Date of Graduation


Document Type


Degree Type



School of Dentistry



Committee Chair

Peter Ngan

Committee Co-Chair

Richard Jurevic

Committee Member

Chris Martin


Background: "The Six Keys to Normal (Optimal) Occlusion" published by Andrews in 1972 identified six common features characteristic of an optimal occlusion. Among these characteristics are flat maxillary and mandibular occlusal planes. Andrews further developed the Straight-Wire Appliance(TM) to facilitate attaining an optimal occlusion in an efficient manner with few if any arch wire bends. In addition to the Six Keys, Andrews proposed that attaining a flat occlusal plane with a straight arch wire is predicated on siting the bracket slots on the FA Points of the tooth crowns (Andrews Plane). Observation of the maxillary and mandibular Andrews plane will reveal that these two planes diverge when both occlusal planes are levelled. This may be attributed to a proportional height discrepancy between the tooth crowns; which requires an adjustment to the sited vertical position of the slots on certain tooth crowns.;Objective: The purpose of this study was to investigate if there is a need to adjusted the FA Points on certain maxillary and mandibular tooth crowns to permit a flat parabolic shaped arch wire to produce level slot alignment and a flat occlusal plane. Correlations between the tooth crown heights and FA Point discrepancies were also analyzed.;Materials and Methods: Casts of twenty patients were scanned and virtually treated using software (ORTHO INSIGHT 3D version 6.0.7036, Motionview Software, LLC). Crown heights of all maxillary and mandibular teeth were digitally measured and recorded. Each sample case was treated virtually to precise level slot alignment with the brackets sited on the FA Points as defined by Andrews. A second treatment was virtually completed on these cases where a flat occlusal plane was not attained with the initial virtual treatment. Bracket positions were adjusted vertically as needed on certain tooth crowns to permit level slot alignment and a flat occlusal plane. The required height adjustment required to attain level slot alignment were recorded as a + or -- vertical height discrepancy between Andrews FA Point and the "adjusted FA Point". Normative statistics was generated for all tooth heights, FA Points, and FA Point discrepancies. Correlations analyses were performed between tooth crown heights, FA Points, and FA Point discrepancies.;Results and conclusions: Mx centrals will likely require an adjustment to the incisal edge of at least 0.5mm ( avg.=1.23 p=<0.0001) Mx laterals will show a positive correlation with crown height and incisal adjustment though not likely to require a change greater than 0.5 mm(avg=0.43mm p=. Md incisors will require an adjustment greater than 0.5mm (laterals avg =0.77mm p=0.0001 centrals avg=0.87mm p=<0.0001) Proclination of lower incisors do not yield a significant change from previously discovered adjustment (lateral avg= 1.34mm p=<0.0001 central avg=1.04mm p=<0.0001) retroclining lower incisors requires no significant adjustment from FA (lateral avg=-0.23mm p=<0.0001 central avg=-0.27mm p=<0.0001) all other teeth found no significant need for occlusal or gingival adjustment.