CHAPTER 7: PART II

ERRORS IN ACCESS CAVITY PREPARATION & CLASSIFICATIONS OF C-SHAPED / PULP FLOORS

safety-tip tapered diamond bur

used to blend and funnel the axial wall from the cavosurface margin to the orifice

used to shape the axial wall in one plane from the orifice to the cavosurface margin

mouse hole effect

orifice that lies completely on the pulp floor

caused by extension of the orifice into the axial wall

cause of loss of significant clinical crown structure

untreated caries, which undermine the tooth

fractures from occlusal stress in badly decayed teeth

trauma, sometimes shearing the crown to the free gingival margin

teeth heavily restored with amalgam, composite, or glass ionomer, which provide no extra-coronal support

access preparation on heavily restored teeth is challenging due to:

reduced visibility — because most restorative materials block light from reaching the pulp chamber

altered external anatomical landmarks — as restorations and full crowns rarely reproduce the original tooth anatomy

changed crown-to-root angulation — especially when large restorations or crowns were placed to correct occlusal discrepancies

reasons for complete removal of restorations:

facilitate treatment of calcified canals (under class V restorations)

prevent coronal leakage: loose fragments can be vibrated or displaced during drilling

avoid canal contamination: fragments can be carried into the canal during shaping, creating metal or composite filings

improve visibility: removal allows direct access to root canals and helps detect recurrent caries, fractures, or calcifications

chamber floor

darker than walls

developmental grooves

lighter than floor

additional aids for locating calcified root canals

canal bleeding points

1% methylene blue staining

sodium hypochlorite “champagne bubble” test

common problems if rotated tooth is not considered:

failure to locate additional or extra canals

instrument separation during canal location attempts

incomplete removal of pulp tissue from the chamber

excessive gouging of coronal or radicular tooth structure

mistaking one canal for another → searching in the wrong direction

poor access placement / inadequate mesial extension

mesial orifices left uncovered

causes:

• failure to correctly locate pulp chamber

• inadequate evaluation of tooth anatomy

prevention for poor access placement / inadequate mesial extension

carefully plan access outline

assess CEJ and tooth morphology

use pretreatment radiographs (especially bite-wings)

inadequate distal extension

distobuccal canal orifice unexposed

causes:

• developmental grooves not traced to termination; cavity not extended distally

prevention for inadequate distal extension

• trace all developmental grooves full

• ensure distal access reaches canal orifices

gross overextension

weakens coronal tooth structure, compromises restoration

causes:

• improper bur angulation

• incorrect determination of pulp chamber position

prevention for gross overextension

avoid excessive removal

follow correct access cavity guidelines

evaluate pulp chamber position and angulation

debris in canal orifices

blocks canals, hinders shaping and cleaning

allowing amalgam or dentin fragments to fall into orifices

prevention for debris in canal orifices

completely remove restorations; perform copious irrigation before locating canals

failure to remove pulp chamber roof

pulp horns exposed

underextension; incomplete access

prevention for failure to remove pulp chamber roof

ensure roof and pulp horns fully removed

use bite-wing radiographs to determine vertical depth

mistaking pulp horns for canal orifices

causes:

• roof remains

• shallow cavity

• shallow depth

• absence of grooves

• lack of developmental grooves

• color differences not recognized

prevention for mistaking pulp horns for canal orifices

remove roof completely

identify whitish roof color

remember true orifices are at or slightly apical to CEJ

overzealous tooth removal

causes:

• weakens / mutilates coronal structure

• risk of coronal fracture

• improper bur angulation

• failure to recognize lingual inclination

prevention for overzealous tooth removal

• evaluate tooth angulation

• adjust bur orientation

• remove dentin gradually and conservatively

inadequate opening

causes:

• access too gingival

• pulp horn retention

• poor instrumentation

• leads to bur/file breakage

• ledging, apical transportation

• access cavity misplaced or too small

• insufficient extension & no incisal extension

prevention for inadequate opening

check pulp chamber depth

ensure proper incisal extension

follow straight-line access principles

labial perforation

causes:

• failure to extend preparation incisally before bur penetration

prevention for labial perforation

plan cavity outline carefully

extend incisal wall before full penetration

confirm with radiographs

furcation perforation

opening into periodontal tissues, weakens tooth

cause:

• incorrect depth measurement between occlusal surface and furcation

prevention for furcation perforation

• use careful bur control

• confirm with radiographs

• repair immediately if occurs

• measure occlusal-to-furcation distance

mesial perforation

often in crowned teeth

causes:

• bur not aligned with long axis

• failure to recognize tooth tipping

• causes long-term periodontal problems

prevention for mesial perforation

align bur with long axis

radiographic confirmation

cautious preparation in crowned teeth

evaluate crown angulation preoperatively

entering the wrong tooth

high risk of medical / legal consequences

causes:

• incorrect dental dam placement

• visually similar crowns

prevention for entering the wrong tooth

mark the correct tooth with a felt-tip marker before placing the dental dam

verify tooth identity carefully

broken burs or files

can lock in canal

causes:

• improper motion

• excessive pressure

• may require excessive tooth removal

prevention for broken burs or files

using instruments before proper access

handle instruments carefully

use correct motion and pressure

ensure proper access cavity preparation first

main cause of C-shape roots and canals

failure of Hertwig’s epithelial root sheath to fuse on either the buccal or lingual root surface

C-shaped roots and canals

most common in MN 2nd molars

also reported in MN 1st molars, MX 1st & 2nd molars, MN 1st premolars

can vary along the root depth so that the appearance of the orifices may not be good predictors of the actual canal anatomy

2 basic types of C-shaped roots and canals

single ribbonlike canal — from orifice to apex (rare)

multiple distinct canals — below the C-shaped orifice (more common)

feature of a root canal obturation

ribbonlike canal space with an arc of 180 degrees or more

category I (C1) of C-shaped root canal

the shape is an uninterrupted “C” with no separation or division

category II (C2) of C-shaped root canal

should be no less than 60 degrees

the canal shape resembles a semicolon resulting from a discontinuation of the “C” outline

category III (C3) of C-shaped root canal

2-3 separate canals and both angles are less than 60 degrees

category IV (C4) of C-shaped root canal

only one round or oval canal is in the cross-section

category V (C5) of C-shaped root canal

no canal lumen can be observed (is usually seen near the apex only)

MN 2nd molars

where four types of pulpal floors are found

type I of pulpal floors

a peninsula-like floor with continuous C-shaped orifice

type II of pulpal floors

A buccal, striplike dentin connection between the peninsula-like floor and the buccal wall of the pulp chamber that separates the C-shaped groove into mesial (M) and distal (D) orifices.

Sometimes the mesial orifice is separated into a mesiobuccal (MB) orifice and a mesio- lingual (ML) orifice by another striplike dentin connec- tion between the peninsula-like floor and the mesial wall of the pulp chamber (most common)

type III of pulpal floors

only one mesial, striplike dentin connection exists between the peninsula-like floor and the M wall

which separates the C-shaped groove into a small ML orifice and a large MB-D orifice

MB-D orifice was formed by the merging of the MB orifice and the D orifice (second most common)

type IV of pulpal floors

non–C-shaped floors

one distal canal orifice and one oval or two round mesial canal orifices are present (least common)

type I of Three-dimensional classification of C-shaped canal

(merging type)

canals merge to one main canal before exiting at the apical foramen

type II of c-shaped canal

(symmetrical type)

separated mesial and distal canals in each root, which exit as separate canals

type III of c-shaped canal

asymmetrical type

separated mesial and distal canals, with the distal canal having a long isthmus across the furcation area