Data sources PubMed, CINAHL, and Cochrane databases.Study selection Papers reporting a primary study with any population, one or both genders specified, participants of any age, incidence of any cancer subsite of HN, and UADT reported as the health outcome, frequency of dental visits/check-ups prior to the diagnosis of one of these cancers (assessed as the exposure), and availability of sufficient data to estimate the measure of association, ie, unadjusted odds ratio (OR) along with its corresponding 95% confidence interval (CI).
PubMed
Data sources PubMed, CINAHL, and Cochrane databases.Study selection Papers reporting a primary study with any population, one or both genders specified, participants of any age, incidence of any cancer subsite of HN, and UADT reported as the health outcome, frequency of dental visits/check-ups prior to the diagnosis of one of these cancers (assessed as the exposure), and availability of sufficient data to estimate the measure of association, ie, unadjusted odds ratio (OR) along with its corresponding 95% confidence interval (CI).
CINAHL
Data sources PubMed, CINAHL, and Cochrane databases.Study selection Papers reporting a primary study with any population, one or both genders specified, participants of any age, incidence of any cancer subsite of HN, and UADT reported as the health outcome, frequency of dental visits/check-ups prior to the diagnosis of one of these cancers (assessed as the exposure), and availability of sufficient data to estimate the measure of association, ie, unadjusted odds ratio (OR) along with its corresponding 95% confidence interval (CI).
Cochrane databases
Methodological quality of the studies was assessed using the quality assessment tool for quantitative studies developed by the Effective Public Health Practice Project (EPHPP)Results After initial search of 1377 studies, thirty-eight articles were included in the analysis for systemic review including 32 case-control and six other design studies not limited to cross-sectional, observational, case-series, and screening. 
SAS