Robert J. Isaacson

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.

A genetic study of class III malocclusion

Abstract The families of fifty-one probands demonstrating Angle Class III malocclusion were examined. Approximately 13 per cent of the siblings of the probands exhibited the trait, suggesting a strong genetic influence in the transmission of Class III malocclusion. No evidence was found to suggest that the trait is sex linked. The results did not support a simple autosomal dominant mode of transmission. The results also did not support a simple autosomal recessive transmission. The explanation most compatible with the results seems to be a polygenic method of transmission depending on a threshold beyond which persons are at risk. The possibility that different methods of transmission exist in different families or different populations has not been ruled out.

Surgical Orthodontic Treatment Planning: Profile Analysis and Mandibular Surgery

Abstract No Abstract Available. Read at the January, 1975 meeting of the Midwestern Component of the Angle Society.

Tooth diameters and arch perimeters in a black and a white population

This study was undertaken to test the hypothesis that a sample of black patients will have larger mesiodistal tooth diameters and larger dental arch perimeters than a corresponding sample of white patients. In this study, the black samples mean canine, first and second premolar, and first molar mesiodistal diameters were significantly larger than those of the white sample. The dental arches of the black patients were significantly wider and deeper but did not show significantly more crowding. Gender and race differences did exist, but gender differences were controlled by sampling procedures. The black sample also had a larger mean MP-SN angle but this was not accompanied by the increased crowding and the narrower dental arches that had been reported associated with high-angle white samples.

Vertical anterior relapse.

Abstract 1. 1. The purpose of this study was to show that changes in vertical jaw relation produced by mandibular rotation resulting from growth after orthodontic treatment contribute in part to vertical anterior relapse. Twenty-six patients were selected on the basis of return to deep-overbite or open-bite following orthodontic treatment as observed directly from dental casts. Dental casts and corresponding sagittal roentgen head films before orthodontic treatment, at the beginning of retention, and at a subsequent date sometime after the end of retention were analyzed to evaluate the return toward the original overbite or open-bite relationship. 2. 2. Two sets of measurements for each patient were obtained to determine the changes in tooth-to-bone relationship and bone-to-bone relationship occurring during the time interval studied. The first set of measurements was based on constructed lines and planes of reference, the second on structural landmarks. 3. 3. A method was described for superimposition of the head films using structural (anatomic and bony) landmarks to eliminate or reduce the error in measuring from lines and planes constructed through changing landmarks. A method described by Skieller 40 was used to determine mandibular growth rotation. 4. 4. Changes in maxillary and mandibular incisor axial inclination and root apex vertical position producing tooth-to-bone relationship changes were analyzed with respect to their contribution to vertical anterior relapse. 5. 5. Changes in maxillary and mandibular molar vertical position in relation to posterior facial height changes producing bone-to-bone relationship changes were also analyzed and discussed with respect to their contribution to vertical anterior relapse. 6. 6. Those patients who exhibited anterior deep-overbite relapse showed greater posterior facial height increase than combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible. In contrast, those patients who exhibited anterior open-bite relapse showed greater combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible than posterior facial height increase. 7. 7. The patients showing deep-overbite relapse exhibited forward mandibular growth rotation, whereas those showing anterior open-bite relapse exhibited backward mandibular growth rotation. 8. 8. Depression of elongated posterior teeth was not found to contribute to anterior deep-overbite relapse. 9. 9. Possible sources of error in this study and the time to begin orthodontic treatment were discussed briefly. Type of retention, based on the original vertical anterior relation and on the type of mandibular growth rotation, was also discussed. Finally, the length of retention based on the age when growth of the jaws is complete was suggested.

Effects of rotational jaw growth on the occlusion and profile.

S tudies using cephalograms employ a method of tracing skeletal structures on a radiograph exposed at one time point, tracing these structures again on a second radiograph exposed at a second time point, superimposing the two tracings on some central reference point, and connecting presumed identical landmarks with a straight line .6p 6 This technique produces a self-fulfilling conclusion that the face and jaws grow downward and forward from beneath the cranium in a linear, translatory fashion. This perspective has influenced orthodontists to expect that the dental occlusion will also be carried in a similar, straight-line, downward and forward manner. Interest in vertical facial growth lead BjSrk,lv * Bjiirk and Palling,s Bjork and Skieller,4 e)degaard,*l-I2 Schudy,13-15 and Isaacson and associatess-lo in recent years to focus more attention on nonlinear jaw growth or jaw rotation. Jaw rotation was not recognized by early workers using cephalograms because of surface remodeling bone changes masking rotational effects as they occurred. This phenomenon of bone remodeling in jaws during normal growth has been carefully documented by BjSrk and Skieller,4 using metallic implants, and Enlow and Hunter,s using histologic techniques. Tooth movement also masked changes in dissimilar jaw growth by compensatory movements at the periodontal regions causing the occlusion to remain apparently in nearly constant relations.4 A recent report focused on a mechanism whereby vertical condylar growth can be converted into changes in anteroposterior jaw relationslo This mechanism explains how vertical condylar growth can, under specific conditions, result in significant anteroposterior dental and profile changes. According to this report, the long-held and widely reported concept of linear downward and forward facial growth is the exception rather than the rule. This report noted that, in order for translatory mandibular growth to occur, vertical

Increase in arch perimeter due to orthodontic expansion

A mathematical model was developed to compare quantitatively the effects of various types of orthodontic expansion on mandibular arch perimeter. Mandibular arch form was modeled with spline interpolation to fit a smooth curve between assigned molar, canine, and incisor positions. Starting with average arch dimensions, intermolar width, intercanine width, and midline arch length were increased individually and in combination in millimeter increments up to 5 mm, and the consequent changes in arch perimeter were measured. Increasing midline arch length by incisor advancement was nearly four times as effective in increasing arch perimeter as was molar expansion; canine expansion had an intermediate effect. Arch perimeter increments increased slightly with successive amounts of expansion for the molar, canine, and incisor. Combinations of molar-canine and canine-incisor expansion yielded results comparable to the total effects achieved by expansion of those teeth individually. Combined molar-canine expansion created increases in arch perimeter that were only slightly less than those generated by incisor advancement alone.

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.

Dental and skeletal contributions to occlusal correction in patients treated with the high-pull headgear–activator combination

The purpose of this study was to examine dental and skeletal changes in patients treated with the high-pull headgear-activator combination. A group of 40 consecutively treated subjects with a Class II molar relationship and a minimum of 5 mm overjet was used for this study. The results showed that Class II correction often was achieved by distal repositioning of the maxillary teeth (mean, 0.07 mm) and mesial repositioning of the mandibular teeth (mean, 3.3 mm) with a wide range of variation. Correlation of maxillary molar repositioning with total interarch occlusal change showed a positive relationship; however, a weak correlation suggested that other variables were contributing factors, in addition to distal upper molar positioning. The change in mandibular molar position compared with the movement of pogonion strongly suggests that forward growth of the mandible is important to the correction of the Class II malocclusion. When total molar repositioning in the upper jaw was correlated with total molar repositioning in the lower jaw, a strong inverse correlation was found, indicating that upper molar movement parallels lower molar movement.

Moving an Ankylosed Central Incisor Using Orthodontics, Surgery and Distraction Osteogenesis

When a dentist replants an avulsed tooth, the repair process sometimes results in the cementum of the root and the alveolar bone fusing together, with the replanted tooth becoming ankylosed. When this occurs, the usual process of tooth movement with bone deposition and bone resorption at the periodontium cannot function. If dental ankylosis occurs in the maxillary incisor of a growing child, the ankylosed tooth also cannot move vertically with the subsequent vertical growth of the alveolar process. This results in the ankylosed tooth leaving the plane of occlusion and often becoming esthetically objectionable. This report describes a 12-year-old female with a central incisor that was replanted 5 years earlier, became ankylosed, and left the occlusal plane following subsequent normal vertical growth of the alveolar process. When growth was judged near completion, the tooth was moved back to the occlusal plane using a combination of orthodontics, surgical block osteotomy, and distraction osteogenesis to reposition the tooth at the proper vertical position in the arch. This approach had the advantage of bringing both the incisal edge and the gingival margin of the clinical crown to the proper height in the arch relative to their antimeres. Previous treatment procedures for ankylosed teeth have often involved the extraction of the affected tooth. When this is done, a vertical defect in the alveolar process results that often requires additional bone surgery to reconstruct the vertical height of the alveolar process. If the tooth is then replaced, the replacement tooth must reach from the final occlusal plane to the deficient ridge. This results in an excessively long clinical crown with a gingival height that does not match the adjacent teeth.