Ass.Prof.Dr.Mohamed ALsakkafAss.Prof.Dr.Mohamed ALsakkaf 11

Endodontic Cavity Preparation

.Careful cavity preparation and canal obturation are the keystones to successful root canal therapy .

.Apical moisture – proof seal, the first essential for success, is not possible unless the space to be filled is carefully prepared and debrided to receive the restoration .

.Endodontic cavity preparation begins the instant the involved tooth is approached with a cutting instrument, and the final obturation of the canal space will depend on the care and

accuracy exercised in this initial preparation .

22

Divisions of Cavity Preparation

For descriptive convenience, endodontic cavity preparation may be separated into

two anatomic divisions: a. Coronal preparation.b. Radicular preparation.

.If one thinks of an endodontic preparation as a continuum from enamel surface to apex, Blacks Principle of Cavity Preparation –Outline, convenience, retention, and resistance forms – may be

applied.

33

.The entire length of the preparation is the full outline form. In turn, this outline may have to be modified for the sake of convenience to accommodate canal

anatomy or curvature and/or instruments.

.Resistance must be developed at the apical terminus of the preparation, the So – Called "apical stop", the barrier against which virtually every canal filling must be

compacted.

44

Basic Coronal Instruments

.Two handpieces are usually required.

.The ideal cutting instrument is the round – end Carbide Fissure bur, with this instrument, enamel,resin, ceramic, or metal perforation is easily accomplished, and surface extensions may be rapidly completed.

.Precious metal alloys can be cut with tungsten carbide burs.

55

.Tapered instruments should never be forced, but should be allowed to cut their own way with a light touch by the operator. If a tapered instrument is forced it will act as a wedge. This causes the enamel to "chech"

or "craze" and will weaken the tooth.

.If a Porcelian Jacket Crown is to be entered, a small diamond bur should be used. Again care must be exercised not to split the

Jacket by forcing the action.

66

. As soon as the enamel or restorative . As soon as the enamel or restorative penetration and minor surface extensions penetration and minor surface extensions are complete, the high – speed handpiece is are complete, the high – speed handpiece is put put aside, and the slow – speed with a round bur aside, and the slow – speed with a round bur is is used. Three sizes of round burs No. 2, 4, 6, used. Three sizes of round burs No. 2, 4, 6, and two lengths, and two lengths, regularregular and and surgicalsurgical are are routinely used. routinely used. . The regular – length round bur in a conventional latch – type contra – angle handpice will "reach" 9.0mm from the nose of

the contra – angle.

66

77

.The surgical – length bur will "reach" 14 or

15mm and is necessary in some deep

preparations.

.The round burs are for dentin removal in both anterior and posterior teeth – these burs are first used to drill through the dentin and "drop" into the pulp chamber. The same bur is then used in the removal of the roof of the pulp

chamber .

.The size of the round bur is made by estimating the canal width and chamber size and depth

apparent in the initial radiograph.

88

.The No.2 round bur is generally used in preparing mandibular anterior teeth and most maxillary premolar teeth with

narrow chambers and canals.

.The No.4 round bur is generally used the maxillary anterior teeth and mandibular premolar teeth, and in "young" maxillary premolars and "adults" molars in both

arches.

99

.The No.6 round bur is used only in molars with large pulp chamber.

.A No.1 round bur is used in the floor of the pulp chamber to seek additional canal

orifices.

.UltraSonic units with specially designed endodontic tips, allow clinicians to more precisely remove dentin and expose

orifices.

1010

.As soon as the bulk of the overhanging dentin is removed from the roof of the chamber, the Law – speed round bur is put aside, and, once again the high – speed fissure bur is used to finish and slope the side walls. Endoz Carbide fissure bur is recommended. It is safe – ended and will not scar the pulpal floor. Moreover it is longer bleded (9mm) for

sloping the access cavity.

High – Speed burs should not be used to penetrate into, or initially enlarge, the pulp chamber unless the operator is skilled in

endodontic preparation.

1111

Principles of Endodontic Cavity Preparation

.By slightly modifying G.V. Black Principles of Cavity Preparation, a list of principles of endodontic cavity preparation may be established.

.Black G.V dealt with cavity preparation limited to the crowns of teeth, however his principles can be applied to radicular

preparations as well.

1212

.Endodontic preparations deal with both coronal and radicular cohorts – each prepared separately but ultimately flowing

together into a single preparation.

For convenience of description, Blacks principles are therefore divided into the

following.

1313

Endodontic Coronal Cavity Preparation

I. Outline Form.

II. Convenience form.

III. Removal of the remaining carious dentin ( and defective restoration).

IV. Toilet of the cavity.

1414

Endodontic Radicular Cavity Preparation

I. and II outline form and convenience form (continued).

IV. Toilet of the cavity (continued).

V. Retention Form.

VI. Resistance Form.

1515

Outline Form

.The outline form of the endodontic cavity must be correctly shaped, and positioned to establish complete access for instrumentation, from cavity margin to apical foramen.

.External outline form evolves from the internal anatomy of the tooth established

by the pulp.

1616

.Because of this internal – external relationship, endodontic preparations must of necessity be done in a reverse manner, from the inside of the tooth to the outside. This means, the external outline form is established by mechanically projecting the internal anatomy of the pulp onto the external surface.

1717

.This may be accomplished only by drilling into the open space of the pulp chamber and then working with the bur from the inside of the tooth to the outside, cutting away the dentin of the pulpal floor and walls overhanging the

floor of the chamber.

.Intracoronal preparation is contrasted to the extracoronal preparation of operative dentistry, in which outline form is always

related to the external anatomy of the tooth.

1818

Factors that govern Endodontic outline form

1 .Size of pulp chamber: .The outline form affected by the size of the pulp

chamber. In young patients, these preparations must be more extensive than in older patients, in whom the pulp has receded

and the pulp chamber is smaller.

.In youngsters teeth the root canals are larger, so they require larger instruments.

1919

2 .Shape of pulp chamber:

.Final outline form should reflect the shape of the pulp chamber.

Examplea. The floor of the pulp chamber in a molar tooth is usually triangular in shape, owing to the triangular position of the orifices of the canals. This triangular shape is extended up the walls of the cavity and out onto the occlusal surface, so the final occlusal cavity outline form is generally triangular.

2020

b. The coronal pulp of a maxillary premolar is flat mesiodistally, but is elongated buccolingually. The outline form is, an elongated oval that extends buccolingually rather than mesiodistally, as does Blacks operative cavity

preparation.

2121

3 .Number, position and carveture of the root canals.

.To prepare each canal efficiently without interference, the cavity walls often have to be extended to allow unstrained

instrument approach to apical foramen.

2222

Self Study

1 .Convenience form.

2 .III Principle (Removal of remaining carious dentin).

3 .IV Principle Toilet of the cavity.

2323

Endodontic Preparation Of Maxillary Anterior Teeth

A. Access opening is always gained through the lingual surface of all anterior teeth. Initial penetration is made in the exact center (X). Avoid intering the cavity too far gingivally.

B. Enterance is prepared with a round – point tapering fissure bur in high – speed handpice, operated at a right angle to the long axis of the tooth. At this step only enamel is penetrated. Don’t apply any pressure.

2424

C. Convenience extension toword the incisal continues the initial penetrating. Enamel and dentin are beveled toward the incial – Entrance into the pulp chamber should not be made with a high – speed

handpice.

D. The outline is fanned incisally with a fissure bur, a "nest" is prepared in the dentin to receive the round bur to be

used in penetration.

2525

E. A surgical – length No 2 or 4 round bur in low – speed is used to penetrate the pulp chamber. Take advantage of convenience extension toward the incisal to allow for the shaft of the bur, operated nearly

parallel to the long axis.

F. Working from inside the chamber to outside, a round bur is used to remove the lingual and labial walls of the pulp

chamber.

2626

CavityAccess TRIANGULAR SHAPE

(YOUNG TEETH)

2727

G. When the outline is completed, the surgical – length bur is carefully passed into the

canal.

Working from inside to outside, the lingual "shoulder" is removed to provide continuous, smooth – flowing penetration. Often a long, tapering diamond point bur to

be used for this purpose.

2828

H. A No 1 or 2 round bur must be used laterally and incisally to eliminate pulpal horn debris (This will prevent future

discoloration).

I. In a "young" tooth with a large pulp, the outline form reflects a large triangular internal anatomy – an extensive cavity that allows cleansing of the chamber as well as passage of large instruments. Extension incisally provides greater

access to the midline of the canal.

2929

Cavity Access. Canine

Extensive ovoid, funnel-shaped coronal preparation

3030

J. In "adult" teeth with the chamber obturated with secondary dentin, are avoid in shape. The difficalty is to reach to this depth with a round bur. Therefore, when the X – Ray reveals advanced pulpal recession, convenience extension must be advanced further incisally to allow the bur shaft to operate

in the central axis.

3131

K. Final preparation with the reamer. The shaft clears the incisal cavity margin and reduced lingual "shoulder", providing good approach to the apical third of the canal. An optimal, round, tapered cavity

may be prepared in the apical third.