Historically, self-etch systems are good at bonding to dentin but have not performed as well when bonding to enamel because there is not a strong etching component to maximize the enamel etch.
Therefore, when bonding a restoration to a preparation that is all or mostly enamel, a self-etch system may not be the best choice. Self-etching systems are improving in adherence. However, some researchers are concerned that seventh-generation systems involve complex chemistry and, thus, potential risk variables may be present. Complex chemistry is being used to bond important restorations. The directions are designed by the chemists to maximize the bond strengths of the materials, so it is essential to take advantage of their research and specific products.
Bonding agents will continue to change and improve—therefore, it is important to remain up-to-date on their clinical applications and mechanisms. Understanding the different types of bonding agents is important in order to know which ones to use for which types of restorations. Radz has no financial relationships with the manufacturers mentioned in this article.
Gary M. Navigation Home Publications Publications. Don't miss an issue! Q: When using three-step bonding in bottles, e. A: The product must be used prior to the expiry date. The problem is that solvent evaporates from the primer bottle, making it a little thicker than usual. It no longer flows and wets the surface well enough. It loses its functionality. The bottles should then be replaced and not used. This phenomenon creates bubbles or voids in the material.
These voids weaken the material and attract water which eventually leads to degradation of the matrix by hydrolysis. A: It is not necessary as long the dentine is not desiccated over-dried. Not too dry, not too wet, just moist. The restoration was light cured 20 seconds from the occlusal, then 10 seconds from both the buccal and palatal aspects.
The matrix was removed and the occlusion was checked. Finally, the restoration was polished Figures 11 to Any excess powder was blown out with compressed air Figure The application of Futurabond U was mixed Figures 16 to 19 and placed into the crown for 20 seconds. The crown was then air-dried for 5 seconds to remove the solvent, and then to thin the material. The bonding agent was then light cured for 10 seconds Figure A resin cement Breeze [Pentron] was dispensed into the crown and then the crown was placed into the mouth.
Next, the margins were light cured for one second. The excess cement in a gel state was then removed with an explorer, then the remainder of the cement was allowed to cure for 4 minutes until fully set.
He is president of Dental Technology Solutions, a lecture and consulting company, and he writes a column for drbicuspid. Consulting with various high technology companies, he is involved with the process of improving established products and testing new products and techniques. He consults with dental offices on implementing dental technology into their practices, and he enjoys promoting the use of technology in the dental office with an emphasis on improving patient care.
Jablow can be reached at marty dentaltechnologycoach. Disclosure: Dr. Share on Facebook Share on Twitter. CASE 1 Figure 1. Preoperative photo of the mandibular left first molar with incipient caries. Figure 2. Figure 3. Tooth after acid-etching the enamel. Figure 4. Application of Prelude One Danville Materials universal bonding agent. Figure 5. CASE 2 Figure 6. Figure 7. Removal of the amalgam. Figure 8. Placement of matrix band, wedge, and Triodent V3 Ring.
Figure 9. Figure Placing of SonicFill Kerr bulk fill composite. SonicFill composite after curing. Postoperative photo. CASE 3 Figure Air abrasion of a monolithic zirconia crown BruxZir [Glidewell Laboratories]. Removal of air abrasion powder using air. Pressing the package to mix the bonding agent prior to application. Piercing the package with the brush to access the bonding agent. Application of Futurabond U to the zirconia crown. Light curing the thinned bonding agent. The chemical structures of these acidic monomers are shown later in Figure and Figure Another requirement for achieving lasting intraoral bonds is hydrolytic stability resistance to chemical degradation by water.
Enamel and dentin are hydrated, hydrophilic, and permeable to water. Even if an enamel or dentin surface is initially dried before applying an adhesive, inadvertent contamination and diffusion can easily result in water becoming strongly bound to both the hard tissue and the adhesive. Thus, for an adhesive monomer to wet hard tooth tissue as well as form a durable bond in the moist environment of the mouth, it must be both hydrophilic for water compatibility and hydrolytically stable to ensure longevity.
Whenever both enamel and dentin tissues are mechanically cut, especially with a rotary instrument, a layer of adherent grinding debris and organic film known as a smear layer is left on their surfaces and prevents strong bonding. Different quantities and qualities of smear layer are produced by the various cutting and instrumentation techniques, as occurs, for example, during cavity or root canal preparation.
In dentin, the smear layer becomes burnished into the underlying dentinal tubules and lowers dentin permeability, which is a protective effect. However, it is also a very weak cohesive material and interferes with strong bonding. Therefore, various cleaning or treatment agents and procedures are employed to either remove the smear layer or enhance its cohesive strength and other properties.
As explained in greater detail below, application of acid is used to remove the smear layer from both enamel and dentin. Alternatively, in dentin the smear layer can be left partially in place and modified such that adhesive resins penetrate through it and bond to the intact dentin structures below.
One of the surface conditioning agents he used, phosphoric acid, is still the most widely used etchant today for bonding to both enamel and dentin. Depending on the concentration, phosphoric acid removes the smear layer and about 10 microns of enamel to expose prisms of enamel rods to create a honeycomb-like, high energy retentive surface Figure The higher surface energy ensures that resin monomers will readily wet the surface, infiltrate into the micropores, and polymerize to form resin tags.
The pattern of etching enamel may vary from selective dissolution of either the enamel rod centers type I etching as shown in Figure , or the peripheral areas type II etching as indicated by the resin tags in Figure Prior to the introduction of enamel acid etching and the use of enamel bonding agents, restorative materials were placed directly on the smear layer of the prepared tooth.
It is evident that the apparent bond strength is the cohesive strength 5—10 MPa of the smear layer, which is not sufficient to withstand the daily mechanical forces experienced in the mouth.
As a result, debonding and leakage of oral fluids within the microscopic space between prepared teeth and restorative materials was an ongoing problem. Unlike other types of dental restorative products, resin-based composites have no mechanism to counteract the effects of marginal leakage e. Stronger and longer lasting bonds result if the smear layer is removed, because resins can then directly bond to the intact hard tissue.
As illustrated in Figure , dentin etching did not gain wide acceptance until Fusayama introduced the total-etch concept in His study demonstrated that not only was restoration retention substantially increased but also pulp damage did not occur as had been generally assumed. A subsequent study by Nakabayashi et al. Such a hybrid layer structure forms very strong resin bonds through the development of an interpenetrating network of polymer and dentinal collagen, together with numerous micromechanical interlocks at the resin—hybrid layer interface.
By the early s, dentin etching had gained worldwide acceptance. Since the total-etch technique usually involves etching with an acid followed by rinsing to remove the acid, this technique is also known as the etch-and-rinse technique. Dentin etching is more technique sensitive than enamel etching because of the complexity of the dentin structure. Acid etching removes hydroxyapatite almost completely from several microns of sound dentin, exposing a microporous network of collagen suspended in water.
Whereas etched enamel must be completely dry to form a strong bond with hydrophobic adhesive resins, etched dentin must be moist to form a hybrid layer. The amount of water left in etched dentin is critical. If insufficient water is present, the collagen network will collapse and produce a relatively impermeable layer that prevents resin infiltration and subsequent hybridization.
If too much water remains, resin infiltration cannot fully replace the water in the collagen network and, consequently, sets the condition for later leakage into those locations. Therefore, a priming step is required to maintain a hydrated collagen network while removing excess water see details in the following sections.
Several aspects of the total-etch, etch-and-rinse, and related techniques are critical to the success or failure of bonding systems, as discussed below. The optimal application time for the etchant may vary somewhat, depending on previous exposure of the tooth surface to fluoride and other factors.
For example, a permanent tooth with a high fluoride content may require a somewhat longer etching time, as do primary teeth. In the latter, increased surface conditioning time is needed to enhance the etching pattern on primary tooth enamel that is more aprismatic than permanent tooth enamel. Currently, the etching time for most etching gels is approximately 15 seconds.
The advantage of such short etching times is that they yield acceptable bond strength in most instances, while conserving enamel and reducing treatment time.
Once the tooth is etched, the acid should be rinsed away thoroughly with a stream of water for about 20 seconds, and the rinsed water must be removed. When enamel alone is etched and is to be bonded with a hydrophobic resin e. Dentin, in contrast, cannot withstand such aggressive drying, which would cause bond failure because of the formation of impermeable, collapsed collagen fibers. In the total-etch technique, a dentin bonding agent and primer must be used that are compatible with both moist dentin and moist enamel.
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