vi. orthognathic arrangement of artificial teeth according ... · posterior teeth: the placement of...

V. Selection of artificial teeth

and esthetic aspects of the

dentition.

VI. Orthognathic arrangement of

artificial teeth according to Gysi.

* The posterior part of the arch form will be determined to a great extent by the neutral zone between the cheeks and the tongue.

Neutral zone is the area between the tongue on one side and the cheeks and lips on the other, where opposing soft tissue displacing forces create a zone of neutral or minimal muscular force, the teeth should be placed as far as possible with respect for these muscle forces.

* Post extraction changes may lead to a gradual shifting of the neutral zone with the tongue spreading laterally. In other words the buccolingual space available for placing teeth is reduced. This is of particular importance in the case of the lower denture. The artificial teeth used are considerably narrower than the natural teeth and this allows them to be placed so that the denture is stable.

Position of maxillary posterior teeth:

The maxillary 1st premolar:

The maxillary first premolar is placed with its long axis perpendicular to the occlusal plane (vertically upright).The buccal cusps are raised 0.5mm from the occlusal plane.

The maxillary 2nd premolar:

The long axis is perpendicular to the occlusal plane ( parallel to the vertical axis). The buccal cusp is 0.5 mm above the occlusal plane and the palatal cusp touches the occlusal plane.

The maxillary 1st molar:

The long axis (viewed from side ) may

slightly incline mesially. When viewed from

the front the tooth slopes buccally. The

mesiobuccal cusp of the first molar is

raised 0.5 mm above the occlusal plane.

The mesiopalatal cusp is in contact with

the occlusal plane. The distobuccal cusp is

raised about 1 mm above the occlusal

plane.

The maxillary 2nd molar:

The long axis ( viewed from side, cervical

area) may slightly incline mesially. The

mesiobuccal cusp of the 2nd molar is

raised

1 mm above the occlusal plane. The

distobuccal cusp 1.5 mm above the

occlusal plane. No cusp touches the

occlusal plane. When viewed from the

front the tooth slopes buccaly (more than

the 1st molar).

The maxillary teeth viewed from the occlusal surface should follow the following guidelines:

- The distobuccal surface of the canine, the buccal surfaces of the premolars and the mesiobuccal surface of the 1st molar should follow a straight line. Buccal surfaces of the 2nd molar are slightly inwards and are placed so that all buccal surfaces of the 1st and 2nd molars follow a straight line.The posterior teeth should be placed so that the central grooves of the maxillary posterior teeth follow the line of the crest of the mandibular residual ridge.

The position of the mandibular

posterior teeth: The placement of the mandibular posterior

teeth determines how well the teeth occlude, both in centric occlusion and in lateral and protrusive excursions. The mandibular 1st molar is first placed in position followed by the 2nd molar, and then the two bicuspids. After placing each mandibular tooth in the correct position the incisal guide pin should be checked to insure that it is in contact with the guide table.

Position of the mandibular 1st molar:

The mesibuccal cusp of the maxillary 1st

molar fits into the buccal groove of the

mandibular 1st molar. The mesiolingual

cusp of the maxillary 1st molar fits into the

central groove of the mandibular 1st molar.

This provides proper buccal overjet.

Position of the mandibular 2nd molar:

The mandibular 2nd molar is placed with the

mesiobuccal cusp fitting between the

maxillary 1st and 2nd molars and contact

with their marginal ridges. The lingual

cusps of the maxillary 2nd molar fit into the

central groove of the mandibular 2nd molar.

Position of the mandibular 2nd premolar:

The mandibular 2nd premolar is placed with

the buccal cusp fitting between the

maxillary 1st and 2nd premolars and in

touch with their marginal ridges. The

lingual cusp fits in between the palatal

cusps of the maxillary bicuspids.

Position of the mandibular 1st premolar:

The buccal cusp of the mandibular 1st

premolar fits between the maxillary canine

and the 1st premolar. Usually this tooth is

not placed until the anterior and posterior

teeth are placed. If there isn’t sufficient

space for the placement of this tooth it

may be trimmed and made narrower to fit

into the available space rather than alter

the placement of anteriors.

In centric occlusion the buccal cusps of the mandibular teeth contact the central fossae of the maxillary teeth while the lingual cusps of the maxillary teeth fit into the central fossae of the mandibular teeth.

Occlusal contacts during lateral movements:

Contacts on the working side i.e. the side to which the mandible is moving.

Working or functional occlusion occurs when the buccal cusps of the maxillary teeth meet the buccal cusps of the mandibular teeth, and the palatal (lingual) cusps of maxillary teeth meet the lingual cusps of the mandibular teeth. However the relationship is not cusp tip to cusp tip, but cusp tip into cusp “valley” with each maxillary cusp distal to the corresponding mandibular cusp.

There should be contact of anterior maxillary and mandibular teeth on the working side.

Balancing occlusion: The balancing side is the opposite side to the side which the mandible has moved.

Balancing occlusion occurs simultaneously on the opposite side from the working occlusion.`In balancing occlusion, the palatal cusps of the maxillary teeth contact the buccal cusps of the mandibular teeth. Balancing occlusion functions to maintain the dentures in position during excursive movements. There will be no contact of the anterior teeth on the balancing side.

Balancing contacts in protrusive

occlusion:

Balancing contacts in protrusive excursions

permit the posterior teeth to touch when

the anterior teeth are in contact. The distal

inclines of the maxillary buccal cusps

contact the mesial inclines of the

mandibular buccal cusps.

Compensating curve of spee:

Anatomic curvature of the occlusal alignment of the natural teeth beginning at the tip of the lower canine and following the buccal cusps of the natural premolars and molars is called curve of spee.

The anterior height of the lower posterior teeth can be checked clinically. The height of the 1st mandibular premolar usually coincides with the height of the resting lower lip at the corner of the mouth.

Curve of spee

Curve of wilson

vi. orthognathic arrangement of artificial teeth according ... · posterior teeth: the placement of...

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