Do amalgams fracture teeth more than composite?

Do amalgams fracture teeth more than composite?

 There are not many good studies on this important topic but the answer appears to be yes.  However, it appears that the age, dental habits, and the size of the restoration are more important.  Also the type of crack, cusp fracture or vertical root fracture, seem to differ.
Several of the common types of cracks we see everyday in amalgam filled teeth

12 year study dental student placed amalgam and composites 2 surface only. Naghipur JPD 2016

  • In the short term the amalgams did fracture the teeth at a higher rate than the composite.
  • Amalgams did not fracture the teeth at significantly higher rates looking at the 12 year data.
Opdam 2012 12 year study of 1202 amalgams and 747 composites  Full study
  • 57% of amalgam failures were fracture v. 62% composite failures were due to caries
  • Composite repairs held up about twice as well as amalgam repairs
  • Failure rate of amalgam was three times that of composite in this study
  • Fractures occurred in 7%  of the amalgams in this study while only 1.5% of composites fractured
  • So this study appears to show that amalgam does fracture teeth more.

 

Hansen 1988 Study on RCT premolars shows the difference in fracture rates between amalgam and resin-restored teeth was highly significant at the 0–3 year interval.

 

“The type of restorative materials used may be a more important factor for the occurrence of longitudinal tooth fractures than the size or classification of the restorations. According to the present study, the use of bonded material like resin or porcelain is recommended to prevent cracks.”
The Results = Compared with resin (4.7%) or porcelain (0.9%), the use of non-bonded inlay restoration materials such as gold (20.5%) or amalgam (18.7%) increased the occurrence of longitudinal tooth fractures.

While I do personally agree with their statement I am not sure if their study truly shows this to be accurate or not. It does not appear they qualified percentages of restorations in their patient base.  If they had recorded the total number of each restoration in each patient they saw for endo they could have used that data as a baseline for how many of each type of restorations they were seeing.  Their data may just reflect the fact that they saw patients with more gold inlays and amalgams than porcelain inlays and composites.  Depending on their patient base there is a high likelihood that the majority of the fillings were in fact amalgam.  Giving the % of cracked teeth by material without reference to how often a certain type of material is seen or how old those fillings are is pretty useless.  To truly test this one would need to know both the age AND the relative number of restorations seen in the sample base.  It seems to me that this study may show nothing more than the fact that amalgam and gold were popular in the past.

Wahl 2004 August in JADA found that existing amalgams fracture teeth slightly less than existing composite (both about 2%)
  • “Our results indicate that cusp fracture rates are influenced by age and by the number of surfaces of a tooth that have been restored. The findings provide no evidence that fracture rates are higher in (EXISTING) amalgam-restored teeth than in composite-restored teeth”

I added existing to the above statement.  This study is a shame because after all their effort the whole study is useless because they do not know the longevity of the fillings placed (which they talk about) or the history of the tooth.  Due to the fact that an older person would likely first have had a smaller amalgam placed for many years then later have it replaced by the then more popular composite, many of the teeth with composites they saw in the year they started recording data had likely already had amalgams for a long time (thus the expansion damage of amalgam had already begun.)

 

Bryan Bauer, DDS, FAGD
630-665-5550

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