Cosmetic or esthetic dentistry is generally used to refer to any dental work that improves the appearance (though not necessarily the function) of a person's teeth, gums and/or bite. This era started with the great advancements in adhesive dentistry or mainly in due to the rapid advancements in the bonding technology which made is possible to achieve acceptable bond strengths of tooth color materials to natural teeth and restorations. There can be no clinic in present times where bonding agent is not used several times each day. Let us look and understand this bonding process has evolved. We also shed light on often confusing issue of different generations of bonding agents.
The first- and second-generation bonding agents used during the 1960s and 1970s did not recommend etching the dentin, but instead relied on adhesion to the attached smear layer. The weak bond strength (2MPa–6MPa) to the smear layer still allowed dentin leakage with clinical margin stain.
The third-generation systems of the 1980s introduced acid etching of dentin and a separate primer designed to penetrate the dentin tubules as a method to increase bond strength. These systems increased bond strength to dentin (12MPa–15MPa) and decreased dentin margin failure. With time, however, margin staining caused clinical failure.
The fourth-generation adhesive systems of the early 1990s used chemistry that penetrated both etched and decalcified dentin tubules and dentin substrate, forming a “hybrid” layer of collagen and resin. Fusayama and Nakabayashi described the penetration of resin into dentin as giving high bond strengths and a dentin seal. In fact, Kanca introduced the idea of “wet bonding” with these systems. Products in this category include All-Bond® (Bisco), OptiBond® FL (Kerr), and Adper™ Scotchbond™ Multipurpose (3M ESPE). These bonding agent systems have the longest track record as far as research goes and they perform well clinically. In fact, OptiBond FL, an 18-year-old product, received the Product of the Year award from Reality magazine.8 Bond strengths for these adhesives were in the low- to mid-20MPa range and significantly reduced margin leakage compared to earlier systems. This system was very technique sensitive and required an exacting technique of controlled etching with acid on enamel and dentin, followed by two or more components on both enamel and dentin. Because of the complexity of multiple bottles and steps, dentists began requesting a simplified adhesive system. Fourth generation adhesive systems were very technique sensitive. Examples
To overcome the technique sensitive aspect was the main goal of developing the fifth-generation bonding systems, introduced during the mid 1990s, which combined primer and adhesive in one bottle while maintaining high bond strengths. Unit-dose packaging introduced during this era provided fresh chemistry for each procedure. Yet controlled etching, surface wetness, and resin placement continued to be a clinical challenge for some clinicians. These are still being used and give us very good bond strenths. Examples are
The sixth-generation bonding systems introduced in the latter part of the 1990s and the early 2000s—also known as the “self-etching primers”—were a dramatic leap forward in technology. The separate acid-etching step was eliminated by incorporating an acidic primer that was placed on the enamel and the dentin after tooth preparation. Several variations involved either mixing the acidic primer and adhesive before placement on the dentin and enamel, or leaving the primer on the tooth and then placing the adhesive over the primer.
These systems were also reported to reduce the incidence of post-treatment sensitivity found in previous systems. However, the bond strength to dentin and enamel is lower than fourth- and fifth-generation systems. Product in this category are
All-In-One is a single-component, self-etch adhesive that eliminates multiple steps when bonding direct and indirect restorations. Clinicians have everything they need for etching, priming and bonding in one material. These have been improving quality rapidly. Examples are
A self-adhering flowable composite combines the benefits of adhesive and composite technology into one product, bringing restorative techniques to new unprecedented heights. Simply syringe into the preparation, agitate, and light-cure. Immediately upon application it conditions, bonds, and seals without the need for an etchant or an adhesive. Two examples of this kind of product areFusio™ Liquid Dentin from Pentron Clinical
In an excellent overview of factors that affect the bond strength of bonding agents, Powers et al point out that the type of substrate (ie, superficial dentin, deep dentin, permanent/primary dentition, carious dentin), phosphoric acid/acidic primers, preparation by air abrasion and laser, moisture, contaminants, desensitizing agents, and self-cured/light-cured restorative materials all affect the bond strength; bond strength is reduced by more than 50% when bonding conditions are not ideal.
Further, when lasers are used to prepare hard tissues, studies show that bonding to these surfaces may be more problematic than bonding to conventionally bur-prepared preparations.
Rushing to complete such procedures by reducing the priming time from 20 to 5 seconds can cause a 17% reduction in mean bond strength. In contrast, using a 20-second application time to agitate a self-etch adhesive significantly improves the shear bond strength to dentin. In addition to agitation, rather than applying a single coat of adhesive resin on dentin, up to four additional coatings increase the bond strength and decrease nanoleakage.
Multiple research reports attest to the existence of material incompatibilities that depend on formulation, and that bond strengths can be reduced by 45% to 90% or more when incompatible combinations are applied clinically.
Acetone-based adhesives show a high degree of technique sensitivity, and over- or under-drying the acid-etched dentin compromises the bond. Simplification of the bonding procedure does not necessarily lead to improved bonding performance, especially in the long term. Alex perhaps has stated it best: “The bottom line is, it is incumbent on every dentist to learn about their specific adhesive system, its idiosyncrasies, its strengths and weaknesses, and how to maximize its performance.”
[an error occurred while processing this directive]