Access Cavity Preparation Lecture Notes PDF

By Dr. Einas Osman Sharfi BDS, MSc U of K introduction  A successful outcome in endodontic treatment essentially depends on three factors: Ø 1) cleaning and shaping Ø 2) disinfection Ø 3) three-dimensional obturation of the root canal system. introduction  However, there is one other step...

By Dr. Einas Osman Sharfi BDS, MSc U of K introduction  A successful outcome in endodontic treatment essentially depends on three factors: Ø 1) cleaning and shaping Ø 2) disinfection Ø 3) three-dimensional obturation of the root canal system. introduction  However, there is one other step that precedes these three.  An error in this preliminary step would compromise all subsequent work. introduction  This preliminary step is the preparation of the access cavity,  the opening in the dental crown that permits localization, cleaning, shaping, disinfection, and three-dimensional obturation of the root canal system. Objectives 1. Remove all caries when present, 2. Conserve sound tooth structure, 3. De-roof the pulp chamber completely, 4. Remove all coronal pulp tissue (vital or necrotic), 5. Locate all root canal orifices, and 6. Achieve straight- or direct-line access to the apical foramen or to the initial curvature of the canal. PRE OPERATIVE ASSESSMENT  An assessment of the following features can be made after visual examination of the tooth, and study of a pre-operative periapical radiograph taken with a paralleling technique: PRE OPERATIVE ASSESSMENT 1. The number of canals present. 2. The length, direction and degree of curvature of each canal. 3. Any branching or division of the main canals. 4. The relationship of the canal orifice(s) to the pulp chamber and to the external surface of the tooth. PRE OPERATIVE ASSESSMENT 5. The presence and location of any lateral canals. 6. The position and size of the pulp chamber and its distance from the occlusal surface. 7. Any related pathology.  Before beginning the access cavity preparation, it is wise to check the depth of the preparation by aligning the bur and handpiece against the radiograph, The stages of access cavity preparation 1. The initial entry is made with a tungsten carbide or diamond bur in a turbine handpiece and the outline form completed as required.  The bur is advanced towards the pulp horns until the roof of the pulp chamber is just penetrated.  round diamond burs round carbide burs fissure carbide bur Round-end cutting tapered diamond bur 2. At this point, the rubber dam should be applied if it is not already in place.  The use of a rubber dam is almost mandatory in modern endodontic practice for three reasons:  Firstly, it provides an aseptic operating field, isolating the tooth from oral and salivary contamination.  Secondly, rubber dam facilitates the use of the strong medicaments necessary to clean the root canal system.  Finally, it protects the patient from the inhalation or ingestion of endodontic instruments. 3. The removal of the entire roof of the pulp chamber, and the tapering of the walls, is now carried out with a safe-tipped endodontic access bur, 4. The walls of the pulp chamber may now be gently flared out towards the occlusal surface. 5. Any remaining pulp tissue and debris is cleared with an excavator from the floor of the pulp chamber and the canal orifices 6. The access cavity should be flushed with a solution of sodium hypochlorite to remove any residual debris. 7. The canal orifices may be located with endodontic probe. 8. Once the canal orifices have been identified, the preparation of the coronal part of the root canals should be commenced. 9. Any alteration to the access cavity outline form may now be undertaken to ensure a direct line of approach to the canal orifices.  It can only be repeated that access is success. Anterior Teeth 1. External Outline Form  Removal of caries and restorations and establishing sound tooth margins,  an initial external outline opening is cut on the lingual surface of the anterior tooth  An outline form is developed that is similar in geometry to an ideal access shape for the particular anterior tooth.  The bur is directed perpendicular to the lingual surface as the external outline opening is created X 2. Penetration of the Pulp Chamber Roof  Continuing with the same round or tapered fissure bur, the angle of the bur is rotated from perpendicular to the lingual/palatal surface to parallel to the long axis of the root  Penetration into the tooth continues along the root’s long axis until the roof of the pulp chamber is penetrated; frequently, a drop into the chamber effect is felt when this occurs. 3. Removal of the Chamber Roof  Once the pulp chamber has been penetrated, the remaining roof is removed by catching the end of a round bur under the lip of the dentin roof and cutting with outward stroke. 4. Removal of the Lingual Shoulder and Coronal Flaring of the Orifice  Once the orifice or orifices have been identified and confirmed, the lingual shoulder or ledge is removed.  This is a shelf of dentin that extends from the cingulum to a point approximately 2 mm apical to the orifice  Its removal improves straight-line access and allows for more intimate contact of files with the canal’s walls for effective shaping and cleaning. Lingual shoulder  In addition, its removal from mandibular anterior teeth may often expose an extra orifice and canal.  flaring the orifice involves the use of : Ø Gate glidden burs Ø safety-tip diamond bur Ø Or rotary nickel-titanium (NiTi) orifice openers 5. Straight-Line Access Determination  Ideally, a small intracanal file can reach the apical foramen or the first point of canal curvature with no deflections.  Without straight-line access, procedural errors (e.g., ledging, transportation, and zipping) may occur. Deflected instrument 6. Visual Inspection of the Access Cavity  Appropriate magnification and illumination should be used to inspect and evaluate the completed access cavity. 7. Refinement and Smoothing of Restorative Margins  The final step in the preparation of an access cavity is to refine and smooth the cavosurface margins. Access cavity for individual anterior teeth Maxillary Central Incisor  The external access outline form for the maxillary central incisor is a rounded triangle with its base toward the incisal aspect Maxillary Lateral Incisor  The external access outline form for the maxillary lateral incisor may be a rounded triangle or an oval, depending on the prominence of the mesial and distal pulp horns. Maxillary Canine  The external access outline form is oval or slot shaped because no mesial or distal pulp horns are present Mandibular Central and Lateral Incisors  The mandibular incisors, because of their small size and internal anatomy, may be the most difficult access cavities to prepare. Mandibular canine  The access cavity for the mandibular canine is oval or slot shaped (similar to maxillary canine) Posterior Teeth 1. External Outline Form  Removal of caries and existing restorations from a posterior tooth requiring a root canal procedure often results in the development of an acceptable access outline form.  However, if the tooth is intact, the access starting location must be determined for an intact tooth.  in maxillary premolars, the point of entry that determines the external outline form is on the central groove between the cusp tips X  Crowns of mandibular premolars are tilted lingually relative to their roots therefore, the starting location must be adjusted to compensate for this tilt.  In mandibular first premolars, the starting location is halfway up the lingual incline of the buccal cusp on a line connecting the cusp tips.  Mandibular second premolars require less of an adjustment because they have less lingual inclination.  To determine the starting location for molar access cavity preparations, the clinician must establish the mesial and distal boundary limitations  The mesial boundary for both the maxillary and mandibular molars is a line connecting the mesial cusp tips. Pulp chambers are rarely found mesial to this imaginary line.  A good initial distal boundary for maxillary molars is the oblique ridge.  For mandibular molars, the initial distal boundary is a line connecting the buccal and lingual grooves. Maxillary molar Mandibular molar  The final outline shape for molars is approximately triangular (for three canals)  or rhomboid (for four canals);  however, the canal orifices dictate the position of the corners of these geometric shapes.  Therefore, until the orifices have been located, the initial outline form should be left as roughly oval. 2. Penetration of the Pulp Chamber Roof  Once initial penetration into the pulp chamber has been achieved, the angle of penetration changes from perpendicular to the occlusal table to an angle appropriate for penetration through the roof of the pulp chamber.  In premolars the angle is parallel to the long axis of the root or roots  In molars the penetration angle should be toward the largest canal because the pulp chamber space usually is largest just occlusal to the orifice of this canal.  Therefore, in maxillary molars, the penetration angle is toward the palatal orifice, and in mandibular molars, it is toward the distal orifice 3. Removal of the Chamber Roof  The bur of choice is used to remove the roof of the pulp chamber completely, including all pulp horns  The goal is to funnel the corners of the access cavity directly into the orifices, and a safety-tip diamond or carbide bur performs this task nicely. A, Pulp roof/pulp horn removal. The round bur hooks under the lip of the pulp horn. A B, The bur is rotated and withdrawn in an occlusal C direction to remove the lip. C, Removal of a cervical dentin bulge. A Gates-Glidden bur is placed just apical to the orifice and withdrawn in a distoocclusal direction. B D, A safety-tip tapered diamond bur is used to blend D and funnel the axial wall from the cavosurface margin to the orifice. 4. Identification of All Canal Orifices  Ideally, the orifices are located at the corners of the final preparation to facilitate all of the root canal procedures  Internally, the access cavity should have all orifices positioned entirely on the pulp floor and should not extend into an axial wall. 5. Removal of the Cervical Dentin Bulges and Orifice and Coronal Flaring  The cervical bulges are shelves of dentin that frequently overhang orifices in posterior teeth, restricting access into root canals  These bulges can be removed with safety-tip diamond or carbide burs or Gates Glidden burs  The instruments should be placed at the orifice level and leaned toward the dentin bulge to remove the overhanging shelf 6. Straight-Line Access Determination  Files must have unimpeded access to the apical foramen or the first point of canal curvature to perform properly. 7. Visual Inspection of the Pulp Chamber Floor  The floor and walls must be inspected, using appropriate magnification and illumination, to ensure that all canal orifices are visible and no roof overhangs are present 8. Refinement and Smoothing of the cavity Margins  In both temporary and interim permanent restorations, the restorative margins should be refined and smoothed to minimize the potential for coronal leakage. Maxillary First Premolar  The access preparation for the maxillary first premolar is oval or slot shaped  The palatal orifice is slightly larger than the buccal orifice.  The buccal extension typically is two thirds to three fourths up the buccal cusp incline. The palatal extension is approximately halfway up the palatal cusp incline. Maxillary First Premolar Access cavity for a maxillary first premolar as viewed through the dental operating microscope. Maxillary Second Premolar  When two canals are present in this tooth, the maxillary second premolar access preparation is nearly identical to that of the first premolar.  If only one canal is present, the buccolingual extension is less Maxillary Second Premolar Access cavity for a maxillary second premolar as viewed through the dental operating microscope Maxillary First Molar  The pulp chamber’s cervical outline form has a rhomboid shape, sometimes with rounded corners.  The mesiobuccal angle is an acute angle; the distobuccal angle is an obtuse angle; and the palatal angles are basically right angles.  B D M P Maxillary First Molar  The palatal canal orifice is centered palatally; the distobuccal orifice is near the obtuse angle of the pulp chamber floor; and the main mesiobuccal canal orifice is buccal and mesial to the distobuccal orifice and is positioned within the acute angle of the pulp chamber. Maxillary First Molar  The second mesiobuccal canal orifice (MB-2) is located palatal and mesial to the mesiobuccal orifice.  Because the maxillary first molar almost always has four canals, the access cavity has a rhomboid shape, with the corners corresponding to the four orifices  B M D P Maxillary Second Molar  The maxillary second molar closely resembles the maxillary first molar  Four canals are less likely to be present in the second molar than in the first molar.  The three main orifices (MB, DB, and P) usually form a flat triangle and sometimes almost a straight line  When four canals are present, the access cavity preparation of the maxillary second molar has a rhomboid shape and is a smaller version of the access cavity for the maxillary first Molar  If only three canals are present, the access cavity is a rounded triangle with the base to the buccal. DB MB P Mandibular First Premolar  The oval external outline form of the mandibular first premolar typically is wider mesiodistally than its maxillary counterpart, making it more oval and less slot shaped  Because of the lingual inclination of the crown, buccal extension can nearly approach the tip of the buccal cusp to achieve straight-line access.  Lingual extension barely invades the poorly developed lingual cusp incline.  Mesiodistally the access preparation is centered between the cusp tips. L B Mandibular Second Premolar  The access cavity form for the mandibular second premolar varies in at least two ways in its external anatomy.  First because the crown typically has a smaller lingual inclination, less extension up the buccal cusp incline is required to achieve straight-line access.  Second, the lingual half of the tooth is more fully developed, and therefore the lingual access extension typically is halfway up the lingual cusp incline.  Mandibular second premolars require less of an adjustment because they have less lingual inclination. L B Mandibular First Molar  The access cavity for the mandibular first molar typically is trapezoid or rhomboid regardless of the number of canals present.  When four or more canals are present, the corners of the trapezoid or rhombus should correspond to the positions of the main orifices.  Mesially the access need not invade the marginal ridge.  Distal extension must allow straight-line access to the distal canal(s).  The mesial canal orifices usually are well separated within the main pulp chamber and connected by a developmental groove.  The MB orifice commonly is under the mesiobuccal cusp,  whereas the ML orifice generally is found just lingual to the central groove.  On occasion an MM canal orifice is present in the groove between the MB and ML orifices  When only one distal canal is present, the orifice is oval buccolingually and the opening generally is located distal to the buccal groove.  This orifice usually can be explored from the mesial with either an endodontic explorer or a small K-file.  If the file tip takes a sharp turn in a distobuccal or distolingual direction, the clinician should search for yet another orifice. D M Mandibular Second Molar  Mandibular second molars may have one to six canals, although the most prevalent configurations are two, three, and four canals.  When three canals are present, the access cavity is similar to that for the mandibular first molar.  The second molar may have only two canals, one mesial and one distal, in which case the orifices are nearly equal in size and line up in the buccolingual center of the tooth.  The access cavity for a two-canal second molar is rectangular, wide mesiodistally and narrow buccolingually. Two canals Three canals Guidlines to determine the number and location of orifices on the chamber floor  Centrality: Ø The floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ.  Concentricity: Ø The walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ; that is, the external root surface anatomy reflects the internal pulp chamber anatomy.  Location of the CEJ: Ø The distance from the external surface of the clinical crown to the wall of the pulp chamber is the same throughout the circumference of the tooth at the level of the CEJ.  Symmetry: Ø Except for the maxillary molars, canal orifices are equidistant from a line drawn in a mesiodistal direction through the center of the pulp chamber floor.  Color change: Ø The pulp chamber floor is always darker in color than the walls.  Orifice location: Ø The orifices of the root canals are always located at the junction of the walls and the floor. Errors in access cavity preparation  Unfortunately , errors can occur in the preparation of an access cavity  Most are the result of failure to follow the access guidelines; others reflect a lack of understanding of the internal and external tooth morphology Thanks