Instrumented Analysis of Jaw Movements Dental

Instrumented Analysis of Jaw Movements Dental

By the expression "instrumented analysis of jaw movements" is meant the dynamic tracing of mandibular movements and their diagnostic interpretation. According to our current understand­ing, this is a supplemental analytical element that provides limited information useful for com­plementing the patient history and manual functional analysis. Instrumented analysis of jaw movements is especially useful for:

determining the joint values of the individual patient (curve and inclination of the condylar
path, Bennett angle, course of the mediotrusive and laterotrusive tracks) for programming the
joints of an articulator, and

describing the paths of condylar movements during both active and manipulated mandibular
movements, as well as for analyzing condylar displacements caused by the occlusion.

Mechanical and electronic recording systems

Left: SAM Axiograph for making direct mechanical tracings of hinge axis movements. This system can also be further modified to form an electronic recording system (e.g. Axiotron).

Right: The String Condylocomp LR3 for making computerized record­ings of hinge axis movements with­out contacting the joint regions.

Every mandibular movement can be defined as a rotation around an imaginary stationary or moving transverse axis through the temporomandibular joints. This hinge axis, as a nearly constant element of mandibular function, forms the frame of reference for all joint-related registration methods (Le Pera 1964, Winstanley 1985).

If the imaginary axis of rotation of the mandible is deter­mined exactly, then mandibular movements that are a com­bination of rotation and translation can be reproduced as a pure movement of the hinge axis. When corrected to the patient's intercondylar distance (distance from the right to the left condyle) the tracing of hinge axis displacement cor-

responds to the true glide path. This is the basic principle of all hinge-axis-related registration systems.

Any procedure may be suitable if it can record mandibular movements in two or three dimensions and, depending upon the stringency of the diagnostic demands, in some cases also their speed. Electronic and computerized regis­tration systems offer the possibility of convenient data stor­age. An additional advantage is that these can adjust mea­surements made outside the joints to conform to the intercondylar distance and thus correct the projected path tracings and render them as actural condylar translations. An important diagnostic benefit is the ability to directly

Instrumented Analysis of Jaw Movements

compare movement paths that were drawn both with and without tooth contact (Slavicek 1981).

This assumes, of course, that the registration system is mounted independently of the occlusion (Kubein et al. 1979, Janig et al. 1980, Slavicek 1981). The patient must be able to freely assume his static and dynamic occlusion and execute movements without interference from the recording appara­tus. If the tooth-guided and non-tooth-guided paths of a defined movement (e.g. protrusion or mediotrusion) coin­cide, then the occlusion is exerting no clinically relevant forced guidance upon the temporomandibular joint. This can

be considered evidence of occlusoarticular harmony. In addi­tion, tracings of active and passive movements can be super­imposed to complement the manual functional analysis.

With the aid of instrumented analysis of movements, dis­turbances in the course of mandibular movements and occlusion-induced displacements of the condyles can be verified earlier and with higher resolution than would be possible through clinical manipulation. Important from the legal standpoint is the ability to document and store graph­ically or electronically each patient's movement patterns for later evaluation and comparison.

Transverse hinge axis of the mandible

The range of motion of any point on the mandible can be defined by the extent and coordination of rotation and translation of the transverse hinge axis (red).

Principle of movement of the condyle in the sagittal plane

The temporomandibular joint can be described not just as a rotating and sliding joint, but also as a dou­bly rotating joint.

One rotational movement of the condyles takes place around their functional transverse axis, while the other occurs as they orbit around a second axis located in the temporal bone (Kubein-Meesenburg 1985).

Anatomical preparation of a temporomandibular joint in protrusive condylar position

Macroscopic sagittal section of a human temporomandibular joint. The protrusive path of the hinge axis, represented by the red line, is largely determined by the radii of curvature of the contacting func­tional surfaces of the articular emi­nence, articular tubercle, and condyle.

Instrumented Analysis of Jaw Movements

Mechanical Registration of the Hinge Axis Movements (Axiography)

The movement of any given point in the mandible can be defined by the magnitude and coordination of rotation and translation of the transverse hinge axis. The static and dynamic displacements of the mandible in the three dimen­sions of space must be recorded in their relation to defined measuring points on the hinge axis. Only in this way can the translatory movement of the mandible executed in combi­nation with rotation be measured without paraxial distor­tion effects. In contrast to classic pantography, in which the mediotrusive and laterotrusive pathways were recorded on

registration plates placed beside the axis, axiography per­mits spatial measurements of mandibular movements to be made from the hinge axis (Mack 1979,1980). The tracings of movements are called axiograms. Axiography, with its mechanical tracings, serves primarily to gather data on the individual patient's joints in preparation for programming the joints on the articulator. Usually, protrusive axiographic tracings are adequate for evaluation of the curvature and inclination of the sagittal condylar path. Measurement of the medial displacement of the mandible that accompanies

Schematic drawing of the SAM Axiograph, Type III

Flag bow

Nasion relator

Anterior rod

Upper sidearm

Alignment flag with ear piece
and alignment pin

Recording flag

Mastoid and vertex support rod
assembly

Mastoid support

Vertex support

Flag sidearm extension rod

Posterior   crossbar (reference
alignment gauge)

Elastic neckband

Recording bow

Tray clutch

Anterior rod of the recording
bow

Sidearm of the recording bow

Alignment tube

Universal clamp for anterior rod

Hinge axis locating styluses

Hinge axis marking stylus

Recording assembly with lead
holder

Dial gauge with lead holder

Placing the flag bow

After loosening the thumbscrews, the side-arms are pushed medially until the ear pieces of the align­ment flags are securely placed in the orifices of the ears.

Right: Placement of the ear pieces and the lateral alignment pins has defined an arbitrary hinge axis.

Axiography

lateral movements serves to determine the Bennett angle and the basic form of the Bennett movement of the mediotruding condyle (e.g. immediate side shift). The clini­cian should be able to find these same mediotrusive paths through additional manipulation. Only in this way can one document the condylar border movements that may be experienced by the patient during parafunctional activity.

For tracing the movements relevant to the programming of the articulator it is usually adequate to use a tray clutch,

which is closed on its occlusal surface, to attach the mandibular recording bow to the lower dental arch. This of course precludes registration of tooth-guided mandibular movements. If axiography is to also provide information on the influence of the occlusion upon the dynamic function of the temporomandibular joints, however, then the mandibu­lar registration bow must be fixed to the buccal and labial surfaces of the lower teeth with a special adapter that leaves the occlusal surfaces free (Slavicek 1981).

Adapting the nasion relator

The nasion relator is adjusted by means of the anterior thumbscrew clamp until the flag bow is held against the head.

Left: If necessary, the nasion relator can be prefitted with a little silicone putty.

Attaching the vertical bars

The alignment of the flag bow to the skull is determined by the ear pieces and the nasion relator.

Left: Attaching the vertical rods for the mastoid and vertex supports.

Attaching the sidearm extension rod

The flag bow is fitted with a vertical rod on each side.

Left:    The    extension rods are screwed onto the side-arms.

Instrumented Analysis of Jaw Movements

Adjusting the posterior crossbar

The distance between the fixation screws of the posterior crossbar (= reference alignment gauge) is ad­justed so that it is the same as that between the fixation screws on the anterior bar.

Attaching the posterior crossbar

The previously adjusted posterior bar is slipped passively over the ex­tension rods.

Right: The posterior crossbar fur­ther increases the rigidity of the flag bow.

Placement of the vertex and mastoid supports

The screw clamps of the vertex sup­port are slipped over the vertical rods and, using light pressure, at­tached by tightening the thumb-

Rlght: Finally the lateral mastoid supports are brought into flat con­tact with the skin and fixed in this position.

The assembled flag bow in place

The elastic band that is lightly stretched from one mastoid sup­port to the other at the hairline gives the flag bow additional stabil­ity. The vertex and mastoid sup­ports provide transverse stability to the flag bow so that now the poste­rior crossbar and the flag side-arm extension rods can be removed.

Axiography

Insertion of the tray clutch

Soft wax strips are placed inside the tray at the midline and along the lingual flange to serve as intention­al fracture lines during removal of the tray after it is filled with impres­sion plaster.

Right: To minimize interference with the occlusion, the tray clutch filled with impression plaster is aligned with the midline and seated until it rests against the chewing surfaces. The patient then closes against the tray in the retruded mandibular position until the plas­ter has hardened.

Preparation of the
mandibular recording bow

Both side-arms are set in their sagit­tal planes at the zero mark and the vertical adjustment screws are brought to their middle positions. The alignment tubes are attached to the side-arms, and the side-arms are made parallel with one another. Left: The side-arms are positioned on the anterior cross rod (near top of photograph) so that the align­ment tubes rest securely, but with­out strain, in the seats milled into the sides of the thumbscrew clamps of the posterior crossbar. The posterior crossbar has been previously adjusted on the patient.

Placement of the recording
bow

The T-handle clamp connected to the center of the anterior rod is slid over the sagittal rod of the tray clutch. The side-arms are connect­ed to the flag bow by the alignment tubes. Any mechanical stress is re­lieved by gentle rotation of the an­terior rod.

Left: The alignment tubes are slid medially until they contact the alignment pins of the flag bow.

Fixation of the recording bow

While the side-arms are held so that the alignment tubes are in stable contact with the alignment flags, the recording bow is fixed to the posteriorly positioned mandible by tightening the clamps and thumb­screws.

Instrumented Analysis of Jaw Movements

Ideal orientation of the recording surfaces to the tracing axis

An essential precondition for an ar­tifact-free tracing of the hinge axis movements is that the recording surfaces be positioned perpendicu­lar to the hinge axis in centric jaw relation (Lotzmann 1990b).

Principle of coaxial mounting

The principle of coaxial mounting of the Axiograph III automatically leads to correct orientation of the recording bow to the flag bow.

Lateral view of the flag bow and recording bow

The arbitrary hinge axis passes through the recording surfaces at right angles.

Top view of the flag bow and recording bow

In the horizontal plane, too, the ar­bitrary hinge axis is perpendicular to the recording surfaces. The dis­tance between the two recording surfaces, necessary for later evalua­tion of the paths of movements, is measured and recorded.

Axiography

Attachment of the recording flags

Left: After removal of the two small alignment tubes, the alignment flags are removed from both side-arms.

Right: The recording plates, cov­ered by adhesive-backed graph paper, are attached to the flag bow through the same threaded holes that were used for the alignment flags.

Location of the hinge axis

Location of the hinge axis should be performed under cautious manual guidance of the mandible to mini­mize translational movements. (Movements are monitored with magnifying loupes!)

Left: The hinge axis locating stylus with a black or silver-colored collar is slid into the sidearm of the recording bow and fixed in place.

713 Avoidance of tooth contact against the tray clutch

The clinician carefully guides the patient's lower jaw posteriorly with the thumb as the index and middle fingers give support nearthe angles of the jaw in an anterosuperior di­rection. The patient should hold the mouth nearly closed, but must avoid contacting the tray with the teeth.

Relaxed opening of the jaws without translation

The patient opens the mouth ap­proximately 12 mm with as contin­uous a movement as possible. Ex­cessive jaw opening will lead to a pronounced forward bodily move­ment of the mandible, while insuffi­cient opening will make the preci­sion of the axis location appear greater than it actually is.

Instrumented Analysis of Jaw Movements

Principle for correcting the location of the hinge axis locating stylus

The direction and magnitude of movement of the hinge axis locat­ing stylus allow one to close in on the position of the imaginary axis (S). During the procedure the movements are paused and the po­sition of the stylus is corrected as necessary (Bosman 1974).

Vertical correction of the hinge axis locating stylus

By turning the knurled screw for tilting the side-arm vertically, the point of the locating stylus can be moved up or down to bring it near­er to the imaginary hinge axis.

Horizontal adjustment of the locating stylus

The knurled screw for moving the sidearm horizontally serves similar­ly to adjust the anterior-posterior position of the locating stylus.

Locating the individual hinge axis

Once the tip of the locating stylus no longer travels in a visible arc as the patient makes opening and closing movements (approximately 12 mm amplitude), it is lying on or in close proximity to the hinge axis of the mandible.

Axiography

Tracing the protrusive movement

Lateral view at the starting point with the mandible in centric.

Left: The hinge axis locating stylus is replaced by the tracing attachment with the yellow collar. The mandible is now guided into centric, and the assistant places the spring-loaded black pencil lead against the record­ing flag.

Maximal protrusion

Lateral view at maximal protrusive position.

Left: During the protrusive move­ment, the pencil lead traces the protrusive path of the hinge axis.

Normal joint function

Sagittal section of a human tem­poromandibular joint. The path of the axis drawn on the label corre­sponds closely to the functional joint surface of the temporal bone seen in the enlarged photograph.

Left: This hinge axis tracing, normal in length and curvature, is evidence of undisturbed joint function.

Marking the centric hinge axis point

To mark the centric hinge axis point, the yellow tracing assembly is replaced by the red attachment containing the flat-tipped axis marking stylus. The mandible is guided into centric, and the posi­tion of the hinge axis is marked on the recording label with red articu­lating film.

Left: Tracing of the protrusive path with the centric axis point marked in red.

Instrumented Analysis of Jaw Movements

723 Mounting the axiograph on edentulous patients

In cases in which the alveolar ridge is still well formed, it is possible to attach the recording bow to the edentulous lower jaw with suffi­cient stability by using the special mandibular clamp (AXO 350, SAM).

Intraoral central bearing pin and recording adapter

To impart adequate positional sta­bility to the mandibular record base during the registration procedure it is recommended that an intraoral central bearing pin and plate system be used (here: Gerber-Set). The registration adapter (Axiodapt, SAM) is adapted to the facial surface of the lower wax rim and anchored into the resin record base by means of the side screws.

Mandibular clamp in place

The mandibular clamp is connected to the registration adapter. It press­es against the inferior border of the mandible on both sides and there­by stabilizes the position of the mandibular record base.

726 Recording of the protrusive hinge axis path

The recording bow is attached to the registration adapter, as de­scribed above. The spring-loaded pencil lead traces the sagittal hinge axis path on the recording flag as the patient executes a protrusive movement with the central bearing pin sliding over the central bearing plate.

Axiography

Recording the mediotrusive hinge axis path

To record the mediotrusive hinge axis path (Bennett angle, "side shift") the patient performs a lat-erotrusive movement to the oppo­site side.

Left: In the mechanical version of the axiograph an analog dial dis­plays the magnitude of the medial movement of the condyle.

Principle of geometric
measurement of the
mediotrusive path

The magnitude of the condyle's medial shift can be calculated from the analogous displacement of the hinge axis point against the record­ing flag. If the distance between the flags (A) and the intercondylar dis­tance (B) are known, the actual movement of the condyle can be calculated.

Left: The individual mediotrusive path can be constructed from the incrementally measured values, as will be explained in the following figures.

Guided mediotrusion

The recording assembly with pencil lead has been replaced by the dial gauge with lead holder. Starting in centric position, the patient's jaw is carefully guided in a slow mediotru­sive movement.

Left: With attention to the starting point, the resulting tracing is cov­ered by a transparent, adhesive-backed millimeter grid.

730 Incremental determination of the medial shift with the aid of the dial gauge

Left: The patient is guided into centric. The dial gauge is read at this starting point and the value entered in the axiograph record book (see p. 260).

Center: Medial shift at 5 mm of mediotrusion.

Right: Medial shift at 8 mm of mediotrusion.

Readings of the medial shift must be made at intervals of at least 1, 2, 5, and 10 mm of mediotrusion.

Instrumented Analysis of Jaw Movements

Induced mediotrusion I

To determine the medial border movements of the condyle, it is rec­ommended that registration of the mediotrusive path also be carried out under manipulation. One of the dentist's hands exerts a controlled, medially directed force over the angle of the jaw, while the other hand braces the head.

Induced mediotrusion II

In this grasping technique for ma­nipulating a mediotrusion, the index and middle fingers rest on the zygomatic arch on the opposite side while the thumb exerts a medi­ally directed force on the angle of the jaw.

Record of the measured values and the graphic conversion

Each individual measurement is subtracted from the starting mea­surement. Black: measurements of an unguided mediotrusion. Red: measurements from a manipulated mediotrusion.

Each of these values is converted to an angular value and plotted graph­ically by using the conversion table (Fig. 734) and factoring in the dis­tance between the flags.

Conversion table

The section of a conversion table for an inter-flag distance of 160 mm is shown here. This allows the mea­surements of the medial shift of the condyle made outside the joint to be corrected to the intercondylar distance of the articulator and con­verted to degrees of angle.

Evaluating the Axiograms and Programming the Articulator 2&\_

Evaluating the Axiograms and Programming the Articulator

Articular factors have no meaning in the fabrication of occlusal splints with initial anterior/canine guidance and flat posterior occlusion, and in these cases the use of aver­age values for the condylar inclination and the Bennett angle settings are sufficient. The condylar inclination rela­tive to the Frankfort horizontal plane or the nearly equiva­lent axis-orbital plane is adjusted to the average setting of 45° and the incisal guidance to 10°. For the final instru­mented occlusal analysis or as a prelude to extensive prosthodontic restoration, the articulator should be pro-

grammed to the patient's individual parameters. This is even more important when the patient does not have the use of definite eccentric guiding surfaces. The clinical rele­vance of programmed articulator joints depends not only upon the quality of the movement tracings, but also on the precision of the centric jaw relation record. The adjustment of the articulator for analysis of movements only serves to approximate a perfect movement simulation. It is only the mobility of the teeth that limits the possibility of a perfect reproduction of the patient's individual jaw movements.

Drawing the reference plane

Left: The reference guide (Axiomat­ic) is mounted on the inner aspect of the right side-arm of the flag bow and adjusted so that the lower edge of the guide lies at the same level as the tip of the orbital pointer.

Right: The metal ruler is positioned to form a line from the reference guide to the red starting point of the hinge axis path, and this refer­ence line is drawn on the registra­tion grid.

736 Measuring the curvature and inclination of the condylar path

Left: The special measuring loupe is used to measure the condylar path.

Right: The base line of the angle scale covers the reference line on the registration grid. The zero point of the angle scale lies over the marked axis point. The angle of the condylar path is read from the 10-mm mark. Any curvature of the path is determined by comparison with the radii of curvature in the measuring loupe.

Estimation of the mediotrusive paths

Left: With the aid of the overlay film, the Bennett angle is deter­mined and the closest matching Bennett guide is selected.

Right: In the SAM system, Bennett guides with four different curva­tures and condylar paths with three different curvatures are available for customizing the articulator joints.

Instrumented Analysis of Jaw Movements

Hinge Axis Tracings (Axiograms) as Projection Phenomena

During extra-articular tracing procedures a distance exists between the place of registration (tip of the tracing pencil or receiving sensors) and the joint being analyzed. Therefore exaggerated tracings of the hinge axis paths (axiograms) can easily arise through projection phenomena (Klett 1982a). It is important that, in addition to the paraxial effect of an incorrectly located axis, this projection phenomenon be taken into account for a correct interpretation of the trac­ings. The only situation in which there is no projection dis­tortion on the axiogram is one in which both condyles start their protrusive and retrusive movements simultaneously

and with equal speed over condylar paths that are identical in curvature and length. If, on the other hand, the two condyles are asynchronous in their movements and travel asymmetrical paths, as is the rule, then the axiographic tracing will be malproportioned, flattened, shortened, or lengthened. This effect is especially noticeable in mediotru-sion in which the movement of the working condyle is reproduced as a distorted, backward-curving laterotrusion path. This projection phenomenon increases with increased distance of the recording point from the temporomandibu­lar joint.

Parallel movement of the hinge axis

Left: The condylar pathways can be accurately reproduced without re­gard to the distance between recording flag and joint only if both condyles move synchronously along paths that are identical in di­rection, length, and curvature.

Right: The same situation viewed from above.

Unequal protrusion

Left: If one condyle (here the left) follows a path that is flatter than that of the other condyle, the re­sulting tracings will be even flatter than the actual path on the first side and steeper than the actual path on the opposite side.

Right: If one condyle lags behind the other in its protrusive move­ment, the axiograph tracing of the slower condyle (here the left) will be flatter and shorter than the actu­al condylar path while the tracing of the leading condyle will be drawn longer and steeper.

Mediotrusion and laterotrusion

Left: An axiograph of the mediotru-sive side (right) will be steeper and longer than the actual condylar path, while the movement of the laterotrusive condyle will be com­pletely misrepresented by the trac­ing as a posterosuperior retrusive path.

Right: Superior view of the same situation.

Effect of an Incorrectly Located Hinge Axis on the Axiograms

Effect of an Incorrectly Located Hinge Axis on the Axiograms

Mandibular movement registration procedures that make tracings from an incorrectly located hinge axis run the risk of producing a distorted representation of the actual move­ment of the axis. Thus a clinically significant change in posi­tion of the condyle can be reduced to an almost point-like marking, while a pure rotation can appear as a gliding movement. Combined rotating and translating movements of the mandible may be traced incorrectly depending upon the rotational component. This phenomenon can be used to test for correct location of the axis. Precise determination of the axis is proven when there is minimal difference

between the tracings of protrusive and opening movements (Kohno 1972, Lotzmann 1987, Nagerl et al. 1991). If protru­sive and retrusive mandibular movements are not accompa­nied by opening and closing of the mouth, then the preci­sion of the hinge axis location bears no clinical relevance to the quality of the axiograms. The curvature and length of the tracings are unchanged. On the other hand, with mediotrusive movement the measurement of the Bennett angle can be affected.

Effect of an incorrectly located axis on a rotation-free protrusive tracing

A protrusive tracing (II) starting from an incorrectly located hinge axis (a) is identical in curvature, length, and inclination to a tracing (I) made from a point over the true axis (r).

Effect of an incorrectly located axis on an opening tracing

Depending on the position of the tracing axis (a) relative to the true axis (r), the axiograph will be more or less distorted. The path may be either elongated or run above or below the true path (red). From this it follows that a direct comparison of the protrusive and opening trac­ings can serve to test the correct­ness of the axis location. Both trac­ings should be virtually identical (Lotzmann 1990a).

Effect of an incorrectly located axis on the mediotrusive tracing

If the axiographic tracings are made over an incorrect axis (broken lines), which lies either posterior or anterior to the true hinge axis (red), the Bennett angle will appear either smaller (II) or greater (III) than when measured over the true axis (I).

Instrumented Analysis of Jaw Movements

Electronic Paraocclusal Axiograpy

In recent years a number of electronic registration proce­dures for recording mandibular movements, both close to the axis and at a distance from the axis, have been described (Gillings 1967, Korber 1971, Burckhardt 1982, Klett 1982b, Meyer and dal Ri 1985). Systems in which new attachments can be made to the conventional axiograph will be of spe­cial interest to practitioners already familiar with mechani­cal axiography. The principle of electronic axiography can be traced back to Meyer and dal Ri (1985). They replaced the mechanical analog dial with a high-resolution electronic sensor and substituted a resistance foil for the recording

graph paper. This made it possible for the first time to elec­tronically record a point on the hinge axis in three dimen­sions. Similarly operating systems that are commercially available are the Axitron (by SAM) and the Cadiax System (by Gamma). Complementing the conventional axiograph with electronic sensors offers the advantage of computer­ized determination of measurements, data processing and documentation of axis displacements. Besides the improved spatial resolution of the movement paths, a decisive advan­tage is that the movements recorded outside the joint, and therefore distorted, can be corrected to coincide with the

Electronic axiography

The Cadi ax-Record ing-System (by Gamma), consisting of two sensors with double styli, two recording flags, insulation amplifier, and a foot pedal, allows computerized determination of hinge axis move­ments. Simultaneous tracing of both axis points makes direct cor­rection of the axiograph for the pa­tient's intercondylar distance possi­ble.

Axiograph of a tooth-guided right lateral movement

Graphic PC representation of the hinge axis paths assisted by the Ca­diax software. The two lower sys­tems of coordinates represent movements in the sagittal plane while the upper systems plot the same movements in the horizontal plane. In the lower margin of the picture the numerical values are given for the positions of the crosshairs.

Profile of hinge axis movement

In this type of display, the lines con­necting the right and left axis points (hinge axis) at different points in time are projected in both the horizontal plane (top) and frontal plane (bottom). This pro­vides information on the relative acceleration of the two condyles.

Electronic Paraocclusal Axiograpy

actual paths of movement within the joint. This correction of the tracings for the intercondylar distance naturally requires that recordings for the two joints be made simulta­neously.

Still another advantage is the analysis of the speed and acceleration of movements of the axis which can provide information on the neuromuscular coordination of move­ments and mechanical obstructions of the joint. Both the Cadiax System and the String Condylocomp System can also measure rotation of the hinge axis and thereby determine, although with reduced precision, the calculated representa­tion of any point on the mandible (e.g. incisal point). To be

able to fully utilize the diagnostic capabilities, the face bow should be attached to the teeth without obscuring their occlusal surfaces. Only in this way can tracings of free and tooth-guided movements be compared directly with one another to determine whether or not the occlusal guidance exercises dominance over the temporomandibular joints. Axiograms of movements made by passive manipulation techniques can add worthwhile information to a manual functional analysis by providing, for example, documenta­tion of the loading direction.

747 Occlusion-free attachment of the mandibular recording bow

After the adapter is fitted to the teeth it is attached with a zinc phosphate cement (e.g. Harvard) or a polycarboxylate cement (e.g. Durelon).

Left: The paraocclusal registration adapter (Axiodapt) is adapted to a cast of the mandibular arch by adding cold-cure acrylic. An upper cast is placed in maximal occlusion against the lower cast to ensure that the adapter will not interfere with the occlusion.

Paraocclusal axiography of a left lateral excursion

Cadiax sensors are attached to the Axiograph III. In addition to transla-tional movements, the double styluses also permit registration of rotation of the hinge axis.

749 Testing the influence of the occlusion

The axiograph, corrected for pro­jection errors, reveals that during a tooth-guided movement of the mandible to the left a strong bal­ancing contact is causing a slight distraction of the condyle on the balancing side (circled in red).

Left: The nonworking interference on the upper and lower second mo­lars causes a distinct discussion of the other teeth, both anterior and posterior.

Instrumented Analysis of Jaw Movements

Superimposition of multiple axiographs

The Cadiax software also allows the overlaying of multiple color-coded tracings of jaw movements. The wide distribution of the tracings shown here could indicate record­ing artifacts (loosened adapter, loose flag bow), pronounced neu­romuscular incoordination, and/or "greater than normal play in the joints."

Direct comparison of tooth-guided and free protrusive tracings

Movements made with the teeth in contact can be compared directly with movements made in the same direction without tooth contact to determine whether there is harmo­ny between tooth guidance and joint guidance. The asymmetrical pattern of free protrusive move­ment shown here leads one to suspect that neuromuscular adap­tation to asymmetrical tooth guid­ance has taken place.

752 Bimanual grasp technique for upward manipulation of the mandible

By using the Dawson grasp, an ad­ditional superior or anterosuperior force can be exerted on the tem­poromandibular joints. If the re­silience of the joint does not allow a slight superior displacement of the axis points, then this indicates the presence of a functional compres­sion of the joints.

Display of the space for retrusive movement in the temporomandibular joints

These paths of movement dis­played in the sagittal plane (lower rectangles) and horizontal plane (upper rectangles) begin from the maximal intercuspation position. The mandible was guided manually into its rearmost position (green crosses). The retrusion paths should appear equal and should not ex­ceed 1.5 mm in length.

Electronic Paraocclusal Axiograpy

Manipulation technique to induce mediotrusion

To record the space of the temporo­mandibular joint used predomi­nantly for parafunctional move­ments, the tracing of the free medial excursion is supplemented by a manipulated medial condylar movement.

Tracing of an induced medial excursion

When a medially directed force is applied to the angle of the jaw, the condyle on that side initially moves medially and downward.

Recording of the opening movement

Because of the elastic deformation of the arch of the mandible, there is a chance that when the mouth is opened wide the registration adapter may become loosened from the teeth. For this reason, tracings of the maximum opening and closing movements should be made at the conclusion of the recording appointment.

Diagram of translating and rotating movements

The Cadiax software offers the ca­pability of representing the transla-tional and rotational components of a movement in diagram form. From this, conclusions can be drawn about the coordination of the mandibular movements.

Instrumented Analysis of Jaw Movements

758 Axiographic representation of deranged temporomandibular joint function

The left protrusive and retrusive tracings suggest anterior disk dis­placement with repositioning. Manual functional analysis confirms this suspicion. Presumably the striking difference in the paths on the right side is of neuromuscular origin. At the present time there is no conclusive evidence that the cause of joint clicking phenomena can be reliably discerned from axio­graphic tracings alone (Rammels-berg 1998).

Defining the treatment position of the mandible

In individual cases paraocclusal ax-iography may also be helpful in defining the treatment position of the hinge axis points, and thereby of the condyles.

Right: Here, the most retruded condylar position at which the disk is in its correct relation to the condyle has been determined by using the axiographic tracing (red dot).

Interocclusal registration

The axiograph is removed. The an­terior bite index serves to keep the mandible in the treatment position while the interocclusal relation is recorded with a firm-setting sili­cone or other suitable material.

Right: While monitoring the jaw re­lationship with the axiograph, the defined mandibular position is fixed by means of an anterior index made of cold-curing resin.

Mounting the casts

The interocclusal record is used to mount the mandibular cast in the therapeutic position previously de­termined with the help of the axio­graph. The occlusal splint for oc­clusal stabilization is fabricated at this intermaxillary relationship.