The effect of artificial aging on water sorption, solubility, flexural strength and compressive strength of materials used as orthodontic band cementation in pediatric dentistry

Luting cements should have mechanical and physical properties that can resist the forces during mastication. Luting cements are expected to have sufficient flexural strength and compressive strength, when exposed to chewing forces and to transmit stresses from the restoration to the tooth without breaking. As a result of fractures and cracks in the cement, the orthodontic band or restoration may become loosened or decementated and resultant caries can be observed. The aim of this study is to evaluate the effects of artificial aging on water sorption, solubility, flexural strength and compressive strength of a conventional glass ionomer luting cement (Meron [Voco, Cuxhaven, Germany]), a multi cure glass ionomer band cement (UnitekTM [3M Unitek, Monrovia, USA]), and compomer band cements ((Ultra Band-LokTM Blue [Reliance Orthodontic Product, Itasca, IL, USA], TransbondTM Plus [3M Unitek, Monrovia, USA]) which are used for orthodontic band cementation in pediatric dentistry. For water sorption and solubility experiment, the luting cements were prepared in accordance with ISO 4049:2009, (15 mm in diameter, 1 mm in depth, n=10). Samples were kept in desiccator until they reach a constant mass, and then aged for 4 weeks in artificial saliva. 1st day, 1st week and 4th week weight measurements made and then kept in desiccator again, and the mass and volumes of the samples were measured. A total of 96 samples were prepared for the flexural strength test in accordance with ISO 4049:2009, 25 X 2 mm in length and 2 mm in depth each group. Half of the prepared samples were aged for 24 hours and the other half for 6 months in artificial saliva and placed to INSTRON 3345 device and three-point bending test was performed. A total of 96 samples were prepared for the compressive strength test in accordance with ISO 9917:2017 with a height of 6 mm and a diameter of 4 mm. Half of the prepared samples were aged for 24 hours and other half for 6 months in artificial saliva and placed to INSTRON 3345 device and compressive strength test was performed. In the statistical analysis of the study, one-way variance analysis was used to make multiple time comparisons of normally distributed variables. In addition, Newman Keuls multiple comparison test in subgroup comparisons, one-way variance analysis in intergroup comparisons, Tukey multiple comparison test in subgroup comparisons, and independent t test was used in paired comparisons. For intergroup comparisons of non-normally distributed variables, Kruskal Wallis test was used and for subgroup comparisons, Dunn's multiple comparison test was used. The results were evaluated at a level of significance at p<0.05. The results of the study revealed that all the materials tested had water sorption characteristics to a degree. Accordingly, while the multi cure Unitek showed the highest water sorption at all time periods, it was followed by Meron, Ultra band-lok blue and Transbond groups, respectively. The difference between water sorption values of all groups except Ultra band-lok blue and Transbond was found significant. It was found that water sorption of all groups increased with time and this increase was significant. As a result of the 4-week solubility test, negative solubility values were obtained in Meron and multi cure Unitek groups; the highest solubility value was found in Ultra band-lok blue group. The difference between all groups was found significant. The flexural strength and compressive strength test results of this study revealed consistent results in the 24th hour and 6th month measurements. The mechanical properties of Ultra band-lok blue and Transbond cements, which are compomer cements, were found higher than multi cure Unitek, which is RMGIC and Meron, which is the traditional GIC. As a result of flexural strength test, the highest flexural strength was observed in the Ultra band-lok group at the end of 24 hours and 6 months, followed by Transbond, multi cure Unitek, Meron, respectively. At the end of 24th hour and 6th month, the difference between Ultra band-lok blue and Transbond groups was not significant. At the end of 6th month, the difference between Meron and multi cure Unitek groups was not found statistically significant. As a result of compressive strength test, the highest values were observed in the Transbond group after 24 hours and 6 months, followed by Ultra band-lok blue, multi cure Unitek and Meron, respectively. Similar to the flexural strength test at the end of the 6th month, the difference between Ultra band-lok and Transbond groups and between Meron and multi cure Unitek groups were not significant. As a result; it was concluded that artificial aging in artificial saliva exerted negative effects on water sorption and solubility of the luting cements used in the band cementation that may cause physical and mechanical changes affecting the clinical durability of these materials. It was observed that materials exhibiting more water sorption properties had weaker mechanical properties.