Depth of cure of dental composites submitted to different light-curing modes

Shrinkage Stress and Temperature Variation in Resin Composites Cured via Different Photoactivation Methods: Insights for Standardisation of the Photopolymerisation

The literature has shown that there is no consensus regarding the best resin composite photoactivation protocol. This study evaluated the efficiency of the conventional, soft-start, pulse-delay and exponential protocols for photoactivation of resin composites in reducing the shrinkage stress and temperature variation during the photopolymerisation. The photoactivation processes were performed using a photocuring unit and a smartphone app developed to control the irradiance according each photoactivation protocol. These photoactivation methods were evaluated applying photoactivation energies recommended by the resins manufactures. Three brands of resin composites were analysed: Z-250, Charisma and Ultrafill. The cure effectiveness was evaluated through depth of cure experiments. All results were statistically evaluated using one-way and multi-factor analysis of variance (ANOVA). The use of exponential and pulse-delay methods resulted in a significant reduction of the shrinkage stress for all evaluated resins; however, the pulse-delay method required too long a photoactivation time. The increases on the temperature were lower when the exponential photoactivation was applied; however, the temperature variation for all photoactivation protocols was not enough to cause damage in the restoration area. The evaluation of the depth of cure showed that all photoactivation protocols resulted in cured resins with equivalent hardness, indicating that the choice of an alternative photoactivation protocol did not harm the polymerisation. In this way, the results showed the exponential protocol as the best photoactivation technique for practical applications.

Properties of Experimental Dental Composites Containing Antibacterial Silver-Releasing Filler

Secondary caries is one of the important issues related to using dental composite restorations. Effective prevention of cariogenic bacteria survival may reduce this problem. The aim of this study was to evaluate the antibacterial activity and physical properties of composite materials with silver sodium hydrogen zirconium phosphate (SSHZP). The antibacterial filler was introduced at concentrations of 1%, 4%, 7%, 10%, 13%, and 16% (w/w) into model composite material consisting of methacrylate monomers and silanized glass and silica fillers. The in vitro reduction in the number of viable cariogenic bacteria Streptococcus mutans ATCC 33535 colonies, Vickers microhardness, compressive strength, diametral tensile strength, flexural strength, flexural modulus, sorption, solubility, degree of conversion, and color stability were investigated. An increase in antimicrobial filler concentration resulted in a statistically significant reduction in bacteria. There were no statistically significant differences caused by the introduction of the filler in compressive strength, diametral tensile strength, flexural modulus, and solubility. Statistically significant changes in degree of conversion, flexural strength, hardness (decrease), solubility (increase), and in color were registered. A favorable combination of antibacterial properties and other properties was achieved at SSHZP concentrations from 4% to 13%. These composites exhibited properties similar to the control material and enhanced in vitro antimicrobial efficiency.

Mechanical and Physical Properties of Two Different Resin-based Materials: A Comparative Study

AIM

The purpose of this study was to evaluate the degree of conversion (DC) of two different resin-based composite materials (nanofill composite and ormocer) and correlate it with some mechanical properties of these two restorative materials.

MATERIALS AND METHODS

Two different resin-based materials (Filtek Supreme XT and Admira) were tested. A total of 30 samples of each type of selected composite were prepared. Specimens were immersed in distilled water for 24 hours. Then, the specimens were subjected to DC, hardness, and diametral tensile strength (DTS) measurements. The data obtained were tabulated for statistical analysis. The t-test was used to detect the significant difference among the variables tested in this study. Furthermore, the interrelationship between the studied parameters was investigated using a simple correlation coefficient statistical test.

RESULTS

Statistically significant differences were observed regarding DC, hardness, and DTS. Filtek Supreme XT presented the highest values. There was a positive correlation between DC and hardness. Also there was a correlation between DC and DTS, but it was not significant.

CONCLUSION

Under the tested experimental conditions, the DC of Filtek Supreme XT was higher than that of ormocer. Accordingly, Filtek Supreme XT showed better mechanical properties.

CLINICAL SIGNIFICANCE

Filtek Supreme XT showed superior mechanical properties. Therefore, orthodontic bracket-based composite combinations may also be expected to perform well clinically over the lifetime of a bonded orthodontic appliance.

Effects of light curing modes and ethanol-wet bonding on dentin bonding properties

OBJECTIVE

This study explored the effects of different light curing modes and ethanol-wet bonding on dentin bonding strength and durability.

METHODS

A total of 54 molars were randomly divided into three groups: Single Bond 2, Gluma Comfort Bond, and N-Bond. Based on the three light-curing modes and presence or absence of ethanol pretreatment, the samples were assigned to six subgroups: high-light mode, ethanol pretreatment+high-light mode, soft-start mode, ethanol pretreatment+soft-start mode, standard mode, and ethanol pretreatment+standard mode. All samples were bonded with resin based on the experimental groups. After 24 h and 6 months of water storage, a universal testing machine was used to measure microtensile bond strength. Scanning electron microscopy (SEM) was applied to observe mixed layer morphology.

RESULTS

The 24-h and 6-month microtensile bond strengths of the ethanol pretreatment groups were significantly higher than those of the non-ethanol pretreatment groups at the same light modes (P<0.05). With or without ethanol pretreatment, the microtensile bond strengths of the high-light modes were significantly lower than those of the soft-start modes and standard modes (P<0.05). The microtensile bond strengths of samples from the 6-month water storage group significantly decreased compared with those of samples from the 24-h water storage group (P<0.05). The soft-start groups and standard groups formed better mixed layers than the high-light mode groups, whereas the ethanol pretreatment groups formed more uniform mixed layers than those without ethanol pretreatment.

CONCLUSIONS

Ethanol-wet bonding technique, soft-start, and standard modes could improve dentin bonding properties.

Depth of cure of bulk fill composites with monowave and polywave curing lights

PURPOSE

To measure and compare the depth of cure (DOC) of two bulk fill resin composites using a monowave and polywave light curing unit (LCU) according to ISO 4049 and using custom tooth molds.

METHODS

The DOC of Tetric Evoceram Bulk Fill and Filtek Bulk Fill Posterior were measured using a monowave LED LCU (Elipar S10) and a polywave LED LCU (Bluephase G2). Metal molds were used to fabricate 10 mm long DOC specimens (n = 10) according to ISO 4049. Uncured composite material was scraped away with a plastic instrument and half the length of remaining composite was measured as the DOC. Custom tooth molds were fabricated by preparing > 10 mm long square- shaped (4 x 4 mm) holes into the mesial/distal surfaces of extracted human molars. Resin composite was placed into one end of the prepared tooth and light polymerized. Uncured resin composite was removed from the opposite side from which the tooth was irradiated and the tooth was sectioned mesio-distally. Half the length of remaining cured composite was measured as the DOC. Data were analyzed by three-way ANOVA (α = 0.05) for factors material, LCU, and mold.

RESULTS

The main effect LCU was not significant (P = 0.58). The interaction effect between material x mold was significant (P = 0.0001). The DOC of the composites differed significantly only with the stainless steel mold in which Tetric Evoceram Bulk Fill showed a deeper DOC than Filtek Bulk Fill Posterior (4.03 ± 0.14 vs 3.56 ± 0.38 mm, P < 0.0001).