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© Borgis - Nowa Stomatologia 1/2017, s. 39-44 | DOI: 10.5604/14266911.1235810
*Wioletta Bielas1, Agnieszka Mielczarek2
The impact of endodontic procedures on mechanical properties of root dentine – a literature review
Wpływ procedur endodontycznych na własności mechaniczne zębiny korzeniowej – przegląd piśmiennictwa
1Doctoral student at the Department of Conservative Dentistry, Medical University of Warsaw
Head of Department: Agnieszka Mielczarek, DMD, PhD
2Department of Conservative Dentistry, Medical University of Warsaw
Head of Department: Agnieszka Mielczarek, DMD, PhD
Streszczenie
Jednym z celów leczenia endodontycznego jest eliminacja bakterii i ich toksyn z przestrzeni wewnątrzkanałowej i zębiny korzeniowej. Jest to możliwe poprzez wdrożenie odpowiednich procedur, takich jak: mechaniczne poszerzenie światła kanału z zachowaniem jego pierwotnego przekroju i przebiegu, chemiczne opracowanie ścian środkami płuczącymi oraz szczelna, ostateczna odbudowa części koronowej. Czynności związane z leczeniem kanałowym nie pozostają obojętne dla biomechanicznych właściwości tkanek zęba. Prognoza leczenia kanałowego jest zależna nie tylko od efektywności oczyszczania ścian kanałów korzeniowych, ale również od ilości i jakości pozostawionych tkanek zęba. Czynnikami mogącymi osłabiać ząb jest uzyskanie dostępu do kanałów korzeniowych, ich mechaniczne opracowanie oraz aplikacja chemicznych środków leczniczych. Ciągły postęp technologiczny zwiększa dostęp do nowych narzędzi endodontycznych i preparatów dezynfekujących. Jak dotąd dysponujemy jednak ograniczoną wiedzą na temat ich wpływu na właściwości mechaniczne zębiny korzeniowej. Różnice obserwowane pomiędzy systemami mogą mieć istotny wpływ nie tylko na ilość skrawanej zębiny, ale również na naprężenia powstające w kanale i mikropęknięcia zębiny. W pracy zaprezentowano przegląd aktualnych doniesień na temat wpływu wybranych procedur endodontycznych na charakterystykę twardych tkanek zęba. Wiedza w tym zakresie jest istotnym elementem planowania rekonstrukcji zębów po leczeniu kanałowym.
Summary
One of the purposes of root canal treatment is the elimination of the bacteria and their toxins from the intracanal space and root dentine. It is possible through the implementation of appropriate procedures, i.e.: mechanical extension of the canal in its crown, central and periapical part with maintenance of the original section and course, a chemical working of the walls using rinse agents and tight final reconstruction of the crown part. The actions connected with endodontic treatment are not neutral for the biomechanical properties of the tooth tissue. The prognosis of the root canal treatment is dependent not only on the efficiency of cleaning the walls of the root canals, but also on the number and quality of the left dentine tissue. The factors that can weaken the tooth are access to the root-canal, its mechanical preparation and the application of intracanal medicaments. Continuous technological progress increases access to new endodontic instruments and disinfectants. However, we have limited knowledge of their effects on the mechanical properties of the root dentine. The differences between the systems can have a significant impact not only on the number of the cut dentine but also the tension in the canal that can cause microcracks of the dentine. This study presents a review of current literature on the impact of selected endodontic procedures on the characteristics of the tooth hard tissue. This knowledge is an essential element of planning the reconstruction of teeth after root canal treatment.
Introduction
Endodontic treatment constitutes an alternative to surgical methods of teeth treatment, which are covered by the inflammation of the pulp or lesions in the periapical tissues. Maintaining a sufficient amount of hard tissue following the end of endodontic procedures is a necessary factor to ensure long-term reconstruction of the crown part of the tooth. The condition for success of canal treatment is the implementation of appropriate procedures, i.e.: mechanical canal dilation in its crown part, central part and apex along with preserving its primary section and course, chemical preparation of the walls with rinsing agents and tight, final restoration of the crown part. Regardless of the selection of the techniques of the mentioned procedures, they do not remain neutral for the biomechanical properties of tooth tissues and breaking the tooth following endodontic treatment are third most common reason for tooth loss, right after caries and periontium diseases (1).
In the opinion of practitioners, a tooth following endodontic treatment has a limited hard tissue stroma, is more brittle and susceptible to breaking (2). The following have an impact on the fact: loss of tissues and change in their properties in the course of endodontic procedures. Actions related to obtaining an access to canals, i.e.: opening the roof of the pulp cavity and performing dilation of the part leading to the cavity of the canal means the loss of approx. 25% of hard tooth tissues (3). The use of medicinal products reduces microhardness of the dentine by 20-27% (4) and the use of chelating agents by 50% (5).
Owing to a real revolution that took place in the field of endodontic devices and procedures within the last 100 years, there is a possibility to select many instruments from among a wide range of stainless steel tools, NiTi tools, oscillatory files, rotary files or the ones adjusting to the shape of the canal. Differences observed between the systems may have a significant impact not only on the amount of processed dentine, but also the tension created in the canal and microcracks of the dentine (6, 7).
Marketing machine files has significantly increased the efficiency and comfort of a doctor’s job. Machine files, owing to increased taper, come into contact with a larger area of the canal walls while working. Increased working area may, however, have an adverse impact on the strength parameters of the root dentine.
The share of machine and manual files in lowering strength parameters of root dentine
Ashwinkur et al. have studied the creation of microcracks in the root dentine of the first molars in the mandible following the use of 4 groups of tools: hand files ProTaper and K-files NiTi and machine files Wave One and ProTaper (8). Control group were teeth subject to canal treatment. After preparing, the roots were divided into three even parts and subject to observation in a Scanning Electron Microscope (SEM). In the control group and the group of roots prepared with hand K-files NiTi, there were no microcracks observed within the dentine. In all the remaining groups, there were lesions in the root dentine in the form of microcracks, in every out of the assessed root fragments. Far more defects in the dentine were observed having used rotary files ProTaper (8).
Similar results of studies were obtained by Liu et al. comparing machine and hand files (9). The authors have carried out studies on 240 incisor teeth of the mandible, which prior to the preparation were divided into 12 groups. 3 types of files were selected for analysis: rotary files K3 and ProTaper and hand NiTi flex K-files. Canals were subjected to preparation on four various lengths: to the apex opening, 1 mm before the apex opening, 2 mm before the apex opening and 1 mm out of the apex opening. The application area of the roots was observed in a stereoscopic microscope. Microcracks were observed in 1 out of 80 teeth prepared with the use of manual tools and 31 out of 160 teeth prepared with the use of rotary tools. Instrumentation at the distance shorter by 1 mm and 2 mm from the distance to the apex opening generated less defects in the dentine as compared with the remaining preparation protocols.
Studies in the field of strength properties of the dentine were continued by Celik et al. (10). The authors assessed resistance to breaking of teeth treated endodontically with the use of machine files ProTaper Universal and Profile and manual flex K-files. The analysis covered 112 two-root premolar teeth. They were divided into 2 groups depending on the working length: 14 and 16 mm, and later into 3 subgroups, each of which was prepared with the use of a different kind of file. Resistance to breaking was measured with the use of a testing machine Lloyd Instruments, Fareham, with the speed of feed 1 mm/min. The lowest resistance was presented by the group prepared with machine files ProTaper at the working length 16 mm.
The creation of microcracks in the root dentine depending on the manner of machine tools operation

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Piśmiennictwo
1. Kishen A: Mechanisms and risk factors for fracture predilection in endodontically treated teeth. Endod Topics 2006; 3: 57-83.
2. Kishen A, Kumar GV, Chen NN: Stress-strain response in human dentine: rethinking fracture predilection in postcore restored teeth. Dent Traumatol 2004; 20(2): 90-100.
3. Reeh ES, Messer HH, Douglas WH: Reduction in tooth stiffness as a result of endodontic and restorative procedures. J Endod 1989; 15(11): 512-516.
4. Yassen GH, Eckert G, Platt J: Effect of intracanal medicaments used in endodontic regeneration procedures on microhardness and chemical structure of dentin. Restor Dent Endod 2015; 40(2): 104-112.
5. Skórska-Jasak A, Klimek L, Pawlicka H: Wpływ kwasu cytrynowego i EDTA na mikrotwardość zębiny korzeniowej. Czas Stomat 2007; LX(10): 650-655.
6. Helvacioglu-Yigit D, Aydemir S, Yilmaz A: Evaluation of dentinal defect formation after root canal preparation with two reciprocating systems and hand instruments: an in vitro study. Biotechnol Biotechnol Equip 2015; 29: 368-373.
7. Shemesh H, Bier CA, Wu MK et al.: The effects of canal preparation and filling on the incidence of dentinal defects. Int Endod J 2009; 42(3): 208-213.
8. Ashwinkur V, Krithikadatta J, Surendran S, Velmurugan N: Effect of recirpocating file motion on microcrack formation in root canals: an SEM study. Int Endod J 2014 Jul; 47(7): 622-627.
9. Liu R, Kaiwar A, Shemesh H et al.: Incidence of apical root cracks and apical dentinal detachments after canal preparation with hand and rotary files at different instrumentation lengths. J Endod 2013 Jan; 39(1): 129-132.
10. Celik D, Serper A, Er K et al.: Fracture resistance of roots after instrumentation with two nickel-titanium rotary systems at different working lengths. Clin Den Res 2015; 39(2): 49-55.
11. Ravi AB, Parabath Singh VP, Sreeram SR et al.: Comparison of root microcrack formation after root canal preparation using two continuous rotational file systems and two reciprocating systems- an invitro study. IOSR-JDMS 2015; 14: 15-18.
12. Jalali S, Eftekhar B, Paymanpour P et al.: Effects of Reciproc, Mtwo and ProTaper instruments on formation of root fracture. IEJ 2015; 10(4): 252-255.
13. Monga P, Bajaj N, Mahajan P, Garg S: Comparison of incidence of dentinal defects after root canal preparation with continuous rotation and reciprocating instrumentation. Singapore Dental J 2015; 36: 29-33.
14. Kansal R, Rajput A, Talwar S et al.: Assessment of dentinal damage during canal preparation using reciprocating and rotary files. J Endod 2014 Sep; 40(9): 1443-1446.
15. Patil CR, Uppin V: Effect of endodontic irrigating solutions on the microhardness and roughness of root canal dentin: an in vitro study. Indian J Dent Res 2011; 22(1): 22-27.
16. Marcelino A, Bruniera JF, Rached-Junior FA et al.: Impact of chemical agents for surface treatments on microhardness and flexural strength of root dentin. Braz Oral Res 2014; 28(1): 1-6.
17. Perez-Heredia M, Ferrer-Luque CM, Gonzalez-Rodriquez MP et al.: Decalcifying effect of 15% EDTA, 15% citric acid, 5% phosphoric acid and 2.5% sodium hypochlorite on root canal dentine. Int Endod J 2008; 41: 418-423.
otrzymano: 2017-01-18
zaakceptowano do druku: 2017-02-08

Adres do korespondencji:
*Wioletta Bielas
Zakład Stomatologii Zachowawczej Warszawski Uniwersytet Medyczny
ul. Miodowa 18, 00-246 Warszawa
tel. +48 (22) 502-20-32
sekretariat.zachowawcza@wum.edu.pl

Nowa Stomatologia 1/2017
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