Influence of ceramic thickness on masking ability of discolored substrates

Method: 25 ceramic disks (10 mm diameter, thickness 0.3, 0.6, 0.9, 1.2, 1.5mm), (n=5), of IPS e.max® Press MO 0 (Ivoclar Vivadent) were evaluated upon five shades (ND1-ND5) of light cured composite  material that simulate the shade of prepared teeth (IPS Natural Die Material Kit, Ivoclar Vivadent) ( disks 10mm diameter, 5mm thickness). Color parameters L*, a*, b* were recorded by using a spectrophotometer (VITA Easyshade® Advance, VITA Bad Säckingen, Germany), for each natural die composite disk (“reference”=R) and for each ceramic disk against the composite disks (“ceramic on reference”=CR). The data were taken into account when 3 similar measurements were obtained. Color differences DE between the R and the respective CR samples were calculated. Statistical analysis was performed in order to assess: 1. correlation between the ceramic disk thickness and its masking abilities; 2. mean DE distribution in each thickness group.

Result: The DE overall values range 8,84 to 48,93. 1. Considering the relationship between the thickness of ceramics and the masking abilities , strong statistical correlation was found between the ceramic disk thickness and  DE in the case of each composite shade (ND1-r=0,79, ND2-r=0,97, ND3-r=0,92, ND4-r=0,92, ND5-r=0,89). 2. For the CR upon various degrees of discolored R, DE vary less for disks with reduced thickness(0,3mm – DE=9,45-18,97, 0,6mm – DE=8,84-34,30, 0,9mm - DE=9,59-41,52, 1,2mm - DE=1,16-46,36, 1,5mm – DE =12,54-48,93).

Conclusion: 1. Color masking capacities of IPS e.max® Press MO ceramics increase with the increased thickness of the ceramic layer, with a more important variation in the range of reduced thickness. 2. More discolored substrates are less successfully masked by ceramic layers of the same thickness.