OBJECTIVES: Conventional approaches to comparing dental cements use standard property tests under manufacturers' specified conditions. Zinc phosphate cements are supplied in powder/liquid form and manipulation frequently involves mixing the components by eye so a range of mixing ratios will inevitably occur in practice. Unfortunately, the physical, chemical, biological and mechanical properties of cements are known to be dependent on the mixing ratio. METHODS: Forty dental nurses prepared a series of three cement samples to a luting consistency they considered acceptable for use in practice. RESULTS: It was found that each dental nurse produced consistent cement mixes, although, the mixing ratios varied from 1.7 to 3.2 g/ml between nurses. The mean compressive strength, standard deviation and associated Weibull Moduli (m) of the cements were determined as a function of this mixing ratio range and showed considerable variation ranging from 33.5 +/- 3.2 MPa (m = 11.0) at 1.7 g/ml to 71.4 +/- 8.4 MPa (m = 8.6) at 2.6 g/ml and 42.5 +/- 10.0 MPa (m = 5.0) at 3.2 g/ml. SIGNIFICANCE: An analytical approach was adopted which facilitated an integrated analysis of the mixing ratio variability with the strength data. It was found for the test group of dental nurses that 25% of cement mixes produced would have achieved strengths below 40 MPa whilst strengths below the standard value were produced in at least 70% of mixes. These results indicate that a simple analysis of the properties of cements manipulated under optimum conditions, provides little information on the material characteristics obtained in practice because of clinically induced variability.
OBJECTIVES: Conventional approaches to comparing dental cements use standard property tests under manufacturers' specified conditions. Zinc phosphate cements are supplied in powder/liquid form and manipulation frequently involves mixing the components by eye so a range of mixing ratios will inevitably occur in practice. Unfortunately, the physical, chemical, biological and mechanical properties of cements are known to be dependent on the mixing ratio. METHODS: Forty dental nurses prepared a series of three cement samples to a luting consistency they considered acceptable for use in practice. RESULTS: It was found that each dental nurse produced consistent cement mixes, although, the mixing ratios varied from 1.7 to 3.2 g/ml between nurses. The mean compressive strength, standard deviation and associated Weibull Moduli (m) of the cements were determined as a function of this mixing ratio range and showed considerable variation ranging from 33.5 +/- 3.2 MPa (m = 11.0) at 1.7 g/ml to 71.4 +/- 8.4 MPa (m = 8.6) at 2.6 g/ml and 42.5 +/- 10.0 MPa (m = 5.0) at 3.2 g/ml. SIGNIFICANCE: An analytical approach was adopted which facilitated an integrated analysis of the mixing ratio variability with the strength data. It was found for the test group of dental nurses that 25% of cement mixes produced would have achieved strengths below 40 MPa whilst strengths below the standard value were produced in at least 70% of mixes. These results indicate that a simple analysis of the properties of cements manipulated under optimum conditions, provides little information on the material characteristics obtained in practice because of clinically induced variability.
Authors: Maria Cristina Carvalho de Almendra Freitas; Ticiane Cestari Fagundes; Karin Cristina da Silva Modena; Guilherme Saintive Cardia; Maria Fidela de Lima Navarro Journal: J Appl Oral Sci Date: 2018-01-18 Impact factor: 2.698
Authors: Sharali Malik; Felicite M Ruddock; Adam H Dowling; Kevin Byrne; Wolfgang Schmitt; Ivan Khalakhan; Yoshihiro Nemoto; Hongxuan Guo; Lok Kumar Shrestha; Katsuhiko Ariga; Jonathan P Hill Journal: Beilstein J Nanotechnol Date: 2018-03-05 Impact factor: 3.649