Maxillomandibular Relations

Maxillomandibular Relations

Maxillomandibular relations are divided into:

Vertical relations.Orientation relations.Horizontal relations.

DEFINITIONS:Vertical dimension:A vertical measurement of the face between any two arbitrary Selected points conveniently located, one above and one below the mouth usually in the midline .

Vertical dimension of rest:The vertical dimension of the face with jaws in the rest relation .Interocclusal distance(freeway space):The distance between the occluding surfaces of the maxillary and mandibular teeth when the mandible is in its physiologic rest position.physiologic rest position:The habitual bostural position of the mandible when the patient is sitting comfortably in the upright position and the condyles are in aneutral unstrained position in the glenoid fossae.

Vertical dimension of occlusion:The occlusal vertical dimension is the vertical dimension of the face when the teeth or occlusion rims are in contact in centric occlusion

Factor affect postural rest position:A.short term factors:1.head posture2.stress3.mouth content4. mouth pain or pain in muscles supporting the mandible5.respirationLong term factors:1.age and health status2.bruxismVertical relations:Vertical relation is the relation of the mandible to the maxilla in a vertical direction.Vertical dimension is the distance between two selected points, usually one on the tip of the nose and the other is on the chin (one on a fixed member and other on a movable member) in a vertical direction.

Establishment of this dimension is by using occlusal rims, which include surfaces that are fabricated on an interim or final denture base for the purpose of making maxillomandibular relation records and arranging the teeth.

It is made up of a record base and a wax rim. The record base must be rigid, accurate and stable,

preferably made up of autopolymerized or light-cured acrylic resin to be adjusted according to the need, while the rim is made up of a base plate wax or a bite rim wax.

In completely edentulous patients, it is difficult to determine the position of the natural teeth; therefore, we use some anatomical landmarks as guides.

Clinical sequencesBefore recording the maxillomandibular relation, occlusal rim serves to determine:Arch form design: the width of occluding surfaces and the contour of the arch form of the occlusal rim should be individually established for each patient to desire each form of the artificial teeth. Arch form generally rounded, square, V-shaped or tapered. Shaping the occlusal rim similar to the ridge allows good support for the lips and cheeks and allows for a proper tongue movement.

Some authors believe that the position of the natural teeth is the location where the forces exerted by the tongue from one side is equal to the forces exerted by the lips and cheeks. Positioning the artificial teeth in that position would make the denture function properly without interferences. In some cases, we block the undercuts, but this blocking must be done in a precise organized way. Over blocking may affect the stability of the record base and this would cause some difficulties in the recording of maxillomandibular relations.

Establishing the level/height of the occlusal plane: determination of the occlusal plane is the most important clinical procedure in the rehabilitation of the edentulous patients. This plane with arch form are the basis for an ideal tooth arrangement. Anteriorly, this plane helps in achieving an esthetic, phonetics while posteriorly, it forms a milling surface. Incorrect occlusal plane would affect the esthetics, phonetics and mastication.

By using a fox bite, the maxillary incisal plane of the occlusal rim would be made parallel to the interpupillary line at a height that allows for the length of the natural teeth (using upper lip, if it is of average length, as a guide, incisors are extended 2 mm occlusally to the upper lip).

Posteriorly, the plane is made parallel to the ala-tragus line. The lower occlusal rim is adjusted to meet evenly the upper occlusal rim with even contact all around.

The lower rim is leveled with the lower lip anteriorly and zero level posteriorly with the retromolar pads.

Modifying the height of the occlusal rims at the desired vertical dimension: establishing the vertical jaw relation requires the measurement of two types of a vertical dimension:

Vertical dimension at rest position.Vertical dimension of occlusion.

Values of the vertical dimension at rest is more than the vertical dimension at occlusion by about 2-4 mm. this distance which is demonstrated by a space between the occlusion rims is known as free way space or interocclusal rest space, which is the different between the vertical dimension of the rest position and the vertical dimension of occlusion. This space is very important for preservation of the supporting tissue.

Vertical dimension at rest position is the amount of jaw separation at rest when the maxillofacial musculature is in a state of a tonic equilibrium. In this position, all the muscles of opening, closing, mastication, speaking, swallowing and breathing are involved. It is believed that this position is measurable and repeatable and can be used as a reference during the establishing vertical dimension of the occlusion; therefore, this must be taken first.

To determine the vertical dimension of the rest position, the patient should sit upright, with the head erected and unsupported and he/she should look straight ahead, this is the relaxed position of the mandible. If or when the patient is intense, under strain, tired or irritable, the value of the measurement is questionable. Rest position is a position in space, which cannot be maintained for a definitive period of time, the duration is usually short and therefore, you have to prepare for the measurement to have a correct result.

Importance of vertical dimension:Functional role: as in mastication, respiration, deglutition and phonetics.Physiological role: for maintaining the health of tissues.Esthetics importance.Psychological importance.

Errors in vertical dimension record are either increased or decreased vertical dimension:Increased vertical dimension will cause the following:Loose of biting force or power.Inability to open the mouth widely.Interferences and clicking on speech.Difficulties on swallowing and mastication.Premature contacts produce soreness to the underlying tissues and produce longer leverage, making the denture easily displaced.

Increased vertical dimension makes the dentures contact for longer period of time and increase the applied forces; this would lead to a rapid bone resorption.Muscular tension and fatigue.Destructive changes in the TMJ.Inharmony of the facial appearance.Lips are not in contact and excessive teeth appearance.Feeling of excessive bulk.Stretched skin and muscles of the lower and middle parts of the face.Psychological problems.

Decreased vertical dimension would case the following:Reduced biting force and make the jaws not in effective and efficient range of muscle function and loose muscles power.Cheek biting.Reducing the oral cavity space and pushing the tongue backward.Incorrect speech and phonation.

TMJ changes.

Wrinkles or folds in the lips which is not due to aging and the vermillion border is reduced.

Angular cheilitis.

Nasolabial angle is less than 90 degrees with the prominence of the lower jaw.

Method of determining vertical dimensionMechanical methods:-parallelism of posterior ridge-measurement of the former denture-pre-extracrion records:1-Profile radiograph2-profile photograph3-articulating study cast4-facial measurements:i-Willis gaugeii-profile silhoutteiii-face maskIv-tattooParallelism of the ridge: parallelism of the maxillary and mandibular ridges plus a 5-degree opening in the posterior region may be regarded as a correct amount of jaw separation. However, in most of people, the teeth are lost at different times; therefore, the ridges are no longer parallel.

Physiological methods:1.physiological rest position2.esthetics3.phonetics4.swallowing5.patient tectile sense6.boos biameter7.electromyographyMethods of measuring the vertical dimension at rest position:Facial measurement: instruct the patient to sit comfortably upright with the eyes looking straight ahead at some object which is in the same level. Insert well-contoured upper rim and mark a point on the patient's nose and other one on the chin. Ask the patient to swallow and relax. When the mandible drops to the rest position, measure between the two points by using a millimeter ruler. It is advisable to repeat this measurement till you have consistent values.

Previous denture: former dentures may be used in the determination of the vertical dimension of occlusion but it is advisable to use other methods to determine the vertical dimension of occlusion and compare it with the old denture measurement. Old denture measurement cannot be accepted in all situations because changes like resorption and attrition may give false records.

Methods of measuring the vertical dimension at occlusion:Pre-extraction records: this includes a profile photograph and radiograph. It helps to measure the distance between some anatomical landmarks and compare it with a measurement made at the treatment time. To have a correct measurement, you have to be sure that the teeth are in contact and an accurate technique was used in taking and processing the radiograph.

Articulated casts may also be useful in the same way but for a patient who had a severely resorbed ridge or sacrificed during teeth extraction, this comparison could be questionable. All the pre-extraction records must be used with caution of their limitations to have proper measurements.Facial measurement: measure the distance between two points after assessment of the facial expressions and compare it with that when the jaws are at rest.

Tactile sensation: seat the patient in the same previous position and instruct him/her to open the jaws widely until strain is felt in the muscles.

When the opening becomes uncomfortable, ask the patient to close slowly until the jaws reach a comfortable relaxed position, then measure the distance between the two points.

Phonetics: it is useful method to establish the rest position by speech. Ask the patient to repeat the letter "M" or the name "Emma" until he/she is aware of the contacting of the lips as the first syllable "em" is pronounced, then ask the patient to stop all jaws movements when the lips touch, then measure the distance between the two points.

Facial expression: in normally relaxed jaws, the lips would be even anteroposteriorly in a slight contact. If the mandible is protruded, the lower lip would be anterior to the upper lip and not in contact. Also when the mandible is detruded, the lower lip would be distal to the upper lip and not in contact too. Also relaxation of the skin around the eyes, over the skin and around the nose all are an evidence of the rest position; therefore, the measurement of the vertical dimension can be established. This method requires some experience.

Anatomical landmarks: Willis guide is designed to measure from the pupils of the eyes to the rima oris and the distance between the anterior nasal spine to the lower border of the mandible. If the two measurements are equal, the jaws are considered at rest, so measurements can be established.Vertical dimension at occlusion Vertical dimension at occlusion is a distance between two points when the occluding members are in contact.

Closest speaking space: closest speaking space is defined as the space between the anterior teeth that should not be less than 1-2 mm between the upper and lower teeth (occlusal rim) when the patient is unconsciously repeats the letter "S". This space is very critical; many patients whistle during "S" phonation or pronounce as "SH" or "TH". It measures vertical dimension when the mandible and muscles involved are in a physiological function of speech.

This method is useful also in proper positioning of the upper and lower anterior teeth, especially when the patient repeats the letter "F" or "V" and "S".

Incisive papilla and mandibular incisors: incisive papilla is a stable landmark that changes little with the resorption of the alveolar ridge. The distance of the papilla from the mandibular incisors averages 4 mm in the natural dentition. The incisal edge of the maxillary central incisors is an average 6 mm below the incisive papilla; therefore, the mean vertical overlap of the opposing central incisors is about 2 mm. This method should be used with caution in patients with severe resorption.

Swallowing threshold: the position of the mandible at the beginning of the swallowing action has been used as a guide to the vertical dimension of occlusion. At the beginning of the swallowing cycle, the teeth come together with a very light contact. The technique involves building a cone of soft wax on the lower denture base in such a way that it contacts the upper rim when the jaws are opened widely.The repeated swallowing of saliva would gradually reduce the height of the wax cone till the mandible reaches the level of vertical dimension of occlusion. This method is limited because, relatively, it takes long time and the softness of the wax may affect the result. However, we have to confirm the reading with other methods to be sure that the record is right.

Tactile sense and patient-perceived comfort: by using adjustable central-bearing screw attached to one of the occlusal rims and a central-bearing plate attached to the other rim. The screw is adjusted until the patient indicates that the length is about right height. The procedure must be repeated for maximum accuracy. The presence of the foreign objects may affect the measurement precision.

Note: Always use more than one method to decide a favorable vertical dimension. (using 3 methods is the best).