Alaa S. El-Ashkar, Maha A. Taymour And Adel M. El-Tannir,

ABSTRACT
Statement Of The Problem: The Precision Of Fit Of Chair-side CAD-CAM Zirconia Reinforced Lithium Silicate Crowns Is Still Under Research And The Effect Of Post Milling Protocol On The Marginal Adaptation Is Not Yet Clearly Stated In Literature.

Purpose: The Aim Of This Study Was To Evaluate The Marginal Adaptation Of Fully Crystallized Versus Partially Crystallized Zirconia Reinforced Lithium Silicate (ZLS) Ceramic Computer-aided Design/computer-aided Manufacturing (CAD/CAM) Fabricated Crowns Using Stereomicroscope.

Materials and Methods: A Total Of 16 Ceramic Zirconia Reinforced Lithium Silicate Crowns. They Were Divided Into Two Groups According To The Degree Of Crystallization. The Marginal Adaptation Of The Fully Crystallized Zirconia Reinforced Lithium Silicate CELTRA DUO (Dentsply, Sirona, Germany), Were Compared With The Partially Crystallized Zirconia Reinforced Lithium Silicate VITA SUPRINITY (VITA Zahnfabrik,Germany) After Its Crystallization. The 16 Crowns (n=8 Each Group) Were Fabricated Using A Chair Side CAD-CAM System. The Crowns And Die/crown Assembly Were Viewed Under Stereomicroscope. 36 Measurements Were Made For Each Crown, 9 Measurements On Each Surface. The Vertical Marginal Gap Was Directly Viewed And Measured Using Stereomicroscope. Data Were Recorded And Statistically Analyzed Using The T- Test And Two-way ANOVA Test. The Significance Level Was Set At P ? 0.05.

Results: It Was Found That Partially Crystallized ZLS Crowns Recorded Statistically Significant Higher Marginal Gap Mean Value (99.52 ? 6.67 ?m) Than Fully Crystallized ZLS Crowns (85.88?3.79?m), (P=0.0002< 0.05). Conclusion: Within The Limitations Of This In-vitro Study, The Vertical Marginal Gap Values Were Within A Clinically Acceptable Range For All Tested Crowns. The Fully Crystallized ZLS Crowns Showed Better Marginal Adaptation Than The Partially Crystallized ZLS Crowns.