Coronal Access Cavity Preparation 2018 PDF

2018 Coronal Access Cavity Preparation BY: Dr/Mohamed Samir ENDODONTICS DIVISION BMC 10/1/2018  Coronal Access Cavity Preparation - An old axiom in endodontics states that (what you remove from the root canal is more important than what you place inside). -...

2018 Coronal Access Cavity Preparation BY: Dr/Mohamed Samir ENDODONTICS DIVISION BMC 10/1/2018  Coronal Access Cavity Preparation - An old axiom in endodontics states that (what you remove from the root canal is more important than what you place inside). - The endodontic cavity preparation has been divided into coronal and radicular cavity preparations. The principles of cavity preparation established by G.V.Black have been modified by John Ingle to suit the endodontic cavity preparation.  The objectives of access cavity preparation are to: 1- Permit the removal of all the chamber contents (the endodontic contents from the pulp chamber, its horns and chamber roof). - If the chamber roof is not completely removed, it will not be possible to perform proper cleaning of the pulp horns. There are two consequences:  Contamination or infection of the endodontic space that the dentist is trying to clean.  Discoloration of the endodontically-treated tooth (especially the front teeth). 2- Permit complete and direct vision of the floor of the pulp chamber and canal openings. 3- Facilitate the introduction of canal instruments into the root canal openings. 4- Provide access as direct as possible to the apical one-third of the canal for both preparation instruments and canal filling instruments. 2  5- Provide a positive support for temporary fillings in order to withstand any displacing forces. 6- Always to have four walls. The four walls of the access cavity serve several purposes:  Correct positioning of the rubber dam so that the clamp is stable and the rubber dam isolates the field well.  Keeping the pulp chamber constantly flooded with as much irrigating solution as possible.  Defining easily recognizable, stable reference points for the rubber stops on the endodontic instruments.  Introducing the temporary medication without affecting the interproximal papillae, as would occur if one tried to use the temporary cement to fill a class II cavity.  Principles of coronal access cavity preparation: I- Outline form II- Convenience form III- Removal of remaining carious dentin and defective restorations IV- Toilet of the cavity(Cleansing of the Cavity) 3  I- Outline form: -The external outline form progresses from the internal anatomy of the pulp chamber. That is to say, the external outline form is established by mechanically projecting the internal anatomy of the pulp onto the external surface. -This can be accomplished by drilling into the open space of the pulp chamber and then working with the bur from inside of the tooth to the outside, cutting away the dentin of the pulpal roof as well as the overhanging walls. To achieve proper outline form, three factors must be considered: 1- The size of the pulp chamber 2- The shape of the pulp chamber 3- The number, position, and curvature of individual root canal 1- The size of the pulp chamber: Larger pulp chambers require larger outline forms than smaller pulp chambers. Since the size of the pulp chamber is usually affected by age, younger patients require more extensive outline forms than older patients where pulp recedes. Trauma, extensive caries as well as medications such as calcium hydroxide are other factors that could affect the size of pulp chamber Fig. (1). 2- The shape of the pulp chamber: The finished outline form should accurately reflect the shape of the pulp chamber. For example, the oval shape of the pulp chamber of maxillary first premolar extend up the walls of the cavity on the occlusal surface, hence revealing the final outline form to be oval as seen in Fig. (2). 4  3- The number, position, and curvature of individual root canal: The access cavity walls should be extended enough to expose orifices of all canals present Fig. (3) as well as facilitate the entrance of the instrument into each root canal without interference and allow instrument approach to the apical foramen without strain. Fig. (1) Fig. (1) Fig. (2) 5  Fig. (3) II- Convenience form: It is the form given to the access cavity to improve visibility, instrumentation and obturation of the root canal by providing a straight line access (SLA) from the occlusal surface to the apical foramen. Four important benefits are achieved through the convenience form: 1- Unobstructed access to the canal orifice: Enough structure must be removed to allow instruments to be easily inserted into the orifices of each canal without interference from the overhanging walls. In some cases, the outline form could be modified to facilitate the search for additional canals as lower incisors, premolars, maxillary first molars, and mandibular molars. 6  2- Direct access to the apical foramen: Enough structure must be removed to allow freedom of the instruments within the coronal cavity allowing them to extend down into the canal in an unstrained position. This is especially true in severely curved canals. Occasionally total decuspation could be required. Fig. (4). Fig. (4) 3- Complete authority over the enlarging instrument: If the instrument is interrupted at the canal orifice by tooth structure that should have been removed, the clinician will lose control of the direction of the tip of the instrument that will be directed instead by the intervening tooth structure. On the other hand, removal of enough tooth structure around the orifice allows the instru- ment to be controlled by two factors only; the clinician’s fingers holding the handle of the instrument and the canal walls touching the tip of the installment. Failure to properly modify the access cavity outline will ultimately lead to failure as ledge, root perforation, instrument fracture, improper cleaning, and shaping. 4- Extension to accommodate filling technique: Enough structure must be removed to facilitate the use of obturating instruments 7 as well as the application of various obturation techniques (e.g. softened gutta- percha technique). III- Removal of remaining carious dentin and defective restorations: Carious structure and defective restorations must be removed to prevent obstruction of the orifices by loose pieces of restoration, to reduce mechanically the bacterial population; to eliminate discolored tooth structure as well as to reduce the possibility of bacteria overloaded saliva leaking into the prepared cavity. IV- Toilet of the cavity: All caries, calcified debris and necrotic material should be removed by irrigation from the pulp chamber before radicular preparation is begun to avoid obstruction of the root canals by metallic or calcified debris or increasing bacterial population by infected soft debris. The use of round burs and long blade endodontic spoon excavators, as well as the irrigation with sodium hypochlorite, are excellent measures for cleansing the chamber. The chamber is finally wiped out with cotton. Air blasts must never be aimed down the canals to avoid emphysema of oral tissues. 8  Guidelines For Access Cavity Preparations 1. Visualization of the likely internal anatomy a- Position of the pulp chamber b- Approximate canal length c- Degree of chamber calcification d- Number of roots and canals -This visualization requires evaluation of angled periapical radiographs and examination of tooth anatomy at the coronal, cervical, and root levels. - The clinician uses the information from these assessments to choose the direction of initial bur penetration. 2. Evaluation of the cementoenamel junction and occlusal anatomies - Complete reliance on the occlusal anatomy is dangerous because this morphology can change as the crown is destroyed by caries and reconstructed with various restorative materials. - Cementoenamel junction (CEJ) is the most important anatomic landmark for determining the location of pulp chambers and root canal orifices. 3. Access through lingual and occlusal surfaces - Access cavities on anterior teeth usually are prepared through the lingual tooth surface, and those on posterior teeth are prepared through the occlusal surface. These approaches are the best means of achieving straight-line access and diminishing esthetic and restorative concerns. 9  4. Removal of all defective restorations and caries before entry into the pulp chamber - The clinician must remove all defective restorations before entering the root canal system. With an open preparation, canals are much easier to locate, and shaping, cleaning, and obturation are much easier to perform. - Working through restorations also allows restorative debris to become more easily lodged in the canal system -All carious dentin must be removed during access preparation. This removal prevents irrigating solutions from leaking past the rubber dam into the mouth and prevents carious dentin and its bacteria from entering the root canal system. -Sometimes removal of extensive defective restorations and carious dentin may not leave enough tooth structure for placement of a rubber dam clamp to seal against salivary contamination. A crown lengthening procedure should be performed to correct this situation before the root canal procedure is begun. 5. Removal of unsupported tooth structure - The clinician should remove all unsupported tooth structure to assess restorability and to prevent tooth fracture. Unnecessary removal of sound tooth structure should be avoided. 6. Creation of access cavity walls that do not restrict straight- or direct-line passage of instruments to the apical foramen or Initial canal curvature - Complete clinician control over all enlarging and filling instruments is vital. - Sufficient tooth structure must be removed to allow instruments to be placed easily into each canal orifice without interference from canal walls. 10  -The walls of the root canal, rather than the walls of the access preparation, must guide the passage of instruments down the canal. Failure to follow this guideline results in treatment errors, including root perforation, misdirection of an instrument from the main canal (ledge formation), instrument separation, or creation of an incorrect canal shape (apical transportation). 7. Delay of dental dam placement until difficult canals have been located and confirmed - Difficulty can arise in gaining access into teeth that are crowded and rotated, fractured to the free gingival margin, heavily restored and calcified, or part of a fixed prosthesis. In these situations, the clinician’s best course of action may be to prepare the initial part of the access cavity before placing the dental dam. 8. Location, Flaring, and Exploration of all root canal orifices -A sharp endodontic explorer is used to locate canal orifices and to determine their angle of departure from the pulp chamber. Next, all canal orifices and the coronal portion of the canals are flared to make instrument placement easier. -The canals are then explored with small, pre-curved K-files (#6, #8, or #10). - The clinician must take care to keep these instruments within the confines of the canal system until the working length has been accurately determined. 9. Inspection of the pulp chamber, using magnification and adequate illumination - Magnification and illumination are particularly important in root canal therapy, especially for determining the location of canals; negotiating constricted, curved, and calcified canals and removing tissue and calcifications from the pulp chamber. 11 - Enhanced vision allows the clinician to see internal dentin color changes and subtle landmarks that may not be visible to the unaided eye. Surgical loupes, endodontic endoscopes, 12 and the DOM are some of the commercially available instruments that can help the clinician accomplish these goals. 10. Tapering of cavity walls and evaluation of space adequacy for a coronal seal - A proper access cavity generally has tapering walls with its widest dimension at the occlusal surface. Armamentaria - Magnification and illumination - Handpieces - Burs Fig.(5) -Endodontic explorer (DG-16, DE-17) - Endodontic spoon - #17 operative explorer - Ultrasonic unit and tips. - (No. 2, 4, 6 round carbide, No. 557 carbide, Transmetal , Endo Z bur, and Endo Access bur.) 12 -Mueller burs exhibit a round cutting head attached to a long shank. The long shank is not designed to drill deep into the root but to extend the head of the slow- speed handpiece away from the tooth and permit better visibility. Fig (5) Burs: #2, #4, and #6 round carbide burs Safety-tip tapered diamond bur & safety tip tapered carbide bur -Round carbide burs (sizes #2, #4, and #6) are used extensively in the preparation of access cavities. They are used to remove caries and to create the initial external outline shape. They also are useful for penetrating through the roof of the pulp chamber and for removing the roof. Some clinicians prefer to use a fissure carbide bur ) or a diamond bur with a rounded cutting end to perform these procedures. - Fissure carbide and diamond burs with safety tips (i.e., noncutting ends) (Fig. 5) are safer choices for axial wall extensions. - Round diamond burs (sizes #2 and #4) are needed when endodontic access must be made through porcelain or ceramometal restorations. Diamond burs are less traumatic to porcelain than carbide. - Once the orifices have been located, they should be flared or enlarged and blended into the axial walls of the access cavity. This process permits the intracanal instruments used during shaping and cleaning to enter the canal(s) easily 13 and effortlessly. Gates-Glidden burs can be used for this purpose, starting with smaller sizes and progressing to the larger sizes. Fig (6) Fig(6 )Gates-Glidden burs Anterior Access Cavity Preparations After visualization of the likely internal anatomy and evaluation of the cementoenamel junction. 1. Removal of Caries and Permanent Restorations - Caries typically is removed early, before the pulp chamber is entered. -This is to minimize the risk of contamination of the pulp chamber or root canal with bacteria. -To prevent coronal leakage from contaminating the pulp chamber, the root canal(s), or both after the endodontic appointment. - Permits straight-line access and prevents restorative fragments from becoming lodged in the root canal system. - evaluate restorability. 14 NB: Clinicians were about 40% more likely to miss fractures, caries, and marginal breakdown if restorations were not completely removed. 2. Initial External Outline Form Once caries and restorations have been addressed, the clinician creates an initial external outline opening on the lingual surface of the anterior tooth. 1. Begin in the center 2. #2 or #4 round bur or tapered fissure bur is used to penetrate through enamel and 1mm into the dentin 3. Create outline form: - For the incisors, the outline form of the cavity is triangular in shape with its base towards the incisal edge and its apex towards the cingulum. For the canines, the outline form is oval in shape in an inciso-gingival direction. - The cavity extends between the two marginal ridges. - The lingual/palatal surface is divided into 3 thirds and the initial penetration is carried out in the center of the middle third just above the cingulum Fig. using a round carbide bur #2 at a right angle to the long axis of the tooth until the enamel is penetrated and dentin is reached. Fig. (7). - It is one half to three quarters the projected final size of the access cavity. 15  Fig. (7) Initial External Outline Form 3. Penetration of the Pulp Chamber Roof Fig. (8). 1. High speed/ low speed. 2. Round or tapered fissure bur. 3. Change the angle to parallel to the long axis of the root. 4. Drop-in effect is felt. 5. If the drop-in effect is not felt at this depth, the clinician should evaluate the situation carefully to prevent a gouge or perforation. The depth and angle of penetration should be assessed for any deviation away from the long axis of the root in both the mesiodistal and buccolingual dimensions, and the penetration angle should be realigned if necessary. If all looks good, the clinician should probe the access opening with an endodontic explorer. 16  Fig. (8) 4. Complete Roof Removal Fig. (9) - Deroofing i.e. complete removal of the roof of the pulp chamber is then carried out using a round bur or a tapered stone with round end or Endo Z bur. -The instrument is held parallel to the long axis of the tooth while cutting on withdrawal i.e. working from inside the chamber to the outside without applying any pressure. - In vital cases, pulp tissue hemorrhage can impair the clinician’s ability to see the internal anatomy. In such cases, as soon as enough roof has been removed to allow instrument access, the coronal pulp should be amputated at the orifice level with an endodontic spoon or round bur. - Complete roof removal is confirmed with a #17 operative explorer if no “catches” are discovered as the explorer tip is withdrawn from the pulp chamber along the mesial, distal, and facial walls. 17  Fig. (9) 5. Identification of all Canal Orifices The cavity is then irrigated with sodium hypochlorite 2.5% to flush away the debris. The endodontic explorer can be used to detect any overhanging walls that should be then removed till the explorer can be freely placed into the canal. 6. Removal of the Lingual Shoulder and Orifice and Coronal Flaring A lingual projection of dentin (lingual shoulder) corresponding to the lingual cingulum (to a point approximately 2 mm apical to the orifice) is a common feature in anterior teeth. Fig. (10 a) The removal of this shoulder would provide a smooth transition between the pulp chamber and the canal. Its removal aids straight-line access. The lingual shoulder can be removed with a tapered safety tip diamond or carbide bur. 18  The tip of a fine safety-tip diamond bur is placed approximately 2 mm apical to the canal orifice and inclined to the lingual during rotation to slope the lingual shoulder. The clinician must be careful when using this bur to avoid placing a bevel on the incisal edge of the access preparation Fig. (10 b) When Gates-Glidden burs are used, the largest that can passively be placed 2 mm apical to the orifice is used first. Fig. (10) Lingual shoulder (a) & incisal bevel (b) a b 7. Straight-Line Access Determination Fig. (11) Straight-line access is evaluated by inserting into the canal the largest file that fits passively to the apical foramen or the point of the first canal curvature. 19  -The final position of the incisal wall of the access cavity is determined by two factors: (1) Complete removal of the pulp horns (2) Straight-line access. Fig. (11) Straight-line access 8. Visual Inspection of the Access Cavity The axial walls at their junction with the orifice must be inspected for grooves that might indicate an additional canal. The orifice and coronal canal must be evaluated for a bifurcation. 20 9. Refinement and Smoothing of Restorative Margins The final step in the preparation of an access cavity is to refine and smooth the cavosurface margins. Rough or irregular margins can contribute to coronal leakage through a permanent or temporary restoration. - Definite, smooth cavosurface margins allow the clinician to place and finish a composite resin final restoration with the precision necessary to minimize coronal leakage. Posterior Access Cavity Preparations 1. Removal of Caries and Permanent Restorations 2. Initial External Outline Form 3. Penetration of the pulp chamber roof 4. Complete roof removal 5. Identification of all canal orifices 6. Removal of the cervical dentin bulges and orifice and coronal flaring 7. Straight-line access determination 8. Visual inspection of the pulp chamber floor 9. Refinement and smoothing of the restorative margins 1- Removal of Caries and Permanent Restorations The discussion of caries and permanent restoration removal presented in the previous section, Anterior Access Cavity Preparations, applies equally to posterior teeth. 21  2 - Initial External Outline Form  Premolars (Fig. 12) -In maxillary premolars, the point of entry is on the central groove between the cusp tips (Fig.12 A). - Crowns of mandibular premolars are tilted lingually relative to their roots, and 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. (Fig.12 B) - Mandibular second premolars require less of an adjustment because they have the less lingual inclination. The starting location for this tooth is one third the way up the lingual incline of the buccal cusp on a line connecting the buccal cusp tip and the lingual groove between the lingual cusps. (Fig.12 C) A B C (Fig. 12 A,B,C) Access starting location 22   Molars (Fig. 13) - Establish the mesial and distal boundary limitations: (Fig. 13) 1-The initial distal boundary for maxillary molars is the oblique ridge 2- The initial distal boundary for and mandibular molars is a line connecting the buccal and lingual grooves. 3- The mesial boundary for both the maxillary and mandibular molars is a line connecting the mesial cusp tips.  Armamentaria #2 round bur for premolars #4 round bur for molars -The bur is directed perpendicular to the occlusal table, and an initial outline shape is created at about one half to three fourths its projected final size. -The premolar shape is oval and widest in the buccolingual dimension. -The molar shape is also oval initially; it is widest in a buccolingual dimension for maxillary molars and in a mesiodistal direction for mandibular molars. -The final outline shape for molars is triangular (for three canals) or rhomboid (for four canals) 23  MAX MOLARS MAND MOLARS MB cusp tip MB B MP ML cusp tip Access starting location Fig. (13) 3. Penetration of the Pulp Chamber Roof (Fig. 14) -Continuing with the same round or tapered fissure bur -In premolars, the angle is parallel to the long axis of the root(s) both in the mesiodistal and buccolingual directions. -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. (Fig. 14) - As with anterior teeth, penetration is limited to the distance measured on a pretreatment radiograph to just penetrate the roof of the pulp chamber. If the drop- 24 in effect is not felt at this depth, the clinician should carefully evaluate the angle of penetration before drilling deeper. 4. Complete Roof Removal -A round bur, a tapered fissure bur, or a safety-tip diamond or carbide bur 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; it can be set on the pulp floor and the entire axial wall shaped at one time with little chance of gouging (Fig.15). -The safety-tip diamond or carbide bur is passed between the orifices along the axial walls to remove the roof, taper the internal walls, and create the desired external outline shape simultaneously. (Fig.15) 5. Identification of all Canal Orifices - Ideally, the orifices are located at the corners of the final preparation to facilitate the shaping and cleaning process. Internally, the access cavity should have all orifices positioned entirely on the pulp floor and should not extend into an axial 25 wall. Extension of an orifice into the axial wall creates a mouse hole effect (Fig.16A,B). A B (Fig.16) A Mouse hole effect caused by extension of the orifice into the axial wall. B, Orifice that lies completely on the pulp floor. Laws of Access Cavity Preparation for Locating Canal Orifices Law of Centrality Law of Cementoenamel Junction Law of Concentricity Law of Color Change Law of Symmetry Law of Orifice Location Law of Centrality - The floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ. 26  Law of Cementoenamel Junction - 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, making the CEJ is the most consistent repeatable landmark for locating the position of the pulp chamber. Law of Concentricity - 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. Law of Color Change -The pulp chamber floor is always darker in color than the walls. Law of Symmetry - Canal orifices are equidistant from a line drawn in a mesiodistal direction through the center of the pulp chamber floor - Canal orifices lie on a line perpendicular to a line drawn in a mesiodistal direction across the center of the pulp chamber floor. NB: -Except for maxillary molars. 27  Law of Orifice Location -The orifices of the root canals are always located at the junction of the walls and the floor. -The orifices of the root canals are always located at the angles in the floor–wall junction. 6. Removal of the cervical dentin bulges and orifice and coronal flaring (Fig.17) -In posterior teeth, the internal impediments are the cervical dentin bulges and the natural coronal canal constriction. -The cervical bulges are shelves of dentin that frequently overhang orifices in posterior teeth, restricting access into root canals and accentuating existing canal curvatures. -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. (Fig.17) 28 7. Straight-line access determination -Files must have unobstructed access to the apical foramen or the first point of canal curvature to perform properly during shaping and cleaning. The clinician must assess each canal for straight-line access and make all adjustments necessary to achieve this goal. 8. Visual inspection of the pulp chamber floor - As discussed in anterior teeth 9. Refinement and smoothing of the restorative margins -In both temporary and interim permanent restorations, the restorative margins should be refined and smoothed to minimize the potential for coronal leakage. - The final permanent restoration of choice for posterior teeth that have undergone root canal therapy is a crown or onlay. 29  Consequences Errors during endodontic access cavity preparation in maxillary and mandibular anteriors: The following errors could occur during access preparation in anterior teeth (Fig. 18): 1 - Gouging of the labial wall due to failure to notice the lingual axial inclination of anterior teeth. 2- Gouging of the distal wall due to failure to notice the mesial axial inclination of anterior teeth 3- Labiocervical perforation due to lack of convenience extension incisally. 4-Ledge due to underextension and incomplete authority over the instruments due to insufficient convenience extension. 5-Missed canal due to insufficient convenience extension. 6-Discoloration caused by failure to completely remove pulp debris and necrotic Fig.(18) tissue due to incisal underextension of the cavity. 30  Errors during endodontic access cavity preparation in maxillary and mandibular premolars: Fig. (19) 1- Perforation at the mesio-cervical region due to failure to recognize the distal axial inclination of the tooth. 2- Underextended preparation exposing only the pulp horns due to lack of knowledge about the position of the floor of the pulp chamber. The light color of dentin is a clue to a shallow cavity. 3- Overextended preparation could be due to searching for canal orifices and failure to recognize the recessed pulp in the preoperative radiograph. 4- Failure to explore, and obturate a second canal due to under extended cavity or lack of knowledge of anatomy. 5- A fractured instrument as a result of the loss of instrument control due to lack of sufficient convenience extension. Fig. (19) 31 Errors during endodontic cavity preparation in maxillary and mandibular molars Fig. (20) A- Underextended preparation where only pulp horns have been exposed. The entire pulpal roof is unremoved due to lack of knowledge of the difference between the floor of the pulp chamber and the dentinal roof with its lighter color indicating a shallow cavity. B- Furcal perforation due to failure to notice the narrow pulp chamber or applying pressure during deroofing. C- Overextended preparation and gouging of the crown due to failure to observe pulp recession in the pre-operative radiograph. D- Perforation at the mesio-cervical region in lower molars caused by failure to orient the bur parallel with the long axis. E- Missed canal due to underextended endodontic cavity preparation leaving part of pulpal roof unremoved. F- Ledge due to the underextended cavity. 32  Fig. (20) Perforation -Perforation of the mesial tooth surface caused by failure to recognize that the tooth is tipped and failure to align the bur with the long axis of the tooth. - Labial perforation caused by failure to extend the preparation to the incisal before the bur shaft entered the access cavity. - Furcation perforation caused by failure to measure the distance between the occlusal surface and the furcation. Diagnosis: -If above the PDL , It Is recognized by leakage. -If into the PDL , bleeding into the access cavity is the first indication. 33 -To confirm, place a file, a radiograph will show that file is not in the canal. Prevention: -Examination of preoperative radiograph -Aligning the long axis of the access cavity with that of the tooth Correction: -Perforation above the alveolar crest can be repaired intracoronally using restoration as GI -Perforation into the PDL should be repaired as soon as possible with a good sealing repair material as MTA Prognosis depends on : -Size -Location -Periodontal condition -Length of time -Accessibility NB: the Success rate of perforation repair is high. GOOD LUCK 34