Surface Tension of Different Dentin Bonding Resin Systems

 
Mariane GONÇALVES
Jesus Djalma PÉCORA
Dionisio VINHA
Reginaldo Santana SILVA
 
Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil


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.


Introduction

Since the 1950s great emphasis has been placed on the study and development of dental materials especially in terms of dentin bonding due to the intense commitment of researchers and industry to obtaining products of proven efficiency (Buonocore et al., 1956; Bowen, 1965; Solomon and Beech, 1983; Youngson et al., 1990). At the same time, more profound knowledge about dentinal structure is necessary so that dentin bonding resin systems can be developed in such a way that their properties are compatible with the characteristics of dental tissue, with special reference to dentinal structure.

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.


Material and Methods

The following 4 fourth generation adhesive resin systems and a resin cement with metal affinity were used in the present study: All Bond 2, Denthesive Bond, Scotchbond Multi-Purpose, Optibond and Panavia Ex. The composition and manufacturers of these bonding systems are described in Table 1.

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.


Results and Discussion

According to Erickson (1992), when adhesive systems are applied to the dental structure, a high surface tension and low viscosity are necessary for the formation of a uniform adhesive film. However, the surface tension value of the adhesive agent must not exceed that of dentin, and the viscosity should be sufficiently low so that the equilibrium point of optimal wetting can be rapidly achieved. Therefore, the use of primers to obtain adhesion becomes extremely important for adequate superficial wetting of dentin, given that these solutions present surface tension values lower than 42.23 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.


Acknowledgments

The authors are indebted to Albertina A. Teixeira, Antonio de Campos and Edna A.S. Moraes for technical assistance.


References

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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


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