Effects of incorporation of 2.5 and 5 wt% TiO₂ nanotubes on fracture toughness, flexural strength, and microhardness of denture base poly methyl methacrylate (PMMA)

PURPOSE: The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes (n-TiO2) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. MATERIALS AND METHODS: TiO2 nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each TiO2:PMMA ratio, 15 specimens were fabricated for each experiment. Effects of n-TiO2 addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. RESULTS: SEM images of n-TiO2 exhibited the presence of elongated tubular structures. The XRD pattern of synthesized n-TiO2 represented the anatase crystal phase of TiO2. Moderate to very strong significant positive correlations were observed between the concentration of n-TiO2 and each of the 3 physicomechanical properties of PMMA (Pearson's P value ≤.001, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% n-TiO2 were significantly higher than those of control (P≤.001). Fracture toughness of samples reinforced with 5 wt% n-TiO2 (but not those of 2.5% n-TiO2) was higher than control (P=.002). CONCLUSION: Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.

The effects of dentin bonding agent formulas on their polymerization quality, and together with tooth tissues on their microleakage and shear bond strength: an explorative 3-step experiment

PURPOSE: Bonding agents (BA) are the crucial weak link of composite restorations. Since the commercial materials' compositions are not disclosed, studies to formulize the optimum ratios of different components are of value. The aim of this study was to find a proper formula of BAs. MATERIALS AND METHODS: This explorative experimental in vitro study was composed of 4 different sets of extensive experiments. A commercial BA and 7 experimental formulas were compared in terms of degree of conversion (5 experimental formulas), shear bond strength, mode of failure, and microleakage (3 experimental formulas). Statistical analyses were performed (alpha=.05). The DC of selected formula was tested one year later. RESULTS: The two-way ANOVA indicated a significant difference between the shear bond strength (SBS) of two tissues (dentin vs. enamel, P=.0001) in a way that dentinal bonds were weaker. However, there was no difference between the four materials (P=.283). The adhesive mode of failure was predominant in all groups. No differences between the microleakage of the four materials at occlusal (P=.788) or gingival (P=.508) sites were detected (Kruskal-Wallis). The Mann-Whitney U test showed a significant difference between the microleakage of all materials (3 experimental formulas and a commercial material) together at the occlusal site versus the gingival site (P=.041). CONCLUSION: A formula with 62% bisphenol A-glycidyl methacrylate (Bis-GMA), 37% hydroxy ethyl methacrylate (HEMA), 0.3% camphorquinone (CQ), and 0.7% dimethyl-para-toluidine (DMPT) seems a proper formula for mass production. The microleakage and SBS might be respectively higher and lower on dentin compared to enamel.

vitro comparison of coronal micro-leakage of three temporary restorative materials by dye penetration

It is necessary to seal the dental access cavity which is under root canal treatment with temporary restorative materials. For this purpose, the main attention in selecting the temporary restorative material during endodontic treatments is drawn to the sealing ability. The purpose of this study is to investigate the coronal sealing ability of 3 temporary filling materials, Cavizol, Coltosol, and Zonalin through DPI [Dye Penetrant Inspection]. In this study, 98 extracted with no decay mandibular and maxillary molar teeth were used. The teeth were divided into 3 experimental groups of 30 teeth and two positive and negative control groups of 4 teeth. In the experimental group, 4x4mm endodontic access cavity was created on the occlusal surface and in each experimental group the teeth were filled with Cavizol, Coltosol, and Zonalin. In the positive control group, access cavity was created but restorative material was not used. In the negative control group, access cavity was not created. Experimental groups [teeth] were placed in normal saline for 2 hours. Then, the first, second and third groups were immersed in methylene blue dye for 24 hours, 1 week, and 4 weeks, respectively. Zonalin showed significantly more [micro] leakage than Coltosol and Cavizol. Cavizol also showed more leakage than Coltosol, but there was no significant difference between them. According to the results of the study, Coltosol and Cavizol are suitable for dressings with less than one week duration because of better sealing. In case the interval between treatment sessions lasts more than a week, the dressing should be replaced

[Degree of conversion of micro-hybrid, nano-hybrid and Ormocer composites using LED and QTH light-curing units]

The aim of this study was to measure the degree of conversion [DC] of three types of composite resins [micro-hybrid, nano-hybrid and Ormocer] with different light curing units [LED LCU and QTH LCU] in two depths. Three commercially available dental resin composites were used in this study: [Tetric Ceram, Ivoclar Vivadent, Liechtenstein-A2 shade], [Tetric Evoceram, Ivoclar Vivadent, Liechtenstein-A2 shade], [Ceram X, Dentsply, Germany-M[2] shade]. Specimens were divided into two groups, 5 specimens were photo-activated by QTH unit [Coltolux 75-Colten] and the other five specimens were cured by LED [Demi-Kerr]. Then each specimen was sectioned at the top surface and at 2-mm depth. The DC was measured by FT-IR [Bruker-tensor 27]. The data were analyzed by 3-way ANOVA test. There was significant difference between tested composite resins [P<0.001]. The results of top surfaces were significantly different from those observed at 2-mm depth [P<0.001]. The type of curing unit affected the polymerization of Ceram X resin composite. This study showed a significant difference in the degree of conversion in different thicknesses within three groups of resin composites

Polymerization behavior and thermal characteristics of two new composites at five temperatures: refrigeration to preheating

PURPOSE: Heat of composite polymerization (HP) indicates setting efficacy and temperature increase of composite in clinical procedures. The purpose of this in vitro experimental study was to evaluate the effects of 5 temperatures on HP of two new composites. MATERIALS AND METHODS: From each material (Core Max II [CM] and King Dental [KD]), 5 groups of 5 specimens each were prepared and their total HPs (J/gr) were measured and recorded, at one of the constant temperatures 0degrees C, 15degrees C, 23degrees C, 37degrees C and 60degrees C (2 x 5 x 5 specimens) using a differential scanning calorimetry (DSC) analyzer. The data were analyzed using a two-way ANOVA, a Tukey's test, an independent-samples t-test, and a linear regression analysis (alpha=0.05). RESULTS: No polymerization reactions occurred at 0degrees C; then this temperature was excluded from statistical analyses. The mean HP of the remaining 20 KD specimens was 20.5 +/- 14.9 J/gr, while it was 40.7 +/- 12.9 J/gr for CM. The independent-samples t-test showed that there were significant differences between the HP of the two materials at the temperatures 15degrees C (P=.0001), 23degrees C (P=.0163), 37degrees C (P=.0039), and 60degrees C (P=.0106). Linear regression analysis showed statistically significant correlations between environment temperatures and HP of CM (R2=0.777). CONCLUSION: Using CM is advantageous over conventional composite because of its better polymerization capacity. However due to its high HP, further studies should assess its temperature increase in vivo. Preheating KD is recommended. Refrigerating composites can negatively affect their polymerization potential.