Braz Dent J (1997) 8(1): 43-47 ISSN 0103-6440
| Introduction | Material and Methods | Results and Discussion | Acknowledgments | References |
Surface tension together with the hybridization process is one of the factors required to attain hybrid layer formation in dentinal tissue when bonding resin systems are used. The objective of the present study was to determine the surface tension of primers and fluid resins of 4 fourth generation bonding systems (All Bond 2, Denthesive Bond, Scotchbond Multi-Purpose and Optibond) and of one resin cement with metal affinity (Panavia Ex), all of them commonly used by Brazilian dentists. All primer solutions presented a lower surface tension than dentin, suggesting that all bonding systems are capable of wetting the tissue and probably cause tissue hybridization. The resin cement demonstrated the highest value, about 2 times that of dentin, which leads us to suppose that it is inefficient in deeply wetting the dentinal structure, without implying inefficient bonding since its analysis is multi-factorial.
Key Words: surface tension, dentin bonding systems, primer.
Therefore, the presence of primer solutions in third and fourth generation dental adhesive systems is justified by the need to achieve “wetting” of dentinal tissue by the hydrophilic monomers of these systems, permitting the subsequent infiltration of hydrophobic monomers, constituents of the fluid resins or dentin bonding agents, which in turn results in the formation of the hybrid layer (Nakabayashi et al., 1991). In order to obtain wetting of the dentinal surface, the liquids or solutions involved in the bonding process should present, among other properties, a surface tension compatible with that of dental tissue. Dentin in particular, due to its peculiar composition and structural arrangement (Marshall Jr., 1991; Butler, 1992), can only be moistened by a liquid with a surface tension equal to or lower than 42.23 dynes/cm (Erickson, 1992). If the primers and bonding resins satisfy this requirement in addition to having adequate viscosity, the equilibrium point of optimal wetting can be achieved, with a consequent truly effective bonding system (Baier, 1992; Erickson, 1992).
The objective of the present study was to determine the surface tension of primer agents and fluid resins of different fourth generation dentin bonding resin systems and of a resin cement with metal affinity, which are currently available in Brazil and are frequently used by professionals.
The surface tension of the products was determined by the method described by Moore (1968) and used by Pécora et al. (1991). Measurements were carried out at a standard temperature of 25oC in a special chamber using the capillary method. Two glass capillary tubes with an internal diameter predetermined by microscopic measurement were used. The mean surface tension values were then calculated and are reported as dynes/cm.
Table 2 shows that, except for the resin cement Panavia Ex which does not include a primer in its formulation, all primer solutions of the products analyzed had mean surface tension values lower than 42.23 dynes/cm, i.e., they fulfilled their function of “wetting” the dentinal surface adequately in terms of preparing the surface for the fluid resin. Once dentin becomes compatible with the fluid resin due to the presence of hydrophilic monomers in the primers, the fluid resins applied to the dentinal structure are capable of forming the hybrid layer since they possess a monomeric composition chemically compatible with that of the primers.
Regarding the values obtained for the fluid resins of the adhesive systems, we observed that only Optibond had the ability to wet the dentinal structure with a value of 34.07 dynes/cm. However, although the results obtained for All Bond 2, Denthesive Bond and Scotchbond MP were higher than desired, the wetting process of the dentinal structure and attainment of hybridization would have been already initiated by the previous application of the primer solution, and all of these products, as mentioned above, are capable of wetting the dentin.
In turn, the resin cement with metal affinity, Panavia Ex, presented the highest surface tension value (107.27 dynes/cm). This material is a powder-liquid system that, when manipulated, demonstrates higher viscosity compared to a liquid resin system, which may be associated with the high mean value observed, suggesting probable inefficiency in terms of wetting the dentin and penetration of the dental cement.
It is important to emphasize that hybridization and the type of hybrid layer formed in terms of dentinal impregnation depth, formation of tags or even bond strength cannot be evaluated by taking only one aspect into account, since this process suffers a multi-factorial influence.
According to the literature, the establishment of an effective adhesive interface is influenced by innumerable factors related to both the dental substrate and the proper material (Tyas et al., 1988; Uno and Asmussen, 1992; Van Meerbeek et al., 1992; Elíades, 1994; Swift Jr. and Fortin, 1995). Among these factors are the specific composition of the product, hydrophilic-hydrophobic equilibrium of the primer, thickness of the adhesive film, surface tension of the adhesive system solutions, polymerization type, polymerization contraction, degree of dental humidity, calcification level of the dentin, presence of a smear layer, conditioning type of the dental structure, and others.
Therefore, the resin cement Panavia Ex and its supposed inefficiency in terms of superficial wetting do not necessarily imply inefficient bonding. The adhesive monomer MDP (methacryloyloxydecyldihydrogen phosphate) present in this material yields satisfactory results in adhesive amalgam techniques and in cases of cementation in fixed prostheses (Atta et al., 1990; Alberton et al., 1993; Cantarelli et al., 1996).
Finally, we emphasize that knowledge and understanding of the hybridization process as well as of the adhesive interface is a continuous learning process depending on constant updating on the basis of the innumerable studies currently related to this topic.
Atta MO, Smith BGN, Brown D: Bond strengths of three chemical adhesive cements adhered to a nickel-chromium alloy for direct bonded retainers. J Prosthet Dent 63: 137-143, 1990
Baier RE: Principles of adhesion. Operat Dent (Suppl 5): 1-9, 1992
Bowen RL: Adhesive bonding of various materials to hard tooth tissues. The effect of a surface-active comonomer on adhesion to diverse substrates. J Dent Res 44: 1369-1373, 1965
Buonocore MG, Wileman W, Brudevold F: A report on a resin composition capable of bonding to human dentin surfaces. J Dent Res 35: 846-851, 1956
Butler WT: Dentin extracellular matrix and dentinogenesis. Operat Dent (Suppl 5): 18-23, 1992
Cantarelli MMC, Matos AB, Oda M: Amálgama adesivo. Rev Odontol USP 10: 137-144, 1996
Elíades G: Clinical relevance of the formulation and testing of dentine bonding systems. J Dent 22: 73-81, 1994
Erickson RL: Surface interactions of dentin adhesive materials. Operat Dent (Suppl 5): 81-94, 1992
Marshall Jr GW: Dentin: microstructure and characterization. Quintessence Int 24: 606-617, 1993
Moore WJ: Fisico-química. Universidade de São Paulo, Rio de Janeiro, 1968
Nakabayashi N, Nakamura M, Yasuda N: Hybrid layer as a dentin-bonding mechanism. J Esthet Dent 3: 133-138, 1991
Pécora JD, Guimarães LF, Savioli RN: Surface tension of several drugs used in Endodontics. Braz Dent J 2: 123-127, 1991
Solomon A, Beech DR: Bond strength of composites to dentin using primers. J Dent Res 62: 677, Abstract 253, 1983
Swift Jr EJ, Fortin D: Update on enamel and dentin bonding. J Dent Québec XXXII: 91-97, 1995
Tyas MJ, Alezander SB, Beech DR, Brockhurst PJ, Cook WD: Bonding - retrospect and prospect. Austral Dent J 33: 364-374, 1988
Uno S, Asmussen E: Selected variables in bonding to dentin. Scand J Dent Res 100: 130-132, 1992
Van Meerbeek B, Lambrechts P, Inokoshi S, Braem M, Vanherle G: Factors affecting adhesion to mineralized tissues. Operat Dent (Suppl 5): 111-124, 1992
Youngson CC, Grey NJA, Martin DM: In vitro marginal microleakage associated with five dentine bonding systems and associated with composite restorations. J Dent 18: 203-208, 1990
Correspondence: Mariane Gonçalves, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, 14040-904, Ribeirão Preto, SP, Brasil.
Accepted January 5, 1997
Electronic publication: September, 1997