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FAQs -> laboratory

question (id # 1349)

Hello, really need this answered please: Before I had my seven upper front crowns fitted last week, my dentist recommended A2 shade but as I had bleached my bottom teeth and they came up good, I thought the A1 shade was much fresher - so we compromised and agreed that the main front four would be A1 and the rest A2. During fitting he informed me the technician had done them all A2! I was in a daze (lifelong fear of dentist) and couldn't respond with numbness and drilling etc. When I got home I thought they were ok but looked dead and yellow in most light. My bottom teeth are more like A1 but will not be in a hurry to bleach them again as so painful and gums bled. Really anxious as cost me huge ammount of money. Do I stick with the A2 knowing my bottom teeth will eventually darken? Or can I say to dentist about original plan and have the front four redone? I feel bad as they are lovely shape and fit and my dentist is also lovely. Please advice. Many thanks.

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question (id # 1038)

I am look for a portable shade matching light system.  It will be used in a mobile ceramic lab.  Need some direction.  Thanks.

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question (id # 1037)

I am looking for a portable shade matching light system. It will be used in a mobile ceramic lab. Need some direction. Thanks




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question (id # 650)

I have been looking for a computer program to manage all the paperwork and invoicing in my lab. "Can you recommend anything?"


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question (id # 470)

Is the dentist's choice of laboratory important?

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question (id # 468)

How often should crowns  be replaced?

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The following questions were not orginally posted in this category, but may be related:

question (id # 1252)

All-in-One ( Procera Implant Bridge PIB) verses Soldering and the Laser/Phaser welder.

Lets start in the beginning.

Once upon a time there was soldering; it was good, it was not easy but it worked and it worked well. It required years of experience and attention to technique, which certainly resulted in some phenomenal fits, almost always only delivered by the experienced. Those were the days when precision gold work on all implants were achievable; when you could hear, hour upon hour, the melodious drone of technician after technician chanting "the impression is probably not accurate anyway!"... "the impression is probably not accurate anyway!"

For those who are not sure, soldering is the joining of metals with a complimentary metal that has a slightly lower melting temperature so it flows into the connecting space fusing the metals together in one unit.   The additives in the solder affect the properties in the solder and influence its corrosion resistance in the oral environment.

The technique sensitivity lay in-

*      The gap between the two metal parts being easily too large.

*      Getting the gap in the correct place perpendicular to the solder contracting forces.

*      The solder not flowing  as the metal may have oxidised prematurely, or the metal was too cold

*      Contraction, as the solder distorts the framework on cooling

*      Investment models that can easily distort

In my experience the most accurate and the strongest joins, have resulted from using solder, I therefore :-

*      Split my castings down the centre of a pontic giving a much larger joining area than a welded one (not possible when you weld)

*      Cast my framework in separate castings so that the 0.2mm joining space is parallel and perpendicular to the forces of soldering contraction

*      Apply my flux on my joins before I transfer it  to my metal reinforced investment model, and only then do I heat the investment model so that  I have no oxidation

*      Let my metal melt the solder not the flame used

The results are second to none; when firing porcelain the solder joint is stable, as they are large connections through the pontic. As the solder joint is not exposed to the oral environment (because it is covered in porcelain or a composite) we have no corrosion issues. Where does that leave the strength of post-ceramic soldering? Oh - too much to consider - too much responsibility - just tell me what to do!!

 I can hear the crunch of pliers, the bang of a hammer, all to deliver yet another passive substructure. After all this Wirz,et al concluded  Soldered joints are described as having a clear reduction in corrosion resistance, not to mention tissue irritation. (and so will lead to fracture, due to elements in solders that help to reduce the temperature) At the time it was all we had and it still has its place today in modern dentistry today. 

Technicians lived and technicians retired and died. There were those who could solder in this way and who thought it was good. There were those who were not so good at it and who looked for other ways so that they didn't have to do it any more. Treatment plans changed, as did techniques and so the seed was sown. These were difficult times for those who knew not how.

Then came the birth of 'Titanium' in everyday dentistry. Now, not only could the inattentive and under-trained not solder, but neither could the skilled! The race was on to solve the titanium soldering problem. In a flash - 'Laser Welding' followed, healing all wounds. An intense heat source heats just the area that needs melting together to the maximum depth of 1.5mm (an average connecter on a bridge should be 3mm). Technicians were happy again because -

*      There were no more investment models

*      It was direct on the model

*      There was not more flux

*      It was quick

Although it is always unrealistic to expect perfection, I was surprised when I read a recent article on Laser/Phaser welding, ('Lightening in a Bottle' by Joachim Mosch, Andreas Hoffman and Michael Hopp), in which they make the assertion that 'This development can actually be considered one of the major breakthroughs (advancements) in dental Technology in the last 15 years'. They go on to say -

*       Proper welded joints will lead to a perfect passive fit

*       Consequently, the surface condition of the components to be welded (highly polished or sandblasted) will influence the effect of the laser energy. The shinier the surface the less effective the laser will be, as more of the light energy hitting the object will be reflected away, reducing the melting effect.

*        ...Laser welders typically need service and maintenance once a year and a new laser lamp every three years.

*       In a laser welder, the argon gas needs to be adjusted almost every time before welding and the position of the nozzle is often in the technicians way

*       The energy need to penetrate the 1.5 mm would overheat the alloy

*       Practically, distortion must also be considered. To avoid distortion during the welding process, place the spots carefully

*       The bent bar at the top prevents distortion

I stopped reading at this point because it seems to me that the overwhelming evidence points to the fact that to produce a passive, complicated implant integral structure is but a dream. I personally saw a laser-welded implant bridge where one of the fixtures was shy of the implant replica by 0.5mm. For me, laser welding is not the answer. It can do things which conventional soldering sometime cannot do, but it is still only as good as the technician who is using it. There is still a melting pool contraction at the site of melting the metals. Depending on the user and using conventional soldering, this can be larger than a precision-soldered join at 0.2mm.

After studying articles and trying the process myself, I find laser welding has more applications than conventional soldering but I do think that in conventional work, when repairing holes in castings, the time taken to re-wax and add the new-unit into the next casting ring, is more accurate and less time consuming. In bridge cases, where the metal needs to actually touch on another at the welding join, it will require a much higher level of skill than conventional soldering, in order to ensure that, by adding and subtracting to the join, it touches exactly.... all that sounds troublesome and time-consuming to me. But there again - Laser welding does have its place, because it is one of the only methods that work with titanium. And even now, with experience born out of twelve years of marriage, a little voice is saying in my head "Be constructive... do not just criticise"....

So there it was all along, the answer right from the beginning. As technicians we all do it every day and all the time, on nearly every coping we make. We mill it and trim it!!! No soldering or welding in any shape, way or form. No heat expansion or contraction, no gaps to fill, no flux to contaminate, no technique sensitive preliminary procedures, no material cost. Just hours and hours of milling and cutting until our fingers fall off and we join the exhausted heap of solderers and laser welders of time gone by.

Sorry, but I'm afraid my story is not over yet! I have been over-seeing this method by using cad-cam and a milling machine in the construction of passive units using the Procera All-in-One system for the last four years .Yet it does not seem to be part of our everyday routine and being challenged by other less accurate products on the market. Why doesnt anyone seem to be talking about it? So I wondered... Am I missing out on the miracle of laser welding? Might I need to buy one?

The Procera all-in-one Implant Bridge (PIB)

I used the Noble Biocare OPEN TRAY TECHNIQUE, in which screw retained impression copings are connected and duralayed to one another and a viscous, hard bodied accurate impression material is injected into a custom-made tray. In this impression the soft tissue solid model is poured and on this a diagnostic try-in is created, using metal temporary cylinders that are connected together in acrylic. I then finish the frame-work in acrylic and Sweden does the rest.   My reward is an engaging (single-units), non-engaging zirconia or titanium, all-in-one milled structure that fits.  And boy does it fit!!!!

This fit (Fig 2) is due to its unsurpassed ability to contact-measure simple pure implant replicas of given dimensions and then laser scanning the external frame-work, which does not need the accuracy of contact scanning. Together this arithmatical equation is re-inacted with milling tools, transforming a solid homogeneous titanium block into dentistry at its best. I welcome this form of technology in my profession. It ensures for the patient what would be unachievable by man.

Fig 2 -Three implant level fits at 20 times magnification of a 14 unit 7 implant PIB.

I can now finalise my sub-structure in the lab and start to be creative with much more freedom and expression than ever before. I can fire my titanium porcelain onto some of them and I use Gradia composites on others. I am making single unit substructures through to full arches and they can be made in Zirconia as well as Titanium. The only limitation with this phenomenal product is that with screw retained substructures, you are unable to deviate more than 20 degrees from the implant screw hole opening. (You can also use the Multi-unit Abutment for Noble Biocare Implants that can correct an axial alignment of the implant for the desired positioning of the screw channel etc.,etc. and the list goes on)

We are, however, able to work around most implants head-placement, as implants at bone level mean that the point of rotation allows for a marked relocating potential of the access hole. This deviation, in measure, is about 7mm at 2cm from axis of rotation. The access hole is smaller than some rivals as the screw driver access is the thickness of the screw-head , rather than the screwdriver used. Using a composite case, if you want the screw to be integral in the framework, the hole is much more discrete because the screw driver shaft is only 1.5mm thick.

What I like most about the PIB method is the freedom of aesthetics. It is, at last, a solution which I would use in my own mouth instead of a denture. As a technician for 20 years, I have always maintained that the aesthetics of full arch implants and their emergence profiles with long root effects do nothing for me. Some dentists say It does not matter whats under your lip because you cannot see it. I suspect that many patients, given the choice, would actually have existing work redone for better tissue aesthetics. We have the materials and we have the skills. All we need to do is to educate dentists, technicians and patients and encourage them to use it.

The advantages of PIBs are manifold. They -

*      Have a passive accurate fit, perfect to the model implant analogs

*      Have the best aesthetic potential on the market

*      At implant level are 40 % cheaper than traditional methods to date as the parts are included in the prosthesis

*      Have no more yellow gold and other potential metal allergies

*      Are made in the same metal as the implants themselves (no galvanic potential)

*      Are capable of more combinations of reconstructive solutions over any other product on the market

*      Are able to move access channel holes to enhance the aesthetic result

*      Can be covered with conventional crown and bridge work

*      Can be made in

Procera® Implant Bridge Zirconia

now up to 14 units

Procera® Implant Bridge Titanium

Procera® Implant Bridge Titanium for other implant systems

  • Camlog®, Astra Tech® and Ankylos®
  • Enabled through a new Multi Unit Abutment*
  • Can be used with a wider range of implant systems
  • Already fits Straumann® Regular Neck 4.8 mm and Wide Neck 6.5 mm

*The new Multi Unit Abutment fits with the following implant systems:

  • Camlog® 3.3   3.8   4.3   5.0   6.0
  • AstraTech® 3.5ST   4.0ST   4.5ST 5.0ST
  • Ankylos® 3.5   4.5   5.5   7.0

Ankylos® is a trademark of Dentsply Friadent Group.
Astra Tech® is a trademark of AstraZeneca Group. 
Camlog® is a trademark of Camlog Biotechnologies Group.
Straumann® is a registered


And so, to sum up.

PIBs tick the all the criteria in modern dentistry, both functionally and aesthetically and their longevity record is good. Requiring yearly maintenance they are easy to clean, simple to repair, cost effective and predictable (Tj - would reliable be better than aesthetically predictable?). Every time one is sent to me I am amazed at the fit and I think that in the future, they may well prove to be a primary tool in our profession, just as the primary colours are the foundation of all colours in the rainbow. As I try on yet another framework and look under my 20 times magnification, I marvel that the miracle has happened again. No more waiting for the answer, simply a feeling of great thankfulness, as I look back to the good old days and remember when I tried to solder or laser weld that large case for Mrs Maxilla and how long it took!

And the next step? Stem-cell technologies, successful predictable soft tissue and bone grafts? What an exciting thought! And what good news for the patient - who must always be our first consideration.

BY TJ NICOLAS RDT NHD RSA winner Dental technician of the year 2007-2008


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