|Year : 2020 | Volume
| Issue : 3 | Page : 130-136
Influence of access cavity design on the fracture resistance and root canal filling efficacy in simulated young permanent molars using cone-beam computed tomography: An in vitro study
N Greeshma Reddy, Sreebala G Naga, MG Manoj Kumar, NC H Srinivas, Shanthan Mettu, Dwitha Animireddy
Department of Pedodontics and Preventive Dentistry, Panineeya Institute of Dental Science and Hospital, Hyderabad, Telangana, India
|Date of Submission||13-Mar-2020|
|Date of Decision||05-Apr-2020|
|Date of Acceptance||14-Jun-2020|
|Date of Web Publication||28-Oct-2020|
Dr. N Greeshma Reddy
Road Number 5, VR Colony, Kamala Nagar, Kothapet, Hyderabad - 500 060, Telangana
Source of Support: None, Conflict of Interest: None
Aims: The aim of this study is to evaluate the influence of access cavity designs on the fracture resistance and root canal filling efficacy of simulated young permanent molars.
Methodology: A total of seventy human unerupted impacted mandibular third molar teeth were collected. Ten were allocated as control; the remaining were designated as experimental, which were divided into three groups (20 each) based on access cavity design. All the samples were exposed to cone-beam computed tomography (CBCT) scanner before the access cavity preparation. Group I-The control group. Group IIa-traditional endodontic cavity (TEC), Group IIb-conservative endodontic cavity (CEC), Group IIc-ninja endodontic cavity (NEC). Endodontic access cavities were prepared and exposed to CBCT. Pre- and post-treatment percentage volumes of lost pericervical dentin were evaluated. Then the root canals were filled with calcium hydroxide and subjected to CBCT imaging for the evaluation of root canal filling efficacy. Evaluation of fracture resistance was carried out using a universal testing machine.
Results: On observation, the volume of lost pericervical dentin was (14.8%) in TEC, (8.3%) in CEC and (6.8%) in NEC. There was no statistically significant difference (P > 0.05) between all the groups on root canal filling efficacy and the number of voids. Fracture resistance of the NEC and control group (P > 0.05) was greater compared to CEC and TEC.
Conclusion: NEC is the accepted method that had better fracture resistance, with a minimum number of voids in the coronal and middle third of the root and had adequate apical seal compared to conservative and TECs.
Keywords: Access cavity designs, calcium hydroxide, conservative endodontic cavity, fracture resistance, ninja, traditional endodontic cavity, young permanent teeth
|How to cite this article:|
Reddy N G, Naga SG, Manoj Kumar M G, H Srinivas N C, Mettu S, Animireddy D. Influence of access cavity design on the fracture resistance and root canal filling efficacy in simulated young permanent molars using cone-beam computed tomography: An in vitro study. Endodontology 2020;32:130-6
|How to cite this URL:|
Reddy N G, Naga SG, Manoj Kumar M G, H Srinivas N C, Mettu S, Animireddy D. Influence of access cavity design on the fracture resistance and root canal filling efficacy in simulated young permanent molars using cone-beam computed tomography: An in vitro study. Endodontology [serial online] 2020 [cited 2021 Jan 20];32:130-6. Available from: https://www.endodontologyonweb.org/text.asp?2020/32/3/130/299287
| Introduction|| |
Pulp necrosis is a frequent complication of dental caries and trauma in immature permanent teeth. The endodontic treatment of these teeth is often complicated. The most important goal in endodontic treatment of young permanent teeth is to induce or create a barrier by placing a medicament, which later will be obturated and given permanent restoration. However, due to nonvitality, the tooth structure becomes brittle, and the resistance of the crown to masticatory force decreases, resulting in fracture of the crown.
Several treatments have been described in order to achieve apical closure. One of them is apexification, and it was first reported by Kaiser and Frank in 1964. The important objective of apexification is to allow apical closure and promote apical healing. To increase the resistance of these immature permanent teeth to fracture, minimal invasive access cavity designs have been introduced, which focuses on the preservation of the pericervical dentin, which is defined as the dentin 4 mm above and 6 mm below the alveolar crest.
The traditional endodontic cavity (TEC) has been introduced several decades before and followed till date. TEC emphasizes straight-line pathways into root canals to increase preparation efficacy and also prevents procedural error.
In recent years, Clark and Khademi have described minimally invasive endodontic cavities or conservative endodontic cavity (CEC), emphasizing the importance of preserving the tooth structure, including peri-cervical dentin. It involves the preservation of the pulp chamber roof and pericervical dentin.
Following this concept, an extremely conservative approach has recently been proposed, which is conventionally known as “Ninja.” This technique may improve the fracture strength of endodontically treated teeth.
Minimal invasive access cavity designs were:
- Conservative endodontic cavity (CEC)
- Ultra-conservative endodontic cavity or “Ninja” cavity (NEC).
Fracture resistance of different access cavity designs following root canal treatment was studied extensively in the literature, but limited research was focused on the evaluation on conservative endodontic cavities and ultra-conservative endodontic cavity (Ninja) to assess the root canal filling efficacy of immature teeth as well as the fracture resistance. The present study was conducted to evaluate pericervical dentin lost, root canal filling efficacy, and fracture resistance with different access cavity designs on simulated immature teeth.
| Methodology|| |
A total of 70 human unerupted impacted mandibular third molar tooth of mean age (22 ± 3 years) was collected for the study. Samples were thoroughly cleaned of its debris, calculus, and soft tissues using an ultrasonic scaler and stored in 0.1% Thymol solution until the study was conducted to avoid dehydration. Samples were observed under a stereomicroscope for the presence of cracks, teeth with cracks were discarded. The following criteria were considered for selecting 70 teeth to be included in the study.
- Intact unerupted impacted mandibular third molars
- Two separate roots.
- Presence of caries.
- Presence of previous restorations
- Presence of cracks
- Visible fracture lines
- Fused roots
- Presence of developmental defects.
Preparation of samples
Seventy extracted samples were sectioned at the apex for about 2 mm with a diamond disc to simulate the immature apex. This preparation helped in the homogeneity of the samples in all the groups.
After the simulation of the teeth, the samples were divided into four groups [Figure 1].
- Group I-control group (n = 10)
- Group IIa-TEC (n = 20)
- Group IIb-conservative endodontic cavity-CEC (n = 20)
- Group IIc-NEC (n = 20).
All the samples were mounted on an arch-shaped modeling wax and were scanned using cone-beam computed tomography (CBCT) before the access cavity preparation.
Access cavities of all the samples were prepared under operating loupes.
Before the access cavity preparation, outlines of the different access cavity designs were marked on the teeth of each group using a black marker pen. Access cavities of all the teeth were drilled with #856 diamond burs mounted on high-speed handpiece with water coolant.
Preparation of teeth in the TEC group involves straight-line pathways achieved by removal of much amount of dentine, flaring of canals' orifices. Thus, TEC preparation increases efficacy and also prevents procedural error.
In the CEC group, teeth were accessed at the mesial quarter of the central fossa and extended apically and distally while maintaining a part of the chamber roof. Circumferential pericervical dentin removal was minimized to ensure the maintenance of the part of the chamber roof. It also localizes all the canal orifices from the same visual angulations.
In the NEC group, the cavity was opened by using a number #1014 diamond round bur perpendicularly at the deepest point of the occlusal surface. Then, when the pulp chamber was reached, the cavity was slightly expanded, buccolingually using a fissure bur. The mesiodistal length of the cavity was set to 2 mm; meanwhile, the buccolingual length of the cavity was 3 mm. The “Ninja” access outline was derived from the oblique projection toward the central fossa of the root canal orifices on the occlusal plane.
After access cavity preparation, no-10 K file was used to locate the canals, and pulp extirpation was done using barbed broaches, irrigated with 5 ml of 5.25% sodium hypochlorite and 5 ml of 17% ethylene diamine tetraacetic acid (EDTA) solution followed by final irrigation with saline. Balvedi et al. suggested removal of the smear layer enhances the mechanical bond between intracanal dressing (calcium hydroxide) and root canal dentin. Hence, the removal of the smear layer was carried out using a 17% EDTA solution. Biomechanical preparation was performed using 6% Endodontic ProTaper file (Dentsply, Switzerland) up to size F3 (25 mm), 2 mm beyond the apex to simulate to the immature apex.
Teeth in TEC, CEC, and NEC were imaged using the CBCT scanner after preparation, and the scans were used to assess different outlines compared with teeth without preparation.
The volume percentage of coronal enamel and dentin lost by TEC, CEC and NEC access cavities was calculated by subtracting the total enamel and dentin crown volume for each tooth type using Insert (On Demand 3D™ software, Daejeon, Korea).
All the samples were dried with paper points and filled with calcium hydroxide and Barium Sulphate in 9:1 ratio mixed with glycerin to form a thick paste to enhance the radiopacity of calcium hydroxide. This paste was carried in 2 ml disposable syringe, and the material was expressed into the canals. The needle was gradually withdrawn from the canal. The coronal access was then restored with Glass Ionomer Cement (type IX) (GC corporation Tokyo, Japan).
The samples, after filling with calcium hydroxide, were exposed to CBCT. Root canal filling efficacy was assessed by the presence of voids in coronal, middle, and apical one-third of each filled root canal.
Seventy samples of all the groups (TEC, CEC, NEC, and CONTROL) were embedded in self-cure acrylic resin up to 2 mm apical to cement-enamel junction using a plastic pipe of 2.5 cm diameter and 20 mm height as a mold. These samples were then subjected to fracture load using universal testing machine. The teeth were loaded at the central fossa at 30° angle from the long axis of the tooth. The continuous compressive force at a crosshead speed of 0.5 mm/min was applied using 8 mm diameter compressive head. The load at which the teeth were fractured was indicated by the software of the testing machine and was recorded in Newtons.
| Results|| |
The mean volume of lost peri-cervical dentin was greater in TEC (14.8%), followed by CEC (8.3%) and NEC (6.8%) [Table 1] and [Graph 1]. The mean load at which fracture occurred was greater in control (2710.3N), followed by NEC (2631.75N), CEC (2150.15N), and TEC had the least resistance to fracture (1835.55N). On inter-group comparison using post hoc Tukey test, a statistically significant difference was observed between all the groups [Table 2] and [Graph 2]. Quality of apical seal and the presence of the mean number of voids were evaluated. When the data were tabulated and analyzed using the Chi-square test, no significant difference on quality of the apical seal was observed. When the number of voids was compared statistically significant difference was observed between TEC and NEC (P < 0.02) [Table 3], [Table 4] and [Graph 3], [Graph 4]. On comparison of the presence of voids in the coronal and middle third of the root by one-way analysis of variance, there was no statistically significant difference (F = 2.24423, P-0.115297) [Table 5].
|Table 1: Comparison of the volume difference in the coronal area with different access cavity designs|
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|Table 2: Intergroup comparison of load at fracture (post hoc Tukey test)|
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|Table 3: Comparison of the quality of apical seal between the three groups by Chi-square test|
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|Table 4: Comparison of mean number of voids between the three groups by Chi-square test|
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|Table 5: Comparison of presence of voids in coronal and middle third of the root between the three groups by one way ANOVA|
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| Discussion|| |
The completion of root development and closure of the apex occurs up to 3 years after the eruption of the tooth. The treatment of pulpal injury during this period provides a significant challenge for the clinician.
Endodontically treated immature teeth are susceptible to fracture depending on their stage of root development, which is directly related to the remaining dentin wall thickness and root length. Therefore, it is important to retain more pericervical dentin, which in turn reinforces the root canal walls of the immature teeth.
Access cavity preparation is considered as a fundamental step in orthograde endodontic treatment. Appropriate access may promote canal detection and enhance instrumentation efficacy by avoiding coronal interferences.
Recently, researchers and clinicians have designed various endodontic access cavity types with minimally invasive therapy. These techniques are aimed at maintaining a sufficient thickness of pericervical dentin. Preservation of pericervical dentin plays an important role in providing ferrule effect and to increase fracture resistance.
The procedure followed for different access cavity preparations and for calculation of the volume of peri-cervical dentin in the present study was described by Plotino et al. The volume percentage of coronal enamel and lost dentin by TEC, CEC, and NEC access cavities were calculated by subtracting the total enamel and dentin crown volume for each tooth type using (CBCT) OnDemand 3D™ software.
It was observed that the mean volume of pericervical dentin lost was greater in TEC (14.8%), followed by CEC (8.3%) and then NEC (6.8%), which is in accordance with the study conducted by Plotino et al. This would be attributed to the fact that TEC resulted in greater loss of tooth structure.
A study conducted by Krishan et al. compared the volume of peri-cervical dentin lost for TEC and CEC groups. He concluded that the mean volume of peri-cervical dentin lost was least in premolars and greatest in molars, ranging from 8.24 ± 1.64 mm 3 (premolars with CEC) to 67.71 ± 14.12 mm 3 (molars with TEC). The results of this study were in accordance with the present study.
Calcium hydroxide remains the compound of choice because of its superior activity and reduced cytotoxicity to the peri-radicular tissues, and it was introduced into dentistry by Hermann in 1930, who confirmed its preference for intracanal use. A major factor in the therapeutic success of Calcium hydroxide is its antibacterial activity.[ 4]
According to Silva (1988), the high molecular weight of the vehicles minimizes the dispersion of calcium hydroxide into the tissue and maintains the paste in the desired area for longer intervals. As a viscous vehicle containing paste may remain within the root canal for a 2–4 month interval, the number of appointments and re-dressings of the root canal is drastically reduced. To increase the rate of dispersion of calcium hydroxide, it is mixed with glycerine. Glycerine in the mix prolongs the action of the paste, and Ca 2 and OH − ions will be given off at lower velocity. Calcium hydroxide is mixed with barium sulfate to enhance the radio-opacity. This enables to assess the filling efficacy effectively.
The first use of calcium hydroxide paste with glycerine in its formula was reported by Steiner et al. (1968). The use of glycerine had extended the dissociation time. Hence, it was employed for root-end closure of immature nonvital teeth.
A study conducted by Staehle et al. compared the three methods, i.e., lentulospiral, disposable syringe system, and endodontic reamer for delivering calcium hydroxide paste into root canals. The quality of the fillings was assessed radiographically and through ground sections, it was concluded that the syringe system yielded better results with respect to the degree of completeness of filling and the porosities, both radiographically and in the ground sections.
Hence to overcome the risk of fracture due to the prolonged treatment time of apical closure with calcium hydroxide in immature teeth, conservative or minimal access designs were introduced to increase the fracture resistance. However, the main disadvantage with this type of minimal access cavity design is inadequate filling efficacy of the canal space. Hence, this study evaluated the filling efficacy with different access cavity designs.
In the present study, a comparison of quality of apical seal was made by (CBCT) On-Demand 3D App ™ software. It was observed that TEC (n = 20) had 5 underfilled teeth, 15 optimal filled teeth, CEC (n = 20) had 10 underfilled teeth, 10 optimal filled teeth, NEC (n = 20) had 11 underfilled teeth, 9 optimal filled teeth. On intergroup comparison of quality of apical seal using Chi-square test, no statistically significant difference was observed among all the three groups (P-0.121959). However, the filling efficacy of root canals was better in TEC compared to CEC and NEC. This might be due to the straight-line axis to all the canals.
On comparison of the presence of voids, NEC (16) had a greater number of voids, followed by CEC (15) and TEC (6). On intergroup comparison using Chi-square test, a statistically significant difference was observed between TEC and NEC (P < 0.02). However, there was no statistically significant difference when TEC and CEC, CEC, and NEC. This could be because TEC design attributed to greater tooth removal for better access to the canals.
In the present study, a comparison of the presence of voids in the coronal and middle third of the root was also evaluated. There was no statistically significant difference observed amongst three groups with respect to the mean number of voids present in the coronal and middle third of the root (F=2.24, P=0.11).
Another parameter evaluated in the present study is fracture resistance; Instron universal testing machine was used to measure tooth fracture resistance because the use of this machine is the simplest and most frequently used method.
According to the findings of the present study, there was a statistically significant difference in the fracture strengths of TEC (1835.556N) and CEC (2150.15N) (P > 0.05). This could be due to more removal of tooth structure in TEC than CEC. Similarly, Plotino et al. found that the fracture strength of teeth prepared with the TEC (733N) was significantly lower than that of teeth prepared with the CEC (1073N) and the NEC (1094N), which is in accordance with the findings of the present study.
Similar findings were observed in a study conducted by Krishan et al., where the fracture load was significantly higher for CEC (1586N) than TEC (641N). In this study, the NEC cavity was not evaluated, and the other tooth types such as (incisors, premolars, and molars) were compared in the study.
However, a study conducted by Moore et al. and Rover et al. found no significant difference in fracture resistance between the TEC (1384N, 937.55N) and CEC (1703N, 996.30N) preparation methods, respectively, which is in contrast to the present study. The differences among various studies could be related to differences in the methodological design, including the type of teeth considered, the use of restoration, the type of material used for restorative procedures, and methodological issues related to the design of the fracture test and cyclic fatigue.
In the present study, the value of fracture resistance of the control group (2710.3N) and NEC (2631.75N) have shown no statistically significant difference, which could be due to minimal tooth structure loss in the preparation of NEC.
| Conclusion|| |
Within the limitations of this study, it could be concluded that minimal invasive endodontic access cavities such as CEC and NEC not only showed greater fracture resistance than TEC but also had an almost same root canal filling efficacy as TEC. Hence, NEC and CEC could be considered as better procedures for endodontic treatment in immature teeth. However, further clinical studies are necessary to determine the effect of root canal filling efficacy and instrumentation efficacy, difficulties during endodontic procedures, and long-term prognosis of endodontically treated immature permanent teeth with minimal access cavity preparations.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]