CONCEPT OF OCCLUSIONS
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INTRODUCTION The goal of modern orthodontics according to Profitt is “the creation of best possible occlusal relationship within the framework of acceptable facial aesthetics and stability of result”. Occlusion – The relationship of maxillary and mandibular teeth when they are in functional contact during activity of the mandible - Dorland’s Medical Dictionary www.indiandentalacademy.com
Dental occlusion varies among individuals according to tooth size and shape, tooth position, timing and sequence of eruption, dental arch size and shape and pattern of craniofacial growth. The position of the teeth within the jaws and the mode of occlusion are determined by developmental processes that interact on the teeth and their associated structures during the period of formation, growth and post natal modification www.indiandentalacademy.com
TERMINOLOGIES USED IN OCCLUSION Normal Occlusion : – Normal occlusion implies a situation commonly found in the absence of disease. It should include not only a range of anatomically acceptable values but also physiological adaptability. – It is always a range never a point.
Ideal Occlusion : – The concept of ideal or optimal occlusion refers both to an aesthetic and physiologic ideal. It includes functional harmony, stability of masticatory system & Neuromuscular harmony www.indiandentalacademy.com
Physiologic occlusion : – The occlusion that shows no signs of occlusion related pathosis. It may not be an ideal occlusion but it is devoid of any pathological manifestations in the surrounding tissues.
Traumatic occlusion : – An occlusion judged to be causative factors in the formation of traumatic lesions of disturbances in the orofacial complex.
Therapeutic occlusion : – It is a treated occlusion employed to counteract structural interrelationship related to traumatic occlusion. www.indiandentalacademy.com
THE DEVELOPMENT OF THE CONCEPTS OF OCCLUSION The development of concept of occlusion can be traced through fiction and hypothesis to fact. The fictional approach was a convenient arrangement of a series of observation and thoughts more or less logically arranged. The hypothetical approach was based on provisional acceptance of certain logical entities. This was to fill in the gaps in empirical knowledge and thus tentatively complete the picture. Fact is a truth known by actual experience or observation. Both the fictional and hypothetical approach are necessary preludes to the establishment of fact. www.indiandentalacademy.com
The development of concept of occlusion thus can be divided into three periods – The fictional period, prior to 1900 – The hypothetical period from 1900 to 1930 – The factual period from 1930 to present
The transition from one period to another was gradual with considerable overlaping There is another trend in the development of the concept of occlusion, the trend from the static to the dynamic www.indiandentalacademy.com
FICTIONAL PERIOD Pioneers like Fuller, Clark and Imrie talked of “Antagonism”, “Meeting” or “Gliding” of teeth. The creation of normal standard, a basis on which to compare departures from normal was lacking. But this served as a working hypothesis or subsequently became established fact after definitive research www.indiandentalacademy.com
Eugene Talbot published his book “Irregularities of the teeth and their treatment� in 1903. he attributes facial deformities to maternal impressions and delineates in great detail the adolescent neuroses of nasal and facial bones, developmental neurosis of eye, the maxillary bone, the palate, tooth position and so forth. The Talbot concept of normal occlusion was that it was a historical event, passed in the decline of the species and normality was possible only with atavism or throwback to our primitive ancestors www.indiandentalacademy.com
HYPOTHETICAL PERIOD Edward H. Angle, – It was him, who channelised orthodontic thinking on occlusion and brought the concept out of realm of fiction – In 1907, Angle summarised his views as ‘occlusion shall be defied as being the normal relation of the occlusal inclined planes of the teeth when the jaws are closed’. – Angle cites the example of a skull of Negro male from Broomell which he names ‘Old Glory’. In ‘Old Glory’ all the teeth are present and arranged in a graceful curve. He emphasizes that all teeth are necessary for maintaining occlusion. He compares ‘Old Glory’ with the profile of Appollo Belvedre a white male www.indiandentalacademy.com
Angle furnished his ‘key to occlusion’ and emphasizes the first permanent molars especially the upper first permanent molar and considers them to be most constant in taking normal position. This formed the basis of Angle’s classification of malocclusion and this has withstood the test of time. From the hypothesis of constancy of first molar and the line of occlusion, Angle developed the concept that all teeth should be present if normal occlusion is to be achived. www.indiandentalacademy.com
Mathew Cryer and Calvin Case Cryer pointed out that Angle showed the straight profile of Apollo Belvedre and chose a skull of negro male ‘Old Glory’ to exemplify ideal occlusion. He questioned how one could mix a prognathic denture with an orthodontic profile. Case took Angle to task for considering bimaxillary protrusion as normal and for not recognizing individual variation. Case accepts Angle’s hypothesis of constancy of first molar. Case related the facile profile to each type of occlusion.
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He proposed the concept of apical base and divided dentofacial area into four segments or zones of movement. He was aware of the role of nose and chin button and their influence on profile. Case proposed the concept of normal and ideal occlusion. Van Loon used plaster cast of the face and teeth in anthropologic manner which Simon developed further. The idea that teeth should be present to obtain normal facial contour was loosing ground. In 1908 Bennett proposed that the condylar movement was primarily rotatary on opening from occlusion to rest position and later on after passing this point became translatory. www.indiandentalacademy.com
Lischer and Paul Simon They bordened the concept of occlusion by relating the teeth to the rest of the face and cranium. They related teeth in occlusal contact to cranial and facial planes outside the denture proper. Though the concept of orbital plane as basis for determining antero-posterior position of dentition did not stand up. It introduced the idea of facial ramification of malocclusion outside the dental area.
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Milo Hellman Hellman showed the racial variation in so called normal occlusion through anthropological studies. Hellman and others studied the prognathism of the human dentition in relation to a cranial base Stages of Dental development Hellman IIA Eruption of 2nd deciduous molar IIC Eruption of permanent incisor IIIA Eruption of permanent 1st molar IIIB Eruption of canines and premolar IIIC Beginning of 2nd molar eruption IVA Eruption of 2nd molar completed VA (Adult) eruptionwww.indiandentalacademy.com of 3rd molar completed
Dimensional change in the phase on the same time scale. Facial depth increases most, height less rapidly and width the least
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FACTUAL PERIOD In 1930 Holly Broadbent and Hans Planer introduced an accurate techniue of roentogenographic cephaolmetry. Investigators were able to follow longitudinally the orofacial developmental pattern and the intricacies of tooth formation, eruption and adjustment. Planer laid emphasis on efficiency of masticating mechanism. He explained physiological rest position and vertical dimension A third element of occlusion, the TMJ has been receiving more attention. There is an intimate relationship between the interdigitation of the teeth, the status of controlling, musculature and the integrity of the TMJ. www.indiandentalacademy.com
DYNAMIC OCCLUSION Recognition of the role played by muscles physiology and the TMJ has firmly entrenched the dynamic functional concept. The 13 muscle attachment to the mandible in addition to articular capsule and tendon provide a high degree of stability of position that occlusal equilibration and full mouth reconstruction can’t change permanently The teeth are in occlusal contact only 2 to 6% of the time. Therefore 94% of the time, they are apart. The largest segment of time is in postural rest position determined by musculature. Postural rest position is a good place to start in an assessment of vertical status and harmony of orofacial features. www.indiandentalacademy.com
Occlusion is a dynamic entity show variation according to age and sex. Most girls by the age of 12 achieve relatively stable occlusion whereas boys achieve that a bit later due to continuing growth pattern. Three components of occlusion can be summed up as 1.
Occlusal position (or) tooth contact position - Masticatory habits, tooth inclination and malposition, shape of teeth, premature contact, faulty restoration, tooth loss, the condition of periodontium affect the occlusal positions
1.
Postural resting position
2.
TMJ www.indiandentalacademy.com
FACTORS & FORCES THAT DETERMINE TOOTH POSITION The alignment of the dentition in the dental arches occur as a result of complex multidirectional forces acting on the teeth during and after eruption. Labial to the teeth are tip and cheeks which provide relatively light but constant lingually directed forces. On the opposite side of the dental arch is the tongue which provides labially directed forces. Hence the labiolingual and buccolingual forces are equal. This is call neutral position. Proimal contact between adjacent teeth helps maintain the teeth in normal alignment Occlusal contact is another important factor that helps to stabilize tooth alignment.
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Intra Arch Tooth Alignment Relationship of teeth to each other within the dental arch. Plane of occlusion A plane comprising buccal and lingual cusp tip of mandibular posterior teeth of both sides as well as the incisal tip of mandibular anteriors the curvature of the occlusal plane is because the teeth are positioned in arches at varying degrees of inclination
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According to Wilson the mandibular arch appears concave and that of maxillary arch convex According to Bonwill, the maxillary and mandibular arches adapt themselves input to an equilateral triangle of similar sides. According to Vonspee, cusp and the incisal ridges of teeth display a curved alignments when the arches are observed from a point opposite to 1st molar Monson connected the curvatures in the saggital plane with compensatory curvatures in the vertical plane and suggested that the mandible arch adopts itself to the curved segment of a sphere of similar radius www.indiandentalacademy.com
Curve of Spee An imaginary anteroposterior line from the cusp tips of the canine extending to the buccal cusps of the posterior teeth – An excessively concave curve of Spee and mandibular core line restrict the occlusal surface available for maxillary teeth. – A flat to slightly concave curve of Spee and mandibular core line bare the proper occlusal surface for optimal occlusion. – A convex curve of Spee and mandibular core line bare excessive portions of the occlusal surface.
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Curve of Wilson It is a mesiodistal curve that contacts the buccal and lingual cusps tips of the mandibular posterior teeth. It helps in two ways – Teeth aligned parallel to direction of medial pterygoid for optimum resistance to masticatory forces. – The elevated buccal cusps prevent food from going past the occlusal table. Curve of Monson It is obtained by extension of the cruve of spee and curve of Wilson to all cusps and incisal edges www.indiandentalacademy.com
Interarch Tooth Alignment Relationship of teeth in one arch to other. The length and width of maxillary arch is higher when compared to mandibular arch. Supporting cusps (or) centric cusps Buccal cusps of the mandibular posterior teeth and lingual cusp of the maxillary posterior are the centric or supporting cusps Non centric cusps The buccal cusp of maxillary posterior teeth and lingual cusp of the mandibular posterior teeth. www.indiandentalacademy.com
Classification of Occlusion Based on Mandibular Position Centric Occlusion – It is the occlusion of teeth in centric relation. Centric relation has been defined as the maxillomandibular relationship in which condyles articulates with the thinnest avascular position of their respective discs with the complex in the anterosuperior position against the shape of articular eminence. This position is independent of tooth contact
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– In orthodontics, diagnosis and treatment planning should be performed by an evaluation of an malocclusion with the mandible in centric relation (CR), i.e. the natural musculoskeletal position of the condyle in the fossa, in order to obtain the true maxillary - mandibular skeletal and dental relations in the three planes of space. www.indiandentalacademy.com
– If this is overlooked an incorrect diagnosis and treatment plan of the actual malocclusion, along with its unfavourable consequences, may result. – During every appointment a patient has to be monitored in CR so that the mechanotherapy is guided to accomplish the final ideal static and functional occlusion with the mandible in position. – If this disregarded several prematurity that may later cause traumatic occlusion or craniomandibular disorders may result. Eccentric occlusion – It is defined as the occlusion, other than centric occlusion. It includes Lateral occlusion Protruded occlusion Retrusive occlusion www.indiandentalacademy.com
Based on relationship of first permanent molar The angulation of upper first permanent molar – the key to functional occlusion. – They are biggest teeth and their anchorage is strongest – Their local position in the occlusal arch supports the main masticatory function – They influence the vertical dimension of upper and lower jaw, the occlusal height and esthetic proportions – They are the first erupting teeth of permanent dentition – The anamolies in dental positing are mostly due to more prominent disloacted positions of the crown of upper permanent molar to normal. www.indiandentalacademy.com
Key Ridges : Infrazygomatic crest. This zygomatic pillar ‘key ridge’ – established during growth directly above the centre of the roots of the first upper molars and proceeds along the outside of the wall of the maxillary cavity upto the zygomatic bone.
Key of Age : Demonstrates the average drift of upper first molar downwards and mesially. All angulation show prominent minus angulation. -17o : 6 – 7 years -8o : 11 years www.indiandentalacademy.com -5o : 17 years
Class I : Neutro Occlusion Mesiobuccal cusps of the upper first permanent molar occludes with the mesiobuccal groove of the lower first permanent molar. This is called the key of occlusion Class II : Disto Occlusion Condition in which the mandibular first Permanent molar is placed posterior in relation to the normal class I condition – Division I – Division II
Class III : Mesio Occlusion Condition in which the mandibular first Permanent molar is placed anterior in relation to the normal class I www.indiandentalacademy.com condition
BASED ON THE ORGANISATION Canine guided (or) protected occlusion – during lateral movements only working side canine comes into contact with the other. This result in disclusion of all posterior teeth – The canine has a good crown root ratio capable of tolerating high occlusal forces – The canine root has a greater surface area then adjacent teeth. Providing greater proprioception. – The shape of the palatal surface of the upper canine is concave and is suitable for guiding lateral movement.
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Mutually Protected : Posterior teeth prevent excessive contact of the anterior teeth in maximum intercuspation anterior teeth disengage the posterior teeth in all mandibular excursive movements. Group Function : During the lateral movement the buccal cusp of the posterior teeth on the working side are in contact
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BASED ON PATTERN Cusp to embrasure / Marginal ridge occlusion : Occlusion of one supporting cusps into a fossa and the occlusion of another cusp of the same tooth into the embrasure area of two opposing teeth. This is a tooth-to-twoteeth relation. Cusp to fossa occlusion : Supporting cusp occluding into fossa. This produces an interdigitation of the cusps and fossa of one teeth with the fossa of only one opposing tooth. This is tooth-to-one-tooth relation. www.indiandentalacademy.com
ANDREWS SIX KEY TO NORMAL OCCLUSION Key I : Molar relationship Key II : Crown angulation Key III : Crown inclination Key IV : Absence of Rotation Key V : Tight Contact Key VI : Curve of Spee Ten characteristics of an organic occlusion Many of the following ten characteristics have been repeatedly observed in well – preserved, unworn dentitions. I. Centric Relation Occlusion Centric relation is the rearmost and midmost hinged position of the mandible. www.indiandentalacademy.com
Centric relation occlusion is the morphologic position of the mandible in centric relation when the posterior teeth are intercusped in occlusion. Centric relation occlusion can only be demonstrated with axis-oriented casts mounted on an articulator. II. Uniform contact in centric relation The elimination of centric prematurities is necessary to establish uniform contact in centric relation. There are four possible effects of the fulcruming effect of premature centric contacts as follows : – – – –
Faceting and wear TMJ Dysfunction Infrabony periodontal bone loss Recession and gingival erosion www.indiandentalacademy.com
III. Cusp-Fossa Occlusion Cusp-to-fossa is a paired relationship between one upper and one lower tooth whereby the teeth, in occlusion, act as a single column-the “unit of occlusion�. This design lends much stability and a reciprocation of forces to the occlusion Cusps-fossa relations are always preferable to cusp-embrasure occlusion, but are not always achievable. IV. Primary Marginal Ridge Contacts This is a sagittal plane projection. Contact on the distal incline of the upper mesial marginal ridges against the mesial marginal ridge of the lower buccal cusp. The distal marginal ridge of the upper lingual cusp has a similar contact with the mesial incline of the opposing distal marginal ridge. If posterior teeth are lost and the vertical dimension decreases, the upper anterior teeth will be splayed. When posterior teeth are present, they prevent wear and possible separation of the front teeth. www.indiandentalacademy.com
V. Tripodism Every cusp has four ridges : Three out of these four ridges can contact an opposing cusp in cusp-fossa occlusion. The cusp tips will be preserved. The ridges will wear evenly and this prevents the formation of non-uniform contacts. VI. Cross – Tooth Stability This is a coronal plane projection of tooth contacts. Posterior cusps in an organic occlusion are shearers of food because they pass close to each other but never close edge – to edge. VII. Forces in the Long Axis Teeth should stand perpendicular to the occlusal plane with their long axis parallel to the long axis of their antagonist Destructive off – axial forces are minimized, which would wear the stamp cusps and cause the teeth to tip, www.indiandentalacademy.com
VIII. Narrow Occlusal table Natural teeth with little wear have narrow occlusal tables. If the occlusal table is kept small the forces of closure will be kept within the perimeter of teeth and directed in the long axis. IX. Maximum Cusp Height and Fossa Depth Teeth with tallest cusps offer greatest shear efficiency. Determinants of cusps height – Angle of eminence – Transtrution
– Vertical laterotrusion of the workin condyle – Inclination of the occlusal plane www.indiandentalacademy.com
X. Disclusion The disclusive characteristic of an organic occlusion allows each part of the dentition to perform that function for which it is best suited Each incisor should be free to contact its antimere at an edge-to-edge relationship without any other tooth in the mouth contacting. When the posterior teeth come into contact in centric relation occlusion, the function is complete and a 0.001� space should separate the anterior teeth. www.indiandentalacademy.com
POSTERIOR GUIDANCE The shape and angle of the slope of the articular eminence of the glenoid fossa are the single most important factors in determining the shape and form of the plane of occlusion. These shapes have been known in dentistry as the curve of Spee, curve of Wilson and curve of Monson. The range of angulation of articular eminence at the midpoint inclined plane is from 17o to 77o. The path of the condylar movement in the TMJ is called the posterior guidance. Mandibular movements are guided by – Shape of TMJ – Contact of anterior tooth – Masticatory muscle www.indiandentalacademy.com
The inclination of the anterior guidance should be equal to the inclination of posterior guidance. If the incisal guidance is flatter than the condylar path, it may cause severe neuromuscular problems. If the inclination of the incisal path is flatter than that of the condylar path, the upper and lower posterior teeth will contact and interfere with the incisive action of the anterior teeth. Anterior Guidance It is defined as “the influence of the contacting surface of anterior teeth – limiting mandibular movements”. There must be proper anterior guidance of the incisal teeth for disclusion of the posterior teeth and harmonious movement of the mandible. www.indiandentalacademy.com
VERTICAL DETERMINANT Condylar guidance
Steeper
Taller the Posterior Cusps
Greater the Vertical overlap
Taller the Posterior Cusps
Greater the Horizontal overlap
Shorter the Posterior cusps
Plane of Occlusion
More parallel the plane to condylar guidance
Shorter the Posterior cusps
Curve of Spee
More acute
Shorter the Posterior cusps
Greater
Shorter the Posterior cusps
Anterior guidance
Lateral translation movement
Greater the immediate side Shorter the Posterior cusps shift More superor the movement of rotating condyle
Shorter the Posterior cusps
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HORIZONTAL DETERMINANT Distance from rotating condyle Distance from midsagittal plane Lateral translation movement Intercondylar distance
Greater
Wider the angle between laterotrusive and Mediotrusive pathways
Greater
Wider the angle between laterotrusive and Mediotrusive pathways
Greater
Wider the angle between laterotrusive and Mediotrusive pathways
Greater
Smaller the angle between laterotrusive and Mediotrusive pathways
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ORTHODONTIC TREATMENT OBJECTIVES The orthodontic treament objectives are to provide good facial esthetics, and an ideal, static and functional occlusion. The static objectives and Andrews’ Six Keys to Normal Occlusion. The functional objectives are obtained with the mutually protected occlusion, which present the following characteristics 1. The teeth should present maximum intercuspation
with the mandible in CR 2. In CR, all posterior teeth should present effective
occlusal contacts through their long axes and the anterior teeth should present a 0.005 inch clearance www.indiandentalacademy.com
3.
During lateral functional movements of the mandible, the cuspid should disclude all posterior teeth, (cuspid guidance)
4.
During protrusion, the six upper anterior teeth should articulate with the six lower anterior teeth and first or second premolars (in first premolars extraction cases) in order to disclude all the posterior teeth.
5.
There should be no balancing side intereferences. This relation of the anterior teeth is known as anterior guidance www.indiandentalacademy.com
CONCLUSION The concept of occlusion has been undergoing sea changes in the course of last century, starting from the days of fiction and passing through the hypothesis proposed by Angle and others, we have reached a factual period of reasoning and proven concepts. With the introduction of the TMJ as component of occlusion the idea of dynamic occlusion and functional harmony have been emphasized. Occlusion, especially in orthodontics during growth, is a process, a process of growing and shifting interactive systems. Orthodontics can be considered as the navigation of those systems www.indiandentalacademy.com
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