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    Help - Partial crown

    Discussion in 'Dental-CAD' started by ps2thtec, Aug 11, 2017.

    1. ps2thtec
      Question

      ps2thtec Well-Known Member Donator Full Member

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      Got this case in and I'm not a removable tech. Any guidance on a design? Thanks!!

      IMG_0478.JPG
       
    2. CoolHandLuke
      Fiendish

      CoolHandLuke Well-Known Member Full Member

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      i can count about 5 ways to make clasp rests, but everything depends on the other side of the mouth.

      ask the dr what kind of rests, and where.
       
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    3. JMN
      Curious

      JMN Christian Member Full Member

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      {Edit:CHL is right, of course, you need more information from the Doc. Some like rest seats on Mes and Dis and do transocclusal clasps in addition to around the back style. Many options.}

      For a rpd to use a tooth as an anchor/abutment, it needs to have a 'rest seat' prepared into the marginal ridge of mesial, distal, or both. A seat is an obvate smooth depression of mildly increasing depth as it extends to the center, about 3-5mm toward the central fossa total mesiaodistal length, from the origin on the distal or mesial wall. The bucco-lingual size is 2-4mm. There should be a sharp, exact, and clear beginning and ending point on the occulsal surface. Think of it like a inlay prep which extends to the marginal ridge.

      The need for this is so that a RPD will focus and transfer the maticatory forces appiled on the prosthetics teeth and structure into the dentition instead of the tissue. The rest seat is where a metal finger will be made to fit intimately into the bowl you create, the mildlymincreasing depth will assist in self seating and centering under dynamic load.

      Next part, the buccal surface should have a well defined height of contour so that a clasp arm can slide over it on intentional removal and insertion. The crown should provide for the buccal surface to have this undercut area of suffienct size the RPD designer is not having to make difficult choices to keep the ancilliary and supporting origin of the clasp arm away from tissue as impingjng on tissue can cause many problems you likely are aware of already.

      The disal wall of the tooth should have a flatter straight wall directly below the rest. This has an angle of slightly less than 90 degrees as measured between the plane of occlusion and itself. This is called a guide plane, and will take some of the transmitted force as well as providing a guide for the path of insertion so the RPD wearer has an easier time and also so the RPD goes smoothly into seated postion without causing excessive frictional dammage to the dentition.

      Anything else? Did that answer all you needed?
       
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    4. victormasi

      victormasi Member Full Member

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      Rest seats in a Zr. crown is too sketchy. You need a PFM with a mesial rest seat on #2. The mesial tooth( #3) is shot and probably being extracted.
       
    5. JMN
      Curious

      JMN Christian Member Full Member

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      Zirc won't handle the force? Interesting. First hand failure, or another source?
       
    6. 2thm8kr
      Devilish

      2thm8kr Beanosavedmysociallife Full Member

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      Zr will handle it fine unless it's paper thin.
      I have no idea what that joker wants you to survey with a quadrant impression??

      From the occlusal view in exocad find a path of draw that is in line with the cuspid. Click save custom view (bottom of right side tool bar).
      After designing and merging the top and bottom, go to expert mode and free form merged construction. In the FF window click ATT and select remove. Scroll down the menu to 'extrusion'. Select a shape that has a flat side.
      Go back to the right side tool bar and select custom view 1 and cut a guide plane into the mesial,distal or both. Now go back to the menu and select 'rotation'. Find a round shape and scale it to about the size of a #8 rd but and position it on the occlusal surface, click apply.
       
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    7. ps2thtec
      Question

      ps2thtec Well-Known Member Donator Full Member

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      Yeah kind of known that after thirty years but thanks !. I was trying to make a point of all the thorough info received.
      I know we all get crap like this.Banghead This a three month old account.
       
    8. JMN
      Curious

      JMN Christian Member Full Member

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      :Top:
       
    9. John C

      John C Member Full Member

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      Thriw a mesial rest on it. Bulk out disto - buccal in the middle 1/3 just enough to create an undercut below it. Call it good enough.
       
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