Fracture Resistance of Upper Central Incisors with Different Endodontic Accesses Restored with Lithium Disilicate Partial Laminate Veneers.

PURPOSE: A treatment protocol involving the root canal treatment with conventional palatal access cavity and the partial veneer application may considerably reduce the fracture resistance of the teeth. On the other hand, labial access cavity within the partial veneer outlines followed with the partial veneer application may more successfully recover the lost fracture resistance of the endodontically treated teeth. In this regard, the present study aims to compare the fracture resistances of upper central incisors endodontically treated with palatal and labial accesses and restored with restorative resin composite and lithium disilicate partial veneers. MATERIALS AND METHODS: Three groups consisting ten specimens each were prepared by using extracted sound human upper central incisors. Root canal treatments with palatal access, resin composite restoration of the access cavities and veneer restorations were applied to the first group (Group P). Root canal treatments with labial access, resin composite restoration of the access cavities and veneer restorations was applied to the second group (Group L). Veneer restorations were applied to the third group (Group C) without root canal treatment. Specimens were thermocycled and loaded to fracture in order to record their fracture resistances. RESULTS: The mean fracture resistance of Group C was observed to be significantly higher, compared to Groups P and L (P < 0.05). Fracture resistance of Group L was observed to be higher, compared to Group P, but the difference was not found statistically significant. Light microscope revealed that the specimens fractured in five different modes. CONCLUSION: Although the mean fracture resistance of the teeth that endodontically treated with labial access cavity prior to the ceramic partial veneer application was higher in comparison with the teeth that endodontically treated with palatal access cavity prior to the ceramic partial veneer application, the difference was found statistically insignificant (P < 0.05).

Evaluation of Different Techniques for Filling Simulated C-shaped Canals of 3-dimensional Printed Resin Teeth.

INTRODUCTION: The purpose of this study was to compare the ability of different root canal filling methods on the C1 root canal anatomy using 3-dimensional (3D) printer technology. METHODS: Mandibular molars were scanned with cone-beam computed tomographic (CBCT) imaging. A mandibular molar tooth with a C1 root canal configuration was selected according to images obtained from CBCT technology. The root canals were shaped with ProTaper Universal rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland) and hand files. After the root canal shaping procedure, the tooth was scanned with micro-computed tomographic imaging, and 80 replicas of the tooth were produced with a 3D printer. Replicas were assigned into 4 groups (n = 20) and were filled using one of the following techniques: a core carrier system (GuttaCore [GC]; Dentsply Tulsa Dental Specialties, Tulsa, OK), a continuous wave obturation system (Elements Free [CW]; Kerr/SybronEndo, Orange, CA), a cold lateral compaction technique (CLC), or the injectable cold filling method (GuttaFlow Bioseal [GFB]; Coltène/Whaledent AG, Altstatten, Switzerland). All specimens were sectioned horizontally at 2, 4, 6, 8, and 10 mm from the apices of the specimens. The sections were examined at 32× magnification under a stereomicroscope, and the percentage areas of gutta-percha, sealer, and voids were measured. Statistical analysis of data was performed using multivariate analysis of variance and Tukey honestly significant difference tests (P < .05). RESULTS: The CW group had the highest mean percentages for void and the least mean percentages for gutta-percha at 2-mm sections (P < .05). A pairwise comparison between the groups showed significantly less void in the CLC and GFB groups and more void in the CW and GC groups at 2 mm (P < .05). In the total area, the CLC and GFB groups showed a significantly lower percentage of gutta-percha and more sealer compared with the other groups (P < .05), and there was no significant difference between the CLC and GFB groups (P > .05). CONCLUSIONS: At the apical part of the canal, the cold lateral compaction and cold injectable filling techniques were more successful compared with the warm gutta-percha filling techniques in C1 root canal configuration.

The efficacy of an experimental single solution versus alternate use of multiple irrigants on root dentin microhardness.

OBJECTIVES: This study was carried-out to evaluate and compare the efficacy of various irrigants when used singly or in combination on the microhardness of root canal dentin. STUDY DESIGN: A total of 50 root-halves were randomly divided into 5 groups immediately after the initial baseline microhardness measurements and treated with: Group-1; 7.5%Ethylenediaminetetraaceticacid (EDTA) + 2.5%sodium hypochlorite (NaOCl), Group-2; 7.5%ethyleneglycol-bis[b-aminoethylether]-N,N,N0,N0-tetraaceticacid (EGTA) + 2.5%NaOCl, Group-3; 7.5%trans1,2diaminocyclohexane NNN',N'tetraaceticacid (CDTA) + 2.5% NaOCl, Group-4; 7.5%EDTA + 2.5% Ethylenediamine (EDA), and Group-5; 1/1 (v/v) EDTA-EDA mixture + 1/1 (v/v) EDTA-EDA mixture. Fifty mL of each solution was used for 1 minute. The reference and post-treatment microhardness values were measured with a Vickers indenter under 80-gram load, 15-second dwell time. Data were analyzed by two-way ANOVA and Bonferroni tests (p=0.05). RESULTS: All solutions decreased microhardness of dentin (p< 0.05). There was statistically significant difference between each group, except Group-1 and 4, after 1st solution application. While Group-2 resulted in a greater reduction of dentin hardness, Group-5 caused the least change in microhardness values, after 1st solution application (p< 0.05). No statistical difference was observed between Groups 1-4, after 2nd solution application. However, Group-5 showed a significant difference compared with all other groups, after 2nd solution application (p< 0.05). CONCLUSIONS: Under the experimental conditions, all tested solutions reduced the microhardness of the root canal dentin. EGTA was the most efficient chelating agent. EDTA-EDA single mixture has led to least change on the microhardness of root dentin. Key words:Microhardness, CDTA, EDTA, EGTA, Ethylenediamine.

The effect of surfactant addition to EDTA on microhardness of root dentin.

INTRODUCTION: The aim of this study was to investigate the effect of different concentrations of cetrimide with or without 5% EDTA solution on the microhardness of human root dentin in vitro. METHODS: Twenty-five recently extracted single-rooted human teeth were selected. The roots were split longitudinally into 2 parts. The specimens were randomly divided into the following 5 groups and were treated with 5% EDTA, 5% EDTA + 0.25% cetrimide, 5% EDTA + 0.50% cetrimide, 0.25% cetrimide, and 0.50% cetrimide immediately after the initial baseline microhardness measurements. A standardized volume of 50 mL of each solution was used for 1 minute. The reference microhardness values of untreated specimens were initially measured with a Vickers indenter under a 50-g load and a 10-second dwell time at the midroot level of the root dentin. Post-treatment microhardness values were obtained in the same manner as the initial ones. The decrease in microhardness was calculated as a percentage. Data were analyzed statistically by 1-way analysis of variance (P = .05) and the post hoc Tukey test for multiple comparisons at the same level of significance. RESULTS: All solutions significantly decreased the microhardness of root dentin (P < .05). Although there was no significant difference among the solutions (P > .05), the specimens in the EDTA + 0.50% cetrimide solution group showed the highest change in microhardness. The plain EDTA and plain 0.50% cetrimide groups had similar values. CONCLUSIONS: The use of surfactants higher than 0.25% in concentration is questionable for clinical conditions.

Deformation of the self-adjusting file on simulated curved root canals: a time-dependent study.

OBJECTIVE: This study examined the surface changes of self-adjusting file after operating in different degrees of canal curvatures with a fixed radius of curvature in different operation intervals. STUDY DESIGN: Artificial canals were manufactured in a 5-mm radius of curvature with 45° and 60° angles of curvature. Forty self-adjusting files were divided into 2 groups and submitted to functional fatigue to failure. Twenty files were tested using the 45° angle and the remaining 20 were tested using the 60° angle at 4 minutes for 7 periods in a total of 28 minutes. The average time frame for each 4-minute inspection period was considered as the moment of failure at 2, 6, 10, 14, 18, 22, and 26 minutes, respectively. Instruments were evaluated using scanning electron microscopy to characterize the material under study. RESULTS: The lattice detachment began at the second period for both groups and continued to increase along with the ongoing testing time. The detachment that occurred in 60° canal curvature was higher at the third and fourth periods when compared with the 45° group (P < .05). For both groups, during the third period, detachment of the arch of the lattice was only one sided; however, this deformation was severe between the fourth and sixth periods with a 2-sided detachment, which was easier to separate. The rough surface became smooth after usage. No full separation of the file was evident for both groups. CONCLUSIONS: In multirooted teeth with severely curved root canals, using more than one self-adjusting file might be recommended to prevent lattice detachment.