Written by Stephen H. Abrams, DDS Sunday, 31 July 2005 19:00
Temporary cementation is not just a small final step in a crown and bridge appointment, but the critical link in creating a well-sealed transitional restoration. The temporary cement creates a microbial barrier between the prosthesis and the tooth, helping to ensure that the pulp remains vital and dentin does not demineralize.
Temporary restorations have a number of important functions. Their primary role is to ensure the vitality of the pulp and keep the patient comfortable while the permanent restoration is being fabricated.1 A properly shaped and contoured temporary restoration will allow the patient and clinician to assess the aesthetics and function of the final restoration. The temporary restoration will also provide support and protection to the gingival tissues. A temporary crown or bridge is not simply a cover for the tooth, but restores the tooth to function on an interim basis. Unfortunately, the temporary prosthesis is usually fabricated at the end of a long appointment when both the clinician and patient are tired and rushed. Errors introduced at this stage will affect the final result. Long-term maintenance of a healthy pulp is the result of atraumatic preparation and the use of biologically acceptable restorative materials that can seal the tooth-restoration interface to prevent or minimize bacterial leakage.2
Temporary cements should have the following characteristics:
• easy removal of excess cement from around the margins upon cementation;
• good marginal seal to help minimize sensitivity;
• good retention but easy removal of the temporary prosthesis;
• low solubility in oral fluids; and
• compatibility with provisional resin restorations, resin core materials, bonding agents, and permanent cements.3
If the cement has these characteristics and the provisional restoration is well-made with good contour and margins, then oral tissues will be protected and remain healthy while the final restoration is being fabricated.
Selecting the right temporary cement for the right clinical situation involves examining a number of factors. One needs to assess the following:
• how long the prosthesis will be in place;
• what types of occlusal and parafunctional forces will be exerted on the prosthesis;
• the shape and parallelism of the preparation, or if multiple abutments, the parallelism of all the abutments;
• the height of the preparation; and
• the thickness of the walls of the preparation.
Each of these factors will influence the type of retention or adhesion a temporary crown will require. For example, a temporary crown placed on a short preparation subject to off-axis occlusal loading may require a very retentive temporary cement. A prosthesis that needs to be in place for a long time may also require a very retentive temporary cement. A temporary crown placed on a long preparation for a short period of time may not require a very retentive temporary cement. In my opinion, there is no one universal temporary cement, but one should have at least 2 types of temporary cements available for use in the office with varying adhesive and retentive properties. One should also become very familiar with the working properties of these cements so that you can determine which cement is appropriate in a particular situation.
|Figure 1. Initial smile showing large restoration on maxillary right lateral incisor.||Figure 2. Cast post core and preparation on the maxillary right lateral incisor.|
In this case we were restoring the maxillary right lateral incisor following the completion of endodontic therapy. The tooth was heavily restored with composite resin, so we fabricated a cast gold post into the root canal system to provide additional support to the coronal tooth structure (Figures 1 and 2).
In this situation we had a short, small preparation that needed to support a temporary crown. There was some degree of occlusal loading in centric occlusion and in lateral excursions. We selected TNE, a noneugenol temporary cement, from Temrex Corporation. It has very good compressive and tensile strength, ensuring that it is very retentive. TNE is based on the diurethane dimethacrylate monomer, one of the most biocompatible resins in dentistry. This chemistry imparts 2 important benefits: excellent biological compatibility and universal ma-terial compatibility. It has negligible solubility in oral fluids and is radiopaque. TNE is now available in an automix dual syringe so that one can quick-mix and dispense the material directly into the prosthesis.
|Figure 3. Applying releasing agent to the incisal edge to decrease the retentiveness of the cement.|
We decided to decrease the retentive properties of TNE by applying a small amount of releasing agent to the incisal edge of the preparation (Figure 3). The releasing agent decreases the bond strength; at times it can also be used to block out undercuts or grooves where the cement can become locked in place.
TNE has a unique, 2-stage set. There is a 1-minute working time and then a 4-minute setting time. As the material sets, it develops a gel state around the margins. It can then be easily peeled away from the crown (Figure 4). This avoids traumatizing the tissue while cleaning away excess cement. TNE also does not stain the surface of temporary crowns.
|Figure 4. After the initial set, TNE easily peels away from the crown margins.||Figure 5. Temporary crown in place 1 week later. Note the good tissue response to the crown.|
If we are careful in our construction of the prosthesis and removal of all residual temporary cement, we find good tissue response at the next visit (Figure 5). In this example after 1 week the gingival tissue is pink and healthy with no sign of bleeding or irritation. When we examined the interior of the temporary prosthesis and the tooth preparation, we found no sign of leakage or residual caries. Open margins allow for bacterial microleakage, which can contribute to postoperative sensitivity and caries. In certain situations this may appear as a black stain that spreads from the crown margins toward the coronal aspect of the tooth. Natural iron pigments in blood or iron-enriched coagulum can be found around the tooth preparation and in the gingival sulcus. These pigments, along with bacteria, saliva, and sulcular fluid, can leak under open crown margins. It is thought that hydrogen sulfide gas, which is produced by this mixture of bacteria as part of metabolism, could react with the iron to form this black stain.4 The solution is to ensure that the preparation is well-cleaned and the margins are sealed both before and after temporary cementation. If a margin appears open, then it can be sealed with a flowable or conventional composite. The tooth preparation should be treated with an antibacterial solution before the crown is placed to reduce the bacterial population on the prepared surface.5 It is the presence of bacteria at the tooth-restoration interface that causes pulpal reactions.6
The black stain can be removed from the tooth surface by using conventional acid etching and bonding with a suitable dentin bonding system. We find that 35% phosphoric acid (Temrex Gel Etch) will remove most black stain. For more persistent stain, removal of the surface layer with a green stone is recommended, ensuring that you do not damage the margins.
The construction of a temporary prosthesis and temporary cementation are key steps in ensuring a successful restoration. A well-designed prosthesis that replicates ideal tooth anatomy will ensure the health of the oral tissues. Care should be taken to ensure that the temporary prosthesis margins are sealed and the tooth preparation is clean and free of bacteria and medicaments. Temporary cementation is a critical part of the provision of any final prosthesis. Care and understanding of the objectives of your temporary prosthesis will create an excellent result.
1. Wassell RW, St George G, Ingledew RP, Steele JG. Crowns and other extra-coronal restorations: provisional restorations. Br Dent J. 2002;192:619-622.
2. Mjor IA, Odont D. Pulp-dentin biology in restorative dentistry. Part 2: initial reactions to preparation of teeth for restorative procedures. Quintessence Int. 2001;32:537-551.
3. Farah JW, Powers JM (eds). Temporary resin cements. The Dental Advisor. 1995;12(3):8.
4. Bailey JH, Fischer DE. Procedural hemostasis and sulcular fluid control: a prerequisite in modern dentistry. Pract Periodontics Aesthet Dent. 1995;7:65-75.
5. Brannstrom M. Reducing the risk of sensitivity and pulpal complications after the placement of crowns and fixed partial dentures. Quintessence Int. 1996;27:673-678.
6. Mjor IA, Ferrari M. Pulp-dentin biology in restorative dentistry. Part 6: Reactions to restorative materials, tooth-restoration interfaces, and adhesive techniques. Quintessence Int. 2002;33:35-63.
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