Application and limitations of configuration factor (C-factor) in stress analysis of dental restorations

OBJECTIVE

The configuration factor (C-factor) is an index used to evaluate the relationship between cavity configuration and the development of polymerization shrinkage stress in dental restorations. Although C-factor has been widely researched, its correlation with stress analysis in dental restorations remains controversial. This review aims to discuss the application and limitations of C-factor and define the restricted conditions under which the C-factor "rule of thumb" is applicable.

METHODS

A thorough literature review was conducted on the application and limitations of C-factor in stress analysis of dental restorations. This was principally based on MEDLINE/PubMed and Web of Science databases and a review of the relevant studies and publications in scientific papers in international peer-reviewed journals for the specific topic of C-factor and polymerization shrinkage.

RESULTS

The C-factor alone cannot provide an accurate prediction of the shrinkage stress of restorations and the mechanical behavior of material-tooth interfaces. C-factor is only applicable under one condition not typically seen in clinical practice: low, near-rigid compliance.

SIGNIFICANCE

Conditions for the application of C-factor have been explicitly defined. A more accurate and precise understanding and utilization of the C-factor is of benefit as it contributes to better understanding of polymerization shrinkage behavior of restorations.

Dentin-composite bond strength measurement using the Brazilian disk test

OBJECTIVES

This study presents a variant of the Brazilian disk test (BDT) for assessing the bond strength between composite resins and dentin.

METHODS

Dentin-composite disks (ϕ 5mm×2mm) were prepared using either Z100 or Z250 (3M ESPE) in combination with one of three adhesives, Adper Easy Bond (EB), Adper Scotchbond Multi-Purpose (MP) and Adper Single Bond (SB), and tested under diametral compression. Acoustic emission (AE) and digital image correlation (DIC) were used to monitor debonding of the composite from the dentin ring. A finite element (FE) model was created to calculate the bond strengths using the failure loads. Fracture modes were examined by scanning electron microscopy (SEM).

RESULTS

Most specimens fractured along the dentin-resin composite interface. DIC and AE confirmed interfacial debonding immediately before fracture of the dentin ring. Results showed that the mean bond strength with EB (14.9±1.9MPa) was significantly higher than with MP (13.2±2.4MPa) or SB (12.9±3.0MPa) (p<0.05); no significant difference was found between MP and SB (p>0.05). Z100 (14.5±2.3MPa) showed higher bond strength than Z250 (12.7±2.5MPa) (p<0.05). Majority of specimens (91.3%) showed an adhesive failure mode. EB failed mostly at the dentin-adhesive interface, whereas MP at the composite-adhesive interface; specimens with SB failed at the composite-adhesive interface and cohesively in the adhesive.

CONCLUSIONS

The BDT variant showed to be a suitable alternative for measuring the bond strength between dentin and composite, with zero premature failure, reduced variability in the measurements, and consistent failure at the dentin-composite interface.

CLINICAL SIGNIFICANCE

The new test could help to predict the clinical performance of adhesive systems more effectively and consistently by reducing the coefficient of variation in the measured bond strength.

Bonding of flowable resin composite restorations to class 1 occlusal cavities with and without cyclic load stress

To examine the bonding of flowable resin composite restorations (F-restoration) to class 1 occlusal cavities with and without cyclic load stress, compared with that of a universal resin composite restoration (U-restoration). Two flowable composites and one universal composite (control) were applied with an adhesive system to 42 standardized class 1 occlusal cavities. The restored specimens were subjected to cyclic load stress and no stress modes. The microtensile bond strength (μ-TBS) of the dentin floor was measured. The U-restoration did not show pretesting failure. The F-restorations exhibited pretesting failure, regardless of the stress mode. The μ-TBS was not significantly different among the three restorations, regardless of the stress mode. The cyclic load stress did not influence the μ-TBS of the F-restorations; however, it significantly reduced μ-TBS in the U-restoration. The bonding reliability of the F-restorations was inferior to that of the U-restoration, for both stress modes.

Comparative evaluation of the bonding efficacy of sixth and seventh generation bonding agents: An In-Vitro study

AIMS

To compare the shear bond strength of sixth generation and seventh generation bonding agents to dentin.

MATERIALS AND METHODS

EIGHTY HUMAN MAXILLARY PREMOLARS WERE REDUCED TO EXPOSE FLAT SURFACE OF DENTIN AND DIVIDED INTO FOUR EQUAL GROUPS, WHICH WERE BONDED USING FOLLOWING BONDING AGENTS: Sixth generation bonding agents, Adper SE Plus and Xeno III and Seventh generation bonding agents, Adper Easy One and Xeno V. Composite cylinders were then built using a plastic mould on these prepared dentinal surfaces. Samples were stored in distilled water for 24 hours and tested for shear bond strength with universal testing machine. Shear force was applied perpendicular to the long axis of composite cylinder at adhesive-tooth interface until debonding occurred. The data so obtained were tabulated and analyzed statistically using independent-samples t test and analysis of variance (ANOVA) test.

RESULTS

The seventh generation adhesives showed significantly higher shear bond strength to dentin compared to sixth generation adhesives (P < 0.01). The highest value of shear bond strength was obtained from Adper Easy One system, while Adper SE Plus gave the lowest shear bond strength values.

CONCLUSIONS

Seventh generation adhesives are more advantageous than sixth generation adhesives in dentin bonding as it requires less time, fewer steps, and better bond strength.

Micro-shear bond strength of adhesive resins to enamel at different relative humidity conditions

This study tested whether exhaled humid conditions would affect the adhesion of etch-and-rinse, two-step and one-step self-etch adhesive resins to enamel. Enamel surfaces of human maxillary anterior teeth (N=240, n=20) were exposed to four humid conditions (H1: 63-68%, H2: 73-78%, H3: 93-98%, H4: 36-45% RH) during bonding with Adper Single Bond 2 (SB2), Clearfil SE Bond (CSE) and Adper Easy Bond (AEB). Specimens were stored in distilled water at 37 ºC for 24 h and tested to failure using micro-shear bond strength (μSBS) test. Data were analyzed using two-way ANOVA and Tukey's test (p<0.05). The μSBS to enamel with SB2, CSE and AEB was not significantly affected by humidity parameters. AEB resulted in significantly lower μSBS in all conditions. The frequency of adhesive failures was the highest at H2, H3 for SB2, H3 for CSE and H1-4 for AEB indicating that humidity conditions may decrease adhesion quality to enamel.

Microleakage of class V resin composites using various self-etching adhesives: an in vitro study

BACKGROUND AND AIMS

Microleakage has been identified as a significant problem with composite restorations because of interfacial gap formation which can result in tooth discoloration, recurrent caries, possible pulpal involvement and restoration replacement. Aim of this study is to evaluate the microleakage of self-etch adhesive system at the coronal and apical margins of class V resin composite restorations under stereomicroscope at 20× magnification.

MATERIALS AND METHODS

Class V cavities were prepared on the facial surfaces of 48 human premolars with coronal margins located in enamel and apical margins located in dentin. Teeth were divided into four groups: Group one-Xeno V; group two- G-Bond; group three-Clearfil S(3) Bond; group four-control. After application of bonding agent and restoration, the teeth were subjected to thermocycling. The teeth were then immersed in 1% aqueous solution of methylene blue dye for 24 hours and sectioned to allow the assessment of microleakage under microscope.

RESULTS

Coronal and apical margins were scored separately using a 0-3 ordinal ranking system and the recorded values were statistically analyzed using Kruskal-Wallis, Mann- Whitney U-test and Wilcoxon signed rank test. Statistical analysis showed that there was less microleakage in Xeno V at coronal region and Clearfil S(3) Bond in apical region, overall Clearfil S(3) Bond showed less marginal permeability in both coronal and apical regions.

CONCLUSION

Specimens restored with the Xeno V and Clearfil S(3) Bond adhesive systems revealed reduced leakage at the coronal margin. At the apical margin, Xeno V showed greater leakage than the other groups, except the control.

CLINICAL SIGNIFICANCE

In class V restorations restored with composite resin, the choice of material affects the microleakage and retention of the restoration. This study theorizes that the self-etch adhesives show less microleakage in the coronal area than the apical margin.

Effect of bur roughness on bond to sclerotic dentin with self-etch adhesive systems

PURPOSE

To evaluate the effect of bur roughness on bond strength values and conditioner pattern of two-step self-etch adhesives applied on sclerotic dentin.

METHODS

The roots of 48 bovine incisors were removed and the crowns were divided into four groups: the control group (CO) teeth were left untreated or the teeth were slightly roughened with coarse-, medium-, or fine-grit diamond burs. Next, the teeth were subdivided and Clearfil SE Bond (CSE) and Adper SE Bond (ASE) were applied according to the manufacturers' instructions. Composite resin (Opallis) buildups were incrementally constructed on the bonded surfaces. After storage for 24 hours in distilled water at 37°C, the teeth were sectioned into sticks (area of 0.8 mm(2)). The sticks were stressed until failure by tensile forces (0.5 mm/min). Additionally, eight bovine teeth were treated as previously described, and after adhesive application, the surface was rinsed off and examined by scanning electron microscopy to measure the relative number of open tubules (OT). Data (MPa) were analyzed by two-way analysis of variance and Tukey test (p=0.05).

RESULTS

CO showed the highest bond strength values (p<0.05). As regards OT, the lowest mean was observed for CO (p<0.05) and the highest was found after application of CSE or ASE (p<0.05).