58 cases of porcelain repair Causes of failure

Porcelain crown and bridge dental defects are repaired and fixed partial denture dentition defect most commonly used method. Its a good biocompatibility, chemical stability, and color of natural teeth and is widely used in a similar clinical effect, but in adapting to syndrome selection, repair, production and production technology, lack of skilled workers, patients and other issues using the method will result in dissatisfied after the completion of restoration. now from May 2007 to November 2010 to my department treatment of 58 patients required re-repair of patients reported as follows.

1 Clinical data
Of porcelain crown, bridge repair are not satisfied, requiring re-repair of 58 patients. 26 males and 32 females. Anterior teeth 67, 65%, posterior 36, accounting for 35% less than a year after the repair, 18 cases, accounting for 31%, more than three years in 36 patients. neck edge black line affect the appearance requirements to re-repair in 23 cases, 40%, porcelain crowns fall off in 12 cases, 20.7%, pulpitis, periapical inflammation in 7 cases, 12.1%, gingivitis, and food impaction in 19 cases, accounting for 32.8%, collapse porcelain 8 cases, accounting for 13.8%.

2 Discussion
2.1 anterior edge of the black lines appear neck causes and preventive measures: the anterior edge of the neck black lines appear, the most important reason is that the metal oxide, nickel-chrome porcelain crown which is more common in its nickel alloy about 73.6% ~ 87.6, chromium about 12.4 to 26.4. nickel-chromium alloy with good mechanical properties and physical properties, cheap, easy production, widespread clinical application. porcelain crown edge of the neck edge of the black line is mainly because the production of nickel-chromium alloy chemical corrosion and electrochemical corrosion. gingival crevicular fluid is an excellent electrolyte, containing a large number of molecular ions, can produce corrosion of the alloy, so that the destruction of molecular structure, free of nickel ion, chromium and other metal ions ion deposition in the gum down to show gray-black or gray gums, gingival margin to form a black line.

In this regard, we recommend the use of titanium porcelain, gold and other precious metal ceramic porcelain and all-ceramic crowns to be addressed. All-ceramic crown because it has no metal base, so there is no metallic black line revealed the problem of the gingival margin, anti-precious metals as high corrosion resistance, can withstand a variety of ions in the oral environment corrosion, will not precipitate the metal ions and stimulate the gums, the formation of the neck edge of the black line, is conducive to periodontal health. porcelain edge technology also can be used in nickel-chrome grill porcelain produced all-ceramic crown neck neck edge, adding a layer of barrier to prevent leakage of metal ions to prevent the neck edge of the dark.

Another clinical preparation and technicians for the production of reasons can lead to neck edge of the black lines occur. One reason is that the neck of prepared abutment width, lack of adequate repair thickness, resulting in porcelain crowns porcelain layer is too thin neck,使金属的颜色能够透出.另一种原因是基牙的颈缘未预备到龈下0.5-1mm的龈沟内,预备过长会压迫牙龈,导致牙龈退缩,最终使修复体的边缘暴露, short neck edge restorations will flush or above the gums, caused cervical margin through the black, red, swollen gums and will cause addition, the edge of the production process mechanics are not in place, clinical bonding adhesive material is too thick, the porcelain abutment crown margin and not seal the neck, can lead to neck edge of the black line. In addition, the repair before the patient fully understand the requirements for appearance, rational choice type of repair is also very important aspects.

2.2 improper color: the color should be natural light than under the method used trichotomy or nine points were recorded. With reference to the patient's age, sex, color, face, lip, adjacent teeth for color selection for non-corresponding shade guide than with the color, two or several ceramic powder can be used to match the case of a conditional can also use the computer colorimeter.

2.3 porcelain crown fall off the causes and treatment measures: the performance of base teeth too much preparation, polymerization degree, the abutment is too short, etc. First, bite force, according to the size of a reasonable choice of abutment, abutment load to avoid excessive , long-term poor results followed the shape of tooth preparation design must meet the requirements of the retention type. will prepare the tooth surface of each shaft nearly parallel to each other is key to retention is also a difficult operation for lack of retention due to loss cases, the binding for the restoration of the body, can increase the nail on the clinical, communication and other retention measures, but most have been unable to prepare a good retention form, and only through the root canal treatment after crown restoration.

Production of porcelain crowns, and tooth paste of the dense and adhesive performance will be the retention of the restoration and long-term effects have significant impact.

2.4 pulpitis, periapical inflammation of the causes and prevention: the body prepared teeth with vital pulp tissue when the cutting teeth too much speed and improper cooling that are likely to stimulate pulp tissue pulpitis, periapical inflammation. Caries for the original Bad handled properly, or the original pulp, root problem is not found, or do comprehensive treatment and processing, prepared teeth do not do temporary crown to protect all possible pulpitis, periapical inflammation symptoms and some teeth missing were not repaired for a long time, in nearly adjacent teeth or distal to the tilt in the repair, in order to bridge the all porcelain crown and porcelain than the corresponding teeth in patients with the long axis aligned cutting too much tilt abutment near the surface or far from the dentin, resulting in pulpitis occurred. Links to free download http://www.hi138.com worn teeth in order to reduce the occurrence of pulpitis apical inflammation, prepare tooth pulp vitality before carefully about the situation of deep caries, cracked teeth, dental trauma, tooth inclination to do the necessary treatment and disposal. Dental anesthesia equipment should be good, cold water cool cutting and grinding, post-vital teeth prepared with fluoride to protect paint and temporary crown to protect them.

2.5 gingivitis, a common cause of food impaction and preventive treatment: gingivitis more common in porcelain crown and abutment neck edge not close together. Abutment can be seen clinically inadequate preparation, not the formation of the neck or shoulder shoulder is not smooth, thick crown edge, the neck is not dense paste, long extended neck edge, oppression gum or adhesive overflow and long-term accumulation and stimulation gingivitis gingival sulcus. a common cause of food impaction is to repair the main body and the adjacent teeth do not touch or close the gap adjacent to the surface appear uneven. In addition, the restoration bad shape, too large, convex side, fullness of the neck and crown can produce lack of food impaction. In these cases, porcelain crowns can be removed after gingivitis, periodontitis has been effectively controlled, the re- to repair the tooth preparation. of gingivitis, the main food impaction is a good preventive measure abutment preparation, craft room is appropriate to make the formation of tooth shape and adjacency relationships, but also to avoid the clinical wear fashionable porcelain crown with o adjacent teeth were ground point too much, causing food impaction.

2.6 collapse porcelain and porcelain collapse: collapse often occurs at the neck edge of the porcelain and cut end. Porcelain crack were more common in clinical practice, there have been reports of clinical failure cases accounted for one fifth of the neck edge of collapse because of shoulder porcelain prepared most of the width is not enough, or skilled workers produce adverse, leading to neck edge of the ceramic layer is too thin. In addition, the restoration and tooth wear do not match and forced into the neck can also easily lead to collapse porcelain. Joint and other deep overbite cases are also prone to bite too tight crack. Preventive measures are a reasonable choice of indications, clinical prepare abutment teeth to ensure adequate retention form, resistance form in the case, try to grind the porcelain crown metal thickness, the model system to take accurate, good bite, try the crown as far as possible, but multi-tone ceramic floor grinding, grinding may be appropriate to adjust the high point of the combined tooth or ridge in the production of ceramic crowns Street take time to ensure strength at the porcelain avoid occlusal function areas, to prevent exposure porcelain mask, make sure the metal support area, so that porcelain was docking in the form, taking into account payments. Porcelain bond strength can be designed to the needs of all the metal surrounding the ceramic form. To account for patient use precautions to avoid biting hard objects such as porcelain can reduce the incidence of collapse.

At present, for a small area of ​​the collapse of porcelain resin can be used to repair, the method is simple, stable and reliable, reducing the workload of doctors and patients to pay the economic and time, regardless of whether the collapse of porcelain tiles intact after the collapse of porcelain repair can be carried out For vital pulp abutment teeth for the porcelain Longbridge collapse of the advantages of porcelain repair is particularly striking is a kind of saving time, effort, economic collapse porcelain clinical effective means of repair. But the collapse of a large area exposed to more porcelain crown base as the collapse of porcelain teeth the size should be carefully repaired, as necessary, with other means to improve the repair of resin bond strength, but large areas of collapse generally need to re-create baked porcelain porcelain crown.

Cracked porcelain Golden ceramic interface due to internal stress and stress concentration inside the ceramic layer, leading to rupture or produce ceramic layer hidden cracks, the failure of ceramic restorations is a common cause of metal substrate and ceramic layers of various types of defects are appearing may lead to the occurrence of crack porcelain. porcelain stripping a variety of reasons, such as gold and one ceramic matching problem, deal with the problem porcelain interface, the interface appearance issues, porcelain layer is too thick (greater than 3ram) or non-uniform problems, ceramic sintering temperature, operational problems on the porcelain bite force problems. the greater the residual stress within the ceramic layer, the greater the likelihood of fracture of metal at the end of the crown shape does not match the requirements easily lead porcelain crack, too thin or uneven thickness of the bottom of the crown, which has a perforated bottom, crown surface of the furrow or acute underlying cause stress concentration. porcelain layer is too thick lead PFM local cooling process, the porcelain surface contraction than the middle of the surface compressive stress applied to the middle of the central tensile stress applied to the surface, the thicker ceramic layer, the surface and Central temperature the greater the tensile stress in the ceramic layer is also greater, will reduce the strength of leading porcelain ceramic layer crack. Ceramic layer thickness generally should not exceed between 1 ~ 1.5mm 3.5mm. Porcelain resin crack repair can also be used, but most of the clinical need to re-create porcelain crowns.

References
[1] Ma Xuan Xiang. Prosthodontics [M]. 5th edition: Beijing: People's Medical Publishing, 2003:114
[2] LIU Hong-chen, Ningjiang Hai. Porcelain repair common problems and treatment [J]. Department of Oral Medicine, 2008,43 (7) :442-444 Links to free download http://www.hi138.com