Recording Jaw Relations
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Direct answer
Recording jaw relations transfers the patient's vertical and horizontal mandibular position from the mouth to the articulator using record blocks (an acrylic or shellac base with a wax occlusal rim). The vertical component fixes the occlusal vertical dimension at 2 to 4 mm below the rest position (the freeway space), while the horizontal component records centric relation — the most retruded physiological position of the condyles — by static check records, functional methods or gothic arch tracing. An error here cannot be corrected later in the denture.
What you must remember
- Vertical dimension at rest is determined by muscle tonus; the interocclusal rest space (freeway space) averages 2 to 4 mm and is subtracted from rest position to obtain occlusal vertical dimension.
- Methods of recording vertical dimension: facial measurement and equal facial thirds (Willis bite gauge), phonetics, swallowing, facial expression and the patient's tactile sense — always combine at least two.
- Silverman's closest speaking space during "S" sounds, asking the patient to count "sixty-six" or say "Mississippi", is about 1 to 2 mm and cross-checks the vertical dimension.
- "M" sounds with the lips gently touching help find the rest position of the mandible before any measurement is taken.
- Centric relation is the most retruded physiological relation of the mandible to the maxillae at the terminal hinge position — reproducible, whereas maximum intercuspation is not.
- Recording methods: static interocclusal check records in wax or paste, functional chew-in records, and graphic tracing — intraoral (Gysi) or extraoral (Stansbury-type) gothic arch, whose apex marks centric relation.
- Occlusal rims are shaped first: the maxillary rim trimmed to lie 1 to 2 mm below the upper lip at rest, its plane parallel to the interpupillary line in front and to Camper's line (ala to tragus) behind.
- A protrusive check record is also made to set the articulator's horizontal condylar guidance; Hanau's formula L = H/8 + 12 derives the lateral inclination from the horizontal one — a classic viva one-liner.
A typical sequence at the chair
After the record bases are verified for adaptation and stability, contour the maxillary rim until the lips are supported naturally, showing 1 to 2 mm below the upper lip at rest; scribe the midline and canine lines on its face. Set the mandibular rim height so that, at first contact, the freeway space measures 3 mm — check by marking dots on nose and chin, having the patient swallow and relax, and measuring the rest distance with a Willis gauge. Confirm with phonetics: counting "sixty-six" should give a clear "S" with 1 to 2 mm of clearance; whistling or lisping signals over-closure or excess height. For the horizontal record, soften a film of wax only on the mandibular rim, guide the patient's chin so the mandible closes on its terminal hinge arc — a gentle backward pressure at the chin with support at the forehead, never forcing — and let the rims indent. Alternatively place a central bearing screw and plate, obtain a Gothic arch tracing, and lock the intraoral tracer at the apex before letting the patient close through a registering medium. Verify any record twice: remove, reseat and confirm the same indentations, because an unverified centric record is the single commonest denture error.
Strain and slip
Forcing the mandible backwards until the chin trembles records a strained, non-physiological position that the patient cannot maintain in function — examiners describe exactly this sign and ask what it means. The second error is testing the vertical dimension only by measurements and skipping the phonetic cross-check; a patient with a long upper lip can hide a 3 mm error from the facial-thirds method. Finally, candidates forget that record bases must be stable first: a rocking base records a false vertical dimension regardless of technique, so the examiner's leading question "what do you check before recording jaw relations?" expects the answer "adaptation and stability of the record base".
Frequently asked questions
What is the freeway space and how much is it?
The interocclusal gap between vertical dimension at rest and at occlusion, averaging 2 to 4 mm; it must be built into complete dentures or the patient feels strained and the muscles tire.
Why is centric relation recorded rather than maximum intercuspation?
In an edentulous patient there is no intercuspation; centric relation is the reproducible terminal hinge position, allowing repeated closure and error-free transfer to the articulator.
What does the apex of a gothic arch tracing represent?
The most retruded position of the condyles — centric relation — where the tracing needle's forward point meets the two lateral excursive arms.
How are the occlusal rim and its plane oriented?
Roughly 1 to 2 mm below the upper lip at rest in front, parallel to the interpupillary line anteriorly and to Camper's line (ala to tragus) posteriorly.
What is Hanau's formula used for?
L = H/8 + 12 estimates the lateral condylar inclination from the recorded horizontal condylar inclination when setting certain semi-adjustable articulators — a favourite short note.