Despite the expectations of patients and the careful and conscientious techniques of dentists, most types of dental restorations do not last a lifetime. In addition, the life expectancy of patients has increased significantly during the past 50 years, making the need for long lasting restorations even more crucial. (The life expectancy of typical dental patients in the United States is nearly 80 years.1) After a few years of service, most direct or indirect dental restorations wear out or break, or tooth structure breaks around them or develops caries. They are similar to tires on an automobile or soles on shoes. Because of the heavy chewing forces to which dental restorations are subjected during service and the ongoing threat of dental decay, it is well-known among dentists that restorations have a predictable life expectancy that, yet, varies significantly from patient to patient because of oral hygiene habits and eating.
When should a dental restoration be replaced and when should it be repaired? What factors are involved in the decision to repair versus replace? How and with what materials should the repair be accomplished? Are some repair materials better than others? What should patients be told about restoration repair versus replacement?
In this column, I will discuss dental restoration failure, how to determine if a repair is feasible, the best repair materials, how to do the repair, and what to tell patients about the potential service to be expected from the repair.
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WHEN TO REPAIR A DENTAL RESTORATION
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It is my opinion that with patients’ increased life expectancy and the long time that dental restorations must serve, repair of failing restorations should be considered whenever possible instead of cutting away tooth structure for crowns. Amalgam has been the major restorative material in dentistry for more than 150 years. It still is used in 68 percent of dental practices in the United States.2 However, resin-based composite (RBC) is the exclusive restorative material in many practices. Some practitioners use either amalgam or RBC, depending on the clinical situation.
Often, caries begins around the margins of amalgam or RBC restorations or on proximal surfaces opposing the initial restoration. Repair of such restorations has been suggested instead of replacement,3 thus preserving tooth structure. Many studies have been completed and consensus conferences conducted on when to consider repairing or replacing amalgam or RBC restorations.4 In such cases, if the new carious lesion is small, it can be removed and another amalgam or RBC restoration placed in the defective area.
When is a defect in a previously placed amalgam or RBC too large to warrant a repair? Most dentists have been taught that any intracoronal cut of a tooth extending further than one-third of the distance from cusp tip to cusp tip should receive a stronger restoration, such as a crown or an onlay. According to that guideline, if the planned repair appears to leave enough tooth structure for adequate tooth strength, the repair probably is justified. However, depending on the repair material used, the resultant restoration may not be pleasing from an esthetic standpoint. Some dentists consider any patched restoration to be inadequate, and they avoid doing such repairs. However, in my opinion, repairs are simple and fast and can be relatively effective when indicated as noted above.
The repair techniques for each of the two most commonly placed restorative materials are different. Amalgam patched into previously placed amalgam requires that its own retentive features be placed in the tooth, because significant molecular bonding cannot be obtained and the strength and retention of the resultant restoration is questionable. Repair of RBC restorations requires removing the newly formed carious lesion, performing appropriate bonding procedures and placing a new RBC restoration. Again, overall strength and retention of the resultant repaired restoration is questionable, despite some minor retention offered by the bonding agent.
If caries is not the main reason for restoration failure, in my opinion, RBC should be considered as a primary material for restoration repair, because it can be placed without difficulty, cured rapidly and finished easily. However, dental caries has been cited as the primary reason for restoration replacement5–8; therefore, does it not make sense to use cariostatic materials for repair? It is nearly impossible for a dentist to determine if the new carious lesion is in fact a new lesion or residual caries left over from the previous, now-failing restoration. In any event, it appears that a tooth-colored cariostatic repair is desirable.
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CURRENT MATERIALS AND TECHNIQUES FOR RESTORATION REPAIR
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Resin-modified glass ionomer (RMGI) is an ideal material for repair in areas observable when the patient is smiling, because the current generation of these materials is relatively pleasing esthetically, is stronger and smoother than in the past and wears better than previous generations; furthermore, the cariostatic activity of glass ionomer (GI) and RMGI has been proved.9–27 However, these materials historically have not been as easy to use as is RBC. Many practitioners elect to use RBC instead of GI or RMGI for restoration repair on the basis of ease of use. Materials containing GI cannot be dispensed in an injectable form; they must be mixed by hand or mechanically. This characteristic discourages some dentists from using them. In addition, the materials can be too sticky or nonputtylike for optimal use. These negative characteristics can be overcome if the practitioner knows how to use the materials. I think that cariostatic activity of the repair material, not ease of placement, should be the clinician’s primary consideration when selecting a material for a caries-active situation. In my opinion, cariostatic materials’ difficulty of use is far outweighed by their positive anticaries activity.
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MATERIALS
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The following information represents my opinions on selection of a restorative material containing GI and the proper placement and finishing of the material in repairing amalgam restorations, RBC restorations and indirect crown or partial crown restorations.
RMGI.
Although numerous RMGI materials are on the international market, two of them are well-known and widely used. They are Fuji Filling LC (GC America, Alsip, Ill.) and Ketac Nano (3M ESPE, St. Paul, Minn.). Both of these products have been formulated to be relatively simple to use. However, practitioners unfamiliar with RMGI find both products more difficult to use than RBC. When using these products, the clinician dispenses the material from a two-barreled dispenser, mixes it and places it using the manufacturer-directed technique. Some dentists complain about the relative fluidity of these products when they first are mixed relative to the more viscous RBC. They are correct. Either RMGI product is easier to use if the mixture is allowed to mature for a few seconds to attain a near-puttylike viscosity before it is placed, making the mixture easier to place in the cavity preparation or repair area.
RMGI requires many hours to reach full chemical maturity.28 As a result, some unknowing practitioners feel that the materials are too soft and weak. I suggest that when the restorative material is placed in the cavity preparation, it should be protected from water contamination for a few minutes. This is an ideal time for the clinician to see another patient briefly. Then, on returning to the first patient, the clinician can finish the restoration with the use of a dull bur such as a previously used no. 7901 or a fine disk. During subsequent observation of the restoration at a follow-up appointment, the clinician will find the RMGI material to be fully cured.
In addition to repairs, RMGI is used routinely in many practices for pediatric and geriatric conventional restorative needs or for any situation in which cariostatic activity is desirable.29
GI.
Dentists have embraced GI materials without resin for placement in clinical situations requiring cariostatic activity. Clinicians have found these materials highly useful in pediatric and geriatric patients needing optimum cariostatic restorations as well as in repair situations. Examples of such materials are GC Fuji IX (GC America) and Shofu Type II Glass Ionomer Cement (Shofu Dental, San Marcos, Calif.).
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ADVISING PATIENTS ABOUT THEIR REPAIRED RESTORATIONS
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Most patients have experienced flat tires on their automobiles. Many of these flats can be patched with success. However, there always is a certain lack of confidence about a tire that has been patched. You can use this analogy to explain to patients that you have done your best to salvage the restoration by placing a decay-preventive repair, but the "patch" that has been placed is just that—a patch—and its longevity is relatively unknown. Most patients accept the repair with relief and will accept a more extensive restoration at a later time, if and when the repaired restoration fails again. I have seen some of my repairs serve for many years, and I have seen some fail soon after placement. However, in many cases, I believe that repairing restorations with cariostatic material is appropriate. It preserves tooth structure, and patients appreciate this conservative clinical approach and its minimal cost.
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SUMMARY
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Repair of restorations has been researched widely and generally is accepted as an adequate procedure for some clinical situations instead of restoration replacement. I have suggested cariostatic materials such as RMGI or conventional GI as appropriate repair materials for restorations that fail because of dental caries.
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WHEN TO REPAIR A...
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