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Lab talk, the good, the bad, and the ugly
All Porcelain-Press
Black Spots on Emax Press restorations
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<blockquote data-quote="Patrick Coon" data-source="post: 300864" data-attributes="member: 11366"><p>Bob,</p><p></p><p>Sorry if it sounded like I was coming at you, that's one of the problems with text based communications. You try to stay brief and you sound curt, if you get into an overly long response it can sound like your talking down or being a "know-it-all", and you can't hear the humor or sarcasm in a written response.</p><p></p><p>And yes those small, thin, "spindly" lower anterior preps can be a PITA. I'm glad you have a technique that works for you now, but for others out there who don't please allow me to give a few tips.</p><p></p><p>So, in my experience it is mostly a sprue placement issue that you can minimize, but not always eliminate this issue. This is because we have to look at two different things in sprue placement and those are: Proper angles to eliminate the gray spot (incisal edges and cusp tips),and proper angle to put the prep in compression during pressing v/s applying a shearing force on the prep (See illustration).[ATTACH=full]32313[/ATTACH]</p><p></p><p>If it happens to be one of the preps like in the Shear force illustration (on right) if we place the sprue in the proper position to eliminate the gray spot then we place the prep at an angle to receive shearing forces (although it may not always be as severe as the illustration). If we place the sprue in a position to put the prep under compression, then we will get the gray spot. So what can we do? One thing is to place a small diameter stainless steel ortho wire (.030") into the prep area of the pattern during investment. This small piece of wire acts like rebar in cement and reinforces the investment helping it to resist breakage when receiving the shearing force (See Illustration). I do put a small loop in the wire end that sticks out of the pattern to secure it in the investment.</p><p>[ATTACH=full]32314[/ATTACH]</p></blockquote><p></p>
[QUOTE="Patrick Coon, post: 300864, member: 11366"] Bob, Sorry if it sounded like I was coming at you, that's one of the problems with text based communications. You try to stay brief and you sound curt, if you get into an overly long response it can sound like your talking down or being a "know-it-all", and you can't hear the humor or sarcasm in a written response. And yes those small, thin, "spindly" lower anterior preps can be a PITA. I'm glad you have a technique that works for you now, but for others out there who don't please allow me to give a few tips. So, in my experience it is mostly a sprue placement issue that you can minimize, but not always eliminate this issue. This is because we have to look at two different things in sprue placement and those are: Proper angles to eliminate the gray spot (incisal edges and cusp tips),and proper angle to put the prep in compression during pressing v/s applying a shearing force on the prep (See illustration).[ATTACH type="full" alt="32313"]32313[/ATTACH] If it happens to be one of the preps like in the Shear force illustration (on right) if we place the sprue in the proper position to eliminate the gray spot then we place the prep at an angle to receive shearing forces (although it may not always be as severe as the illustration). If we place the sprue in a position to put the prep under compression, then we will get the gray spot. So what can we do? One thing is to place a small diameter stainless steel ortho wire (.030") into the prep area of the pattern during investment. This small piece of wire acts like rebar in cement and reinforces the investment helping it to resist breakage when receiving the shearing force (See Illustration). I do put a small loop in the wire end that sticks out of the pattern to secure it in the investment. [ATTACH type="full" alt="32314"]32314[/ATTACH] [/QUOTE]
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Lab talk, the good, the bad, and the ugly
All Porcelain-Press
Black Spots on Emax Press restorations
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