Dentin Enamel Bonding Systems: Generations and Current Trends

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Table of Contents

Introduction
Generations in Dentin Enamel Bonding Systems
Etching in Adhesive Dentistry and Composite Systems
Current Trends in Dentin Enamel Bonding Systems
Conclusion
References

Introduction

Dentin enamel adhesion systems have revolutionized the field of dentistry. The concept of using the natural micro-porosities present in the dentin and enamel structure for micromechanical adhesion has led to creation of a new line of cements and composites that have eliminated amalgam and other macro-retentive restorations. Initial attempts at creating such systems were successful for enamel, but not for dentin due to the unique anatomy and high water content of the structure.

Generations in Dentin Enamel Bonding Systems

The first generation aimed at creating an effective adhesion system for dentin. This led to the creation of dentine adhesive systems such as NPG-GMA and N-phenylglycerine respectively.
The second generation invented the coupling systems, bonding dentin on one end and the composite at the other end. Examples of such systems include bis-GMA and HEMA.
The third generation introduced the primers, which modified the dentinal surface to become more adhesive by retaining the shape of the dentinal tubules. This system included 4-META and BPDM.
The fourth generation introduced complete removal of the smear layer, and proposed the concept of a hybrid layer. In this generation the total etch technique was created where by both dentin and enamel could be etched simultaneously.
The fifth generation reduced the number of steps involved in the preparation of the tooth surface. This generation included the one bottle systems and self etching primer systems respectively.
The sixth generation achieves bonding by using a one solution system.

The many efforts in mastering bonding to enamel and dentine are visible by the number of generations of adhesive systems that were introduced during the years. Essentially, these systems were modified to address etching of enamel, the etching and then conditioning of dentine, the treatment of the smear layers, and creating better handling properties of the composites (Kugel and Ferrari, 2000). Each generation showed one significant improvement towards the current dentin enamel bonding system. The first generation shows one of the first attempts at creating an effective dentinal system such as N-phenylglycerine and glycidyl methacrylate, or the NPG-GMA. These systems however, failed due to lack of bond strength (Kugel and Ferrari, 2000).

The second generation introduced coupling agents aimed to engage dentine at one end and the composite at the other end. These included the bisphenol-A-glycidyl methacrylate or bis-GMA and hydroxymethyl methacrylate or HEMA (Kugel and Ferrari, 2000).

The third generation introduced the primers, which were aimed to modify the smear layer of the dentin in order to make it more adhesive. The primer is composed of hydrophilic resin monomers, such as hydroxymethyl trimellitate anhydrate or 4-META and byphenyl dimethacrylate or BPDM (Kugel and Ferrari, 2000).

The third generation was replaced by the fourth generation, which completely removed the smear layer. Furthermore, the concept of hybrid layer came in to existence. The hybrid later was made up of polymerized meth-acrylate and dentin. This technique came to be known as the total etch technique, as both the dentine and the enamel could be etched simultaneously (Kugel and Ferrari, 2000).

The fifth generation system was aimed at improving the dentin enamel bonding system by reducing the number of steps in the bonding procedure. This generation also aimed to prevent the collapse of collagen in the demineralized dentin. This generation consists of one bottle systems and the self etching primer system (Turkun 2005). The first type uses a combination of the primer and adhesive of 35 to 37 percent phosphoric acid for 15 to 20 seconds. The second system of self etching primer comprises of aqueous solution of 20 percent phenyl-P in 30 percent HEMA (Kugel and Ferrari, 2000).

The sixth generation system is a recent innovation where bonding can be achieved using one solution. These systems can simultaneously be used for both dentin and enamel; however, studies have shown a lesser bond strength to enamel. Further research in this area is underway (Kugel and Ferrari, 2000). These systems however, in clinical studies and researches have shown good performance results when evaluated on the basis of color matching, marginal discoloration, marginal adaptation, initial caries formation, anatomical form, post operative sensitivity and retention loss respectively (Turkun 2005).

Etching in Adhesive Dentistry and Composite Systems

The concept in this system is the etching of the surface of enamel and dentine. This leads to the exposure of porosities in the two structures, which can then be used as retentive tags for resin fillings (Perdigao et al, 2000). Enamel is a relatively dry structure, which is why resin bonding systems bind better with it. The dentine, due to its more complex anatomy, and its water content, is a more difficult structure to etch (Perdigao et al, 2000). Attempts to create an ideal tooth bonding system would include one that is able to bond to both dentin and enamel structures successfully (Perdigao et al, 2000).

Currently there are two types of etching systems available in the market. In the total acid etch system; both dentin and enamel are exposed to direct acid. The acids used in these systems include citric acid, and 20 to 40% ortho-phosphoric acid respectively (Paradella, 2007). In these systems, the acid is then rinsed off, and the tooth surface is dried. On this dried surface a primer is applied. The primer helps in restoring the shape of the collagen fibers present in the dentin which become collapsed due to the application of the acid. The proper shape of the collagen fibrils ensure a better adhesion of the composite to the tooth surface (Paradella, 2007).

The self etching system does not include a separate step for etching of the tooth structure. These systems utilize the smear layer by fixing it to its tubules and thereby strengthening it, and then fix the composite on to it (Paradella, 2007). These systems are further divided into self etching primer systems and the self etching adhesive systems, in which the primer, bond and adhesive are delivered in one bottle, making it a one step system (Paradella, 2007).

The micro-adhesion that is attained in dentin and enamel is due to etching of the tooth surface with an acid. While etching and thereafter bonding to enamel surface is easier, the dentin surface poses problems due to its increased water content. Currently there are two etching systems available: the total acid-etch system and the self etching system respectively. The later system differs from the first as there is no separate etching step required in the tooth surface preparation. The self etching system is further divided in to self etching primer systems and the self etching adhesive systems respectively.

Current Trends in Dentin Enamel Bonding Systems

Current researches are aimed at creating biological and antibacterial properties in the bonding systems in order to prevent the recurrence of caries underneath the fillings, which usually develop due to residual bacteria in the dentinal tubule left behind during preparation time.

With the creation of effective etching and bonding systems, the new areas of research in adhesive dentistry include the addition of antibacterial properties and bio-functional advantages to these systems (Turkun 2005 and Feuerstein et al, 2007). Dentists believe that the retention of bacteria in the uninfected dentin is one of the primary causes of failures in such restorations. New bonding systems therefore are integrating biological systems such as methacryloxy dedecyl pyridinium bromide or MDPB and studying their efficacy (Turkun 2005 and Feuerstein et al, 2007). Such systems promise better results in the field of restorative and adhesive dentistry.

Conclusion

Dental adhesive systems have come a long way since their inception. New researches are underway in order to make them better systems.

The dentine enamel system has revolutionized the field of dentistry, and introduced a new concept of adherence of cements in this field. The concept of using the natural micro-porosities present in the dentin and enamel structure for micromechanical adhesion has led to creation of a new line of cements and composites that have virtually eliminated amalgam and other macro-retentive restorations. Even more so, the major breakthrough in adhesive dentistry came with the introduction of separate dentine and enamel systems (Turkun 2005).

The concept of adhesive dentistry is actually based on the use of micro-porosities as retentive grooves to hold the filling and composite in place. It was easier to gain adhesive properties on the enamel, but was not so in the case of dentine. Enamel is a relatively dry structure. Dentine, on the other hand, comprises of more collagen (17%) and water and fluid content than enamel, which made it very difficult to create a dentinal adhesive system (Kugel and Ferrari, 2000). Dentine was also difficult due to the age changes that affect its porosity. Finally, the presence of smear layer was another impeding factor in ideal dentinal bonding (Turkun 2005).

References

Cachute P T (2007). Current Adhesive Systems in Dentistry- What is being Said and Researched. Odontologia Clin-Cientiff Recife 6(4), 293-298.

Fueurstein O, Shlomo M, Hagay S and Ervin I W (2007). Antibacterial Properties of Self-Etching Dental Adhesive Systems. JADA 138(8), 349-54.

Kugel G and Ferrari M (2000). The Science of Bonding: From First to Sixth Generation. JADA, 131(1), 20S-24S.

Perdigao J, Frankenberger R, Rosa BT and Breschi L (2000). New Trends in Dentin/Enamel Adhesion. Am J Dent Nov13(Spec No), 25D-30D.

Sebnem T L (2005). The Clinical Performance of One and Two-Step Self Etching Adhesive Systems at One Year. JADA 136, 656-664.

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