The fabrication of long-term provisional (fixed) tooth restorations from PMMA (polymethyl methacrylate) (99)

​The fabrication of permanent tooth restorations (crowns, bridges) is always preceded by a pre-prosthetic treatment in which teeth beyond repair are removed and salvageable teeth undergo scaling (tartar removal) and root canal treatments so that the permanent restorations are mounted on clean teeth and fully healed gums. Until such time as the permanent restorations area complete, provisional crowns and bridges are required to protect the tooth preparations.

Demands as regards provisional restorations have greatly increased, what with advances in dentistry. Owing to innovations and the introduction of cutting-edge materials, our prosthodontic inventory has come to include polymer-based provisional tooth replacements. Milling provisional bridges from a PMMA (polymethyl methacrylate) blocks, CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) ensures substantially higher quality and aesthetics (generally intended as long-term provisional tooth restorations).

Provisional PMMA tooth restorations serve as reliable long-term solutions for the healing periods between the treatments. As readily seen from the image above, tartar removal, tooth extractions and other invasive treatments cause a great extent of inflammation and therefore do not allow for the immediate mounting of permanent replacement teeth, mandating a healing period of 2 to 3 months

What to expect from a good provisional tooth replacement?

• High aesthetics.

• To ensure proper masticatory function.

• Resilience to breakage

• Appropriate assistance in phonation.

• With tooth preparations (filed-down live teeth), the protection of the tooth pulp against mechanical, thermal and chemical stimuli, e.g. to prevent toothache during eating.

• Keeps the filed tooth stumps in place to prevent tooth mobility until the permanent tooth restorations are finished.

Provisional crowns and bridges can be of various kinds:

1. Provisional immediate crowns prepared by the dentist straight at the chairside. Provisional immediate crowns are tooth restorations fabricated and mounted on the tooth preparations right after being filed down/prepared, in the same sitting (the Scutan method).
2. Provisional crowns can be fabricated from self-curing acrylate in the dental laboratory, hand-moulded, cast and polished by the dental technician.
3. The provisional crown may also be fabricated with CAD/CAM procedure.

Whatever the type of the provisional crown, it is worn by the patient on their tooth preparations until the permanent crown is complete.

What are the benefits of CAD/CAM processed provisional tooth restorations?

• They are created with a state-of-the-art procedure.

• The tooth restorations thus created are extremely accurate.

• Their cutting-edge material sees to their increased resilience.

• They have a smooth, life-like appearance.

• They are not liable to discoloration.

• They do not wear out.

• They are extremely unlikely to break.

In the front region it is of the utmost importance to provide the patient with enduring, reliable and seamlessly fitting long-term provisional tooth restorations with impeccable aesthetics:

How are PMMA crowns fabricated with CAD/CAM technology?

• Your dentist takes a precision/functional impression of the teeth.

• The impression is forwarded to the dental laboratory where it is cast from gypsum.

• The gypsum cast is digitalised with a 3 dimensional scanner.

• The dental technician designs the provisional crown in 3 dimensions using the digitalised sample with an application serving this end.

• The parameters of the crown designed are fed into a 5-axis CNC milling machine which mills the provisional crown from a single PMMA block. Since the machine can move in 5 axial directions the finished crown will be an exact match of its digital design, with no variance whatsoever. Crowns milled in this fashion fit the tooth preparations with extreme precision.

• The crown removed from the milling machine has a matte finish. It receives its permanent gloss by the dental technician painstakingly polishing it.

• The provisional crowns are transferred back to the dentist, where they are glued on. The timeline of the treatments determines the kind of luting cement to be used. If the ensuing treatments follow one another at short intervals, then they are mounted with provisional luting cement to allow for easy removal of the provisional PMMA crown (e.g. root canal treatments, endodontic treatments). If the treatments follow at longer intervals, months or even years, your dentist may opt for a long-term luting cement, which still ensures easy removal of the provisional crown, but offers longer-lasting retention. A great benefit of PMMA crowns is that the crown can easily be removed without any risk of breaking the tooth stump at intermediate treatments.

The benefits of provisional PMMA tooth restorations made with CAD/CAM technology:

• By virtue of its increased resilience owing to its polymer material, it has increased life-time over conventional chairside provisional materials.

• It is a lot tougher than conventional acrylate (methyl methacrylate, a methyl ester of methacrylic acid), of which the majority of provisional crowns are made.

• Provisional crowns can be taken off and mounted back on the tooth preparations/tooth stumps multiple times without running the risk of breakage.

• The provisional tooth replacement does not get discoloured or wear out, can be polished perfectly and its aesthetic properties match those of natural teeth.

Uses of CAD/CAM processed provisional tooth restorations:

• Provisional crowns or bridges both in front and molar regions

• Implant-borne provisional or fixed tooth restorations.

• Long-term provisional prosthodontic devices for patients treated for occlusal and TMJ issues or periodontitis.

Disadvantages of CAD/CAM processed provisional PMMA dental restorations:

• The most expensive provisional crown.

• It is not ready immediately after polishing, turnaround time is several days.

The future, in all likelihood, is for digitally fabricated tooth restorations, due to the patients having ever increasing aesthetic demands.

Literature:

Kivovics P, Katona I, Csemez A, Németh O, Borbély J: Ideiglenes rögzített fogpótlások készítése CAD/CAM technológia alkalmazásával. Magyar Fogorvos. 2015/1: 24-29.

Fábián T, Götz Gy, Kaán M, Szabó I: A fogpótlástan alapjai. Semmelweis Kiadó, 2001.