ACCESS CAVITY PREPARATION - Major objectives:
- Remove all the caries
- Conservation of tooth structure
- Completely un-roof the pulp chamber
- Remove all coronal pulp tissue, vital or necrotic
- Locate all root canal orifices
- Achieve straight line access
- Establish restorative margins
Weine’s classification of Root Canal Morphology
- Type I: 1->1
- Type II: 1->2->1
- Type III: 2->2 separate early
- Type IV: 1->2 separate late; most challenge
MAXILLARY CENTRAL INCISOR
- single canal and single foramen Most of the times
- Canal form is usually type I
- The pulp in young patients has usually 3 pulp horns
- pulp chamber: MD > FL
- External access outline form: triangular, base toward incisal
- Lingual shoulder must be removed.
MAXILLARY LATERAL INCISOR
- single canal & single foramen
- type I canal form
- young patients usually have two pulp horns & MD > FL.
- canal is tapered
- apex is curved generally distally
- External access outline form: triangle or oval.
- Anomalies: Developmental groove, Dens invaginatus.
- central is shorter than lateral.
- root canal morphology: Type I more common than II or III.
- pulp chamber: smaller replica of upper incisors. MD < FL.
- When single canal, normally straight, but may curve distally.
- canal outline is oval @ CEJ
- External access outline form: triangle or oval.
- Lingual shoulder must be eliminated. A second canal (lingual) may be found underneath.
- The longest tooth (26.5mm)
- Pulp chamber: MD < FL.
- No pulp horn
- Rarely > 2 canals
- Oval Type I.
- Apex tapered and very thin, usually straight but may curve distally.
- External access outline form: OVAL.
- Lingual shoulder must be eliminated.
- Incisal extension of 2-3 mm to incisal edge to allow straight line access.
- Smaller than the max. canine
- Type I form; rarely 2 roots; very few times Type IV with 2 separate apical foraminas.
- MD < FL
- Access cavity OVAL.
- Lingual shoulder must be removed. Possible second canal underneath.
- Incisal extension toward incisal edge for straight line access
MAXILLARY FIRST PREMOLAR
- Root canal: generally 2 roots w/ 2 canals, or 1 root w/ 2 canals w/ a common apical foramen.
- 2 pulp horns: B and P
- Pulp chamber: MD < BP
MAXILLARY SECOND PREMOLAR
- Type I (48% ) w/ apical distal curvature.
- Pulp chamber: MD < BP
- Two pulpal horns.
- Canal orifice is in the center
- One canal 75%, 2 canals 25%
- - a single canal may bifurcate into two in the apical half
- Pulp chamber: MDTwo pulpal horns
- Access preparation in the center of the cusp tips
- Crown tilted to Lingual; access must start closer to the facial of the occlusal surface
Maxillary First Molar
- The most complex root canal anatomy.
- Three individual roots (MB,DB,P).
- Anatomical structures around the root apices makes radiographic interpretation of the roots difficult.
- Palatal root: the longest, larger diameter. One canal, curves buccally at apical third, flat, ribbon-like, and wider in MD direction.
- DB root: conical, 1/2 canals.
- MB root: Usually two canals (1-3). Concavity on the distal aspect, makes this wall thin.
- - 37% or more: two MB canals join into one foramen.
- - 25% or more: two MB canals exit through two separate foramina
- - MB2 canal always smaller in diameter than the other three.
Maxillary First Molar - Access cavity preparation:
- Always assume two MB canals exist until careful examination proves not.
- Rhomboid shape with the corners corresponding to the four orifices (MB1, MB2, DB, P);
- Mesial: not extend into the mesial marginal ridge.
- Distal: not penetrate through the ridge.
- Buccal: parallel to the line connecting MB1 and DB orifices, not to the buccal surface of the tooth.
- The initial point of penetration: over P, the major (largest) canal - Intrapulpal anesthetic injection can best be utilized in this area when anesthesia is a problem; the easiest to locate.
Maxillary Second Molars
- Resemble the coronal anatomy of the maxillary first molars
- •The roots are closer and sometimes fused; when fused, may have only 2 canals, or one in rare cases.
- •The roots are shorted and not as curved as MxM1.
- •Usually each root only has one canal; 4 canals less likely.
- •The three orifices (MB, DB, P) usually form a flat triangle (sometimes a straight line):
- - MB is more buccal and mesial
- - DB is in the midpoint between MB and P.
- - P is at the most palatal aspect of the root.
Maxillary Second Molars - Access cavity preparation:
- •Four canals: rhomboid shape.
- •Three canals: rounded triangle with the base to the buccal.
- •The oblique ridge usually is not invaded.
- •The mesial marginal ridge is not invade.
- •Two canals: oval, widest in the FL dimension.
Mandibular First Molar
- Most frequent for RCT.
- Four pulp horns: MB, ML, DB, DL.
- Two or three roots.
- Distal surface of M root and mesial surface of D root have root concavities, very thin walls - danger zones.
- Three or four canals: two in M root (MB and ML canal) and one (Distal canal) or two (DB, DL canal) in D root
- All Orifices: usually in the mesial two thirds of the crown .
- Pulp chamber floor: trapezoid or rhomboid shape.
Mandibular First Molar - Distal root:
- Flattened MD morphology with complex root canal configuration.
- Conical distal roots: frequently single canal.
- Diameter larger than mesial root.
- Occasionally, orifice extends wide bucco-lingually.
- Wide BL anatomy: indicates a second canal or ribbon-like complex webbing.
- When two separate canals: much thinner than a single distal canal, and located towards buccal and lingual. When a distal canal can not accommodate size #15 file at the initial entrance and is not centrally located, be suspicious of two distal canals.
Mandibular First Molar - Mesial root:
- Wider than Distal.
- Curves mesially from the cervical line to the middle third and then angles distally to the apex.
- Often two independent foramina.
- MB canal always curved, ML canal usually straight and shorter.
Mandibular First Molar - Access cavity preparation:
- Mesial: not to invade the marginal ridge.
- Distal: allow straight line access to the distal canal(s).
- MB orifice: commonly under MB cusp.
- ML orifice: lingual to the central groove.
- Middle mesial canals may be present between MB and ML orifices (1% to 15% of the time).
- If only one distal canal: oval buccolingually and located distal to the buccal groove.
- Initial point of penetration: over the major (largest, distal) canal: Effective Intrapulpal anesthetic injection; the easiest to locate.
Mandibular First Molar - variation in root morphology
Extra distolingual root (common in Asian population). Radix entomolaris (RE): supernumerary root located distolingually in mandibular molars. Each root usually contains a single root canal.
Mandibular Second Molar
- Smaller coronally than M1 and more symmetrical.
- Two roots, close to each other, sometimes fused.
- Pulp chamber and canal orifices are not as large as MdM1.
- One, two, three or four canals.
- Mesial canals: are located closer together.
- Mesial root: less curvature than MdM1; somewhat shorter.
- Easier to treat mechanically.
- Slight mesial inclination -> angle of approach is somewhat easier.
- Anatomy variations: some single or fused roots have C-shaped canal; the two canals are connected by a semicircular slit.
Mandibular Second Molar - access cavity
- Similar to MdM1, a little more triangular and less rhomboid.
- Sometimes only two canals, one M & one D, orifices nearly equal in size and line up in the center of the occlusal surface.
Third Molars (Maxillary And Mandibular)
- Occasionally, the loss of M1 & M2 makes M3 a strategic abutment for fixed/removable appliances.
- Can present problems for RCT, mostly related to accessibility and anatomy.
- Reaching the most posterior tooth with a handpiece and hand instrument can be difficult because of poor visibility and the restricted jaw opening.
- Often tipped mesially - to the advantage of the clinician.
- Keeping in mind the long axis of the tooth and pulp chamber is centrally located will assist in the initial cavity preparation.
Molar Access Opening Errors
- Unroofed preparation: The pulpal horns have merely been exposed and the entire roof of the pulp chamber remains.
- Over extended preparation: undermining the enamel walls; The crown is badly gouged due to the failure to observe recession in the radiograph.
- Perforation into the furcation: using a surgical length bur and failing to realize the narrow pulp chamber had been passed.
- Inadequate vertical preparation: failure to recognize severe buccal inclination of an unopposed molar.
- Perforation at the mesial cervical: failure to orient the bur with the long axis severely tipped to the mesial (mandibular molars)
- Disoriented occlusal outline form exposing only the palatal canal: The faulty cavity has been prepared in a full crown which was placed to “straighten” a rotated molar.
- Disoriented occlusal outline form exposing only the mesiobuccalcanal: The faulty cavity has been prepared in a full crown which was placed to “straighten-up” a lingually-tipped molar.
- Failure to find the second distal canal: lack of exploration for the fourth canal.