Andrew Richardson

Lower third molar development subsequent to second molar extraction

Development and eruption of lower third molars was examined in 63 subjects who were treated by extraction of second molars. Changes in mesiodistal and buccolingual lower third molar angulation were measured on 60 degrees cephalograms taken before extraction and 3 or more years later. The final position of lower third molars was assessed on models at the end of the observation period by using a scoring system. All lower third molars erupted in periods ranging from 3 to 10 years after extraction. Ninety-nine percent of the third molars upright mesiodistally, but few became as upright as the second molars they replaced. Model analysis showed that 96% of the lower third molars erupted in good or acceptable positions.

An investigation into the age of cessation of endocranial growth using the techniques of logetronic copying and photosubtraction

The classical teaching that endocranial growth is dependent on growth of the brain and thus should cease early in life has been questioned by Richardson and Blair who found marked expansive growth between 5 and 15 years in the occipital region. These authors were unable to comment on the age at which endocranial growth ceases because the changes towards the end of the growth period were of the same order of magnitude as the errors involved in digitizing standard cephalometric radiographs. In the present study, aimed at determining the age of cessation of endocranial growth, a very precise technique involving Logetronic copying and photosubtraction was used. Positive and negative Logetronic prints were made from standard 90 degree lateral cephalometric films of 28 normal boys taken at annual intervals between 5 and 15 years. The negative of one stage superimposed on the positive at the next stage revealed any growth changes by photosubtraction. Comparisons were made between films at 5 and 10 years, 10 and 13 years, 13 and 14 years and 14 and 15 years. All superimpositions and recordings were repeated by a second observer. All subjects showed growth changes between 5 and 10 years, 96% changed between 10 and 13 years, 64% changed between 13 and 14 years, and 54% showed growth changes between 14 and 15 years. Endocranial growth has ceased between 14 and 15 years in 46% of normal boys.