Access Is Success

The success of endodontic treatment depends entirely on precise, proper execution of preparation of access cavity. An access cavity that has been prepared improperly in terms of position, depth, or extent will hamper the achievement of optimal results.

Arnaldo Castellucci, M.D, D.D.S

ABSTRACT

In the past, access cavities were standardized mainly dependent on the tooth type. However, with the advent of modern endodontic techniques using a dental operation microscope & loupes providing magnification & better illumination, the ‘ideal’ access cavity preparation has evolved from being based on individual tooth type to the preparation based on the shape of the pulp chamber morphology of the tooth being treated.

Access is the first & arguably the most important phase of non-surgical root canal treatment. However, it can be the most challenging and frustrating aspect of endodontic treatment. Therefore, for successful treatment, good access cavity design and preparation is imperative for quality endodontic treatment, prevention of iatrogenic problems & prevention of endodontic failure.

INTRODUCTION

As novices to root canal therapy ourselves, one of the worst nightmares during access cavity preparation is perforation. Furthermore, there are several aspects of access cavity preparation that could go wrong without the correct knowledge & guidance that plagued us during our graduation days. Now, however, being armed with the correct knowledge & guidance, we can recognise the cause & prevent these procedural errors during treatment by following a set of few simple laws & guidelines that govern & dictate the access cavity preparation.

Access into the pulp chamber and the root canal system is the most critical step in root canal therapy. Unlike other aspects of Dentistry, root canal therapy is carried out with limited visual guidance. This, coupled with complex anatomy of the root canal system & various pathological conditions, makes the preparation of an ideal access a crucial step to gain success in treatment. Therefore, the objective of a well designed access cavity is to create a smooth, straight line path to the root canal system, while retaining as much tooth structure as possible.

Therefore, the purpose of this article is to highlight the common iatrogenic errors by General Dental Practitioners due to the lack of knowledge & awareness of certain internal anatomic features for a given tooth.

What are the common errors during access preparation?

• Incomplete caries removal
• Incomplete de-roofing of the pulp chamber
• Searching the canal with a bur
• Damaging the pulpal floor
• Access cavity perforations
• Missed canals

WHAT DO THE ENDODONTIC PRINCIPLES SAY ABOUT ACCESS CAVITY PREPARATION?

I. Outline form

It is the recommended shape for access of a normal tooth with radiographic evidence of pulp chamber and canal space. External outline form evolves from internal anatomy of the tooth established by the pulp. Therefore, external outline form is established by mechanically projecting the internal anatomy of the pulp onto the external surface.

II. Convenience form

Establishing a straight line access to the apical 1/3rd of the canal for preparation & canal filling instruments. Cavity expansion also accommodates filling techniques & helps to contain the irrigating solutions during chemo-mechanical preparation.

Too narrow access cavity leads to limited visual access and also creates friction of the instrument shaft against the coronal obstruction which in turn leads to application of increased forces by the operator to overcome the obstruction which contributes to fracture of the instrument. Also, the access cavity should provide positive support for temporary filling material between appointments.

III. Removal of remaining carious dentin & Defective restorations

Caries remaining in the endodontic access cavity must be removed for 3 reasons:

1. To eliminate mechanically as many bacteria as possible from interior of the tooth
2. To eliminate the discoloured tooth structure, that may ultimately lead to staining of tooth especially of concern in the anteriors.
3. To eliminate the possibility of any bacteria-laden saliva leaking into the access cavity.

Incomplete de-roofing of the pulp chamber and its content leads to re-infection & incomplete removal of carious dentin leads to microleakage as dentin is porous in nature.

IV. Toilet of the cavity

Removal of residual caries, necrotic tissue, soft and calcified debris should be done before radicular preparation is begun. Sterilize the access cavity with antimicrobial agents like Sodium hypochlorite.

WHAT SHOULD THESE PRINCIPLES MEAN TO A GENERAL DENTAL PRACTITIONER?

The first & foremost thing to do should be to recollect the normal anatomy of the tooth in question. This gives a clear picture of the number of roots, canals, the position of the tooth in relation to the dental arch etc., A good, undistorted radiograph taken using the right technique would aid in making this assessment easier.

While preparing the outline form 3 important factors to be considered are:

• Size of the pulp chamber
• Shape of the pulp chamber
• Number of individual root canals, curvature & their position.

The General Dental Practitioner should always keep in mind the objectives of access preparation that it must permit complete, direct vision of the floor of the pulp chamber and canal orifices especially posterior teeth because the floor has natural grooves at the end of which the canal orifices are located.

Is finding the pulp chamber/canal an arbitrary process?

Absolutely NO!! One can predictably locate the pulp chamber/canal based on scientific evidence.

The studies conducted by Krasner & Rankow have provided the following Laws:

1. Law of Centrality:

The pulp chamber is always located in the center of the tooth at the level of the CEJ.

2. 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.

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

4. Law of Symmetry 1: It states that except for the maxillary molars, canal orifices are equidistant from a line drawn in mesio-distal direction through the pulp chamber floor.

5. Law of Symmetry 2: It states that except for the maxillary molars, canal orifices lie on a line perpendicular to a line drawn in a mesiodistal direction across the center of the pulp chamber floor

6. Law of Color change: It states that the pulp chamber floor is always darker in color than the walls.

7. Law of Orifice location 1: It states that the orifices of the root canal are always located at the junction of the walls and the floor.

8. Law of Orifice location 2: It states that the orifices of the root canals are always located at the angles in the floor-walls junction

9. Law of Orifice location 3: It states that the orifices of the root canals are always located at the terminus of the root,s developmental fusion lines.

What common misconceptions does a General Dental Practitioner have regarding access cavity preparation?

1. Misconception: The purpose of access cavity preparation is to find the canals!

Fact: The purpose of access cavity preparation is & always will be to find the pulp chamber & NOT the canals.

2. Misconception: Canals could be searched using a bur!

Fact: Absolutely not! A bur is never meant for this purpose. A DG16, slow speed handpiece & Ultrasonic tips designed for this purpose can be used to locate the orifices of the canals.

3. Misconception: Each tooth has a specific access cavity shape that is unique for the tooth depending on individual tooth type.

Fact: Well, there may be common access cavity shapes for each tooth type. However, the shape of the access cavity is defined by the pulp chamber morphology rather that the individual tooth type. For example, a maxillary second molar can have an ovoid access cavity shape if it has only two canals as against the common triangular shaped access cavity for this tooth.

4. Misconception: Conventional path of penetration for access is applicable to all cases.

Fact: The conventional path of penetration is lingual for anteriors & occlusal for posteriors. However, this may not be the case always. In conditions such as attrition, abrasion, palatally inclined tooth, crowding etc., access can be from the labial than the conventional lingual approach. It can also be from the cusp tip in a peg lateral.

Also, correct angulations of the bur should always be practised. If the bur is wrongly angulated, it can lead to weakening of the tooth structure and contribute to crown fracture or even perforations.

Lastly, are there any guidelines that a Dentist can follow to avoid these errors?

• Start by taking a diagnostic radiograph and inspect the internal anatomy of the tooth which dictates the access.
• Excavate caries, all unsupported enamel, dentin and any defective restoration.
• If prepared cavity is closer to the chamber, it is better to enter the chamber from the same side itself.
• A palatal entry for upper anteriors, lingual entry for lower anteriors & an occlusal entry for posteriors is advised. Also, follow the ‘Stay lingual rule’ for maxillary lateral incisor and mandibular first premolar.
• Complete de-roofing of the pulp and removal of the pulp horns.
• Irrigate the chamber with antimicrobial solutions like Sodium Hypochlorite & Chlorhexidine.
• Locate the canal orifices with a DG16 and NOT with a bur.
• Establish a glide path with a 10 K file and NOT with any other hand file.
• Extirpation of coronal pulp with sharp spoon excavator & radicular pulp using a barbed broach.
• Coronal flaring of access cavity walls and establishing a straight line access.

Evaluate the access cavity prepared. It can be slightly modified as per case requirements, age, limited mouth opening etc., to give it the so-called ‘convenient shape’

Modification of access should allow introduction of instruments into the entire working length as well as irrigating solutions during endodontic treatment. These modifications, however, can be done during any stage of the treatment according to the instrument/material requirements.

To conclude, a proper access cavity preparation is one of the foundations on which success of root canal treatment rests. Non-surgical endodontic therapy is perceived by the common man as a conservative treatment modality to save the natural tooth. However, several misconceptions about endodontic treatment have lead to most iatrogenic errors that arise during access cavity preparation. Such errors are very common and compromise both the Endodontic as well as the Prosthodontic treatment outcomes. Hence, the objective of this article is that by merely ‘Being aware’ of the internal anatomy & having a scientific approach, one can minimize these errors. Therefore, a properly prepared Access always translates to Success.

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