Key points of clinical application of fiber resin post and core
Since the fiber post came into the market in 1989, it has become more and more popular in clinical medicine. Scholars at home and abroad have also used a large number of literature studies to prove that the fiber post has a good clinical effect
Advantages of fiber resin post and core
The elastic modulus of fiber post is very close to that of natural dentin (18 GPA), which can effectively reduce the stress concentration, make the stress transmit evenly along the root canal wall, and thus reduce the occurrence of root fracture. Other studies have shown that even if the root fracture occurs, the fracture line of fiber post is also above the alveolar bone, and most of them are fracture between the post and the core, so it is conducive to re repair. At the same time, the post core material has a semi permeability similar to the tooth tissue, and the core material has a color similar to the dentin, which can simulate the permeability of natural teeth, and provide a good background color for all ceramic restoration, so as to increase the aesthetic effect of all ceramic restoration.
In addition, compared with metal posts (especially metal posts with ferromagnetic materials, such as cobalt chromium alloy posts), fiber posts will not produce artifacts and affect the results of MRI. When it is necessary to remove the post, the fiber post is easier to remove than the metal post, and it is not easy to cause secondary damage to the tooth tissue.
Selection of fiber pile
Fiber type
Fiber pile is composed of resin matrix and reinforced fiber, which can be divided into carbon fiber pile, glass fiber pile and quartz fiber pile. Among them, glass fiber post and quartz fiber post are widely used in clinic, and quartz fiber post is more recommended because of its better mechanical and aesthetic properties than glass fiber post.
Shape of pile
The shape of fiber pile can be divided into two categories: column pile and cone-shaped pile. Although the column pile has better retention, it needs more preparation at the tip of the root, which weakens the root strength. At the same time, the end of the pile is more likely to lead to stress concentration. The tapered post, especially the double tapered fiber post, which is more suitable for the shape of root canal, can effectively reduce the amount of root canal preparation, increase the cohesion of the fiber post and root canal, and conduct the stress more evenly, which is conducive to the preservation of tooth tissue and the retention of the post.
Diameter of pile
The diameter of the post should be about 1 / 3 of the root diameter, and should change with the change of the root canal shape. The thickness of the root canal wall at the tip of the post should be more than 1mm, so as to ensure the strength of the fiber post and the remaining tooth tissue, and prevent the fracture of the post and the root.
Length of pile
In the selection of the length of the post, because of the existence of apical divergence within 5 mm of the root tip, 4-6 mm of gum should be reserved in the apical area to achieve good apical closure. On this basis, the ratio of post to crown should be at least greater than 1, and the length of the post in the endodontic segment should be at least 1 / 2 of the length of the whole endodontic segment (as shown in Figure 1), so as to ensure the retention and resistance of the post. In clinic, many cases of post crown falling off, post or root breaking are directly related to the insufficient preparation length of post canal.
Fig. 1 based on the length of root supported by alveolar bone, the preparation depth of the post should be more than half of it
Quality of piles
The fiber pile shall contain enough reinforced fiber content and appropriate resin matrix, and be processed by specific processing technology to ensure good mechanical strength of the fiber pile. The fiber post should have good light conductivity, so that the light emitted by the light curing lamp can be transmitted along the fiber post to the root canal, so as to promote the curing of the bonding resin and obtain good bonding strength. The fiber post should also have X-ray radiation resistance to facilitate clinical examination and diagnosis. At the same time, a good fiber pile system should also have excellent precision and be convenient for the operation of clinicians.
Number of piles
The number of fiber posts should be considered according to tooth position, defect and root canal. It is suggested that only one main post should be placed in a single tooth, such as oval, 8-shaped, funnel-shaped root canal, etc., and the auxiliary post system should be considered for restoration. The number of fiber posts in multiple teeth should consider the number of roots, defect range and location. Generally, one fiber post should be placed in one wall defect, two fiber posts should be placed in two walls defect, and more fiber posts should be placed in larger defect.
Clinical use
Indications
Because of its good mechanical, biological and aesthetic properties, fiber post can be used as the first choice in most cases. However, when the tooth defect is too large to obtain enough dentin shoulder collar, and the axial direction of the tooth needs to be changed to a large extent, or when the occlusion is too tight and the fiber post is required to bear a large bite force, the application of the fiber post is also facing challenges.
Pile road preparation
The preparation sequence of the pile road is: first, use GG drill or Peeso drill step by step to determine the depth and direction of the pile Road, and remove all the dental glue and paste fillings within the length of the pile road; then use the reaming drill matched with the fiber pile system to expand the pile Road step by step, starting from the drill with the smallest diameter, and increasing the diameter to the drill with the predetermined diameter step by step to avoid drilling skipping. During the preparation of the pile way, the equipment with tip protection should be selected to avoid side penetration. The author recommends GG drill. Although the tip of the Peeso drill has a safety head, it is hard, which is easy to cause side penetration of the root canal and break of the drill. Care should be taken during the use.
During preparation, the instrument should be rotated in and out of the root canal and pulled to prevent seizure and fracture of the instrument. The conic pile system has obvious advantages in the preparation of the pile Road, because it is matched with the conic pile road preparation drilling needle, which is not easy to jam the needle in the preparation process, and the possibility of the preparation leading to the lateral penetration of the root is greatly reduced. Special attention should be paid to the preparation of the post canal. The time for the instrument to enter the root canal for each preparation should not exceed 2 s, so as to avoid damaging the periodontal tissue due to excessive heat. Repeated use will blunt the drill needle, reduce the cutting and grinding efficiency, and increase the heat production. It should be replaced in time.
Pile road treatment
During the preparation of the post canal, all the dental glue and paste in the pulp cavity and root canal within the length of the post canal must be completely removed. The smear layer will be formed in the cutting process of the inner wall of root canal. Therefore, after the preparation of the post canal, in addition to using wet cotton to wipe the residue on the wall of root canal, effective methods should be selected to wash and disinfect the inner wall of root canal and pre-treatment before bonding. Sodium hypochlorite, hydrogen peroxide and other oxidants may form an oxygen inhibiting layer to inhibit the full polymerization of the adhesive resin, and the phenolic agent may also affect the full polymerization of the resin, so it should be avoided in the process of pile road treatment. Chlorhexidine, as a strong broad-spectrum antibacterial agent, can be directly adsorbed by dentin tubules for sterilization, at the same time, it can inhibit the matrix metalloproteinase activity of dentin bonding interface, protect the mixed layer, and improve the stability of dentin bonding interface.
In the pre-treatment of fiber post bonding, 15% EDTA washing can effectively remove the smear layer on the dentin surface after post cavity preparation, open the dentin tubule mouth, protect the collagen fiber network structure, and facilitate the penetration of resin cement. The use of 35% phosphoric acid etching for 20-30 s can also effectively remove the smear layer on the dentin surface, make the root canal wall surface cleaner and more suitable for the role of adhesives, but the acid etching time should be strictly controlled, and the redundant acid etchants in the root canal should be completely removed (to ensure that the time of water flushing after acid etching is 1.5-2 times of the acid etching time).
Adhesion of piles
Resin cement should be selected for fiber post bonding, so that fiber post, resin adhesive and resin core material can be combined into a whole, because of its almost the same material characteristics, it can produce a strong adhesion. The adhesive system can be divided into full etching adhesive system and self etching adhesive system. It can also be divided into three steps, two steps and one step according to the operation steps. In clinical practice, the factors such as adhesive strength, technical sensitivity and operation time should be considered comprehensively to make a choice.
Nuclear production
At present, the mainstream way is to use the adhesive core repair integrated resin to form the core, which can avoid the formation of the weak interface between the adhesive resin and the core resin in the traditional two-step method, so that the internal and external root canals are connected as a whole, and the shear performance is closer to the dentin, which is more conducive to the distribution of stress. When the defect of tooth is small, the method of gradually adding can be used to mold the core. When the defect of tooth is large, the transparent core forming cap method can be used, which is more efficient and easy to operate.
In the clinical work, the prosthetics often encounter the defective teeth which need to be repaired. No matter two-thirds of the crown is broken or three walls of the teeth are missing after root canal treatment, they are often rejuvenated in the hands of prosthetics.
For the teeth with large area defects, the prosthetics will choose to insert part of the prosthesis into the root canal to obtain retention, which is called the post structure of the prosthesis. In the later stage of development, if the pile is cast by metal and integrated with the retention structure inside the crown, it is called cast pile core; if it is a pre formed semi-finished pile, it is called pre formed pile.
Materials for making piles
Metal (gold alloy, nickel chromium alloy, titanium alloy, etc.), which has good mechanical properties but not very beautiful, especially in the application of all ceramic crown restoration will bring great aesthetic obstacles;
Porcelain post (mainly zirconia) has strong aesthetic performance, but also has high hardness, which is easy to break under the action of stress;
Fiber reinforced resin post (carbon fiber post, glass fiber post, quartz fiber post, etc.) has the best aesthetic performance, the closest elastic modulus to the tooth, is not easy to break, and also reduces the risk of tooth root fracture. It is the mainstream choice of pre formed post at present.
So, which is the ideal choice in the preformed fiber pile?
Preformed fiber pile
In the early days, there were a lot of black carbon fibers in the carbon fiber piles, so the aesthetics was not very good;
The main body of modern carbon fiber pile is generally white and milky white, but there will be a thin black axis, so the aesthetic effect is still not ideal;
At present, it is widely used as glass fiber pile, the color is white, milky white or transparent, without black fiber;
The quartz fiber post with the best fatigue strength has a very excellent light conduction function, which is conducive to the curing of the resin after the post core is placed into the root canal.
Nuclear materials
At present, the main materials for nuclear production are metal, amalgam, glass ionomer cement and composite resin.
Most of the metal cores are usually cast together with the post, which has good strength and won't separate; while the prefabricated post needs a certain retention core on the pile, which has different materials, but most doctors choose to use composite resin for the pile, because of its high strength, beautiful color and easy operation, it can obtain a strong adhesive force through the dentin adhesive, so as to keep up with the residual The remaining teeth formed a good combination and enhanced retention.
To sum up, prosthetics tend to choose the pre fiber post and composite resin nucleation method to repair the teeth and make the crown with good appearance and strength.
Advantages of preformed fiber pile
However, many of the crowns after root canal treatment are incomplete. In this case, can the preformed fiber post ensure its strength requirements?
In fact, different from the common concept, the main purpose of the post is to improve the retention force of the core and crown, and to distribute the stress uniformly. And its direct strength is lower than that of metal, which will not have a great impact on its resistance. Especially on the premise of enough retention force, it can repair the tooth with huge defect even without using post