Etching with EDTA- An in vitro study

ISSN 0970-4388 Etching with EDTA- An in vitro study BOGRA P a, KASWAN S b ABSTRACT: In the present study, 25% EDTA, in gel form, was used to analyse its micromorphological effects on tooth surfaces with the objective to see the effectiveness of EDTA in etching so as to replace phosphoric acid as an etchant. EDTA has neutral ph (6.4-7.4) and is known to open & widen the dentinal tubules as well as remove the smear layer. An invitro study LUQS conducted on orthodontically extracted premolars with 25% EDTA as an etchant which was applied on prepared tooth surfaces for 15 seconds, 1 minute and 3 minutes. The effects of EDTA gel was observed under SEM and results tabulated and evaluated. There was statistically significant differences between the 3 etching time groups and the results indicate that etching with 25% EDTA for 15 seconds is inadequate. The best results were obtained in the 3 minute time etch group. The results so obtained can be attributed to the fact that EDTA acts selectively and / or requires more time for action. Key Words :- EDTA, Etching, Etchant. INTRODUCTION : Acid etching has revolutionized the concept of adhesion in restorative dentistry. The optimization of micromechanical retention by increased roughness of enamel surfaces and exposure of intact dentin associated collagen, achieved by acid etching, are prerequisites for the creation of a hybrid layer. The hybrid layer produces a strong bond between the cavity wall and adhesive restorative material. Acid etching was first tried with 85% phosphoric acid around 5 decades back. Since then various etchants like citric acid, lactic acid, aluminium salt solution, maleic acid, EDTA etc. have been introduced for creating microirregularities in the tooth structure. Phosphoric acid, a strong inorganic acid (30% - 50%) has been most commonly used for etching. Strong acids at low ph denature proteins such as collagen, which leads to a change in their dimensions, or even fragmentation and dissolution. Moreover, the depth of penetration of phosphoric acid is reported to be greater deep inside the tubules. The adhesive systems are not able to penetrate completely up to full length of demineralized dentin and this eventully leads to nanoleakage. a. Professor and Head, b. P. G. Student Department of Conservative Dentistry & Endodontics D.A.V.(C) Dental College, Yamuna Nagar, Haryana So, for achieving microirregularities in the tooth structure, alongwith preservation of the collagenous matrix use of milder acids was introduced. Milder acids are capable of removing smear layer, widening of dentinal tubule orifices and exposure of more stable collages matrix. The most commonly used acids are maleic acid, citric acid, EDTA etc. MATERIALS AND METHOD Fifteen freshly extracted maxillary and mandibular premolars, indicated for orthodontic extraction, were obtained for the study and were stored in normal saline. The roots were seared off at CEJ and the buccal surfaces were ground wet, on silicon carbide 300 and 600 grit paper till a flat surface was obtained exposing both enamel and dentin. The teeth were then thoroughly rinsed. With the help of a diamond disc, a longitudinal / vertical groove was placed through the lingual surface, just 1-1.5mm short of the flat, prepared buccal surface. The prepared samples were randomly divided into 3 groups : Group I - 5 samples to be etched with 25% EDTA for 15 sec. Group II - 5 samples to be etched with 25% EDTA for 60sec Group III - 5 samples to be etched with 25% EDTA for 3 min. The EDTA gel was applied on the prepared surfaces for the required time with the help of applicator brush so as to evenly distribute the gel. The specimens were then rinsed thoroughly with distilled water. Then the samples were split into two by placing chisel in the prepared groove on the linguo-occlusal aspect and given a sharp blow with mallet. Splitting was performed to permit the inspection of dentinal tubules in their depth. The etched samples were then dehydrated by placing them in graded concentration of ethyl alcohol ( 70% - 100%). Then the samples were sputter coated with gold palladium in a sputtering device and placed in vaccum chamber for viewing under SEM. The enamel & dentinal surfaces were viewed and the extent of depth of demineralization in tubules was seen through the split aspect. The results were put to statistical analysis using student s t test. RESULTS The etched enamel surface, for all the 3 etching times of 15 sec, 60sec, & 3 minutes revealed microtopography similar 79-83

to pitted surface falling into the category of type 4 etching pattern 1 (Figs. 1,2,3). The enamel prisms morphology was not delineated in any sample. On the dentinal surface after 15 seconds of etching, (Fig.4) the tubule orifices were open with very minute traces of smear layer. The tubule orifices were open but not sufficiently widened (Mean diameter of the tubule orifices was 1.94µ (Table 1); normal diameter of tubules is 1-2µ). The presence of peritubular dentin was clearly evident in the photomicrographs. The EDTA gel did not cause any discernible demineralization in the depth of tubules(table 1). After 60 seconds of etching, (Fig.5) there was slight widening of the dentinal tubule orifices with mean diameter being 2.67µ (Table 2). Photomicrographs still showed evidence of presence of pertibular dentin thereby indicating partial demineralization by 25% EDTA gel. The dentinal surface appeared smooth and debris free. The mean depth of demineralization in the tubules was 3.92µ (Table 2). After 3 minutes of etching, (Fig.6) the mean widening of the tubule orifices was 3.53µ (Table 3) due to demineralization of pertibular dentin which also extended to a mean depth of 7.86µ (Table 3) into tubules. The depth of demineralization was appreciably seen due to funneled effect of the demineralized tubules (Fig. 7,8,9). When compared statistically, all the 3 groups had statistically significant difference (p < 0.05) in the widening of tubules and the depth of demineralization in dentinal tubules. DISCUSSION The adhesive restorative materials bond micromechanically to the prepared tooth surfaces which is enhanced by etching and conditioning of the tooth surfaces. Etching involves selective removal of component(s) from a solid surface. It increases surface area, surface free energy and wettability of the surface. The various factors that influence the effects of acid etching are chemical composition of tooth structure, the technique used, type, concentration, ph and viscosity of acid used and Fig 1: Shows enamel surface after etching with 25% EDTA gel for 15 seconds. Fig 2: Shows enamel surface after etching with 25% EDTA gel for 60 seconds. Fig 3: Shows enamel surface after etching with 25% EDTA gel for 3 minutes. Fig 4: Shows etching of dentinal surface with 25% EDTA gel for 15 seconds.

Fig 5: Shows etching of dentinal surface with 25% EDTA gel for 60 seconds. Fig 6: Shows etching of dentinal surface with 25% EDTA gel for 3 minutes. Fig 7: Shows effect of 25% EDTA gel application for 15 seconds on depth of demineralization in dentinal tubules. Fig 8: Shows effect of 25% EDTA gel application for 60 seconds on depth of demineralization in dentinal tubules. Fig 9: Shows effect of 25% EDTA gel application for 3 minutes on depth of demineralization in dentinal tubules. 81

Table 1 : Effect of 25% EDTA gel application on prepared specimens for 15 seconds. Table 2 : Effect of 25% EDTA gel application on prepared specimens for 60 seconds. Table 3 : Effect of 25% EDTA gel application on prepared specimens for 3 minutes. 82

time of application of acid 2. Etching was introduced by Buonocure (1955), since then various etching agents like phosphoric acid, lactic acid, nitric acid, EDTA, maleic acid, polyacrylic acid, chloracetic acid, oxalic acid etc. have been used. EDTA (C 10 H I6 N 2 O 8 ) is an insoluble, odourless, crystalline white powder. Various sodium salts of the acid are soluble in water. EDTA is a substance which in an aqueous solution chelates divalent cations such as Ca++, Mg ++, Fe ++, & Pb ++ at neutral ph. For the study, 25% EDTA gel was selected because it has been shown to be more effective than low ph etchants in exposing dentin associated collagen without compromising smear layer removal. 3,4 The etched enamel surfaces did not show any delineated prism morphology in any of the samples. The concentration or time of the etching may be low to obtain a desirable etching effect on enamel. 5,6 The etching on dentinal surfaces after 15 seconds and 60 seconds of etching were inconsistent indicating that EDTA requires more time for reaction. Based on the above mentioned indication the etching time was extended to 3 minutes. This time was chosen because various studies reported favourable surface morphology after 3 minutes of etching. 7,8,9 When the etching time was prolonged from 60 seconds to 3 minutes, there was appreciable increase in the widening of the tubule orifices and in the depth of the demineralization in tubules. The increased depth of demineralization from 3.93µ (60 seconds) to 7.86µ (3 min.) is not essentially of great importance because various studies have concluded that resin tags of 3µ provide adequate bond strength. Moreover increased depth interferes with complete penetration and polymerization of the systems leading to formation of a compromised hybrid layer which is prone to nanoleakage. 2,10 However, there is appreciable increase in the diameter of the widened dentinal tubule orifices when the etching time is increased from 60 seconds to 3 minutes and this helps in increased retention of the adhesive systems. The etching time of 3 minutes seems to be a prolonged time considering the technique sensitivity of the adhesive systems and the value of time of the operator and patient. However, further studies related to the clinical and histopathological biocompatibility. bond strength, microleakage etc. are required prior to establishing and advocating the use of 25 percent EDTA gel for etching. It was concluded from the present study that 1) Etching of enamel surfaces with 25% EDTA gel cannot be recommended because of the negligible non-uniform effect on enamel. 2) On dentinal surfaces, EDTA caused widening of dentinal tubule orifices and the demineralization extended into the depth of tubues. 3) The best results on the dentinal surfaces were obtained in the 3 minutes etching group. REFERENCES 1. Galil K. A., Wright G.Z. : Acid etching patterns on buccal surfaces of permanent teeth. Paediatr Dent 1979; 1: 230-234. 2. Pashely D.H. : The effects of acid etching on the pulpodentin complex. J Oper Dent 1992; 17 : 229-242. 3. Blomlof J. S. P. et al.: Acid conditioning combined with single component and two component dentin bonding agents. Quint Int 2001; 32 : 711-715. 4. Brannstrom M., Jhonson G. : Effects of various conditioners and cleaning agents on prepared dentin surfaces : A SEM investigation. J Prosth Dent 1974; 31 (4) : 422-430. 5. Cehreli Z.C., Altay N.; Effects of a nonrinse conditioner and 17% EDTA on the etch pattern of intact human permanent enamel. The Angle Orthod 2000; 70 : 22-27. 6. Nikiforuk G., Sreebny L. ; Demineralization of hard tissues by or ganic chelating agents at neutral ph. J Dent Res 1953; 32 (6) : 859-867. 7. Blomlof J. P. S. et al: Smear layer formed by different root planing modalities and its removal by an EDTA gel preparation. Int J Periodont Rest Dent 1997; 17 : 243-249. 8. Blomlof J.P.S., Cederlund A.L., Blomlof L.B. et al: A new concept for etching in restorative dentistry? Int J Perio dont Rest Dent 1999 ; 19 :31-35. 9. Brannstrom M., Nordenvall K. J., Glantz P. O.: The effect of EDTA containing surface active solutions on the morphology of prepared dentin : An in vivo study. J Dent Res. 1980; 59 (7) : 1127-1131. 10. Ohhashi M. et al: Duration of cleaning and priming of dentin and contraction gap formation J. Dent 1995; 23: 365-369. Reprint Requests to: Dr. Poonam Bogra Prof. and Head Dept. of Conservative Dentistry and Endodontics, D. A. V. [C] Dental College Yamuna Nagar, Haryana 83