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[eyeloveteeth]

that's not true. CMM probes come in all shapes and sizes i know of some that are 0.25µm accurate. just different grades - Grade 10 is like .30µm tolerance i think

 

[CoolHandLuke]

that's not true. CMM probes come in all shapes and sizes i know of some that are 0.25µm accurate. just different grades - Grade 10 is like .30µm tolerance i think

dental probe. not ruby cmm. the kind dental assistants use to probe margins.

 

[Car 54]

dental probe. not ruby cmm. the kind dental assistants use to probe margins.

That's how I took what you meant in your previous post.

 

[Affinity]

CHL, the goal is not if a probe fits under a crown.. were trying to keep bacteria out... at least I thought thats what a crown was.

 

[Affinity]

Heres a nice pdf on oral microbiology if anyone wants to brush up... Ive been reading too many RKM posts...

http://www.mecourse.com/ecourse/term6/docs/oralmicroflora.pdf

 

[2thm8kr]

CHL, the goal is not if a probe fits under a crown.. were trying to keep bacteria out... at least I thought thats what a crown was.

Crown margin accuracy would need to be better than .02 microns to keep some oral bacteria out.

 

[JMN]

Anyone remember what the basis was for the old metric of 25 microns as a goal for crown/tooth marginal gap?

 

[Car 54]

Anyone remember what the basis was for the old metric of 25 microns as a goal for crown/tooth marginal gap?

I'm not sure. I think the earlier chair-side Sirona/Cerec mills were milling at an accuracy of 50um? and as one clinician Dr mentioned that if the Drs
felt good about the margins, that they were about 50um open, and that an explorer tip was around 100-120+um so that's why the margins
felt good to them.

 

[Affinity]

Crown margin accuracy would need to be better than .02 microns to keep some oral bacteria out.

So you dont think its important for margins to be as closed as humanly possible? Why do we have 'margins' then?

 

[2thm8kr]

So you dont think its important for margins to be as closed as humanly possible? Why do we have 'margins' then?

I don't recall saying margins aren't important. It is a metric that has been beaten into our heads by our mentors and their's before them. IT was extremely important to have the margins as closed as possible to keep the adhesives from washing out over time. Newer adhesives are less prone to that.

I can show you xrays of pfm crowns that have been in the mouth for over 2 decades that have the sh!ttiest open margins you have ever seen. They are still there and no recurrent decay present. I can also show you xrays of crowns with closed margins that have decay around the marginal areas and underneath the crown, the crowns have only been in for a year or two. Has more to do with ph level in the patient's mouth than open or closed margins as well as the bacterial flora in the patient's mouth.

 

[rkm rdt]

now I'm to blame for open margins? wtf dtg ( don't there go)

 

[CoolHandLuke]

CHL, the goal is not if a probe fits under a crown.. were trying to keep bacteria out... at least I thought thats what a crown was.

the probe has to feel below the margin and not drag when pulled through the emergence profile. this is why sometimes letti g the cement fill the tiny open margin gaps is a good idea; these small gaps would not be able to be milled by a 1mm cutter anyway, and in the majority of cam calculations 1mm finishing is all that drags over the margin contours anyway.

0.6 and 0.3 do rest milling and anatomy. not margin refinement unless you want to take 1hr to do a single.

 

[Affinity]

So what youre saying is cerec wins, and all of the bitching everyone has been doing for a decade now was screaming in the wind..

 

[2thm8kr]

No, I'm just saying that margins aren't always the reason crowns live or die.
There have been studies on this.

 

[JMN]

 

[Affinity]

I wouldnt say that a hermetically sealed margin is the reason for caries under a crown. Most times the Dr doesnt remove it, or the prep isnt clean etc. I understand oral Ph is what promotes bacterial growth.
It seems to be a trend however, in my 21 years in dentistry, that materials and techniques have moved towards accuracy, now it seems that it doesnt matter 'as much', because cement is better. Which was the original thought I had, and actually answered my question: Yes we have regressed in technique, and care towards accuracy in exchange for speed. Maybe its what keeps us around to grind another day.

To me, the most sealed 1:1 margin is important because thats how I was trained, but honestly the more time I spend in this field, the more I hate it. Now it comes off the mill and out the door, no need for scope or any handwork. This will be what seals the fate of techs in our industry. (another pun for RKM)

 

[2thm8kr]

Yes we have regressed in technique, and care towards accuracy in exchange for speed.

Courtesy of the insurance companies and bean counters influencing the way patient care is received.

The future of this business isn't in single crowns, the process could already be automated. As I see it the future is leveraging your 21+ years of acquired skills
into TX, DX, SX planning, and executing the plan with available technologies plus your hand skills into a final restoration that fits and functions better than
anything a few bench workers can kluge together at a big box lab.

 

[Affinity]

the only future I see for me is trying to find a way out of this business.

 

[CoolHandLuke]

ive heard that by 2030 it is predicted there will be over 1billion fully edentulous people.

so...

 

[eyeloveteeth]

the argument is that any leftover space will be further sealed by the cement - so the gapage further shrinks.

Like i've been saying - we don't focus on posterior single units - because we cannot win. We charge $195 for our posterior units all day long and if they don't like it, they can go elsewhere and get their open margin crowns instead of our open margin crowns