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| IMC Wiki | Access to root canals: trephining, cavities for endodontic access and uncovering of root canal entries

Access to root canals: trephining, cavities for endodontic access and uncovering of root canal entries

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Minimisation of the pulp cavity

Dentine which develops before the eruption of the teeth is referred to as primary dentine and that which develops following eruption as secondary dentine. Continuous deposition of secondary dentine on pulp walls with advancing age results in a reduction in the size of the pulp cavity.

Furthermore, if the pulp is subjected to exogenic damage (e.g. caries, trauma, cavity preparation), this leads to excessive formation of what is referred to as irritation dentine which can fill the cavity irregularly and sometimes completely. With advancing age of the patient, it can therefore be increasingly difficult to expose the root canal system of a tooth by trephining.
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Diagnostic x-ray

Prior to trephining and subsequent root canal preparation, a diagnostic x-ray is recommended in order to show the tooth concerned together with its roots and the surrounding peri-radicular tissue. Such an overview can supply useful information for the endodontic treatment that will follow, about the number and morphology of the tooth roots, the direction and extent of a possibly twisted course of the root, the shape of the apex and possible root resorption. This diagnostic imaging prior to root canal treatment is immensely important for gaining detailed information.


Trephining should produce straight access of adequate dimensions to all root canals.
Any protrusion of the pulp roof must always be removed in order to be able to remove any possibly infected pulp remnants as well as to obtain optimal vision and access.

Any protrusion of the pulp roof must be removed; the floor of the pulp cavity must not be changed. In order to avoid perforation, a Batt-tip drill (drill with a non-cutting tip) should be used for preparation of the endodontic access cavity.

Only optimal vision and access guarantee that no root canal entries will be overlooked.
Please always bear in mind that on the one hand the floor of the pulp cavity must never be changed in order to not destroy anatomical clues as to the location of canal entries, as well as being able to avoid perforation of the floor of the cavity into the desmodontium as this latter may result in tooth loss.

Considering the above aspects, the Batt-tip drill with its blunt and rounded tip is the ideal instrument for the preparation of the opening for trephining and the endodontic access cavity.

Number, location and shape of root canals

Not only the obstruction of canal entries by irritation dentine but also the great variability in the number, location and shape of the root canals often lead to an insufficient exposure of root canals.

Profound knowledge about the possible number and location of root canal entries is therefore essential.

Maxillary teeth

RC = root canal
mb = mesio-buccal

Maxillary tooth 1 canal 2 canals 3 canals 4 canals Number of roots Particularities
Middle incisor almost always       1  
Lateral incisor almost always       1 relatively frequent deformities:
dens in dente, peg-shaped tooth
Canine tooth almost always       1  
First premolar 8-9 % 85-92 %,
1 buccal RC
1 palatal RC
2 buccal RC
1 palatal RC
Second premolar 48-72 % 28-51 % 1 %
2 buccal RCs
1 palatal RC
First molar rare
(conical root)
  up to 49 % up to 95 %
1-4 fourth RC usually in mb root,
rarely in palatal root
Second molar selten
(conical root)
up to 10 % 63 % 37 % 1–4  

Mandibular teeth

RC = root canal

Mandibular tooth 1 canal 2 canals 3 canals 4 canals Number of roots Particularities
Incisors up to 89 % up to 40 %
1 buccal RC
1 lingual RC
Canine tooth 80-87 % 13-20 %
1 buccal RC
1 lingual RC
First premolar 74 % 23-26 % very rarely   1-2  
Second premolar 86-99 % 1-13 % 0.5 %   1-2  
First molar rare
(conical root)
see Fig. 3
7 % 64 % 29 % 1-3 very rarely enteromolar root possible as additional distal root
Second molar rare
(conical root)
13 % 79 % 8 % 1-3  

Eccentric x-rays

If maxillary or mandibular premolars, or mandibular incisors, have two root canals, these are projected one overlapping the other in an orthoradial projection.
Therefore, it is recommended that one obtains x-rays in a 30° mesial, or a distal-eccentric, angle.

If the root canal instrument is positioned in the centre of the tooth root while x-rays are taken, it can be assumed that there is only one canal in the root. However, if it is not located in the centre, it is very probable that there is an additional root canal.

Initial exposure of root canal entries

Initially, root canal entries should always be exposed using manual instruments, particularly those made of stainless steel.

In contrast to instruments made of nickel-titanium, stainless-steel instruments are more tactile affording greater manual control during the course of root canal treatment.
In calcified and obliterated root canals, special instruments should be used for the initial probing of the root canal. These instruments are characterised by a particular bending stability due to thermal hardening and reduced length. Experiments showed that initial probing of the root canal using manual instruments made of stainless steel lead to a significantly reduced risk of fracture when permanently rotating nickel-titanium instruments are used. Therefore, regardless of the selected preparation technique, any root canal should be probed and penetrated using manual instruments initially.

Dilatation of the coronal root canal entrance

The coronal root canal entrance should preferably be dilated using rotary instruments, such as Gates-Glidden drills or Peeso drills, as well as special, more conical intro files.
As a rule, these mechanical instruments may only be used in a straight section of the root canal that is not bent.