Model surgery prediction for mandibular midline distraction osteogenesis

Mandibular midline distraction osteogenesis is available as a treatment option for the correction of mandibular transverse arch deficiency. A model surgery technique is presented here through a case report that will allow the surgeon to predict the amount of transverse expansion that can be gained by this procedure. Utilizing measurements from a three-dimensional stereolithography model, the mandibular cast is mounted on a semi-adjustable articulator. The maxillary model is mounted onto the articulator using an interocclusal record. Acrylic straps are fabricated that relate the condylar elements of the articulator to the right and left mandibular dental segments. The mandibular model is sectioned at the midline, the hemi-mandibular segments are rotated laterally until the desired midline expansion is achieved and the mandibular model is luted into its new position. The post-expansion relationship of the maxillary and mandibular arches can be visualized on the articulator and provide useful information to the surgeon and orthodontist.     

Fabrication Method for a Mounting Jig and Cast Support for Mounting Complete Dentures

In complete denture fabrication, the definitive maxillary cast is mounted on an articulator using a facebow transfer or mounting jig, and the mandibular cast is mounted using an interocclusal record. The technique presented describes an easy and inexpensive method for fabrication of a mounting jig and rigid cast supports for mounting complete dentures.     

Posterior bilateral condylar displacement: its diagnosis and treatment.

One type of condylar displacement (posterior bilateral) was discussed as an etiologic factor in TMJ dysfunction. Joint noise, tenderness on muscle palpation, and acute TMJ pain are all considered signs of TMJ dysfunction. Any joint noise is considered to be an early dysfunctional symptom because of its higher incidence in association with palpable muscle pain or acute TMJ dysfunction. Sometimes the joint noise will immediately precede acute muscle pain and/or fluctuate with the painful symptoms. The treatment of bilateral posterior condyle displacement has been described. The mandibular anterior teeth were shortened and the maxillary posterior occlusion adjusted so that the mandible could be respositioned in an anterior position without increasing the vertical dimension of occlusion. A silver-plated maxillary cast was obtained and mounted on a semiadjustable articulator (Hanau) with a face-bow. The mandibular cast was mounted in the dysfunctional (retruded) centric relation. The articulator was moved into a protrusive position by the amount of anterior correction that is needed to reposition the condyles into the middle of the fossae symmetrically on both sides. The original TMJ radiographs provide the necessary information for this clinical judgment. Acrylic resin was placed in the space created between the condylar sphere and stop on the articulator. An acrylic resin temporary repositioning prosthesis constructed on the metal cast has two functions. It provides a therapeutic trial for the anterior condylar respositioning, and it holds the mandible in the therapeutic position while TMJ radiographs confirm the corrective position of the condyles in the fossae. After a successful 6 to 8 week trial period with remission of symptoms, a gold prosthesis was constructed on the same cast in the same therapeutic position. It remains to be seen whether, after several years, the condylar suspension system changes from a dysfunctional centric relation to a new functional centric relation in which the patient can no longer return to the posterior displaced condylar position in the fossa. Only with painstaking observations, accurate TMJ radiographs, complete documentation, and after-care can a more scientific approach to the diagnosis and treatment of TMJ dysfunctional pain syndrome be achieved.     

"Myo-Monitor centric": an evaluation

Ten patients had three “Myo-Monitor centric” records made at each of three appointments. Terminal hinge axis determination and interocclusal registration of centric relation were used to accurately mount maxillary and mandibular casts on a modified articulator. The characteristics of “Myo-Monitor centric” were investigated by: evaluation of the reproducibility of “Myo-Monitor centric” records; comparison of “Myo-Monitor centric” position to centric relation contact position and centric occlusion; comparison of the tooth contact on hinge closure from “Myo-Monitor centric” with centric relation contact; evaluation of the effect of the anteroposterior head position on the number and location of tooth contacts during “Myo-Monitor centric” mandibular closure; and a comparison of the anteroposterior relationships among “Myo-Monitor centric,” centric relation, and centric occlusion.Examination and appropriate statistical analysis of the data revealed several characteristics of “Myo-Monitor centric”: The axis of rotation determined by “Myo-Monitor centric” was always anterior and inferior to the patient's terminal hinge axis; “Myo-Monitor centric” registrations within individuals were non-reproducible; with “Myo-Monitor centric” registrations, centric relation contacts on the mandible were anterior to both centric relation and centric occlusion contacts on the maxillae; variation of anteroposterior head position affected Myo-Monitor-produced mandibular closure; and eight of ten patients had “Myo-Monitor centric” contact anterior to their centric relation contact.     

A Comparative Evaluation of Static and Functional Methods for Recording Centric Relation and Condylar Guidance: A Clinical Study

To evaluate and compare the centric relation and horizontal condylar guidance using interocclusal wax and extra oral Gothic arch methods and subjective evaluation of dentures thus fabricated. Centric relation and horizontal condylar guidance was recorded by using interocclusal wax and gothic arch tracing in 28 completely edentulous patients. These records were transferred to the articulator and difference in both values was recorded. After that patients were divided in two groups according to the centric relation and horizontal condylar guidance recording method used to achieve balanced occlusion. Response of the dentures was subjectively evaluated using “Woelfel subjective evaluation criteria”. Centric relation recorded by both the methods did coincide in 7.14 % of patients. Centric relation recorded by interocclusal wax was posterior to Gothic centric relation in 21.43 % of patients, and anterior to Gothic centric relation in 71.42 % patients. Gothic arch tracings gave higher mean guidance values on both the sides as compared to protrusive wax record in all the subjects, although the difference was statistically insignificant (P > 0.05). Subjective evaluation showed statistical insignificance for all the parameters in both groups. Gothic arch method records the centric relation at a more posterior position than the Static method, but it does not make any difference in clinical performance of the complete denture. Horizontal condylar guidance angle was approximately similar by both the methods.     

A comparison of articulator settings obtained by using an electronic pantograph and lateral interocclusal recordings

Articulator settings were obtained for two subjects 10 times in a 2-week period by using both a lateral interocclusal record technique and a Pantronic pantograph. The ORB and PSS articulator settings obtained from the two techniques were compared and the following conclusions drawn. 1. Over a 2-week period, the variance in the Pantronic pantograph ORB and PSS articulator settings was less than the variance in the setting obtained by using lateral interocclusal records. For the Pantronic pantograph technique, 95% of any ORB settings were within 2.5 degrees of the Pantronic pantograph mean and 95% of any PSS settings were within 1.9 degrees of the Pantronic pantograph mean. For the interocclusal record technique, 95% of the ORB settings made with interocclusal records were within 11.9 degrees of the mean for one subject and 13.4 degrees of the mean interocclusal records setting for the other subject. For the PSS settings, 95% of the interocclusal record settings were within 10.1 degrees of the mean setting for one subject and 11.6 degrees of the mean interoccusal record setting for the other subject. 2. In adjusting the ORB and PSS articulator settings, the maximum potential occlusal errors that may be produced by using the Pantronic pantograph are smaller than the maximum errors that may be produced in using the lateral interocclusal record technique.     

The role of the general practitioner in restoring patients with temporomandibular joint dysfunction

Treatment of temporomandibular joint pain, resulting from occlusal dysfunction, is divided into two phases. First, occlusal splint therapy is used to eliminate the initial signs and symptoms and to achieve stability in centric relation. In the second phase of treatment the occlusion is adjusted and, if indicated, restored by means of crown and bridge procedures. Casts, properly mounted in a semi-adjustable articulator, with the lower cast mounted in centric relation, can be extremely helpful for an occlusal analysis and a diagnostic occlusal adjustment in the articulator. Each occlusal adjustment procedure in the mouth should be preceded by an initial study, occlusal analysis and occlusal adjustment on articulator mounted casts. The two main criteria for restoring the occlusion are: maximum intercuspation occurring in centric relation and disocclusion of the posterior teeth during excursive movements by means of anterior guidance. Patients with a history of temporomandibular joint pain and dysfunction usually have a limited adaptive capacity of even the smallest occlusal imperfection. In order to cope with the occlusal restoration of patients with such a low level of occlusal tolerance the final crowns and bridges should be cemented temporarily for a period of at least 3 months. A matt gold surface will be very helpful to locate undesirable occlusal contacts during temporary cementation.     

Movement between centric relation contact position and the intercuspal position.

Casts of 42 patients free from temporomandibular joint problems were mounted on an articulator in centric relation contact position. The movement of the horizontal axis of rotation was measured when the casts were moved from centric relation contact position to the intercuspal position. Measurements of the vertical and horizontal movements of the incisal pin were also made during this movement. There was a highly significant correlation between the movement of the horizontal axis in the horizontal plane and the ratio of vertical to horizontal movement as measured at the incisal pin. The greater this ratio was, the smaller the horizontal movement of the axis was; the smaller the ratio (the larger the horizontal component) was, the larger was the horizontal movement of the axis. The clinical implications are discussed.     

Jaw relation records for fixed prosthodontics

This article discusses and reviews general principles of jaw relation records, including the purpose of a jaw relation record and the concept of a tripod of vertical support with adequate horizontal stability to allow opposing dental casts to be mounted accurately on an articulator. The use of the maximum intercuspal position for the vast majority of patients is favored when the goal of restorative treatment is to maintain a patient's pretreatment intercuspation and vertical dimension of occlusion. In addition, articulator choice, purpose of a face bow, and materials for jaw relation records are discussed. Common errors in making impressions, pouring impressions,mounting casts, and making interocclusal records are elucidated, providing the practitioner important information with which to avoid inaccuracies that may lead to additional time spent making intraoral occlusal adjustments at the insertion of fixed restorations.     

Patient response to variations in denture technique. Part III: Five-year subjective evaluation.

Dentures were constructed for 64 patients by two different techniques. One technique, designated as "complex," involved more complicated procedures such as a true hinge axis location, balanced occlusion, dentures remounted on an articulator after processing with new interocclusal records, and occlusal corrections made on the articulator. The "standard" technique involved an arbitrary mounting of the maxillary cast on the articulator, arranging the occlusion with centric relation coincident with centric occlusion but without a balanced occlusion, and making occlusal corrections in the mouth. Subjective evaluations were made for each of the 64 patients at initial placement of the dentures and for all active patients at five yearly recall visits following placement. The evaluation method was designed to determine clinical differences between the dentures made by the two techniques. At the end of 5 years, the data obtained at five yearly recall visits were subjected to statistical testing. These tests were performed to determine if the technique by which the dentures were made had any effect on the performance of the dentures that could be detected clinically. The results of the test showed that there was no significant difference between dentures made using two denture techniques that could be detected by subjective means.     

Checking the occlusal relationships of complete dentures via a remount procedure

Correct occlusal relationships are part of the successful prosthetic treatment of edentulous patients. Occlusal checking should be performed via a remount procedure because denture base materials and fabrication procedures cannot provide dimensionally accurate complete dentures. Occlusal errors caused by the adjustment of denture bases to the denture foundation after a certain period of wearing can also be corrected by means of remounting. The following remount procedures for complete dentures are described: fabrication of transfer casts, transfer of a maxillary denture with a facebow, centric relation record, and mounting of dentures with transfer casts in an articulator with a dental stone. Deflective occlusal contacts of denture teeth in centric occlusion can be eliminated by selective grinding and by tooth-guided excursive movements. In complete denture treatment, priority is given to anterior/canine-guided occlusion.     

Comparative evaluation of sagittal condylar guidance obtained from a clinical method and with cone beam computed tomography in dentate individuals

Statement of problemProgramming semiadjustable and fully adjustable articulators involves time-consuming clinical steps which can be avoided if an accurate radiographic method can accurately determine the condylar guidance angles.PurposeThe purpose of this clinical study was to compare the sagittal condylar guidance in dentate individuals as determined by a clinical method, protrusive interocclusal record, and a radiographic method, cone beam computed tomography. If the methods show a correlation, then cone beam computed tomography can be used as a time-saving method of programming an articulator for patients requiring a cone beam computed tomography scan.Material and methodsA total of 40 participants (20 men and 20 women) within the 20 to 40 years age group were enrolled according to the inclusion and exclusion criteria. Cone beam computed tomography scans were obtained, and by using an appropriate software program, the sagittal condylar guidance was measured for both sides. A protrusive interocclusal record was obtained by using polyvinyl siloxane material. The maxillary cast of each participant was mounted on a semiadjustable articulator with a facebow transfer, and the mandibular cast was mounted with a maximum intercuspal record. The protrusive record was then transferred to the articulator for programming.ResultsThe right and left sagittal condylar guidance values obtained from both the protrusive interocclusal record and cone beam computed tomography method were comparable, with no significant differences (P>.05). The difference in condylar inclination values for both sexes obtained from both methods for both sides were not statistically different (P>.05). With increasing age, condylar inclination values obtained from both methods tended to decrease. The values for sagittal condylar guidance obtained from both methods (protrusive interocclusal record and cone beam computed tomography) were comparable and correlated.ConclusionsCone beam computed tomography measurement involves stable bony landmarks and can be standardized, whereas clinical methods are time consuming and can provide inaccurate results because of the instability of the materials used to register the maxillomandibular relationship. Thus, cone beam computed tomography can be used to obtain the sagittal horizontal guidance for programming semiadjustable and fully adjustable articulators for patients requiring a cone beam computed tomography scan.     

Procedural problems in using the Denar pantograph as a transfer-bow.

A method has been described for using zinc-oxide/eugenol paste as an interclutch support when the Denar pantograph is used as a transfer-bow. Using this technique a stable centric relation position can be maintained during the maxillary cast mounting procedure and the subsequent setting of the articulator to the pantographic recordings.     

Reliability of a measuring-procedure to locate a muscle-determined centric relation position

Although reproducibility of centric relation position, determined with an anterior deprogramming device, a leaf gauge, is widely accepted among clinicians, data confirming statistical evidence are lacking in the current literature. The objective of this study was to prove clinical reliability of a measuring-procedure to locate the centric relation position, determined with the leaf gauge. A sample of 15 subjects (6 men, 9 women, age 22 to 46), assessed with the Research Diagnostic Criteria to rule out any TMD-signs, was selected. Three observers each took three sequential interocclusal records with the leaf gauge, to mount a set of casts into the centric relation position in an articulator. Out of 15 subjects, 12 (5 men, 7 women) fitted criteria of precision--three out of three interocclusal records for each of the three observers--in a split-cast procedure. The applied statistical method is an analysis of variance model (ANOVA) with two factors for 3 observers and 12 subjects. The variance components estimation procedure is MIVQUE (0). The a was set at 0.05. No significant difference between observers for the measured variables sagittally (XL, XR), transversally (YL, YR), and vertically (ZL, ZR) could be found. MIVQUE variance components estimates for observers is < 0, varies for subjects from 0.04 to 0.20 and varies for error from 0.12 to 0.25 mm. Reliability of a measuring-procedure to locate a muscle-determined centric relation position could be established satisfactory.     

Impact of arbitrary and mean transfer of dental casts to the articulator on centric occlusal errors

When fabricating dental restorations, casts are usually transferred to the articulator based on arbitrary hinge axes or mean values instead of true hinge axis points. Using arbitrary hinge axis points or mean values can lead to occlusal errors if the vertical relation is changed in the articulator (e.g., when a centric record is used). This study predicted the probability of occlusal errors occurring in a group of subjects when casts are mounted based on arbitrary hinge axis points or mean values. In 57 healthy volunteers, true hinge axis points, arbitrary hinge axis points, right infraorbital point, maxillary incisal point, and the palatal cusps of the second molars were determined. Mean hinge axis points were established based on Balkwill angles between 17° and 25°. Occlusal errors evoked by cast mounting in relation to arbitrary or mean axes compared to true hinge axes were calculated. Errors were determined for vertical relation settings of 2 and 4 mm. With 2 mm vertical relation, occlusal errors ≥340 μm occurred with a 10% probability with arbitrary hinge axis mounting. At the same probability level, the error increased moderately to ≥440 μm with mean value mounting and a Balkwill angle of 17°. With a Balkwill angle of 25° occlusal errors ≥1,120 μm occurred with 10% probability. Occlusal errors increased considerably with a vertical relation setting of 4 mm. If vertical relation shall be altered, a transfer of the casts according to arbitrary hinge axes is recommended. If casts are transferred according to mean values, errors are bigger depending on the articulator used.     

Processing changes in complete dentures: posterior tooth contacts and pin opening

Dentures were constructed for 50 patients. The centric relation contacts were marked and photographed before removing the finished trial dentures from the articulator and again on the same articulator and same stone mountings after processing. The amount of incisal pin opening was measured and recorded after processing. An attempt was made to analyze the patterns of centric relation contacts after processing and to determine if there was a correlation of pin opening and tooth contacts. It was found that there was a definite shift of the tooth contacts to the more posterior teeth after processing but that the amount of pin opening did not seem to be related to the number or location of the tooth contacts. The magnitude of pin opening seems to depend upon the amount of shift rather than the direction.     

A new articulator emphasizing centric occlusion and the anterior determinants.

A new articulator is described which has the advantages of the rigidity of a simple articulator in the upper member and the flexibility of an adjustable articulator in the lower member. A link between the members and the frame along with the posterior controls establishes a full range of functional chewing movements and defines the extreme lateral or border paths. The articulator has condylar element controls which permit releasing and remounting the mandibular cast in a manner that serves the same function as the split-cast technique, but this method is faster and shows the amount of discrepancy. The condylar element control is an improvement over existing devices for comparing interocclusal records in that it not only indicates differences in position but it also provides quick remounting of the casts in a working articulator. Other features of the articulator are: (1) a condylar lock mechanism which is activated by only a half turn, (2) adjustable spring tension, (3) precise long centric and wide centric controls, (4) an incisal pain which can be removed and replaced on the articulator without changing its setting, (5) a Bennett movement carefully selected to avoid the complication of a pantograph type of face-bow, and (6) a new sponge wall type of mounting plate which supports both casts for simultaneous mounting.     

Sagittal condylar guidance as determined by protrusion records and wear facets of teeth.

The maxillary and mandibular casts of 45 healthy and dentulous subjects, with conspicuous wear facets on canines and molars, were mounted on a semiadjustable articulator. The sagittal condylar guidance was determined by two methods: (1) using a protrusion wax interocclusal record and (2) by matching the wear facets of opposing canines and contralateral molars. There was a substantial bilateral symmetry of the right and left sagittal condylar guidance angles using both methods. There were, however, significant differences between the mean angles of the two methods, about 31 degrees (protrusion record) versus about 24 degrees (wear facets). This, in association with rather low coefficients of linear determination, suggested that the two methods of recording the sagittal condylar guidance angle were based on totally different phenomena.     

Device for recording the path of insertion for removable partial dentures

Some negative outcomes of oral rehabilitation using removable partial dentures (RPDs) can be prevented when the framework of the RPD is planned with mounted diagnostic casts that have been analyzed in a dental surveyor. Recording the established path of insertion can be difficult when the procedure uses a pin that is cemented in the cast base, and the casts are mounted in an articulator. This article presents a procedure for a pin device to record the path of insertion of RPDs. This device serves the same purpose as the cemented pin but can be easily removed and replaced.     

Principles for selecting interocclusal records for articulation of dentate and partially dentate casts.

Minimizing the orientation error of the working and opposing casts on the articulator should reduce the extent of intraoral adjustment of restorations before their placement. This article defines and reviews principles such as the tripod of vertical support (three widely spaced occlusal contacts) and adequate horizontal stability, which enable opposing dental casts to be held together in a stable and reproducible manner at the time the mandibular cast is mounted to the articulator. During the restoration of the dentate or partially dentate patient, where restoration is to be coincident with pretreatment maximum intercuspation, the goal of the interocclusal record is to provide stability and/or support for the casts. The types of interocclusal records are organized into categories and designs based upon the remaining vertical support and horizontal stability of the dentition. The clinical indications, limitations, design, and composition of a variety of records for each of these categories are reviewed and discussed.