 Hello everyone, welcome back to another session in dentistry and more. So we are continuing our prosanotic sessions So today's topic is the rest and rest seats So today's session will be discussing in detail about various types of rest and rest seats the preparation of rest seats its properties Advantages and disadvantages. So as we all know Rest are kept on tooth restoration only or enamel So appropriate use of teeth requires consideration as to how best to engage teeth for the supportive qualities So the most effective resistance can be provided if the tooth is stressed along its long axis So suppose this is our tooth So it should be the resistance can be provided if the tooth is stressed along its long axis. So It should be parallel to the long axis So the prosthetic framework should engage the tooth in a manner that Encourages axial loading. This is the axial loading So the use of rest with removable partial-danger processes which was developed by Bonwell in 1899 As per definition given by GPT Rest is a rigid extension of a RPD that contacts the occlusion incisal singulum or lingual surface of a tooth or Restoration the surface of which is commonly prepared to receive it Whereas a rest seat It is a prepared recess in a tooth or restoration Created to receive the occlusion incisal Singulum or lingual rest so classification according to McCracken The basis of tooth surface prepared to receive them Can classify it as occlusion singulum rest then incisal rest and Lingual rest this is based on McCracken whereas according to Stuart a classified on the basis of function they serve as primary or Secondary, okay secondaries also known as auxiliary rest And another one more classification is there that is anterior and posterior rest So what are the basic functions of rest? The first function is to provide resistance against the occlusion load then to direct forces of mastication parallel to the long axis of the abutment tooth and To maintain the retentive terminal of the clasp arm in its intended position Then to prevent the danger base from seating past its intended position Then to provide the lateral stability against undue horizontal stress to the soft tissue of the ridges then to close a small space between teeth by bridging the space Using occlusion rest to maintain the occlusion contact with opposing teeth to prevent extrusion of abutment teeth To help where tipping or rotation of tooth has impaired Functional occlusion and to provide indirect retention using auxiliary rest. So these are basic functions of rest so what are the basic considerations while Preparing a rest and rest seat The first thing is forces that are applied to a RPD must be transferred to the supporting teeth and tissues in a traumatic fashion There should not be any trauma while transferring the force to the supporting structures and rest should be sturdily placed in Properly prepared rest seat Sturdily placement basic considerations then rest seat should be within the confines of the Greatest tooth mass and there should be having more periodontal ligament fibers. Okay Should be where we have more periodontal fibers That is a rest seat should be within the confines of the greatest tooth mass and it should not be placed on a inclined tooth surface so inclined Tooth surface we should not keep there should not be any sharp angles Sharp angles so sharp angles and inclined planes sharp angles and The minimum thickness is 1 mm and there should not be any undercuts 1 mm thickness and undercuts There should not be any undercuts So let's see what is the difference between primary rest and Secondary or auxiliary rest so primary rest a rest which is a part of a retentive class Assembly which is known as primary rest it prevent vertical movement of a process is towards the tissues and also help Transmit applied forces to the supporting teeth and it should be shallow and saucer shaped and should be function as Ball and socket joint, you know, what is ball and socket joint? So this is a socket and this is the ball Whereas an auxiliary or secondary rest a rest that is responsible for additional support or indirect retention It is for indirect retention Or for additional support that is known as auxiliary rest or secondary rest. They are used in the extension RPD's such as a class 1 class 2 and class 4 class 4 will be long span Cases so in these type of extension RPD's the secondary auxiliary rest will be used Now, let's see one by one. The first one is occlusion rest Occlusion rest So as you see the picture here, it is a rigid extension of Removable dental processes that contacts the occlusion surface of a tooth or restoration Or the occlusion surface of which may have been prepared to receive it So you can see the form is Triangular shape where the base is the marginal ridge and apex is towards the center You can see the mesiodisthral diameter of a rest that is one third to one half of the Mesiodisthral diameter So the rest should be in that dimension and the buccal ingle dimension It should be one half of the total buccal ingle width and regarding the Angulation. Angulation is very important So angle formed by the occlusion rest and the vertical minor connector should be less than 90 degree So you can see this is less than 90 degree So when the rest it is less than 90 degree and more than 90 degree You can clinically understand it Using a explorer. So when you probe it Approximately the explorer will not slip off if the angulation is less than 90 degree and Explorer will slip off the rest seat if it is pulled Approximately if the angulation is greater than 90 degree and less than 90 degree It is a posterior acid if it is more than 90 degree It is not a positive one and the floor of the occlusion rest seat There should be a reduction of the marginal ridge to a depth of 1.5 millimeter Now, let's see how do we prepare occlusion rest in a sound enamel in an existing restoration or a new restoration or in a crown in lace on lace so When we prepare a rest seat in a sound enamel The preparation of rest seat always must follow proximal preparation never preceded So proximal preparation Should be first, okay, then only Should be first Then only the rest seat Never forget Proximal preparation should be first then we can do the rest seat second First should be the proximal preparation then the rest seat So the occlusion rest see in sound enamel may be prepared with a diamond points Diamond points of approximately the size of number six and eight round bus or even you can use Carbide bus Whereas the occlusion rest seat preparation in existing restoration is same as an enamel There is a proximal preparation should be first then rest seat should be placed rest seat preparation in Amalgam should be avoided because of the Creep problem Whereas occlusion rest seat in new restoration they should be placed in the wax pattern So the location of the occlusion rest should be shown when the tooth is prepared for a crown or an Inlay so that the sufficient clearance may be provided in the preparation for the rest Whereas occlusion rest seat in crown in lace or on lace, okay, so crown Inlays or on lace So most ideal way of getting a positive support it is indicated in rotated inclined tooth mandibular bicuspid with rudimentary cusp or Tooth with abrasion So these are generally made larger and deeper than the enamel and Those made in abutment crowns Supporting tooth toothbound dentures may be slightly deeper than those in abutment supporting a distal extension base That is a abutment crown supporting toothbound dentures They will be slightly deeper than those in abutment supporting a distal extension case. Okay, so the toothbound Cases will be having slightly deeper than the distal extension So what are the types of occlusion rest? The first one is internal occlusion rest internal Occlusion rest I'll just put over that is occlusion rest So so see the picture here a totally tooth support at partial denture may use internal occlusion rest for tooth occlusion support and Horizontal stabilization so the occlusion support is derived from the floor of the rest seat and from an additional occlusion Bevel if provided So the horizontal stabilization is from the near vertical walls of this type of rest seat It should be parallel to the path of placement slightly tapered occlusion. You can see the slight tapering here and Doubtail to prevent dislodgement approximately What are the advantages of this internal occlusion rest that it facilitates the elimination of a visible glass or buckly that is the most Common problem we face with the rest Occlusion visibility so this will not be visible and Permits the location of the rest seat in a more favorable position in relation to the tipping axis of the Abortment because it is inside the second one is long or continuous rest long or Continuous Rest So the rest can be designed to extend entirely across the occlusion surface of Two or more teeth and in some instances across the entire arch Can see here when occlusion force is delivered in one area all the remaining teeth act in unison To provide support because it is a single framework So with planning this type of rest can restore the occlusion plane provide support and spleen the arch The third one is ring rest So for clinical situation with a buckly inclined maxillary molar Serving as a distal terminal abortment for a RPD. Okay, so buckly Inclined maxillary molar which serves as a distal terminal abortment for a RPD The use of a ring rest with a long guiding plane can be considered as a cost-effective and efficient alternative design option So this is a scenario can use it in this scenario where the Maxillary molar which is buckly inclined act as a distal terminal abortment next one is Interproximal occlusion rest Interproximal Occlusion rest which is also known as temperature rest The design of a direct retainer assembly may require that Interproximal occlusion recipe used So these are prepared as individual but adjoining occlusion rest seeds as you see here and Preparations must be extended further link only and adjacent rest Rather than a single rest are used to avoid interproximal wedging by the framework So also to shun the food away from the contact points and we should take care to avoid eliminating contact point of abetment teeth and Sufficient to structure must be removed to allow for adequate bulk of the components to be so shaped that occlusion will not be altered Fifth one is extended occlusion rest Which is indicated in Kennedy's class 2 modification one Kennedy's class 3 situations when the most posterior abortment is a measly tipped molar So this rest should extend more than one half of the measles means your distal width of the tooth It should be approximately one third of the buckling width of the tooth And it should allow for a minimum of one millimeter thickness of the metal and the preparation should be rounded with no undercuts or sharp angles So that was all about the occlusion rest So we learn internal occlusion rest long continuous rest Ring rest Interproximal or m pressure rest or extended occlusion rest. So this can be alone asked as a short essay or short note So it is very important this rest and rest seat and previously we were discussing how to Prepare rest seat on enamel on only crown existing restoration or a new restoration All are important now. We have the lingual or singulum rest lingual or singulum rest a metallic extension of a partial removable dental processes Framework that fits into a prepared depression within an abortment tooth's lingual surface So lingual or singulum rest are used primarily on maxillary canines So the thickness of enamel on the lingual surface of mandibular canine rarely allows a lingual rest to be used That is why it is mostly on the maxillary canines lingual rest provides improve aesthetics. That is a most striking or attractive feature of lingual or singulum rest The outline form as you see picture here a slightly rounded V is prepared on the lingual surface at the junction of the gin chival and middle one-third of the tooth can see the V here The apex of the V is Directed incisely the proximal view Demonstrate the correct angulation of the floor of the rest seat. It should be less than 90 degree Can see from a mesial occlusion and all aspects So the mesial distal length of the preparation should be minimum of 2.5 to 3 mm and labial lingual width about 2 mm. This is labial lingual. This is mesial distal and incisor apical depth minimum of 1.5 mm Okay so the mesial distal should be 2.5 to 3 mm labial lingual should be 2 mm and incisor apical depth should be minimum of 1.5 mm So it is located closer to the rotational center of the supporting tooth and does not tend to tip the tooth Sometimes we need to follow a round lingual seat Form that is mesial of the canine teeth when Typical singulum rest is contraindicated because of any large restoration lack of clearance with the opposing teeth or poor singulum so we might Go with a round lingual seat form Which should be a spoon shaped similar to occlusion rest seat and it is more difficult due to the incline of the lingual surface and Lingual rest seat on a cast restoration. Okay when we do this on a cast restoration When a crown needs to be placed on an anterior tooth and a rest seat is required The rest seat should be placed in the wax pattern first The floor of the rest seat is readily carved to be the most apical portion of the preparation a saddle like shape Which provides a positive rest seat located favorably in relation to the long axis of the tooth So the framework of the denture is made to fill out The continuity of the lingual surface so that the tongue contacts the smooth surface without the patient being conscious of the bulk or the irregularities of this rest and The lingual rest may be placed on the lingual surface of a cast veneer crown a 3 quarter crown an inlay or a laminate veneer or a composite restoration So that was all about the lingual or singulum rest So if we finished the occlusion rest and lingual rest now we have the third one that is incisal rest So incisal rest are placed at the incisal angles of the anterior teeth Which is less desirable than lingual rest and receipts for anterior teeth Nevertheless, they may be used successfully if abutment or sound and cast restoration cast restoration are not indicated So the incisal rest may be used on a canine abutment in either arch But the singulum can be used only on the upper arch So this incisal rest is more applicable to the mantular canine Okay, so this type of rest provides definite support with relatively little loss of tooth structure and little display of metal Unlike the occlusion rest So the labial view demonstrate inclination of the floor of the rest seat Which allow forces to be directed along the long axis of the tooth as nearly as possible can see the floor of the rest seat which is Helping the force to be in a Direction that is parallel to the long axis of the tooth and the proximal edge of the rest seat is rounded rather than straight The lingual view shows that all borders of the rest seat are rounded to avoid any sharp line angles It should appear as a small v-shaped notch located approximately 1.5 to 2 mm from the proximal incisal Ankle can see here. The deepest part of the preparation should be toward the center of the tooth mesiodisterly The notch should be rounded and should extend slightly onto the facial surface to provide a positive seat for the rest So that was about incisal rest. So that was all about rest and rest seats So this session was basically about the occlusion lingual or singulum or incisal rest seat So it can be asked to say long assay short assay or short not anything can be asked as a short not The occlusion rest or its type lingual or singulum rest incisal rest its rest seat preparation on enamel cast restoration or crown or anything so always draw picture It is very helpful when you draw picture and shows the angulation and the size and shape of the rest seat rather than writing up the same thing and Paragraphs, so hope you understood this concept of rest and rest seats. So I'll come with a new topic in prosthodontics. Thank you