Abstract
For obtaining the better retention of a sealant, the necessity of the acid etching of surface enamel is well recognized. However, conventional acid etching would not produce homogeneous and sufficiently etched enamel. A recent study of our collegues has suggested that ultrasonic treatment in addition to the conventional acid etched technique could produce better etched enamel. Etching with phosphoric acid is considered to be no problem clinically and the etched surface, left unsealed, may return to a normal appearance. Horowitz and his collegues suggested that an acid etched, unsealed surface or even a surface from which the sealant has been lost are not more susceptible to decay than uneched surfaces. In the present study, fluoride effects on unsealed acid etched enamel are critically evaluated on an in vitro basis.
Freshly extracted premolars were used and the labial enamel surfaces were given the following treatment and grouped as follows,
A: Conventional acid etching for 60 seconds
B: Ultrasonic acid etching using ultrasonic tip (GOOF, Odontoson,41KHz)
C: Ultrasonic acid etching using ultrasonic cleaner (YOSHIDA, Ultosonic III,42KHz)and then immersed in sodium fluoride solution at different concentrations (9000ppmF-,500 ppmF-,10ppmF-, pH 6.5∼6.8) for different periods of time (3 min.,24 hrs.,1,3,5,7 weeks). Surface changes of the enalmel were then examined with the aid of a scanning electron microscope ( JEOL, JSM-35C), electron probe X-ray microanalyzer (SHIMADZU, EMX-SM), microradiography (NIPPON SOFTEX, Softex-CMR) and changes of crystallinity were exam ined with X-ray diffraction (RIGAKU, Microflex and Microforcus Laue Camera). Also variation of crystallinity was estimated from the half-line breadth value (310), (002) reflections of enamel apatite. The reaction products were also identified with the A. S. T. M. cards.
The result obtained in the present study were as follows:
1) An ultrasonic acid etched enamel surface showed that enamel rods appear clearly throughout, and more etching occured at the periphery of rods.
2) The crystallinity at the etched enamel surface was decreased both in the a-axis and the c-axis.
3) Calcium fluoride was identified on enamel surfaces after being immersed in the 9000 ppmF- and 500 ppmF- fluoride solution for 7 weeks.
4) The intensity of FKand CaKevaluated with an electron probe X-ray microanalyzer was highest in the superficial layer after being immersed in the 9000ppmF- and 500 ppmF- fluoride solutions, and PKα decreased in the superficial layer.
5) The crystallinity of the acid etched enamel apatite was increased both in the a-axis and the c-axis directions when the specimen was immersed in the 500ppmF- and 10 ppmF- solution for 7 weeks.
These results suggested that a low concentration of fluoride solution will be effective for remineralization on acid etched enamel.
