Effect of thermocycling and design parameters on the mechanical properties of dental ceramics

PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.Thesis (D.Sc.D.)--Boston University, Henry M. Goldman School of Dental Medicine, 2006 (Dept. of Restorative Sciences and Biomaterials).Includes bibliographical references: leaves 96-98; 202-207.Introduction: Environmental conditions may negatively affect the mechanical properties of dental restorative materials. Objective: The objective was to evaluate the effect of thermocycling on the flexural strength and surface roughness of porcelain and composite resin dental restorative materials. Materials and methods: Eleven conventional dental porcelains (Alpha porcelain, Omega 900, Response, VMK 95, Finesse, Symbioceram, LFC, d.Sign, Empress classic and Empress 2) and 4 machinable restorative dental materials (Vita Mark II, Procad, Paradigm Z100 and RIPC) were tested. A total of 300 bar specimens were fabricated, 220 from the conventional group fabricated by using hand condensation of a powder-water slurry in a silicone mold. The specimens were then sintered according to manufacturers' recommendations. The other 80 specimens (machinable group) were sectioned from blocks. The test surfaces in maximal tension were polished to a mirror-like finish. Twenty specimens of each material were randomly subdivided into 2 groups, a non-themocycled group (n=10), a themocycled group (n=10) (300 thermocycles between 5 and 55 degrees C). A 4-point-bending test was used to test the conventional porcelains, and 3-point-bending test was used to test the machinable materials with an Instron machine and a crosshead speed of 0.5 mm/min. Results: In the 4-point-bending test, Omega 900 ceramics recorded the highest mean flexural strength (115 [plus or minus] 12.9 MPa), followed by Response (110 [plus or minus] 19 MPa), Empress 2 (90 [plus or minus] 9 MPa), d.Sign (88 [plus or minus] 4 MPa), LFC (86 [plus or minus] 25 MPa), Alpha porcelain (83 [plus or minus] 10 MPa), VMK 95 (81 [plus or minus] 10 MPa), Empress classic (76 [plus or minus] 5 MPa), Symbioceram (73 [plus or minus] 7 MPa), Finesse (68 [plus or minus] 11 MPa), and Soft Spar (63 [plus or minus] 4.9 MPa) materials. Of the machinable materials, Procad ceramics had the highest mean flexural strength (177.5 [plus or minus] 34.9 MPa), followed by Paradigm Z100 (175 [plus or minus] 20.7 MPa), RTPC (129 [plus or minus] 5.5 MPa), and Vita Mark II (117 [plus or minus] 5.6 MPa) materials. No differences were observed for the surface roughnesses of the tested materials. No statistically significant effect was recorded on the flexural strength and surface roughness of the materials before and after thermocycling. Conclusion: Thermocycling did not affect the flexural strength, or the surface roughness of the tested materials