title: Mono or polycrystalline alumina-modified hybrid ceramics.
abstract: OBJECTIVE
  This study evaluated the effect of addition of alumina particles (polycrystalline or monocrystalline), with or without silica coating, on the optical and mechanical properties of a porcelain.
  
  
  METHODS
  Groups tested were: control (C), polycrystalline alumina (PA), polycrystalline alumina-silica (PAS), monocrystalline alumina (MA), monocrystalline alumina-silica (MAS). Polycrystalline alumina powder was synthesized using a polymeric precursor method; a commercially available monocrystalline alumina powder (sapphire) was acquired. Silica coating was obtained by immersing alumina powders in a tetraethylorthosilicate solution, followed by heat-treatment. Electrostatic stable suspension method was used to ensure homogenous dispersion of the alumina particles within the porcelain powder. The ceramic specimens were obtained by heat-pressing. Microstructure, translucency parameter, contrast ratio, opalescence index, porosity, biaxial flexural strength, roughness, and elastic constants were characterized.
  
  
  RESULTS
  A better interaction between glass matrix and silica coated crystalline particles is suggested in some analyses, yet further investigation is needed to confirm it. The materials did not present significant differences in biaxial flexural strength, due to the presence of higher porosity in the groups with alumina addition. Elastic modulus was higher for MA and MAS groups. Also, these were the groups with optical qualities and roughness closer to control. The PA and PAS groups were considerably more opaque as well as rougher.
  
  
  CONCLUSIONS
  Porcelains with addition of monocrystalline particles presented superior esthetic qualities compared to those with polycrystalline particles. In order to eliminate the porosity in the ceramic materials investigated herein, processing parameters need to be optimized as well as different glass frites should be tested.
authors.affiliation: Graduate Program in Dentistry, Federal University of Pelotas, Brazil; School of Materials Engineering, Federal University of Pelotas, Brazil.
authors.forename: Marina R
authors.initials: MR
authors.lastname: Kaizer
authors.affiliation: Graduate Program in Dentistry, Federal University of Pelotas, Brazil.
authors.forename: Ana Paula R
authors.initials: AP
authors.lastname: Gonçalves
authors.affiliation: Graduate Program in Dentistry, Federal University of Uberlândia, Brazil.
authors.forename: Priscilla B F
authors.initials: PB
authors.lastname: Soares
authors.affiliation: College of Dentistry, New York University, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Dentistry, University of São Paulo, Brazil.
authors.forename: Paulo F
authors.initials: PF
authors.lastname: Cesar
authors.affiliation: School of Materials Engineering, Federal University of Pelotas, Brazil.
authors.forename: Sergio S
authors.initials: SS
authors.lastname: Cava
authors.affiliation: Graduate Program in Dentistry, Federal University of Pelotas, Brazil. Electronic address: moraesrr@gmail.com.
authors.forename: Rafael R
authors.initials: RR
authors.lastname: Moraes
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D002516:Ceramics; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D003460:Crystallization; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D006358:Hot Temperature; D008422:Materials Testing; D010316:Particle Size; D018583:Pliability; D016062:Porosity; D013499:Surface Properties
chemical_list: D020099:Coated Materials, Biocompatible; D003776:Dental Porcelain; C023506:Glass ceramics; D000537:Aluminum Oxide
keywords: Ceramics; Composites; Monocrystals; Optical and mechanical properties; Polycrystals; Porcelain; Silica coating; Single crystals