Basic Concepts Of Occlusion mu2c

DEPTT. OF PROSTHODONTICS & CROWN &BRIDGE

CONCEPTS OF OCCLUSION IN COMPLETE DENTURE SEMINAR VIKAS AGGARWAL

INDEX

1. INTRODUCTION 2. DIFFERENCE BETWEEN NATURAL AND ARTIFICIAL DENTITION 3. REQUIREMENTS OF COMPLETE DENTURE OCCLUSION 4. CONCEPTS OF OCCLUSION 5. VARIOUS THEORIES OF OCCLUSION 6. BALANCED OCCLUSION 7. NON BALANCED OCCLUSION/MONOPLANE OCCLUSION 8. LINGUALIZED OCCLUSION 9. ORGANIC CONCEPT OF OCCLUSION 10.TYPES OF OCCLUSAL SCHEMES 11.CONCLUSION

CONCEPTS OF OCCLUSION INTRODUCTION Occlusion is a factor that is common to all branches of dentistry. The study of occlusion and its relationship to function of the masticatory system has been a topic of interest in dentistry since many years. One of the chief aims of preventive and restorative dentistry has been to maintain an occlusion that will function in harmony with the other components of the masticatory mechanism, thereby preserving their health and at the same time providing the optimum, if not maximum masticatory function. OCCLUSION: according. to GPT 8th ed a) Act or process of closure or of being closed or shut off b) The static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth or tooth analogues ARTICULATION: It is defined as the dynamic relationship between the occlusal surfaces of the teeth during function. ( GPT 8th) Sliding occlusion is the ing of teeth in motion. Sliding occlusion occurs when the occlusal surface of the teeth make when the mandible is moving. Centric occlusion is the position of mandible when the relationship of the opposing occlusal surface that provides the maximum planned and / or intercuspation. Centric occlusion with teeth present is the tooth-to-tooth relation whereas centric relation is a static position, is a bone-to-bone relation. Eccentric occlusion is a ing of teeth or occluding surface when the jaws are in any other relation other than centric occlusion

Differences between natural and artificial occlusion: 1. The teeth in natural dentitions are retained by periodontal tissues that are innervated by proprioceptive fibres. In edentulous mouths, both occlusion and proprioceptive mechanism are lost. In complete denture occlusion all the teeth are on bases seated on movable tissues. 2. In natural dentitions the teeth receive individual pressures of occlusion and can move independently to adjust to occlusal pressures. The artificial teeth move as a unit on a base. 3. Malocclusion of natural teeth may be uneventful for years. Malocclusion of artificial teeth evokes an immediate response and involves all of the teeth and the base. 4. Non vertical forces on natural teeth during function affect only the teeth involved, are usually well tolerated, whereas in artificial teeth, the effect involves all of the teeth on the bases and is traumatic. 5. Incising with the natural teeth does not affect the posterior teeth whereas incising with artificial teeth affects all of the teeth on the base. 6. In natural teeth, the second molar is the favoured area for masticating hard foods, owing to more favourable leverage and power. Heavy pressures of mastication in the second molar region with artificial dentition will tilt the base. 7. In natural teeth, bilateral balance is rarely found, and if present it is considered balancing side interference. In artificial teeth bilateral balance is generally considered necessary for base stability.

8. In natural teeth, prematurities are avoided due to neuromuscular system control and establish stable habitual occlusion away from centric relation. In artificial occlusion any prematurity causes instability due to lack of . Requirements of Complete Denture Occlusion According to Ortmann (1971) the requirements of complete denture occlusion which are: 1. Stability of occlusion at centric relation position and in area forward and lateral to it. 2. Balanced occlusal s bilaterally for eccentric s. 3. Unlocking the cusps mesiodistally to allow for gradual but inevitable settling of the bases due to tissue deformation and bone resorption. 4. Control of horizontal force by buccolingual cusp height reduction according to residual ridge resistance form and inter arch distance. 5. Functional lever balance by favourable tooth to ridge crest position. 6. Cutting, penetrating and shearing efficiency of occlusal surfaces. 7. Anterior incisal clearance during posterior masticatory function. 8. Minimum occlusal areas for reduced pressure in communiting food. 9. Sharp ridges or cusps and generous sluice ways to shear and shred food with the minimum of force necessary. These requirements can be applied if the occlusion is divided into 3 distinct units incising, working, and balancing. Requirements for incising units: 1. These units should be sharp in order to cut efficiently.

2. They should not during mastication. 3. They should have as flat incisal guidance as possible considering esthetics and phonetics. 4. They should have horizontal overlap to allow for base settling without interference. 5. They should only during protrusive incising function. Requirements for working occlusal units: 1. They should be efficient in cutting and grinding. 2. They should have decreased bucco-lingual width to minimize the work force directed to the denture foundation. 3. They should function as a group with simultaneous harmonious s at the end of the chewing cycle and during eccentric excursions. 4. They should be over the ridge crest in the masticating area for lever balance. 5. They should have a surface to receive and transmit the force of occlusion essentially vertically. 6. They should centre the work load near the anteroposterior centre of the denture. 7. They should present a plane of occlusion as parallel as possible to the mean foundation plane. Requirements for balancing units: 1. They should on the second molars when the incising units in function.

2. They should at the end of the chewing cycle when the working units . 3. They should have smooth gliding s for lateral and protrusive excursions. Axioms for artificial occlusion were published by Sears in 1952 which have guided the planning of complete denture occlusion for many years: 1. The smaller the area of occlusal surface acting on food the smaller will be the crushing force on food transmitted to the ing structures. 2. Vertical force applied to an inclined occlusal surface causes non vertical force on the denture base. 3. Vertical force applied to an inclined ing tissue causes non vertical force on the denture base. 4. Vertical forced applied to a denture bases ed by yielding tissue causes the base to teeter when the force is not centred on the base. 5. Vertical force applied outside (lateral) to the ridge crest creates tipping force on the base. CONCEPT’S OF OCCLUSION Occlusion must satisfy physiologic requirement and be acceptable to the patient. When considering the concepts of occlusion, one must review certain factors which will govern a satisfactory arrangement of teeth for complete denture. There is no scientific proof that any one concept of occlusion will satisfy the entire requirement of a complete denture in a patient. There is likewise no scientific proof that one tooth form is more efficient than other tooth form. It is almost impossible to conduct a scientific investigation that will

give definite predictable results of the reactions of the basal seat to denture. Clinical observation and evaluation are not always reliable. Competent prosthodontics differs in their evaluations. Theory means observation based on principles and concept is application of theory. In pertinence to occlusion the concept of occlusion for complete denture falls in to two broad disciplines (Heartwell 5th ed) 1) Balanced occlusion. 2) Non-balanced occlusion. Any occlusion other than balanced occlusion is referred to as non-balanced occlusion. This includes arrangement according to, Spherical theory, Organic occlusion, Neutrocentric concept Concepts of occlusion according to Boucher (11th ed) 1. Balanced 2. Monoplane 3. Lingualized

Various Theories of occlusion 1. Bonwill theory of occlusion 2. Conical theory of occlusion 3. Spherical theory of occlusion

1) BONWILL THEORY OF OCCLUSION 1858 He developed the theory of equilateral triangle, in which there was a 4-inch distance between the condyles and between each condyle and incisor point. This theory proposed that teeth move in relation to each other as guided by the condylar controls and the incisal point 2) CONICAL THEORY OF OCCLUSION R.E. Hall (1915) Theory proposed that the lower teeth move over the surfaces of the upper teeth as over the surfaces of a cone with a generating angle of 45 degree and with a central axis of the cone tipped at a 45 degree angle to the occlusal plane. The Hall automatic articulator designed by R.E. Hall is an example of such a theory.

3) SPHERICAL THEORY This theory was proposed by G.S. Monson in 1918 and was based on the observations of natural teeth and skulls made by Von Spee. This form of occlusion is sometimes referred to as having Monson's Curve. The spherical theory shows the lower teeth moving over the surface of the upper teeth as over the surface of a sphere of a diameter 8 inches (20 cms.). The center of the sphere is located in the region of the glabella and surface of the sphere es through the glenoid fossa along the articulating eminences or concentric with them.

VARIOUS CONCEPTS OF OCCLUSION A) BALANCED OCCLUSION Definition: “The simultaneous ing of maxillary and mandibular teeth on right and left and in the posterior and anterior occlusal areas in centric and eccentric positions.”-Heartwell It is defined as “stable simultaneous of the oppoper and lower teeth in centric relation position and a continuous smooth bilateral gliding from this position to any eccentric position within normal range of mandibular function.”-Winkler

Balanced occlusion involves the arrangement of the teeth to provide even tooth between posterior and anterior teeth as the mandible moves to and from centric and eccentric positions. The purpose of this arrangement of the teeth is to provide stabilizing forces to the denture bases on their basal seat when the teeth make and the jaws are in centric and eccentric relation. This type of articulation helps to maintain the stabilizing forces as mandible moves the teeth to and from centric occlusion and eccentric occlusion.

When artificial cusp form teeth are arranged for complete denture it is possible that the occlusal surface of the teeth should be altered to allow freedom of tooth movement in harmony with the rotation when it occurs in fossae. The freedom of tooth is accomplished by altering the fossae of the tooth both anteroposteriorly and mesiodistally. When a non-cusp form posterior tooth is

used this freedom exists. In both situations the anterior teeth are arranged or altered to allow this freedom of movement. The anterior teeth are not arranged in when the jaws are in centric relation. This concept of occlusion is similar to alteration of natural teeth to develop freedom in centric or long centric relation and includes concept of balanced occlusion. This concept does not imply that centric relation is an area; it means that centric occlusion for some individuals may be an area.

a) the most retruded position of mandible with posterior teeth in maximum intercuspation at given vertical dimension. b) Centric occlusion anterior to centric relation: first position of tooth (1): maximum intercuspation of posterior teeth (2) This is often referred to as acquired centric occlusion with natural teeth but the use of centric is confusing C) Long centric occlusion: position of first tooth (1) The freedom of tooth between points 1 and 2 is accomplished by altering the fossae of the tooth both anteroposteriorly and mesiodistally

Concepts Proposed To Attain Balanced Occlusion 1) Gysi’s concept (1914) - for the use of 33 degree anatomic teeth under various movements of articulator to enhance stability of denture. 2) Sear’s concept (1920) - Balanced occlusion for non-anatomical teeth with anteroposterior & lateral curvature or use of second molar ramp. 3) Pleasure’s concept- Also called posterior reverse lateral curve. In 1937, Dr. Max Pleasure described a reverse occlusal scheme in which the posterior teeth are set with buccal tilt providing total lever balance during function. Buccal tilt is given at the premolars , no tilt or flat occlusal surface at first molars and a lingual tilt (Monson curve) to second molars. The reverse curve is created to direct forces of occlusion lingually to favor stability of lower denture. Lingual tilt of the second molar provides a buccal rise to provide for a lateral balancing .A compensating curve is developed in the first and second molar area to provide for protrusive balance. This scheme is especially beneficial for patients with class II jaw relation.The lever balance obtained in the premolar area is nearly at the anterio-posterior center of the denture foundation coinciding with the zone where class II patient functions during light to heavy intermediate chewing..

4) French concept (1954)- Increasing the stability of denture by reducing the occlusal table of lower posterior teeth while maintaining the balanced concept. He arranged upper first premolar with 5 degree of inclination, upper second premolar with 10 degree of inclination, upper molars with 15 degree of inclination.

5)Frush’s concept-1966 – (linear occlusion) One dimensional between opposing posterior teeth that initially could be arranged to balanced articulation on dental instruments followed by interocclusal shaping to obtain balanced articulation. Linear occlusion is a one dimensional between two opposing posterior teeth. The occurs only in one dimension which is the length of the ing blade (not surface). This blade, being always in the form of a straight line, geometrically constitutes “length” in occlusal without either “width” or “depth” of occlusal s. Intent of this occlusion was to remove occlusal deflective s and provide greater stabilization of dentures.

REQUIREMENTS OF BALANCED OCCLUSION 1. All the teeth of working side should glide evenly against the opposing teeth. 2. No single tooth should produce any interference or disocclusion of other teeth. 3. There should be s in balancing side, but they should not interfere with the smooth gliding movement of the working side. 4. There should be simultaneous during protrusion SIGNIFICANCE: Brewer (1963) found in a 24 hour test that: ”Normal individual makes masticatory tooth only for 10 mins in one day compared to 24hrs of total tooth during other functions. So, for these 24hrs of tooth , balanced occlusion is important to maintain denture stability It improves the stability of denture, reduce resorption of the residual ridge and soreness and improve oral comfort & well-being of the patient. BALANCE AS RELATED TO COMPLETE DENTURE

When forces act on a body in such a way that no motion results, then there is balance or equilibrium. This should be the primary aim of the dentist i.e. to achieve a stable base. In order to do so the following axioms have to be followed: by Sears 1. The wider and larger the ridge and closer the teeth are to the ridge, the greater the balance. 2. Conversely, the smaller and narrower the ridge and farther the teeth from the ridge, the poorer the balance 3. The wider the ridge and narrower the teeth buccolingually, the greater the balance. 4. Conversely, the narrower the ridge and wider the teeth, the poorer the balance. 5. The more lingual (with-in limits provided by the tongue) the teeth are placed in relation to alveolar ridge crest, the greater the balance. 6. The more buccal the teeth are positioned, the poorer the balance.

TYPES OF BALANCE Balance may be unilateral, bilateral, or protrusive. 1) UNILATERAL LEVER BALANCE This is present when there is balance of the base on its ing structures when food bolus is interposed between the teeth on one side and a space exits between the teeth on the opposite side. Following points encourages the lever balancea) Teeth placement should be such that to direct the resultant force on the functioning side over the ridge or slightly lingual to it.

b) Having the denture base cover as wide an area on the ridge as possible. c) Placing the teeth as close to the ridge as other factors will permit. d) Using as narrow a buccolingual width occlusal food table as practical.

2) UNILATERAL OCCLUSAL BALANCE This is present when the occlusal surfaces of teeth on one side articulate simultaneously, as a group, with a smooth uninterrupted glide. 3) BILATERAL OCCLUSAL BALANCE This is present when there is equilibrium on both sides of the denture due to simultaneous of the teeth in centric and eccentric occlusion. It requires a minimum of three s to establish a plane of equilibrium. This balance is dependent on the interaction of the incisal guidance, plane of occlusion, angulations of teeth, compensating curve, and condylar guidance 4) PROTRUSIVE OCCLUSAL BALANCE This is present when the mandible moves essentially forward and the occlusal s are smooth and simultaneous in the posterior both on right and left sides and on the anterior teeth. It is slightly different from bilateral balance in that it requires a minimum of three s, one on each side posteriorly and one anteriorly, and is dependent on interaction of the same factors as bilateral occlusal balance.

ADVANTAGES OF BILATERALLY BALANCED OCCLUSION Prime gave the concept of “ENTER BOLUS EXIT BALANCE” which implies that introduction of food on one side will prevent the teeth of opposite side from ing and hence occlusal balance is impossible during mastication. However Sheppard (1964) later gave the concept of ENTER BOLUS ENTER BALANCE according to which even while chewing, the teeth cut through the bolus and come in with each other, for few fractions of a second. Hence the stability of the denture is maintained during various movements of mandible during chewing. Moreover, the bilateral balanced occlusion is even more important during functional and the parafunctional activities like swallowing of the saliva, closing to seat the denture and bruxing of the teeth. Balanced occlusion thus will make such episode less damaging to the ing structures during the times of stress As Winkler stated balancing occlusion in complete dentures is like changing stumbling prose to poetry. 1. Bilateral simultaneous help to seat the dentures in a stable position during mastication, swallowing and maintain retention and stability of the denture and the health of the oral tissues. 2. Due to cross-arch balance, as the bolus is chewed on one side, the balancing cusps will come close or will on the other. The dictum “Enter bolus, exit balance” is therefore refuted. 3. Denture bases are stable even during bruxing activity.

Disadvantages of Balanced Occlusion: 1. It is difficult to achieve in mouths where an increased vertical incisor overlap is present – Class II cases. 2. It may tend to encourage lateral and protrusive grinding habits. 3. A semi adjustable or fully adjustable articulator is required. FACTORS AFFECTING BALANCED OCCLUSION Rudolph.L.Hanau 1930 described nine factors that govern the articulation of artificial teeth .These nine factors are called the laws of balanced articulation. Hanau later condensed these factors to 5 articulation factors and named it the articulation Quint. LAWS OF BALANCED ARTICULATION 1. Horizontal condylar guidance 2. Compensating curve 3. Protrusive incisal guidance 4. Plane of orientation 5. Buccolingual inclination of the tooth axis 6. Sagittal condylar pathway 7. Sagittal incisal guidance 8. Tooth alignment

9. Relative cusp height HANAU’S QUINT 1. Condylar guidance 2. Incisal guidance 3. Orientation of occlusal plane 4. Inclination of the cusps 5. Prominence of the compensating curve

Thielmann subsequently simplified Hanau‟s factors in a formula for Balanced Articulation. [K x I] / [OP x C x OK] Where, K = Condyle guidance. I = Incisal guidance. C = Cusp height inclinations. OP = Inclination of the occlusal plane. OK = Curvature of the occlusal surfaces. TRAPAZZANO CONCEPT Trapazzano (1963) reviewed Hanau‟s five factors and decided only 3 factors were actually concerned in obtaining balanced occlusion. He eliminated need for compensating curve and plane of occlusion and called it Traid of Occlusion. He said that plane of occlusion could be shifted to weaker ridges hence its location is not constant and is variable with in interarch distance. He also dismissed the need of compensating curves, according to him when we arrange cusped teeth in principle these curves are produced automatically.

BOUCHER’S CONCEPT Boucher in (1963) disagreed with Trapazzano and felt that the occlusal plane could be located at various heights to favour 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 confirm to anatomic and functional needs. Boucher, unlike Trapozzano, felt there was a need for a compensating curve and stated, "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. Boucher's concept is that a) There are three fixed factors: The orientation of the occlusal plane, the incisal guidance, and the condylar guidance; b) The angulation of the cusp is more important than the height of the cusp c) The compensating curve enables one to increase the effective height of the cusps without changing the form of the teeth.

LOTT’S CONCEPT Lott (1963) 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. He stated the laws as follows: 1. The greater the angle of the condyle path, the greater is the posterior separation. 2. 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 condyle path. 3. The greater the separation of the posterior teeth, the greater, or higher, must be the compensation curve. 4. Posterior separation beyond the ability of a compensation curve to balance the occlusion requires the introduction of the plane of orientation. 5. The greater the separation of the teeth, the greater must be the height of the cusps of the posterior teeth.

LEVIN’S CONCEPT Bernard Levin (1978) described the laws of articulation in a Quad. Levin‟s concepts are similar to that of Lott‟s, but he eliminates the plane of occlusion. However Hanau‟s five laws are found most acceptable. As described by the Rudolph L.Hanau there are five factors involved in balanced occlusion of CD. These factors are: 1. Inclination of the Condylar guidance 2. Inclination of the Incisal guidance 2. Inclination of the Plane of orientation 3. Prominence of Compensating curve 4. Height of cusps.

1. Condylar Guidance: Is the mandibular guidance generated by the condyles traversing the contours of the glenoid fossa. It is one of the end controlling factors. It is independent of tooth . The condylar path is determined on the patient by a protrusive record and set on the instrument. It acts as a posterior control factor. As defined by G.P.T-8, it is mandibular guidance generated by the condyle and articular disc traversing the contour of glenoid fossae. Of the five factors governing the laws of articulation as given to us by Hanau, the condylar inclination is one of the three most important and necessary factors utilized in securing balanced articulation and forms one of the end-controlling factors

There is controversy that whether condylar path is precise or not. Kurth (1954) claims that condylar path is not same for varying incisal guidance. Payne (1951) has shown that mandible can move to follow steep cusps, modified cusps and zero degree teeth when there is posterior harmony and no anterior interference is present. Weinberg (1976) has demonstrated that the condylar path may vary with the variable pressure of function.

As stated by Hanau (and agreed by Trapozzanno) that the condylar guidance is the factor edentulous patient presents and can no way be modified by the operator. Factors which determine the registration of condylar guidance are – a) Shape of the bony contour of glenoid fossae; b) Muscles attaching to the mandible ; c) Limitation of the movement by attached ligaments. d) The registration method used. i.e. If registration method require bases to rest on tissue of mandible and maxilla, the REALEFF can modify the recordings.(Hanau) 2. Incisal Guidance : As defined by G.P.T- 8 It is the influence of the ing surfaces of the mandibular and maxillary anterior teeth on mandibular movements. And incisal guide angle is defined as the angle formed by the intersection of the plane of occlusion and a line within the sagittal plane determined by the incisal edges of the maxillary and mandibular central incisors when the teeth are in maximum intercuspation.

Trapozanno( 1963) defined it as the steepest angle formed with the horizontal plane by drawing a line between the incisal edges of the maxillary and mandibular incisors and cuspids of both right and left segments when the teeth are in centric occlusion It can be set by dentist in accordance with esthetics and phonetics. If the incisal guidance is steep it calls for steep cusps, steep occlusal plane or a steep compensating curve to affect an occlusal balance. This type of occlusion is detrimental to the stability and equilibrium of the denture base. For complete dentures the incisal guidance should be as flat as esthetics and phonetics will permit. When the arrangement of the anterior teeth necessitates vertical overlap, a compensating horizontal overlap should be set to prevent dominant incisal guidance, from upsetting the occlusal balance on the posterior teeth. Incisal guidance should never exceed the condylar guidance. It is the anterior controlling factor. The above 2 factors determine the movements of the articulator. In order to achieve balance, the other 3 balancing factors are arranged to correspond to these articulator movements. In C.D construction it is largely under the control of the dentist, the limitations governing it area) Ridge relation, b) Arch shape, c) Ridge fullness d) Inter ridge space e) Phonetics and esthetic requirements of the patients.

3) PLANE OF OCCLUSION According To G.P.T -8 it is defined as the average plane established by the incisal and occluding surfaces of the teeth. Generally, it is not a plane but represents planer mean of the curvature of these surfaces. This plane is established in anterior region by the height of lower cuspid which coincides with the commissure of the mouth and in the posterior region by the center (Winkler) or junction of posterior and middle third of the retromolar pad (Boucher). These landmarks also provide a physiologically and functionally acceptable anteroposterior inclination of the occlusal plane that is nearly parallel to the lower mean foundation plane. These landmarks also creates an occlusal plane essentially parallel to the alatragus line (Camper`s plane) Okane (1979) showed that when occlusal plane is parallel is to the ala – tragus line, the closing force during maximum clenching was greater than when it was altered by +/- 5 degree. Tilting of plane of occlusion beyond 10 degree is not advisable.Its position can be altered only slightly without creating serious functional problem. Its role is not as important as are the other determinants 4) COMPENSATING CURVE According To G.P.T -8 , it is defined as (1) the anterio-posterior curving (in median plane) and the medio-lateral curving ( in frontal plane) within the alignment of occluding surfaces and incisal surfaces of artificial teeth used to develop balanced occlusion.

(2) The arc introduced in the construction of complete denture to compensate for the opening influence produced by the condylar and insical guidance's during lateral and protrusive mandibular excursive movements It is determined by the inclination of the posterior teeth and their vertical relationship to the occlusal plane so that the occlusal surface results in a curve that is in harmony with the movement of the mandible as guided by the condylar path posteriorly and incisal guidance anteriorly A steeper condylar path requires a steeper compensating curve. A lesser compensating curve for steeper condylar guidance would result in steeper incisal guidance acting as anterior interference, causing loss of molar balancing s. The primary function thus of compensating curve is to provide balancing s for protrusive mandibular movements. Without this curve it would be necessary to incline the entire occlusal plane at an angle

5) INCLINATION OF THE CUSPS/ CUSPAL ANGULATION It is also a determinant, as it modifies the effect of the plane of occlusion and the compensating curve. The angulation of the cusp is more important than the height of the cusps. The mesiodistal cusp heights that interdigitate lock the occlusion so that reposition of the teeth due to setting of the base cannot take place. To prevent this problem, it is advocated that all mesiodistal cusp heights be eliminated in anatomic type teeth. With the teeth so modified, only the buccolingual inclines need be considered as determinants of balanced occlusion.

Out of the five factors, only four can be controlled by the dentist. 1) The incisal guidance and plane of occlusion can be altered but only slightly because of esthetic and phonetic limitations. 2) The main factors which can be used and changed effectively are compensating curve and inclinations of the cusps of the teeth 3) The inclination of the occlusal plane: Plane of orientation is established in the anterior by height of the lower cuspid and in the posterior by the height of the retromolar pad. Its position can be altered only slightly. 4) The compensating curve is one of the most important factors in establishing a balanced occlusion. The compensating curves eliminate Christensen‟s phenomenon to achieve balance. It is determined by the inclination of the posterior teeth and their vertical relationship to the occlusal plane so that the occlusal results in a curve that is in harmony with the movement of the mandible. The anteroposterior curvature of the occlusal plane is desired to permit protrusive disocclusion of the posterior teeth by the combination of anterior guidance and condylar guidance. Mediolateral curve: It results from the inward inclination of the lower posterior teeth, making the lingual cusps lower than buccal cusps on the mandibular arch and buccal cusps higher than the lingual cusps on the maxillary arch. Aligning the teeth according to the above produces the greatest resistance to masticatory forces. 5) Cusp height and inclination: These are important determinants, as they modify the effect of the plane of occlusion and the compensating curve.

All the five factors of balance interact with each other. The dentist can control only four of the 5 factors, since the condylar path is fixed by the patient. Incisal guidance and plane of occlusion can be altered only slightly. The important working factors for the dentist to manipulate are the compensating curve and the inclinations of cusps on the occlusal surfaces of the teeth. Balance in non anatomic teeth: It can be accomplished in two ways. One can either set the teeth in a compensating curve as is done in anatomic forms, or one can set the teeth in a flat plane, and utilize a balancing ramp just distal to the 2nd molar. This ramp adjusted so that the upper 2nd molar will it eccentric movements and thus provide three point s. Pleasure (1937) set premolars and 1st molars in an anti-Monson curve; this avoids a tipping force and seats the denture. In order to provide eccentric balance during tooth s the 2nd molars are set in the conventional Monson curve. This combination of Monson and anti-Monson curve in posterior occlusion is often referred to as the pleasure curve. Trapozzano (1960) studied the masticatory performance of balanced and non-balanced occlusion in complete denture patients and concluded that masticatory efficiency with balanced occlusion was only slightly greater but the stability was definitely enhanced.

B) Non-balanced occlusion When the requirement for balanced centric and eccentric occlusion and balanced sliding occlusion are accepted as requisites for balanced occlusion, it follows that all other occlusal arrangement are non-balanced occlusion. The arrangement of teeth according to the spherical theory, organic occlusion, and occlusal balancing ramps for protrusive balance and transographic and on a plane may be classified as non-balance occlusion. Non-balanced occlusion is an arrangement of teeth with form or purpose. Acceptance of the concept of non-balanced occlusion includes acceptance of the following 1. The character of the ing foundation makes it almost impossible to harmonize tooth arrangement with mandibular movement in the eccentric relation to the maxillae and to maintain this harmony. 2. The ing of the teeth during masticatory and non-masticatory mandibular movement occurs when the mandible is in centric relation to the maxillae. 3. The artificial teeth should not when the mandible is in eccentric relation to the maxillae because when jaws are eccentrically related and the teeth , horizontal and torqueing forces are directed to . These forces are un stabilizing and potentially destructive to ing tissue. 4. When the jaws are in centric relation and the of the teeth produces no discomfort to the ing tissue or the ts, the patient is encouraged to make similar maxillo mandibular relation repeatedly.

CONCEPTS OF NON BALANCED OCCLUSION Pound's concept -He proposed a monoplane occlusion which stresses the importance of phonetic and aesthetics for anterior teeth. The posterior teeth on the other hand have a sharp upper cusp and a wide lower central fossa. The buccal cusps of the lower posterior teeth were reduced to avoid deflective s. In effect it was lingualized occlusion where in there is no buccal of upper and lower teeth and the occlusal surfaces are reduced such that they lie in a triangle formed between the mesial end of the canine and the two sides of the retromolar pad. Gold surface occlusal concept-33 degree teeth with full occlusal gold surface are used to attain non balanced concept. Extreme vertical overlaps producing cuspid guidance are frequently used resulting in disocclusion of posterior teeth away from maximum intercuspation position. Hardys concept- A straight horizontal occlusal plane using non anatomical teeth is used to establish non balanced occlusion. Occlusal pivots by Sears- The pivots were used to place the mandible in equilibrium by concentrating the load in the molar regions. This scheme reduced the injury to the temporomandibular t and also reduced the stress in the anterior region.

Kurth's concept- He proposed a non-balanced occlusion set with flat posterior teeth in a horizontal plane without any balancing ramps. The teeth were set in a flat plane anteroposteriorly with a reverse lateral curve

Philip M. Jones scheme of non-balanced occlusion 1972 -In this scheme, non-anatomical teeth were arranged with the following modifications: 1. Different articulator that could fit large casts was used. He advocated barn hinge door articulator. 2. The maxillary and mandibular teeth were arranged without any vertical overlap. 3. The jaw relation determined the amount of horizontal overlap. 4. The maxillary posteriors were set first and the occlusal plane must fill certain requirements a) Occlusal plane should divide interarch space equally. b) Occlusal plane should be parallel to mean denture base foundation c) Occlusal plane should lie at middle and upper third of retromolar pad. 5. During final arrangement, there should be complete intercuspation between the upper and lower posterior teeth except the second molar. 6. The occlusal surface of the upper second molar should be 2 mm above the plane of occlusion (hence it is out of occlusion) and parallel to the occlusal surface of the lower second molar. 7. These modifications are done so that the premolars and the first molars are the primary masticators and the second molars are just non-functional space fillers.

NEUTROCENTRIC CONCEPT OF OCCLUSION (MONOPLANE OCCLUSION) Devan in 1954 suggested the concept of neutrocentric occlusion This concept of occlusion assumes that the anterior-posterior plane of occlusion should be parallel to the denture foundation area and not dictated by condylar inclination. The plane of occlusion is completely flat and level. There is no curve of Wilson or Curve of Spee (compensating curve) incorporated into the set up. In mediolateral direction teeth are set flat with no medial or lateral inclination. The patient is instructed to avoid incising with the anterior teeth; therefore there is no need to concern for sagittal condylar inclination. Because there are no cusp on teeth, when incising is avoided and no cusp project above or below the occlusal plane then horizontal condylar guidance may be set to zero. Since teeth are not arranged for balanced when jaws are eccentrically located lateral condylar guidance may be set zero. There is no vertical overlap of the anterior teeth. When using this concept of occlusion the patient is instructed not to incise the bolus. With this tooth arrangement DeVan noted that “the patient will become a chopper, not a chewer or a grinder.” Acc. to DeVan the main objectives of neutrocentric concept areI – Neutralization of the inclines and, II – Centralization of the occlusal forces acting on the denture foundations. In order to attain these objectives, it is necessary to reduce the size and number of teeth and to abandon attempts to secure balancing s in eccentric positions beyond the range of masticatory stroke

According to DeVan, the five factors involved in the relation of the teeth to dental foundation are: (a) POSITION There is probably no single factor as important as position. Acc. to DeVan posteriors should be positioned in as central position on the foundation as allowed by the tongue, this way denture will be more stable due to enhanced lever balance, and more of the osseous foundation will be saved by the harmful tensile and shearing forces acting on bone and the overlying mucosa  Acc. to DeVan the employment of lateral balance intensifies rather than alleviates the problem of stabilizing the denture.  Eccentric balance does help to maintain retention; but if the use of inclines is essential for its establishment, then bilateral balance causes a decrease in stability.  Balancing inclines shift the denture farther toward the side of the mastication, preventing its dislodgement while increasing its side displacement. B) PROPORTION DeVan recommends reduction in the proportion of the artificial teeth as compared to size of natural teeth.  Reduction in proportion is necessary to develop centralization of forces, Reduction of frictional forces developing on occlusal surfaces which will transfer to the underlying mucosa and bone.  Reduction by 40% in width is possible without serious diminution of the food table

C) PITCH  Pitch is synonymous with inclinations or tilt.  In neutrocentric concept the plane of occlusion should be oriented so that it is midway and parallel to mean foundation planes of the maxilla and the mandible.  The compensating curve should be neutralized so that posteriors are placed on a plane rather than on spherical surface. D) FORM  Artificial posterior teeth should be devoid of projecting cusps.  ing occlusal lines should be on a single plane.  This arrangement will avoid interference from TMJ and their inclines. E) NUMBER OF TEETH DeVan recommends reduction in no. of teeth from 8 per denture to 6 per denture.  This will aid in stability by freeing the lower ridge molar incline of occlusion.  Elimination of 2nd molar will result in establishment of centralization and reduction in occlusal area

C) LINGUALIZED OCCLUSION Acc. to GPT-8, lingualized occlusion is defined as the form of denture occlusion in which the maxillary lingual cusps articulate with the mandibular occlusal surfaces in centric, working and balancing mandibular positions. Although S. H. Payne(1941) has being credited for being the first one to describe, it was Gysi (1927) who used this scheme approximately 20 years earlier(1927). Payne 1941 credited Farmer with development of this technique, and provided a brief description of the required laboratory procedures. According to Payne‟s article, a mortar-and-pestle arrangement was created via judicious recontouring of 30-degree teeth. Pound (1970) used maxillary teeth having cusp angles greater than 30 degrees in conjunction with mandibular teeth having cusp angles of 20 degrees or less. He carefully reshaped mandibular fossae to produce cross-arch balance. Like his predecessors, Pound ensured that maxillary buccal cusps did not mandibular teeth during eccentric mandibular movements. He accomplished this by reducing the facial surfaces of the mandibular posterior teeth rather than elevating the buccal cusps of the maxillary teeth. Generally, maxillary teeth with cusp angles of ≥30 degrees are opposed by mandibular teeth displaying cusp angles of ≤20 degrees are used. The posterior teeth selected for lingualized occlusion differ depending upon whether balanced or non balanced occlusion is used. A balanced scheme usually involves maxillary tooth with sharply pointed lingual cusp to oppose mandibular tooth with an uncomplicated occlusal table including only shallow inclines.

For a non balanced lingualized occlusion monoplane mandibular denture tooth is selected. Clough et al 1983 examined chewing efficiency of monoplane versus lingualized occlusion and reported that 67% of the patients in their study preferred lingualized occlusion. PRINCIPLES OF LINGUALIZED OCCLUSION 1. Anatomic posterior teeth are used for maxillary denture. 2. Non anatomic or semi anatomic teeth are used for mandibular denture. 3. Modification of mandibular posterior teeth is accomplished by selective grinding. 4. Balancing and working s should occur only on the maxillary lingual cusps. 5. Protrusive balancing s should occur only between maxillary lingual cusps and lower teeth.

The advantages of lingualized occlusion are:  Lingualized occlusion yielded cross-arch balance. This resulted in improved denture stability and enhanced patient comfort  Occlusal forces can be directed lingually without placing the teeth lingually  It is especially useful where esthetic demands of the patient is high but presenting oral conditions indicate non-anatomic teeth, e.g., severe ridge resorption, class II & III jaw relationships and highly displaceable ing tissues.

 The chewing efficiency is comparable to anatomic (semi) and definitely superior to zero degree teeth  As mesiodistal locking is eliminated by grinding the transverse ridges of the cusp teeth, freedom is provided in the occlusion to accommodate for the settling of denture base.  The lateral thrust control (during functional and para-functional movements) is provided by grinding the buccolingual inclines, which is based on the shape and prominence of the ridge and its ability to withstand lateral forces  The para-functional habits are usually confined to a zone of activity around centric relation. The lingualized occlusion provides for smooth balancing s with excursive movements of 2-3mm around centric relation, owing to creation of common central fossa in mandibular posteriors by selective grinding of transverse ridges in the process of mesiodistal unlocking  Lingualized occlusion creates a more favorable lever by moving the centric s from half tooth to lingual. This allows occlusal forces to move more centrally there by contributing to more stable denture.  It minimizes the frictional between upper and lower occlusal surfaces as there are only one area of .  There is only one point. This creates Mortar pestle type of occlusion that provides a small area of for more efficiency and control of lateral forces. By allowing the maxillary cusp to function against a variety of opposing occlusal surface, the advantage of many other occlusal schemes can be accommodated while their disadvantages can be ignored. Greatest advantage of balanced lingualized occlusion is esthetics. First the presence of cusped tooth in maxillary premolar and first molar region looks

more natural when compared to zero degree teeth. Second the use of occlusal curves for the purpose of balance allows for incisal overlap of anterior teeth. The popularity of lingualized occlusion stems from simplicity and flexibility of the concepts and from its wide application to clinical practice. Indeed this type of occlusion may be used in any type of removable prosthodontic appliance and in most cases, incorporates most of the advantages while eliminating or neutralizing the disadvantages of many occlusal schemes. Lingualized is a truly “OCCLUSION FOR ALL REASONS” MYERSON’S LINGUALIZED INTEGRATION Myerson proposed specialized tooth Molds for arranging teeth in lingualized occlusion. He proposed two different molds for the maxillary posterior namely control (cc) mold and Maximum (Mc) mold. The remaining teeth are common for both these molds. He advocates the use of „Mc‟ Mold for patients who can reproduce accurate centric position and „cc‟ mold for patients with variation in centric position. These teeth provide Maximal intercuspation, good cuspal height to perform occlusal reshaping and a natural and pleasing appearance. The „Mc‟ Mold Maxillary posterior have taller cusps with a more anatomical appearance compared to the „cc‟ mold. The „Mc‟ mold also offers a more exacting occlusion. ORGANIC CONCEPT OF OCCLUSION Mutually protected occlusion is also known as canine protected occlusion or ''organic" occlusion. It had its origin in the work of D'Amico, Stallard and Stuard. (1963)

According to this concept of occlusion, the anterior teeth bear the entire load and the posterior teeth are disoccluded in any excursive position of the mandible. In organic or organized occlusion the arrangement of teeth should relate the occlusal element of teeth so that the teeth will be in harmony with the muscles& ts in function. The muscles & ts should determine the mandibular position of occlusion without tooth guidance. Organic occlusion has three phases of mutually interdependent protection 1. The posterior teeth should protect the anterior teeth in centric occlusal position 2. The maxillary incisor should have vertical overlap sufficient to provide separation of the posterior teeth when the incisors are in end-to-end . 3. In lateral mandibular position outside the masticatory cyclic movement the cuspid should prevent of all other teeth. An articulator capable of receiving and reproducing pantograms in 3 planes is recommended to develop the organic concept of occlusion. This type of occlusion is more applicable in natural dentition and fixed partial denture, than in complete dentures

TYPES OF OCCLUSION SCHEMES Now let us discuss the three main occlusal schemes i.e.  Monoplane occlusion  Classical bilaterally balanced occlusion  Lingualized occlusion It is of interest to note that none of the occlusal scheme has been proved to be superior to other (for all presenting conditions of edentulous mouths), although one type of scheme may offer some advantages over other.

MONOPLANE OCCLUSION Acc. To G.P.T -8 ,it is defined as an occlusal arrangement wherein the posterior teeth have masticatory surfaces that lack cuspal height . Hall (1929) is credited for the introduction of Zero degree teeth calling them inverted cusp tooth, but these teeth have the problem of clogging of food in the depressions onto the occlusal surfaces Myerson later designed a cusp less teeth with series of transverse buccolingual ridges and sluiceways between them.

ADVANTAGES OF MONOPLANE OCCLUSION / ZERO DEGREE TEETH 1. They are more adaptable to unusual jaw relations such as Class II and Class III malocclusions. 2. Zero degree teeth impart to the patient a sense of freedom because they do not lock the mandible in one position only. 3. This is used more easily when variation in the width of upper and lower jaws indicate a cross bite setup. 4. Centric occlusion is more of an area and less of a precise point in these teeth hence they allow closure of jaws over a broad area. 5. Minimal horizontal pressures are created because of elimination of incline plane. 6. Zero degree teeth permit the use of a simplified and less time consuming technique and offer greater comfort and efficiency for longer duration. 7. They accommodate better to the inevitable negative changes in the ridge that occur with aging.

As far as balanced occlusion is concerned in monoplane occlusion two important concepts prevailA) Non Balanced occlusion (in centric relation only) E.g Neutrocentric concept. B) Balanced occlusion in centric relation and lateral excursions This can be achieved with the use of compensating curve, balancing ramps, Tripodization by tilting the 2nd maxillary and mandibular molars, and using monoplane with zero overbite (but this will compromise phonetics and esthetics.)

The 2nd category in monoplane occlusion involves bilateral balance in centric and eccentric relations. A) WITH COMPENSATING CURVE Acc. to this concept – A) No. of posterior teeth should be 3, i.e. mandibular 1st premolar should be omitted. B) Antero-posterior comp. curve begins at the DMR of the 2nd premolar and continues till 2nd molar. The amount of this curve is dependent on steepness of the condylar guidance, but is rarely more than more than 20 degree from horizontal. This curve is used to provide the needed tooth structure for protrusive balancing s Mediolateral compensating curve is also needed to achieve lateral balanced s. This curve is initiated from first replacement tooth and continued till the second molar. The degree to which the facial cusps are elevated to establish this curve will vary with the condylar and incisal guidances. The curve usually does not exceed 5-10 degree B) WITH BALANCING RAMPS (NEPOLA 1958)  Balancing ramps provide a tripodization of the denture base.  As the patient moves the mandible from centric relation to protrusive or lateral positions, there is smooth anteriorly on the teeth and posteriorly on the ramps.  The balancing s give improved horizontal stability to the dentures. Esthetics and phonetics are greatly enhanced because there is more freedom in placing anterior teeth.

 The ramps can be developed after the final try-in of the waxed dentures or at the time of clinically remounting the dentures at the insertion appointment  The procedure is performed on a properly adjusted articulator.  This technique can be applied to existing dentures by clinical remount. C) WITH TILTING THE SECOND MOLARS Acc to C G Porter, mandibular second molar is inclined to provide with maxillary dentures in all excursions. The maxillary molars are also inclined but left out of centric . He recommended the use of French modified posterior teeth which have sub-occlusal surfaces of mandibular buccal cusps directing the occlusal force downward and lingually.

CHARACTERISTICS

ANATOMIC

LINGUALIZED

NEUTROCENT RIC

ESTHETICS

+

+

-

EASE ACCORDINGOF

+

+

-

+

+

-

SIMPLER TECHNIQUE

-

+

+

DECREASED LATERAL

-

+

+

EASE OF ADJUSTMENT

-

+

+

CLASS II & III CASES

-

+

+

STABILITY WITH

-

+

+

PENETRATION OF FOOD BOLUS DENTURE STABILITY (in parafunct movt )

FORCES

CENTRALIZED & NEUTRALIZED FORCE

CONCLUSION Many occlusal schemes have been proposed over the years. Most schemes when correctly used gives satisfactory results. The result is satisfactory, if the patient gets better function, esthetics & comfort without any adverse changes in denture foundation.

REFERENCES: 1. Boucher's Prosthodontic Treatment for Edentulous Patients (12th Edition) 2. Boucher's Prosthodontic Treatment for Edentulous Patients (11th Edition) 3. Essentials of complete denture prosthodontics Sheldon Winkler 2nd ed 4. Textbook of complete denture Arthur O. Rahn, Charles M. Heartwell 5th ed 5. A Text book of occlusion Norman .D.Mohl 1988 1st edn 6. Trapazzano.R.V (1963), Laws of articulation. J Prosthet Dent, 13(1),3444 7. Boucher.O.C (1963), Discussion of Laws of articulation. J Prosthet Dent, 13(1),45-48 8. Ortman.R.H (1971), Role of occlusion in preservation and prevention in complete denture prosthodontics. J Prosthet Dent, 25(2),121-138 9. Becker.M.C, Swoope.C.C, Guckes.A.D (1977), Lingualized occlusion for removable prosthodontics. J Prosthet Dent, 38(6),601-608 10.Levin.B (1978), Reevaluation of Hanau‟s law of articulation and Hanau‟s Quint. J Prosthet Dent, 39(3),254-258 11.Nimmo. A & Kratochvill. J. F (1985), Balancing ramp in non-anatomic complete denture occlusion, J Prosthet Dent, 53(3), 431-433 12.Phoneix.D.R & Engelmeire.R.L (2010), Lingualized occlusion revisited, J Prosthet Dent, 104(5), 342-346