Effect of gamma,ethylene oxide,electron beam,and plasma sterilization on the behaviour of SR-PLLA fibres in vitro

- The aim of this study was to evaluate the effect of various sterilization processes on the physical and mechanical properties of self-reinforced bioabsorbable fibres made out of polylactide (PLLA). The samples were sterilized using plasma, ethylene oxide (one and two cycles), gamma (25 kGy at room temperature, 25 kGy in dry ice, and 2 × 25 kGy at room temperature), and electron beam (15, 25, and 55 kGy) sterilization. The intrinsic viscosity, crystallinity, and mechanical properties (modulus of elasticity, yield strength, and ultimate tensile strength) were tested before and immediately after each sterilization treatment, as well as up to 30 weeks in vitro. Compared with unsterilized fibres, the intrinsic viscosity was markedly decreased after radiation sterilization (gamma and electron beam) and the loss in mechanical properties was accelerated during in vitro degradation. Plasma and ethylene oxide (one and two cycles) did not markedly alter the properties of the samples after sterilization or during in vitrodegradation. These data are important for determining the effect of various sterilization processes on the physical and mechanical properties of polylactidebased materials and can be used to predict how fast degradation of the mechanical properties of the self-reinforced PLLA will occur. They can also be used to tailor the degradation kinetics to optimize implant design.     

Assessment of IGRT variability for lung SBRT

PurposeThe purpose of this project was to assess factors that may influence variability in the pre-treatment kilovoltage cone beam computed tomography (kV CBCT) image matching process for lung stereotactic body radiation therapy (SBRT).Methods and materialsPre-treatment CBCT and planning CT data sets of previously-treated lung SBRT patients were gathered and anonymized from four radiotherapy centers in Alberta. Eight radiation therapists (RTTs) and four radiation oncologists (ROs) were recruited from the same four cancer centers for image matching. Identical data sets were provided to each user, but the order of image sets was randomized independently for each user to remove any learning bias. Inter-user variabilities were then investigated as functions of various factors, including image origin (source institution/machine), user's institution (local matching protocol), profession (RTT vs. RO), years of experience and image quality (presence/absence of added noise).ResultsVery little variation in image matching between different users was observed. The mean differences from the consensus means for different image sets were less than 1 mm in all directions, and cases that exceeded 3 mm (i.e. clinically significant differences) were extremely rare. Image origin, user's institution, and profession (RTT vs. RO) didn't lead to any meaningful clinical differences, while image quality didn't introduce any statistically significant differences. In addition, no discernible trend was seen between user's experience and deviation from the user mean. Overall, no meaningful differences in inter-user variabilities for the different factors investigated were found in this study.ConclusionsThere appears to be an adequate standardization across the province of Alberta in terms of CBCT image matching process. No clinically significant differences were observed as functions of various factors investigated in this study. Consistency in matching between RTTs and ROs in this study suggests that RTTs do not need systematic RO approval of their lung CBCT match. It should be noted that RTTs at the centers in this study receive comprehensive training in CBCT-based image matching.     

Probing the interfacial strength of novel multi-layer zirconias

ObjectivesThe rapidly increasing use of zirconia-based CAD/CAM multi-layer structures in dentistry calls for a thorough evaluation of their mechanical integrity. This work examines the effect of the multi-layering architecture as well as variations in composition and inclusion of pigments among the layers on the flexural strength of multi-layer zirconias.MethodsA modified 4-point bending test, aided by a Finite Element Analysis (FEA), was used to probe the interfacial strength of 3 classes of yttria-partially-stabilized zirconia: Ultra Translucent Multi-Layer (UTML—5Y-PSZ), Super Translucent Multi-Layer (STML—4Y-PSZ), Multi-Layer (ML—3Y-PSZ). In accord with the size limitation (22-mm height) of CAD/CAM pucks, test samples were prepared in the form of “long” (25 × 2 × 3 mm) and “short” (17.8 × 1.5 × 2 mm) beams. Homogeneous beams (both long and short) were produced from either the Enamel (the lightest shade) or Dentin (the darkest shade) layer, whereas multi-layer beams (short beam only) were obtained by cutting the pucks along their thickness direction, where the material components of various shades were stacked.ResultsThe Enamel and Dentin layers exhibited similar flexural strength for a given material class, with ML amassing the highest strength (800–900 MPa) followed by STML (560–650 MPa) and UTML (470–500 MPa). The 3 classes of multi-layer zirconia showed a trade-off between strength and translucency, reflecting different yttria contents in these materials. The failure stress of the cross-sectional multi-layer beams was, however, ∼30% lower than that of their Enamel or Dentin layer counterparts, regardless of material tested.SignificanceThe weakness of interfaces is a drawback in these materials. Additionally, when measuring strength using short beam flexure, friction between the specimen and supporting pins and accuracy in determining loading span distances may lead to major errors.     

Access to original canal trajectory after deviation and perforation with guided endodontic assistance

Procedural accidents are eventualities that may occur during endodontic treatment because of lack of attention to detail or even unforeseeable situations. Knowledge of the root canal anatomy and its variations is a prerequisite for successful endodontic treatment. This case report describes an endodontic treatment where there was an intercurrence, generating deviation and perforation, which was solved with the aid of guided endodontics. A 37 years old, ASA1, was referred to the clinic for localisation and treatment of a calcified canal of the second right upper premolar. The tomographic images revealed the presence of only one canal and deviation with apical perforation. With the help of CBCT and CAD/CAM, it was possible to perform the guided access technique even after deviation and root perforation. Once again, this technique proved to be safe and predictable, allowing for a favourable prognosis in the long term.     

Standardized method to quantify the variation in voxel value distribution in patient-simulated CBCT data sets

Objectives:

To suggest a standardized method to assess the variation in voxel value distribution in patient-simulated CBCT data sets and the effect of time between exposures (TBE). Additionally, a measurement of reproducibility, Aarhus measurement of reproducibility (AMORe), is introduced, which could be used for quality assurance purposes.

Methods:

Six CBCT units were tested [Cranex^® 3D/CRAN (Soredex Oy, Tuusula, Finland); Scanora^® 3D/SCAN (Soredex Oy); NewTom™ 5G/NEW5 (QR srl, Verona, Italy); i-CAT/ICAT (Imaging Sciences International, Hatfield, PA); 3D Accuitomo FPD80/ACCU (Morita, Kyoto, Japan); and NewTom VG/NEWV (QR srl)]. Two sets of volumetric data of a wax-imbedded dry human skull (containing a titanium implant) were acquired by each CBCT unit at two sessions on separate days. Each session consisted 21 exposures: 1 “initial” followed by a 30-min interval (initial data set), 10 acquired with 30-min TBE (data sets 1–10) and 10 acquired with 15-min TBE (data sets 11–20). CBCT data were exported as digital imaging and communications in medicine files and converted to text files containing x, y and z positions and grey shade for each voxel. Subtractions were performed voxel-by-voxel in two set-ups: (1) between two consecutive data sets and (2) between any subsequent data set and data set 1. The mean grey shade variation for each voxel was calculated for each unit/session.

Results:

The largest mean grey shade variation was found in the subtraction set-up 2 (27–447 shades of grey, depending on the unit). Considering subtraction set-up 1, the highest variation was seen for NEW5, between data sets 1 and the initial.

Conclusions:

Discrepancies in voxel value distribution were found by comparing the initial examination of the day with the subsequent examinations. TBE had no predictable effect on the variation of CBCT-derived voxel values. AMORe ranged between 0 and 64.     

下颌第三磨牙萌出状态与第二磨牙远中邻面龋坏的相关性研究

目的:研究下颌第三磨牙萌出状态与第二磨牙远中邻面龋坏的相关性。方法 :临床收集因下颌第三磨牙不适而就诊的患者204例,运用锥形束CT分析下颌第二磨牙远中邻面龋坏与第三磨牙阻生类型(高位、中位、低位)、阻生角度以及两磨牙的釉牙骨质界距离(cementoenamel junction,CEJ)等因素是否存在相关性。结果:在下颌第三磨牙存在的情况下,第二磨牙远中邻面龋坏发生率高达78.4%;性别差异无统计学意义(P=0.165);高位、中位和低位阻生的龋坏发生率差异无统计学意义(P=0.646);而当第三磨近中阻生角度为40~80°时,第二磨牙远中邻面最易发生龋坏,与其他阻生角度组的差异有统计学意义(P<0.001);当第二磨牙与第三磨CEJ距离在6~9 mm时,第二磨牙远中邻面龋坏高于其他组,差异有统计学意义(P<0.001)。结论:下颌第三磨牙近中阻生角度、第三磨牙与第二磨牙的CEJ距离与第二磨牙远中邻面龋坏的发生密切相关。当第三磨近中阻生角度在40~80°间,且两磨牙间的CEJ距离在6~9 mm时,第二磨牙远中邻面更容易发生龋坏,此类阻生齿建议尽早拔除。     

不同垂直骨面型成人下切牙区牙槽骨形态特征的CBCT研究

目的：比较不同垂直骨面型下前牙区牙槽骨形态特征,并初步探讨年龄对牙槽骨形态的影响。方法选取未行正畸治疗的100例患者的CBCT资料,根据患者垂直骨面型进行分组,组内再根据年龄分为青年组及中年组。应用Simplant软件进行下切牙区牙槽骨形态分析,并使用SPSS软件进行数据处理。比较各类骨面型下前牙区骨形态以及年龄对牙槽骨形态的影响。结果下切牙区牙槽骨形态及下切牙倾斜度在不同垂直骨面型间存在统计学差异,增龄也会对牙槽骨形态造成影响。高角组的唇舌侧牙槽骨高度较低,骨厚度较小,下切牙较舌倾。结论不同垂直骨面型之间下切牙区牙槽骨形态存在差异,提醒在正畸矫治设计时予以注意。