Endodontic Instruments

Endodontic Instruments¹²

The Preparation Appointment

• Local Anaesthesia
• Rubber Dam
• Access
• Establish “working length”
• Prepare / instrument the canal
  • With anti-bacterial irrigation
• Medicate the canal
• Temporary restoration

Note

The primary focus of this lecture is on establishing the working length and the process of preparing and instrumenting the canal.

Aims of Root Canal Preparation³⁴

• To remove all of the canal contents, organic or otherwise, that may lead to the growth of micro-organisms or the breakdown of toxic products and their release into the periapical tissues
• To remove the irregularities of the canal walls including obstructions such as calcifications, etc.
• To prepare the canal for its disinfection and to develop a shape that permits a simple and effective root canal filling to be placed.

Note

Root canal preparation is a mechanical procedure with both biological and mechanical objectives. The mechanical objectives are designed to facilitate the achievement of the biological goals.

The aims of root canal preparation can be divided into two categories:

• Biological objectives
• Mechanical objectives

Biological Objectives⁵⁶⁷⁸⁹

• Remove all tissue and other debris
• Avoid periapical irritation
  • Confine instruments to the canals
  • Do not force debris through the ap. foramen
  • Measure & prepare canals at the same visit

Note

To minimize errors in measurement, it is crucial to measure and prepare the root canals in the same appointment. Relying on measurements from a previous appointment increases the risk of error due to variations in reference points and operator positioning.

• Create sufficient space within the canal for intracanal medication

Mechanical Objectives¹⁰¹¹¹²

• Leave the ap. foramen in its original position
• Keep the ap. foramen as small as is practical
• Create a continuously tapering conical shape
  • Narrow apically, tapering to wide orifice
  • Narrowest point at the apical constriction
  • Conical preparation must exist in multiple planes
• Create a shape that is easy to fill

Analogy

An analogy for the ideal prepared shape is the Washington Monument or the state war memorial in Kings Park, which has an even greater taper. The shape features a narrow apical point (apical seat) and a continuous flare towards the coronal end.

An image showing widening of the root canal.

Preparation Techniques and Instruments^13141516

Overview of Techniques

• Hand files - Stainless steel

• Rotary files - Nickel Titanium (NiTi)

• Flexible instruments used in a special low-speed, torque-controlled motor at speeds around 200 RPM.

  • Many different techniques for each are described in books, journals, lectures

Tip

While this lecture focuses on hand files, it is essential to master their use before progressing to rotary systems, as hand files are still required for initial canal negotiation and establishing working length even when using rotary techniques.

Factors Influencing Technique Choice¹⁷¹⁸¹⁹

The technique used should depend on the:

• Instruments used -

  • Design of the cutting blade

• Root filling technique used -

  • e.g. Lateral compaction, vertical compaction, etc.

• A lateral compaction technique requires a different preparation than a vertical compaction technique, which needs a larger canal size.

• Operator -

  • Skill, preference, experience

Examples of File Techniques and Systems²⁰

Hand File Techniques

• Non-serial
• Step-back
• Step-down
• Double-flared
• Crown-down pressureless
• Balanced forces
• Canal Master
• Hybrid techniques
• Continuous wave
• Dr. XXXX’s technique
• Dr. AAAA’s technique
• Etc, etc, etc.

Guiding Principle

However, the most important principle is to base the technique on the instrument’s design.

Rotary NiTi File Systems²¹

Info

There are approximately 80 different rotary file systems available worldwide. These systems come and go from the market frequently. While students will gain experience with specific rotary systems in later years, the foundational knowledge of hand instrumentation is paramount.

File systems	Handpiece systems
Quantec - SC, LX	TriAuto ZX
Axxess Flare	ProFile High Torque
Profile - 29, GT, .04, .06	ATR Tecnika Motor
ProTaper	Nouvag TCM Endo Motor
ProSystem GT	K³ etcm Motor + H/P
K³	Rotary Master Endo H/P
Lightspeed	Endo-Pro Micromotor
Herodent	Endo Gripper H/P
ENDOflash	M4 Safety Handpiece
Navi Flex	Tardie CS
NT McXim	Titan 3
NiTi Roto 360	Sprint TCM
NiTi Flex	Kavo ENDOflash
Microtitane	Herodent
Onyx-R File	Canal Finder
SureFlex	Canal Master
HyFlex etc, etc, etc	Cursor etc, etc, etc

Endodontic Hand Instruments²²²³

ISO Specifications²⁴²⁵

Note

To standardize instruments across manufacturers, the International Standards Organization (ISO) established specifications for hand files in the late 1960s.

Colour	Size	D1
Pink	6	0.06 mm
Grey	8	0.08 mm
Purple	10	0.10 mm
White	15	0.15 mm
Yellow	20	0.20 mm
Red	25	0.25 mm
Blue	30	0.30 mm
Green	35	0.35 mm
Black	40	0.40 mm
White	45	0.45 mm
Yellow	50	0.50 mm
Red	55	0.55 mm
Blue	60	0.60 mm
Green	70	0.70 mm
Black	80	0.80 mm
White	90	0.90 mm
Yellow	100	1.00 mm
Red	110	1.10 mm
Blue	120	1.20 mm
Green	130	1.30 mm
Black	140	1.40 mm

• ==File Size (D1 Diameter): The size of a file is determined by its diameter in hundredths of a millimeter at D1, which is 1 mm from the instrument’s tip. For example, a size 25 file has a diameter of 0.25 mm at D1.==

• ==Size Increments: Sizes increase by 0.05 mm from size 15 to 60. After size 60, they increase by 0.10 mm (e.g., 60, 70, 80).==

• Taper:

  • 0.02 mm / mm

• ==Cutting Blade Length: The fluted or cutting portion of all hand files is a standard 16 mm.==

• Lengths:

  • 21 mm
  • 25 mm
  • 28 mm
  • 31 mm

• ==The clinic primarily stocks 25 mm and 31 mm files.==

• ==Rubber Stoppers: These silicone markers can be moved along the file’s shaft to mark the working length, preventing over-instrumentation.==

Types of Files^2627282930

Instrument	Cross-Section Shape	Cutting Angle
HEDSTROEM FILE / H-File	Circle / Circle with a leaf-like inner shape	$90^{\circ }$
K-FILE	Square	$60^{\circ }$
REAMER	Triangle	$60^{\circ }$
TRIOCUT™	Three-lobed
UNIFILE®	S-shape
K-FLEX®	Diamond

Hedström Files³¹

• ==Manufacture: Ground from a round stainless-steel wire blank, creating a series of sharp, spiraled cutting edges.==
• ==Properties: Very efficient at cutting on the pull stroke. More flexible than K-files due to the round cross-section. These are the files used in the clinic.==

Mechanism of Use³²³³³⁴

Based on the overall design of the file and its cutting edges.

• Three actions used simultaneously:

  1. Slight Rotation (⅛) → To engage dentine

• ==A maximum 1/8th of a turn clockwise is used to engage the file’s cutting flutes into the dentin wall.==

Caution

Over-rotation, especially the 1/4 turn often cited for K-files, can cause the file to lock and break.

2. Push-Pull

• ==The primary cutting action occurs on the pull (withdrawal) stroke. The push stroke is passive. This motion shaves dentin from the canal wall.==

  3. Circumferential Filing

• Because most canals are oval or irregular, the file must be moved around the entire periphery of the canal. After each push-pull stroke, the instrument is repositioned against an adjacent part of the wall. This action ensures the entire canal is cleaned and shaped, maintaining its original cross-sectional form while enlarging it.

• These actions are used together to enlarge & flare.

Slight Rotation to Engage

Push-Pull action

Circumferential filing

Action of Files in Canals^{35363738394041}

• Passive
• Pull

Pre-curving Files⁴²

• Pre-curve ALL files prior to use

Tip

Over 95% of root canals have some degree of curvature. Therefore, it is safest to assume all canals are curved and to pre-curve files before insertion.

• > 95% of canals are curved **>**5°

• Reproduce the canal’s curve

• Can help by-pass obstructions

• But - curved files can CAUSE PROBLEMS if are rotated too much

Potential Complications^{43444546474849}

• Canal Transportation - Apically

  • ==The inherent stiffness of a file causes it to try and straighten itself within a curved canal. This can cause the file to preferentially cut the outer wall of the curve apically and the inner wall of the curve coronally,

• Strip perforation

  • ==In multi-rooted teeth (e.g., mandibular molars), canals are often located closer to the thin furcation side of the root. Excessive transportation towards this

• Ledging of canal

  • ==If a file is forced or rotated excessively when it meets resistance, it can dig into the canal wall, creating a ledge

• Shortening of “working length”

  • Occurs as the canal curvature is reduced
    • A 10-degree curve can shorten the working length by approximately 0.5 mm. This must be accounted for by progressively shortening the instrumentation length for larger files.

• File acts like a “plunger” or a piston

  • Debris created during instrumentation can be packed into the apical third if not properly removed, creating a blockage. This can be prevented by always instrumenting to the full working length with each file, using copious irrigation, and pre-curving files.
  • Can lead to a “false canal” or a perforation

Irrigation⁵⁰⁵¹⁵²

 MUST Irrigate Between Each File

• ==The canal should be flushed with an irrigant (e.g., EDTAC) between every file.==
• The irrigant helps to float debris out of the canal, lubricate the instrument, and begin the disinfection process.
• When instrumenting a multi-canal tooth, it is efficient to use the same size file in all canals before irrigating them all and moving to the next larger file size.

Gates-Glidden Burs⁵³⁵⁴⁵⁵

Properties⁵⁶

• Rotary instrument - for a low speed handpiece

• Made from: Steel or stainless steel

  • Steel versions are considered single-use.
    • They have a small, flame-shaped, side-cutting head on a long, thin shaft.

• Side cutting bur

  • End does not cut - only guides the instrument

• Six sizes – numbered 1 - 6

  • Should NEVER use No. 1 - too fragile

• ==Sizes are identified by rings on the shaft (e.g., 3 rings = size #3). Sizes #2 and #3 are most common.==

• Designed to break at top of shaft if too much pressure used

  • But - does not always happen !!

Risk of Fracture

Although designed to break at the shaft, they can corrode if reused and break near the cutting head, making retrieval extremely difficult. For this reason, they should be treated as single-use instruments.

Usage⁵⁷⁵⁸⁵⁹

• Use “passively” only - i.e. NO pressure
• Cut on withdrawal stroke only
• Use as an orifice opener & to flare the coronal few millimetres of the canal
• This creates a funnel shape for better access to the apical regions.
• NB - Will widen an existing hole but will not create a hole or opening that is not already there !!

Risks⁶⁰⁶¹

• **Take care to avoid
  • ==Aggressive use or using too large a size can cause a strip perforation, especially on the thin furcation side of a root. Cutting should be directed away from this

Instrument Characteristics & Risks⁶²

• oid “strip perforations”
• Designed to break at top of shaft if too much pressure used

But - does not always happen !!

Preparation Appointment⁶²

• Local Anaesthesia

• Rubber Dam

• Access

• Establish “working length”

• Prepare / instrument the canal

  • With anti-bacterial irrigation

• Medicate the canal

• *Temporary restoration

• Ultimately, every clinician develops their own variation of a standard technique.

Footnotes

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