Erosion of water-based cements evaluated by volumetric and gravimetric methods.
OBJECTIVE
To compare the erosion of glass ionomer, zinc phosphate and polycarboxylate cements using volumetric and gravimetric methods.


METHODS
For the volumetric method, the eroded depth of cement placed in a cylindrical cavity in PMMA was measured using a dial gauge after immersion in an eroding solution. For the gravimetric method, the weight of the residue of a solution in which a cylindrical specimen had been immersed was measured. 0.02 M lactic acid solution (0.02 M acid) and 0.1 M lactic acid/sodium lactate buffer solution (0.1 M buffer) were used as eroding solutions. The pH of both solutions was 2.74 and the test period was 24 h.


RESULTS
Ranking of eroded depth and weight of residue was polycarboxylate>zinc phosphate>glass ionomers. Differences in erosion were more clearly defined by differences in eroded depth than differences in weight of residue. In 0.02 M acid, the erosion of glass ionomer using the volumetric method was effected by the hygroscopic expansion. In 0.1 M buffer, the erosion for polycarboxylate and zinc phosphate using the volumetric method was much greater than that using the gravimetric method. This is explained by cryo-SEM images which show many holes in the surface of specimens after erosion. It appears that zinc oxide is dissolved leaving a spongy matrix which easily collapses under the force applied to the dial gauge during measurement.


CONCLUSIONS
The volumetric method that employs eroded depth of cement using a 0.1 M buffer solution is able to quantify erosion and to make material comparisons.
Nomoto
Rie
R
Department of Dental Engineering, Tsurumi University School of Dental Medicine, 2-1-3 Tsurumi, Tsurumi-Ku, 230-8501, Yokohama, Japan. nomoto-r@tsurumi-u.ac.jp
Uchida
Keiko
K
Momoi
Yasuko
Y
McCabe
John F
JF
D002021:Buffers; D003343:Corrosion; D003738:Dental Cements / Q000737:chemistry*; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007101:Immersion; D019344:Lactic Acid / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011076:Polycarboxylate Cement / Q000737:chemistry; D019354:Sodium Lactate / Q000737:chemistry; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D017155:Wettability; D015036:Zinc Phosphate Cement / Q000737:chemistry
D002021:Buffers; D003738:Dental Cements; D005899:Glass Ionomer Cements; D011076:Polycarboxylate Cement; D014867:Water; D019344:Lactic Acid; D015036:Zinc Phosphate Cement; D019354:Sodium Lactate