title: Porcelain monolayers and porcelain/alumina bilayers reinforced by Al2O3/GdAlO3 fibers.
abstract: OBJECTIVE
  This work tested the effect of the addition of Al(2)O(3)/GdAlO(3) longitudinal fibers in different contents to veneering porcelain of two dental all ceramic systems.
  
  
  METHODS
  Fibers (0.5 mm diameter) obtained by the Laser Heated Pedestal Growth (LHPG) method were added to bar-shaped specimens made by veneer porcelain (monolayers) or both the veneer and the core ceramic (bilayers) of two all-ceramic systems: In-Ceram Alumina-glass infiltrated alumina composite (GIA) and In-Ceram 2000 AL Cubes-alumina polycrystal (AP) (VITA Zahnfabrik). The longitudinal fibers were added to veneering porcelain (VM7) in two different proportions: 10 or 17 vol%. The bars were divided into nine experimental conditions (n=10) according to material used: VM7 porcelain monolayers, VM7/GIA, VM7/AP; and according to the amount of fibers within the porcelain layer: no fibers, 10 vol% or 17 vol%. After grinding and polishing the specimens were submitted to a three point bending test (crosshead speed = 0.5 mm/min) with porcelain positioned at tensile side. Data were analyzed by means of one-way ANOVA and a Tukey's test (α=5%). Scanning electronic microscopy (SEM) was conducted for fractographic analysis.
  
  
  RESULTS
  Regarding the groups without fiber addition, VM7/AP showed the highest flexural strength (MPa), followed by VM7/GIA and VM7 monolayers. The addition of fibers led to a numerical increase in flexural strength for all groups. For VM7/GIA bilayers the addition of 17 vol% of fibers resulted in a significant 48% increase in the flexural strength compared to the control group. Fractographic analysis revealed that the crack initiation site was in porcelain at the tensile surface. Cracks also propagated between fibers before heading for the alumina core.
  
  
  CONCLUSIONS
  The addition of 17 vol% of Al(2)O(3)/GdAlO(3) longitudinal fibers to porcelain/glass infiltrated alumina bilayers significantly improved its flexural strength. 10 vol% or 17 vol% of fibers inclusion increased the flexural strength for all groups.
authors.affiliation: Departmento de Materiais Dentários, Faculdade de Odontologia, Universidades de São Paulo, São Paulo, Brazil. risgura@hotmail.com
authors.forename: Ricardo
authors.initials: R
authors.lastname: Sgura
authors.forename: Igor Studart
authors.initials: IS
authors.lastname: Medeiros
authors.forename: Paulo Francisco
authors.initials: PF
authors.lastname: Cesar
authors.forename: Adeliani Almeida
authors.initials: AA
authors.lastname: Campos
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Hernandes
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D005682:Gadolinium / Q000737:chemistry*; D005898:Glass / Q000737:chemistry; D055595:Mechanical Phenomena
chemical_list: D003776:Dental Porcelain; D005682:Gadolinium; D000537:Aluminum Oxide