Scope & Macroscopic Anatomy of Endodontics PDF

The scope of endodontics Definition: It is the art and science of prevention, diagnosis, and treatment of pulp and periradicular diseases. Objectives of endodontics: Endodontic treatment is performed to render the affected tooth 1) Biologically acceptable. 2) Symptom free. 3)...

The scope of endodontics Definition: It is the art and science of prevention, diagnosis, and treatment of pulp and periradicular diseases. Objectives of endodontics: Endodontic treatment is performed to render the affected tooth 1) Biologically acceptable. 2) Symptom free. 3) Functioning without any diagnosable pathosis. Phases of endodontic therapy: Three basic steps of endodontic treatment can be identified 1- Diagnostic phase. 2- Preparatory phase. 3- Obturation phase. 1- Diagnostic phase: - The cause of the diseases is identified. - The treatment plan is developed. 2- Preparatory phase: The contents of the pulp chamber and root canals are removed and the root canal space itself is shaped to receive a three-dimensional filling. 3- the obturation phase: In which the root canal system is filled with an inert material to ensure a fluid tight seal. Indications for endodontic therapy: a. Endodontic therapy can be successfully done in the majority of teeth suffering from pulpal or periradicular pathosis. 1      b. However there are some teeth, indicated without pulp or periapical pathosis. 1) Teeth that need post and core to rebuild the missing coronal portion of the tooth. 2) Traumatic pulp exposure due to dental work or accidental fracture. 3) Internal resorption. 4) Overerupted and mesially drifted teeth where crown reduction may cause pulp exposure. 5) Teeth retained in the mouth to support overdenture. 6) Esthetic requirement: which means that all teeth should be in the same harmony. Contraindications for endodontic therapy: Modern Endodontics can solve many problems of what was considered as contraindications of Endodontic treatment. However, there are some conditions to be considered when planning for endodontic treatment 1) Teeth with insufficient periodontal support and tooth will not be functioning well. Unless good periodontal support is present to ensure retention of the tooth, endodontic treatment is specially planned. 2) Teeth with vertical root fracture. Extraction may be the only solution for single rooted teeth. 3) Teeth with extensive internal or external resorption or large perforations which cannot be treated surgically. 4) Non restorable tooth which cannot function properly after treatment. 5) Teeth with root canals not suitable for instrumentation such as calcified canals making passage of the endodontic instruments to the apex impossible. If apical surgery is also inadvisable because of health considerations, extraction of the tooth becomes the inevitable result. 6) Patients with systemic disease contraindicating surgical endodontics. 2      Macroscopic anatomy of the pulp space The hard tissue surrounding the dental pulp can take a variety of configurations and shapes. A throughout knowledge of tooth morphology, careful interpretation of radiograph, and adequate access and exploration of tooth anterior are important for the success of treatment. Therefore, to master the anatomic concept of the pulp space morphology, the operator must develop a mental, three- dimensional image of the inside of the teeth. Pulp space: It is the entire internal space which contains the pulp it consists of the following entities: 1) Coronal pulp: a- Pulp chamber: it is the part of pulp cavity lying in the crown of the tooth. It consists of: 1- The roof of the pulp chamber: the dentin covering the pulp chamber occlusally or incisally. 2- The floor of the pulp chamber: the dentin bordering pulp chamber in the furcation area. 3- The walls of the pulp chamber: located axially (mesially, distally, buccally, lingually) b- Pulp horns: accentuation of the pulp chamber directly under a cusp or a developmental lope. 2) Radicular pulp: a- Root canals: most of root canals have curvature this varies for gradual curvatures to sharp curvatures. 1) Anatomical apex: it is the most tapered portion of the root. 3     2) Apical constriction: It ends at cemento-dentinal junction, and considered the narrowest part of the root canal. The distance between anatomic apex and radiographic apex ranges from (0.5 1mm). 3) Apical foramen: the exit of the neurovascular bundle which supply the tooth. It is possible to have many apical foramina in one root. b- Lateral canals: canals that are located approximately at right angles to the main canal extending from the main canal to the outer surface of the root. 3) Root canal orifice: Opening in the floor of the pulp chamber leading to the root canal. Types of roots: Type I: These types have mature root canals (having apical constriction). Type II: These types have mature root canals but not straight, it could be: a- Slightly curved. b- Severely curved. c- Dilacerated. d- Bayonet. 4     Type III: These types having immature root canals, it could be: a- Tubular b- Blunderbuss They could be either straight or curved roots. Root canal systems: (Weine classification) Class I: Single root canal, single orifice, and single apical foramen. Class II: Two root canals, two orifices, and single apical foramen. Class III: Two root canals, two orifices, and two apical foramina. 5     Class IV: Single root canal, single orifice, and two apical foramina. Class V: Single root canal, single orifice, and single apical foramen. There is branching in the middle one third surrounding dentin island. Class VI: Two root canals, two orifices, and two apical foramina. Canals unite in the cervical one third to from single canal, then they divide again in the apical one third. 6      Macroscopic anatomy and tooth morphology To describe the pulp space, 5 points should be fulfilled: 1. The clinical view. 2. The proximal view. 3. The cross section view. 4. Root canal configuration (types of root canal system). 5. Outline form of the access cavity. Maxillary central incisor a. Labial view (mesiodistally): 1. Wide pulp chamber mesiodistally. 2. Three pointed pulp horns in recently erupted tooth. 3. Uniform tapering towards the root. 4. 2-degree mesial-axial inclination of the tooth. 5. Apical-distal curvature (8% of the time). b. Proximal view ( labiolingually): 1. Pointed pulp chamber incisally. 2. Pulp chamber widens cervically and tapers towards the apical one third. 3. Presence of a lingual shoulder at the point where the chamber and canal join. 4. 29-degree lingual-axial angulation of the tooth. c. Cross-sections: 1. Cervical: triangular in shape. 2. Middle: ovoid in shape. 3. Apical: round in shape. d. Average length: 23.5 mm e. Root canal configuration: 7     Almost 100% of the cases have class I root canal system. f. Outline form of access cavity: Triangular in shape with the base incisally and the apex cervically. Maxillary lateral incisor a. Labial view: 1. Wide mesiodistal pulp chamber. 2. Apical-distal curvature (53% of the time). 3. 16-degree mesial-axial inclination of the tooth. b. Proximal view: 1. Presence of a lingual shoulder at the point where the chamber and canal join. 2. 29-degree lingual-axial angulation of tooth. 3. Relatively broad labiolingual extent of the pulp. c. Cross-sections: 8      1. Cervical: triangular in shape. 2. Middle: ovoid in shape. 3. Apical: round in shape. d. Average length: 22.5 mm e. Root canal configuration: Almost 100% of the cases have class I root canal system. f. Outline form of access cavity: Triangular in shape with the base incisally and the apex cervically. Maxillary canine It has the longest and strongest root in the oral cavity. a. Labial view ( mesiodistally): 1. Narrow mesiodistal width of the pulp chamber. 9     2. Single pointed pulp horn extended toward the cusp tip. 3. 6-degree distal-axial inclination of the tooth. b. Proximal view ( labiolingually): 1. Wide pulp chamber labiolingually and narrow mesiodistally. 2. Presence of a labial shoulder just below the cervical level. 3. One pointed pulp horn. 4. 21-degree lingual-axial angulation of the tooth c. Cross-sections: 1. Cervical: oval in shape in labio-lingual direction. 2. Middle: ovoid in shape. 3. Apical: round. d. Average length: 26 mm. e. Root canal configuration: Class I root canal system. f. Outline form of access cavity: Oval in shape in a labio-lingual direction. 10      Mandibular incisors The smallest tooth in the oral cavity. a. Labial view: 1- Three pointed pulp horns. 2- The root may be straight or with apical distal curvature (23%of the time). 3- Narrow pulp chamber mesiodistal. 4- Mesial-axial inclination of the tooth (central incisor 2 degrees, lateral incisor 17 degrees). b. Proximal view: 1- Pulp chamber pointed incisally. 2- Pulp chamber wide labio-lingually. 3- Lingual shoulder at the point where the chamber and canal join. 4- 20-degree lingual-axial angulation of the tooth. c. Cross sections: 1. Cervical: oval in labio-lingual direction. 2. Middle: oval in labio-lingual direction. 3. Apical: round. d. Average length: 21.5 mm e. Root canal configuration: Has one root canal with a single foramen (class I) 60 %, may be with two root canals and two apical foramina (class III) 30 % or two root canals ending with one apical foramen (class II) 10 %. f. Outline form of access cavity: Triangular with base incisally and apex cervically. 11      Mandibular canine Similar to maxillary but smaller in size. a. Labial view: 1. Narrow mesio-distal width of the pulp. 2. Apical-distal curvature of the root (20% of the time). 3. 13-degree mesial-axial inclination of tooth. b. Proximal view: 1. Broad labio-lingual extent of the pulp. 2. Narrow canal in the apical third. 3. 15-degree lingual-axial angulation of the tooth. 4. Apical-labial curvature (7% of time). c. Cross sections: 1. Cervical: oval in the labio-lingual direction. 2. Middle: ovoid. 3. Apical: round. d. Average length: 25 mm. 12     e. Root canal configuration: Mostly has one root canal (class I) 94% but 6 % may show two root canals class II, class III. f. Outline form of access cavity: Oval in shape in the labio-lingual direction. Maxillary first premolar a. Buccolingual view: 1. Narrow mesiodistal width of the pulp chamber. 2. Pointed pulp horn. 3. 10-degree distal-axial inclination of the tooth. b. Proximal view: 1. Broad Bucco-lingually with two pointed pulp horns. 2. Buccal horn is more prominent. 3. Two widespread and separate roots, each with a single straight canal. 4. 6-degree buccal-axial angulation of the tooth. c. Cross sections: 1. Cervical: oval Bucco-lingual direction. 13      2. Middle: ovoid. 3. Apical: round. d. Average length: 22 mm e. Root canal configuration: 85% of the cases have two root canals, either birooted with each root has one canal (class I) 72%, or single root with two root canals 13% class III or II. Also single root canal in 9% of the cases. Rarely 6% of the cases may show three root canals. f. Outline form of access cavity: Oval in Bucco-lingual direction. Maxillary second premolar a. Buccal view: 1. Narrow mesiodistal width of the pulp. 2. Apical-distal curvature 34%, and may have bayonet curve in 20% of cases. 3. 19-degree distal-axial inclination of the tooth. 14     b. Proximal view: 1. Broad Bucco-lingually with two pointed pulp horns. 2. Buccal horn is more prominent. 3. 9-degree lingual-axial angulation of the tooth. c. Cross sections: 1. Cervical: oval Bucco-lingual direction. 2. Middle: ovoid. 3. Apical: round. d. Average length: 21 mm e. Root canal configuration: 75-85% of cases have one root. Class I is more frequent 75% of the cases, also class II, III may be present. Two roots may be present each with one root canal (class I). Three root canals are very rare. f. Outline form of access cavity: Oval in Bucco-lingual direction. 15      Mandibular first premolar a. Buccal view: 1. Narrow mesio-distal width. 2. Presence of one pulp canal, relatively straight canal. 3. 14-degree distal-axial inclination of the root. b. Proximal view: 1. Broad buccolingual extent of the pulp. 2. Extended buccal pulp horn. 3. Apical-buccal curvature 2%. 4. 10-degree lingual-axial angulation of the root. c. Cross sections: 1. Cervical: ovoid. 2. Middle: ovoid. 3. Apical: round. d. Average length: 21 mm e. Root canal configuration: About 75-85% have single root canal (class I), Class II, III, IV may also be present. f. Outline form of access cavity:Ovoid in Bucco-lingual direction. 16      Mandibular second premolar a. Buccal view: 1. Narrow mesiodistal width of the pulp chamber. 2. Apical-distal curvature (40% of the time). 3. 10-degree distal-axial inclination of the root. b. Proximal view: 1. Broad buccolingual “ribbon-shaped” coronal pulp. 2. Single-root, bifurcated canal at the mid-root level and a single apical foramen. 3. 34-degree buccal-axial angulation of the root. c. Cross sections: 1. Cervical: ovoid. 2. Middle: ovoid. 3. Apical: round. d. Average length: 21.5 mm e. Root canal configuration: Generally it has a single root canal (class I) 85%, Class III, IV may also be present 15%. f. Outline form of access cavity:Oval in Bucco-lingual direction. 17      Maxillary first molar a. Buccal view: 1. It has three roots: mesiobuccal, distobuccal, palatal. The palatal root is the longest and strongest root. 2. Each root contains one root canal. 3. The mesio-buccal root may contain the fourth canal in 96% of the cases. 4. Straight palatal root, mesio-buccal and distobuccal curved towards distal. b. Proximal view: 1. Large pulp chamber with four prominent pulp horns under each cusp. 2. The buccal horns are more prominent than the palatal ones. 3. Palatal canal may have a buccal curve (55% of the time). c. Cross sections: 1. Cervical: a) Triangular in shape with base buccally and apex palatal in case of three root canals orifices. b) Trapezoidal in shape with base buccally in case of four root canal orifices. A dark cavity floor with lines connecting orifices is in marked contrast to white walls. Second mesiobuccal (MB2) present in a groove like a comma extending from mesiobuccal orifice. 2. Middle: Palatal is oval mesiodistally and the rest are round. 3. Apical: All canals are round. d. Average length: mesiobuccal 20 mm, distobuccal 19.5 mm, palatal 20.5 mm. e. Root canal configuration: 1. Mesiobuccal root mainly contain two canals MB1, MB2 with percentage 96% either in class II or III. 2. Distobuccal root contains one canal class I. 3. Palatal root contains one canal class I. 18     f. Outline form of access cavity: In case of four canals trapezoidal in shape. In case of three canals triangular in shape with base buccally and apex palatal. Maxillary second molar It is similar to the first molar but, there is possibility of fusion between the two buccal roots to have one buccal and one palatal roots. In this case the buccal root have two root canals class II or III or single canal class I. The outline form may be trapezoidal in case of four root canals, triangular with base buccal and apex palatal in case of three root canals, or ovoid in case of two canals. 19      Mandibular first molar a. Buccal view: 1. It has two roots one mesially and one distally. 2. The mesial root shows curvature distally (84% of the time). 3. The distal root is usually straight (75%) but may show mesial curve (20%). 4. Distal-axial inclination of the tooth. b. Proximal view: 1. The mesial root is broad Bucco-lingually and contains two root canals mesiobuccal and mesiolingual. 2. The distal root mostly contains single canal, however, about 30% of distal roots has an extra canal, so the names will be distobuccal and distolingual. 3. 58-degree buccal-axial inclination of the roots. 20     c. Cross sections: 1. Triangular with base mesially and apex distally if there are three root canal orifices. 2. Trapezoidal if there are four root canal orifices. Mesial root canals are rounded in cross sections while distal is large kidney shaped in Bucco-lingual direction. Average length: mesial root 21 mm, distal root 21 mm. d. Root canal configuration: Mesial root contains two root canals which may be class III or II. Distal root may contain one root canal 70% class I or class III or II. e. Outline form of access cavity: Triangular in case of three root canals or trapezoidal in case of four root canals. 21      Mandibular second molar The pulp chamber and root canals are nearly similar to the mandibular first molar. The roots are often gradually curved distally. The mesial root has two canals class II 50% or class III 40%. At least frequency it could has one single canal class I. The distal root usually has a single root canal class I 92%. It may have two canals class II 5% or class III 3%. The second molar also may has one root with one root canal, which has a C- shaped cross section. 22      Endodontic cavity prepration Endodontic cavity prepration include 2 steps: 1. Coronal cavity prepration (access cavity). 2. Radicular cavity prepration. Access cavity prepration It is the efficient uncovering of the roof of the pulp chamber & providing the direct access to the apical foramina by the way of the pulp canals. Principles of access cavity prepration: I. Outline form. II. Convenience form. III. Removal of carious dentin and defective restoration. IV. Toilet of the cavity. I- Outline form: The external outline form evolves from the internal anatomy of the tooth. 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. Straight line access should be correctly shaped and positioned to establish a straight line access for instrumentation, from the cavity margin to the apical foramen. Factors affecting outline form: 1. Size of the pulp chamber: The outline form of endodontic access cavities is 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 all three dimensions 2. Shape of Pulp Chamber: The finished outline form should accurately reflect the shape of the pulp chamber. For example, 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 23     and out onto the occlusal surface; hence, the final occlusal cavity outline form is generally triangular. 3. Number, Position, and Curvature of Root Canals: To prepare each canal efficiently without interference, the cavity walls often have to be extended to allow an unstrained instrument approach to the apical foramen. When cavity walls are extended to improve instrumentation, the outline form is materially affected. II- Convenience form: Modification of the outline form to establish greater convenience for instrumentation and obturation. The term straight line access (SLA) describes a prepration that provides a straight unimpeded path from occlusal surface to the apex. This allows the enlarging instrument to reach the apex with minimal deflection. Benefits of convenience form modifications: 1) Unobstructed access to the canal orifices: In endodontic cavity preparations of all teeth, enough tooth structure must be removed to allow instruments to be placed easily into the orifice of each canal without interference from overhanging walls. Extra precautions must be taken to search for additional canals as in lower incisors, maxillary molars, and lower premolars. 2) Direct access to apical foramen: To provide direct access to the apical foramen, enough tooth structure must be removed to allow the endodontic instruments freedom within the coronal cavity so they can extend down the canal in an unstrained position. 3) Extension to Accommodate Filling Techniques: If a softened gutta-percha technique is used for filling, wherein rather rigid pluggers are used in a vertical thrust, then the outline form may have to be widely extended to accommodate these heavier instruments. 4) Complete Authority over the Enlarging Instrument: It is important that the clinician maintain complete control over the root canal instrument. If the instrument is impinged at the canal orifice by tooth structure the dentist will lose control of the direction of the tip of 24     the instrument, and the intervening tooth structure will dictate the control of the instrument. Therefore two factors will be controlling the instrument when the tooth structure around the orifice is removed: 1) Clinicians fingers on the handle of instrument. 2) Wall of the canal at the tip of the instrument. III- Removal of carious dentin and defective restorations: Caries and defective restorations remaining in an endodontic cavity preparation must be removed for three reasons: 1) To eliminate mechanically as many bacteria as possible from the interior of the tooth. 2) To eliminate the discolored tooth structure, that may ultimately lead to staining of the crown. 3) To eliminate the possibility of any saliva leaking into the prepared cavity. IV- Toilet of the Cavity: All of the caries, debris, and necrotic material must be removed from the chamber before the radicular preparation is begun. Excavators, round burs, and irrigation with sodium hypochlorite (NaOCl) are excellent for cleansing the pulp chamber. Objectives of toilet of the cavity: 1) Improve visibility. 2) Antimicrobial. 3) Dissolution of pulp tissues (decrease bleeding). 4) Lubrication. 25      Access cavity prepration in anterior teeth 1. Entrance is always gained through the lingual surface of all anterior teeth in the middle middle third. 2. Initial entrance is prepared with a round-point tapering fissure bur in an accelerated-speed contra- angle handpiece with air coolant, operated at a right angle to the long axis of the tooth. 3. Convenience extension toward the incisal continues the initial penetrating cavity preparation. Maintain the point of the bur in the central cavity and rotate the handpiece toward the incisal so that the bur parallels the long axis of the tooth. Enamel and dentin are beveled toward the incisal. 4. The preliminary cavity outline is funneled and fanned incisally with a fissure bur. 5. A surgical length round bur 2 or 4 with slow speed contra-angle is used to penetrate the pulp chamber, working from inside to outside. 6. Round bur must be used laterally and incisally to eliminate pulpal horn debris and bacteria. This also prevents future discoloration. 7. Finally, dentine walls are smoothed with tapered fissure. 8. The outline in Maxillary and mandibular incisors triangular with base incisally and the apex cervically. 9. The outline in Maxillary and mandibular canines oval labiolingually. 26      Errors in access cavity prepration in maxillary anterior teeth a) Perforation at the labiocervical caused by failure to complete convenience extension toward the incisal, prior to the entrance of the shaft of the bur. b) Gouging of the labial wall caused by failure to recognize the 29- degree lingual-axial angulation of the tooth. c) Gouging of the distal wall caused by failure to recognize the 16- degree mesial-axial inclination of the tooth. 27     d) Pear shaped transportation of the apical canal caused by failure to complete convenience extensions. The shaft of the instrument rides on the cavity margin and lingual shoulder. Inadequate débridement and obturation ensure failure. e) Discoloration of the crown caused by failure to remove pulp debris. The access cavity is too far to the gingival with no incisal extension. f) Ledge formation at the apical-labial curve caused by failure to complete the convenience extension. The shaft of the instrument rides on the cavity margin and shoulder. 28      Errors in access cavity prepration in mandibular anterior teeth a) Gouging at the labiocervical caused by failure to complete convenience extension toward the incisal prior to entrance of the shaft of the bur. b) Gouging of the labial wall caused by failure to recognize the 20- degree lingual-axial angulation of the tooth. c) Gouging of the distal wall caused by failure to recognize the 17- degree mesial-axial angulation of the tooth. d) Missed canal caused by inadequate inciso-gingival extension of the access cavity. e) Discoloration of the crown caused by failure to remove pulp debris. f) Ledge formation caused by complete loss of control of the instrument passing through the access cavity prepared in proximal restoration. 29      Access cavity in premolars 1. Entrance is always gained through the occlusal surface of all posterior teeth. Initial penetration is made parallel to the long axis of the tooth in the exact center of the central groove of the maxillary premolars using tapering fissure bur in high-speed contra-angle hand piece. 2. No. 2 or 4 round bur is used to open into the pulp chamber. The bur will be felt to drop when the pulp chamber is reached. 3. An endodontic explorer is used to locate orifices to the buccal and lingual canals in the first premolar or the central canal in the second premolar. 4. Working from inside the pulp chamber to outside, a round bur is used at low speed to extend the cavity buccolingually by removing the roof of the pulp chamber. 5. Finishing of cavity walls are completed with fissure bur at high speed. 6. For maxillary premolars: The buccal orifice located under the buccal cusp tip, the palatal orifice located under the base of the palatal cusp. 7. Final outline form: a) Oval in buccolingually for maxillary premolars. b) Ovoid in buccolingually for mandibular premolars. 30      Errors in access cavity prepration in maxillary premolar teeth a) Underextended preparation exposing only pulp horns. b) Overextended preparation searching for a receded pulp c) Perforation mesio-cervically due to failure to observe the distal-axial inclination of the tooth. d) Faulty alignment of the access cavity through full veneer restoration e) Broken instrument twisted off in a crossover canal. This can be avoided by flaring the internal preparation f) Missing the third canal of the maxillary first premolar (6% of the time) g) Missing the second canal of the maxillary second premolar (24% of the time). 31      Errors in access cavity prepration in mandibular premolar teeth a) PERFORATION at the disto-gingival caused by failure to recognize that the premolar has tilted to the distal. b) Incomplete preparation and possible instrument breakage caused by total loss of instrument control. Use only occlusal access, never buccal or proximal access. c) Missed canal caused by failure to adequately explore the canal with a curved instrument d) Apical perforation. e) Perforation at the apical curvature caused by failure to recognize, by exploration, buccal curvature. 32      Access cavity prepration in maxillary molars 1. Access prepration is made in the occlusal surface. 2. The initial penetration is started midway between the mesial ridge and the oblique ridge using round bur directed towards the palatal. It will be felt to drop when the pulp chamber is reached 3. Using a round bur the roof pulp chamber is removed by Working from inside to outside. 4. Final finish and funneling of cavity walls are completed with a tapered diamond points at high speed. 5. An endodontic explorer is used to locate orifices of the palatal, mesiobuccal, and distobuccal canals. 33     6. The mesiobuccal (MB1) orifice is located beneath the mesiobuccal cusp tip. The second mesiobuccal (MB2) is located 1 mm mesial and palatal to the MB1. 7. The distobuccal orifice is located 2 mm distal and palatal to the mesiobuccal orifice. 8. The palatal orifice is located under the base of the mesiopalatal cusp. 9. The outline form in case of four canals trapezoid or triangle with base towards buccal and apex palatal. 10. The access cavity is located in the mesial half of the tooth or slightly crossing the oblique ridge. 34      Errors in access cavity prepration in maxillary molars teeth a. Underextended preparation leading to failure in locating the orifices of the root canal. b. Overextended preparation undermining enamel walls. c. Furcation perforation failing to realize that the narrow pulp chamber had been passed. d. Inadequate vertical preparation related to failure to recognize severe buccal inclination of an unopposed molar. e. Disoriented outline form in full crown, which was placed to straighten a rotated molar. f. Ledge formation due to failure to provide straight line access. g. Perforation of a palatal root commonly caused by assuming the canal to be straight. 35      Access cavity prepration in mandibular molars The same as in the maxillary molars, with the following differences: 1. Initial penetration is made in the central pit where the round bur is slightly directed towards the distal. 2. The mesiobuccal orifice under the mesiobuccal cusp tip. The mesiolingual orifice is located 2 mm lingual to the mesiobuccal orifice. Distal orifice is 1 mm distal to the central pit. 3. Extra canal distally either distobuccal or disto-lingual. 4. Outline form: triangular with base mesially and apex distal in case of three orifices, or trapezoidal in case of four orifices. 36      Errors in access cavity prepration in mandibular molars teeth a. Overextended preparation undermining enamel walls. b. Perforation into furcation caused by failure to realize that the narrow pulp chamber had been passed. c. Perforation at the mesial-cervical caused by failure to orient the bur with the long axis of the molar severely tipped to the mesial. d. Disoriented outline in full crown, which was placed to straighten up lingually tipped molar. e. Missed second distal canal. f. Ledge formation due to failure to provide straight line access. g. Perforation of the curved distal root. 37      38