Preparation tips (long axis of a typodont teeth/abutment)

Aug 14, 2020
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When working on a typodont teeth for a crown (be it ceramic crown requiring a chamfer margin, PFM requiring a partial slice preparation or e-max with a shoulder prep), I struggle with getting the walls of the typodont to be tapered 6 degrees (convergent) with the path of insertion. I think I have a problem with the location the ideal path of insertion (which often is the long axis of the tooth on typodonth teeth). I typically place my bur perpendicular at the midpoint of th occlusal surface on molars and bicuspids and define this as my long axis of the tooth. When doing preparation on the incisors I place my bur facially at the midline that divides the tooth in two halfs and try keeping my bur as straight as possible with the path of insertion. Despite this, I always end up with buccal or lingual walls being convergent and the other being either too straight/parallell which gives me undercuts, or too tapered (15-20 degrees).

I think this is maybe due to not angling the bur adequately with the path of insertion (long axis of the tooth). How does one find the long axis of the tooth and path of insertion on typodont teeth? I try not to angle the bur too much since the burs have a intrinsic taper which will give me the 5-6 degrees required, so it's just a case of angling the burs to be parallell with the long axis of the tooth. How does one place the bur on the sound tooth (i.e. finding the right bur angulation that is neither too parallell (crown will not seat) and not too over tapered (poor retention and resistance form)?

Also when doing a knife-edge margin I sometimes cannot detect a physical margin and hence tend to get undercuts often on the palatal side; how can I avoid this? With regards to inter proximal reduction; how does one avoid the rookie mistake of creating too tapered walls (mesio-distal?) and at the same time don't hit the adjacent teeth. I try to leave a thin enamel shell inter proximally.

I will be happy if someone could give me few pointers on angling the bur/holding the dental handpiece towards the long axis of the tooth; finding the correct path of insertion when doing a prep on the typodont
 
Aug 14, 2020
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To my question:

Could you give me some pointers on how to keep the burr parallell with the path of insertion (how do you find the ideal path of insertion and keep the burr aligned) when doing the axial reduction on the typodont?



I usually do the incisal/occlusal followed by the buccal and inter proximal and at last the palatal/lingual surface. But I will implement your suggestion!
 
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bracketbuster68

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Jul 26, 2018
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To my question:

Could you give me some pointers on how to keep the burr parallell with the path of insertion (how do you find the ideal path of insertion and keep the burr aligned) when doing the axial reduction on the typodont?



I usually do the incisal/occlusal followed by the buccal and inter proximal and at last the palatal/lingual surface. But I will implement your suggestion!
Lock your wrist and cut with your arm, holding the bur at the same angle throughout. Practice a bunch so you get the muscle memory to cut quick.
 

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