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Dr. Karl Woodmansey explores the difficulty of obtaining complete apical debridement and disinfection, and the subjective judgment dentists must use to achieve appropriate apical size and taper.
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Educational aims and objectivesThe purpose of this article is to compare the volume, lateral surface areas, and apical perimeters of various theoretical apical root canal preparations and discuss known effects of apical preparation design on the efficacy of root canal instrumentation and disinfection.Expected outcomesCorrectly answering the questions, worth 2 hours of CE, will demonstrate you can:• describe how treatment philosophy, canal morphology, and the instruments and techniques used affect apical root canal preparations.• explain how to predict and calculate the theoretical geometries of ideally prepared canals.• compare the parallel and tapering preparation techniques.
AbstractApical root canal preparations vary depending on treatment philosophy, canal morphology, and the instruments and techniques used. The diameter and taper of the apical root canal preparation can be varied to meet the operator’s design. This article compares the volumes, lateral surface areas, and apical perimeters of various theoretical apical root canal preparations and discusses known effects of apical preparation design.IntroductionMicroorganisms retained in the apical segment of root canals are related to periapical disease.1,2 Consequently, disinfection of the apical 3-mm of root canals is critical for endodontic success. Chemomechanical disinfection of this area is complicated by varied apical canal morphologies, including the presence of curvatures, isthmuses, and lateral canals.3,4
Apical root canal preparations differ depending on canal morphology, treatment philosophy, desired obturation technique, instruments used, and instrumentation techniques employed. Some practitioners desire a minimally instrumented apex, preserving the apical constriction. Others prefer larger apical diameters to completely instrument the apical canal walls, removing more potentially infected dentin. Nickel-titanium (NiTi) rotary instruments are commonly used for apical canal preparations because they can machine relatively predictable shapes into root canal dentin.
To date, minimal clinical research has examined the effects of apical preparation size and shape, leaving much speculation regarding potential consequences. The theoretical geometries of ideally prepared canals can be predicted mathematically. This paper compares the volumes, lateral surface areas, and apical perimeters of theoretical apical root canal preparations and discusses known effects of apical preparation design.
Regardless of apical diameter, two apical preparation designs are common: the parallel preparation and the tapering preparation. Parallel apical preparations have no taper (.00). These preparations are associated with LightSpeed® LSX (Discus Dental) instrumentation and Simplifill® (Discus Dental) obturation techniques. A parallel preparation may or may not enlarge the apical constriction.
In a tapering preparation, the apical canal is prepared to a tapering form that may or may not enlarge the apical constriction. Tapers are expressed as the diametric increase (in mm) per mm of canal length. Common tapers are .02, .04, .06, .08, and .10. Tapering preparations can be created with sequential instrumentation using hand files or with tapered NiTi rotary files. Common tapered NiTi rotary instrument systems include: ProFile® (Dentsply Tulsa Dental), K3™ (SybronEndo), EndoSequence™ (Brasseler USA), ProFile® GT® (Dentsply Tulsa Dental), GT® Series X™ (Dentsply Tulsa Dental), ProFile® Vortex™ (Dentsply Tulsa Dental), and Twisted Files™ (SybronEndo). Not all instrument systems offer all tip sizes and tapers. Tapering preparations are commonly utilized with lateral or vertical compaction or carrier-based obturation techniques. CalculationsThe volumes, lateral surface areas, and apical perimeters of the apical 3 mm of theoretical, idealized parallel and tapering root canal preparations can be calculated. Illustrated are apical sizes of 20, 25, 30, 35, 40, and 45 with constant tapers of .00, .02, .04, .06, .08, and .10.
The calculations for parallel preparations were calculated using the formulas for a right circular cylinder (r = radius; R = radius at larger end of the cone).5 Volume was calculated as V = π r2h, and lateral surface area was calculated as S = 2π rh, and apical perimeter as P = 2π r (Figure 1). In these calculations, h = 3 mm and r = ½ the apical diameter.
The calculations for tapering preparations were calculated using the formulas for the frustum of a right circular cone. Volume was calculated as V = π (R2+rR+r2)h/3, lateral surface area was calculated as S = π (r+R)s, and apical perimeter as P = 2π r (Figure 2). In these calculations, h = 3 mm, r = ½ the apical diameter, and R = the ½ the preparation diameter 3 mm from the apex. R is calculated using the apical diameter and the taper. The calculated apical perimeters varied from 0.63 mm for a size 20 apical diameter to 1.4 mm for a size 45 apical diameter (Figure 3). The calculated lateral surface areas varied from 1.88 mm2 for a 20/.00 preparation to 5.66 mm2 for a 45/.10 preparation (Figure 4). The calculated preparation volumes varied from 0.09 mm3 for a 20/.00 preparation to 0.87 mm3 for a 45/.10 preparation (Figure 5). Volumes and lateral surface areas increased directly with apical diameter and taper. Apical perimeter increased directly with apical diameter, but was not related to taper. DiscussionThe formulas for preparation volume and surface area are based on apical diameter, preparation taper, preparation height (or length) and π. For these calculations, the height of the idealized apical preparations was standardized at 3 mm. Consequently, height is a constant in the calculations and has no influence. The same is true for the unchanging constant π. The apical diameter and preparation taper were the only variables for these calculations and demonstrated direct relationships with preparation volume and lateral surface area.
Although the geometries of actual canal preparations have been measured using cone-beam CT, the data presented here represents idealized, theoretical preparations.6 Actual preparations vary greatly depending on root morphology (including canal curvature) and instruments and instrumentation techniques utilized. The range of apical sizes studied here was selected as being typical of many canal preparations. However, actual parallel canal preparations created with LightSpeed® LSX instruments commonly exceed size 45. Regardless, the formulas used here can be extrapolated to these and other constantly tapering preparations. These formulas, however, do not apply to variably-tapering preparations.
In 2005, Baugh and Wallace provided a review of apical instrumentation.7 Some particulars from that review are highlighted here. Related information is also presented.
Using a variety of instrumentation techniques, Weller et al found that no technique was able to predictably create an idealized round cross-sectional shape in irregularly-shaped canals.8 Kerekes and Tronstad observed canal diameters (largest dimension) of up to 5 mm.9 Wu et al further demonstrated the propensity for canals to be cross-sectionally ovoid in the apical third.10 This greater dimension of non-round canals was termed the “working width” to illustrate the difficulty of complete mechanical preparation of canals.11
Round, rotating instruments have difficulty removing dentin from the entire wall surfaces of non-round canals. Of course, instrumentation can enlarge the canal to include all dimensional ramifications. However, excessive apical preparations may unnecessarily weaken root structure. A number of authors have examined the balance between apical enlargement, debris removal, and remaining dentin thickness.8 In general, instrumentation should conserve healthy dentin to avoid perforations and weakening of tooth structure.12, 13
Some dentists utilize the arbitrary criteria of enlarging canals to three sizes larger than the first file to bind at the working length.14 However, others have found this technique to be unreliable.15,16 Anatomic studies have provided average pre-treatment apical dimensions, which have been extrapolated into recommended minimal post-instrumentation sizes.9,10,15,17,18
Depending on initial canal size, larger apical preparations generally remove more infected dentin and debris, including microbial biofilms.19-21 Mechanical instrumentation removes infected dentin circumferentially, with bacterial reduction related to apical file size.16,22,23 Usman et al, demonstrated enhanced debridement of the apical 3 mm with ProFile® GT® 40/.06 compared to 20/.06 preparations.20 A similar study by Albrecht et al examined debris at both the 1-mm level and the 3-mm level of apical preparations created using ProFile® GT® instruments and showed a significant relationship between debris removal and apical size and taper.21 Interestingly, Aydin et al found no difference in bacterial reduction with greater volumetric mechanical preparation, and Lussi has questioned the need for any mechanical debridement.24,25
Larger apical preparations permit greater volumes of irrigants and contribute to microbial reductions.26-28 Shuping et al found no difference in bacterial reduction with saline or NaOCl at size 25/.06.23. A size 35/.04 apical preparation was minimally required for a significant antimicrobial effect of sodium hypochlorite. Khademi found a size 30 apical size was required for penetration of irrigants to the apical third.29 In theory, apically enlarged canals may permit better access of irrigants into lateral ramifications and un-instrumented canal walls, disinfecting areas untouched by instrumentation. However, because much of the microbial load in the apical third exists in the form of microbial biofilms, irrigation alone is generally insufficient for thorough canal debridement.
Canals with larger perimeters and lateral surface areas may offer more potential space for apical infiltration and bacterial microleakage. However, this has not been well-established. Theoretical apical perimeters were calculated here, but the coronal perimeter may actually be more important with relation to coronal microleakage.ConclusionThe reality is that complete apical debridement and disinfection is difficult. Using idealized theoretical models, the volumes, lateral surface areas, and apical perimeters of apical preparations were calculated. Dentists should consider these variables when preparing apical root canals. More clinical studies are needed to compare the outcomes of differing apical preparation sizes and tapers. The antimicrobial effects of mechanical instrumentation and irrigation must also be independently assessed. Until evidence-based research enlightens these issues, dentists must use subjective judgment regarding appropriate apical size and taper.
References1. Sjogren U, Hagglund B, Sundqvist G, et al (1990) Factors affecting the long-term results of endodontic treatment. J Endod 16(10):498-504.2. Kakehashi S, Stanley HR, Fitzgerald RJ (1965) The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surg Oral Med Oral Pathol 20(3):340-349.3. Vertucci FJ (1984) Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 58(5):589-599.4. Dummer PD, McGinn JH, Rees DG (1984) The position and topography of the apical canal constriction and apical foramen. Int Endod J 17(4):192-198.5. Burrington, RS (1940) Handbook of Mathematical Tables and Formulas, 2nd edition. Handbook Publishers, Inc., Sandusky, Ohio:11-15, 20-21.6. Bernardes RA, et al (2010) Root canal area increase promoted by the EndoSequence and ProTaper Systems: comparison by computed tomography. J Endod 36(7):1179-1182. 7. Baugh D, Wallace J (2005) The role of apical instrumentation in root canal treatment: a review of the literature. J Endod 31(5):333-340.8. Weller PJ, Svec TA, Powers JM, et al (2005) Remaining dentin thickness in the apical 4mm following four cleaning and shaping techniques. J Endod 31(6):464-467.9. Kerekes K, Tronstad L (1977) Morphometric observations on root canals on human molars. J Endod 3(3):114-118.10. Wu MK, Roris A, Barkis D, et al (2000) Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 89(6):739-743.11. Jou YT, Karabucak B, Levin J, et al (2004) Endodontic working width: current concepts and techniques. Dent Clin North Am 48(1):323-335.12. Gutmann JL (1977) Preparation of endodontically treated teeth to receive a post-core restoration. J Prosthet Dent 38(4):413-419.13. Trope M, Ray HL Jr (1992) Resistance to fracture of endodontically treated roots. Oral Surg Oral Med Oral Pathol 73(1):99-102.14. Grossman LI, Oliet S, del Rio CE (1988) Preparation of the root canal: equipment and technique for cleaning, shaping and irrigation. In: Endodontic Practice, 11th edition. Lea & Febinger, Philadelphia:179-227. 15. Wu MK, Roris A, Barkis D, et al (2002) Does the first file to bind correspond to the diameter of the canal in the apical region? Int Endod J 35(3):264-267.16. Mickel AK, Chogle S, Liddle J, et al (2007) The role of apical size determination and enlargement in the reduction of intracanal bacteria. J Endod 33(1):21-23.17. Trope M, DebelianG (2009) Microbial control: The first stage of root canal treatment. Gen Dent 57(6):580-588.18. Senia ES (2008) Determining the final apical size (FAS). The EndoFiles: Practical information for the smart endodontics community. Summer;4: http://endofiles.wordpress.com/about/19. Tan B, Messer H (2002) The quality of apical canal preparation using hand and rotary instruments with specific criteria for enlargement based on initial apical file size. J Endod 28(9):658-664.20. Usman N, Baumgartner JC, Marshall JG (2004) Influence of instrument size on root canal debridment. J Endod 30(2):110-112.21. Albrecht LJ, Baumgartner JC, Marshall JG (2004) Evaluation of apical debris removal using various sizes and tapers of Profile GT files. J Endod 30(6):425-428.22. Siqueira J, Lima K, Magalhaes F, et al (1999) Mechanical reduction of the bacterial population in the root canal by three instrumentation techniques. J Endod 25(5):332-335.23. Shuping G, Orstavik D, Sigurdsson A, et al (2000) Reduction of intracanal bacteria using nickel-titanium rotary instrumentation and various medications. J Endod 26(12):751-755.24. Aydin C, Tunca YM, Senses Z, et al (2007) Bacterial reduction by extensive versus conservative root canal instrumentation in vitro. Acta Odontol Scand 65(3):167-170.25. Lussi A, Messerli L, Hotz P, et al (1995) A new non-instrumental technique for cleaning and filling root canals. Int Endod J 28(1):1-6.26. Salzgeber RM, Brilliant JD (1977) An in vivo evaluation of the penetration of an irrigating solution in root canals. J Endod 3(10):394-398.27. Ram Z (1977) Effectiveness of root canal irrigation. Oral Surg 44(2):306-312.28. Chow T (1983) Mechanical effectiveness of root canal irrigation. J Endod 9(11):475-479.29. Khademi A, Yazdizadeh M, Feizianfard M (2006) Determination of the minimum instrumentation size for penetration of irrigants to the apical third of root canal systems. J Endod 32(5):417-420.
Karl Woodmansey, DDS, is a practicing endodontist and owner of Bozeman Endodontics in Bozeman, Montana. Dr. Woodmansey is a dental and endodontic graduate of Texas A&M University’s Baylor College of Dentistry in Dallas, Texas. He is a Fellow of the Academy of General Dentistry, the Academy of General Dentistry International, the American College Health Association, the American College of Dentists, and the International College of Dentists. Dr. Woodmansey also serves as a member of the US Air Force Reserve Dental Corps. He can reached at (406) 587-7668 or
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