Comparison of shear bond strength of amalgam ...

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ISSN 0970 - 4388

Comparison of shear bond strength of amalgam bonded to primary and permanent dentin MAHDI S.a, BAHMAN S.a, ARGHAVAN A. B.b, FATEMEH M.c

Abstract Amalgam’s non-adhesive characteristics necessitate cavity preparations incorporating retentive features, which often require the removal of non-carious tooth structure. Use of adhesives beneath amalgam restorations, would be helpful to overcome this disadvantage. This study was undertaken to compare the mean shear bond strength of amalgam bonded to primary and permanent dentin, to evaluate the efficacy of amalgam adhesives in pediatric dentistry.27 primary and 28 permanent posterior teeth with intact buccal or lingual surfaces were grounded to expose dentin and wet-polished with 400-grit silicone carbide paper. Scotchbond Multi Purpose Plus adhesive system was applied to the dentin surfaces and light cured. Amalgam was condensed onto the treated dentin through a plastic mold.shear bond strength testing was done using an Instron Universal testing machine, at a crosshead speed of 0.5 mm/min.The data were analyzed by independent samples t-test The difference among the two groups was not statistically significant (p>0.05) Bonded amalgam showed the same level of bond strength to primary and permanent dentin; so, application of amalgam bonding agents in pediatric dentistry can be recommended. Keywords: Missing?????

Introduction

bonded amalgam technique in primary teeth.[3-24] This in vitro study was undertaken to compare the mean shear bond strength of amalgam bonded to primary and permanent dentin, using a 4th generation adhesive system, to evaluate the efficacy of bonded amalgam restorations in pediatric dentistry.

Despite the advances in resin-based composite and adhesive systems, amalgam, after more than a century of proven clinical performance, remains the most popular restorative material for posterior restorations in both primary and permanent teeth. Its long and successful use has been the result of its relative ease of manipulation, good wear resistance, and reasonable cost to the patients.[1-4] However Lack of adhesion and early micro leakage, are significant disadvantages to its use as a restorative material. Since amalgam does not bond to tooth structure, cavity preparations for amalgam restorations traditionally has incorporated mechanical retentive features requiring additional removal and possible weakening of remaining tooth.[5,6]

Materials and Methods In this study, 28 permanent and 27 primary extracted human posterior teeth with intact buccal or lingual surfaces were used. The teeth were stored in tap water at room temperature after extraction. After separation of all debris, specimens were mounted in acrylic resin and the buccal or lingual enamel removed to produce a flat dentin surface parallel to the long axis of the tooth. In order to obtain a uniform flat surface and fresh smear layer, dentin surfaces were ground wet with 400-grit silicone carbide paper and rinsed with water prior to adhesive procedures.

Since the mid-1980’s, adhesive resin systems have been advocated for use in bonding amalgam to tooth structure. Dentin adhesives, used as liners in amalgam restorations, reportedly improve retention, strengthen restored teeth in vitro, and may allow a more conservative approach to cavity preparation.[4,7] Reduction of micro leakage is another reported benefit of using dentin adhesives for amalgam bonding. Micro leakage at the tooth/restoration interface can lead to sensitivity, recurrent caries, marginal staining, pulpal damage and ultimate failure of the restoration.[4] Despite the large amount of research on the efficacy of bonded amalgam technique in permanent teeth, little research has addressed

Dentin was etched with 35% phosphoric acid for 15 seconds, and dried for 1-2 seconds, leaving the surface visibly moist. Scotchbond Multi Purpose Plus activator was applied on the etched dentin surface, left for 5 seconds and air dried with a gentle. Air stream for 5 seconds. Scotchbond Multi Purpose Plus primer was brushed on the surface, and gently air dried for 5 seconds. One drop of Scotchbond Multi Purpose Plus adhesive was mixed with one drop of Scotchbond Multi Purpose Plus catalyst and applied in a thin layer and light cured for 10 seconds prior to triturating and hand-condensing the amalgam.

a

Assistant Professor, bDentist, cDDs, MSC Degree Student of Pediatric Dentistry, Department of Pediatric, School of Dentistry, Tehran University of Medical Science, Tehran, Iran

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Shear bond strength of amalgam bonded

A cylindrical plastic mold of 3 mm in diameter was secured onto the dentin surface, and a pre-dosed capsule of high copper admixed alloy (Sinalux) was triturated and immediately condensed into the mold. After storage in distilled water for 24 hours, the mold was cut off and carefully removed. All specimens were stored in the room temperature distilled water for 7-10 days and thermo cycled 500x between 5 and 55ºC, with a dwell time of 15 seconds in each bath and a transfer time of 10 seconds. A shear strength test was performed with an

these variations could be responsible for the high standard deviations and wide ranges obtained in the present study. As mentioned before, in this study, the adhesive was lightcured for 10 seconds before placing the amalgam. The results of a study by Cobb et al indicated that light curing of Scotchbond Multi Purpose Plus adhesive system, significantly increases the bond strength of amalgam to dentin.[4] The results of another study by Winkler et al also revealed that the bond strength of dual-cure amalgam adhesives to dentin is more than the self-cure ones.[26]

Instron Universal testing machine (model # 1195) at a crosshead speed of 0.5 mm/min until fracture.

The mean shear bond strength obtained in this study for permanent teeth was 6.59±2.64 MPa, which is significantly less than the result obtained by Cobb et al which was 10.3±2.3 MPa.[4] It can be attributed to the different method and materials used in these two studies, such as amalgam type, condensation force, type of testing machine etc. which can possibly influence on the results.

Results For The results of shear bond strength testing the two test groups evaluated are provided in Table 1. Independent samples t-test indicated no statistically significant difference between two groups. (P>0.05)

The results of this study showed no significant difference between shear bond strength of amalgam to primary and permanent dentin. These results are comparable to the results obtained by Baghdadi which suggested that the bond strength of amalgam bonded to primary and permanent dentin by a 5th generation light-cure dentin adhesive was equal.[24] It can be attributed to the mode of failure usually reported in the studies on bonded amalgam in primary and permanent teeth. In these studies the failures occur in the interface between amalgam and the adhesive resin and so is independent to the dentin type, at least when the dentin is normal.[3-24]

Discussion Preservation of primary teeth in the arch is important for the management of the developing dentition and in nurturing a positive attitude in children toward dental health.[24] In nations where there are millions of patients (adults and children) who show a high caries prevalence and the people often are just discovering the potential problems of dental disease with little or no funded public health strategy for its prevention, dental amalgam is a very important part of their dental care plan for the foreseeable future.[24]

It can be explained by the mechanism of bonding amalgam to tooth structure. The adhesive interface between the tooth and amalgam restorations relies on micromechanical retention of the bonding agent to the both dentin and amalgam. The nature of adhesive bond to tooth structure has been well documented. Previous comparative studies of adhesives, reported higher dentin shear bond strength to composite than those found to amalgam. These findings suggest that the weak link in the bonded amalgam may be the micromechanical bond formed between the resin and amalgam. Scotchbond Multi Purpose Plus includes a self-curing adhesive component for amalgam bonding. Micromechanical retention is based upon the amalgam mixing with resin during condensation and subsequently interlocking upon polymerization.[4]

This in vitro study measured the shear bond strength of an admixed amalgam alloy to primary and permanent dentin, using the 4th generation bonding system: Scotchbond Multi Purpose Plus. Unfortunately, comparison of one-bottle adhesives to multi-bottle adhesives reveals that the former still are not quite as versatile as those with two or more bottles, which also are less technique sensitive.[24] Bond strength studies are quite rough categorizing tools for evaluating the efficacy of bonding materials. Several factors influence in vitro bond strength to dentin, such as the type and the age of the teeth, the degree of dentin mineralization, the dentin surface being bonded, the type of bond strength test (shear or tensile), the storage media, and the environmental relative humidity.[25] In substrates and testing conditions,

This in vitro study as well as all other studies, was performed on noncarious surfaces of teeth. In vivo conditions may not be as ideal. Normal dentin is more permeable than carious or sclerotic dentin.[24] At least two studies showed that bond strength of current bonding systems to caries -infected and caries-affected dentin, were significantly different from those to normal dentin.[27,28]

Table 1: Mean shear bond strength (MPa) and standard deviation of two groups Group Primary Permanent

N 27 28

Mean (MPa) 6.2926 6.5904

S.D. (MPa) 2.32136 2.46484


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P-value 0.647

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Shear bond strength of amalgam bonded

Conclusion

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According to the results obtained within the limitations of this laboratory study, it was determined that Scotchbond Multi Purpose Plus adhesive system gave the same level of bond strength to primary and permanent dentin. Although laboratory testing of adhesive systems provides a mechanism to screen newly developed systems, or evaluate the new applications of current adhesives, clinical trials are essential to document long-term clinical performance. Therefore, the system also should be evaluated clinically.

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McDonald RE, Avery David R. Dentistry for the child and adolescent. 8th ed. St. Louis: Mosby; 2004, chap 4, 16. John GA, Luiz BN, Monteiro S, Ritter AV. Adhesive restorations with amalgam: Guidelines for the clinician. Quintessence Int 1994;25:687-95. Myaki SI. Micro leakage in primary teeth restored by conventional or bonded amalgam technique. Braz Dent J 2001;12:197-200. Cobb DS, Denehy GE, Vargas MA. Amalgam shear bond strength to dentin using single-bottle primer-adhesive systems. Am J Dent 1999;12:222-6. El-Kalla IH, Garcia-Godoy F. Fracture strength of adhesively restored pulpotomized primary molars. J Dent Child 1999;66:23842 Rasheed AA. Effect of bonding amalgam on the reinforcement of teeth. J Prosthet Dentist 2005;93:51-5. Zidan O, Abdel-Keriem U. The effect of amalgam bonding on the stiffness of teeth weakened by cavity preparation. Dent Mat 2003;19:680-5. Staninec M, Holt M. Tensile adhesion and micro leakage of resin bonded amalgam restorations. J Prosthet Dent 1988;59:397402. Torii Y. Inhibition of caries around amalgam restorations by bonding amalgam to tooth structure. Oper Dent 1989;14:142-8. Staninec M. Retention of amalgam restorations: Undercut versus bonding. Quintessence Int 1997;28:717-23. Charlton DG, Moore BK, Swartz ML. In vitro evaluation of the use of resin liners to reduce micro leakage and improve retention of the amalgam restorations. Oper Dent 1992;17:112-9. Eakle WS, Staninec M, Lacy AM. Effect of bonded amalgam on the fracture resistance of teeth. J Prosthet Dent 1992;68:257-60. Hadavi F, Hey JH, Strasdin RB, McMeekin GP. Bonding amalgam

Reprint requests to: Dr. Seraj Bahman Department of Pediatric, School of Dentistry, Tehran University of Medical Science, Tehran, Iran

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