Objetivo: avaliar a resist?ncia ? fratura de coroas cer?micas monol?ticas com diferentes espessuras e cimentadas sobre pilar s?lido e tiBase. As hip?teses apresentadas s?o que (i) a presen?a do orif?cio do parafuso de fixa??o diminui a resist?ncia ? fratura das coroas, (ii) o material restaurador influencia na resist?ncia ? fratura, (iii) a espessura da restaura??o influencia na resist?ncia ? fratura das restaura??es. Materiais e m?todos: Um total de 64 coroas de segundo pr?-molar superior foram confeccionadas para os pilares S?lido e Variobase C? (tiBase) sobre o an?logo do implante Straumann Tissue Level. As coroas foram confeccionadas em dissilicato de litio (IPS e.max CAD) e zirc?nia (Incoris ZI) com 0,5 mm e 1,5 mm de espessura na face oclusal, e divididas em 8 grupos (n=8): SE05, SE15, SZ05, SZ15, VE05, VE15, VZ05, VZ15. As coroas foram cimentadas com cimento resinoso e o acesso ao parafuso restaurado com resina composta. Ap?s ciclagem mec?nica, os corpos de prova foram submetidos ao ensaio de resist?ncia ? fratura na m?quina de ensaio universal e a for?a m?xima registrada em Newtons (N). Os resultados obtidos foram submetidos ao teste de Shapiro-Wilk seguido de ANOVA 3-way e Tukey (a= 5%). Resultados: SZ15: 5368,6 N ? 536,74 A; SZ05: 4809,8 N ? 857,55 A; SE15: 2068,8 N ? 359,77 B; SE05: 1887,4N ? 276,94 B; VZ15: 1935,5N ? 274,51 B; VZ05: 1759,4 N ? 334,34 B; VE15: 963,5 N ? 198,92 C; VE05: 924,8 N ? 152,01 C. Conclus?es: A presen?a do canal de acesso ao parafuso reduziu pela metade a resist?ncia ? fratura das coroas quando comparados com as coroas cimentadas sobre pilar s?lido. A zirc?nia Incoris ZI apresentou maior resist?ncia ? fratura do que o IPS e.max CAD independente do pilar e da espessura. As diferentes espessuras das restaura??es tiveram pouca influ?ncia na resist?ncia ? fratura. Objective: to evaluate the fracture strength of monolithic ceramic unit crowns with different thickness and cemented on solid abutment and tiBase. The hypotheses presented are that (i) the presence of the fixing screw hole decreases the crown fracture strength, (ii) the restoring material influences the fracture resistance, (iii) the restoration thickness influences the fracture resistance of the restorations. Materials and methods: A total of 64 upper second premolar crowns were made for the solid abutment and Variobase C? abutment over the implant analog Straumann Tissue Level. The crowns were made of lithium dissilicate (IPS e.max CAD) and zirconia (Incoris ZI) with 0,5 mm and 1,5 mm thickness in the occlusal, and divided into 8 groups (n = 8): SE05, SE15, SZ05, SZ15, VE05, VE15, VZ05, VZ15. The crowns were cemented with resin cement and the screw access restored with composite resin. After mechanical cycling, the specimens were submitted to the test of fracture resistance in the universal test machine and the maximum force recorded in Newtons (N). The results were submitted to the Shapiro-Wilk test followed by 3-way ANOVA and Tukey (a= 5%). Results: SZ15: 5368,6 N ? 536,74 A; SZ05: 4809,8 N ? 857,55 A; SE15: 2068,8 N ? 359,77 B; SE05: 1887,4N ? 276,94 B; VZ15: 1935,5N ? 274,51 B; VZ05: 1759,4 N ? 334,34 B; VE15: 963,5 N ? 198,92 C; VE05: 924,8 N ? 152,01 C. Conclusions: The presence of the screw access channel reduced in half the fracture strength of the crowns when compared to the crowns cemented on a solid abutment. Incoris ZI showed higher fracture resistance than the IPS e.max CAD independent of the abutment and thickness. The different thicknesses of the restorations had little influence on fracture resistance. Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES