How does direct composite resin compare with amalgam for filling permanent posterior teeth?

Question:
How does direct composite resin compare with amalgam for filling permanent posterior teeth?
Clinical Answer:
There is insufficient randomized controlled trial evidence to draw firm conclusions as to how direct composite resin compares with amalgam for filling permanent posterior teeth.

Low-quality evidence suggested that, when placed in permanent posterior teeth, amalgam restorations had a lower failure rate (failure occurred in on average 75 versus 142 per 1000 people) than resin composite restorations and also reduced the risk of secondary caries (on average 57 versus 122 per 1000 people). These findings were based on two parallel group trials (involving 1006 participants and 3010 restorations, 5-7 years follow-up).These results were not supported by an additional five split mouth trials (1620 composite restorations and 570 amalgam restorations, 3-5 years follow-up) that suggested similar rates of failure and caries in both groups; the analysis of caries was underpowered. One of the trials found no clear evidence of a difference in adverse events between groups.