Assist prof Dr Emad Farhan Alkhalidi B D

Assist prof. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D. Conservative Department

Access Cavity Preparation Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation 1. The objective of entry is to give direct access to the apical foramina, not merely to the canal orifices. Since it is the apical foramen of each canal that must be sealed, the access cavity must allow for removal of any tooth structure that might impede the preparation and filling of that area. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation 2. Access cavity preparation are different from typical operative occlusal preparations. The typical occlusal cavity preparations used in operative dentistry are based on the topography of occlusal grooves, pits and fissures and on the avoidance of underlying pulp. The access cavity preparations for endodontic therapy are designed for efficiently uncovering the roof of the pulp chamber and providing direct access to the apical foramina by way of the pulp canals. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation 3. The likely interior anatomy of the tooth under treatment must be determined. Each tooth has a typical length, number, and configuration of roots and canals. Before starting the access, radiographs taken from at least two different angles must be studied. This information gained before initiation of preparation will greatly facilitate the entry as well as further treatment. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation 4. When canals are difficult to find, the rubber dam should not be placed until correct location has been confirmed. It is often difficult to prepare access in a malposed tooth or one that is part of a bridge or splint. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation The occlusal anatomy, which ordinarily gives excellent clues to the position of the underlying canals, may be considerably altered. Teeth with large and / or deep restorations causing heavy dentinal sclerosis also may cause problems. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation Therefore it is best to make the initial portion of the access preparation before the placement of the rubber dam so that the shape and inclination of the adjacent teeth, the gingival tissues, and the hard structures covering the roots are of aid in determining the position of the canals. If the tooth to be treated is part of a bridge or splint, water spray may be used to keep the adjacent abutments from overheating until the gold is penetrated. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation 5. Endodontic entries are prepared through the occlusal or lingual surface – nerve through the proximal or gingival surface. To be conservative, the dentist may elect to perform endodontic therapy through an already existing proximal or gingival restoration or carious lesion. When proximal or gingival tooth destruction occurs, affected areas should be excavated and restored, with either a temporary seal or a permanent filling material. Then the normal access is prepared through the occlusal or lingual surface. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for proper access preparation 6. As part of the access preparation, the unsupported cusps of posterior teeth must be reduced. Endodontic therapy requires the removal of much of the central portion of the treated tooth, greatly reducing resistance to stress. Although this problem is solved by the placement of a proper restoration after treatment, the tooth is severely weakened until that time. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• Therefore, as part of access preparation, all unsupported cusps must be reduced by trimming with a tapered fissure carbide or diamond stone until a definite clearance in occlusal and lateral movement is obtained. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Rules for Access Cavities Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Removal of roof • The first step is to locate and remove the entire roof of the pulp chamber so that its walls are continuous with the access cavities. • Any pulpal remnants left in the pulp chamber will break down and cause the crown of the tooth to discolour. • In addition, during preparation of the canal the debris left in the pulp chamber may be pushed down the canal by instrumentations and cause infection. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Direct line access • The shape of the access cavity should be cut so that the coronal walls do not deflect instrumentations during root canal preparation. • Access should be in a direct line with the apical third of the root canal. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• The radiograph taken from the mesio – distal direction (Figure) shows that direct line access into incisor, canine and mandibular premolar teeth involves the incisal edges and in mandibular premolars the buccal cusp. So as not to compromise with the restoration of the crown of the tooth, the access cavity should be cut close to, but not involving, the incisal edge. • The two photographs (Figures) show a case for overdentures where the crowns of the teeth are to be removed. It is evident that direct line access is on the labial surface. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Avoid damage to floor • Particular care must be taken not to damage the floor of the pulp chamber. The photograph. shows that the floor of the pulp chamber in the molar has been flattened with a bur which makes the location of the canal orifices much more difficult. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Avoid damage to floor • The natural floor tends to guide an instrument into the canal orifice. The floor of the pulp chamber in the mandibular molar is illustrated. • Note the hump in the centre of the floor which deflect the point of an instrument. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Conserve tooth substance • The access should not be made so large that the walls of the tooth will be unnecessarily weakened. The tooth must be capable of being restored. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Resistance form • The access cavity should be beveled to prevent the coronal filling material from being depressed into the tooth and so breaking the seal. The temporary amalgam restoration has been displaced because no bevel was made. The access cavity in the second illustration has been altered to provide resistance form for the filling. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Cutting the Access Cavity Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• Cutting the access cavity may be divided into three stages; locating the pulp chamber with a bur, secondly removing the roof of the pulp chamber, and finally completing the shape of the cavity. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• Stage 1: A tapered tungsten 701 friction grip is used to locate the pulp chamber. In anterior and premolar teeth the bur is held in the main axis of the tooth. If the preoperative radiograph shows a fine canal this stage is carried out before the rubber dam is placed so that the orientation of the tooth is not lost. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

In posterior teeth the handpiece head and bur are held in front of the preoperative radiograph which has been taken with a paralleling technique. The depth and angle of penetration from the occlusal surface may be estimated. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• The initial penetration in posterior teeth is directed towards the main axis of the largest canal, that is the palatal canal in the maxillary teeth and the distal canal in the mandibular teeth. The pulp chamber wil be at its widest in his area. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• Stage 2: A No. 6 round bur in a slow handpiece is used to remove the pulp cornua and remainder of the roof of the pulp chamber. The bur is placed in the pulp chamber and a cutting action used only on the withdrawal stroke so that the roof is lifted off the chamber Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• Stage 3: The access cavity shape is completed using a non – end cutting, tapered, diamond friction grip bur. • It is important to ensure that the walls of the pulp chamber are continuous with the walls of the access cavity and that the cavity is beveled to provide resistance form for the temporary restoration Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Final Shape of Access Cavity Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

• Diagrams and extracted teeth have been used to illustrate the shape of access cavities. In the younger patient the access will tend to be larger and in the older patient it will be smaller. It should be mentioned that the cavities illustrated are classical in outline. In practice many restorations will be removed to prevent contamination of the root canal. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Maxilla Central and lateral incisors • To achieve direct line access to all parts of the canal the cavity will encroach almost onto the incisal edge (Figure 19). The cingulum should be preserved as far as possible as this portion of the tooth is important in providing retention for a jacket crown. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Maxilla Canine: • The cavity is similar to that of the incisors except that the palatal cut involves more of the cingulum. This will allow instrumentation of the bulge in the palatal wall which lies above the cingulum. The buccal extent of the cavity should be almost to the incisal edge. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Maxilla First and second premolars: • The oval outline is similar for both premolar teeth. The buccal and palatal extensions end approximately in the middle of the cuspal slopes. The width of the cavity will be about one third of the mesio – distal width of the occlusal surface. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Maxilla First molar: • The shape is rhomboidal rather than triangular and lies nearer the mesial aspect of the tooth. The mesio – buccal extension of the cavity cuts into the mesio – buccal cusp. Most of the palatal cusp is preserved due to the direction of the palatal canal. The palatal wall is broader as this follows the shape of the pulp chamber. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Maxilla Second molar: • The outline is similar to the first molar except that it is flattened mesio – distally in keeping with the pulp chamber and the occlusal surface of the tooth. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Mandible Central and lateral incisors: • Direct line access would be through the incisal edge and this coupled with the high incidence of two canals means that the access cavity must be wide bucco – lingually and up to the incisal edge. If the tooth is to be crowned following root treatment then the incisal edge may be removed. Note that the cavity is relatively narrow mesio – distally. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Mandible Canine: • Same as central and lateral incisors. The incidence of two canals in mandibular canines is lower than centrals and laterals but still significant Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Mandible Premolars: • The buccal cusp tip lies over the central axis of the tooth so the oval – shaped cavity should lie as far buccally as possible encroaching towards the tip of the buccal cusp. If the tooth is to be cusp – covered following root treatment the access may involve the buccal cusp tip. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Mandible First molar: • The access is rhomboidal in shape lying in the mesial part of the occlusal surface with the bucco – mesial corner of the cavity involving the mesio – buccal cusp. The distal aspect of the access must be wide enough to allow for the high incidence of two canals in the distal root or one broad canal Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.

Mandible Second molar: • The position of the access cavity is similar to the first molar. The distal aspect of the cavity is narrower due to the low incidence of two canals in the distal root. The overall shape is triangular rather than rhomboidal. Dr. Emad Farhan Alkhalidi B. D. S. , M. Sc. , Ph. D.