بسم الله الرحمن الرحيم The doctor gave us three handouts: No1: all of it is required and in pages 21-30 there are exercises try to solve them and the doctor will put the correct solutions in the clinic. No2: required pages are 5-8 No3: required pages are 238-258 The doctor began the lecture by saying that we should say: metal framework partial denture instead of Cr-Co partial denture, because it could be made from Cr-Co, Ni-Ti, type4 gold alloy or titanium. In the last lecture we talked about Kennedy classification that is based on the frequency and the design principles for example in class1 the denture is tooth-tissue supported but class 3 is tooth supported. Today we will talk about some specific design principles for each class. Now we will continue what we started talking about which is the indirect retention:
When we talk about indirect retention we are trying to prevent rotation around a specific rotation axis. We have two types of fulcrum line: 1. Fulcrum line axis (primary fulcrum line): imaginary line that connects the most distal occlusal rests and this axis of rotation is important in occlusal forces. 2. Retentive fulcrum axis: it is the imaginary line that connects the retentive tips, and this is important when eating sticky food. The importance of this: When we have free end saddle and we have RPI on the premolars (if the case is that we have from premolar to premolar) look at picture below, when the patient eat sticky food the free end saddle move upward and the anterior part will move down, so there will be rotation around the retentive fulcrum access, so to prevent this we have to put a rest on the anterior teeth, and this is the indirect retention.
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As we said in the previous lecture the indirect retainer usually I try to put it at the longest right angle line from the retentive fulcrum access, in our case it will be on the central incisor, but its root is not the best to support partial denture, so we put the rest at the canine. A student asked about the rest that is on the canine and the premolar, and the doctor answered that we can put it on the canine, premolar or both. In case of class 4 we have two types, short span and long span, the long span act as reverse Kennedy class 1, we need to put distal rests on the second molars to prevent rotation of the denture. So indirect retention implies in Kennedy class 1, 2, and long span class 4.
Mandibular: In conventional class1 (if the case is that we have from premolar to premolar) there is RPI system on the premolar (mesial rest, guiding plane and I bar), and indirect retainer on the canine, some times the lingual sulcus is small and I have to put lingual plate instead of lingual bar so the plate will help in indirect retention, but we should use rests with this plate to prevent it from pushing the lower anterior teeth out. *Here I have to extend the denture base to retro molar pad Maxillary: We can use the mesial rest and distal rest for indirect retention; here I have to extend the denture base to the hamular notch to get the maximum support. If we have canine abutment in the mandible: I will get my indirect retention by using lingual plate instead of lingual bar and singulam rest on anterior teeth (the lower) If the canine is rotated: Here the cingulam rest is contraindicated, and indicated to use incisal rest on the canine If we have canine abutment in the maxilla:
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In this case it is better to cover the anterior teeth completely to get indirect retention When we have modifications: It will be difficult to design because I would have multiple paths of insertion and getting parallel guiding plane is difficult, sometimes it is indicated to close the anterior modification space with bridge to keep the design simpler, however if the path of insertion in the anterior edentulous space is close to the path of insertion in the posterior edentulous space I can use the rest that is located adjacent to the edentulous space for indirect retention, that what the doctor said!.
When I have posterior edentulous space: If it is class 1 I can use RPI
Here the axis of rotation is on the most distal abutments, so if I have a case with anterior teeth until canine in one side and until molar in the other side, so the fulcrum axis is between the mesial of canine and distal of the molar, because the rests in this case are on the mesial of canine and distal of molar. Sometimes we can place a clasp assembly on the premolar and molar to give additional retention so that there is equivalent retention to balance out the edentulous space on the opposite side.
The doctor said that we don’t have best design and the others are wrong, so as many as there are doctors there will be designs, but all of them depend on the basic biological and mechanical underlying factors. If we have modification space, the rests will be adjacent to the modification space, and one in front to provide indirect retention. The more the modification spaces the more difficult the design. If we have a class2 with anterior modification space, and we have a lone standing premolar (pear abutment), in this case we can’t use it for indirect retention because its root is short and conical (can’t give enough support), and if we make the partial denture with rest on the premolar, the denture will apply force on the tooth mesial and distal back and forth, so in this case we have distribute the force on the other teeth.
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It is the simplest class, so all what we do is placing rests adjacent to the edentulous area with clasp assembly (it is not necessary to put clasp for the four teeth adjacent to the edentulous areas). The retention of class3 partial denture in addition to the clasps it depends on the frictional retention from the parallel guiding plane. Sometimes the teeth wears down without reaching the pulp, and the patient does not want to put a crown so we can dome over the tooth and cover it and use it for support but not for retention. In class 3 if we have edentulous areas on the left side and the anterior teeth (as the picture in the right side), here I have to include the right side with the design, but why we include this area that doesn’t have missing teeth? We need this for cross arch stabilization, even though there is no rotation. Now in maxillary denture we could have palatal bars, straps, and plates. As the area covered by the major connecter is less, the thickness of it will be more and it will be more irritating to the tongue, so in some cases it is better to cover the whole palate to avoid irritation of the tongue.
We place the rest seats like in class 3 adjacent to the edentulous area, but if the rests affect the esthetics I can put it away from the edentulous area. In the upper: sometimes it is difficult to place rest on the teeth because of tight contact on the teeth, so in this case we put the rest on the distal of the second molar that is out of occlusion(if the lower second molar is the last standing tooth ).
When we place rests on the premolars? And when we place them on the most distal molar? When the missing teeth are 4 or less we put it on the premolar, but if the missing teeth are 6 teeth we should extend them to the molar. In the lower: Few cases we may use labial bar if the teeth are lingually inclined but the disadvantage of the major connector that it is flexible and unaesthetic.
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Basic guide lines for removable partial denture design:
First: keep the design as simple as possible: The more the components of RPD the more difficult for the technician to make it, and more difficult for the patient to clean it and difficult for the clinician to maintain it.
Second: Cover as less of soft tissues as possible: The minimum space between minor connectors is 5mm; if this space is present I can put 2 minor connectors, other wise I have to put plate, but doctor Isam prefers the plate because he doesn’t want the denture to be as spider. Third: Broad tissue support: to have the maximum support I have to extend the denture base to the maximum extension specially in class 1 and 2
Forth: Use as less as possible of frame work elements: If I have two minor connectors adjacent to each other I can combine them with a plate to be more comfortable to the patient (in this case I could have plate with bar). Fifth: Plan for the future: If I have a case where some teeth are mobile, so I exclude them from the design and place lingual plate reaching them so if they are extracted in the future I can put teeth on the plate instead of the extracted teeth. Another example is when I have a bridge and I anticipate the extraction of the distal abutment, when I make the mesial abutment I can make rest seat in it so when the distal abutment is extracted, I can remove the bridge but keep the mesial abutment that already has rest seat. Sixth: Don’t design using the cast alone: You have to take measurement in the patient’s mouth not on the cast, and depending on these measurements I will make the design (I have to measure the frenal attachment and the lingual sulcus depth) For example when the buccal frenum is within 3mm from free gingival margin so in this case it is contraindicated to use I bar, and for the lingual sulcus if it is less than 7mm so it is contraindicated to use lingual bar and I have to use lingual plate (the minimum is 7mm)
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Seventh: I have to check mounted casts: You can’t draw the design on one hanging cast; when you mount the casts you can know where the opposing teeth will hit, to know where to put the rests. Eighth: Avoid using incisal rest: It will cause tilting of the teeth, and unaesthetic. Ninth: Avoid rests on restorations: The restorations are not suitable to place rest on them, except if there is amalgam restoration that there is 2mm thickness of amalgam remaining after I do the preparation of the rest seat (2mm of amalgam below the rest). Ideally the most suitable restoration for rests is the porcelain fused metal crown, but the problem is that the porcelain will lead to wearing of the metal. Tenth: Avoid rests on heavy occlusal contacts: The rests should not interfere with the opposing dentition, so I have to put the casts on each other and draw a line to know where the occlusion is (look at handout No3 page 249 figures 7-90 and 7-91) Caries susceptibility: the partial denture increase the susceptibility to caries multiple fold Eleventh: You should make the correct design for the clasps: The circumferential clasps: it should start in the undercut, go above the maximum bulge of the tooth and end up in the rest, and it is the first choice in class 3 and 4 The I bar: it should have curve, no sharp angles and no double right angle (look to the figure below), and it is first choice in class 1 and 2 (RPI)
How many direct retainers (clasps) do we need?
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4 clasps: In Kennedy class 3 mod 1, we put them on the four corners, but we can omit one of the anterior clasps if we have supplemental retention from the guide planes.(look at figure7-72 page 242 in handout No3) 3 clasps: it is less retentive but still acceptable 2 clasps: it is the minimum number of clasps and it is used in class 1 Note: here we don’t talk about indirect retainers, but we are talking about the direct retainers Major connectors: The doctor said that he will not talk about indications, contra-indications, advantages and disadvantages of each type of major and minor connector but these are required from us in viva and exams. (You can find them in the handouts from doctor ziad from last year) Twelfth: Avoid abrupt changes in the couture of the prostheses: You need smooth continuous contours between the metal and the acrylic (See figure at the right), and the minor connector doesn’t need to be extended from one embrasure to the next but they need to contact the tooth where the rest is located. (See picture below). If we can’t use I bar we can use the alternative, which is wrought wire clasp.
Principles of RPD design: keep it as simple as possible (KISS) (Keep It Simple Stupid) eliminate anterior modification space by putting bridge 2. Determine weather the case is fulcrum type (tooth-tooth born or tooth-tissue born).
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The sequence of RPD design: Decide the path of insertion on a surveyor 7
Need to know where the support is (rests) Major connector 4. To connect the major connector with the rests we use minor connector, and the denture base that is part of the minor connector, and the guiding plane. Direct retention (clasp) Indirect retention in class 1,2, and long span class 4
The surveying: The doctor didn’t talk about it and he said that it is present in the handout and it is required, but he talked about few points. Tripoding: Tri: three, pod: foot, so it means three feet We put three points on the cast to have a reference of the tilt that is used in surveying
The last thing: The doctor talked about a design made by stewert and this design is explained totally in the handout No3 from page 246 to page 258, under the title step by step procedure, and this explanation is better than what I can write here so read the text and see the pictures wile reading what is written under them. Note: here stewert made the rests on the distal side of the abutments because he used wrought wire, but we always put the rests on the mesial side in free end saddle.
تمت بحمد الله Done by: Khalid Mousa Feery
The exams timetable:
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Date
Exam
Time
Labs
22/11
radio
2.15
29/11 2/12 15/12 17/12
surgery prostho cons perio
4.15 12.30 1.30 4.00
21/12
ortho
4.00
10H
24/12
pedo
2.15
10H
1, 2,4,5,6 4,5,6,7,8 10H3+4 10H 10H3+4 10H
Best wishes in the exams
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