Preliminary report on tooth movement after loss of the first permanent molar in 500 adolescents

• 1.

  Correlated according to the number of molars in each age group. As the age when each child was examined increased, the percentage of one and two molars lost in the respective age groups decreased. The contrary was true of the percentage of three molars lost, which increased with the rise in age at the time of examination from 15 to 18 years. The four molar percentage was fairly constant in the age groups from 15 to 18 years but increased at 18 to 19 years.

• 2.

  When correlated according to percentages showing 1, 2, 3 and 4 molars lost at the time of examination, the percentage frequency of distribution according to age at the time of examination, 15 to 19 years, was the same for the “one molar lost” group as for the “two molars lost” group. This type of correlation was true also of the three and four molars lost groups respectively.

• 3.

  When correlated to the age when the first molars were lost, we find the peak for the one molar group at age 13; the two molar group at 14 years; the three molar group also at 14 years and the four molar group at 15 years.

  1. Download : Download full-size image

• 4.

  The mandibular left first molar is most frequently lost. The mandibular right is second; the maxillary left, third and the maxillary right is fourth in order of decreasing frequency. What is the reason for this condition? Does it have anything to do with the side most frequently used for chewing? Is it related to right and left handedness? Why are the mandibular teeth more frequently lost? If the answer is that these teeth are the first permanent teeth to erupt, then the conditions present in the mouth of the child at that age should be better known to us. These questions have not as yet been satisfactorily answered. The average number of first molars lost is 1.88 per child examined.

• 5.

  At the time when the first and second premolars and the second molar in the 941 quadrants studied were examined, less than 1.5 per cent showed no movement (O-O-O position). Less than 1 per cent were in the O-D-O position. The percentage of D-D-O was greater in the mandibular than in the maxillary quadrants. The percentage of O-O-M positions was greater in the maxillary than in the mandibular quadrants. From 66 to 68.8 per cent of all quadrants showed the D-D-M position. There was hardly any difference between the right and the left quadrants in each jaw.

• 6.
  • (a)

    Fifty per cent of O-O-O were in the three-month interval group and 78 per cent within six months; none in O-O-O later than one year after extraction.

  • (b)

    O-D-O showed 84 per cent in the intervals within one year. None later than three years.

  • (c)

    D-D-O had 75 per cent at the three-year interval and none later than eight years.

  • (d)

    O-D-M had 71 per cent at the three-year interval and none after eight years.

  • (e)

    O-D-M showed higher percentages than D-D-M in the intervals up to three years but lower than D-D-M after three years.

  • (f)

    D-D-M was fairly evenly distributed between 1 and 8 years.

  When the correlation of position of the first and second premolars and the second molar to the interval of time elapsed and first molar space remaining is made, we may be able to tell more accurately whether any of the positions other than D-D-M are present or whether they all are substations, as they seem at present, on the road to D-D-M. At present, we can say that after 9 years of age there were no cases in any position other than D-D-M. In other words, given sufficient time, premolars and second molars in jaw quadrants from which first molars had been lost will tend to show change of position. This provides the answer to those who would extract first molars with the thought that the second molars will move forward by themselves to occupy the space thus left, while the premolars stand still.

• 7

  Weighted median correlation showed faster closure of space in max- illary than in mandibular quadrants in the intervals between 3 months to 10 years. There was a steady and definite decrease of space between the second premolar and the second molar as the interval between extraction and the taking of the impression increased.

• 8

  The range of variance and the amount of space left between the second premolar and the second molar at each interval decreased as the interval after extraction increased. This seems to indicate that, while the space tends to get smaller, it does not necessarily close at the same rate in all cases. It is possible that other local factors are responsible for the persistence of the space for an undue length of time as well as for the rate of closure in all cases.