Abstract
Quite recently, standardized roentgenographic data for 34 pairs of like— sexed twins discordant for cleft of lip and/or palate became available for study. As part of the analysis of this quite unusual sample of matched— pair subjects an investigation was undertaken to examine the effects of clefting on crown~root lengths and on eruption of the buccal teeth in grow~ ing children. While it is generally accepted that children with clefts are shorter and lighter than non—cleft children (5, 6) and may erupt their teeth more slowly, the evidence for the latter is not conclusive. A definitive answer was therefore sought amongst those of the sample whose dentitions were developing. The data were obtained from left and right 45° cephalograms for 28 pairs of like—sexed twins discordant for cleft of lip and/or palate from the eastern half of the United States. The age range was from 3 years to 15 years. These were selected from the total sample of 34 discordant twin pairs* on the basis of age. The sample is therefore of matchedpair design with respect to age and sex; the genetic component is matched to varying degrees depending principally upon the zygosity of the twins. The composition of the sample according to sex and zygosity is shown in Table 1. Method Crown—root length was measured from the tracings parallel to the long axis of each buccal tooth (Pml, ng, N11 and M2, both sides) using the mesial cusp tips and mesial root apices as end points. Eruption was measured as the distance from the mesial cusp to the mandibular border perpendicular to Functional Ocelusal Plane expressed as a percentage of the total distance for each position from Functional Ocelusal Plane to mandibular border as shown in Figure 1. It may be noted that the percent obtained for each twin by this method could never Dr. Hunter is affiiliated With the Division
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