journal of dentistry 38 (2010) 290–295

available at www.sciencedirect.com

journal homepage: www.intl.elsevierhealth.com/journals/jden

A suitable base material for composite resin restorations: Zinc oxide eugenol Li-Hong He *, David G. Purton, Michael V. Swain Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, New Zealand

article info

abstract

Article history:

Objective: This in vitro study evaluated the effects of a zinc oxide eugenol (ZOE) base on the

Received 30 September 2009

mechanical properties of a composite resin restoration.

Received in revised form

Methods: Class I cavities were prepared on plastic teeth and filled with ZOE plus composite

25 November 2009

resin, following standard clinical procedures. The samples were sectioned sagittally and the

Accepted 30 November 2009

ZOE–resin interface was exposed. After polishing, nanoindentation was performed on the region near the interface, and elastic modulus and hardness were plotted in the form of a color contour map. SEM was employed to observe the interface between composite resin

Keywords:

and ZOE base.

Zinc oxide eugenol

Results: In the region close to the ZOE base, the elastic modulus and hardness of composite

Composite resin

resin reduced to the values of 9.71  0.54 and 0.51  0.05 GPa, respectively. Eugenol from

Dental base

ZOE had detrimental effects on the composite resin only to a distance of less than 100 mm

Nanoindentation

from the ZOE base. Conclusion: Although eugenol suppresses polymerization slightly, by considering the biological advantages of ZOE, together with the results of the current investigation, ZOE may still be considered a suitable base material for composite resin. Bonding is essential for composite resin restorations over ZOE bases to avoid shrinkage detachment. # 2009 Elsevier Ltd. All rights reserved.

1.

Introduction

With increasing demands for aesthetic restorations and development of tooth colored materials, composite resin has replaced amalgam and become the dominant plastic restorative material. However, zinc oxide eugenol (ZOE) cement, the traditional base for amalgam restorations may not be appropriate, as eugenol suppresses the polymerization of composite resin. The suppression effect appears to be due to the interaction between free radicals and eugenol.1 As a result, eugenol reduces the mechanical properties of composite resin.2,3 The prior use of a eugenol-containing temporary restoration (IRM) has been shown to affect the resin–dentin bond strength of etch-and-rinse (Single Bond, 3M ESPE, St.

Paul, MN, USA) and self-etch systems (Clearfil SE Bond, Kuraray Medical Inc., Tokyo, Japan and iBond, Heraeus Kulzer, Hanau, Germany).4 However, eugenol-containing materials have several advantages as bases for restorations. Eugenol can penetrate through the dentin and reach the pulp. Its diffusion from ZOE appears to depend more on the hydrolysis of eugenol than on dentin permeability.5 Eugenol is claimed to have sedative effects on the inflamed pulp and ZOE is considered an effective option for a dental cavity base, especially for deep cavities in teeth with reversible pulpitis.6 Eugenol released from ZOE has been shown to inhibit the biosynthesis of lipoxygenase products and the early chemotactic accumulation of leucocytes.7 Recent investigation of the influence of eugenol on

* Corresponding author at: Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, PO Box 647, Dunedin 9054, New Zealand. Tel.: +64 3 479 7084; fax: +64 3 479 5079. E-mail address: [email protected] (L.-H. He). 0300-5712/$ – see front matter # 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2009.11.009

journal of dentistry 38 (2010) 290–295

human macrophages (U937) under the stimulation of lipopolysaccharide (LPS) illustrated that eugenol was able to block the release of bone resorbing mediators, including interleukin1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and prostaglandin E2 from LPS-stimulated macrophages, suggesting a potential anti-inflammatory effect of eugenol in acute pulpitis and apical periodontitis.8 An electro-physiological study proved that eugenol inhibits P2X(3) activity, a pain receptor expressed in the trigeminal ganglion, which contributes to its analgesic effect.9 An in vitro study revealed that eugenol could inhibit macrophage function by impairing adherence capacity, and modulate immune and inflammatory reactions in dental pulp and periapical tissues.10 Investigation of the antibacterial effects of different liner materials illustrated that ZOE had the most marked inhibitory effect against Streptococcus mutans, which indicated that the material has the potential to prevent secondary caries.11 Another study on the antibacterial effects of root end filling materials identified that ZOE had the overall best antibacterial effects on both aerobic and anaerobic bacteria, among all the candidates including MTA, EBA and amalgam.12 An earlier investigation illustrated that ZOE had the potential to stimulate the remineralization of carious dentin.13 Moreover, ZOE is a better thermal insulator than most other lining materials including resin modified glass polyalkenoate, dentin bonding resins, and calcium hydroxide.14 All of the above factors suggest that ZOE is a suitable option as a base material for deep cavities, especially in those cases where it is difficult to remove all the affected dentine and in those with pulp inflammation, including preparations where some bacteria remain. Research has proven that the inhibitory effect of eugenol on the polymerization of composite resin is concentration dependent.1 Although low concentration of eugenol exerts anti-inflammatory and local anesthetic effects on the dental pulp tissue, high concentration of eugenol is cytotoxic.5,15 Therefore, in the clinical situation, the concentration of eugenol should not be too high, for reasons of biocompatibility and biosafety. The question is, to what extent does a ZOE base inhibit the polymerization of composite resin and reduce the mechanical performance of the fillings placed over it? The aims of the study were to use an ultra-micro-indentation system to investigate the mechanical properties of light-cured composite resin, placed over a typical eugenol-containing base material, and to verify the influence of eugenol on the polymerization of resins.

2.

Materials and methods

2.1.

Sample preparation

Class I cavities with a depth of around 5 mm were prepared in plastic molar teeth (model A5A-500, Nissin Dental Products Inc., Kyoto, Japan) in a simulation model. IRM (Dentsply, York, PA, USA) (Batch No. 0710011) was mixed by following the manufacturer’s instructions (one flat scoop of powder with one drop of liquid, which equals to 7 g of power with 1 g of liquid) and placed as a 2 mm thick base on the pulpal wall of the cavities. This thickness was chosen to facilitate mechani-

291

cal testing. Filtek Supreme XT (3M ESPE, St. Paul, MN, USA) (Batch No. 3910A4D), A4 shade, was chosen as the test composite resin. Three samples were prepared with different procedures. (1) Control sample: composite resin placed in a cavity with no base. (2) Standard sample: composite resin bonded over a ZOE base using 3-step etch-prime-bond Adper Scotchbond Multipurpose system (3M ESPE, St. Paul, MN, USA) (Expiry date: 2011-04). (3) No-bonding sample: composite resin placed over a ZOE base with no bonding. All restorations were done following standard procedures. The restored teeth were left on a laboratory bench for 24 h before cutting and polishing. The restored teeth were embedded in cold-curing epoxy resin (Epofix, Struers, Copenhagen, Denmark) and cut sagittally into halves using a high-speed cutting machine (Accutom-50, Struers, Copenhagen, Denmark) with a diamond cutoff wheel (331CA, Struers, Copenhagen, Denmark) at a spindle speed of 3000 rpm, under water irrigation. The cut surfaces of the samples were polished (TegraPol-21, Struers, Copenhagen, Denmark) to 1 mm diamond polishing paste.

2.2.

Nanoindentation test

The indentation experiments were performed using a nanobased indentation system (Ultra-Micro-Indentation System, UMIS-2000, CSIRO, Australia). The finished specimens were mounted on a metal base with wax. The mounting base contained a strong magnet to ensure adequate contact was obtained with the test base in the UMIS. The nanoindentation tests were performed at a load of 10 mN with a calibrated Berkovich indenter. The maximum load was held for 10 s to minimize the effect of creep on the unloading curve. The Oliver–Pharr analysis method16 was used by the software to calculate the elastic modulus and hardness. For each sample, 10  10 indentation arrays were made on the sample with an interval of 50 mm between indents to cover the ZOE–resin interface. Later, the elastic modulus and hardness values of each indent were plotted against its x and y coordinates to generate a color-coded contour map. For further comparison, additional indents were made on the composite resin 25 mm away from the designated ZOE–resin interface zone.

2.3.

SEM observation

All samples were then gold coated for scanning electron microscope (SEM) observation. A Cambridge S360 SEM (Cambridge Instruments, Cambridge, UK) with a secondary electron detector was employed to observe the samples.

3.

Results

3.1.

SEM observation

In Fig. 1A, near the ZOE interface in the standard sample, there is a less polymerized layer in the composite resin with a depth of 20 mm. In contrast, there is no similar layer in the composite resin of the sample without bonding (Fig. 1B). Bonding agent created an adhesive bonder layer of 10 mm in the standard sample and there was a gap of 20 mm between the ZOE base and the composite resin without bonding.

292

journal of dentistry 38 (2010) 290–295

sample has higher mechanical properties than the bonded sample at the same distance.

4.

Fig. 1 – SEM images of ZOE–resin interfaces of (A) standard sample and (B) no-bonding sample.

3.2.

Nanoindentation

From the control sample, Filtek Supreme XT composite resin had an elastic modulus of 15.47  0.98 GPa and a hardness of 1.03  0.16 GPa. The ZOE base had an elastic modulus and hardness of 7.58  0.70 and 0.17  0.02 GPa, respectively. From Fig. 2, it is obvious that ZOE base did not influence the polymerization and mechanical properties of the bulk of the composite resin. The region of reduced mechanical properties was restricted to the ZOE–resin interface. For the no-bonding sample, the composite resin detached from the ZOE base and there was a gap of around 20 mm. The black regions in the maps with elastic modulus less than 2 GPa and hardness less than 0.1 GPa are the reflection of this gap. The standard sample illustrates the compromised region of 50 mm away from the ZOE–resin interface (the region with the y coordinate of 300–350). For further comparison, data points of composite resin at different distances from the ZOE–resin interface were extracted and compared with the control values (Table 1). Table 1 illustrates that eugenol did have a suppression effect on the polymerization of the composite resin because the resin 25 mm away from the interface had significantly lower mechanical properties than the control. However, the effect of the eugenol is restricted to a region within 100 mm of the interface, at which point the mechanical properties are very similar to the control sample. Moreover, the no-bonding

Discussion

Although it has been widely accepted that eugenol suppresses the polymerization of polymers including composite resins, in practice, eugenol in IRM reduces the mechanical properties of composite resin within a limited range (less than 100 mm from the interface). Moreover, the less polymerized composite resin close to the interface (Fig. 1A) generates a graded region and provides a smooth transition from hard resin to soft ZOE base. From an engineering point of view, functionally graded materials are specifically designed to reduce the sharp mismatch of material properties at interfaces, to improve stress distribution and to limit detachment and cracking at the material interface.17,18 Furthermore, finite element analysis has indicated that both optimum stress magnitude and distribution are best served with low modulus restorative materials.19 In short, the suppressed region at the base of the composite resin restoration may have beneficial effects on the restorations. In addition, it is reasonable to assume that less polymerized material will have higher creep ability, which will be able to compensate for the curing shrinkage of the composite resin and help to maintain an intact bonding interface. When it comes to the influence of eugenol on the bonding strength of resin bonding systems, although it has been claimed that eugenol-containing temporary cements compromise the resin–dentin bond strength of the following permanent resin based cements,4 the overall effects were controversial and technique sensitive.20 Moreover, finite element analysis on class II MOD restorations has illustrated that the greatest von Mises stress was on the lateral walls, buccal and lingual, of the cavity.19 Therefore, the shear stresses at the interface between the ZOE base and composite resin restoration are less critical. In addition, after mixing following the manufacturer’s instruction, the IRM material was in a putty form which was very easy to place without contaminating the lateral walls of the cavity. The clean walls should ensure the effective bonding and a successful composite restoration. It has long been a concern that some components of restorative composite resins and adhesives are toxic.21 The mechanisms of cytotoxicity are related firstly to the shortterm release of free monomers during polymerization and secondly to the long-term release of leachable substances by erosion and degradation over time.22 Therefore, from biocompatibility and biosafety points of view, it would be better to have a base or liner under composite resin restorations, especially in deep cavities. Although there might be a higher residual monomer level within the composite resin near the ZOE–resin interface, the ZOE base will be able to block the penetration of the residual monomer into the pulp tissue. From Fig. 2 and Table 1, it is apparent that the sample without bonding was less affected by the eugenol. One possible reason is, without bonding, the polymerization shrinkage of the composite resin pulled the material from the surface of the base and generated a gap between the two

293

journal of dentistry 38 (2010) 290–295

Fig. 2 – Colored contour maps of elastic modulus and hardness across the interface of the three different samples investigated (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.).

Table 1 – Comparison of mechanical properties of composite resin at different distances from the ZOE–resin interface. Distance to ZOE–resin interface

25 mm 50 mm 100 mm *

Standard

No bonding

Control

Elastic modulus (GPa)

Hardness (GPa)

Elastic modulus (GPa)

Hardness (GPa)

Elastic modulus (GPa)

9.71  0.54* 14.28  0.71* 14.95  0.73

0.51  0.05* 0.90  0.09* 0.97  0.07

14.79  0.77* 14.65  1.04 15.60  1.02

0.96  0.14 0.95  0.11 1.19  0.22

15.47  0.98

Data have statistical difference to the control value (P < 0.05 by t-test).

Hardness (GPa) 1.03  0.16

294

journal of dentistry 38 (2010) 290–295

Table 2 – Mechanical properties of typical glass ionomer materials under wet conditions. Glass ionomers 23

Vivaglass Vitremer23 Fuji II LC23 Photac-Fil Quick24

Manufacturer

Elastic modulus (GPa)

Vivadent, Schaan, Liechtenstein 3M, St. Paul, MN (USA) GC, Tokyo, Japan 3M-ESPE, Seefeld, Germany

3.5  1.1 9.1  1.1 6.6  1.8 10

materials (Fig. 1B). Without the direct contact, it is reasonable to assume that the polymerization procedure was less disturbed by diffusion of the eugenol. However, in a clinical situation, gaps between the materials or between the tooth and restorations are not acceptable. Therefore, standard bonding procedures are essential for composite resin restorations. The current investigation revealed the elastic modulus and hardness of ZOE as 7.58  0.70 and 0.17  0.02 GPa, respectively. From previous investigations of typical glass ionomers (GI) (Table 2), ZOE has comparable elastic modulus and lower hardness than popular GI base materials.23,24 However, by considering the working location of a restoration base, which is an enclosed chamber, the hardness of the material is not critical. The pressure transmitted from an occlusal contact through the composite will primarily produce compression but not generate local stresses sufficiently high to cause permanent deformation. Therefore, mechanically, ZOE should be strong enough to act as a base and it has long been a choice of base for amalgam restorations. Moreover, if there is any microleakage around the restoration, the acidic buffering capacity and the antibacterial property of ZOE may help to reduce the chance of secondary caries.

5.

Conclusions

By considering the biological advantages of ZOE, together with the results of the current investigation, it can be concluded that, although eugenol slightly suppresses the polymerization, ZOE may still be considered as a suitable base material for composite resin. A bonder is essential for composite resin restorations over ZOE bases to avoid shrinkage-induced detachment.

Acknowledgement The authors would like to thank Mrs. Dianne Fox for the help with material preparation and Ms. Liz Girvan for the assistance with SEM.

references

1. Fujisawa S, Kadoma Y. Action of eugenol as a retarder against polymerization of methyl methacrylate by benzoyl peroxide. Biomaterials 1997;18:701–3. 2. Millstein PL, Nathanson D. Effect of eugenol and eugenol cements on cured composite resin. Journal of Prosthetic Dentistry 1983;50:211–5.

Hardness – 60 HV  0.6 GPa 58 HV  0.58 GPa 40 HV  0.4 GPa

3. Cohen BI, Volovich Y, Musikant BL, Deutsch AS. The effects of eugenol and epoxy-resin on the strength of a hybrid composite resin. Journal of Endodontics 2002;28:79–82. 4. Carvalho CN, De Oliveira Bauer JR, Loguercio AD, Reis A. Effect of ZOE temporary restoration on resin–dentin bond strength using different adhesive strategies. Journal of Esthetic and Restorative Dentistry 2007;19:144–52. 5. Abou Hashieh I, Camps J, Dejou J, Franquin JC. Eugenol diffusion through dentin related to dentin hydraulic conductance. Dental Materials 1998;14:229–36. 6. Hume WR. Pulp protection during and after tooth restoration. In: Mount GJ, Hume WR, editors. Preservation and restoration of tooth structure. London: Mosby International Ltd.; 1998. p. 203–10. 7. Hashimoto S, Maeda M, Yamakita J, Nakamura Y. Effects of zinc oxide-eugenol on leukocyte number and lipoxygenase products in artificially inflamed rat dental-pulp. Archives of Oral Biology 1990;35:87–93. 8. Lee YY, Hung SL, Pai SF, Lee YH, Yang SF. Eugenol suppressed the expression of lipopolysaccharide-induced proinflammatory mediators in human macrophages. Journal of Endodontics 2007;33:698–702. 9. Li HY, Lee BK, Kim JS, Jung SJ, Oh SB. Eugenol inhibits ATPinduced P2X currents in trigeminal ganglion neurons. Korean Journal of Physiology & Pharmacology 2008;12:315–21. 10. Segura JJ, Jimenez-Rubio A. Effect of eugenol on macrophage adhesion in vitro to plastic surfaces. Endodontics & Dental Traumatology 1998;14:72–4. 11. Boeckh C, Schumacher E, Podbielski A, Haller B. Antibacterial activity of restorative dental biomaterials in vitro. Caries Research 2002;36:101–7. 12. Torabinejad M, Hong CU, Ford TRP, Kettering JD. Antibacterial effects of some root end filling materials. Journal of Endodontics 1995;21:403–6. 13. Shimizu A, Hishida E, Shibatani T. A comparison of hardness between unsealed and sealed carious dentin. Journal of Osaka University Dental School 1981;21:153–63. 14. Little PAG, Wood DJ, Bubb NL, Maskill SA, Mair LH, Youngson CC. Thermal conductivity through various restorative lining materials. Journal of Dentistry 2005;33:585–91. 15. Markowitz K, Moynihan M, Liu MS, Kim S. Biologic properties of eugenol and zinc oxide-eugenol—a clinically oriented review. Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontics 1992;73:729–37. 16. Oliver WC, Pharr GM. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. Journal of Materials Research 1992;7:1564–83. 17. Kashtalyan M, Menshykova M. Three-dimensional elastic deformation of a functionally graded coating/substrate system. International Journal of Solids and Structures 2007;44:5272–88. 18. Pompe W, Worch H, Epple M, Friess W, Gelinsky M, Greil P, et al. Functionally graded materials for biomedical applications. Materials Science and Engineering 2003;A362:40– 60. 19. Ausiello P, Rengo S, Davidson CL, Watts DC. Stress distributions in adhesively cemented ceramic and resincomposite class II inlay restorations: a 3D-FEA study. Dental Materials 2004;20:862–72.

journal of dentistry 38 (2010) 290–295

20. Ganss C, Jung M. Effect of eugenol-containing temporary cements on bond strength of composite to dentin. Operative Dentistry 1998;23:55–62. 21. Geurtsen W. Biocompatibility of resin-modified filling materials. Critical Reviews in Oral Biology & Medicine 2000;11:333–55. 22. Goldberg M. In vitro and in vivo studies on the toxicity of dental resin components: a review. Clinical Oral Investigations 2008;12:1–8.

295

23. Cattani-Lorente MA, Dupuis V, Payan J, Moya F, Meyer JM. Effect of water on the physical properties of resinmodified glass ionomer cements. Dental Materials 1999;15: 71–8. 24. Wang XY, Yap AUJ, Ngo HC, Chung SM. Environmental degradation of glass-ionomer cements: a depthsensing microindentation study. Journal of Biomedical Materials Research Part B Applied Biomaterials 2007;82B: 1–6.

ID 3146115

Title A suitable base material for composite resin restorations: Zinc oxide eugenol

http://fulltext.study/journal/2838

http://FullText.Study

Pages 6