Apical Base Relationship Research Articles

The JYD angle: a modified method of establishing sagittal apical base relationship.

The reliability of angular measurements used for the evaluation of sagittal jaw relationship is affected by a number of factors including the degree of facial prognathism, the rotation of the jaws and the anterior face height. A method of establising apical base relationship is presented which eliminates the effect of the facial prognathism and permits the effect of the remaining factors to be approximately estimated. The JYD angle is recommended for use in determining sagittal apical base relationship.

Adjusting A-N-B angles to reflect the effect of maxillary position.

Abstract The angle A-N-B is a popular indicator of apical base relationships. Maxillary protrusion also has a major influence on that angle that is superimposed on the apical base effect. These effects are algebraically additive, so they may cancel each other in one patient and add together to produce a large reading for the A-N-B angle in mother, A simple method of compensation for these misleading effects is presented here. Read in part at the July, 1980 meeting of the Southwest Component of the Angle Society.

A modified technique for evaluating apical base relationships

1. The ANB difference is not always an accurate method of establishing the actual amount of apical base divergence. In addition to the geometric shortcomings previously pointed out, the results of this study indicate that the ANB landmarks are subject to growth and treatment mechanics which cause corresponding variations in the measurements used. 2. The AXD method described in this study demonstrates a method of relating apical bases which eliminates two of the variables, nasion and point B. The AXD angle is a more critical evaluation and was found to correspond significantly with a linear measurement of the actual apical base difference. 3. This study and others have demonstrated conclusively that angular measurements cannot compensate for divergence of apical bases resulting from variations in vertical facial height. For this reason, a set of linear measurements was proposed which would offer an accurate method of evaluating the pre- and posttreatment changes taking place. 4. The linear measurements introduced in this study demonstrate an accurate method of assessing apical base relationships. The use of these measurements provides a critical evaluation of treatment and places proper emphasis on favorable growth and treatment mechanics. 5. The study of the pre- and posttreatment linear measurement concerning point A determined that this landmark remained remarkably constant during orthodontic treatment. It would appear from this study that treatment mechanics for Class II cases do not actively relocate point A but actually hold it in position while the middle face is growing forward. 6. The A-D' measurement is concerned with the actual distance, in millimeters, between the apical base landmarks. In the fifty cases studied, the mean pretreatment measurement of A-D' was reduced 15.8 per cent as the Class II malocclusion was corrected. The mean pretreatment ANB underwent a reduction of 43.1 per cent on these same cases. While the A-D' pre- and posttreatment change may not be as dramatic as the ANB evaluation, the major point to consider is the critical degree of accuracy which this measurement brings into an analysis.

Changes in the relationship o f nasion, point A, and point B and the effect upon ANB

1. 1. The ANB difference is not always a true indication of the apical base relationship. 2. 2. The A-B′ measurement offers an accurate means of making this assessment and provides a more critical evaluation of the changes taking place at points A and B. 3. 3. Certain changes in the relative position of nasion to points A and B influence the degree to which ANB fails to reflect apical base relationship. 4. 4. ANB varies according to facial divergence; cases with an SNA of 86 degrees and over were found to have the largest average ANB value, while those with an SNA of 77 degrees and less had the smallest. 5. 5. Conversely, the A-B′ measurement averaged slightly less in the forward-divergents, even though their average ANB value was the greatest. 6. 6. The greatest degree of ANB reduction occurred in the forward-divergent cases (those in which SNA was 86 degrees and over). 7. 7. The average changes for ANB, A-B′, and the horizontal expression of point A were all negative values (reductions of the measurements concerned), an indication of orthodontic influence upon the relationship of point A to point B. 8. 8. Mandibular rotation was evidenced in specific cases, suggesting that orthodontic treatment also had a definite influence upon the relationship of point B to point A. 9. 9. Considerable variation was noted in the cases studied and seems to confirm that variation, rather than constancy, is the rule when applied to the individual patient. 10. 10. Cases were selected for a broad ANB range rather than a normal distribution, resulting in a high standard deviation. Therefore, the average changes noted in this study should not be used for making individual comparisons or predictions with any significant degree of accuracy.

Serial dentition and apical base relationships in Class I malocclusion: By Alan L. Gans, University of Michigan, Ann Arbor, Michigan

Serial dentition and apical base relationships in Class I malocclusion: By Alan L. Gans, University of Michigan, Ann Arbor, Michigan