What’s the best way to protect the tooth during temporization

Research shows a simple procedure can prevent sensitivity, protect the tooth against secondary caries and pulpal irritation, and even eliminate the need to numb the patient when you cement the finished crown.

by Nelson Gendusa, DDS
Director - Research

In a recent survey roughly 30% of the dentists reported that at least 5% of their patients complained of sensitivity during the temporization stage (and 3% of the respondents said the number was more like 15%!)¹

Someone (I can’t remember who) once calculated that a molar preparation can open as many as 6-million tubules. That’s 6-million mini-exposures to the oral environment. 6-million potential passageways for chemical irritants, bacteria and their endotoxins.

Tubules radiate from the pulp like the spokes of a wheel, and widen as they approach the pulp. Dave Pashley once figured that as much as 22% of deep dentin consists of big wet holes.

Once a crown prep has been cut, those tubules must be resealed, or the patient may suffer sensitivity during the provisional period. If the temporary crown leaks, the pulp may be in jeopardy from pathogens and the toxins they produce.

And the fact is, all temporary cements leak.² When they’re cemented with temporary cement even great-fitting gold crowns will leak. One study suggested that 14 days was plenty of time for bacterial toxins to penetrate under provisionally-cemented gold crowns.³

That’s why dentists in increasing numbers are applying a bonding agent to the prep before cementing the temp - not for retention, but to armor-plate the preparation. That way, when the temp inevitably leaks, the schmutz will remain trapped between the restoration and the bonding agent. 38% of Touch&Bond users and 41% of Brush&Bond users tell us they apply the material to crown preparations in order to protect them during the provisional period.

A quick aside to illustrate that not all bonding agents provide the same protection: Researchers at the Tokyo Medical and Dental Hospital recently published research demonstrating that Touch&Bond’s ultrathin 3-micron film was extremely effective in resisting caries ... significantly better than 3M’s SingleBond. The other standout was Clearfil SE. However Clearfil comes with a 90-micron film thickness - That’s THIRTY TIMES the thickness of Touch&Bond - which limits its usefulness in indirect restorations.⁴

In past articles I suggested that Touch&Bond’s miniscule 3-micron film thickness gave it a slight advantage over our Brush&Bond (9-microns) for indirect applications. However, talking to dentists actually doing the procedure makes me suspect I was wrong. They report routinely applying a second coat of Brush&Bond with no fit problems at all during final cementation.

This was an important discovery, because if the additional film thickness isn’t a problem, Brush&Bond is probably the better choice for protecting crown preparations. Brush&Bond occludes tubules better than Touch&Bond.5 And because it forms a more robust film, Brush&Bond is more likely to prevent discomfort during temporary crown removal and final cementation.

So why didn’t B&B’s thicker film cause fit problems?

It’s amazing how things you hear when you’re young and impressionable stay embedded in your brain. In dental school I was taught that a well-fitting crown has a marginal gap of just 25-microns. In fact, this is nonsense ... presumably dreamed up by the same guy who conceived of the “ideal 4° crown taper.” In the real world 25-micron marginal gaps and 4-degree tapers do not occur. (Okay, maybe they occur. But only rarely and mostly by chance.)

When I quickly tore through the research on marginal gaps (see sidebar), I found that real crowns have marginal gaps of 40-100 microns.
Furthermore, do you know how small 18 microns is? It’s 18 thousandths of a mm!! Let’s contemplate that. A human hair is about 70 microns in diameter. A salt crystal measures about 100 microns per side. In other words, if your crown fits absolutely perfectly with no marginal gap at all - adding two coats of Brush&Bond after the impression would cause the crown to sit high just 1/4th the thickness of a human hair. You’d never see it on a film. It wouldn’t affect the bite or create a plaque trap. I’d argue that it wouldn’t be clinically high.
While I was digesting this information, the latest Journal of Adhesive Dentistry appeared on my desk. In it was an in vitro study exploring the use of Brush&Bond as a prep protector.

Researchers found that when

o Brush&Bond was first applied to dentin
o then temporary cement was applied over it and covered with provisional material
o everything was later removed and the surface cleaned with acid
o and an indirect restoration was bonded without another application of B&B

the final bond was indistinguishable from the bonds created when direct composite was bonded immediately after preparation. No difference.

Protection that keeps on ticking even if your restoration doesn’t

After these researchers had measured the bond strength, they microscopically examined all the fractured surfaces to determine where the resin bond had failed. And in every single indirect case, the fracture occurred within the cement or at the interface between the cement and the Brush&Bond. In other words, even after the restoration was pulled off, the dentin remained sealed with Brush&Bond polymer.

Those researchers suggested that if the B&B-sealed prep was well-cleaned with acid, the original bonding agent could be used to bond the final restoration. Maybe, but I’ve seen some micrographs which suggest that scrubbing with acid may damage the protective film. (And remember, the primary reason we apply the stuff is to protect - not necessarily to bond!) So instead, I recommend applying another coat of B&B.

Fewer needles at cementation

I was reading responses to a young dentist who complained on the internet that he was sensing a lot of patient discomfort during cementation.

Several dentists recommended that he routinely numb the patient before cementing. One respondent said he used the needle on 99% of his vital insertions, and suggested that any dentist who did less was causing needless pain.

At this point Dr. Jason Robert Tanoory (Canandaiga, NY) jumped in -

“I can’t believe what I’m hearing! I KNOW your patients don’t want a shot for a 10-minute appointment! There’s a better way out there. Just seal the prep with Brush&Bond: PROBLEM SOLVED. I only have to numb about 5% of my patients for cementation.”

Another dentist volunteered that he too used B&B to protect the prep. He estimated that it eliminated 90% of the shots.

As Dr. Tanoory observes, if there’s an alternative, most patients would rather not get the needle. Furthermore, once you’ve numbed them, you lose an important source of information during the crown adjustment.

So let’s summarize -

The benefits of routinely protecting the preparation with Brush&Bond are

1) Eliminate sensitivity during the provisional period

2) Keeps black scuzz off the tooth during the provisional period

3) Prevent secondary caries during the provisional period

4) Protect the pulp from bacteria and their by-products that can sneak under the temporary crown margin

5) Dramatically reduce the need to anethesize the patient at final cementation

6) Make more reliable adjustments at cementation because the unanesthetized patient can give reliable feedback

7) Fewer complaints of post-cementation discomfort

Several dentists even tell me they’ve seen a drop in those embarassassing post-cementation RCTs. However, that’s purely anecdotal.

So what exactly is the procedure for protecting preparations?

The table below shows what I’d do ... I’m not saying this is the only way to do it ... It’s just what I’d do.