Articulators in Restorative Dentistry

• Articulators, transfer records, and study casts are important in restorative dentistry

Articulators

• Articulators are mechanical devices with upper and lower components used to attach maxillary and mandibular casts
• They reproduce the static relationship of the maxilla to the mandible, and permit limited lateral and protrusive movements
• Articulators are used to study individual teeth and dental arches for diagnosis and treatment planning
• They allow adjustment of fixed and removable prostheses and indirect dental restorations
• There are four general types of articulators: simple hinge, average value, semiadjustable, and fully adjustable
• Simple hinge articulators offer single hinge movement without lateral movements
• Average value articulators have a fixed condylar angle of 30 degrees and may have adjustable incisal guidance
• Semiadjustable articulators allow the adjustment of condylar inclination and side shift (Bennett angle)
• They can be arcon or nonarcon in design
• Arcon articulators have the condylar elements designed with the fossa box in the upper member, similar to the temporomandibular (TM) joints
• Nonarcon articulators have a ball-and-slot mechanism with the condylar ball attached to the upper member
• Fully adjustable articulators are complex and duplicate TM joint features through condylar adjustments

Transfer Records

• A facebow is an instrument used to record the relationship of the maxilla to the hinge axis of rotation of the mandible
• It enables a maxillary cast to be placed in an equivalent relationship on the articulator
• To identify the hinge axis, a hinge axis locator and hinge axis facebow are needed
• Arbitrary axis facebows may be used with an arbitrary hinge axis point
• Facebows also allow the transfer of intercondylar distance

Occlusal Records

• Used to articulate casts for diagnosis and treatment planning
• The centric relation (CR) is recorded with the teeth slightly apart to avoid deflection by tooth contacts
• Retruded contact position (RCP) or CR is used for complex or multiple restorations and complete denture construction

Lateral and Protrusive Records

• Used to set the condylar angles of the articulator
• Can be done with graphical analysis systems to record condylar inclination, and side shift measurement (Bennett movement and angle)

Dynamic Records

• Single plane dynamic recordings can be made with tracing plates or acrylic clutches attached to the teeth
• Pantographic tracings involve a device used with a fully adjustable articulator to trace border paths of jaw movement in three planes
• Stereographic recordings are used with the TM joint articulator

Study Casts

• Casts should be obtained from impressions that record the complete dental arch and ridge and fossa areas
• Alginate impressions are generally used and produce accurate casts if poured promptly

Selecting an Articulator Type

• Simple hinge articulators have limited value but allow preliminary evaluation of tooth arrangement and patient discussion
• Average value articulators approximate condylar movements
• Semiadjustable articulators are appropriate for most restorative purposes and allow examination of RCP (CR) features and RCP to ICP differences
• Fully adjustable articulators allow replication of mandibular movement but are complex and require pantographic tracings