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 impres-sion 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.

Introduction: Endodontic rotary systems may result in Dentinal Cracks. They may propagate to vertical root fracture that compromises the outcome of endodontic treatment. This study aimed to compare Neolix and Reciproc (single-file systems), Mtwo and ProTaper (conventional rotary systems) in terms of Dentinal crack formation in root canal walls. Methods and Materials: This in vitro study was conducted on 110 extracted human singlerooted teeth. The teeth were randomly divided into four experimental groups (n=25) for root canal preparation with Neolix, Reciproc, Mtwo and ProTaper systems and two control groups (n=5). The first control group underwent root canal instrumentation with hand files while the second control group received no preparation and was only irrigated. After instrumentation, root canals were horizontally sectioned at 3, 6 and 9 mm from the apex and inspected under a stereomicroscope under 12× magnification for detection of Cracks. The data were analyzed using chi-square, GEE test and Bonferroni tests (P<0. 05). Results: No crack was found in the control groups. All rotary systems caused Dentinal Cracks. ProTaper, Reciproc, Mtwo and Neolix caused Cracks in 92%, 80%, 68% and 48% of samples. ProTaper caused significantly more Cracks than Neolix and Mtwo (P<0. 05). No significant differences were noted between other groups (P>0. 05). Conclusion: All rotary systems cause Dentinal Cracks and it is significantly different in apical, middle and coronal third of the root. Neolix appears to be a suitable alternative to other rotary systems since use of this single-file system saves time and cost and minimizes trauma to Dentinal walls.

Cervical Dentinal hypersensitivity is a widespread disease with tremendous adverse effects on the patients’ comfort.Between 8%-57% of the total population is affected by this disease. Literature even states a prevalence of over 90% in patients with periodontal disease.Conservative treatment techniques provide, in most cases, no satisfying results because the seal of Dentinal tubules and surface coatings are ephemeral due to tooth brushing and abrasive and erosive food particles. General practitioners have to face this problem in their daily business.To increase our patients’ comfort, innovative and new treatment strategies are needed.This presentation shows a new approach for the reduction of cervical Dentinal hypersensitivity with lasers, it deals with different wavelengths and possible materials that help to seal the cervical regions. It summarizes the effects of lasers and shows the advantages as well as the limitations of different wavelengths.

A novel micromechanical based theory for the determination of the stress intensity factors (SIFs) of three-dimensional interacting Cracks is proposed. The pioneering work of Eshelby"s equivalent inclusion method (EIM) in conjunction with Hill"s theorem on discontinuities of elastic fields across the interfaces are utilized in this analytical approach. The important feature of the present theory lies in its generality in treating modes I, II, III, and mixed mode fracture, and handling interacting Cracks with various geometries subjected to non-uniform far-field applied stress (strain), in a unified manner. For illustrations arbitrarily oriented penny shape Cracks under far-field normal and shear loading are examined. Comparisons with other analytical solutions, whenever available, established the remarkable accuracy and robustness of the proposed theory.

Objective: This study investigated the effect of glide path preparation and different instruments in creating Dentinal Cracks during root canal instrumentation. Methods: Eighty maxillary molars were divided into four groups (n=20). The mesiobuccal root canals were prepared using two rotary systems (Group 1: Hyflex EDM and Group 2: ProTaper Gold) and two reciprocating systems (Group 3: WaveOne Gold and Group 4: Reciproc Blue R25). In each group, ten specimens were prepared using the designated glide path files. Methylene blue dye was injected into the root canals to highlight Dentinal Cracks. The samples were then sectioned and examined under a microscope to count the number of Dentinal Cracks at the apical, middle, and coronal thirds. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests (P<0.05). Results: When glide path files were not used, the number of Cracks was comparable across the groups in coronal, middle and apical sections (P>0.05). Among the samples prepared with glide path files, those instrumented with WaveOne Gold showed a significantly higher number of Dentinal Cracks in the coronal section compared to ProTaper Gold (P<0.05), and in the middle section compared to both HyFlex EDM and ProTaper Gold (P<0.05). In the apical section, no significant difference in the number of Cracks was observed among the groups (P=0.627). Conclusions: Glide path preparation with rotary systems (ProTaper Gold and HyFlex EDM) resulted in fewer Dentinal Cracks in the mesiobuccal root canals of maxillary molars compared to a reciprocating system (WaveOne Gold).

Introduction: This study aimed to compare the incidence of Dentinal crack formation by instrumentation with ProTaper Universal system (rotary, multi-file system), SafeSider (reciprocation movement, multi-file system) and Neolix (rotary, single-file system). Methods and Materials: In this in vitro study, 60 freshly extracted mandibular first molars were randomly divided into three experimental groups (n=15) and a control group containing unprepared teeth (n=15). Instrumentation in different groups was accomplished using either ProTaper, Neolix or SafeSider systems up to 25/0. 08. The teeth were then sectioned at 3, 6 and 9 mm from the apex, and observed under a stereomicroscope for presence of Dentinal Cracks. Data were analyzed with Chi square test, Fisher’ s exact test and Bonferroni correction. Results: Micro Cracks were seen in all experimental groups (13. 3% in ProTaper, 26. 7% in SafeSider and 40% in Neolix). There was a significant difference between Neolix and the control groups in microcrack formation (P=0. 042). Micro Cracks mainly occurred in the coronal section (9 mm). No microcrack occurred in the control group. Conclusion: Neolix rotary single-file system caused more Dentinal Cracks compared to the unprepared roots. All the instrumentation systems increased the number of micro Cracks compared to unprepared teeth.

Introduction: The aim of this study was to compare the formation of Dentinal crack and craze lines in the root dentin during root canal preparation with three different NiTi endodontic systems, naming Reciproc (RCP), ProTaper Universal (PTU) and Mtwo.Methods and Materials: One hundred extracted mandibular premolars with single canals were selected and decoronated. The teeth were randomly divided into four groups of 25 each (n=25). In groups 1, 2 and 3 the teeth were prepared using Mtwo, PTU and RCP, respectively. While in group 4 (control group) the samples were left unprepared. After preparation, all specimens were sectioned perpendicular to the long axis of root at 3, 5 and 9-mm distances from the apex.The sections were then individually observed under 12× magnification using stereomicroscope. The data was analyzed using the chi-square and Fisher’s exact tests. The level of significance was set at 0.05.Results: No Cracks were observed in the control group.All engine-driven systems caused Dentinal Cracks. Mtwo and PTU caused Cracks significantly more than RCP (P<0.05). There was no significant difference between RCP and control group (P>0.05).Conclusion: All three engine-driven systems created Dentinal defects. Reciproc caused less Cracks than Mtwo and ProTaper Universal.