Effect of prepolymerized composite megafiller on the marginal adaptation of composite restorations in cavities with different C-factors: An SEM study.

Aim: To evaluate the effect of prepolymerized custom-made composite megafiller and configuration factors (C-factor) on marginal adaptation of resin composite restorations. Materials and Methods: Forty extracted human mandibular molars were divided into four experimental groups consisting of 10 samples each. In groups I and III, class V (configuration factor 5) and in groups II and IV, class II box-shaped cavities (configuration factor 2) were prepared. Groups I and II were restored with a nanofilled composite (Filtek™ Z350 3M ESPE, St Paul, MN, USA) placed in horizontal increments. In groups III and IV, preformed composite megafiller was placed and cavities were restored with nanofilled composite Z-350. After curing, the samples were finished and prepared for examination under low vacuum scanning electron microscope. The data were analyzed with one-way analysis of variance. The significance between the individual groups was calculated by Post hoc test using the Holm-Sidak method ( P≤0.05). Results: The marginal gap values in groups III and IV were significantly lower than in groups I and II, respectively ( P≤0.05). Minimum gap values were seen in group IV. Conclusion: Use of prepolymerized composite megafiller and a lower C-factor decreased the marginal gaps between the tooth and composite restorations.

The influence of cavity configuration on the microtensile bond strength between composite resin and dentin / 대한치과보존학회지

This study was conducted to evaluate the influence of the C-factor on the bond strength of a 6th generation self-etching system by measuring the microtensile bond strength of four types of restorations classified by different C-factors with an identical depth of dentin. Eighty human molars were divided into four experimental groups, each of which had a C-factor of 0.25, 2, 3 or 4. Each group was then further divided into four subgroups based on the adhesive and composite resin used. The adhesives used for this study were AQ Bond Plus (Sun Medical, Japan) and Xeno III (DENTSPLY, Germany). And composite resins used were Fantasista (Sun Medical, Japan) and Ceram-X mono (DENTSPLY, Germany). The results were then analyzed using one-way ANOVA, a Tukey's test, and a Pearson's correlation test and were as follows. 1. There was no significant difference among C-factor groups with the exception of groups of Xeno III and Ceram-X mono (p < 0.05). 2. There was no significant difference between any of the adhesives and composite resins in groups with C-factor 0.25, 2 and 4. 3. There was no correlation between the change in C-factor and microtensile bond strength in the Fantasista groups. It was concluded that the C-factor of cavities does not have a significant effect on the microtensile bond strength of the restorations when cavities of the same depth of dentin are restored using composite resin in conjunction with the 6th generation self-etching system.

Analysis of gap formation at tooth-composite resin interface: effect of C-factor and light-curing protocol

OBJECTIVE: The aim of this study was to evaluate the effect of C-factor and light-curing protocol on gap formation in composite resin restorations. Material and METHODS: Cylindrical cavities with 5.0 mm diameter and three different depths (A=1.0, B=2.0 and C=3.0 mm) were prepared on the occlusal surface of 30 human molars and restored in a single increment with P 60. The composite resin was light-cured according to two protocols: standard - 850 mW/cm² / 20 s and gradual - 100 up to 1000 mW/cm² / 10 s + 1000 mW/cm² / 10 s. After storage in distilled water (37°C/7 days), the restorations were cut into three slices in a buccolingual direction and the gap widths were analyzed using a 3D-scanning system. The data were submitted to ANOVA and Student-Newman-Keuls test (alpha=0.05). RESULTS: ANOVA detected a significant influence for the C-factor and light-curing protocol as independent factors, and for the double interaction C-factor vs. light-curing protocol. Cavities with higher C-factor presented the highest gap formation. The gradual light-curing protocol led to smaller gap formation at cavity interfaces. CONCLUSIONS: The findings of this study suggest that the C-factor played an essential role in gap formation. The gradual light-curing protocol may allow relaxation of composite resin restoration during polymerization reaction.

Effect of cavity shape, bond quality and volume on dentin bond strength / 대한치과보존학회지

The aim of this study was to evaluate the effect of cavity shape, bond quality of bonding agent and volume of resin composite on shrinkage stress developed at the cavity floor. This was done by measuring the shear bond strength with respect to iris materials (cavity shape; adhesive-coated dentin as a high C-factor and Teflon-coated metal as a low C-factor), bonding agents (bond quality; Scotchbond(TM) Multi-purpose and Xeno(R)III) and iris hole diameters (volume; 1 mm or 3 mm in diameter x 1.5 mm in thickness). Ninety-six molars were randomly divided into 8 groups (2 x 2 x 2 experimental setup). In order to simulate a Class I cavity, shear bond strength was measured on the flat occlusal dentin surface with irises. The iris hole was filled with Z250 restorative resin composite in a bulk-filling manner. The data was analyzed using three-way ANOVA and the Tukey test. Fracture mode analysis was also done. When the cavity had high C-factor, good bond quality and large volume, the bond strength decreased significantly. The volume of resin composite restricted within the well-bonded cavity walls is also be suggested to be included in the concept of C-factor, as well as the cavity shape and bond quality. Since the bond quality and volume can exaggerate the effect of cavity shape on the shrinkage stress developed at the resin-dentin bond, resin composites must be filled in a method, which minimizes the volume that can increase the C-factor.

Influence of cavity size and restoration methods on the cusp deflection in composite restoration / 대한치과보존학회지

The aim of this study was to measure the cusp deflection during composite restoration for MOD cavity in premolar and to examine the influence of cavity dimension, C-factor and restoration method on the cusp deflection. Thirty extracted maxillary premolar were prepared to four different sizes of MOD cavity and divided into six groups. The width and depth of the cavity were as follows. Group 1; 1.5 x 1 mm, Group 2; 1.5 x 2 mm, Group 3; 3 x 1 mm, and Group 4-6; 3 x 2 mm respectively. Group 1-4 were restored using bulk filling method with Z-250 composite. However, Group 5 was restored incrementally, and Group 6 was restored with an indirect resin inlay. The cusp deflection was recorded at the buccal and lingual cusp tips using LVDT probe for 10,000 seconds. The measured cusp deflections were compared between groups, and the relationship between the cube of the length of cavity wall/the cube of the thickness of cavity wall (L3 / T3), C-factor and cusp deflection or %flexure (100 x cuspal deflection / cavity width) was analyzed. The cusp deflection of Group 1-4 were 12.1 microm, 17.2 microm, 16.2 microm and 26.4 microm respectively. The C-factor was related to the %flexure rather than the cusp deflection. There was a strong positive correlationship between the L3 / T3 and the cusp deflection. The cusp deflection of Group 5 and 6 were 17.4 microm and 17.9 microm respectively, which are much lower value than that of Group 4.

The effect of cavity wall property on the shear bond strength test using iris method / 대한치과보존학회지

OBJECTIVES: In the unique metal iris method, the developing interfacial gap at the cavity floor resulting from the cavity wall property during polymerizing composite resin might affect the nominal shear bond strength values. The aim of this study is to evaluate that the iris method reduces the cohesive failure in the substrates and the cavity wall property effects on the shear bond strength tests using iris method. MATERIALS AND METHODS: The occlusal dentin of 64 extracted human molars were randomly divided into 4 groups to simulate two different levels of cavity wall property (metal and dentin iris) and two different materials (ONE-STEP(R) and ALL-BOND(R) 2) for each wall property. After positioning the iris on the dentin surface, composite resin was packed and light-cured. After 24 hours the shear bond strength was measured at a crosshead speed of 0.5 mm/min. Fracture analysis was performed using a microscope and SEM. The data was analyzed statistically by a two-way ANOVA and t-test. RESULTS: The shear bond strength with metal iris was significant higher than those with dentin iris (p = 0.034). Using ONE-STEP(R), the shear bond strength with metal iris was significant higher than those with dentin iris (p = 0.005), but not in ALL-BOND(R) 2 (p = 0.774). The incidence of cohesive failure was very lower than other shear bond strength tests that did not use iris method. CONCLUSIONS: The iris method may significantly reduce the cohesive failures in the substrates. According to the bonding agent systems, the shear bond strength was affected by the cavity wall property.

The effect of viscosity, specimen geometry and adhesion on the linear polymerization shrinkage measurement of light cured composites / 대한치과보존학회지

OBJECTIVES: The aim of study was to investigate the effect of flow, specimen geometry and adhesion on the measurement of linear polymerization shrinkage of light cured composite resins using linear shrinkage measuring device. METHODS: Four commercially available composites - an anterior posterior hybrid composite Z100, a posterior packable composite P60 and two flowable composites, Filtek flow and Tetric flow - were studied. The linear polymerization shrinkage of composites was determined using 'bonded disc method' and 'non-bonded' free shrinkage method at varying C-factor in the range of 1~8 by changing specimen geometry. These measured linear shrinkage values were compared with free volumetric shrinkage values. The viscosity and flow of composites were determined and compared by measuring the dropping speed of metal rod under constant load. RESULTS: In non-bonded method, the linear shrinkage approximated one third of true volumetric shrinkage by isotropic contraction. However, in bonded disc method, as the bonded surface increased the linear shrinkage increased up to volumetric shrinkage value by anisotropic contraction. The linear shrinkage value increased with increasing C-factor and approximated true volumetric shrinkage and reached plateau at about C-factor 5~6. The more flow the composite was, reduced linear shrinkage was measured by compensation radial flow.