Aim: To systematically review current evidence comparing the use of mineral trioxide aggregate and calcium hydroxide for direct pulp capping in permanent teeth with mature root development. Materials and methods: A search of multiple databases was undertaken for randomised controlled trials comparing use of mineral trioxide aggregate and calcium hydroxide for direct pulp capping. Other sources, including trial registries and reference lists, were also searched. Three reviewers independently conducted the screening, data extraction and critical appraisal. Following screening, four studies were identified and analysed. Results: Three of the four studies were identified as being at high risk of bias. Two studies reported statistically significant superiority of mineral trioxide aggregate over calcium hydroxide, although one of these studies had the highest risk of bias. Two studies demonstrated the superiority of mineral trioxide aggregate over calcium hydroxide for direct pulp capping, which was not statistically significant. Conclusions: There is evidence from the randomised controlled trials that mineral trioxide aggregate performs better than calcium hydroxide for direct pulp capping of permanent teeth with complete root development following pulp exposure during caries removal, but not in cases of iatrogenic or traumatic exposures. This supports the European Society of Endodontology 2019 position statement on the management of deep caries and the exposed pulp. There are indications that the superiority of mineral trioxide aggregate over calcium hydroxide for direct pulp capping becomes more pronounced over time; the need for longer-term studies is questionable given the weight of evidence already available from short- to medium-term randomised controlled trials. Keywords: calcium hydroxide, dental pulp exposure, direct pulp capping, mineral trioxide aggregate, systematic review