Evaluation of physical/mechanical properties of an experimental dental composite modified with a zirconium-based metal-organic framework (MOF) as an innovative dental filler.

OBJECTIVES: This study aimed to modify an experimental dental composite using a synthesized nano-structured methacrylated zirconium-based MOF to enhance physical/mechanical properties. METHODS: The previously known Uio-66-NH2 MOF was first synthesized and post-modified with Glycidyl Methacrylate (GMA). Fourier Transform Infrared (FTIR) Spectroscopy and CHNS analysis confirmed the post-modification reaction. The prepared filler was investigated by XRD, BET, SEM-EDS, and TEM. The experimental composite was prepared by mixing 60% wt. of resin matrix with 40% wt. of fillers, including silanized silica (SS) or Uio-66-NH-Me (UM). The experimental composites' depth of cure (DPC) was investigated in five groups (G1 =40% SS, G2 =30%SS+10%UM, G3 =20%SS+20%UM, G4 =10%SS+30%UM, G5 =40%UM). Then flexural strength(FS), Elastic Modulus(EM), solubility(S), water sorption(WS), degree of conversion(DC), polymerization shrinkage(PS), and polymerization stress(PSR) of the groups with DPC of more than 1 mm were investigated. Finally, the cytotoxicity of composites was studied. RESULTS: The groups with more than 20% wt. UM, filler (G4, G5) had lesser than 1 mm DPC. Therefore, we investigated three groups' physical and mechanical properties with lower than 20% UM filler (G1-G3). Within these groups, G3 has a higher FS, EM (P < 0.05), and lower WS and S (P < 0.05). DC dropped in G2 and G3 compared to G1 (p < 0.05), but there was no significant difference between G2 and G3 (P = 0.594). SIGNIFICANCE: This new filler is an innovative coupling-agent free filler and can be part of dental filler technology itself. It can also introduce a new group of dental fillers based on MOFs, but it still needs a complete investigation to be widely used.

Comparison of the Success Rate of Filled and Unfilled Resin-Based Fissure Sealants: A Systematic Review and Meta-Analysis.

Objectives: Incorporation of fillers might improve the physical properties of sealants. This systematic review and meta-analysis evaluated the retention and caries development rate of filled and unfilled fissure sealants. Materials and Methods: This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. The PubMed, Scopus, Embase, Cochrane Database of Systematic Reviews, and ISI Web of Knowledge were searched until October 24, 2019. The risk of bias (ROB) was assessed for the included studies based on the Cochrane collaboration common scheme for bias, and the meta-analysis was performed through a random effects model. Results: The search resulted in 6,336 unrepeated relevant studies. After the title, abstract and full-text screening, 19 studies with 26 comparing groups were finally included in this systematic review and meta-analysis. According to the included studies, both retention rate and caries development in filled and unfilled resin-based sealants did not significantly differ within 2 years of follow-up. Conclusion: Since there was no significant difference in the retention rate and caries development between filled and unfilled sealants, it seems that the final decision should be made uniquely for each patient according to the type of fissure, patient's age, habits, etc.

Resistance to demineralisation of adjacent enamel and dentine, fluoride release and dentine bond strength of fluoride-containing self-etch adhesive systems.

BACKGROUND: The current study aimed to assess the amount of fluoride released from fluoride-containing dental adhesives and its effect on micro-tensile bond strength (µTBS) and on resistance to demineralisation of dentine and enamel. MATERIAL AND METHODS: Two fluoride-containing dental adhesives, and a fluoride-free adhesive were used as experimental adhesives. After thermal cycling the µ-TBS of adhesives to dentine and the failure mode were assessed. The fluoride release and cross-sectional microhardness (CSMH) of specimens were measured before and after one day, 7 and 28 days of pH-cycling. The data were analysed using one-way ANOVA, Weibull statistics and repeated measures ANOVA. RESULTS: The results indicated a significant difference between the group of FL and both the SE and LBF groups (p≤0.001). The CSMH values of both the dentine and enamel underneath the adhesives was reduced at 28 th day of the pH-cycling compared to the baseline (p≤0.001). From day 1 to day 28, the released fluoride declined in both the fluoride containing dental adhesives (p≤0.001). CONCLUSIONS: Based on the results, the released fluoride from dental adhesives may adversely influence the bond strength and durability of the resin/dentine interface. Moreover, the released fluoride didn't improve the resistance to demineralisation of adjacent enamel and dentine to bond interface. Key words:Fluoride release, micro-tensile bond strength, microhardness, fluoride-containing adhesives.

In-vitro bioactivity evaluation and physical properties of an epoxy-based dental sealer reinforced with synthesized fluorine-substituted hydroxyapatite, hydroxyapatite and bioactive glass nanofillers.

The purpose of this study was to evaluate the physical properties and bioactivity potential of epoxy-based dental sealers modified with synthesized bioactive glass (BAG), hydroxyapatite (HA) and fluorine substituted hydroxyapatite (FHA) nanoparticles. The synthesized powders were incorporated at 10% and 20% into the epoxy-based dental sealer. The setting time, flow and solubility and microhardness of the modified and unmodified samples were examined. The bioactivity was evaluated using FESEM-EDX and elemental mapping, ATR-FTIR and XRD. The flow value of all of the experimental groups except the FHA modified samples, was greater than 20 mm. Concerning solubility, no specimens exhibited more than 1% weight loss. The solubility value of the FHA groups was statistically significant lower than other groups (p ≤ 0.001). The mean hardness values of all of the modified samples were significantly higher than the unmodified group (p ≤ 0.001). Regarding bioactivity, in vitro study revealed that after 3 days immersion in SBF a compact and continuous calcium phosphate layer formed on the surface of epoxy sealers containing BAG and HA nanoparticles. Based on these results, the addition of BAG and HA nanoparticles did not adversely alter the physical properties of epoxy sealers. Additionally, they improved the in vitro bioactivity of the epoxy sealer.

Comparative assessment of the crystalline structures of powder and bulk human dental enamel by X-ray diffraction analysis.

OBJECTIVES: The aim of this study was to assess and compare the crystalline structures of both powder and bulk human dental enamel by X-ray diffraction analysis (XRD). METHODS: The buccal surfaces of 60 selected noncarious third molars were divided into two groups of powdered and bulk enamel specimens. To prepare enamel powders, the enamel tissues were ground and powdered manually using a mortar and pestle. For bulk samples, the enamel slabs were sectioned using a low-speed diamond saw. The crystalline structures of samples were analyzed by XRD, and the obtained data were analyzed. The values of the lattice parameters were obtained using the equation of hexagonal crystalline structures. The crystal sizes and microstrains of crystallites were calculated using both the Scherrer and Williamson-Hall (W-H) methods. The total area under the peaks was considered as the criterion for assessing crystallinity. The data were analyzed by a parametric independent t-test and nonparametric Mann-Whitney test using SPSS for Windows at a significance level of 0.05. RESULTS: The results of the current study revealed significant differences between the crystallinity values and crystal sizes of the two study groups (p ≤ 0.001). The powdered samples showed higher crystallinity and smaller crystal sizes than those of the bulk samples. The obtained strain values of the powder samples were nearly twice those of the bulk samples. This difference was not statistically significant (p = 0.76). CONCLUSIONS: The results of this study revealed that the sample preparation method for human tooth enamel can affect the crystalline data obtained from XRD analysis.

Shear Bond Strength of Molar Tubes to Enamel Using an Orthodontic Resin-Modified Glass Ionomer Cement Modified with Amorphous Calcium Phosphate.

OBJECTIVES: This study aimed to assess the shear bond strength (SBS) of molar tubes to the enamel surface of molar teeth using a resin-modified glass ionomer (RMGI) cement modified with amorphous calcium phosphate (ACP). MATERIALS AND METHODS: In this in-vitro study, 60 extracted human third molars were randomly divided into four groups for bonding of molar tubes to the enamel surface. Fuji Ortho LC and Fuji Ortho LC modified with ACP (1.55 wt%) were used in groups 1 and 2, respectively. In group 3, the enamel surface was sandblasted, and bonding was then performed using Fuji Ortho LC glass ionomer modified with ACP. In group 4, molar tubes were conventionally bonded using Transbond XT composite. The SBS was measured using a universal testing machine. RESULTS: The mean SBS of groups 1 to 4 was 10.22, 6.88, 9.4, and 13.68 MPa, respectively. Only the SBS of group 1 was not significantly different from that of groups 3 and 4 (P>0.05). Comparison of adhesive remnant index (ARI) scores of the groups revealed significant differences only between groups 1 and 4 (P<0.001) and between groups 1 and 2 (P=0.002). CONCLUSION: The results revealed that the addition of ACP to Fuji Ortho LC significantly decreased the SBS of molar tubes bonded to enamel compared to the conventional resin bonding system. Sandblasting of the enamel surface significantly increased the bond strength. Fuji Ortho LC modified with ACP is recommended for bonding of molar tubes to posterior teeth considering its cariostatic property.