What is the most common type of provisional coverage used for crown and bridge preparations?

By Mary Govoni, CDA, RDA, RDH, MBA

Making provisional or temporary crowns and bridges is both interesting and challenging for dental assistants. If the state dental practice allows the delegation of this function, and dental assistants have proper training, the assistant can greatly enhance productivity in the practice during crown and bridge procedures. If the assistant is able to make the temporary, the doctor's time is freed up to see other patients, while the assistant provides his or her services to the patient.

Assuming that the chairside assistant is going to fabricate provisionals for patients, what factors will affect his or her success in completing the procedure and providing the highest quality of service for the patient? These factors are selection of the matrix material, selection of the provisional material, chairside technique, finishing or polishing the restoration, and cementing the provisional restoration.

Matrix selection

The types of materials typically used as matrices are wax, alginate impressions, thermoplastic buttons, aluminum crowns (sometimes lined with an acrylic wash), polycarbonate preformed crowns, putty or silicone impressions, and light-cured tray material or "stents." The type of matrix material selected should be convenient to use, cost-effective, and provide a smooth surface, which will allow the provisional material to cure with a smoother surface that requires less polishing once the material has cured.

My choices for matrix materials that provide theses characteristics are thermoplastic matrix buttons, putty (3M ESPE Express™ Impression Material), and vinyl poly siloxane (VPS) impression materials (3M ESPE Position™ Penta™ Quick Impression Material). Putty is supplied as a two-component system (the base and catalyst) which are mixed by hand until the material is consistent in color and free of streaks. The material should not be mixed while wearing latex gloves, as the latex will retard the setting of the material. Once the material is mixed, it is placed over the teeth prior to preparation, allowing material to extend one tooth mesial and one tooth distal to the preparation(s). Forming the putty over the teeth will look very similar to an impression tray. Approximately one teaspoon each of the base and catalyst materials is adequate for a single crown to a three-unit bridge. For longer-span bridges, using the measuring scoops that come with the putty, which hold slightly more material, will provide adequate coverage for a quadrant matrix. The cured surface of the putty is very smooth, which makes the surface of the provisional material set up very smooth. In addition, the putty is stable, unlike an alginate impression, and can be saved for future use if necessary. This is extremely helpful for patients who may be wearing their provisional restorations for a month or longer.

VPS materials for preliminary impressions and provisionals include products such as Position Penta Quick impression material (3M ESPE). This material is dispensed from foil bags that are placed in cartridges and loaded into the Pentamix™ Mixing Unit (3M ESPE). Mixing this material is simple and automatic, the impression material has a short set time and it provides a very smooth surface for the provisional material. This type of material also can be saved for future use.

Thermoplastic matrix buttons (Matrix Buttons from Advantage Dental Products) are also great for matrices. They are simple to use, do not require any mixing, and are very inexpensive. The opaque thermoplastic buttons are placed in hot water (approximately 150 degrees) for about 45 seconds to melt the plastic material. Once the material has turned clear, it is should be rolled into an oval shape and placed over the teeth to be prepared, occlusal surface first, in the same fashion as the putty (one tooth mesial and one tooth distal to the prep). As the plastic cools and hardens, it will turn opaque again, indicating that it is set and can be removed. The setting time can be accelerated by gently blowing air from the air/water syringe on the material. One thermoplastic button is typically enough material for one to two adjacent crowns. Three (or more) crowns or a three (or more) unit bridge likely will require melting two buttons together to provide enough material. If the matrix has been formed, but does not provide adequate coverage for the teeth to be prepared, the button(s) can simply be melted down again and reformed. This is a distinct advantage of this type of matrix material. If an acrylic material is used in this type of matrix, a separating agent must be used. This matrix also can be saved for future use if necessary.

Selection of provisional materials

I believe that the selection of the provisional material is the single-greatest factor in the success of the provisional restoration. Many people believe that the material is not so important since it's only "temporary," but I disagree. The use of a high-quality product will provide better ease of use for the assistant, and that makes the process more efficient and less time-consuming. It also provides a much more durable, pleasing restoration for the patient.

Factors to consider in the choice of provisional products: shade selection, strength, ease of use, cost effectiveness, and ease of polishing. The types of provisional materials available are methacrylate resins (typically called "acrylics") and bis-acrylic materials formed in a matrix of preformed aluminum, stainless steel, and polycarbonate crowns. For most uses, my recommendation is the selection of a bis-acryl material, such as Protemp™ 3 Garant™ Temporization Material from 3M ESPE.

Bis-acryl products will provide greater strength, color stability, no objectionable odor or taste during fabrication, no heat release during curing, and very smooth surface prior to polishing. In fact, the use of resins in putty or thermoplastic matrices can nearly eliminate the need to polish the restoration to achieve the smooth finish necessary for patient comfort.

A distinct advantage in using bis-acryl materials is that the material will bond to itself, which is very important if the provisional has bubbles or voids after it is removed from the matrix. The ability to add to the temporary in case of voids helps to avoid re-makes and wasted material. Protemp 3 Garant temporization material has "add-on" material provided in a convenient syringe (see photo at left). One also can use additional material from the cartridge or a restorative resin material.

Some practitioners object to the increased cost of the bis-acryl materials. However, if chair time is decreased because of the more "user-friendly" characteristics of these materials, then the products are actually more cost-effective.

Chairside techniques

When dispensing material from a cartridge, always dispense a small amount of the material (until you see the white catalyst) on a towel or other surface outside of the matrix before filling the matrix. This should be done because a small amount of the first material that comes out of the mixing tip may not be adequately mixed and may interfere with the material setting. In addition, it also is critical that dentists know and understand that bleeding through the mix tip (a pea-sized amount) is a requirement — before every use prior to dispensing into the matrix.

When filling the matrix, always keep the dispensing tip in contact with the surface of the matrix and immersed in the material. This prevents air bubbles from forming in the material, which can cause voids in the temporary. Fill the prepped area just to the margin of the prep. Overfilling wastes material and will require more trimming once the material has set.

Finishing and polishing

Every dentist and assistant will have his or her own preferences about what to use for finishing provisional restorations. Whether you prefer finishing diamonds, polishing stones, or discs is not as important as to remember to always use a fulcrum or finger rest while using a bur or stone in a handpiece to stabilize your working hand. The fulcrum can be established on a work surface or on your opposite hand and provides better control with the handpiece. It is also important to remember to wear safety glasses to prevent getting pieces of material in the eye.

Cementing temporaries

Cementing provisional restorations seems slightly contrary. While we want the temporary to stay on the tooth for the planned time, we also want the temporary to be easy to remove when it's time to remove it. For this reason, I like zinc oxide cements. Since these cements have the lowest solubility, they typically make temporaries easier to remove and the cement that remains on the prepped tooth is also easier to remove. Zinc oxide cements with eugenol, however, are not recommended for use with bis-acryl materials since they can cause the material to soften. This is especially important with long-term provisional restorations (RelyX Temp NE, formerly known as Procem from 3M ESPE, Zone).

From matrix and material selection, every step of the process of fabricating provisional restorations is an important one. It's not just a temporary. In the patient's mind, it's a preview of the restoration that will follow. The better the quality of the temporary, the more confidence your patient will have.

Mary Govoni is a Certified and Registered Dental Assistant and a Registered Dental Hygienist, with over 28 years of experience in the dental profession as a chairside assistant, office administrator, clinical hygienist, educator, consultant, and speaker. She is the owner of Clinical Dynamics, a consulting company dedicated to the enhancement of the clinical and communication skills of dental teams. She can be reached at .