INTRODUCTION: The exact reasons for failure of the inferior alveolar nerve (IAN) 
block are not completely known, but red hair could play a role. The genetic 
basis for red hair involves specific mutations, red hair color (RHC) alleles, in 
the melanocortin-1 receptor (MC1R) gene. The purpose of this prospective 
randomized study was to investigate a possible link between certain variant 
alleles of the MC1R gene or its phenotypic expression of red hair and the 
anesthetic efficacy of the IAN block in women.
MATERIALS: One-hundred twenty-four adult female subjects (62 red haired and 62 
dark haired) participated in this study. Dental anxiety was determined in each 
subject using the Corah Dental Anxiety Questionnaire. The subjects were given 2 
cartridges of 2% lidocaine with 1:100,000 epinephrine via the IAN block. Pulpal 
anesthesia was measured in the posterior and anterior teeth in 4-minute cycles 
for 60 minutes using an electric pulp tester. The MC1R alleles were genotyped 
for each subject from cheek cells containing DNA collected using buccal swabs.
RESULTS: Women with red hair and women with 2 RHC alleles reported significantly 
higher levels of dental anxiety compared with women with dark hair or women with 
0 RHC alleles. No significant differences in anesthetic success were found 
between any of the groups for any of the teeth.
CONCLUSIONS: Red hair and the MC1R gene were significantly linked to higher 
levels of dental anxiety but were unrelated to success rates of the IAN block in 
women with healthy pulps.