| Abstract|| |
A good access cavity preparation is the gateway to success in endodontic treatment. This article presents occlusal landmarks that can be used as the boundary for the endodontic access at the occlusal surfaces of maxillary and mandibular molars. Further this article gives a structure or landmark guided three simple stages of preparation to reach the pulp chamber. This assures an ideal access cavity reducing the risk of dentin gouging and eliminating iatrogenic deleterious events. All canal orifices will be within this boundary and can often be located easily.
Keywords: Boundary, guided molar access preparation, structure
|How to cite this article:|
Balagopal S, Chandrasekaran C. Structure bound guide to access cavity preparation for molar root canal treatment. Indian J Dent Res 2020;31:621-4
|How to cite this URL:|
Balagopal S, Chandrasekaran C. Structure bound guide to access cavity preparation for molar root canal treatment. Indian J Dent Res [serial online] 2020 [cited 2020 Oct 30];31:621-4. Available from: https://www.ijdr.in/text.asp?2020/31/4/621/298423
| Introduction|| |
A well-prepared access cavity is the opening to successful root canal treatment. This has been mentioned by almost all clinicians in the past and it predominates in the present too. Instruments have taken different shapes and instrumentation techniques have undergone varied forms but the requirement for an ideal access cavity has remained as a prerequisite for safe, easy, and efficient instrumentation. It has been accepted that unnecessary tooth removal compromises final restoration. It has been evinced that the final quality of restoration and its longevity is directly proportional to the tooth structure remaining after the access cavity preparation. It is also mandatory that a good coronal seal after the root canal obturation is equally important for the long-term success of a root treated tooth and this will depend to a large extent on the remaining coronal tooth structure after the root canal treatment.
The ideal requirements for an optimum access cavity has been described in many text books. The advantages and disadvantages of over cutting and deficient preparations have also been listed out in most text books. Many clinicians have also made generalized statements such as, the access cavity for a molar will lie in the mesial third and it would be quadrilateral or triangular in shape. Further, preservation of structures like the crossing ridges and retention of as much portions of the roof of the pulp chamber to retain integrity and fracture resistance of the tooth through “L” and “I” beam principles have been discussed and presented by a few workers.,,, There have also been suggestions to follow the decay in the tooth and as the decay is removed that will lead to the pulp chamber (Caries guided access). Musikant and associates have showed endodontic odontometrics that do help understand the average location of the various structural landmarks within the tooth., Works of Krasner and Rankow have also provided a number of descriptions of the pulp chamber and canal orifices in relation to the cemento-enamel junction. But so far none have given a stepwise preparation of access cavity specifically for mandibular and maxillary molars that can be universally followed.
This article is aimed at providing a stepwise preparation of access cavity through integration of the works of various authors and clinicians with clinical experience of over 29 years and teaching experience of over 25 years. The stepwise procedures mentioned here have been initially experimented and studied in over 200 extracted teeth before executing it in clinical practice. Further, it has been the method of teaching and training in all programs conducted since over 5 years and was observed to be successful. It has been observed that the technique works very well with the new students and practitioners. Hence the objective of this article is to present the technique in detail, which has perfect practicalities and strong scientific foundations.
General pre-requisites before access preparation in molar teeth
A thorough visual examination of the subject tooth, its morphology, and its relationship with the adjacent teeth and jaw is essential. The buccal plate for root position, tooth angulation, drifting, and inclination are to be examined and kept in mind. In the crown the number of cusps, anomalous cusps and coronal clefts must be kept in mind. It is also mandatory to probe and understand the structure of the cemento-enamel junction (CEJ). This gives multiple clues regarding the anatomy of the pulp chamber particularly the floor of the pulp chamber and the canal orifice locations.
Reading of the pre-operative radiograph is essential to record the relationship of the tooth to the jaw bone and neighbouring teeth. The radiograph also helps to measure the approximate thickness of the roof of the pulp chamber, the thickness of the mesial and distal walls, the morphology and thickness of the floor of the pulp chamber and the overall size of the pulp chamber. In addition to the above, the radiograph also provides immense information regarding the root and canal morphology and their variances.
| Structure Bound Guide (Sbg) to Access Cavity|| |
Step 1. Mapping the landmarks on the occlusal surface
The preparation is begun by marking the definite landmarks on the occlusal surface of the molar tooth.
The external outline should include the [Figure 1].
- Cuspal eminence of the mesio-buccal cusp of the tooth.
- 1 mm buccal and distal to the mesio-lingual cuspal eminence.
- 2 mm buccal and 1 mm lingual to the central groove at about 1 mm mesial to the height of the distal transverse ridge.
These points may be joined to get the quadrilateral external outline of the access cavity on the occlusal surface.
The external markings should include the [Figure 2]a, [Figure 2]b
|Figure 2: Maxillary Molar (a) Imaginary markings (b) Clinical markings (c, d, e) shape varies from near Equilateral to Scalene triangle depending on the occlusal external outline|
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- The cuspal eminence of the mesio-buccal cusp like in the mandibular molar.
- 1 mm buccal and distal to the mesio-palatal cuspal eminence.
- The distal wall of the access cavity should run along and 1 mm mesial to the height of the oblique ridge.
To what distance the distal wall will extend from the palatal point towards the buccal will depend upon the external morphological outline of the tooth.
If the tooth that is rhomboidal, appears more like a square, then the disto-buccal point is marked to get an almost equilateral triangle [Figure 2]c.
If the bucco-palatal width of the tooth is visibly longer [Figure 2]d, then the distal wall runs a shorter distance and the large base of the triangle is towards the mesial.
In situation where the bucco-palatal width of the tooth appears markedly longer with an insignificant disto-palatal cusp [Figure 2]e then the distal wall runs still shorter distance and the final access cavity may appear like a scalene triangle or have an almost oval outline.
The above-mentioned points or landmarks are made first and then the access cavity preparation is begun with the dental bur. The ideal bur to begin with may be a diamond fissure BUR, SF-41 running at high speed in an airotor.
Step 2. Initiation of access cavity [Figure 3]a, [Figure 3]b, and [Figure 4]a, [Figure 4]b
|Figure 3: (a) Occlusal surface mapping (b) Initial 2 mm deep cuts at the marked points. (c) Connecting the landmark points (d) Second level of penetration (e) Establishment of flat floor (f) Penetration of the pulp chamber (g) Finished access preparation|
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|Figure 4: (a) Occlusal surface mapping (b) Initial 2 mm deep cuts at the marked points (c) Connecting the landmark points (d) Second level of penetration (e) Establishment of flat floor (f) Penetration of the pulp chamber (g) Finished access preparation|
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Two significant scientific evidences are used in this method of access cavity preparation in molars. The first one is the report of the study by Bradford Johnson, on Endodontic Access. In this study, the author has reported that the thickness of the roof of the pulp chamber is about 7 mm. The second significant scientific evidence that is integrated with this procedure is the “Law of Centrality” described by Krasner and Rankow. The law states that the pulp chamber of every tooth is in the centre of the tooth at the level of the cemento-enamel junction (CEJ). It should be noted that extrapolation of the centre of the tooth at the CEJ towards the occlusal surface will not lie in the centre at the occlusal surface and vice-versa. When these two evidences are kept in mind and the bur depth and orientation are adhered to during the drilling, it should not result in unnecessary dentin removal (gauging) and should never result in the occurrence of lateral perforation (an iatrogenic negative event).
The initial preparation of the access cavity is begun by making 2 mm deep cuts at the marked landmark points [Figure 3]a, [Figure 3]b
Step 3. First level preparation [Figure 3]c, and [Figure 4]c
The landmark cuts are connected with the fissure bur SF-41 and if any portion of the tooth remains unremoved within the cut boundary that is also removed to get a flat floor. At this stage, it can be inspected to see that the cavity prepared is within the mapped area. Any correction can be done if there is deficiency or deviations in the preparation. Any errors at this stage is not likely to affect the preparation much. This is because this 2 mm of tooth structure is likely to be removed during preparation of the tooth for post endodontic restoration, which usually is an occlusal full coverage restoration that requires about 2 mm of occlusal reduction.
Step 4. Second level preparation [Figure 3]d, [Figure 3]e, [Figure 4]d, [Figure 4]e
The landmarks corresponding to the previously marked points are again deepened to another 2 mm to 3 mm with the fissure bur, this time with the bur oriented to travel towards the centre of the tooth. This is done in compliance with the Law of Centrality. The marked and deepened points are connected and if any portion of tooth remains unremoved within the mapped area it is flattened. At this stage, it once again gives an opportunity to correct the preparation if it is deviating from the mapped outline and/or is deviating from the expected movement of the bur towards the centre of the tooth, as the cavity approaches the CEJ. This prevents errors such as lateral perforation, overcutting, and dentin gouging. Such errors can result in perennial periodontal disease or weaken the crown and reflect deleteriously in the crown restoration.
Step 5. Penetration of the roof of the pulp chamber [Figure 3]f and [Figure 4]f
This is the last stage in the gross access cavity preparation. The coronally mapped and progressed cavity is now once again deepened to 2 mm to 3 mm at the points which are currently inclined towards the centre of the tooth during the second stage. These points are connected as before. During this preparation one or more pulp horns get exposed or often the entire roof of the pulp chamber is removed. If the entire roof is not yet removed, then a non end-cutting tapered fissure bur is introduced into the pulp horn and with a painting stroke the roof is cut following the external boundary and maintaining the inclination of the bur towards the centre of the tooth.
Step 6. Finishing of access preparation [Figure 3]g and [Figure 4]g
The non end-cutting tapered fissure bur is inserted into the pulp chamber and the portions of (shoulders of) the roof is cut and removed making the walls of the pulp chamber confluent with the walls of the prepared cavity. This also prepares the access cavity with an occlusal divergence, which enhances visibility and accessibility. Care is taken to see that the tip of the bur is not damaging the floor of the pulp chamber. This completes a conservative endodontic access cavity preparation in any molar tooth.
Advantages of the structure bound guided (SBG) stepwise preparation of the access cavity
- This method provides definite coronal landmarks, which in turn provides definite access cavity outline.
- This method helps make precise de-roofing of the pulp chamber
- This preparation method uses strong scientific foundations integrating the tooth morphology and endodontic odonto-metrics.
- This prevents inadvertent gouging of dentin.
- There has not been any such precise guide in the access cavity preparation in maxillary and mandibular teeth.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. Sundaresan Balagopal
Department of Conservative Dentistry and Endodontics, Tagore Dental College and Hospital, Chennai - 600 127, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]