There are many types of porcelain teeth, currently commonly used are all-ceramic porcelain teeth, precious metal porcelain teeth (gold, silver, palladium), semi-precious metal porcelain teeth (cobalt-chromium alloy), non-precious metal porcelain teeth (nickel-chromium alloy) . At present, the most clinical application is the semi-precious metal porcelain crown, especially the cobalt-chromium alloy porcelain, which has the advantages of low price, good mechanical strength, beautiful appearance and avoiding gingivitis and periodontitis.

 

Metal porcelain needs to make wax-up first. Traditional wax-up production relies on manual work and experience. It is necessary to coat a layer of separating agent on the surface of the abutment, and immerse it in wax water with a temperature of 85~95 degrees for one second to make the abutment. Apply an even layer of yellow wax to the surface. After the yellow wax has cooled, take it out and check for smoothness and cracks. After the completion, add a layer of green wax evenly on the original yellow wax, and the wax must be smooth.

Then, a layer of trapezoid-like shoulder with a thickness of about 0.6 mm and a width of 1.0 to 1.2 mm is evenly added to the lingual neck margin of the abutment. Use red wax to restore the basic shape of the edentulous area, and then cut back to reserve the position of porcelain on each surface of the tooth, about 1.5-1.8mm. It is required that the wax-up does not have any sharp corners. The thickness of the wax-up is about 0.35-0.4mm in the anterior teeth and 0.4-0.45mm in the posterior teeth.

Apply a layer of separating agent on the surface of the abutment, and immerse it in wax water with a temperature of 85-95 degrees for one second, so that the surface of the abutment adheres a uniform layer of yellow wax. After the yellow wax has cooled, take it out and check for smoothness and cracks. After the completion, add a layer of green wax evenly on the original yellow wax, and the wax must be smooth.

Then, a layer of trapezoid-like shoulder with a thickness of about 0.6 mm and a width of 1.0 to 1.2 mm is evenly added to the lingual neck margin of the abutment. Use red wax to restore the basic shape of the edentulous area, and then cut back to reserve the position of porcelain on each surface of the tooth, about 1.5-1.8mm. It is required that the wax-up does not have any sharp corners. The thickness of the wax-up is about 0.35-0.4mm in the anterior teeth and 0.4-0.45mm in the posterior teeth.

The traditional production of wax-up is inefficient, the cost of a single production is high, and it is difficult to meet modern production requirements. If the light-curing 3D printing method is used to make wax-up, it will be an easy process, with low cost and high production efficiency.

 

After the waxing is completed, it enters the casting process. Due to the high melting point cobalt-chromium alloy used, it is difficult for ordinary gypsum powder to meet such high temperature requirements, and special dental casting embedding powder is required.

Place the removed wax shape on the cast ring 2/2 to 3/5 of the way into a circular shape, which must be neatly arranged, similar to the top of an umbrella. The distance between the wax model and the edge of the apron is 5-7mm, and a circle cannot exceed 60 grams, that is, the total weight of the wax model must be less than 6 grams. Spray waxing water to clean the wax. Before embedding, dry it with an air gun, pour the water and swelling water into a mixing tank in proportion to mix, add an appropriate amount of embedding material, quickly stir with a plaster knife for 8 to 10 seconds, and then stir with a vacuum cleaner mixer for 40 to 60 seconds, Then pour the mixed embedding material into the casting ring at a uniform speed, and use a vibrating screen to assist in embedding.

Note air bubbles and proper ratios in the embedding medium. Embedding is proportional to the weight of the wax. For example, if the wax weighs 5 grams, 300-350 grams of embedding powder and 70-84 ml of swelling water should be prepared.

The baking temperature standard is determined according to the embedding material. Porcelain, steel teeth, steel brackets and other nickel-chromium alloys are 950-980 degrees, gold 800-850 degrees, and titanium alloys 900-950 degrees. The first temperature is 300 degrees, the heating time is 1 hour, and it is kept for 30 minutes, with the runner facing down. The second time is the final temperature, maintained at 950 degrees for 30 minutes, on the runner. Casting begins as soon as the temperature reaches the above criteria.

 

Shake the centrifuge 3 to 4 times. When casting, the flame length is 3 to 4 cm, the distance between the alloy and the flame tip is 2 cm, and the oxygen is controlled at 3.5 to 3.8 bar, not exceeding 4 bar. As the metal begins to melt into a dazzling sight, there are instant bright spots and wobbles.

Note that the alloys should be stacked together with a small amount of flux added to melt the alloys. The melting temperature should not be too high, otherwise it will easily lead to tooth perforation and steel embrittlement. After casting, the castings were taken out and sandblasted after cooling at room temperature.

In addition to using the appropriate embedding powder and pouring temperature, it is also necessary to connect a suitable pouring runner. The position of the runner and the diameter of the runner will affect the final pouring effect.

The whole process is a complete system, which needs to be continuously optimized in practice in order to produce beautiful works!