Glass ionomer bond polyacrylic acid Edmond R. Hewlett, Douglas C. Wrobelc
A. Caputo, MS, PhD,b and
University of California, School of Dentistry, Los Angeles, Calif. This investigation compared the effect of smear layer removal using various treatments with polyacrylic acid on the shear bond strength of glass ionomer restorative materials to dentin. Three brands of glass ionomer were applied to prepared dentin surfaces of extracted human molars, after one of four treatments with polyacrylic acid. Samples using dentin surfaces with the smear layer left intact served as controls. Comparison of mean shear bond strength values for all possible combinations of restorative material and polyacrylic acid treatment indicated that samples produced using 25% polyacrylic acid had lower (p < 0.05) values in some instances. No other significant differences were found when test values were compared with each other or with control values. The authors concluded that removal of the smear layer does not enhance the dentin-glass ionomer restorative bond strength, as has been suggested by other investigators. Scanning electron photomicrographs indicate that treatment with higher concentrations of polyacrylic acid produces higher degrees of dentlnal tubular orifice patency. (J PROSTHET D~~~1991;68:767-72.)
lass ionomer restorative material has been proposed as an alternative to amalgam alloys for surfaces not subjected to direct occlusal forces, particularly class V restorations.‘, 2 Although these materials have lower wear resistance and hardness than amalgam or composite resin,3,4 the advantages of glass ionomer are an ability to seal a cavity through its chemical bond to dentin,5* 6 and a potential cariostatic effect by means of fluoride release.7ls Removal of the dentinal smear layer prior to placement of glass ionomer material has been shown to improve both the shear bond strength of the material to dentin,g and the clinical retention rate of glass ionomer restorations.iO Polyacrylic acid (PAA) is an effective smear removal agent, and by limiting the time of its application to dentin, it is possible to leave smear debris in the dentinal tubular orifices, thereby occluding them.‘l It has been postulated that these “plugs” of smear debris may play a role in preventing the introduction of pulpal irritants into the tubules.12 Many manufacturers of glass ionomer materials recommend PAA for smear layer removal, but there exists no consensus as to which PAA concentration is optimal. This article reports the shear bond strengths produced between glass ionomer restorative materials and prepared dentin surfaces when varying treatments with PAA are used to condition the dentin. The treatments varied with respect
Presented at the American Association for Dental Research, San Francisco, Calif. *Assistant Professor, Section of Operative Dentistry. bProfessor and Chair, Section of Biomaterials Science. cDental student.
Fig. 1. Assembly for shear testing. Table I. Application methods for PAA smear removal
agents PAA agent 10% (G. C. Dentin Conditioner) 25% (Ketac Conditioner) 40 % (Durelon Liquid) 48% (Shofu SGC Liquid)
20 set (scrub w/cotton swab) 10 set (passive application) 10 set (passive application) 15 set (scrub w/cotton swab)
to PAA concentration, time, and method (active versus passive) of PAA application to dentin. It was anticipated that an optimal combination of glass ioriomer restorative and PAA pretreatment could be found.
Fig. 2. Ketac-Fil material mean values.
Table II. Mean shear bond strengths (in MPa) lO%PAA
Ketae-Fil Shofu Type II Fuji Type II
4.1 (1.6) 3.0 (1.1)
2.7 (1.1) 1.9 (0.9) 3.1 (0.9)
MATERIAL AND METHODS Specimen preparation Fifty-five freshly extracted human molar teeth were stored in normal saline at 3’7”C. Longitudinal sections (one or two per tooth, depending on tooth size) of the teeth were made using a hard tissue saw equipped with a water-cooled O.OlO-inch thick blade. Tooth sections were embedded in autopolymerizing acrylic resin, leaving the flat surfaces of proximal coronal dentin exposed. Dentinal surfaces were progressively finished on a flat circular sander (Buehler -Scientific, Lake Bluff, Ill.). Gross sanding was done first, using sandpaper of 180 grit, to remove excess resin from the dentinal surface, leaving the surface flush with the surrounding resin. Grits of 240, 320, 400, and 600 were then used. For each grit, the specimen was oriented such that the grinder rotated from the coronal to the apical aspect. Each specimen was sanded for 10 seconds with each grit. A standard smear layer was thus produced using the sanding pr;>cedure. F’our concentrations of PAA were used to remove the dentinal smear layer: 10% (G. C. Dentin Conditioner, G. C. Dental Industrial Corp., Tokyo, Japan); 25% (Ketac Condztioner, Espe-Premier, Norristown, Pa.); 40% (Durelon L1ciuid, Espe-Premier); and 48% (SGC Liquid, Shofu Inc., KT;a)to,,Japan). Manufacturers’ instructions for time and pra;.hod of application were followed for each PAA agent, awl are listed in Table I.
0.021 0.063 0.207
Scanning electron photomicrographs (Figs. 6 through 10) indicate the dentin surface morphology produced by each of the PAA treatments. All PAA treatments appear to remove smear layer debris when compared with the untreated sample (Fig. 6), but vary in the resulting amount of tubular orifice opening. Both 40% and 48% PAA (Figs. 9 and 10) produced a uniform opening of dentinal tubules across the test surface. The 25% PAA (Fig. 8) left virtually all tubules occluded with smear debris, in addition to leaving what appears to be a fine smear layer remnant on the surface. The 10% PAA (Fig. 7) produced varied small amounts of tubular opening, leaving most of them largely but not completely occluded.
DISCUSSION All four pairs of sample means that were found to differ significantly involved passive treatment with the 25% PAA. The mean values for the samples receiving the 25% PAA were consistently lower than the other means in each of these pairings. This tendency is illustrated in Fig. 5, which summarizes the results. This finding, along with the microscopic appearance of the treated dentin surface (Fig. 8), suggests that passive treatment of cut dentin with 25% PAA for the relatively short (10 second) duration used here serves to reduce the affinity of the smear layer for the dentin, leaving behind a more poorly-attached layer of smear debris, rather than removing it. It is hypothesized that this debris covering the cut dentin and occluding the tubules leads to the lower bond strengths seen here. The more thorough removal of smear debris by a lower concentration of PAA (10%) Fig. DECEMBER
Fig. 6. SEM photograph of untreated (smear layer intact) dentin surface. (Original magnification x3000.)
Fig. 8. SEM photograph of dentin surface treated with 25% polyacrylic acid. (Original magnification x3000.)
Fig. 7. SEM photograph of dentin surface treated with 10% polyacrylic acid. (Original magnification X3000.)
Fig. 9. SEM photograph of dentin surface treated with 40% polyacrylic acid. (Original magnification x3000.)
‘7) is likely due to the fact that longer application time as well as an active (scrubbing) application method were used in this procedure. It can also be postulated that the lo%, 40%, and 43% PAA test groups benefited from mechanical retention because of the opened dentinal tubules. This retention, however, would not explain the fact that mean values for untreated samples did not differ significantly from those for these three groups. Mean values for untreated samples were either higher than or not significantly different from the means for any of the test groups, suggesting that the removal of the dentinal smear layer prior to the placement of a glass ionomer restorative material does not enhance the shear bond strength of the material to dentin. The controls tended to have greater intragroup variability, however, than did most test groups, as indicated by a tendency toward higher standard deviations. This finding is possibly related to
Fig. 10. SEM photograph of dentin surface treated with 48 % polyacrylic acid. (Original magnification x3000.)
-tated ~~~r~6’ instins 88 01 for the various PAA e and method (active versus wirkl for all PAA agent8 a&iveapglication of IO 5 %PAA pebble procedure to optimize the jokzomer lining cement~to dentin. An apgdyiag such a protocol to glass kkveswould be of value. if#iSB ~~~~~~~~~$ active pretreatment of cut dentin with ement of a glw ionomer restorative material appears to provide the best combination of shear bond strength and dentinal tubuler occlusion of any of the treatm$nta tested, regardless of which restorative material is used. While removal of the dentinal smear layer does not apmr to ~~*~~~t~y enhance the shear bond strength of the mktar&d to dentin, pretreatment of the dentin with a P&A ~~~~~ more consistent results.
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Reprintrequeststo: DR. EDMOND R. HEWLETT SCHOOL OF DENTISTRY UNIVJMBITY OF CALIFORNIA Los ANGELES, CA 90024-1668
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