The current study evaluated the surface roughness changes for three different hybrid ceramic materials after immersion in Listerine mouth wash, then after repolishing. Standardization of all procedures followed in the current study to maintain study validity and reliability. The three hybrid ceramic materials were cut 1mm thick by isomet low speed sectioning machine which showed very minimal waste and deformation of the cut materials.[16]
The selected thickness of the tested sample was 1mm which simulates the thickness of clinically applied full coverage crown and confirmed with digital caliber for standardization. Moreover, it is difficult to get accurate cut of the tested materials less than 0.8mm as it would subject to cracks, deformation or even fracture.[17]
Hybrid ceramics have been developed of ceramic and polymer materials together which combines the advantages of ceramics (strength, durability, color stability) and improved flexure strength (flexibility) of composite resin.3 so, in this study the tested materials were Vita enamic, Shofu HC and Nacera Hybrid. These materials have differences in its chemical composition and the percentage of contained resin and glass that expected to have impact on surface roughness changes of each material.[18]
Surface roughness measurements were done using non-contact optical profilometer to fulfill the need of quantitively characterization of the surface topography without contact as Ra value is the most used method of calculating the average roughness of ceramic surfaces but, it doesn’t mean that there is no defect in the local area of the surface.[19]
Listerine mouth rinse widely used with patients suffering from gingivitis as it has antibacterial effect as it reduces streptococcus mutans count, but long time of exposure to these oral hygiene solutions with acidic content and low PH may affect on the surface topography of dental ceramic restorations in the oral cavity.[20]
So, this study examined the effect of Listerine mouth rinse on the surface roughness of three hybrid ceramic materials (Vita Enamic, Shofu HC, Nacera Hybrid) after immersion in 20 ml for 120 days at 37 C, replenishing every 12 hours which equals 2min daily mouth wash using for ten years.[14]
The null hypothesis of this study was rejected as, the results of the current study showed increase in the Surface roughness measurements (Ra) value of the three hybrid materials in comparison to its base line values after immersion in mouth rinse, with the highest value in shofu HC then followed by Nacera Hybrid and Vita Enameic respectively.
Higher polymeric content in Shofu Hc and Nacera Hybrid (40%, 50%) respectively cause low surface hardness and greater surface roughness than other glass ceramic materials as its exposure to acidic solutions for long periods of time weakens its structure and cause release some of its inorganic contents, while increasing surface roughness of Shofu Hc than Nacera hybrid may be due difference in its chemical composition, structural organization and particle size and shape.[17, 21]
These findings in agreement with El Zayat el al studied the impact of two energetic drinks on color stability and surface roughness and microhardness of some ceramic and hybrid materials (Celtra Duo, IPS e. max and Nacera hybrid). The results showed that significant increase in surface roughness of Nacera hybrid in comparison to other two materials.[17]
Also, the current study in accordance with Hamdy TM et al who studied the effect of different mouthwashes on the surface microhardness and color stability of dental nanohybrid resin composite and found that mouthwashes chemical composition had a strong effect on the surface hardness of resin composite materials.[22]
The results of current study disagreed with Bohner et al who evaluated the surface roughness of resin composite and ceramic material after immersion in mouthwashes and concluded that mouthwashes did not have significant change in surface roughness of composite resin and ceramic materials.[23]
Repolishing is critical for smooth surface, less plaque retention, facilitates hygiene, more esthetic, decrease tissue inflammation and comfortable surface of restoration.[24]
The current study showed a significant decrease in surface roughness after repolishing with ceramic polishing kit in the three hybrid materials that become closer to its base line Ra values.
Vita Enamic showed the lowest value of surface roughness after repolishing followed by Nacera Hybrid ad Shofu HC as the microstructure of the material is a very critical factor affecting on surface roughness.
These hybrid materials composed of polymer infiltrated ceramic networks as feldspathic ceramic crystal network is supported by an acrylate-based polymer mesh (increasing the polymer % decrease the wear resistance of the materials and increase its surface roughness.[25]
The materials with interpenetrating network structure, the filler responsible for its physical and mechanical properties with close network structure to each other, when the fillers wear away move away from the structure, the network can maintain its existence in the structure as it is in the form of mesh and more durable. In this condition this increase the surface roughness.[19]
Vita Enamic (80% by weight ceramic network, 14% by weight polymer network) while Shofu HC (61% zirconia silicate, 39% densely packed nanofiller), Nacera Hybrid (50% nano glass,50% polymer network)
The current study in agreement with Makkeyah F and Al A Nkily MM who studied the effect of different polishing systems on surface roughness of lithium disilicate ceramics and found an enhancement of surface topography with reduction in surface roughness after polishing process.[26]