The effect of coping/veneer thickness on the fracture toughness and residual stress of implant supported, cement retained zirconia and metal–ceramic crowns
Dental Materials
Volume 28, Issue 10 , Pages e250-e258, October 2012
Abstract
Objectives
The aim of the work was to assess the influence of coping and veneer thickness on the fracture resistance of porcelain–metal and porcelain–zirconia crowns in a clinically representative model.Methods
A total of 30 zirconia and 30 precious metal copings were fabricated. There were 10 copings in each group of 0.5
mm, 1mm and 1.5mm
thickness. Each group of 10 was further divided into two groups with a
total thickness of three and four millimeters inclusive of veneering
ceramic. The specimens were cemented to a titanium abutment with zinc
oxide cement and tested using a microindenter. Crack length, hardness
and spalling (chipping) were recorded using an optical microscope from
which fracture toughness was calculated.Results
Kruskal–Wallis tests and simple linear regression analysis were used to analyze the results, revealing a significant difference between zirconia (ZrCC) and metal (MCC) specimens for crack length. 0.5mm
coping thicknesses and MCC specimens showed the highest fracture
toughness values. Simple linear regression analysis showed a limited
effect of the overall thickness or veneer thickness on crack length and
hardness; however coping thickness showed a positive correlation with
both. Spalling was higher in zirconia specimens.Residual stresses were higher for ZrCC specimens and showed a positive correlation with crack length. The ratio of veneer to coping thickness was negatively correlated with residual stress.
Comments