With the promotion of zirconia market, its application is more and more: single crown, inlay, implant abutment, triple crown, multi crown, half crown and even full crown. So far, zirconia has accounted for 50% or more of the goods of many processing plants.
After continuous testing, research and close communication with customers for many years, the Technology Department of aerchuang company hopes to share some experience with you. Previously, it shared the analysis of zirconia crown cracking in the company's internal journal. Today, it makes a summary and share on how to avoid crown cracking and deformation when making a long bridge with zirconia in the details of each step in the standard manufacturing process of zirconia.
1. Avoid stress concentration, and design the jaw curve according to the opposite dentition and occlusion;
2. There are at most three missing positions of anterior teeth, two missing positions of posterior teeth and no more than one missing position of free end;
3. When the abutment conditions are not suitable for making zirconia, such as no common approach for the bridge, too small distance between the bridge and the gingiva, too large undercut of the abutment and unreasonable preparation of the abutment, the doctor should be contacted in time;
4. The minimum thickness of the lingual side of the crown should be greater than 0.8mm, and the thickness of the incised end or occlusal surface adjacent to the missing body should be greater than 1.0mm;
5. The cross-sectional area of anterior tooth connector ≥ 9mm² and posterior tooth connector ≥ 12mm²
1. During typesetting, the supporting rod should be placed symmetrically between 1 / 3 and 1 / 3 of the crown neck;
2. Support rods shall be placed on the bridge body as far as possible, and shall not be placed on the connecting body as far as possible;
3. Add the tongue side reinforcing bar (the thickness of the tongue side reinforcing bar is recommended to be about 2mm), and the design method of the tongue side reinforcing bar is as follows:
The software does not support the automatic addition of lingual reinforcement plate, which can be manually trimmed through tooth arrangement and other methods (the thickness of the rest should be as uniform as possible, controlled at about 2mm);
4. We can choose whether to add the sintering bar of the occlusal surface or not;
5. Check the use of the needle. For long bridge machining, it is better to replace the new needle and process after the equipment is calibrated;
6. When the dental bridge is removed from the porcelain block, only the labiobuccal side of the dental bridge and the lateral support bar of the cross bar need to be removed. When the support bar is removed, it needs to be operated carefully, and the removal amount should not exceed 0.5mm each time, so as to prevent the fracture of the dental bridge or the internal hidden crack during the removal process. It is suggested that the removal sequence of the support bar should be crown labiobuccal side support bar, bridge labiobuccal side support bar and lateral support bar of the cross bar in turn;
7. The lingual strut of the bridge can be selectively removed 1 / 2-1 / 3 of the diameter of the partial strut, and the removal starts from the neck of the bridge.
1. According to the clinical requirements for staining, it is recommended to use brushing method for staining;
2. Before dyeing, take out the dye 30-60 minutes in advance and cool it to room temperature before dyeing;
3. After dyeing, the bridge needs to be dried for more than 60 minutes, and the drying temperature of the bridge is 90 ℃; after drying, wait for the temperature of the crown surface to cool to room temperature, and then place it in a crucible for sintering.
1. Curve setting, according to different furnace corresponding to different parameter settings:
2. When sintering, it should be placed vertically on the crucible or the lid of the crucible;
3. After sintering, the crown should be taken out when the furnace temperature is lower than 200 ℃.
Removal of lingual reinforcing bar
Use a high-speed water jet to grind the support rods between the lingual side and the lingual side of the bridge one by one, pay attention to the gradual grinding with light pressure, and try to avoid grinding to local heating.
Shape adjustment and occlusion
1. Use special grinding tools for zirconia of high-speed mobile phones or slow mobile phones to carry out shape dressing, occlusion and adjacency adjustment;
2. During grinding, pay attention to one-way and light pressure grinding to prevent hidden cracks during grinding;
3. When opening the tooth seam, pay attention to point cutting instead of direct cutting. Use special slotting tools to handle it gently, so as to reduce the grinding amount of slotting as much as possible;
4. After full crown grinding, it is recommended to use 50 μ m (270 mesh) high-purity alumina sand for sandblasting at 2-2.5bar (0.2-0.25mpa). The sandblasting function is: cleaning and restoring material strength (with experimental data proving that the strength of zirconia can be greatly improved under this condition), at the same time, the process is also convenient for subsequent dyeing and glazing;
5. After the internal crown is polished, it is suggested to use a porcelain furnace to heat treat the crown, so as to reduce the content of monoclinic phase on the crown surface, improve the strength and increase the bonding force of zirconium porcelain. The heat treatment temperature curve is as follows:
Porcelain / glaze
1. It is suggested that the temperature rise rate of glaze should not be too fast;
2. The frequency of entering the porcelain furnace should be controlled within 3 times as much as possible, and frequent sintering is easy to lead to hidden crack;
3. The furnace temperature shall be cooled to below 200 ℃ before being taken out.