BT-Race — Biologic and conservative root canal instrumentation with the final restoration in mind

Drs. Gilberto Debelian and Martin Trope explore the BT-Race system

Intracanal microbes are the cause of endodontic disease.^1-3 The prevention or removal of microbes from the root canal system during treatment is the factor that determines if the treatment will be successful or not.^4-5

Root canal instrumentation is one of the major tools to ensure the long-term success of root canal therapy.^6-7 The aim is to mechanically disrupt as much biofilm as possible so that with the addition of irrigants and/or intra-canal medicaments, a very low microbial count can consistently be achieved before root canal filling.

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Another aim/challenge of root canal instrumentation is to achieve the microbial reduction goals previously mentioned without unnecessarily weakening the root by over-instrumentation, i.e., reduction of the dentin wall thickness. Preservation of native tooth structure, especially in the cervical region of the tooth, has been demonstrated to correspond to better long-term survivability from a loading and restorative standpoint. It is well established that as the remaining dentin thickness decreases, so the root decreases in its resistance to fracture.⁸

What is the ideal root canal instrumentation size?

The axiom: The file alone does not remove the maximum amount of biofilm but works with irrigation in a synergistic effect with the file.  The key question is, What is the ideal instrumentation size to achieve the desired goal of biofilm elimination? In order to answer this question, we need to analyze anatomical studies and evaluate whether and how it is possible to remove biofilm from these canals.

When evaluating the anatomical studies, it is interesting to note how consistent they are! (Figure 1) best summarizes the anatomical aims for a mandibular molar.

First, let’s look at the mesio-buccal and mesio-lingual canals at the 1 mm measurement from the apical foramen, which corresponds most closely to the dentino-cemental junction. In the mesial-distal direction, the diameters are 0.21 and 0.28, respectively. Thus, finishing at a No. 25 file would appear to be sufficient when viewed with a periapical radiograph since the mesio-distal direction is what we see on the radiograph. However, if we look at the bucco-lingual direction, the correct sizes are between No. 35 and No. 40! For the distal canal, a No. 35 would look adequate on the radiograph (mesio-distal view), but the correct size would be No. 50.

Thus, we might take a popular saying from our colleagues who advocate thermoplastic obturation: “If we want to clean in three dimensions, we need to instrument in the bucco/lingual dimension also.” Just as important, if we look at the measurements at 2 mm and 5 mm from the end of the root, it is apparent that if we in fact do instrument to the apical sizes required (No. 35 or No. 40 mesial and No. 50 distal), then a 0.04 taper is all that is needed to contact the walls in these areas farther from the apex. Using tapers larger than 0.04 is not required to remove microbes and unnecessarily weakens the root. Anatomical studies of all roots follow this basic biological rule;  i.e., No. 35 or No. 40 for the “smaller” canals and No. 50 for the “larger” canals.^9-11

Ideal shape for an instrumented canal?

Adequate biological sizes with minimal taper with the least number of files

Thus, in order to achieve the aims stated above, i.e., maximal biofilm disruption with minimal weakening of the root, we should aim for No. 35, No. 40, or No. 50 apical sizes with no more that 0.04 taper.^9-11 These biological sizes with the addition of an adequate irrigation protocol will ensure a consistently low microbial count to ensure maximal success.

BT-Race system — biologic and conservative

BT-Race files (Brasseler USA) are sterilized in individual blisters so that sterility is ensured for every file. (Figure 2)

The biologic sizes mentioned previously can be achieved in three files every time after a glide path is achieved. The system is designed so that these sizes are attained with minimal removal of unnecessary dentin coronally so as to maintain the strength of the root.

The BT-Race file has a non-screw-in design, triangular cross section to increase flexibility and cutting efficiency and is electro-polished to decrease the effects of torsional and cyclic fatigue. (Figure 3)

Booster Tip (BT) 

The booster tip is the key feature of these files that allows them to follow curvatures in canals without undue stress on the file or the root. The Booster Tip files start as a non-cutting tip from 0 mm to 0.17 mm diameter, and the cutting edges start from 0.17 mm and upward on the file. This allows these files  to safely follow a canal even with a very narrow diameter. The final size of the file is achieved within 0.5 mm of the tip. Thus, for example, the BT2 (see Figure 4), which is a non-tapered file with a cutting size of 0.35 mm, can still easily advance into the canal prepared by the glide path file, which is 0.15mm in diameter.

The booster tip allows a file of any diameter to follow the shape of a canal that has been prepared with a No. 15 glide path stainless-steel file. However, the protocol of three files (see Figure 5) is designed to relieve undue stress on the root and files while instrumenting the canal to biologically accepted sizes.

Essentials for successful use of the BT-Race sequence

1. Glide path. 

In order to guarantee a minimal number of file breakages, a glide path to No. 15/0.02 taper is essential. Hand files can usually achieve this aim. However if a No. 6 or No. 10 is extremely difficult to get to working length, then ScoutRace files (Brasseler USA) allow endodontists  to achieve this requirement more quickly.

2. Speed of 800–1000 RPM 

A high speed reduces the risk of breakage due to torsional fatigue, and since these files are for single-patient use only, the chances of breakage from cyclic fatigue is also reduced. Thus, by using high speed and limiting the number of usages to one, we are limiting the chances of breakage of these files.

BT1 – 10/0.06 

This file establishes the final glide path and determines the coronal diameter. In any canal in which a No. 15/0.02 glide path has been achieved, the file will contact mainly the coronal third of the canal. At 12 mm from the working length, the diameter will be 0.82 mm. These files have no booster tip since the tip diameter is already 0.10 mm and smaller than the glide path established with a K-File No. 15/0.02.

BT2 – parallel No. 35 file with Booster Tip

The BT2 file is used to prepare the apical third of the canal.  The file is extremely flexible due to its non-tapered design and yet easily and efficiently penetrates into the narrow canal due to the BT Tip.

BT3 – No. 35/0.04 with Booster Tip

This file is used to join the coronal and apical preparations created by the BT1 and BT2 and thus create a No. 35/0.04 final shape that allows maximal irrigation and a tight-fitting cone fit. The file is able to get to working length with minimal stress since the coronal has been cleared by BT1 and the apical cleared with BT2 file.

Importantly, in this canal the maximum diameter at the 12 mm level is 0.83 mm. Thus, the removal of coronal dentin is minimal allowing for the strongest root possible after restoration.

Conclusion

With this unique file system, all canals can be conservatively instrumented to the correct biological sizes while maintaining maximum cervical tooth structure that remains following instrumentation. The booster tip ensures that the original canal shape is maintained, thus, keeping even the larger files centered in the canal. With this centering advantage, in addition to the minimal taper required to achieve these biologic sizes, the canal is maximally cleaned without weakening or stressing the root.

Case studies

Note that these cases fulfill the objective of biologic apical sizes with conservative coronal removal of dentin. Thus, they have a high probability of endodontic success and survivability.

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