الفهرس 
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Abstract
Porcelain laminate veneers (PLVs) were introduced in 1980 as a result of continuous demand of esthetics. PLVs have undergone a continuous evolution of both techniques and materials. They have become the corner stone on esthetic dentistry, due to its characteristics of biocompatibility, longevity, conservation and maintaining of tooth structure.
Three preparation designs of PLVs have been introduced in regard to the incisal edge, but in this study feather edge and overlapped edge designs were used.
Several new ceramic materials have been introduced to provide optimal characteristics of optical, physical and biological properties.
VITA Enamic has been introduced as a hybrid ceramic that has a dual network structure and combines the best properties of ceramic and composite materials. Also, Super high translucent zirconia has been developed that have undergone many changes in microstructure and composition to increase their translucency to be used as an esthetic material in manufacturing crown, veneers and ultrathin veneers.
Microleakage affects the durability of PLVs and it is affected by the cementation, preparation design and type of restoration.
The current study was designed to assess the effect of two designs of preparation and two different ceramic materials on the microleakage of laminate veneer at the incisal and cervical margins.
The following materials were used in this study:
-Two types of commercially available ceramics (Vita Enamic –Super high translucent Zirconia).
-Self adhesive resin cement.
Forty recently extracted caries free human upper central incisors were collected, cleaned then disinfected. The teeth were divided randomly regarding the design of preparation into 2 groups n=20.
• group I : design 1 (feather edge ) n=20
• group II : design 2 (overlapped incisal edge) n=20
Each group further divided into 2 subgroups according to the material (Vita Enamic and High translucent zirconia) n=10.
• Subgroup En: Vita Enamic material.
• Subgroup Zr: Super-high translucent zirconia material.
According to the thermal treatment each subgroup was divided into 2 classes n=5.
- Control class: it represented five teeth that were not subjected to any thermocyling procedure.
- Thermocycled class: it represented five teeth which were subjected to thermocycling procedure.
Then the laminate were designed and milled by CAD CAM system. Vita Enamic veneers were cleaned then etched using hydrofluoric acid followed by silane coupling agent application.
Super high translucent zirconia veneers were sandblasted by aluminum oxide particles 50 µm.
The porcelain laminate veneers were cemented to the prepared teeth using self-adhesive resin cement, thermocycled, stored in fuchsine dye for 24 h and then sectioned labiopalatally. The samples were investigated incisally and cervically for dye penetration by the stereomicroscope. The microleakage was measured in microns. The obtained data were then statistically analyzed.
Using the independent samples T test and 3 way Anova test, the results showed that:
- There was significant increase in incisal microleakage of overlapped edge design than feather edge design in both control and thermocycled groups using both Enamic and Zirconia material.
- There was significant increase in incisal and cervical microleakage of Zirconia material than Enamic for both designs in both control and thermocycled classes.
Conclusions
Within the limitation of this study, the following conclusions could be drawn:
- Feather edge preparation showed better marginal sealing than overlapped design.
- Control groups showed a better marginal sealing than thermocycled groups in both designs and both materials.
- Vita Enamic has better marginal sealing than Zirconia.
Recommendations for further investigations:
• Further studies using different ceramic materials.
• Using different designs of preparation of laminate veneers.
• Using different artificial aging methods.
• Further in-vitro studies together with long term in-vivo investigation are needed to confirm the clinical implication of these findings.
Clinical implications:
- Feather edge design is recommended over overlap design except in some clinical situations as presence of diastema, the need for enlarging the teeth size.
- Hybrid ceramic is recommended over Zirconia material except in some clinical situations as the need for enforcement of the restored teeth and the presence moderate occlusal stresses on the laminate veneers.