Assessment of tooth discoloration induced by biodentine and white mineral trioxide aggregate in the presence of blood.

INTRODUCTION: In clinical dental application, using silicate-based cements is extremely popular. These materials come into direct contact with blood during or after placement and may cause tooth discoloration.
OBJECTIVES: The purpose of this study was to compare the coronal tooth discoloration induced by white mineral trioxide aggregate (MTA) and biodentine in the presence of blood.
MATERIALS AND METHODS: Seventy specimens were chemomechanically prepared and divided into four experimental and two control groups. In the experimental groups, the pulp chambers were filled with white MTA angelus or biodentine. Blood or saline saturated cotton pellets were placed within the canals. Saline or blood alone was used in the control groups. Color was assessed with a spectrophotometer at baseline, 1 week, and 1 and 3 months, and color change values were calculated. Tukey's honestly significant difference and Sidak tests were used for statistical analysis.
RESULTS: The color change was significantly less with biodentine/saline than MTA/saline and MTA/blood (P < 0.05). Regardless of the material type and blood presence, discoloration increased after 3 months (P < 0.05).
CONCLUSION: Discoloration induced by biodentine/saline may not be clinically noticeable and it was less than MTA-containing groups. Irrespective of blood presence or absence, MTA caused perceptible color change.

INTRODUCTION

Poor esthetic appearance of endodontically treated teeth significantly affects the patients’ quality of life.[1] Therefore, endodontic treatments should not focus only on biological and functional aspects but should also consider esthetic aspects.[2]

Some endodontic procedures such as pulp capping, pulpotomies, and regenerative endodontics involve the placement of mineral trioxide aggregate (MTA) in the coronal third of the tooth, which may have the potential for discoloration.

MTA was first introduced in a gray form MTA (gMTA), which was associated with discoloration.[34] To overcome this shortcoming, white MTA (wMTA) was developed by removing or lowering the concentration of various metal oxides implicated in color change.[5] However, some studies have reported undesirable postoperative tooth discoloration after the use of wMTA.[67] Moreover, the presence of blood adjacent to the setting wMTA can exacerbate this discoloration.[89]

Biodentine, a new calcium silicate-based material, is a bioactive dentine substitute with endodontic indications similar to those of MTA.[10111213] Biodentine powder mainly consists of tricalcium silicate, calcium carbonate, and zirconium oxide as the radiopacifier and its liquid contains a water reducing agent and calcium chloride as the setting accelerator.[14] A previous study showed that the teeth restored with biodentine maintained color stability, whereas those treated with wMTA exhibited discoloration.[15]

In another study, when left in the canal for 6 months, both gMTA and wMTA caused significant coronal tooth discoloration, but biodentine did not induce a perceptible color change in the tooth structure.[16] Nevertheless, a recent study showed that, in the presence of blood, there was no significant difference between tooth discoloration induced by biodentine and MTA.[17]

Therefore, this ex vivo study was designed to compare the coronal discoloration induced by wMTA and biodentine and also to assess the influence of blood on this discoloration.

MATERIALS AND METHODS

A closed system previously described by Felman and Parashos[8] was modified and adopted for this study. Seventy human single-rooted permanent maxillary anterior and mandibular premolar teeth extracted for periodontal or orthodontic reasons were selected for this study. The teeth were fully formed and inspected to ensure the absence of cracks, fractures, caries, and coronal restoration. The selected teeth were disinfected by immersion in 5.25% sodium hypochlorite solution for 1 h and then kept in normal saline solution until use. The teeth were cleansed with an ultrasonic scaler and polished with pumice and water to remove extrinsic debris and stains. The root ends were sectioned to obtain standard specimens with 10-mm root length from the buccal cementoenamel junction. Root canals were prepared from the apical aspect to the most coronal part of the pulp chamber (pulp chamber roof) to provide a closed system for the prevention of coronal microleakage. Canal enlargement was initially performed with stainless steel K-type files (MANI, Tochigi-Ken, Japan) followed by # 2–6 Gates Glidden drills (MANI, Tochigi-Ken, Japan). Finally, a ParaPost drill (Coltene/Whaldent, Alstatten, Switzerland) size 7 was used to produce a canal with 1.75-mm diameter. Between each instrument change, the canals were irrigated with 2 mL 2.5% sodium hypochlorite solution using a 27G needle. At the end of root canal preparation, root canals were irrigated with 10 mL 2.5% sodium hypochlorite solution to remove any pulp tissue remaining followed by 17% EDTA (CERKAMED, Poland) for 1 min to remove the smear layer. Canals were finally irrigated with 10 mL of normal saline.

Blood collection

This study was approved by the Ethics Committee of the relevant authority (Grant No. 10813). Whole fresh blood sample was collected from a healthy, consenting volunteer by a trained member of medical staff in accordance with Helsinki ethical principles for medical research involving human subjects.[18] The blood collection tubes were sterile and coated with K2 EDTA as an anticoagulant agent to prevent clotting during the experiment.

Experimental setup

The teeth were randomly assigned to four experimental (n = 15) and two control (n = 5) groups [Table 1]. MTA Angelus (Angelus, Londrina, Brazil) and BIODENTINE (Septodont, Saint Maur Des Fosses, France) were prepared according to the respective manufacturer's instruction. In the experimental groups, either Angelus MTA or biodentine was packed through the apical aspect to the most coronal aspect of the standardized preparation up to the buccal cemento-enamel junction with an endodontic plugger. Sterile, customized cylindrical cotton pellets (size 4; Richmond Dental, Charlotte, NC) were loosely placed within the canals from the apical access and saturated with normal saline solution or blood. In the control groups, only cotton pellets were placed within the canals and then saturated with 0.5 mL of normal saline or blood. The apical openings were sealed with sticky wax. Every specimen was placed into a single vial-containing 1 mL of saline as the humidifying agent [Figure 1]. The vials were stored in an incubator at 37°C during the experiment.

Table 1

∆E values for the experimental groups in different time intervals (mean±standard deviation)

Groups	∆E1 (t1-t0)	∆E2 (t2-t0)	∆E3 (t3-t0)
Biodentine/saline (n=15)	2.28±1.62	2.38±1.84	3.24±2.23
Biodentine/blood (n=15)	3.20±2.11	3.06±2.38	4.20±2.89
wMTA/saline (n=15)	4.53±2.30	4.84±1.76	5.82±2.47
wMTA/blood (n=15)	3.68±2.23	5.61±4.55	6.72±4.98
Saline moistened cotton pellets (negative control n=5)	1.92±1.59	3.23±1.76	2.90±1.70
Blood moistened cotton pellets (positive control n=5)	5.50±4.21	6.00±3.97	8.32±5.78

wMTA: White mineral trioxide aggregate, SD: Standard deviation

Figure 1

Each specimen was placed into a single vial during experimentation

Tooth color assessment

Color change was evaluated with a spectrophotometer (Spectroshade MHT S.p.A., Verona, Italy) at four-time points: immediately before materials placement, and at 1 week, 1 month, and 3 months after material placement. Technical specifications of the spectrophotometer are as follows: Emitted light: 410–680 nm, Lighting: 2° × 45°; polarized and telecentric, Resolution: 640 × 480, Sensor: CCD B/W [Figure 2].

Figure 2

Color change was evaluated with Spectroshade MHT

A mounting system was developed to allow positioning of the spectrophotometer at an angle of 0° relative to the vertical axis with an approximately 1 cm distance from the buccal surface of the specimens. Color measurements were carried out by a single operator and repeated three times for each sample and the mean values were calculated. Data were reported using the Commission International de I’Eclairage's L*a*b* color system, and the color change between two measurements was calculated using the following formula:

ΔE* = ([L1−L0*] + [a1−a0*] + [b1−b0*]²)½

L* values represent lightness, ranging from black (0) to white (100), a* and b* represent greenness/redness and blueness/yellowness, respectively. The proposed limit for color matching adopted in this study was set at 3.7 ΔE* units (perceptibility threshold). Differences beyond this limit were considered clinically perceptible.[19]

Statistical analysis

Multi-sample repeated measures analysis of variance was used to assess the effects of material type and blood contamination over time. The main effects were further investigated with pairwise between-group and within-group comparisons using Tukey's honestly significant difference and Sidak tests, respectively. The level of statistical significance was set at 0.05.

RESULTS

Means and standard deviations of color changes (ΔE*) at each period are shown in Figure 3 and Table 1.

Figure 3

Trend of ΔE changes at different measurement time intervals

There was no statistically significant interaction effect between the experimental groups and periods (P = 0.419). In other words, the experimental groups showed a similar trend of color changes over time.

Regardless of the effect of time, the color change in the biodentine/saline group was significantly less than that of MTA/saline and MTA/blood group (P < 0.05).

Irrespective of the type of material and the presence of blood, greater ΔE* values were recorded after 3 months than at 1 month and 1 week (P < 0.05).

DISCUSSION

In this study, extracted human teeth were used and the samples were prepared from the apical aspect. This method provides a closed system that prevents the potential complication of coronal microleakage and also allows standardization of the thickness and volume of the tested materials.[9] However, in some studies, typical access cavities were prepared and filled with composite resin after application of calcium silicate-based cements.[171920] Although preparing an access cavity is similar to the clinical situation, filling the access cavities with composite resin may affect the results of studies. It has been reported that irradiation with a curing light causes discoloration in wMTA but not in biodentine.[21]

In the present study, the greatest color change was observed in the positive control group (blood), at all-time points. Some degree of discoloration, although not perceptible for human eyes, was also observed in the negative control group. The reasons for discoloration of the negative control teeth are uncertain; however, a similar phenomenon has been reported by some previous studies.[151720]

In the present study, irrespective of the type of material and blood contamination, increasing discoloration was observed over time. Previous studies have also demonstrated similar increasing discoloration patterns for some calcium silicate-based materials.[1517]

Among the experimental groups, biodentine/saline exhibited the lowest ΔE* value which did not exceed the human eye perceptibility threshold[37] at any time interval. The clinical implication of this finding is that complete hemostasis of pulp in direct pulp capping cases before the application of biodentine may prevent perceptible tooth discoloration. The biodentine/saline group also showed statistically significant differences with MTA/saline and MTA/blood. This finding is in accordance with the results reported by Kohli et al.[16] They showed that, in contrast to gMTA and wMTA, biodentine did not induce perceptible color changes in the tooth structure when left in the canal for extended periods. Vallés et al.[15] also reported that teeth treated with wMTA exhibited discoloration, whereas those treated with biodentine maintained color stability during a 6-month period. Another study by Shokouhinejad et al.[17] also confirmed that, in the absence of blood, biodentine exhibited less tooth discoloration than one type of MTA (OrthoMTA).

The exact mechanisms by which wMTA induces tooth discoloration are currently unknown. One possible mechanism may relate to the oxidation of the iron content of wMTA powder to the calcium aluminoferrite phase of the set wMTA cement.[8] Other mechanisms are related to the presence of bismuth oxide as a radiopacifier in wMTA powder. Vallés et al.[21] investigated the color stability of five different calcium silicate materials influenced by the combination of light and anaerobic conditions. Materials without bismuth oxide did not exhibit discoloration under any given light or oxygen conditions. On the other hand, bismuth-oxide-containing materials exhibited dark discoloration after light irradiation in an oxygen-free environment. Bismuth oxide may also react with sodium hypochlorite,[2223] if present in the canal, or with amino acids in dentine collagen,[24] leading to subsequent discoloration. The adverse effect of bismuth oxide was supported by Kang et al.,[25] who reported that the newly introduced MTA-based materials which contain zirconium oxide as radiopacifier were associated with less discoloration than those containing bismuth oxide were biodentine contains zirconia as a radiopacifier and the lack of bismuth oxide was hypothesized to be the reason for its color stability.[151621]

In this study, the mean ΔE* value for the biodentine/blood group exceeded the human perceptible threshold of 3.7 after 3 months. Moreover, no significant differences were observed between this group and the MTA/saline and MTA/blood groups. These results support the findings of Shokouhinejad et al.[17] who found no significant difference between the tooth discoloration of biodentine and two types of MTA (ProRoot MTA and OrthoMTA), in the presence of blood. Regarding the impact of blood contamination on tooth discoloration, however, our results are inconsistent with those obtained by Shokouhinejad et al. They showed that blood contamination, regardless of the incubation time and type of material, significantly increased the ΔE* of materials, whereas in our study, neither MTA nor biodentine was associated with significantly greater color changes in the presence of blood.

Direct comparison of the two studies cannot be performed because of the different experimental methodologies used, including the preparation of specimens (preparation from apical aspect versus preparation of typical access cavities), type of material (MTA Angelus versus ProRoot MTA and OrthoMTA), and period (3 months versus 6 months). Therefore, further research is required to determine the influence of blood on the tooth discoloration induced by biodentine and MTA.

CONCLUSION

Within the limitations of this ex vivo study, the tooth discoloration induced by biodentine/saline may not be clinically noticeable and it was less than those induced by MTA/saline and MTA/blood. Irrespective of the presence or absence of blood, MTA caused a clinically perceptible color change.

Financial support and sponsorship

This work was supported by the vice-chancellery of Shiraz University of Medical Sciences (Grant # 10813).

Conflicts of interest

There are no conflicts of interest.