TRAUMA
Injuries to teeth are common. In a prospective study where all dental injuries occurring from birth to the age of 14 were registered, it was found that 30% of children had sustained injuries to the primary dentition and 22% to the permanent dentition1. These statistics are age-related. In the primary dentition, the prevalence of injuries ranges from 31 to 40% in boys and from 16 to 30% in girls. In the permanent dentition, the prevalence of dental trauma in boys ranges from 12 to 33% compared with 4 to 19% in girls. Most injuries affect the maxillary incisors and in the majority of cases, only one tooth is affected. An increased overjet with prominent incisors and incompetent lips have been found to be predisposing factors.
Prevention
Patients with an increased maxillary overjet have a significantly greater risk of traumatic dental injuries. An additional trauma factor is insufficient lip protection. Collision sports have been the cause of many injuries to the head and neck. It is clear that protection of the oral and dental tissues is needed for all participants in active contact sports. This is best provided by a gum shield made by a dentist.
Effects
Traumatic injuries may affect the teeth in various ways including:
• Chipped enamel or enamel infraction
• Fracture into dentine
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• Fracture exposing pulp
• Fracture involving both crown and root
• Root fracture
• Avulsion
• Tooth loosened in socket (intrusion/extrusion/luxated) History
This should include a medical and dental history, age, time of accident, cause, pain, previous trauma history, loss of consciousness and treatment already carried out for the injury including information about the storage conditions of the tooth.
Pulp sensibility testing
Pulp testing following traumatic injuries can be unreliable. These procedures require cooperation and a relaxed patient in order to avoid false responses. Pulp sensibility testing, however, is important at the time of injury for establishing a point of reference for evaluating pulpal status at later follow-up examinations. It is essential to review traumatised teeth clinically and radiographically before instituting endodontic therapy.
Radiographs
These are important for initial diagnosis and later comparisons. Films must be dry, and radiographs should also be available of the contralateral teeth. It is essential to look for root development, fractures, widening of the periodontal membrane space, size of the pulp, proximity of the pulp to any fracture, damage to adjacent teeth, coincidental pathology and foreign bodies.
Treatment options
Chipped enamel
The degree of damage depends on energy dissipation. Infractions usually require no treatment. The trauma may have affected the periapical tissues and there is the possibility that the pulp will become non-vital. Pulp sensibility tests should be performed 3-monthly for 1 year and radiographs 6-monthly for at least three recalls.
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Fracture into dentine
As dentine is exposed, there are two priorities – to protect the exposed dentine and prevent possible migration of a tooth that has lost contact with its neighbours. This may be done with a directly bonded restoration or fragment.
Fracture exposing pulp
A complicated crown fracture implies exposure of the pulp to the oral environment. Healing is not spontaneous and untreated exposures lead to total pulp necrosis. The aim of pulp capping or pulpotomy treatment is to preserve a vital pulp, which is biologically walled off by a continuous hard tissue barrier. The maturity of the tooth is most significant. It is agreed that the exposed pulp should be maintained in young teeth with incomplete root formation and removed in mature teeth when constriction of the apical foramen allows adequate obturation of the root canal.
Fracture involving both crown and root
A decision must be taken as to whether the tooth can be root filled and a satisfactory restoration ultimately provided, or the tooth should be extracted.
Root fracture
Although the reported incidence of these injuries is low the true number may well be higher as ‘unknown’ fractures are sometimes revealed. They most commonly occur in the middle third of a fully erupted, fully formed tooth and healing is possible along similar lines to healing of a fractured bone.
The avulsed tooth
This most commonly occurs in males, in upper incisors and particularly in younger patients with protrusive teeth. In the majority of cases, reimplantation is carried out but no guarantee of success should be given to the patient. Replanted teeth are often subject to resorption which may be either inflammatory or replacement (ankylosis).
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The loose tooth
Any tooth loosened in its socket may become non-vital as a result of damage to apical blood vessels. Regular reviews are thus required to assess clinical and radiographic changes.
Splinting
Splints are used to stabilise teeth loosened in their sockets, teeth with root fractures, teeth lost (avulsed) and replanted, fractures of the alveolus and fractures of facial bones. Splinting is ideally provided directly by joining adjacent teeth together with an adhesive restorative material (such as glass-ionomer cement or bonded composite), or a piece of wire (for example orthodontic wire) retained on the teeth by an adhesive restorative material or orthodontic brackets. Other techniques such as the use of interdental/eyelet wires have been described, though these may be traumatic to the gingival tissues and may extrude a tooth if inappropriately applied. Teeth may also be splinted with a removable appliance constructed on a cast. The most suitable method will vary in each case, but generally that which is least intrusive whilst fulfilling its role should be used.
The duration of splinting varies depending on the type of injury.
Where soft tissue only has been injured (for example a luxation injury) then the period of splinting may be as little as one week or less. Where there is significant hard tissue injury (for example alveolar fracture or root fracture) a much longer period of wear (up to 3 months) is required. Whatever method of splinting is employed, care must be taken that the splint is neither too rigid nor placed for too long as both these will increase the risk of ankylosis.
Injuries to developing teeth
The close relationship between the apices of primary teeth and their permanent successors explains why injuries are easily transmitted from the primary to the permanent dentition. Traumatic injuries to developing teeth may influence their future growth and maturation.
When the injury occurs during the initial stages of development, enamel formation can be seriously disturbed owing to interference with a number of stages in ameloblast development.
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Resorption
Transient root resorption occurs frequently in traumatised teeth2 and in those undergoing orthodontic treatment. It is normally without clinical significance. Pressure resorption in the permanent dentition seen during tooth eruption is also seen in orthodontic movement of teeth3 and usually manifests as a shortening of the roots. It may be quite destructive if diagnosed late.
Root resorption sustained by infection is the most important clinical condition from an endodontic point of view. It can occur either on the root surface (external resorption), or in the root canal (internal resorption). Replacement or endosteal root resorption is seen in teeth that have suffered dentoalveolar ankylosis because of necrosis of the periodontal ligament.
Internal root resorption
It has been shown that bacterial infection is a prerequisite for internal resorption4. This process seems to be elicited by irritation from bacteria or their products within the dental tubules derived from caries, fractures or anatomical defects. Sometimes, resorptive defects are noted radiographically in root-filled teeth and this may be attributed to percolation of oral fluids via a defective coronal restoration or periodontal pocket and lateral canals etc. When seen radiographically, internal resorption is a definite indication that endodontic treatment is required. Clinically, there is necrosis in the pulp chamber and in the root canal to a level coronal to the resorption lacunae. Root treatment is complicated by the problems associated with removal of tissue from a resorptive defect and any remnants may contribute to failure.
The treatment of choice is to use sodium hypochlorite as an irrigant and to dress the canal with calcium hydroxide paste, replacing at 2–3-week intervals before filling with gutta-percha. A thermo-softened filling method may be indicated if there is extensive resorption.
Cervical root resorption
This appears to follow injury to the cervical attachment apparatus of the tooth. It is most often an inflammatory type of resorption and if local necrosis of the periodontal ligament takes place ankylosis may ensue. Cervical resorption is not a pulpal reaction, but is of importance if it penetrates the root canal. It then becomes an endodontic problem.
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External inflammatory root resorption
This is a commonly occurring complication following trauma to the teeth. The condition can be recognised radiographically as a peri-radicular radiolucent area encompassing areas of the root and adjacent alveolar bone. It is important that endodontic therapy is instituted as soon as there are clinical or radiographic signs that resorption is in progress as the resorptive process may destroy the tooth in a few months. Treatment is similar to that for treatment of non-vital teeth and the success is related to removal of the necrotic pulp. There is clinical evidence that long-term treatment with calcium hydroxide provides the most predictable results5.
Replacement resorption
Damage to the periodontal structure can result in surface resorption when the root surface is seen to demonstrate the presence of super-ficial lacunae with new cementum formation. It has been proposed that this is a response to localised injury to the periodontal ligament.
This may be self-limiting and spontaneously repair. Extension of this process may result in direct union between bone and root substance.
Clinically, dentoalveolar ankylosis will be recognised because of the lack of tooth mobility. Radiographically, there will be an absence of periodontal space. Also, there may be a ‘moth eaten’ appearance of the root. There is at present no treatment for this condition although the speed with which the root is replaced by bone is relatively slow and may take several years.
PERIO-ENDO CONNECTIONS
The pulp and the periodontal ligament are closely connected via:
• The apex or apices
• Other vascular channels (e.g. lateral and furcation canals)
• Dentinal tubules
Therefore, it is not surprising that there should be a relationship between diseases of the pulp and the periodontium. In determining the treatment for a particular tooth it is essential to know whether the initial lesion is of periodontal or endodontic origin (Fig. 4.1).
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Fig. 4.1 Origin and passage of infection in combined perio-endo lesions.
Classifications
The following classifications of endodontic and periodontal lesions have been proposed:
• Lesions of endodontic origin
• Periodontal lesions
• Primary endodontic/secondary periodontal
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• Primary periodontal/secondary endodontic
• Combined endodontic/periodontal lesions
Lesions of endodontic origin
Lesions of endodontic origin are simple periapical or lateral periodontal granulomas (chronic apical/lateral periodontitis characterised by aggregations of macrophages, lymphocytes and plasma cells) and abscesses (acute apical/lateral periodontitis) recognised by the usual clinical and radiographic features.
Periodontal lesions
Periodontal lesions are diagnosed on the basis of generally accepted criteria including derangement of gingival architecture and loss of gingival attachment as demonstrated by pocket probing and radiographs.
Primary endodontic/secondary periodontal
Endodontic disease may masquerade as periodontal disease in several ways:
• Drainage of a periapical lesion via the periodontal ligament, perhaps perforating the gingivae at, or near to, the mucogingival junction, or exiting via the gingival crevice.
• Endodontic lesions formed via lateral canals at places on the root surface other than at the apex.
• Lateral perforation of the root during root canal or post preparation leading to a lateral periodontal abscess which may drain via the gingival crevice.
• Endodontic lesions in furcation areas formed via ‘lateral’ canals leading to abscesses, sinuses and radiographic bone loss, which may look like periodontal disease.
Primary periodontal/secondary endodontic
Chronic periodontitis may lead to pulpal disease by means of direct bacterial invasion, or trauma during root surface instrumentation as part of treatment. Chemicals and obtundents used to relieve dentine sensitivity may irritate the pulp, as may the exposure of root surfaces by gingival recession. There is some disagreement in the literature about whether this really happens, mainly because many teeth with
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significant periodontal disease also have large restorations, so it is impossible to know whether the pulpal lesion was caused by caries, restoration or periodontitis.
Combined endodontic/periodontal lesions
Combined endodontic/periodontal lesions may be:
• Independent of one another
• Coalescing
Differential diagnosis
Differential diagnosis is based upon interpretation of information gained from the following:
• History:
—
pain (duration and character)
• Clinical examination:
—
swelling (site, type and character)
—
discharge (type of fluid, blood, pus etc.)
—
percussion (gentle percussion in several directions)
—
mobility
• Special tests:
—
vitality/sensibility testing (electrical and/or thermal, mechanical)
—
periodontal probing
—
test cavity
—
radiographs (parallax views if necessary)
Treatment planning
In determining the treatment to be provided, an assessment of the vitality of the tooth in question is required. In some instances, it may not be clear whether the pulp is vital or not. In these cases a judgement must be made based on the available evidence from the history and clinical appearance (including special investigations) and treatment instigated. The options for treatment are summarised below:
• Pulp judged to be healthy:
—
periodontal therapy
—
reassessment: if unsuccessful commence endodontic
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therapy.
If successful no further treatment.
• Pulp judged to be unhealthy:
—
endodontic therapy
—
reassessment: if unsuccessful commence periodontal therapy. If successful no further treatment.
ELECTIVE ENDODONTICS
Elective devitalisation is the procedure that involves the purposeful extirpation of healthy (i.e. non-inflamed, non-infected) pulpal tissue as a prelude or aid to provision of a restoration. Pulpal tissues comprise part of a dentino-pulpal complex and can normally respond dynamically to stimuli and may play a role in proprioception. As such, the needless removal of this important tissue should be avoided; however there are certain situations in which elective devitalisation may still have a role.
Rationale for devitalisation
In general terms, the basis for elective devitalisation of a tooth may be due to biological considerations, mechanical considerations or as an aid to specific treatments.
Biological considerations
A tooth that has an extensive restoration is likely to have had multiple previous restorations, the placement of each having caused trauma to the pulpal tissues. These injurious insults to the tooth are thought to be cumulative6 (termed ‘stressed pulp syndrome’) and further restorations or preparation for an indirect restoration will further stress the pulpal health. In such a situation the likelihood of subsequent loss of vitality is obviously increased. When the tooth in question is to be restored indirectly, the problems of performing root canal treatment through the restoration are axiomatic. The problems are further compounded if the unit in question forms part of a larger restoration, such as a bridge retainer. In addition to the problems of performing root canal treatment, the indirect restoration itself is also compromised with lower survival7. Given the situation of an extensively restored tooth that requires restoration with an indirect restoration and has uncertain or doubtful vitality, it is sometimes
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prudent to perform root canal treatment before provision of the restoration.
There are also a number of other situations in which elective devitalisation may be performed for biological reasons: continued sensitivity not amenable or not responsive to treatment, evidence of progressively sclerosing canals, root resorption and treatment for periodontal disease that involves root amputation or hemisection.
Mechanical considerations
When insufficient coronal dentine remains to provide for retention and resistance, placement of a restoration is problematic. In this situation, placement of a corono-radicular core will allow for the retentive and resistance form to be provided by the radicular dentine.
This may be achieved through placement of the restorative material alone (such as an ‘amalgam–dowel core’) or in combination with an intra-radicular post. Obviously, using the radicular dentine for retention will necessitate root canal treatment.
When a tooth is extensively restored and/or has a poor crown to root ratio due to bone loss arising from periodontal disease, elective devitalisation and crown reduction will reduce the influence of any lateral forces acting upon the tooth. This is of particular relevance when the tooth in question is a potential abutment for a partial denture. The reduced tooth may then be utilised as an overdenture abutment, providing support and stability for the prosthesis as well as maintenance of alveolar bone.
Aid to treatment
Occasional situations may arise in which devitalisation of teeth will aid provision of treatment. Although uncommon, such situations include gross adjustment of occlusal irregularities or major realign-ment of tooth axes.
Risks and complications
Although the above arguments for elective devitalisation are per-suasive for some situations, such a procedure is not without its drawbacks. The primary consideration is that the success of root canal treatment cannot be guaranteed. Despite advances in endodontic treatment, the potential for failure of the root canal treatment should be weighed carefully against the risks/problems of restoring the tooth
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without devitalising it. Although root canal treatment and placement of an intra-radicular post was once thought to strengthen a root (even being advocated for otherwise healthy teeth that were planned to act as bridge abutments!) it is now accepted that this will, in fact, predispose to root fracture8. Although there is no conclusive evidence that endodontically treated teeth are more brittle, the procedure itself will weaken the tooth due to the amount of coronal and radicular dentine that will be removed.
Teeth that have been root filled have shown poor performance as bridge abutments and especially so if an intra-radicular post is present. Such poor performance is even more likely when root-filled teeth support a distal extension, whether this is a removable partial denture or a cantilever bridge9,10. This may in part be as a result of a decreased proprioceptive mechanism following pulpectomy.
It should also be remembered that elective devitalisation before definitive treatment will increase the time required to complete the treatment and also increase costs.
Making a decision
Whether or not to perform elective devitalisation should not be an empirical decision but each tooth should be assessed individually.
Such assessment should include not only a careful clinical examination regarding current status of the tooth, but also the history of the tooth. Radiographs and sensibility (vitality) testing are essential aids.
The aim of assessment is to determine the risks involved in not devitalising the tooth, primarily with respect to the chance of requiring root canal treatment once the definitive restoration has been placed, compared with the increase in complications such as failure of the root canal treatment and potential for higher failure of the tooth or restoration itself.
In situations in which elective devitalisation is being considered, alternative treatment options should be explored. Such options may include surgical crown lengthening, orthodontic movement or use of a bonded restoration. Advances in multi-purpose bonding systems may allow for placement of restorations (direct or indirect) whereby retention is provided solely by the bond to tooth structure. Although little long-term clinical data exist for this technique it has obvious advantages if the longevity of the tooth can be increased.
There will be situations in which significant doubt exists over the potential for continued vitality of a tooth or when a restoration cannot be placed without utilising radicular dentine to provide retention.
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Careful planned elective devitalisation and appropriate restoration may prove wise in such instances.
RESTORATION OF THE ROOT-FILLED TOOTH
Once a tooth has undergone endodontic treatment it is then necessary to restore the tooth in order to:
• Provide a coronal seal (this has a significant effect on the outcome of the endodontic treatment)11,12.
• Return the tooth to function.
• Protect the remaining tooth from fracture.
In most instances, teeth that have undergone endodontic treatment will be doubly weakened. By the very nature of factors resulting in loss of vitality, the majority of endodontically treated teeth will already have suffered from a significant loss of tooth structure as a result of the cumulative ravages of caries and previous restoration.
To enable endodontic access these already weakened teeth then have a significant further amount of tooth structure removed. In addition, it has been suggested that endodontically treated teeth are more brittle. More recent studies dispute this, though some change in physical properties do occur.
Anterior teeth
In anterior teeth, the amount of tooth structure removed to gain access to the pulp space is not overly large and does not have a large effect on the fracture resistance of the tooth. Thus for most anterior teeth, the only restorative need is to provide a coronal seal and return to function. In many cases this may be achieved simply by removing the obturant (gutta-percha) to a level slightly below the gingival margin or cemento-enamel margin, placing a ‘sealing’ material (such as a resin-modified glass-ionomer cement) 1–2 mm thick and then restoring the access cavity with a resin composite (Fig. 4.2). Where the existing loss of tooth structure is extensive, more attention should be given to the retention of the ‘core’ restoration and an indirect restoration such as a full coverage crown should be provided.
Posterior teeth
The restoration of root-filled posterior teeth is complicated by the
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Fig. 4.2 Direct restoration of (a) posterior and (b) anterior root filled teeth (Am =
amalgam, GP = gutta-percha, Co = composite, RmGIC = resin-modified glass-ionomer cement).
axial stress placed on any restoration distal to the canines. The preparation of the access cavity and removal of the roof of the pulp chamber acts to increase the stresses at the base of the cusps during function and predisposes these cusps to fracture. In addition, in most root-filled posterior teeth, removal of caries and defective restorations will have resulted in disruption of the marginal ridge, which further weakens the tooth. The overall result of this is that the compromised cuspal tissue cannot withstand the ‘wedging’ forces developed during function and is liable to fracture13.
When restoring endodontically treated posterior teeth, consideration needs to be given to the high risk of cuspal fracture. Although some protection may be given to weakened cusps by placing a bonded restoration14, in any tooth in which the existing restoration and access cavity combined involves more than the occlusal surface, some form of cuspal protection is required. As discussed in Chapter 5, although cuspal coverage may be provided with a direct restoration, practically this need is best served by provision of an indirect restoration that overlays the cusps at risk of fracture. Thus most endodontically treated posterior teeth require restoration with a suitable core followed by provision of an indirect restoration such as
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a crown or cuspal coverage inlay.
The choice of core restoration depends primarily on the amount of coronal dentine available to assist in retention of the core, or, more exactly, an assessment of the quantity of sound coronal dentine that will remain following subsequent preparation for the indirect restoration. It is of interest that the amount of residual coronal dentine is often overestimated in the clinical setting15.
Teeth requiring endodontic treatment have typically lost tooth structure (due to previous restorations and/or current caries): further loss of coronal dentine is necessary for endodontic access. As a result, there is often a lack of coronal dentine in which to prepare retentive features without compromising the strength of the remaining tooth structure. Nayyar and his co-workers described a technique whereby 2–3 mm of the coronal root filling is removed and an amalgam core placed to fill not only the coronal preparation, but also to fill the pulp chamber and extend into the roots16. Utilisation of the radicular portion of the tooth in this way provides good retention and resistance without the need to remove any more coronal tooth structure (Fig. 4.2). In the initial report, a very high success rate was reported.
This technique has been widely adopted and is also suitable for premolars as well as molars. Although it is usual to remove root-filling material from the coronal aspect of the root, in situations in which there is a large pulp chamber, extension of the amalgam into this space alone is sufficient. A core of this type will function well even when as little as one sound cusp remains and careful application of this technique can overcome problems related to limited retention of a direct core, while reducing the need for placement of an intraradicular post and associated problems.
The main disadvantage of this technique is the difficulty of endodontic retreatment and the lack of any ‘sealing’ material between the root filling and the coronal restoration. The latter problem may be overcome if the technique is used with resin-modified glass-ionomer cement (RmGIC) as the core material, though a significant amount of coronal dentine must remain, as RmGIC is a weaker material and less suitable for use as a structural core.
If there is little remaining coronal dentine, then further retention for the core will need to be provided by the placement of an intraradicular post. If some coronal dentine remains to provide some support, then a direct post in conjunction with a corono-radicular direct core should be placed. If very little coronal dentine remains then a cast post (indirectly constructed) should be provided. If a cast post is to be provided and more than one canal needs to be utilised
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to provide retention, as the canals are likely to be divergent, the core should be constructed in more than one piece (i.e. two or three, depending on how many intra-radicular posts are placed). Such a core is termed a ‘split core’.
Intra-radicular posts
Historically it was understood that the placement of an intraradicular post would reinforce the root and provide greater resistance to root fracture. Clinical studies have not shown reduction in fracture incidence by the placement of a post in pulpless teeth10; the bulk of remaining tooth structure rather than the presence of a post is important in providing resistance to fracture. The only exception to this is when a tooth has a very large canal space with thin root dentine walls at risk of fracture. Such a situation may typically arise in an upper incisor that became non-vital at a young age (typically due to trauma). The radicular dentine will be thin with a very large pulp space. It is possible that bonding techniques may allow for reinforcement for the root via placement of a low viscosity resin composite into the root with a light-transmitting intra-radicular post to allow for light-activated polymerisation of the resin composite to the full depth17. Although evidence for this is limited at present, it would seem to be a useful technique to reduce the potential for fracture of such teeth.
From available evidence it would appear that the only true indication for post placement in a tooth is to retain a core, more specifically:
• To retain a restoration when a lack of coronal tooth structure remains following root canal treatment. This lack of tooth structure would not enable satisfactory resistance or retentive form for a direct or indirect restoration without the placement of a post in order to retain a core.
• There is insufficient crown tissue left on a vital tooth to accommodate placement of a core (to support a crown). In such cases elective root treatment may be undertaken.
The term ‘post-crown’ is often used but perhaps ‘post-retained core’ is more appropriate.
Design requirements
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Length
There is a direct relationship between post length and retention and in addition, the post must also be long enough to minimise internal stresses on the root. The exact dimensions of the ideal post have been considered in detail and these include:
• Equal to the length of the clinical crown18,19
• Half the length of the root20
• Longer than the final clinical crown8
• Midway between the apex and the height of the alveolar crest21
• Leaving 3–5 mm of root filling material22
While a disparity of opinions exists as to the length of post preparation, most investigators and clinicians agree that the post length must not interfere with the apical seal. Microleakage is considerably reduced if an excess of 4 mm of gutta-percha remains in the canal apical to the post23,24.
Diameter
With respect to retention, diameter is not as important as post length with little or no increase in retention seen with increasing diameter.
Post diameter should therefore not be increased in the hope of gaining retention but should solely be dictated by the physical properties of the post and canal morphology, in order to avoid removing an excess of sound tooth structure. Increasing the diameter unnecessarily weakens the remaining root and may predispose it to fracture.
Shape
Posts may be generally classified as tapered or parallel, threaded or non-threaded and with a variety of surface finishes. The post shape is an important factor in determining retention and stress distribution, and selection of post type is usually dictated by the clinical situation.
With respect to retention, tapered posts usually fare poorly; the greater the taper, the lower the retention. Due to the tapered design, these posts allow cement to flow and vent easily and hence perform favourably during cementation and before loading (as shown in photoelastic stress studies). However, during loading tapered posts demonstrate unfavourable stress distribution compared with parallel-sided posts25, and are more likely to split the root due to wedging
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forces. Parallel-sided posts offer increased retention compared with tapered posts along with a more favourable stress distribution pattern on loading.
To alleviate hydrostatic pressure during cementation, cylindrical posts usually incorporate vents along their long axes. The resistance of cylindrical posts to torsional/rotational forces is low and hence whenever possible an anti-rotational feature should be included in the final post-core unit to improve resistance to these forces. A circular cross-sectional configuration of the prepared post space will not offer any significant resistance to rotation of the post, thus the normal eccentricity of the coronal portions of the canal should be accentuated to provide an anti-rotational feature. This may also act as a positive seat for the core at the coronal portion of the canal, thus preventing over seating and wedging within the root that could lead to vertical fracture.
Indirectly constructed intra-radicular posts are made from a replica or ‘pattern’ of the desired shape: this pattern may be custom made or constructed from preformed shapes. Custom posts are essentially posts made from a pattern of a freehand preparation of the canal space: this pattern is usually made indirectly on a cast (obtained from an impression of the preparation) but may be made directly in the mouth. Preformed shapes usually entail the use of a drill and matching post components. Such components may consist of ‘blanks’ used for impression taking, burnout patterns for construction of a pattern (either indirectly on a model or directly in the mouth) or may be prefabricated posts with a core either built up directly or a core cast onto the prefabricated post.
Surface finish
The threaded or screw post has been in use for the longest time26,27.
Although increased retention is provided, care must be taken during insertion to avoid fracture of the root or post. Photoelastic studies have demonstrated high levels of residual stress with threaded posts in both loaded and unloaded states, and as such the increased retention afforded by use of threaded posts must be weighed against the potential for creating stress fracture of roots. Some studies have shown that posts with larger threads are less passive and such posts, especially if tapered, are more likely to be involved in root fractures28,29.
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The provision of serrations or roughening can increase the surface area of a post. Smooth posts demonstrate the lowest retentive values, while sandblasting smooth surfaces doubles their retentive value.
The retentive value of smooth and sandblasted posts can be further increased by the addition of circumferential grooves, but such features may weaken the post itself.
Post material
Custom cast metal posts (type III yellow gold, base metal alloys or silver–palladium alloys) are the only universal way of achieving accurate adaptation to all root canal configurations, but as discussed above are not as retentive as parallel posts. Prefabricated post systems may utilise a burnout replica to construct a one-piece cast post and core or a wrought post onto which a core is cast. A wrought post is stronger than a cast post for a given diameter. However, wrought posts with cast-on cores are not consistently more resistant to fracture30.
The strength advantage afforded by wrought gold is lost during casting; however a complete casting with fewer voids is more likely, especially with smaller diameters. The use of differing metals in such a situation offers the potential for corrosion and this may even lead to root fracture due to build up of pressure from corrosion products, especially if the post contains tin31. Wrought posts are also generally more expensive.
Direct intra-radicular posts are designed to be cemented into the tooth and a core built up intra-orally. Prefabricated wrought metal posts offer the advantage of superior strength compared with cast posts, particularly in diameters less than 1.5 mm, and they are also clinically convenient. As well as wrought gold, direct posts may be composed of titanium, stainless steel or newer materials such as fibre posts (posts with a resin matrix and carbon or quartz fibre) or ceramic.
A post fabricated from carbon-fibre reinforced epoxy resin became commercially available in 199232, and several fibre posts are now available, with quartz fibres being the most common. It is claimed that the physical properties of such posts are similar to that of dentine, although it has been suggested that the flexibility of the post in situ will not match that of the root, even if the elastic modulus is the same, due to the influence of the cement layer and core33. There also remains disagreement as to whether a stiffer post leads to more even distribution of stress or whether a post with low stiffness is preferred34.
Increased longevity of the restoration is claimed due to the decrease
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in stress concentration35, though there is no clinical evidence to support this statement. There are a number of large studies showing a reduction in incidence of root fracture when fibre posts are compared with more rigid posts36–38 and thus it is wise to consider placement of a fibre post to retain a core in situations in which the root is at significant risk of fracture (e.g. a short root, short post and thin radicular dentine). However, there are few well controlled clinical studies and no reliable randomised controlled trials39, though this is an area of research interest at present and more data may soon be available.
In response to the need for a post possessing optical properties compatible with an all-ceramic crown, an all-ceramic post has been developed. The post is made from zirconium polycrystals and has a high flexural strength and fracture toughness. Although designed for use with a composite core, a technique has been described to combine the post with a pressed glass core. Due to the brittle nature of these posts, they are extremely difficult to remove.
Choice of direct or indirect post-retained core As with all indirect techniques, an indirect post will require an unim-peded path of insertion with no undercuts. In some situations in which a reasonable amount of dentine remains, placement of a direct post and direct core material (amalgam, resin composite etc.) will avoid unnecessary removal of sound tooth structure. When little Fig. 4.3 Direct and indirect intra-radicular posts.
POOC04 02/18/2005 04:35PM Page 101
(in suitable canal)
No
Amalgam dowel core
Yes
Yes
Prefabricated post
and amalgam dowel core
Eccentric/elliptical/
very tapered/very large canal?
supported cusps remaining with
Yes
No
No
Canal(s) suitable for post placement?
Yes
Cuspal coverage required, place core first
One or more well-
reasonable amount of coronal dentine?
ability to restore
No
Any coronal dentine?
No
Custom cast post-core
Consider split core if more than
one canal can be utilised
Reconsider
?Amalgam dowel core
OR bonded core
No
Yes
Yes
Access cavity/existing restoration small occlusal?
Yes
No
Flow chart for restoration of molar teeth.
Canal(s) suitable for post placement?
No cuspal coverage required
Bonded restoration
Eccentric/elliptical/
very tapered/very large canal?
Cast post-core with prefabricated pattern
(e.g. ParaPost) OR consider split core if
more than one canal can be utilised
Fig. 4.4
POOC04 02/18/2005 04:35PM Page 102
No
Consider fibre post
and direct composite core
IF post
Prefabricated post and direct
composite/amalgam core
Luscent Anchor / DT light post
/
Yes
Reconsider options:
XLA, OD, Proceed with post and crown
completely intact walls remaining)
over denture).=
no
Consider root re-inforcement
e.g. Luminex
No
Large core required?
(i.e.
No
Yes
Yes
High risk of root fracture?
(short root, thin root dentine)
extraction, OD =
Eccentric/elliptical/
very tapered/very large canal?
Yes
Yes
Yes
No
Large canal with thin periphery of root dentine?
No
No
Restore access
With bonded restoration
Post required to retain core
Sufficient height of coronal dentine to allow for ferrule?
Custom cast post-core
Cast post-core with prefabricated
pattern (e.g. ParaPost)
Yes
No
No
Can this be corrected with
surgical crown lengthening?
Yes
Reconsider options:
XLA, OD, Proceed with post and crown
IF post
OR
No
Crown required?
(i.e. Premolar with more than occlusal cavity or anterior tooth with large access cavity/restoration) Yes
Eccentric/elliptical/
Consider fibre post
Flow chart for restoration of premolar and anterior teeth (XLA very tapered/very large canal?
Sufficient coronal dentine to act as/support core?
No post, direct core
(composite or amalgam)
Fig. 4.5
POOC04 02/18/2005 04:35PM Page 103
Endodontics – further considerations 103
coronal dentine remains to provide strength and aid in retention of a core, then an indirect post with integral core is indicated (Fig. 4.3).
In all cases, it is essential that the margin of the subsequent indirect restoration passes beyond the junction of the core and tooth, i.e. a ferrule is present (see Chapter 5).
The above principles for restoration of root-filled teeth are summarised in the flow diagrams in Figs 4.4 and 4.5.
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