Evaluation of the effect of preheating or precooling on compressive strength and fluoride release of five different glass ionomer based restorative materials

Glass ionomer cements have good aesthetic properties, biocompatibility and are easy to apply. These materials have been often used in pediatric dentistry due to their fluoride release and anti caries properties. However, low mechanical properties limit the usage of glass ionomer cements in clinical seting. Many studies have been conducted to improve the mechanical properties of glass ionomer cements. The aim of this study, was to evaluate the effect of pre-heating or pre-cooling on the compressive strength values and the amounts of fluoride release of five different glass ionomer-based restorative materials (resin-modified glass ionomer cements [Photac Fil Quick Aplicap and Fuji II LC Capsule], polyacid modified composite resins [Dyract XP and F2000] and a conventional glass ionomer cement [Ionofil molar AC]). 7 capsules from each of the glass ionomer-based restorative materials were immersed to water bath at 40°C for 90 sec after placing into a water impermeable plastic bag, stored refrigerator at 4°C for 30 min and the other group was kept at room temperature before the mixing. This study was carried out two hundred and ten specimens. Of these, one hundred an five specimens (4 mm diameter and 6 mm height) were prepared for compressive strength experiment and one hundred and five specimens (10 mm diameter and 2 mm height) were prepared for fluoride release experiment. The prepared specimens were placed in plastic test tubes containing 3 ml de-ionized water and than put into an incubator at 37°C. The specimens which are prepared for compressive strength experiments were tested using INSTRON 3345 instrument until failure. Test speed was set at 1.0mm minˉ¹. For the fluoride release experiment, the specimens were measured at 1st, 2nd, 3rd, 4th, 7th, 14th, 21st and 28th days by ion selective electrode connected to an ion analyzer. Orion 720A + and Orion Fluoride electrode were used for fluoride release mesurements. The statistical analysis was performed with NCSS 2007 software program. Data were analysed by using the descriptive statistical methods (mean average, standart deviation, median, interquartil range). Newman Keuls and Tukey multiple comparison tests were also performed. The level of significance was set at p<0,05. For resin-modified glass ionomer cement group (Photac Fil Quick Aplicap, Fuji II LC) heating or cooling did not show any significant effect on the compressive strength. In one of the materials of in this group (Photac Fil Quick Aplicap) cooling significantly increased the fluoride release compared with heating and room temperature. For the other material (Fuji II LC) heating significantly increased the fluoride release compared with cooling and room temperature. In the compomer group, one material (F2000) was not affected heating or cooling regarding compressive strength values , where as the other material (Dyract XP) revealed significantly higher the compressive strength value after heating. In one of the material in this group (Dyract XP) heating or cooling did not create any significant difference on the amount of fluoride release, where as in the other material (F2000) heating significantly increased the fluoride release compared with cooling and room temperature. The conventional glass ionomer cement (Ionofil Molar AC) revealed significantly lower compressive strength value after cooling. Heating and cooling significantly increased fluoride releasing compared to room temperature. In conclusion, this study supports that the effects of heating and cooling and their effects on the materials phsical, chemical and mechanical properties in clinical condition should be stated in the product instruction manual by the manufacturing company.