Background <p>Wedge-shaped defects are rarely reported in single mandibular denture (SMD). This report describes an unusual unilateral wedge-shaped defect observed in an SMD and discusses its possible etiological factors.</p> Case presentation <p>A 58-year-old woman presented with sensitivity in the left maxillary posterior teeth. Clinical examination revealed wedge-shaped defects in the left maxillary molars and a unilateral wedge-shaped defect approximately 3 mm in depth on the left side of the mandibular denture base. The patient denied bruxism or traumatic injury to the prosthesis but reported a long-standing habit of unilateral mastication.</p> Conclusion <p>This case suggests that long-term unilateral mastication may be associated with the development of localized wedge-shaped defects in SMDs. Comprehensive occlusal assessment and regular prosthesis maintenance may help prevent similar complications.</p>