the advantage of microscope is

1.The oversight of the root canal decreases.
2.easy to discover fracture line.
3.easy to repair perforation
4.easy to remove the broken instruments.
5.A root end filling with apicoectomy becomes accurate.

The greatest threat might be root fracture for the endodontically treated tooth.The prognosis of vertically fractured tooth is very bad and there are a lot of cases of the extraction.
The possibility of the root fracture will possibly rise when it is used for
largely loaded tooth such as abutment tooth of bridge, or anchored tooth of denture.

Resistance to fracture of restored endodontically treated teeth. Endod Dent Traumatol. 1985 Jun;1(3):108-11.

Endodontically treated teeth as abutments. J Prosthet Dent. 1985 May;53(5):631-6.

Classifications of root fracture
direction (Vertical or Horaizontal)
part (Crown,or Root)

The recovery method is different by the type of fracture. Vertically fractured root is almost hopeless.

A. Before treatment: radiolucent image is present at arrow

B. After root canal filling

C. 2years later: radiolucent image have been disapeared

Radiolucent image on x-ray films which suggests periapical lesions needs over 6 months to be diminished.

Criteria for diagnose

#Good on x-ray films (a year after treatment)

１．normal or periodontal ligament space within 1mm
２．radiolucent image has not seen
３．normal lamina dura
４．root resorption has not been recognized

#Doubtful on x-ray films (a year after treatment)

１．periodontal ligament space extended to within 2mm
２．radioluceny  has been equal to before treatment , or improved slightly.
３．hypertrophic lamina dura
４．root resorption has been indicated

#Unacceptable on x-ray films (a year after treatment)

１．periodontal ligament space extended to over 2mm
２．radioluceny has been increased
３．lamina dura has not been recovered
４．root resorption has been recognized

Recovery forms of  wound

It is preferable to recover to original organization.

In endodontically treated tooth,  it is ideal that newly cementum attach on apical foramen and root surface. As well, regeneration of bone are expected to take place in the part of bone resorption area, but recovery of wound will possibly be occurred in the form of fibrous granulation.

Under filling

Dead space beyond the filling material might be place for bacteria growing.

Over filling

Overfilling might cause postoperative pain and continued inflammation disturb normal recovery

a.Gums are incised, and inflammatory tissue is seen.
b.The apex of the root is cut by about 3mm, and the inflammatory tissue is taken out.
c.The root is shortened.
d.The root end is filled with cement.

America Association of Endodontist

Coronal leakage is widely acknowledged as a cause of the failure of the root canal treatment.

The influence of the method of canal preparation on the quality of apical and coronal obturation.
[J Endod. 1979]

The crown restoration is more important than the root canal filling.

Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration.
[Int Endod J. 1995]

Guttapercha and sealer alone can not prevent coronal leakage.

The influence of orifice sealing with various filling materials on coronal leakage.　[Dent Mater J.　2004]

purpose of rubber dum
１．Antiseptic treatment
２．Specification of operative field
３．Prevention of aspiration of instrument
４．Protection of surrounding soft tissue
５．Dampproof

Neither the decayed tooth nor the pulp disease occur in the germfree animal.
It is needless to say that the purpose of the root canal treatment is to make the root canal an asepsis, and aseptic treatment is necessary for the root canal treatment.

Prevention of secondary infection, or reinfection.
1.Use of sterilized instruments
2.Use of rubber dam

Prevention of focal infection.

Chronic odontogenic pain are mostly caused by introgenic injury or infection, and characterized by pain elimination with local anesthesia.

Major causes of chronic pain

The refractory pain are composed by complexity of causes described below.
1.Pain by continued stimulation

2.Abnormality of neural fiber related to pain transmission (neuropathic pain)

The stump pain (phantom limb pain and determination edge nerve etc. )are included in the neuropathic pain.
In the root canal treatment, if the neural fibers that distribute in the dental pulp or the periodontal tissue are injured, it is possible to happen.

3.Systematic disorder, mental disease

The inflammation which cannot be controlled because of systematic disorder, steroid taking, or immunosuppressive agent’s taking.

4.Psychogenic pain

Uneasiness to continuation of pain

#What is the Wind up phenomenon(central sensitization)?

An example of non-associative learning in which the progressive amplification of a response follows repeated administrations of a stimulus. An everyday example of this mechanism is the repeated tonic stimulation of peripheral nerves that will occur if a person rubs his arm continuously. After a while, this stimulation will create a warm sensation that will eventually turn painful. The pain is the result of the progressively amplified synaptic response of the peripheral nerves warning the person that the stimulation is harmful. Sensitization is thought to underlie both adaptive as well as maladaptive learning processes in the organism.