Measurement of Radiopacity of Modern Commercial Glass Ionomer Cements

One of the drawbacks of the original glass ionomer (GIC) Aspa was that it lacked radiopacity making it difficult to differentiate the restoration from any underlying caries. Most modern GICs overcome this drawback by including radiopacyfying elements in the glass composition in order to impart a degree of radipacity to the cement.

Objectives: To measure and compare the radiopacity of 10 modern commercial GICs.

Materials and Methods: Nine restoratives (Chemfil Rock, Chemfil Superior, Ionofil Molar, Ketac Molar, Ketac Fil , Zero Glass, Amalgomer, Riva Selfcure, Fuji IX)  , one luting cement (Ketac Cem) and Aspa were mixed and formed into 1x10mm discs. The discs were allowed to set for 15 minutes at 37^oC. Thereafter a radiograph was taken by placing the discs on a digital radiographic detector along with an aluminium step-wedge. A calibration curve was produced by plotting the grey-scale values from the aluminium step-wedge against the thickness of aluminium. Grey scale values from the sample discs were then converted to mm of Al using this curve.

Results: With the exception of ASPA, Amalgomer and Chemfil Superior, all GICs showed a degree of radiopacity either greater or equal to the ISO requirement of 1 mm of Al.

Barium and strontium containing Zeroglass had the lowest radiopacity equivalent to 1mmof Al. Ketac Fil and Fuji IX, both of which contain strontium, showed radiopacity equivalent to 3.5 and 2.7 mm of Al, respectively. Ketac Molar which contains lanthanum and Chemfil Rock which contains zinc showed radiopacity equivalent to 2.8 mm of Al.

Conclusions: The radiopacity of Zeroglass matches that of human dentine. All other radiopaque GICs showed radiopacity levels greater than that of tooth enamel (2-2.5 mm of Al). The radiopacity of GICs is dependent on the glass composition.