3-11 An air-activated pantograph for recording mandibular movements.
Fig 3-12 Tracings are shown for a pantograph in which all recording tables are attached to the mandible and all styli are attached to the maxilla. Styli are shown in their initial positions. (a) Left lateral excursion; (b) right lateral excursion; (c) protrusive excursion.
Registration of Condylar Movements
To faithfully simulate the condylar movement on an articulator, it is necessary to obtain a precise tracing of the paths followed by the condyle. This can be achieved most accurately by means of a pantographic recording, which will capture all of the characteristics of the mandibular border movement from its optimum position to its most forward and most lateral positions.
The pantograph consists of two facebows. One is affixed to the maxilla and the other to the mandible, using clutches that attach to the teeth in the respective arches. Recording styli are attached to the one member, and small tables upon which the tracings are made are attached to the other member of the instrument, opposite the styli. There are both horizontal and vertical posterior tables attached in the vicinity of the hinge axis on each side of the pantograph. There are also two tables attached to the anterior member of the bow, one on either side of the midline (Fig 3-11).
The mandible goes through a series of right and left lateral, as well as protrusive, excursions. The styli on one facebow scribe on the recording tables the paths followed by the condyles in each movement (Fig 3-12). When the pantograph is attached to the articulator, various adjustments are made until the movements of the articulator will follow the same paths scribed on the tracings during mandibular excursions.
The pantographic tracing can only be utilized to full advantage when used with a fully adjustable articulator. To adjust the settings of a semi-adjustable articulator, wax interocclusal records are used. The patient closes into a heatsoftened wax wafer in a right lateral protrusive position and maintains that posture until the wax has hardened. The procedure is repeated with another wax wafer for a left lateral protrusive position. The wax wafers are then placed, first one and then the other, on the articulated casts. After the right lateral wafer is used to adjust the condylar inclination for the left condyle, the left lateral wafer is used to adjust the right condylar inclination. Complete details of the technique are described in chapter 4.
Advances in electronics and computers have brought about the introduction of new electronic pantographs that determine the condylar settings of the articulator. One type of electronic pantograph is similar to a traditional pantograph, with the styli and recording tables replaced by electronic senders and receivers. Another type utilizes a sender unit located at the end of a bite fork that is attached to the mandibular teeth. A receiver unit is suspended from a facebow mechanism directly above it. With both types of instruments, as the patient moves the mandible through the border movements, information is recorded and displayed on a small computer. This information can then be used to adjust the condylar settings on a fully adjustable or semi-adjustable articulator.
References
1. Posselt U. Physiology of Occlusion and Rehabilitation, ed 2. Oxford: Blackwell Scientific, 1968:55.
2. Hobo S, Shillingburg HT Jr, Whitsett LD. Articulator selection for restorative dentistry. J Prosthet Dent 1976;36:35–43.
3. Hodge LC, Mahan PE. A study of mandibular movement from centric occlusion to maximum intercuspation. J Prosthet Dent 1967;18:19–30.
4. Weinberg LA. An evaluation of the face-bow mounting. J Prosthet Dent 1961;11:32–42.
5. McCollum BB, Stuart CE. Gnathology—A Research Report. South Pasadena, CA: Scientific Press, 1955:39.
6. Kornfeld M. Mouth Rehabilitation: Clinical and Laboratory Procedures, ed 2. St Louis: Mosby, 1974:48,336.
7. Schallhorn RG. A study of the arbitrary center and the kinematic center of rotation for face-bow mountings. J Prosthet Dent 1957;7:162–169.
8. Beyron H. Orienteringsproblem vid protetiska rekonstruktioner och bettstudier. Sven Tandlak Tidskr 1942;35:1–55.
9. Beck HO. A clinical evaluation of the arcon concept of articulation. J Prosthet Dent 1959;9:409–421.
10. Lauritzen AG, Bodner GH. Variations in location of arbitrary and true hinge axis points. J Prosthet Dent 1961;11:224–229.
11. Gysi A. The problem of articulation. Dent Cosmos 1910;52:1–19.
12. Teteruck WR, Lundeen HC. The accuracy of an ear face-bow. J Prosthet Dent 1966;16:1039–1046.
13. Bergstrom G. On the reproduction of dental articulation by means of articulators—A kinematic investigation. Acta Odontol Scand Suppl 1950;9(suppl 4):1–131.
14. Guichet NF. Procedures for Occlusal Treatment—A Teaching Atlas. Anaheim, CA: Denar, 1969:35.
15. Whitsett LD, Shillingburg HT Jr, Keenan MP. Modifications of a new semi-adjustable articulator for use with a caliper style ear face-bow. J Calif Dent Assoc 1977;5(4):32–38.
Table 3-1 Accuracy of arbitrary hinge axis points*
| Measurements and landmarks for arbitrary hinge axis points | Arbitrary points within 6 mm of kinematic hinge axis points (%) | Investigator(s) |
|---|---|---|
| 13 mm from posterior margin of tragus to canthus | 98.0 92.158.3 | Schallhorn7 Beyron8 Beck9 |
| 13 mm in front of anterior margin of meatus | 16.7 40.0 | Beck9 Lauritzen and Bodner10 |
| 13 mm from foot of tragus to canthus | 33.0 | Teteruck and Lundeen12 |
| 10 mm anterior to center of external auditory meatus and 7 mm below Frankfort plane | 83.3 | Beck9 |
| Ear axis | 75.5 | Teteruck and Lundeen12 |
*Data from Whitsett et al.15
4 Interocclusal Records
After the maxillary cast has been accurately affixed to the articulator using a facebow, the mandibular cast must be oriented to the maxillary cast with equal exactitude to be able to diagnose the patient’s occlusion.1,2 Centric relation records are used to replicate, on the articulator, the relationship between the maxillary and mandibular arches that exists when the condyles are in their most anterosuperior position in the glenoid fossae. Lateral interocclusal records are used to adjust the condylar guidance of the articulator. Then, it is possible to observe tooth relationships and identify deflective contacts and/or other occlusal discrepancies from the casts on the articulator. When this information has been gathered and assessed, a determination can be made as to what corrective measures, if any, will be performed on the occlusion.
A distinction must be made between mounting for diagnosis and mounting for treatment. The attachment of casts to an articulator for diagnosis will be done with the condyles in a centric relation position. When casts are articulated for restoration of a significant portion of the occlusion, it also may be done with the condyles in the centric relation position. However, the beginning operator usually restores only limited segments