A Study On The Root Canal Taper Of Mandibular First Premolars Of Chinese With Single-canal

It is widely accepted that root canal preparation is one of the major components of root canal therapy. The root canal preparation is to taper the canal in the way so that the largest diameter is at the orifice and smallest is at the apical foramen. Thereby it allows effective irrigation and filling. During the last decade, instruments with tapers ranging from .02 to .10 became popular as they created tapered shapes with adequate volume, which allows effective irrigation and filling.However it is challenging process to select the correct taper instruments. During root canal preparation, the final 3-dimensional preparation shape of the canal should completely encompass the initial or untreated shape of the canal. The clinician must decide on using instruments that either have an inherently smaller, or larger taper based on the structure of a given canal. This is determined by the operator's subjective decision. Choosing a smaller taper may reduce the risk of procedural accidents and potential problems during cleaning and shaping; but it may compromise the hygiene of the canal system and placement of the filling material. Choosing too large a taper may better protect canal hygiene, but may also increase the potential for strip perforations, other procedural accidents, and may predispose the root to vertical fracture since greater reduction of root structure may increase the stress on the canal wall . Therefore, a thorough knowledge of the root canal anatomy, especially of the taper of different types of teeth at different ages is essential in helping the clinician to choose the correct taper instrument. However such information is limited. Recently taper research has attracted increase interest, many focus on to exam the shaping ability of tapered instruments in different kind of root canals,or focus on to develop different design. But limited research has been conducted to determine the initial tapers of teeth. In a close related study , tapers of the apical third of 180 canals were calculated. However, the teeth were randomly selected, no information was available as to the ages of these teeth. The influence of age on the shape of the canals was not considered. It is known that root canal show complicated morphological changes owing to the addition of the secondary dentine with age. This can make canal more different among groups of age.The aim of the present study is to measure the anatomical taper of mandibular first premolars of younger group ranging from ages 13-23 years. First 46 single-root mandibular first premolars at the ages were selected. Then, with the use of Micro-computed tomography (MCT) and digital X-ray system , diameters at three levels (apical; middle; orifice) were measured in two direction and tapers at three levels were calculated. Then six teeth in various ages were scanned by MCT, diameters at three levels were measured and tapers were calculated. Therefore,such information will be valuable for clinician to use correct taper instruments。Results.With MCT , the average taper of cervical, middle , and apical third of these root canals :46 teeth from ages 13-23 years were: .14,.27,.25 bucco-lingually and .07,.10,.06 mesio-distally. 38 of them from 13-19 years were: .14,.27,.27 bucco-lingually and .08,.10,.07 mesio-distally.11 teeth from ages 20-29 years were: .15,.33,.17 and .03,.09,.04 respectively. 2 teeth from 30-39 years were: .26,.50,.09 and -.04,.12,.00. And one of 78 year old were: .71,.28,.09 and .05,.01,.00. Conclusion:1. The results showed that long oval canal in common in the mandibular first premolar. The long and narrow oval canals would be impossible to instrument completely without significantly weakening the roots. Obviously, that the taper of instruments are for .06 is suitable for preparing the mandibular first premolar from ages 13-23 years .2. By digital X-ray system with parallel project, we can obtain the canal's taper precisely .3. The taper of the middle third reaches a maximum during the period of middle age in two orientations.4. The apical third of canal will present gradually tubulous when the age become older and older.