title: Photoconductive method for measuring light transmission to the root of metal-ceramic and all-ceramic restorations.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  The photoconductive method was proven to be a reliable technique for measuring the light transmitted through restorations into the adjacent tissue.
authors: School of Dentistry, National Yang-Ming University, Taipei, Taiwan.
authors: Yun-Lin
authors: YL
authors: Hsieh
authors: Yu-Lin
authors: YL
authors: Lai
authors: Hui-Lin
authors: HL
authors: Chen
authors: Cheng-Yuan
authors: CY
authors: Hung
authors: Xiu-Ling
authors: XL
authors: Chen
authors: Shyh-Yuan
authors: SY
authors: Lee
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D019187:Cadmium Compounds; D002858:Chromium Alloys / Q000737:chemistry; D003442:Crowns; D003738:Dental Cements / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D003804:Dentin / Q000033:anatomy & histology; D006801:Humans; D007180:Incisor; D008027:Light; D018020:Lithium Compounds / Q000737:chemistry; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D055095:Optics and Photonics / Q000295:instrumentation; D017680:Potassium Compounds / Q000737:chemistry; D011874:Radiometry / Q000295:instrumentation; D015203:Reproducibility of Results; D013440:Sulfides; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000145:classification; D014092:Tooth Root / Q000033:anatomy & histology*
chemical_list: D000538:Aluminum Silicates; D019187:Cadmium Compounds; D002858:Chromium Alloys; D003738:Dental Cements; C118557:Empress 2; C483026:In-Ceram Alumina; D018020:Lithium Compounds; D016876:Metal Ceramic Alloys; D017680:Potassium Compounds; D013440:Sulfides; C034939:cadmium sulfide; D003776:Dental Porcelain; C016447:feldspar