Fixed prosthodontics has become a major portion of American dental practice. Placement of routine crowns and fixed prostheses is not difficult for experienced dental practitioners. However, it poses many challenges to some dentists, and especially to inexperienced staff personnel, to whom certain aspects of the fixed-prosthodontic procedure may be delegated.
One of the most frustrating aspects of the fixed-prosthodontic procedure is the cementation, because it involves a number of unpredictable steps. It is my observation that most American dentists delegate a significant portion of the cementation procedure to staff members and, depending on the education and experience of the staff member, delegation may further confound the procedure.
In this article, I identify most of the frustrating aspects of the cementation procedure and make recommendations to prevent occurrence of these problems.
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INADEQUATE EDUCATION ABOUT CORRECT CEMENT INDICATIONS AND USE
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The importance of adequate staff education is brought clearly to mind with the realization that the longevity of a crown costing several hundred dollars is directly related to the proper or improper use of a few dollars’ worth of cement. New staff members should receive education on cement mixing and its use as soon as they begin their employment. Previous experience and education may be acceptable, but you need to evaluate it before trusting a new staff member to prepare the cement for an expensive crown or fixed prosthesis. I suggest having an in-service education session on this important subject whenever a new employee is hired.
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IMPROPER MIXING
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Some cement brands are available only in hand-mix form, while others may be triturator-activated. If your staff members have had difficulty with hand mixing, I suggest triturator-activated materials. Triturator-activated brands are well worth the slight extra cost for a dental staff with cement-mixing inconsistencies.
Hand mixing can be mastered rapidly with practice. If you prefer to use this form of cement, in-service education and constant monitoring of mixing procedures are mandatory.
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INCOMPLETE SEATING OF RESTORATIONS
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After seating thousands of crowns, I still occasionally find that a crown does not seat completely. It is more critical now, since popular resin and resin-reinforced glass ionomer cements have high early strength. At the time of pre-cementation evaluation of the restoration’s fit, remember the fit of the margins in specific locations. As soon as the restoration has been seated, reevaluate the fit. Place significant load on the restoration, rock it and evaluate it once more. If any misfit is present, remove the restoration immediately. Waiting even a few minutes makes removal of the crown impossible. If a restoration has been seated incorrectly, and this problem is determined almost immediately after cementation, gently tapping on the restoration may help you remove it. However, when resin or resin-reinforced glass ionomer has been used, it is doubtful that the restoration can be removed. Just cut it off and do better next time.
The all-ceramic crowns and restorations made using computer-aided design/computer-aided manufacturing require special care in seating. I suggest extremely careful preseating evaluation, a homogeneous load, more rocking than normal, and ensuring continued load during cement setting to ensure that the restorations fit well after cementation. These restorations have a less accurate internal fit than do porcelain-fused-to-metal restorations; this causes slight movement in all directions before seating. Seating more than two contiguous units of these restorations at the same time is not advised. Because of these crowns’ slight internal freedom of movement, contact areas may be inadequate if restorations are seated incompletely. Contact areas may be inadequate if the seated restorations are even slightly off mesially or distally.
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CEMENT THAT SETS TOO RAPIDLY OR TOO SLOWLY
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Dentists work at different speeds. Practitioners should select cement brands not only on the basis of the cement type, but also in relation to the speed of set. Each category of cement has various setting times.
Check with manufacturers about the setting times of their cements. If after using a specific brand for a while you find that it is too slow or too fast for you, change brands.
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TOOTH SENSITIVITY AFTER CROWN CEMENTATION
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Postcementation tooth sensitivity has existed during the entire history of fixed prosthodontics. Fortunately, the resin-reinforced glass ionomer cements have had the least postoperative tooth sensitivity of any popular cement category for many decades. RelyX Luting Cement (3M ESPE, St. Paul, Minn.) and FujiCEM (GC America, Alsip, Ill.) have shown unprecedented lack of postoperative tooth sensitivity, as well as clinical success. This probably accounts for their high popularity. If postoperative tooth sensitivity continues after changing to these cements, use of a desensitizing agent such as Gluma Desensitizer (Heraeus Kulzer, South Bend, Ind.) is indicated for use before cementation with future patients.
Resin cements are especially prone to producing postoperative tooth sensitivity.
Using self-etching primers before cementation and avoiding the total-etch procedure on teeth receiving resin-cemented restorations can reduce or eliminate this problem. One of the most popular products is Panavia F cement used after ED Primer (Kuraray America, New York).
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SET CEMENT REMAINING IN THE CONTACT AREA
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All cements can produce this objectionable condition. The two most popular cements, resin-reinforced glass ionomer and resin, are the worst of all cements for producing this problem. However, it can be avoided. Leave a competent dental assistant or the dentist with the patient as the cement is setting. As soon as the cement is in the putty stage, remove the excess immediately. Some of the new cement brands, especially resin, have a "snap set." This requires rapid cement removal at exactly the right time. Do not leave the patient biting on an object and return later. The chance of cement’s remaining in the contact areas will increase greatly if you do not supervise the cement setting.
In the case that cement has been allowed to set in a contact area, remove the most coronal cement between the observable occlusal contact area. After clearing the most coronal aspect with a sharp instrument or an explorer, have someone place gentle force between the teeth with a blunt instrument such as a beaver-tail burnisher and push waxed dental floss through the partially open contact area to remove the cement.
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CEMENT IN THE GINGIVAL CREVICE
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Everybody has encountered from time to time the embarrassing situation of finding cement in the gingival crevice at a subsequent recall appointment. When using a strong, fast-setting cement, employ the following technique to reduce the occurrence of remaining cement.
After gross, supragingival set cement removal, use an instrument to retract the gingiva to provide clear vision to the marginal area. A Zekrya Gingival Protector (Zenith/DMG, Englewood, N.J.) retracts the gingiva easily and well and allows for excellent vision of the margins and the excess cement. It usually can be removed without difficulty.
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SUMMARY
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Restoration cementation is a routine procedure, but it commonly is accomplished improperly. In this article, I have discussed several of the most frequently occurring problems with restoration cementation and have made suggestions about how to prevent them.
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INADEQUATE EDUCATION ABOUT...
IMPROPER MIXING
