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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 14  |  Issue : 1  |  Page : 25-29

Fracture resistance of roots obturated with a single expandable polymer cone


1 Department of Endodontics, Faculty of Dentistry, Assiut University, Assiut, Egypt
2 Department of Endodontics, Faculty of Dentistry, Ain Shams University, Cairo, Egypt

Date of Web Publication14-Mar-2017

Correspondence Address:
Abeer A Elgendy
Department of Endodontics, Faculty of Dentistry, Ain Shams University, Cairo
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tdj.tdj_57_16

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  Abstract 

Endodontically treated teeth are considered to be more susceptible to fracture than vital teeth, therefore various obturation materials and methods have been used to reinforce them and decrease the incidence of vertical root fractures. The aim of this study was to compare root fracture resistance after filling either with smartseal system (PropointPT cone and Smart-paste Bio sealer) or with gutta-percha in combination with either MTA Fillapex or AH Plus sealers.
Sixty single-canal extracted teeth were selected. The crowns were removed and the roots were prepared with ProTaper rotary system to size F4, roots were divided into four groups according to obturation system (n = 15). Group 1: smartseal system, specimens were filled with a bioceramic sealer (Smart-paste Bio), and F4 PropointPT. Group 2: were filled with MTA Fillapex and F4 gutta-percha single cone. Group 3: were filled with AH Plus sealer and F4 gutta-percha single cone. In group 4, the roots were neither shaped nor filled and served as negative control. All specimens were tested in a universal testing machine as the force at the time of fracture was recorded in Newtons. Data were analyzed using the one-way analysis of variance.
Roots in the negative control group and smartseal group showed significantly higher values (380.7 ± 59 N) and (347.2 ± 56 N) respectively. There was no significant difference between the MTA Fillapex/gutta-percha and AH Plus/gutta-percha groups (227.4 ± 43 N) and (254.4 ± 55 N), respectively.
It can be concluded that the smartseal system did improve the fracture resistance of the endodontically treated roots more than MTA Fillapex/gutta-percha or AH Plus/gutta-percha combinations.

Keywords: AH Plus, bioceramic sealer, MTA Fillapex, single cone, smartseal


How to cite this article:
Elayed MA, Elgendy AA. Fracture resistance of roots obturated with a single expandable polymer cone. Tanta Dent J 2017;14:25-9

How to cite this URL:
Elayed MA, Elgendy AA. Fracture resistance of roots obturated with a single expandable polymer cone. Tanta Dent J [serial online] 2017 [cited 2017 Jun 22];14:25-9. Available from: http://www.tmj.eg.net/text.asp?2017/14/1/25/202058


  Introduction Top


Endodontically treated teeth are believed to be more susceptible to fracture than vital teeth. Various factors may contribute to the acquired weakness of endodontically treated teeth including excessive loss of tooth structure because of caries or trauma, dehydration of dentin, extensive cavity preparation, method of canal preparation, irrigation of the root canal, applying excessive pressure during root obturation, and preparation of intraradicular posts [1],[2]. As a result, considerable researches have been done to investigate the potential of several obturation methods, to reinforce the endodontically treated teeth and minimize the risk of vertical root fractures [3],[4],[5].

Obturation materials are considered the key elements in supporting strength of the endodontically treated teeth. Gutta-percha, in combination with a sealer, is among the most commonly used root canal filling material [6], however gutta-percha has a low elastic modulus than dentin, therefore has a little effect in reinforcing roots after endodontic treatment [7]. Hence the use of sealer with the ability to bond to the root canal dentin surface will strengthen the remaining tooth structure, thus increasing resistance to fracture [8].

Bioceramic sealers are biocompatible, nontoxic, chemically stable, do not shrink, form hydroxyapatite and create a bond between dentin and the filling material [9]. Recently smartseal system was introduced, which is a new epoxyamine resin-based filling system utilizing a single filling point (Propoint) and a bioceramic sealer (Smart-paste Bio). Propoint consists of a polymeric core with a hydrophilic polymer sheath designed to absorb internal water in root canal and swells only laterally [10]. Smart-paste Bio is a premixed hydrophilic biocompatible resin-based sealer, which uses bioceramic as one of its constituents to improve the dimensional stability and render it nonresorbable inside the root canal. Smatpastebio produces calcium hydroxide and hydroxyapatite as byproducts of the setting reaction [11]. According to the manufacturer, the hydrophilic nature of the cement makes it a perfect companion to use with self-sealing propoint, allowing the point to hydrate and swell to fill any voids.

Additionally, there are mineral trioxide aggregate (MTA) based sealers, which are composed primarily of tricalcium oxide, tricalcium silicate, bismuth oxide, tricalcium aluminate, tricalcium oxide, tetracalcium aluminoferrite and silicate oxide with other mineral oxides. MTA sealer could provide effective seal and promotes biological repair. Once MTA sealer is compacted against dentin in presence of phosphate, it forms an interfacial layer resembles hydroxyapatite in composition. Moisture (i.e., biological fluids) is essential to allow the setting reaction and to induce bioactivity process with the formation of apatite precipitates. Similarly, MTA Fillapex sealer composed of MTA, salicylate resin, natural resin, bismuth oxide, and silica and was shown to have similar properties [12]. The aim of the present in-vitro study was to investigate the effect of using Smartseal system, MTA Fillapex/gutta-percha or AH Plus/gutta-percha on fracture resistance of dentin after root canal obturation.


  Materials and Methods Top


Specimen selection and preparation

Sixty-five freshly extracted, single rooted human mandibular premolar teeth with approximately the same dimensions were selected and stored in distilled water till the time of use. Teeth were collected from endodontic clinic affiliated with academic institution. The use of the extracted teeth and the protocol of the study were approved by the institutional research ethics board. Teeth were examined using an operating microscope (×25 magnifications; Zeiss, Oberkochen, Germany) to exclude any teeth with pre-existing root fractures or cracks. All teeth were radiographed from mesiodistal and buccolingual; first, to confirm the presence of single and straight canal and absence of internal resorption or any other defects and second; to measure mesiodistal and buccolingual dimensions. All the roots were of similar dimensions measuring 5.3 ± 0.5 mm buccolingually and 4.3 ± 0.5 mm mesiodistally. Specimens that showed 10% or more deviation from the mean were discarded. All teeth were disinfected using 2.6% sodium hypochlorite solution for half an hour and then stored in physiological saline solution until used. All crowns were sectioned using diamond disk to obtain a standardized root length of 16 mm. Fifteen samples were excluded without instrumentation or obturation to be considered as the negative control group. In the remaining roots, the working length was established by placing a k-file size #15 into the canal until we observed it at the apical foramen, then decreasing the file length by 1 mm. Sixty roots were instrumented with ProTaper rotary system (Dentsply Maillefer, Ballaigues, Switzerland) to a master apical file F4 which equal to Iso size 40 with 6% tapering, using a torque and speed-controlled electric motor (X Smart; Dentsply Maillefer). The speed and torque values were set as recommended by the manufacturer. Irrigation was done using 3 ml of 2.6% NaOCl between each two successive files using a 27 G needle. Recapitulation was performed with a file size 10. After instrumentation, all specimens received a final flush with 5 ml of SmearClear (Sybron Endo, Orange, California, USA), after that, 5 ml of sterile water was used to remove any residue, and then canals were dried with sterile paper points.

Sample classification

Specimens were randomly assigned into three experimental groups according the root canal filling material and one negative control group (n = 15/group). In all experimental groups, the canals were obturated with sealer by using the matched taper, single-cone technique.

Group 1: Smartseal system (DRFP Ltd, Stamford, UK) specimens were filled with a bioceramic sealer (Smart-paste Bio), which was introduced into the root canal via its intracanal tip. An F4 smartpoint PT (equal to Iso size 40 and have 6% tapering) with a good tug-back was then coated with sealer and slowly inserted into the canal until the working length was reached.

Group 2: MTA Fillapex (Angelus, Londrina, Brazil)/gutta-percha: the sealer was introduced into the root canal by using a lentulo spiral. F4 gutta-percha master point (Dentsply Maillefer) with a good tug-back action was coated with sealer and inserted slowly into the canal until reached the working length.

Group 3: AH Plus sealer/gutta-percha (Dentsply Maillefer): sealer was introduced into the root canal via its intraoral tip. F4 gutta-percha master point with a good tug-back was then coated with sealer and slowly inserted into the canal until the working length was reached.

Group 4 (negative control): this group received neither instrumentation nor obturation and served as a negative control. After root canal filling, excess gutta-percha were seared off, then canals' openings were sealed with Cavit temporary filling (3M ESPE, St Paul, Minnesota, USA). The roots were stored in 100% humidity for 2 weeks to allow for complete setting of the sealer.

Mechanical testing

After 2 weeks, the apical 5 mm of all roots was covered with wax to obtain a 0.2- to 0.3-mm-thick layer before embedding the roots into acrylic resin to simulate the periodontal membrane space, all the roots were mounted vertically in copper rings (20 mm high and 20 mm diameter) and filled with self-curing acrylic resin (Meliodent; Bayer Dental, Leverkusen, Germany). The apical 9 mm part of the root was embedded individually, while the 7 mm of the coronal part remained exposed. A carbide bur was used to shape the root canal access to accept the loading fixture. The mounted cylinders were placed in the universal testing machine (Model 4502; Instron, Canton, Massachusetts, USA) one at a time. The acrylic blocks were placed with the vertically aligned roots on the lower plate of the machine while the upper plate included the round tip that had a diameter of 4 mm. This round tip contacted the coronal surface of the specimen and was subjected to a slowly increasing vertical force of 1 mm/min until fracture occurred, and the values were recorded in Newtons. For this study, we defined 'fracture' as the point at which a sharp drop greater than 25% of the applied load, or frank fracture of the specimen was observed. For most specimens, an audible crack was also observed. The data were collected, tabulated and the mean and SD were calculated for each group. Statistical analysis was performed by SPSS software, version 17 (SPSS Inc., Chicago, Illinois, USA).


  Results Top


[Table 1] presents the mean ± SD of the force required to fracture the roots. Group 1 (filled with Smart-paste Bio and PropointPT) showed a significant difference and had the highest fracture resistance of the three experimental groups (347.23 ± 56.642) followed by group 3 (filled with AH Plus/gutta-percha). The negative control group (unprepared/unfilled) revealed the highest fracture strength (380.77 ± 59.213 N) but there was no statistically significant difference in fracture resistance between group 1 and the negative control group (P>0.05), while the minimal force required to fracture the roots was seen in group 2 (filled with MTA Fillapex/gutta-percha) (227.43 ± 43.092 N). There was statistically significant difference between groups 2 and 3 (P < 0.001). Analysis of variance and Tukey's honest significance difference post-hoc tests were run on the data to determine significant differences between the groups at P value less than 0.05 ([Table 1]).
Table 1: Mean±SD of fracture strength for each group (in Newtons)

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  Discussion Top


Biomechanical preparation of the root canal system is achieved by utilizing both mechanical instrumentation and chemical disinfection of the root canal system. Excessive removal of tooth substance during mechanical instrumentation and the effect of root canal irrigants result in dentin dehydration, reducing the elastic modulus and flexural strength of dentin that might contribute to the weakening of endodontically treated teeth [13]. Likewise, the filling technique used during obturation plays a key role on the fracture resistance of the treated teeth [14].

One of the most important requirements of the root canal filling is to reinforce and strengthen the weakened root against fracture. Different endodontic filling materials showed improvement in the fracture resistance of endodontically treated teeth [15],[16]. It has been demonstrated that gutta-percha has no influence on the fracture resistance of endodontically treated teeth [17],[18],[19]. MTA, as a main core, has been shown to increase the resistance to fracture in some studies [18],[20] and have no influence in another [19]. Though, the use of root canal sealer in addition to the main core is considered mandatory as it fills the gaps between gutta-percha cones and the root canal dentinal walls, also fills the voids between individual gutta-percha cones [21]. Recently, the smartseal system (was introduced, this system consists of obturation points (propoints) and an accompanying sealer (Smart-paste Bio). The effectiveness of smartseal obturation system on fracture resistance of the treated roots is still unclear so in the present study it was evaluated and compared with gutta-percha cone with either MTA Fillapex or AH Plus sealer.

In root canal dentin; the presence, density, and diameter of the dentinal tubules may be variable hence, standardization of samples is an important factor in mechanical testing regarding dimension, extraction time, and storing conditions. In this study like previous fracture load studies [22],[23],[24]. Buccolingual and mesiodistal dimensions were measured so that the selected samples were standardized regarding the remaining dentin thickness of samples subjected to fracture tests.

During mechanical testing; forces transmitted to teeth has been shown to vary between studies. Force might be applied to the facial surface of the tooth at 90° to its long axis to induce cervical fracture [25],[26]. Also force might be directed 45° to the long axis of the tooth to simulate a traumatic blow on the middle third of crowns from a labial direction [20]. Hammad et al. [27] used a finger spreader fixed to a load cell of a universal testing machine to penetrate the root canal filling and induce fracture by wedging effect. The method used in the present study following Madarati et al. [19] who used a 4 mm steel ball fixed to a metal cylinder to induce a wedging effect and eventually vertical fractures.

The results of the present study showed that the roots filled using smartseal system have an improved fracture resistance more than those obturated using AH Plus/gutta-percha or MTA Fillapex/gutta-percha combinations. This improvement might be attributed to the components of the smartseal system. Regarding to its propoints, it contains a polyamide core with an outer bonded hydrophilic polymer coating, which are designed to expand laterally without expanding axially by absorbing residual water from the instrumented root canal space and the naturally present moisture in the dentinal tubules. When hydrated in the root canal, the propoints expand, conforming to canal irregularities and pressing the hydrophilic sealer, Smart-paste Bio (introduced as HySeal-bio in USA), into concavities, lateral portals of exit and the dentinal tubules [10]. The lateral expansion of propoint is claimed to occur nonuniformly, with the expandability depending on the extent to which the hydrophilic polymer is prestressed (i.e. contact with a canal wall will decrease polymer expansion) [10].

Polymers of have a controlled expansion force, which below the tensile stress of dentine. This gentle expansion occurs within the first 4 h after placing the point into the canal and allows the point to gently adapt to any irregularities in the root canal.

In addition to the sealer of this system, Smart-paste Bio, has a delayed setting time (4–10 h) and hydrophilic in nature, allowing the propoint to hydrate and swell to fill any voids [28]. Also this sealer like any other bioceramic sealer, has the ability to produces calcium hydroxide and hydroxyapatite as byproducts of the setting reaction [29]. These byproducts allow chemical bonding to root canal dentin walls [3]. Cobankara et al. [30] reported that chemical bonding enhances the fracture resistance of teeth with root canal filling. The results of the present study came in accordance to Celikten et al. [31] who compared the fracture resistance of roots filled with smartseal system to other bioceramic sealers, results showed that all the materials increased the fracture resistance of the instrumented roots.

Regarding to the other tested sealers, AH Plus, as an epoxy resin-based sealer, can penetrate better into the microirregularities because of its creep capacity and long polymerization period [32]. Different studies revealed the reinforcing capability of the AH Plus [16],[33],[34]. However; the results of the present study revealed that AH Plus and MTA Fillapex did not improve the fracture resistance of the treated roots, counter to Smart-paste Bio. This might be explained as the hydrophilic nature of the Smart-paste Bio [35] resulted in more intimate contact with the canal walls than the hydrophobic AH Plus sealer [36]. The results of the present study came in line with a study by Ersoy and Evcil [37] who showed that both AH Plus and MTA Fillapex did not have any effect on the fracture resistance of the treated roots. Also, Tanalp et al. [38] found that MTA Fillapex did not improve the fracture resistance of immature teeth. In contrast, it was found that MTA Fillapex increase the fracture resistance of endodontically prepared teeth [3]. This disharmony in results of MTA Fillapex in regard to fracture resistance of the treated roots, could be explained by its lowest bond strength to root dentine, because of low adhesion capacity of its tag-like structures [39]. On the other hand the use of gutta-percha, as a main core, either with AH Plus or MTA Fillapex might be the cause of low facture resistance of the treated roots in these two groups, as gutta-percha has different disadvantages including its poor adaptation to the canal walls, and lack of rigidity which limits its ability to fill canal irregularities, voids, and lateral canals [11].

Within the limitation of the present study, it can be concluded that the polymer propoint cones plus a bioceramic sealer (Smart-paste Bio) did improve the fracture resistance the endodontically treated roots more than the regular gutta-percha cone either with MTA based sealer (MTA Fillapex) or with epoxy resin-based sealer (AH Plus). However, it is recommended to evaluate the long term effect and the ability of this obturation system to enhance the resistance to facture of the endodontically treated roots.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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