title: Effect of Zirconia and Alumina Fillers on the Microstructure and Mechanical Strength of Dental Glass Ionomer Cements.
abstract: BACKGROUND
  Glass-ionomer cements perform a protective effect on the dentin-pulp complex considering the F ions release and chemical bonding to the dental structures. On the other hand, those materials have poor physic-mechanical properties in comparison with the restorative resin composite. The main aim of this work was to evaluate the influence of zirconia and/or alumina fillers on the microstructure and strength of a resin modified glass-ionomer cement after thermal cycling.
  
  
  METHODS
  An in vitro experimental study was carried out on 9 groups (n = 10) of cylindrical samples (6 x 4 mm) made from resin modified glass-ionomer (Vitremer, 3M, USA) with different contents of alumina and/or zirconia fillers. A nano-hybrid resin composite was tested as a control group. Samples were mechanically characterized by axial compressive tests and electron scanning microscopy (SEM) coupled to energy dispersive X-ray spectrophotometry (EDS), before and after thermal cycling. Thermal cycling procedures were performed at 3000, 6000 and 10000 cycles in Fusayama´s artificial saliva at 5 and 60 (o)C.
  
  
  RESULTS
  An improvement of compressive strength was noticed on glass-ionomer reinforced with alumina fillers in comparison with the commercial glass ionomer. SEM images revealed the morphology and distribution of alumina or zirconia in the microstructure of glass-ionomers. Also, defects such as cracks and pores were detected on the glass-ionomer cements. The materials tested were not affected by thermal cycling in artificial saliva.
  
  
  CONCLUSIONS
  Addition of inorganic particles at nano-scale such as alumina can increase the mechanical properties of glass-ionomer cements. However, the presence of cracks and pores present in glass-ionomer can negatively affect the mechanical properties of the material because they are areas of stress concentration.
authors.affiliation: Center for Microelectromechanical Systems (CMEMS)-Uminho, Universidade do Minho, P-4800-058, Guimarães, Portugal; Post-Graduation Program in Dentistry (PPGO), Edif. CCS, School of Dentistry, Universidade Federal de Santa Catarina (UFSC), 88040-900, Florianópolis/SC, Brazil.
authors.forename: Júlio C M
authors.initials: JC
authors.lastname: Souza
authors.affiliation: School of Dentistry, School of Health Sciences (FCS), Universidade Fernando Pessoa (UFP), Porto, Portugal.
authors.forename: Joel B
authors.initials: JB
authors.lastname: Silva
authors.affiliation: Department of Materials Engineering, Universidade Federal do Rio Grande do Norte (UFRN), 59072-970, Natal/RN, Brazil.
authors.forename: Andrea
authors.initials: A
authors.lastname: Aladim
authors.affiliation: Center for Microelectromechanical Systems (CMEMS)-Uminho, Universidade do Minho, P-4800-058, Guimarães, Portugal.
authors.forename: Oscar
authors.initials: O
authors.lastname: Carvalho
authors.affiliation: Post-Graduation Program in Dentistry (PPGO), Edif. CCS, School of Dentistry, Universidade Federal de Santa Catarina (UFSC), 88040-900, Florianópolis/SC, Brazil.
authors.forename: Rubens M
authors.initials: RM
authors.lastname: Nascimento
authors.affiliation: Center for Microelectromechanical Systems (CMEMS)-Uminho, Universidade do Minho, P-4800-058, Guimarães, Portugal.
authors.forename: Filipe S
authors.initials: FS
authors.lastname: Silva
authors.affiliation: Department of Materials Engineering, Universidade Federal do Rio Grande do Norte (UFRN), 59072-970, Natal/RN, Brazil.
authors.forename: Antonio E
authors.initials: AE
authors.lastname: Martinelli
authors.affiliation: Center for Microelectromechanical Systems (CMEMS)-Uminho, Universidade do Minho, P-4800-058, Guimarães, Portugal; Post-Graduation Program in Dentistry (PPGO), Edif. CCS, School of Dentistry, Universidade Federal de Santa Catarina (UFSC), 88040-900, Florianópolis/SC, Brazil; Ceramic and Composite Materials Research Group (CERMAT), Universidade Federal de Santa Catarina (UFSC), Campus Trindade, Florianópolis/SC, Brazil.
authors.forename: Bruno
authors.initials: B
authors.lastname: Henriques
keywords: Alumina; glass-ionomer cement; strength; thermal cycling; zirconia