Introduction - Materials and methods.
D. Da Silva, U. Endal, A. Reynaud, I. Portenier, D. Orstavik & M. HaapasaloDepartment of Endodontics, Dental Faculty, University of Oslo, Oslo.
NIOM, Scandinavian Institute of Dental Materials, Haslum, Norway.Introduction.
Root filling, particularly of curved canals, is often regarded as technically demanding and difficult. This is reflected by the high number of existing root-filling techniques and by the frequency of new techniques being developed. Heat-softened gutta-percha on a solid carrier is a method that has rapidly gained popularity. It is an easy and rapid technique. The quality of root fillings produced in this way, including apical and coronal leakage has been evaluated in a number of studies during the last 15 years (Lares et al. 1990, Gencoglu et al. 1993a, Gutmann et al. 1993 a,b, Bhambhani & Sprechman 1994, Dalat & Spangberg1994, Dummer et al.1994, Hata et al. 1995,Weller et al.1997,Taylor et al.1997, Gulabivala et al. 1998, Lee et al. 1998, Cohen et al. 1999, Kytridou et al. 1999). Although the methods used as well as the design of the carriers has varied between the different studies, there seems to be agreement that the method is simple to use and produces root fillings of good quality (Dummer et al.1993,Gencoglu et al.1993b, Gutmannet al. 1993b, Dummer et al. 1994, Leung & Gulabivala 1994, Gulabivala et al.1998). However, the majority of studies where overfilling has been addressed, indicate that the possibility of extrusion of gutta-percha/sealer is higher than with several other methods, including lateral condensation (Clark& ElDeeb1993, Dummer et al.1993, Gutmann et al. 1993b, Kytridou et al. 1999). Combining the speed and ease of the softened gutta-percha method with the apical precision of a master cone would seem advantageous. Therefore, the aim of the present study was to evaluate a backfilling technique with Thermafil in comparison with lateral condensation and Thermafil, with special emphasis on the occurrence and control of over- filling and voids. Materials and methods.Preparation.
Sixty plastic blocks (Endo-training-block 015_035, Maillefer, Ballaigues, Switzerland) with curved canals 17 mm in length were prepared with the ProFile system (Maillefer) to size 04/40 in the apical canal. The largest instrument, ProFile 06/40, was used to 14 mm (3 mm short of preparation length). The taper of the prepared canals was 04 between D0 (0.40 mm) and D9 (0.76mm), and 06 between D9 and D17 (1.24 mm).The following ProFile instruments were used in order: 06/ 40 (OS3), 06/30 (OS2), 06/25, 04/25, 06/20, 04/30, 04/35, 06/40, 04/40. The same instrument set was used to prepare five canals. A micromotor (Tecnica, ATR srl, Pistoia, Italy) was used at 300 r.p.m. with pre-programmed settings for the various instrument sizes, as recommended by the manufacturer. Apical patency after ProFile preparation was ensured with a size 15 hand K-le (Maillefer). Root filling.
The canals were examined under a stereomicroscope (Olympus SZ40, Olympus Optical, Tokyo, Japan) at a magnification of 10x for the quality of the preparations. The criteria for acceptable preparations were: absence of steps, transportation of the canal and over instrumentation that would result in a poorer apical stop. The canals were then divided into three groups of 20 each and coded randomly. The canals were then filled using one of the three different techniques: Thermafil (TF group, 20 canals) (Maillefer), backfilling with Thermafil (BF group, 20 canals), and lateral condensation (LC group, 20 canals). An oven (Thermaprep Plus, Maillefer) was used to soften the gutta-percha on the Thermafil points as recommended by the manufacturer. In the TF group, a thin layer of sealer (AH Plus, Dentsply, Tulsa, USA) was applied to the canal walls with a size 35 paper point (taper .02, Maillefer), before filling with a size 40 TF point (taper .04) following the manufacturers instructions. Excess coronal gutta-percha and the plastic handle were removed with a round bur (ISO 016, Maillefer) at 2000 r.p.m. without water cooling, and the gutta-percha was vertically condensed with pluggers (model LM 41-42 XSi, LM-Dental, Naantali, Finland).
In the BF group, a gutta-percha master point (ISO size 40, taper .02, Maillefer), coated with sealer (AH Plus, Dentsply) was first introduced into the canal. The master point was condensed with a size C finger spreader (Maillefer), and a Thermafil point size 04/30was used for back-filling of the canal. Excess coronal gutta-percha and the plastic handle were removed with a round bur and the root filling was vertically condensed as with TF. In the LC group, a master point size 02/40 (Maillefer), coated with sealer (AH Plus, Dentsply) was introduced into the canal, condensed with finger spreader C (Maillefer, Dentsply) followed by three accessory gutta-percha points of size C (Maillefer) with sealer. Excess guttapercha was removed using a warm excavator, and thefilling was vertically compacted as above. Assessment of the root fillings.
The presence or absence of extruded sealer/gutta-percha through the apical opening was assessed through a stereo microscope at a magnification of 10x (Olympus SZ40, Olympus Optical). The quality of the root fillings was assessed on digital radiographs (CCD sensor, 0.04 s, 70 kV) (RVGui, Trex-Trophy Radiology Inc., Marne-la-Valle. e, France) studied on a computer screen. Two projections with a 908 difference were used for each filling. The occurrence of voids in the apical, middle and coronal third of the root filling was registered and the total length (_SD) of the voids per canal was measured to the nearest 0.5 mm.
The blocks were cut into four sections under water cooling (Accutom, Struers, Denmark) that allowed the cross-section of six surfaces in each root filling to be evaluated. The sectioning levels are indicated in Fig. 1. Alight microscope (Leitz Aristoplan, Leitz Wetzlar, Oberkochen, Germany) was used at a magnification of 25x under reflected light. The sections were studied for the presence of voids and sealer. Statistical analysis.
Fisherâ€™s exact tests (two-sided) were used to assess the probability of a hypothesis of no difference between the backfilling with thermafil versus the Thermafil and versus the lateral condensation technique.
Figure 1. Sectioning of the root filled plastic block. The sections were done 2, 7 and12 mm from the apex. Ca.1 mm was lost in each section because of the thickness of the cutting blade.