Pulp Space Anatomy and Access Cavities

Sumamry This lesson will help you to visualise where the root canal system is and will therefore aid your endodontic access.

Key words¹

Orifice - the opening to the canal

Overview

It is essential to know the pulp space anatomy in order to achieve a high level of standard of endodontic treatment. Understanding access cavity design allows for conservative cavity preparation and prevents excessive tooth destruction. Magnification and enhanced illumination are extremely helpful during access cavity preparation and allow detailed examination of the pulp space.

General pulp space anatomy

The pulp space is split into two parts: Pulp chamber: within the crown ReviseDental.comThe outline follows the shape of the crown Root canal: within the root The outline follows the shape of the roots The canals have a similar tapering form to the roots Pulp space is surrounded by dentine Dentinal tubules make up 20-30% of the total volume of dentine² The concentration of tubules increase from the amelodentinal junction to the pulp Therefore the permeability of dentine is significantly larger closer to the pulp The tubules are an important reservoir for microorganisms and these microorganisms may persist even after root canal treatment Shape Since the roots tend to be broader buccolingually than they are mesiodistally, the pulp space is usually oval in cross-section Deposition of minerals With age, the pulp space becomes smaller, with an increase in deposition of fibrous and mineral components In response to irritation from caries, restorations or tooth wear, tertiary dentine is produced by odontoblasts. This causes the pulp space to become smaller and canal orifices difficult to locate The use of magnification and illumination will reveal the different colours of circumpulpal and tertiary dentine to aid access The pulp space is complex The root canals may divide and re-join Eight separate pulp space configurations were identified by Vertucci (1984)³ (See drawing below), however it is now known that even more categories also exist (Gulabivala).

Diagrams to show eight separate pulp space configurations ReviseDental.com

Apical foramina and constriction

The foramina Is the opening at the apex of the root of a tooth Rarely opens at the exact anatomical or radiographic apex of the tooth The apical constriction Is where the canal constricts at the end, before emerging at the apical foramina, near the root end The apical constriction should ideally be used as the natural end point in root canal treatment, however in apical periodontitis cases, this has often been resorbed The integrity of the constriction should be maintained to avoid complications This position can be accurately located with an apex locator

Drawing to demonstrate the location of apical foramen and apical constriction

Accessory and lateral canals:³

Lateral canal are found anywhere along the length of the root and they tend to be at right angles to the main root canal Patent lateral canals are present in the coronal or middle third of 59% of molars Accessory canals usually branch off the main root canal somewhere in the apical region The presence of lateral canals in the furcation areas of molar teeth is well documented, andReviseDental.com their incidence is relatively high A total of 76% molars are reported to have openings in the furcation

Variations in Pulp Space

Variations are likely to occur and can include: Multiple roots e.g. mandibular first molar can present with three roots (a mandibular molar may have an additional disto-lingual root, known as radix entomolaris) Dens invaginatus Malformation where there is an infolding of enamel into dentine There is a deep pit into the pulp space which can be a route of infection into the pulp Dens evaginatus A protuberant cusp develops There is a high risk of this cusp fracturing creating a route for infection into the pulp

Access Cavities

Access cavities vary between each tooth You must ensure that you have detailed knowledge of each tooth and cavity morphology before cutting an access cavity As well as avoiding unnecessary removal of tooth tissue, you must ensure that caries removal is complete, all restorations removed to assess restorability and must ensure that the roof of the pulp chamber is completely removed It is important to ensure that you achieve straight line access in order to prevent complications and achieve the best preparation possible There have been a number of laws produced to guide clinicians with cutting access cavities and locating root canal orifices

Krasner andReviseDental.com Rankow's Anatomic Laws:⁴

Anatomic laws relating to the pulp chamber: Law of centrality: the floor of the pulp chamber is always located in the centre of the tooth at the level of the CEJ Law of concentricity: the walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ

The diagram demonstrates the centrality of the pulp chamber and how the walls of the pulp chamber follow the pattern of the external wall whilst having the same central point

ReviseDental.com Law of the CEJ: the CEJ is the most consistent, repeatable landmark for locating the position of the pulp chamber

The diagram demonstrates how the distance from the external surface of the clinical crown to the wall of the pulp chamber is the same throughout the circumference of the tooth at the level of the CEJ Anatomic laws regarding the pulp chamber floor:

Law of symmetry 1: except for maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial distal direction through the pulp-chamber floor

The diagram demonstrates how the mesial canals are the same distance from the line drawn

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Law of symmetry 2: except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial-distal direction across the center of the floor of the pulp chamber

The diagram demonstrates the the two lines drawn are perpendicular to each other

Law of Colour Change: the colour of the pulp-chamber floor is always darker than the walls Law of orifice location 1: the orifices of the root canals are always located at the junction of the walls and the floor

The diagram demonstrates the darker colour of the pulpal floor and the junction between the wall and the floor

ReviseDental.com Law of orifice location 2: the orifices of the root canals are located at the angles in the floor- wall junction Law of orifice location 3: the orifices of the root canals are located at the terminus of the root developmental fusion lines

The diagram shows the developmental fusion lines and demonstrates that the orifices are located at the angle of the floor-wall junction and at the end of the fusion lines

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Specific pulp space anatomy

Average length and number of canals specific to each tooth:⁵ Maxillary teeth

Maxillary tooth Average length (mm) Number of roots Number of canals Central incisor 22.5 1 1 Lateral incisor 22.0 1 1 Canine 26.5 1 1 1 (6%) First premolar 20.6 2-3 2 (95%) 3 (1%) 1 (75%) Second premolar 21.5 1-3 2 (24%) 3 (1%) 4 (93%) First molar 20.8 3 3 (7%) 4 (37%) Second molar 20.0 3 3 (63%) Third molar 17.0 1-3

Mandibular teeth

Mandibular tooth Average length (mm) Number of roots Number of canals 1 (58%) Central incisor 20.7 1 2 (42%) 1 (58%) Lateral incisor 20.7 1-2 2 (42%) 1 (94%) Canine 25.6 1 2 (6%) 1 (73%) First premolar 21.6 1 2 (72%) 1 (85%) Second premolar 22.3 1 2 (15%) 3 (67%) First molar 21.0 2-3 ReviseDental.com4 (33%) 2 (13%) Second molar 19.8 2 3 (79%) 4 (8%) Third molar 18.5 1-2 Pulp space anatomy and access cavities specific to each tooth

Maxillary teeth

Maxillary Incisors: An abnormality is most likely to occur with maxillary lateral incisor and may present with:Dens invaginatus, germination or fusion Pulp Chambers The central incisors of young patients normally have three pulp horns The canals of lateral incisors are often curved distally/ palatally at the apex Root Canals Extremely rare to have more than one root or canal Oval shape in cross-section, only round near the apex Access cavities Triangular in shape, prepared from the palatal aspect An access cavity that is too small and close to the cingulum leads to Severe stresses on the instrument Instrument binding against the access cavity walls Risks of ledge formation apically The access cavity should extend far enough incisally without excess removal of tooth tissue Sometimes the incisal edge may be involved if access is to be adequate Once initial access has been carried out, the cervical constriction should be removed and the dentine lip adjacent to the pulp horns should be removed Maxillary Canines: Pulp Chamber Quite narrow The canals of canines may have a distal apical curvature Root Canal Oval shape in cross-section Circular in the apical third Access cavity Prepared from the palatal aspect, from the cingulum to the edge Narrow mesio-distally Maxillary Premolars PulpReviseDental.com Chambers Wide buccopalatally, narrow mesiodistally with two pulp horns Root Canals First premolars: Two canals within two roots Many configurations (described above) can be found Prevalence of lateral canals can be as high as 49%² Root canal orifices lie buccally and palatally Second premolars: One canal within one root Variation of configurations with the most prevalent being Types II and III (25%) and IV and VII (25%)² Ribbon shaped Access cavities Cut occlusally Wider buccolingually Maxillary Molars Pulp Chambers First molars: Four pulp horns Root Canals First molars: Usually three-rooted with four root canals (always assume the fourth canal is present) The fourth canal is in the mesiobuccal root: in up to 90% of first molars² This canal configuration is usually Type IV, however Type IV has been prevalent too Mesiobuccal canals: Superimposed on a radiograph Leaves the chamber mesially Then curves distopalatally Distobuccal canal: Leaves the chamber distally Curves mesially in the apical half Palatal canal: Curves buccally in the apical third Second molars: Similar to first molars, but less divergent Three canals, sometimes possesses an extra mesiobuccal canal Fusion between roots is much more common Third molars: May have three separate roots Partial or complete fusion occurs often Access cavities Triangular in shape (more of a trapezoid shape for first molars) Within the mesial two-thirds of the occlusal surface The oblique ridge can remain intact Less tissue removal required from the distobuccal surface in comparison to the mesiobuccal surface due to the location of the orifices ReviseDental.com Diagrams to show the access cavities of maxillary teeth

Mandibular teeth

Mandibular Incisors Pulp chambers Similar to the maxillary incisors Three pulp horns are present Root canals Can show Types I to IV configurations Two canals can be present: up to a prevalence of 41%² May curve distally but mostly straight Access cavities Similar to maxillary incisors Likely to involve the incisal edge Mandibular Canines Pulp chamber Similar to maxillary canine, but smaller Root canal Type I configuration is prevalent Similar to maxillary canine, but smaller Access cavity Lingual aspect ReviseDental.comOval in shape Likely to involve the incisal edge Mandibular Premolars Pulp chambers Wide buccolingually Two pulp horns Root canals Both are usually single rooted First premolar Second premolar Two canals may be present Access cavities Wide buccolingually through the occlusal surface It may be necessary to involve the buccal surface if two canals are present Mandibular Molars Pulp chamber First molars: May have five pulp horns Root canal First molars: Two roots with three root canals Two canals are usually found in the mesial root, but a third mid-mesial canal may also be present. Two canals can also sometimes be found in the distal root The mesial canal has one apical foramen in 40-45% of cases² Distal canal is more oval The distal canal curves buccally The mesiobuccal canal leaves the pulp chamber mesially and alters distally in the mid third The mesiolingual canal is straighter but may curve mesially at the apical third Second molars: Mesial root has two canals These tend to fuse in the apical third Only one distal canal Horse-shoe shaped, otherwise incomplete division gives rise to a C-shaped canal Third molars Many root canals Access cavity Mesial three-quarters of the occlusal surface Triangular First molars More rectangular due to a possible second distal canal

ReviseDental.com Diagrams to show the access cavities of mandibular teeth

Access Procedure

Burs used for access

Fissure bur With a rounded edge Used for axial wall removal Round burReviseDental.com Can identify and undercuts and remove dentine surrounding pulp horns Endo access bur: Combination of round and tapered fissure bur Safe-ended endo access bur Has a non-cutting edge to ensure that the floor of the pulp chamber is untouched Used for axial wall removal Tungsten carbide bur Can be used for axial wall removal Method of access

Anterior teeth

Bullet points correlate with diagrams below from left to right: 1. Entrance is achieved through the lingual surface of anteriors 2. Initial access is carried out and only enamel is penetrated 3. The bur angulation changes – the handpiece is rotated towards the incisal edge so that the bur parallels the long axis of the tooth. 4. The cavity outline is funnelled and fanned incisally. This will help to remove pulpal horn debris and bacteria 5. The labial lip and wall of the pulp chamber is removed to ensure that the cavity is smooth and continuous with the canal orifice 6. The lingual shoulder is removed to allow a continuous preparation 7. Straight line access has been achieved ReviseDental.com Diagrams to show the method of access of anterior teeth⁶

Posterior teeth

Bullet points correlate with the images below from left to right: 1. Entrance gained through the occlusal surface 2. The bur may feel as though it has ‘dropped’ when the pulp chamber has been reached. The pulp chamber is opened up. The roof of the pulp chamber is removed 3. Funnelling of the cavity walls are completed 4. An endodontic explorer (DG-16) is extremely useful in aiding to locate orifices

ReviseDental.com Diagrams to show the method of access of posterior teeth⁶

Complications of poor access Perforation A hole or break through dentine and enamel Can occur in the crown, floor of the pulp chamber and root Caused by: Misdirection of the bur Loss of orientation Using straight instruments in a curved canal Gouging Artificially created cavity in the crown of the tooth Caused by: Misdirection of the bur during access preparation Ledge Iatrogenic irregularity in the root canal system Causes: Failure to adequately prepare the coronal flare Using straight instruments in a curved canal Skipping file sizes or moving up sizes too quickly Fractured instrument A broken instrument caused by too much stress Causes: Failure to adequately prepare the coronal flare Skipping file sizes or moving up sizes too quickly Discolouration Caused by: Inadequate removal of the pulp horns

Diagrams to showReviseDental.com complications of poor access⁶

Access through crown and bridge

It is important to remove the crown and bridge (and any other restoration) prior to commencing root canal treatment rather than accessing through the restoration because: There may be caries or cracks underneath You lose anatomical markers used for access The angulation of the tooth may be different to how it appears and therefore may increase risk of perforation/ excessive tooth removal

Conclusion There is a huge variety of different sizes and shapes of pulp spaces. It is important to have good knowledge of these differences in order to cut access cavities and ensure that unnecessary removal of tooth tissue is avoided. Pulp spaces become smaller with age and after trauma due to deposition of minerals.

Third Party Links

References Specific references: ¹Farlex, Medical Dictionary. The Free Dictionary Accessed May 1st, 2020. ²San Chong B. Harty's Endodontics in Clinical Practice E-Book. Elsevier Health Sciences; 2016 Jul 28 pp. 36-53 ³Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology. 1984 Nov 1;58(5):589-99. ⁴Krasner P, Rankow HJ. Anatomy of the pulp-chamber floor. Journal of endodontics. 2004 Jan 1;30(1):5-16. ⁵Carrotte P. Endodontics: Part 4 Morphology of the root canal system. British dental journal. 2004 Oct;197(7):379-83. ⁶Dentinal Tubules (no date supplied) Endodontic Cavity Preparation. Available at: Dentinal Tubules: Access Cavity Pictures (Accessed: 29 May 2020) General references used for this information: Hargreaves KM, Berman LH. Cohen's pathways of the pulp expert consult. Elsevier Health Sciences; 2015 Oct 2. link San Chong B. Harty's Endodontics in Clinical Practice E-Book. Elsevier Health Sciences; 2016 Jul 28. link Tronstad L. Clinical endodontics: a textbook. Stuttgart; New York: Thieme,; 2009. link Darcey J, Taylor C, Roudsari RV, Jawad S, Hunter M. Modern endodontic planning part 2: access and strategy. Dental update. 2015 Oct 2;42(8):709-20.

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