FUNCTIONAL MALOCCLUSION
INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
TERMS Occlusion – The relationship of maxillary and mandibular teeth as that are brought into functional contact. Centric occlusion – Mandibular position dictated by maximum and habitual intercuspation of maxillary and mandibular teeth. It is dentally determined position independent of condylar position. Also called as intercuspal position. www.indiandentalacademy.com
Centric Relation Occlusion. The simultaneous even contact between maxillary and mandibular teeth into maximum interdigitation with the mandible in its most unstrained and retruded position. Also called as Retruded contact position. According to Dawson : Centric relation can be defined as the most superior position the condyles can assume in the glenoid fossa.
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It is not unstrained because it is achieved by firm contraction of the elevator muscles. It is not most retruded as it is possible to force the condyles distal to centric relation, but such a displacement occurs only with a downward movement away from centric relation.
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Centric Relation Occlusion. The simultaneous even contact between maxillary and mandibular teeth into maximum interdigitation with the mandible in its most retruded position – when centric relation and centric occlusion coincide. Considered to be the ideal occlusal relationship. However, it does not usually occur in individuals unless they have had an occlusal equilibration or a complete dental arch rehabilitation.
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Centric cusps/Supporting cusps : Primarily responsible for maintaining the distance between maxilla and mandible. They are buccal cusps of mandibular posterior teeth and lingual cusps of maxillary posterior teeth. Occlude with opposing central fossa areas. Non centric or Guiding cusps : Buccal cusps of maxillary posterior teeth and lingual cusp of mandibular posterior teeth. www.indiandentalacademy.com
Centric cusps are broad & rounded whereas non centric cusps are sharp. Non centric cusps also give the mandible stability so that when the teeth are in full occlusion, a tight definite occlusal relationship results. This is called maximum intercuspal position. If mouth is opened, then closed, the non centric cusps will help the mandible back to the intercuspal position. Therefore , the non centric cusps are appropriately referred to as guiding cusps. www.indiandentalacademy.com
Freedom in Centric: Provides for freedom for the mandible to close into maximum intercuspation in centric relation anteriorly to centric occlusion, and in between as well as slightly lateral and anterior to this area of occlusal contacts. In this concept , “ there is a flat area in the central fossae upon which opposing cusps contact which permits a degree of freedom in eccentric movements uninfluenced by tooth inclines�. www.indiandentalacademy.com
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Also known as ‘long centric’. This allows the mandible to close into an intercuspal position without the need for gross neuromuscular responses to premature occlusal contacts. Point Centric : In long centric , supporting cusps make contact with flat areas prepared in the restored teeth, not only when condyles are in centric relation but also when slightly anterior to centric relation. However in the concept of point centric supporting cusps must make occlusal contact at a point when the condyles are only, and precisely in centric relation.
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Ideal occlusion : An ideal relationship of maxillary and mandibular teeth combining a functional occlusion along with the absence of malocclusion as described by the six keys of occlusion Ash and Ramfjord (1995) defined ‘ideal occlusion’ as: 1. The coincidence of centric occlusion in centric relation (CO = CR), when there is freedom for the mandible to move slightly forwards from that occlusion in the same sagittal and horizontal plane (freedom in centric). 2. When the mandible moves, there is immediate and
lasting posterior disclusion (anterior guidance on front teeth)
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The concept of normal occlusion emphasizes the functional aspect of occlusion and the capability of the masticatory system to adapt to or compensate for some deviations within the range of tolerance of the system. A description of normal occlusion involves occlusal contacts, alignment of teeth, overbite and overjet, arrangement and relationship of teeth within and between the arches, and relationship of teeth to osseous structures.
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Functional Occlusion – A static and dynamic relationship of the teeth combining minimum stress on TMJ, optimal function of the orofacial complex, stability and esthetics of the dentition and protection and health of periodontium. Also known as Physiological occlusion. Dynamic or Functional occlusion refers to the occlusal contacts that are made while the mandible is moving relative to the maxilla i.e. during speech, mastication and swallowing.
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The mandible is moved by the muscles of mastication, and the pathways along which it moves are determined by these muscles, as well as by two guidance systems: • Posterior guidance system • Anterior guidance system.
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The Posterior Guidance System is provided by the temperomandibular joints. As the head of the condyle moves downward and forward the mandible is moving along a guidance pathway that is determined by the intra-articular disc and the articulatory surfaces of the glenoid fossa, all of which is enclosed in the joint capsule.
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If teeth are touching during a protrusive or lateral movement of the mandible, then those teeth also provide a guidance to the mandibular movement. This is the Anterior Guidance and is provided by whichever teeth touch during eccentric movements of the mandible.
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Thus, Anterior guidance or Anterior coupling can be defined as the tightly overlapping relationship of the opposing maxillary and mandibular incisors and canines which produces disclusion of the posterior teeth when the mandible protrudes and moves to either side from 1-4mm. Anterior guidance can be further classified into: • Canine guidance • Group function www.indiandentalacademy.com
Canine Guided Occlusion – during the lateral excursion, contact occurs only between the upper and lower canine, and first premolar on the working side. There is no contact between the teeth on the nonworking side. The theory of canine protected occlusion was put forward by Nagao (1919), Shaw (1924) and D’Amico (1958). www.indiandentalacademy.com
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It is based on the impression that the canine is the most appropriate tooth to guide the mandibular excursion, because: 1) The canine has a good crown: root ratio, capable of tolerating high occlusal forces. 2) The canine root has a greater surface area than adjacent teeth, providing greater proprioception. 3) The shape of the palatal surface of the upper canine is concave and is suitable for guiding lateral movements. www.indiandentalacademy.com
Group function Occlusion (Shyler, 1929) – during the entire lateral movement, the buccal cusps of the posterior teeth on the working side are in contact. There is no contact on the non-working side. This is also known as Unilateral Balanced Occlusion.
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Balanced Occlusion – during the entire lateral movement, all of the posterior teeth on the working side, and one or more teeth on the non-working side contact simultaneously. Present day thinking has completely dismissed this concept for restoring the natural dentition. However, it is desirable in a patient wearing a set of complete dentures.
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• Eccentric Relations.
Refers to any deviation of the mandible from the centric occlusion position. This includes lateral and protrusive movements and any combination of these. Protrusive relation. It is that position with the mandible moved anteriorly and downward, so that both mandibular condyles and discs are forward in their glenoid fossa. www.indiandentalacademy.com
As the mandible moves forward, the incisal edges of the mandibular anterior teeth glide against the lingual fossae of the maxillary anteriors. When the mandible is fully protruded, the incisal edges of the mandibular incisors are in front of the maxillary anterior teeth. The average maximum forward protrusion of the mandible is 8.3mm (range 2.5 to 16mm)
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Lateral Relation. In lateral relation, the mandible is moved to the right or left side and slightly downward (as in mastication). If the mandible moves to the right side, the right condyle remains relatively stationary (while rotating), and the left condyle and disc move downward, forward and inward within the articular fossa.
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• Working Side.
The side towards which the mandible moves during function. Usually, the posterior upper and lower teeth are aligned with the upper buccal cusps directly over the lower buccal cusps and with the lower lingual cusps directly beneath the upper lingual cusps during working side tooth contacts (group function). The condyle only rotates on its vertical axis and moves laterally 1-2mm or less . Minimal movement www.indiandentalacademy.com
Maxillary Dynamic Occlusion
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• Balancing/Non-working Side.
It is the side away from which the mandible moves. On the balancing side, the upper lingual cusps are aligned over the lower buccal cusps, but usually do not contact during the opposite side working tooth relation. Any balancing side tooth contacts are thought to be destructive to both the involved teeth and damaging to the TMJ on the opposite side. The balancing side mandibular condyle moves medially, downward and forward 5-12 mm. www.indiandentalacademy.com
The features of an ‘ideal’ functional occlusion include: a) Bilateral occlusal contacts in the retruded contact position. b) Coincidence in the retruded contact position and the intercuspal position, or a short slide between the two (<1mm). c) Contact between opposing teeth on the working side during lateral jaw movements – canine protected or group function. d) No contact between teeth on the non-working side during lateral excursions. www.indiandentalacademy.com
Posseltâ&#x20AC;&#x2122;s Envelope of Motion Posselt (1957) described the extreme or border movements of the mandible as an envelope of motion. The occlusion achieved during the normal functional movements, such as swallowing and chewing, occurs within this relatively small space.
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Sagittal Movement Frontal Movement
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During lateral movement of the mandible, the condyle of the working side rotates and moves laterally, as well as upwards, downwards or backward. The lateral component is called the Bennett Movement. On an average, it measures 0.5mm. It is also called the Bennett shift, Lateral shift, or Immediate side shift. www.indiandentalacademy.com
The condyle of the non-working side moves downwards, forwards and inwards, creating the Benett Angle. It is also called the Progressive side shift www.indiandentalacademy.com
Mandibular Deviation â&#x20AC;&#x201C; refers to the direction and movement of the mandible from the first tooth contact with the jaw in centric relation to the centric occlusion position. The direction of deviation is usually upward and forward (1.25mm), with or without a lateral component. Mandibular Deflection â&#x20AC;&#x201C; refers to any contact of opposing teeth which guides or directs the mandible away from centric relation, either forward or to one side or both, as the teeth slide into centric occlusion www.indiandentalacademy.com
Disclusion â&#x20AC;&#x201C; refers to the separation of all the posterior teeth on one side as the mandible moves to that side. It is caused by the opening component produced by a deep vertical overlap of the canines
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Functional Cross bite Usually associated with unilateral posterior crossbite with mandibular shift. Clinical presentation is a unilateral crossbite with a functional shift of the mandible toward the crossbite side. A centric occlusion (CO) to centric relation (CR) discrepancy is evident in an Functional cross bite, whereas CO and CR are usually coincident in a true unilateral crossbite. A bilateral crossbite due to skeletal imbalance between maxillary and mandibular transverse dimensions differs from an Functional cross bite only in degree of severity; the maxillary to mandibular width discrepancy is less with functional cross bite. www.indiandentalacademy.com
Lateral shift of the mandible in an functional cross bite results in a mandibular skeletal (and often dental) midline deflection to the crossbite side. The maxillary arch is usually symmetrical with coincident maxillary dental and skeletal midlines. The maxilla is transversely constricted in an Functional cross bite with marginal ridges in line and absence of simple dental crossbite. Because of this transverse maxillary deficiency, frequently more crowding is seen in the maxilla than in the mandible. www.indiandentalacademy.com
The crossbite side in an Functional cross bite often shows a partial or full Class II molar relationship; the non-crossbite side shows a Class I relationship due to rotational closure of the mandible. Pretreatment tomograms reveal an asymmetric condyle position; the non-crossbite side is down and forward in the fossa and the crossbite side is centred in the fossa. Early correction of posterior crossbites may help prevent signs and symptoms of temporomandibular disorder (TMD). www.indiandentalacademy.com
Children with unilateral posterior cross bites have been reported to have lower maximum bite forces and lower numbers of occlusal contacts than children without malocclusions. However , the bite force does not seem to vary between Angle malocclusion types. Orthodontic treatment may be needed to improve function. www.indiandentalacademy.com
Treatment Posterior crossbites in the deciduous dentition showed self-correction of between 0% and 9% Removal of functional interferences has been shown to be useful only in patients under the age of 5, with success rates ranging from 27% to 64% In a study of 76, 4-year-old children with posterior crossbite, Lindner (1989) reported 50% correction after functional grinding www.indiandentalacademy.com
Success rates for treatment with expansion appliances in the early mixed dentition stage range from 84% to 100%. Advantage of early treatment (deciduous or very early mixed dentition) is improvement of maxillary arch length deficiency secondary to maxillary constriction, because the permanent incisors are afforded more space before or during eruption than if the crossbite is treated at a later age. www.indiandentalacademy.com
When expansion is carried out during the late deciduous dentition, the first permanent molars usually erupt into satisfactory transverse positions
Overexpansion is desired to the point where the lingual cusps of upper molars contact the buccal cusps of lower molars. Other treatment involves removal of occlusal interferences & elimination of functional shift. www.indiandentalacademy.com
There is a growing body of evidence that untreated crossbites will lead to permanent growth alteration, making early treatment crucial. Evidence from tomographic studies has shown that the condyles in child crossbite patients are related asymmetrically within the fossa, but that symmetry is restored after early treatment. www.indiandentalacademy.com
It has been inferred that the glenoid fossa and condyle will undergo remodelling during growth to compensate for condylar asymmetry if left untreated, although no longitudinal research has provided conclusive evidence of glenoid fossa and condylar skeletal adaptation. Symmetry of the mandible and its rotational position relative to the cranial base is altered in adult patients with untreated posterior crossbites.
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Correction of functional cross bite with maxillary expansion in growing patients has been shown to establish condyle and dental symmetry and to realign the mandibular rotation. Once these adaptations are firmly established in adulthood, treatment may combined orthodontic and surgical approach. To achieve the potential benefits of correcting functional cross bite, maxillary expansion must be performed early, before fusion of the palatal halves. www.indiandentalacademy.com
Occlusal Interference Defined as: A cuspal contact forcing the mandible to deviate from a normal pattern of movement â&#x20AC;&#x201C; Posselt (1968). Undesirable occlusal contact that may produce mandibular deviation during closure to maximum intercuspation, or may hinder smooth passage to and from the intercuspal position â&#x20AC;&#x201C; Glossary of orthodontic terms (2000).
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Features of occlusion that are likely to interfere with function or parafunction: 1. Occlusal contacts on the non-working side. 2.
Unilateral contacts in the retruded contact position.
3.
Long slides (>1mm) between the retruded contact position and the intercuspal position.
4. Asymmetry in the slide between the retruded contact position and the intercuspal position.
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Working side interferences Occlusal interference on the working side may be detected during lateral excursion with the teeth in contact, but such an interference may not cause overt clinical symptoms if the patient does not use the working side during function or parafunction.
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Protrusive interferences : Usually are on the distal facing inclines of maxillary teeth and mesial facing inclines of maxillary teeth. Interferences between the maxillary and mandibular anterior teeth in lateral or in protrusive excursions should be corrected by grinding on the lingual aspect of maxillary incisors & cuspids along the path of interference.
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Balancing side interferences : are those that occur between maxillary & mandibular supporting cusps & their occlusal inclines. Since these cusps maintain centric stops and thus are essential to the stability of the tooth position, removal of interferences has to be done with great care. Main rule is to do the whole grinding on only one of the 2 interfering cusps or inclines if they both serve as centric stops for the teeth. www.indiandentalacademy.com
Common interference sites in Orthodontic cases In orthodontic cases, there are some factors that usually tend to present interferences during the finishing stages. The most common are : a) lingual crown torque of the upper second molars; b) accentuated lingual crown torque of the lower second molars; c) incorrect anteroposterior relation between the maxilla and the mandible; and d) incoordination of the upper and lower arch widths. www.indiandentalacademy.com
These factors can induce interferences in the balancing side. During treatment, these potential interference factors should be corrected by orthodontic mechanotherapy.
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Lower Incisor extraction and. Functional Occlusion Cases in which there is a severe Bolton discrepancy, with disproportionately larger lower anterior teeth than upper anterior teeth, usually present a good relation of these teeth at the end of treatment, when one lower incisor is extracted. On the other hand, if the discrepancy is not severe enough, the anterior guidance will be compromised because the upper anterior teeth curvature radius will be disproportionately larger than the lower anterior teeth curvature radius as long as there is a normal buccal intercuspation.. www.indiandentalacademy.com
The anteroposterior distance of the lower to the upper anterior teeth will be increased, and consequently the anterior teeth will not be able to disclude the posterior teeth on the beginning of protrusion. As a result, many interferences on posterior teeth may develop. Cuspid guidance will also be compromised, because the ideal relation of 0.0005 inch between these teeth will not be established. Moreover, there will be a tendency for relapse of the overbite and overjet www.indiandentalacademy.com
Occlusal interference & bruxism Lindqvist (1973) examined 78 , 14 yr old children, 34 children had bruxofacets & reported tooth grinding. Types of functional malocclusion recorded in the study were lateral shift of the mandible & nonfunctional side interferences. Results showed significantly higher frequency of occlusal interferences in subjects with bruxism than in those without it.
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Nilnerâ&#x20AC;&#x2122;s (1983) examination of 440 children aged 7-14 years investigated the relationship between functional malocclusion & bruxism. Types of functional malocclusion recorded in the study were interferences in terminal hinge movement, mediotrusion interferences , and cuspid rise. It was found that dental wear in lateral sections was more pronounced in bites with mediotrusion interferences than in bites without them.
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However Vanderas et al (1995) from review of studies regarding relationship between malocclusion & bruxism concluded that statistically significant correlations reported by the reviewed studies are inconsistent & without biological significance.
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TMD & Functional malocclusion Liu , Tsai (1998) investigated the role of functional malocclusion in temporomandibular disorders (TMD) in untreated orthodontic patients. A total of 508 orthodontic patients were enrolled. All patients were evaluated for the presence of various types of functional malocclusion and clinical signs of TMD before treatment. The frequencies of TMD were 44.2% in patients with retruded position (RP) interference and 38.1% in those without such interference . www.indiandentalacademy.com
The frequency of TMD in patients with protrusive interference was greater than those without (32.2% vs. 18.4%). Patients with balancing interference had a significantly higher frequency of TMD than those without (49.2% vs. 23.9%). Authors concluded that patients with functional malocclusion of balancing or protrusive interference type have an increased risk for developing TMD.
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Seligman & Pullinger (1991) assessed the published research literature concerning the relationship of functional movements of the mandible to the TMD. They reported that most controlled surveys fail to demonstrate any association between working and non working contacts and TMD signs or symptoms. These types of eccentric occlusal contacts are so common & variable that they lack the sensitivity & specificity for defining a present or potential TMD population.
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The following is a list of signs or symptoms from occlusal interferences: 1. Occlusal wear. 2. Excessive tooth mobility. 3. Temporomandibular joint sounds. 4. Limitation of opening or movement. 5. Myofascial pain. 6. Contracture of mandibular musculature, making manipulation difficult or impossible. 7. Some types of tongue-thrust swallow.
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If a patient has any of these signs or symptoms and the mandible is difficult to manipulate, it would be wise to pursue a cautious course of action and use a splint to see if the symptoms can be eliminated or alleviated and what changes occur in mandibular position, before placing orthodontic appliances. According to Roth : â&#x20AC;&#x2DC;It is important to realize that a "little bit of clicking" of the TMJ's is abnormal. That occlusal wear is abnormal, unless the patient is chewing whale hides for a living. We must be aware that when occlusal harmony is present, most of these signs are not presentâ&#x20AC;&#x2122;. www.indiandentalacademy.com
â&#x20AC;&#x153;We must realize that the patients we are treating, for the most part, are children with exceptionally high tolerance levels and adaptive capacities. We must also realize that tolerance levels decrease with age. Therefore, what the child patient can tolerate in terms of occlusal interferences at the age of 14 or 15, he may not be able to tolerate at age 20 or 25, without symptomsâ&#x20AC;?. Patients do not adapt to occlusal interferences, they tolerate them; but they tolerate them less well as they get older. www.indiandentalacademy.com
OCCLUSAL INTERFERENCES TEND TO MAKE TEETH AND JAWS A FOCUS FOR VENTING PSYCHOLOGICAL STRESS. When the teeth and jaws are stressed by gnashing, clenching, and grinding, the weakest link or links of the chain will break down. If the patient is prone to periodontal disease, the working over of occlusal interferences in the presence of plaque will start periodontal breakdown. www.indiandentalacademy.com
If the periodontium and hygiene are good, the patient may experience occlusal wear. If the joints are the weakest link in the chain, then the patient may develop temporomandibular joint dysfunction or disease. Patients may develop symptomatology in any or all of these areas simultaneously.
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The patient with "minor" or subclinical symptomatology could be just waiting for someone to subject him to orthodontic tooth movement, before the symptoms become overt. Once this has happened, there is usually no turning back. The orthodontist has now got the ball and he'd better know which way to run. www.indiandentalacademy.com
In terms of their reactions to occlusal interferences, patients could be classified into three categories: 1. Those with symptomatology. 2. Those that are either psychologically and/or physically predisposed to developing a problem. 3. Those that are neither symptomatic nor predisposed to developing symptoms
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Examination On initial examination, the orthodontist should attempt to manipulate the mandible into clinical centric relation . Recording of centric relation jaw position. - Bilateral manipulation of mandible into centric relation. - Use of leaf gauge (anterior deprogrammer). - Use of sliding guiding inclined gauge (or sliding guide) for anterior deprogramming and recording CR. www.indiandentalacademy.com
Manual guidance of the mandible into centric relation
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If the discrepancy is a large one, a mounting on a simple anatomical articulator (such as a WhipMix or Hanau) is indicated, so that the discrepancy can be studied and steps for its correction can be integrated into the treatment plan. If the mandible is difficult to manipulate and upon attempting to hinge the mandible closed a fair amount of resistance is encountered; and then, once the teeth are contacted, there is no centric prematurity, do not believe what you are looking at in the mouth. www.indiandentalacademy.com
The patient has closed into his habitual centric occlusion and the musculature is in a state of contracture, to posture or accommodate the mandible to the existing occlusion. It will require splint therapy to free the musculature, so that the true discrepancy can be revealed. The temporomandibular joints should be palpated for popping or grating sounds. The musculature should be examined for tenderness. www.indiandentalacademy.com
If these signs are present, then splint therapy and cephalometric TMJ tomograms are indicated, prior to attempting to begin orthodontic treatment. The occlusion should be inspected for wear facets and checked to see if the patient can contact these areas of wear or faceting. The patient should be checked for his ability to execute left and right lateral excursions and protrusive movements. www.indiandentalacademy.com
If the patient cannot execute gliding movement on the anterior teeth in all excursions : there are posterior interferences or incorrect anterior coupling, even though this may not look like the case intraorally. For instance, if the patient cannot keep the anterior teeth together in a protrusive movement either from centric forward or protrusive back, there is a severe enough posterior interference present to prevent him from making this movement without separating his teeth. www.indiandentalacademy.com
The amount of maximum opening should be noted as it is an indicator of the state of contracture of the mandibular musculature. Normal maximum opening from the incisal edge of the lower incisors to the incisal edge of the upper incisors averages approximately 45 to 50mm.
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Diagnosis & Treatment planning Whenever any of the symptomatology mentioned is found on examination, it is wise to utilize splint therapy to unearth the true maxillomandibular relationship prior to placing orthodontic appliances. Once the discrepancies are apparent, the orthodontist will make a treatment plan to deal with all of the discrepancies present in the case; not just one to cover only those discrepancies he can see intraorally. www.indiandentalacademy.com
Standard orthodontic models and cephalometric headfilms have been traditionally taken in habitual centric occlusion. We must have records taken in centric relation as well, if any significant centric discrepancy exists in a particular case. This is necessary for us to evaluate how much of the discrepancy lies in which planes of space, so that we can elect to use the appropriate mechanics that will deal with each of the discrepancies. www.indiandentalacademy.com
For instance, we may have a case in which there appears to be unilateral Class II molar relationship, but in centric relation of the mandible there is really a bilateral Class II molar relationship end-on. If we base our mechanics upon a unilateral Class II relationship and treat accordingly, we will wind up with a case treated out of centric that is bilateral Class I in habitual centric closure and unilateral end-on Class II on the side opposite the original habitual centric Class II in centric relation. www.indiandentalacademy.com
If it is bilateral end-on Class II then our mechanics must deal with a bilateral Class II situation, in order to be able to finish the case in bilateral Class I and in centric relation occlusion. TMJ tomograms : Cephalometric tomography of the joints is of great diagnostic benefit www.indiandentalacademy.com
In the large majority of cases, gnathologic centric relation will yield a normal looking position on a cephalometric tomogram. But it is important to realize that a normal looking position on a cephalometric tomogram does not necessarily mean that the patient has a centrically related occlusion. This is because the 3-d relationship of the condyles in the fossae is reduced to two dimensions on the tomogram. www.indiandentalacademy.com
Therefore, slight movement of the condyles, particularly lateral or vertical axis rotary movements will be difficult, if not impossible, to discern when this type of movement occurs in small amounts between centric relation and centric occlusion.
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Repositioning Splint The purpose of the repositioning splint is to enable the operator to find "true" centric (which is stable and comfortable); to test the patient's response to change in the occlusion, prior to embarking upon a complex course of occlusal therapy; and, finally, to see if the mandibular centric relation position can be stabilized. Eugene Dyer popularized the use of the repositioning splint, which he now calls a craniomandibular orthopedic appliance. Dyer also pointed out a number of years ago that, in centric relation, the condyles are usually in the superior-anterior portion of the fossae. www.indiandentalacademy.com
The splint is used whenever a patient is symptomatic and/or when the mandible is difficult to manipulate or, better yet, when the mandible is not easy to manipulate. Initially, splint treatment is directed toward alleviation of pain-dysfunction symptoms and the diagnosis of the true maxillomandibular relationship. The splint is a means of relaxing the mandibular musculature and resolving the inflammatory changes within the joint capsules. www.indiandentalacademy.com
Allows remodeling of the joints to occur, if there have been some previous degenerative changes. It tests the patient's response to occlusal change without actually changing the occlusion; and allows the operator to know if the mandibular position can be stabilized, and what the exact extent of the discrepancy is that must be corrected. www.indiandentalacademy.com
It puts the patient to the test in terms of his or her desire to undergo complex occlusal therapy. It also allows the patient to know what he might expect, in terms of comfort, if the complete correction of the occlusion is undertaken. Usually done prior to any type of irreversible occlusal treatment.
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The objective in making the repositioning splint is to seat the condyles in the most superior position possible on every visit, and to adjust the occlusal surface of the splint to achieve maximum intercuspation at this position of the mandible at the most closed vertical dimension obtainable.
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The mandibular postural changes during splint therapy are of three different types: 1. Changes due to relaxation of the musculature that postures the mandible incorrectly due to muscle contracture or spasms. 2. Changes due to elimination of intracapsular inflammatory fluid. 3. Changes due to remodeling or recontouring of the bony parts of the joints (e.g. condyles or fossae). www.indiandentalacademy.com
Splint therapy must be continued until there has been no change in mandibular positioning in centric relation for at least three months. In some of the more difficult cases, where there is some radiological evidence of recontouring of bony parts of the joints, six months stabilization on the splint is a good indicator that it is all right to proceed with more definitive treatment. www.indiandentalacademy.com
Gnathological Objectives Historically, gnathology has been associated with restorative dentistry and prosthetics and, although there have been some orthodontists involved in the early gnathological research, no one until recent years has attempted to describe the occlusion of the natural dentition in terms of tooth positions necessary to achieve an occlusion that meets gnathological goals. www.indiandentalacademy.com
The gnathological objectives are aimed at harmonizing the occlusal morphology or natural tooth positions with closure of the mandible in centric relation, and with border excursions of the mandible.
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First objective : Obtain a stable centric relation of the mandible and have the teeth intercusp maximally at this mandibular position. All centric stops should hit equally and simultaneously and the stress of closure should be directed, as nearly as possible, down the long axes of the posterior teeth. There should be no actual contact of the anterior teeth in centric closure (.0005" clearance). www.indiandentalacademy.com
Second Objective : to have a harmonious glide path of anterior teeth working against each other to separate or disclude the posterior teeth immediately, but gently, as soon as the mandible moves out of centric closure. The glide path provided by the anterior teeth must be in harmony with the way in which the mandible moves through border excursions. There should be sufficient overbite and overjet at the maxillary incisor tips to allow for a gentle glide path.
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The cuspids should be the main gliding inclines on lateral excursion and the six maxillary anterior teeth should articulate with the six mandibular anterior teeth and the mandibular bicuspids (first bicuspid in nonextraction cases), so that the protrusive load is spread over 14 teeth.
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The gentle lateral and protrusive lift is not only necessary from the standpoint of mandibular movement, but necessary from the orthodontist's point of view in terms of posttreatment stability of the tooth positions. Excessive lateral stress on the cuspids may cause lingual movement of the lower cuspids and resultant lower anterior crowding, and/or labial movement of the maxillary cuspids .
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Since the maxillary anterior teeth are retracted in most cases, an improper anterior guidance in protrusive will tend to enhance the chances of relapse of the maxillary anterior teeth labially. This is very commonly seen in posttreatment orthodontic cases, because of bracket placement that tends to elongate the maxillary central incisors. Thus, the central incisors become the only teeth in contact in an incisive relationship.
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In addition to this, most treated cases exhibit insufficient torque of the maxillary central incisors, thus creating too steep an anterior lift and an insufficient glide path in protrusive .
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Inadequate labioaxial inclination of the maxillary central incisors can also cause them to be overstressed upon lateral and lateroprotrusive movements, as well as pure protrusive. In posttreatment orthodontic cases, the anterior teeth will tend to move to accommodate mandibular movement, if the anterior tooth positions interfere with these movements. www.indiandentalacademy.com
A "mutually protective" occlusal scheme needs to be established , where the anterior teeth protect the posterior teeth from lateral stress during movement and the posterior teeth protect the anterior teeth from lateral stress during closure into centric relation occlusion. The anterior teeth are subjected to a minimum of stress during movements, only if a gentle glide path is provided that is in harmony with the manner in which the mandible moves. www.indiandentalacademy.com
A centrically related occlusion and a mutually protective excursive occlusal scheme are dependent upon: 1. Proper individual tooth positioning. 2. Knowing when the mandible is in centric and when it is not. 3. Coordination of arch form and arch width. 4. Control of the vertical dimension. 5. Anteroposterior correction between maxilla and mandible. 6. Clinical awareness of excursive interferences www.indiandentalacademy.com
In addition, Roth advocated the concept of overcorrection : so that settling into centric relation and ideal intercuspation is most likely to occur. This is necessary because - 1. Teeth will move after appliance removal, no matter where they are placed. 2. The curve of Spee will return or deepen after appliance removal. 3. Teeth that are slightly tipped distally in the buccal segments will tend to settle better than teeth that are already mesially inclined. 4. As teeth in the buccal segments settle they will tip mesially and rotate mesially. www.indiandentalacademy.com
5. As band spaces close, there is a corresponding loss of torque of the anterior teeth. 6. Teeth adjacent to an extraction site will tend to rotate towards the extraction site. 7. Teeth adjacent to the extraction sites tend to tip into the extraction sites.
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8. Maxillary lingual cusps will tend to migrate downward until they find an occlusal stop against the opposing teeth (since the maxillary lingual cusps are the centric supporting cusps of the upper teeth). Because these factors seem to occur most of the time, it seems only logical to plan for these things to happen during treatment and set up a detailing or finishing goal that will overcome these factors, thus allowing every conceivable opportunity for the teeth to settle into the most ideal occlusion after appliance removal. www.indiandentalacademy.com
Overcorrection is built in for all areas except for buccolingual torque of the lower buccal segment. This is one area that is absolutely critical in terms of exact positioning, because torque errors in the lower buccal segments will not settle out of the occlusion. The lower buccal segment torque must be correct, to act as a template for the maxillary teeth to occlude with and to settle to. www.indiandentalacademy.com
AFTER CENTRIC IS OBTAINED Check tooth detailing (by having patient to go through test excursions â&#x20AC;&#x201D; right lateral, left lateral, protrusive) for: 1. Torque of upper incisors. 2. Artistic tip of upper incisors and cuspids. 3. Overbite and overjet. 4. Flatness of curve of Spee. 5. Second molar positions. 6. Look for anterior group function, posterior clearance (minimal), cuspid guidance, and balancing interferences. www.indiandentalacademy.com
At the end of appliance therapy, the occlusion should almost resemble a "bilaterally balanced" occlusal scheme during the excursions. In other words, the anterior guidance should almost not be quite adequate. This is because the curve of Spee is leveled and the overbite has been overcorrected. After appliance removal, the curve of Spee will return and the overbite will deepen to provide a more ideal anterior guidance.
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Selective Grinding - In the centric relation, all premature contacts are identified. Grinding is performed on the inclines to alter or reshape all inclines into cusp tips or flat surfaces. Contacts of cusp tips to flat surfaces direct the occlusal forces through the long axes of the teeth.
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During lateral excursions, on the balancing side, if there is an interference between a cusp tip and a cusp incline, the incline should be ground. If the contact occurs between two centric stop cusp tips, the least stable in centric should be ground. www.indiandentalacademy.com
On the working side, the sites to be ground are the tips or inclines of the upper buccal and lower lingual cusps, irrespective of the interference spot (BULL law). - During protrusive movement, interferences usually occur between the mesial inclines of lower cusps and the distal inclines of upper cusps. Here, the inclines of the guide cusps should be ground.
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Criteria for judging outcome of equilibration â&#x20AC;&#x201C; 1) There is no aymmetric shift from CR to CO. If present, it is smooth, symmetric ,less than 1mm in magnitude. 2) The completed adjustments have light or no contact between the incisor teeth & firm contact between as many posterior teeth as possible. 3) Patient perceives bilateral contact when closing the teeth to centric relation occlusion. 4) Sharp occlusal sounds are produced when the patient taps slowly or firmly into occlusion.
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5) Tooth guidance under lateral & protrusive contact is smooth & without effort. 6) The displacement of mobile teeth is minimized under closure & guiding movements.
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Conclusion In recent years , orthodontists have voiced more interest in occlusion and functional occlusion. Treating a case to functional occlusion requires thorough understanding of the concepts and clinical mastery of the techniques To treat to centric , the case must be diagnosed in centric, monitored thoroughly & a clear end of treatment goal must be established. www.indiandentalacademy.com
In today's consumer oriented practice it is better to give our patients a functionally sound treatment plan where the goal of every case should be a centric relation occlusion. Proffit summed up the goal of modern orthodontics as â&#x20AC;&#x153;the creation of the best possible occlusal relationships within the framework of acceptable facial esthetics and stability of resultsâ&#x20AC;?. www.indiandentalacademy.com
References 1) Valiathan A, Srivastava AK. Oclusal equilibration following orthodontic therapy. J Ind Orthod Soc 2000; 33: 17-22. 2) Prashanth VK & Ashima Valiathan: Ideal treatment results - Is it an orthodontists dream or reality? Kerala Dental Journal, 1995; 18(1): 1059-1061. 3) Liu JK, Tsai MY: Association of functional malocclusion with temporomandibular disorders in orthodontic patients prior to treatment. Funct Orthod. 1998 ;15(3):17-20.
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4) Roth RH : Functional occlusion for the orthodontist part I .- part III. JCO 1981, 15 (1-3) ; 32-50, 100-123, 175-198. 5) Milosevic A. Occlusion: I. Terms, mandibular movement and the factors of occlusion. Dent Update 2003; 30:359-361. 6) Ash M. Philosophy of occlusion: past and present. Dent Clin North Am 1995; 39(2): 233255.
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7) Vlachos CC. Occlusal principles in orthodontics. Dent Clin North Am 1995; 39(2): 363-378. 8) Okeson JP : Occlusion and functional disorders of the masticatory system. Dent Clin North Am 1995; 39(2): 285-300. 9) Clark JR, Evans RD : Functional occlusion: I A Review. Journal of Orthodontics 2001,28(1); 76-81. www.indiandentalacademy.com
10) Nilner M: Relationships between oral parafunctions and functional disturbances and diseases of stomatognathic system among children 7-14 years. Acta Odontol Scand 1983(41) : 167-172. 11) Lindqvist B : Occlusal interferences in children with bruxism. Odontol Revy 1973(24);141-148. 12) Vanderas AP, Manetas KJ : Relationship between malocclusion and bruxism in children and adolescents : a review. Pediatric Dentistry 1995, 17 (1) ; 7-11. www.indiandentalacademy.com
13) Parker WS. Centric relation and centric occlusal â&#x20AC;&#x201C; an orthodontic responsibility. Am J Orthod 1978; 74(5): 481-499. 14) Viazis AD. Atlas of orthodontics. 1998 15) Daskalogiannakis J. Glossary of orthodontic terms. 2000, Quintessence Publishing Co. 16) Christensen GJ. The major part of dentistry you may be neglecting. J Am Dent Assoc 2005; 136: 497-499.
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17) Ramfjord S, Ash M. Occlusion. 4th Ed., 1996, W.B.Saunders Co. Pg- 141-158. 18) Okeson JP. Management of temperomandibular disorders and occlusion. 5 th Ed., 2003, Mosby.pg- 464-472, 567-581. 19) Moyers RE. Handbook of orthodontics. 4th Ed., 1988, Year Book Medical Publishers. Pg â&#x20AC;&#x201C; 108-117.
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20) Seligman DA, Pullinger AG : The role of functional occlusal relationships in temperomandibular disorders: A review. J. Craniomandibular disorders Facial Oral Pain 1991,5:265. 21) Kennedy DB, Osepchook: Unilateral posterior crossbite with mandibular shift: A review. JCDA 2005, 71(8): 569-573. 22) Bakke M: Bite force and occlusion. Semin Orthod 2006,12 (2) : 120-126. www.indiandentalacademy.com
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