CHAPTER 7: ACCESS CAVITY PREPARATION

access cavity preparation

create an opening to the tooth

essential to achieve proper biomechanical preparation (BMP) cleaning and shaping of the root canal system, and obturation sealing and closure after BMP

used by:

• high/low speed handpiece

• endodontic access burs (long shank)

characteristics of ideal access

straight entry into the canal orifice

line angles form a funnel that drops smoothly into the canal(s)

• projection of the canal center line to the occlusal surface:

  • indicates location of line angles

• connection of line angles:

  • creates the outline form

objectives of access cavity preparation

to remove all caries

to locate all root canal orifices

to remove all coronal pulp tissue

to conserve sound tooth structure

to completely unroof the pulp chamber

to establish restorative margins to minimize marginal leakage of the restored tooth

to achieve straight- or direct line access to the apical foramen or to the initial curve of the canal

[ SLA is the main objective – the opening that you create would help you enter the RCS w/out hindrances ]

fissure carbide & diamond burs (with safety tip)

safer for axial wall extensions

can extend to pulp floor safely

produce axial walls free of gouges

• used to:

  • extend axial walls

  • favorably orient axial walls

  • level cusp tips

  • level incisal edges (reference points for working length)

round carbide burs

create initial external outline

penetrate pulp chamber roof

remove chamber roof & caries

• risk (in inexperienced hands):

  • gouging pulp floor and axial walls

round bur #2 & #4

used to access through porcelain or ceramometal restorations

• advantages:

  • less traumatic to porcelain than carbide burs

  • less likely to crack or fracture porcelain

• reminders:

  • must be used with water spray

  • after penetrating porcelain:

    • switch to carbide bur for metal or dentin (greater cutting efficiency)

medium- or fine-grit diamond burs

bur used for zirconia restorations as carbide burs do not cut zirconia efficiently or safely with the use of copious water spray

• zirconia is brittle:

  • cutting may create cracks

  • cracks may propagate and cause restoration failure

transmetal bur

bur used for metal restorations

• benefits:

  • uses new bur

  • excellent cutting efficiency

  • use with water spray for maximal cutting effect

extended-shank round burs

improves visibility

moves handpiece head away from tooth

• alternative:

  • ultrasonic units

• examples:

  • LN bur

  • mueller bur

  • munce discovery bur

bur used for intial RCT

round bur & fissure bur to enlarge and create a proper form

—regular bur will block visualization

special endodontic burs

diamendo

endo Z bur

howard martin bur

howard martin bur

round bur and a taper-fissured body

diamendo

diamond bur for refining the walls of the canals

endo Z bur

cutting the walls of the access prep

used for canal exploration

K-files (patency files)

canal probe: #12 orange

endodontic explorer (DG-16)

endodontic explorer (DG-16)

identify canal orifices

determine canal angulation

endodontic explorer (JW-17)

thinner, stiffer tip than DG-16

• useful for:

  • identifying calcified canals

patency files of K-files

initial files that would enter the canal

#6 → pink, #8 → gray, #10 → violet

canal probe: #12

created to bridge the gap between #10 & #15 files for smoother canal enlargement

NeoProbe → tip diameter of 0.12 and a taper of 1% (varies on the brand)

pulp extirpation

the removal of vital pulp using nerve broach

when inserting nerve broach, avoid touching dentin

canal preparation

used of irrigating syringe and irrigating needles

size of irrigating syringe used

10–20mL

size of Irrigating needles used for anterior

25-gauge

size of irrigating needles used for posterior

27 or 30 gauge

side-venting needles

23 gauge

to flush out debris or root canals in a whirlpool effect w/out hitting the apical foramen = efficient cleaning

reminders for canal preparation

isolation – to prevent contamination

preoperative x-ray – to assess canal anatomy

canal patency – use small files (#6, #8, #10) to locate and confirm canals

instrumentation/shaping – use hand or rotary files, noting canal bifurcations and curvatures

obturation – final step, filling the canal (the “end game” of RCT)

laws of access cavity prep

law of centrality

law of concentricity

law of the CEJ

law of symmetry

law of color change

law of orifice location

law of centrality

floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ → most stable landmark as reference during access prep

file – prepare ; bur – access

law of concentricity

walls of the pulp chamber are always concentric to the external surface at the CEJ

—> that is, the external root surface anatomy reflects the internal pulp chamber anatomy

law of the CEJ

distance from the external surface of the clinical crown to the wall of the pulp chamber is the same throughout the circumference at the CEJ

making the CEJ the most consistent repeatable landmark for locating the position of the pulp chamber

first law of symmetry

except for the mx molars

canal orifices are equidistant from a line drawn in a mesiodistal direction through the center of the pulp chamber floor

second law of symmetry

except for the mx molars

canal orifices lie on a line perpendicular to a line drawn in a mesiodistal direction across the center of the pulp chamber floor

law of color change

the pulp chamber floor is always darker in color than the walls.

from enamel: white – yellow → dentin: brownish – yellow → pulpal floor: grayish color

first law of orifice location

the orifices of the root canals are always located at the junction of the walls and the floor

second law of orifice location

the orifices of the root canals are always located at the angles in the floor-wall junction

third law of orifice location

the orifices of the root canals are always located at the terminus of the developmental fusion lines of roots

distal

rubber clamp bow is always located at the __

fast break

sudden disappearance of the canal along its length

signifies:

• splitting of the canals

• presence of a bifurcation / trifurcation

pulp canal obliteration (PCO)

calcify itself as a defense-mechanism

pulp canal has been calcified in response to injury

average length of teeth (mm)

oval access opening

mx canine

mx 1st premolar

mx 2nd premolar

mn canine

mn 1st premolar

mn 2nd premolar

mn incisors

oval-triangular access opening

mx incisors (central/lateral)

triangular access opening

mx 1st molar

mx 2nd molar

trapezoidal access opening

mn 1st molar

mn 2nd molar

from the lingual surface to the incisal surface

entry of access for mn incisors

• benefits:

  • better access to the lingual canal

  • improved straight-line access

  • improved canal debridement

reminders for cavity access preparation

recommended average length is the actual canal length

rubber stopper placed at the highest reference point of the clinical crown, not on the orifice

slight extrusion of root canal sealer through the apical foramen is generally not a major concern, as macrophages and the body’s immune system can gradually dissolve it

apical constriction: natural stop for RCT

• 0.5–1.5 mm from the apical foramen (AF)

• 0.5–1 mm short of the radiographic apex

access cavity prep by doc g

area of internal resorption due to trauma (that burot gi mark ni doc g)

anterior tooth:

• initial entry: lingual surface

• use: long shank round bur

• penetration technique:

  • advance slowly

  • you will feel a sudden drop when entering the pulp chamber

  • then reorient the bur perpendicular to the long axis

posterior tooth:

• initial entry: occlusal surface

• based on the law of centrality

after entering the chamber:

• extend the preparation to form a triangular outline form (especially in anterior teeth)

• use an explorer to:

  • remove debris

  • locate canal orifices

• how do you know you’ve found the canal?

  • use patency files (small K-files)

  • if the file advances smoothly down the canal → you are in the canal

why not an oval access opening?

• an oval prep:

  • removes only the middle pulp chamber

  • may leave mesial and distal pulp horns behind

• has big opening access but orifice is small!

  • use gates glidden drill or SX (canal orifice opener) → to create a smooth transition

gouging

iatrogenic mistake during access cavity preparation on the lateral walls or pulp chamber floor, it should be straight

treatment: fill it

root canal walls

must guide instruments, not access cavity walls

failure to follow root canal walls may cause:

root perforation

ledge formation

apical transportation

incorrect canal shape

instrument separation

micro-openers

offset handles enhance visualization

flexible stainless steel hand instruments

used for locating canal orifices before dam placement