broken screw head

[Tom Moore]

Lots of exposure for a very few bucks. I get no blow-back from the customers over the inclusion and price of a new screw. I never what to be worked over by a helix on an axis if I can help it.

 

[dmonwaxa]

Condescending...! So by loading you mean torqueing right, and when torqued the screw is in tensile stress right? Slight almost immeasurable deformation ...yes? So by over torquing what happens? Increased deformation? Now combine that with a repeated load...cyclic fatigue....failure. Seen it happen over and over with gold screws fron the olde braenemark days, definitely don't ned no funny fuzzy math to determine that. Heres an experiment ,,,take a piece of wire and bend it back and forth repeatedly, see what happens.

 

[TheLabGuy]

Yeah ter, that's going to be a tough sell in my lab. How much is a (patient price) implant these days? 2,500 total? Tough sell to a Doctor or patient about a ten dollar screw that may or may not fail. In addition, I'm not knocking your research or your mindset, but unless you can confidently say you researched every single screw out there from all the various manufacturers, it would be hard to convince me let alone my Docs.

 

[Tom Moore]

The top of screw threads are pulled against the upper part of the threads in the implant and held there by the slight stretching under load from the part of the screw without threads. This works like a spring holding everything in place. This load and stretch is only optimum one time. The fist implants I did was a full mouth on blades 39 years ago so this is not my first rodeo. I have done a lot of implants and attended lots of schools on implants over those 4 decades. It's the way they are designed to function.

 

[rkm rdt]

Tom , the screw wasn't invented back when you were doing blade implants.

 

[ter01475]

When a screw is properly loaded there is NO deformation... period. The clamping comes from the mechanical advantage between the leading edge of the thread and the head of the screw and it's seat. Threads have a leading flank and a following flank, the leading flank carries the load. The pitch of the thread and the lead are equal...normally, but not always. This is a boring subject and I am sure you are wrong. Let me recommend some reading material for you.

Screw Threads . Design. Selection. Specification (For Fastening, Motion Translation, Power Transmission ) by Robert V. MacKenzie Go to a good library and find the book or buy it on Amazon.

This text will explain every thing from the history, design, torque formulas, and will take the mystery out of threaded fasteners for you. 3I started this bull with lab screws and final screws and I assure you it is not necessary. Seems a shame to charge an extra 40 dollars per implant for a part that is not needed, but knock your self out. Send me all the screws you are throwing away though!

 

[Tom Moore]

There is always deformation when force is applied.

 

[[email protected]]

Our philosophy is to try to restore original on original when possible. As long as the screw is cared for at the bench and not loaded it will perform as designed. The bigger concern is damage to the screw head itself. Usually inexperience or laziness I see other techs grabbing any driver near by to tighten or remove the screw (a worn unigrip will remove just about any screw except Ankylos). They shove it down into the abutment hoping to get a bite of the screw and move on. This is where a lab screw is most beneficial, to protect the screw from lab damage like wrong/worn driver, sandblasting, dirt, cross threading etc. I work with a highly trained and talented team and they know what will set me off, a damaged screw which is as bad as a lost screw.

 

[dmonwaxa]

When a screw is properly loaded there is NO deformation... period. The clamping comes from the mechanical advantage between the leading edge of the thread and the head of the screw and it's seat. Threads have a leading flank and a following flank, the leading flank carries the load. The pitch of the thread and the lead are equal...normally, but not always. This is a boring subject and I am sure you are wrong. Let me recommend some reading material for you.

Screw Threads . Design. Selection. Specification (For Fastening, Motion Translation, Power Transmission ) by Robert V. MacKenzie Go to a good library and find the book or buy it on Amazon.

This text will explain every thing from the history, design, torque formulas, and will take the mystery out of threaded fasteners for you. 3I started this bull with lab screws and final screws and I assure you it is not necessary. Seems a shame to charge an extra 40 dollars per implant for a part that is not needed, but knock your self out. Send me all the screws you are throwing away though!

Dear Mr. ter01475, thanks for the suggestions for reading. That really is a nice homework assignment. Did you get your homework assignment finished yet? The repeated bending of a piece of wire? Surely that would take only a few minutes at most compared to hours of reading on my part. BTW do you have any knowledge of screws backing out or becoming loose? What gives please enlighten us.

I agree with you regarding the mathematical equations and formulas involved, and surely most are way above my we wittle brain. Heres the thing though common sense prevails. Most anything can be argued (proven) mathimatically,,,,true! For example, take a miscast using a broken arm casting machine, too little centrifugual force and you get an incomplete casting (voids short margins etc) too much force and and you end up with a miscast (blowout). Both scenarios can be proven mathematically, using formulas and equations, no doubt. Equally, the proper amount of force required to achieve a complete casting could be derived. Now here is the issue,,,,variables (wildcards); proper temperature for instance, time, and human error. Surely those can be factored in also. And this is where statistics come in and the element of probability, means and deviation. Surely you understand that. They cannot tell you with 100% certainty, (oxymoron) hence deviations. Statistically the idiot who to always get a miscast no matter what, might screw up and get lucky. Believe me I know.... The only thing that is 100% is that it will not always work.

So you see my friend, human intelligence an human stupidity are both infinite. Factor in common sense or a lack of it, then who knows. Surely there's merit in your position,,, but like many on here, we know, what we know, what we know,,, and that's certainty

Here's a little reading if you care to oblige. We surely didn't need a math degree to come up with this.

http://products.asminternational.org/fach/data/fullDisplay.do?database=faco&record=2039&search=

Once again common sense.

 

[dmonwaxa]

Our philosophy is to try to restore original on original when possible. As long as the screw is cared for at the bench and not loaded it will perform as designed. The bigger concern is damage to the screw head itself. Usually inexperience or laziness I see other techs grabbing any driver near by to tighten or remove the screw (a worn unigrip will remove just about any screw except Ankylos). They shove it down into the abutment hoping to get a bite of the screw and move on. This is where a lab screw is most beneficial, to protect the screw from lab damage like wrong/worn driver, sandblasting, dirt, cross threading etc. I work with a highly trained and talented team and they know what will set me off, a damaged screw which is as bad as a lost screw.

You posted as I was writing the above post, and I agree. You just proved my point in an indirect way,,,,the human element,,,,Thanks

 

[Tom Moore]

Yes your honer I did explain that a new pristine never used before screw was available at less than .01 percent of what the patient paid for the implant and the crown on top of it. I also explained that it would reduce the chance of screw failure and loosening of the screw after placement. The dentist said the lab screw used in our production would do just fine. We did our do diligence.

This seems much easier than explaining implants to a layman and quoting books on those screwy screws.

 

[ter01475]

The comparison of bending a wire vs the function of a screw is like comparing apples and oranges. The rules for and math involved for determining torque levels are not random. We do this all the time in the lab...why do you select the alloy that you use for bridge work?
One factor is strength or tensile strength, because we don't want the bridge to bend or fracture. We also use alloys that will flex but not fracture, and this is measured by modulus of elasticity...for instance a clasp.

To say they every time a load is applied to metal it deforms is not correct. We select alloys that can carry loads without deforming or fracturing. The same is true for most everything around us. Your deck in you home is built with lumber that has a tensile strength rating. The loads are once again figured out using math for the static load and the live load (people, furniture, and snow for some of us up north). Like screws we don't want the floor joists to bend or deform. What about your car...we you hit a bump in the road the car does not deform...hit a tree, which would be an overload for sure, it will bend and break. Your roof on your home...rigid and no deforming. There a huge difference in lumber for a home up north vs a home down south, due to snow loads.

There are ways to design screws that will bend, but won't fracture under a normal functional load. One design is what you see with the fastening screw for a Straumann Bone Level implant. There is the head with a bevel seat, then a long unthreaded shaft, and then the threaded portion. The bending movements are designed to happen in the unthreaded shaft. There is a point when the load exceeds the tensile strength of the alloy and it deforms. When that happens the unit has been stretched and it becomes loose. The worse outcome is it fractures. Most screws are designed to have a fracture point generally just below the head, so if there is an overload the broken portion can be removed and replaced.

For the subject of common sense....common sense told the citizens of Salem, Ma that there were some "ladies" in their town that should be burned at the stake...so what we might think as common sense is not always true. Take a look at a jumbo jet and watch them load it with freight... common sense tells me that there is no way that thing should be able to fly. How can a sailboat sail into the wind??

Well time to go out and get the boat clean for the weekend....I may re tighten all the screws and bolts the more I think about it, Have a great Memorial Day and HI to Chris...nice to see you here

 

[Tom Moore]

For every action there is a equal and opposite reaction unless that law of physics has somehow been repealed in the arena of the implant screw.

The act of burning people because of fuzzy headed religious beliefs is not common sense any more you can apply force and there is no effect on what you apply it to is common sense.

 

[CoolHandLuke]

Ratings carry the connotation that up to this point any deformation under stress is normal, and at this point or beyond, the subject cannot withstand the applied forces.

with screws its as much a torsional force as a bending force. the longer the length of tooth on the implant, the more stress is applied to the head of the screw even during simple biting force.

so with every bite, torque and bending force is applied to the screw, the interface, and the bone. when all the forces are within acceptable levels, nothing breaks, but it is all under a load and is deforming. eventually it will break being weakened by too much force over time.

this is so often why Titanium screws are commonplace, and gold screws are not. gold bends too easily. titanium is quite a lot more dense but more tan that when subjected to force it is springy. it bounces back to its cured shape.

its probably why nobel has had such longstanding success; they simply use bigger screws.

 

[CoolHandLuke]

Understand that screws don't wear out if properly torqued. They only "deform" when over torqued... or over loaded, therefore using new screws for an abutment is a waste of money. Torque levels are determined with a mathematical formula that includes tensile strength, thread pitch, screw design, etc.. How many times have you changed out the lug nuts on your car wheels??? Never!! Torque levels provide a preload for threaded fasteners so that they don't fail from a functional load.

if this was at all true, you'd never hear of truck tires popping off and killing people, or airplanes coming apart at the seams mid flight. unfortunately it is almost a daily occurrence in trucks and planes all over the world.

you don't hear about it much with cars unless of course they are quite old and weathered by years of ... weather.

 

[2thm8kr]

Ratings carry the connotation that up to this point any deformation under stress is normal, and at this point or beyond, the subject cannot withstand the applied forces.

with screws its as much a torsional force as a bending force. the longer the length of tooth on the implant, the more stress is applied to the head of the screw even during simple biting force.

so with every bite, torque and bending force is applied to the screw, the interface, and the bone. when all the forces are within acceptable levels, nothing breaks, but it is all under a load and is deforming. eventually it will break being weakened by too much force over time.

this is so often why Titanium screws are commonplace, and gold screws are not. gold bends too easily. titanium is quite a lot more dense but more tan that when subjected to force it is springy. it bounces back to its cured shape.

its probably why nobel has had such longstanding success; they simply use bigger screws.

Titanium is Not more dense than gold. Check your periodic table.
Density really has nothing to do with strength, lead is more dense than titanium as well and is easily deformed.

 

[CoolHandLuke]

yes, i don't know what word i was reaching for but "dense" sure wasn't the right one.

 

[2thm8kr]

http://www.pcbloadtorque.com/pdfs/engineering fundamentals.pdf

For all the doubters out there.

 

[dmonwaxa]

The comparison of bending a wire vs the function of a screw is like comparing apples and oranges. The rules for and math involved for determining torque levels are not random. We do this all the time in the lab...why do you select the alloy that you use for bridge work?
One factor is strength or tensile strength, because we don't want the bridge to bend or fracture. We also use alloys that will flex but not fracture, and this is measured by modulus of elasticity...for instance a clasp.

To say they every time a load is applied to metal it deforms is not correct. We select alloys that can carry loads without deforming or fracturing. The same is true for most everything around us. Your deck in you home is built with lumber that has a tensile strength rating. The loads are once again figured out using math for the static load and the live load (people, furniture, and snow for some of us up north). Like screws we don't want the floor joists to bend or deform. What about your car...we you hit a bump in the road the car does not deform...hit a tree, which would be an overload for sure, it will bend and break. Your roof on your home...rigid and no deforming. There a huge difference in lumber for a home up north vs a home down south, due to snow loads.

There are ways to design screws that will bend, but won't fracture under a normal functional load. One design is what you see with the fastening screw for a Straumann Bone Level implant. There is the head with a bevel seat, then a long unthreaded shaft, and then the threaded portion. The bending movements are designed to happen in the unthreaded shaft. There is a point when the load exceeds the tensile strength of the alloy and it deforms. When that happens the unit has been stretched and it becomes loose. The worse outcome is it fractures. Most screws are designed to have a fracture point generally just below the head, so if there is an overload the broken portion can be removed and replaced.

For the subject of common sense....common sense told the citizens of Salem, Ma that there were some "ladies" in their town that should be burned at the stake...so what we might think as common sense is not always true. Take a look at a jumbo jet and watch them load it with freight... common sense tells me that there is no way that thing should be able to fly. How can a sailboat sail into the wind??

Well time to go out and get the boat clean for the weekend....I may re tighten all the screws and bolts the more I think about it, Have a great Memorial Day and HI to Chris...nice to see you here

ter01475, I agree with you that under normal load the does not deform. ...at least in a manner that would lead to premature failure. Also under normal rated torque values when correctly applied. ..should not lead to failure agreed.

The rest of your post you basically restated what I said in a roundabout way.

The southern spec roof will function up north ...just not long-term. It may be capable of holding the ssme amount of snow as a northern spec roof ...momentarily and fail prematurely as should be expected because its functioning outside its rated spec.

Cars ... metal flexes (bend and twist );even if its ever so slightly more so now with unibody design. We usually dont feel it because of shock absorbers. But drive that vehicle continuously without shock absorbers over rough terrain repeatedly an see what happens. Common sense tells me all the squeaking and rattling of metal might mean its functioning outside the parameters of its intended design.

Now sailing....yes sailing ... you can never sail directly into the wind, you tack...at an angle. I'm almost certain the first sailor to do so used some common sense (his common knowledge) of what he knew. Later im sure it developed into more of a science for repeatable results.
However.. Now If you do manage to sail headlong directly into the wind ...just dont spit into the wind...common sense.

 

[Tom Moore]

If there is a chance of failure should it be engineered to be the implant,the abutment or the screw?