1, old dental trauma, the roots of the teeth appear slow extradental intradental resorption, imperfect endodontic treatment and other factors will lead to a variety of discomfort symptoms, can be diagnosed by clinical and X-ray dental examination. 2, such as dental preparation (grinding) poor – shoulder abrasion quality is not in place, or do not use the gingival row gingival technology, the edge of the porcelain teeth will appear plaque retention caused by gingival recession, the edges of the teeth will appear blackened, especially in the gums of the thinner anterior teeth position. 3, porcelain teeth material selection: front teeth should be selected biocompatibility and stability of good materials such as precious metals, all baked. 4, and the bite of the opposing teeth should not be too tight, resulting in excessive force on the porcelain teeth. 5.Some bad biting habits.