The Bond Strength of Nanohybrid and Nanoceramic Composites to Feldspathic Porcelain.

BACKGROUND: Porcelain fracture is the most important problem in fixed prosthetic restorations. The replacement of fractured restoraions isn't often prefer by patients and dentists. Intraoral repair of fractured porcelain is a big alternative for patient and dentist. For this reason, dentists try to improve different surface treatments to increase the bond strength between porcelain and repair materials such as composite resins. AIMS: The aim of this study was to evaluate the shear bond strength (SBS) of nano-hybrid (Nh.com) and nano-ceramic composite resins (Nc.com) to this feldspathic porcelains (Vita and Ivoclar). SETTINGS AND DESIGN: 120 ceramic disc were fabricated from feldspathic porcelain. MATERIALS AND METHODS: The following surface treatment was applied on the ceramic surface: 1) Hydrofluoric acid+silane, 2) Air-abrasion+silane, 3) Air-abrasion=Control group. Nh.com and Nc.com was placed on the porcelain surface. Half of the specimens were stored in 37 ± 2oC distilled water and another half were subjected to thermocycling before SBS. The samples placed in an universal testing machine and applied shear force until seperation occured. STATISTICAL ANALYSIS USED: The data were analyzed by multi-way analysis of variance (ANOVA) and Duncan test (P <0.05). RESULTS: The results show that Ivoclar and Vita had almost equal fracture values. Nh.com showed high bond strength than Nc.com. In the Ivoclar porcelain, hydrofluoric acid etching had highest fracture values than other surface treatments, and in the vita porcelain air-abrasion had a little difference from hydrofluoric acid etching. CONCLUSIONS: Different surface treatments show different effect on SBS between feldspathic porcelain and composite resins.

Effect of sealer coating and storage methods on the surface roughness of soft liners.

STATEMENT OF PROBLEM: A soft lining is applied under a removable prosthesis for various reasons. The porosity of the lining material may increase colonization by microorganisms and cause tissue inflammation. PURPOSE: The purpose of this in vitro study was to evaluate the effect of sealer coating on the surface roughness of soft lining materials under 4 different conditions. MATERIAL AND METHODS: A total of 125 specimens were prepared. One high-temperature silicone-based soft lining material and 2 room-temperature-polymerized soft lining materials (1 silicone-based and 1 methacrylate-based) were used. Twenty-five specimens of each room-temperature soft lining material were coated with 2 layers of surface sealer. Additionally, 5 specimens of each material were stored in either distilled water, Coca-Cola, denture cleanser, saliva, or air. The surface roughness was measured at baseline and after 1, 7, 14, and 28 days. Surface roughness values were analyzed with repeated measures analysis of variance, and the Bonferroni multiple comparison test was performed using time-dependent groups and storage methods. RESULTS: In the time-dependent groups, methacrylate-based sealer-coated soft liners exhibited a significant increase in roughness (1.74-2.09 µm, P<.001), and silicone-based sealer-coated soft liners exhibited a decrease in roughness, but it was not significant (2.16-2.02 µm, P>.05). Therefore, the sealer coating was not effective in reducing surface roughness. Among the time-dependent storage methods, the denture cleanser exhibited an almost significant increase in roughness (1.83-1.99 µm, P=.054). Coca-Cola and artificial saliva did not show a significant difference (P>.05). However, a significant decrease in roughness was found with distilled water (P=.02) and air (P<.001). CONCLUSIONS: Statistically significant differences in surface roughness were found among the different types of soft liners. The sealer coating had no significant effect, and denture cleanser slightly increased the surface roughness. Contrary to expectations, the roughness did not increase in all groups over time.

Evaluation of the flexural strength of dual-cure composite resin cements.

The aim of this study was to evaluate of flexural strength of some adhesive resin cements. Three dual-cure composite resin cements (Nexus 3; Variolink II, Panavia F) were prepared. The manufacturer's mixing directions for the cements were followed. Adhesive resin cement was mixed, placed in the rectangular portion of the mold. Fifteen specimens were prepared for each cements. The cements were light-activated with light lamp for 40 s on both and top and bottom surfaces. The each cement specimens were divided into three groups according to time of storage and stored in distilled water for 24 h, 15, and 30 days. Total 45 specimens were stored at 37°C (98.6 0F) in distilled water for 24 h, 15, and 30 days prior to tests. The flexural strength was tested with a universal testing machine at a crosshead speed of 0.5 mm/min (0.02 in.) The maximum load was recorded as MPa. The results were analyzed by Analysis of Variance and Duncan test. The Panavia F resin cements content Bisphenol A was showed the highest flexural strength (80.80 MPa) (11.71 ksi) for 24 h. The lowest flexural strength was observed in Nexus 3 (51.00 MPa) (7.39 ksi). It was found significant interaction of material and time (p < 0.05). The types of cement and time of storage was statistically significant on the flexural strengths (p < 0.001).

The effect of staining solutions on the color stability of provisional prosthodontic materials.

OBJECTIVES: The aim of this study was to evaluate the effects of staining solutions on the color stability of self-cure provisional resin materials. METHODS: The specimens were prepared for each of three auto-polymerized bis-acryl resin and auto-polymerized methyl methacrylate provisional resin material. The baseline color values were measured with a colorimeter according to the CIE L(*)a(*)b(*) color scale. After the first measurement (T(0)), specimens were placed in staining solutions (coffee, coca-cola, burn and distilled water for control group) and the other measurements were taken after 24h (T(1)), 1 week (T(2)) and 4 weeks (T(3)). RESULTS: Data were analyze statistically by (a) repeated measures (ANOVA), (b) one and two way ANOVA, and (c) Tukey HSD multiple comparison tests. At the 24h immersion period, the post hoc analysis indicated that AccessCrown-coffee revealed the highest ΔE(*) values (4.4). At the second immersion period (1 week), Structur2 SC-coffee had the highest ΔE(*) values compared with other materials (5.4). CONCLUSIONS: The degrees of discoloration were increased with immersion time. The methylmethacrylate resin was more resistant to discoloration than bis-acryl resins. After immersion for 30 days, the coffee solution resulted in unacceptable discoloration for all the tested materials.

A comparison of the fracture resistance of core materials using different types of posts.

OBJECTIVE: The purpose of this in vitro study was to determine the fracture resistance of 3 core materials (silver amalgam, resin composite, glass-ionomer cement) supported by 1 custom cast post (nickel-chromium alloy) and 2 prefabricated posts (Radix and Safix posts). METHOD AND MATERIALS: A sum of 45 recently extracted single-rooted human incisors and canines were placed in 0.5% sodium hypochlorite. Before the experiments, the anatomic crowns of teeth were removed below the cementoenamel junction to obtain a standard root length. The roots were endodontically treated by the manual condensation method. The teeth were randomly divided into 9 groups with 5 samples per group. The posts were luted in the corresponding root canals with zinc polycarboxylate cement. Each core reconstruction was prepared with diamond instruments, and the height of cores formed was 6.0 mm. The tooth and post-core combinations were mounted in acrylic resin blocks. Each tooth and post-core combination was placed in a special jig at a 45-degree angle to the buccal/lingual axis and then subjected to a load on an electronic pull-tension-compression testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed using one-way analysis of variance. RESULTS: The resistance to fracture for prefabricated posts was significantly higher for resin composite core than for the other post-core combinations (P <.001). For prefabricated posts, the composite core and amalgam core materials were significantly stronger than the glass-ionomer core material (P <.001). The differences between the core materials were statistically significant (P <.001). CONCLUSION: The glass-ionomer core with custom post was the weakest post-core system, while the prefabricated posts (Safix and Radix) with resin composite and amalgam cores were the strongest post-core systems.

The investigation of solubility values,water sorption and bond strength of auto-polymerising and heat-polymerising acrylic resin materials.

In this study the solubility, water sorption and the bond strength of auto-polymerising and heat-polymerising acrylic resins were investigated. Two auto-polymerising and five heat polymerising acrylic resin materials were used for this study. Thirty-five specimens were prepared (50 mm in diameter and 0.5 +/- 0.01 in thickness) for water sorption and solubility tests. In order to examine bond strength, specimens were prepared in 2.5 x 10 x 64 mm dimensions. These specimens were repaired with QC and major repair acrylic. Some specimens were kept in distilled water for 50 hours, and others for 30 days. The strength of the bond was measured by a Pull-Compress device. As a result of the variance analysis; water sorption, solubility and the bond strength between acrylic resins were identified as statistically significant (P < 0.001). The water sorption of the major acrylic resin specimens were lower than the other materials (P < 0.001).

Determination of the occlusal vertical dimension: use of maxillary and mandibular posterior teeth measurement in edentate subjects.

Determination of the occlusal vertical dimension (OVD) is one of the most important steps in making dentures. Various techniques have been used to make these measurements. Unfortunately, there is no universally accepted method available for clinical use. The aim of this study was, therefore, to develop a technique to determine OVD for complete dentures by using parameters obtained from natural posterior dentition. The silicon impressions were made from the posterior region of the mouth from dentate patients in maximum intercuspation. The measurements were made to determine the distance between the depth of maxillary and mandibular mucobuccal reflections and the relations of the posterior teeth to the mucobuccal reflections. The mean distance between the mucobuccal reflections was 36.14 mm. in the first premolar region, 35.57 mm. in the second premolar region and 32.44 mm. in the first molar region for the right side. The findings of this study can be used as a guide for the construction of record bases and occlusal rims and for establishing the occlusal vertical dimension in edentulous patients.

Influence of a thickness and processing method on the linear dimensional change and water sorption of denture base resin.

The purpose of this study was to evaluate the influence of a thickness and processing method on linear dimension change and water sorption in a denture base resin after storage in water for 24 hours, one week, and four weeks. Sixty wax specimens 65 mm long and 10 mm wide were fabricated in three thicknesses, 1.5, 3, and 4.5 mm. Three dimples were made in each wax specimen. A travelling microscope was used to measure the total distance from the uppermost dimple to the lowest dimple to the nearest 0.01 mm. Acrylic resin blocks were polymerized with 2 processing cycles (short and long-cured). Immediately after processing, all samples were measured by the same investigator. They were then weighed by an electronic precision balance capable of measuring to 0.001 g. Data were analyzed by analysis of variance. Thickness and time of storage were statistically significant on the dimensional change (linear and weight changes) of denture-base resin (p < 0.01), showing the influence of the processing method.