Effect of core ceramic grinding on fracture behaviour of bilayered lithium disilicate glass-ceramic under two loading schemes.
OBJECTIVE
The purpose of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered lithium disilicate glass-ceramic (LDG) under two loading schemes.


METHODS
Interfacial surfaces of sandblasted LDG disks (A) were ground with 220 (B), 500 (C) and 1200 (D) grit silicon carbide (SiC) sandpapers, respectively. Surface roughness and topographic analysis were performed using a profilometer and a scanning electron microscopy (SEM), and then underwent retesting after veneer firing. Biaxial fracture strength (σf) and Weibull modulus (m) were calculated either with core in tension (subgroup t) or in compression (subgroup c). Failure modes were observed by SEM, and loading induced stress distribution was simulated and analyzed by finite element analysis. Statistical data analysis was performed using Kruskal-Wallis, one-way ANOVA, and paired test at a significance level of 0.05.


RESULTS
As the grits size of SiC increased, LDG surface roughness decreased from group A to D (p<0.001), which remained unchanged after veneer firing. No difference in σf (p=0.41 for subgroups At-Dt; p=0.11 for subgroups Ac-Dc), m values as well as failure modes was found among four subgroups for both loading schemes. Specimens in subgroup t showed higher σf (p<0.001) and m values than subgroup c. Stress distribution between loading schemes did not differ from each other. Cracks, as the dominant failure mode initiated from bottom tensile surface. No sign of interfacial cracking or delamination was observed for all groups.


CONCLUSIONS
Technician grinding changed surface topography of LDG ceramic material, but was not detrimental to the bilayered system strength after veneer application. LDG bilayered system was more sensitive to fracture when loaded with veneer porcelain in tension.


CONCLUSIONS
Within the limitations of the simulated grinding applied, it is concluded that veneer porcelain can be applied directly after technician grinding of LDG ceramic as it has no detrimental effect on the strength of bilayered structures. The connector areas of LDG fixed dental prosthesis are more sensitive to fracture compared with single crowns, and should be fabricated with more caution.
Department of Prosthodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangdong Provincial Key Laboratory of Stomatology, Guangzhou, China.
Xiao-Dong
XD
Wang
Institute of Stomatological Research, Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China.
Yu-Tao
YT
Jian
Department of Prosthodontics, School of Dentistry, Albert-Ludwigs University, Freiburg, Germany.
Petra C
PC
Guess
Department of Prosthodontics, School of Dentistry, Albert-Ludwigs University, Freiburg, Germany.
Michael V
MV
Swain
Department of Metallic Materials Science and Engineering, School of Materials Science and Engineering, South China University of Technology, Guangzhou, China. Electronic address: mexzhang@scut.edu.cn.
Xin-Ping
XP
Zhang
Department of Prosthodontics, Guanghua School of Stomatology, Sun Yat-sen University, Guangdong Provincial Key Laboratory of Stomatology, Guangzhou, China. Electronic address: zhaoke@mail.sysu.edu.cn.
Ke
K
Zhao
D017554:Carbon Compounds, Inorganic / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D045662:Dental Etching / Q000379:methods*; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D003801:Dental Veneers; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006358:Hot Temperature; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D061848:Optical Imaging / Q000379:methods; D010316:Particle Size; D018583:Pliability; D011897:Random Allocation; D017655:Silicon Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties
D017554:Carbon Compounds, Inorganic; D003764:Dental Materials; C508050:IPS e.max Press; D017655:Silicon Compounds; C493120:lithia disilicate; D003776:Dental Porcelain; C023506:Glass ceramics; C022088:silicon carbide
Dental porcelain; Finite element analysis; Fractography; Fracture strength