Pyruvic acid as an etching agent

Variations in acid-etch patterns with different acids and etch times

Research has shown that mandibular premolars have the highest rate of orthodontic bracket bond failure. Bond strength is thought to depend on the quality and quantity of enamel etch produced by the acid. Phosphoric acid is the most commonly used acid for etching before bonding. Nitric acid is also commercially available for etching enamel; however, it has not been studied specifically for etching in orthodontic bonding. This ex vivo study compared the enamel etch patterns achieved on the orthodontic bonding area of extracted mandibular premolars treated with 37% wt/wt phosphoric acid and 2.5% wt/wt nitric acid applied for 15, 30, or 60 seconds. The etch patterns were viewed with a scanning electron microscope and assessed with a 5-point etch scale. Statistical analysis showed that increasing the duration of acid application (irrespective of acid type) significantly increased the amount of better quality etch. Phosphoric acid at 37% concentration was more effective at producing a good-quality etch than was nitric acid at 2.5% for all 3 application times. The quantity of good-quality etch produced by phosphoric acid at 37% was time specific, with 15 seconds being significantly less effective than 30 or 60 seconds. However, 60 seconds was not significantly better than 30. Comparing the upper half of the orthodontic bonding area with the lower half showed no statistically significant differences for either acid type or length of application (P >.005). These findings support the use of 37% wt/wt phosphoric acid and indicate an optimum application time of 30 seconds.

Michael Buonocore and the Eastman Dental Center: a historic perspective on sealants

Dr. Michael Buonocore is known for his innovative research on the preparation of the enamel surface with a weak acid to enhance adhesion of an organic plastic chemical sealant and the polymerization in situ of a sealant with ultraviolet light. His co-workers at Eastman Dental Center aided and extended his research findings. The purpose of his original research was the development of a sealant to prevent occlusal caries on posterior teeth. However, the major impact of his work has been the development of adhesive restorative techniques. Although it has been demonstrated that (i) bacteria tend to die out and caries does not progress if early caries lesions are inadvertently sealed, (ii) sealant retention rates are favorable, and (iii) sealants are cost-effective, the use of sealants by the profession is still far short of early expectations.

Effect of trichloracetic acid on the microhardness and surface morphology of human dentin and enamel

Trichloracetic acid is recommended for the treatment of external cervical root resorption. The present study examined the effect of 90% trichloracetic acid on the microhardness and surface morphology of human dentin and enamel. Intact extracted human teeth were sectioned and embedded in acrylic resin. Each tooth was grinded and highly polished exposing a flat surface of dentin and enamel. The teeth were treated with 90% trichloracetic acid for 30, 60 and 90 s. Vicker's microhardness of the dentin and enamel was assessed for each tooth before and after each treatment. In addition the surface morphology of a trichloracetic acid treated tooth was examined via SEM. The results showed that 90% trichloracetic acid caused a second order type reduction of the microhardness, as well as structural changes in both dentin and enamel.

Effect of acidic pretreatment on adhesion to dentin mediated by Gluma

Tensile bond strengths between dentin and a typical restorative resin were measured after the dentin was treated with Gluma. Solutions of phosphoric, pyruvic, nitric, or oxalic acid, also containing various amino acids, were used as pretreatments. Without amino acids in the solutions, the pretreatments conferred bonds of low strength. Use of acidic solutions containing glycine or N-phenylglycine was found to give bonds of high strength to both dentin and enamel.

The continuous brushing acid-etch technique

The continuous brushing of an acid-etching agent onto the enamel surface of an extracted tooth resulted in a more debris-free surface. SEM photomicrographs showed dissolution of some of the apatite crystals and a reduction in size of the remaining crystals, thus increasing the potential space between them for retention of unfilled composite.

Direct bonding comparing a polyacrylic acid and a phosphoric acid technique

The purpose of this study was to compare in vitro a polyacrylic acid technique (crystal bonding) with a conventional phosphoric acid-etch technique for the preparation of teeth for bonding. The potential value of the polyacrylic acid technique was evaluated for bond strength, enamel loss, cleanup, and fracture location--with and without the use of a sealant. Ninety-six premolars were evenly divided into two groups. Group A was preconditioned with polyacrylic acid and group B with phosphoric acid. Half of each group was treated with a sealant before direct bonding of orthodontic brackets. Sealant was not used on the other half of each group and brackets were bonded directly to the conditioned labial surfaces with a composite cement. Bonding and rebonding shear strength tests were carried out for both groups. Results indicated that shear bond strength values for the polyacrylic acid group were approximately one third those of the phosphoric acid group using a composite cement as the adhesive. Enamel loss was measured on the lingual surfaces of 30 of the 96 premolars. The lingual surfaces were conditioned with polyacrylic acid. Following debonding and cleanup procedures, the polyacrylic acid treated surface was left slightly pitted with no resin tags remaining. Cleanup procedures required only a rubber-cup silicate prophylaxis. The total enamel loss was minimal (4.5 micron), thus preserving most of the outermost fluoride-rich layer of enamel.

Pyruvic acid as an etching agent in clinical dentistry

The objective of this study was to evaluate the use of pyruvic acid as an alternative etching agent to phosphoric acid (H3PO4). Solutions containing 5, 10, 15, 20, 25, and 30 m/m % pyruvic acid and 50% m/m H3PO4 were prepared. The tensile bond strengths of a composite resin to enamel surfaces etched with the respective etching agents were determined. The rates of etching of enamel surfaces by each of the etching solutions were evaluated. Unground and polished enamel surfaces were etched with the respective etching solutions and the surfaces examined by scanning electron microscopy. The tensile bond strengths of the resin to enamel surfaces etched with 10-30% pyruvic acid exceeded those obtained on enamel surfaces etched with 50% H3PO4. The rates of etching of all the pyruvic acid solutions were significantly less than of H3PO4. Well-defined etching patterns were observed on the enamel surfaces etched with all the etching solutions. The results of this laboratory study suggest that pyruvic acid may be a suitable alternative to phosphoric acid as an etching agent in clinical dentistry.

The effect of salivary contamination on fissure sealant--enamel bond strength

The effect of accidental salivary contamination on the retention of fissure sealants is investigated via in vitro bond tests and scanning electron microscopy. The strength of the bond between sealant and saliva contaminated and washed enamel (168 +/- 14 kg cm-2) is not found to be significantly different from the bond strength to uncontaminated enamel (174 +/- kg cm-2). Unwashed contaminated enamel gives significantly reduced bond strength (68 +/- 11 kg cm-2).

Bonding of polymers to enamel: influence of deposits formed during etching, etching time and period of water immersion

A technique for measuring the shear bond strength of composites to etched enamel was developed. The importance of thorough washing of the enamel surface to remove deposits formed during etching was demonstrated by measurements of bond strength and by scanning electron microscopy. One of three orthodontic adhesive systems showed a highly significant increase in bond strength after immersion in water for three months. Etching times as short as five seconds gave a bond strength not significantly different from that obtained after a one-minute etch.

Possible factors in the adhesion of fissure sealants to enamel

The type of aqueous solution used to wash the enamel surface immediately after etching with orthophosphoric acid affected the tensile bond strength obtained. Washing with a 1% potassium chloride solution was found to effect an improved bond strength, but no difference was observed when different types of water were employed for this purpose. A similar finding of no difference in bond strength was obtained when the possible influence of electrostatic forces was eliminated.

Pulpal response to pyruvic acid

Etching of enamel surfaces produces a marked increase in the bond strength of dental materials to tooth structure. The results of recent studies have indicated that pyruvic acid may be used in preference to phosphoric acid, because of its milder etching effect on enamel surfaces, without adversely affecting the bond strength. The pulpal responses elicited by 10% pyruvic acid applied for 90 seconds to freshly prepared cavities in monkey teeth, were examined after 4, 14 and 42 days. The differences between some of the ariteria used to evaluate the pulpal responses in acid-treated and control teeth at the three post-operative time intervals were statistically significant. These results suggest that exposed dentin should be protected with a lining before etching adjacent enamel surfaces with 10% pyruvic acid.