A Comparative Evaluation of the Surface Roughness, Surface Hardness and Microleakage of a Pure Ormocer with an Ormocer-Based Composite and a Nanocomposite Restorative Material

Abstract

Introduction: Resin composite is a popular, universally used, tooth coloured direct restorative material. Although much progress has been made to the filler technology in resin composites over the years, no fundamental changes have been made to the composition of the monomer matrix since Bowen introduced dimethacrylates in the early 1960s. As an alternative group of polymers, ormocers were developed as a new material class. Ormocer is an acronym for Organically Modified Ceramic. The first generation of ormocers were expected to combine both the advantages of inorganic polymers and organic polymers. However, due to the ongoing challenges to improve handling properties and to incorporate filler particles, conventional dental monomers, such as Bis-GMA and UDMA, had to be added to the ormocer matrix, diminishing the initial promising advantages of this material. It therefore becomes necessary to refer to this added dimethacrylate, first generation ormocer materials as ormocer-based composites. Pure ormocers are organically modified, non-metallic, inorganic compounds that are dimethacrylate-diluent-free. This unique material group differ from conventional composites in that the matrix has an organic but also an inorganic component. Ormocers are expected to combine both the advantages of inorganic polymers such as mechanical strength and thermal stability, as well as the advantages of organic polymers such as impact resistance and flexibility. Disadvantages such as polymerization shrinkage, high wear and leaching of monomers may be reduced by the large size of the ormocers’ monomer molecules. Aim: The aim of this in vitro study was to determine whether a new generation of pure ormocers offer any clear differences when compared to a first generation ormocer-based composite and conventional nanocomposite in terms of surface roughness, surface hardness and microleakage. Materials and Methods: A pure ormocer (Admira Fusion) a first generation ormocer-based composite (Admira) and a nanocomposite (Filtek Z350 XT) were evaluated. Twelve disk samples (10mm x 2mm) of each material were prepared for both surface roughness and surface hardness. For surface roughness, all samples were finished and polished strictly according to the manufacturers’ instructions and measured with a profilometer. For surface hardness, samples were stored in an incubator, polished and a Vickers diamond indenter (500g load and dwell time of 40sec) was used to record values. For microleakage, 36 standardised, Class V cavities were prepared and randomly divided into three groups. Restored teeth were thermally fatigued, immersed in 2% methylene blue solution for 48 hours, sectioned and scored for occlusal and gingival microleakage. Results: Statistical significance was set at p<0.05. With surface roughness, there was no statistical significant difference between the experimental conditions after curing the materials through a Mylar strip and before polishing. The one-way analysis of variance (ANOVA) identified no significant difference in terms of surface roughness between the three material groups (p>0.05) when polished with water-cooling. There was however a statistical significant difference when the ormocer-based composite (p=0.003) and the nanocomposite (p<0.001) was compared with the pure ormocer when polished dry. A significant statistically higher surface hardness was identified for the nanocomposite compared to both the pure ormocer (p<0.001) and ormocer-based composite (p<0.001). Fisher’s exact test identified no significant difference in terms of occlusal microleakage (p=0.534). Gingival microleakage revealed a marginal significant difference with the nanocomposite leaking marginally less compared to the pure ormocer (p=0.093). Conclusion: Based on the comparative evaluation and statistical analysis of the surface roughness and microleakage, there is no difference in using a pure ormocer compared to an ormocer-based composite or nanocomposite. The surface hardness of the nanocomposite was statistically significantly higher than for the pure ormocer and ormocer-based composite. The choice of material would be subject to the clinical condition and the practitioner’s preference; however, the nanocomposite should be used in areas, which require increased surface hardness.