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J Am Dent Assoc, Vol 131, No 2, 173-177.
© 2000 American Dental Association |  |
RESEARCH |
A CLINICAL SURVEY
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ABSTRACT |
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 TOP ABSTRACT Caries.Complex amalgam restorations.MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Methods. The causes of failure for 706 cuspal-coverage amalgam restorations were determined through the use of a questionnaire. Dentists from a variety of dental schools; Army, Navy, Air Force, Public Health and Veterans Affairs dental clinics; and private practice were asked to record pertinent information regarding patients and restoration failures from choices provided on a survey form.
Results. The survey documented 706 failed restorations. Mandibular first molars accounted for 36.25 percent of all failures. The majority of failures were caused by fractured teeth (24.3 percent), caries (20 percent) and fractured restorations (17.1 percent). Among all of the failed restorations, 82.15 percent were restorable, 9.35 percent were repairable and 8.50 percent were nonrestorable. Among the fractured teeth, 80 percent were restorable, 14.5 percent were nonrestorable and 5.5 percent were repairable. Among the carious teeth, 84 percent were restorable, 8 percent were nonrestorable and 8 percent were repairable. A 
2 analysis revealed that tooth fracture was more likely to be associated with nonrestorability than either caries (2 = 5.013, P < .05) or restoration fracture (2 = 6.202, P < .05).
Conclusions. The leading cause of failure among the 706 restorations was tooth fracture, which resulted in significantly greater numbers of non-restorable teeth than either caries or fractured restorations.
Clinical Implications. Tooth fracture creates a greater risk of nonrestorability than any other cause of failure. Replacement or coverage of fracture-prone cusps is likely to improve the life expectancy of complex amalgam restorations.
Complex amalgam restorations, defined as restorations that cover or replace at least one cusp, have been shown to provide a longevity of clinical service approaching that of more conservative Class II restorations. A survey conducted by Klausner and colleagues1 determined the following mean (± standard deviation) ages of various types of amalgam restorations at the time of replacement: Class I, 11 years (± 7 years); Class II, 11 years (± 6 years); and complex amalgams, 10 years (± 7 years).
Similarly, in a retrospective study, Robbins and Summitt2 examined 128 complex amalgam restorations in 86 patients and found the 50 percent survival rate to be 11.5 years. Moffa3 conducted a 19-year study of 1,727 amalgam restorations and found the 50 percent survival rate for Class I restorations to be more than 19 years and for Class II restorations, 13 years. Smales4 reported the results of an ongoing prospective clinical study that compared the longevity of complex amalgams with that of amalgam restorations that had no cuspal coverage. He reported that 72.6 percent of the complex amalgams and 72.8 percent of the non–cuspal-coverage amalgam restorations were clinically acceptable at the 13-year point.
For purposes of the study, failure was defined as a deficiency that required repair or replacement of the restoration to remedy existing pathosis or to prevent the development of pathosis. Participants were asked to return the questionnaire after eight weeks. The first completed questionnaire was returned four weeks after the questionnaires had been sent and the last was received at 15 weeks. We tabulated the data, ranked causes of failure in order of prevalence and performed a
Survey participants reported 706 complex amalgam restoration failures and 1,278 causes of failure. Of these restorations, 177 had been placed by private practitioners, 367 by military providers and the remainder by practitioners in teaching institutions, Veterans Affairs clinics, public health services or unspecified locations. The mean age of patients was 41.9 years, with a range from 16 to 86 years. The largest number of failed restorations (119) were found in patients in the 31- to 35-year-old age group, followed by 95 failed restorations in the 41- to 45-year-old age group and 90 failed restorations in the 36- to 40-year-old age group.
Mandibular first molars accounted for 36.26 percent of all failures (256 teeth), followed by mandibular second molars (19.97 percent, 141 teeth) and maxillary first molars (15.01 percent, 106 teeth) (Table 1
Caries.
TOP
ABSTRACT
Caries.
Complex amalgam restorations.
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
REFERENCES
Among amalgam restorations of various classes, caries consistently has been reported to be a major cause of failure. Mjor and Toffenetti5 compiled data via a survey and found that 59 percent of failures among amalgam restorations were due to caries. Assessing the failure modes of Class I and Class II amalgam restorations, several investigators1,3,6 found caries to be the chief cause of restoration failure. Among these investigations, failures were reported in the following ranges: caries, 27.3 to 54 percent; amalgam bulk fracture or restoration margin fracture, 19 to 33 percent; and tooth fracture, 9 to 10 percent.
Complex amalgam restorations.
TOP
ABSTRACT
Caries.
Complex amalgam restorations.
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
REFERENCES
Few published data exist regarding the failure mechanism of complex amalgam restorations. Klausner and colleagues1 examined more than 500 defective complex amalgam restorations and found the major causes of failure to be caries (43 percent), tooth fracture (32 percent), poor marginal integrity (9 percent) and isthmus fracture (3 percent). On the basis of this single investigation, we find that the most discernible difference between complex and noncomplex amalgam restorations with regard to causes of failure is the relatively high percentage of failures due to tooth fracture among complex restorations. Using a survey questionnaire for data acquisition, we initiated this study to determine the causes of failure among a large number of complex amalgam restorations.
MATERIALS AND METHODS
TOP
ABSTRACT
Caries.
Complex amalgam restorations.
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
REFERENCES
General dentists from Air Force, Army, Navy and Veterans Affairs dental clinics, dental schools and private practices were asked to collect data using a questionnaire to classify the cause of failure of any complex amalgam restoration they encountered during the study. Practitioners received questionnaire packets containing detailed instructions for the completion of the requested information, the definition of a cuspal-covered amalgam, a universal numbering system chart for teeth, an explanation of the purpose of the study, an example of a completed survey page and a return envelope that was addressed and stamped. 2 analysis to assess the relationship between cause of failure and tooth restorability.
RESULTS
TOP
ABSTRACT
Caries.
Complex amalgam restorations.
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
REFERENCES
Of the 891 survey packets mailed to practitioners and clinics, 83 (9.32 percent) were returned for data compilation. A total of 102 practitioners took part in the study by entering the number of failed restorations and the causes of their failure (some of the returned packets contained multiple surveys). 
). Because participants listed all contributing causes of failure, it was not possible to determine the primary cause of restoration failure in all instances. Table 1 lists the number of restoration failures according to tooth number. Table 2 provides the causes of failure for the 706 complex amalgam restorations.
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Of the 309 fractured teeth, 247 (80 percent) were restorable, 45 (14.5 percent) were nonrestorable and 17 (5.5 percent) were repairable. Among 255 carious teeth, 214 (84 percent) were restorable, 20 (7.8 percent) were nonrestorable and 21 (8.2 percent) were repairable. Of the 219 fractured restorations, 186 (85 percent) were reported to be restorable, 15 (6.8 percent) were nonrestorable and 18 (8.2 percent) were repairable.
A 2 analysis revealed that tooth fracture was more likely to be associated with nonrestorability than either caries (2 = 5.013, P < .05) or restoration fracture (2 = 6.202, P < .05). Of 105 complete occlusal-coverage amalgam restorations that failed, only two (1.9 percent) were associated with tooth fracture, while 30 (28.6 percent) involved caries and 48 (45.7 percent) involved fractured restorations. The remaining 25 restorations (23.8 percent) failed as a result of several other causes.
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DISCUSSION |
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TOPABSTRACTCaries.Complex amalgam restorations.MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Tooth fracture vs. caries. A notable finding of this study was the high number of restoration failures that were related to tooth fracture rather than caries. This contrasts with the findings of investigators1,3,6 who examined the failure of Class I and Class II amalgam restorations and found caries to be the predominant cause of failure. However, in their evaluation of complex amalgam restorations, Klausner and colleagues1 found a much greater incidence of failure as a result of tooth fracture than caries, a finding that corroborates those of our study.
A notable finding of this study was the high number of restoration failures that were related to tooth fracture rather than caries.
One possible interpretation of the data from our study is that clinicians may be too conservative when preparing teeth for complex amalgam restorations and fail to remove unsupported tooth structure, leaving weakened teeth subject to fracture under occlusal stress. We found a greater association between failed cuspal-coverage restorations and tooth fracture than between failed restorations and caries. However, the number of restorations that failed because of caries and fracture may be the result of caries weakening a tooth and predisposing it to fracture; likewise, a fractured restoration may result in an increased risk of caries.
Removal of tooth structure. Researchers evaluating Class I and II restorations consistently have reported that the conservative removal of tooth structure provides a tooth with greater resistance to occlusal forces than less-conservative preparation techniques. Larson and colleagues7 found that in mesio-occlusodistal cavity preparations, teeth were weakened significantly when the isthmus was increased from one-fourth to one-third the intercuspal distance.
In this study of cuspal-coverage amalgam restorations, we found that tooth fracture was the leading cause of failure, which resulted in significantly greater numbers of non-restorable teeth than did failures resulting from caries or restoration fracture. These findings imply that teeth that are inadequately prepared in the course of being restored with complex amalgams (that is, unsupported tooth structure is left) are at increased risk of fracture. The small number of failed complete-coverage amalgam restorations reported by respondents in this study, as well as the increased risk of nonrestorability associated with failure due to tooth fracture, suggests that weakened tooth structure exposed to occlusal forces should not be retained, but should be removed and replaced with restorative material to protect the tooth from fracture.
Determining which portions of the tooth require further reduction for protection is a subjective decision; however, evidence from this study indicates that clinicians err, too frequently, on the side of conservatism. The result is the need for restoration repair or replacement. Of greatest concern is the incidence of nonrestorability among complex amalgam restorations that incur cuspal fracture. The possibility of catastrophic failure (that is, the tooth becomes nonrestorable) should be a consideration when clinicians elect to leave fragile cusps unprotected when placing large amalgam restorations.
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CONCLUSIONS |
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TOPABSTRACTCaries.Complex amalgam restorations.MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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FOOTNOTES |
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REFERENCES |
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TOPABSTRACTCaries.Complex amalgam restorations.MATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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