Selecting the best materials for long-lasting provisional prostheses
Nathaniel Lawson, DMD, PhD | Amir H. Nejat, DDS
An ideal provisional restoration would be fabricated quickly, withstand fracture during function, maintain vertical dimension and an esthetic appearance during use, allow modifications for reline and recontouring, and not irritate the pulp during fabrication or function. For cases with immediately loaded implants or functional prototypes in full-mouth rehabilitation, provisional materials are required to remain in function for many months. As clinicians require longer service time for provisional prostheses and patients expect normal function and optimum appearance, we must explore new materials and techniques to fabricate and maintain long-lasting, esthetic provisional restorations.
Classification of Provisional Materials
Broadly, provisional materials can be classified as resin-based composite materials (ie, bis-acryl) and polymer-based materials (ie, polymethyl methacrylate—PMMA, and polyethyl methacrylate—PEM).
Bis-acryl (ie, ProTemp™ Plus, 3M, www.3m.com; Luxatemp Automix Plus, DMG America, www.dmg-america.com; Integrity® Multi-Cure, DENTSPLY Caulk, www.dentsply.com) is the material of choice for single unit provisional restorations that function for a short period of time. These materials are easy to use because of their paste-paste delivery system that allows fast fabrication, low shrinkage during set (making for a good fit), and low exothermic reaction, which is less likely to irritate the soft tissue or pulp of the patient. These materials are not well suited for multi-unit provisional prostheses because they do not have the toughness of PMMA materials.1 Bis-acyl materials do not perform well for long-term provisionals because they are difficult to repair and have poor color stability.1 These materials are also considerably more expensive than PMMA or PEM temporary materials.
PMMA (ie, Jet, Lang, www.langdental.com; Alike™, GC America, http://gcamerica.com) is a preferred material for long-term or long-span provisional prostheses due to its toughness, good color stability, and ease of repair.1 During set, however, it has a high exothermic reaction, which could cause pulpal irritation and undergo considerable shrinkage, which could alter its internal fit. These unfavorable qualities hinder its use for direct fabrication of provisional prostheses in the mouth. PMMA is well suited for use as a shell fabricated on a cast that can be relined in the mouth with a PEM.
PEM (Trim II, Harry J Bosworth Co., http:// dental.keystoneindustries.com; Snap™, Parkell, http://parkell.com) is more biocompatible, emits less heat during curing, and undergoes less setting shrinkage than PMMA. It is well suited as a relining material for PMMA shells, as it forms a strong bond with PMMA. PEM can also be used alone as a provisional material, however it is less color stable and less tough than PMMA.1
New Options for Long-Term Provisionals
One option for fabrication of long-span or long-term provisional materials is the use of laboratory-processed provisionals (ie, Cercon base PMMA, DENTSPLY; CAD-Temp®, VITA, www.vita-zahnfabrik.com) that can be relined intraorally with PEM or PMMA. These materials are typically fabricated out of highly cross-linked PMMA or bis-acryl with laboratory CAD/CAM milling. They have a higher reported strength than traditional PMMA.2 It is also possible to fabricate highly cross-linked PMMA provisionals with chairside CAD/CAM (Telio CAD, Ivoclar Vivadent, www.ivoclarvivadent.us). Other in-office solutions for high-strength provisionals include materials like Radica VLC (DENTSPLY Caulk), which is a composite resin that is cured with a laboratory light cure unit or Tuff-Temp™ Plus (Pulpdent Corporation, www.pulpdent.com), which is a provisional based on a rubberized urethane molecule.
How to Repair Provisional Materials
To maintain provisional restorations for extended periods of time, repairing these materials may be necessary. Repairing PMMA and PEM provisional materials can be accomplished by reapplication of similar material.3 If the provisional restoration has been worn in the mouth, it can be roughened by air abrasion or bur roughening. The surface of the old prosthesis is then wet with the liquid followed by application of new material.
Repair of bis-acryl material is not ideal, however it can be accomplished by air abrasion of the old prosthesis followed by application of a flowable composite.4 Roughening the old provisional prosthesis with a diamond bur may suffice if an air abrasion unit is not accessible. The use of an intermediate coat of adhesive is not necessary, and can even reduce the bond between the flowable material and the old provisional material.4 Repair of a bis-acryl provisional material with additional bis-acryl material also does not work well as the bond takes approximately 24 hours to develop and will likely debond immediately or soon after the patient leaves the office.5
How to Make Esthetic Modifications to Provisional Materials
Long-term provisional restorations used to restore anterior teeth will require natural optical and esthetic properties to meet the demands of many patients. Achieving a high gloss and low roughness of the provisional prosthesis is important not only for cosmetics but it also offers biologic benefits by reducing the accumulation of plaque and preventing inflammation of surrounding soft tissue.