The Cochrane review of surgical removal versus retention of asymptomatic disease-free impacted wisdom teeth suggests that the presence of asymptomatic impacted wisdom teeth may be associated with increased risk of periodontal disease affecting adjacent 2nd molar (measured by distal probing depth > 4 mm on that tooth) in the long term. Few studies, however, met the criteria to be included in the Cochrane review and those that were included provided very low quality evidence and had a high risk of bias. Another study which was at high risk of bias, found no evidence to suggest that removal of asymptomatic disease-free impacted wisdom teeth has an effect on crowding in the dental arch.