Influence of Simulated Hot and Cold Dietary Temperatures on the Microleakage Resistance of Smart Dental Restorative Materials

Abstract

Background: Dental restorations were considered inert. More recently, there has been an effort to create restorative materials that respond to environmental stimuli and modulate the biologic response of the tissue they interact with. One of the risks associated with the use of restorations in the oral cavity is the effect of repeated cycles of thermal expansion and contraction of restorations exposed to hot and cold foods and beverages. The cyclic nature of these temperature fluctuations may adversely affect the quality of the interface of the dental restoration and put it at risk for marginal leakage. Objective: This study evaluated the effect of simulating hot and cold foods and beverages on smart dental restorative materials. Methods: 160 sound human premolar teeth were mounted in acrylic resin, and a Standardized Class V cavity was prepared. Four groups of each twenty teeth were formed and individually restored with Activa BioACTIVE, Cention N, and EQUIA Forte HT; a nanohybrid control composite was also used. All materials were light cured for 40 seconds. Each material group was sub-divided into five sub-groups. The first four sub-groups of each material group were exposed to heat (hot), cold (cold), and alternating heat and cold (alt hot/cold) temperature cycles. A fifth, control, sub-group was not thermally exposed.  Each sub-group was allowed to age in a thermal cycling device for a total of 1,500 cycles. The device had a temperature range of 5° to 55° Centigrade, and a dwell time of 30 seconds at each temperature. To evaluate marginal microleakage, the restorations were immersed in methylene blue for 24 hours. Stereomicroscopy was used to assess the quality of the restoration. The data were statistically analyzed using a pairwise comparisons. Results: In both the restorative material and the thermal exposure condition, significant differences in microleakage were observed (p < 0.05). The combined hot and cold exposure condition resulted in greater microleakage than the single exposure conditions. Of the test materials, Activa BioACTIVE showed the lowest mean microleakage with repeated thermal expansion/contraction, followed by Cention N and EQUIA Forte HT. The conventional composite demonstrated the greatest microleakage. In the single temperature condition, no differences in mean microleakage were observed among the materials. In the alternating temperature condition, Activa BioACTIVE and EQUIA Forte HT showed less microleakage than the other materials. Conclusion: It can be concluded that repeated exposure to oral temperature extremes, as may occur with food and beverage, can result in microleakage of restorations. Of the materials evaluated, Activa BioACTIVE and EQUIA Forte HT, demonstrated the ability to maintain marginal integrity and closure with the greatest resistance to food and beverage-induced temperature changes. Further studies on the effects of food and beverage temperature changes and other clinical conditions are necessary to better assess the long-term behavior of restorative materials.