With the increasing presence of zebra crowns in the market, in addition to the color issue, zebra crown cracking is also a hot topic at present. The influencing factors of total zirconium crown crack are mainly the following three points: clinical objective reasons, operation process problems, and daily use of patients.
1 Objective clinical reasons
1. The clinical preparation of teeth is unreasonable or the abutment conditions are not suitable for zirconia
Such as shoulder table, concave shoulder table, unclear edge line, double edge line, insufficient tooth preparation space, indented abutment or bridge not in common position, abutment incision or jaw edge too sharp, etc.
Solution: Prepare the abutment according to the requirements
- Prepare the abutment into a rounded beveled shoulder or a horizontal right-angle shoulder with a blunt axis-neck line. It is recommended to prepare the shoulder width of 0.5~1.0mm.
- The jaw face and the cut ends need to be ground 0.8~1.5mm, the axis aggregation angle is 3°~6°, the connection between the shaft wall and the jaw surface should be rounded, and the corner radius is greater than 0.5mm.
- The opening angle of 120°~140° of the maxillofacial surface can ensure that the surface of the inner crown is accurately copied during cutting, so as to achieve a perfect fit.
- When preparing the bridge, it is necessary to have a common seating channel between the abutments to avoid concavity.
2. Clinical modeling is not clear
In fixed repair, the accuracy of clinical modeling is the first key to successful repair. In addition to the requirements for the user’s technology, the selection of stamping materials is also particularly important.
The ideal stamping material should be safe, non-toxic, and non-irritating, smooth and dense surface, good elasticity, fluidity and plasticity, certain strength and chemical stability, proper solidification time and high accuracy, and not easy to deform.
- Improper selection of stamping materials causes deformation of the model or inaccurate abutment increases the difficulty of production
- When the mold is taken, the edges are not clear due to incomplete gums or incomplete gums
2 Operation process and process issues
1. Improper handling of plaster models
The moral model refers to the male mold formed by injecting the model material into the oral impression in its plasticity or flow state. It is the basis for making various prostheses.
China Dental Outsource must pay attention to the factors that may cause excessive local stress of the crown, such as bubbles, sharp corners, and flying edges when repairing plaster models.
2. Unreasonable design or parameter settings
A qualified prosthesis should have a certain thickness, connection strength, sufficient porcelain stacking space, normal crown size and form, reasonable occlusion relationship, and appropriate tightness for trying on.
Zirconia must ensure at least 0.6mm or more to ensure that the repair body has a certain strength, the connector needs to ensure the thickness of 3*3 or 4*4 to achieve a certain connection strength, occlusion should pay attention to the extension, lateral movement, the clearance agent should be set according to the abutment condition to avoid excessive polishing in the late stage leading to excessive local stress of the crown.
3. Abnormal processing
Improper design layout, problems with design and processing files, abnormal equipment, cutting fluid composition, etc., will lead to a decrease in the strength of the porcelain block, too long tool use time and insufficient sharpness, equipment loss, etc., will also lead to increased processing resistance and increase the probability of hidden cracks inside the crown.
4. Improper prefixation leads to loss of crown strength
Each grinding equipment has its specified speed, should follow the instructions of the equipment, the mobile phone rotates too fast, too much force when cutting the support rod, the crown falls or bounces on the wall of the porcelain block, the use of tools is insufficient cutting force, deepening the groove too deep across the maxillofacial edge ridge, etc.
5. Dyeing and sintering details are not paid
Porcelain blocks and staining fluids should be operated in accordance with the process details specified by China Dental Outsourcing. Insufficient drying time, too high drying temperature, improper drying tools, too fast sintering procedure (temperature lifting rate), etc. will lead to subtle cracks inside the crown bridge.
All zirconium crown bridges dry naturally after dyeing and sintering using a slow burn procedure to achieve the best color, permeability, and strength of crowns and bridges.
6. The process is too rough after sintering
Polishing Use zirconia special car stone or water-cooled mobile phone emery car to trim the elegant edge and shape (the reinforced restoration should be polished strictly according to the speed of the tool used, and excessive pressure cannot be used during the grinding process to prevent internal cracking caused by excessive local heating). Mobile phone speed too fast, too much force, use of inferior coarse sand tools, local polishing too much heat, sandblasting use of alumina sand particles too thick will affect the final strength of the repair body, polishing too thin will also lead to insufficient support, open teeth too deep, groove deepening too much, too much jaw adjustment or contact too tight and other fine-tuning links also easily lead to dental crown cracking.
7. Glazing or porcelain procedures too fast
Remove the crown from the porcelain table if it heats up and cools down too fast and the temperature is too high.
3 Reasons for daily use by patients
Patients biting hard objects or not wearing bridges after trying on them caused excessive local stress on the zirconium crown.
The completion of a zirconium crown must perfectly combine technical and scientific aspects. It is necessary to be proficient in various operational skills and to systematically grasp the basic theories, and rely on good communication and cooperation among doctors, technicians and other personnel and daily maintenance of patients.
In short, China Dental Outsourcing reminds everyone that the quality of zirconium crowns is the responsibility of all participants. Problems in every part of the denture repair process will affect its final use.