sharp or rounded amalgam preps

[nug]

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Does your school teach you to have sharp or round internal line angles on your amalgam preps? Our oper faculty stressed sharp angles, but all the text books said rounded angles are better.

 

[saahakhan]

hello dear friend,
im new at this forum and this my first mail. i am 3rd prof. BDS student.
well as far as i have seen my teachers doing amalgam fillings. those that make round angles for amalgam fillings are better and have a long life than others and pt. is also comfortable with round angle amalgam fillings.
this only my observation. i hope some fully qualified proffesional wil be able to gave more appropriate answer
bye

 

[gpg]

Its best to have well-defined internal line angles which are rounded.If they are left real sharp there is a good chance that some debris will be left there and chances are good that there will be secondary decay there.

 

[tinker bell]

Round & smooth, all the way

 

[toothcaries]

..to resist fracture with amalgam u want the enamel margins at 90degrees(or slightly greater) and rounded internal line angles in general...

(if i remember correctly)

 

[UBTom]

The way it was taught at my school: The retention form for amalgam is parallel walls with sharply defined line angles with the pulpal floor because it resists displacement a bit better than rounded angles. I vaguely remember this from studying for the NBDE part-II's too, but my recollection is fuzzy. 😛

Rounded line angles are good for resins though, because unlike amalgam which depends on the shape of the prep for retention, resins depend largely on bonding with enamel (and to a lesser extent, dentin) for retention as per Dr. Michael Buonocore's research on the topic. The rounded internal line angles is better for smooshing the resin into the cavity without leaving a void.

HTH!

 

[ItsGavinC]

Yeah, they've got to be parallel walls with sharp angles to the pulpal floor. If viewing the prep from the occlusal surface, however, the angles of the prep are anything but sharp and are rounded (dovetails, etc.) to give better retention to the amalgam.

 

[booshwa]

We are taught to use rounded line angles because it has been shown (I haven't actually read it anywhere, just what the operative profs say) that sharp angles create "stress fractures in the amalgam." As far as the angulation, we are taught that the buccal/lingual-occlusal walls should be at 90 deg. or slightly undercut (very slight otherwise unsupported enamel) for retention.

We are taught using 256 burrs, which are rounded, but a lot of the faculty still used 556 burs which are not rounded. Ultimately, it probably doesn't make that much of a difference in the durability of the amalgams.

 

[UBTom]

We are taught to use rounded line angles because it has been shown (I haven't actually read it anywhere, just what the operative profs say) that sharp angles create "stress fractures in the amalgam."

Yep, that does indeed happen at the line angle where the pulpal floor meets the axial wall in a Class-II prep. Which is why that line angle should be rounded or beveled (I use a gingival margin trimmer to do that). Everywhere else should be sharp though..