I. Definition of Pile Core Crown Pile core crown is a common restoration method for repairing large dental defects. A large defect is the loss of a large portion of the hard tissue of the affected tooth’s crown. Even the root of the tooth is involved. Due to the small amount of remaining tooth tissue, good retention cannot be obtained with a full crown alone. To increase retention, a portion of the restoration is inserted into the root canal to obtain retention, and this portion of the restoration inserted into the root canal is called a pile. In the early days, the pile and the crown were integrated, and these crown restorations with a pile inserted into the root canal to obtain retention were called pile crowns. The pile crown used today is a modification of the traditional pile crown, in which the pile and the outer full crown are made separately and independently, called the pile crown. What kind of teeth need pile core restorative crowns? When there is a large area of tooth tissue loss in the crown, simple filling, full crowns and inlays are not effective, the pile core system makes it possible to restore the residual roots and crowns, avoiding alveolar bone resorption and loss of proprioceptive receptors caused by tooth extraction, and improving chewing efficiency. What is residual crown and residual root: most of the crown of a tooth is missing due to decay and other reasons, which is called residual crown, while the crown is basically missing and only the remaining root is called residual root. 1.Residual crown: most of the clinical crown is missing and cannot be restored directly with crown 2.Residual root: the clinical crown is completely missing the residual root, even up to subgingival, but can be extended by crown or orthodontic traction 3.Mismatched reversed teeth that need to change the direction and not orthodontic indications 4.Malformed teeth with poor direct preparation and retention 3. Timing of pile core crown restoration Before pile core restoration of dental defects requires careful and perfect preoperative preparation, that is, the affected tooth The tooth must have undergone perfect root canal treatment, and generally needs to be observed for one to two weeks after root canal treatment to confirm that there are no clinical symptoms such as spontaneous pain and percussion pain, and that the original fistula has completely healed before the restoration of the pile crown can be performed. The length of time required for observation varies according to the pulp condition of the tooth before treatment: 1. Pile crown restoration should be started only when the apical lesion is significantly reduced and there are no clinical symptoms. The ideal core material should meet the following requirements: suitable strength, close to the modulus of elasticity of dentin, good retention, good aesthetics, good corrosion resistance, no discoloration, good biocompatibility, does not affect magnetic imaging, easy to use, etc. (1) Classification 1, according to the different materials, piles can be divided into: (1) metal piles including base metal piles (nickel-chromium alloy, cobalt-chromium alloy, titanium alloy and pure titanium), semi-precious metal piles and precious metal piles (gold alloy). (2) Non-metallic piles, non-metallic material pile cores including ceramic piles, composite resin piles, fiber reinforced resin piles (carbon fiber, glass fiber, quartz fiber and quartz plastic coated carbon fiber), etc. 2. According to different manufacturing methods, the piles can be divided into: (1) Casting piles Casting piles are individually cast using the lost wax method, and are metal pile cores with one core (2) Pre-formed piles Pre-formed piles are semi-finished piles with different shapes and sizes, which are used according to the specific conditions of the roots. （Cast metal piles have good physical and mechanical properties and can be easily machined into a precise shape. For patients with severe labial tilt and severe lingual tilt requiring reorientation, cast metal pile cores are suitable. However, because its elastic modulus is much higher than that of natural dentin, when the restoration is subjected to a large load, it will easily lead to stress concentration in the local area of the dentin in the root canal and cause root fracture; during the clinical use of cast metal pile cores, the gingiva and porcelain crown or all-ceramic crown can be stained due to the metal ions released after electrolytic corrosion. In addition, metal pile nucleus has the ability of blocking, affecting x-ray and magnetic resonance imaging. If the metal pile fails, the root may need to be extracted. For residual roots with little residual dental tissue and thin root canal walls, casting pile cores should be avoided as much as possible. 1) Common metal pile cores are mainly composed of nickel-chromium alloy or cobalt-chromium alloy, which are hard, and the pile itself is very strong, but they are very easy to lead to splitting of the root, and are easy to corrode and have poor biocompatibility, so they should be chosen carefully. (2) pure titanium pile titanium has stable chemical properties and excellent biocompatibility, does not react with human tissue; light weight; titanium because of its extremely low magnetic permeability, no interference with magnetic resonance imaging, when the head and neck need to do MRI examination, no need to remove the pure titanium pile nucleus to avoid pain and inconvenience to patients, does not affect the future medical examination; its elastic modulus is lower than ordinary metal pile nucleus; pure titanium also has certain disadvantages, that is It is not easy to process; because of the transparent metal color, it is difficult to meet the aesthetic requirements of all-ceramic restorations. (3) Precious metal pile Gold alloy pile core is a more ideal inert pile core material, elastic modulus and thermal expansion coefficient basically match the enamel, and the compressive strength is sufficient to meet the general occlusal force. The disadvantage of using precious metal pile cores in anterior teeth is that it is difficult to meet the aesthetic requirements of all-ceramic restorations and affect the nuclear magnetic examination. Porcelain piles Ceramic materials have high compressive strength, fracture resistance, superior biocompatibility, ceramic pile cores also have no effect on future MRI, good aesthetic properties, especially for anterior all-ceramic crown restorations. CAD-CAM processing of zirconia pile cores and lost wax casting method can be used to complete the individual porcelain pile cores, the strength of which can meet the clinical requirements. Ceramic core pile modulus of elasticity of about 200GPa, while the root modulus of elasticity of 9-10GPa, ceramic pile nucleus of high strength, high elastic modulus determines that it almost does not bend, the external force is easy to concentrate in the apical part of the formation of the local high-pressure strong, easy to cause root fracture, and zirconia ceramic hardness is particularly high, simply can not use the turbine to directly grind the porcelain pile, once broken can not be removed, may lead to tooth extraction. . In addition, its price is more expensive than ordinary pile core, the production is also more complex. The long-term restorative effect of porcelain piles, especially the fatigue resistance is worthy of attention. 3. fiber pile 1) advantages glass fiber pile modulus of elasticity and tooth tissue is similar, conducive to stress transfer to the root surface, thereby reducing the concentration of stress in the root, when the force can be fractured before the tooth tissue, thus playing a role in protecting the tooth tissue, reducing the risk of root fracture, so that the affected tooth has the possibility of restoration again; good light transmission and natural color so that the all-ceramic restorations made on its aesthetic performance is good. The clinical production of fiber pile resin cores is carried out by the doctor at the chairside, and can be completed in one visit, reducing the number of visits; glass fiber piles have good biocompatibility; glass fiber piles have stable physicochemical properties in the oral cavity, have strong corrosion resistance, and do not release metal ions such as nickel or beryllium in the oral environment to produce toxicity or cause human Good repeatability, the fiber pile can be easily removed with a drill after the nucleus is broken, and can be restored twice, with good long-term restorative effect; fiber pile super mechanical properties, with stronger bending strength and tensile strength than metal piles; excellent bonding performance fiber pile with resin bonding performance far exceeds that of metal piles. Metal in the oral cavity can cause some effect on MRI images, while fiber pile restoration has no effect. (2) Disadvantages Pre-formed piles are not suitable for crown restorations that require a change in restoration direction; limited strength, not suitable for restorations with little remaining dentin or small restoration gaps such as deep overdentures; relatively coarse diameter, care should be taken to prevent lateral penetration when applied to posterior root canal preparation; (3) Selection of pile core materials 1 If the cervical dentin is high (height greater than 1.5 mm), a hoop effect can be obtained and If the diameter and length of the root and the height of the alveolar bone are good, then there is no big difference between using fiber or ceramic or metal pile cores. 2 If the cervical dentin is low (less than 1.5 mm in height) and the barrel effect cannot be obtained, but the root is in good condition, it is more reasonable to use ceramic or metal cores. 3 If the root is in poor condition and the cervical portion is good, then fiber pile cores are more reasonable. There are no absolute advantages and disadvantages of fiber, ceramic and metal pile cores, but they are chosen according to the different conditions of the patient, and the correct grasp of the indications is the key. (1) X-rays must be taken before the preparation of the affected tooth to understand the length, diameter and shape of the root, the morphology and thickness of the root canal, the root canal treatment, as well as the periapical and alveolar bone; (2) Preparation of the remaining tooth tissue: according to the requirements of the selected final full crown restoration, remove the thin-walled weak tip, the original filling, the carious tissue, etc.; (3) Preparation of the remaining tooth tissue: according to the requirements of the selected final full crown restoration, remove the thin-walled weak tip, the original filling, the carious tissue, etc. (3) Removal of root filling material; (4) Root canal preparation; routine root canal preparation of the affected tooth with reference to x-ray and root canal length measured during root canal treatment, with a length of 2/3-3/4 of the root length, or at least equal to the crown length, and a diameter of about 1/3 of the root diameter, and preserving at least 2 mm of the dentin shoulder collar as much as possible. (5) Finishing; (6) Making of impressions; (7) Making of casts; (8) Completion of intraoral cementation of the pile core, full crown preparation, taking of impressions, infusion of working models, full crown fabrication, and cementation after clinical trial. (1) X-ray must be taken before the preparation of the affected tooth to understand the length, diameter, and shape of the root, the morphology and thickness of the root canal, the root canal treatment, and the periapical and alveolar bone conditions; (2) Preparation of the remaining tooth tissue: prepare the tooth according to the requirements of the chosen final full-crown restoration, removing thin-walled weak tips, original fillings, carious tissue, etc.; (3) (4) Root canal preparation: The tooth should be prepared with a length of 2/3-3/4 of the root length, or at least as long as the crown length, with a diameter of about 1/3 of the root diameter and at least 2 mm of the dentin shoulder collar preserved as much as possible, with reference to the root canal length measured by X-ray and root canal treatment. (5) Pre-pile cementation; (6) Resin core molding; (7) Full crown preparation, impression taking, working model infusion, full crown fabrication, and cementation after clinical trial wear is completed. (1) When most of the patient’s posterior teeth are missing, extra caution should be exercised when restoring the upper anterior teeth with pile crowns, as tooth fracture or pile crown loss can easily occur. The patient should be advised to repair the missing posterior teeth before restoring the upper anterior teeth. (2) When restoring upper anterior teeth with pile crowns, the orthodontic dentition should be adjusted to close contact with the posterior teeth and no contact or light contact with the anterior teeth; the anterior extension dentition should be adjusted to equal contact between the tooth and the adjacent teeth.