Occlusal planes and compensating curves

A detailed review on two very important topics in the field of dentistry used in case of processing a dental prosthesis.

1. Occlusal planes & compensating curves. Presented by- Moderated by- NAYANJIT TALUKDAR - Dr. Jogeswar Barman Roll No.- 16 - Dr. Rajdeep Paul 2 nd year BDS Regional Dental College.

2. Occlusion According to GPT 9- The static relationship (process of closure) between the incising or masticating (occluding) surfaces of the maxillary or mandibular teeth or tooth analogues.

3. Difference between natural teeth and complete denture occlusion.

4. Centric relation It is the maxillomandibular relationship, independent of tooth contact, in which the condyles articulate in the anterior-superior position against the posterior slopes of the articular eminences, and are resting in the most retrussive unstrained position in the glenoid fossa.

5. It is the occlusion of the opposing teeth when the mandible is in centric relation, which may or may not coincides with the maximum intercuspation during swallowing and the terminal position of a masticatory stroke. Centric occlusion

6. Types of cd occlusion * Balanced occlusion * Monoplane occlusion * Lingualized occlusion

7. Definition:- It is defined as the bilateral simultaneous, anterior and posterior occlusal contact of teeth in centric and eccentric positions. - GPT-9 Balanced occlusion in complete denture is unique, as it doesn't occur with the natural teeth . If it occurs with the natural teeth, it is considered as a premature contact on nonworking side and is considered as pathologic. balanced occlusion

8. Significance. This concept was originally put forth to enhance the retention as well as the stability of the denture during mastication. It is deemed necessary during many excursive movements like swallowing saliva, closing to reseat dentures and bruxism, performed by patients in between meals. If balance is not present, the denture base could tip, shift or torque on their foundation during the eccentric movements and cause soreness and inflammation, leading to accelerated bone resorption. Equal contact of all posterior teeth in centric relation is definitely essential to the healthy mucosa, though the same cannot be stated for contact in eccentric relations.

9. Factors affecting Balanced Occlusion. Condylar guidance. Incisal guidance. Orientation of the occlusal plane. Compensating curves. Cuspal inclination.

10. Importance. The determination off the occlusal plane is one of the most important steps in prosthodontics rehabilitation of edentulous patients. The position of occlusal plane forms the basis for ideal tooth arrangement. The 3D arrangements of dental cusps and incisal edges in the natural human dentition are classically described as spherical, with the occlusal surface of all teeth touching a segment of the surface of the sphere, called as Curve of Monsoon. It is divided into an anteroposterior curve and a mediolateral curve called as curve of Spee and curve of Wilson respectively. Reestablishment of these curves of natural dentition is essential during rehabilitation of a patient in prosthodontics. Replacement of natural occlusal curves with artificial teeth are collectively known as compensating curves which hold an important place in complete denture fabrication.

11. Occlusal Plane. Occlusal plane or plane of occlusion refers to an imaginary average plane that is theoretically established by the incisal edges of the incisors and the tip of the occluding surface of the posterior teeth. -- GPT-9 Generally, it is not a plane but represents the planar mean of the curvature of these surfaces.

12. Orientation. It is established anteriorly by the height of the lower canine, which nearly coincides with the commissure of the mouth. Posteriorly, it is established by the height of the retromolar pad. It is also related to the ala-tragus line. It must be orientated in the same relation as when natural teeth existed, and hence, there is not much scope to manoeuvre this factor

13. Significance of Occlusal Plane. The configuration of the occlusal plane is important as slight variation will lead to occlusal instability. It should be in harmony with the other components of the masticatory system. It forms the basis by which occlusal surfaces of teeth can be related to one another and to other structures of the head.

14. Different occlusal planes. Thayers in 1990 AJO has given three different occlusal planes . They are- Bisected occlusal plane. Functional occlusal plane. Lower incisor occlusal plane. Upper/lower occlusal plane.

15. Compensating Curves. They are defined as the anteroposterior curvature (in the median plane) and the mediolateral curvatures (in the frontal plane) within the alignment of the occluding surfaces and the incisal edges of artificial teeth that is used to develop balanced occlusion. --- GPT-9 . The arc introduced in the construction of complete removable dental prosthesis to compensate for opening influences produced by the condylar and incisal guidance's during lateral and protrusive jaw movements. --- GPT-9.

16. They are determined by the inclination of the posterior teeth and their vertical relationship to the occlusal plane. This results in curve that is in harmony with the mandibular movements as dictated by condylar guidance – both protrusive and lateral. A steep condylar guidance requires steep compensating curve for occlusal balance; otherwise, it will lead to loss of balancing molar contact during protrusion and lateral excursion.

17. The curves that assist in producing balanced occlusion are as follows-

18. Curve of Spee. It is the anatomic curve established by the occlusal alignment of the teeth, as projected to the median plane, beginning with the cusp tip of the mandibular canine and following the buccal cusp tips of the premolar and molar teeth, continuing through the anterior border of the mandibular ramus, ending with the anterior-most portion of the mandibular condyle. -- GPT-9 It was first described by Ferdinand Graf Spee, German anatomist, in 1890. Spee suggested that this geometric arrangement is the most efficient pattern for maintaining maximum tooth contact during chewing & considered as an important tenet in denture construction.

19. This curve assist in obtaining protrusive balance. Without this curve, it would be necessary to tilt the entire occlusal plane at an angle and raising it distally, to obtain balance. This will destabilize the upper denture and cause damage to the rugae area, increasing bone resorption in this area. This radius or steepness of the curve necessary to achieve balance is dependent on the incisal and condylar guidance. It is functionally and mechanically advantageous to keep it as modest or shallow as possible.

20. In the theory that the occlusion should be spherical, the curvature of the cusps as projected on the frontal plane expressed in both arches; the curve in the mandibular arch being concave and the one in the maxillary arch being convex. -- GPT-9 It is named after George Wilson , who described it in 1911. The curve of Wilson also permits lateral mandibular excursions free from posterior interferences. Curve of Wilson.

21. Curve of Wilson.

22. This is curve that is convex downwards . It is used to arrange the molar teeth. This curve results from the lingual inclination of the mandibular posterior teeth; making the lingual cusps lower than the buccal cusps and bringing them in heavy occlusal contact with the upper buccal cusps during lateral movements of the working side, which are placed higher than its palatal cusp due to the buccal inclination of maxillary arch.

23. It is a curve of occlusion that is convex upwards . This is used to arrange the 1 st premolars. 1 st proposed by Avery Brothers. Reverse curve or Anti-Monsoon curve .

24. This is the curve of occlusion in which each cusp and incisal edge touches or conforms to a segment of the surface of a sphere 8 inches in diameter with its centre in the region of the glabella. -- GPT-9 This curve in three dimensions is a combination of the ‘ curve of Spee’ and ‘curve of Wilson’. This curve is named after George S. Monson in 1932. Curve of Monsoon.

25. Bonwill was the 1 st to describe the dental arches, noted that an equilateral triangle of 4 inch sides existed between the centres of condyles and the mesial contact areas of the mandibular central incisors. In 1932, Monsoon, used Bonwill’s triangle and proposed a theory of a sphere and curve formed from that sphere was later known as Curve of Monsoon. Bonwill triangle.

26. This is a helicoid curve of occlusion that, when viewed in the frontal plane, conforms to a mediolaterally convex curve in which the lingual surfaces of the teeth are more coronal to the buccal surfaces, except for the last molars, which reverse that pattern. -- GPT-9 1 st proposed by Max Pleasure in 1937. This is a combination of Monsoon and anti-Monsoon curves. Hence, it is not a single curve but a combination of curves. It is used for arranging non-anatomic teeth in balanced occlusion. Curve of Pleasure.

27. The premolars and 1 st molars are set in a reverse curve to prevent buccal tipping and seat the denture. 2 nd molars are set in a conventional Monsoon’s curve to provide eccentric lateral balance. This curve increases the total efficiency and stability of the upper dentures during speech, laughter, coughing, sneezing, etc. Enhanced stability of the lower denture during closure against a morsel of food. Unimpaired balancing contacts, increased cutting efficiency because of longitudinal sliding movements of the lower cutting ridges. Reduced occlusal pressure and tissue trauma.