Topic number 18
Apparatus for jaws motion reproduction. Rules of fixation models in occluders and articulators.
Dentistry
The mandible articulates with the skull at the temporomandibular joints. The condyle of the mandible fits into the mandibular fossa on the underside of the temporal bone, thus the name temporomandibular articulation or joint.
The articular tubercle or eminence is a rounded projection which forms the anterior boundary of the mandibular fossa. The articular disc is composed of tough fibrous tissue and lies between the mandibular fossa and articular eminence above and the condyle below. The disc is attached to the capsular ligament which surrounds the joint and is also attached to part of the external pterygoid muscle, one of the four major muscles of mastication. Synovial cavities filled with a lubricating fluid lie above and below the articular disc.
The structure of the temporomandibular joint permits the mandible to make many movements. There are two basic movements, a hinge or rotary movement and a sliding or translatory movement. The hinge movement takes place between the condyle and the articular disc while the translatory movement takes place between the articular disc and the mandibular fossa.
The mandible is shifted from side to side and opened and closed by coordinated movements of the muscles of mastication (massctcr, temporalis, internal pterygoid and external pterygoid and other muscles). In lateral excursions of the mandible, one condyle is held in position while the other slides forward down the articular eminence. A slight side-shift (Bennett movement) accompanies these excursions. The lateral excursions of the mandible permit food to be grasped and crushed between the teeth.
The teeth, muscles, and joints all work in harmony or decreased function and/or pain result. Likewise, denture teeth must be in harmony with thejoints and muscles. For thisreason, jaw movements are considered when planning the occlusion for artificial replacements.
Adjustable and semi-adjustable articulators simulate jaw movements. The Hanau H-2 articulator is a widely used semi-adjustable articulator. This instrument has adjustable horizontal condylar guides which, when adjusted by means of a protrusive jaw relationship record, represent the inclination of the mandibular fossa. The lateral condylar guidance, a mechanical equivalent of Bennett movement, is introduced by rotating the posts of the articulator.
All articulator is a “mechanical device that represents the temporomandibular joints and jaw members to which maxillary and mandibular casts may be attached.” (CCDl) By definition it is evident that an articulator is any instrument which has a movable joint on which casts of maxillary and mandibular arches may be mounted. Articulators arc available in many forms from the simplest hinge-type instruments to very complicated and expensive instruments.
For case of description it is best to classify articulators. The simplest type of articulator is the nonadjustahle or hinge-type articulator. This type accepts only centric relation maxillomandibular records for mounting casts and can be opened and closed only.
The second type is the semi-adjustable articulator. These articulators have adjustable horizontal condylar guides and accept both centric relation and protrusive maxillomandibular relation records. These articulators are similar in design and use, the only difference being that the Model H-2 has longer posts and an orbital plane guide. The orbital plane guide allows the casts to be mounted in ielation to the axis-orbital plane of the patient and orients the casts on the articulator in the same relationship to the bench top as the dental arches are in the patient.
The semi-adjustable type of articulator is the most widely used articulator in dental schools throughout the . By adjusting the condylar elements, better dentures and restorations can be constructed than are possible on simple, non-adjustable articulators. The Hanau Model H-2 articulator is the one which has been selected for the balance of illustrations in this manual. This articulator is relatively inexpensive, is sturdily constructed, and is widely used throughout the .
The third type of articulator is the fully adjustable articulator. These articulators accept not only centric relation maxillomandibular records, but also piolrusive and right and left lateral maxillomandibular relation records. These articulators are more complex than the semi-adjustable articulators and are more expensive.
The Stewart articulator is another fully adjustable articulator similar in appearance and use to the Gnatholator. The Whip-Mix articulator is a student model of the Stewart articulator. The Whip-Mix instrument is a semi-adjustable articulator in that it accepts centric and protrusive jaw relation records only, lateral jaw relation records may be used but the arbitrary intercondylar distances will not permit accurate adjustment to all of these records.
When the dentist has completed recording the maxillomandibular records and making the face-bow transfer, the occlusion rims, casts, face-bow and a prescription containing instructions, tooth shade and mold are sent to the laboratory.
Some precautions must be observed when mounting casts. The articulator must be checked to be sure it is adjusted correctly. The condylar elements must be locked in centric position. There must be no lateral “play” in the articulator. The mounting rings must be firmly attached. The casts must be seated completely in their respective occlusion rims. Failure to observe these precautions will result in having the casts mounted in an improper relationship.
The equipment required for mounting casts on a Ganau articulator. Note the cast support directly behind the maxillary cast. This is attached to the articulator in place of the lower mounting ring to support the maxillary occlusion rim during mounting procedures.
The face-bow has been mounted and centered on the articulator. The condylar roils on the face-bow are adjusted so that they lit snugly on the condylar roil of the articulator but the face-bow is not distorted. Note that the mounting support has been placed on the articulator and that the jack screw on the assembly holding the bite fork has been lowered until the orbital indicator is on the same level as the orbital plane guide, the semicircular device attached to the upper member of the articulator.
The articulator has been opened ready for application of plaster to the base of the maxillary cast.
A medium thin mix of impression plaster is prepared. The plaster is placed on the base of the cast and piled up until it extends above the level of the mounting plate.
The upper bow of the articulator is brought over the top of the cast and pressed into the mounting plaster. The articulator must be closed until the incisal guide pin touches the incisal guide table.
The plaster is smoothed and the excess removed. A wet finger can be used to smooth the plaster after the excess is removed.
After the plaster has set, the face-bow is removed from the articulator. The bite fork is heated with a torch and removed from the occlusion rim. (The bite fork is the portion of the face-bow which attaches to the maxillary occlusion rim.) Care should be exercised so that the lines which have been placed by the dentist on the occlusion rim are not obliterated.
The maxillary cast and mounting ring are removed from the articulator. The maxillary and mandibular occlusion rims are placed on their respective casts and the casts are placed together to check clearance in the posterior region of the casts. As can be seen in this illustration there is interference in this region. This the proper seating of the casts into their respective occlusion rims.
The interference is eliminated by carefully removing some of the nonanalomical portion of the cast. The anatomical portion or denture-bearing area of the cast is not altered.
The casts are again reassembled with the occlusion rims to assure that proper clearance is present in the posterior part of the casts. Enough clearance must lie provided so that a definite space is present when the casts are seated in their base plates.
The maxillary and mandibular occlusion rims and casts are sealed together with wax. Any wax which will attach the mandibular and maxillary occlusion rims to each other and to the casts is satisfactory.
The maxillary cast and mounting are replaced on the articulator and the articulator inverted on a plastering stand. Any device which will support the articulator in this fashion is acceptable if a plastering stand is not available.
A mix of plaster is placed on the base of the mandibular cast and the articulator closed on this plaster. Before closing the articulator, some plaster must be pushed down into the spaces in the mounting ring adjacent to the bottom of the articulator. Note that the mandibular cast has been soaked to provide better adhesion of the mounting plaster to the cast.
The articulator is closed onto the mounting plaster so that the incisal pin touches the incisal guide table. The excess plaster is removed with a plaster spatula and the plaster smoothed with a wet finger.
The mounting of the mandibular cast is completed.
The mounting plaster is smoothed to produce a neat appearance. The incisal guide pin extension has been replaced and the articulator is now ready for the arrangement of artificial teeth and/or the mounting of a central bearing device.
1 class
One or several defects, when at least one of them is limited only based on one side
1 sub-class - one-sided end defects
2 sub-class - bilateral end defects
One or several defects, when they all are limited as far as teeth based on both the sides
1 sub-class - absence to 3 teeth
2 sub-class - absence is more than 3 teeth
An articulator is an instrument which simulates movements of the mandible. The records made with occlusion rims are used to mount the master casts and to adjust the articulator. The type of articulator used is determined by the complexity of the restoration and the desires of the dentist.
An articulator is a “mechanical device that represents the temporomandibular joints and jaw members to which maxillary and mandibular casts may be attached.” (CCDT) By definition it is evident that an articulator is any instrument which has a movable joint on which casts of maxillary and mandibular arches may be mounted. Articulators are available in many forms from the simplest hinge-type instruments to very complicated and expensive instruments.
For ease of description it is best to classify articulators. The simplest type of articulator is the nonadjus table or hinge-type articulator. This type accepts only centric relation maxillomandibular records for mounting casts and can be opened and closed only.
Bibliography:
“Propedeutics of orthopedic stomatology” Z. H. Rodmann
“Wady zgryzu, Podręcznik dla studentów ” K. Głowacki