What is a metal core? (What's Metal core?)
It refers to the construction of a metal abutment.
If an appropriate abutment tooth form can not be obtained only by the formation of the dental crown tooth due to the tooth loss of the dental crown or endodontic treatment, etc., build up the shortage with artificial material. It is said to build a kite.
Above all, cast abutment construction is a method of recovering the abutment tooth form by asking for retention in the pulp cavity and the root canal, taking an impression of the abutment tooth, and making it using a working model. Metals for casting support construction include gold alloys, gold-silver-palladium alloys, and silver alloys.
The features of the cast-in-place construction method include the following.
1. Full cast crowns can be worn after construction of cast abutments, even for teeth with pronounced crown collapse.
2. Can protect vulnerable residual tooth quality.
3. The improvement of the shape of the abutment tooth increases the holding power of the crown.
4. The simplification of the abutment tooth configuration can improve the crown compatibility.
5. The crown axis can be improved, and it can also be applied to the adjustment of the attachment / detachment direction of the bridge abutment.
6. The procedure at the time of crown re-production can be simplified.
7. Equalization of crown thickness can be achieved.
Materials
Model trimmer, super hard plaster, ordinary plaster, die lock tray, unity articulator, plaster split saw, vaseline, round bar, wax separating material, inlay wax soft (rod), lab silicone putty, sprue wax, truncated cone, thickness 0.7mm casting liner, stainless ring, vacuum kneader, furnace, gypsum investment material, centrifugal caster, match, gas blow pipe, low melting point flux, dental silver alloy (for metal core), cutting disc, carbide Bar, paper cone, brown silicone point.
Method of fabrication
1. The model base is removed with a model trimmer so that the base of the dentition model is parallel to the occlusal plane and the thickness is 7 to 10 cm.
2. Form maintenance holes in the base surface.
3. Add super hard gypsum to a large lock tray with appropriate mixing ratio, pour, and set a dentition model on it.
4. Once the super hard gypsum hardens, attach the working model to the articulator.
5. Divide each abutment tooth with a plaster split saw.
6. Perform margin trimming.
7. Apply wax separation material to the abutment teeth.
8. The post portion is formed by a soft pressure welding method.
The tip of pressing the wax to the back of the root canal is to first make a wax block larger than the external shape of the abutment teeth. Next, a portion about 2-3 mm hard from the outside is made, and the central portion of the wax block is heated with a heated wax instrument. Then, the softened wax is pressed in at the timing when the surface of the heating part turns dark and cloudy.
9. Once the post is complete, make the crown profile wax-up.
10. A core of the contour is made of silicone putty to record the crown contour.
11. Referring to the putty, the crown wax is removed so that the thickness of the crown is uniform and the axial taper is 2 to 8 °. And it forms in the simplest possible abutment tooth form.
12. Once waxing up is complete, plant thick and short sprue wax on the occlusal surface of the wax core.
13. Put a wax pattern on the frustum and wrap a casting liner inside the stainless steel ring.
14. Buried with gypsum-based investment material (standard mixing ratio)
15. Make mold according to manufacturer's specification (lost wax method)
16. Cast the specified metal.
17. Once the mold has cooled, index the cast.
18. After sprue cut, after mobile correction with a straight bar, it is finished by grinding to the roughness of the brown silicon point.
Discussion
1. About working model
In case of manufacturing only the abutment construction, the accuracy of the positional relationship of the dentition model is not required so much. Therefore, this time, a divided tooth row model using a die lock tray was manufactured. Super-hard gypsum was used in the tray because it is desirable to produce a working model that is as accurate as possible in positional relationship. In addition, if dust such as gypsum scraps and wax adheres to the inner surface of the tray, the accuracy of the positional relationship significantly deteriorates.
The split dentition model using the die lock tray can have a slightly shorter working time than producing a split dentition model using the dowel pins. In addition, it is an advantage that there is no concern of penetrating the post when drilling holes for dowel pin planting.
2. About wax up
There are several conceivable ways to wax up the post section. One is the softening pressure welding method used this time. This method requires sense and skill, and it is presumed that few dental technicians can use this method at present. Another method is to pour the wax into the post and heat the wax into a liquid state, and immediately insert a resin or metal rod so that the wax in the post can be removed. This method is simpler as a method, but has the disadvantages that it is difficult to pour the wax to the back of the post, that bubbles are mixed in, and the wax in the post part is difficult to remove. As another method, there is a method of pouring a pattern resin into a post portion, etc., but when an undercut exists in the post portion, removal of the pattern is difficult, so it can not be used so much.
Abutment tooth part is considered to be able to produce the abutment construction which considered the clearance of the front crown, if the silicon core is produced after waxing up the crown external shape once and the clearance is confirmed and manufactured. . Without the silicon core, it is surmised that technical errors such as non-uniform thickness of the crown formed on the abutment construction and misalignment of the tooth axis are likely to occur. Of these errors, the tooth axis misalignment is likely to occur as well when the working model is not a parallel model.
3. About casting
This time, dental low melting point silver alloy was used. This differs from the gold-silver-palladium alloy in the casting process because the melting point is about 600 ° C. When casting a gold-silver-palladium alloy, the mold heated to 700 ° C is cast when it is in the red state, whereas when casting a low melting point silver alloy for dental use, the mold heated to 700 ° C is cast as a match It is necessary to cool the metal to a temperature that does not ignite and then melt and cast the metal. Also, it is necessary to use a special low melting point type flux. Even when heating and melting the low melting point silver alloy, it is necessary to stop the heating for about 3 to 4 seconds after the alloy is rounded after adding the flux and then centrifugally cast it.
About the production of metal core using 4.3D printer
If a resin-made base construction model with excellent heat dissipation is formed using liquid tank photopolymerization method and inkjet 3D printer technology, existing dental alloy products can be made by using the lost wax casting method in combination Abutment construction of the can be produced. It is necessary to verify the adaptation accuracy to the model in the future.
Conclusion
A high-precision, high-quality metal core could be manufactured by making full use of the ideal abutment construction by the silicon core method, the formation of the post by the soft welding method, and the special casting technology of the low melting point alloy.
