The Demarco review found that the main reasons cited for failure of posterior composite restorations are secondary caries (i.e. cavities which develop subsequent to the restoration), fracture, and patient behavior, notably bruxism (grinding/clenching.) Causes of failure for amalgam restorations reported in the Manhart "et al."review also include secondary caries, fracture (of the amalgam and/or the tooth), as well as cervical overhang and marginal ditching. The Demarco "et al." review of composite restoration studies noted that patient factors affect longevity of restorations: Compared to patients with generally good dental health, patients with poorer dental health (possibly due to poor dental hygiene, diet, genetics, frequency of dental checkups, etc.) experience higher rates of failure of composite restorations due to subsequent decay. Socioeconomic factors also play a role: "People who had always lived in the poorest stratus ["sic"][stratum?] of the population had more restoration failures than those who lived in the richest layer."