To evaluate and compare the compressive strength of root dentin exposed to calcium hydroxide, mixed with various vehicles for a period of 30 days - An in vitro study.

Background: Long-term use of intracanal medicaments such as calcium hydroxide (CH) reduces the fracture resistance of dentin. Aim: This study aimed to evaluate and compare the compressive strength of root dentin exposed to CH, mixed with various vehicles after 30 days of placement. Settings and Design: Sixty single-rooted extracted human permanent premolars were collected, and complete instrumentation was done. Samples were divided into six groups. Materials and Methods: In Group I, no medicament was placed. In Group II, Group III, and Group IV, the root canals were filled with CH powder mixed with normal saline, distilled water, and local anesthetic solution. In Group V and Group VI, the root canals were filled with Metapaste and RC-Cal. Access cavities were sealed using IRM and were stored for 30 days. Teeth sectioned to obtain a 5 mm thick dentin cylinder subjected to compressive loading to evaluate the fracture resistance using a universal testing machine. Statistical Analysis: Results were analyzed using one-way ANOVA and multiple comparisons using Bonferroni test. Results: Highest mean compressive strength was recorded in Group I followed by Group II, Group IV, Group VI, Group III, and Group V. Conclusions: CH when used as a root canal dressing material will reduce the compressive strength of the teeth irrespective of the form of CH and vehicle.

A comparative evaluation of the effect of 8% and 17% ethylenediaminetetraacetic acid exposure for 1 min and 10 min on the fracture resistance of endodontically treated roots: An in vitro study.

OBJECTIVE: The objective of this study was to evaluate the effect of 8% and 17% ethylenediaminetetraacetic acid (EDTA) exposure for 1 min and 10 min on the fracture resistance of endodontically treated roots. METHODOLOGY: Sixty human single-rooted teeth were decoronated and divided into six groups (n = 10). Canal preparation was carried out except in negative control group, using the ProTaper rotary file system. Final irrigation was performed using distilled water, 17% EDTA for 1 min and 10 min, 8% EDTA for 1 min and 10 min. Thereafter, roots were obturated with ProTaper F3 Gutta-percha points and AH Plus sealer using a single-cone technique. The specimens were loaded vertically at 1 mm/min crosshead speed until vertical root fracture occurred. Results were evaluated statistically with one-way analysis of variance and post hoc Tukey test. RESULTS: Analysis of results showed that the unprepared roots showed the highest fracture resistance and roots irrigated with 17% EDTA for 10 min showed the lowest fracture resistance. The mean fracture resistance of unprepared roots, roots irrigated with 8% EDTA for 10 min and 17% EDTA for 1 min was significantly higher than roots irrigated with 8% EDTA for 1 min, 17% EDTA for 10 min and distilled water. CONCLUSION: From a clinical viewpoint, if EDTA has to be used, it is safer to use higher concentration for a shorter application time or a low concentration with a longer application time. Prolonged use of high concentrations of EDTA might increase the risk of root fracture.

Effect of Instrumentation Length and Instrumentation Systems: Hand Versus Rotary Files on Apical Crack Formation - An In vitro Study.

INTRODUCTION: Stresses generated during root canal instrumentation have been reported to cause apical cracks. The smaller, less pronounced defects like cracks can later propagate into vertical root fracture, when the tooth is subjected to repeated stresses from endodontic or restorative procedures. AIM: This study evaluated occurrence of apical cracks with stainless steel hand files, rotary NiTi RaCe and K3 files at two different instrumentation lengths. MATERIALS AND METHODS: In the present in vitro study, 60 mandibular premolars were mounted in resin blocks with simulated periodontal ligament. Apical 3 mm of the root surfaces were exposed and stained using India ink. Preoperative images of root apices were obtained at 100x using stereomicroscope. The teeth were divided into six groups of 10 each. First two groups were instrumented with stainless steel files, next two groups with rotary NiTi RaCe files and the last two groups with rotary NiTi K3 files. The instrumentation was carried out till the apical foramen (Working Length-WL) and 1 mm short of the apical foramen (WL-1) with each file system. After root canal instrumentation, postoperative images of root apices were obtained. Preoperative and postoperative images were compared and the occurrence of cracks was recorded. Descriptive statistical analysis and Chi-square tests were used to analyze the results. RESULTS: Apical root cracks were seen in 30%, 35% and 20% of teeth instrumented with K-files, RaCe files and K3 files respectively. There was no statistical significance among three instrumentation systems in the formation of apical cracks (p=0.563). Apical cracks were seen in 40% and 20% of teeth instrumented with K-files; 60% and 10% of teeth with RaCe files and 40% and 0% of teeth with K3 files at WL and WL-1 respectively. For groups instrumented with hand files there was no statistical significance in number of cracks at WL and WL-1 (p=0.628). But for teeth instrumented with RaCe files and K3 files significantly more number of cracks were seen at WL than WL-1 (p=0.057 for RaCe files and p=0.087 for K3 files). CONCLUSION: There was no statistical significance between stainless steel hand files and rotary files in terms of crack formation. Instrumentation length had a significant effect on the formation of cracks when rotary files were used. Using rotary instruments 1 mm short of apical foramen caused lesser crack formation. But, there was no statistically significant difference in number of cracks formed with hand files at two instrumentation levels.

Antimicrobial effect of three disinfecting agents on Resilon cones and their effect on surface topography: An in vitro study.

AIM: The objective of this study was to evaluate the effectiveness of 5.25% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), and 2% peracetic acid (PAA) in disinfecting Resilon cones and to evaluate topographical changes microscopically under scanning electron microscope (SEM) after rapid chemical disinfection. MATERIALS AND METHODS: Resilon cones were disinfected in an ultraviolet (UV) light chamber for 20 min and contaminated by immersing in a microbial suspension of Enterococcus faecalis for 30 min. The contaminated cones were then immersed in the 5.25% NaOCl, 2% CHX, and 2% PAA for 1 min, 5 min, and 10 min, separately. The cones were then incubated at 37°C in thioglycollate broth for 7 days and examined for turbidity. The samples showing turbidity were subcultured on blood agar and incubated at 37°C for 48 h. Gram staining was done to confirm that the cultured bacteria were E. faecalis. Surface changes of disinfected Resilon cones were evaluated under SEM. STATISTICAL ANALYSIS USED: The data were analyzed statistically using Kruskal-Wallis, analysis of variance (ANOVA), and Mann-Whitney U-test. RESULT: In eliminating E. faecalis, 5.25% NaOCl was most effective followed by 2% PAA and 2% CHX. Topographic examination of tested Resilon cones revealed some surface deposits after disinfection with 5.25% NaOCl and 2% CHX, whereas 2% PAA caused surface erosion. CONCLUSION: In disinfecting Resilon cones, 5.25% NaOCl is most effective followed by 2% PAA and 2% CHX.

Evaluation of smear layer removal from ultrasonically prepared retrocavities by three agents.

OBJECTIVES: To evaluate the efficacy of 35% orthophosphoric acid, 24% ethylenediaminetetraacetic acid (EDTA) and 10% citric acid in the removal of smear layer from retrocavities prepared with ultrasonic retro-tips using scanning electron microscopy. MATERIALS AND METHODS: Root canals of fifty single-rooted teeth were cleaned, shaped, and obturated with gutta-percha and AH plus sealer. The apical 3 mm of each root was sectioned with a diamond disc and retrograde cavities were prepared with Kis # 1 ultrasonic retro-tips to a depth of 3 mm. Retro cavities in Group I were treated with a gel of 35% orthophosphoric acid for 15 seconds, Group II were treated with a gel of 24% EDTA at neutral pH for 2 minutes, and Group III were treated with a gel of 10% citric acid for 2 minutes, followed by 1 minute rinsing with distilled water for all groups. The samples were prepared for scanning electron microscopic observation. Scoring was performed for the presence of the smear layer on the walls of the retrocavity. RESULTS: In the orthophosphoric acid group, it was observed that all dentinal tubules were open in 70% of the samples. The majority of analyzed samples in EDTA and citric acid group showed dentinal tubules covered with the smear layer. CONCLUSIONS: Application of 35% orthophosphoric acid gel for 15 seconds on retrocavities prepared with ultrasonic retro-tips is the most effective means for removal of smear layer.

An in vitro evaluation of effect of eugenol exposure time on the shear bond strength of two-step and one-step self-etching adhesives to dentin.

OBJECTIVES: To evaluate the effect of the eugenol exposure time of an eugenol-based provisional restorative material on the shear bond strength of two-step and one-step self-etching adhesives to dentin, at three different time intervals of 24 h, 7 days, and 14 days. MATERIALS AND METHODS: Forty extracted human posterior teeth were sectioned mesiodistally to obtain two halves and the resulting 80 halves were randomly assigned into four groups of 20 specimens each (Group-I, -II, -III, and -IV). Cavities of specified dimensions were prepared to expose dentin surface. In Group-I, temporarization was carried out with noneugenol cement (Orafil-G) for 24 h (control group). In Group-II, -III, and -IV, temporarization was carried out with eugenol cement (intermediate restorative material (IRM)) for 24 h, 7 days, and 14 days, respectively. Each group was further divided into two subgroups of 10 teeth each for two-step (Adper SE Plus) and one-step (Adper Easy One) self-etch adhesive systems, respectively. A plastic tube loaded with microhybrid composite resin (Filtek Z-350, 3M) was placed over the dentin surface and light cured. The specimens were subjected to shear stress in universal testing machine. RESULTS: Group-II yielded low shear bond strength values compared with Group-III, -IV, and Group-I, which was statistically significant. CONCLUSIONS: The prior use of eugenol containing temporary restorative material reduced the bond strength of self-etch adhesive systems at 24-h period. No reduction in bond strength at 7 or 14 days exposure was observed with either two-step or one-step self-etch adhesive.

Evaluation of effect of different cavity disinfectants on shear bond strength of composite resin to dentin using two-step self-etch and one-step self-etch bonding systems: a comparative in vitro study.

AIM AND OBJECTIVES: To evaluate the effect of 2% chlorhexidine, 2% sodium hypochlorite, 3% hydrogen peroxide on shear bond strength of composite resin to dentin using two-step and onestep self-etch bonding systems and to study the mode of failure of specimens under stereomicroscope. MATERIALS AND METHODS: Eighty extracted sound human posterior teeth were used. The occlusal surfaces were ground to expose the dentin and were then randomly divided into 4 main groups. In group I, no cavity disinfectant was used and served as control. In groups II, III, IV, 2% chlorhexidine, 2% sodium hypochlorite and 3% hydrogen peroxide were used as cavity disinfectants respectively. Each group was then divided into two subgroups of 10 teeth each according to the bonding agent used, two-step self-etch (Adper SE Plus) and one-step self-etch (Adper Easy One) respectively. A transparent cylindrical plastic tube was loaded with microhybrid composite and placed over the dentin and light cured for 40 seconds. The specimens were subjected to shear stress in the universal testing machine. RESULTS: Pretreatment with 2% chlorhexidine, 2% sodium hypochlorite and 3% hydrogen peroxide, had a negative effect on the shear bond strength of self-etching bonding systems. CONCLUSION: The highest bond strength was found in 2% chlorhexidine group followed by 2% sodium hypochlorite group and the lowest bond strength was found in 3% hydrogen peroxide group. CLINICAL SIGNIFICANCE: All three cavity disinfectants used in this study reduced the shear bond strength and hence should be used with caution.

Influence of restorative technique, Bevelling and aging on composite bonding to sectioned incisal edges: A comparative in vitro study.

AIM: To evaluate the effect of direct and indirect technique, bevel placement, and aging on the fracture resistance of composite restorations bonded to sectioned incisal edges. MATERIALS AND METHODS: Incisal thirds of 80 human maxillary incisors were sectioned. Four treatment groups of 20 teeth each were formed as follows: Direct composite with bevel and without bevel (Adper single bond 2/Filtek Z350); indirect composite with bevel and without bevel (prepolymerized Filtek Z350 cemented with Adper single bond 2/Relay × ARC). Ten teeth from each group were stored in distilled water for 24 h. The remaining ten teeth were stored in distilled water for 180 days with two thermocycling treatments. The specimens were subjected to shear testing using universal testing machine. Fractured specimens were examined with a stereomicroscope at ×10 magnification to evaluate the failure patterns. The obtained data were statistically analyzed by using ANOVA, Bonferroni test, and Student's t-test. RESULTS: Beveled restorations exhibited higher fracture resistance values than nonbeveled restorations. Long-term water storage decreased the fracture resistance. CONCLUSION: The use of bevels resulted in improved fracture resistance of composite restorations and reduced the impact of aging.

A comparative study of different bleaching agents on the morphology of human enamel: an in vitro SEM study.

UNLABELLED: The purpose of the study was to compare two different commercial bleaching agents, Opalescence with Colgate Platinum, and 30% phosphoric acid used as aggressive agent on the morphology of human enamel. MATERIALS AND METHODS: Ten freshly extracted, noncarious, human maxillary central incisors extracted for periodontal reasons were used in this study. The labial surface of the disinfected teeth were polished using a polishing paste with the help of rubber cup and a slow speed handpiece. Each tooth was sectioned at cement-enamel junction and the crown was separated into four specimens, all taken from labial surface. Group 1 was treated with Colgate Platinum for 7 hours, group 2 with Opalescence for 7 hours, group 3 was treated with 30% phosphoric acid for 30 seconds and group 4 was untreated and used as control. After the treatment period, the specimens were washed with normal saline and stored in sterile bottle and sealed. Photomicrographs obtained from the scanning electron microscopy (SEM) after surface treatments were examined for no alteration, slight alteration, moderate alteration and severe alterations. RESULTS: The specimens treated with commercial bleaching agents revealed no enamel surface morphologic alterations compared to control group. The specimen treated with phosphoric acid showed severe alterations. CONCLUSION: Ten percent carbamide peroxide evaluated in this study does not etch tooth enamel or alter enamel surface morphology as do conventional etching techniques. CLINICAL RELEVANCE: Carbamine peroxide is a safe and effective tooth whitening agent even when used for extended period of time. The enamel surface remains smooth which reduces caries due to plaque collection.