The rationale of extraction as an adjunct to orthodontic mechanotherapy and the sequelae of extraction in the absence of orthodontic guidance

Abstract

1. 1. Extraction is a recognized and widely accepted adjunctive procedure in orthodontic mechanotherapy. The indications for extraction, while basically clear-cut, are necessarily modified in their application to the individual patient by the subjective esthetic standards of the practitioner. 2. 2. There is a direct correlation between the number of permanent first molars showing caries or fillings and the number of carious filled or extracted teeth in the mouth as a whole. Children with permanent first molars extracted, however, average a higher incidence of carious, filled, and extracted teeth for the mouth as a whole than similar age groups having an equal number of permanent first molars filled or carious but retained in the mouth. The incidence of carious, filled, or missing teeth in the mouth is intensified with each additional extraction of a first permanent molar. 3. 3. Carious, filled, and extracted teeth are almost evenly distributed among the four jaw quadrants when the first permanent molars are retained in the mouth. In boys and girls with one to all four first permanent molars extracted, the average number of decayed, missing, or filled teeth in the mouth as a whole is increased and is higher in the maxillary than in the mandibular teeth, regardless of the jaw from which the first permanent molars are extracted. 4. 4. The rate of distal shifting of the first and second premolars is more rapid even in the maxilla than in the mandible. The distal shifting of the maxillary first and second premolars, as is indicated in the foregoing, is accompanied by loss of contact points. In the mandible the difference in the rate of shifting between the premolars is greater than in the maxilla and is accompanied by definite spacing of the teeth. 5. 5. In spite of the fact that the permanent first molar space was closed in one group of cases, the respective amount of shifting of the adjacent teeth responsible for the space closure in the mandible varied with the age of the patient at the time the permanent first molar was extracted. It would seem that if the first molar is extracted before the premolars erupt, the molar space will close by extreme distal shifting of the premolars but only moderate mesial shifting of the second molars. If the mandibular first molar is extracted after the premolars have erupted, the space is closed more by the mesial shifting of the second molars than by distal shifting of the premolars. 6. 6. Loss of first molar teeth in mouths with normal occlusion, without subsequent control of the direction of shifting of the adjacent and other remaining teeth left in the mouth, leads to malocclusion. 7. 7. Extraction of permanent first molar teeth in mouths showing malocclusion, without control of the direction of shifting of the remaining teeth, almost invariably leads to aggravation rather than improvement of the existing malocclusion (Fig. 14). 8. 8. Closure of the space after extraction of the permanent first molars in the maxilla is due to a slight distal shifting of the premolars and a proportionately greater mesial shifting of the second molars, therefore, loss of maxillary first molars in Class I (Angle) malocclusion can cause such malocclusion to change to Class II, Division 2, although the classification of the malocclusion in these cases was usually found to remain the same. When mandibular first molars are lost in Class I (Angle) malocclusion, these usually are transformed into Class II, Division 1, or Class II, Division 2, subdivision malocclusion, depending on whether the loss of the first molar is unilateral or bilateral and on the relationship of the lower lip to the maxillary incisors. Additional factors in this connection are muscular pressure, masticatory strength, and other local influences. 9. 9. Loss of maxillary permanent first molars in Class II (Angle) cases is not followed by self-correction because of the comparatively slight distal shifting of the premolars and the relatively greater mesial shifting of the adjacent second molars. Loss of the mandibular first molars in Class II (Angle) cases increases the protraction of the maxillary incisors because of lingual collapse of the mandibular incisor teeth. 10. 10. Loss of maxillary first molar teeth in Class III (Angle) cases increases the malocclusion. Because of the tendency of mandibular premolars to shift singly, resulting in interdental spacing, in addition to other local conditions present, extraction of mandibular first molar teeth without subsequent orthodontic guidance does not benefit Class III (Angle) cases.