Etch & Rinse

Bonding agents or adhesives, as the name implies, are products that allow us to adhere various types of dental materials to enamel, dentin, and even other dental materials. Unlike the old hydrophobic materials used to bond to enamel, virtually all of the current bonding agents are typically hydrophilic to some extent to be compatible with dentin. However, it is this need to be hydrophilic that has caused most of the problems when it comes to bonding. Therefore, success or failure with these products depends as much on how they are applied as which product you choose to use.

Types of Adhesives

There are many ways to categorize bonding agents. One popular method uses the "generations" nomenclature. But, unless you are a dental historian, there is really no value in using the "generations" system. Who really cares if an adhesive is a "fifth generation" or "sixth generation" or "seventh generation"? Who is counting anyway?

Another way to separate these products is by the number of components. This system became popular (and has been used by us in the past) during the years that the single-component products were being introduced. We still use this nomenclature to describe the products, but not for categorization.

We used to categorize these products as to whether they could be used for all procedures or just those for light-cured, direct procedures. These latter products were not effective when self-cured composites and/or indirect restorative procedures were used. However, even these products can usually be transformed into all-purpose by using various chemical activators. Therefore, we have dropped this separation.

This brings us to the categorization we have chosen to use: etch & rinse (previously known as total-etch), self-etch, and universal. This category covers the etch & rinse products.

What makes these products etch & rinse

They utilize at least two steps, with the first one being the application of a phosphoric acid gel to the entire tooth surface that will be overlaid with the restorative material. This application is followed by a thorough water lavage of the tooth. Then the actual bonding agent is applied. Arguably the most versatile and reliable especially on enamel, etch & rinse bonding agents can be used for virtually any type of restoration and have the track record to prove it. The main reason many dentists stop using these adhesives is due to their patients suffering from postoperative sensitivity. However, if you apply them carefully following our simplified instructions, we are confident that you can greatly minimize or eliminate the sensitivity problem in the vast majority of patients.

Components and Composition

As noted previously, etch & rinse bonding agents usually have one to three components (other than the etchant). These components typically include:

Primer

Applied first, contains a solvent (making it hydrophilic), and usually (but not always) does not have any light-curing capabilities. This component is typically premixed and packaged in one bottle, syringe, or unidose, but some primers may have two components that require mixing.

Bonding Resin

Applied after the primer. Can enhance adhesion by its wetting agent function or it can also have hydrophilic qualities and thus can actually contribute to enhancing the hybrid layer (see below). On the other hand, another theory is that the bonding resin should be hydrophobic to prevent formation of water trees (see below). If its companion primer is one component, the bonding resin may have two components that need to be mixed when it needs self-cured capability. Conversely, if the primer is in two components and needs to be mixed, the bonding resin may only need to be one component. And, in the products that only have a single-component, the primer and bonding resin are mixed together in one bottle.

Filled Adhesives

Some adhesives add different types of fillers to the normally unfilled product for the following reasons:

  1. Fluoride release if the filler glass has this capacity. While this is a noble goal, it is highly unlikely that there will be enough fluoride released by the adhesive to be of clinical value.
  2. Lower modulus of elasticity to impart added flexibility to a restoration done with a stiff material such as a universal (nanohybrid) composite. Materials with more elasticity, such as microfills, may be better retained in Class V lesions due to their higher flexibility, compared to hybrids. The flexibility could also help to reduce the stress at the interface between the restoration and tooth caused by polymerization shrinkage. In other words, the elasticity of the adhesive could absorb within itself some of the curing stresses. By reducing this stress at the tooth-restoration interface, the restoration could be expected to have better retention. While this theory sounds feasible, it has yet to be proven.
  3. Filler could actually reinforce and strengthen the hybrid layer.
  4. Filler could help the adhesive cover the dentin surface in one application rather than multiple ones.

Radiopacity

Our tests have shown that it is virtually impossible to visualize a bonding agent on an x-ray image when the bonding agent is placed in the very thin layer (about 10 microns) typical of the current products on the market. Therefore, we suggest ignoring radiopacity claims when choosing a bonding agent.

Working Time

While working time limitations are well-known with light-sensitive restorative materials, this issue has not been investigated thoroughly when it comes to bonding agents. And, although some bonding agents have light-protected dispensing wells as part of their intro kits, this is not universal with all products.

However, based on lab tests and clinical experiences, we have found working times of various bonding agents can fluctuate greatly. Therefore, to overcome working time problems, please follow these rules:

1. Dispense your bonding agent immediately before using it.

2. Use a light filter on your headlight or dental unit light.

3. If you apply a bonding agent on multiple preparations simultaneously, even the ambient light in your treatment room may begin to polymerize highly reactive materials prematurely, possibly before you have had a chance to evaporate the solvent. Therefore, using a light filter shield positioned over the intraoral treatment area to restrict as much as possible the ambient light.

Enamel vs. Dentin

Enamel

While dentin is the substrate that has garnered most of the interest, enamel is still the most reliable tooth tissue for bonding. Although some initial dentin bond strengths may even exceed those of enamel, the long-term bonding stability favors enamel. In addition, microleakage testing usually shows significantly lower scores on enamel compared to those on dentin/cementum.

The main reason bonding to enamel is more reliable is that it is primarily inorganic. You etch it, you dry it, you bond to it. There is nothing complicated or very technique-sensitive about this procedure. Etching creates micromechanical retention by selectively demineralizing the surface. Once dried, low viscosity resin penetrates into the microscopic spaces in its surface that were created by the etching process. After curing the resin, it tenaciously adheres to the enamel.

However, when a hydrophilic adhesive is used, drying the enamel is not necessary and may not even be beneficial. Our tests have shown moist or wet protocols, developed for dentin, are usually also effective on enamel. Nevertheless, if no dentin is exposed, a hydrophilic adhesive probably offers no benefits over a simple, unfilled resin applied to dry, etched enamel.

Dentin

Unlike enamel, dentin is primarily organic, mainly collagen and water, making it a much different substrate for bonding. It is also in direct contact with the pulp, which tells us that whatever we do to dentin must be done in a way that it doesn't injure the pulp.

Most efforts to bond to dentin have focused on both mechanical and theoretical chemical adhesion. The early adhesives tried to bond to the smear layer, which is basically the layer of preparation debris that is difficult to remove with conventional cleaning procedures, but, paradoxically, is not firmly attached to the dentin for bonding purposes. This means that trying to bond to the smear layer has been unreliable and not very successful.

As mentioned previously, etch & rinse bonding agents use a phosphoric acid etchant to remove the smear layer and to demineralize the dentin surface. This leaves a lattice of unsupported collagen. The adhesive then infuses the collagen with resin, locking into it to form a micromechanical bond, similar to that of enamel. This complex of resin-reinforced dentin has been termed the hybrid layer.

Another issue of dentin bonding is the stability of the bond. This topic rarely arises with enamel, but the question is: Do dentin bonds get weaker or start to hydrolyze over time? There is evidence that does, indeed, suggest this is happening, but its effect on the longevity of restorations is uncertain.

In addition, studies performed by Editorial Team Member Dr. Franklin Tay have shown that enzymes called matrix metalloproteinases (MMPs) can break down the collagen scaffolding that is essential for stable bonds. However, these same studies have found that MMPs can be inactivated by treating etched dentin with products containing glutaraldehyde or chlorhexidine. These products are applied and not rinsed off. To inhibit MMP activity, the evidence suggests that in the case of chlorhexidine, concentrations as low as 0.01% or even less are effective. Therefore, it seems applying aqueous chlorhexidine (such as Consepsis) or a product containing glutaraldehyde (such as Gluma Desensitizer) after etching but before applying the primer/adhesive is a prudent procedure.

Bond Strength Tests

These are the most common tests done on bonding agents. They can be done relatively quickly and are especially valuable when trying to distinguish between technique variations. Many manufacturers tout the superiority of their adhesives based on these scores. Indeed, there have even been conferences devoted to "battle of the bonds", which are sort of like bond strength Olympiads!

The most common yardstick to judge whether a specific bonding agent has an adequate bond strength is to compare it to an enamel control. Since bonding to frosty, dry, etched enamel using a conventional unfilled resin has been validated with over 30 years of clinical use, equivalent dentin values should be an indication that the product will perform satisfactorily, at least initially.

In the RRL, we periodically test bond strength to dry, frosty enamel using an unfilled, hydrophobic resin (Heliobond). While consistency is our goal, there have been variations in this bond strength test over the years based on the temperature and humidity in the lab, as well as differences in human extracted teeth. The range of these bond strengths have been from 20MPa to 27MPa. Therefore, bond strengths for adhesives that produce similar values should be clinically acceptable.

However, the clinical significance of bond strength tests (and just about all in vitro tests) continues to be debated. No one really knows how much bond strength is enough. It is also unknown whether bonding agents with bond strengths, which exceed that of the enamel control, have any clinical advantages over those with equivalent values.

Therefore, we continue to use bond strength tests as screening devices. For example, when we first discovered clinically that self-cured core materials were debonding when a single-component adhesive was used, we tested this combination in the lab and confirmed that there is a basic incompatibility between most one-component adhesives and self-cured composites.

Spotting trends and discovering uses of these materials that just don't work are really the main purposes of these tests. Consequently, while bond strengths falling below that of the enamel control may cause some justifiable concern, we do not use these values as the sole determinant in ranking the products, unless the scores are significantly lower than the average in the group.

Equipment

Our usual testing apparatus (developed by Ultradent) employs a mold that produces a small cylinder of composite about 2.2mm in diameter and 2.0mm in height. While this is adequate for testing bonding agents in the light-cured mode using typical 2.0mm increments of composite, it does not permit testing when bulk filling a deep preparation for a core build-up. To solve this problem, we developed molds that are wider (3.8mm in diameter) to allow easier insertion of the restorative material and in various depths (2mm, 3mm, 4mm, and 5mm). These deeper and wider molds are manufactured by 3M.

Tooth Specimens

All bond strength testing in our lab is done on extracted teeth that have been embedded in acrylic and then flattened. While flattened teeth really do not simulate cavity preparations, this protocol is essential to conduct these tests. The only exception to this "flat tooth" rule is when unprepared enamel is tested. In this case, we select the extracted teeth that are as flat as nature would allow, but the variables of some surface curvature and irregularities are unavoidable. Consequently, we do not perform bond strength tests on unprepared enamel as a rule. Although dentin is the substrate that we are most often testing, all bonding agents are also tested on enamel.

Immediate vs. Delayed Testing

Immediate

Since we usually begin to stress a restoration with finishing procedures as soon as it is light cured, it is important to know this early bond strength. Consequently, we test each bonding agent as soon as light curing the restorative material is completed. This is our most common test.

5 Minutes

Typically used for self-cured products such as core materials and cements to simulate the usual waiting time for these materials to chemically polymerize in the mouth. Some testing of dual-cured materials is also done at this time, but not routinely since we have found only small differences in bond strength between immediate and five minutes. The time starts after the mold is filled and the specimen is placed in an incubator set at 37°C/95% humidity in an effort to simulate the oral environment if a patient is allowed to close during the polymerization period. (While the intraoral temperature and humidity may not perfectly match these parameters in all cases, it should be reasonably close.) Teeth used for these tests are typically warmed to body temperature prior to testing.

24 Hours

Most common test reported by manufacturers. It may produce higher values compared to those recorded immediately. In addition, many research facilities do not have their equipment conveniently arranged for immediate testing, so the 24 hour test is done due to logistical considerations. We use this time delay typically only for dual-cured and self-cured products such as core materials and cements, the latter of which is consistent with the typical advice given to patients to be careful with what they eat for the first 24 hours after luting a restoration. However, some light-cured products are additionally tested at this time interval, the results of which can then be compared to those achieved immediately.

Specific Tests

Moisture Status of Preparation

After rinsing the phosphoric acid etchant, you need to know the optimal moisture status of the preparation. Our tests show that this can be one of the most critical steps during the adhesive process. However, the directions from many manufacturers either omit this description entirely or it is covered inadequately. Therefore, we test all bonding agents using three protocols:

•Dry

Air syringe is used to produce forceful air for 2-3 seconds for a small preparation or longer until the cavity is completely void of visible moisture, but not totally desiccated.

•Moist

Blot with a lint-free, dry 2x2 gauze, mini-sponge, or virtually any absorbent product that will not leave a residue on the tooth surface. The result should be a tooth surface with no visible moisture, but appears to have either a matte or slightly shiny appearance (depending on the character of the dentin and type of instrument used to prepare it).

This protocol will leave necessary moisture in the demineralized dentin (created by the etching process). Clinically, you would have to cut the 2x2 gauze (if used) into small sections or use other products such as an applicator tip or mini-sponge to siphon off the excess moisture in small areas. For large areas, such as a complete crown preparation, draping an intact 2x2 gauze over the preparation may be more effective and expeditious.

•Wet

Use the same type of blotting material described under Moist and dip it into distilled water. Then blot this wet material with a dry 2x2 to create a "damp" blotting material. Use this "damp" material to blot the cavity preparation, leaving tooth surface with a definite sheen of water on it, but be sure all puddles of water are removed.

Note: To create the moist or wet status, many manufacturers will tell you to use your air syringe. Typical instructions will tell you to "dry lightly for 2-3 seconds" or some variation thereof. Our tests show that using air to create moist or wet options is not effective. From a clinical perspective, it is even more difficult. For example, if you are trying to "dry lightly" an MOD preparation, you may merely be blowing the excess water from one proximal box to another. Therefore, the blotting techniques we have developed have proven to be much more effective and easier to calibrate.

In addition, when using the moist or wet option, you should apply the adhesive or primer immediately after blotting the tooth. If you wait even 15 seconds (especially if you are using the rubber dam), some of the moisture could evaporate, which could affect the performance of the adhesive.

Furthermore, if you choose to apply a product containing either chlorhexidine or glutaraldehyde to inactivate MMPs, use the Moist protocol prior to applying this product. Then follow our suggested technique when applying the adhesive or primer, treating the MMP inhibitor that you applied as if it were water.

Method and Time for Applying the Primer/Adhesive

The manner by which you apply a primer or adhesive can vary from the simple "let sit" of some manufacturers to literally scrubbing it into the surface of the preparation. "Let sit" may be effective in the laboratory on flat test teeth, but it rarely works with the complex surfaces found in many preparations, especially vertical ones. "Scrubbing" is a relative term and the force by which it is accomplished is limited by the application instrument. In other words, the applicator tips that are usually supplied with bonding agents are rarely stiff enough to allow vigorous "scrubbing".

"Gentle agitation", which refers to applying the primer/adhesive and then basically moving it around on the preparation surface to ensure that there is optimal contact in all areas, is in-between "scrubbing" and "let sit". "Rubbing" is basically the same as "scrubbing", but it is presumably accomplished in a less aggressive manner, although from a clinical perspective, trying to differentiate between "rubbing" and "scrubbing" is virtually impossible.

Application time can also vary the effectiveness. Our tests found the best method and optimal time to apply the bonding agent. Be aware that the size of the preparation will affect the application time. While the stated times are application for small Class V preparations, you should extend the times for large Class IIs. In addition, don't start your timer until the preparation is thoroughly wet with primer or adhesive.

Method of Evaporating the Solvent

The monomers in the primers or bonding resins are typically dissolved in solvents (usually ethanol, acetone, and/or water), which carry these monomers into the demineralized surface of the preparation. Etching with phosphoric acid creates this demineralized surface. These solvents, besides being the vehicle in which the monomers are dissolved, need to be hydrophilic since the demineralized dentin surface contains moisture to prevent the collagen network from collapsing.

The solvents also tend to be "water-chasing." This property refers to the solvent being attracted to the moisture content of the dentin. As the solvent "chases the water", it literally brings the active monomers with it. Once this job is done, however, the solvent needs to be evaporated, since it can actually interfere with adhesion if it remains in the adhesive.

Part of the reason for the interference is the dilution factor. In other words, solvents literally water-down the adhesive. But even more important is that the hydrophilic nature of a solvent can prevent the bonding of the hydrophobic materials such as composites and cements subsequently being placed.

After application of an adhesive or primer, the excess is usually first removed by suctioning, being careful to allow a continuous coating to remain on the tooth. If you don't suction the excess, there is a tendency to just blow the primer or adhesive from one part of the cavity to another section or onto the soft tissue, which can cause untoward reactions that are typically self-limiting but may provoke undesirable questions from the patient. After suctioning the excess, the solvent needs to be evaporated using air.

The typical method is to place the tip of the air syringe about 1.0cm from the tooth and direct a gentle stream of air (like a breeze) at the preparation surface. Some adhesives, however, require a more forceful air flow, not only to evaporate the solvent, but also to keep the film thickness as minimal as possible so the layer of adhesive does not interfere with the complete seating of an indirect restoration.

When using forceful air, be careful not to blow the primer or adhesive completely off the tooth. This can usually be done by starting the evaporation procedure with gentle air and proceed to forceful. We have determined the optimal technique for each adhesive.

The result of this evaporation effort should be a layer of primer that appears dry (you can't move it around with the air syringe) and the preparation surface appears shiny. This air-evaporation effort may take five or more seconds, depending on the size of the cavity.

If the dentin surface is not shiny, it may not be sealed. Therefore, it seems prudent to apply additional adhesive and repeat the evaporation process. Typically, the reapplication is merely applying the material and immediately beginning the evaporation process – you don't need to wait as you may have when you applied it initially. If, after the second application, the dentin surface is still not shiny, we recommend applying the adhesive one final time.

Light Curing the Primer/Adhesive

If this is the final component of the bonding agent (such as when you are using a single-component product), you would typically cure it at this time. The conventional curing time has always been 20 seconds. However, this may be overkill for some adhesives. We tested the optimal curing time for each adhesive. But be aware that even these times may need to be altered based on the distance from the tip of the light to the tooth surface. For some bonding agents used in the dual-cured or self-cured mode, in which an activator is mixed with the main component of the kit, you may need to wait until the restorative material or indirect restoration is placed to cure the adhesive or allow it to cure concurrently along with the dual-cured or self-cured composite or cement.

Method of Applying the Bonding Resin

As this component does not typically contain any solvents and, indeed, is usually primarily hydrophobic, you do not have to apply air other than to thin out the layer. While this will work, overaggressive use of the air can lead to overthinning, which, in turn, can affect the performance of the bonding agent. You can alternately remove the excess by using the same applicator, but blotting it with a 2x2 each time you remove more excess. This is known as the "brush on, brush off" technique and works well.

Component(s) to use when bonding a dual-cured core or an indirect restoration such as an onlay

It has been thought that, if you are using a dual-cured core material to build up a tooth or dual-cured cement to lute a thick, indirect restoration, you also need to use a dual-cured adhesive (two components) for compatibility and just in case the light doesn't penetrate to the tooth surface. However, if you can light cure all the way through the core or to the bottom of the indirect restoration (especially if you position the tip of the curing light on the facial, lingual, and occlusal surfaces and use a high-powered light), then a single-component, light-cured adhesive or the light-cured version of a multi-component product may be quite satisfactory. In addition, a light-cured cement may also work instead of a dual-cured version for the indirect restoration.

Component(s) to use when bonding a self-cured core or an indirect, metal-based restoration such as a ceramometal crown

Similar to the dual-cured core test, this test is done by using the self-cured version of the adhesive (if it has one). The test simulates a direct, self-cured core build-up or indirect restoration cemented with a self-cured resin cement if you waited five minutes after placement to allow the material to chemically-cure.

Miscellaneous Adhesive Issues

Effect of Moisture on Restorative Materials

If a restoration fractures, not only do we have to bond to the remaining section of the restoration, but also to any exposed tooth surface. If dentin is exposed, you would typically want to use an adhesive that will bond securely to the restorative material and to the tooth itself. If your typical bonding agent requires you to leave the tooth moist or wet for optimal bond strength, then it may be difficult to leave the tooth moist or wet but dry the fractured area of the hydrophobic restoration.

We tested the effect of moisture on bond strength to several restorative materials. Our tests confirm that composites and ceramic materials should be repaired dry. Therefore, the use of an adhesive that bonds to dry enamel and dentin reasonably well would be the product of choice.

Effect of Silane on Tooth Structure

When a repair is done, silane is typically applied to the fractured surface of a ceramic restoration and may also be effective on certain composites. The silane would be applied prior to applying the bonding agent on the tooth and restorative material. However, silane is a liquid and, during its application on the fractured surface of a restoration, some of it may flow onto the adjacent tooth surface that also needs to be repaired. With this in mind, it would be important to know if silane could have an effect on the bond of the repair material to dentin.

Our test results show that silane can interfere with the bond of the composite to dentin. Therefore, when applying silane, make every attempt to confine its application just to the fractured restorative material. This confinement will not be possible if you merely douse the tooth with silane. But if you apply it with a fine brush, keeping it off the tooth is certainly a possibility.

Water Additives

With the increased concern about contaminated water lines, products are being added to self-contained water reservoirs on dental units. However, some of these products have not been tested properly as to their effects on adhesion. Our own testing of one product showed bond strengths decreased 22% compared to the untreated control. Therefore, we strongly suggest not adding any disinfectant to your water reservoir without having reliable data on its effect on issues such as adhesion.

Water Trees

Even when the dentin is shiny and appears to be totally sealed, bonding agents that do not employ a final layer of a hydrophobic bonding resin may be subjected to a phenomenon called the "semi-permeable membrane effect". Discovered by Editorial Team Member Dr. Franklin Tay, this effect is characterized by a porous hybrid layer, which allows pulpal fluid to diffuse onto the dentin surface and potentially interfere with the bond between the hydrophobic restorative material and hydrophilic adhesive. This diffusion effect simulates branches on a tree, thus the term "water trees" was created to describe it.

However, while this effect has been shown to exist clinically, it remains to be seen what its long-term sequelae may be. Nevertheless, using a multi-component adhesive that includes a final layer of a hydrophobic bonding resin will presumably prevent this problem from occurring and is one reason that the multi-component adhesives are making somewhat of a comeback.

Hybridizing the Dentin at the Preparation Appointment

There is a trend to create a hybrid layer at the preparation appointment for an indirect restoration. This is also known as "IDS (immediate dentin sealing)". The purposes of the hybrid layer in this instance are to protect the pulp by sealing the dentin surface, minimize or eliminate sensitivity between the preparation and seating appointments, and allow seating of the definitive restoration without having to anesthetize the tooth. While these are noble goals, there are also some downsides to this procedure.

In the first place, the hybridizing procedure is done before taking the impression. Depending on the type of adhesive used to create the hybrid layer, the sharp margins of the preparation could be less distinct and more difficult for the lab to see. Second, applying an adhesive after preparing a tooth especially for full coverage may be difficult due to the challenges of adequately isolating the preparation.

Third, the adhesive could bond with the provisional cement if a resin version is used. Fourth, bonding to this precured adhesive layer may not be as adhesive as starting with fresh tooth structure. And, finally, unless you are using a hydrophobic layer over your hydrophilic adhesive, this presumably sealed dentin surface may be susceptible to the formation of water trees. Therefore, this procedure may not produce all of its presumed benefits and may not be worth the effort it takes.

Shaking the bottle/Stirring the Unidose

Many bonding agents suffer from phase separations of their components in bottles and unidose vessels. This means that most bottles should be shaken before dispensing and the contents of unidose vessels should be stirred before applying to the preparation. Some bottles even have a small ball inside to act as a shaker to help mix the components. When in doubt, shake or stir.

Application Techniques

In each product commentary, we have listed the application techniques that we have found to be most effective and practical for clinical use. In some instances, these procedures may vary from the manufacturer's directions. However, we feel strongly that our techniques will give you the best chance for success and will minimize failures.

Application Steps

1. Clean Preparation (Photos 1 – 4)

Pumice, applied to the tooth using a prophy cup in a slowspeed handpiece, is the time-honored method to clean a tooth after completing a cavity preparation. However, there are more contemporary materials and methods to accomplish this goal. Please see CAVITY CLEANERS/DISINFECTANTS for guidance.

Photo 1 Tooth has been prepared for a direct MOD restoration.

Photo 2 After rinsing off any loose preparation debris, tooth is dried for a few seconds.

Photo 3 Preparation is scrubbed with cleaner/disinfectant (Consepsis). While there is virtually no evidence that there is any clinical benefit using an antimicrobial agent as a cleaner, our tests show there is no disadvantage either. Therefore, since a cavity preparation is an open wound, we believe it is prudent to debride it with a product that has a disinfecting effect, no matter how minimal an effect it may be.
Photo 4 Plain pumice used with a StarBrush can also be used for extra cleaning power. This could be the technique of choice if carious dentin was removed using a slowspeed, round bur, which would most likely result in a heavy layer of prep debris.

2. Dry Tooth Prior to Etching (Photo 5)

After rinsing the cleaning material off the tooth, you typically need to dry the preparation before applying the etchant. Suction the excess water and then dry with air, but don't desiccate the tooth. The preparation should look dry, without any visible moisture.

Photo 5 Preparation is dried prior to applying etchant. You do not need to desiccate the preparation, but visible moisture should be eliminated to prevent diluting the etchant.

3. Place Matrix (Photo 6)

Even though it is widely recommended to delay the placement of the matrix until after adhesive application (although we have never figured out the basis of this recommendation), we believe that it is much more advantageous to place it at this point in the procedure. This is due to the fact that a matrix:

A. Keeps etchant off the adjacent teeth.

B. Better isolates the gingival margins from sulcular fluid and/or bleeding caused by the preparation.

C. Prevents any contamination of the preparation that can occur during the placement of the matrix.

Photo 6 Matrix is placed and wedged.

4. Etch Tooth (Photos 7 – 10)

Apply a gel etchant first to the enamel and then the dentin. Start the timer for 15 seconds and begin gently agitating the etchant with a brush or applicator tip to ensure complete coverage of the cavity preparation especially at the margins. See ETCHANTS for more information.

Photo 7 Etchant is applied, starting with the enamel.

Photo 8 Enamel in the preparation and several mm beyond the margins has been totally covered with etchant.

Photo 9 Etchant has been applied to the dentin.

Photo 10 Disposable brush is used to agitate the etchant, ensuring that it wets the entire cavity surface.

5. Rinse Etchant (Photos 11 & 12)

Rinse for at least five seconds using a forceful air-water spray, paying particular attention to narrow areas where matrices meet tooth structure. Inspect the preparation carefully to be sure all the etchant has been rinsed off before moving onto the next step.

Photo 11 Suction the bulk of etchant first and then rinse thoroughly using a forceful air-water spray.

Photo 12 Preparation should be left wet, but no traces of etchant should remain after rinsing.

6. Suction excess water (Photo 13)

Prior to deciding whether you are going to leave the prep dry, moist, or wet, you need to suction the excess rinse water, leaving the prep with just a thin, shiny layer of water. If you are going to apply an MMP inhibitor, you would do it now.

Photo 13 Excess water is suctioned after rinsing etchant.

7. Create drymoist, or wet cavity prep

The etching process leaves the collagen scaffolding largely unsupported. At the bottom of the demineralized zone, there is a layer of irregular hydroxylapatite. To allow the penetration of adhesives through this demineralized zone and into the hydroxylapatite base, the dentin must typically not be overly dried or the collagen lattice will most likely collapse. When this happens, the adhesive presumably cannot infiltrate throughout the collagen. Therefore, with most adhesives, the dentin should not be dried with air prior to application of the primer (if you are using a multi-component product) or the single-component adhesive. However, some adhesives contain water, which seemingly rehydrates this demineralized zone even if it has collapsed due to overdrying. Our tests found the best "wetness" level for each adhesive.

DRY (Photos 14-16)

Dry with air for five seconds (or until the cavity is completely dry, but not desiccated).

 

Photos 14 & 15 Air is used to dry the preparation. Note the positions and angles of the air syringe tip.

Photo 16 Preparation after drying. Note absence of visible moisture.

MOIST (Photos 17-21)

Blot with a lint-free, dry 2x2 gauze or mini-sponge, which slightly outperformed the 2x2 in our tests. The tooth surface should have no visible moisture and may have either a matte or slightly shiny appearance (depending on the character of the dentin and type of instrument used to prepare it), but the demineralized dentin will still be moist. Clinically, you would have to cut the 2x2 gauze (if used) into small sections or use other products such as an applicator tip or mini-sponge to siphon off the excess moisture in small areas. For large areas, such as a complete crown preparation, draping an intact 2x2 over the preparation may be more effective and expeditious.

   

Photos 17-20 Preparation is left wet after rinsing, followed by blotting with a dry section of a nonlinting 2x2.

Photo 21 Preparation after blotting to create Moist Option. There is no visible moisture, but the dentin looks remarkably different than when it was dried with air.

WET (Photos 22-26)

Dip 2x2 or mini-sponge in distilled water and then blot it on a dry 2x2 to make it slightly damp. Then blot the cavity preparation with this damp 2x2, leaving surface with a definite sheen on it, but no puddles.

   

Photos 22-25 Preparation is left wet after rinsing the etchant (same as with the Moist Option), but the section of 2x2 is dipped in distilled water, followed by blotting with another 2x2 to create a slightly damp condition. Then this damp section of 2x2 is used to blot the preparation.

Photo 26 Preparation after blotting to create the Wet Option. Note the thin layer of water glistening on the surface of the preparation, but there are no puddles.

8. Apply Adhesive or Primer (Photos 27 – 29)

There are three general protocols when applying an adhesive or primer (when using a multi-component system). Some adhesives seem to bond to dentin better when they are literally scrubbed into the demineralized surface. Scrubbing, however, is a relative term and the force by which it is accomplished is limited by the application instrument. For example, you can scrub the Ultradent adhesives into the dentin surface with significant force by using the Inspiral Brush that fits onto the end of the dispensing syringe. But you cannot apply the same force when an applicator tip is used. Our tests found the best method and optimal time to apply the adhesive.

Note: When using the moist or wet option, you should apply the adhesive or primer immediately after blotting the tooth. If you wait even 15 seconds (especially if you are using the rubber dam), some of the moisture could evaporate, which could affect the performance of the adhesive.

 

Photos 27 & 28 Adhesive or primer is applied using an applicator tip.

Photo 29 Preparation after adhesive or primer has been applied.

9. Remove Excess Adhesive or Primer and Evaporate the Solvent (Photos 30 – 35)

After application of an adhesive or primer, the excess must first be removed by suctioning, being careful to allow a continuous coating to remain on the tooth. If you don't suction the excess, there is a tendency to just blow the primer or adhesive from one part of the cavity to another section. After suctioning the excess, the solvent needs to be evaporated.

Although there are a few products claiming to be solvent-free, the monomers in most primers of multi-component adhesives and in the single-component adhesives themselves are dissolved in solvents. While directing a gentle stream of air at a distance of about 1.0cm from the tooth to evaporate the solvent works best for most materials, others require starting out this process with gentle air and gradually increasing it to forceful. Unfortunately, gentle air is an ambiguous term and an action difficult to calibrate.

An alternative to using a difficult to calibrate air syringe for evaporating the solvent is the A-dec Warm Air Dryer. With this instrument, the amount of air delivered to the tooth is always the same. To get warm air, however, it needs to be activated from a cold start for about 30 seconds before going to the mouth. Our tests show that it is a viable alternative to an air syringe for evaporating the solvent, but the air stream is typically not forceful enough if you are trying to thin out the adhesive.

 

Photos 30 & 31 Excess primer or adhesive is being suctioned. Note that the suction tip is at an angle and/or slightly off the prep. If it is placed directly over the prep, it could possibly remove too much material.

 

Photos 32 & 33 Air is being used to evaporate the solvent in the primer or adhesive. Note that the position of the air syringe is about 1cm away from the preparation.

Photo 34 Dull surface after evaporating solvent may be an indication that the dentin is not sealed. Additional layers of adhesive or primer may be indicated.

Photo 35 Shiny surface of dentin after evaporating the solvent gives you a certain amount of peace of mind that the dentin has been sealed, but it's still not a perfect guarantee due to the semi-permeable membrane effect.

10. Light Cure the Adhesive (Single-component) for 10-20 seconds (Photo 36)

Photo 36 A large diameter tip that overlaps the prep is best for curing. However, many of the newer LEDs do not have tips larger than 10mm in diameter. Therefore, if you are curing an MOD in a molar, its mesiodistal width could be 12mm or more. This means you would have to cure the mesial half of the prep and then perform an additional cure for the distal half. You should also keep the light tip as close as possible to the occlusal surface of the prep.

11. Apply the Bonding Resin (if using a multi-component system) (Photos 37-44)

   

Photos 37-40 Bonding resin is being applied using a disposable brush, making sure to cover the entire preparation.

Photo 41 Preparation after being covered with bonding resin.

Photo 42 Disposable brush is blotted with a dry 2x2.

Photo 43 Brush is used to remove excess bonding resin. While air can also be used for this function, overthinning is a concern. Brushing off the excess may be safer.

Photo 44 Preparation after thinning out bonding resin.

12. Light cure bonding resin

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Tenure4G
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All-Bond 3
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