title: Transient and residual stresses induced during the sintering of two dentin ceramics.
abstract: OBJECTIVE
  To characterize the stress induced deformation of bi-axial flexure strength (BFS) test specimens during processing to provide an insight into sintering effects and associated BFS determination.
  
  
  METHODS
  40 Vitadur-Alpha and 80 IPS e.max Ceram disc-shaped specimens were condensed and a sintered on a silicon nitride refractory tray under controlled firing and cooling parameters. The mean of the maximum deflection (μm) and Ra values (μm) were determined using a high resolution profilometer and were related to the orientation of the measured surface within the furnace. BFS testing of the subsequent groups (n = 20) was performed and the data related to the measured deformation of the sintered specimens. A two-way analysis of variance (ANOVA) where factors were identified as surface state and firing orientation with post hoc Tukey's tests was complemented by pair-wise comparisons with a Student's t-test for each measurement (P < 0.05).
  
  
  RESULTS
  The mean of the maximum deflection values and the mean BFS for Vitadur Alpha discs were not significantly influenced by firing orientation (P = 0.248 and P = 0.284, respectively). However, the Ra values were significantly different (P < 0.001). The two-way ANOVA revealed a significant impact on the mean of the maximum deflection measurements for surface state (P < 0.001) and firing orientation (P < 0.001) during sintering (P < 0.001). The mean Ra values were not significantly influenced. The BFS of sintered IPS e.max Ceram discs was sensitive to firing orientation (P < 0.001).
  
  
  CONCLUSIONS
  Conventional glass theory explains that residual thermal stress gradients induced during sintering can cause test specimen deformation which can alter the expected BFS data. The study demonstrates that variability such as firing orientation during sintering which is very rarely reported in the literature can have a significant impact on the reported BFS data and can confound its interpretation.
authors.affiliation: Materials Science Unit, Division of Oral Biosciences, Dublin Dental School & Hospital, Trinity College Dublin, Ireland.
authors.forename: G
authors.initials: G
authors.lastname: Isgró
authors.forename: O
authors.initials: O
authors.lastname: Addison
authors.forename: G J P
authors.initials: GJ
authors.lastname: Fleming
mesh_terms: D000465:Algorithms; D002516:Ceramics / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003890:Desiccation; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D013997:Time Factors
chemical_list: C483027:vitadur alpha; D003776:Dental Porcelain; C023506:Glass ceramics