In utero partial liver resection in the rabbit model: a study on fetal tissue regeneration

This study compared step-back preparations in curved canals of resin blocks using nickel-titanium K-files and stainless steel K-files. Forty canals in resin blocks were cross-sectioned at 3 levels: 1 to 2 mm from the apical foramen, middle of the curve, and coronal. Direct digital computer images were recorded before and after instrumentation. Superimposition of the images combined with digital subtraction computer software allowed direct measurement of area instrumented, distance of transportation, and shape analysis. Time for instrumentation was recorded. Results showed Ni-Ti files to cause significantly less transportation and remain more centered at the apical level (p < 0.05). Area removed by instrumentation was significantly greater for stainless steel files at the middle level (p < 0.05). Cross-sectional shape of the instrumented canal was not significantly different (p < 0.05). It took significantly longer to prepare a canal with Ni-Ti K-files in resin blocks compared to stainless steel (p < 0.05). Resin simulated canals showed similar results compared to canals in extracted roots using an identical methodology.     

Lichen myxoedematosus associated with human immunodeficiency virus infection--report of two cases and review of the literature

The transportation produced in the apical and middle areas of 30 mesiobuccal root canals of human mandibular molars was evaluated after circumferential instrumentation using stainless steel K-files (group A), nickel-titanium K-files (group B), and clockwise/counterclockwise file rotation using Flexogates (group C). The canals were instrumented with files #15 to #35 in size. Apical transportation was assessed radiographically while that occurring in the middle area was studied microscopically in cross-sections. Although apical transportation was greatest in the canals of group A, this difference was not statistically significant (P > 0.05). With respect to the middle area of the root canal, considerable transportation was observed in 7 of the 30 instrumented roots. Of these, five belonged to group A and two to group B, a difference which was not statistically significant (P > 0.05). The best results for transportation in the middle area of the canal were obtained in group C, in which no transportation occurred. This difference was significant when compared with the transportation observed in group A (P = 0.02) but not with that in group B (P > 0.05).     

High frequency catheter ablation in young patients with permanent junctional reentry tachycardia and ectopic atrial tachycardia]

A total of 160 simulated canals of various angles and positions of curvature were prepared by hand using either Mani Flexile Files, Mani SEC-O Files, Maillefer Flexofiles, or Zipperer Flexicut Files. After orifice enlargement, each file type was used to prepare 40 canals employing a balanced force motion and a modified double-flared technique. Pre- and postoperative images of the canals were taken with a videocamera, and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount of material removed as a result of preparation were determined from composite images of superimposed pre- and postoperative views. Significant differences (p < 0.001) in preparation time were observed, with Flexile Files being quickest and SEC-O Files being slowest. Overall, Flexofiles and Flexicut Files deformed significantly more (p < 0.001) than Flexile and SEC-O Files. The incidence of canal blockage was not influenced by instrument type, but the incidence of apical extrusion was significantly greater (p < 0.001) with SEC-O Files. SEC-O Files created significantly fewer (p < 0.001) and significantly narrower (p < 0.001) zips, with significantly less (p < 0.001) removal of material from the outer aspect of the curve and thus significantly less (p < 0.001) transportation. Flexicut Files created the widest canals apically, with the greatest removal of material from the outer aspect of the curve and the most transportation. Flexofiles created significantly more (p < 0.001) perforations. Under the conditions of this study, obvious differences between instruments were highlighted with SEC-O Files preparing canals more safely and with least destruction. The unique rounded tip of the SEC-O Files may have had an influence on the outcome.     

A comparative study on the effect of three methods of instrumentation on the shape of root canal (an in-vitro study)

This study compared the ability of three types of engine driven instrumentation techniques to negotiate and prepare small, slightly curved root canals. Forty five mesial roots of extracted maxillary and mandibular first permanent molars were classified into three groups. Group (I) was prepared by Canal Leader system, group (II) was prepared by Nickel Titanium files and group (III) was prepared by Canal Master technique. Radiographs of the root canal space before and after preparation was carried out by the aid of an experimental model. Enlarged photographic prints obtained from radiographs were scored for shaping effectiveness of the three techniques in respect to canal course, position & width of apical constriction and lack of ledge formation. The results indicated that the Canal Leader system was an efficient technique in maintaining canal curvature, absence of zipping, transportation or ledge formation in almost all of the specimen tested, followed by the Nickel Titanium files and then the Canal Master technique which produced more straightening and destruction of apical constriction.     

Comparison of two endodontic handpieces during the preparation of simulated root canals

The objective of this in vitro study was to compare and assess two endodontic handpieces during the preparation of simulated root canals. One hundred and sixty simulated root canals in clear resin blocks, of two angles and positions of curvature, were prepared using either Shaper files activated by the MM1500 Sonic Air handpiece (Micro-Mega, Besan?on, France) or Excalibur files activated by the W & H Excalibur 969 handpiece (W & H, Bürmoos, Austria). Files of 21-mm or 25-mm length were used. When preparing the canals, the files were used either in line with or perpendicular to the canal curvature. Preparation of the canals was carried out using a technique described in the manufacturers' literature. A variety of parameters were used to compare the handpieces, including an assessment of the canal preparation time, the deformation or fracture of instruments, loss of canal length, weight loss from the resin blocks and the overall postpreparation canal shape. Both handpieces provided an efficient and easy method of preparing and shaping the root canal with little operator fatigue. The MM1500 Sonic Air handpiece took significantly more time (P < 0.001) to prepare the canals and was associated with both more loss of working length (P < 0.05) and more loss of weight (P < 0.001). Both handpieces created a high percentage of aberrations in the shapes of prepared canals. The MM1500 Sonic Air handpiece created significantly more aberrations than the Excalibur handpiece (P < 0.05 for zip and elbow, P < 0.05 for danger zone and coronal narrow). The effects of the variables, canal curvature, file length and the plane of use of the file, on the performance of the handpieces, were also assessed.     

Influence of membrane oxygenators on the pulsatile flow in extracorporeal circuits: an experimental analysis

The vertical force applied to an endodontic spreader generates stress along the canal walls. Recognizing the potential for this stress may reduce the incidence of vertical root fractures. A photoelastic acrylic model was fabricated to exhibit the stress produced during obturation of curved canals using the lateral condensation technique. Twenty standardized models simulating curved canals (32 degrees) were formed within PL-2 photoelastic acrylic resin blocks. The canals were fitted with a gutta-percha point, and either a stainless-steel or nickel-titanium finger spreader was inserted. An Instron 4502 universal testing machine applied a vertical force of 20 Newtons to the spreader. Quarter wave and polarizing filters were used with backlighting to generate the fringe patterns in the models. Photographs of the resulting stress lines showed that the stainless-steel spreaders created three areas of concentrated stress. The nickel-titanium spreaders induced stress patterns spread out along the surface of the canals, thus reducing the concentration of stress and the potential for vertical root fracture.     

Incidence of Lightspeed separation and the potential for bypassing

It is important for endodontic instruments to have a low fracture rate. If a fracture does occur, it would be desirable to have the ability to bypass the broken segment and complete the root canal treatment. One hundred sixty-two root canals in 52 maxillary and mandibular first molars were cleaned and shaped with Lightspeed instruments by three endodontists in their private practices. The canals were instrumented using the technique recommended by the manufacturer. All canals were instrumented to at least a size 45 at the working length. Six instruments separated during treatment. All six had been used more times than recommended by the manufacturer. Five of the six were easily bypassed and treatment completed.     

Effect of two obturation techniques on the filling of lateral canals and the main canal

The three-dimensional obturation of the root canal system is widely accepted as a key factor for successful endodontic therapy. The purpose of this study was to evaluate the obturation of lateral canals and the main canal using cold lateral condensation versus the gutta-percha coated rigid carrier. Thirty epoxy blocks with five lateral canals placed at varying angles from the main canal were used. Each experimental group was obturated by a board certified endodontist with clinical experience in the respective obturation technique. The length of gutta-percha and sealer in the lateral canals was measured under a microscope (x30, Unitron) to the nearest 0.5 mm. The blocks were sectioned with an Isomet Plus precision saw (Buehler, Lake Bluff, IL) and copious water irrigation perpendicular to the main canal at the apex, the height of contour, and at 0.8, 1.6 and 2.4 mm from the canal apex. A microscope (x100, Leitz, Switzerland) was used to determine voids. There was significantly (p < .001) more gutta-percha in the lateral canals with the gutta-percha coated rigid carrier technique. In contrast, the cold lateral condensation technique had significantly (p < .001) more sealer in the lateral canals. However, there was no significant (p < .05) difference, in gutta-percha-plus-sealer filling of the lateral canals, between the two techniques. In the apical 1 mm of the main canal there were significantly (p < .011) fewer voids with the gutta-percha coated rigid carrier technique compared to the cold lateral condensation. In the model chosen, the gutta-percha coated rigid carrier technique and the cold lateral condensation technique were equally effective in filling lateral canals. In filling the main canal, however, the coated rigid carrier technique was more effective.     

Antibacterial activity of calcium hydroxide-containing endodontic sealers on Enterococcus faecalis in vitro

Nickel-titanium instruments purportedly resist deformation and loss of sharpness better than do stainless steel instruments but may be more susceptible to breakage. The processes of wear and breakage of nickel-titanium and stainless steel instruments were examined. Sixty files of five types (12 each) and three manufacturers were used. All were used repeatedly in curved canals until failure or for a maximum of 22 minutes. Each instrument was examined with scanning electron microscopy both new (control) and at spaced intervals for evidence of wear and fatigue. All new instruments were of good quality. Stainless steel instrument tended to wear the most rapidly, and next were nickel-titanium rotary instruments; the most resistant to wear were nickel-titanium hand instruments. There were few instrument separations. In general, nickel-titanium (particularly hand) instruments resisted deterioration better than did stainless steel. Nickel-titanium rotary instruments (2 of 12) had the most breakage.     

The challenge of preparing the curved root canal

Heavily restored teeth which become pulpally involved are now often root canal treated rather than extracted. While this is laudable it has a significant impact on the practice of endodontics today. The curved calcified canal can prove very difficult to prepare to its natural shape by conventional techniques and there is always the likelihood of iatrogenic damage. To compensate for this many clinicians tend to under-prepare these canals, perhaps leaving them inadequately cleaned and certainly remarkably difficult to fill to length. The purpose of this article is to outline the stages of and the rationale behind a hand instrumentation preparation method which uses the balanced force method of movement of files from canal entrance to apical constriction. In the authors' experience this technique has gone a long way towards solving the problem of cleaning and shaping the fine curved canal. With some practice, but no extra expense, the technique described will not only speed up canal preparation but will also make it more predictable.     

Morphometric video analysis of the engine-driven nickel-titanium Lightspeed instrument system

Two hundred and sixteen Lightspeed instruments were evaluated microscopically for the presence of corrosion, surface debris, and alloy defects. The instruments were assessed morphometrically for consistency of physical design and dimensions by measuring and analyzing eight parameters of the instrument pilot tips, heads, and shafts. Results from visual inspection showed that none of the instruments were corroded; 23 presented surface porosities, and 17 had sharp strips of alloy. Data obtained by morphometric analysis indicated the mean diameter of the head of only 7 of 18 sizes met the +/- 0.02 mm allowable tolerance set forth by the American Dental Association (ADA) Specification No. 28. Observation and video analysis indicated that instruments of the same size adhere to the same basic design, but that morphometric variations do exist. The visual and intersize analysis indicated that the Lightspeed is not an instrument of any one determined shape that changes only in diameter. Rather, it is a series of instruments that show gradual shifts in both size and shape as the instrument size increases. Lightspeed instruments are a new type of nickel-titanium endodontic instrument that cannot be evaluated using the standards proposed by the American National Standards Institute/ADA Specification No. 28 for files and reamers.     

In vivo model for assessing the functional efficacy of endodontic filling materials and techniques

Endodontic fillings were challenged with bacterial ingress in mandibular premolars of 4 beagle dogs. Groups 1, 2, and 3 (n = 9), had canals filled with gutta-percha and sealer, gutta-percha alone, and sealer alone, respectively. After 2 wk, pulp chambers were inoculated with plaque. Group 4 (n = 9) and group 5 (n = 5) had canals either filled as in groups 1 to 3 or unfilled, respectively, but not inoculated. Group 6 (n = 5) had canals unfilled and inoculated. Teeth were radiographed periodically for 14 wk, dogs terminated, and jaw blocks retrieved and processed for light microscopic examination. Rarefying osteitis appeared in group 6 at 3 wk and in groups 2, 3, and 5 at 11 wk. Periradicular inflammation was none, mild, or severe. Occurrence of severe inflammation in groups 1 to 6 was 0, 11%, 33%, 0, 60%, and 100%, respectively. Groups 1 to 3 combined differed significantly from group 4 (repeated-measures ANOVA, p < 0.05). This model could be used to assess the functional efficacy of endodontic fillings in vivo.     

Results of surgical treatment of oesophageal cancer

The objective of this laboratory study was to compare root-end cavities prepared with sonic Retro-prep tips in a MM1500 Sonic Air handpiece with those created by burs in a conventional handpiece. A total of 80 single-rooted extracted human teeth with mature apices and straight canals were included in the study. Four groups of 20 extracted teeth were prepared as follows: I, a 3-4 mm root-end resection perpendicular to the long axis of the root, with a size 40 sonic Retro-prep tip creating an apical cavity 3 mm into root canal system; II, a 45 degrees bevel of the root-face removing a 3-4 mm root segment and root-end preparation as per group I; III, root-end resection as per group I, with an apical cavity prepared using a size 010 inverted cone bur 3 mm down the long axis of the root; IV, resection as per group II, followed by an apical cavity preparation with a size 010 inverted cone bur 3 mm into the root canal system. The apical root portion and root-end cavities were replicated and prepared for SEM analysis at x 20 and x 80 magnification. The degree of chipping associated with the margin of the root-end cavities, as evaluated with a standard grading system, and the incidence of root-face cracks were noted. Marginal chipping of root-end cavities prepared using sonic instrumentation was significantly worse than that produced by burs (P < 0.001). Perpendicular root-end resections showed significantly better scores than bevelled root-end resections (P < 0.005). The incidence of root-face cracking was low with no significant difference between the experimental groups.     

双曲面弯晶X射线分析仪器及应用进展

弯晶X射线技术历经近百年发展,已成为当今X射线荧光光谱(XRF)技术的主要研究方向之一。始于晶体X射线衍射技术,几代学者前仆后继从概念设想、理论推导,推动着弯晶X射线技术的进步;成于人工晶体和曲面晶体加工工艺的成熟,从平面晶体、柱面晶体、双曲面晶体到全聚焦双曲面晶体;拓于微探针分析、实验室能谱仪器、临床成像等应用,双曲面全聚焦弯晶能够将照射到晶体上、满足Bragg定律和罗兰圆结构的X射线单色化并全聚焦,弯晶X射线技术和仪器性能获得了本质提升。文章回顾了弯晶X射线技术和仪器的研制和应用历程,追寻前人在晶体及仪器研制方面的宝贵经验,探讨了未来弯晶X射线仪器的发展方向。     

Three-dimensional reconstruction of the membranous vestibular labyrinth in the toadfish, Opsanus tau

Membranous vestibular labyrinths from the oyster toadfish, Opsanus tau, were fixed, dissected from the animal, stained, and embedded in rectangular blocks of clear histological resin. Photomicrographs of complete embedded labyrinths were taken from six orthogonal directions and used to construct three-dimensional (3D) geometrical models of the semicircular canals, ampullae, utricular vestibule and common crus. Membraneous ducts and ampullae were modeled using a set of cross-sectional elliptical curves laced together to generate curved tubular models of each structure. The ensemble of these curved tubes was used to generate a complete 3D reconstruction of the outside surface of the membranous labyrinth. When viewed from six orthogonal directions, reconstructions closely matched the embedded tissue. Dimensions of the reconstruction and histological sections were compared to measurements of fresh tissue taken from the same animals prior to fixation and used to correct the reconstructions for tissue shrinkage. Results provide estimates of the endolymphatic volumes, local cross-sectional areas and elliptical eccentricities as well as 3D orientations of the geometric canal planes relative to the skull. Ten micrometer histological sections of the material were also prepared to measure wall thickness in various regions of the labyrinth.     

Oral antihyperglycaemics. Considerations in older patients with non-insulin-dependent diabetes mellitus

Various instrumentation techniques have been proposed and examined with conflicting results. They include hand and ultrasonic techniques and combinations of the two. In the present study we assessed the effectiveness of four preparation methods for cleaning small, curved root canals, using backscattered-imaging scanning electron microscopy (SEM). The methods were: (i) step-back without initial coronal flaring; (ii) step-back with coronal flaring; (iii) step-back with initial coronal flaring and finished by ultrasonic irrigation; and (iv) ultrasonics only. Eighty freshly extracted maxillary and mandibular molars were randomly placed into four treatment groups of 20 teeth each. After preparation, roots were sectioned longitudinally and examined wet by SEM. Each canal was qualitatively evaluated and the groups compared for removal of debris and smear layer, both overall and at each level (apical, middle and coronal). There were no statistically significant differences between the techniques, either overall or within any of the regions. When comparing regions (regardless of technique) the middle level was cleaner than the apical or coronal levels. In conclusion, efficacy differed little among the techniques; none of them completely removed smear layer and all left debris.     

An in vitro comparison of thermoplasticised gutta-percha obturation techniques with cold lateral condensation

This study compared the apical sealing ability, obturation time and extrusion of gutta-percha and sealer when root canals were obturated using either cold lateral condensation or one of the three methods using thermoplasticised gutta-percha (Alpha Seal, Thermafil or JS Quick Fill) in vitro. One hundred and thirty-one root canals from 78 extracted human teeth were used; 116 canals were divided into five groups so that they were balanced with respect to prepared canal anatomy, and the remaining 15 canals were used as positive and negative controls. The canals in the first four groups were prepared with hand files using the step-down technique to a standard apical size and flare. The last group was prepared using engine-driven rotary nickel-titanium files (McSpadden) to a similar apical size and flare. One of the four obturating techniques was used to fill the canals in each of the first four groups. The fifth group was obturated using the Alpha Seal technique. The roots were immersed in india ink, demineralised and rendered transparent to assess the extent of maximum lincar dye penetration. The Alpha Seal groups had the highest number of specimens without any leakage. There was a significant difference in the proportions of specimens that did not leak when the Alpha Seal (P < 0.01) and cold lateral condensation groups (P < 0.05) were compared with JS Quick Fill. Cold lateral condensation had a higher proportion of specimens with leakage in canals with curvature greater than 20 degrees than in canals with curvatures less than 20 degrees (P < 0.05). The curvature of canals had no effect on the sealing ability of the other techniques. The method of canal preparation had no effect on the sealing ability of Alpha Seal. Alpha Seal, Thermafil and JS Quick Fill were significantly quicker to perform than cold lateral condensation.     

Laparoscopic versus open Nissen fundoplication: outcome of surgery in monozygotic twins

Many clinicians use ultrasonics for root-end preparations. The purpose of this study was to evaluate resected root-end surfaces of bilaterally matched human teeth for cracks before and after ultrasonic root-end preparation. Twenty matched pairs of extracted single rooted teeth were divided into two experimental groups. In group 1, root-end resection was performed on uninstrumented teeth. In group 2, root-end resection was performed after the canals were instrumented and filled with gutta-percha. All teeth in both groups received root-end preparations using ultrasonic instrumentation at low power. Two examiners evaluated the root-ends after root-end resection and again after root-end preparation using zoom magnification of 20x to 63x. The number, types, and location of cracks were mapped. There were no significant differences when gutta-percha filled roots were compared to uninstrumented roots with regard to the number or type of cracks after root-end resection or root-end preparation. In addition, there were no significant differences in the number or type of cracks following root resection and ultrasonic root-end preparation when compared to teeth with root resection alone.     

A new ultrasonic canal preparation system with electronic monitoring of file tip position

A new ultrasonic root canal preparation system has been developed that electronically monitors the location of the file tip during all instrumentation procedures. The Root ZX has been adapted for this purpose, and its filter circuit effectively cuts out the large spike noise of the ultrasonic unit. During enlargement of the canal, the ultrasonic vibration of the file can be stopped at any desired position on the meter. Extracted human tooth models with electronically measurable canals were used to test the device. Pre- and postoperative shapes of the root canals were evaluated using contact microradiography. The autostop mechanism worked correctly. Using a weak power and fine files, straightening, ledge formation, and file breakage were minimal. It seems that this system minimized the danger of overinstrumentation and could be safely applied in clinical practice.     

Epidemiologic Evidence of Radiofrequency Radiation (Microwave) Effects on Health in Military, Broadcasting, and Occupational Studies

Tennis elbow afflicts 40% to 50% of the average, recreational tennis players; most of these players more than 30 years of age. Tennis elbow is thought to be the result of microtrauma, the overuse and inflammation at the origin of the ECRB as a result of repeated large impact forces created when the ball hits the racket in the backhand stroke. Several authors have found that EMG activity in the ECRB, the muscle and tendon complex afflicted in tennis elbow, is high during the acceleration and early follow-through phases of the groundstrokes and during the cocking phase of the serve. Unfortunately, none of the authors gave evidence to support the claim that muscle activity in the ECRB at ball contact is high. In the one-handed backhand, the torques at impact (17-24 nm) will be absorbed by the tendons of the elbow. Giangarra and his colleagues observed that the two-handed backhand "allows the forces at ball impact to be transmitted through the elbow rather than absorbed by the tissues at the elbow." Other authors have reported that players using a two-handed backhand will rarely develop lateral epicondylitis, because the helping arm appears to absorb more energy and changes the mechanics of the swing. As seen by Morris and colleagues, Giangarra and associates, and Leach and colleagues, players who utilize the two-handed backhand have a very low incidence of tennis elbow. These three studies conclude that the two-handed backhand stroke is probably the most effective backhand stroke to prevent lateral tennis elbow. Studies show that wrist extensors are highly involved in all strokes (serve, forehand, and both one- and two-handed backhand strokes). This relatively high involvement (40%-70% MVC) throughout play may result in overload of this muscular group. Thus, tennis elbow may be caused simply by continued use of this muscular system in all strokes, and not just because of the high forces absorbed at impact. Another theory concerning impact states that if the extensor group is already at near maximum contraction, vibrations and twisting movements are transferred directly through the muscle (muscle stiffness at this point would be great) to the tendinous insertion, causing repeated microtrauma. If the muscle is the stiffest element in the system, the force will be transferred to the tendon. It is evident that a need exists for specific study of muscular response during impact. More microanalysis of the impact phase needs to be conducted specifically for the one-handed backhand groundstroke.