The ideal preparation for root canal treatment helps to disinfect and fill the root canal. On the contrary, inadequate preparation and errors in the process, such as the generation of steps, root canal deviation, lateral penetration and other problems, will directly affect the success of the treatment. The traditional stainless steel K file, generally with a taper of 0.02, is difficult and time-consuming to prepare the general root canal to reach a continuous taper shape. In addition, the elasticity of the stainless steel material itself is insufficient, and the preparation problem is even more difficult.
With the advent of nickel-titanium instruments and improvements in technology, the preparation of root canal treatment has undergone tremendous changes. A large number of studies have shown that the fracture resistance, elasticity and deformation resistance of nickel-titanium instruments are significantly better than those of stainless steel instruments. The root canal used to prepare curved root canals can maintain the original root canal shape and reduce the fatigue of doctors. The crown-down method is recommended for root canal preparation. Its advantages are:
(1) The crown-root preparation first expands the root canal orifice and establishes a straight path. After the straight path is established, the curvature is reduced, which can reduce the stress accumulation of the instrument, thereby reducing the degree of root canal deviation; The reduction of root canal curvature also avoids changes in working length during root canal preparation.
(2) Reduce the coronal resistance of the root canal, making the apical part preparation faster, easier and safer.
(3) Due to the enlargement of the root canal, the irrigation needle can easily enter a deeper position, which enhances the irrigation effect.
(4) Before root canal preparation, removing most of the pulp tissue and other infectious substances in the upper part of the root canal can reduce the chance of the infected tissue being pushed out of the apical foramen and reduce the possibility of acute postoperative pain.
The study also pointed out that the probability of pulp tissue and other infectious substances being pushed out of the apical foramen was relatively reduced if the rotary nickel-titanium preparation technique was used.
Although nickel-titanium instruments have significant advantages over traditional endodontic instruments, they also have certain problems. Nickel-titanium instruments differ from stainless-steel instruments in that deformation of the stainless-steel file is easily detectable. However, due to the characteristics of the material, nickel-titanium instruments are not easily found to be damaged or deformed, so they will break when they are pressed again in the next use.
There are two types of nickel-titanium device fractures: torsional fractures and fatigue fractures.
(1) Correct case selection: steep apical curvature, double curved root canal, calcification and obstruction in the root canal are all inappropriate cases.
(2) The dentin is removed first, and the root canal orifice is prepared for the straight approach, which can reduce the resistance when preparing the apical part; do not use force during preparation to reduce the pressure on nickel-titanium devices; often use a small (No. 10 or 15) file to insert into the root canal to remove internal debris.
(3) Only nickel-titanium instruments can be used in unobstructed root canals. It is recommended to use K-file to prepare the root canal to size 20 and prepare enough preparation paths before using rotary nickel-titanium instruments; if the canal has a sharp bend, use manual preparation.
(4) Limit the number of uses of nitinol files to prevent the instrument from breaking due to metal fatigue, which is why nitinol files rarely break on the first use. At the same time, studies have pointed out that the rotational speed of the machine tool is related to the chance of breaking.
(5) Use a motor handpiece with automatic reversal, torque control program function, it can prevent the risk of needle sticking and breaking; During use, the instrument should be kept continuously rotating in the root canal. After each withdrawal from the root canal, the debris on the instrument should be carefully cleaned, and any deformation of the instrument should be checked. If any problem is found, the instrument should be discarded in time.
(6) The root canal wall should be lubricated with irrigation fluid and lubricants. Most of the lubricants specially used for root canal treatment contain calcium chelating agents such as EDTA, which can soften the dentin of the root canal wall. Effectively lubricate the root canal wall, which is beneficial to the operation of root canal preparation instruments, reduces the resistance during work, and prevents breakage.