T. Michael Speidel

Extreme Variation in Vertical Facial Growth and Associated Variation in Skeletal and Dental Relations

Abstract No Abstract Available. Presented by Dr. Robert Isaacson as the fourth Wendell L. Wylie Memorial Lecture at the University of California, November 1970.

Tooth-size discrepancy in mandibular prognathism

A Bolton analysis of seventy-eight cases of Angle Class III malocclusion, twenty-six cases of Angle Class I malocclusion, and twenty-six cases of Angle Class II malocclusion was recorded. Frequency of excess mandibular tooth structure, magnitude of the excess, over-all ratios, and anterior segment ratios were computed and analyzed. Two clinical cases were presented to show the advantage of tooth-size harmony in mandibular prognathism. Analysis of the data as presented above suggests the following conclusions: 1. The frequency of mandibular tooth-size excess (over-all ratio) in this sample was greater in cases of mandibular prognathism than in Angle Class I and Angle Class II cases. 2. In those cases with mandibular tooth-size excess, there was a suggestion that the magnitude of the excess was greater in cases of mandibular prognathism than in Angle Class I and Angle Class II cases. 3. A tooth-size discrepancy analysis should be included as one part of the diagnostic records for mandibular prognathism.

A Laminagraphic Study of Cuspid Retraction versus Molar Anchorage Loss

Abstract No Abstract Available. Given before the Midwestern Component of the Angle Society, January, 1969.

Measurement of tooth movement

1. Tooth movement relative to the alveolar bone can be precisely described only by superimposing on fixed points in the bone. Implants are the best known way today. Over short-term studies laminagraphy and the use of bony trabeculations are also useful. Remodeling occurs extensively on bony surfaces, making them too labile for use as stable landmarks. To project small amounts of tooth movement based on the use of such methods is so questionable as to represent little better than a guess or a clinical impression. 2. Growth can be separated into vertical and anteroposterior vectors with respect to the dentition. Since the occlusion is the concern, orientation of vertical and anteroposterior vectors to the occlusal plane is a reasonable baseline. The vertical and anteroposterior dental changes may not show a linear relationship in the anterior and posterior parts of the mouth when jaw rotations are occurring. 3. Growth can be disproportionate in either the vertical and/or the anteroposteroir plane of space. If the vertical increments of the anterior face differ from the vertical increments at the posterior face, mandibular rotations occur. This growth is accompanied by dental compensations that tend to mask the rotation. Therefore, open bite and deep bite are frequently skeletal growth problems. 4. Disproportional forward growth of the maxilla or mandible in an anteroposterior direction can lead to Class II or III relations. The growth that leads to Class II or Class III is accompanied by dental migrations that tend to mask this disproportionate growth. Orthodontic treatment of growth disproportionalities usually represents attempts to make the teeth further compensate. If surgical options are elected, the dental compensations should be removed prior to surgery in order to achieve a full surgical correction. 5. The teeth tend to move and grow in the opposite direction of the growth disproportionality. The teeth tend to mask the disproportionality. Thus, in an open bite, the incisors tend to move vertically further than in deep bites. Vertical imbalances may be more difficult to mask. Backward rotation of the mandible requires more vertical movement at the incisor than at the molar just to maintain vertical incisor relationships.

The effects on speech of surgical premaxillary osteotomy

Patients were tested before and after undergoing surgical premaxillary osteotomy for correction of skeletal and soft-tissue discrepancies. Both structural and speech measurements were made before surgery and for a year after surgery. The role of hearing and oral sensation in adaptation to surgery was evaluated. Immediately after surgery, speech was disrupted. Distortions of /s/ predominated. However, there were non long-term effects on speech. Hearing and oral sensation played little role in adaptation.

Enamel surface abrasion from ceramic orthodontic brackets: A special case report

The purpose of this report is to present a dramatic case of enamel abrasion from ceramic orthodontic appliances that was discovered only after appreciation of the initial findings of a study underway at the Department of Orthodontics, University of Minnesota. An artificial oral environment used in this study to simulate mastication also is described. The potential detrimental effects of ceramic appliances on tooth contact are discussed. All aspects of any new material should be investigated before its clinical application to prevent undesired side effects.

Comparison of three methods of profile change prediction in the adult orthodontic patient

Potential changes in the contour of the facial profile that accompany tooth movement can be important considerations in developing an orthodontic treatment plan. The objective of this study was to compare the accuracy of three different methods of predicting horizontal soft-tissue changes. Eighty-three nongrowing, orthodontically treated patients comprised the sample. Pretreatment and posttreatment lateral cephalometric hard- and soft-tissue landmark points were digitized. A coordinate system was defined, landmark coordinates were corrected for magnification, and then hard- and soft-tissue, angular, and linear measures were calculated by computer programs developed on a DEC PDP 11/44. The accuracy of prediction of soft-tissue landmark changes was compared for three prediction methods: (1) use of ratios of means of soft-tissue changes to corresponding hard-tissue changes, (2) use of a bivariate regression equation on corresponding hard-tissue landmark changes, and (3) use of stepwise multiple regression with hard-tissue changes and initial hard- and soft-tissue facial characteristics as predictor variables. For predicting changes of four soft-tissue points, multiple regression equations were slightly more accurate than ratio of means predictions. The standard errors of the estimate ranged from 0.7 to 1.1 mm for the multiple regression predictions; these were from 0.2 to 1.4 mm lower than those obtained for ratio of means predictions. The accuracy of the bivariate regression prediction technique fell between that of the other two methods. Examination of the residuals showed that the multiple regression equations consistently underpredicted the most extreme soft-tissue facial changes.

Location of the mandibular center of autorotation in maxillary impaction surgery

Controversy exists about the location of the center of autorotation of the mandible after maxillary impaction surgery. This investigation focuses on the problems associated with locating that center of autorotation and identifies factors that can increase the probability of accurately identifying its location for predicting surgical outcomes. The reliability of the Rouleaux technique for calculating the centers of rotation is established and is shown to be acceptable, as long as the landmarks used for determining the center are properly selected, and the magnitude of the rotation required is sufficient. The location of the centers of autorotation of the mandibles after maxillary impaction surgery for 46 patients was used to investigate the errors associated with landmark selection and amounts of rotation. Although there is much variation in its location, the center does not lie within the body of the condyle but instead lies away from the condyle. Guidelines for maximizing the reliability of predicting surgical outcomes on the basis of autorotation of the mandible after maxillary impaction surgery are given.

Differential treatment planning for mandibular prognathism

The treatment records of thirty-eight cases of mandibular prognathism treated by orthodontics means only (ORTHO) were evaluated. The pretreatment records of twenty cases of mandibular subapical esteotomy (SUB) and twenty cases of mandibular setback (SET) were evaluated for comparison and contrast with the pretreatment ORTHO records and with each other. Dental, skeletal, and soft-tissue parameters in the vertical and horizontal planes of space were recorded. Statistical analysis of means of parameters of the pretreatment records provided documentation of the discriminant variables in each of the following paired groups: ORTHO-SUB, ORTHO-SET, and SUB-SET. Analysis of the data as indicated above led to the following conclusions: 1. Three discriminant groups of mandibular prognathism of various degrees of severity were discernible when comparisons of treatment categories simulating clinical decisions were made. The ORTHO group was distinguished from the SUB group in the horizontal plane and, more strongly, in the vertical plane. The ORTHO group was distinguished from the SET group in the vertical plane and, more strongly, in the horizontal plane. The SUB group was distinguished from the SET group in the horizontal plane. 2. The physiologic developmental status of the patient should be carefully evaluated. 3. Anteroposterior dysplasias should be assessed relative to the cant of the mandibular plane. True denture base discrepancies can be noted relative to the occlusal plane. 4. Documentation of vertical dysplasias should include measurements of craniofacial divergence (SN-MP, FH-MP, and OP-MP). 5. In assessing the profile evaluation of the patient with mandibular prognathism, particular attention should be focused on facial contour angle (FCA), nasolabial angle (NLA), and relative lower lip protrusion (LLP). 6. Any numerical values obtained in the evaluation of the dental, skeletal, or soft-tissue characteristics of mandibular prognathism should be considered only as descriptive, diagnostic guides and not as components of a diagnostic formula.

Treatment-induced errors in occlusion following orthognathic surgery

Posttreatment occlusion following orthognathic surgery is often different from that predicted in the treatment plan. Differences between intended and actual occlusion may be treatment-induced occlusal errors caused by mismatches between the centers of rotation of the mandible and of the articulated models. Discrepancies in the position of the articulator center of rotation (relative to the position of the center of rotation of the patients mandible) influence the magnitude of occlusal errors. A computer model was developed to quantify these errors. As the center of rotation of the articulated models becomes more divergent from the patients center of rotation, the magnitude of the occlusal errors increases. This magnitude increases most rapidly along the line that is perpendicular to the line joining the patients center of rotation and a preselected mandibular landmark (incisor tip or molar cusp, for instance). For small changes in vertical dimension, clinically insignificant errors result, independent of the degree of mismatch between the centers of rotation. Clinical implications of these findings are discussed.