulp capping [DPC], miniature pulpotomy [MP], and full pulpotomy [FP]) using calcium-enriched mixture cement for deep caries management of mature permanent molars including teeth with clinical signs of irreversible pulpitis and the presence of apical periodontitis. METHODS: Blinded participants (N = 302) were randomly allocated to 4 study arms. Random allocation was disregarded when visible pulp exposures did not happen after complete caries removal and the tooth was transferred to the IPC arm. Pre- and intraoperative data including vitality test results, pulpal/periapical status, and exposure type/location were recorded. Pain was measured using a numeric rating scale before treatment initiation up to 1 week postoperatively. Participants were followed up for 1 year. RESULTS: The groups were homogenous in terms of age, sex, marital status, education, and practitioner; pre- and intraoperative conditions were similar in all arms and did not affect the long-term success. Preoperative pain and apical periodontitis were significantly different among arms (P < .05); however, it was not the case when the IPC group was excluded. After baseline pain adjustment, pain relief was continuous with similar patterns in all treatment groups. The 3- and 12-month success rates of the VPT techniques were comparable in the IPC (98.7% and 100%, respectively), DPC (98.4% and 94.7%, respectively), MP (98.4% and 91.4%, respectively), and FP (93.5% and 95.5%, respectively) arms, respectively (P > .05). CONCLUSIONS: In deep caries management of mature permanent molars, the 4 VPTs were associated with favorable/comparable clinical and radiographic outcomes. The pulpal and periapical status as well as pulpal exposure type/location had no effect on treatment outcomes.

Effect of incorporation of zinc oxide nanoparticles on mechanical properties of conventional glass ionomer cements.

AIM: The aim of this study is to investigate the physical properties of conventional and resin-modified glass ionomer cements (GICs) compared to GICs supplemented with zinc oxide (ZnO) nanofiller particles at 5% (w/w). METHODS: In this in vitro study, ZnO nanoparticles of different morphologies (nanospherical, nanorod, and nanoflower) were incorporated to glass ionomer powder. The samples were subjected to the flexural strength (n = 20) and surface hardness test (n = 12) using a universal testing machine and a Vickers hardness machine, respectively. Surface analysis and crystal structure of samples were performed with scanning electron microscope and X-radiation diffraction, respectively. The data were analyzed using one-way ANOVA, Shapiro-Wilk, and Tukey's tests (P < 0.05). RESULTS: Flexural strength of glass ionomer containing nanoparticles was not significantly different from the control group (P > 0.05). The surface hardness of the glass ionomer containing nanospherical or nanoflower ZnO was significantly lower than the control group (P < 0.05). However, the surface hardness of glass ionomer containing nanorod ZnO was not significantly different from the control group (P = 0.868). CONCLUSIONS: Incorporation of nanospherical and nanoflower ZnO to glass ionomer decreased their surface hardness, without any changes on their flexural strength. Incorporation of nanorod ZnO particles caused no effect on the mechanical properties.

Determinants of oral health behaviour among Iranian dentists.

AIM: To study the oral health behaviour of Iranian dentists. DESIGN: A cross-sectional study. SETTING: Two annual dental meetings in Tehran, Iran. PARTICIPANTS: 1,033 dentists responded, 980 were eligible for this study. METHOD: Data were collected using a self-administered questionnaire which covered dentists' oral self-care, dental attendance, and smoking. Recommended oral self-care (ROSC) included tooth brushing > 1/day, eating sugary snacks < daily, and regularly using fluoride toothpaste. Knowledge of preventive dental care was assessed by nine Likert-scale statements. Dentist's gender, age, and professional reading were recorded. Statistical evaluation was by the Chi-square test and logistic regression. RESULTS: In total, 59% of respondents reported brushing their teeth at least 2/day, 59% consumed sugary snacks < daily, 74% used fluoride toothpaste regularly, and 76% were non-smokers. Of all, 27% followed ROSC. Women reported desirable behaviours more frequently than did the men (p < 0.01). Female gender (OR 1.4-2.3), being a non-smoker (OR 1.3-1.5), and wider professional reading (OR = 1.2) were the major factors that contributed to dentists' desirable oral health behaviour. CONCLUSIONS: That only a small number of Iranian dentists follow the ROSC calls for more attention to behavioural contributions to oral diseases and its consequences with general and oral health, regarding both dental curriculum and continuing education.

Effect of delayed light-curing on solubility, color stability, and opacity of Fuji II LC glass ionomer cement: original article / Efeito da fotopolimerização tardia na solubilidade, estabilidade de cor e opacidade do cimento de ionômero de vidro Fuji II LC: artigo original

Objective: Resin-modified glass ionomer (RMGI) cements are among the commonly used restorative materials in low stress-bearing areas and also for temporary restorations. The competition between acid-base reactions and light polymerization reactions in delayed curing of RMGIs can affect their physical and mechanical properties, as well as their degree of conversion. Since solubility, color stability, and opacity are among the main physical properties affecting the durability and clinical service of RMGI restorations, this study aimed to assess the effect of delayed curing on solubility, color stability, and opacity of Fuji II LC RMGI. Material and Methods: This in vitro, experimental study evaluated 80 Fuji II LC RMGI specimens (10 specimens per each in 4 groups) in terms of solubility, color stability, and opacity at 6 months later. Specimens were cured immediately or were cured with 1, 5 and 10 min delay. Results: Maximum solubility and minimum change in opacity and color stability at 6 months were noted in the group with delayed curing by 10 min. A significant difference was noted in the solubility of specimens cured after 10 min and 1 min. Significant differences were also noted in the opacity and color stability of specimens cured after 10 min and all other groups (P < 0.05). Conclusion: Delayed curing by 1 min decreased the solubility of RMGI specimens compared with immediate curing or curing after 5 min. Although this difference did not reach statistical significance. Color stability and changes in opacity are mainly influenced by the acid-base reactions rather than polymerization reactions.(AU)

Objetivo: Cimentos de ionômero de vidro modificado por resina (CIVMR) estão entre os materiais restauradores mais comumente utilizados em áreas de baixa tensão e também para restaurações temporárias. A competição entre reações ácido-base e reações provenientes da fotopolimerização tardia dos CIVRMs podem afetar suas propriedades físicas e mecânicas, bem como seu grau de conversão. Uma vez que a solubilidade, estabilidade de cor e opacidade estão entre as principais propriedades físicas que afetam a durabilidade e o tempo de serviço clinico de restaurações de CIVMR, este estudo teve como objetivo avaliar o efeito da fotopolimerizaçao tardia na solubilidade, estabilidade de cor e opacidade do CIVMR Fuji II LC. Material e Métodos: Este estudo experimental in vitro avaliou 80 espécimes de CIVMR Fuji II LC (4 grupos com 10 espécimes cada) em termos de solubilidade, estabilidade de cor e opacidade apos 6 meses. As amostras foram fotopolimerizadas imediatamente ou com 1, 5 e 10 min de atraso. Resultados: Máxima solubilidade e mínima alteração na opacidade e estabilidade da cor em 6 meses foram observadas no grupo com fotopolimerização tardia em 10 min. Uma diferença significativa foi observada na solubilidade das amostras fotopolimerizadas após 10 min e 1 min. Diferenças significativas também foram observadas na opacidade e estabilidade de cor das amostras fotopolimerizadas após 10 min e em todos os outros grupos (P <0,05). Conclusão: A fotopolimerizaçao tardia em 1 min diminuiu a solubilidade das amostras CIVMR em comparação com a fotopolimerizaçao imediata ou após 5 min. Embora essa diferença não tenha alcançado significância estatística. A estabilidade da cor e as mudanças na opacidade são influenciadas principalmente por reações ácido-base, em vez de reações causadas pela polimerização(AU)

Effect of water storage on flexural strength of silorane and methacrylate-based composite resins.

OBJECTIVES: This study assessed the effect of water storage on the flexural strength (FS) of low shrinkage composites. MATERIALS AND METHODS: A total of 165 bar-shaped specimens (2 × 2 × 25 mm) were fabricated of 2 low shrinkage composites (Filtek P90 [3M ESPE], GC Kalore [GC International]) and a conventional methacrylate-based composite (Filtek Z250 [3M ESPE]). The specimens were subjected to 3-point bending test at 6 time intervals, namely: immediately after curing, at 24 hours, 1 week, 1 month, 6 months, and 1 year following storage in wet and dry conditions. The FS of the specimens were measured by applying compressive load at a crosshead speed of 1.0 mm/min. Data was analyzed using 3-way analysis of variance (ANOVA) and Tukey's test. RESULTS: Three-way ANOVA revealed significant interactions between time, type of composite, and storage condition (p = 0.001). Tukey's multiple comparison test revealed significant reductions in FS of all composites after 6 months and 1 year of storage in distilled water compared to dry condition. CONCLUSIONS: Filtek P90 showed the highest and GC Kalore showed the lowest FS after 1 year storage in distilled water. The immediate high strength of Filtek Z250 significantly decreased at 1 year and its final value was lower than that of Filtek P90.

Effect of decontamination on micro-shear bond strength of silorane-based composite increments.

AIM: The aim of the present study was to evaluate the micro-shear bond strength of silorane-based composites after saliva/blood decontamination. METHODS: A transparent mold (1 × 2 × 1 cm) was used to make 11 flat, silorane-based composite blocks. One block served as the control. After contamination, the blocks were treated as follows: group 1: 10-s air spray; group 2: 10-s water spray + 10-s air spray; group 3: 10-s water spray + 10-s air spray + 10-s etching with phosphoric acid; group 4: 10-s air spray + 10-s etching + bonding; group 5: 10-s water spray + 10-s air spray + 10-s etching + bonding; and groups 6-10: treated the same as groups 1-5, the only difference being that blood was used instead of saliva. Ten tubes (0.7 mm × 1 mm) containing silorane-based composites were attached to each decontaminated block and light cured for 40 s. After 24-h storage in distilled water, specimens were tested under micro-shear loading at a cross-head speed of 0.5 mm/min. Data were analyzed using one-way anova and Tukey's honest significant difference (HSD) test (P < 0.05). RESULTS: One-way anova showed significant differences in the micro-shear bond strength among the experimental groups (P < 0.001). Tukey's HSD test revealed that the bond strengths in groups 5, 9, and 10 were similar to the control group (P > 0.05). CONCLUSION: Decontamination by water and air spray, etching, and bonding was effective in restoring the bond strength of silorane-based composite increments.

Shear Bond Strength of a Resin Cement to Different Alloys Subjected to Various Surface Treatments.

OBJECTIVES: Micromechanical retention of resin cements to alloys is an important factor affecting the longevity of metal base restorations. This study aimed to compare the bond strength and etching pattern of a newly introduced experimental etchant gel namely Nano Met Etch with those of conventional surface treatment techniques for nickel-chrome (Ni-Cr) and high noble alloys. MATERIALS AND METHODS: A total of 120 discs (8×10×15 mm) were cast with Ni-Cr (n=20), high noble BegoStar (n=50) and gold coin alloys (n=50). Their Surfaces were ground with abrasive papers. Ni-Cr specimens received sandblasting and etching. High noble alloy specimens (BegoStar and gold coin) received sandblasting, sandblasting-alloy primer, etching, etch-alloy primer and alloy primer alone. Cylindrical specimens of Panavia were bonded to surfaces using Tygon tubes. Specimens were subjected to micro-shear bond strength testing after storing at 37°C for 24 hours. RESULTS: In gold coin group, the highest bond strength was achieved after sandblasting (25.82±1.37MPa, P<0.001) and etching+alloy primer (26.60 ± 5.47 MPa, P<0.01). The lowest bond strength belonged to sandblasting+alloy primer (17.79±2.96MPa, P<0.01). In BegoStar group, the highest bond strength was obtained in the sandblasted group (38.40±3.29MPa, P<0.001) while the lowest bond strength was detected in the sandblast+ alloy primer group (15.38±2.92MPa, P<0.001). For the Ni-Cr alloy, bond strength in the etched group (20.79±2.01MPa) was higher than that in the sandblasted group (18.25±1.82MPa) (P<0.01). CONCLUSIONS: For the Ni-Cr alloy, etching was more efficient than sandblasting but for the high noble alloys, higher Au content increased the efficacy of etching.