The effect of disinfectants on the properties of dental gypsum: 1. Mechanical properties.
OBJECTIVE
This study was conducted to evaluate the effect of selected disinfectants incorporated in the liquid of dental stones on material strength properties with the aim of developing a material with acceptable mechanical properties.


METHODS
Two types of dental stone (types III and V) were mixed with aqueous solutions of 0.525% sodium hypochlorite, 0.1% and 10% povidone-iodine, and 2% glutaraldehyde, and with water as a control. The liquid/powder ratios recommended by the manufacturer were used. These materials were subjected to further modification by adding a mixture of 1.0% gum arabic and 0.132% calcium hydroxide to the hemihydrate powders before mixing with the disinfectant solutions at 2 different liquid/powder ratios for each. Both the regular and the modified materials were tested for compressive and diametral tensile strength after 1 hour and 1 week from the start of the mix. The structure of set materials was determined by scanning electron microscopy examination of fracture surfaces.


RESULTS
The disinfectants often reduced the strength of both types of dental stone. However, using either 0.1% povidone-iodine or 0.525% sodium hypochlorite resulted in strength values comparable with that of the control. The addition of gum arabic and calcium hydroxide helped reduce the mixing liquid/powder ratios, improving the strength properties of the disinfected materials.


CONCLUSIONS
Chemical disinfectants reduce the strength of dental gypsum when used as mixing water substitutes. Gum arabic and calcium hydroxide additives permit a lower liquid/powder ratio and can help offset this weakening.
Abdelaziz
Khalid M
KM
Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota School of Dentistry, Minneapolis, USA.
Combe
Edward C
EC
Hodges
James S
JS
D000704:Analysis of Variance; D002126:Calcium Hydroxide / Q000737:chemistry; D002133:Calcium Sulfate / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D019245:Compressive Strength; D003461:Crystallography; D019551:Dental Disinfectants / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D005976:Glutaral / Q000737:chemistry; D006170:Gum Arabic / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D016062:Porosity; D011206:Povidone-Iodine / Q000737:chemistry; D011208:Powders; D012973:Sodium Hypochlorite / Q000737:chemistry; D012996:Solutions; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013718:Tensile Strength; D013997:Time Factors; D014867:Water / Q000737:chemistry
D019551:Dental Disinfectants; D003764:Dental Materials; D011208:Powders; D012996:Solutions; D014867:Water; D011206:Povidone-Iodine; D006170:Gum Arabic; D012973:Sodium Hypochlorite; D002126:Calcium Hydroxide; D005976:Glutaral; D002133:Calcium Sulfate