Compensating Curves in Prosthodontics

This presentation deals with role of compensating curves in prosthodontics. Its implications in teeth arrangements, occlusion and in prostheses

1. Compensating Curve PRESENTED BY- DR. PARTHA SARATHI ADHYA (1st year PGT, Dept. of Prosthodontics and Crown & Bridge) Under the guidance of :- Prof.(Dr.) Jayanta Bhattacharyya.(H.O.D) Prof.(Dr.) Samiran Das. Dr. Sayan Majumdar . Dr. Saumitra Ghosh . Dr. Preeti Goel .

2. contents Introduction Compensating Curve. Curve of Monson . Curve of Wilson Curve of Spee Curve of Pleasure . Compensating curve formula. Hanau’s Quint. Role of Compensating Curve in Fixed Denture Prosthesis. Review of literature

3. The determination of the occlusal plane is one of the most important steps in prosthodontic rehabilitation of edentulous patients . The position of the occlusal plane forms the basis for ideal tooth arrangement. The three dimensional arrangements of dental cusps and incisal edges in the natural human dentition are classically described as spherical, with the occlusal surfaces of all teeth touching a segment of the surface of a sphere, called the curve of Monson. It is divided into an anteroposterior curve called the curve of Spee and a mediolateral curve called the curve of Wilson . 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. Introduction

4. Compensating Curve T he anteroposterior curving (in the median plane) and the mediolateral curving (in the frontal plane) within the alignment of the occluding surfaces and incisal edges of artificial teeth that is used to develop balanced occlusion.-GPT-9 T he arc introduced in the construction of complete removable dental prostheses to compensate for the opening influences produced by the condylar and incisal guidance’s during lateral and protrusive mandibular.-GPT-9

5. Curve of Monson [George S. Monson, U.S. dentist, 1869-1933] 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 center in the region of the glabella.- GPT-9 if jaw development was ideal, an equilateral triangle would be formed by straight lines drawn connecting the centers of both condyles and connecting these centers and a point at the mesioincisal angle of the lower central incisors. – Bonwill . the points on the lower jaw teeth which move in contact with those in the skull lie on the surface of a sphere.- Von Spee .

6. Bonwill triangle was equilateral, ideal conditions seldom prevailed and that usually an isosceles triangle resulted, with the short side between the condyle centers. the center of a sphere with a radius of approximately 4 inches is equidistant from the occlusal surfaces of the teeth and the center of the condyles and that lines drawn from the center of this sphere must pass through the long axis of each tooth. This “spherical theory” has been modified and further interpreted by Morton, Maxwell.

7. Validity of Curve of Monson Although Monson’s principles apply in ideal conditions, the latter, again, are seldom found in the adult dentitions. Growth and development and environmental factors (i.e., the physiologic condition of the dental structure) have caused a deviation from the “ideal” because of loss of teeth, malposed and malaligned teeth, periodontal disease, altered muscular function, habit patterns.

8. Curve of Wilson [George H. Wilson, U.S.1855-1922 ] In the theory that 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 the curve of Wilson also permits lateral mandibular excursions free from posterior interferences

9. The curve of Wilson results from lingual inclination of the mandibular posterior teeth, making the lingual cusps lower than buccal cusps on the mandibular arch; the buccal cusps are higher than palatal cusps on the maxillary arch because of the buccal inclination of maxillary posterior teeth.

10. Role of Curve of Wilson in occlusion The curve of Wilson also permits lateral mandibular excursions free from posterior interferences. Aligning both maxillary and mandibular posterior teeth with the principal direction of muscle contraction produces the greatest resistance to masticatory forces and creates the inclinations that form the curve of Wilson. the curve of Wilson was positively correlated to intercanine , interpremolar , and intermolar distances . This means that as the curve of Wilson became steeper, these distances became smaller.

11. Role of Curve of Wilson in mastication When the curve of Wilson gets altered, masticatory function may be impaired because increased activity is required to get the food onto the occlusal table.

12. Curve of Spee [Ferdinand Graf Spee , Prosector of Anatomy, Germany, 1855-1937]: The anatomical curve established by the occlusal alignment of the teeth, as projected onto 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 and ending at the anterior aspect of the mandibular condyle.- GPT-8 The arc of a curved plane that is tangent to the incisal edges and the buccal cusp tips of the mandibular dentition viewed in the sagittal plane.

13. Proposition one: Spee indicated that from a profile view, the molar surfaces lie on the arc of a circle which, continued posteriorly , touches the anterior border of the condyle. Proposition two: It is easy to demonstrate the curve in cases with marked attrition than in cases with well-preserved cusps. Proposition three: When other points besides molars were included in measurements from the line of occlusion, they, along with the condyle, could be on a common arc . Spee suggested that this geometric arrangement defined the most efficient pattern for maintaining maximum tooth contacts during chewing and considered it an important tenet in denture construction.

14. Role of Curve of Spee in mastication Osborn reported that the curve of Spee had a positive correlation with the inclination of masseter muscle. This forward tilt of the mandibular posterior teeth arrangement maximizes the muscular efficiency during chewing. The axis of each lower tooth on the curve of Spee is aligned nearly parallel to its individual arc of closure around the condylar axis to align each tooth for maximum resistance to functional loading

15. Role of Curve of Spee in occlusion The curve of Spee permits total posterior disclusion on mandibular protrusion, given proper anterior tooth guidance. The curve of Spee may be pathologically altered due to rotation, tipping, or extrusion of teeth. Mew quotes that whenever the curve of Spee is increased, the margins of the tongue will be seen to overlay the lingual cusps of the mandibular premolar, and the greater the curve, the more likely it is to overlay both the lingual and buccal cusps, often with scalloping .

16. Analysis of the curve of Spee and the curve of Wilson in adult Indian population: A three‑dimensional measurement study Sowmya Velekkatt Surendran , Sharmila Hussain1, S. Bhoominthan , Sanjna Nayar , Ragavendra Jayesh . The Journal of Indian Prosthodontic Society | Oct-Dec 2016 | Vol 16 | Issue 4. Hydrocollied impression of 60 subjects (30 male, 30 female ) taken and master casts are obtained. The cusp tips of canines, buccal cusp tips of premolars and molars , and palatal/lingual cusp tips of second molars of 60 maxillary and 60 mandibular casts obtained were marked with an indelible marker

17. Three dimensional (x, y, z) coordinates of the cusp tips of the molars, premolars, and canines of the right and left sides of the maxilla and mandible were obtained with three dimensional coordinate measuring machine. In Indian population, males have a greater radius of the curve of Spee and curve of Wilson compared to females. For males and females, the mean radius of curve of Spee and curve of Wilson are greater in maxillary arch than mandibular arch.

18. Deepest cusp tip was the distobuccal cusp of the first molar in the maxillary arch and the mesiobuccal cusp of the first molar in the mandibular arch in both males and females. In maxillary and mandibular arches, the mean radius of the right and left curve of Spee was similar. This was observed in both the genders . In the selected subjects, the radius of the curve of Spee and curve of Wilson are greater than the 4 inch (100 mm) radius proposed by Monson.

19. Curve of Pleasure [Max A. Pleasure, U.S. dentist, 1903-1965] 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 in excessive wear of the teeth, the obliteration of the cusps and formation of either flat or cuppedout occlusal surfaces, associated with reversal of the occlusal plane of the premolar, first and second molar teeth (the third molars being generally unaffected), whereby the occlusal surfaces of the mandibular teeth slope facially instead of lingually and those of the maxillary teeth incline lingually .- GPT-9

20. 1 st proposed by the Avery brothers in 1929. It increases total efficiency. The stability of the upper denture 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 the longitudinal sliding movement of the lower cutting ridges. Reduced occlusal pressure and tissue trauma .

21. COMPENSATING CURVE FORMULA When the two buccal cusp tips and the highest-situated lingual cusp tip are connected with straight lines, these lines circumscribe a small plane which is called the “cusp plane .” The inclination of the cusp plane to the plane of occlusion is called the “cusp plane angle .”

22. The tips of the incisors, the cuspid , and the cusp plane of the bicuspids are on the line PP’,. The cusp plane of the molars is on the line MM’,. These lines each form an angle with the plane of occlusion. This angle ( ω ) is identical with the cusp plane angle.

23. of the protrusive facets with various condylar guidance inclinations is calculated in relation to the plane of occlusion. On varying the cusp plane angle, the cusp angulation of the protrusive facets has to be altered accordingly to retain the Same incline of the facets to the plane of occlusion . The action of the compensating curve is as follows. The cusp angulation of the protrusive facets of the molars (calculated in accordance with the cusp incline table) must be reduced with an angle equal to the cusp plane angle (w) . This relation can be expressed by means of the formula : C= Ԑ- ώ where C is the cusp angulation, Ԑ= the cusp angulation according the table and, ώ = the cusp plane angle. This formula is called the “formula for the compensating curve

24. BICUSPID ARRANGEMENT The angul.ation of the bicuspid plane to the condylar guidance is: ß’= β + ω which is greater than the inclination of the condylar guidance ( β ). Therefore, the cusp angulation may be steeper to attain antagonistic contact for protrusive movement. Consequently , the curve of occlusion decreases the cusp angulation for the molars and increases the cusp angulation of the bicuspids.

25. we do not use high cusps for the bicuspids. In the region of these teeth, therefore, the antagonists lose their contact during protrusive gliding movements . This is also true on the balancing side during lateral movements. The advantages of this arrangement are the possibility of chewing hard food in the bicuspid region and the coincidentally obtained antagonistic contact in the front and in the molar region.

26. Hanau’s Quint Rules for balanced denture articulation including incisal guidance, condylar guidance, cusp length, the plane of occlusion, and the compensating curve.-GPT-9 [K × I]/[OP × C × OK]. K = the inclination of condylar guidance, I = the inclination of the incisal guidance, C = the height of the cusps, OP = the inclination of the plane of orientation, OK = the prominence of the compensating curve.

27. In order to obtain a smooth, balanced occlusion, the compensating curve must be in harmony with the other factors of occlusion. This relationship is expressed in Hanau’s Quint.

28. TRAPOZZANO CONCEPT His Triad of Occlusion, which is simpler than Hanau's Quint but eliminates the important compensating curve. the plane of orientation since its location is highly variable within the available inner ridge space. Incisal guidance Condylar guidance Cusp angle.

29. BOUCHER CONCEPT Trapozzano's concept that the occlusal plane could be located at various heights to favor a weaker ridge, and he recommended that the occlusal plane "be oriented exactly as it was when the natural teeth are present. '' He believed that this must be done to conform to anatomic and functional needs. There are three fixed factors: The orientation of the occlusal plane, the incisal guidance, and the condylar guidance. " The value of the compensating curve is that it permits an alteration of cusp height without changing the form of the manufactured teeth . . . . If the teeth themselves do not have cusps, the equivalence of cusps can be produced by using a compensating curve. '‘ The compensating curve enables one to increase the effective height of the cusps without changing the form of the teeth . The angulation of the cusp is more important than the height of the cusp.

30. Lott concept Lott studied Hanau's work and clarified the laws of occlusion by relating them to the posterior separation that is the resultant of the guiding factors . The greater the angle of the condyle path, the greater is the posterior separation. The greater the angle of the overbite (vertical overlap), the greater is the separation in the anterior region and the posterior region regardless of the angle of the condylar path The greater the separation of the posterior teeth, the greater, or higher, must be the compensation curve

31. Posterior separation compensation curve to balance the occlusion requires the introduction of the plane of orientation The greater the separation of the teeth, the greater must be the posterior teeth . Levin concept The condylar guidance is fixed and is recorded from the patient. The incisal guidance is usually obtained from the patient’s esthetic and phonetic requirements. However, it can be modified for special requirements. The compensating curve is the most important factor for obtaining balance. Monoplane or low cusp teeth must employ the use of a compensating curve. Cusp teeth have the inclines necessary for obtaining balanced occlusion but nearly always are used with a compensating curve.

32. My concept of the laws of articulation is quite similar to Lott's, but I would eliminate the plane of orientation . I am in agreement with Boucher 3 as to the need for the compensating curve and that the occlusal plane should be included only in its correct anatomic position, i.e., in the position that conforms to the patient's anatomy, esthetics, and function .

33. Role of Compensating Curve in Fixed Denture Prosthesis Cones should follow an anteroposterior curve (of Spee ) and a lateral curve (of Wilson).

34. Role of Compensating Curve in Fixed Denture Prosthesis Pankey -Mann-Schuyler (PMS) philosophy The incisal guidance was the developed intraorally with acrylic resin to satisfy esthetic and functional requirements . Optimal occlusal plane is selected as dictated by the curve of Monson and mandibular posterior teeth are restored in harmony with the anterior guidance such that they will not interfere with the condylar guidance. Group function occlusion on the working side during lateral excursions . Maximum number of contacts on posterior teeth in centric relation.

35. Maxillary posterior occlusal surfaces are developed after the completion of mandibular restorations by the functionally generated path technique (FGP ). Use of FGP records allows eliminating all occlusal interferences and establishing functional form of the occlusal surfaces of the restoration.

36. Hobo concept Hobo and Takayama in their study revealed that anterior guidance influenced the working condylar path and concluded that they were dependent factors. cusp angle be considered as the most reliable determinant of occlusion as cusp angle does not deviate and is 4 times more reliable than the condylar and incisal path which show deviation.

37. Boardrick’s Occlusal Plane Analyser (BOPA ) BOPA is used to determine and achieve an occlusal plane that fulfills both the functional, occlusal as well as the aesthetics requirement in cases that require full mouth rehabilitation. It was based on an anthropological study in 1919, that Monsoon proposed the anteroposterior curve of the teeth forms a sphere, with the center of rotation located in the region of the glabella. The Broadrick Flag allows the construction of the Curve of Spee in perfect harmony with the anterior condylar guidance allowing total posterior tooth disclusion on mandibular protrusion

38. Anterior survey point (ASP) was selected on midpoint of disto-incisal edge of mandibular canine, from which long arc of 4-inch radius was drawn on flag with use of compass. Posterior survey point (PSP) was located on disto-buccal cusp of distal mandibular molar. If position of this tooth were deemed unacceptable, anterior border of condylar element on articulator could be selected as PSP.

39. Short arc of 4-inch radius was drawn from PSP on flag to intersect long arc at center of curve of Spee . Point of compass was placed at center of flag, and 4-inch radius was drawn through buccal surfaces of mandibular teeth . The angle of the condylar guidance is not less than the curve of Spee , as this would introduce posterior protrusive interferences The center should always lie along the long arc drawn from the anterior survey point, but it may be moved in an anterior or posterior direction from the intersection of this arc with that drawn from the posterior survey point.

40. Significance of BOPA Preliminary determination of an acceptable plane of occlusion on the study models as an aid in treatment planning. Preliminary determination of the amount of reduction that will be required when each tooth is prepared. In the laboratory wax-up and final metal ceramic restoration, determination of the height of each cusp tip, which helped in establishing the curve of Spee and the curve of Wilson.

41. Simplified Occlusal Plane Analyser (SOPA ) Composed of a compass of 4 inch radius. Touch the compass lead (C) to the tip of the lower cuspid . Position the compass point (D ) on the center line (for the 4” radius) of the SOPA flag. Arc the compass lead to the back molar . This establishes the optimum occlusal plane height for the posterior teeth.

42. The role of occlusal curvatures and maxillary arch dimensions in patients with signs and symptoms of temporomandibular disorders Georgios Kanavakisa ; Noshir Mehtab . Angle Orthodontist, Vol 84, No 1, 2014. 100 subjects were taken randomly and impression were taken of both arches. For the investigation of TMJ disorders RDC-TMD criteria was used along with various joint sounds were also investigated. Measurements on plastermodels were performed with the use of a digital caliper. The depth of the curve of Spee was measured at the most distal premolar and at the molar level. The highest value on each side was recorded.

43. The curve of Wilson (COW) on each side was measured as the angle between the frontal projected buccal -lingual plane of the cusp tips on the first mandibular molars, according to Ali et al. Results- This finding was consistent on both sides, so it can be concluded that people with a flatter curve of Spee present a higher incidence of joint sounds during lateral excursions . The curve of Wilson was positively correlated to intercanine , interpremolar , and intermolar distances. subjects with a steeper COW presented narrower maxillary arches. Conclusion Subjects with TMJ sounds present a flatter COS . Deep occlusal curvatures are not associated with TMJ pain or pain of muscular origin.

44. Association between occlusal curvature and masticatory movements with different test foods in human young adults with permanent dentitions Kenji Fueki , Eiko Yoshida, Kota Okano, Yoshimasa Igarashi. Archives of Oral Biology (2013 ). Forty-six subjects (21 females, 25 males, mean age 25.0 years, range 20–32 years), with completely natural dentition and Angle Class I molar relationship were taken. Upper and lower dental casts of each subject were mounted on a semi-adjustable articulator. The mandibular cast mounted on the lower member of the articulator was fixed to a threedimensional measuring gauge (QM-measure 353, Mitsutoyo Mfg ., Tokyo, Japan). The coordinates of the mid-points of the canine cusps, and the buccal and lingual cusps of the premolars , first and second molars were measured and digitized .

45. The approximate spheres were calculated from the measurements according to the Broadrick Occlusal Plane Analyzer using a custom made software . Mandibular movements during unilateral chewing of six test food items (chewing gum, cheese, kamaboko , boiled beef, gummy jelly and raw carrot) until the subjects felt ready to swallow were recorded using a six-degrees-of-freedom mandibular movement recording system.

46. Conclusion- subjects with larger SR tended to show masticatory cycles with greater vertical and lateral amplitude, faster opening/closing velocity, shorter opening/closing/ oc - cluding /cycle duration, and they tended to chew the test foods until ready to swallow with less number of chewing strokes and chewing time compared to those with smaller SR. The mean value of curve of spee is 112mm which is greater than 4 inch as described by Mansoon .

47. Conclusion Difference of opinions exist regarding importance of compensating curves during fabrication both removable denture prosthesis and (tooth supported or implant supported) fixed denture prosthesis. From experts’ opinion, literature reviews and case reports, i t is evident that prosthodontist should have a sound knowledge about the occlusal curves of natural dentition and compensating curves. To achieve success in clinical practice, establishment of compensating curves in dental prosthesis is one of the important key factors which increases patients’ compliance as well as longevity of the restoration.

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