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Biomedical subjects

R J Isaacson

Publications and source records attributed to R J Isaacson.

At least 19 recordsLinked to original sources
PubMed2001

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.

Alveolar Process↗
PubMed1999

Condylar positional changes after mandibular advancement surgery with rigid internal fixation.

The purpose of this retrospective investigation was to describe condylar positional changes in patients after mandibular advancement surgery. By superimposing on clearly identifiable cephalometric landmarks (ie, mandibular symphysis and rigid fixation screws), condylar positional changes from immediately after surgery to orthodontic appliance removal were extrapolated. Although the mandibular symphysis generally moved in either an anterior or posterior direction after surgery, condylar movements were exclusively in an upward vertical direction. Correlations were found between several measured variables, including a tendency for increased superior postsurgical movement of the condyles with increasing magnitudes of surgical advancement of the mandible. This long-term instability of skeletal relationships may be caused by a wide variety of interacting factors and events.

Adolescent↗
PubMed1997

Lower arch perimeter preservation using the lingual arch.

The purpose of this investigation was to determine whether the placement of a mandibular lingual arch maintained arch perimeter in the transition from the mixed to the permanent dentition, and if so, whether it was effective at preventing mesial migration of first permanent molars, or whether this migration still occurred en masse, by increased lower incisor proclination. Thirty patients were randomly assigned to either a treatment group (N = 14, mean age = 11.5 years) or a control group (N = 16, mean age = 11.3 years). Study models, cephalograms, and tomograms of the patients, taken at the beginning and at the end of the study period, were examined. Statistically significant differences between groups were found for positional changes of mandibular first molars and incisors, and changes in arch dimensions. The results indicate that the lingual arch can help reduce arch perimeter loss, but at the expense of slight mandibular incisor proclination.

Cephalometry↗
PubMed1997

Variability of facial photographs for use in treatment planning for orthodontics and orthognathic surgery.

Facial photographs are commonly used preoperatively for recording and analyzing skeletofacial and dentofacial deformities prior to orthodontics and/or orthognathic surgery. This study was undertaken to determine the reproducibility of facial photographs over time in any individual patient. Twenty subjects had full-facial frontal and lateral, frontal smile, and lip-to-tooth length (incisor show at rest) photographs taken on 5 different days over a 7- to 14-day period. A total of 18 linear and angular measurements were made on each set of photographs. Standard errors of the 18 measurements over time were generally moderate but varied widely, suggesting that facial photographs have the potential to provide reliable diagnostic information in some cases. In any individual patient, however, there were some variations within measurements that were clinically unacceptable. Measurements made from pictures of the smile were significantly less reliable than those taken at rest, and measurements of vertical head posture and lower lip length were found to be the least reliable. This study suggests that some measurements from facial photographs are generally reproducible over time, but significant individual variations do occur.

Adult↗
PubMed1995

Condylar movement and mandibular rotation during jaw opening.

Inaccurate description of mandibular rotation can have profound effects on orthognathic surgical treatment planning and surgical outcome, as well as affect the precision of appliances fabricated on articulators. Disagreement exists concerning movements of the condyle during jaw opening. Although mandibular function is often described as rotation around an instantaneous center located outside of the condyle, many believe that jaw opening occurs around an axis of rotation that remains fixed at the center of the condylar head. In this study, condylar movements and centers of mandibular rotation during jaw opening were examined in normal subjects with the Dolphin Sonic Digitizing System. All of the subjects demonstrated both translation and rotation of the condyle during initiation of jaw opening, and none had a center of mandibular rotation located at the condylar head. The findings support the theory of a constantly moving, instantaneous center of jaw rotation during opening that is different in every person. There were also differences in movement within the subjects between experimental trials. The uncertainty of predicting mandibular rotation for a given patient should be considered when planning surgical treatment and fabricating orthodontic appliances.

Cephalometry↗
PubMed1995

The ground rules for arch wire design.

All force systems applied to a tooth are composed of either single forces and/or couples. The application of a force through the center of resistance of a tooth will result in translation of the tooth. The application of a force to act at points other than through the center of resistance of a tooth will produce different tendencies for rotation. Tooth rotation resulting from the application of a force always creates a simultaneous tendency to move the center of resistance of a tooth in the direction the force is acting. In contrast, the location of a couple on a tooth is irrelevant to the resulting tooth movement. A couple can never move the center of resistance, and with a couple the center of rotation and the center of resistance will always be coincident. The equilibrium forces, associated with a moment of a couple, also are single-point forces and can produce different tooth movements depending on where they are applied. All tooth movement must be either translation and/or rotation as defined at the tooth's center of resistance.

Dental Stress Analysis↗
PubMed1995

One-couple orthodontic appliance systems.

One-couple orthodontic appliances are capable of applying well-defined forces and couples to effect controlled tooth movement during treatment. There are two sites of attachment: one in which the appliance is inserted into a bracket or tube where both a couple and force is generated, and one at which the appliance is tied as a point contact where only a force is produced. Using relatively simple designs, powerful biomechanical force systems that are easy to discern clinically can be applied to move teeth according to a prescribed plan. Several one-couple appliances are described to move individual or groups of teeth in all three dimensions. A complete biomechanical analysis of each appliance is presented and clinical reports follow each description.

Cuspid↗
PubMed1995

Two-couple orthodontic appliance systems: torquing arches.

Twists placed in an arch wire between incisor brackets are often used in an attempt to obtain root torque. This is only partially effective because of the equal and opposite reciprocals acting on the adjacent teeth. Alternatively, a V-bend in a torquing arch, inserted at only the molar and incisor brackets, may use the bending properties of the arch wire to create dissimilar moments in a two-bracket system. If the greater moment is present at the incisors, all of the incisors are rotated en masse in the same direction, with the associated equal and opposite vertical equilibrium forces directed at the incisors and molars. The lesser moment at the molar also usually has equilibrium forces that may reduce or supplement vertical forces at the molar and incisor depending on the magnitude and direction of the moment present. If the arch wire is unrestrained the resulting tooth movement shows rotation of the incisors around the CRes and movement of the CRes in the direction of the vertical equilibrium force present. The alternative use of a single force to rotate incisor crowns facially results in a reciprocal distal force at the posterior teeth and rotation of the incisors with a center of rotation apical to the CRes.

Dental Stress Analysis↗
PubMed1995

Creative arch wires and clinical conclusion.

When two successive couples are present, the absolute value of the moment at each bracket cannot be clinically determined. The larger moment can be identified, however, and this will show the direction of the associated equilibrium forces. If the couples at two adjacent brackets produce moments in opposite directions, the associated equilibrium forces are also in opposite directions. The net equilibrium force present at each bracket is in the direction of the equilibrium force associated with the larger moment, but the magnitude of the force is reduced by the oppositely directed equilibrium force associated with the lesser moment. If the couples at two adjacent brackets produce moments in the same direction, their associated equilibrium forces are also in the same direction and the net equilibrium force present at each bracket is the sum of the equilibrium force associated with each moment.

Dental Stress Analysis↗