DISCUSSION
fracture, discoloration, Ceramic veneer failure
SECONDARY, CAVITY
Ceramic with high crystal content, such as yttria‐stabilized tetragonal zirconia polycrystal (TZP‐Y), is primarily engaged in manufacturing structures of fixed crowns and bridges because of its high fracture toughness properties. Recently, conversely, zirconia has witnessed a plethora of changes to its microstructure, which increased its translucency without losing its fracture resistance. Henceforth, its clinical utilizations are expanded. Consequently, translucent zirconia is widely considered to be an esthetic material, particularly in making anterior and posterior crowns and bridges, along with veneers.This type of ceramic has been found to offer incredibly satisfactory esthetic outcomes when used in veneers; it reduces the risk of layered porcelain fracture throughout clinical applications and experimentation. TZP‐Y affords lower cost compared to other used materials; zirconia structures provide sufficient areas of shading to hide the underlying discolored abutment due to its high density and homogeneity even when the region thicknesses are scarce. Hence, the idea of research revolved originally around evaluating the clinical performance of veneers manufactured from both e.max and high‐translucency zirconia. The investigators of this current study faced limited clinical research in the medical literature addressing the use of zirconia in veneer manufacture. Such a shortcoming was accompanied by another lack of clinical research that studied the clinical evaluation of the esthetic, functional, and biological aspects of veneers also manufactured from these two materials, namely the Ceramic veneer failure can be categorized as either absolute or relative. Absolute failure is when there are irreparable cracks that make the veneer unacceptable and require a complete remake. Relative failure, on the other hand, is when there are cracks that are still clinically acceptable or when the ceramic attachment fails but can be rebonded (Guess & Stappert, One common issue in dentistry is bonding failure when using resin cement to attach ceramic veneers, regardless of whether the veneers are made of e‐max ceramic or cubic zirconia. This can be caused by various factors, such as microleakage, secondary carriers resulting from the dissolution of resin cement, and the dissolution of bonding agents due to chemical and mechanical factors within the oral cavity (Huang et al., On the other hand, the effectiveness and polymerization time of a light cure device has a significant impact on the curing process of resin cement (Rasetto et al., In our research, we noted that there were no de‐bonding occurrences in either group. This could be attributed to following an accurate cementation protocol, and case selection which had a good occlusion and a precise fit of the ceramic veneers onto the enamel surfaces, which exhibited a comparable elastic modulus to the veneers. Moreover, the exceptional robustness and mechanical precision of the glass ceramics, fortified with lithium disilicate crystals and zirconia porcelain, further amplified these outcomes.When evaluating the surface discoloration criteria in this study, no discoloration was observed in the veneers' surface in both study groups (e.max and zirconia), except for two veneers in the (e.max) group after 3 months of observation. The discoloration was simple and could easily be removed by polishing: the surface of e.max veneers was more discolored compared with the zirconia surface.No discoloration was observed in the veneers' margins in both study groups through the observation periods. This agrees with Ozel and Aykor's study, in which it was found that there was no marginal discoloration of lithium disilicate crystal (e.max) veneers (Nejatidanesh et al., Color matching and translucency were good in both of the study groups, namely e.max and zirconia. The results of our study disagreed with Nejatidanesh et al., who found that a large percentage of the veneers (IPS e.max) had discoloration over time. The reason was attributed to the fact that the discoloration occurred on the adjacent natural teeth, not on the veneers (Nejatidanesh et al., The bonding to zirconia has been a focus of scientific research during the past period. Various treatment methods have been used: sandblasting using aluminum oxide, nanostructured alumina coating, tribochemical silica coating followed by silanization, and application of resin cement containing 10‐MDP monomer, among others. In this current study, there were no cases in which fracture or loss of veneer bonding was verified in either of the study groups. The results of this study come in accordance with Nejatidanesh et al. They did not record any fracture or cracking in the e.max veneers; this was ascribed to the high flexural strength of the material used, which can reach up to 420 MPa (Nejatidanesh et al., Our results also agreed with Nejatidanesh et al. (