Patient Satisfaction and Clinical Performance of Ultra-translucent Multi-layer Monolithic Zirconia and Lithium Disilicate Ceramic Laminate Veneers. Randomized Control Clinical Trial

Preservation of tooth structure and prevention of needless tooth structure removal are basic and important principles in prosthodontics. Striving to achieve the cosmetic aspect is also a basic requirement, especially in the modern world Fawakhiri et al. (2023) Porcelain laminate veneers are one of the most popular cosmetic and minimally invasive dental treatments. These veneers can change the color, contour, shape, and size of the teeth they cover and bond to tooth structure with the use of adhesive cements. A thin layer of enamel (0.5-.8 mm) is removed to provide space for each veneer Piemjai and Donpinprai (2023) Several ceramic materials are currently indicated for veneers: lithium disilicate, feldspathic ceramic, feldspathic reinforced with leucite, fluorapatite, and lithium silicate reinforced with zirconia. All of these ceramics exhibit high translucency characteristics due to the high content of glassy matrix in their composition, thus providing highly satisfactory esthetics in addition to excellent adhesion to resin cement through the conditioning with hydrofluoric acid (4%-10%) followed by silanization Souza et al. (2017) Lithium disilicate ceramics belong to the silica-based ceramics family. They are commonly used for the fabrication of laminate veneers owing to their excellent optical properties, including their superior translucency and strong bonding to the tooth enamel surface when etched with hydrofluoric acid and then silanized Ojeda et al. (2023) Longevity is one of the most important factors to predict the survival and success of restorations. Many longitudinal clinical studies have evaluated the performance of ceramic veneer restorations and have confirmed good clinical performance, excellent aesthetics, and a high level of patient satisfaction. Major clinical complications commonly resulting in the failure of ceramic veneer restorations are fracture and debonding (Monaraks, 2018) The long-term clinical success of ceramic-based restorations is strongly dependent on their retention to teeth or abutment substrates by using adhesive systems and resin-matrix cements in vitro research has shown that load-to-fracture values of monolithic zirconia are higher than those of LS2; the latter, in turn, are higher than those of ZLS Zarone et al. (2019) ,(Souza et al., 2023) 6 The excellent biocompatibility and superior mechanical properties of zirconium dioxide (zirconia) ceramics make them a material of choice in prosthetic dentistry. Nevertheless, zirconia ceramics have not been used for the fabrication of laminate veneers because the opaqueness and low translucency of zirconia ceramics yield undesirable esthetic results. Due to the absence of any glassy matrix, zirconia is free from silica and, consequently, cannot be conditioned with conventional acid etching techniques, differently from glass-ceramics. Kusaba, Kosuke et al., (2018) , Zarone et al. (2019) Lately, the ultra-translucent multilayered zirconia has been introduced to the market. This material structured to replicate the naturality of teeth according to each anatomical region, keeping translucency at the incisal edge and a higher opacity at the cervical area. The multilayer blanks are pre-layered and thus contain different shades. There is scientific evidence reporting that the darker the color the higher the degree of opacity, that's to say the lower the translucency becomes. The color of the blanks is increasingly lighter and thus more translucent towards the incisal area. The dental technician can use CAD software to help to determine color sequences and intensities by positioning the constructed restoration in the blank. One advantage resulting from the combination of highly esthetic (color and translucency values are similar to those of natural teeth) and highly stable materials is better treatment with restorations with low space requirements. This Ultra-translucent Zirconia ceramic veneers have a minimum thickness of 0.1-0.3 mm, a more conservative option than glass-ceramic restorations Alqutaibi et al. (2022), Gomes et al., (2022), ("Three Generations of Zirconia: From Veneered to Monolithic. Part I.," 2017)

Inclusion criteria

1- Age between 18 and 50 years. 2. Absence of abnormal functional habits such as bruxism. 3. Good condition of gingival and periodontal tissues. 4. Good oral health. 5. A clear indication for patients for treatment with ceramic laminate veneers: Presence of diastema, moderate discolored dental restorations, slight modification of color in the discolored teeth, and modification of shape and sizes of the teeth.

• Patient commitment for attending follow up session

Exclusion criteria

• Age under 18 years
• Bad oral hygiene
• Dysfunctional habits and bruxism
• Periodontal diseases
• High risk of caries
• Inadequate enamel for bonding
• Extreme staining and color change in tooth -