 Welcome to everybody. Today, I'll be talking about working length determination. I'll be talking about this particular topic. And the following contents. I'll begin with introduction. I will go on with the definitions involved in working length. Anatomy of the root apex clinical significance of working land different methods of working in determination and the most common methods in our clinical practice. In radiograph, like such as radiographic and non radiographic methods. Let us begin with introduction. One of the main concerns in root canal treatment is to determine how far the instrument should be advanced within the root canal. And at what point preparation and filling should terminate. Winning shaping and obturation cannot be accomplished unless working length is determined precisely. Next coming on to the most common definitions to understand working length concept. Working length is defined as the distance from the coronal reference point to a point at which canal preparation and obturation should terminate. The reference point, it is a site on occlusion or incisal surface from which measurements are made. This point is used throughout canal preparation and obturation. Anatomic apex is defined as a tip or end of the root determine morphologically and the radiographic apex is defined as a tip or end of the root determine radiographically. Next coming on to the major and minor diameter. Now major diameter or apical foramen. It is the main apical opening of the root canal. It is frequently essentially located away from the anatomic or radiographic apex. Now, can you see how this is the major apical diameter. Now coming on to the apical construction or a minor diameter. It is it is the apical portion of the root canal having the narrowest dimension. Now, can you see this particular figure? Now, this is the apical construction or a minor diameter. Now, next is a cemento-dental junction. It is a region where the cement and dentine are united. Now, to understand the cemento-dental junction, as we all know, there's a dentine in the root canal. Now, this dentine means the cement of the root apex and that location where they both unite is called the cemento-dental junction. Next, we will understand the anatomy of the apex. Now, this understanding or this knowledge is very important to understand the concept of working length. So, if understood properly, we can establish an accurate working length. So, to understand this particular anatomy of the root apex, we need to know certain components of this root apex. Now, the root apex generally comprises of apical foramen, apical constriction, cemento-dental junction, lateral canals. Then there is a canal curvature and there are different types of root apex. So, I'll be talking about all this under the following slides. Let me begin with the apical foramen. Apical foramen is rounded edge like a funnel or a crater that differentiates the termination of the cemento-dental canal from the exterior surface of the root. So, this is the apical foramen. Okay, foramen is nothing but an opening. As we know, in astrology, we all have heard about the various foramans in our skull. So, to understand it better, it's just an opening of the root towards the apex. Now, the location and shape of fully formed apical foramen vary in each tooth and in the same tooth at different periods of life. Next, coming to the apical constriction. Now, apical constriction is the narrowest part of the root canal with the smallest diameter of blood supply. As you can see here in this particular figure, it's the narrowest part of the root canal system. Now, preparation to this point results in a small wound site and optimal healing conditions, means to say that if you try to prepare your canal like a biomechanical preparation, or if you try to operate the root canal to this point, it can create an optimal healing condition. Now, apical foramen is not always the most constricted part of the root canal. From the apical constriction, the canal widens as it approaches the apical foramen. Now, if you can see here, it widens when it approaches the apical foramen. Now, this shape can be compared to a funnel shape or it can be compared to a hyperbolic shape or the shape of the morning glory flower. Next, the important landmark in the root anatomy is the cementodentinal junction. I've already explained about the cementodentinal junction as to what it means. So, it basically means the dentin meeting the cement of the root apax. Now, it is a histological landmark. It cannot be located clinically or radiographically because it is present in the canal system. So, we cannot really determine it morphologically or clinically. Next, coming to the various lateral canals or accessory canals present in the main root canal. The knowledge of lateral canals is very important to determine the working length precisely. So, we need to know the exit, the origin of the lateral canals. So, a lateral canal is located at right angles to the main root canal. You can see here it is the lateral canal originates at right angles to the main root canal. Now, accessory canal. Now, here is the accessory canal. It branches off from the main root canal in the apical region and the forkation canal originates in the forkation area. Now, these canals are areas for interchange of metabolic and breakdown products between the pulp and the periodontal tissue. So, if any disruption of this area or if any infection results in the pulp, which it can reach the periodontal tissue, also the vice versa, if the infection is existing in periodontal tissue, it can reach the pulp. Now, we need to know two important canals, which is lateral canal and an apical delta. Now, if you can see in this particular radiograph, this is nothing but a lateral canal, which is right angle direction from the main root canal. Now, where is the apical delta can be seen in the root apex? So, this is a branching pattern of small accessory canals, which can be seen at the tip or apex of the sum two. Now, in this particular radiograph, you can see a mandibular molar showing in apical delta. So, sometimes this apical delta is very critical to obture it because sometimes if any irritants or bacterial byproducts are there in this particular apical delta, chances of reinfection or it can, you know, the obturation, it really determines the success rate of the root canal treatment. Next, moving on to the significance of working and determination. It determines how far into the canal the instruments are placed and well and thus how deeply the tissues, the debris and metabolites are removed. It limits the depth to which the canal filling may be placed. It affects the degree of pain and discomfort that the patient will feel following the appointment. If calculated within correct limits, it will play an important role in determining the success of the treatment and conversely, if calculated incorrectly, may cause the treatment to fail. Next, coming on to failure to accurately determine and maintain the working length. Now, what are the main causes of failure? Suppose the length too long. Now, suppose if you have calculated working length and the length of the working length is too long can lead to perspiration through apical constriction. It can lead to overfilling or overextension of the gutter pressure points. It can lead to increased incidence of postoperative pain. It can lead to a prolonged healing period and low success rate owing to incomplete regeneration of cementum, baritone ligament and alveolar bone. Now, problems associated with the shorter working length. It can lead to incomplete cleaning that is incomplete debridement of the bacteria and its byproducts from the main root canal. It can cause underfilling of the root canal. It can cause a persistent discomfort to the patient. It can cause incomplete apical seal, apical leakage, which supports the existence of viable bacteria and contributes to a periratical and lesion. And also the main factor or main point to be noted here if the short working length is present in root canal treatment, it can lead to a lower success rate. Now, how to measure working length? Now, measurement should be made from a secure reference point on the ground that can be identified and monitored accurately in close proximity to the straight line path of the instrument. Now, reference points in anterior teeth are usually the incisal edges and in posterior they are the cusp tips. The reference point must be definite and reliable point or surface to ensure exactness in all subsequent measurements. Means the reference point should not be changed in but in following appointments. So it should be a reliable point. Now incisal edges or cusp that are undermined or fractured should be ground until a sound surface is attained. So the statement means if suppose there is uneven surface or there is a up and downs in particular incisal edges or a cusp tip. So it should be made flattened so that that particular point can be used also in the next upcoming appointments. The reference point is the site on the occlusion or incisal surface from which measurements are made. A reference point is chosen that is stable and easily visualized during the preparation. Reference point that will not change during or between appointments is selected. Do not use weakened enamel or diagonal lines or fractured as a reference site for length of tooth measurement. Weakened cusp or incisal edges are reduced to a well supported tooth structure. You can see here there is a fractured anterior tooth which has made stabilized to which has made even so that a proper attainable reference point is achieved. So this reference point will not be changed in subsequent steps of the root canal treatment. Next moving on to the different methods of working-line determination. Now there are basically two different types of working-line determination. One which involves a radiograph and one which does not involve the radiograph. Now radiographic methods can be different types. Now there are so many types which are mentioned here. Starting with best method, Brickmans, Bramante's, Grossman's formula, Engels method, Wien's method, Cutler's method, radiographic grid, Euclidean endometry, zero radiography, direct digital radiography, subtraction radiography and endometric probe. Now the most common used radiographic methods in our clinical practice will be either Grossman's formula, Engels method and Wien's method. Whereas non-neutographical methods are becoming more popular as in the current era of practicing endodontics which can be digital tactile sense, apical periodontal sensitivity, electronic apex locator and paper point method. So in this the electronic apex locator with the different generations of apex locator available, it is becoming easier for us to accurately determine the working-lines. Now let us understand the most commonly used radiographic methods first and then we will move on to non-neutographical methods. Now this is the basic idea of radiographic method of determination of working length. Now in this particular slide you can understand there is a radiograph which will be exposed. That is that preoperative radiograph will be exposed and then files will be placed in the root canal and then one more radiograph will be exposed and with the addition or subtraction principle we can accurately determine the working length. Now there are two techniques of radiography which is involved in assess our determination of working length. The first technique is paralleling technique and the next technique is bisecting angle technique. Now I am not going to the oral medicine aspect or oral radiology aspect to give you the insights about the both techniques. So whichever technique is feasible to our practice or wherever you are practicing or you want to calculate the working length you can choose either of the technique. Now coming to the Grossman's method. In Grossman's method it involves a series of radiographs which can be a preoperative radiograph and placing the file inside the canal and taking a radiograph later on. So the correct length of the tooth can be determined by the Grossman's formula. It can be calculated by correct length of the tooth is equal to known length of the instrument in the tooth into apparent length of the tooth on the radiograph. That is after exposing the radiograph while placing the file on the root canal divided by apparent length of the instrument on the radiograph. So with this formula you can calculate the working length of the tooth. The next which is the most commonly used in our clinics is Ingle's method. Now this method is very simple like first we have to measure the tooth on the preoperative radiograph. So this is the first step wherein you measure the tooth length in the preoperative radiograph. Then you subtract 1 mm as a safety allowance for possible image distortion or magnification and then you place the file. Now suppose this particular length of the tooth is 23 mm. Now we have subtracted 1 mm and we adjust the length to be 22 mm and with this file the endodontic file is placed in the root canal and one more radiograph is exposed. Now another radiograph on the other radiograph measure the difference between the end of the instrument and end of the root end and add this amount to the original measured length. Now suppose if the instrument is at the apex there will be no need to change the root canal length. If suppose there is a difference in the length. Like suppose if you find that there is a 1 mm short of the length you can adjust it according to the preoperative radiograph. If the instrument has gone beyond the apex, subtract this difference from the adjusted length of the tooth and subtract 1 mm. Now safety factor to confirm with the apical termination of the root canal at the apical constriction. Now the safety factor is nothing but you have to subtract 1 mm from the actual length of the tooth. That is only because that major and minor diameter are always separated by a distance of 0.5 to 1 mm. So we always give a safety allowance of 1 mm. Now suppose you calculate the working length in the radiograph and it is 23 mm. So for the safety factor you need to subtract 1 mm and you need to keep your working length as 22 mm. Okay that is about the Engels method of working length determination. Now for this, Veen has given some modifications in a length subtraction. Now he says that if there is no resorption in the first picture you can see if there is no resorption, if there is an optimal periapical condition, you can subtract 1 mm. And suppose if there is any periapical bone loss present you can subtract 1.5 mm and if there is any periapical bone loss with root apex resorption you can subtract 2 mm. So these are the Veen's modification which is very very very important for us to know wherein in those particular three conditions to subtract how much length from the main calculated working length. Now according to Cutler what he has told is like anatomy of the root apex he has divided or he has given some facts about the distance between the major minor diameter, the apex of the tooth and the minor diameter. So the main point to be remembered here is the distance between the major and minor diameter is 0.5 mm in 18 to 25 year old and 0.7 mm in 55 years or above. Okay and the distance between 1 and 3 that is the apex and the minor constriction is in the range of 0.1 to 2.7 mm. Okay so it can be from very minimal to maximum of 2.7 mm. Now coming to the advantages and disadvantages of this radiographic method. The advantages of being you can see the anatomy of the tooth. You can see if any curvatures of the tooth roots present if present it can see a relationship between adjacent teeth and anatomic structures. Disadvantages being it varies with different observers it can superimpose the anatomical structures. It can give a 2D view of a 3D object and it leads to a radiation exposure. It cannot interpret if apical foramen has buccal or lingual exit and also it has limited accuracy. So with all this disadvantages kept in mind the researchers have gone from radiographic to non-radiographic. So now we will see the most commonly used methods in our critical practice which involves no radiography. The first one is digital tactile sense. Now this method is very simple method wherein with the digital tactile sensation we can feel the apex of the root. Okay you can just take a file and you can just feel the apex of the root and also to keep in mind this comes with experience. Suppose if you have an experience you can really feel the root apex. So you can try it out in the extracted tooth models and then you can try it out on the patient. So advantages being for this method it is a time saving and there is no radiation exposure but also there are some disadvantages. Suppose in cases of a narrow canals one may feel increased resistance as the file approaches the apex. Also in cases of teeth with immature apex the instrument can go very apically 2 to 3 mm beyond. In case of anatomical variations in apical constriction or sclerosis or resorption and age this method becomes unreliable. So this method should be considered supplementary to high quality carefully aligned parallel working length radiograph or an apex locator. So this is a supplemental method. Next is the Paradontal Sensitivity Test. This method does not provide accurate readings for example in case of narrow canals instrument may feel increased resistance in apical 2 to 3 mm. Now this Paradontal Sensitivity Test is mainly a test wherein you can get the patient's response of pain. Suppose when you put a file inside the tooth now you can proceed or you can advance your file to a point wherein patients ask you to stop it because it will be very painful for him to experience that particular you know the situation. So this also can be used as a supplemental method in working length determination. Next is the Paperpoint Measurement Method. This method however may give unreliable data. If the bulk is not completely removed like suppose this is nothing but using a paper point and we can place it in the canal. So you can advance this paper point to a point wherein you can see a bleeding or suppose in the apex of the root canal when there is a bleeding point it makes the working length determine accurately. Suppose I can give you an example that suppose in a patient wherein you have extirpated the bulb correctly you can place this paper point and this paper point when it reaches the apex there is a bleeding point noted. So that is how we measure the working length in this particular method. But this method cannot be reliable if suppose the tooth is pulplis and a periobacterial lesion rich in blood supply is given because if such thing is there the entire paper point will become red in colour. Also if the paper point is left in canal for a long time it gives you an unreliable result. Next coming on to the Electronic Apex Locator. In addition to radiography tactile sensation has been used with questionable success. The drawbacks cited about radiographic length determination, the introduction and development of apex locators was received with enthusiasm. This device does not assess the position of the root apex and the name electronic apex locator is not appropriate. Electronic apical foramen locator or electronic root canal length measurement device as a generic name would be more appropriate. So it is basically electronic device which can be used to determine the apical foramen or minor constriction using electric current. So we will understand the mechanism of how it accurately determines the root length. It uses the human body to complete an electrical circuit. One side of the circuitry is connected to an endodontic instrument that is here. If you can see one side is connected to an endodontic instrument and the other side to the patient's body. So this is the other side which is a lip or a chin or a buccal mucosa here and is connected to the patient's body. The patient's lip or by an electrode held in the patient's hand. You can also make patients hold it or keep it in its hand. The functionality is based on the fact that the electrical conductivity of tissue surrounding the apex of the root is greater than the conductivity inside the root canal system provided the canal is dry. Now the length of this is measured by the electrical difference between the canal, the canal conductivity of the current in the canal and also in the pellet apex. So differences in this both situation will lead to a determination of a point wherein you can look at the minor constriction. The parts of the apex locator. Now it has four parts. It is the lip clip, the file clip, the electronic device and the cord which connects above three parts. Coming to the uses of the apex locator, it provides objective information with high degree of accuracy. If there are suppose any overlapping routes in cases of mandibular or maxillary molars, it can determine the working length. If there is an excessive bone density present in the apical portion of the root, it can determine the working length. It can be used in patients with gag reflex and cannot tolerate x-ray films. It can be used in pregnant ladies to reduce the radiation exposure. It can be useful in children, disabled patients, heavily sedated patients, etc. So these are the basic uses of the apex locator. The conditions for the accuracy of electronic apex locator can be like basic conditions to for accurately it has to be present to accurate for the accuracy of this particular apex locator. The canal should be relatively dry. The canal should be free from debris. There should be no cervical release. There should be no blockage or calcification of canals. There should be proper contact of file with the canal walls and the periapics. These are the basic conditions required. Coming to the different generations of electronic apex locator with some of the examples. Now coming to the first generation, it was mainly the main principle involved and its working was resistance. So it used to determine the resistance between the flow of the current in the apex and the canal system. So the examples were endometer as the dendometer, then also there is a cofinken by Denmark company. Next was second generation was impedance. Now impedance, the principle involved here is impedance, which was used and the examples being the Sono Explorer and Digipex 2. Whereas the third generation is the frequency, which is most commonly used in our clinical practice. It gives you different frequencies in the root canal and also in the apex. So the most common example for this can be the ND 5000. Also the index are up to the apex locator. The next thing the fourth generation apex locator, it has dual frequencies which are involved to accurately determine the working length. It can be root ZX and propex to fifth generation. It involves the multiple frequencies and it is one of the recent advanced type of an apex locator, which determines the root apex 90 with 99.9% accuracy. And the last being the sixth generation or an active type of apex locator. So this is still under the research stage, but soon the days are not far that we can get a apex locator which can accurately determine and which can replace the radiographic method. Finally the conclusion the minor diameter is a practical and anatomy termination point for the preparation and obturation of the root canal and this cannot be determined radiographically. Modern apex locators can determine this position with accuracies greater than 90% but with some limitations. No individual method is truly satisfactory in determining endodontic working length. Therefore the combination of the methods should be used to assess the accurate working length determination. So that's all about the walking and determination. I thank all of you to attending or listening to this lecture. Thank you.