Study of Congenitally Missing Second Premolars and Space Factors in the Arches

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Abstract
Among 3699 persons on whom complete oral examinations and radiographs were made, 4.8% had congenital absences of teeth, including 2.4% lacking one or more second premolar and 2.1% having anomalies of the upper second incisor. In these and earlier records, 153 persons failed to develop 330 permanent second premolars; the quadrant incidences show that the premolars were missing more often in the lower than in the upper arch and in the left quadrants more often than in the right. Of the group, 64 retained 115 deciduous premolars which provide more than ample space for the missing permanent premolars; 32 others had lost all their deciduous premolars but retained ample space for the missing permanent premolars. In only 36 persons was the space between first premolars and first molars completely closed. It was concluded that lack of space is not a factor in the congenital absence of second premolars. It was suggested that the factor responsible for the absence of premolars is probably responsible for the absence of the other types which are frequently congenitally absent.

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