The Lewis offset is a term for the portion of the central groove on a permanent mandibular first molar

Mandibular first molar

The mandibular first molar or six-year molar is the tooth located distally from both the mandibular second premolars of the mouth but mesial from both mandibular second molars...

 which lies between the two central pits. It lies at an angle to the mesio-distal axis of the tooth, and causes the mesial portion of the central groove to be located further buccally than the distal portion. This bucco-lingual shift correlates with a relative difference in size between the mesial and distal cusps on these teeth - the mesiolingual cusp is larger than the mesiobuccal cusp, but the distobuccal cusp is larger than the distolingual cusp. It also allows for the buccal groove to be located mesial to the lingual groove which is mandatory to accommodate the relative sizes of the three cusps on the buccal and two cusps on the lingual of the occlusal surface of the tooth.

The offset is named for Dr. Christopher S. Lewis, a Mercer Island, WA dentist and longtime faculty member in Dental Anatomy at the University of Washington School of Dentistry

University of Washington School of Dentistry

The University of Washington School of Dentistry is located in Seattle, and is the only school of dentistry in Washington State. The school emphasizes research in anxiety, orofacial pain, tissue repair and regeneration, immune response to bacteria, and practice based research.- History :A part of...

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