 as the direct retainer. Now once the direct retainer is attached to the cast partial length of framework when I apply a vertical dislodging force what you see is there is some amount of resistance. There is so hello everyone today we'll be looking at the topic of indirect retainers and I understood that this was slightly difficult in the undergraduate level so I have tried my best to declutter the topic for you. Now before we can jump into the topic of indirect retainers I have I wanted to make a few things clear and the first one is the difference between a cast partial denser and a acrylic partial or a treatment partial denser. What has been described in the books is cast partial denser that is what you see over here it has a metal framework an acrylic part and a denser teeth whereas what you see over here is the treatment or the acrylic partial denser. So what is described in the books is cast partial denser but what we follow and give to the patients on a regular basis is acrylic or treatment partial denser. So after having understood what is the difference between a cast partial denser and an acrylic partial denser let us try to understand the fundamentals the three fundamental concepts which is retention stability and support. So retention is defined as the ability of the framework or the cast partial denser to resist forces that are directed in the vertical aspect that is when you try to dislodge it in the path of insertion the ability of this cast partial denser to resist to that force is called as the retention. The ability of this cast partial denser to resist horizontal forces horizontally horizontal displacement is called as stability and the ability of the cast partial denser to resist forces directed towards the tissue surface that is if there is a framework that is sitting over here and if a force is applied towards the tissue surface it is called as the ability to resist that is called as support. So now let us try to understand the the principle of indirect container. Let us consider this pencil to be the cast partial denser framework. So this is the cast partial denser and the background that you see is the tissue surface. So now when I apply a vertical dislodging force what you see is the pencil or the cast partial denser is offering no resistance to the vertical dislodging force that means the retention is absolutely nil okay. So to enhance the retention what we do is we add the first component that is going to resist the vertical dislodgement force as you can see at the bottom that is going to act as the direct retainer. Now once the direct retainer is attached to the cast partial denser framework when I apply a vertical dislodging force what you see is there is some amount of resistance. There is some amount of resistance to the vertical dislodging force but what you see here is if this is the anterior portion this anterior portion has started to rotate that means the direct retainer that has been attached is acting as the fulcrum and the anterior portion of the cast partial denser framework has started to rotate. Now this rotation can cause undesirable and detrimental forces on the abutment and that has to be prevented. So that is what that is where the indirect retainer comes into the picture. So what I have done is to prevent the lifting or the movement of the anterior portion I have attached a indirect retainer that is going to prevent the rotation of the anterior portion. So now what you see here is when I am applying a vertical dislodging force what you see is the pencil is not raising up and the anterior portion is also not rotating. So this is the principle of indirect retainer and this gives us the definition of indirect retainer which says that indirect retainer is a component of cast partial denser framework that is going to assist the direct retainer in preventing the component from vertical dislodgment forces through a lever action acting on the opposite side of the fulcrum. It is a huge definition but if you split it up and if you can understand this principle and go back and read the definition it will be easier to understand. Now let us try to dive deeper into the other concepts of indirect retainer. Now if you see this refractory cast wax pattern has been adapted and we will be trying to understand what is a fulcrum line on this cast now. A fulcrum line is basically an imaginary line that is connecting the distal surface of the most posterior abutment that means it is an imaginary line that is going to connect to the distal surface of the first premolar on this side and the second molar on this side. So if this is the fulcrum line indirect retainer is always placed perpendicular and far away from the fulcrum line that means if this is the perpendicular and it has to be placed far away anteriorly. So an indirect retainer will be something like this occlusal rest that is there on this premolar. Why it has to be placed far away is only if it is placed far away anteriorly it is going to resist the anterior rotation as we saw on the principle of indirect retainer. So that is why indirect retainer is placed perpendicular and far away anteriorly to the fulcrum line as possible. So now let us try to understand the different types of indirect retainer. Before we jump into understanding the different types what we have to know is like any other component be it a major connector or a direct retainer or an occlusal rest indirect retainer does not necessarily have to be placed as a separate component. So a direct retainer or a major connector by itself can also act as an indirect retainer that is why understanding the principle of indirect retainer is essential to know if a separate indirect retainer has been incorporated in the design or if any other component that is there is going to act as the indirect retainer. So coming to the first one or the most commonly used indirect retainer is a auxiliary occlusal rest. So what you see over here is a Kennedy's class 2 classification and if this is the fulcrum line the indirect retainer has been placed perpendicular, anterior and far away from the fulcrum line. So auxiliary occlusal rest is the most commonly used indirect retainer. Next moving on to the canine extensions if this is again a Kennedy's class 2 classification and what has been done is a rest has been incorporated that is an auxiliary occlusal rest has been incorporated and since if this premolar is weak or it cannot take the entire load a small extension, a small line or a preparation will be done on the canine so that is going to act as the canine extension and similarly in the same way if a rest is not incorporated on the premolar and if a rest is incorporated on the singulum of the canine so that is going to be a canine rest indirect retainer. So thus these three are the most commonly used one moving on to the less commonly used indirect retainers. Now this is a Kennedy's class 1 classification on a mandible and the major connector that has been incorporated here which is the linguo plate or the continuous lingual plate is going to act as the indirect retainer. So this is the fourth type of indirect retainer which is the linguo plate indirect retainer. Now coming to the next one which is the indirect retainer that is coming in the modification areas so this is a Kennedy's class 2 mod 1 classification in this the fulcrum line is going to be somewhere like this and the direct retainer that has been incorporated in the modification area that is the direct retainer given on this premolar is going to act as the indirect retainer also. So in a modification area we have to keep in mind that there might or might not be a indirect separate indirect retainer but most commonly the direct retainer the class presumably that has been incorporated in the modification area is going to act as your indirect retainer also and the least commonly used indirect retainers are going to be the rugae support here the major connector is taking the support of a well established rugae and this rugae support is going to provide and function as a indirect retainer and the last and the most least commonly used one is going to be the major connector itself acting as the indirect retainer here what you see is a antero posterior palatal strap now this major connector is going to act as an indirect retainer it is not very effective but this major connector is going to act as the indirect retainer in a Kennedy's class 1 classification on a magzela. So these are the most commonly used and the different types of indirect retainers that are existing and described in the books now let us try to understand indirect retainers in two special situations one is Kennedy's class 1 classification and second is Kennedy's class 4 classification if you see a Kennedy's class 1 what is happening is this is the fulcrum line and ideally an indirect retainer should be placed perpendicular and anterior to the fulcrum line that means an indirect retainer should rest on the lingual aspect of the incisors but since incisors are a weak tooth to take that much amount of load what we are doing is we are splitting the indirect retainers and giving it as auxiliary or crucial rest one side on the first premolar and other side on the first premolar again so what is happening is the indirect retainer in a Kennedy's class 1 will not sit on the incisors but rather be split and divided into two indirect retainers each side on the first premolar so that is in a Kennedy's class 1 situation and now if you look at Kennedy's class 4 the fulcrum line is somewhere here and that means indirect retainer cannot be given anteriorly there is no position for indirect retainers anteriorly so we are going to incorporate indirect retainers posteriorly and just like how we saw in a Kennedy's class 1 we will split the indirect retainers into two halves that has been incorporated in the most posterior abutment here being the molars so here a direct retainer assembly a direct retainer class assembly is going to provide the indirect retention that is going to be incorporated in a Kennedy's class 4 so these are two different situations that has to be kept in mind and indirect retainers are going to be split rather than being placed at a convenient position so I hope this video was helpful in understanding the different types and the principle of indirect retainer so that's it for this video thank you