A pilot study of lactic acid as an enamel and dentin conditioner for dentin-bonding agent development Mohammed F. Ayad, BDS, MSD,” Stephen F. Rosenstiel, BDS, MSD, and Ali M. Farag, BDS, MSD, PhD” College of Dentistry, The Ohio State University, Columbus, Ohio, and University of Tanta, College of Dentistry, Tanta, Egypt The purpose of this pilot study was to determine how lactic acid solution at various concentrations and etching times affected prepared human enamel and dentin surfaces and to assess whether it could be used in place of phos- phoric or maleic acid as an etchant. The occlusal surfaces of extracted molar teeth were ground wet with 600.grit silicon carbide paper and treated with various aqueous solutions of lactic acid. Random samples were prepared for observation by scanning electron microscopy. The rest were used to determine shear bond strength of bonded dental composite cylinders. The micrographs revealed that lactic acid dissolved the smear layer with various degrees of etching and demineralization. The degree of smear layer and matrix removal was proportional to the concentration of the acid and the length of application time. A 20% lactic acid concentration applied for 10 seconds produced a clearly etched surface with minimal demineralization. A 30% concentration not only removed the smear layer and enlarged the dentin tubule orifices but also appeared to affect the collagen matrix. The shear bond strength to enamel treated with 50% lactic acid (17.5 2 1.5 MPa) and All-Bond 2 etchant (18.9 2 1.3 MPa) were not significantly different (p > 0.05). However, mean dentin bond strengths for all groups of lactic acid etchant and AR-Etch etchant (10% phosphoric acid) were statistically similar. (J Prosthet Dent 1996;76:254-9.) Al though lactic acid is a normal product of the fermentation of many vegetable materials and it is a fuel produced by some muscles and used by others1 the ac- tion of lactic acid as an alternative to phosphoric or ma- leic acid as a dentin etchant has not been reported.2 Acid etching of dentin is recommended with many dentinal bonding systems to remove the smear layer and to per- mit bonding directly to the dentin matrix. The smear layer, an incidental consequence of cavity preparation with rotary instruments, has been the sub- ject of considerable investigation3 The particles that remain on the surface of dentin after tooth preparation vary in size from 0.05 to 10 um.4a5 Although they tend to be irregular, the larger particles have plate-like conurations that permit them to stack into a layer that is seldom more than 1.0 pm thick. The composition of these particles is similar to the dentin from which they were formed.6 Intentional removal of the smear layer during restorative procedures remains controversial. One school of thought suggests that, because the smear layer occludes the dentinal tubules, it precludes bacterial in- Wisiting Scholar, Section of Restorative and Prosthetic Den- tistry, College of Dentistry, The Ohio State University. “Associate Professor and Chairman, Section of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University. “Assistant Professor, Section of Restorative, Fixed Prosthodontic and Endodontic Dentistry, College of Dentistry, University of Tanta. 254 THE JOURNAL OF PROSTHETIC DENTISTRY vasion. Others advocate removal of the smear layer to enhance the bonding of adhesive restorative materials and encourage the ingress of tags into the enlarged of- fices of the dentinal tubules. A further argument in fa- vor of removal is that the smear layer, although com- posed primarily of inorganic material,7,s may have a sig- nificant organic component including viable bacteria and their byproducts g~lothat might provide a reservoir of ir- ritants.ll Thus complete removal of the smear layer would be consistent with the elimination of irritants. Improved restoration retention and reduced micro- leakage is the goal of current resin-bonding systems. It is accomplished by allowing a hydrophilic resin to infil- trate both tubules and intertubular dentin. Resin infil- tration into intertubular dentin can only occur if some of the mineral phase of dentin is removed by an acidic conditioner.‘2 Many acid-etching protocols have been suggested as suitable for dentin conditioning,13 includ- ing 37% phosphoric acid for 15 seconds,l” 10% citric acid for 60 seconds, 25% tannic acid for 15 to 60 seconds,15J6 10% polyacrylic acid for 20 seconds,17 and 10% maleic acid for 10 seconds.ls In 1984 Mountlg suggested that dentin etchants should be (1) isotonic to avoid osmotic pressure changes, (2) neutral pH or at least between pH 5.5 and pH 8.0, (3) nontoxic to dentin, pulp, and gingival tissue, (4) compatible with the chemistry of the cemen- tation agents, (5) water soluble and easily removed, (6) unable to deplete the enamel or dentin chemically, and (7) able to enhance the surface chemically in prepara- VOLUME 76 NUMBER 3