Ask Dr. Christensen: Resin cement and bonding
Question ...
I am concerned about using light-cured bonding materials when seating tooth-colored inlays and onlays or all-ceramic crowns. I can’t cure the bonding materials before placing the restorations because pooling of the bonding material will not let the restoration seat. If I don’t use a bonding agent, extreme tooth sensitivity is present. Will the resin cement chemistry make the bonding material harden if I don’t cure it before seating the restoration with resin cement?
Answer from Dr. Christensen ...
I share your frustration. For years, I have suggested to manufacturers that they provide the option for dentists to use their bonding materials with either a light-cure or dual-cure method. Most still don’t understand why this is necessary.
Tooth-colored inlays and onlays and some types of all-ceramic crowns, including pressed ceramic crowns, are best cemented with resin cement. The resin cement is stronger than other commonly used cements, such as resin modified glass ionomer, and it provides additional strength to the overall indirect restoration.
Quite obviously, when placing a direct restoration, light-curing bonding agents are no problem. They are cured, and the subsequently placed putty restorative material adapts to the bonding agent and its inevitable and unpredictable film thickness. However, when an indirect restoration is seated, it should fit the previously made tooth preparation. When a light-cured bonding agent is placed in the tooth preparation at the seating appointment, the film thickness of the air-thinned bonding agent inadvertently pools in the line and point angles and does not allow proper seating of the restoration. The various bonding materials have significantly different film thicknesses. Some are extremely thin (less than 10 microns), while others can be as thick as 100 microns. Some manufacturers claim that an air stream, blown on the bonding agent, thins it to an acceptable level. But my clinical experience refutes that statement. Pooled bonding material, blown into the intricacies of the tooth preparation and cured with a light, can inhibit proper fit of indirect restorations when the thicker agents are used.
I have some suggestions for you. Several companies provide dual-cure catalysts for their bonding agents. Among them are OptiBond® Solo Plus™ SE (Kerr), Prelude (Danville Materials), and the grandfather of self-etching primers, CLEARFIL LINER BOND 2V (Kuraray America). When using any of these products, the previously described problem does not exist. The bonding agent need not be cured before cementing the indirect restoration. It cures by itself after cementation.
Another solution is to use a very thin bonding material such as Brush&Bond™ (Parkell). The film thickness of this product is so thin (~10 microns) that challenges in seating indirect restorations are not present. Additionally, reports from clinicians verify that this product prevents postoperative tooth sensitivity.
Use of indirect restorations is growing. Eventually manufacturers will have to recognize and correct the problem described by your question.
One of our new video productions, V1502 “The New Generation of Tooth-Colored Inlays and Onlays,” shows how to seat indirect restorations with resin cement, and includes a discussion of the bonding and desensitizing challenge. For more information, contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.
Question ...
When making an interocclusal record (IOR) to mount an upper and lower cast for fabrication of a three-unit fixed partial denture, what is the recommended procedure? I have heard conflicting opinions expressed by dentists and laboratory technicians.
Answer from Dr. Christensen ...
Both lab technicians and dentists have their favorite methods to relate upper and lower casts on an articulator. In my experience, some of the techniques are accurate and others are inaccurate. My own techniques - proven over many years - are as follows:
One or two units
I prefer using a double-arch impression tray, which automatically makes the correct interocclusal relationship. The trays that have been most successful in our research and clinical experience are the Sideless Triple Tray® (Premier Dental) and the QUAD-TRAY® (Clinician’s Choice).
Three-unit fixed prosthesis
• Make an accurate alginate impression and a well-poured stone cast for the opposing arch. These are two of the most inaccurate portions of the fixed prosthodontic procedure, and they often are performed incorrectly because they are delegated to an inexperienced person.
• Make the full-arch impression of the prepared teeth very carefully in vinyl polysiloxane or polyether, ensuring that the impression is accurate and that it duplicates all of the details of the tooth preparations.
• Make an IOR only on the side of the arch where you have prepared teeth. It should extend over the prepared teeth and at least two teeth that are not prepared. By far the most used material today is Blu-Mousse® (Parkell). More than 30 years of research has shown that a partial IOR for a full arch mounting of casts is more accurate than a complete arch “bite.” The partial IOR only replaces the tooth structure you have removed and one or two unprepared teeth.
• Using a disposable scalpel, trim off all of the material that touches either soft tissue or extends into undercuts. I do not have the laboratory technician do this trimming. It requires a few seconds, and only you know the characteristics of the mouth. Try the trimmed record back into the mouth to verify the fit and the accuracy of the IOR.
Full-arch
The most accurate IOR method for this situation is to prepare all of the teeth, except a few that have stable occlusion, and to use these teeth to retain the vertical dimension of occlusion while an IOR is made in vinyl polysiloxane.
For these situations where all of the teeth have been prepared and the vertical dimension of occlusion has not been retained, I prefer the following:
• Make an accurate alginate impression and a well-poured stone cast for the opposing arch.
• Make a judgment about where the vertical dimension of occlusion should be and place a resin “stop” in the anterior portion of the mouth to prevent closure at the predetermined point. Using a dual-handed technique, carefully guide the mandible into a nonstressed centric-relation hinge position, with the IOR material of your choice in place.Trim it after setting as described above.
Some PCC presentations that will assist in answering this question include V19-90 “Multiple Unit Fixed Prosthodontics,” C502A “Pouring & Trimming Casts,” and C902B “Simple Double-Arch Impressions for Technicians & Dentists.” For more information, contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.
