Dental Traumatology 2015; 31: 385–389; doi: 10.1111/edt.12185
Fracture resistance of weakened bovine teeth after long-term use of calcium hydroxide Marcia Carneiro Valera1, Maria Tereza Pedrosa Albuquerque2, Mayra via Nicolle Cristina Yamasaki3, Fla Stefani Vassallo4, Denise Almeida e Silva Alves da Silva4, Juliana Yuri Nagata5 ~o Jose dos Campos Dental School, Sa ~o Sa ~o Jose dos Paulo State University, UNESP; 2Sa ~o Paulo State Campos Dental School, Sa University, UNESP; 3Piracicaba Dental School, ~o State University of Campinas, UNICAMP; 4Sa ~o Paulo Jose dos Campos Dental School, Sa ~o Paulo; 5Dentistry State University, UNESP, Sa Department, Endodontics Area, Federal University of Sergipe, Lagarto, Brazil 1
Key words: calcium hydroxide; fracture resistance; irrigant solution; permanent tooth; root fracture; prognosis Correspondence to: Marcia Carneiro Valera, ~o Jose dos Faculdade de Odontologia de Sa Campos, UNESP - Institute of Science and ~o Jose dos Campos, SP Technology, 777 Sa CEP 12-245-000, Brazil Tel.: +55-12-39238902 e-mail: [email protected]
Abstract – Background/Aim: In some parts of the world, revascularization may not be the most feasible treatment option for necrotic immature teeth. Therefore, apexification remains the most widely utilized treatment option for these cases. This study aimed to evaluate the fracture resistance of weakened bovine tooth roots treated with various irrigant solutions as well as long-term application of calcium hydroxide intracanal medication (ICM). Material and methods: One hundred seventy bovine teeth were randomly divided into three experimental groups (n = 50) and two control groups (n = 10). Group SS was irrigated with physiologic solution; group CHX was treated with 2% chlorhexidine gel and group NaOCl was irrigated with 1% sodium hypochlorite. After instrumentation, root canals were dressed with calcium hydroxide and evaluated at different periods (15, 60, 90, 180, and 360 days). The specimens were loaded at a 45° angle to measure fracture resistance through the use of an EMIC test machine. Results: A decrease in fracture resistance was observed during the time of ICM dressing. The highest values of fracture resistance were observed in group SS with 15 days of ICM, not differing from the control group. Irrigation with NaOCl associated with ICM for 15 days presented the lowest fracture resistance; however, a statistically significant difference was not observed when compared with SS and CHX in the same time period. In longer periods of exposure to ICM (180 and 360 days), root canals irrigated with NaOCl and CHX showed significantly lower fracture resistance than SS (P < 0.05). Conclusion: Apexification with periodic changes of calcium hydroxide medicament leads to weakness of the teeth independent of the irrigation solution used.
Accepted 27 January, 2015
Immature teeth have thin and weak root walls, making them susceptible to fractures from minor impacts (1). When pulpal necrosis occurs in these teeth, root development is interrupted. Therefore, the ideal treatment option should promote apical closure and/or root development to increase fracture resistance and overall longevity of the teeth (2). Traditionally, apexification therapy has been the most widely indicated treatment for necrotic cases of immature teeth through the use of calcium hydroxide or mineral trioxide aggregate (3–5). Typically, apexification is achieved by root canal treatment with periodic changes of intracanal medication until an apical barrier is formed. This allows biologic sealing and root canal obturation of immature teeth. Although apexification is widely used, it has some associated disadvantages. These include the long duration of treatment and the requirement for many appointments (6). Furthermore, apexification involves extensive exposure to root canal dressings, which increases the © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
risk of fracture due to the weakness of root walls (6). Lastly, apexification does not induce continued root development, but rather only apical closure (6). Within the apexification protocol, bacteria elimination is provided by irrigant solutions. Studies state that some of these chemical solutions may interfere with the mechanical properties of dentinal walls (7, 8). Sodium hypochlorite is the most widely used endodontic irrigant due to its antimicrobial and tissue dissolution properties (9). However, endodontic literature reports that sodium hypochlorite may modify the dentin matrix through the degradation of organic compounds (10). In addition, high concentrations of sodium hypochlorite (3% and 5.25%) are capable of reducing the modulus of elasticity and flexural resistance of dentin, which may compromise fracture resistance of dentin wall integrity (11, 12). Chlorhexidine is another chemical substance commonly used during root canal instrumentation and has been extensively studied due to substantivity and 385
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low toxicity. This irrigant may be indicated in cases of immature teeth and represents an alternative for allergic patients to sodium hypochlorite, but it does not have the ability to perform organic tissue dissolution (13, 14). In addition, studies have shown that 2% chlorhexidine also reduces dentin microhardness (15). Besides the use of irrigant solutions, intracanal medications are commonly used to complement the disinfection of root canals and induce apical closure. Intracanal medications may also interfere with the fracture resistance of dentin walls, as they remain in direct contact with dentin for long periods of time (1). Calcium hydroxide is the most widely used intracanal medication, presenting antimicrobial action due to its high pH, as well as the capacity of inducing remineralization of periapical tissues (1). However, the literature suggests that long-term dressing with calcium hydroxide may reduce fracture resistance of radicular dentin (>60%) (16,17), and this effect is probably promoted by alterations in organic dentin matrix (1, 6). Considering these limitations, pulp revascularization has been proposed as an alternative to induce root end development and to increase fracture resistance of immature teeth (18). Both Ca(OH)2 and an antibiotic paste (e.g., metronidazole, minocycline, and ciprofloxacin) have been indicated as intracanal medications in the revascularization protocol; however, antibiotic paste has offered more encouraging results in terms of root canal wall thickening and root development (19– 23). Although revascularization has demonstrated promising outcomes, apexification still represents the most widely indicated treatment for immature teeth with pulp necrosis, and the literature shows few studies evaluating the influence of irrigant solutions and intracanal medications in fracture resistance of weakened root walls (24, 25). It is quite an important consideration based upon the widespread use of irrigants throughout endodontic treatment. The aim of this study was to evaluate the action of irrigant solutions (physiologic solution, sodium hypochlorite, and 2% chlorhexidine gel) as well as the longterm use of calcium hydroxide on the fracture resistance of weakened bovine teeth. Material and methods Specimen selection and preparation
One hundred seventy bovine incisors with similar size, shape, and the absence of cracks were selected by measuring the buccolingual and mesiodistal widths in millimeters, allowing a maximum deviation of 10% from the average (26). The teeth were cleaned in water and stored in 0.1% thymol until the beginning of the experiment. The crowns of all teeth were coronally and apically sectioned up to 10 mm from the cemento-enamel junction and at a distance of 5 mm from the most apical limit of root using a slow-speed diamond precision saw with a water coolant (Isomet 1000; Buehler, Lake Bluff, IL, USA) to simulate immature teeth. Total length of specimens was standardized at 25 mm 2 mm.
Preoperative radiographs were taken in the mesiodistal and buccolingual directions to confirm the thickness of initial dentin. All radiographs were taken with condensation silicon (3M, Sumare, Brazil) molds that were manufactured for each specimen with the buccal surface directed toward the film receptor to standardize the images. The samples were then positioned with the lingual surface directed toward the film. Radiographic positioner (Indusbello, Londrina, Brazil) was used to standardize the distance between each tooth and the radiographic equipment. Root canals were instrumented using Gates-Glidden drills sizes # 2, 3, 4, and 5 (Dentsply Maillefer, Ballaigues, Switzerland) in the cervical and middle thirds of the root canal (until 20 mm of extension), simulating immature teeth. The apical third was instrumented with manual Kerr files using an ascending order until no. 150 (Dentsply Maillefer). One hundred fifty teeth were randomly assigned into three experimental groups (n = 50 for each group) according to the tested irrigant solution: (i) sterile physiological solution (SS); (ii) 2% chlorhexidine gel (CHX); and (iii) 1% sodium hypochlorite (NaOCl). The canals were rinsed with 10 ml of the corresponding irrigant group solution between each instrument. After instrumentation, the smear layer was removed by flushing the root canals with 5 ml of 17% EDTA solution followed by irrigation with 10 ml of saline solution. The root canals were dried with sterile paper points, and intracanal medications were placed. The final radicular thickness was standardized at 2 mm 0.5 in the cervical third and at 1.5 mm 0.5 in the apical third, measured using a digital caliper (Teknikel, Istanbul, Turkey). After instrumentation and irrigation, root canals were dressed with calcium hydroxide (Biodin^ amica, Ibipor~ a, Brazil) and propilenoglycol [Ca(OH)2]. The intracanal medication (ICM) was manipulated at 1:1 proportion in creamy consistency and was inserted in the full length of root canal through the use of manual file no. 80 (Dentsply Maillefer). Mesiodistal and buccolingual radiographs were taken to confirm complete filling with intracanal medication. The root canals were evaluated in different periods of intracanal medication permanency (15, 60, 90, 180, and 360 days), with periodic changes every 30 days. During intracanal medication changes, root canals were rinsed using 10 ml of the same irrigant solution. In addition, twenty teeth were randomly selected to be assigned into two control groups: (i) without instrumentation and without intracanal medication (NI) and (ii) with instrumentation and without intracanal medication (I). Control group #2 was irrigated with saline solution, following the same instrumentation protocol as in the experimental groups. Fracture resistance
The external surfaces of the root were covered with wax 2 mm below the CEJ to the root apex to simulate a periodontal membrane. To achieve this, the roots were dipped into molten wax, resulting in a wax layer 0.2–0.3 mm thick. Afterward, the wax-covered roots were embedded in acrylic resin (Cl assico, Rio de © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Calcium hydroxide long-term use in immature teeth
periods of intracanal medication maintenance. Treatment with sterile saline solution (SS) associated with calcium hydroxide as ICM during 15 days showed the highest fracture resistance (118.78 19.16) when compared to the instrumented control group. In the same period of time, root canals irrigated with CHX (105.59 14.05) showed stronger resistance than NaOCl (89.13 23.14); however, both irrigants did not significantly differ from control group 2. In the periods of 60, 90, 180, and 360 days, a significant decrease in fracture resistance was observed for almost all analyzed groups when compared to control and to 15-day medicated groups (P < 0.05). Only SS group in 180 days (75.96 27.64) had a higher fracture resistance than the 90-day group (69.23 26.44); however, no significant difference was observed between the two. Fracture resistance values of root canals irrigated with different irrigant solutions were also compared and statistically analyzed using Tukey testing (Table 3). Root canals irrigated with SS and dressed with intracanal medication for 15 days presented stronger mean force required to fracture the roots than root canals irrigated with CHX and NaOCl. At 60 days, only group NaOCl presented significant reduction in frac-
Janeiro, Brazil) cylinders. As soon as polymerization of the acrylic resin started, the roots were removed from the resin, and the wax was cleaned from the root surfaces using a curette. The cleaned root surfaces were coated with a thin layer of polyvinylsiloxane impression material (Coltene\Whaledent AG, Altstatten, Switzerland) embedded into acrylic resin and positioned at 45° to the buccolingual long axis. A universal testing machine (Instron Corp., Canton, MA, USA) was used for the fracture resistance test. The compressive loading was applied at a speed of 1.0 mm min 1 until fracture occurred. Testing was initiated at 0 Kgf and was continuous until fracture. The fracture moment was determined when a sudden drop in force occurred that was observed on the testing machine display. The maximum force required to fracture each specimen was recorded and analyzed statistically using one-way analysis of variance with Tukey post hoc test for multiple comparisons. The level of significance was set at P < 0.05. Results
Mean values and standard deviations of the force required to fracture the roots of control groups are presented in Table 1. Root canal instrumentation decreased fracture resistance of the control group 2 (instrumented) when compared to control group 1 (no instrumentation), with significant difference. Table 2 shows the mean fracture resistance values and standard deviations for each experimental group. There was reduction in fracture resistance associated with longer
Table 3. Different periods of intracanal medication (ICM) maintenance in the groups SS. CHX and NaOCl. Mean fracture resistance values according to Tukey test (significance level of 5%)
Table 1. Control groups. Descriptive statistical data of fracture resistance (kgf) Without intracanal medication Statistic
Without instrumentation
With instrumentation
N Mean Standard deviation Minimum Median Maximum
10 109.74 A 16.13 80.94 109.05 134.45
10 93.50 B 14.27 81.05 91.08 132.16
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The same letters indicate no significant differences (P > 0.05).
ICM—time
Irrigant solution
n
Mean
Groups
15 15 15 60 60 60 90 90 90 180 180 180 360 360 360
SS CHX NaOCl SS CHX NaOCl SS CHX NaOCl SS CHX NaOCl SS CHX NaOCl
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
118.8 105.6 89.1 70.4 59.3 41.0 69.2 66.0 64.7 76.0 50.6 44.6 44.1 30.4 17.2
A AB ABC CDE CDEF EFG CDE CDE CDE BCD DEF DEFG EFG FG G
The same superscript letters indicate no significant differences (P > 0.05).
Table 2. Fracture resistance (kgf) comparing different irrigant solutions to control group (without medicament and with instrumentation) at different time periods of intracanal medication (ICM) dressing Irrigant solution ICM (days)
Control
SS
Initial 15 60 90 180 360 Total (m SD)
93.50 14.27 A
– 118.78 70.39 69.23 75.96 44.06 67.20
NaOCl
19.16 14.61 26.44 27.64 20.93 37.62
The same letters indicate no significant differences (P > 0.05). © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
A B B B B
– 89.13 41.03 64.73 50.60 17.21 55.43
CHX
23.14 A 11.57 B 20.60 B 33.50 B 7.74 B 29.59
– 105.59 59.30 66.02 44.56 30.43 66.77
14.05 A 14.04 B 23.92 B 24.08 B 8.28 B 30.13
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ture resistance when compared to group SS (P < 0.05). And in longer times of intracanal medication maintenance (180 and 360 days), root canals irrigated with NaOCl and CHX showed significantly lower fracture resistance than root canals irrigated with SS (P < 0.05). There were two fracture modes, a split vertical fracture that extended along the long axis of the root and a comminuted fracture that shattered the root into fragments. The most common fracture mode was the split vertical fracture in buccolingual direction in all groups. Discussion
The current endodontic options of treatment for immature teeth are apexification and revascularization. Both treatments are performed using intracanal medications to help with disinfection and to induce apical closure. Apexification requires a longer duration of intracanal calcium hydroxide placement and irrigant solution contact with dentinal walls to complete treatment when compared to revascularization. The literature reports show that during apexification therapy, calcium hydroxide generally remains inside the root canals between two and 12 months (27). Considering the fragility of root canal walls in immature teeth, particularly in the cervical third, it has been demonstrated that endodontic treatment may increase this weakness (28, 29). It has been reported that 60% of all endodontically treated immature teeth have suffered fractures due to minor impacts (1, 28, 29). In addition, calcium hydroxide dressings placed for long periods have resulted in 20% of root fractures (28). In the present study, it was observed that calcium hydroxide dressing for 15 days did not promote a significant reduction of fracture resistance for all irrigant solutions. However, when it remained for longer periods of time, a reduction in fracture resistance was noted. The consequences of long-term use of intracanal medication were reported in a study of luxated teeth treated with calcium hydroxide between 3 and 54 months (16). A 20% cervical root fracture rate was observed over 3.5 and 5 years of follow-up (16). This finding was also duplicated in the present study that showed a remarkable reduction in fracture resistance of teeth dressed with calcium hydroxide for periods longer than 180 days. It may be explained due to the action of calcium hydroxide to promote protein denaturation and hydrolysis of the dentin organic matrix, which may interfere with the mechanical properties of dentin (30, 31). Besides intracanal medications, irrigant solutions used in the present study also interfered with fracture resistance as some studies have shown that the microstructural organization of the organic matrix might be modified by NaOCl (29). Irrigation with NaOCl promotes damage in collagen and proteoglycans of dentin matrix with consequent reduction in the elastic modulus and fracture resistance of dentin. Thus, endodontically treated teeth irrigated with NaOCl generally present lower mechanical resistance, leading to a greater risk of fractures. In the present study, the NaOCl group that remained with intracanal medication for longer periods (60, 180, and 360 days) presented signifi-
cant reduction in fracture resistance, differing from control and SS groups. Considering the fragility of immature teeth and the observed damage produced by NaOCl in reducing root mechanical resistance, it may be suggested that a shorter duration of use, or the irrigation with alternative solutions, may help minimally interfere with the dentin collagen matrix. Chlorhexidine has also been used for root canal irrigation, due to its antimicrobial action with residual effects (32). However, in the present study, this irrigant also reduced root canal wall fracture resistance. This finding was previously reported in teeth irrigated with NaOCl or CHX, which showed decreased dentin microhardness after their use (15, 33). Despite these unfavorable features, there is no consensus regarding the influence of CHX in contact with dentin matrix at the current time. According to the results of the tested irrigant solutions, sterile physiologic solution presented lower interference with the fracture resistance of weakened roots after 15 days. Considering that both irrigant solutions and intracanal medications used during long periods may bring problems to the resistance of immature teeth, pulp revascularization has been currently studied as a promising alternative (34, 35). This therapy has promoted root development with increased root length and thickness of root walls in immature teeth (36, 37). In addition, this treatment may be concluded in a shorter timespan than apexification. Additionally, the literature has suggested that 15–30 days of calcium hydroxide intracanal dressing may be sufficient to promote the beneficial antimicrobial effects (38). Considering this information, the results of the present study demonstrated that calcium hydroxide dressing for only 15 days did not promote a significant reduction in dentin fracture resistance. Therefore, the shorter period of intracanal medication dressing required in revascularization therapy has demonstrated to be another advantage of this treatment when compared to apexification. However, further studies comparing intracanal medications and irrigant solutions used in revascularization should be designed to better define the most effective period of time for the antimicrobial action without interfering with the mechanical properties of the weakened roots. Although revascularization has been studied widely and has showed promising results, it may not be considered the first treatment choice in some world realities. The healthcare systems in developing countries generally lack the available materials and professionals that may not be in knowledgeable at the most recent studies. Apexification with periodic changes of intracanal medication may weaken root canal walls that do not indicate this therapy; however, it may still be considered the most widely performed treatment in the global population. Within the limitations of this in vitro study, it may be concluded that the use of NaOCl or CHX as irrigant solutions as well as calcium hydroxide as an intracanal medication for long-term periods may reduce the fracture resistance of weakened tooth roots. Therefore, apexification utilizing repeated placement of calcium hydroxide medicament is associated with weakening of tooth roots, independent of the irrigant solution used. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Calcium hydroxide long-term use in immature teeth Acknowledgement
The authors deny any conflict of interests.
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Fracture resistance of weakened bovine teeth after long-term use of calcium hydroxide Marcia Carneiro Valera1, Maria Tereza Pedrosa Albuquerque2, Mayra via Nicolle Cristina Yamasaki3, Fla Stefani Vassallo4, Denise Almeida e Silva Alves da Silva4, Juliana Yuri Nagata5 ~o Jose dos Campos Dental School, Sa ~o Sa ~o Jose dos Paulo State University, UNESP; 2Sa ~o Paulo State Campos Dental School, Sa University, UNESP; 3Piracicaba Dental School, ~o State University of Campinas, UNICAMP; 4Sa ~o Paulo Jose dos Campos Dental School, Sa ~o Paulo; 5Dentistry State University, UNESP, Sa Department, Endodontics Area, Federal University of Sergipe, Lagarto, Brazil 1
Key words: calcium hydroxide; fracture resistance; irrigant solution; permanent tooth; root fracture; prognosis Correspondence to: Marcia Carneiro Valera, ~o Jose dos Faculdade de Odontologia de Sa Campos, UNESP - Institute of Science and ~o Jose dos Campos, SP Technology, 777 Sa CEP 12-245-000, Brazil Tel.: +55-12-39238902 e-mail: [email protected]
Abstract – Background/Aim: In some parts of the world, revascularization may not be the most feasible treatment option for necrotic immature teeth. Therefore, apexification remains the most widely utilized treatment option for these cases. This study aimed to evaluate the fracture resistance of weakened bovine tooth roots treated with various irrigant solutions as well as long-term application of calcium hydroxide intracanal medication (ICM). Material and methods: One hundred seventy bovine teeth were randomly divided into three experimental groups (n = 50) and two control groups (n = 10). Group SS was irrigated with physiologic solution; group CHX was treated with 2% chlorhexidine gel and group NaOCl was irrigated with 1% sodium hypochlorite. After instrumentation, root canals were dressed with calcium hydroxide and evaluated at different periods (15, 60, 90, 180, and 360 days). The specimens were loaded at a 45° angle to measure fracture resistance through the use of an EMIC test machine. Results: A decrease in fracture resistance was observed during the time of ICM dressing. The highest values of fracture resistance were observed in group SS with 15 days of ICM, not differing from the control group. Irrigation with NaOCl associated with ICM for 15 days presented the lowest fracture resistance; however, a statistically significant difference was not observed when compared with SS and CHX in the same time period. In longer periods of exposure to ICM (180 and 360 days), root canals irrigated with NaOCl and CHX showed significantly lower fracture resistance than SS (P < 0.05). Conclusion: Apexification with periodic changes of calcium hydroxide medicament leads to weakness of the teeth independent of the irrigation solution used.
Accepted 27 January, 2015
Immature teeth have thin and weak root walls, making them susceptible to fractures from minor impacts (1). When pulpal necrosis occurs in these teeth, root development is interrupted. Therefore, the ideal treatment option should promote apical closure and/or root development to increase fracture resistance and overall longevity of the teeth (2). Traditionally, apexification therapy has been the most widely indicated treatment for necrotic cases of immature teeth through the use of calcium hydroxide or mineral trioxide aggregate (3–5). Typically, apexification is achieved by root canal treatment with periodic changes of intracanal medication until an apical barrier is formed. This allows biologic sealing and root canal obturation of immature teeth. Although apexification is widely used, it has some associated disadvantages. These include the long duration of treatment and the requirement for many appointments (6). Furthermore, apexification involves extensive exposure to root canal dressings, which increases the © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
risk of fracture due to the weakness of root walls (6). Lastly, apexification does not induce continued root development, but rather only apical closure (6). Within the apexification protocol, bacteria elimination is provided by irrigant solutions. Studies state that some of these chemical solutions may interfere with the mechanical properties of dentinal walls (7, 8). Sodium hypochlorite is the most widely used endodontic irrigant due to its antimicrobial and tissue dissolution properties (9). However, endodontic literature reports that sodium hypochlorite may modify the dentin matrix through the degradation of organic compounds (10). In addition, high concentrations of sodium hypochlorite (3% and 5.25%) are capable of reducing the modulus of elasticity and flexural resistance of dentin, which may compromise fracture resistance of dentin wall integrity (11, 12). Chlorhexidine is another chemical substance commonly used during root canal instrumentation and has been extensively studied due to substantivity and 385
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low toxicity. This irrigant may be indicated in cases of immature teeth and represents an alternative for allergic patients to sodium hypochlorite, but it does not have the ability to perform organic tissue dissolution (13, 14). In addition, studies have shown that 2% chlorhexidine also reduces dentin microhardness (15). Besides the use of irrigant solutions, intracanal medications are commonly used to complement the disinfection of root canals and induce apical closure. Intracanal medications may also interfere with the fracture resistance of dentin walls, as they remain in direct contact with dentin for long periods of time (1). Calcium hydroxide is the most widely used intracanal medication, presenting antimicrobial action due to its high pH, as well as the capacity of inducing remineralization of periapical tissues (1). However, the literature suggests that long-term dressing with calcium hydroxide may reduce fracture resistance of radicular dentin (>60%) (16,17), and this effect is probably promoted by alterations in organic dentin matrix (1, 6). Considering these limitations, pulp revascularization has been proposed as an alternative to induce root end development and to increase fracture resistance of immature teeth (18). Both Ca(OH)2 and an antibiotic paste (e.g., metronidazole, minocycline, and ciprofloxacin) have been indicated as intracanal medications in the revascularization protocol; however, antibiotic paste has offered more encouraging results in terms of root canal wall thickening and root development (19– 23). Although revascularization has demonstrated promising outcomes, apexification still represents the most widely indicated treatment for immature teeth with pulp necrosis, and the literature shows few studies evaluating the influence of irrigant solutions and intracanal medications in fracture resistance of weakened root walls (24, 25). It is quite an important consideration based upon the widespread use of irrigants throughout endodontic treatment. The aim of this study was to evaluate the action of irrigant solutions (physiologic solution, sodium hypochlorite, and 2% chlorhexidine gel) as well as the longterm use of calcium hydroxide on the fracture resistance of weakened bovine teeth. Material and methods Specimen selection and preparation
One hundred seventy bovine incisors with similar size, shape, and the absence of cracks were selected by measuring the buccolingual and mesiodistal widths in millimeters, allowing a maximum deviation of 10% from the average (26). The teeth were cleaned in water and stored in 0.1% thymol until the beginning of the experiment. The crowns of all teeth were coronally and apically sectioned up to 10 mm from the cemento-enamel junction and at a distance of 5 mm from the most apical limit of root using a slow-speed diamond precision saw with a water coolant (Isomet 1000; Buehler, Lake Bluff, IL, USA) to simulate immature teeth. Total length of specimens was standardized at 25 mm 2 mm.
Preoperative radiographs were taken in the mesiodistal and buccolingual directions to confirm the thickness of initial dentin. All radiographs were taken with condensation silicon (3M, Sumare, Brazil) molds that were manufactured for each specimen with the buccal surface directed toward the film receptor to standardize the images. The samples were then positioned with the lingual surface directed toward the film. Radiographic positioner (Indusbello, Londrina, Brazil) was used to standardize the distance between each tooth and the radiographic equipment. Root canals were instrumented using Gates-Glidden drills sizes # 2, 3, 4, and 5 (Dentsply Maillefer, Ballaigues, Switzerland) in the cervical and middle thirds of the root canal (until 20 mm of extension), simulating immature teeth. The apical third was instrumented with manual Kerr files using an ascending order until no. 150 (Dentsply Maillefer). One hundred fifty teeth were randomly assigned into three experimental groups (n = 50 for each group) according to the tested irrigant solution: (i) sterile physiological solution (SS); (ii) 2% chlorhexidine gel (CHX); and (iii) 1% sodium hypochlorite (NaOCl). The canals were rinsed with 10 ml of the corresponding irrigant group solution between each instrument. After instrumentation, the smear layer was removed by flushing the root canals with 5 ml of 17% EDTA solution followed by irrigation with 10 ml of saline solution. The root canals were dried with sterile paper points, and intracanal medications were placed. The final radicular thickness was standardized at 2 mm 0.5 in the cervical third and at 1.5 mm 0.5 in the apical third, measured using a digital caliper (Teknikel, Istanbul, Turkey). After instrumentation and irrigation, root canals were dressed with calcium hydroxide (Biodin^ amica, Ibipor~ a, Brazil) and propilenoglycol [Ca(OH)2]. The intracanal medication (ICM) was manipulated at 1:1 proportion in creamy consistency and was inserted in the full length of root canal through the use of manual file no. 80 (Dentsply Maillefer). Mesiodistal and buccolingual radiographs were taken to confirm complete filling with intracanal medication. The root canals were evaluated in different periods of intracanal medication permanency (15, 60, 90, 180, and 360 days), with periodic changes every 30 days. During intracanal medication changes, root canals were rinsed using 10 ml of the same irrigant solution. In addition, twenty teeth were randomly selected to be assigned into two control groups: (i) without instrumentation and without intracanal medication (NI) and (ii) with instrumentation and without intracanal medication (I). Control group #2 was irrigated with saline solution, following the same instrumentation protocol as in the experimental groups. Fracture resistance
The external surfaces of the root were covered with wax 2 mm below the CEJ to the root apex to simulate a periodontal membrane. To achieve this, the roots were dipped into molten wax, resulting in a wax layer 0.2–0.3 mm thick. Afterward, the wax-covered roots were embedded in acrylic resin (Cl assico, Rio de © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Calcium hydroxide long-term use in immature teeth
periods of intracanal medication maintenance. Treatment with sterile saline solution (SS) associated with calcium hydroxide as ICM during 15 days showed the highest fracture resistance (118.78 19.16) when compared to the instrumented control group. In the same period of time, root canals irrigated with CHX (105.59 14.05) showed stronger resistance than NaOCl (89.13 23.14); however, both irrigants did not significantly differ from control group 2. In the periods of 60, 90, 180, and 360 days, a significant decrease in fracture resistance was observed for almost all analyzed groups when compared to control and to 15-day medicated groups (P < 0.05). Only SS group in 180 days (75.96 27.64) had a higher fracture resistance than the 90-day group (69.23 26.44); however, no significant difference was observed between the two. Fracture resistance values of root canals irrigated with different irrigant solutions were also compared and statistically analyzed using Tukey testing (Table 3). Root canals irrigated with SS and dressed with intracanal medication for 15 days presented stronger mean force required to fracture the roots than root canals irrigated with CHX and NaOCl. At 60 days, only group NaOCl presented significant reduction in frac-
Janeiro, Brazil) cylinders. As soon as polymerization of the acrylic resin started, the roots were removed from the resin, and the wax was cleaned from the root surfaces using a curette. The cleaned root surfaces were coated with a thin layer of polyvinylsiloxane impression material (Coltene\Whaledent AG, Altstatten, Switzerland) embedded into acrylic resin and positioned at 45° to the buccolingual long axis. A universal testing machine (Instron Corp., Canton, MA, USA) was used for the fracture resistance test. The compressive loading was applied at a speed of 1.0 mm min 1 until fracture occurred. Testing was initiated at 0 Kgf and was continuous until fracture. The fracture moment was determined when a sudden drop in force occurred that was observed on the testing machine display. The maximum force required to fracture each specimen was recorded and analyzed statistically using one-way analysis of variance with Tukey post hoc test for multiple comparisons. The level of significance was set at P < 0.05. Results
Mean values and standard deviations of the force required to fracture the roots of control groups are presented in Table 1. Root canal instrumentation decreased fracture resistance of the control group 2 (instrumented) when compared to control group 1 (no instrumentation), with significant difference. Table 2 shows the mean fracture resistance values and standard deviations for each experimental group. There was reduction in fracture resistance associated with longer
Table 3. Different periods of intracanal medication (ICM) maintenance in the groups SS. CHX and NaOCl. Mean fracture resistance values according to Tukey test (significance level of 5%)
Table 1. Control groups. Descriptive statistical data of fracture resistance (kgf) Without intracanal medication Statistic
Without instrumentation
With instrumentation
N Mean Standard deviation Minimum Median Maximum
10 109.74 A 16.13 80.94 109.05 134.45
10 93.50 B 14.27 81.05 91.08 132.16
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The same letters indicate no significant differences (P > 0.05).
ICM—time
Irrigant solution
n
Mean
Groups
15 15 15 60 60 60 90 90 90 180 180 180 360 360 360
SS CHX NaOCl SS CHX NaOCl SS CHX NaOCl SS CHX NaOCl SS CHX NaOCl
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
118.8 105.6 89.1 70.4 59.3 41.0 69.2 66.0 64.7 76.0 50.6 44.6 44.1 30.4 17.2
A AB ABC CDE CDEF EFG CDE CDE CDE BCD DEF DEFG EFG FG G
The same superscript letters indicate no significant differences (P > 0.05).
Table 2. Fracture resistance (kgf) comparing different irrigant solutions to control group (without medicament and with instrumentation) at different time periods of intracanal medication (ICM) dressing Irrigant solution ICM (days)
Control
SS
Initial 15 60 90 180 360 Total (m SD)
93.50 14.27 A
– 118.78 70.39 69.23 75.96 44.06 67.20
NaOCl
19.16 14.61 26.44 27.64 20.93 37.62
The same letters indicate no significant differences (P > 0.05). © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
A B B B B
– 89.13 41.03 64.73 50.60 17.21 55.43
CHX
23.14 A 11.57 B 20.60 B 33.50 B 7.74 B 29.59
– 105.59 59.30 66.02 44.56 30.43 66.77
14.05 A 14.04 B 23.92 B 24.08 B 8.28 B 30.13
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ture resistance when compared to group SS (P < 0.05). And in longer times of intracanal medication maintenance (180 and 360 days), root canals irrigated with NaOCl and CHX showed significantly lower fracture resistance than root canals irrigated with SS (P < 0.05). There were two fracture modes, a split vertical fracture that extended along the long axis of the root and a comminuted fracture that shattered the root into fragments. The most common fracture mode was the split vertical fracture in buccolingual direction in all groups. Discussion
The current endodontic options of treatment for immature teeth are apexification and revascularization. Both treatments are performed using intracanal medications to help with disinfection and to induce apical closure. Apexification requires a longer duration of intracanal calcium hydroxide placement and irrigant solution contact with dentinal walls to complete treatment when compared to revascularization. The literature reports show that during apexification therapy, calcium hydroxide generally remains inside the root canals between two and 12 months (27). Considering the fragility of root canal walls in immature teeth, particularly in the cervical third, it has been demonstrated that endodontic treatment may increase this weakness (28, 29). It has been reported that 60% of all endodontically treated immature teeth have suffered fractures due to minor impacts (1, 28, 29). In addition, calcium hydroxide dressings placed for long periods have resulted in 20% of root fractures (28). In the present study, it was observed that calcium hydroxide dressing for 15 days did not promote a significant reduction of fracture resistance for all irrigant solutions. However, when it remained for longer periods of time, a reduction in fracture resistance was noted. The consequences of long-term use of intracanal medication were reported in a study of luxated teeth treated with calcium hydroxide between 3 and 54 months (16). A 20% cervical root fracture rate was observed over 3.5 and 5 years of follow-up (16). This finding was also duplicated in the present study that showed a remarkable reduction in fracture resistance of teeth dressed with calcium hydroxide for periods longer than 180 days. It may be explained due to the action of calcium hydroxide to promote protein denaturation and hydrolysis of the dentin organic matrix, which may interfere with the mechanical properties of dentin (30, 31). Besides intracanal medications, irrigant solutions used in the present study also interfered with fracture resistance as some studies have shown that the microstructural organization of the organic matrix might be modified by NaOCl (29). Irrigation with NaOCl promotes damage in collagen and proteoglycans of dentin matrix with consequent reduction in the elastic modulus and fracture resistance of dentin. Thus, endodontically treated teeth irrigated with NaOCl generally present lower mechanical resistance, leading to a greater risk of fractures. In the present study, the NaOCl group that remained with intracanal medication for longer periods (60, 180, and 360 days) presented signifi-
cant reduction in fracture resistance, differing from control and SS groups. Considering the fragility of immature teeth and the observed damage produced by NaOCl in reducing root mechanical resistance, it may be suggested that a shorter duration of use, or the irrigation with alternative solutions, may help minimally interfere with the dentin collagen matrix. Chlorhexidine has also been used for root canal irrigation, due to its antimicrobial action with residual effects (32). However, in the present study, this irrigant also reduced root canal wall fracture resistance. This finding was previously reported in teeth irrigated with NaOCl or CHX, which showed decreased dentin microhardness after their use (15, 33). Despite these unfavorable features, there is no consensus regarding the influence of CHX in contact with dentin matrix at the current time. According to the results of the tested irrigant solutions, sterile physiologic solution presented lower interference with the fracture resistance of weakened roots after 15 days. Considering that both irrigant solutions and intracanal medications used during long periods may bring problems to the resistance of immature teeth, pulp revascularization has been currently studied as a promising alternative (34, 35). This therapy has promoted root development with increased root length and thickness of root walls in immature teeth (36, 37). In addition, this treatment may be concluded in a shorter timespan than apexification. Additionally, the literature has suggested that 15–30 days of calcium hydroxide intracanal dressing may be sufficient to promote the beneficial antimicrobial effects (38). Considering this information, the results of the present study demonstrated that calcium hydroxide dressing for only 15 days did not promote a significant reduction in dentin fracture resistance. Therefore, the shorter period of intracanal medication dressing required in revascularization therapy has demonstrated to be another advantage of this treatment when compared to apexification. However, further studies comparing intracanal medications and irrigant solutions used in revascularization should be designed to better define the most effective period of time for the antimicrobial action without interfering with the mechanical properties of the weakened roots. Although revascularization has been studied widely and has showed promising results, it may not be considered the first treatment choice in some world realities. The healthcare systems in developing countries generally lack the available materials and professionals that may not be in knowledgeable at the most recent studies. Apexification with periodic changes of intracanal medication may weaken root canal walls that do not indicate this therapy; however, it may still be considered the most widely performed treatment in the global population. Within the limitations of this in vitro study, it may be concluded that the use of NaOCl or CHX as irrigant solutions as well as calcium hydroxide as an intracanal medication for long-term periods may reduce the fracture resistance of weakened tooth roots. Therefore, apexification utilizing repeated placement of calcium hydroxide medicament is associated with weakening of tooth roots, independent of the irrigant solution used. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Calcium hydroxide long-term use in immature teeth Acknowledgement
The authors deny any conflict of interests.
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