Photoconductive method for measuring light transmission to the root of metal–ceramic and all-ceramic restorations

Hsieh, Yun-Lin; Lai, Yu-Lin; Chen, Hui-Lin; Hung, Cheng-Yuan; Chen, Xiu-Ling; Lee, Shyh-Yuan

doi:10.1016/j.dental.2008.01.015

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Volume 24, Issue 9 , Pages 1230-1235, September 2008

Photoconductive method for measuring light transmission to the root of metal–ceramic and all-ceramic restorations

Yun-Lin Hsieh
- School of Dentistry, National Yang-Ming University, Taipei, Taiwan
Yu-Lin Lai
- School of Dentistry, National Yang-Ming University, Taipei, Taiwan
- Dental Department, Taipei Veterans General Hospital, Taipei, Taiwan
Hui-Lin Chen
- Dental Department, Taichung Veterans General Hospital, Taichung, Taiwan
Cheng-Yuan Hung
- School of Dentistry, National Yang-Ming University, Taipei, Taiwan
Xiu-Ling Chen
- School of Dentistry, National Yang-Ming University, Taipei, Taiwan
Shyh-Yuan Lee
- School of Dentistry, National Yang-Ming University, Taipei, Taiwan
- Dental Department, Taipei Veterans General Hospital, Taipei, Taiwan
- Corresponding author at: School of Dentistry, National Yang-Ming University, Taipei 112, Taiwan. Tel.: +886 2 28267235; fax: +886 2 28264053.

Received 9 April 2007; accepted 17 January 2008.

Abstract

Objectives

In this study, the authors attempted to develop a photoconductive method for measuring light transmission through a crown restoration to the root dentin; metal–ceramic crowns with four coping designs (metal collar, and metal framework ending 0, 1, and 2mm coronal to the axiogingival line angle) and two all-ceramic crowns (Empress II and In-Ceram Alumina) were compared.

Methods

According to pre-registered templates, 36 crowns were fabricated for an extracted central incisor. A cadmium sulfide (CdS) photoconductive cell was secured onto the root of a tooth, which was fixed in a light box. The validity and reliability of the experimental design were verified, and the impedance of the cell was recorded when the crowns were placed on the prepared tooth with or without try-in pastes under a constant luminance.

Results

A significant correlation (r=−0.99, p<0.001) was found between the light intensity and impedance of the CdS cell, and a 1.15% coefficient of variation between repeated measurements was observed. In this study, Empress II crowns had the smallest impedance, indicating that they provided the best light transmission. Conventional metal–ceramic crowns had the least light transmission, which was significantly improved by reducing the metal collar (p<0.05). The framework of metal–ceramic crowns which ended 2mm coronal to the axiogingival line angle showed as much light transmission as the In-Ceram crowns. The impedance increased when try-in pastes were employed in all test groups.