title: Colour stability and opacity of resin cements and flowable composites for ceramic veneer luting after accelerated ageing.
abstract: OBJECTIVE
  Colour changes of the luting material can become clinically visible affecting the aesthetic appearance of thin ceramic laminates. The aim of this in vitro study was to evaluate the colour stability and opacity of light- and dual-cured resin cements and flowable composites after accelerated ageing.
  
  
  METHODS
  The luting agents were bonded (0.2 mm thick) to ceramic disks (0.75 mm thick) built with the pressed-ceramic IPS Aesthetic Empress (n=7). Colour measurements were determined using a FTIR spectrophotometer before and after accelerated ageing in a weathering machine with a total energy of 150 kJ. Changes in colour (ΔE) and opacity (ΔO) were obtained using the CIE L*a*b* system. The results were submitted to one-way ANOVA, Tukey HSD test and Student's t test (α=5%).
  
  
  RESULTS
  All the materials showed significant changes in colour and opacity. The ΔE of the materials ranged from 0.41 to 2.40. The highest colour changes were attributed to RelyX ARC and AllCem, whilst lower changes were found in Variolink Veneer, Tetric Flow and Filtek Z350 Flow. The opacity of the materials ranged from -0.01 to 1.16 and its variation was not significant only for Opallis Flow and RelyX ARC.
  
  
  CONCLUSIONS
  The accelerated ageing led to colour changes in all the evaluated materials, although they were considered clinically acceptable (ΔE<3). Amongst the dual-cured resin cements, Variolink II demonstrated the highest colour stability. All the flowable composites showed proper colour stability for the luting of ceramic veneers. After ageing, an increase in opacity was observed for most of the materials.
authors.affiliation: Professional and Technological Education Center, Federal University of Parana, R. Dr. Alcides Vieira Arcoverde, 1225, 81520-260 Curitiba, PR, Brazil.
authors.forename: Lucí Regina Panka
authors.initials: LR
authors.lastname: Archegas
authors.forename: Andrea
authors.initials: A
authors.lastname: Freire
authors.forename: Sergio
authors.initials: S
authors.lastname: Vieira
authors.forename: Danilo Biazzetto de Menezes
authors.initials: DB
authors.lastname: Caldas
authors.forename: Evelise Machado
authors.initials: EM
authors.lastname: Souza
mesh_terms: D000538:Aluminum Silicates; D000704:Analysis of Variance; D003116:Color; D003124:Colorimetry; D003188:Composite Resins; D003287:Contrast Media; D003776:Dental Porcelain; D003799:Dental Stress Analysis; D003801:Dental Veneers; D008027:Light; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D019279:Resin Cements; D012212:Rheology; D055116:Self-Curing of Dental Resins; D017550:Spectroscopy, Fourier Transform Infrared; D018709:Statistics, Nonparametric; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D003188:Composite Resins; D003287:Contrast Media; C075815:IPS-Empress ceramic; D019279:Resin Cements; D003776:Dental Porcelain