balanced occlusion and its importance contents in complete
TRANSCRIPT
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DR DEVENDRA PAL
BALANCED OCCLUSION AND ITS IMPORTANCE
IN COMPLETE DENTURE FABRICATION
Contents
◼ Introduction◼ Definitions◼ Requirements of complete denture occlusion◼ Concepts of occlusion
◼ Balanced occlusion: DefinitionPre-RequisitesPro and Cons
◼ Parameters to success of occlusal balance
◼ Types
◼ Hanaus Law of articulation
◼ Steps
◼ Occlusal adjustment in balanced occlusion: Selective grinding
◼ Problems / Correction in balanced occlusion
◼ Balancing Ramps
◼ Review of literature
◼ Summary & conclusion
◼ References
Introduction
Definitions:
Occlusion:
Is defined as any contact between the incising or masticating surfaces of the maxillary and mandibular teeth.-GPT
According to Heartwell this is a static position and the jaws can be in either centric or eccentric relation. Every time the teeth contact there is a resultant force which may vary in magnitude and direction.
Dental Articulation:
The static and dynamic contact relationship between the occlusal surfaces of the teeth during function.-GPT
Centric Occlusion:
Refers to the relationship of the mandible to the maxilla, when the teeth are in maximum occlusal contact, irrespective of the position or alignment of the condyle disk assemblies. This is also referred to as the acquired position of the mandible or the maximum interocclusal position. (MIOP).
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Requirements of complete denture occlusion:
-Stability of occlusion at centric relation position and in an area forward and lateral to it.
-Balanced occlusal contacts bilaterally for all eccentric mandibular movements.
-Unlocking the cusps mesio-distally to allow for gradual but inevitable settling of the bases due to tissue deformation and bone resorption.
-Control of the horizontal force by buccolingual cusp height reduction according to residual ridge resistance form and interarch distance.
-Functional lever balance by favorable tooth to ridge crest position.
Theories of occlusion
◼ Spherical theory
◼ Equilateral triangle theory
◼ Conical theory
Spherical theory of occlusion
▪ This was given by Monson(1918) and the conceptwas derived from an idea by Von spee.
▪ Positioning of teeth with antero-posterior andmedio-lateral inclines in harmony with a sphericalsurface. Some times referred to as having Monsoncurve.
▪ Lower teeth moves over the surface of upper teethas over the surface of sphere with a diameter of8inches(20cm).
▪ Centre of sphere is in gabella.
▪ Surfaces of the sphere passes through glenoidfossa along the articular eminences.
Equilateral Triangle TheoryThis theory was proposed by Bonewill
Average 4inch between each condyles and incisal guidance form the shoulder of the equilateral triangle
Conical theoryThis theory was proposed by Hall
Lower teeth move over the surfaces of the upper teeth as over the surfaces of cone with a generating angle of 45 degree and with the central axis of cone tip opened at 45 degree angle to the degree of occlusal plane.
The occlusal spectrum and complete dentures:
occlusal schemes in use today:
-Balanced occlusion: -Non-balanced Anatomic Spherical occlusionSemi-anatomic Organic occlusion.Non-anatomic Transiographics.Lingualised Nuetrocentric.
Occlusal form
◼ 330 bucco-lingual inclines of anatomic teeth for patients with strong, well formed ridges
◼ 200 bucco-lingual inclines of semi-anatomic teeth for patient with ridge contour is reduced by resorption
◼ 00 non-anatomic teeth for patient with flat, knife edge ridges
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Anatomic (Balanced) Occlusion
Semi-anatomic (balanced)
Lingualized Occlusion
Non-anatomic (balanced)
Neutrocentric Occlusion
Advantages Disadvantages1. Better Esthetics 2. Ease of Penetration (Decreased
vertical stress) 3. Denture stability during
parafunctional movements
1. Less esthetic 2. Poor penetration (Feel dull,
increased vertical forces on ridge)3. Encourage lateral chewing
component. Disadvantages Advantages
1. Precise records, Exact mountings required.
2. Greater lateral forces on inclines (more bone deformation)
3. Results short level4. Harder to adjust
1. Simpler technique, less precise records.
2. Decreased lateral forces 3. Faster to adjust (sandpaper)4. Permits area of closure 5. Good for class II and III jaw
relations. 6. Good stability, forces centralized
and neutralized.
Organic occlusion
▪ Based on the work of Angelo D Amico (Gnathological Society)
▪ It is that concept where in any jaw movement away from centricocclusion will result in separation of all posterior teeth.
▪ The ridge and groove directions of the posterior teeth are determinedas result of the movements of the condyles. The cusp height, fossadepth of posterior teeth and the proper concavity at the lingualsurfaces of the maxillary anterior teeth are determined as a result ofmandibular movements.
▪ The aim of this occlusion is to relate the occlusal elements of teeth sothat the teeth will be in harmony with the muscles and joints infunction.
▪ In organic occlusion three phases of mutually interdependentprotection are present.
▪ The posterior teeth should protect the anterior in the centricocclusal position.
▪ The maxillary incisors should have vertical overlapsufficient to provide separation of the posterior teeth whenthe incisors are in edge to edge contact.
▪ In lateral mandibular position outside the masticatorymovements, the cuspids should prevent contact of all otherteeth.
Transographic Occlusion
◼ Given by Shwelzer
◼ Eccentric balancing contacts are not considered since they are believed to be outside the mandible
◼ This theory is dependant on Split Theory where each condyle is considered to be independent
◼ According to Schweitzwer this theory agreed in principle with tenets of gnathology, but differed in its concept of the problem.
Neutrocentric conceptProposed by DeVan(1954)Key objectives: -Neutralization of inclines
-Centralization of forcesFeatures :◼ Arrangement of teeth on a plane parallel to basal support and without
compensating curves.◼ Not dictated by horizontal condylar guide◼ Bucco-lingual direction teeth are set flat without B-L inclination◼ Horizontal condylar guidance and lateral condylar set zero◼ Reduced bucco-lingual width of teeth◼ Second molar is eliminated◼ Patient advised to avoid incising in anterior teeth◼ No cusp in posterior teeth Advantages: -simple and less precise records are required
-lateral forces are reduced-easy to adjust
Balanced Occlusion:
It is defined as “The simultaneous contact of opposing upper and
lower teeth in centric relation position and a continuous smooth bilateral gliding from this position to any eccentric position with in normal range of mandibular function”-GPT
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Need for balanced occlusion
◼ Improved stability of denture
◼ No interference of cusp during mastication
◼ Preservation of ridges by better distribution of forces
Goals of balanced occlusion
◼ Simultaneous contact in centric relation
◼ Working side contact
◼ Balancing contact in protrusion
◼ Balancing contact in lateral excursion
Following axioms should be considered:1. The wider and larger the ridge and closer the teeth are to the ridge, the greater the
lever balance.
2. Conversely, the smaller and narrower the ridge and the farther the teeth are placed from the ridge the poorer the lever balance.
3.The wider the ridge and the narrower the teeth, the greater the balance.
4.Conversely, the narrower the ridge and wider the teeth the poorer the balance.
5.The more lingual the teeth are placed in relation to the ridge the better the balance.
6.The more buccal the teeth are placed to the ridge crest, the poorer the balance.
7.The more centered the force of occlusion anterior-posteriorly, the greater the stability of the base.
Pre-Requisites for balancing:
1.Mandibular posterior teeth must be set so that occlusal surfaces are horizontal.
2.Plane of occlusion must have a proper orientation.
3.A compensating curve must be set.
4.Teeth must be modified so that there are no interlocking transverse ridges.
Pros and Cons –Bilateral Balanced Occlusion:
“Enter bolus, exit balance” has cast suspicion as to
whether smooth, gliding, non-interfering, bilateral tooth contacts are possible. It implies that occlusal balance is impossible during mastication.
Brewer and Hudson (1961) have shown that complete denture teeth do contact at times during mastication.
Pros:
1.The contact varies in frequency with different foods and different persons. If this contact is interruptive and deflective; and not bilateral, the denture base will not be stable. Hence, bilateral balanced contacts during the terminal arc of closure help to seat the denture in a stable position.
2.Also bilateral balanced occlusion is important during activities such as swallowing saliva, closing to reseat the dentures, and the bruxing of the teeth during times of stress.
3.Patient with a balanced design do not upset the normal static, stable and retentive qualities of their dentures.
4.In bilateral balance the bases are stable during bruxing activity.
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Cons:There are some possible disadvantages of bilateral balanced occlusion:
1. It may tend to encourage lateral and protrusive grinding, although this habit may be confined to those people who are subjected to irrelevant muscle activity.
2. It is difficult to achieve in mouths where an increased vertical incisor overlap is indicated, and is better to retain the vertical overlap, than to sacrifice it in order to achieve articular balance.
3. A semi-adjustable or fully adjustable articulator is required.
Parameters to success of occlusal balance:
1.Accurate record of relation of maxilla to T.M.J. (which is registration of 3 dimensional spatial relation of maxilla to T.M.J. to maintain biological soundness of the joint.)
2.Optimal relation of condyles.
3.Bilateral muscle balance of horizontal movers of the mandible.
4.Eccentric relation record of functional protrusion of the mandible.
Types of Balanced Occlusion:
Balance may be: Unilateral, bilateral, or protrusive.
Unilateral lever balance:
This is present when there is equilibrium of base on its supporting structures when a bolus of food is interposed between teeth on one side and space exists between teeth on the opposite side.
Unilateral occlusal balance:
This is present when occlusal surfaces of the teeth on one side articulate simultaneously with smooth uninterrupted glide.
Bilateral occlusal balance:
-This is present when there isequilibrium on both sides of denturedue to simultaneous contact of teethin centric and eccentric occlusion.
-It requires a minimum of threecontacts. The more the contacts themore assured the balance.
Protrusive occlusal balance:
-This is present when the mandible moves essentially forward and occlusal contacts are smooth and simultaneously in posterior region both on right and left sides as well as anterior teeth.
-It requires a minimum of three contacts, one on each side posteriorly and one anteriorly
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Total concept of balanced 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.
-Occlusal balance with stable contacts at the retruded border position and in an area anterior to it.
-Right and left eccentric occlusal balance by simultaneous contacts at the limit of functional and parafunctional activity.
-Intermediate occlusal balance for all positions between centric occlusion and all other functional or parafunctional excursions to the right and left and protrusive.
FACTORS THAT AFFECT THE
OCCLUSAL BALANCE
Condylar Guidance
◼ It is post end controlling factor.◼ It represents angles of downward and forward
movement of condyle relative to axis-orbital plane.◼ It is obtained by movement of protrusive registration.◼ It should be recorded and transferred to articulator as
closely as possible as given by the patient.◼ In contrast to other four factors it cannot be modified◼ Steeper the condylar- decreased incisal guidance, to
reduce the amount of jaw separation during protrusion
◼ More the condylar guidance more will be the cuspal height
◼ Condylar pathway depends on bone contour of T.M.J., muscle of mastication, ligament of T.M.J. and neuromuscular control of the patient.
◼ Average condylar guidance is about 25-30 degree.
Incisal guidance
This is defined as “The influence of
the contacting surfaces of the mandibular and maxillary anterior teeth on mandibular movements”-GPT.
It is usually expressed in degrees of angulation from horizontal by a line drawn in the saggital plane between the incisal edges of the upper and lower incisor teeth when closed in centric occlusion.
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It is directly proportional to vertical overlap and indirectly proportional to horizontal overlap.
In complete dentures the incisal guidance should be as flat as possible as
the esthetics and phonetics permits. If the incisal guidance is steep, it requires steep cusps, a steep occlusal
plane, or a steep compensating curve to affect an occlusal plane
It depends upon following factors:
◼ Phonetic
◼ Esthetic
◼ Shape of residual ridges
◼ Ridge relation
◼ Inter-alveolar distance
◼ On average it is about 10-20 degree.
Orientation of occlusal plane
◼ It is purely geometrical factor.◼ This plane is assumed to pass through 3 dental landmark
central incisal point and summit of mesio-buccal cusp of last molar on either side.
◼ It is parallel to Ala- tragus line.
◼ It is transferred to articulator with help of facebow.◼ Steep increase in inclination of occlusal plane will result
in movement of upper denture backward and lower denture forward during function.
◼ Decrease in inclination will result in opposite of above movement.
◼ 2-5 degree angle between this plane and horizontal plane of reference.
Cuspal Inclination
◼ The angle formed by the incisal slope of mesio- buccal cusp to horizontal plane is defined as cuspal inclination.
◼ According to that there are 3 types of posterior teeth.
◼ a) 0 degree posterior teeth.
◼ b) 20 degree posterior teeth.
◼ c) 33 degree posterior teeth.
◼ If the condylar guidance is steep, higher cuspal height tooth are used to gain in balanced occlusion.
◼ Effective cuspal angle can either be increased or decreased by mesial or distal tilt of tooth.
Compensating Curves
◼ It refers to Antero- Posterior and lateral curve produced in the alignment and arrangement of occluding surfaces of the teeth.
◼ Compensating curve allows the dentist to alter cusp height without changing the form which supplied by the manufacturers.
◼ It compensates for opening called as “CHRISTENSEN’S
phenomenon” that occurs in
posterior region when protrusive movements are made.
Christensen’s Phenomenon Antero-Posterior / Lateral Compensating curves
◼ CURVE OF SPEE: ANTERO -POSTERIOR curved arrangement of occlusal surfaces and incisal edges of natural teeth when viewed saggitally is called curve of spee, if it is in denture it is called A-P compensating curve.
◼ MEDIO-LATERAL CURVE OR CURVE OF WILLSON: It is transverse curve made by lingual inclination of posterior teeth (Manson’s curve)
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◼ Factors affecting protrusive balance:◼ Inclination of the condylar path on the articulator as
recorded from patient
◼ Incisal guidance taken from the patient
◼ Inclination of the plane of occlusion set to physiological factors
◼ Compensating curve set to harmonize condylar and incisal guidance
◼ Control of cusp height and tooth inclination
◼ Factors affecting lateral balance◼ Condylar inclination on the balancing side
◼ Inclination of the incisal guidance and cuspid lift
◼ Inclination of plane of occlusion on balancing and working side
◼ Compensating curve on balancing and working side
◼ Bennett side shift on working side
◼ Buccal cusp height or inclination on balancing side
◼ Lingual cusp height or inclination on the working side
‘Rudolph L.Hanau’ proposed nine factors that govern the articulation of artificial teeth.
-Laws of articulation.
-Hanaus Quint
Hanau’s Quint Trapozzano’s Concept:
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Bouchers concept:
Occlusal plane to be located exactly as it was when the natural teeth were present.States that:-There are 3 fixed factors :1. The orientation of the occlusal plane, the incisal guidance, and the condylar guidance.
2. The angulation of the cusp is more important than the height of the cusp.
3. The compensating curve enables one to increase the effective height of the cusps without changing the form of the teeth.
The lott’s Concept
◼ He related the laws as follows ◼ The greater the angle of the condylar path, the greater is the
separation
◼ The greater the angle of the of the overbite, the greater is the separation in the anterior region and the posterior region.
◼ The greater is separation of the posterior teeth, greater is the compensating curve.
◼ Posterior separartion beyond the ability of compensating curve to balance the occlusion requires the plane of orientation.
◼ The greater the separation of the posterior teeth, the greater must be the height of the cusps….
Bernard Levin Concept
◼ Eliminated plane of orientation.
◼ Guiding factors increase the posterior separation.
◼ Controlling factors decrease the posterior separation.
The Quad: The laws of protrusive and lateral
balanced occlusionSteps involved in balancing:
-The teeth have to be inclined to develop a balanced occlusion.
-The upper and lower incisal units meet only when the mandibular teeth are protruded and protrusive balancing unit functions only when upper and lower units contact.
-To develop a balanced occlusion one needs an adjustable articulator which should:
-Receive a face-bow transfer.-Adjust to individual inter condylar guidance.-Have an adjustable incisal guide table.
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To adjust the articulator requires:
-A centric relation record.
-Eccentric protrusive record.
-Right and left lateral relation records are desirable if the articulator is capable of accepting the records.
-If the articulator will not receive the lateral records (Hanau type) then lateral condylar guidance is calculated as:
L = H/8 + 12
Selective Grinding
Definition: The modification of the occlusal forms of the teeth with the intend of equilibrating occlusal stress, producing simultaneous occlusal contacts/ harmonizing cuspal relations.
Rational :◼ Eliminate occlusal interferences ◼ Achieve balanced occlusion ◼ Contacts in harmony with TMJ and neuromuscular system◼ Failure to achieve it
-soreness-loss of supporting bone -TMJ problems
Principles :◼Eliminate interlocking transverse ridges
◼Functional cusp not subjected to selective grinding
◼Lower buccal cusp inclines can be reduced but not the cusp
◼Maxillary buccal cusp out of contact during centric occlusion and eccentric positions.
-“BULL’s law-
-In anterior teeth, lingual of upper and labial surface of lower teeth is grinded to eliminate any interference.
-Final result should be smooth gliding lateral excursion with five working and five balancing contacts.
-The multiple contacts should be smooth, uniform and in harmony with the TMJ’s and the neuro-muscular activity.
Steps at which grinding is performed:
◼ At the time of teeth arrangement
◼ Lab remount procedures
◼ Clinical remount procedures
Methods of detecting errors
◼ Articulating paper
◼ Carbon paper
◼ Wax paper
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Selective grinding for centric contacts:
-After the complete arrangement of teeth, place an articulating paper and tap the articulator.
Only the lower central fossa or marginal ridges should be ground not the upper lingual cusps.
-If any upper buccal cusps or inclines are in contact, they should be ground out of contact.
“The final result should be upper lingual cusp in contact with the lower central fossa”.
Occlusal and incisal stops in centric occlusion
Premature contacts in centric relation Removal of premature contacts
Selective grinding for working and balancing contacts:
There should be working and balancing contacts that are in harmony with guidance of condylar inclination and incisal guidance.
If the mandible moves to left, the upper left lingual cusps should contact lower left lingual cusps (on working side) and the upper right lingual cusps contact lower buccal cusps (balancing side).
‘If any prematurity exist, selective grinding is done’.
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Selective grinding for the protusive contacts
◼ Maxillary lingual cusp gliding over the distal lingual cusp of the mandibular teeth.
◼ The upper second molars riding up the distal inclines of the lower second molars created by the compensating curves.
◼ All the premature contacts are gently ground off.
◼ Anterior teeth prematurities- anterior mandibular teeth are being
modified keeping esthetics in mind
After completion of the grinding
Remedies for error in occlusion
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Absence of contact in the posterior region with the cast in a protrusive relation
◼ Increase the prominence of the antero-posterior curve
◼ Increase the cusp height
◼ Raise the plane of orientation in the posterior region
Premature contact in the posterior region with the cast in protrusive relation
◼ Decrease the prominence of the antero-posterior compensating curve
◼ Decrease the cusp height
◼ Lower the plane of orientation in the posterior region
◼ Absence of contact on the balancing side with the cast in a lateral relation
◼ Increase the lateral cusp height on the balancing side
◼ Increase the prominence of the lateral compensating curve on that side
◼ Raise the plane of orientation
◼ Premature contact on the balancing side with the cast in a lateral relation
◼ Decrease the lateral cusp height on the balancing side
◼ Decrease the prominence of the lateral compensating curve on that side
◼ If extreme, lower the plane of orientation in the posterior region on that side
Balancing side interferences are removedCorrection of balancing side interferences
◼ Absence of contact on the working side with the cast in a lateral relation
◼ If all the contacts are correct, increase the lateral cusp height on the working side
◼ If the error is very slight, spot-grind on the balancing side, or
◼ Decrease the prominence of the lateral compensating curve on the working side
◼ Premature contact on the working side with the casts in a lateral relation
▪ Increase the prominence of the lateral compensating curve on that side
◼ Grind the teeth on the working side, but first decide whether to do it by decreasing lateral cusp height or by increasing anteroposterior cusp height
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PREMATURE CONTACT OF THE ANTERIOR TEETH WITH THE CASTS IN THE PROTRUSIVE RELATION
◼ Rearrange the lower anterior teeth closer to the lower ridge.
◼ Use shorter lower anterior teeth
◼ Shorten them by grinding
ERRORS IN OCCLUSION DISCOVERED WHEN TRIAL DENTURE ARE EXAMINED IN THE PATIENTS MOUTH
◼ AN INCREASE OR DECREASE OF THE VERTICAL DIMENTION OF THE OCCLUSION FROM THAT ORIGINALLY ESTABLISHED ON THE PATIENTS.
CAUSES
◼ This could result from failure to have the lower end of the anterior pin in contact with the platform of the anterior guide at the time the mandibular cast was mounted in the articulator
TO CORRECT◼ If the change was accidental after mounting the mandibular cast in the
articulator, reestablish the desired occluding vertical dimension on the patient, return to the articulator and firmly lock he anterior pin in its position. And rearrange the teeth.
FAULTY CENTRIC OCCLUSION WHEN THE JAW IS CLOSED IN THE CENTRIC RELATION.
CAUSE◼ A faulty centric relation record
TO CORRECT.◼ First check all feature listed as equivalent, make a new centric
record on the patient and remount the mandibular cast. Make a new protrusive record and readjust the condylar elements of the articulator rearrange the teeth to proper occlusion.
ABSENCE OF CONTACT ON THE POSTERIOR REGION IN PROTRUSIVE RELATION.
CAUSE◼ The condylar inclines on the articulator are flatter than the
condylar path of the patient.TO CORRECT◼ Make a new protrusive jaw relation record on the patient and
readjust the condylar elements. Rearrange the teeth as follows◼ Increase the height progressively towards the posterior.◼ Increase the prominence of the antero- posterior compensating
curve.◼ Raise plane of occlusion in the posterior region.
PREMATURE CONTACT IN THE POSTERIOR REGION IN PROTRUSIVE JAW RELATION.
CAUSE◼ The patient’s condyle path is flatter than the condylar guidance in
the articulator.TO CORRECT◼ Make a new protrusive jaw relation record. Adjust the condylar
elements of the articulator. Rearrange the teeth as follows.◼ Decrease the cusp height progressively to the posterior region◼ Decrease the prominence of antero-posterior compensating curve◼ Lower the plane of orientation in the posterior region.
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ABSENCE OF CONTACT ON THE BALANCING SIDE.
CAUSE◼ The condylar inclination on the articulator is too flat, probably due
to protrusive jaw relation. TO CORRECT◼ Increase the lateral cups height on the balancing side ◼ Increase the prominence of the lateral compensating curve on that
side.◼ Raise the plane of orientation in the posterior region on that side
PREMATURE CONTACT ON THE BALANCING SIDE
CAUSE◼ The condylar guidance inclination in the articulator is steeper than
the condylar path inclination. of the patient probably due to faulty protrusive record
TO CORRECT◼ Make a new protrusive jaw relation record on the patient. Readjust
the condylar guidance elements and rearrange the teeth.◼ Decrease the lateral cusp height on the balancing side.◼ decrease the prominence of the lateral compensating curve on the
side◼ If the errors are slight, set the condylar guidance inclination 5 degree
flatter. And spot grind the teeth on the side.
OTHER TYPES OF OCCLUSION
LINGUALISED OCCLUSION
◼ GYSI in 1927 introduced this type of concept.
◼ POUND used it for non balanced articulation.
◼ PAYNE in 1941 used it for balanced articulation.
Definition : Lingualised occlusion uses the maxillary lingual cusp as a dominant functional element, against the corresponding portion of the mandibular teeth
Indications for Lingualised occlusion:
◼ Lingualised occlusion can be used in most denture combinations.
◼ It is particularly helpful when the patient places high priority onesthetics but non-anatomic occlusal scheme is indicated by oralconditions such as severe alveolar resorption, a Class II jawrelationship, or displaceable supporting tissue.
◼ If the non-anatomic occlusal scheme is used, esthetics in the premolarregion are compromised.
◼ With Lingualised occlusion, the esthetic result is greatly improvedwhile still maintaining the advantages of a non-anatomic system.
◼ Lingualised occlusion also can be used effectively when a completedenture opposes a removable partial denture.
Principles of Lingualised occlusion
◼ Anatomic posterior (30 or 33°) teeth are used for the maxillarydenture. Tooth forms with prominent lingual cusps are helpful.
◼ Non-anatomic or semi-anatomic teeth are used for the mandibulardenture. Either a shallow or flat cusp form is used. A narrow occlusaltable is preferred wherever resorption of the residual ridges hasoccurred.
◼ Modification of the mandibular posterior teeth is accomplished byselective grinding which is always necessary regardless of specifictooth or material.
◼ Upper lingual cusps should contact lower teeth in centric occlusion.
◼ Balancing and working contacts only on maxillary lingual cusps.
◼ Protusive contacts only between upper lingual cusps and lower teeth.
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Advantages of Lingualisedocclusion◼ Most of the advantages attributed to
both the anatomic and non-anatomicforms are retained.
◼ Cusp form is more natural inappearance compared to non-anatomictooth form.
◼ Good penetration of the food bolus ispossible.
◼ Bilateral mechanical balancedocclusion is readily obtained for aregion around centric relation.
◼ Vertical forces are centralized on themandibular teeth.
Monoplane Occlusion
MAIN FEATURES◼ Non anatomic tooth form may be occlusion of choice for given situation
like poor neuro-muscular control, highly resorbed residual ridge. ◼ Tooth inclines are eliminated and balance is produced by combination
antero-posterior and medio-lateral curves or by the use of a balancing ramp leading to a three –point balance
◼ Anterior teeth primarily set for length and proper lip support.◼ Elimination of cuspal inclines and teeth must be set in flat monoplane
arrangement,◼ zero incisal guidance should be established ADVANTAGES◼ Preservation of structure of basal seat.◼ Efficient occlusal form.◼ Simplicity of technique involved ◼ Good for patients with cross-bite or class 3 relationships and
especially for patient with class 2 relationships who have an extremely long functional path.
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Balancing ramps in non-anatomic complete denture occlusion
-Non anatomic teeth with no cuspal inclination.
-flat plane with no overbite.
-An improvement on inclined molar technique for balancing protrusive and lateral excursion is the use of customized balancing ramps is placed posterior to most distal mandibular second molar
-Tripodization of the dentures
Review of Literature
Finn Tengs Christensen (1960) described the importance of balanced occlusion in arrangement of teeth. He stressed the introduction of compensating curves for achieving balance.
-In order to achieve balance, the compensating curve must be in harmony with other factors
-By means of compensating curves, complete antagonist contact during protrusive movements can be obtained with lower cusp angulation.
-’So the orientation in one factor influences the other’.
Vincent R. Trappozano (1960) carried out tests to check the efficiency of balanced and non-balanced occlusion.
-He selected few patients depending on inter-ridge space, intelligence and experience of wearing dentures and on basis of type of residual ridge. Patients were from 55 years to 70 years.
-All had worn dentures with 23degrees posterior teeth in balanced occlusion.
- Comparative chewing tests of occlusal efficiency were made with carrots and freshly roasted peanuts.
-These were selected as test foods because they don’t readily disintegrate into fine particles.
-The number of strokes made upto time of deglutition were counted and averaged.-The average was noted for each patient and this was the number of strokes permitted.
-A 100 mesh screen was used as sieve to study the size of remaining particles and weight changes in test materials after mastication by the patient.
-Out of 12 patients examined, 9 patients had greater efficiency of chewing with balanced occlusion.
- In 3, efficiency was greater with non balanced occlusion when carrots were chewed. When peanuts were chewed no difference was noticed.
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Honorato Villa (1962) recommended a technique for the use of non-anatomic posterior teeth. He used the incisal guidance for attaining balanced occlusion. ◼The lower bicuspids were placed first on lower occlusal rims. The two bicuspids represent the central transverse axis.
◼When cusps are placed against a flat plane, there will be balancing contacts only in working position and not in protrusive and balancing positions.
◼A groove is made in upper denture where the lower cusp will occlude, in order to overcome the difficulty and this makes the balanced occlusion possible in protrusive and lateral occlusion.
◼The logistic behind this arrangement is that balancing incline requires less inclinations when it is placed on upper first bicuspid instead of second molar because of anterior position of bicuspid.
H.O. Beck (1973) grouped the balanced and non-balanced occlusions into five categories each.
Non-balanced occlusions are:a. Modified cusp teeth with upper lingual cusps opposing widened
lower fossa and a reduction of buccal cusps of lower posterior teeth.
b. Cusp teeth arranged in typical occlusion with disocclusion by cuspid guidance in eccentric positions.
c. Non-anatomic teeth arranged in flat occlusal plane anteroposteriorly and laterally.
d. Non-anatomic teeth arranged high in second and first molar regions.
e. Non-anatomic teeth arranged in flat plane anteriorly but with reverse lateral curve.
Five balanced occlusions are:a. Anatomic and semi-anatomic teeth arranged in classic interdigitations.
b. Semi anatomic teeth with buccal reduction of lower posterior teeth.
c. Non-anatomic teeth arranged on curves anteroposteriorly and laterally.
d. Non-anatomic teeth arranged reverse curve laterally but with second molar ramps for balancing contacts.
e. Semi-anatomic teeth with only a linear contact of lower posterior teeth with upper occlusal surfaces balanced anteroposteriorly and laterally.
He concluded: Occlusal designs and their resulting functions are of concern to the dentist so that loss of the remaining tissues of the mouth, which may be attributed to the occlusion, can be minimized
Summary
The nature of the supporting structures for the complete dentures and the forces directed to them by the occlusion creates a special biomechanical problem.
Balanced occlusion is one of the most important factors which will favor the stability of the base; and help in preservation of the supporting structures by reducing the lateral forces.
“ Thereby signifying its importance in complete denture fabrication.”
Conclusion
◼ Necessity of the balanced occlusion is not universally subscribed by the Prosthodontics. Patient doesn’t require a
balanced occlusion in order to wear the denture successfully. A physiological consideration like interocclusal distance, centric relation is mandatory for the success of the denture.
◼ Denture and its supporting structures will not be tolerated unless the occlusion established accommodates their idiosyncrasies; in such cases balanced occlusion is imperative.
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19
References
-Arthur N.: Balancing ramps in non-anatomic complete denture occlusion. JPD,1985;53:431-433.-Beck H.O.: Occlusion as related to complete removable prosthodontics. JPD,1972;27:246-256.-Becker C.M., Swoop P.C.: Lingualised occlusion forremovable prosthodontics. JPD,1977;38:601-608.Bernard Levin: Reevaluation of Hanaus Laws of Articulation and the Hanaus Quint. JPD,1978;39:254-258.-Bolender-Zarb: Prosthodontic Treatment For Edentulous Patient,12th Edition, 2004 Mosby.-Dawson P.E.: Evaluation, diagnosis and treatment of occlusal problems,2nd edition, 1989 Mosby.
Gregory R.P., Gerald H.L.: The Occlusal Spectrum and Complete Dentures.-Heartwell Charles M.: Sylabbus of complete dentures.-Kydd W.L.: Comlete denture base deformation with varied occlusal tooth form. JPD., 1959;6:714-718.-Kurth L.E.: Balanced Occlusion. JPD’1954’4:150-167.-Ramjford S. and Ash: Occlusion-Sharry J.J.: Complete Denture Prosthodontics; 1962 McGraw-Hill Book Company.Sheldon Winkler: Essentials of complate denture prosthodontics2nd Edition;2000, Ishiyaku EurAmerica Inc. U.S.A.-Trappozano V.R.: An experimental study of the testing of occlusal patterns on the same denture bases. JPD.;1952; 440-457.
As classically told by Heartwell balancing an occlusion is like converting “the stumbling prose into poetry”.
Thank you
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1
DUPLICATING AND REFRACTORY MATERIALS USED IN
REMOVABLE PARTIAL DENTURES
BY- DR DEVENDRA PAL SINGH
Contents
1. DEFINITION
o Duplication
o Refractory cast
2. DUPLICATION MATERIALS
o Agar agar
o Alginate
o Silicones
o Aqueous acrylamide gel
o Polyvinyl chloride
3. REFRACTORY MATERIALS
o Phosphate bonded
o Ethyl silicate bonded
o Gypsum bonded
4. REVIEW OF LITERATURE
5. SUMMARY AND CONCLUSION
6. BIBLIOGRAPHY
INTRODUCTION
In preparing partial dentures , a
duplicate should be made of the stone
cast of the patient mouth. This duplicate
is required for two reasons:
1) The cast on which the wax pattern of
the metal framework is to be formed
must be made from the refractory
investment, because it must withstand
the the casting temperatures
2) The original cast is needed for checking
the accuracy of the metal framework
and for processing the plastic portion of
the partial denture.
Duplication:
◼ The procedure of accurately reproducing a
cast.
Refractory Cast:
◼ A cast made of materials that will
withstand high temperatures without
disintegrating and, when used in partial
denture casting techniques, has expansion
to compensate for metal shrinkage.
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2
Materials used for duplication:
◼ Agar agar
◼ Alginate
◼ Silicones
◼ Aqueous acrylamide gel
◼ Polyvinyl chloride
Agar agar:
◼ Agar is the material of choice to make the
mold for duplication, as it is a reversible
hydrocolloid and can be used many times.
Composition :
◼ The basic constituent of the hydrocolloid
impression material is agar.
◼ Agar is an organic hydrophilic colloid
extracted from certain types of seaweed.
◼ It is a sulfuric ester of a linear polymer of
galactose.
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3
◼ The principle ingredient by weight is water
(>80%)
◼ A small percentage (0.2% - 0.5%) of
borax is added to strengthen the gel.
◼ To counteract the effects of water and
borax, potassium sulfate is added because
it accelerates the setting of gypsum.
◼ Some products contain filler particles for the control
of strength, viscosity, and rigidity. E.g., fillers used are
diatomaceous earth, clay, silica, wax, rubber and
similar inert powders.
◼ Other ingredients like thymol as bactericide and
glycerin as plasticizer may be added
◼ Pigments and flavors are also be added.
Gelation process:
◼ The setting of a reversible hydrocolloid often called
gelation is a solidification process.
Sol Gel
◼ The physical change from the sol to gel and vice
versa is induced by a temperature change.
However the hydrocolloid gel does not return to the
sol at the same temperature at which it solidifies.
Gelation process:
◼ The setting of a reversible hydrocolloid often called
gelation is a solidification process.
Sol Gel
◼ The physical change from the sol to gel and vice
versa is induced by a temperature change.
However the hydrocolloid gel does not return to the
sol at the same temperature at which it solidifies.
◼ The gel must be heated to a higher
temperature known as the liquefaction
temperature (70° to 100°C) to return it
to the sol condition.
◼ When cooled from this temperature
range, the sol transforms into gel at a
point known as gelation temperature
(37° to 50°C).
◼ The temperature lag between the gelation
temperature and the liquefaction
temperature of the gel makes it possible
to use agar as a impression material.
◼ The molten colloid can be stored for a
few days in a hydrocolloid storage unit at
57°C – 60°C.
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4
Alginate
◼ A Chemist from Scotland noticed that a certain
brown seaweed (algae) yielded a peculiar
mucous extraction and named it as Algin.
◼ This natural substance was later identified as a
linear polymer with numerous carboxyl acid
groups and named an hydro-b-d- mannuronic
acid (also called alginic acid).
The advantage of alginate over agar is:
◼ Its easy to manipulate
◼ Relatively less duplication time
◼ Relatively inexpensive because it does
not require elaborate equipment like agar.
Modified alginates:
◼ The traditional alginate is used as a two
component system, a powder and liquid.
◼ However the alginate is also available in the
form of a solution containing the water but no
source of calcium ions.
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5
◼ A reactor of plaster of Paris can then be added
to the solution.
◼ There is yet another form that is available. The
two component system which is in the form
of two pastes : one contains the alginate
solution and the other contains the calcium
reactor.
Composition:
◼ The chief active ingredient of the irreversible
hydrocolloid is one of the soluble alginate such as
sodium, potassium or triethanolamine alginates.
◼ Other components like diatomaceous earth, and zinc
oxide act as filler particles are added which can
increase the strength and stiffness of the alginate gel,
produce a smooth texture.
◼ CaSO4 dihydrate or hemihydrate can be
used as a reactor.
◼ A fluoride, such as potassium titanium
fluoride, is added as an accelerator for
the setting of the stone
◼ NaPO4 acts as a retarder.
Gelation process:
◼ The typical sol-gel reaction can be described
simply as a reaction of soluble alginate with
calcium sulphate and the formation of an
insoluble calcium alginate gel.
◼ CaSO4 reacts rapidly to form insoluble calcium
alginate from the potassium or sodium alginate in
an aqueous solution.
◼The production of the calcium alginate is so rapid
that it does not allow sufficient working time. Thus,
a third water soluble salt, such as trisodium
phosphate, is added to the solution to prolong the
working time.
◼ The reaction between CaSO4 and the soluble alginate
is prevented as long as there is unreacted trisodium
phosphate.
2Na3PO4 + 3CaSO4 → Ca5(PO4)2 + 3Na2SO4
◼ When the supply of trisodium phosphate is
exhausted, the calcium ions begin to react with the
potassium alginate to produce calcium alginate.
K2n Alg + n CaSO4 → n K2SO4 + Can Alg
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6
Controlling gelation time:
◼ It is the time measured from the beginning of
mixing until gelation occurs.
◼ The optimal gelation time is between 3-4 min at
room temperature.
◼ Gelation time is best regulated by the amount of
retarder or by altering the temperature of the
water.
Silicones:
Two types of silicones are used as rubber
impression materials and are identified on
the basis of their chemical reactions as
◼ Condensation Silicone
◼ Addition Silicone
Condensation silicones
◼ They are supplied as a base and an accelerator.
◼ The base contains a moderately low molecular
weight silicone called a dimethyl siloxane, which has
reactive terminal hydroxyl groups.
◼ Fillers like silica or copper carbonate are added to
the liquid silicone polymer to form a paste.
◼ Accelerators like stannous octate or alkyl silicate
are used.
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7
◼The condensation polymerization of this material
involves a reaction with trifunctional and
tetrafunctional alkyl silicates, commonly tetraethyl
orthosilicate, in the presence of stannous octate.
◼These reactions can take place at ambient
temperatures; thus, the materials are often called
room temperature vulcanization silicones.
Ethyl alcohol is a by product of
the condensation setting reaction.
Its subsequent evaporation probably
accounts for condensation silicones biggest
disadvantage which is poor dimensional
stability.
Addition silicones
◼ They are frequently called as polyvinyl siloxane.
◼ In contrast with the condensation silicones, the
addition reaction polymer is terminated with vinyl
groups and is cross linked with hydride groups
activated by a platinum salt catalyst.
◼ Both base and catalyst pastes contain a form of
the vinyl silicone.
◼ The base paste contains polymethyl hydrogen
siloxane as well as other siloxane
prepolymers.
◼ The catalyst paste contains divinyl
polydimethyl siloxane and other siloxane
prepolymers.
◼ If the catalyst paste contains the platinum salt
activator, then the base paste must contain the
hybrid silicone.
◼ Both pastes contain fillers, and retarders are
present in paste containing the activator.
◼ One of its disadvantage is its inherent
hydrophobicity.
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8
Aqueous acrylamide gel:
The time necessary for performing the duplicating
procedure using agar which is used successfully in
dental laboratory duplicating procedures is 2 to 3
hours.
There are situations however in which a duplicating
material is needed that can produce a cast in a very
short period of time.
◼Aqueous acrylamide gel was produced from a
mixture of two organic monomers,
acrylamide and N, N – methylenebis
acrylamide in water.
◼ When these substances are catalysed by the
addition of ammonium persulfate and
b-dimethylaminoprionitrile, a transparent
gel forms by a polymerization – cross linking
reaction.
◼ This material is commercially available under the
trade name of CYANOGUM 41 or AM-9
chemical group.
◼ Potassium alginate is added for the purpose of
preventing sticking between the acrylamide gel
and the master or refractory cast.
◼ It is a duplicating material that allows a mold to
be made of a master cast within 15 min.
Polyvinylchloride
◼ It is a reversible plastic gel.
◼ The main advantages of this material are:
◼ High strength properties
◼ High chemical stability, which permit a
large number of duplications before replacement.
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9
Properties and requirements of duplicating
material
ANSI / ADA specification no. 20 for dental
duplicating materials includes 2 types
1. Thermoreversible (Type I)
- Hydrocolloidal (Class I)
- Nonaqueous organic (Class II)
2. Non reversible (Type II)
- Hydrocolloidal (Class I)
- Nonaqueous organic (Class II)
▪ The specification sets requirements of freedom
from foreign material and impurities and
It should be suitable for duplication of
plaster, stone or investment casts of the oral
tissues.
◼ Pouring temperature and the temperature
of gel formation are defined for the
thermoreversible products.
◼ Working and setting times are specified for
the non-reversible material.
◼ Compatibility with at least one type of
investment and the ability to reproduce detail
satisfactorily are required.
◼ Type I products should be dimensionally stable after
inoculation under controlled conditions.
◼ Requirements for permanent deformation, strain in
compression, and resistance to tearing are
described.
◼ Packaging must include instructions that indicate
the type of investment that can be used with
the material.
◼ For type I products, must also include (1) method
of liquefying (2) tempering or storing
temperature and (3) pouring temperature.
Refractory materials:
The rapid growth in use of cast removable
partial dentures , the increased use of
higher melting alloys and the use of less
expensive base metal alloys have resulted
in an increased use of phosphate or
silicabonded refractory material.
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10
Phosphate bonded:
Composition:
▪ These investments consist of refractory fillers and a
binder.
◼ The filler is silica, in the form of Cristabalite, Quartz, or a
mixture of the two and in a concentration of approx 80%.
◼ The binder consists of magnesium oxide and a phosphate
that is acid in nature.
▪ It is fortunate that the colloidal silica suspensions
became available in time for use with the phosphate
investments in place of water to compensate for the
greater contraction of the high fusing alloys during
solidification, as it increases the setting expansion of the
investment.
◼ Carbon is often added to the powder to produce clear
castings and facilitate the divesting of the casting from the
mold.
◼ But the latest evidence indicates that palladium does react
with carbon at temperature above 1504°C. Thus if the
temperature exceeds this temperature during casting, a
carbon free investment should be used.
Setting reactions
◼ Magnesium ammonium phosphate formed is
polymeric. Although the stoichiometric quantities are equal
molecules of magnesia and monoammonium phosphate, an
excess of magnesia is usually present, and some of it is
never fully reacted.
◼ What is thus formed is a predominantly colloidal
multimolecular aggregate around excess MgO and fillers.
On heating, the binder of the set investment undergoes
thermal reactions.
Setting and thermal expansion:
◼ Theoretically, the reaction should entail a shrinkage, but inpractice there is a slight expansion by using a colloidal silicasolution instead of water.
◼ The early thermal shrinkage of phosphate investments isassociated with the decomposition of the binder, magnesiumammonium phosphate, and is accompanied by evolution ofammonia.
◼ Some of the shrinkage is masked because of theexpansion of the refractory filler especially in the case ofcristobalite
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11
Working and setting time:
◼ Phosphate investments are affected by temperature.
◼ The setting reaction itself gives off heat, and this
further accelerates the rate of setting.
◼ Increase in mixing time and mixing efficiency results
in faster set.
◼ Increase in w:p ratio, increases the working time.
Ethylsilicate-bonded:
losing popularity - complicated and time
consuming procedures involved.
Binder is a silica get that reverts to silica on
heating. Several methods may be used to
produce the silica or silicic acid gel binders.
◼ Another system for binder formation is based
on ethyl silicate. A colloidal silicic acid is
formed by hydrolyzing ethyl silicate in the
presence of hydrochloric acid, ethyl alcohol and
water.
◼ A polymerized form of ethyl silicate is used a
colloidal solution of polysilicic acid is formed. This
solution is mixed with quartz or cristabolite to which is
added a small amount of finely powdered MgO to
render the mixture alkaline.
◼ A coherent gel of poly silicic acid then
forms, accompanied by a setting shrinkage.
◼ This soft gel is dried at a temperature below
168°C. During the drying process, the gel loses
alcohol and water to form a concentrated, hard
gel.
This contraction is known as “green shrinkage”
and it occurs in addition to the setting shrinkage.
Investments of this type are designed to reduce the
layer of silica gel around the particles.
This type of investment can be heated to 1090°C
to 1180°C and is compatible with the higher
fusing alloys.
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12
Gypsum bonded:
◼ When casting gold alloys gypsum bonded
investment material can be used. Most materials
now contain alpha-hemihydrate because of
their greater strength.
◼ This gypsum product serves as a binder to hold
the other ingredients together and to provide
rigidity.
◼ The strength of the material is dependent on
the amount of binder present. The material
may contain 25% to 45% of gypsum.
◼ In addition to silica certain modifying
agents, coloring matter and reducing
agents, such as carbon and powdered copper
are present.
Some of the modifiers such as boric acid and sodium
chloride
- not only regulate the setting expansion and
the setting time but
- they also prevent most of the shrinkage of
gypsum when it is heated above 300°C.
◼ But all forms of gypsum dehydrate between
200-400°C. A slight expansion occurs
between 400°C – 700°C and then a large
contraction occurs.
◼ This latter shrinkage is most likely caused by
decomposition of sulfur gases, such as
sulfur dioxide
This decomposition not only causes
shrinkage but also contaminates the
castings with the sulfides of the non-noble
alloying elements, such as silver and copper.
Thus it is imperative that gypsum bonded
material not be heated above 700°C.
◼ Silica is added to provide a refractory
during the heating of the material and to
regulate the thermal expansion.
◼ If proper forms of silica like quartz or
crystabolite are used in the material, the
contraction during the heating can be
eliminated and changed to an expansion.
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13
◼ F.A Peyton and R. G. Craig (1962)
conducted a study to test the compatibility of
duplicating compounds and casting
investments. This study was designed to establish
the surface hardness, surface roughness and thermal
expansion of different investment material poured
against different duplicating media.
REVIEW OF LITERATURE
◼ Measurements of surface detail showed that
Gypsum bonded investment were
incompatible with all the duplicating materials.
◼ Phosphate bonded investments were
compatible with plastic duplicating compound.
◼ Silicate bonded investment were compatible
with agar duplicating compound.
REVIEW OF LITERATURE
◼ PBI were harder when produced against
plastic duplicating media.
◼ GBI showed variable results and
◼ SBI were weak and cannot be tested
E. R. Dootz, R. G. Craig, F. A. Peyton (1965)
Conducted a study to see the
influence of investments and duplicating
procedures on the accuracy of partial denture
castings. This study was designed to see the effect
of changing duplicating materials, soaking refractory
cast in water, applying the paint-on layer and outer
layer of investment on casting accuracy.
REVIEW OF LITERATURE
◼ The results revealed that the total
compensating expansion through the base
of the refractory cast may not be equal to
the expansion through the tissue surface
of the cast.
◼ The compensating expansion was
increased by soaking the refractory cast
in water and by applying a paint-on layer.
REVIEW OF LITERATURE
◼ Peter R. Likeman, David R. Radford, Andrzej
S. Juszczyk(1996)
Conducted a study to investigate the
surface of investments poured against
different duplicating media. In this study they
used two PBI material and compared their
surface characteristics with duplicating gel
and poly (vinyl siloxane) duplicating medium
REVIEW OF LITERATURE
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14
◼ The hardness of samples poured in poly(vinyl
siloxane) was greater than that of same
investment poured in duplicating gel
◼ Microscopic examination revealed greater
surface irregularity of samples poured in
duplicating gel than in poly(vinyl siloxane).
REVIEW OF LITERATURE
Robert W.Rudd and Kenneth E.Rudd in their
review article (2001) stated that problems
encountered during duplicating due to
REVIEW OF LITERATURE
◼ Using contaminated material
◼ Failing to seal the definative cast to bottem of
the flask
◼ Pouring over heated material
◼ Delaying the pouring the stone or investment.
Summary and ConclusionsIn this seminar the commonly used
duplicating and refractory materials were described.
Agar agar and phosphate bonded materials are
used extensively as duplicating and refractory
materials respectively because of their advantages
over the other materials.
Knowledge of these materials is a pre-requisite
for obtaining acceptable refractory casts.
References◼ Craig R.G. and Powers J.M. ; Restorative Dental
Materials, 11th edition, Mosby publishers, 2002
◼ Dootz E.R., Craig R.G., Peyton F.A. : The influence of
investments and duplicating procedures on the accuracy of
partial denture castings.
J. Prosthet. Dent. 1965; 15: 679-690.
◼ Dootz E.R., Craig R.G. and Peyton F.A. ; Aqueousaccrylamide gel duplicating material
J. Prosthet. Dent. 1967;17: 571-577
◼ Kenneth J.Anusavice ; Phillip’s Science of Dental
Materials, 11th edition, W.B. Saunders publishers,
2003
◼ McCracken’s ; Removable Partial Prosthodontics,
11th edition,Mosby publishers, 2005
◼ Peyton F.A., Craig R.G. : Compatibility of duplicating compound and casting investments.
J. Prosthet. Dent. 1962; 12: 1111-1124.
◼ Peter R. Likeman, David R. Radford, Andrzej S.
Juszczyk : The surface of investment poured against
different duplicating media.
J. Prosthet. Dent. 1996; 9: 572-579.
◼ Phillips R.W. : Skinner’s Science of Dental
Materials. Ed. 9, Philadelphia : Saunders, 1991; 406-
410.
◼ Rudd, Morrow and Rhodes ; Dental laboratory
procedures – vol.3, 2nd edition, C.V. Mosby
publishers, 1986
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15