Vertical dimension of occlusion, or VDO, also known as occlusal vertical dimension (OVD), is a term used in dentistry to indicate the superior-inferior relationship of the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

and the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

when the

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

are occluded in

maximum intercuspation In dentistry, maximum intercuspation refers to the occlusal position of the mandible in which the cusps of the teeth of both arches fully interpose themselves with the cusps of the teeth of the opposing arch. This position used to be referred to ...

. A VDO is not only possessed by people who have teeth, however; for completely

edentulous Toothlessness, or edentulism, is the condition of having no teeth. In organisms that naturally have teeth, it is the result of tooth loss. Organisms that never possessed teeth can also be described as edentulous. Examples are the members of the ...

individuals who do not have any teeth with which to position themselves in maximum intercuspation, VDO can be measured based on subjective signs related to

esthetic Aesthetics, or esthetics, is a branch of philosophy that deals with the nature of beauty and taste, as well as the philosophy of art (its own area of philosophy that comes out of aesthetics). It examines aesthetic values, often expressed thr ...

s and

phonetics Phonetics is a branch of linguistics that studies how humans produce and perceive sounds, or in the case of sign languages, the equivalent aspects of sign. Linguists who specialize in studying the physical properties of speech are phoneticians. ...

In terms of esthetics, an appropriately measured VDO will appear to a layman's eye as an ordinary configuration of the patient's nose, lips and chin. An excessive VDO will appear as though the patient has something stuffed into their mouth, and the patient may not even be able to close their lips. A telltale indication of an excessive VDO is a patient straining to close their lips around the wax rims during VDO determination. Conversely, a deficient VDO will appear as though the patient's mouth has collapsed, and the chin appears too close to the nose; in essence, the patient would be over-closing their mouth because there would not be enough wax on the wax rims to maintain the proper vertical dimension of occlusion. In terms of phonetics, certain sounds are made by configuring the mouth in specific ways. The two sounds most commonly used to establish a patient's VDO are

sibilant Sibilants are fricative consonants of higher amplitude and pitch, made by directing a stream of air with the tongue towards the teeth. Examples of sibilants are the consonants at the beginning of the English words ''sip'', ''zip'', ''ship'', and ...

and

fricative A fricative is a consonant produced by forcing air through a narrow channel made by placing two articulators close together. These may be the lower lip against the upper teeth, in the case of ; the back of the tongue against the soft palate in t ...

sounds. Sibiliant sounds are made by allowing the maxillary

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...

s to nearly touch the mandibular incisors, while fricative sounds are made by allowing the maxillary incisors to touch the slightly inverted lower lip at the wet-dry line. By having the patient count upwards from fifty and then upwards from sixty, the dentist can watch and listen to the patient attempting to make first fricative and then sibilant sounds and adjust the wax rims accordingly. A common trick is to ask the patient to say the name "Emma," as the position of the mandible immediately after completing the word is a rough estimate of the patient's proper VDO. The position after saying "Emma" is referred to as the vertical dimension at rest, or VDR. Historically, the VDO has been estimated at 3 mm less than VDR because a person will generally maintain their mandible at an opening of 3 mm when at rest.Bhat, VS; M Gopinathan, M: Reliability of determining vertical dimension of occlusion in complete dentures: A clinical study, ''JIPS'' 2006 6:1:38-42
/ref> There is another rule that applies to many mammals which give us a very practical way to find a suitable VDO. Take the distance between the inner corner of the eye and the same corner of the lips (in older people the measurement should be done a little more medially (closer to the nose) to avoid a down-pointing lip corner). Using a ruler, apply this measurement between the center bottom of the nose (that rises from the upper lip) and lower tip of the mandible center. (In the completely edentulous (those with no teeth), do as referred.) Maintain a centric position.

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