 Hello everyone, welcome back to another session in dentistry and more. Today's topic in process roundics is objectives of impression making. So, we have five objectives. The first one is retention, then stability, support, aesthetics and the last one is preservation of remaining structures. The first three are very much confusing and important that is retention, stability and support. The last two is aesthetics and preservation of remaining structures. The name itself gives a self explanation about it. So, we will be dealing in detail about the first three, retention, stability and support. So, let's learn one by one. So, we will start with retention. Okay, so, retention is defined as that quality inherent in the processes which resist the force of gravity or adhesiveness of food substances or the forces associated with opening of the jaws. Okay, so, it is a quality of that danger to resist the gravitational force that is especially in the maxilla or the food adhesiveness and also forces associated with mouth opening. So, it is the ability of danger to resist the displacement against the vertical forces that is the tissue away dislodgement. So, this is the tissue we have tissue here with this is the denser maxilla denser. This is the mandible denser. Okay, this is the maxilla denser. So, it is the ability of the denser to resist the displacement against the vertical force. So, there will be vertical forces like this, like this. Okay, that is tissue away dislodgement. So, this is the tissue and it is moving away from the tissue. So, this is mandible and this tissue and the denser is going up. There is a tissue away dislodgement that is retention. Okay, don't get confused this retention that is away. It is moving away from the tissue that is from maxilla or mandible. So, we have retentive forces act through the three surfaces of a denser. So, we know the three surfaces of a denser that first one is occlusion surface, then the Polish surface, then the impression surface. Okay. So, these are the three surfaces of a denser and the retentive forces act through these three surfaces. Okay. So, through the occlusion surface, the force of mastication, force of mastication. Okay. Then the Polish surface, there will be muscular forces, muscular forces and the last one that is the impression surface which is in contact with the tissue. There will be physical forces. So, these three forces are act through these three surfaces that is occlusion surface, Polish surface and the impression surface. Okay. So, there are many dislodging forces. So, there are many dislodging forces which is acting on the densers. It could be mastication or adhesive foot like pizza or chewing gum or gravity that is gravitational force but it acts only on the maxilla or the surrounding musculature or it could be occlusion, prematurities or it can also be para functional habits. All these things can dislodge the denser from the tissue. Okay. So, that is a retention dislodging forces which is basically against gravity. So, there are many factors which is affecting retention. It can be classified as primary factors and secondary factors. So, primary factors and secondary factors. Primary factors involves physical factors or mechanical factors, physical and mechanical. Whereas the secondary factors includes muscular factors, anatomic factors, physiological factors, psychological factors. So, all these includes in secondary factors. Okay. So, we will start with the physical factors. Okay. So, which involves adhesion, then cohesion, then interfacial surface tension. So, interfacial surface tension. Then we have the capillary attraction, capillary attraction. Then atmospheric pressure, viscosity and finally gravity. Okay. So, these are the primary factors of retention and the physical factors. So, adhesion. So, we will start with adhesion. Adhesion is attraction of unlike molecules. Okay. Unlike molecules and cohesion is the force between similar molecules or like molecules. So, adhesion, it acts when saliva sticks to the denger base and to the mucus membrane of basal seat. Okay. So, there will be adhesion or adhesi force between the denger base and the mucus membrane of the basal seat. So, this quality of adhesion depends on the close adaptation of the denger. Size of denger bearing area, the type of saliva and the direction of displacing force. Okay. So, the amount of retention provided by the adhesion is directly proportional to the area covered by the denger. So, if you have more area, maxilla will be having more retention compared to mandible. Because mandible surface area is less compared to maxilla. Okay. So, similarly, patients with small jaws or very flat alveolar edges cannot expect a good retention compared to the patients with large jaws or prominent alveoli. Okay. So, the most adhesives saliva is thin serous. Okay. Thin serous saliva will be most adhesive one whereas the thick saliva is very adhesive but tends to build up so that it is too thick in palatal area and which further interferes with the oral adaptation. So, always the thin serous mucosa will be best for the maximum retention. So, it is a force between or the physical attraction of unlike molecules and it acts when saliva sticks to the denger base and to the mucous membrane. Okay. Now, we have cohesion. Cohesion is a force between like molecules or similar molecules. That is, it occurs within the layer of fluid or within saliva. It is a molecule, same molecules within saliva. So, it is present between the denger base and mucosa but the normal saliva is not very cohesive. So, therefore, most of the retentive forces of denger mucosa interface come from the adhesive and the interfacial surface tension. So, these two are the main retentive force because the cohesion or cohesive force is too low for saliva. So, we are mainly taking the retentive force from adhesion and interfacial surface tension. Okay. So, just take an example. So, we have a substrate here and we have adhesive in between. Okay. So, the adhesive force or the adhesion is between the substrate and the adhesive. That is happening here. Okay. These unlike molecules. That is, the substrate is one and the adhesive, the second one. There is a different, different molecules but the cohesive forces within the adhesive is the same molecule. These are the same molecules. So, the force between these two is the cohesive force and between these two is the adhesion force. That is the difference. Okay. So, cohesive force is too less for saliva with respect to our denger. So, we are mainly focusing on the adhesion force and the interfacial surface tension. So, the next one is interfacial surface tension. It is a resistance to separation of two parallel surfaces that is imparted by a film of liquid between these two. Okay. So, this is a film of liquid between two parallel surfaces. So, that is the resistance for separation of these two. So, this is commonly we see when we have two plane surfaces just like glass and we have a thin layer of liquid in between these two. The force which we apply to separate this is very greater than if the water is not present in between. Okay. So, that is the interfacial surface tension. So, this roll of surface tension is through the capillary attraction. Okay. So, there will be capillary attraction, capillary force between these two. So, when the adaptation of denger base to mucosa is sufficiently close, the space filled with a thin film of saliva act like a capillary tube. So, this is a bone and we are adapting the denger very close to the bone or maxilla or mantable. The saliva within these two act like a capillary tube. Okay. And this liquid which seeks to increase its contact with both the denger and mucosal surface. So, there will be a capillary action and increased surface tension because of the presence of saliva. Okay. So, that is why the adhesive force and interfacial surface tension are very much crucial for the retention not the cohesion. Okay. So, that is the third one interfacial surface tension. We also talked about the capillary attraction because it both comes in same concept. And the next one is atmospheric pressure. So, atmospheric pressure which resist dislodging forces to denger with an effective seal. Okay. Because no air entrapped between the fitting surface of the denger and the mucous membrane. So, it is called nothing but suction. That is a resistance to removal from the basal seat. And the sixth one is viscosity. Saliva is drawn into a space being created beneath the denger. Okay. So, it gives a valve-like action of the soft tissue. It depends on the saliva quality that is consistency and quantity. We already spoken thin, serious saliva is very good compared to thicker one. Okay. And the last one is gravity. So, it acts like a retentive force for the mantibular denger. But it is a displacy for the maxillary denger. Okay. So, these are the physical factors for the retention. Now, we have the mechanical factors. Mechanical factors, first one is surface area. Okay. Surface area of the denger base that is as it increases the peripheral seal. It will increase adhesion. So, there will be more retention than the shape of polished surface. Shape of polished surface. So, the shape of polished surface and teeth positioning in the neutral zone will give more retention. We already studied what is neutral zone where the forces are being neutralized from the cheek and lip forces, which is counterbalanced by the tongue muscle forces. So, shape and polish surface at the neutral zone, then the undercuts. Undercuts, modest undercuts and less severe ones increases retention. Okay. Not the very severe one. Modest ones increases retention. The most common undercuts are lateral tuberosities. Lateral tuberosities. Then maxillary primolar area. Maxillary primolar area. Then the distal lingual areas and lingual mantibular meat body areas all are undercuts, which gives more retention. So, that is the mechanical factors than the denger extension. Denger extension. The body should be extended properly to increase the surface area and the peripheral seal. It should not be too much beyond the peripheral palatal seal or the toothed of the citromolar pad. It will give proper retention. So, these are the mechanical factors that is coming under primary retentive factors. Then we have factors affecting retention, that is anatomical factors, which is coming under secondary. Anatomic factors, that is the size of the denger bearing area, quality of denger bearing area, palatal vault, soft palate, tongue size, inter arch distance, rich form. Then physiological involves saliva quantity and its quality. So, muscular factors we talked about the neutral zone. So, that is all about retention. Now, let us move on to the second one that is stability. So, retention is the ability to resist the gravitational force. The second one is stability. So, stability is nothing but resistance against the horizontal forces. Retention was vertical forces, horizontal forces. So, it is a resistance of a denger to moment on its tissue foundation, especially to the lateral or horizontal forces. So, the quality of denger to be firm, steady or constant to resist the displacement by functional stresses are not to be subject to change your position when force is applied. This is nothing but the ability of the denger to withstand the horizontal forces. So, the retention was tissue away forces. It was like this, that is the gravitational forces. This is in the horizontal direction. So, what are the factors affecting stability? Similarly, we have many factors in stability just like retention. The one is retention quality, the vertical height of the residual ridge, then the quality of soft tissue covering the ridge, occlusion plane, quality of the impression, teeth arrangement, contour of the poly surface, ridge relation, then proper relief of hard areas, width of occlusion table. So, all are affecting the stability. So, if we have written T force greater than the displacing force with good support, we have not learned yet, it will give good stability. That is the concept. So, if we have good written T force with adequate support, it will give good stability. Then the vertical height, if we have more vertical height, it will be good stability, lesser vertical height less stable. So, that is about stability. Now, let us move on to the third one that is support. The next one is support. So, support it is the resistance to vertical forces of mastication and to occlusion or other forces applied in a direction towards the basal seat. So, that is like this, that is this tissue word forces. This was tissue away forces and that was retention. So, tissue word forces is support and the lateral forces is stability. So, this is the concept, retention, support and stability. Retention is tissue away forces. Tissue towards forces, support and lateral forces is stability. So, support is nothing but the resistance to vertical force of mastication and to occlusion or other forces which is being applied towards the basal seat. Okay, like this towards the basal seat. This is the basal seat, this is the maxilla, this is the mantel. So, when the natural teeth are missing, the alveolar ridge and the covering of mucosal tissue become the supporting elements. Okay, so these are the supporting elements. So, we can divide the supporting area into primary supporting area and secondary supporting area. So, the primary and secondary, the primary are area of irringulus ridge which are at right angle, 90 degree angle, the ridge part of the ridge which is at my right angle to the occlusion force and areas which is not resolved easily such as the dense cortical bone and areas which is covered with keratinitis mucosa. Whereas the secondary supporting areas involves the area of irringulus ridge which is not resolved easily, again the dense cortical bone and again the keratinized mucosa. But the problem is here the occlusion forces would not be at right angle. Okay, it will not be at right angle. So, this is nothing but primary stress bearing area and this is secondary stress bearing area. So, this is the concept, the retention. So, this is the retention, this is the support, this is the stability. But act like this, if we have good retention, good support and good stability, there will be perfect denture. Okay. And the fourth one, aesthetics. For aesthetics, the thickness of the denture flanges is one of the important factor that gives good aesthetics. Thicker denture flanges are preferred in long-term edengulus patients to give required labial fullness. So, we need to take impression perfectly to reproduce the width and height of the entire circles, entire sulcus for the proper fabrication of the flanges. Okay. And the last one, we have the preservation of structures, preservation. That is a preservation of that which remains is of at most importance and not the meticulous replacement of that which has been lost. So, this was stated by D Van in 1952. Okay. So, he said the preservation that which remains is of at most importance and not the meticulous replacement of that which has been lost. So, impression should record the details of the basal seat and peripheral structures in an appropriate form to prevent injury to the oral tissues. So, that is all about the objectives of impression making. So, we learned about retention, support, stability, aesthetics and preservation of structures. So, retention was a much detailed one because it has many factors such as adhesion, coercion, interfacial surface tension, then the capillary action, atmospheric pressure, everything and again the secondary factors, then the stability, it is horizontal force, then support, it is a tissue word force. Okay. And the aesthetics and the preservation of structures. So, the retention, support and stability is most repeatedly a commonly asked question. It could be asked as a short knot or short assay or long assay. Long assay will be as objectives of impression making. Okay. Hope you understood this concept. So, I will come up with a new topic in top surroundings. Thank you.