Key Engineering Materials Vols. 264-268 (2004) pp. 2035-2038 online at http://www.scientific.net © 2004 Trans Tech Publications, Switzerland
Effects of Different Acid Treatments on Dental Ceramic Surfaces D. Şen1, G. Sınmazışık2, E. Poyrazoğlu1, B. Tunçelli1, B. Özkal3, M. L. Öveçoğlu3 1
Dept. of Prosthodontics, Faculty of Dentistry, Istanbul University, Çapa, Istanbul, Turkey
2
Vocational School of Health Related Professions, Marmara University, Nişantaşı Istanbul, Turkey
3
Dept. of Metall. and Materials Eng., Istanbul Technical University, Maslak 34469, Istanbul, Turkey
Keywords: Acid treatment, core ceramic, flexural strength.
Abstract. In this study, effects of etching on a dental ceramic material were investigated. 9.6% hydrofluoric acid solution was used to etch 28 specimens which were prepared from the FinesseTM (trademark of Dentsply Inc.) core ceramic fabricated through ceramic hot pressing routes followed by ingot casting. The specimens were randomly divided into four groups. Three groups were etched at different times. The fourth group was the control group. 4-point bending tests and scanning electron microscopy (SEM) investigations were carried out on these specimens to determine the effects of etching on the flexural strength. Whereas the control group had better flexural strength values, there were no statistically significant differences between the strength values of the specimens of the three groups etched at different times. Introduction Effective acid treatment of the ceramic surface is considered as an essential step for the clinical success of indirect ceramic bonded restorations and direct ceramic procedures[1]. Etching increases the surface roughness and improves the retentive force between restorations and teeth[2]. Alteration of the surface topography by etching will result in changes in the surface area and in the wetting behaviour of the porcelain. This may also change the ceramic surface energy and its adhesive potential to resin[1]. Type of etchant, concentration of etchant and etching time, all influence bond strength[3]. Etching of dental ceramic with hydrofluoric acid or ammonium hydrogen difluoride is a common procedure used to achieve a clean microretentive surface. It is very important to choose the optimal clinical etching time for ceramic restorations[2]. This study aims to investigate the effect of different etching time on the surface roughness and flexural strength of FinesseTM (trademark of Dentsply Inc.) core ceramic material. Materials and Methods A total of 28 specimens all having the dimensions of 30 mm x 3 mm x 3 mm were prepared from the FinesseTM (trademark of Dentsply Inc.) core ceramic following the instructions given by the manufacturer. The specimen surfaces were wet ground using 400, 600 and 800 grit size silicon carbide papers and polished using fine alumina powders progressively down to 0.5 µm. This is followed by ultrasonical cleaning for 5 min in acetone before and after etching using 9.6 % HF acid gel followed by immersing in a neutralizer for 20 seconds, as recommended in clinical procedures [2,4]. The specimens were randomly divided into four groups. The etching times were 1.5 min, 2 min and 2.5 min., respectively and the fourth group was the control group. Scanning Electron Microscopy (SEM) investigations were carried out to examine the surface morphologies of the specimens and energy dispersive spectrometry (EDS) analyses were conducted to determine their surface chemistry. The specimens were carbon coated under vacuum. A Jeol T-330 SEM was used in the secondary imaging mode (SEI) operated at 15 kV and linked with an energy dispersive
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[email protected]) - Istanbul Technical University - Turkey All rights reserved. No part of the contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 160.75.44.50-27/10/04,12:39:15)
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spectrometry (EDS) attachment. Four point bending tests were carried out in a 100 KN Servohydraulic DartecTM Universal Testing Machine (Dartec Ltd., U. K.) using a self-aligning test fixture accommodating an inner span of 8 mm and an outer span of 37 mm at a crosshead rate of 0.01 in/min. The bars were broken such that the greatest tensile force was applied opposite to the treated surface. The flexural strength was calculated using the following equation :
σ = 3P(L - M)/2w.h²
(1)
where P: applied load, L: outer span, M: inner span, w: width, h: height of specimen. The results of four point bending mechanical test were examined with the paired samples T test. Results Figures 1(a)- 1(c) present the SEM micrographs of specimens etched with HF for 1,5, 2, 2.5 minutes. As seen in these figures, although the samples etched with three different times may have similar retentive surfaces, longer etching time produced increased surface roughness of the porcelain.
a
b
c Figure 1. SEM micrographs of the FinesseTM core ceramic specimens etched with 9.6 % HF for a) 1,5, b) 2 and c) 2.5 minutes. The EDS results of the SEM micrographs of Figure 1 are shown in Table 1. As seen in Table 1, there are slight differences differences in the EDS profiles of the etched and unetched samples. Etching increased the CaO content nearly 1 wt%, decreased the Al2O3 content nearly 3 wt% and increased the BaO and K2O contents nearly 2 wt%.
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Table 1. SEM/EDS Chemical analysis of the FinesseTM (trademark of Dentsply Inc.) core ceramic specimens etched with 9.6% HF for a) 1,5 min (Group 1) and b) 2 min (Group 2),. c) 2.5 min.(Group 3) and unetched – control group.(Group 4).
Na2O K2O CaO SiO2 Al2O3 BaO
Group 1 10.44 8.41 2.34 60.87 14.81 3.12
Group 2 8.53 9.09 2.08 62.05 15.06 2.04
Group 3 10.83 8.44 2.30 61.21 15.44 1.78
Group 4 10.61 7.54 1.49 61.47 18.09 1.01
Figure 2 shows the flexural strength values of the four groups of the present investigation. As seen in Fig. 2, Group 4 – the control group has the highest flexural strength values around 84 MPa and the other groups have values around or less than 80 MPa. The four-point bending test results of paired samples T test showed that the differences between the groups are not statistically significant. (Fig. 2, Table 2).
Figure 2. Flexural strength (4-point bending) values of the test groups of the FinesseTM (trademark of Dentsply Inc.) core ceramic specimens etched with 9.6% HF for a) 1,5 min (Group 1) and b) 2 min (Group 2),. c) 2.5 min.(Group 3) and unetched – control group.(Group 4).
Table 2. The flexural strength results of paired samples T test. GROUPS Group 3 and Group 4 Group 1 and Group 2 Group 1 and Group 3 Group 1 and Group 4 Group 2 and Group 3 Group 2 and Group 4
n 7 7 7 7 7 7
p 0,083>0,05 0,717>0,05 0,373>0,05 0,293>0,05 0,629>0,05 0,136>0,05
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Discussion Different types of treatment methods have been used to prepare the porcelain surfaces for resin bonding. Among these, HF acid etching is a well accepted pretreatment method that produces an irregular surface topography. After acid treatment, microporosities are formed on the ceramic surface for the penetration of the composite resin [3]. Many researchers reported that SEM findings of the etched porcelain surfaces with HF acid showed that etching by HF acid may be adequate and produce pronounced morphological changes compared with time[5, 6]. The choice of etching time and an HF gel concentration depends on the authors. Stangel et al. [5] evaluated the effect of 52 % HF for 90 seconds and 20% HF for 2.5 minutes and noted distinct microstructural differences for each concentration, which indicated preferential dissolution in one of the phases of porcelain. Calamia et al. [7] examined the effects of three concentration of HF (5%, 7.5%, 10%) on different porcelain surfaces at 2.5 and 20 minutes. They found significantly better bond strength in the porcelain samples etched for 2.5 and 20 minutes. In the present study, a 9.6% HF gel concentration was applied at different etching times of 1.5, 2 and 2.5 minutes. The etchant of 9.6%HF was chosen on the basis of the reported literature on dental ceramics[2,4]. The results of the SEM study showed that although the samples etched with three different times may have similar retentive surfaces, longer etching time produced increased surface roughness of porcelain. HF selectively dissolves the glass matrix and produces a porous irregular surface which increases the surfaces area and facilitates the penetration of repair materials into the microundercuts of the etched porcelain surfaces. The results of this study clearly indicate that the application of the HF acid for three different times produced the desired surface as determined by other researchers [4]. Based upon the quality of etched surface it was concluded that an etching time 1.5 min can provide adequate roughness. Increasing the etching time to 2.5 min produce sharper irregularities on the porcelain surface that can lead to fracture within the porcelain substrate. Although etching of ceramic increases the surface roughness and improves the retentive force between restorations and teeth. It has also the potential to remove significant amounts of ceramic that could affect the clinical fit of the restoration and its strength. [2]. Further studies are needed to investigate the effects of increasing etching time to bonding to the resin cements Conclusions 1) On the basis of the results of the present study, it is concluded that acid treatment of FinesseTM ceramic core material had no effect on the flexural strength of the material statistically significant within the limits of the time interval and the concentration of HF acid. 2) The effect of the size and the surface depth of the microporosities on the bonding with composite resins and on the strength of the composite resin-ceramic compound should be investigated. References [1] A. D. Bona, K. J. Anusavice: Int J Prosthodont Vol.15 (2002), p. 159-167. [2] X-P. Luo, N. Silikas, M. Allaf, N.H.F.Wilson, D.C.Watts: Surface Science (2001), p. 388-394. [3] Ş. Canay, N. Hersek, A. Ertan : J. of Oral Rehabilitation Vol. 28 (2001), p. 95-101. [4] A. Al Edris, A. Al Jabr, R. L. Cooley, N. Barghi: J. Prosthet Dent. Vol.64 (1990), p. 734-739. [5] I. Stangel, D. Nathanson, C.S. Hsu: J Dent Res. Vol.66 (1987), p. 1460-1465. [6] V. Jardel, M. Degrande, B. Picard, G. Derrien : Int J. Prosthodont. Vol.19 (1999), p. 415-418. [7] J. R. Calamia, R. J. Simonsen: J Dent Res Vol.63 (1984), p. 179.
