Translucency of IPS e.max and cubic zirconia monolithic crowns

doi:10.1016/j.prosdent.2017.09.007

The Journal of Prosthetic Dentistry

Volume 120, Issue 2, August 2018, Pages 269-275

Presented at the 94th general meeting of the International Association of Dental Research and received the Frechette Award, materials category, Seoul, Republic of Korea, June 2016.

https://doi.org/10.1016/j.prosdent.2017.09.007 Get rights and content

Abstract

Statement of problem

Although several monolithic zirconia ceramics have recently been introduced, the need for improved optical properties remains. The newest cubic-zirconia has been claimed to have optimal translucency characteristics for esthetic restorations.

Purpose

This in vitro study evaluated the optical properties of novel cubic ultratranslucent (UT) and supertranslucent (ST) zirconia by comparing them with lithium disilicate (L-DIS) glass-ceramic for the manufacture of monolithic computer-aided design and computer-aided manufacturing (CAD-CAM) molar crowns.

Material and methods

The UT and ST multilayered zirconia and the low-translucency grade L-DIS were milled. Eighty monolithic crowns were made from 2 CAD files, corresponding to thicknesses of 1.0 and 1.5 mm, and subdivided (n=20) into 4 groups: UT1.0, UT1.5, ST1.0, and L-DIS1.5. All groups were shaded using A2 color standard. Translucency of the crowns was measured by total transmission, using a photoradiometer in a dark chamber; furthermore, the contrast ratio was analyzed using a dental spectrophotometer applied to the buccal surface of the crowns. Data were analyzed using the Kruskal-Wallis and post hoc multiple Mann-Whitney U tests with Bonferroni correction (α=.05 divided by the number of tests performed in each set).

Results

When the ceramic types were analyzed, using total transmission and contrast methods, they showed significantly different translucency levels: UT1.0>ST1.0>UT1.5>L-DIS1.5 (total transmission P<.001). Contrast ratio evaluation yielded similar results (P≤.006); however, the differences between ST1.0 and UT1.5 were not significant.

Conclusions

Both the ST1.0 and UT1.0 crowns, even at the maximum thickness tested (UT1.5), showed significantly higher translucency than L-DIS. Zirconia translucency was improved by eliminating the tetragonal phase, which is responsible for the toughening effect; thus, further studies are advocated to investigate the mechanical resistance of cubic zirconia.

Section snippets

Material and Methods

A mandibular right first molar was scanned with an intraoral scanner (Lava Chairside Oral Scanner; 3M ESPE) to obtain a standard tessellation language (STL) file of the tooth. Using CAD software (Dental System; 3Shape), the virtual tooth crown was digitally reduced, first by decreasing the height of the cusp tips and central fossae by 1.0 mm and then by extending the reduction to the axial walls. Once the 1.0-mm STL file was obtained, further reduction by 0.5 mm created the second 1.5-mm file;

Results

Both the Tt and CR methods differed significantly between groups. Tt values decreased in the following order: UT 1.0 > ST 1.0 > UT 1.5 > L-DIS 1.5; all differences between groups were significant (P<.001). When analyzed using CR, the lowest value (highest translucency) was found for the UT 1.0 group, whereas L-DIS 1.5 showed the highest CR (P≤.006). No statistically significant differences were observed between the ST 1.0 and UT 1.5 groups (P=.099).

The Tt and CR values are summarized in Tables 2

Discussion

Because the crowns had different levels of translucency when measured using the Tt method (P<.001), the null hypothesis was rejected. Using CR analysis, the null hypothesis was partially rejected as only the ST 1.0 and UT 1.5 groups were not significantly different (P=.099).

No consensus has been reached in dental studies about the different methods adopted to quantify translucency.⁶ Calculation of the translucency parameter is one of the most common approaches to evaluating light interactions

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

1.
Tt evaluation showed that both Katana ST and UT cubic zirconia crowns are more translucent than L-DIS crowns (LT) when a white light beam with predominantly blue-violet wavelengths is used (P<.001),
2.
CR analysis closely confirms the Tt results (P≤.006),
3.
Owing to their higher translucency, cubic zirconia ceramic appears to be a promising material for highly esthetic, anatomic contour restorations.

Acknowledgments

The authors wish to thank Dr Antonio Corradi, Scientific Manager (Kuraray Europe Italia S.r.l) for materials supply and technical assistance; and Mr Alfredo Rizzati, Dental Technician, Certified InLab Trainer Sirona, (Digital Dentists Unite and Academy of Digital Dentistry, Italy) and Mr Davide Cantoni, New Ancorvis Srl, Bologna, Italy, for the ceramic crowns milling.

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Research and EducationTranslucency of IPS e.max and cubic zirconia monolithic crowns

Abstract

Statement of problem

Purpose

Material and methods

Results

Conclusions

Section snippets

Material and Methods

Results

Discussion

Conclusions

Acknowledgments

J Prosthet Dent

J Prosthet Dent

J Prosthodont

J Dent

J Prosthet Dent

J Prosthet Dent

Dent Mater

Dent Mater

Dent Mater

Acta Biomater

Scripta Mater

J Prosthet Dent

Dent Mater

J Eur Ceram Soc

J Eur Ceram Soc

J Prosthet Dent

Acta Biomater

Dent Mater

Research and Education
Translucency of IPS e.max and cubic zirconia monolithic crowns