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J Am Dent Assoc, Vol 136, No 2, 201-203.
© 2005 American Dental Association |
OBSERVATIONS |
When you purchase a set of tires, an automobile or a pair of shoes, one of the characteristics you probably consider is the item’s potential longevity. Manufacturers and retailers often advertise the expected longevity of their products to consumers, and it is not uncommon for the consumer to object when the purchased item wears out or breaks before the expected time.
Are estimations of the expected longevity of restorations explained to dental patients? Although the longevity of dental restorations is somewhat predictable, it has been my observation that most dentists do not inform their patients about the expected service period of restorations. Should we be doing so? In my opinion, dental practitioners would generate greater patient satisfaction if they informed patients about the expected longevity of treatment rendered. This concept has been addressed from a legal standpoint and often is referred to as "informed consent."1
In this column, I will discuss the most commonly used dental restorations intended for posterior teeth, candidly appraise the potential service period for these materials and predict their expected modes of failure. I hope that the information will motivate dentists to inform patients about the service potential of dental restorations, thus avoiding future patient confrontations and legal activity.
It is known that all types of restorations for posterior teeth have a variable but finite longevity. When patients know the expected potential service period, redoing the restorations at a later time is not unexpected or upsetting to them.
Amalgam.
Amalgam still is the most used dental material globally, although a growing percentage of U.S. dentists do not use it. Additionally, some patients will not accept the unsightly appearance of amalgam.2 Nevertheless, I predict that amalgam will continue to compose a significant portion of dental restorations for the immediate future.
Amalgam restorations, placed at an average level of quality, serve for many years. Studies on amalgam show widely varied failure and longevity statistics. This variability probably is related to the care with which the restorations were placed, the appropriateness of placing amalgam in the specific tooth preparations, and the oral conditions under which the amalgam was placed. It has been my experience, after placing and observing thousands of amalgam restorations over several decades, that few of them have failed. I predict that a moderately sized mesioocclusal-distal amalgam restoration, placed by a dentist with average ability, will last for at least 10 years in a typical patient; I have seen some last for 40 years or more.
The cost to a patient per year of service for an amalgam restoration is low when compared with that for any other posterior tooth restoration. If failure occurs, it is related to dental caries around margins, fracture of tooth cusps, infrequent fracture of the amalgam itself or darkening of the remaining tooth, which motivates the patient to seek a more esthetically pleasing restoration.
Resin-based composite.
The first resin-based composite material was introduced as a Class II restorative in 1968. Our own clinical research on resin-based composite in Class II locations started in 1968, although it was crude research compared with the studies of today. It is well-known that those early restorations soon failed because of excessive wear, tooth sensitivity and/or pulpal death, recurrent caries, open contact areas or fracture of the restorative material.
Although there are some earlier exceptions, by about 1985—nearly 20 years after the introduction of resin-based composite as a Class II restorative material—improved resin-based composite materials with small particle-sized fillers became commonly used. Successful Class II composite restorations started to be observed and accepted by the profession. Failure still was observed frequently in some brands. The most common causes of failure still were excessive wear, postoperative tooth sensitivity, open contact areas and recurrent caries.3
By now, resin-based composite materials have evolved to the level that properly placed restorations are serving successfully for many years. These restorations require extreme care during placement, including meticulous techniques to prevent postoperative tooth sensitivity, open contacts and the dreaded "white line" at margins, which generally is related to relaxation of polymerization shrinkage stress in the tooth structure caused by aggressive finishing techniques.
How long should a Class II resin-based composite restoration serve when current brands of composite are used and the clinical expertise of the clinician is at least average? It has been our observation in worldwide clinical studies conducted on Class II resin-based composite restorations that predictions for longevity range widely. My own observation about the treatment of dentists who have average or higher clinical ability is that the restorations serve clinically at least 10 years. The current generation of Class II resin-based composites has similar, but less frequent, failure modes to those described previously for the older generations of materials. Improved materials and enlightened and experienced practitioners have reduced failures significantly during the past few years. However, most clinicians agree that placement of Class II composite restorations requires more careful attention to detail than does placement of similarly sized amalgam restorations.
In my opinion, resin-based composite used in Class II situations still needs two improvements. Polymerization shrinkage needs to be reduced to as close to zero as possible, thus reducing stress in remaining tooth structure, and wear of the resin needs to be improved to be close to that of enamel. Manufacturers are working to improve these properties.
Porcelain-fused-to-metal (PFM) crowns.
These relatively esthetically acceptable restorations have served the public for more than 40 years.4 They are easily made by technicians of average ability, and the tooth preparation and scaling procedures are simple. However, they abrade opposing tooth structure significantly, lose their superficially applied stains within a few years, and become esthetically less acceptable as gingiva recedes.
It is my own conclusion that PFM crowns have an esthetic longevity of about 10 years, and because of the degeneration described previously, they have a functional longevity of about 20 years. It is apparent that PFM crowns cost patients significantly more per year of service than do crowns of amalgam or resin-based composite, since the average cost of a PFM crown is about five or six times more than that of an amalgam or composite crown.
PFM crowns are relatively trouble-free. Their most common modes of failure are infrequent fracture of pieces of fired ceramic from the metal understructure, recurrent caries on the margin areas or need for endodontic therapy. Additionally, as expected during a period of years, gingival recession occurs, and esthetically unacceptable PFM crown margins are exposed to view.
Cast gold alloy restorations.
The lost-wax cast gold restoration has served the public for more than 100 years. However, in recent years, patients have objected to display of gold in their teeth, and use of cast gold alloy restorations—including inlays, onlays and crowns—is diminishing.5 This trend is disturbing, because any practitioner experienced in the use of cast gold alloy restorations knows that these restorations can be placed with minimal display of metal and serve well for several decades. In my own practice experience, I have seen many of these restorations serve for more than 40 years.
Although cast gold alloy restorations can be placed with minimal display of gold alloy, the trend is for patients to reject any display of metal. It is remarkable that most dentists I treat prefer gold alloy restorations in their own posterior teeth, but they place PFM restorations in the teeth of most of their patients. In locations of the mouth where the display of metal can be kept to a minimum, cast gold alloy restorations have no peer with regard to long-term service and minimal wear of opposing teeth, and their use is encouraged.
The mode of failure of cast gold alloy restorations is predictable: wear of the metal through to underlying tooth structure, recurrent caries and, in the case of inlays, occasional fracture of remaining tooth cusps.
All-ceramic restorations.
All-ceramic restorations for posterior teeth have had an unpredictable service record when used as inlays, onlays, crowns and fixed prostheses. During the past several decades, numerous all-ceramic posterior tooth restoration types have come and gone because of frequent failure. Notable exceptions are the pressed-ceramic restorations and the computer-directed milled-ceramic restorations, which have had an acceptable service record with observable but minimal failure when placed properly.6 It is impossible to extrapolate an expected overall generic longevity for all-ceramic posterior tooth restorations because of the varied physical characteristics among the types of materials.
Currently, several brands of computer-directed milled zirconia substructure, all-ceramic crowns and fixed prostheses are on the international marketplace. In terms of in vitro strength, it is easy to predict that the service potential of these restorations may rival that of PFM crowns. Longer and in-depth clinical research is needed to make valid predictions about the longevity potential of these restorations. However, the strength characteristics of the current generation of zirconia-based all-ceramic crowns and fixed prostheses make the predictions for future longevity highly promising.
The failure mode of the older all-ceramic restorations is well-known. It usually is catastrophic fracture of the complete structure. It is the hope of the profession that the newer generation of these restorations will have significantly better service potential. Until these restorations have proven positive longevity characteristics, patients should be informed about their unpredictable longevity potential.
POSTERIOR TOOTH RESTORATIONS: SERVICE POTENTIAL AND EXPECTED FAILURE MODE
TOP
POSTERIOR TOOTH RESTORATIONS:...
SUMMARY
REFERENCES
The dental literature and folklore contain highly diverse and confusing predictions regarding longevity of posterior tooth restorations. The following information is based on my own observations from many years of practice, teaching, research, discussion with dentists throughout the world and mentoring many dentists in clinical study clubs. I suggest that the exact number of years that restorations are expected to serve not be expressed to patients, in case the exact predictions are not accurate. I usually explain service potential to patients using one of four categories of longevity expectations: "This restoration should serve (a few years) (several years) (many years) (indefinitely [in the event of an elderly person])." When the treatment includes restoration of many teeth, I suggest that the patient receive a formal completion letter from the practitioner explaining his or her feelings about the expected longevity of the restorations, the necessity for recall appointments and suggested preventive procedures.
SUMMARY
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POSTERIOR TOOTH RESTORATIONS:...
SUMMARY
REFERENCES
Several forms of restorative techniques are used for posterior teeth. They vary significantly in cost and longevity. The following restorative concepts are the most commonly used: amalgam, resin-based composite, PFM, cast gold alloy restorations and all-ceramic restorations. I suggest that patients be informed about the potential longevity of restorative treatment for posterior teeth as they make decisions about treatment for their oral restorative needs.
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FOOTNOTES |
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TOPPOSTERIOR TOOTH RESTORATIONS:...SUMMARYREFERENCES |
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  J. W. Simecek, K. E. Diefenderfer, and M. E. Cohen An Evaluation of Replacement Rates for Posterior Resin-Based Composite and Amalgam Restorations in U.S. Navy and Marine Corps Recruits J Am Dent Assoc, February 1, 2009; 140(2): 200 - 209. [Abstract] [Full Text] [PDF]
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C. D. Lynch, R. J. McConnell, and N. H.F. Wilson Teaching the placement of posterior resin-based composite restorations in U.S. dental schools J Am Dent Assoc, May 1, 2006; 137(5): 619 - 625. [Abstract] [Full Text] [PDF]
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