Compensating Curves in Prosthodontics Short Notes

Compensating Curves in Prosthodontics Short Notes

Compensating curve is defined as, “The anteroposterior and lateral curvatures in the alignment of the occluding surfaces and incisal edges of artificial teeth, which are used to develop balanced occlusion.” –GPT

Types Of Compensating Curves

• Anteroposterior curves
• Lateral curves.

In complete dentures compensating curves similar to the curve of Spee, Wilson’s curve, and Monson’s curve are incorporated to produce balanced occlusion. Ideally, these curves are present in natural dentition.

Anteroposterior Compensating Curves

• They compensate for the Curve of Spee seen in natural dentition and are incorporated in a
  anteroposterior direction.
• Curve of Spee is defined as, “Anatomic curvature of the occlusal alignment of teeth beginning at the tip of the lower canine and following the buccal cusps of the natural premolars and molars, continuing to the anterior border of the ramus as described by Graf von Spee”. –GPT
• It is an imaginary curve joining the buccal cusps of the mandibular posterior teeth starting from the canine and passing through the head of the condyle.
• Significance: In protrusion, the posterior teeth arranged to incorporate this curve will remain in contact without disocclusion as in Christensen’s phenomenon.

Lateral compensating curves

• Seen transversely from one side of the arch to the other.
• Monson’s curve is defined as, “The curve of occlusion in which each cusp and incisal edge touches or conforms to a segment of the sphere of 8 inches in diameter with its center in the region of the Glabella”. –GPT
• This curve runs across the palatal and buccal cusps of the maxillary molars. During lateral movement, the mandibular lingual cusps on the working side should slide along the inner inclines of the maxillary buccal cusp.
• On the balancing side, the mandibular buccal cusps should contact the inner inclines of the maxillary palatal cusp. This relationship forms a lateral balance. Wilson’s curve is defined as, “A curve of occlusion which is convex upwards”. –GPT
• This curve runs opposite to the direction of Monson’s curve. This curve is followed when the first premolars are arranged. The premolars are arranged according to this curve so that they do not produce any interference with lateral movements.
• A reverse curve is defined as, “A curve of occlusion which in transverse cross-section conforms to a line which is convex upward”. –GPT was originally developed to improve the stability of the denture. The reverse curve was modified by Max. A pleasure to form the pleasure curve.
• A pleasure curve is defined as, “A curve of occlusion which in transverse cross-section conforms to a line which is convex upward except for the last molars”. –GPT
• It was proposed by Max Pleasure. He proposed this curve to balance the occlusion and increase the stability of the denture.
• Hence the first molar is horizontal, the second premolar is lingually tilted and the second molar is buccally tilted. This curve runs from the palatal cusp of the first premolar to the distobuccal cusp of the second molar.

Factors Affecting Compensating Curves

• Condylar guidance
• Incisal guidance
• Occlusal plane
• Cuspal inclination.

Compensatory curve Condylar Guidance: Condylar guidance can be defined as, “Mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossa”. GPT 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.

Compensatory curve Cuspal Angulation: Cusp angle is defined as “The angle made by the average slope of a cusp with the cusp plane measured mesiodistally or buccolingually”. –GPT

• The mesiodistal cusps lock the occlusion, such that repositioning of teeth does not occur due to settling of the base.
• If locking need to be prevented then mesiodistal cusps are reduced during occlusal reshaping. When mesiodistal cusps are reduced the buccolingual cusps are considered as a factor for balanced occlusion.
• In cases with a deep bite (steep incisal guidance), teeth with high cuspal inclines are required to produce posterior contact during protrusion. The inclination of the posterior teeth and their vertical relationship to the occlusal plane results in a curve that is in harmony with the movement of the mandible as guided posteriorly by the condylar path.

Compensatory curve Incisal Guidance: It is defined as, “The influence of the contacting surfaces of the mandibular and maxillary anterior teeth during mandibular movements”. –GPT

• Incisal guidance is expressed in degrees of angulation from the horizontal by a line drawn in the sagittal plane between the incisal edges of the upper and lower incisor teeth when closed in centric occlusion. If the incisal guidance is steep, it needs steep cusps, a steep occlusal plane, and a steep compensating curve to produce occlusal balance.
• Ideally, the incisal guidance should be as flat as esthetics and phonetics will permit. If the anterior teeth necessitate a vertical overlap, a compensating horizontal overlap should be set to prevent anterior interference.

Compensatory curve Occlusal Plane: It is defined as, “An imaginary surface which is related anatomically to the cranium and which theoretically touches the incisal edges of the incisors and the tips of the occluding surfaces of the posterior teeth. It is not a plane in the true sense of the word but represents the mean curvature of the surface”. –GPT

• It is established anteriorly by the height of the lower canine, almost coinciding with the commissure of the mouth, and posteriorly by the height of the retromolar pad. It is usually parallel to the ala-tragus line or Camper’s line. The tilt of the plane of occlusion beyond 10° is not advisable.
• If the occlusal plane is too low, tongue interference can cause tongue biting. At rest, after swallowing, the tongue with its tip should gently touch the lingual surfaces of the lower anterior teeth, the tongue assumes a position in which its lateral border, at the junction of the keratinized and non-keratinized mucosa, is at the level of the lingual contour of the lower natural posterior teeth. The dorsal surface of the tongue is nearly level with the occlusal surfaces of the posterior teeth.

Compensatory Curve Incorporation Of Compensating Curve

• The compensating curve incorporated in a properly oriented plane of occlusion starts with the first molar by raising it at the distal and continuing this initiated curve with a further rise in the second molar.
• The radii of the curve needed to achieve balance depend on the angle of the incisal guidance and the condylar guidance.
• It is easier to set the correct compensating curve when the lowers are set first because the determining factors of the incisal guidance and condylar inclination can be readily analyzed and related to the mandibular cast, which is in a fixed relationship to them on the articulator.
• This is accomplished by setting as shallow an incisal guide angle as phonetics, esthetics and function of the anterior teeth will permit.

Compensatory curveSignificance Of Compensating Curves

• To provide balancing occlusal contacts for protrusive mandibular positions.
• Enhances retention, and stability of the denture.
• As the forces distributed are uniform while compensatory curves are incorporated the residual ridge resorption is decreased.
• Masticatory efficiency is improved.