Condylar Guidance And Incisal Guidance Short Notes

Condylar Guidance And Incisal Guidance Short Notes

Condylar Guidance (posterior Determinant)

• Condylar guidance is defined as, “Mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossa”.—GPT
• It is the path of movement taken by the condyle in the glenoid fossa. The glenoid fossa and the condyle are the articulating surfaces of the temporomandibular joint.
• The condyle moves along the surface of the glenoid fossa during mandibular movement so the glenoid fossa determines the path of movement of the condyle.
• The slope of the glenoid fossa is a ‘S’ bend. Hence the condyle also moves along a ‘S-shaped path. This shape of the glenoid fossa, which determines the path of movement of the condyle, is called condylar guidance.
• The condylar guidance can be measured using a protrusive interocclusal record.
• Protrusive interocclusal record is defined as, “The influence of the contacting surfaces of the mandibular and maxillary anterior teeth during mandibular movements”. –GPT

Importance of condylar guidance

• A steep condylar path needs a steep compensating curve for occlusal balance.
• If a lesser compensating curve is substituted for a steep condylar guidance it would result in a steep incisal guidance resulting in loss of molar balancing contacts.

Setting the condylar guidance in the articulator (Hanau)

• A protrusive record is placed on the mandibular occlusal rims and the condylar thumb nuts on the articulator are made loose so that the upper member of the articulator can be easily guided into the imprint of the protrusive record perfectly.
• Rotate the right and left guidances back and forth to accurately seat the upper and lower rims into the protrusive record.
• After checking the value on both sides of the condylar guidance on the articulator, tighten the thumbnut. The approximate value is within +30 degrees and almost the same value on both sides.

Incisal guidance

• When the mandible is protruded the incisal edge of the lower anterior slide along the slope of the lingual surface of the upper anterior teeth before reaching edge-to-edge contact. The lingual surface of the maxillary anterior guide the mandible during protrusive movement and is called Incisal guidance.
• Incisal guide angle is defined as, “The angle formed in the horizontal plane by drawing a line in the sagittal plane between the incisal edges of the maxillary and mandibular central incisors when the teeth are in centric occlusion”. –GPT

Importance of Incisal guidance

• In complete denture patients, incisal guidance is not present and it is arbitrarily set using a standard incisal guide value while arranging the anterior teeth. It is modified during esthetic anterior try-in.
• If the incisal guidance is steep, it requires steep cusps, a steep occlusal plane, or a steep compensating curve to effect an occlusal balance.
• A steep inclined plane is detrimental to the stability and equilibrium of the denture base hence the incisal guidance should be as flat as esthetics and phonetics will permit.
• When the arrangement of the anterior teeth necessitates a vertical overlap, a compensating horizontal overlap should be set to prevent dominant incisal guidance (anterior interference) from upsetting the occlusal balance on the posterior teeth.

Condylar Guidance  Preparation of anteroposterior guides

• The occlusion rims should be removed to evaluate the interridge space and arch form. A mark is placed on the occlusal rim as a projection of a line running from the incisal tip of the mandibular canine to the apex of the retromolar pad.
• This reference line is checked in relation to the arch form as in the palatal surfaces of the upper incisors. This is known as the protrusive incisal path or incisal guidance.
• The angle formed by this protrusive path to the horizontal plane is called the incisal guide angle.
• If the incisal guidance is steep, steep cusps or a steep occlusal plane or a steep compensatory curve is needed to produce balanced occlusion.

Setting up the Incisal guidance

• The upper six and lower six teeth are set by esthetics, function, and phonetics. Lock the articulator in centric. Occlusal rims are seated in vertical and centric relation.
• The incisal pin is placed at zero horizontal incisal guide and the lateral wings are also placed at zero with the chisel end of the pin resting on the center of the incisal table. Lock the thumb screw. Loosen the locknut for protrusion and release the centric locks.
• Guide the upper cast into a straight protrusion with the lingual edge of the upper central incisors in contact with the incisal edges of the lower incisors. The incisal guide is rotated antero- posteriorly to make contact with the incisal pin. Tighten the locknut to maintain angulation.
• The upper cast is guided into the right lateral canine to canine and the lateral wing on that side is elevated to contact the incisal pin and the lateral wing locknut adjusted thence is tightened. Repeat with the other side. The normal value is within 5 degrees.

Factors affecting Incisal and condylar guidance

As the occlusal plane, condylar guidance, incisal guidance, compensatory curves, and cuspal inclination are all interrelated, any alteration to one of the factors affects the rest also