Access cavity

preparation for maxillary

caninesPresented by-

Khushboo ChansoriaKritika Sarkar

INTRODUCTION

Parts of root canal system

Anatomy of apical root

• The classic concept is based on 3 anatomic & histologic landmarks: Apical Construction(AC), Cemento-dentinal junction & apical foramen(AF).

• Acc to Kuttler’s description of the anatomy of root apex has root canal tapering from orifice to AC is 0.5mm-1 mm inside the AF.

Clinical significance

• The AC generally is considered the part of root canal with smallest diameter also a reference point used most often as apical termination for shaping, cleaning & obturation.

• Post-op discomfort generally is greater when this area is violated by instruments of filling materials & the healing may be compromised.

• From the minor diameter the canal widens as it approaches the AF (major diameter).

• The space between major & minor diameter has been described as funnel shaped of hyperbolic or having the shape of “morning glory”.

• The mean distance between major & minor diameter is 0.5mm in a young person & 0.67mm in an older individual (distance is greater because of build-up of cementum.

Maxillary Canine•Longest human tooth.•Average tooth length is 26mm.•A specimen of 33.5 mm in length has been reported.

Developmental and anatomic data Average time of eruption-: 10-12YearsAverage age of calcification-: 13-15YearsAverage tooth length-: 22-27mmAverage crown length-: 10mmAverage root length-: 17mmM-D of crown-: 7.5mmM-D of crown at cervix-: 5.5mmLabio-lingual diameter of crown-: 8mmLabio-lingual diameter at cervix-: 7mm

Pulp chamber It has the largest pulp

chamber than any single rooted tooth.

Labio-palatally triangular in shape, apex is toward the single cusp and base toward the cervical third of crown.

Mesio-distally it is narrower and may resemble like flame.

In cross-section it is ovoid in shape, with greater diameter labio-palatally.

Only one pulp horn is present.

Root and root canal Single root canal of

maxillary cuspid is larger than that of maxillary incisor.

It is wider labio-palatally than its mesio-distal diameter, and on reaching middle third, it taper gradually to an apical constriction.

In cross-section, root canal is ovoid in the cervical and middle third and generally round in the apical third

Incidence

RootStraight : 39%Distally curved : 32% Palatally curved : 7%Labially curved: 13%“S-shaped” or bayonet curved Apical foramen: 7%Apical delta : 3%

Anatomic relationship in situ The root of maxillary cuspid

is positioned in the cancellous bone of the maxilla between the nasal cavity and the maxillary sinus, called the canine pillar.

It has an average of 6 degree disto-axial inclination.

Labial surface of the root lies under the labial cortical plate and may fuse with it- most prominent bulge: canine eminence (fenestration & dehisence).

• An abscess originating in a maxillary canine usually perforates the labial cortical plate below the insertion of levator muscles of the upper lip and drains into buccal vestibule.

• If the perforation occurs above the insertion the abscess will drain into the canine space and will cause cellulites.

• Apical curettage may be difficult during peri-radicular procedures because of length of tooth.

Objectives of access cavity preparation

• Most important phase of non-surgical root canal treatment.

• Without adequate access, instruments & materials become difficult to handle in the highly complex and variable root canal system.

Objectives

To achieve a straight line access to apical

foramen/ initial curvature of canal.

To locate all root canal

orifices

To conserve sound tooth

structure

Access opening

External access outline form is oval or slot shaped because no mesial or distal pulp horn are present

Mesio-distal slope is determined by the mesio-distal width of pulp chamber.

Inciso-gingival diameter is determined via straight line access factor and removal of the lingual shoulder.

Incisal extension is approached with in 2-3 mm of the incisal edge to allow for straight line access.

All internal walls funnel to the orifice.

Access cavity

• Is defined as an endodontic coronal preparation which enables unobstructed access to the canal orifices, a straight line access to apical foramen, complete control over instrumentation and to accommodate obturation technique.

Armamentarium• Ruler• X-ray film• Pencil• High speed handpiece• High speed fissure bur or round bur• Slow speed handpiece• Slow speed long-shank #2, #4, #6 bur• Endodontic explorer• Slow speed long shank #4 or #6 round bur• Irrigating syringe• Sodium hypochlorite• Irrigating needle (with 45 degree bend at tip)

Steps

Step 1: Visualization of likely internal anatomy• Begin with an x-ray of the unprepared tooth. This

start x-ray is important in making a diagnosis, as well as estimating the initial measurement of the canals. Study the radiograph as a blueprint to establish the:– size,– shape– location of the pulp canal(s) and– their relative positions.

• Palpation along the attached gingiva aids the determination of root location.

Step 2:Pencil Access• Outline the coronal access on the

tooth in pencil, using the coronal preparation slides as a guide.

• The access outline for a maxillary canine is similar to an upside-down triangle shape, with the base of the triangle parallel to the incisal edge.

Step 3: Cut Through Center

• First, remove all caries and fillings that obstruct the view or that can cause leakage.

• Undermined enamel should also be removed together with any parts of the crown that make accessibility to the canal(s) difficult.

• Using a high-speed fissure bur or round bur held perpendicular to the lingual surface, cut just through the enamel in the center of the pencil-marked area. A common error is to begin cavity too far gingivally. Do not force the bur.

Step 4: Extend Access• Extend the opening laterally to the

designated outline by maintaining the point of the bur in the central cavity and rotating the hand piece toward the incisal so that the bur continues to parallel the long axis of the tooth.

Step 5: Cut Through Dentin• With a low-speed long-shank #4 or #6 bur

(depending on the size of the pulp chamber), make a cut with the long axis of the tooth and cut directly through the dentin into the large pulp horn, or the largest area of the pulp chamber.

• This procedure makes the access cavity walls confluent with the lateral & the incisal walls of the pulp chamber & renders the cavity a lingual extension of pulp chamber with a “straight line” penetration to the apical root canal.

• The bur should be used with a pull stroke from the chamber in and out.

Step 6: Explore Access• Use the endodontic explorer to check

for the canal. • If the explorer meets constant

resistance, the pulp chamber has not yet been reached.

Step 7: Cut into Chamber• Continue drilling apically through the

dentin. • The operator will feel a slight drop as

the bur breaks through the roof and drops into the pulp chamber.

Step 8: Explore Access• When the pulp chamber has been

penetrated, probing with the explorer will often produce a "catch" along the ledges, or overhangs, created by the lingual walls or roof of the pulp chamber.

Step 9: Remove Undercuts• Expand the coronal cavity access slightly.• Avoid perforating the floor of the pulp chamber.• Penetrate the pulp chamber using a slow-speed

long-shank round bur (No. 4 or 6 Gates Glidden).• Working from inside the chamber to outside in a

sweeping motion, remove undercuts, or lingual and labial walls of pulp chamber.

• The access on the tooth is extended more toward the cingulum. Additional beveling of the incisal wall is also completed by working from inside to outside to remove the lingual "shoulder" of the canal, thus allowing for the continuous access from the coronal cavity into the canal.

• The ideal access consists of smooth walls without ledges. The use of fissure burs very often creates ledges in the floor and walls of the cavity access preparation, which can make canal instrumentation more difficult. Moreover, ledges in the dentin can diminish the tensile strength of the tooth.

• In general, the No. 2 is used for working within the canals, while Nos. 4 and 6 are for working within the chamber, using a sweeping motion to avoid gouging the floor of the pulp chamber and creating the illusion of a canal which may lead to perforation.

• Remove debris from the chamber as you proceed, using a No. 2, No. 4 or No. 6 bur to eliminate pulpal horn debris and bacteria.

• If the canal or chamber is calcified, remove dentin with the slowspeed hand piece and appropriate bur.

• Step 10: Irrigate• Irrigate periodically to flush out debris. • Fill an irrigating syringe with "sodium

hypochlorite" and attach an irrigating needle, the tip of which should be bent at approximately a 45 degree angle to the long axis of the needle.

• The distance from the bend to the tip of the needle should equal 20 mm.

• Using this needle, gently flush fillings and debris from the chamber.

• The needle should fit in the canal very loosely, and the solution should be introduced very slowly, so that it can run back out of the access opening and is not forced through the apex.

Step 11: Straight-Line Access• The resulting cavity should be smooth and

continuous, flowing from cavity margin to canal orifice; this is referred to as straight-line access.

• The incisal wall meets the lingual surface of canine in a butt joint to provide adequate thickness for a restorative material because this tooth is heavily involved in excursive occlusal guidance.

• Verify that you have achieved straight-line access by rotating a file within the canal.

• The file should have direct and unimpeded access to the canal, achieving 360 degrees of unrestrained motion; you should be able to rotate the file 360 degrees about the cavity outline without encountering resistance within the pulp chamber due to ledges or ridges.

Bibliography

• Pathways to pulp- Cohen• Grossman’s endodontics• Endodontics by John Ingle• Textbook of endodontics by Nisha Garg• Endodontics by Pittford• Endodontology by Gunner• Google.com• Columbia.edu• Universityofmichigan.edu• Googlebooks.com

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