Evaluation of titanium mesh and fibers in reinforcing endodontically treated molars: An in vitro study.

Aim/Objective: We aimed to evaluate the fracture resistance of titanium mesh and fibers that could aid as a substitute for crown coverage. Materials and Methodology: Forty extracted human mandibular molar teeth were selected for this study and were divided into four groups (n = 10). Access cavity preparation was done in all experimental teeth (Groups 2-4) maintaining 1.2-1.5 mm diameter of tooth structure around the circumference to mimic the structural loss of teeth due to the extent of dental caries. Group 1 consisted of intact teeth which were assigned as control. Group 2 was reinforced with titanium mesh. Group 3 was reinforced with glass fiber. Group 4 was reinforced with polyethylene fiber. The access cavities in all the experimental teeth were later filled with nanohybrid composite and were subjected to fracture resistance using a universal testing machine.
Results: The results of the study were evaluated statistically using the Kruskal-Wallis test. There was no statistically significant difference among the experimental and control groups.
Conclusion: Within the constraint of this in vitro study, an inference can be given that fiber-reinforced composite and titanium mesh could rule out the mandatory procedure of crown placement for endodontically treated molars. Copyright:

INTRODUCTION

The restoration of endodontically treated posterior teeth is considered a very important stage in determining the prognosis of the treated tooth. Fractures are more common in endodontically treated teeth due to extensive loss of tooth structure as the progression of dental caries increases with time.[12] Nevertheless, comprehensive studies have been carried out on this subject; it has been a dilemma to select an appropriate restorative procedure that could result in achieving considerable success and also to address the query of whether the placement of a crown is mandatory.[34]

Although placement of a crown has been routinely advised for an endodontically treated tooth as a method to strengthen it, tooth fractures have been unpreventable despite the full-crown coverage placement.[5] The subject of deliberation for some time now has been as to whether full cast crowns, especially in posterior teeth, are indeed compulsory or not after endodontic treatment. The emergence of newer and more reliable restorative materials has pushed clinicians to shift the thought process from mandatory crown coverage to an innovative approach of restoring endodontically treated teeth with advanced restorative materials and techniques.[6]

The study presented was carried out to assess whether titanium mesh and fibers reinforced with composites could rule out the compulsory requirement of crown coverage in endodontically treated posterior teeth.

MATERIALS AND METHODOLOGY

Forty human first and second molars which were extracted due to periodontal reasons were collected for this study from the department of maxillofacial surgery. The teeth collected were free of caries and without any fracture lines or cracks. An operating microscope (Global Surgical Corporation, Saint Louis, USA) at ×12.8 magnification was used to confirm the same. All the teeth had similar mesiodistal (10.5 ± 1 mm) and buccolingual (9.5 ± 1 mm) dimensions to rule out the effect of size and shape on the results and also to maintain a standardization protocol. According to OSHA guidelines, 0.1% thymol was used to disinfect the teeth, and were later segregated into three experimental and one control group.

The control group was comprised of intact teeth (n = 10). Access cavity preparation was done in all experimental teeth (Groups 2–4) maintaining 1.2–1.5 mm diameter of tooth structure around the circumference to mimic the structural loss of teeth due to the extent of dental caries [Figure 1a]. Canal preparation in all the experimental groups (Groups 2–4) was done up to master apical file size of 25/0.4 (Blue Flex, Mumbai). All the mandatory protocols required during the biomechanical preparation were carried out meticulously.

Figure 1

(a) Marking of the extent of access cavity preparation, (b) Access cavity reinforced with titanium mesh, (c) Access cavity reinforced with Everstick crown and bridge fiber, and (d) Access cavity reinforced with polyethylene fiber

In Groups 2, 3, and 4, all the teeth were conditioned with 37% phosphoric acid (3M ESPE, Bangalore, India). The inner circumference of the access cavities in all experimental teeth was reinforced with different reinforcing materials. Group 2 was reinforced with premeasured titanium mesh (Bombay Ortho Industry, Mumbai) which was bonded to the nanohybrid composite Filtek Z 350 (3M ESPE) using 4-META bonding agent [Figure 1b]. In Group 3, the teeth were reinforced with premeasured Everstick C&B fiber (GC, India) [Figure 1c], and final restoration was done with nanohybrid composite Filtek Z 350 (3M ESPE). In Group 4, the teeth were reinforced with premeasured polyethylene fiber (Ribbond, Seattle, USA), and final restoration was done with nanohybrid composite Filtek Z 350 (3M ESPE, Mumbai, India) [Figure 1d]. In order to simulate the periodontal ligament, polyvinyl siloxane impression material (EXAFLEX, GC America Inc., USA) was coated around each tooth and was fixed in a block of self-cure acrylic resin (Tempron, GC, India) with the long axis of the tooth perpendicular to the base of the block. To prevent the teeth from drying, they were placed in an incubator at 37°C and 100% humidity until they were subjected to fracture resistance. All the teeth were tested for resistance to fracture using a universal testing machine (Instron India Pvt. Ltd., Mumbai) with a 5-mm diameter round tip which was placed parallel to the long axis of the teeth until the bar slightly contacted the occlusal surface. The compressive load applied was at a speed of 1 mm/min, and the fracture resistance values were recorded in Newtons. Statistical analysis of the recorded values was done using SPSS 11.5 statistical software (SPSS Corp., Chicago, IL, USA). Kruskal–Wallis test was applied.

RESULTS

The mean values with their standard deviations as well as the intergroup comparisons were noted and calculated [Tables 1 and 2]. The mean fracture resistance value of all the groups did not show any statistically significant difference from the control group.

Table 1

Fracture resistance under static loading of endodontically treated molar

	N	Mean	Std. Deviation	Minimum	Maximum
Intact Tooth	10	849.6	185.1	642	1114
Titanium Mesh	10	836.7	226.7	576	1270
Everstick Fiber	10	865.7	148.2	672	1137
Ribbond FIber	10	701.7	118.1	527	867

Table 2

Intergroup comparison of fracture resistance under static loading of endodontically treated molar

Groups	N	Mean Rank	Kruskal Wallis test
Intact Tooth	10	23.05	Chi square	P value
Titanium mesh	10	20.90	5.85	0.119 (NS)
Everstick Fiber	10	24.90
Ribbond Fiber	10	13.15
Total	40

Test: Kruskal Wallis test. NS – Non-Significant

DISCUSSION

The amount of tooth structure remaining dictates the success of the longevity, as well as the need to reinforce an endodontically treated tooth. It is well documented that the coronal pulp tissue contributes to the structural integrity of the tooth and hence the root canal procedure hampers the strength of posterior teeth.[2]

Various works of literature have suggested methods to reinforce an endodontically treated tooth with newer and advanced restorative materials, which has given rise to an interesting argument as to whether crowns are mandatory in endodontically treated posterior teeth.[78]

This in vitro study was taken up to suggest some innovative methods in reinforcing endodontically treated teeth simulating extensive loss of tooth structure due to caries.

Various studies have been conducted to evaluate whether crown coverage was mandatory after endodontically treated teeth. It was observed that coronal coverage did not potentially improve the fracture resistance of anterior teeth which were endodontically treated with a follow-up of 25 years.[9] Another study concluded that composite resin restoration would effectively strengthen an endodontically treated tooth with minimal loss of tooth structure.[10]

Zelic et al. conducted a finite element analysis study and concluded that the biomechanical preparation of the root canal did not attribute to weakening of the tooth structure, but it was rather the extent of the access cavity preparation which resulted in loss of tooth structure that had a greater impact on determining the tooth strength.[11]

This in vitro study was conducted to assess whether titanium mesh and fibers reinforced with composites could rule out the compulsory requirement of crown coverage for endodontically treated posterior teeth. The mandibular molars were selected for this in vitro study, bearing in mind the functionary requirement and placement of the tooth in the arch.[12]

The materials used in this study were titanium mesh (Bombay Ortho Industry, Mumbai, India) and fibers. Polyethylene fiber (Ribbond, Seattle, USA) was used as a reinforcing material by placing it against the inner circumference of the access cavity. The material was chosen considering its good flexibility and the ability to dissipate the stress at the restoration/adhesive resin interface.[13]

The material did not demonstrate any statistical significant difference in the mean values among experimental groups, but its values were at par with the control group.

Everstick C&B is an example of unidirectionally oriented E-glass fibers impregnated with linear polymers (polymethyl methacrylate) and cross-linking monomers (bis-GMA) which are locked to each other. Each bundle contains approximately 4000 individual glass fibers. E-glass fibers are cost-effective and possess low density. These are insensitive to moisture, heat resistant, nonflammable, and maintain strength over an extensive range of conditions. Considering the mechanical properties and flexibility, the fiber was chosen to reinforce the inner circumference of the experimental tooth. The mean values of fracture resistance of Group 3, Glass Fiber (Everstick C&B), were slightly more than that of Group 2, titanium mesh, and marginally greater than the Group 4, polyethylene fiber (Ribbond), although statistically there was no significant difference found amongst them.[14]

In dentistry, titanium is widely used in surgical operations due to its high stiffness, low density, corrosion resistance, and good biocompatibility. Titanium mesh can adapt to various shapes through bending due to its plastic property. An adult human male can produce an occlusal force that averages from 45 to 68 kg (441.3–666.8 MPa) on molar sites. When comparing the values of ultimate flexural strength of titanium mesh (503-900 Mpa) and elastic modulus (10-20 Gpa) was at par with that of human occlusal force, this material was chosen to reinforce the inner cirumference of experimental group 2. Considering the mechanical properties of titanium mesh, this material was chosen to reinforce the inner circumference of experimental Group 2. The mean values of titanium mesh were at par with Group 3 and the control group.[1516]

CONCLUSION

Within the limitation of this in vitro study, it can be concluded that the three experimental materials titanium mesh, Everstick C&B, and polyethylene fiber can provide an appropriate option against crown coverage in endodontically treated molar teeth.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.