Results - Discussion - References.
The results of the different procedural errors are presented in Fig.1.With the ‘8-step method’, significantly (P < 0.0001) more root canals (136, 91%) maintained their original shape with no deviation compared to the conventional ‘serial step-back technique’ (87, 61%). The following procedural errors were detected in the‘8-step method’: 10 canals with transportation (5%) and five root perforations (2%); there were no canal obstructions. With the ‘serial step-back technique’, significantly (P < 0.0001) more errors occurred: 28 canals were transported (17%), 10 had root perforations (7%) and16canals had obstructions (6%).
The percentage of canals maintaining their original shape with both techniques in anterior and posterior teeth is presented in Fig. 2.All anterior teeth maintained the original canal shape when treated with the ‘8-step method’. Only 78% of the anterior teeth had no deviation when prepared with the ‘serial step-back technique’. In molars, 88% maintained the original curve when treated with the ‘8-step method’ and only 49% when prepared with the ‘serial step-back technique’ (P < 0.0001).
Figure 1. Procedural errors examined during instrumentation of root canals by junior dental students using the '8-stepmethod' (n =149) compared with the'serial step-back technique' (n =142). A significant difference was observed between the two groups (P < 0.0001).Discussion.
Figure 2. Maintenance of the original root canal shape during instrumentation of anterior and posterior teeth by junior dental students using the'8-step method' (n =149) compared with the'serial step-back technique' (n =142). A significant difference was observed between the two groups (P < 0.0001).
There are a variety of innovative instruments and techniques available to prepare root canals. However, each has its advantages and disadvantages. The acquisition of knowledge to allow the selection of the appropriate instruments and techniques for improved quality and efficient treatment requires time and experience. Dental schools worldwide are faced with the challenge of providing undergraduate students with the skills to prepare root canals safely and to expose them to a diversity of new instruments and techniques within a limited time period, normally 2-3 years.
The new ‘8-step method’ was developed to integrate the various instruments and techniques in one method. During the 3-year programme, undergraduate students are exposed to traditional stainless steel instruments as well as the modern rotary NiTi ones. Furthermore, the students become familiar with different instrumentation motions in the root canal (e.g. filing and reaming) and different techniques (e.g. ‘serial step-back technique’ or ‘balanced force technique’). After graduation, they are expected to recognize the advantages and disadvantages of each instrument, motion or technique and select which is best for their practice needs.
Flaring of the coronal third of the root canal before determining the working length has several advantages (Morgan & Montgomery 1984, Stabholtz et al. 1995). It removes coronal curvatures, improves tactile feel and allows irrigation of the coronal two-thirds of the canal to minimize extension of infected debris beyond the apical constriction. With this method, the unskilled student could block the canal. Therefore, students in this school were instructed in traditional techniques to determine the working length first and then instrument the canal to the apical constriction. With the‘8-stepmethod’, each student practices flaring of the coronal third with hand or rotary instruments on extracted teeth before treating patients. In the present study, the careful approach by the unskilled student prevented obstructions with the ‘8-step method ’compared to the traditional ‘serial stepback technique’. It should be emphasized that the blunt tip design of modern hand and rotary instruments make coronal flaring easier and safer (Miserendino et al. 1985, 1986).
Preparation of the apical third using the ‘8-step method’ is divided into two steps. The narrow canals are first instrumented to size 25 and then evaluated by both the student and instructor for procedural errors. The canal is further enlarged according to average initial diameter, tactile feeling, anatomy of the root canal and type of instrument used. The average size of the master apical file (MAF) is limited for some techniques and instruments to size 25 for simple canals. However, some instruments are designed to enlarge safely the apical third of the root canal to average sizes within the range of 40-60 depending on the initial diameter of the root canal. The present study demonstrated that preparing the apical third to larger sizes did not necessarily increase the incidence of the procedural errors provided the correct method was selected. For example, the average size of MAF for the MB root of maxillary molars was 35 using the ‘balanced force technique’ with the ‘8-step method’ and only 25 for ‘serial step-back technique’, and the procedural errors detected in the new method were significantly less.
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