Course Goals (overall aim): This course aims at educating the students about the following : Methods of working length determination The different techniques for root canal preparation The different root canal irrigants Obturation techniques and materials Mishaps during cleaning and shaping of root canals Mishaps during obturation

Intended Learning Outcomes (ILOs): a-Knowledge and Understanding: By the end of the course every student will be able to: describe the different methods of working length determination describe commonly used irrigating solutions and their properties. describe the different techniques of root canal preparation list requirements, indications and available types of sealers. describe the different obturation techniques list errors that might occur during root canal preparation, their prevention and treatment if possible. recognize errors that might occur during obturation, their prevention and treatment if possible.

b-Intellectual Skills: By the end of the course every student will be able to: compare the different root canal preparation techniques compare the different root canal obturation techniques

c-Professional and Practical Skills: By the end of the course every student will be able to: determine the working length for each individual tooth Perform root canal preparation for single and multiple canalled teeth apply principles of root canal irrigation obturate single rooted as well as multirooted teeth interpret radiographs use the different intracanal instruments

Distribution of Scores: written exams 40% practical exams 20% Oral exams 20% periodic quizzes } course work } 20% assignments }

Working Length Determination

Reference point It is the site on the occlusal or incisal surface from which measurements are made. This point is used throughout canal preparation & obturation. The measurement should be made from a secure reference point on the crown, in close proximity to the straight-line path of the instrument, a point that can be identified and monitored accurately (usually the incisor edge in anterior teeth , the cusp tip in posterior teeth).

The first step in cleaning and shaping is working length determination. The word “length” is defined as the distance between two fixed points.

There are two apices recognized for any root: 1) Radiographic apex: which is the external border of the root tip & is seen radiographically. 2) Anatomical apex: which is the natural apical constriction formed by the cemento-dentinal junction (narrowest part in the canal).

The tooth length is the distance between a reference point coronally (such as the incisal edge for anterior teeth and the cusp tip for posterior teeth) and the radiographic apex. The working length is the distance between the reference point coronally and the anatomical apex.

Significance of working length determination: 1) Determine the instrument length in the canal. 2) Limits the depth to which the canal filling maybe placed. 3) Limits the postoperative pain & discomfort as instrumentation shorter than the apical constriction leaves uncleaned space.

4) Determination of the success of treatment. While beyond the apical constriction irritate the periapical tissues, violate the apical zone and affect the compaction of the filling material against the apex. 4) Determination of the success of treatment.

Failure to accurately determine & maintain working length lead to: a- Length too long can lead to: 1. Perforation through apical constriction 2. Traumatize the periapical tissue leading to inflammation, pain and swelling. 3. Overfilling or over extension 4. Increased incidence of post-operative pain and failure.

Failure to accurately determine & maintain working length lead to: b- Short working length can lead to: 1. Incomplete cleaning and debridement of the root canal 2. Shelfing the canal: a ledge in a root canal formed during instrumentation, which will catch an instrument tip. 3. Under filling 4. Persistent discomfort 5. Incomplete apical seal, apical leakage which supports the existence of viable bacteria and contributes to a periradicular lesion and lead to failure.

b) Bone but no root resorption 1.5mm from the apex. Variation in the position of the apical constriction in relation to the radiographic apex: The distance between the anatomic and radiographic apex ranges from 0.5-2mm, depending on; a) Apical foramen is usually found 0.5-1mm short from the radiographic apex ( no bone or root resorption). b) Bone but no root resorption 1.5mm from the apex. c) Bone and root resorption: 2mm from the apex.

Different methods used for working length determination: 1- Average Length of Teeth: 2- Digital Tactile Perception: 3- Patient Sensation: 4- Paper point evaluation

Methods of working length determination: 5) Radiographic method : - Proper preoperative radiograph is taken. - Proper sized file is inserted into the root canal from the reference point to the: * Estimated average length. * Apical constriction as felt by the dentist. * Patient sensation if healthy apical tissues are present.

- Adjusted working length should be checked radiographically. - Provisional working length x ray is taken while the file is inserted in the canal. - Adjustment for the working length is made by subtraction or addition to the used file length according to the proximity of the file to the anatomical apex. - Adjusted working length should be checked radiographically.

2) Buccal object rule for posterior teeth: This method is used for the working length determination in multi-rooted teeth. If the radiograph is taken with zero horizontal angulation this will lead to superimposition of the buccal and palatal canals on the film. This is why the buccal object rule is used through directing the x ray cone mesially or distally.

N.B: same lingual opposite buccal. - It states that “the most distant object from the cone (always the lingual) moves towards the direction of the cone in the film. - Meaning that when the x ray cone is directed from the mesial side, the lingual canal comes mesially on the film while if the x-ray is directed from the distal, the lingual canal becomes distally on the film. N.B: same lingual opposite buccal.

Limitations of Radiograph: Two dimensional image for three dimensional object so palatal or buccal curved roots can’t be seen. Wrong vertical angulation will lead to super imposition of anatomic structures. Procedural errors during imaging & processing Radiation hazards. Difficult of film placement in patient with high gaging sensation. Time consumption. Limited ability for proper determination of anatomic apex.

6) Electronic apex locators: - They are electronic devices which are designed to determine the canal length by giving a reading when the file tip is at the apical foramen as it reaches vital tissues. - The principle is based on the electrical resistance of different tissues. When the circuit is complete, resistance decreases and current begins to flow.

All apex locators function by using the human body to complete an electrical circuit. One side of the apex locator’s circuitry is connected to an endodontic instrument. The other side is connected to the patient’s body either by a contact to the patient’s hand or cheek. The electrical circuit is completed when the endodontic instrument is advanced apically inside the root canal until it touches periodontal tissue. The display on the apex locator indicates that the apical area has been reached

Advantages of electronic apex locators Accurate (80%-97% accurate), Easy and fast Reduction of x-ray exposure so can be used in pregnant women – because of no risk of radiation. Shortens the preparation time. Affordable, painless and safe. Artificial perforation can be recognized Can used in patient with gagging reflex Can be used when dense zygomatic arch is over lapping the apices of upper molars.

Disadvantages of electronic apex locators Requires a special device with fully charged battery as weak battery affect the accuracy of reading. Accuracy is limited to mature fully formed apices. Accuracy is influenced by the electrical conditions in the root canal (touching a metallic restoration will affect the performance of electronic apex locator) Difficult in tooth with open apex that will give reading at shorter length Contraindicated to be used in patients with cardiac artificial pacemaker.

Classification and Accuracy of Apex Locators: This classification is based on the type of current flow and the opposite to the current flow, as well as the number of frequencies involved.

First-Generation Apex Locators Also known as “resistance apex locators”, measure opposition to the flow of direct current or resistance. Their major drawback was the need for the canal to be thoroughly debrided and dry. E.g. sono-explorer.

Second-generation apex locators Also known as “impedance apex locators”, measure opposition to the flow of alternating current or single frequency impedance. The major disadvantage of second-generation apex locators is that the root canal has to be reasonably free of electroconductive materials to obtain accurate readings. The presence of tissue and irrigants in the canal changes the electrical characteristics and leads to inaccurate, usually shorter measurements. E.g. Endocater.

Third –Generation Apex Locators The third-generation apex locators are similar to the second-generation except that they use multiple frequencies to determine the distance from the end of the canal. These units have more powerful microprocessors and are able to process the calculations required to give accurate readings. E.g. Endex and Root ZX.

Fourth- Generation Apex Locators The apex locaters are similar to Impedance-type because it measures the impedance of the tooth at two different frequencies. As the file is advanced apically, the difference in the impedance value begins to differ greatly with maximum difference at the apical area. The disadvantages of devices 4th generation is the difficulty on working in dry canals and necessarily of compulsory, additional wetting.

Fifth-Generation Apex Locators These were developed in 2003. It measures the capacitance and resistance of the circuit separately. It is supplied by diagnostic table that includes the statistics of the values at different positions to diagnose the position of the file. Devices employing this method experience considerable difficulties while operating in dry canals.

Sixth-Generation Apex Locators The sixth generation Adaptive Apex Locator overcomes as the disadvantages of the popular apex locators 4th generation low accuracy on working in wet canals. Adaptive Apex Locator continuously defines humidity of the canal and immediately adapts to dry or wet canal. This way it is possible to use it dry and in additional wetted canals as well, canals with blood or exudates, canals with still not extirpated pulp.

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