Models are mounted with a facebow in two stages: The maxillary model is first inserted, then the mandibular model is mounted over a centric record.
How well movement is duplicated in articulators depends directly on the precise positioning of the occlusal field relative to the joint axis and equally on precise setting of the joint values in relation to this positioning. Models can be mounted in an articulator as follows:
The centric position is established with a Gothic arch tracing (intraoral interocclusal record registration) by a method developed by Gysi, Mc-Grane, and Gerber. This arch is formed when the horizontal border movements of the mandible are traced. A tracing stylus is attached to a baseplate and inscribes the horizontal mandibular movements on the tracing plate of the other baseplate. The advantage of this method is that it cancels out all uncontrollable occlusal contacts and reduces them to a central point. At the same time, a relaxed neuromuscular resting position can be adopted in which the joints are relieved of any loading.
The jaw relation is any position that the movable mandible can adopt relative to the fixed maxilla. In definition terms, jaw relation in a healthy occlusal system means the constantly reproducible, centric position of the mandible where the condyles are located deep in the mandibular fossae without pressure or tension and where maximal intercuspation and centric loading of the teeth exist. Jaw relation registration is intended to rediscover this centric occlusion or habitual intercus-pation position.
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 quality of a mechanical articulator must be measured by what system errors occur and the seriousness of the individual errors. The best and most expensive equipment will not achieve the desired results if it is operated incorrectly or carelessly. Any system errors will be compounded by operating errors.
An attempt is made with these devices to optimize the simulation of movements achieved with average-value articulators. These devices can be adjusted to different reference planes. The fixed geometric values are the following:
Average-value articulators are fixed-value devices whose overall size is defined by the average Bonwill triangle (approximately 11-cm side length) and an average Balkwill angle (approximately 22 degrees). The Camper plane is the reference plane. The horizontal condylar inclinations are generally at an angle of 30 to 34 degrees to the occlusal plane. A Bennett angle of 0 to 20 degrees is also firmly set (Figs 8-11 to 8-13).
The possibilities and limitations of movement replication with mechanical articulators depend on the aforementioned joint replication and furthermore on the use of anatomical geometric values of the masticatory system. Accordingly, all articulators can be classified as fixed-value, semi-adjustable, or fully adjustable devices. The values that can be individually measured and variably applied are the following:
In the natural masticatory system, the mandible moves in condylar, tooth, and neuromuscular guidance against the fixed maxilla; however, the conventional design of articulators only allows the upper arm to be moved in relation to the fixed mandibular model holder, imitating only condylar and tooth guidance. This means that relative movements with calculable variations are possible.