Provisional Crowns Made Simple

[DrAnil]

A patient presents with recurrent decay under a mesio-occlusal porcelain inlay on tooth # 31.  There is also a large buccal amalgam restoration, so the tooth was treatment planned for a full-coverage crown.

#31 planned for full-coverage crown

While waiting for the anesthesia to take effect, take an impression of the tooth before it has been prepared.  Use alginate in a quadrant tray for a single tooth.

Alginate in a quadrant tray, pre-operatively

If the tooth is going to be in a provisional for a long time, use a material like Template instead of alginate.  The Template matrix can remain in a  safe place for months if you need to fabricate a new one.  Alginate, on the other hand, would distort to the point of being useless after one day.

Now have fun and prepare the tooth.

Okay, provisional time.  Use bis-acryl most of the time.

Re-seat the tray in the mouth just to ensure it can be easily placed all the way down.  Squirt the first bit of bis-acryl onto the tray and the rest in the matrix for tooth #31 up to the brim.

Squirt!

Now wait until the little bit of bis-acryl on the tray is set.  Remove the tray and check the fit in the mouth.  Do not evaluate the bite just yet- the material is not fully set and may break. Just evaluate the marginal fit.  Trim the excess with a diamond bur.

Diamonds are your best friend with bis-acryl

Almost done!  Now you can check the occlusion and cement with your favorite temporary cement.

That’ll do. That’ll do.

This is a pretty simple technique.  Most of the early challenges may be due to not being familiar with the differences between bis-acryl and regular acrylic.

        

[DrAnil]

 Protemp, Luxatemp, Telio, Integrity are some of the most popular brands of bis-acryl resins.

Acrylic resins, also known as polymetheyl methacrylate and polyethyl methacrylate, have been the gold standard for provisional fabrication for decades.  But the advantages of using bis-acryl instead of acrylic resin are numerous.  They include:

(a) lower temperatures during curing

(b) low shrinkage

(c) no powder and liquid means more consistent mixtures

(d) less porous means lower bacterial contamination

(e) no nasty monomer smell

Despite these and other advantages, bis-acryl may cause you some headaches if not handled properly.  Here are some tips to avoid the pitfalls:

 

(1) Trim with diamonds, not acrylic burs

Acrylic burs generate too much action on the bis-acrylic temporary and can lead to unwanted chipping.  This is due to the fact that bis-acryl resin is more brittle than acrylic resin.  A nice diamond bur will gently and smoothly trim excess material.

Don’t use diamonds to trim acrylic resin because the acrylic tends to stick and clog the diamond.  This doesn’t happen with bis-acrylic resin!

(2) Do not have the patient bite while it is setting

As I just mentioned, bis-acrylic resin is more brittle than acrylic resin, especially while it is curing.

When fabricating an acrylic resin provisional, instruct the patient to bite down.  This simple set helps further seat the curing provisional but also reduced the amount of occlusal adjustment you’ll need to do.

Do not do this with bis-acryl! You may split the curing provisional into pieces.  Wait for full curing and then adjust.

(3) Apply Vaseline to cores

If you’ve just placed a core build-up on the tooth in question, care must be used when fabricating a provisional with bis-acryl.  Depending on the exact material you’ve used for the core, the bis-acryl may actually bond to the core.  Not good.

To avoid this, apply a light coating of Vaseline to the prepared tooth and core before fabricating your bis-acryl provisional.

Thin layer of Vaseline being added

 

(4) Bond before relines and additions

One of the greatest advantages of working with bis-acryl resin is that it can easily be modified with more bis-acryl or even flowable composite.  Relining provisional crowns, sculpting emergence profiles around temporary implant abutments, developing pontic sites, repairing chips in the provisional, etc.

Place and cure bonding agent to the surface of the bis-acryl provisional that you would like to modify.

Step 1: Apply bonding agent

Step 2: Bis-acryl reline

        

[Author]

Posts