AN INVESTIGATION OF GROWTH ROTATIONS OF THE JAWS STEPHEN DAVID SPRINGATE B.D.S.(Hons)., M.D.S., M.Sc., Ph.D., F.D.S., D.Orth., M.Orth.R.C.S.(Eng). Department of Orthodontics UCL Eastman Dental Institute A thesis submitted in fulfilment of the requirements for the degree of Doctor of Medicine (Research) of University College London February, 2019 1 DECLARATION. I, Stephen David Springate, confirm that the work presented in this thesis is my own and that this thesis is the one on which I expect to be examined. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. 2 ABSTRACT 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. 3 IMPACT STATEMENT During normal growth the stable cores of the upper and lower jaws gradually rotate in an anti-clockwise direction when viewed from the patient’s right hand side. On average the lower jaw rotates by about 15 degrees and the upper jaw rotates by half this amount. However, in a small proportion of the population there is a much more marked forward rotation (-20 degrees) or, less commonly, a marked backward rotation (+15 degrees). These extreme forms of growth rotation are disproportionately associated with some of the most difficult orthodontic treatment problems often necessitating surgical correction in adult life. The present research examined the co-ordination between growth rotations of the jaws and growth changes throughout the facial bones and dentition to locate possible causal factors. This required the accurate measurement of the intra-individual patterns of sequential growth increments which has not generally been possible previously because of two confounding effects: 1) the doubling of the random error in locating the end points of the increments; and 2) the negative serial correlation between adjacent increments. A new method of radiographic analysis was developed to suppress the serial correlation and to reduce the random error thereby allowing intra-individual patterns of incremental growth to be accurately recorded without the introduction of artifacts induced by the standard curve-fitting and smoothing procedures. As a result of the study evidence was found that contradicts the prevailing theories of the causation of growth rotation and which, instead, points strongly to the postural relationship of the mandible to the cranium as being the primary underlying cause. This suggests the possibility of developing orthodontic treatments to intercept and reduce the most severe forms of growth rotation by influencing cranio-mandibular posture during childhood and adolescence. If this could be achieved it should avoid the need for complex surgery to correct the effects of the most severe forms of growth rotations of the jaws. 4 ACKNOWLEDGMENTS The writing of this thesis and the work that preceded it could not have taken place without the help and support of many people, too many to properly acknowledge them all. The work contained in this thesis could not have been undertaken without access to the priceless radiographic records of the Mathews longitudinal growth study of the University of California. For this reason I wish to record my sincere gratitude to two people. First, to the late Dr J. Rodney Mathews (lead researcher of growth study that bears his name) for his great kindness in allowing access to the records of that study. A kindness that I can never repay. Secondly, to the late Dr Sheldon Baumrind the custodian of the records who arranged for the transfer of the remaining records to me and whose long discussions with me deepened my understanding of the problems of extracting accurate growth data from serial radiographs. I would like to warmly thank Professor Nigel Hunt and Professor Susan Cunningham who agreed to act as my supervisors without any coercion and whose unfailing courtesy and kindness over many years is truly appreciated. My sincere thanks also go to Professor Sir David Cox for his help in statistical analysis of the error studies and for his mathematical brilliance. I am also grateful to Professor Peter Diggle for help in interpreting time-series data. Finally, I thank my wife, Clare and my sons, Oliver and Henry, for allowing me to rob them of the time that has been used in the preparation of this work – thank you for being tolerant, yet again, of my selfishness and for not shouting at me too much when I left so many other things undone. 5 LIST OF FIGURES Figure Title Page No. Figure 2.1 Diagrammatic representation of Björk's classification of growth Rotations of the mandible defined by the centre of rotation (COR). 33 Figure 5.1 Locations of the tantalum implant markers. 70 Figure 5.2 Examples of the serial cephalometric radiographs used in the study 72 Figure 5.3 The age distribution of the radiographs for (a) the Initial Survey; and (b) the Time-Series study. 74 Figure 5.4 Diagrammatic representation of the procedure used to locate the correct coupling of the implant images across the three radiographic projections. 78 Figure 5.5 The cardinal axes used in the orientation of the head and in the descriptions of the directions of growth displacements and tooth migrations. 82 Figure 5.6 The points, lines and planes in the lateral cephalometric radiograph. 89 Figure 5.7 The regions analysed on the oblique cephalometric radiograph. 91 Figure 5.8 Analysis of the eruption and migration of the buccal teeth from the oblique cephalometric radiograph. 92 Figure 5.9 The regions analysed and measurements made on the frontal cephalometric radiograph. 94 Figure 5.10 Examples of the composite plots and colour coding used in the analysis of the radiographic growth sequences. 100 Figure 6.1 The sequence of the stages in the construction of the discrete time-series. 107 Figure 7.1 The results of the initial survey showing the locations of significant associations after correction for multiple inference. 128 Figure 7.2 Initial Survey: comparison of the nature and location of growth changes statistically significantly correlated with the indices of growth. 129 Figure 7.3 Mean facial diagrams for subjects at the extremes of the range of mandibular growth rotation. 130 13 Figure 7.4 Centres of growth rotations of the jaws in subjects from the extremes of the range of mandibular rotation: (a) lowest rotators; and (b) highest rotators. 131 Figure 7.5 The results of the main study showing the time-series variables in statistically significant synchrony with the indices of growth. 134 Figure 7.6 Time-series study: comparison of the nature and location of growth Changes in statistically significant synchrony with the indices of growth. 135 Figure 7.7 Time-series plots of the 10 variables in statistically significant synchrony with the temporal patterning of mandibular growth rotation (r-MGR) for subjects with the: maximum; median; and minimum cumulative growth rotation of the mandible. 136 Figure 7.8 Time-series plots of the pattern of general somatic growth (r-CervSp) versus the pattern of mandibular growth rotation (r-MGR) for all subjects in the study. 139 Figure 7.9 Time-series plots of additional selected variables without statistically significant synchrony with the temporal patterning of mandibular growth rotation (r-MGR) for subjects with: maximum; median; and minimum cumulative growth rotation of the mandible. 141 Figure 8.1 Comparison of the locations of significant associations for CervSp and Cond-Mag. 155 Figure 8.2 Time-series plots showing examples of the modulation of condylar magnitude by the direction of condylar growth for subjects with the: maximum; median; and minimum cumulative growth rotation of the mandible. 163 Figure 8.3 Time-series plots of total maxillary growth displacement and the ratio of horizontal to vertical growth displacement relative to the patterns of: mandibular growth rotation; and general somatic growth.