title: Fracture toughness testing: A discriminatory mechanical testing performance indicator for glass-ionomer restoratives?
abstract: OBJECTIVE
  To investigate the single-edge notched (SEN) bend fracture toughness (KIC) testing methodology as a reproducible and discriminatory mechanical testing protocol for encapsulated and hand-mixed glass-ionomers (GI).
  
  
  METHODS
  SEN bend test-pieces (35.0±0.1mm length, 6.0±0.1mm width, 3.0±0.1mm thickness with a sharp notch formed at mid-length by embedding a scalpel blade) were prepared for KIC testing using three encapsulated GI products (Chemfil Rock, Fuji IXGP Fast Capsule and Ionofil Molar AC). In addition, test-pieces were prepared from a hand-mixed GI product (Ionofil Molar) which contained between 100% and 20% of the manufacturer's recommended powder content (in 10% decrements) for a constant weight of liquid. Groups of 20 test-pieces were prepared for each encapsulated GI product (n=3) and hand-mixed GI powder:liquid mixing ratio (n=9). Data were statistically analyzed and the coefficients of variation (CoV) determined for each encapsulated GI product and hand-mixed GI powder:liquid mixing ratio.
  
  
  RESULTS
  The KIC testing methodology failed to discriminate between the encapsulated GI products that were investigated (p=0.225). For the hand-mixed GI, the KIC testing methodology also failed to discriminate between the powder:liquid mixing ratios investigated (R(2)=0.576). The pooled CoV (10%) for the encapsulated GI products and for the powder:liquid mixing ratio groups (12%) identified the reproducibility of the test for this experiment. For the hand-mixed GI mixing ratio groups with between 100% to 50% of the recommended powder content, no trend could be discerned.
  
  
  CONCLUSIONS
  The KIC testing methodology failed to discriminate between different encapsulated GI products and hand-mixed GI powder:liquid mixing ratio groups investigated, despite KIC being an intrinsic material property and the coefficient of variation being acceptable.
authors.affiliation: Materials Science Unit, Dublin Dental University Hospital, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Mirza Shahzad
authors.initials: MS
authors.lastname: Baig
authors.affiliation: Division of Oral and Maxillofacial Clinical Sciences, Dundee Dental Hospital and School, Park Place, Dundee DD1 4HR, Scotland, United Kingdom.
authors.forename: Charles H
authors.initials: CH
authors.lastname: Lloyd
authors.affiliation: Materials Science Unit, Dublin Dental University Hospital, Trinity College Dublin, Dublin 2, Ireland. Electronic address: garry.fleming@dental.tcd.ie.
authors.forename: Garry J P
authors.initials: GJ
authors.lastname: Fleming
mesh_terms: D000538:Aluminum Silicates; D019245:Compressive Strength; D003799:Dental Stress Analysis / Q000295:instrumentation*; D005899:Glass Ionomer Cements / Q000737:chemistry*; D006244:Hardness; D008422:Materials Testing; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D000538:Aluminum Silicates; C439808:Fuji IX GP Fast; D005899:Glass Ionomer Cements; C541507:ionofil U; C039733:Chemfil
keywords: Encapsulation; Fracture toughness testing; Glass-ionomer restorative; Hand-mixed; Powder:liquid mixing ratio