Influence of mixing method on the porosity of resin cements

Introduction: The significant attempt in dentistry was followed by introduction of resin based cements in every day practice. One of the most relevant feature of resin cements is low design porosity. On the other hand, the importance of open porosity is in its impact on possibility of penetration of undesired oral fluids, bacterial toxins and bacteria into underlying dentin structure. Objective: According to the previous state, the purpose of this study was to evaluate the effects of mixing methods on the porous structure of commercial resin cements. Method: Testing was performed on cylindrical specimens made of three self adhesive resin cements: first product, hand mixed, consisted of two paste (Rely X U100), second cement, auto-mixed also consisted of two paste (Rely X Unicem2, Auto-mix) and the third resin cement was encapsulated and prepared for the experiment mechanically by shaking (Rely X Unicem Aplicap).The porous structure of cements was estimated by mercury intrusion porosimeter (Carlo Erba 2000) using Milestone software system. This apparatus operates in the interval .1-200MPa, enabling the detection of pores in interval 7,5-15000nm. Results: All samples had very low porosity, particularly sample of encapsulated resin cement that can be regarded as nonporous. All parameters of porous structure of encapsulated sample resin cement have values within values of experimental error of the instrument. Somewhat more expressed porosity (< 2%) of hand mixed and auto mixed samples could be considered almost negligible. Distribution of pore size diameter indicated that ~ 75 % pores were in the mesoporous region (7.5-50 nm) for all investigated samples, also indicating less expressed porous structure. Conclusion: Based on results of this study it is possible to concluded that capsulation should enable uniform proportioning and mixing of dental cements so the functional properties of cementitious mass will not be susceptible to clinically induced variability.