Annotation to the lesson №2,3 Topic: Endodontic instruments, its application. Methodic of preparing pulp access cavities in mandibular teeth. Endodontics is the branch of clinical dentistry associated with the prevention, diagnosis and treatment of the pathosis of the dental pulp and their sequelae. Aims and objectives of the endodontic therapy are:

1. Diagnosis of various pulpal diseases. 2. To identify various etiological factors for pulpal and periapical diseases. 3. Maintain vitality of the pulp. 4. Preserve and store the tooth with damaged and necrotic pulp. 5. Preserve and restore the teeth which have failed to the previous endodontic therapy, to allow the tooth to remain functional in the dental arch.

1. Endodontic instruments and their types. ISO-FDI (Federation Dentaire International) grouped root canal instruments according to their method of use: Group I : Hand use only, for example K and H-files, reamers, broaches, etc. Group II : Latch type Engine driven: Same design as group I but can be attached to hand piece. Group III : Drills or reamers Latch type Engine driven, for example Gates- Glidden, Peeso reamers. Group IV : Root Canal points like gutta-percha, silver point, paper point.

Motions of Instrumentation – Also referred to as envelops of motion 1. Filing motion - push and pull action 2. Reaming motion - clockwise or right hand rotation 3. Turn and pull - combination of reaming and filing 4. Watch winding - back and forth oscillation of a file and left as the instrument is being pushed forward into the canal 5. Watch winding and pull - used with H-file 6. Balanced force instrumentation: - Most efficient to cut dentine - Positioning and preloading the instrument through a clockwise rotation and than shaping the canal with counter clockwise rotation

2. Standardization principles of instruments.

Fig. 1. Diagrammatic representation of an endodontic instrument

All manufacturers make their brand of instruments according to a standard or specification for root canal instruments as determined by standardization organizations. The numbering of the instruments is identical with the diameter of the instruments at their tip (D1) expressed in hundredths of a millimeter (Fig. 1). Thus, no. 40 instrument has a diameter at the tip (D1) of 40/100 mm, which is 0.4 mm. The standardized instruments are manufactured in numbers or sizes from 10–150. In the sizes 10–60 there is an instrument for each 5/100 mm increment at Dl, whereas from size 60 and above the increment is 10/100 mm. K-type instruments are available in a size 8 as well. The standardized instruments are made in lengths of 21, 25, and 31 (30) mm. However, the length of the part of the blade with cutting flutes is always the same, namely 16 mm. Also, the flare of the blade is always the same regardless of the size of the instrument. Thus, the diameter of the blade where the cutting flutes end (D2) is the diameter at the tip (D1) plus 0.32 mm. This means that the taper of the instruments is 0.02 mm per mm. The manufacturing tolerance is 0.02 mm. Accordingly, the diameter of two instruments with the same number may vary as much as 0.04 mm. The colors white, yellow, red, blue, green, and black are used on the handles of the instruments to indicate their size. Since originally instrument no. 15 was the smallest instrument, the standardized color coding begins at this size. Thus, no. 15 instruments are white, no. 20 yellow, no. 25 red, no. 30 blue, no. 35 green, and no. 40 are black. No. 45 instruments have white handles again, and the color coding is repeated. In addition, no. 10 instruments have purple-colored and no. 8 instruments have silver-colored (grey) handles (Fig. 2).

All instruments for preparing canals come from three basic forms: K-reamer, K- file, and Hedstrom file.

3. K – files. Methods of use.  It is square in cross section, manufactured from stainless steel wire, which is grounded into desired shape. (Fig. 3)  Tighter twisting of the file spirals increases the number of flutes in file. Functions:

- To clean inside walls of canal - To contour inner walls of canal

Files are predominantly used

Fig. 3. Diagrammatic representation of K – file. with filing or rasping action in which there is little or no rotation in the root canals. It is placed in root canal and pressure is exerted against the canal wall and instrument is withdrawn while maintaining the pressure.

H-files (Hedstrom file). Methods of use  Hedstrom files have flutes which resemble successively triangles set one on another (Fig.4).  • Hedstrom files cut only when instrument is withdrawn because its edges face the handle of the instrument.  When used in torquing motion, their edges can engage in the dentin of root canal wall and causing H-files Fig. 4. Diagrammatic representation of H – file. to fracture.  Since they lack the flexibility and are fragile in nature, the H-files tend to fracture when used in torqueing action.

4. K – reamers.  Twisted triangular cutting edge (similar to K-type file, but cutting edge is farther apart and has fewer twists per millimeter). Triangular cross sectioned files show superior cutting and increased flexibility than the file with square blank (Fig. 5).  Used with twisting motion  Handles—Color coded according to size  Range of sizes—To accommodate width of canal; diameter increases with size  Available in different lengths

Fig. 5. Diagrammatic representation of K – reamer.

Broach.  Broaches are manufactured from round wires, smooth surface of which has been notched to form barbs (Fig. 6)  They are specifically designed to remove the pulp.  Broach does not cut the dentin but can effectively be used to remove cotton or paper points which might have lodged in the canal.  !!!For single use only!!!

Fig. 6. Diagrammatic picture of broach.

Technique of Pulp Extirpation (Healey, 1984) Irrigate the canal with 5.2% solution of sodium hypochlorite ↓ Penetrate the barbed broach along the canal wall towards the apex ↓ As it reaches to the apical constriction, move it into the center of mass of pulp tissue ↓ Rotate the broach several times in a watch winding manner to entrap the pulp which is then withdrawn from the canal.

Engine – driven instruments. Gates-Glidden Burs 1. Traditional engine driven instruments include Gates- Glidden drills which have flame shaped cutting point mounted on long thin shaft attached to a latch type shank (Fig.7). 2. Gates-Gliddens are available in a set from 1 to 6 with the diameters from 0.5 to 1.5 mm. 3. Due to their design Gates-Glidden drills are side cutting instruments with safety tips. 4. If its cutting tip jams against the canal wall, fracture should occur at the junction of shank and the shaft but not at the tip of the instrument. This makes the easy removal of fractured drill from the canal.

Fig. 7. Gates – glidden burs.

Peeso Reamers They are rotary instruments used mainly for post space preparations (Fig. 8). Disadvantages of using peeso reamers are: 1. They don’t follow the canal curvature and may cause perforation by cutting laterally. 2. They are stiff instruments. 3. They have to be used very carefully to avoid iatrogenic errors.

Fig. 8. Peeso Reamers

Access cavity preparation in mandibular incisors, premolars and molars. Preparation of the access cavity is opening through the coronal portion of tooth which allows localization, cleaning, shaping, disinfection and a three dimensional obturation of the root canal system. Objectives: 1. To gain the direct access to the apical foramen. 2. Pulp chamber debridement. 3. Conserve as much sound tooth structure as possible and as consistent with treatment objectives. Before going for access cavity preparation, a study of preoperative periapical radiograph should be done to know: i. Morphology of the tooth. ii. Anatomy of root canal system. iii. Number of canals. iv. Curvature of branching of the canal system. v. Position of apical foramen. vi. Calcification, resorption present if any.

Overall view of possible canal location in mandibular teeth.

Access preparations in mandibular teeth

Mandibular anterior teeth Premolars are opened with a In mandibular molars the have two root canals in up to buccolingually oriented oval- opening should be 25% of cases. A triangular shaped access preparation trapezoidal, usually wider preparation is made from the through the occlusal surface. mesially than distally, and lingual. bordered mesially by the marginal ridge.