Simulated Periodontal Ligament Research Articles

Food impaction on three-dimensional printed models with periodontal ligament simulation.

This study aims to evaluate food impaction on three-dimensional (3D) printed models with periodontal ligament simulation. Based on a commercial typodont pair, 3D maxillary and mandibular models were created with no teeth and with tooth sockets that were 1 mm wider than the original ones from 24 to 27 or 34 to 37 for periodontal ligament simulation with vinyl polysiloxane impression material. In total, 35 pairs of 7 combinations, including maxillary/mandibular typodonts in occlusion with maxillary/mandibular 3D models with/without a distal gap of canines on 3D models (tooth 23 or 33) were mounted on hinge articulators and divided into seven groups (n = 5). Each sample experienced the same manual chewing simulation on a customized device. The proximal surfaces were photographed to measure the percentage of food impaction area using ImageJ software. Group with fixed maxillary and mandibular teeth showed more food impaction than other groups with significant differences in the average of maxilla and the average of all proximal areas. The flexibility of the periodontal ligament and the degree of freedom of the teeth in their sockets may contribute to the extent of food impaction in proximal spaces.

An in vitro evaluation of dentinal microcrack formation during root canal preparations by three different nickel–titanium systems: ProTaper Gold, HyFlex CM, and Silk

Aim: This study aimed to compare the frequency of dentinal microcracks after root canal shaping with three different nickel–titanium (NiTi) systems, namely, ProTaper Gold (PG), HyFlex CM (HCM), and Silk. Methods: One hundred mandibular premolars with a single canal were chosen for this study. All specimens were decoronated and divided into four groups of 25 each. Teeth were mounted in the acrylic block with simulated periodontal ligaments. Group I served as a negative control Group, in which no treatment was performed. Biomechanical preparation was done in the Group II, using the Protaper gold file system. Group III, using the Hyflex CM file system and Group IV, using the Silk file system. Specimens were horizontally sectioned at 3, 6, and 9 mm from the apex using the low-speed diamond disc under water cooling. The slices were then viewed under a stereomicroscope at ×25 to determine the presence of cracks. The absence or presence of cracks was recorded, and the data were analyzed with a Chi-square test. The significance level was set at P < 0.05. Results: Coronal section showed lesser crack formation in all three groups after biomechanical preparation. More number of dentinal microcracks were seen in the apical sections, followed by the middle and the coronal sections in Group II (PG), followed by Group IV (Silk), and Group III (HCM), respectively. Group II showed more microcracks at all three levels of the root canals when compared with Groups III and IV. Intergroup analysis showed no statistically significant difference in microcrack formation. Conclusion: Within the limitation of this in vitro study, it can be concluded that NiTi instruments may cause cracks on the root surface. HCM and Silk files tend to produce a less number of cracks as compared to PG instruments.

Evaluation of Bond Strength and Fracture Load of Teeth With Flared Root Canals Restored With Prefabricated, Anatomical, and Computer-aided Design and Computer-aided Manufacturing Fiber Posts.

This study compared the use of anatomical glass fiber posts using bulk-fill composite resin with computer-aided design and computer-aided manufacturing (CAD/CAM) milled glass fiber post in oversized root canals, through bond strength (BS) and fracture resistance (FR) tests (fracture load). A total of 48 mandibular premolars were selected, half of them had their crowns removed at the cemento-enamel junction (CEJ) and the other half were sectioned 2 mm above the CEJ. Subsequently, teeth were endodontically treated. After 1 week, the standard preparation of the canals was carried out, and the roots were divided into three groups (n=16), according to the use of different restorative techniques (control: prefabricated glass fiber post [PFP], direct anatomical glass fiber post [AFP], and CAD/CAM milled glass fiber post [MFP]). After luting procedures using Single Bond Universal and RelyX Ultimate (3M ESPE), for eight teeth in each group, six specimens were obtained (two slices from each root third: cervical, middle, and apical). For the remaining eight roots of each group, standardized preparations for metal-free crowns, milling of 5 mol% yttria-stabilized tetragonal zirconia polycrystalline, cementation of the crowns, and periodontal ligament simulation were performed. Then, for each group, the BS was evaluated through the push-out test, and the FR was evaluated in compression. The data obtained from BS were submitted to two-way analysis of variance (ANOVA; group vs root region) and Tukey (α=0.05) and from FR to one-way ANOVA (group) and Tukey (α=0.05). For the BS test, the MFP group was statistically superior to the PFP group in all root regions and was statistically superior to the AFP group only in the cervical region, being statistically similar in the middle and apical root regions. For the FR test, the MFP group was statistically superior to the PFP and AFP groups. The milled fiber post technique can be a legitimate alternative in the restoration of weakened roots with flared root canals.

A new orthodontic force simulation system with a simulated periodontal ligament to measure the delivered force at the root apex.

To develop a new orthodontic force simulation system with a simulated periodontal ligament (PDL) that enables measurement of the delivered force at the root apex and to clarify the relationship between the applied orthodontic force and the delivered force at the root apex. In vitro study. Orthodontics department of a university, Tokyo, Japan. A new orthodontic force simulation system that enables measurement of the force at the root apex of the maxillary central incisor, was developed. Lingual and intrusion movements were simulated with applied orthodontic force at three levels: 50, 100 and 200 gf. The delivered forces at the root apex were compared between the two movements. Furthermore, the ratio of delivered force at the root apex to the applied orthodontic force (the apex force ratio) was calculated. The magnitudes of delivered forces at the root apex were significantly greater in intrusion movement than in lingual movement (P < 0.01). The apex force ratios were in the range of 47.3%-56.2% for lingual movement and 85.6%-86.2% for intrusion movement. The present study, of a newly developed orthodontic force simulation system, showed that the characteristics of the delivered force at the root apex differed according to the direction of tooth movement.

Identification of the periodontal ligament material parameters using response surface method

The orthodontic treatment can be guided by the finite element (FE) simulation of periodontal ligament (PDL) mechanical properties, and the biomimetic degree of FE simulation can be primarily affected by the material properties of the PDL. According to the principle of parameter inverse, a method: response surface (RS) method and FE inverse method were proposed to identify the material parameters of PDL. The Prony series viscoelastic FE model was established based on the relaxation experiment. With root mean square error of simulation results and experimental results as the objective function, the optimal parameter combination was obtained by RS method, and the FE simulation result were compared with the experimental result. The result showed that the optimal parameters of the PDL were elastic modulus: 3.791 MPa, Poisson's ratio: 0.42, temperature: 29.294°C separately, and the simulation result of optimal combination maintained consistency with experiment with the correlation coefficient of 0.97258, indicating that the method proposed in this paper could well identify of PDL material parameters. The parameter identification method used in this paper can significantly improve the calculation efficiency, and reduce the parameter identification error compared with the simple FE inverse method, which has scientific significance and theoretical value.

Influence of Methodological Variables on Fracture Strength Test Results of Intact Premolars: an ex-vivo study

The present ex vivo study evaluated the influence of periodontal ligament simulation, load inclination, and tip morphology on fracture strength test results on intact premolars. Forty maxillary premolars were divided into four groups, Group 1, with a 90° load inclination, spherical tip with a diameter of 3mm and periodontal ligament simulation (PDL+); Group 2, with a 90° load inclination, flat tip with a diameter of 2mm, PDL+; Group 3, with a 45° load inclination, flat tip with 2mm of diameter, PDL+; Group 4, 90° load inclination, spherical tip with 3mm diameter, without periodontal ligament reproduction. Interactions among variables and intergroup significance were tested with Wilcoxon rank-sum and Kruskal Wallis’s tests (p≤0.05). Statistically significant differences were found between groups B and C, but they were not found for the others. A 90° load inclination significantly increases fracture strength, while periodontal ligament simulation and tip morphology did not significantly influence the results.

Effect of hand files, rotary protaper universal and protaper retreatment files on crack formation in dentin

Background: The aim of the study was to compare the effect of hand files, rotary protaper universal files and protaper retreatment files on crack formation in dentin. Methods: Eighty mandibular premolar teeth with single canals are selected and mounted on resin blocks with simulated periodontal ligaments. The teeth were divided into four groups of twenty samples in each group. Un-instrumented group serves as control group while group two and three consists of hand file and rotary protaper universal file system respectively. Group 4 consists of retreatment group consisting of two sub groups of ten samples in each group. Subgroup 4a consist of samples prepared with hand file while subgroup 4b consist of samples prepared with rotary protaper universal system. Thereafter, retreatment is performed with protaper retreatment file system in both the sub groups. All the roots were sectioned perpendicular to the long axis at 4mm from apex using a low speed saw (Isomet) under water cooling. Digital images of each sections were captured at 25X magnification using a digital camera attached to a stereomicroscope and cracks were noted. Results: Although the result is statistically non significant, hand files show less number of cracks as compared to rotary protaper universal file.

Glass Fiber Post lengths and adhesive strategies to restore extensively damaged canines

The aim of this study was to evaluate different post lengths and adhesive strategies for restoring extensively damaged canines. Sixty human canines were randomly distributed into two groups (n=30), according to the resin cement used: self-adhesive or conventional. Each group was further distributed into 3 groups (n=10) based on the intracanal post lengths: 5, 7.5 and 10 mm. The radicular portion was endodontically filled, the cervical third was enlarged to simulate extensive damage and the coronal portion was reconstructed with composite resin. The samples were prepared with a simulated periodontal ligament and submitted to fatigue loading (160N – 1,200,000 cycles), followed by fracture resistance testing. The results were submitted to two-way ANOVA and Tukey tests (α=5%). The assessed glass fiber post lengths have not influenced on the fracture resistance (p&gt;0.05). However, the performance of the conventional cements was better than the self-adhesive cements when the same post length was compared (p&lt;0.05). Repairable fractures were prevalent (70-90%) in all groups tested. Conventional resin cement yielded higher fracture resistance than self-adhesive cement, regardless the post length adopted.

Effects of Adjacent Tooth Type and Occlusal Fatigue on Proximal Contact Force of Posterior Bulk Fill and Incremental Resin Composite Restoration.

To measure the proximal contact force in newtons (N) between incremental and bulk fill class II resin composite restorations and implant molar teeth or adjacent premolar teeth with simulated periodontal ligament. The model used was created with a typodont first molar tooth with two bilateral occlusal-proximal class II cavities, an adjacent tooth simulating an implanted molar tooth (Titamax CM, Neodent, Curtiba, PR, Brazil) and a premolar with simulated periodontal ligament. Two resin composite restorative techniques were used: Inc-Z350XT, (Filtek Z350, 3M Oral Care, St. Paul, MN, USA) inserted incrementally and Bulk-OPUS, (Opus Bulk Fill APS, FGM, Joinville, SC, Brazil) high viscosity bulk fill resin composite (n=10). As a control, a typodont having intact teeth without restorations was used. After the restorative procedure, each specimen was radiographed using a digital system (Dürr Dental, Bietigheim-Bissingen, Germany). The proximal contact force (N) was measured using dental floss with a microtensile machine (Microtensile ODEME, Luzerna, SC, Brazil). The specimens were then subjected to mechanical fatigue cycling to simulate 5 years of aging. All the parameters were measured after aging. The X-rays were blindly qualitatively analyzed by two operators to identify the loss of proximal contact. One-way ANOVA was used for comparing the initial contact force between restored and intact teeth. Two-way ANOVA followed by Tukey testing was performed for contact area data and for the contact force/contact area ratio. The proximal contact force data were analyzed using one-way repeated measurement ANOVA followed by Tukey testing (α=0.05). The X-ray proximal contact analyses were described by the frequency. The initial proximal contact force was similar for intact and restored teeth. The contact force and contact area with the molar were significantly higher than with the premolar; however the contact force/contact area ratio was similar for all tested groups. The bulk fill technique showed a contact force similar to the incremental filling technique. Fatigue resulted in a significant reduction in the proximal contact force (p<0.001), irrespective of the region analyzed or restorative material used. The digital X-rays detected no alteration in the proximal contact after occlusal fatigue. Larger contact area resulted in higher proximal contact force. Proximal contact force decreased with 5 years of simulated occlusal fatigue. The bulk fill technique showed a proximal contact force similar to that of the incremental filling technique.

Mathematical validation of measurement of root fracture resistance: an in vitro study

BackgroundThe aim of this study was to develop a mathematically valid method of assessing fracture resistance of roots. The model developed used mesial roots of lower molars instrumented using stainless steel hand files (SS) and two rotary nickel-titanium (NiTi) systems.MethodsEighty human lower molars were selected and randomly divided into four groups (n = 20). After instrumentation, the root canals were obturated using thermoplasticized gutta percha. The roots were covered with a simulated periodontal ligament and mounted vertically in autopolymerizing acrylic in PVC tubes. Using a universal testing machine, the force to fracture (N) was applied and the maximum load (FL) was recorded. Remaining dentine volume was calculated and the fracture resistance (FR) was recorded. The data were analyzed using SPSS version 22 with P < .05.ResultsThere were no significant differences among the instrumentation methods for FL but in FR the roots instrumented using rotary NiTi showed significantly lower values than control groups and SS files (P < 0.001).ConclusionsConsidering the effect of root length, volume of the root, and volume of the instrumented canal as well as the maximum failure load may be a more objective method of reporting fracture resistance of roots.

Root Microcracks Formation during Root Canal Instrumentation Using Reciprocating and Rotary Files

The aim of this study was to compare the formation of dentinal cracks with nickel-titanium (NiTi) instruments working in continuous rotation and reciprocating motion. One hundred sixty extracted human mandibular first molars were selected for the study. The mesial roots were resected and mounted in resin blocks with simulated periodontal ligaments. Those teeth were randomly assigned to five groups (n = 32 teeth/group). The first one was treated with K-files and served as control group, and the remaining 128 teeth were divided into 4 groups depending on the root canal preparation technique. Group 2 samples were prepared by sequential ProTaper Universal (PTU), group 3 samples with rotary ProTaper Universal (RPTU), group 4 achieved by the One Shape (OS), and group 5 with the WaveOne (WO) primary files. Roots were then horizontally sectioned at 3, 6, and 9 mm from the apex, and the slices were then observed under a stereomicroscope at ×40 magnification to determine the presence of internal dentinal microcracks. The presence or absence of dentinal defaults was recorded and the statistical analysis was performed by Pearson Chi-square test. The significance level was set at p < 0.05. The study was made in the oral biology and biotechnology research laboratory of the faculty of medical dentistry of Rabat, Morocco. No dentinal defect was seen with the stainless steel hand file (group 1). The manual PTU (group 2), the RPTU (group 3), the OS (group 4), and the WO (group 5) in reciprocating motion caused cracks in 15.6%, 12.4%, 21.9%, and 6.2% of samples, respectively. The highest percentage of dentinal defect was showed in group 4 but without significant difference with the other group (p > 0.05). Dentinal cracks are produced indifferently of motion kinematics. Within the limits of this study and the current literature, such incidence is less with instruments working in reciprocating motion compared with those working in continuous rotation. Manual and rotary NiTi sequential systems showed fewer microcracks than the single file system working by continuous rotation motion.

Development of apical root microcracks following different root canal preparation systems

Context: The most critical step in root canal therapy is cleaning and shaping of the root canal. A vast array of instruments both handheld and engine driven are available for root canal preparation. There are very few studies to compare the effect of different types of instruments on the development of apical root cracks. Hence, the aim of the study was to compare the development of apical root cracks following different root canal preparation techniques and instruments.Aims: The aim of this study is to compare the development of apical root cracks following different root canal preparation techniques and instruments.Settings and Design: This is an in vitro study.Subjects and Methods: Forty extracted mandibular premolar teeth were selected and mounted on resin blocks with simulated periodontal ligaments, after which the apex was exposed. All teeth were randomly divided into four groups; each group was earmarked for a specific technique and instrument used for root canal preparation. Digital images of external apical root surfaces of every tooth were taken before and after apical enlargement through optical microscope (×40). These images were compared, and the presence of cracks was evaluated.Statistical Analysis Used: Chi-square exact test was used to compare the four groups.Results: Overall P value was 0.167 which is not statistically significant and indicates that the proportion of teeth developing cracks was not statistically significant among the four groups.Conclusions: More cracks were developed with rotary system. However, the results were not statistically significant among the four groups.

Effect of apexification on occlusal resistance of immature teeth

BackgroundStrain distribution was investigated to assess the occlusal resistance alterations in immature teeth under different occlusal force.MethodsIn vitro apexification models of teeth with a funnel-shaped immature apex were obturated with mineral trioxide aggregate (MTA; ProRoot MTA) using different combinations of core materials (10/group): group 1, full-length orthograde obturation of MTA; group 2, a 5-mm MTA apical plug with a composite core; group 3, a 5-mm MTA apical plug and back-filling with warm gutta-percha. Teeth with calcium hydroxide (CH)-medicated canals and untreated teeth with normal apices were tested as controls. The teeth were arranged between two adjacent normal-apex teeth, embedded in a resin mold with a simulated periodontal ligament space. Strain data were recorded from the 3-unit teeth assembly under static compressive occlusal forces (50, 100, 200, and 300 N). Measurements were repeated 20 times for each condition, and the data were statistically analyzed.ResultsThe immature teeth showed altered occlusal force resistance, placing increased strain on adjacent teeth. Teeth with CH-medicated canals showed significantly inferior occlusal resistance under all tested forces (P < 0.05). Application of an MTA plug with deep composite resin core resulted in significantly better stress-bearing capacity especially under forces of 50 and 300 N (P < 0.05).ConclusionsThe pattern of occlusal force distribution in immature teeth differed according to the canal obturation materials used for apexification. Immature teeth with an MTA apical plug showed more favorable occlusal force resistance than those with CH-medicated canals.

In vitro Simulation of Periodontal Ligament in Fatigue Testing of Dental Crowns.

Objective Fatigue testing of restorative material has been appreciated as an appropriate method to evaluate dental restorations. This study aims to investigate the influence of periodontal ligament (PDL) simulation on fatigue and fracture tests results of zirconia crowns. Materials and Methods A standard tooth preparation for all ceramic zirconia crown was made on a typodont mandibular molar. The prepared master die was duplicated using epoxy resin to produce 40 replicas. PDL simulation was made by surrounding the root of 20 dies with a 0.3-mm thick silicon layer. The other 20 specimens had no PDL simulation. Zirconia crowns were fabricated using computer-aided design/computer-aided manufacturing technology and cemented to the epoxy resin dies. Ten crowns from each group were subject to chewing simulation with simultaneous thermocycling (5–55°C). All specimens were then loaded until failure in universal testing machine. Statistical Analysis Statistical analysis was conducted using SPSS software. Shapiro–Wilk test confirmed the normal distribution of data. Descriptive statistic was performed and differences between the groups were analyzed using paired samples t -test. Results All fatigued crowns survived chewing simulation; no failure was observed after finishing simulation. The highest mean fracture load recorded was 3,987 ± 400 N for the no fatigue/no periodontal simulation group. Comparing the mean fracture load of the two groups with periodontal simulation and the two groups with no periodontal simulation showed no statistically significant difference ( p > 0.5). Conclusion Considering the testing set-up applied in this study, simulating PDL using resilient materials does not affect the in vitro survival and fracture resistance of zirconia crowns.

Systematic review of chewing simulators: Reality and reproducibility of in vitro studies.

BackgroundThe aim of this systematic review was to analyze the types of human chewing simulator described in scientific literature. Material and MethodsAn electronic search was conducted in the databases PubMed, Embase and Scopus. The search strategy included 10 search terms: “in vitro”; “dental materials”; “shear strength”; “fatigue fracture”; “bite force”; “prosthetic materials”; “chewing simulator”; “chewing machine”; “simulated mastication”; and “dental wear simulator.” Two researchers worked independently to assess the titles and abstracts of the articles. The quality of the in vitro trials selected was evaluated by means of the Consolidated Standards of Reporting Trials scale. ResultsThe electronic search identified 80 articles related to the topic of interest. After reading the full texts, ten works were selected. The articles focused mainly on the design of chewing simulators. Most of them were considered of moderate quality. Regarding the characteristics that an ideal chewing simulator should encompass, the devices described in articles varied greatly in terms of movement, periodontal ligament simulation, force sensors, and the materials tested. ConclusionsNo chewing simulator offers all the characteristics necessary to reproduce human masticatory movements and forces under the humidity and pH conditions of the oral cavity. A simulator that encompasses all these characteristics would make it possible to standardize trials involving simulated mastication. Key words:In vitro, dental materials, dental wear simulator.

Influence of Different Implants on the Biomechanical Behavior of a Tooth-Implant Fixed Partial Dentures: A Three-Dimensional Finite Element Analysis.

This study analyzed the biomechanical behavior of rigid and nonrigid tooth-implant supported fixed partial dentures. Different implants were used to observe the load distribution over teeth, implants, and adjacent bone using three-dimensional finite element analysis. A simulation of tooth loss of the first and second right molars was created with an implant placed in the second right molar and a prepared tooth with simulated periodontal ligament (PDL) in the second right premolar. Configurations of two types of implants and their respective abutments-external hexagon (EX) and Morse taper (MT)-were transformed into a 3D format. Metal-ceramic fixed partial dentures were constructed with rigid and nonrigid connections. Mesh generation and data processing were performed on the 3D finite element analysis (FEA) results. Static loading of 50 N (premolar) and 100 N (implant) were applied. When an EX implant was used, with a rigid or nonrigid connection, there was intrusion of the tooth in the distal direction with flexion of the periodontal ligament. Tooth intrusion did not occur when the MT implant was used independent of a rigid or nonrigid connection. The rigid or nonrigid connection resulted in a higher incidence of compressive forces at the cortical bone as well as stress in the abutment/pontic area, regardless of whether EX or MT implants were used. MT implants have a superior biomechanical performance in tooth-implant supported fixed partial dentures. This prevents intrusion of the tooth independent of the connection. Both types of implants studied caused a greater tendency of compressive forces at the crestal area.

Critical evaluation of fracture strength testing for endodontically treated teeth: a finite element analysis study.

ObjectivesThe aim of this study was to investigate whether the diameter and direction of the plunger and simulation of the periodontal ligament (PDL) affected the stress distribution in endodontically treated premolars.MethodsA fracture strength test was simulated via finite element analysis. A base model was set up, and the following parameters were modified: plunger diameter (3 mm vs. 6 mm), plunger direction (vertical vs. 135° angular to the central fossa), and PDL simulation. The analysis was conducted using the CosmosWorks structural analysis program, and the results are presented in terms of von Mises stresses.ResultsThe smaller plunger increased the stresses at the contact area of the crown, but the plunger diameter had no effect on the stress distribution within the root. An angular plunger direction increased stresses within the root, as well as at the buccal cusp of the crown, compared with the vertical direction. Simulation of the PDL caused higher stress accumulation, especially in the cervical region of the root.ConclusionsThe plunger diameter had no effect on the stress distribution in the roots, whereas the plunger direction and PDL simulation did affect the stress distribution. More stringent standards can be established by taking such parameters into account when performing fracture testing in future studies.

Influence of testing parameters on the load-bearing capacity of prosthetic materials used for fixed dental prosthesis: A systematic review and meta-analysis

The aim of this study was to systematically review the literature to assess static fracture strength tests applied for FDPs and analyze the impact of periodontal ligament (PDL) simulation on the fracture strength. Original scientific papers published in MEDLINE (PubMed) database between 01/01/1981 and 01/06/2010 were included in this systematic review. Data were analyzed considering the test method (static loading), material type (metal-ceramic-MC, oxide all-ceramic-AC, fiber reinforced composite resin-FRC, composite resin-C), PDL (without or with) and restoration type (single crowns, 3-unit, 4-unit, inlay-retained and cantilever FDPs). The selection process resulted in the 72 studies. In total, 377 subgroups revealed results from static load-bearing capacity of different materials. Fourteen metal-ceramic, 190 AC, 121 FRC, 45 C resin groups were identified as subgroups. Slightly decreased results were observed with the presence of PDL for single crowns (without PDL=1117±215 N; with PDL=876±69 N), 3-unit FDPs (without PDL=791±116 N; with PDL=675±91 N) made of AC, 3-unit FDP (without PDL=1244±270 N; with PDL=930±76 N) and inlay-retained FDP (without PDL=848±104 N; with PDL=820±91 N) made of FRC and 4-unit FDPs (without PDL=548±26 N; with PDL=393±67 N) made of C. Overall, for single crowns, fracture strength of FRC was higher than that of AC and MC; for 3-unit FDPs FRC=C&gt;AC=MC; for 4-unit FDPs AC&gt;FRC&gt;C and for inlay-retained FDPs, FRC=AC. An inclination for decreased static fracture strength could be observed with the simulation of PDL but due to insufficient data this could not be generalized for all materials used for FDPs.

Effect of different periodontal ligament simulating materials on the incidence of dentinal cracks during root canal preparation.

Background. The present study was undertaken to evaluate the incidence of dentinal cracks during root canal preparation with different periodontal ligament simulating materials in vitro. Methods. Seventy freshly extracted human mandibular first premolars were selected and divided into 7 groups in terms of simulating material: group 1: polyether impression material; group 2: polyvinyl acetate adhesive; group 3: polyvinyl siloxane impression material; group 4: cyanoacrylate adhesive; group 5: epoxy resin adhesive; group 6: positive control, without any periodontal ligament simulation; and group 7: negative control, where neither a periodontal ligament simulating material was used nor canal preparation was carried out. Root canal preparation was carried out in all the groups followed by sectioning of roots at 3 mm, 6 mm and 9 mm. The sections were evaluated under a stereomicroscope at ×2.5 for the presence or absence of cracks. Chi-squared test was used to compare the appearance of defective roots between the different experimental groups. Results. The least number of cracks were found in the negative control group, followed by group 1 where polyether impression material was used for periodontal ligament simulation. The difference was significant with a P-value of 0.002 for coronal sections. Conclusion. Under the limitation of the present study, polyether and polyvinyl siloxane (light body) can both be used for simulation of periodontal ligament.

In vitro comparative evaluation of dentinal microcracks formation during root canal preparation by different nickel-titanium file systems

Aim: The aim of this study was to evaluate and compare dentinal microcracks formation during root canal preparation by different commercially available nickel-titanium (NiTi) file systems. Materials and Methods: Eighty-four single-rooted mandibular premolars were selected. All specimens were decoronated and divided into seven groups of 12 each. Teeth were mounted in the acrylic block with simulated periodontal ligaments. Twelve teeth served as a control in which no treatment was performed. Experimental groups were instrumented with Hand NiTi, ProTaper universal, ProTaper Next, Silk, WaveOne, and self-adjusting files (SAF). Roots were then sectioned 3, 6, and 9 mm from the apex, and the cut surface was observed under a stereomicroscope and checked for the presence or absence of dentinal microcracks. Results: SAF group and Hand NiTi group showed no cracks formation along with control group. ProTaper rotary files showed more number of cracks than ProTaper Next, Silk and WaveOne used in the study. However, no statistically significant difference was found among ProTaper rotary, ProTaper Next, Silk, and WaveOne (P > 0.05). Conclusion: All rotary files created microcracks in the root dentin at all three levels, whereas the SAF and hand files presented with satisfactory results with no dentinal microcracks.