Journal of the International Clinical Dental Research Organization

ARTICLE
Year
: 2009  |  Volume : 1  |  Issue : 3  |  Page : 37--48

Fracture resistance of endodontically treated roots filled with resilon and guttapercha - A comparative in-vitro study


Rajesh R Shetty1, Moksha Nayak2, Jimmy Thomas3,  
1 Department of Conservative Dentistry & Endodontics, Dr. D. Y. Patil Dental College & Hospital, Pimpri, Pune, India
2 K.V.G. Dental College, Sullia, Karnataka, India
3 Al-Azhar Dental College, Perumpillichira, Thodupuzha, Kerala, India

Correspondence Address:
Rajesh R Shetty
Department of Conservative Dentistry & Endodontics, Dr. D. Y. Patil Dental College & Hospital, Pimpri, Pune
India

Abstract

Aims and objectives: The purpose of this study was to evaluate and compare in vitro the fracture resistance of endodontically treated roots filled with Resilon and Gutta-percha. Methodology: Eighty extracted single canal teeth were selected and randomly assigned to five groups of sixteen teeth each. Teeth were sectioned using a diamond disc so as to obtain a root length of 14±1 mm. Roots were instrumented using .04 taper Profile rotary system to an apical size of 40 and obturated using .04 taper single cone (size 40) as follows: Group 1: Resilon .04 taper cone and Epiphany Self etching sealer, Group 2: .04 taper gutta-percha cone and AH Plus sealer ,Group 3: .04 taper gutta-percha cone and Roeko Seal Automix sealer, Group 4: .04 taper gutta-percha cone and Zinc oxide Eugenol sealer , Group 5: .04 taper gutta-percha cone without the use of a sealer. Following obturation, teeth were mounted in Poly Vinyl Chloride jigs using self cure acrylic resin such that 9mm of the root remained exposed. Fracture resistance testing was done using Instron testing machine using a vertical load applied perpendicular to the root surface. Statistical analysis was done using ANOVA, Tukey HSD and Student«SQ»s «SQ»t«SQ» test. Results: Very highly significant difference was observed between the groups (P=.001). Resilon with Epiphany group demonstrated highest mean fracture resistance value and gutta-percha without sealer displayed the least, comparative results were highly significant. Resilon compared to gutta-percha with Roeko Seal Automix (P=.037) and Zinc Oxide Eugenolsealers (P=.029) showed statistically significant difference. AH plus group showed significantly higher value compared to gutta-percha without sealer. Conclusions: Filling the root canals with Resilon increased the in vitro fracture resistance of endodontically treated roots compared to standard gutta-percha techniques. Adhesive sealers are more beneficial in increasing the fracture resistance of endodontically treated teeth.



How to cite this article:
Shetty RR, Nayak M, Thomas J. Fracture resistance of endodontically treated roots filled with resilon and guttapercha - A comparative in-vitro study.J Int Clin Dent Res Organ 2009;1:37-48


How to cite this URL:
Shetty RR, Nayak M, Thomas J. Fracture resistance of endodontically treated roots filled with resilon and guttapercha - A comparative in-vitro study. J Int Clin Dent Res Organ [serial online] 2009 [cited 2019 Aug 26 ];1:37-48
Available from: http://www.jicdro.org/text.asp?2009/1/3/37/77022


Full Text

 Introduction



Endodontically treated teeth are widely considered to be more susceptible to fracture than are vital teeth. The reasons most often reported have been the dehydration of dentin after endodontic therapy, excessive pressure during obturation and the removal of tooth structure during endodontic treatment. It is commonly believed that the loss of dentin creates an increased susceptibility to fracture [1] . According to Bender and Freedland, vertical root fracture is one of the most serious complications after root canal therapy with an unfavorable prognosis, resulting almost inevitably in extraction of the teeth or resection of the affected root [2] .

Gutta-percha with an insoluble root canal sealer can be seen as the gold standard of root canal fillings and is offered the status as a time honored standard for endodontic obturation. The ability of these materials to reinforce an endodontically treated root is discussed with some controversy.

Many methods have been utilized to increase the fracture resistance of teeth. One such technique is the utilization of an obturating material which bonds to the root canal walls and the coronal tooth structure. This can be achieved with the use of resin cements via bonding procedures. Recently improvements in apical and coronal seals and strengthening of endodontically treated teeth have been proposed by establishing monoblocks via bonding of the root filling materials to intraradicular dentine .This is similar to contemporary adhesive strategies used for intracoronal restorations that attempt to eliminate micro leakage and strengthen coronal tooth structures by creating similar monoblocks between tooth substrates and restorative materials [3] .

Resilon a thermoplastic synthetic polymer based material introduced in 2004 performs similar to gutta-percha and has the same handling characteristics. A tight adhesion between Resilon cone and the resin based sealer form a "monoblock" and have potential to strengthen the walls against fracture and decrease the microleakage [4] .

The purpose of this in vitro study was to compare the fracture resistance of endodontically treated roots filled with Resilon with that of conventional gutta-percha using different sealers like AH plus, Roeko Seal Automix and Zinc oxide Eugenol.

 Aims and Objectives



Assessing root reinforcement has been a critical step in predicting the outcome of endodontic treatment. To date no literature with regard to assessing and comparing the fracture resistance of teeth prepared with rotary system and filled with single cone gutta-percha with different sealers like resin based, silicon based or zinc oxide eugenol based to that of Resilon is available.

 Materials and Methods



[INLINE:1]

 Investigation Design



80 extracted human maxillary anterior teeth were selected and teeth were disinfected and stored according to OSHA* regulations. Cleaning and shaping done on all teeth using .04taper Profile rotary instrumentation to an apical size of 40. All 80 teeth were divided into 1 control group and 4 experimental groups of 16 teeth each.

[INLINE:2]

All 80 teeth were mounted in acrylic resin in PVC jig. Fracture strengths were measured using instron testing machine and load recorded in kilogram force. Statistical analysis were done using ANOVA and Tukey HSD test.

 Preparation for Mechanical Testing



The root ends were embedded in self cure acrylic resin in a Poly Vinyl Chloride jig in such a way that coronal 9mm of the root remain exposed. Poly Vinyl Chloride jigs of one inch diameter and one inch height was used. The long axis of the root was vertically aligned using a protractor. The specimens were stored in 100% humidity until testing.

A carbide bur was used to remove the temporary material and to shape the root canal opening to accept the loading fixture.

The testing for fracture resistance was done using an instron testing machine (Model 3365,Instron, Canton Mass).

A spherical tip of radius 2mm was used to apply a vertical loading force at a crosshead speed of 1mm per minute until fracture occurred. Fracture resistance was defined as the point at which a sharp decline and instantaneous drop greater than twenty five percent of the load applied was observed.

Statistical analysis was performed using Analysis of Variance (ANOVA) and Comparisons were done using Tukey HSD and Student's 't' test using the statistical package, SPSS Version 11.5 for Windows. [Figure 1]{Figure 1}

 Results





The maximum load require to fracture was in group 2.Highly significant difference between group1 and group 5 (P=.003).Group 1 compared to group 3 and group 4 showed significant difference.Group 1 compared to group 3 and group 4 showed significant difference.However there was no significant difference between group 1 and group2.Group 2 in comparison with group 5 showed statistically significant difference where as no statistically significant difference was observed between group 2 vs groups 3 and 4. No statistically significant difference was observed between group 3 vs groups 4 and 5. Similarly no statistically significant difference was observed between group 4 and group 5. [Graph 1][SUPPORTING:1], [Graph 2] [SUPPORTING:2] and [Graph 3] [SUPPORTING:3]

 Discussion



Root canal treatment weakens tooth structure and predisposes teeth to fracture is a known perception . It has been reported that incidence of vertical root fracture is greater in root filled teeth [5] .Previous studies have demonstrated the reinforcement of root filled teeth with bonded restorative materials [6],[7] . Johnson et al. recommended the use of adhesive sealers in the root canal system to reinforce the root filled teeth [8] .

Root canal instrumentation is an essential step in endodontic treatment. Studies have shown instrumentation alone to significantly weaken the root. Hence it is logical to remove as little dentin as possible during instrumentation without jeopardizing long-term success [2] .

A new obturation system; Resilon was introduced in 2004 which is a thermoplastic synthetic polymer based material. It performs similar to gutta-percha and has the same handling characteristics [2] . It was reported that Epiphany sealer bonds both to root dentine and Resilon cones forming a 'monoblock' that has good adaptation to the canal walls and thereby reinforcing the tooth [1] . The purpose of this in vitro study was to compare the fracture resistance of endodontically treated roots filled with Resilon with that of conventional gutta-percha using different sealers like AH plus , Roeko Seal Automix and Zinc oxide Eugenol.

Instrumentation of all eighty specimens followed the same technique and a uniform size profile instrumentation upto .04 taper 40 size with a slow speed rotary Anthogyr hand piece so as to decrease the uncontrollable variation and to standardize as much as possible. As was done in previous studies the length of the roots were standardized to 14±1 mm and roots with similar bucco-lingual dimensions were selected to eliminate variations in dimensions. Selection of specimens tested were almost similar in size, shape and thickness and assigned to groups randomly.

Sodium hypochlorite though reported to weaken the tooth structure, is a gold standard for root canal irrigation since it acts on the organic portion of the tooth and is the most commonly used irrigant. The present study utilized 2.5% Sodium hypochlorite. Canals were lubricated with EDTA (RC-PREP) as it aids in instrumentation with rotary endodontic system. Weiger and colleagues recommended using EDTA followed by NaOCl to optimize adhesion of sealers to the root canal walls. A final rinse with EDTA is used because remaining NaOCl might inhibit the setting of resin materials and it also aids in removal of smear layer which is thought to be important for resin based sealer to form adhesion and thus increase the fracture strength. The removal of smear layer has been shown to increase the sealing effect and adaptation of the root canals to dentin [9] . The best combination suggested with rotary instruments is EDTA followed by NaOCl. The present study utilized the same protocol.

In several studies test for facture strength were performed using the cyclic loading (Heydecke etal, Fokkinga et al) [6] applying the force in different directions in order to simulate the clinical conditions. However in many studies, it has been reported that applying the force vertically to the long axis of the tooth, transmits the force uniformly (Chen et al, Lindermuth et al, Dias de Souza et al). In the present study a single load to fracture was applied vertically as in many other studies that evaluated the effect of root canal sealer on the fracture resistance of root filled teeth ( Apicella et al, Cobankara et al, Lertchirakarn et al, Texiera et al) [10] .

Gutta-percha is considered to be the gold standard and has been in use for over hundred years and a suitable substitute has not yet emerged. Rotary instrumentation (Profile) results in a canal shape with minimal canal transportation conducive to obturation. This is in agreement with Imura et al, Peters et al and Ayar and Love. This type of preparation allows for effective obturation using the matched taper single cone technique which is reported as high gutta-percha fill percentages [11] . In the present study root canal instrumentation was done using .04 taper Profile instrument upto size 40 and single cone obturation was performed using .04 taper cone (size 40).

The concept of dentine bonding in restorative dentistry has been introduced in endodontic treatment and promising results have been reported in methylmethacrylate tributyl borane or MMA/TBB based resin sealer producing consistently high bond strengths [1] . Adhesive sealers have been introduced to obtain dentinal tubular penetration, bond to collagen matrix and consequently adhesive strength to dentine. The present study compared fracture resistance of teeth obturated using single cone gutta-percha using adhesive (AHPlus) and non adhesive sealers (RoekoSeal Automix, Zinc oxide eugenol) instrumented with rotary instrumentation. The comparative results of gutta-percha with AHPlus (group 2) showed higher mean values compared to gutta-percha with RoekoSeal Automix (group 3) and Zinc oxide eugenol based sealers (group 4) although the results were not statistically significant. Use of EDTA along with NaOCl removes the organic and inorganic content results in open dentinal tubules. The resin forms tags into these open dentinal tubules. Thus resin based sealers have been proposed to adhere to the root canal dentin and therefore reinforce endodontically treated teeth. These materials have the potential to enhance endodontic seal by reducing microleakage from both apical and coronal directions thereby contributing to the success of orthograde endodontic treatment [1] . Our present results confirm those of Hammad etal [2] . Showing a higher mean fracture resistance value for resin based sealers compared to non adhesive sealers.

RoekoSeal Automix a silicon based sealer utilized in the present study is a thixotropic material and has an added advantage of raving, good biocompatibility, low film thickness, and good adaptation to dentine. There is no literature regarding the fracture resistance of gutta-percha with RoekoSeal. The present study showed roots obturated with gutta-percha and RoekoSeal Automix (group 3) to have a better fracture resistance than gutta-percha with Zinc oxide eugenol sealer(group 4) although the mean value was not statistically significant.

Root canal sealers are necessary to seal the space between the dentinal wall and the obturating core interface, to fill voids and irregularities in the root canal, to fill lateral and accessory canals, and spaces between gutta-percha points used in lateral condensation. Sealers also serve as lubricants during the obturation process. Present study showed gutta-percha with AHPlus sealer to have a significantly higher fracture resistance compared to gutta-percha without sealer. Guttapercha with RoekoSeal Automix(group 3) and Zinc oxide eugenol based sealers(group 4) also showed higher mean values than gutta-percha without sealer even though the values were not statistically significant.

In the present study gutta-percha with Zinc oxide eugenol based sealer (group 4) showed lesser mean value of fracture resistance compared to resin based and silicon based sealers which is in accordance with the study of Lertchirakarn etal [5] .

The reasons for not using resins have centered on questionable results, difficult and un predictable method of delivery into root canal system and inability to retreat the canal if necessary. Evaluation of a new thermoplastic synthetic polymer based on polyester- Resilon was utilized in the present study which allows the bonding agent (sealer), to attach to the resin core and dentine wall, thus forming a monoblock. Resilon can be removed for retreatment by softening with heat or dissolved with solvents like chloroform [12] . Results of the present study showed highly statistically significant difference in the mean fracture value between resilon (group 1) and control group (group 5) and significant differences with gutapercha using Roeko Seal (group 3) and Zinc oxide eugenol sealer (group 4). The mean value was higher in resilon group compared to gutta-percha with AHPlus (group2) although it was not Statistically significant. The results of the study is in accordance with that of Teixeira et al [1] and Schafer et al [4] .

Lack of correlation with the study of Sagsen et al [9] may be attributed to the length of the specimens exposed to force during the mechanical testing. In the present study 9mm of roots was exposed to force and in the study of Sagsen et al 6mm of roots was exposed to the force. Further more it has been stated by Johnson et al that the small amount of the materials used with in the root canal might be insufficient to reinforce the filled roots [12] . The high fracture resistance values observed in the present study compared to previous studies [1],[2],[4],[9] may be due to the variations between structures of root dentine of the tested samples related to age or dentinal sclerosis. It can also be assumed that the chemical coupling of resin based sealer to Resilon is weak which may be due to the fact that the amount or method of dimethacrylate incorporated in resilon may not be optimized for predictable coupling [3] .

The clinically relevant comparison between resilon and gutta-percha groups according to the present study showed highly statistically significant difference indicating that the monoblock concept is important not only to resist bacterial penetration through the material but also to hold the roots together, thereby increasing the resistance to fracture.

The present in vitro study was regarding the fracture resistance of endodontically treated teeth .Care should be taken in transfer of these findings to long term clinical situation since previous studies [13],[14] have pointed out that resilon seems to be biodegradable under the attack of hydrolytic ester bond cleaving enzymes which may exist as a component of salivary enzymes or as extracellular enzymes from endodontically relevant pathogens such as pseudomonas aeruginosa, enterococcous faecalis and several actinomyces strains. Moreover there is some evidence that resilon is also susceptible to alkaline hydrolysis.

Clinical long term studies are necessary to collect evidence based data to support the confident use of these materials.

 Conclusion



This in vitro study evaluated the fracture resistance of endodontically treated teeth obturated using Resilon and gutta-percha using different sealers. Within the limitations of this in vitro study, the following conclusions were drawn.



Root canals filled with Resilon increased the in vitro resistance to fracture of single canal extracted teeth compared to other experimental groups and results were statistically significant. The mean fracture resistance value for the experimental groups in ascending order was as follows: gutta-percha with out sealer, gutta-percha with Zinc oxide eugenol sealer, guttapercha with Roeko Seal Automix sealer, guttapercha with AH Plus sealer and Resilon with Epiphany.

Within the limitation of this study, it can be concluded that the monoblock concept is important not only to resist bacterial penetration through the material but also to hold the roots together, thereby increasing the resistance to fracture.

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