Effect of Biomineralization Ability on Push-out Strength of Proroot Mineral Trioxide Aggregate, Mineral Trioxide Aggregate Branco, and Calcium Phosphate Cement on Dentin: An In vitro Evaluation.

CONTEXT: Biomineralization is a process which leads to the formation of an interfacial layer with tag-like structures at the cement-dentin interface. It is due to interaction of mineral trioxide aggregate (MTA) and Portland cement with dentin in phosphate-buffered solution (PBS). This study is aimed to evaluate the effect of influence of biomineralization process on push-out bond strength of ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK, USA), MTA Branco (Angelus Soluc¸o˜es Odontolo´gicas, Londrina, PR, Brazil) and calcium phosphate cement (BioGraft CPC). AIM: The aim of this study was to evaluate the effect of biomineralization process on the push-out strength of ProRoot MTA, MTA Branco, and CPC after mixing with 0.2% chlorhexidine gluconate solution (0.2% CHX) and 2% lidocaine solution (2% LA) on the bond strength of MTA-dentin.
MATERIALS AND METHODS: Dentin discs with uniform cavities were restored with ProRoot MTA, MTA Branco, and calcium phosphate cement after mixing with 0.2% CHX solution and 2% lidocaine solution. The samples were uniformly distributed into two groups. Experimental group being immersed in PBS solution and control group being immersed in saline for 2 months. Instron testing machine (Model 4444; Instron Corp., Canton, MA, USA) was used to determine the bond strength. STATISTICAL ANALYSIS USED: A two-way analysis of variance and post hoc analysis by Bonferroni test.
RESULTS: All samples immersed in experimental group displayed a significantly greater resistance to displacement than that observed for the samples in control group (P < 0.05). MTAs displayed a significantly greater resistance to displacement than calcium phosphate cements.
CONCLUSION: The main conclusion of this study was that the push-out bond strength of the cements, mainly the MTA groups, was positively influenced by the biomineralization process.

INTRODUCTION

Perforation is the leading cause for endodontic failure.[1] An incidence of perforation in endodontic treatment ranges from 3% to 10%.[2] An ideal perforation repair material should provide an adequate seal and should resist the dislodging forces, such as mechanical loads of occlusion or the condensation of restorative materials over it.[34]

Many materials such as amalgam, super EBA, IRM, Cavit, composite resin and glass Ionomer cements had been used in the past to seal perforation sites. These materials have their own disadvantages such as microleakage, toxicity, and sensitivity to the presence of moisture.[5]

Researches in the field of biomaterials have overcome these barriers and have led to the development of new biomaterials such as CPC, mineral trioxide aggregate (MTA), biodentine, and bioaggregate.

Calcium phosphate cements (CPC) were first reported by Brown and Chow in 1986 as a self-setting, bioactive and biodegradable[6] material which is comprised equimolar amounts of tetracalcium phosphate and dicalcium phosphate anhydrous was shown to be biocompatible[7] and osteoconductive.

MTA promotes biomineralization in the presence of phosphate-buffered solution (PBS).[8] It forms apatite at cement-PBS system which gets accumulated inside collagen fibrils, stimulates controlled mineral nucleation on dentin, and induces the organization of an interfacial film with tag-like structures at the cement-dentin interface.[9] Refinement in the marginal seal of MTA apical plugs after immersion in PBS over time could be attributed to biomineralization process.[10]

MTA exhibits very good biocompatibility and superior sealing ability.[11] The resistance to displacement raises over a period and may get affected in the presence of blood contamination.[12] To overcome this drawback, CPC was experimented.

Conventionally, distilled water had been used to mix these cements. An acidic pH in the environment impedes MTA and CPC setting and reduces its strength and hardness.[13] To improve the efficacy of MTA and CPC, CHX and 2% lidocaine solution had been used in this study.

Chlorhexidine (CHX) is a dicationic bisguanide cholorophenyl ring that was initially used as a general disinfectant because of its broad antibacterial action.[14] It is also used as an irrigant to sterilize the root canal system.[1516] It has been shown that mixing of MTA with CHX increases the antibacterial efficacy of MTA.[17] Lidocaine 2% containing 1:50,000 epinephrine (Astra pharmaceutical products) was used to enhance hemostasis in the surgical sites. There are inconsistent results in the literature regarding effect of CHX and LA on the physical properties of MTA and CPC.

The objective of this study was to compare and evaluate the effect of 0.2% CHX and 2% LA on the bond strength of PROROOT-MTA, MTA Branco, and CPC dentin ex vivo.

MATERIALS AND METHODS

One hundred and twenty sound human premolars extracted for orthodontic purposes were used in the present study.

The crowns were removed [Figure 1] and midroot dentin was horizontally sectioned into 2.00 mm thick slices with a water-cooled low-speed carborundum disc [Figure 2]. With a spherical diamond bur, the space of the canal was enlarged and two complete passes of a #5 Gates-Glidden bur was done to obtain 1.3 mm diameter standardized cavities. The sections were initially immersed in 17% EDTA for 3 min followed by 1% sodium hypochlorite for 3 min. They were then washed in distilled water and dried.

Figure 1

Decoronated specimens

Figure 2

Tooth being sectioned

One hundred and twenty sectioned teeth samples were divided into two groups equally, one being control Group A (saline solution) and the other being experimental Group B [Figure 3], i.e., phosphate-buffered solution (PBS). Each group was further divided into 6 subgroups.

Figure 3

Sectioned specimens

MTA Branco, CPC, and ProRoot MTA powder was mixed with 0.2% CHX solution and 2% LA on a glass slab with a cement spatula following the manufacturer's recommendations. When the mixture showed putty consistency, with the help of a Dovgan carrier (G. Hartzell and Son, Concord, CA, USA) placed in root canals and compacted with pluggers (Dentsply Tulsa Dental). All specimens were examined using a microscope at 16 × magnification. Specimens with cracks, defects, or gaps between the material and dentin walls were excluded from the study.

Immediately after filling, samples from the control group (A) were placed in a saline solution of 15 ml (PH = 7.2) for 2 months at 37° centigrade [Figure 4] and experimental group (B) were placed in PBS of 15 ml for 2 months at 37° centigrade [Figure 5]. The solution was replaced once in every 5 days.

Figure 4

Specimens in saline solutions

Figure 5

Specimens in phosphate-buffered solution

Push-out test

After experimental periods, samples were placed in a steel holder which was tightened to an aligning apparatus that held it centered beneath a steel piece with a cylindrical punch. Using an MTS testing machine, the bond strengths were measured [Figure 6].

Figure 6

Specimens subjected for universal testing machine

The barrel-shaped end of a 2/4 hand blogger with 1 mm diameter was used as a force probe mounted on the moving head of the MTS. The force probe travelling at a speed of 0.2 mm/min, applied pressure to the surfaces of MTA in each specimen until the substance was dislodged. The ultimate force utilized to MTA before dislodgement occurred was recorded as N force.

All measurements investigated by means of SPSS 16.0 system for windows. (SPSS Inc, US). A two-way analysis of variance (ANOVA) compared with the 5% significance level was performed to compare the differences in dislodgement force among the twelve subgroups.

RESULTS

Two-way ANOVA analysis showed that the mean values demonstrated a statistically significant variance in the mean expulsion force among the CPC and all other subgroups [Table 1].

Table 1

Demonstrates the comparison between the mean bond strength of each subgroup

The mean dislodgement force of MTA-dentin decreased in the control group. The highest degree of mean dislodgment force was shown by MTA subgroups.

Bonferroni test was used to do a comparison between individual groups.

The results show that compared to the samples immersed in the control group (P > 0.05), samples immersed in experimental group displayed a significantly greater resistance to displacement as shown in Table 2.

Table 2

Comparison of saline (control) with other groups

Bond strength was significantly greater in subgroup 1B, 2B, 5B, and 6B than in the others (P > 0.05).

No statistically significant difference in the mean dislodgment force between the 0.2% CHX solution and 2% LA subgroups was documented. Subgroups 3B and w4B showed significantly least amounts of bond strengths than other subgroups shown in Graph 1.

Graph 1

Demonstrates the subgroup comparison using Bonferroni test

DISCUSSION

A MTA was developed at Loma Linda University for the sealing between the tooth and the external surfaces of tooth.[18] MTA has been used in both surgical and nonsurgical utilization, along with root-end fillings,[192021] direct pulp cappings,[2223] perforation repairs in roots or furcation and apexification.[24] Root perforations can be repaired using other materials such as calcium phosphate cement (CPC). They possess the property of biocompatibility and moldability.[25] The above cements can be mixed using saline, CHX, and 2% lidocaine solution. However, the question as to whether these medications would potentially initiate chemical reactions to degrade MTA and CPC or interfere its bond to dentin has not been well addressed in the previous literatures.

Saline and 2% lidocaine solutions are often used because they are easier to use and more convenient alternatives to sterile water in clinical routine.[12] PBS is a buffer solution containing sodium chloride, sodium phosphate, and (in some formulations) potassium chloride and potassium phosphate. It helps maintain a constant pH. The osmolarity and ion concentrations of the solution usually match those of the human body.

The mean values of push-out bond strength of all the experimental groups are in agreement with the findings of previous studies.[12]

Our results showed that compared to the control group, all samples immersed in experimental group showed a significantly greater resistance to dislodgement and showed a significant difference in the mean dislodgment force between the MTA and CPC subgroups. No significant difference was observed among 2% LA and 0.12% CHX groups.

MTA stimulates the precipitation of carbonated apatite, promoting a controlled mineral nucleation on dentin as the formation of an interfacial layer with tag-like structures.[9] Although all cement forms tag-like structures when immersed in PBS, it is important to note that the samples of ProRoot MTA and MTA Branco exhibited significantly superior resistance to displacement than the CPC.

Poor mechanical properties of CPC are the main disadvantage of this material. Since the material is weak under tensile forces.[26] On the other hand, the superior performances of ProRoot MTA and MTA Branco produced the overall highest amount of precipitates and thus, positively influenced the formation of an interfacial layer with tag-like structure.[9] This effect could be responsible for the superior bond strength of the MTAs when compared with the CPC. CPC groups showed significantly least amount of resistance to displacement than the MTA groups.

Our results show that all PBS-immersed samples displayed a significantly greater resistance to dislodgement than that observed for control group.

Based on this ex vivo study, it may be possible to improve the retention of MTA apical plugs to dentin using PBS as an intracanal dressing or as a final rinse in prepared root canals as suggested by Martin et al.[10] In view of this finding, further research is needed to establish a new protocol to encourage the precipitation of carbonated apatite and subsequently the formation of an interfacial layer with tag-like structures.

CONCLUSION

The main conclusion of this study was that the PBS solution showed higher resistance to dislodgement than compared to saline solution. Biomineralization process showed positive influence on the resistance to dislodgement from dentin of all cement tested. More than CPC, MTA cement, however, benefited more from the process. Lidocaine 2% and 0.12% CHX did not significantly alter the physical properties of the cements. MTA Branco and ProRoot MTA both showed no significant difference in push-out bond strength.

However, further studies are recommended before this mixture can safely be used in clinical situations.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.