Fully Adjustable Articulators System Errors
Using these articulators, it is possible to mimic the individual movements of dynamic occlusion as far as possible, provided all the relevant geometric values have been determined following special registration and model transfer methods. Devices of this kind might also be referred to as simulators of masticatory movement. The variations from the actual movement paths are so minimal that they can be disregarded in practice.
The reference plane for fully adjustable articulators is preferably the hinge-axis orbital plane (auriculo-infraorbital plane, Frankfort plane); the Camper plane and the midface horizontal or patient horizontal plane also act as reference planes for some articulators. The devices are supplied in arcon or nonarcon versions.
Precise mounting of models requires timeconsuming registration methods. All the values must be measured and transferred individually. Discrepancies between the individual and the simulated movement paths are usually due to handling and measuring errors.
When using a fully adjustable articulator (or individually adjustable articulator), it must be possible to perform all the movements out of centric occlusion that are possible for the patient while maintaining tooth contact. Therefore, articulators must meet the following conditions:
Individually adjustable values for:
- Sagittal condylar path inclination, left and right
- Bennett angle, separately left and right
- Shaping of individual incisal guidance or variably adjustable incisal guide table
- Intercondylar distance
- Position of the occlusal plane relative to joint axis or cranium, ie, the exact position of the occlusal field in relation to the hinge axis in all spatial directions
- Specially shaped condyles and condylar paths
- Distraction adjustment for relieving compressed TMJs
- Exact replication of the individual Bennett movement
- Analogous movement directions
- Adequate working space for working models
In an articulator, the primary aim is to simulate mandibular movements with tooth contact. Open mandibular movements are of minor importance in denture fabrication, namely when shaping the denture base: The denture base must not impinge on muscle attachments and ligaments that tighten during open mandibular movement. This movement of muscle attachments and ligaments cannot be reproduced with the articulator.
Intercondylar distance is the distance between the two condyles, which is only individually adjustable with very elaborate devices. However, the distances between the joints differ considerably from patient to patient. The intercondylar distance of articulators is based on the side length of the Bonwill triangle as a fixed value (Fig 8-22). This can result in substantial shifts in the occlusal field, because different movement curves of the centric stops can arise during lateral movements, depending on the difference from the individual case.
Condylar path inclinations in the sagittal direction can be accurately adjusted on nearly all articulators. However, it is more difficult to replicate the precise Bennett movement. If the Bennett movement is imitated by setting the condylar paths in the horizontal plane more toward the middle, the Bennett movement occurs as a pure axial shift, whereas in the anatomical case it follows a curved path or may even run dorsally to cranially or ventrally to caudally with the condyle in a resting position (Fig 8-23).
If the Bennett movement is incorrect, tooth contacts will also occur on the nonworking side during lateral movement, even though none are present in the articulator because they have not been incorporated. In a complete denture, for instance, it is exactly these balancing contacts still present in the articulator that are missing.
Functions of the articular disc and the joint capsule and naturally the neuromuscular system can only be mimicked indirectly or very inadequately. The neuromuscular system is the system unit of nerves and muscles, or in a wider sense, the movement habit. Thus, denture reconstructions are only ever checked in a "gentle" sliding state, never under masticatory loading.