Confocal laser scanning microscopic analysis of microleakage in class II restorations: zirconia-incorporated glass ionomer versus bulk-fill composite 

Introduction
Durability and marginal integrity of composite resin in class II restorations raise concerns when dealing with caries that extend apically to the cementoenamel junction (CEJ). Hence, a new generation of glass ionomer cement (GICs) exemplified by Zirconomer aims to address the limitations observed in previous tooth-colored restorative materials.

Objectives
To evaluate and compare microleakage in class II restoration with Zirconomer Improved and Tetric® N-Ceram Bulk Fill composite using a confocal laser scanning microscope.

Material and methods
A total of 46 extracted teeth were collected, and standardized mesial class II box cavities were prepared 1 mm below the CEJ. They were then randomly divided into 2 groups with Zirconomer Improved as the experimental group and Tetric® N-Ceram Bulk Fill composite as the control group, and restored accordingly. Restorations were finished and polished, after which the specimens were prepared for microleakage testing both occlusally and cervically. The samples were immersed in 0.5% rhodamine B dye and sectioned longitudinally. Microleakage was measured under confocal laser scanning microscope at 10x magnification, followed by software analysis.

Results
Zirconomer showed greater degree of microleakage at both cervical and occlusal levels as compared with bulk-fill composite, with statistically significant results (p < 0.05).

Conclusions
No material was able to completely eliminate microleakage. However, the least was seen in the bulk-fill resin composite, followed by the highest in the Zirconomer Improved group.