11 IntroductionOcclusion in complete denture must be developed to function effeciently and with the least amount of trauma to the supporting tissues.
12 Objectives Preservation of the remaining tissues Proper masticatory efficiencyEnhancement of denture stability, retention and supportEnhancement of phonetics and esthetics
13 Difference Between Natural and Artificial Occlusion The teeth in natural dentitions are retained by periodical tissues that are uniquely innervated and structured. In complete artificial occlusion all the teeth are on bases seated on slippery tissues.In natural dentitions the teeth receive individual pressures of occlusion and can move independently.
14 Difference Between Natural and Artificial Occlusion 3. Malocclusion of natural teeth may be uneventful for years. 4. Non vertical forces on natural teeth during function affect only the teeth involved and are usually well tolerated, whereas in artificial teeth the effect involved all of the teeth on the bases. It is usually traumatic to the supporting structures.
15 Difference Between Natural and Artificial Occlusion 5. Incising with the natural teeth does not affect the posterior teeth. Incising with artificial teeth affects all of the teeth on the base. 6. In natural teeth the second molar is the favored area for masticating hard foods. 7. In natural teeth bilateral balance is rarely found; If present it is considered balancing side interference.
16 Difference Between Natural and Artificial Occlusion 8. In natural teeth proprioception gives the neuromuscular system control during function.
17 Requirement of Complete Denture Occlusion Stability of occlusion in centric relation.Balanced for all eccentric contacts bilaterally for all eccentric mandibular movements.Unlocking the cusp mesiodistally to allow for gradual but inevitable settling of the bases due to tissue deformation and bone resorption.Control of horizontal forces by buccoligual cusp height reduction according to the residual ridge resistance and interridge space.
19 Requirement of Complete Denture Occlusion 5. Functional lever balance by favorable tooth to ridge crest position
20 Requirement of Complete Denture Occlusion 6. Cutting and shearing effeciancy of the occlusal surface (sharp cusps or ridges) 7. Anterior clearance of teeth during mastication. Minimum occlusal contact between the upper and lower teeth to reduce pressure during function (linguilized occlusion)
21 Requirements for Incising Units These units should be sharp in order to cut effeciently. They should not contact during mastication. They should have as flat an incisal guidance as possible considering esthetics and phonetics. They should have horizontal overlap to allow for base settling without interference. They should contact only during prostrusive incising function.
22 Requirements for the Working Occlusal Units They should be effecient in cutting and grinding. They should have decreased buccal- lingual width to minimize the work force directed to the denture foundation. They should function as a group with simultaneous harmoniuos contacts at the end of the chewing cycle and during eccentric excursions.
23 Requirements for the Working Occlusal Units They should be over the ridge crest in the masticating area for lever balance. They should center the work load near the anteroposterior center of the denture. They should present a plane of occlusion as parallel as possible to the mean foundation plane.
24 Fundamentals for Artificial occlusion The smaller the area of the occlusal surface acting on food, the smaller will be the crushing force on food transmitted to the supporting structures. Vertical force applied to an inclined occlusal surface causes non vertical force on the denture base.
25 Fundamentals for Artificial occlusion Vertical force applied to a denture base supported by yielding tissue causes the base to slide when the force is not centered on the base. Vertical force applied outside (lateral to) the ridge crest creates tipping force on the base.
26 Balance occlusionBalance as related to complete denture occlusion: Balance occlusion in complete dentures can be defined as stable simultaneous contact of the opposing upper and lower teeth in centric relation position and a continuous smooth bilateral gliding from this position to any eccentric position within the normal range of mandibular function.
27 Balance occlusionBalance in complete dentures is unique and man made. The physical factors that apply to the relationship of the teeth to each other and that apply to the position of the teeth in the denture base as related to the ridge must be understood. The application of these physical laws can be expressed by the following:
28 Balance occlusionThe wider and larger the ridge and the closer the teeth are to the ridge, the greater the level balance.Conversely, the smaller and narrower the ridge and the farther the teeth from the ridge, the poorer the level balance.The wider the ridge and the narrower the teeth buccolingually, the greater the balanceThe more lingual (inside) the teeth are place in relation to the ridge crest, the greater the balance
29 Balance occlusion5. The more centered the force of the occlusion anteroposteriorly, the greater the stability of the base.
30 Types of BalanceLever Balance – This is present when there is equilibrium of the base on its supporting structures when a bolus of food is interposed between the teeth on one side and a space exist between the teeth on the opposite side. This state of equilibrium is encouraged by the following:1. Placing the teeth so that the resultant direction of force on the functioning side is over the ridge or slightly lingual to it.
31 Types of Balance2. Having the denture base cover as wide an area on the ridge as possible. 3. Placing the teeth as close to the ridge as other factors will permit. 4. Using as narrow a buccolingual width occlusal food table as practical.
32 Types of Balance(b) Occlusal Balance Bilateral occlusal balance – this is present when there is equilibrium on both sides of the denture due to simultaneous contact of the teeth in centric and eccentric occlusion. It requires a minimum of three contacts for establishing a plane of equilibrium.
33 Types of Balancec)Protrusive occlusal balance – this is present when the mandible moves essentially forward and the occlusal contacts are smooth and simultaneous in the posterior both anterior teeth. It is slightly different from bilateral balance in that it requires a minimum of three contacts, one on each side and one anterior, and is dependently on the interaction of the same factors.
34 Types of BalanceThis total concept of balanced complete denture occlusion must be considered in terms of the following:The tooth size and position in relation to the ridge size and shape.The extent of denture base coverage.Occlussal balance with stable contacts at the retruded border position and in an area (long centric)
36 Types of BalanceN.B. – In both natural and artificial dentition, when centric relation and centric occlusion do not coincide, it is desirable to create an area within the fossae that will allow freedom of tooth movement from centric relation to centric occlusion (this is called long centric or freedom in centric)
37 Types of Balance4. Right and left eccentric occlusal balance by simultaneous contacts at the limit of functional and parafunctional activity. 5. Intermediate occlusal balance for all positions between centric occlusion and all other functional or parafunctional excursion to the right, left and protrusive.
38 Advantages of Balanced Occlusion Distribution of loadStabilityReduced traumaFunctional movementEfficiencyComfort
39 Factors Affecting the balanced occlusion (Laws of Articulation Hanau quint) There are five factors involved in eccentric occlusal balance in complete dentures.Condylar guidanceIncisal guidanceThe occlusal planeThe compensatory curvesCusp angulation
40 Condylar guidance – it is definite anatomic feature that depends on the inclination of the floor of the glenoid fossa. It should be determined on the patient and set on the articulator by eccentric records so that the patients TMJ is in harmony with the occlusion programmed on the articulator. If the condylar angle (angle between the path of condyle and the Franfort horizontal plane) is steep, its difficult to produce balance occlusion because when the condyle travel downward and forward large space is created posteriorly when the anterior teeth are edge to edge. So compensation should be made by altering the other factors to otain the desired balanc.
41 2. Incisal guidance – Incisal guidance is the effect of the contact of the upper and lower anterior teeth on the movement of the mandible. It is usually expressed in degrees of agulation 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 requires steep cusp, a steep occlusal plane, or a steep compensating curve to effect an occlusal balance.
42 Factors affecting the incisal guidance angle. 1 Factors affecting the incisal guidance angle. 1. Vertical overlap (over bite): the vertical overlap is directly proportional with the incisal angle. For complete dentures the incisal guidance should be as flat as esthetic and phonetics will permit.
43 For the following reasons: 1 For the following reasons: 1. To guard against loss of posterior teeth contact during prostrusive movement. 2. To allow the use of posterior teeth with reduced cusp angle and this will reduce the lateral stresses transmitted to the ridge. 3. To reduce the downward movement of the mandible during edge to edge position.
44 The incisal guidance is reduce by: Setting the upper anterior teeth outside the ridgeSetting the lower anterior teeth inside the ridge without encroaching on the tongue spaceShorten the upper and lower anterior, if esthetics and phonetics allows.
45 When the arrangement of the anterior teeth necessitates a vertical overlap, a compensating horizontal overlap should be set to prevent anterior interference.
46 3. Plane of Occlusion – the occlusal plane is established in the anterior by the height of the lower cuspid, which is nearly coincident with the commissure of the mouth, and in the posterior, by the height of the retromolar pad. It is also related to the related to the ala- tragus line. Its role is not as important as are the other determinants.
47 4. Compensating curves -- Compensating curve is one of the more important factors in establishing a balanced occlusion so that the occlusal surface results in a curve that is in harmony with the movement of the mandible as guided posteriorly by the condylar path. A steep compensating curve for occlusal balance. A lesser compensating curve for the same condylar guidance would result in a steeper incisal guidance (anterior interference), which would cause loss of molar balancing contacts.
48 Height of cusps on teeth or inclination of cusp less teeth Height of cusps on teeth or inclination of cusp less teeth. Cusp angle – the angle made by the slopes of a cusp with a perpendicular line bisecting the cusp, measured mesio-distally or buccolingullay. Cusp Height – the shortest distance between the tip of a cusp and its base plane. Altering the cusp height by widening or narrowing a tooth alters the length of the cusp incline but does not change the relationship to the mean occlusal plane, i.e. cusp angle is not affected by a change in cusp width.
49 when we select a tooth with a certain xusp height or angle, it doesn’t mean anything until the tooth is positioned in the denture. For example, a particular tooth may be manufactured with a 30 degree inclination. However, by tilting the tooth in relation to the mean occlusal plane, one may create an effective inclination of greater or less than 30 degrees.
50 Interaction of the five factor Of the four that he can control two of them (the incisal guidance and the plane of occlusion) can be altered only a slight amount because of esthetic and physiologic factors. The important working factors for the dentist to manipulate are the compensating curve and the inclinations or cusp on the occlusal surfaces of the teeth.
51 Selection of Posterior Tooth Forms Factors affecting the selection of posterior teeth forms:The capacity of the ridge to receive and resist forces of mastication.Inter ridge distance.Ridge relationshipEstheticsPatients age and neuromuscular coordinationPrevious denture wearing experience.
54 Posterior artificial teeth are classified according to their oclusal form into anatomic, semi- anatomic and non anatomic. 1. Anatomic Teeth – the standard anatomic tooth has inclines of approximately 33. The cuspal inclination is measured by the angle formed by the mesiobuccal cuspal incline to the horizontal plane when the long axis of the tooth is vertical.
55 2. Non Anatomic Teeth (0) – Non anatomicteeth have a flat occlusal surace (without cusps) this type of teeth does not function efficiently unless the occlusal surface is provided with cutting ridges and spill ways this types of teeth were designed to eliminate the problems evolved with using anatomic teeth.
56 Semi Anatomic Teeth – Examples of the semi anatomic teeth are twenty degree teeth.
57 Problems with Anatomic Tooth Forms In edentulous mouths, these same cusps can cause trauma, discomfort, and instability to the bases because of the horizontal components they generate. The basic problem initiallly is the coordination of their cusps to harmonize with one another and the mandibular movements.
58 The problem of unmodified, cusped teeth for complete dentures can be summed up as follows: It is mandatory to use an adjustment aritculator.Eccentric records must be made for articulator adjustments.Mesiodistal interlocking will not permit settling of the base without horizontal forces developing. So reduction of cusp height and performing long centre concept becomes mandatory.
60 4. Harmonious balanced occlusion is lost when settling occurs. 5 4. Harmonious balanced occlusion is lost when settling occurs. 5. The base need prompt and frequent refitting to keep the occlusal stable and balanced. 6. The presence of cusps generates more horizontal force during function.
61 Problems with Non anatomic Tooth Forms 1. Non anatomic (flat) teeth occlude in only two dimensions (length and width), but the mandible has an accurate three dimensional movement due to its condylar behavior. 2. This form loses shearing efficiency. 3. Bilateral and protrusive balance are not possible with a purely flat occlusaion. Non anatomic teeth set on inclines for balance require as much concern as anatomic teeth for jaw movements.
62 the flat teeth do not function efficiently unless the occlusion surface provides cutting ridges and generous spillways.
63 Balanced Occlusion with Non Anatomic or Flat Teeth Balanced occlusion with cupless teeth can be achieved by several ways:Zero-degree teeth with inclination of the lower second molarZero-degree teeth with balancing ramps placed posterior to the most distal molar.
64 3. Zero-degree teeth set to steep compensatory.
65 Occlusal Designs for Balanced Occlusal Lingualized Occlusion This method of lingualizing the occlusaion was suggested as a method to achieve bilateral balanced occlusion. The lingulaized occlusaion utilizies only the upper lingual cusps on each side to act as cutters operating in the central fossa of the lower teeth this gives mortar and pestle type contact that lingualizes the resultant force without moving the teeth in relation to the ridges.
66 Lingualized occlusion is indicated when the patient places high priority on esthetics but a non anatomic occlusal scheme is indicated by oral conditions suchs as sever alveolar resorption, class II jaw relation or displaceable supporting tissues.
67 Advantages of lingualized occlusion Most of the advantages attributed to both anatomic and non anatomic forms are retainedCusp form is more natural in appearanceGood penetration of the bolus is possibleBilateral balanced occlusion is readily obtained
68 Linear Occlusion concept In this type of occlusion the teeth are arranged so that the masticatory surfaces of the mandibular posterior teeth have straight long, very narrow occlusal form resembling that of a line articulating with apposing monoplane teeth.
69 Monoplane Teeth with Compensating Curve The arrangement of monoplane teeth in a compensating curve of occlusion is similar to that for anatomic teeth.
70 Non-Balanced Occlusion When the foundation tissues is compromised, i.e. severely resorbed ridge, knife-edge, thin wiry ridge or one that is covered with thick movable flabby tissues, favorable control of occlusal forces can be utilized by the use of non-anatomic teeth arranged following the monoplane occlusion concept.
71 Monoplane Occlusion Concept The monoplane occlusion concept utilizing non- anatomic teeth with flat occlusal surfaces set to a flat occlusal plane. The posterior limit of the extent of lower posterior teeth is the point at which the mandibular ridge begins to curve upward, with elimination of contact between the upper and lower second molars, which are considered as space fillers. The patients should avoid incising with their anterior teeth, as the purpose of the anterior teeth is to produce a desired appearance. If they recognized this limitations, no balancing contact will be necessary for protrusive occlusion.