Showing posts with label Restorative Dentistry. Show all posts
Showing posts with label Restorative Dentistry. Show all posts

Sunday, April 1, 2012

A note on Jacket crowns, Indications, Alternatives, Assessment of teeth and Tooth preparation


A note on Jacket crowns
Indications
Discolored teeth

Fractured teeth

Grossly carious teeth

Hypoplastic teeth

Tooth wear

As part of a bridge

Alternatives to JCs
Bleaching

Composite veneering

Porcelain veneering

Composite restorations
Resin bonded bridges
Assessment of Individual teeth
Vitality / status of the pulp
Size of the pulp in vital teeth
Resting lip line and smile line
Aesthetics
Pre operative work up
Finalize the material/s
Depth of preparation
Path of insertion
Appropriate burs, trays and materials
Local anesthesia if tooth is vital
Shade selection

Stages of tooth preparation

Depth orientation grooves

           Labial, incisal reduction

              Interdental reduction



























           Palatal cervical collar

            Cingulum reduction

              Gingival margin




Saturday, March 24, 2012

Methods for Removal of root filling material in preparation for posts


Methods for Removal of root filling material in preparation for posts

Obturation techniques
Gutta-percha is today the universally accepted core material used for root canal obturation. However, the techniques for placement differ, but all require the use of sealing cement. Obturation techniques include cold lateral compaction of gutta-percha points, compaction of gutta-percha that has been heat softened in the canal and compacted (eg System B), thermoplastisised gutta-percha which is injected into the canal (eg Obtura and UltraFil) and finally compaction of gutta-percha which has been placed in the canal and softened by mechanical means (eg McSpadden compactors). These obturation techniques are unlikely to have an impact on the final apical seal once post space preparation has been carried out. An alternative obturation technique also exists which involves heated gutta-percha surrounding a plastic or metal carrier (eg Thermafil). The carrier ensures that the gutta-percha passes to the correct working length and is left in situ with the gutta-percha. During mechanical gutta-percha removal of this system, there is greater potential to disrupt the apical gutta-percha and a number of dye leakage studies have supported this hypothesis. It would therefore be prudent not to use such obturation techniques if placement of a post is anticipated.

Chemical removal
Solvents such as oil of eucalyptus, oil of turpentine and chloroform have been used to soften gutta-percha for removal, with the latter two being the most effcicient. However, some of these materials and especially chloroform are hazardous to use as they are toxic and potentially carcinogenic. Oil of turpentine is less toxic, but there is concern that solvents in general lead to a dimensional change in the gutta-percha, leading to increased microleakage. This together with the fact that it is difficult to control the depth of softening of the gutta-percha and potential leakage of the solvents into the periradicular tissues should be sufficient to discourage their use for gutta-percha removal for post placement. They are however a necessary adjunct in root canal re-treatment cases.

Thermal removal
A heated instrument such as a lateral compactor can be inserted into the gutta-percha to the desired length to soften and remove the gutta-percha. However, in narrow canals, fine instruments lose their heat quickly and gutta-percha removal can be difficult. A System B spreader is ideal for removal of gutta-percha.
System B with heated plugger (200°C) in foreground, with rubber stop placed at the desired length for gutta-percha removal  
From a pre-operative radiograph a plugger should be chosen of the correct dimensions that is likely to bind at the desired post length and this position should be marked on the plugger with a rubber stop. The tip should be placed in the gutta-percha and with the heat applied driven slowly to the desired post length in about 2–3 seconds. The heat should be removed and the plugger allowed cooling for about 7–10 seconds, twisted and then removed with the coronal gutta-percha. Alternatively, a short burst of heat to the plugger will allow for easy removal. It is important that the plugger is sufficiently hot to completely soften the gutta-percha. If too cool, it will result in the gutta-percha remaining sticky with the risk of dislodging the apical gutta-percha. An instrument such as a Buchanan plugger can then be used to vertically compact the softened gutta-percha. Such a technique is useful in removing old gutta-percha which can become quite hard.
Buchanan plugger  
Some authors would suggest that gutta-percha should be removed with heated techniques as a routine and mechanical removal only used if heat is insufficient.If mechanical removal is used, a heated instrument can be used to soften the most coronal gutta-percha, so that it can be vertically compacted and adapted to the canal walls to create a seal.

Mechanical removal
Mechanical removal of gutta-percha is efficient and probably the most commonly used technique, but it is a technique that can result in the most damage to tooth tissue. If done incorrectly, it can weaken the root unnecessarily, damage the periodontium and in some cases lead to root perforation.
Periapical radiograph showing teeth 13 and 12 used as double abutments for a fixed-fixed conventional bridge 

 Periapical radiograph of tooth 23 with a post that poorly fits the prepared post hole 
A non-end cutting bur such as a Gates-Glidden or Peeso reamer should be used for gutta-percha removal, as these will cut and remove the relatively softer gutta-percha preferentially to the dentine of the canal walls.

The sequence in which the burs are used is important so that a rise in temperature at the root surface, which could damage periodontal cells, is avoided and the risk of preferentially cutting away root dentine to one side of the root canal is reduced.
 Periapical radiograph of root filled central incisor teeth (top left) from which the diameter of the post to be used can be estimated  
Temperature rise on the root surface has been investigated in a number of studies. A Gates-Glidden bur rotating at 8,000 rev min-1 results in a small rise in temperature at the root surface. However, both tapered and parallel-sided post drills produce a significant increase in temperature in excess of 17°C. Peeso reamers also generate significant rises in temperature, higher than that reached with Gates-Glidden burs and Parapost twist drills. To reduce this temperature increase, which could potentially damage cells in the periodontal ligament, it is important that the smaller sized Gates-Glidden burs are used first, working up through the sizes in turn, until no gutta-percha is removed apically. At this stage the smallest post drill can be used, again working up through the size sequence until the final post size is reached.

Thursday, November 10, 2011

A Note On Definition, Diagnosis, Treatment & Prognosis Of Dental Trauma


Enamel Infraction

Definition: incomplete fracture (crack) of the enamel without loss of tooth structure.
Diagnosis: normal gross anatomic and radiographic appearance; craze lines apparent, especially with transillumination.
Treatment objectives: to maintain structural integrity and pulp vitality.
General prognosis: Complications are unusual.

Crown fracture–uncomplicated

Definition: an enamel fracture or an enamel-dentin fracture that does not involve the pulp.
Diagnosis: clinical and/or radiographic findings reveal a loss of tooth structure confined to the enamel or to both the enamel and dentin.
Treatment objectives: to maintain pulp vitality and restore normal esthetics and function. Injured lips, tongue, and gingiva should be examined for tooth fragments. When looking for fragments in soft tissue lacerations, radiographs are recommended. For small fractures, rough margins and edges can be smoothed. For larger fractures, the lost tooth-structure can be restored.
 General prognosis: The prognosis of uncomplicated crown fractures depends primarily upon the concomitant injury to the periodontal ligament and secondarily upon the extent of dentin exposed. Optimal treatment results follow timely assessment and care.

Crown fracture–complicated

Definition: an enamel-dentin fracture with pulp exposure.
Diagnosis: clinical and radiographic findings reveal a loss of tooth structure with pulp exposure.
Treatment objectives: to maintain pulp vitality and restore normal esthetics and function. Injured lips, tongue, and gingiva should be examined for tooth fragments. When looking for fragments in soft tissue lacerations, radiographs are recommended.
• Primary teeth: Decisions often are based on life expectancy of the traumatized primary tooth and vitality of the pulpal tissue. Pulpal treatment alternatives are pulpotomy, pulpectomy, and extraction.
• Permanent teeth: Pulpal treatment alternatives are direct pulp capping, partial pulpotomy, full pulpotomy, and pulpectomy (start of root canal therapy). There is increasing evidence to suggest that utilizing conservative vital pulp therapies for mature teeth with closed apices is as appropriate a management technique as when used for immature teeth with open apices.
General prognosis: The prognosis of crown fractures appears to depend primarily upon a concomitant injury to the periodontal ligament. The age of the pulp exposure, extent of dentin exposed, and stage of root development at the time of injury secondarily affect the tooth’s prognosis. Optimal treatment results follow timely assessment and care.

Crown/root fracture



















Definition: an enamel, dentin, and cementum fracture with or without pulp exposure.
Diagnosis: Clinical findings usually reveal a mobile coronal fragment attached to the gingiva with or without a pulp exposure. Radiographic findings may reveal a radiolucent oblique line that comprises crown and root in a vertical direction in primary teeth and in a direction usually perpendicular to the central radiographic beam in permanent teeth. While radiographic demonstration often is difficult, root fractures can only be diagnosed radiographically.
Treatment objectives: to maintain pulp vitality and restore normal esthetics and function.
• Primary teeth: When the primary tooth cannot or should not be restored, the entire tooth should be removed unless retrieval of apical fragments may result in damage to the succedaneous tooth.
• Permanent teeth: The emergency treatment objective is to stabilize the coronal fragment. Definitive treatment alternatives are: to remove the coronal fragment followed by a supragingival restoration or necessary gingivectomy, osteotomy, or extrusion (surgical or orthodontic) to prepare for restoration. If the pulp is exposed, pulpal treatment alternatives are pulp capping, pulpotomy, and root canal treatment.
General prognosis: Although the treatment of crown-root fractures can be complex and laborious, most fractured permanent teeth can be saved. Fractures extending significantly below the gingival margin may not be restorable. 

Root fracture

Definition: a dentin and cementum fracture involving the pulp.
Diagnosis: Clinical findings reveal a mobile coronal fragment attached to the gingiva that may be displaced. Radiographic findings may reveal 1 or more radiolucent lines that separate the tooth fragments in horizontal fractures. Multiple radiographic exposures at different angulations may be required for diagnosis. A root fracture in a primary tooth may be obscured by a succedaneous tooth.
Treatment objectives:
• Primary teeth: Treatment alternatives    include extraction of coronal fragment without insisting on removing apical fragment or observation. It is not recommended to reposition and stabilize the coronal fragment.
• Permanent teeth: Reposition and stabilize the            coronal fragment in its anatomically correct position as soon  as possible to optimize healing of the periodontal ligament and neurovascular supply while maintaining esthetic and functional integrity.
General prognosis: Pulp necrosis in root-fractured teeth is attributed to displacement of the coronal fragment and mature root development. In permanent teeth, the location of the root fracture has not been shown to affect pulp survival after injury. Therefore, preservation of teeth with root fractures occurring in the tooth’s cervical third should be attempted. Young age, immature root formation, positive pulp sensitivity at time of injury, and approximating  the dislocation within 1 mm have been found to be advantageous to both pulpal healing and hard tissue repair of the fracture.

Concussion

Definition: injury to the tooth-supporting structures without abnormal loosening or displacement of the tooth.
Diagnosis: Because the periodontal ligament absorbs the injury and is inflamed, clinical findings reveal a tooth tender to pressure and percussion without mobility, displacement, or sulcular bleeding. Radiographic abnormalities are not expected.
Treatment objectives: to optimize healing of the periodontal ligament and maintain pulp vitality.
General prognosis: For primary teeth, unless associated infection exists, no pulpal therapy is indicated. Although there is a minimal risk for pulp necrosis, mature permanent teeth with closed apices may undergo pulpal necrosis due to associated injuries to the blood vessels at the apex and, therefore, must be followed carefully.

Subluxation

Definition: injury to tooth-supporting structures with abnormal loosening but without tooth displacement.
Diagnosis: Because the periodontal ligament attempts to absorb the injury, clinical findings reveal a mobile tooth without displacement that may or may not have sulcular bleeding. Radiographic abnormalities are not expected.
Treatment objectives: to optimize healing of the periodontal ligament and neurovascular supply.
• Primary teeth: The tooth should be followed for pathology.
• Permanent teeth: Stabilize the tooth and relieve any occlusal interferences. For comfort, a flexible splint can be used. Splint for no more than 2 weeks.
General prognosis: Prognosis is usually favorable. The primary tooth should return to normal within 2 weeks. Mature permanent teeth with closed apices may undergo pulpal necrosis due to associated injuries to the blood vessels at the apex and, therefore, must be followed carefully.

Lateral luxation
Definition: displacement of the tooth in a direction other than axially. The periodontal ligament is torn and contusion or fracture of the supporting alveolar bone occurs.
Diagnosis: Clinical findings reveal that a tooth is displaced laterally with the crown usually in a palatal or lingual direction and may be locked firmly into this new position. The tooth usually is not mobile or tender to touch. Radiographic findings reveal an increase in periodontal ligament space and displacement of apex toward or though the labial bone plate.
Treatment objectives:
• Primary teeth: to allow passive or spontaneous repositiong if there is no occlusal interference. When there is occlusal interference, the tooth can be gently repositioned or slightly reduced if the interference is minor. When the injury is severe or the tooth is nearing exfoliation, extraction is the treatment of choice.
• Permanent teeth: to reposition as soon as possible and then to stabilize the tooth in its anatomically correct position to optimize healing of the periodontal ligament and neurovascular supply while maintaining esthetic and functional integrity. Repositioning of the tooth is done with digital pressure and little force. A displaced tooth may need to be extruded to free itself from the apical lock in the cortical bone plate. Splinting an additional 2 to 4 weeks may be needed with breakdown of marginal bone.
General prognosis: Primary teeth requiring repositioning have an increased risk of developing pulp necrosis compared to teeth that are left to spontaneously reposition. In mature permanent teeth with closed apices, pulp necrosis and pulp canal obliteration are common healing complications while progressive root resorption is less likely to occur.

Intrusion
Definition: apical displacement of tooth into the alveolar bone. The tooth is driven into the socket, compressing the periodontal ligament and commonly causes a crushing fracture of the alveolar socket.
Diagnosis: Clinical findings reveal that the tooth appears to be shortened or, in severe cases, it may appear missing. The tooth’s apex usually is displaced labially toward or through the labial bone plate in primary teeth and driven into the alveolar process in permanent teeth. The tooth is not mobile or tender to touch. Radiographic findings reveal that the tooth appears displaced apically and the periodontal ligament space is not continuous. Determination of the relationship of an intruded primary tooth with the follicle of the succedaneous tooth is mandatory. If the apex is displaced labially, the apical tip can be seen radiographically with the tooth appearing shorter than its contralateral. If the apex is displaced palatally towards the permanent tooth germ, the apical tip cannot be seen radiographically and the tooth appears elongated. An extraoral lateral radiograph also can be used to detect displacement of the apex toward or though the labial bone plate. An intruded young permanent tooth may mimic an erupting tooth.
Treatment objectives:
• Primary teeth: to allow spontaneous reeruption except when displaced into the developing successor. Extraction is indicated when the apex is displaced toward the permanent tooth germ.
• Permanent teeth: to reposition passively (allowing re-eruption to its preinjury position), actively (repositioning with traction), or surgically and then to stabilize the tooth with a splint for up to 4 weeks in its anatomically correct position to optimize healing of the periodontal ligament and neurovascular supply while maintaining esthetic and functional integrity. For immature teeth with more eruptive potential (root ½ to ²/³ formed), the objective is to allow for spontaneous eruption. In mature teeth, the goal is to reposition the tooth with orthodontic or surgical  extrusion and initiate endodontic treatment within the first 3 weeks of the traumatic incidence.
General prognosis: In primary teeth, 90% of intruded teeth will re-erupt spontaneously (either partially or completely) in 2 to 6 months. Even in cases of complete intrusion and displacement of primary teeth through the labial bone plate, a retrospective study showed the reeruption and survival of most teeth for more than 36 months. Ankylosis may occur, however, if the periodontal ligament of the affected tooth was severely damaged, thereby delaying or altering the eruption of the permanent successor. In mature permanent teeth with closed apices, there is considerable risk for pulp necrosis, pulp canal obliteration, and progressive root resorption. Immature permanent teeth that are allowed to reposition spontaneously demonstrate the lowest risk for healing complications. Extent of intrusion (7 mm or greater) and adjacent intruded teeth have a negative influence on healing.

Extrusion
Definition: partial displacement of the tooth axially from the socket; partial avulsion. The periodontal ligament usually is torn.
Diagnosis: Clinical findings reveal that the tooth appears elongated and is mobile. Radiographic findings reveal an increased periodontal ligament space apically.
Treatment objectives:
 •Primary teeth: to allow tooth to reposition spontaneously or reposition and allow for healing for minor extrusion (<3 mm) in an immature developing tooth. Indications for an extraction include severe extrusion or mobility, the tooth is nearing exfoliation, the child’s inability to cope with the emergency situation, or the tooth is fully formed.      
• Permanent teeth: to reposition as soon as possible and then to stabilize the tooth in its anatomically correct position to optimize healing of the periodontal ligament and neurovascular supply while maintaining esthetic and functional integrity. Repositioning may be accomplished with slow and steady apical pressure to gradually displace coagulum formed between root apex and floor of the socket. Splint  for up to 2 weeks.
General prognosis: There is a lack of clinical studies evaluating repositioning of extruded primary teeth.6 In permanent mature teeth with closed apices, there is considerable risk for pulp necrosis and pulp canal obliteration. These teeth must be followed carefully.

Avulsion
Definition: complete displacement of tooth out of socket. The periodontal ligament is severed and fracture of the alveolus may occur.
Diagnosis: Clinical and radiographic findings reveal that the tooth is not present in the socket or the tooth already has been replanted. Radiographic assessment will verify that  the tooth is not intruded when the tooth was not found.
Treatment objectives:
•Primary teeth: to prevent further injury to the developing successor. Avulsed primary teeth should not be replanted because of the potential for subsequent damage to developing permanent tooth germs.     
• Permanent teeth: to replant as soon as possible and then to stabilize the replanted tooth in its anatomically correct  location to optimize healing of the periodontal ligament  and neurovascular supply while maintaining esthetic and functional integrity except when replanting is contra-indicated by:
1.  The child’s stage of dental development (risk for ankylosis where considerable alveolar growth has to take place);
2.   Compromising medical condition; or
3.   Compromised integrity of the avulsed tooth or supporting tissues.
 Flexible splinting for 2 weeks is indicated. Tetanus  prophylaxis and antibiotic coverage should be considered. Treatment strategies are directed at avoiding inflammation that may occur as a result of the tooth’s attachment damage and/or pulpal infection.
General prognosis: Prognosis in the permanent dentition is primarily dependent upon formation of root development and extraoral dry time. The tooth has the best prognosis if replanted immediately. If the tooth cannot be replanted within 5 minutes, it should be stored in a medium that will help maintain vitality of the periodontal ligament fibers. The best (ie, physiologic) transportation media for avulsed teeth include (in order of preference) Viaspan, Hank’s Balanced Salt Solution (tissue culture medium), and cold milk. Next best would be a non-physiologic medium such as saliva (buccal vestibule), physiologic saline,  or water. Although water is detrimental to cell viability due to its low osmolality and long term storage (ie, more than 20 minutes) in water has an adverse effect on periodontal ligament healing, it is a better choice than dry storage. Limited tooth storage in a cell-compatible medium prior to replantation has produced similar healing results as compared with immediately-replanted teeth.
The risk of ankylosis increases significantly with an extraoral dry time of 20 minutes An extraoral dry time of 60 minutes is considered the point where survival of the root periodontal cells is unlikely. In permanent avulsed teeth, there is considerable risk for pulp necrosis, root resorption, and ankylosis.
Additional considerations: Recent evidence suggests that success of replantation is dependent upon many factors, some of which the clinician can manipulate in a manner that favors more successful outcomes. Decision trees for acute management of avulsed permanent incisors have been developed with up-to-date information in an easy to use  flowchart format.
Revascularization: An immature (ie, open apex) tooth has  the potential to establish revascularization when there is a minimum of a 1.0 mm apical opening. Complete pulpal revascularization has been shown to occur at a rate of 18% among immature teeth. It appears that antibiotic treatment reduces contamination of the root surface and/or pulp space, thereby creating a biological environment that aids revascularization. On the other hand, a mature tooth (ie, closed apex or apical opening <1 mm) has little or no chance of revascularization. Researchers have demonstrated that immature teeth soaked in doxycycline solution have a greater rate of pulp revascularization.
Periodontal ligament (PDL) management – transitional therapy: When a tooth has been out of the oral cavity and in a dry environment for greater than 60 minutes, the PDL has no chance of survival. If such a tooth is replanted, it is likely to undergo osseous replacement resorption and, over time, the tooth will become ankylosed and ultimately will be lost. Because pediatric dentists need to consider the growth and development of the child patient, the goal for a tooth that has been avulsed for greater than 60 minutes with dry storage is to delay the osseous replacement and, hence, ankylotic process as long as possible. To slow down this process, the remaining PDL should be removed because otherwise it becomes a stimulus for inflammation that accelerates infection-related resorption. The remaining PDL can be removed by several methods: gentle scaling and root planning, soft pumice prophylaxis, gauze, or soaking the tooth in 3% citric acid for 3 minutes. This should be followed by a sodium fluoride treatment for 20 minutes. The rationale for this fluoride soak is based upon evidence that this procedure will delay, but not prevent, ankylosis; fluoroapatite is more resistant to ankylosis than hydroxy-apatite. When teeth are soaked in fluoride before replantation, it has been shown to reduce significantly the risk of resorption after a follow-up of 5 years. Despite these recommendations, teeth that have been out of the  oral cavity for greater than 60 minutes with dry storage  have a poor prognosis and will not survive long term.
Possible contraindications to replantation: There are possible contraindications to tooth replantation. Examples are  immunocompromised health, severe congenital cardiac anomalies, severe uncontrolled seizure disorder, severe mental disability, severe uncontrolled diabetes, and lack of alveolar integrity.
Current research: Antiresorptive-regenerative therapies may have potential for enhancing the prognosis of avulsed teeth.
Treatment strategies are directed at avoiding or minimizing inflammation, increasing revascularization, and producing hard barriers in teeth with open apices. New treatment strategies also are directed at specific clinical challenges that include decoronation as an approach to treat ankylosis in growing children and transplantation of premolars as an approach for replacing avulsed teeth. Dental practitioners should follow current literature and consider carefully evidence-based recommendations that may enhance periodontal healing and revascularization of avulsed permanent teeth.

Friday, November 4, 2011

Root Canal Obturation Techniques



Aims and objectives of obturation
  1. To established barrier to passage of micro-organisms from the oral cavity to the radicular tissue
  2. To entomb and isolate any micro-organisms organisms that may survive the cleaning and shaping process
  3. To prevent leakage into the canal system of potential nutrients that would support the microbial growth
  4. To reduce the risk of bacterial movement or fluid percolation in to the canal system space from the gingival sulcus or periodontal pockets.
Root Canal Obturation Techniques ppt


Friday, October 21, 2011

A Note onExamination of the occlusion


Introduction
As stated in the previous section, the principle function of the concept of ideal occlusion in everyday dentistry is to provide a benchmark against which any patient’s occlusal pattern can compared. This does not infer that the provision of an ideal occlusion is the treatment objective for that particular patient nor for patients in general.
The three question examination
Question 1.
Does Centric Occlusion occur in Centric Relation?
Centric relation describes a relationship between the two jaws, it has nothing to do with teeth; it is not an occlusion. When the head of the condyle is moving purely in the rotational phase of its movement, then the mandible is in a terminal hinge axis. This concept provides one of the three pillars of the definition of centric relation that is given in the previous section. If the head of the condyle is the stationary centre about which the mandible is rotating, then the mandible, during this phase of movement will describe an arc. Whereas if the mandible is not in terminal hinge axis, then the head of the condyle will not be purely rotating, because there will be an element of translation; and as a consequence of the fact that the head of the condyle is, therefore, not stationary (in the antero-posterior plane)  the mandible will not describe an arc.
Manipulation of patient to find the Centric Relation
 It is feeling that the patient’s mandible is describing a perfect arc during manipulation that gives the experienced operator the confidence that the terminal hinge axis of the mandible  has been found.
 Illustration of the relationship between the condyles 
It is certain that in reality the mandible is not describing a perfect arc because unlike on an articulator the condyle is never a perfect sphere and the glenoid fossa is never a hemisphere. There is, however, one important test that provides confidence that Centric Relation has been found. This test is based upon the fact that because the Centric Relation is a jaw relation-ship not guided by teeth nor by the patient’s muscles but by the operator arcing the mandible in its terminal hinge axis towards the maxilla, and that the end point of this arc will be consistent.  The end point of this arc occurs when the first teeth touch and this is known as the premature contact in the Centric Relation. Centric Relation is the only ‘Centric’ which is consistent. It is the fact that the Centric Relation has been found to be consistent in any one patient irrespective of time or operator that makes it so significant as a concept. It may be that the end point of the closing arc of the mandible whilst it is in terminal hinge axis (Centric Relation) is not a premature contact but rather an even contact of all of the teeth (Maximum Intercuspation). In this case the Centric Relation and Centric Occlusion coincide. If, however, as is usually the case this ideal situation does not occur then the Centric Occlusion will not occur in Centric Relation. It will then be possible discover where the premature contact in Centric Relation is.
How to find the Centric Relation
The positional difference between Centric Relation and Centric Occlusion can further be examined by noting the direction of slide of the mandible when the patient is asked to clench his or her teeth together whilst resting on the Centric Relation premature contact.
If Centric Relation (CR) and Centric Occlusion(CO) do not coincide, in many ways it would make more sense to describe the relationship between the jaws when the teeth are in Centric Occlusion, and not the other way round; but that is impossible to do because there are no landmarks on the jaws that can be examined whilst the patient is holding his or her teeth in Centric Occlusion. So the question has to be: ‘ Does CO occur in CR?’.
Question 2.
Does the patient have Freedom in Centric Occlusion?
This investigation will answer the question: ‘Is the patient’s Centric Occlusion locked in?
This means when the patient is biting together normally, do his or her incisor teeth prevent those teeth moving slightly forward, or are they prevented from doing so (locked), by the fact that the lower incisor teeth heavily contact the palatal surfaces of the upper incisor teeth?
It can be examined by in one of three ways:
1. Marking the occlusal contacts and seeing if the anterior contacts are heavier than the posterior ones
2. Asking the patient to close together slowly and reporting which teeth hit first
3. Feeling for tremors on the upper incisor teeth with our finger nail whilst the patient repeatedly taps up into Centric Occlusion.
This was easier in the days before routine use of gloves.
Question 3.
Where is the patient’s Anterior Guidance?
It  has already been discussed that the term ‘anterior guidance’ should not be taken to mean the guidance that is on the front teeth: it is the mandible that is being guided, by the temporo-mandibular joints (posterior guidance) and by the teeth (anterior guidance). Therefore, which ever teeth touch during excursive movements of the mandible provide the anterior guidance or the dynamic occlusion.
However,  the benchmarch against which the patient’s occlusion is measured is ideal occlusion, and in an occlusion which is ideal for the rest of the articulatory system the anterior guidance is on the front teeth.
How to examine anterior guidance
When the anterior guidance is on the back teeth the terminology used is posterior interference. This may be either on the working or non-working side. If interferences are present then they may extend beyond the crossover position. If there are no posterior interferences, then the anterior guidance will be on the front teeth, and this is described as being either ‘canine guidance’ (where the contact between the upper and lower teeth during an excursive movement of the mandible is against the upper canine and then eventually on the upper central incisors); or it is described as a ‘group function’ where the anterior guidance is on several teeth. In a group function these contacting teeth are usually the canines and first and second pre-molars; the more anterior teeth of the group should provide the earlier and harder contacts, otherwise the contact could be considered as a working side interference.

A Video on Mandibular movement

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