Hand files, Working length, Radiographs

Lecture given on 8/18/2025

*explain an overview of Kakehasi 1965

a space was drilled into the teeth of mice and the mice were fed 2 different diets (conventional food and the other was germ free food)

the bottom line is that it determined that the presense or absence of microbial flora is the major determinant in the healing of exposed pulps

*what happened to the conventional rats in Kakeshashi 1965?

by the 8th day the only vital tissue was in the apical half

complete pulpal necrosis with granulomas and abscess formation occured in all older rats

no dentinal repair occured

*what happened to the germ free rats in Kakeshashi 1965?

no devitalized pulps, apical granulomas, or abscesses were found

dentinal bridging repair began at 14 days and by 21-28 days it was complete

explain the threshold of endodontic treatment

there is a threshold that determined the success of endodontic treatment

treatment just needs to reduce the bacterial load below the threshold for the treatment to be successful, it does not need to sterilize the root canal fully

t/f deep cavities bacteria travel faster than surface level cavities- and why?

true- tubular diameter increases from 0.6-0.8 um close to the DEJ to about 3 um at the pulp

how does age affect the permeability of dentin?

the width of peritubular dentin increases causing a reduction in tubular lumen or sclerosis

how does caries in dentin affect the permeability of dentin?

the tooth tries to remineralize which causes a decrease in permeability

what is the objective of a root canal?

address the problem by disinfection and sealing of the root canal system

what are the major goals of root canal treatment?

removal of vital and necrotic tissue from the main root canals, creation of sufficient space for irrigation and medication, preservation of the integrity and location of the apical canal anatomy, avoidance of iatrogenic damage to the canal system and root structure, facilitation of canal filling, avoidance of further irritation or infection of periradicular tissues, and preservation of sound root dentine to allow long-term function of the tooth

*what are schilders 5 objectives of a root canal?

continuously tapering funnel from the apex to the access cavity

cross-sectional diameter should be narrower at every point apically

the root canal preparation should flow with the shape of the original canal

the apical foramen should remain in its original position

the apical opening should be kept as small as practical

what are the 4 biological objectives of root canal treatment?

confinement of instrumentation to the roots themselves

no/minimal forcing of necrotic debris beyond the foramen

removal of all tissue from the root canal space

creation of sufficient space for intra-canal medicaments

what is the purpose of the endodontic explorer?

exploring- locate orifices, and as a tool to remove calcification

*what is the purpose of a barbed broach?

extirpating- engages the pulp tissue and removes it from the canal

it is not an enlarging instrument

*t/f a barbed broach should fit tightly in the canal

false- should fit freely and loosely, it is not an enlarging instrument

what is the purpose of gates-glidden drills?

enlarge the coronal canal area, only in the straight part of the canal (upper 1/3-1/2)

how should gates-glidden drills be used?

they should cut on the outstroke only, so they should fit loosely so that they do not cut on the instroke

when misused, they can dramatically reduce the radicular wall thickness because they are side cutting instruments

measurement control technique

instruments should always be used with a rubber stop as a measurment control

how long is the working part of a hand file?

16mm- it is standardized

what is the standard taper on hand files?

0.2mm

what is the D0, D10, and D16 of a #30 hand file?

D0 is 0.30mm

D10 is 0.50mm

D16 is 0.62mm

Understand how this calculation is done!

*which hand files have the greatest percent increase in tip diameter?

10 to 15 handfile (50% increase)

what is the purpose of a patency file?

a small K file (often #10) that is passively extended just through the apical foramen

why is a patency file a good thing to use?

helps to ensure working length is not lost and that the apical portion is not packed with tissue and debris

what size file is ideal for a glide path?

at LEAST a #15 k file but 20-25 is better

glide path

a file (at least #15) can be passively and smoothily inserted to working length with long in and out movements

this needs to be established before the use of a rotary

why does a glide path need to be established before using the rotary?

it reduces the contact area of the rotary, reducing taper lock

also minimizes the screw-in effect and reduces the risk of torsional fracture

watch winding

reciprocating back and forth (cw and ccw), light apical pressure is applied to gently move the file deeper into the canal

reaming

cw, cutting rotation of the file

placed into the canal until binding is encountered and then rotated cw 180-360 to plane and enlarge the canal space

filing

pressing laterally while withdrawing along the path of insertion to scape the walls

removes tissue and cuts superficial dentin from the wall on outstroke

k-files / reamers

twisting square or triangular metal blank along its long axis

what motion should be used with k-files?

in and out motion

what motion should be used with reamers?

rotational

h types (hedstrom file)

milled from round, stainless steel blanks

what motion should be used with h type?

filing strokes

not in rotational movement because of increased chance of fracture

c-type files

stiffer than k files, recommended for calcified canals

when comparing a reamer to a file, a reamer is…

more flexible, has less flutes, used mainly in reaming action, less effective in filing action because of less flutes

when comparing a reamer to a file, a file is…

less flexible, has more flutes, used mainly in filing action, can be used in a reaming action

balanced force technique (overview, not steps)

creates least canal abberations, provides excellent canal-centering ability, superior to other techniques with hand instruments

what are the 3 steps to the balanced force technique

1- after passive insertion of a file, a cw rotation of 90 to engage dentin

2- the file is held in the canal with adequate axial force and rotated ccw to break loose the engaged dentin chips from the canal wall

3- the file is removed with a cw rotation to be cleaned

step back technique

attempts to reduce procedure errors and improve debridement

some claims that it extrudes more debris

what are the steps for the step back technique?

after determining the initial file that binds at the working length, the succeeding files are shortened by 0.5-1.0mm from the previous file length

creates a flared, tapering preparation hopefully reducing procedural errors

step down technique

shaping the coronal aspect first before apical instrumentation

intended to minimize the amount of necrotic debris extruded during instrumentation

by first flaring the coronal 2/3s of the canal the apical instruments are less impeded through most of their length, maybe less chance of zipping

crown down technique

modification of step down, relies more on coronal flaring and then determination of the working length later in the procedure

you can only take a rotary…

where you have a guide path

*NiTi

1959 by Buehler and Wang at Naval Ordinance Lab

can deform 10-30x other metals and return to its shape

has shape memory and superelasticity (depending on temperature!)

*shape memory

the ability to undergo deformation at one temperature, stay in its deformed shape when the external force is removed, and then recover its original/undeformed shape upon heating above its transformation temperature

*superelasticity

the ability for the metal to undergo large deformations and immediately return to its undeformed shape upon removal of the external load

when was NiTi introduced to endo?

1980s by Walia et al

what is special about the passive preparation of rotary designs?

cross section shows radial lands- keeps rotary in the center, fairly safe regarding preparation errors, less efficient, has more of a reaming action instead of cutting

what is special about the active preparation of rotary designs?

no radial lands, higher cutting effiency, higher potential for procedure errors

what is special about the reciprocating rotation of rotary designs?

needs a special motor, tries to eliminate the problems with continuous rotation (taper lock, fatigue fracture, threading in)

tries to mimic balanced force

torsional fracture

due to frictional resistance

an example is locking the flutes in the canal wall while continuing to rotate the coronal portion

cyclic fatigue

occurs in curved canals, results when strain develops in the metal, areas of tension and compression alternate and fracture occurs

what are common iatrogenic errors in root canal preparation?

zip, elbow, ledging, perforation, strip perforation, outer widening, apical blockage, damage to the apical foramen

zipping/tearing/transportation

over enlargement of the canal along the outer side of the curvature and under-preparation of the inner aspect of the curvature at the apical end point

ledging

a blockage or ledge created, often on the outer side of the curvature as a platform

may be difficult to bypass and the original pathway of the canal is lost

how can you prevent ledging?

extension of access cavity to provide unobstructed access to the canals

precurving and not forcing instruments

using NiTi files

using passive step-back and balanced force technique

instrumenting the canal to its full length

how can you bypass a ledge?

use a small file with distinct curve at the tip

a slight rotation of the file combined with a picking motion can often help advance the instrument

perforation

destruction of the root cememntum and irritation/infection of the PDL, difficult to seal

strip perforation

overpreparation and straightening along the inner aspect of the root canal curvature

happen in the midroot/danger zone

apical blockage

packing of tissue or debris and results in a loss of working length and root canal patency

complete disinfection of the most apical part of the root canal system is impossible

what can happen if the apical foramen is damaged (displaced or enlarged)?

irritation of the periradicular tissues by extruded irrigants or filling materials may occur because of the loss of an apical stop

what is the desirable final size of apical preparations?

there are 2 main proposals (keep as small as possible or 3 sizes larger than the first file) but at the end of the day you need to decide for yourself

what are the benefits of a narrow apex preparation?

minimal risk of canal transportation and extrusion or irrigants or filling material, can be combined with tapered preparation to counteract some drawbacks

what are the drawbacks of a narrow apex preparation?

little removal of infected dentin, questionable rinsing effect in apical areas during irrigation, possibly compromised disinfection during interappointment medication, not ideal for lateral compaction

what are the benefits of a wider apex preparation?

removal of infected dentin, access of irrigants and medications to apical third of root canal

what are the drawbacks of a wide apex preparation?

risk of preparation errors and extrusion of irrigants and filling material, not ideal for thermoplastic obturation

overfilling

total obturation of the root canal space with excess material extruding beyond the apical foramen

overextension

filling material beyond the apex, but the canal may not have been filled adequately within its confines

t/f the root of a tooth has one diameter and that is the apical foramen

false- it has a minor diameter (apical constriction) and a major diameter (apical foramen)

are the anatomical apex and the radiographic apex the same thing?

no, and there is a 1-2 mm difference between the two locations

t/f the numbers on an apex locator do not correspond to the mm from the apex you are

true

SLOB

same lingual, opposite buccal