Computer aided detection of natural reference markers in serial radiographs of growing bone

This thesis describes the theoretical and experimental development and testing of a computer-based image processing system for the detection of stable structural features in serial radiographs of growing bone. The study is divided into three parts. First, a simple theoretical model for the detection of stable structures in a radiographic sequence was developed together with a more detailed statistical model of the processes which hinder detection. Analysis of the models indicated that the processing procedures needed to perform the detection were those described by the so-called "matched filter equation". Secondly, the assumptions of the model were tested in a series of experiments using serial radiographs of 24 children with implanted tantalum markers, drawn from the files of the University of Washington, USA. Information gained from these experiments prompted changes to the detection method to allow the radiographic data to comply with these assumptions and provide robustness against image noise. The method was implemented as a semi-automatic image processing system on a Sun 3/160 computer. The system was tested in a further series of experiments using a second sample of radiographs of 28 children with implanted markers and with radiographs of dried human skulls. The results of these experiments indicated that the system could detect persistent structural features whose positions were consistent with the stable tantalum markers and that the system was robust against minor changes in projection between radiographs. Finally, the detection system was applied to the investigation of mandibular incisor eruption from intra-alveolar to pubertal eruption stages using serial lateral cephalometric radiographs of 11 children. This investigation revealed two new features of incisor eruption: first, the eruption paths deviated lingually at, or just prior to, alveolar emergence; and second, post-emergence eruption was characterised by a labio-lingual oscillation of the crowns of the incisors

An investigation of growth rotations of jaws

This thesis describes an investigation into the origin and mechanism of growth rotations of the jaws. The materials comprised serial lateral, frontal and oblique cephalometric radiographs of 11 untreated children (5 males and 6 females) with tantalum markers in the mandible and both maxillae. The radiographs were recorded annually over an average period of 9.6 years (mean age at initial records 7.21 years) and were drawn from the archives of the Mathews Longitudinal Growth Study of the University of California, USA. The investigation comprised two separate but related studies: (i) an initial survey examining the correlations between growth rotations of the jaws and growth changes at sites throughout the face; and (ii) an in-depth investigation of the patterning of the sequences of annual increments of growth employing time-series analysis to detect intra-individual co-ordination of growth. The initial survey revealed a series of associations that matched those found in previous implant studies but some exceptions. The main study extended these results and indicated that the vertical growth displacements of the ramus and anterior maxilla combined to produce growth rotation of the mandible while the horizontal to vertical distribution of maxillary growth displacement produced growth rotation of the maxilla. Growth rotations of the jaws were found to be co-ordinated with: vertical growth displacement of the ramus (p=0.030) and anterior maxilla (p=0.009); horizontal growth displacement of the mandible (p<<0.001) and maxilla (p=0.015); horizontal migration of the maxillary molars (p=0.034); changes in angulation of the maxillary molars (p=0.009); and changes in the postural height of the tongue (p=0.048). The patterning of the co-ordination between rotational and translational growth displacements of the jaws and growth related changes in the dentition suggests a linkage to postural changes in the mandible and tongue. Based on these findings an explanatory model is proposed for the origin and control of growth rotations of the jaws