Restorative Notes on Bonding to Sclerotic Dentin and Removing All-Ceramic Crowns 

By Lee Ann Brady, DMD 

Bonding to Sclerotic Dentin 

Bonding to sclerotic dentin is difficult, if not close to impossible. If the lion’s share of the tooth’s surface is sclerotic, you may not have the longevity that you’re hoping for. I’m specifically thinking of some lower anterior restorative cases I’ve seen over the years, where the veneers just haven’t held up and we’ve had to go to full coverage. 

I don’t trust some of the self-etching adhesives to result in a strong bond on sclerotic dentin, even the newer ones in the eighth generation. Fortunately, one thing we don’t need to worry about is sensitivity because the dental tubules are closed. Since I’m not worried about sensitivity, I can apply the same techniques I would with enamel with the intent of improving the probability of a strong bond. I can do a light prep, get rid of the sclerotic surface, and etch it with phosphoric acid for 25 or 30 seconds. Alternatively, I can use 30- to 50-micron aluminum oxide in an abrasion unit.  

Removing All-Ceramic Crowns 

Removing dental crowns can be a delicate and time-consuming procedure. In a world of so many different materials, it’s helpful to have an idea of which bur to use and how long removing the crown could take. One of the biggest challenges is determining whether a crown is a lithium disilicate or zirconia restoration. The radiograph and visual inspection will give us clues but afterwards, we must go through a process to understand what may be involved. 

Our First Clue: Zirconia looks like metal on a radiograph, and lithium disilicate looks radiolucent like natural tooth structure.   

Our Second Clue: If the crown is partial coverage, it’s much more likely to be bonded and I plan to prep down the entire restoration.  

Lithium disilicate restorations are often easier to cut through or section but they could be bonded and impossible to remove in pieces. Even if we can cut four pieces, we may have extensive prepping to do.  

On the other hand, zirconia can be harder to cut through, especially the 3y or 4y variety. But at least once you get to the cement layer, you can normally break it into pieces and remove them instead of having to extensively prep the entire tooth.  

If the restoration is full coverage, I can easily remove it in sections. In this case, I attempt to make my cuts all the way from buccal to lingual across the occlusal surface without bothering to stop. At this stage, I can pick up a crown remover and apply some general pressure to crack it off. If the crown is not budging at all, I assume it is bonded to the tooth, and the next thing I do is pick up a big flat-top diamond to do my occlusal reduction as if I were prepping a natural tooth. Once all the occlusal is off the glass, the pieces on the buccal, lingual, and interproximal fall off. 

The goal of treating severely worn teeth is to extend the life and function of the teeth while improving their function and aesthetics. For the patient’s optimal comfort and health, we seek to achieve a stable posterior occlusion and efficient anterior guidance.

This article is written for the purpose of inspiring dentists to learn indicators for using this technique, and the no-prep “index technique” of diagnosing and restoring worn teeth with composite restorations.

The Benefits of the Index Technique

Conservation of the natural tooth structure—Whenever possible, dentistry should be additive, not subtractive-additive. The adhesion of composite resin is now so reliable that retentive cavity preparations are not always necessary. The digital index technique protocol proposes a conservative and alternative approach based mainly on minimally or noninvasive copy-and-paste composite restorations on both ante¬rior and posterior teeth. In anterior sextants with undercuts, a direct molding technique allows the clinician to be extremely conservative.

Simple repair—Another positive trait of this technique is the relative ease with which chipping or restorative failure can be managed by applying a simple adhesive protocol. Full loss or detachment of the restoration is an unlikely occurrence. Partial failure can be easily repaired with fresh composite following proper surface treatment: sandblasting, salinization, and bonding all surfaces.

Less clinical time and expense—This technique shortens the time to finalize a case. The technique requires a wax-up for planning the case and the fabrication of a transparent index but no other digital or analog lab expense. (See accompanying images above.) With this technique, you can avoid or postpone a more biologically invasive and financially costly solution.

Long-lasting aesthetics—Nano hybrid composite has good wear characteristics. Its superficial gloss lasts, and the composite can be easily repolished during patient re-calls.

Reversibility—With the index technique, you can remove the composite to restore the patient’s teeth to the occlusion they had before treatment if necessary. It should be noted that it is not easy to remove composite after adhesion due to bonding strength and composite chromatic integration with the natural tooth.

Join me for “Worn Dentition: Direct & Indirect Adhesive Management through a Non-Invasive Approach”

In October 2023, I will present an in-depth, two-day workshop at The Pankey Institute. During this workshop, you will learn the indications and protocols for diagnosing and treating severely worn dentition using the new direct “Index technique” approach. The course also will cover when and how to bond on worn dentition using additive partial indirect restorations (onlays/overlays) in composite and/or ceramic. The step-by-step protocols for digital and analog workflows will be addressed during the workshop through step by step images and videos on patients in order to understand this “hybrid approach”. I look forward to being back at the Institute, and I hope you will join me there!

The photos below refer to an INDIRECT additive adhesive ceramic cementation case:

while these photos refer to a DIRECT additive adhesive molding copy&paste protocol through the “Index Technique” protocol:

Not every tooth that has been endodontically treated requires a crown to insure it has great longevity and doesn’t crack or fracture.

Molars

Very clearly the literature supports that molar teeth in the posterior absolutely must have four cusp coverage—a four-cusp onlay or a full coverage crown. We are trying to use the phenomenon of containment with strong ceramic or metal material around the entire circumference of the tooth. We are holding the buccal and lingual together and replacing the top of the root chamber, so the tooth doesn’t fracture.

Bicuspids

Bicuspids that have been endodontically treated do not need two-cusp coverage if there have been no previous restorations and the endo access is very conservative. In the case of a premolar that has never had an MO, a DO, or an MOD, and has a tiny access hole, you can do a composite buildup or chamber retaining composite restoration. If the patient has high functional risk, a reasonable decision would be to restore the tooth with an onlay or crown

Anterior Teeth

There is no scientific support for doing a crown on an anterior tooth just because it has had endodontic therapy. We do a crown on an anterior tooth that has had endo when it is already structurally compromised, for example with previous mesial lingual and distal lingual composite fillings, missing tooth structure, and significant structural compromise between the endo access and other restorations.

Restorations are the foundation of a thriving dental practice because they keep you challenged and motivated while ensuring patient satisfaction. Indirect bonded anterior restorations provide patients with functional and aesthetic solutions to improve their smiles.

But “veneers” are more complicated than they seem when you see the finished product: bonded anterior restorations.

Before you decide on the type of restoration you are going to offer your patients in the anterior region, here are four questions you should be asking to get the most from your restorative process:

1. Can indirect bonded anterior restorations strengthen worn-down, eroded, or chipped teeth?
2. Should teeth be whitened before they are veneered?
3. Should endodontically treated teeth be veneered?
4. Are crowns stronger than veneers?

If you are hungry for more guidance on indirect bonded anterior restorations, check out my upcoming course at Pankey Online. On Friday, August 20th, 2021, from 2-4 pm ET, I will be hosting a live, 2-hour virtual course, “Indirect Bonded Anterior Restorations.” You can easily register for my course, which provides 2 CE credits, at Pankey Online.

Join me as we discuss useful concepts like three-dimensional functional and esthetic mock-ups, provisional fabrication, preparation design for adhesive restorations, and more. See you there!

The question of whether it is better to have a rough or smooth tooth preparation for indirect restorations pops up from time to time, and dentists relate to me they have heard conflicting opinions.

I go to the research literature to become better informed when questions arise, and this is one question research has answered convincingly for me.

What is the impact of texture on the predictability of your restorations?

When we think about the surface texture of a tooth preparation, there are two considerations.

1. How does the surface texture have an impact on bond strength or retention of an adhesively placed restoration? Do coarser surface textures on preps increase bond strength, or is it exactly the opposite?
2. How does the surface texture impact the accuracy of a VPS or Polyether impression and therefore the fit of the restoration?

It turns out that smoother is better.

If you go to the literature and look up the research studies in PubMed, you will find there is a high correlation between high bond strength and extremely smooth surface texture. To achieve an extremely smooth surface texture, multiple studies used carbide burs that are in the same shape that we use in doing crown and veneer preparations.

The other piece of the puzzle (the second consideration) has to do with the contact angle of VPS or Polyether impression materials and the tooth preparation. The smoother the preparation surface is, the more accurate the impression will be. The more accurate the impression is, the more accurate the die will be. And the more accurate the die is, the more accurate the fit of the final restoration will be.

So, in both categories, bond strength for adhesives and accuracy of physical impressions, smoother preps win over coarser preps.

All restorative materials have wear properties. We need to understand both how they wear and survive in the oral environment and how they impact opposing natural teeth.  

The wear of enamel is the basis for comparison.

Despite what we sometimes see clinically, enamel is highly resistant to wear (attrition and abrasion), with average annual wear rates of 30-40 microns. The range is from as low as 15 microns to as high as 100+ microns, and there is variability depending on the tooth position in the arch.  

Unlike enamel, which basically all has the same structure and properties, composites come in many different formulas. The chemical and physical properties of the material have a direct impact on its wear resistance and impact on other teeth. Some examples of this include: 

• Size, shape, and hardness of filler particles 
• Quality of the bond between filler particles and polymer matrix 
• Polymerization dynamics of the polymer 

These same properties affect the other physical and handling properties of the material and have to be balanced to create a composite that works clinically.  

Creating improvements in the physical properties of composites has eliminated the high degree of wear in non-contact areas we witnessed years ago. The loss of restorative material gave the appearance of fillings losing their shape and contour. Today our primary concern is in areas of direct occlusal contact.  

One approach might be to avoid using composite that has direct occlusal contact.

I would say this is not only not practical but not necessary. We have a variety of materials available today, with a range of handling and physical properties, and wear rates that are between 30-200 microns a year.  

We need to choose a composite based on things like wear versus polish–ability, anterior versus posterior, and the properties of the particular material we are using. In addition, we can manage the occlusion to maximize the success of the natural teeth as well as the composite. 

Both dentin and enamel can be worn down at a more than normal pace when exposed to very abrasive toothpastes.

We have learned that this damage is not being caused by the toothbrush, but the material being put on the toothbrush. As the desire to have whiter and whiter teeth has become popular, manufacturers have increased the abrasiveness of toothpaste to more effectively remove the external stains. In addition, tarter control and other newer versions of toothpaste designed to grab market share of consumers can also tend to be more abrasive. 

Ideally, we would like to be brushing with a material that has an RDA (relative dentin abrasiveness) of less than 80, but the FDA allows toothpaste to be sold with an RDA up to 200. The original Colgate toothpaste has an RDA in the 70’s. Most Sensodyne have RDA’s below 85, but several of the 2 & 1 tarter control and whitening have an RDA close to the maximum of 200. The abrasiveness can damage restorations, increase wear of exposed dentin and exacerbate sensitivity. At my Scottsdale, AZ practice, we keep a list of the most common toothpastes with their RDA, so we can discuss this with our patients. 

Prophy paste, even the fine, is generally more abrasive then over the counter toothpastes.

In addition, it is applied using a prophy cup going at 20,000 rpm’s with much more pressure. Even though the incidence is much less frequent, being 2 to 4 times per year instead of every day, this can still be a significant issue. 

A cool little experiment is to take some microscope slides and using your fingers rub prophy paste around on them and then rinse. Look at the slides with light behind them. You’ll be surprised to see a slide is scratched after just one application. This is the same thing that will happen to ceramic restorations. The glaze will be easily scratched. The surface of the crown or veneer will begin to deteriorate. 

Similarly, abrasive prophy paste will increase a patient’s sensitivity if used on exposed roots, accelerate the wear on exposed dentin or cementum, and can damage other restorative materials. The RDA of prophy paste can range from 150 for fine to up over 300 for coarse. Alternatives are to use products like Clinpro 5000 or MI Paste as a prophy product, both of which are low in abrasiveness. In my office, we use a product called Proxyt, from Ivoclar. It is a non-abrasive prophy product and is available in 3 grits and with and without fluoride. All three of the varieties have RDA’s between 7-83 and are safe to use on dentin, cementum, and ceramic. 

When we nose breathe, our tongue is elevated against the anterior portion of the palate and held there with gentle pressure. This position mechanically pulls the base of the tongue forward increasing the size of the airway. At the same time, the gentle pressure and movement of the tongue to this position helps to strengthen the tongue and keep it strong. A strong tongue is less likely to collapse backwards and obstruct the airway, so nose breathing is important for airway.

There is also great research today that breathing through your nose promotes better health. It creates higher levels of oxygenation of the blood, it cleans and humidifies the air for better lung health. Studies also show that mouth breathing suppresses the immune system and can have other adverse health effects. To this end, one of the current trends is to work with patients to train them to nose breath, including using a mouth taping technique.

A simpler way that may be effective is to use behavior modification and have people actively work on nose breathing. Many of the step tracking devices today can be set to vibrate every 15 minutes, to remind the person to move. I use this to remind people who parafunction to check if their teeth are touching, and for mouth breathers so they can check-in and nose breath instead.

Capturing an exquisite final impression is our goal every time. Getting this result can be one of the most challenging things we do in dentistry. In addition to being masterful in taking an impression and handling the materials, we also must manage the oral environment properly.

Improving the Gingival Tissue Prior to the Impression Appointment

For crown and bridge impressions this process has to begin with optimal tissue management, and tissue management always begins before tooth preparation. Old restorations with poor margins often compromise hygiene with resultant irritated and inflamed gingival tissues. If the tissue is inflamed at the time, we recommend the tooth be crowned, we apply chlorhexidine varnish (Cervitec Plus – Ivoclar Vivadent). When the patient returns for impressions, tissue health is vastly improved.

Managing the Gingival Tissue for Tooth Preparation

Tooth preparation itself can result in difficulty managing the tissue. My preference is always to leave margins supragingival if that is clinically appropriate. My second choice is equigingival, where the margins are right at the crest of the tissue. If the margins are to be placed subgingival, I want to avoid cutting the tissue and then having to manage bleeding. If my initial margin placement is equigingival, I place a primary cord to move the tissue out of the way. This allows me to now drop the margin subgingival with minimal trauma to the tissue.

Retraction of the Gingival Tissue for the Impression

Once tooth preparation is complete, retraction creates a space for the impression material to go past the margin apically so that we can create the proper emergence profile of the restoration. There are many ways to retract prior to an impression. I personally use a second or top cord with a larger diameter than the primary cord I placed to move the tissue for subgingival preparation. If the tissue is bleeding after the placement of the top cord, I place 3M’s “Retraction paste” as a hemostatic agent. This allows for optimal control of bleeding without worry of negatively impacting the set of my impression materials or staining the prep or gingival tissues.

Taking the Final Impression

The final impression is taken with Flexitime impression material (Kulzer). I have my assistant load the tray with heavy body material. I first wet the top cord, so I do not cause bleeding upon removal. The area is now thoroughly dried to allow for proper contact of the impression material to the tooth and tissue surfaces. I inject Flexitime CorrectFlow (Kulzer) and then seat the impression tray. I hold the tray for the full intra-oral set time and do not allow patients to close or bite on the tray, as movement can negatively impact the accuracy of the impression.

Is the impression perfect?

Once removed I inspect the impression using magnification to assess that I have adequate flash beyond the margins of the light body, no pulls, voids, drags or evidence that the impression moved. There is no way to correct an impression for errors. If errors occur, we repeat the process from the beginning to take a new impression.

Check out some of my short videos about impressions on Restorative Nation at https://restorativenation.com/?s=impression.

I believe that some wear is normal. I base this on the fact that I have very few if any patients who are in their seventies or eighties and still have mamelons on their incisors. Wear is a concern when the amount of tooth structure being lost is out pacing the patient’s age.

In Part 1 of this series, I wrote about determining when wear leaves the physiologic category and becomes something we need to discuss with patients. Both attrition and erosion can cause severe tooth wear, but they pose different long-term risks. Once we have a sense of the cause of tooth wear, we can partner with the patient to treat the damage and manage the progression.

These are the guidelines for discerning attrition from erosion.

Attrition is the loss of tooth structure caused when the patient rubs two tooth surfaces together. You will observe:

· Matching facets on upper and lower teeth

· Facets on tooth surfaces that occlude

· Enamel and dentin worn evenly

Erosion is caused by the presence of acid from issues like GERD and eating disorders. You will observe:

· Facets that may or may not match on upper and lower teeth

· Facets on tooth surfaces that are not in occlusion

· Dentin cupped out and wearing faster than enamel

· Tooth structure wearing around restorations that remain unchanged

Note that attrition can be seen in addition to erosion, often giving us a false sense of how much the patient truly parafunctions, as the etched tooth structure wears away more easily.