Implications of the inclination of the mandibular first molars in the extractionist versus expansionist debate.

Some orthodontic expansionists (versus extractionists) hold a notion that in the decision to treat nonextraction, expansion treatment can be predicated and dictated based on the degree of facial-lingual inclination of the mandibular molars (particularly the mandibular first molars). For instance, some modern-day expansionists argue that mandibular first molars with a facial crown lingual inclination of approximately -30 degrees (based on Andrews' measurement) indicate that the mandibular arch, and subsequently the maxillary arch, needs to be developed or expanded to allow for more arch and tongue space. However, this thinking is based on a false premise; the mandibular first molars are normally lingually inclined approximately -30 degrees and not naturally found in an upright facial-lingual position of approximately -12 degrees.