الفهرس 
Wear characteristics and clinical performance of lithium-silicate versus monolithic zirconia crowns
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Abstract
Aim: The aim of the present study was to evaluate: The wear characteristics of lithium-silicate crowns in comparison to monolithic zirconia crowns after one year of function. The quality of the overall restorations was also evaluated at baseline and after one year according to the modified United States Public Health Service (USPHS) criteria, including the following outcomes: Color match, sensitivity of the natural tooth opposing to crown, marginal adaptation, as well as, anatomic form, integrity of the restoration, secondary caries and retention.The gingival and periodontal response to the tested all- ceramic crowns was also assessed at baseline and 1 year follow up period.Methodology A total of twenty-two patients (age range 21-45 Y) requiring full-coverage restorations for endodontically treated 1st molars opposed by natural antagonistic teeth were selected for the present study. The patients were divided into two groups according to the crown materials (N=11 patients per each group): group I (Comparator group) fabricated from monolithic zirconia crowns (STML MZ) and group II (Intervention group) fabricated from lithium silicate crowns (Obsidian). After cementation of the crowns and after one year of follow up, vinyl polysiloxane impressions of the crowns and their antagonist teeth were taken, and replica stone casts were fabricated. For surface roughness quantification nalysis of replica casts, the optical profilometer was used. The replicas (baseline and after one year) were scanned and digitally superimposed in order to evaluate the wear of the crowns and their antagonist{u2019}s enamel. The quality of the overall restorations was evaluated according to (USPHS) criteria at the same timeframes as gingival and periodontal health were also evaluated. All data was collected,checked, revised, tabulated and entered into the computer. Statistical analysis was performed by using t-test vii Comparison between 2 groups (qualitative data) was performed by using the Chi square test.Results: Statistically insignificant difference in the surface roughness between the both tested groups at base line and after 1 year follow up. Concerning the results of enamel wear (vertical loss in mm) opposing both ceramic crowns after 1 year of cementation, the results showed that the amount of enamel wear opposing STML monolithic zirconia crowns was (0.0655 ± 0.0116 mm), which was significantly higher than the amount of enamel wear opposing lithium silicate crowns which was (0.0457± 0.0099 mm) p<0.05