FAQs
1.What parts are used?
2. Who supplies the API kits?
3. Is it only suitable for the Astra system?
4. How much do the API kits cost?
5.Who can be a Design lab?
6. What tools does the Design lab need?
7.What does Tyler Crown & Bridge (the Precision Lab) do?
8. How much does Tyler Crown & Bridge charge?
9. How much time does Tyler Crown & Bridge need?
10. How much vertical height is needed?
11. Which alloys can be used?
12. Does the casting need to fit the model properly before it is sent to Tyler Crown & Bridge.
13. What if I have a miscast?
14. What does the Design lab need to send to Tyler Crown & Bridge?
15. Can the Design lab smooth over the laser welds?
16. Can the Design lab fire porcelain over the laser weld joint?
17. What if the bridge doesn’t fit passively in the mouth?
18. Is it better than a CAD CAM bridge?
19. Are there situations where this technique is unsuitable?
1.What parts are used?
The API kit contains the parts needed to take an impression, pour the machining model, create the wax pattern and perform the machining process. In practice it is usually necessary to pour a second model which can be mounted on an articulator. The Design lab can use the second model for waxing up and veneering while the first model, conforming to the specifications in the laboratory manual, is reserved for the machining process.
The second set of replicas can in most cases be the usual parts supplied by the implant manufacturer, but if they are unsuitable, there are spare replicas available from Astratech for all the API kits.
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2. Who supplies the API kits?
Since the dentist will normally need access to the kit first, they will order them from Astratech and pass on the laboratory items, with the impression, to the Design lab. Once the wax pattern or casting has been made, the remaining parts - the bridge support and screw, are included in the list of items sent to the Precision lab.
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3. Is it only suitable for the Astra system?
Look at the Astratech website list of implant systems and platform widths and matching API kits.
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4. How much do the API kits cost?
Phone Astratech for up to date prices.
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5.Who can be a Design lab?
Any lab that has the required tools and knowledge to produce wax patterns or castings suitable for the Cresco technique is qualified. There is no certification required. See the Cresco laboratory manual.
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6. What tools does the Design lab need?
The "Wax tube bending kit" and the Cresco laboratory screwdriver are the only essentials. See the Cresco laboratory manual.
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7.What does Tyler Crown & Bridge (the Precision Lab) do?
The model and casting are mounted on metal plates and new fitting surfaces are screwed to the replicas prior to machining both the bridge and bridge supports. Then the machined surfaces are laser-welded together. See the Cresco laboratory manual.
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8. How much does Tyler Crown & Bridge charge?
See the price list for up to date prices. Postage to, but not from, the Design lab is included.
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9. How much time does Tyler Crown & Bridge need?
The "Express" turn-round time is two working days, which includes the day the work arrives and the day it leaves the Precision lab. The normal turn-round time is four working days including arrival and despatch days. We do appreciate it if you are able to book your cases in advance.
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10. How much vertical height is needed?
The legs of the bridge should have 3mm of unmodified cylindrical shape to permit machining and welding. The remaining structure is the same as any other screw retained bridge and depends upon the distance between Implants, occlusal space, alloy strength and veneering considerations. See the Cresco laboratory manual.
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11. Which alloys can be used?
Any alloy which can be machined , laser-welded and is accepted for use intra-orally can be used.
Titanium is easy to machine and weld and is biocompatible. Tyler Crown and Bridge can cast wax patterns in titanium and then machine them to fit before return to the Design lab. Please allow four more working days for casting.
This alloy can be veneered with composite or porcelain, or acrylic teeth can be bonded on with denture base.
Select an API kit with a titanium bridge support.
Welding wire is provided by Tyler Crown & Bridge.
Chrome-cobalt (Bego’s Wirobond C, supplied by Metrodent) machines and welds well and is recommended for large span porcelain fused to metal cases, to avoid sagging in the furnace. Cr-Co is stiffer than titanium for the same cross-section and can be useful for close-bite cases.
Select an API kit with a chrome-cobalt bridge support.
Welding wire is provided by Tyler Crown & Bridge.
Precious metal alloys are more popular in the UK than in Sweden, where this technique was developed, but they can be used. High gold content alloys can be difficult to machine, with smearing of the metal surface and clogging of the cutting blades occurring. Please phone for advice.
Select an API kit with a burnout bridge support pattern, which should be cast by the Design lab in the same alloy as the bridge. The Design lab should provide welding wire, recommended by the alloy manufacturer, for each case.
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12. Does the casting need to fit the model properly before it is sent to Tyler Crown & Bridge?
No, in fact it is better not to try as the replicas and screws may be damaged if there is a misfit. The Precision lab can manage with the normal dimensional inaccuracies associated with wax warpage and investment expansion. In fact there is less need for dimensional accuracy than is required with a cement retained bridge.
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13. What if I have a miscast?
It’s a good idea to have some spare waxing tubes available, as this has been scientifically proven to be the best way of ensuring that they are not required. In the event of the screw access hole being significantly blocked by a casting bubble it will be quicker to recast, but small defects around the screw seat don’t matter, as they will be machined away.
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14. What does the Design lab need to send to Tyler Crown & Bridge?
The machining model.
The casting (or wax pattern), neither screwed to the model.
The impression – accidents do happen.
The bridge supports and screws (plus Lot number).
Telephone number and return address.
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15. Can the Design lab smooth over the laser welds?
Although the weld won’t be smooth it shouldn’t be necessary to do more than remove a few high spots in aesthetically critical areas. Excessive reduction will reduce the cross section of joined metal, reducing the strength of the weld.
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16. Can the Design lab fire porcelain over the laser weld joint?
The bridge, welding wire and new fitting surfaces are all of the same composition for the purposes of firing porcelain, so there is no restriction. Grains of porcelain powder fired onto the fit surface are a risk, so a small metal margin is advisable.
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17. What if the bridge doesn’t fit passively in the mouth?
If the bridge still fits the machining model, then a new impression should be taken and poured. The new model and bridge are returned to Tyler Crown & Bridge. The original casting can be remachined and welded on the new model, free of charge, by the Precision lab, using free bridge supports from Astratech. If the misfit is apparent after veneering, provided the bridge legs are long enough, it is sometimes possible to remachine without removing much of the porcelain, composite or acrylic.
In the case of porcelain it may be possible to cover the exposed welds with pink composite to avoid another firing.
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18. Is it better than a CAD CAM bridge?
The passive fit will be the equal of a CAD CAM bridge, but with further advantages.
The screw access hole can be moved, giving the opportunity to improve aesthetics and function.
There is greater freedom of alloy choice.
For the Design lab, more of the work is performed in-house, thus retaining more of the profit from each case.
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19. Are there situations where this technique is unsuitable?
This technique is only for screw retained bridges using a metal alloy – not single units and not all ceramic.
The technique won’t work if the case doesn’t have enough space for at least 2.5mm of cylindrical leg, however, if a metal occlusion is possible, most situations can be restored.
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