Y3 L4 Preparing and shaping

Question 1

What is shaping?

Answer 1

Controlled removal of dentine to produce a suitable shape to facilitate irrigation, placement of medicament, and insertion of a dense root filling without compromising the integrity of the tooth. (Using files).

Question 2

What is cleaning?

Answer 2

Removal of all inorganic debris, organic substrate and microorganisms. (Using irrigation techniques).

Question 3

What approach is used in RCT?

Answer 3

Crown down approach: shaping and disinfecting coronally before insturmenting apically.

Question 4

What are the advantages of the crown down approach?

Answer 4

• Straight line access achieved early on, before reaching the apical region
• Eliminates dentinal interferences
• Reduces the risk of extruding infected debris
• Better penetration of irrigating solution
• Decreases the risk of apical blockage and other procedural errors

Question 5

Summarise the corono-apical approach (crown down).

Answer 5

• Negotiate the coronal portion of canals using hand files
• Use rotary instruments for coronal flare
• Negotitate the apical protion using hand files
• Determine working length
• Use rotary instruments for apical prep

Question 6

What are Schilder’s mechanical objectives?

Answer 6

• To develop a continually tapering funnel from the access cavity to the apical foramen (smooth-flowing preparation). Widest at orifice level. Most narrow apically.
• To maintain the path of the original canal e.g. straight or curved
• To keep the apical foramen as small as possible
• To retain the apical foramen in its original position

These principles reduce risk of procedural errors.

Question 7

Give examples of procedural errors.

Answer 7

• Ledge formation
• Apical transportation
• Perforation
• Apical zip

Question 8

What is a ledge?

Answer 8

• Lack of smooth flowing tapered
• Cannot bypass a ledge, area beyond ledge will not be adeqautely shaped and cleaned
• Can occur due to forcing large files down a curved canal, or skipping file sizes instead of gradually widening the canal

Question 9

What is apical transportation?

Answer 9

• Preparation should be centred around the path of the canal (red line) from the orifice level to the apical constriction
• The black outline shows how the root canal has been prepared, can see it is not centred.
• Caused by inflexible file being rotated in a curved canal, has a tendency to want to straighten and not keep to the path of the canal. Pushes preparation further off the path of the canal, creates its own path.

Question 10

What is a perforation?

Answer 10

• Continuing along the wrong path
• Root material present in periapical region

Question 11

What is strip perforation?

Answer 11

• A perforation on the inner region of the curved root due to over instrumentation
• More common in L6s due to narrow roots
• In this inner aspect at the curve there is a thinner region of dentine called the danger zone
• If instrumentation focuses on this inner part, a strip perforation can occur

Question 12

What is an apical zip?

Answer 12

• Where the preapration (green) moves further and further from the route of the canal (black)
• Preparation gets wide towards the apex, the narrowest part of the preparation is called the elbow.
• Preparation must be centred around the original path of the canal.

Question 13

What are the consequences of not following Schilder’s mechanical objectives?

Answer 13

• Inadequately cleaned root canals, which will harbour debris and residual microorganisms that will cause treatment failure
• Over-reduction of sound dentine can cause weakened roots and reduce fracture resistance
• Apical or strip perforation gives poorer prognosis as you cannot achieve an adequate seal

Question 14

Where is the apical constriction usually located?

Answer 14

0.5-2mm from the apex
The apical constriction is the narrowest part of the canal apically and this is where the preparation should finish.

Question 15

What is the difference between the apical foramen, the apex and the apical constriction?

Answer 15

• Apical foramen: the opening of the canals on the surface
• Apex: radiographic or anatomical feature which is the most prominent part of the root end
• Apical constriction: narrowest part of the canal apically

Question 16

What is the difference between estimated and true working length?

Answer 16

Question 17

What are the issues with radiographic/estimated working length?

Answer 17

• Inability to visualise canal terminus
• Inability to visualise apical constriction
• In 20% of cases, the canal terminates buccal or lingual to the apex, when you radiograph the tooth you will not be able to see the tip of the instrument out of the canal

Question 18

How does an EAL work?

Answer 18

• Used to identify apical constriction
• Works based on electrical difference between tissues
• Place file down canal, attach file to device, as you advance further down the canal the device tells you when you’re reaching the end of the canal, and when you reach periapical tissues

Question 19

What is the apical stop?

Answer 19

• Prepare canals to the determined true working length and do not exceed this length.
• The apical stop is created by preparing the root canals according to the working length.
• Ensure the canal is narrowest at the apical stop, and then develop a continually tapering conical form in the canal.

Question 20

What instrumentation techniques do we use to shape the canals?

Answer 20

• Hand instruments (stainless steel)
• Mechanical rotary devices (NiTi)

Question 21

What are the 3 types of stainless steel hand instruments?

Answer 21

• Hedtrom
• K files
• Reamers

Question 22

Describe the stainless steel hand instruments.

Answer 22

• Adaptable, able to be used in a variety of canal configurations
• Colour coded
• Length of cutting part is 16mm
• 2% tapered
• File lengths range in size and shape

Question 23

What are the disadvantages of stainless steel hand instruments?

Answer 23

• Alloy and design tend to lead to more procedural errors unless the operator is well experienced
• Not predictable/reliable, large degree of variation between dentists
• Complicated: numerous techniques developed and found in literature in order to overcome the design flaws created by the complex instrument sequences
• Inefficient as there are a large number of instruments required and long method of instrument manipulation = slow process
• Difficult to learn to use

Question 24

Describe NiTi instruments.

Answer 24

• Come in a hand driven version, and a rotary version
• Safe
• Super elastic (flexible) which reduces incidences of operator error
• They have shape memory, return to original shape once they leave canal
• Held in handpiece, prevents instruments being dropped into canals
• Predictable: standardised methods, reduced operator variability
• Simple sequence to follow, fewer instruments required to complete preparation
• Easier to learn how to use, inexperienced operators can produce well shaped canals, fewer problems with instrument manipulation
• Efficient: rapid removal of dentine, smaller number of instrument changes required

Question 25

What are the disadvantages of NiTi instruments?

Answer 25

• Rotary files cannot be used alone, must be used after hand files have been used, (hand files generate a glide path)
• Can deform and fracture if overused or used incorrectly
• Cannot be used in cases of severe apical curvature or double curved canals
• More expensive, require hand pieces to drive them
• Cannot pre-bend

Question 26

What are the sizes of the ProTaper files?

Answer 26

Question 27

What is pre flaring/coronal flaring?

Answer 27

Question 28

State the general guidelines for using NiTi rotary instruments.

Answer 28

250-300rpm (slow)
Light continous pressure, passive, brushing motion on withdrawal