Apical Curvature Research Articles

Clinical insights into tooth extraction via torsion method: a biomechanical analysis of the tooth-periodontal ligament complex.

Traditionally, extracting single, flat- or curved-rooted teeth through twisting is unfeasible. However, our clinical practice suggests that such teeth can be extracted efficiently through moderate twisting in a minimally invasive manner. Given the lack of studies on biomechanics of the tooth-periodontal ligament (PDL) complex during torsion, which has further constrained its application, we assessed the feasibility of the torsion method for extracting single-rooted teeth and evaluated its minimally invasive potential. Using three-dimensional finite element analysis, we examined the stress distribution of the tooth and PDL during torsion. Then, we examined changes in the optimal torsion angle (OTA) and stress distribution across various anatomical scenarios. During torsion loading, stress concentration was primarily observed on the sing-rooted tooth surface near the alveolar crest, whereas molars at the root furcation. The OTA was found to increase under conditions such as narrowing of root width, decrease in the root apical curvature, change from type I to IV bone, alveolar bone loss, and shortening of root length. Moreover, the clinically validated model demonstrated that 74% of outcomes fell within the standard OTA range. In conclusion, the decrease in PDL area necessitated a larger angle for complete PDL tearing. Single-rooted teeth with root width-to-thickness ratios of ≥0.42 and apical curvatures of ≤30°are suitable for extraction using the torsion method. This study confirms the feasibility of the torsion method for minimally invasive tooth extraction and expands its indications, laying the theoretical foundation and essential insights for its clinical application.

Segmental range-of-motion by vertebral level in fused and unfused patients with adolescent idiopathic scoliosis: a systematic review of the literature.

This study aims to understand global and segmental spinal ROM in surgical and nonsurgical AIS patients. This systematic review examined segmental vertebral ROM in AIS patients using PubMed, SPORTDiscus, MEDLINE, and Web of Science until October 8th, 2023. Inclusion criteria were articles on segmental motion in AIS patients, both operative and non-operative, under 18years old. Seventeen articles met eligibility criteria from 2511 initially retrieved. All patients (n = 996) had AIS (549 non-operative; 447 were operative), with a frequency-weighted mean age of 15.1 ± 1.6years and a baseline Cobb angle of 51.4 ± 13.3 degrees. Studies showed heterogenous segmental flexibility in the unfused spine, with the apical curve and upper thoracic segments being more rigid and lower segments more flexible at -5 disk segments from the apex. Most studies showed a predictable loss of motion in fused spinal regions postoperatively and a variable loss of global motion depending on the LIV and number of fused segments. A 7° global loss of total trunk flexion per level was observed with increasingly caudal LIV, starting at L1. Anterior vertebral body tethering (AVBT) preserved motion post-surgery but reduced coronal plane motion. AVBT saw less motion loss compared to posterior spinal fusion (PSF) but had higher revision and complication rates. Preservation of spinal segments correlated with improved motion postoperatively. Increasing caudal LIV in PSF showed sagittal flexion loss. AVBT preserved more sagittal ROM than PSF but increased coronal motion loss, complications, and revision rates, with the largest benefit at LIV L4. Data on segmental motion are limited and further research on postoperative segmental ROM is required.

The flaring efficiency of the Profile and Protaper on resin simulated root canals

Forty resin simulated root canals with standardized curvature prepared for thisstudy, divided into four groups ten canals for each group. Thirty canals were preparedwith rotary endodontic instruments, profile 04, profile 04, 06 and protaper, ten canalsfor each type, with slow speed contra angle hand piece (300 rpm) using crown — downtechnique the other l0 canals were prepared with stainless steel k-flexo handinstrument using step — back technique. The total time required for preparation wascalculated. The resin blocks were scanned; the pre-instrumented and post -instrumented images were stored in the computer and superimposed for twodimensional evaluation of canals preparation using Adobe photoshope 8.0 and Coreldraw 9. For the coronal portion the amount of canal substance removed wascalculated at 7mm, 9mm, llmm levels from the working length. For the apicalcurvature the centering ratio was calculated at 2mm and 4mm level from the workinglength. The results showed that the amount of canal substance removed from thecoronal portion by protaper was statistically higher than other groups with statisticallyless ability to stay center in the canal than profile rotary instruments but more abilityto preserve apical curvature than k-flexo hand instruments with less time required forpreparation. K-flexo files showed statistically less amount of canal substance removalat coronal portion and statistically higher centering ratio than other groups, andrequire more time for canals preparation .

Impact of Angle of File Access and Location of Canal Curvature on the Dynamic Cyclic Fatigue of Nickel Titanium Rotary Instruments.

To evaluate the impact of different file access angles and root canal curvature's location on the fatigue failure of One Curve (OC) and E3 Azure (EZ) NiTi files using a dynamic model at simulated body temperature. Eighty new instruments with similar tip sizes and taper (#25/0.06) from two NiTi rotary systems, One Curve and E3 Azure, were tested at simulated body temperatures (37°C) using a custom-made dynamic cyclic fatigue device. Instruments were divided into four subgroups according to the location of root canal curvature (a coronal curve 5 mm from the root canal orifice and an apical curve 10 mm from the root canal orifice) and the angle of file access (0° or 30°). Instruments were operated in simulated stainless-steel canals having a 60° curve and a 3 mm radius. A custom-made device produced controlled vertical pecks during file rotation. Time to failure (sec) was registered, and the length of the fragment segments was measured (mm). Data were analysed statistically with One-Way ANOVA and Tukey post hoc tests. The significance level was set at 5%. All separated instruments were examined by scanning electron microscope. One-way ANOVA (p<0.05) found a significant difference among the tested instruments. Post Hoc analysis revealed lower cyclic fatigue resistance when the angle of file access was 30º, and the root canal curvature was located coronally for both files (p<0.0001). Three-way ANOVA showed that the angle of file access was the most influential contributor to cyclic fatigue, followed by the location of file curvature and, finally, the file type (p<0.0001). The fractographic examination revealed a predominantly ductile fracture mode for all tested instruments. The lengths of all fractured segments showed no significant difference (p>0.05), indicating an accurate trajectory during testing. OC files had superior cyclic fatigue resistance than EZ files; coronal curvatures negatively impacted cyclic fatigue resistance compared to apical curvatures, while the angle of file access presented the highest impact on dynamic cyclic fatigue.

Effect of preset torque setting on torque/force generation, shaping ability and surface changes of nickel titanium rotary instrument in different root canal curvature locations: An ex vivo study.

The aim of this study was to evaluate how preset torque settings influence the torque, vertical force, and root canal-centering ability of ProGlider and ProTaper NEXT nickel-titanium rotary instruments in canals with different curvature locations. Based on micro-computed tomography, mesial roots of human mandibular molars (25°-40° curvature) were allocated to the apical curvature (apical 1-5 mm) or the middle curvature (apical 5-9 mm) groups, and mandibular incisors (curvature <5°) to the straight canal group. Each group was subjected to automated instrumentation and torque/force measurement with the preset torque of 1, 2.5, or 5 N•cm. Canal-centering ratios were determined with micro-computed tomography. Instrument fracture occurred only in the 2.5 and 5 N•cm groups in curved canals. The preset torque setting and curvature location did not influence canal shaping ability.

An Alternative Method of Management of a Separated Endodontic File Beyond the Apex - A Case Report

Endodontic instrument fracture is a prevalent challenge in root canal therapy, often leading to treatment complications and increased procedural difficulty. This case report presents an alternative way of treating an endodontic file separated in the apical third of the mesio-buccal canal of a lower molar. Due to the strategic importance of the tooth, the considerable apical curvature and patient’s requirements, the clinicians opted for deliberate extrusion of the broken fragment into the periodical tissues, thus hermetically sealing the endodontic space. This approach has the potential to offer a less traumatic treatment option under certain conditions. Keywords: separated, file, fracture, management, alternative

Effect of foraminal enlargement on microcrack formation and apical transportation: a nano-CT assessment

The aim of this study was to evaluate the foraminal enlargement and its influence on microcrack formation and apical transportation in root canals with apical curvature. Eighteen maxillary lateral incisors with apical curvature were selected by using micro-CT images. Root canals were randomly divided in two groups (n = 9) according to root canal preparation using two working lengths: 1 mm short of the apical foramen (control group) and 1 mm beyond the apical foramen (foraminal enlargement). For both groups Reciproc Blue R40 was used for root canal instrumentation. Specimens were scanned by nano-CT (UniTOM HR) before and after root canal preparation. Percentage, length, and width of microcracks, and apical transportation were assessed. Kappa, chi‐square and McNemar tests were used for qualitative analyses while paired and unpaired t-test were used for quantitative analyses (α = 0.05). For both groups, rather similar and low percentages of microcracks were observed before root canal preparation (P > 0.05). The foraminal enlargement promoted new microcracks, not observed in the control group. An increase in microcrack length was observed when the foraminal enlargement was performed (P < 0.05). Higher apical transportation was observed when foraminal enlargement was performed (P < 0.05). Foraminal enlargement using a heat-treated reciprocating file size 40 promoted microcracks and higher apical transportation than root canal preparation up to 1 mm short of apical foramen.

Shaping Ability of Protaper Gold and Protaper Ultimate in Simulated Root Canals: A Comparative Study

This study aimed to compare the shaping ability of ProTaper Gold (PTG) and the newly developed ProTaper Ultimate (PTU) systems in artificial S-shaped canals. Both files are manufactured via gold thermal treatment methods and have variable taper along their working part. Thirty-Two S-shaped canals in clear resin blocks were prepared up to an apical size of 25 using PTU and PTG instruments (n = 16 canals/group). Resin blocks were filled with ink and photographed before &amp; after instrumentation to develop composite images by superimposition. The amount of removed resin was measured perpendicularly to the canal surface in 18 points, in addition to the canal transportation and centering ratio. Statistical analysis was performed by using Manne-Whitney U-test (α = 0.05). No broken files or aberrations were recorded during instrumentation. PTG significantly removed a higher amount of resin at 4, 6, 8, and 9 mm from the apex, but at 1 mm PTU significantly cut a higher amount (p &lt; 0.05). Concerning transportation &amp; centering ability, both files deviated from the center and at 3 mm PTU yielded significantly higher deviation, while at 4 mm PTG recorded a higher value (p &lt; 0.05). In conclusion, PTU produced more conservative preparation than PTG especially in the coronal third, while for maintaining the original canal curve, PTG caused lesser deviation at the beginning of the apical curvature.

A novel model to evaluate the fatigue resistance of NiTi instruments: Rotational and axial movement at body temperature.

To develop a model to test cyclic fatigue resistance of TruNatomy instruments undergoing rotational and axial movement at body temperature. A total of 288 Prime and Medium instruments were subjected to cyclic fatigue testing in simulated canals (at 37°C) using a model with either rotational movement only or rotational and axial movement simultaneously. Two different sized canals and three different types of curvatures were tested for each instrument (30/0.04 and 30/0.06 for Prime; 38/0.04 and 40/0.06 for Medium). The number of cycles to failure (fatigue resistance) was recorded. Rotational and axial movement of instruments led to greater fatigue resistance compared with rotational movement alone. Apical curvatures led to greater fatigue resistance than curvatures in the coronal and middle third. The developed dynamic model at body temperature to evaluate fatigue resistance of instrument closer simulates clinical scenarios.

Effect of kinematics on the torque/force generation, surface characteristics, and shaping ability of a nickel‐titanium rotary glide path instrument: An ex vivo study

AbstractAimTo evaluate the effect of various rotational motions on the torque/force generation, surface wear, and shaping ability of the ProGlider glide path instrument (Dentsply Sirona).MethodologyMesiobuccal and mesiolingual canals of mandibular molars were selected based on the canal volume, length, angle of curvature (25°–40°), and radius of curvature (4–8 mm) after micro‐computed tomographic scanning. The samples were randomly assigned to four groups (n = 13, each) according to movement kinematics [continuous rotation (CR; 300 rpm), optimum torque reverse motion (OTR; 180° forward and 90° reverse when torque &gt;0.4 N cm), time‐dependent reciprocal motion (TmR; 180° forward and 90° reverse), and optimal glide path motion (OGP; a combination of 90° forward, 90° reverse, 90° forward, and 120° reverse)]. Instrumentation was performed with an automated root canal instrument and torque/force analysing device. Maximum torque/force values, canal volume changes, and canal‐centring ratios at 1, 3, 5, and 7 mm were evaluated. Surface defects (pits, grooves, microcracks, blunt cutting edges, and disruption of cutting edges) and spiral distortion on the ProGlider instrument were scored at the tip and 5 mm short of the tip before and after five consecutive uses with scanning electron microscopy. The Kruskal–Wallis test followed by Dunn's post‐test with Bonferroni correction and Wilcoxon signed‐rank test were used to analyse the data (α = 0.05).ResultsOptimal glide path motion generated significantly less clockwise torque and greater upward force than other groups (p &lt; .05). OGP resulted in significantly fewer surface defects than CR (p &lt; .05). In OGP and CR, the tip exhibited more surface defects than 5 mm short of the tip (p &lt; .05). CR resulted in greater volume changes than OGP and TmR (p &lt; .05) and greater centring ratios (i.e., more deviation) than OGP at 1 mm and OTR at 3 mm (p &lt; .05).ConclusionsUnder laboratory conditions using the ProGlider instrument, OGP generated significantly less clockwise torque and greater upward force than the other rotatory motions. OGP generated fewer superficial defects than CR, and the three modes of reciprocal rotation better maintained the apical curvature of root canals than CR with the ProGlider instrument.

Comparison of Cyclic Fatigue Resistance of Novel TruNatomy Files with Conventional Endodontic Files: An In Vitro SEM Study

To compare and analyze the cyclic fatigue resistance of novel TruNatomy files against the conventionally used rotary files and reciprocating files in a simulated canal system with curvatures in the middle, apical portions root, and S-shaped canal employing scanning electron microscopy. Endodontic files tested in the study include ProTaper, HyFlex EDM, Reciproc blue, and TruNatomy files operated in a simulated root canal system. A total of 96 files were employed in this study. They were categorized into four groups. Group 1 employed 24 TruNatomy files, group 2 employed 24 ProTaper gold files, group 3 employed 24 HyFlex EDM files, and group 4 employed 24 Reciproc blue files. All the groups employed eight files each under three subgroups namely A, B, and C representing middle, apical, and double curvatures, respectively. Artificial grooves were incorporated in the stainless steel blocks having three different curvatures. All the file systems were operated with a torque-controlled electric motor. The files were engaged in the artificial canal until the occurrence of fracture. The time required for the fracture was noted. Length of fractured tip was measured using the digital Vernier caliper. The number of cycles of failure (NCF) was calculated. The fractured parts were subjected to scanning electron microscope to analyze the mode of fracture. TruNatomy files had the highest mean NCF values of 588.01 in middle curvature, 1,321 in apical curvature, and 642.5 in S-shaped curvature HyFlex EDM and Reciproc blue file system exhibited comparable cyclic fatigue resistance among them. ProTaper gold file system exhibited least mean NCF values of 158.13 in the middle, 196.5 in the apical curvature, and 116.88 in the S-shaped canal system. Middle portion fractured first than the apical curvature. The mean length of fractured segments was found to be insignificant among the experimental study groups tested. All the file systems employed in the study had good cyclic fatigue resistance while TruNatomy files had the highest cyclic fatigue resistance while HyFlex EDM and Reciproc blue had comparable fatigue resistance. ProTaper gold file system had the least fatigue resistance at different radius of curvature in the simulated canal system in the apical and middle portions and S-shaped root canal. The selection of file systems in cleaning and shaping protocols is an enigma to the endodontics. This in vitro study explored the selection protocols for the execution of root canal preparation. Heat treatment of nickel-titanium (NiTi) endodontic files had improved the cyclic fatigue résistance significantly enhancing the clinical life of file systems.

Root Canal Morphology of Mandibular First Premolars using Radiography: An in vitro study

Objective: The goal of this study was to document the Root Canal morphology of the first mandibular premolars using radiography.&#x0D; Materials and Methods: The trial took place at the LUMHS Operative Dentistry Department. Two hundred removed permanent mandibular first premolars that met all of the study's inclusion criteria were gathered from LUMHS Jamshoro/Hyderabad and nearby private dental clinics in Hyderabad. All debris, soft tissues, and calculus were removed from the teeth, which were then preserved in a 10% formalin solution. Each tooth's length was measured from the crown's tip to the root's apex. An removed tooth, on the other hand, was examined from all angles, including buccal, lingual, and proximal. Root concavities and grooves, as well as bifurcation and apical curvature, were found.&#x0D; Results: Comparison between both views showed 189 teeth have 1 root in and 186 have 1 canal in buccolingual view, while 182 teeth have 1 root and 179 have 1 canal in mesiodistal view. 11 teeth on buccolingual and 18 teeth on mesiodistal view showed 2 roots and 14 teeth on buccolingual and 21 teeth on mesiodistal view showed 2 canals. 110 teetj showed type I canal pattern.&#x0D; Conclusion: It is concluded that mandibular first premolar teeth have a wide range of radicular traits, with the majority of them having one root and one canal.

Pertinence of the Tactile Controlled Activation(TCA) technique in the management of severely curved root canals - A report of two cases

Canal curvatures such as dilacerated canals, bayonet-shaped canals, and acute curvatures in the apical third pose a therapeutic challenge to the clinician. Pre-treatment determination of the degree of curvature, usage of scrupulous instrumentation techniques facilitate successful negotiation of the bends and enhance the quality of the treatment. The following case series chronicles the application of a novel instrumentation technique known as Tactile Controlled Activation(TCA) technique in the management of sharp apical curvatures in a molar and a premolar, thus upholding its accountability in the management of canal curvatures without any iatrogenic mishaps, besides maintaining the original trajectory of the canal. Keywords curved canals, dilacerations, novel instrumentation technique, root canal curvatures, rotary files

Static Cyclic Fatigue Resistance in Abrupt Curvature, Surface Topography, and Torsional Strength of R-Pilot and ProGlider Glide Path Instruments

IntroductionThis study aimed to compare ProGlider (Dentsply Sirona, Ballaigues, Switzerland) and R-Pilot (VDW, Munich, Germany) instruments in terms of their cyclic fatigue resistance using an artificial stainless steel canal showing an abrupt apical curvature, torsional resistance according to the ISO specification, and topographic changes on the instrument surface after glide path management in mesial canals of mandibular first molars with the abrupt curvature selected based on their micro–computed tomographic examination. MethodsEighty instruments were used: 40 ProGlider (size 0.16, .02v taper) and 40 R-Pilot (size 0.125, .04 taper) instruments. The cyclic fatigue resistance was tested in a static test model using an artificial canal with an abrupt apical curvature (angle of curvature of 90° and radius of curvature of 2 mm). The torsional resistance test was performed according to ISO 3630-1 specifications. To determine surface topography of the unused and used instruments, mesial root canals of mandibular molars with an abrupt apical curvature were selected to prepare a glide path with either the ProGlider or R-Pilot instrument. An optical profilometer and scanning electron microscopy were used to determine the surface properties. Normally distributed torsional and cyclic resistance data were analyzed using the Student t test, whereas quantitative data obtained by the optical profilometer were analyzed with the Kruskal-Wallis H test with a 5% significance threshold. ResultsThe R-Pilot showed significantly higher cyclic fatigue and torsional resistance than the ProGlider (P < .05). Angular deflection values were similar between instruments (P < .05). Measurements made from the blade area showed that the surface roughness values of the ProGlider were larger. Cutting blade measurements showed that unused instruments had significantly greater roughness values than used ones (P < .05). Although there was a 14% increase between the blade edge radii of the used and unused R-Pilot instruments, this difference was determined as 61% in ProGlider instruments. ConclusionsThe R-Pilot exhibited greater cyclic fatigue strength than the ProGlider when tested in an artificial canal with an inner diameter of 1.0 mm and an abrupt apical curvature. Torsional resistance of the R-Pilot was higher than the ProGlider, but the angular deflection values were similar. Glide path preparation in a mesial root canal with an abrupt apical curvature did not increase the surface roughness of both instruments but resulted in a greater blade edge radius.

Shaping ability of ProTaper Gold and WaveOne Gold nickel-titanium rotary instruments in simulated S-shaped root canals

Background/purposeGold metal technology improves flexibility and the resistance to cyclic fatigue of the endodontic mechanical files. This study compared the performance of ProTaper Gold (PTG) multiple file system and WaveOne Gold (WOG) single file system in simulated S-shaped root canals, which represents one of the most challenging root canal morphology. Materials and methodsForty S-shaped canals (n = 20 canals/per group) in resin blocks were instrumented to an apical size of 0.25 mm using PTG and WOG Primary, respectively. The total amount of resin removal, canal transportation, centering ratio, and the degree of canal straightening were measured in Photoshop CS6 software. Statistical analysis was performed by using Mann–Whitney U-test (α = .05). ResultsNone of the files fractured during the instrumentation. The WOG group removed significantly less amount of resin at 0, 3, 6, 7 and 9 mm from the apex (P < .05). The WOG group remained more centered in canals at 0 mm from the apex (P < .05). The PTG group showed a better centering ability and less canal transportation at 4, 5 and 6 mm from the apex (P < .05). In the coronal curvature portion, the use of WOG Primary significantly decreased curvature angle and increased radius compared with PTG instruments (P < .05). There was no significant difference between the two groups in terms of the apical curvature angle and radius change (P > .05). ConclusionThe WOG Primary file has a less aggressive dentin cutting and more centered apical preparation. The PTG system is more advantageous in shaping the coronal curvature of S-shaped canal.

Efficacy of five irrigation techniques in removing calcium hydroxide from simulated S-shaped root canals

Background/purposeCalcium hydroxide [Ca(OH)2], a wildly used intracanal medicament, should be completely removed from the root canal before obturation to avoid negative effects on the treatment. This study evaluated the effectiveness of conventional needle irrigation (CNI), passive ultrasonic activation (PUI), photon-induced photoacoustic streaming (PIPS), XP-endo Finisher (XP) and EDDY for the removal of Ca(OH)2 from S-shaped root canal. Materials and methodsEighty-four S-shaped root canals in resin blocks were prepared using Protaper Gold up to size #25/0.08 and filled with Ca(OH)2. Five groups were established according to the removal techniques (n = 16): CNI, PUI, PIPS, XP and EDDY group. The positive and negative control group (n = 2) were also established. Sodium hypochlorite 3% was used as the irrigant. Digital radiographs were used to measure the remaining Ca(OH)2. Statistical analysis of the data was performed by using the Kruskal–Wallis test, followed by Dunn's post hoc test with Bonferroni correction (α = 0.05). ResultsAll the tested techniques completely removed Ca(OH)2 from the straight portion and coronal curve of the S-shaped root canal in 100% of cases. Regarding the apical curve, PUI, EDDY, PIPS and XP removed significantly more Ca(OH)2 than CNI (P < 0.05), with no significant differences among these four groups (P > 0.05). The complete clearance of Ca(OH)2 from the apical curve was observed in 75%, 62.5%, 56.3%, 43.8% and 0% of cases of PUI, EDDY, PIPS, XP and CNI group, respectively. ConclusionIrrigant activation enhanced Ca(OH)2 removal from the apical region of the S-shaped root canal. CNI was significantly less effective than all activation techniques.

Cone-beam computed tomographic analysis of apical transportation and centering ratio of ProTaper and XP-endo Shaper NiTi rotary systems in curved canals: an in vitro study

BackgroundCleaning and shaping of the root canal system is an important step of endodontic treatment. Canal transportation is a common procedural error in preparation of curved canals. This study aimed to compare the canal transportation and centering ratio of two rotary files in curved canals using cone-beam computed tomography (CBCT).MethodsForty-four extracted human mandibular first molars with mature apices and 10° to 30° apical curvature were selected. The samples were randomly divided into two groups (n = 22) with similar curvature. The canals were prepared with ProTaper and XP-endo Shaper file systems according to the manufacturers’ instructions. The CBCT images were obtained using Cranex 3D CBCT scanner before and after root canal preparation, and canal transportation and centering ratio of the files at 3, 4 and 5 mm levels from the apex were calculated. Data were compared between the two groups using independent t-test at 0.05 level of significance.ResultsThe ProTaper Universal caused greater canal transportation and had lower centering ratio than XP-endo Shaper in both mesiodistal and buccolingual directions at all levels from the apex. The difference between the two groups regarding canal transportation was significant at all levels from the apex in buccolingual direction (P < 0.05) except for 3 mm from the apex (P > 0.05). The difference between the two groups regarding centering ratio was not significant (P > 0.05) in mesiodistal direction at all levels except for 4 mm from the apex (P < 0.05).ConclusionThe ProTaper Universal causes greater canal transportation in both buccolingual and mesiodistal directions than XP-endo Shaper.

Comparison of Low Degree/High Degree and Zernike Expansions for Evaluating Simulation Outcomes After Customized Aspheric Laser Corrections.

PurposeThe purpose of this study was to compare the low degree/high degree (LD/HD) and Zernike Expansion simulation outcomes evaluating the corneal wavefront changes after theoretical conventional and customized aspheric photorefractive ablations.MethodsInitial anterior corneal surface profiles were modeled as conic sections with pre-operative apical curvature, R0, and asphericity, Q0. Postoperative apical curvature, R1, was computed from intended defocus correction, D, diameter zone, S, and target postoperative asphericity, Q1. Coefficients of both Zernike and LD/HD polynomial expansions of the rotationally symmetrical corneal profile were computed using scalar products. We modeled different values of D, R0, Q0, S, and ΔQ = Q1 to Q0. The corresponding postoperative changes in defocus (Δz20 vs. Δg20), fourth order (Δz40 vs. Δg40) and sixth order (Δz60 vs. Δg60) Zernike and LD/HD spherical aberrations (SAs) were compared. In addition, retrospective clinical data and wavefront measurements were obtained from two examples of two patient eyes before and after corneal laser photoablation.ResultsThe z20, varied with both R0 and Q0, whereas the LD/HD defocus coefficient, g20, was relatively robust to changes in asphericity. Variations of apical curvature better correlated with defocus and ΔQ with SA coefficients in the LD/HD classification. The impact of ΔQ was null on g20 but induced significant linear variations in z20 and fourth order SA coefficients. LD/HD coefficients provided a good correlation with the visual performances of the operated eyes.ConclusionsSimulated variations in postoperative corneal profile and wavefront expansion using the LD/HD approach showed good correlations between defocus and asphericity variations with variations in corneal curvature and SA coefficients, respectively.Translational RelevanceThe relevance of this study was to provide a clinically relevant alternative to Zernike polynomials for the interpretation of wavefront changes after customized aspheric corrections.

Shaping ability of three thermally treated nickel-titanium systems in S-shaped canals.

This study aimed to compare the shaping ability of ProTaper Next (PTN), HyFlex EDM (HEDM) and One Curve (OC) systems manufactured via different thermal treatment methods in simulated S-shaped canals. Sixty S-shaped canals in clear resin blocks were enlarged to a final apical size of 25 using PTN, HEDM and OC instruments (n = 20 canals/group). Composite images were obtained by superimposing pre- and post-preparation images. The amount of removed resin was measured perpendicularly to the canal surface in 22 points. Prepared canal width and canal transportation at different levels were determined. Canal aberrations were also recorded. Data were statistically analysed using analysis of variance, the Kruskal-Wallis and the chi-square tests at a 0.05 significance level. OC produced the most conservative enlargement and better maintained particularly the apical curvature of the S-shaped canals than HEDM and PTN. OC and HEDM better maintained the canal terminus and coronal curvature than PTN.

Influence of sodium hypochlorite and chlorexidine on the dynamic cyclic fatigue resistance of XP-Endo Finisher instruments

Aim: This study evaluated the cyclic fatigue resistance of XP-Endo Finisher (XPF), associated with two different irrigation solutions: sodium hypochlorite 6% (NaOCl) or chlorhexidine digluconate gel 2% (CHX) in a dynamic model. The null hypothesis tested was that there was no statistically significant difference. Methodology: 30 new files were divided into three groups (n=10) based on the irrigation solution used. Group 1: XPF using CHX as an irrigation solution; Group 2: XPF using NaOCl as an irrigation solution; Group 3 (control group): XPF using lubricating oil (LO). The artificial canal was manufactured measuring 1.5 mm wide, 20 mm long, and 3.5 mm deep with a straight cervical segment measuring 14.29 mm. A curved apical segment 4.71 mm with 3 mm radius and 90° of curvature and an ending with straight apical portion measuring 1 mm long. Resistance to cyclic fatigue was determined by recording time to fracture, and the file surface was examined under scanning electron microscopy. Results: Data were tabulated and subjected to statistical analysis of variance. Student-Newman-Keuls test for multiple comparisons, with a significance level of 5%. The average time took for file fracture was 306.7 seconds for 2% chlorhexidine and 67,6 for 6% sodium hypochlorite. 2% CHX was significantly different from the NaOCl and LO groups (P< .001). Conclusions: XPF presented the best results of fracture time and the number of cycles to fracture when used along with 2% chlorhexidine in canals with severe apical curvature, and there was no statistical difference in fragment size.