Preclinics of Dental Prosthetics · MU Sofia

13. Gnathology. Rest vertical dimension - RVD. Occlusion and articulation. Basic positions of the mandible.

Covers the gnathology triad of TMJs, teeth and muscles, then rest vertical dimension with its freeway space and how occlusal vertical dimension follows from it. Compares occlusion with articulation in a table, then sets out the basic mandibular positions (centric occlusion, centric relation, myocentric occlusion, terminal posterior occlusion) in a table by introducer, priority and condyle position. Ends with freedom in centric, the small forward slide from centric relation into centric occlusion.

Inside: 5 sections · 2 labelled pictures · 2 tables · 13 flashcards · 4 min

Topic 13 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 5 sections, about 393 words (4 min of reading), with 13 flashcards.

In this note

  1. Introduction
  2. Gnathology and occlusodontics
  3. Rest vertical dimension (RVD)
  4. Occlusion and articulation
  5. Basic positions of the mandible

Introduction

Almost every restoration rebuilds part of an occlusal surface; a crown or bridge replaces all of it. If the new surface meets the opposite teeth in the wrong place, the whole system feels it. Gnathology is the study that keeps restorations in harmony with the joints and muscles.

Gnathology and occlusodontics

Gnathology studies the form, function and disorders of one functional triad:

  1. The craniomandibular joints (TMJs)
  2. The teeth arranged in their dental arches
  3. The masticatory and facial muscles

It gives priority to the position of the condyles in their fossae. Gnathologists locate the patient's transverse hinge axis and transfer it with a facebow to an articulator, so that restorations are built around the patient's own jaw movements. Occlusodontics deals with the occlusal surfaces and contacts themselves: the goal is posterior contacts that hold the mandible steady and spread the load evenly.

Rest vertical dimension (RVD)

The mandibular rest position is where the mandible hangs when its muscles are relaxed and the head is upright. The lips just touch, and the condyles sit slightly rotated at the foot of the eminence. It is set by muscles and nerves, not by teeth.

  • Freeway space (interocclusal clearance): the gap between the teeth at rest, 2–5 mm, about 3 mm on average.
  • Occlusal vertical dimension (OVD): the face height with the teeth together, so OVD = RVD minus the freeway space.
  • RVD stays almost the same with age and tooth loss. That makes it the starting point for building a new bite: in a completely edentulous patient, measure RVD, subtract about 3 mm, and that is the height for the dentures.

Too high a bite leaves no freeway space: tired muscles, sore ridges, clicking teeth. Too low a bite makes the face look old and the corners of the mouth fold.

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