Post and core reconstruction for fixed prosthodontic restoration

If the previous restorative therapy or dental caries has resulted in substantial loss of tooth structure, the abutment teeth for fixed prosthodontic restorations require a core reconstruction or a post and core. Small dentin defects can be restored with bonded cores; more extensive dentin defects that are often accompanied by previous endodontic treatment generally require additional support for the core material. A direct procedure with a bonded post is a viable treatment method. The decision to use either light-conducting all-ceramic zirconium or titanium as a post material depends on the aesthetic requirements present. The indications for a cast post and core as an indirect procedure for prosthodontic reconstructions appear to be decreasing. The learning objective of this article is to review the past and current post and core materials and techniques. Indications for core reconstruction with vital teeth and posts and cores for pulpless teeth are discussed.     

Porcelain-fused-to-metal post and core: an esthetic alternative

Custom cast metal post and cores used to retain all-ceramic restorations are indicated in endodontically treated teeth when little clinical crown remains. The metal cores of these post and core restorations block light transmission and create a graying effect when used in support of all-ceramic restorations. This article describes a technique to minimize this effect using custom cast porcelain-fused-to-metal post and cores to achieve a more natural esthetic result.     

Strength of roots before and after endodontic treatment and restoration

The resistance to fracture of mandibular premolar roots before and after endodontic and restorative procedures was tested. Seven treatment groups were evaluated. A Universal testing machine was used to apply vertical and lateral (45-degree) forces. Overall, the untreated roots showed the highest resistance to fracture. Factors of importance to prevent fracture were found to be (a) the amount of remaining tooth structure; (b) strength of post and core; and (c) bonding between core material and dentin. These factors suggest that a composite core following the use of EDTA to remove the smear layer may be a successful treatment when sufficient tooth structure remains.     

82B盘条拉伸试验中黑心白点断口的成因

大规格的 82B 盘条在拉伸试验中发现,力学性能差的断口均为脆性平齐断口,并且断口上总有1~2个黑心,每个黑心上均有1个白点,将这种断口称为 黑心白点断口(简称BCWPF).对常用直径(10.0、12.5、14.0 mm)的这种黑心白点断口,用体式显微镜观察宏观形貌,用电镜观察微观形貌,用能谱进行微区元素分析,对断口材料本身的组织和夹杂物进行定性定量分析,发现断口的黑心白点主要由氧化铝类和硫化物类非金属夹杂物组成,部分还有球状氧化物类和硅酸盐类夹杂物.通过使用不含铝的硅锰脱氧剂来降低氧化铝夹杂,深脱硫来降低硫化物类夹杂,夹杂物的塑性改造后,拉伸断口的黑心白点现象明显减少,盘条的力学性能得到显著提高.     

Slip-Form Application to Concrete Structures

Because of superior speed and productivity, slip forms were extensively utilized as a potential formwork candidate in constructing concrete structures for the past few decades. Typical projects that employ this formwork technique are: Core of high-rise buildings, silos, telecommunication towers, cooling towers, heavy concrete offshore platforms, etc. The research presented in this paper aims at studying slip-form application to cores and silos, assessing its productivity, and determining its appropriate speed as well as auxiliary resource combinations. Simulation models are developed in which the potential control units in a slip-form system are described for cores and silos. Data are collected from several case study projects. A set of charts has been developed to predict productivity considering different stoppages, core cross section area, slipping (jacking) rate, and concrete placing methods. These charts play an essential role in managing slip-form application to cores and silos. Results show that the developed simulation models predict the productivity of case study projects with 99.70 and 99.30% accuracy for cores and silos, respectively. The presented research is relevant to both researchers and practitioners. It provides practitioners with charts that assist in scheduling and managing the required resources for slip-form application. In addition, it provides researchers with simulation models and framework for implementing slip forms to core and silo construction.     

Effect of mechanical versus thermal removal of gutta-percha on the quality of the apical seal following post space preparation

The objective of this study was to compare the effects of a flame-heated endodontic plugger, an electrically-heated endodontic spreader, Peeso reamers, and GPX burs on the apical seal when gutta-percha was removed from the root canal for post space preparation. Eighty-nine human canines were instrumented and obturated with gutta-percha and sealer to a standardized working length of 15 mm. An 11-mm segment of gutta-percha was removed from the roots in each of the four experimental groups of 20 teeth to simulate post space preparation. The teeth were immersed in India ink for 7 days and rendered transparent. The extent of linear dye leakage was measured with a stereomicroscope. There was no statistically significant difference in linear dye leakage among any of the experimental groups when 4 mm of gutta-percha remained.     

Long-term evaluation of endodontic and periodontal treatment

One hundred and ninety-five teeth in 35 patients with periodontitis who had received both endodontic and periodontal treatment were evaluated 9 years after endodontic treatment and 8 years after periodontal treatment. Some 91.4% of cases were well maintained and 8.6% showed a deterioration in their periodontal condition. Twelve of the 195 teeth with endodontic treatment were lost, eight for periodontal reasons, three as a result of fracture and one because of caries, and the periodontal condition of 10 teeth had worsened. An apical lesion formed on one tooth. The results indicate that the risk of endodontic failure in this group of 195 teeth is very low, and that there is little risk of tooth loss for periodontal reasons, provided that the patients receive supportive periodontal treatment.     

Hemobilia: a rare complication of cholecystitis and cholecystolithiasis. Case report

Rectified turpentine oil can be used to soften or dissolve gutta-percha in the root canal space to facilitate endodontic retreatment or preparation of space for a post. For endodontic retreatment, the turpentine oil can be heated to 71 degrees C which significantly increases its ability to dissolve gutta-percha. For removing only a portion of the gutta-percha while leaving the rest intact, as for the preparation of space for a post, the turpentine oil is delivered to the canal at body temperature (37 degrees C).     

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.     

Definitive injuries to the teeth. Lesions of hard tissue and pulp

Tooth infraction and enamel fracture are the most simple traumatic crown lesions. When necessary the lesions can be covered with composite material. Follow-up of the traumatized tooth is necessary since pulp necrosis and obliteration can develop. In case of an uncomplicated fracture involving enamel and dentine immediate protection of the dentinal wound is important for the preservation of tooth vitality. In case of a negative vitality test, an endodontic treatment will be performed in case of a tooth with open apex only when supplemental clinical and or radiological signs of pulp necrosis are present. When a complicated enamel-dentine fracture is present, an endodontic treatment will be performed when root formation is complete. In case of a wide open apex, a pulp capping, partial pulpotomy or cervical pulpotomy will be performed in order to preserve vitality of pulpal tissues at the level of the root. Crown root fractures can be superficial, deep or vertical. In case of a superficial localisation of the fracture line, restoration with composite material or with the fractured tooth segment is indicated. Deep crown-root fractures can only be restored when the fracture line is localized not deeper than at 1/3 of the length of the root. In case of a vertical fracture, extraction is the only possibility. Root fractures on immature teeth are in most cases unilateral and have a good prognosis. In teeth with completed root formation, fractures at the level of the cervix have a poor prognosis. The fractured segment will be removed. Only when the remaining root segment is long enough, this part can be maintained. In case of a fracture at the mid-root level, repositioning and rigid splinting for a period of 8 weeks is necessary. When the tooth becomes non-vital, endodontic treatment is performed on the coronal part. Root fracture in the apical part does not necessary result in enhanced tooth mobility and immobilisation is not always necessary. Healing of a root fracture is only possible when the tooth is immobilized for a sufficiently long period. Regular control of tooth vitality is necessary since pulp necrosis can lead to an inflammatory reaction at the level of the fracture line.     

Sleep disturbance in spinocerebellar ataxias: is the SCA3 mutation a cause of restless legs syndrome?

OBJECTIVE: We sought to determine possible technical causes of inconclusive results on CT-guided core biopsies of lesions suggestive of malignancy and to determine the frequency with which such lesions are eventually found to be malignant. MATERIALS AND METHODS: We retrospectively reviewed 116 consecutive CT-guided thoracic and abdominal core biopsies performed with a 20-gauge automatic biopsy system. Biopsy results were conclusive (n = 94) if pathology confirmed malignancy and inconclusive (n = 22) if pathology results were negative for malignancy or were nondiagnostic. Lesion volume, location, number of cores, and biopsy technique (paraxial or coaxial) were compared for the conclusive and inconclusive biopsy results. Malignancy within the group of inconclusive biopsy results was determined from a second biopsy, radiographic follow-up, or surgery. RESULTS: Regression analysis identified only the biopsy method as a significant factor affecting biopsy outcome: The paraxial method was more likely to yield a conclusive result than the coaxial method (p < .002). For the two biopsy methods, lesions had similar volumes, locations, and numbers of cores obtained. For single core biopsies, both methods were equivalent. However, if two or more cores were obtained, a conclusive result was achieved in more than 90% of biopsies with the paraxial method versus 65% for the coaxial method. On follow-up, results of 14 (64%) of 22 inconclusive biopsies were malignant, indicating an overall false-negative rate of 12%. CONCLUSION: CT-guided core biopsy performed with 20-gauge automatic biopsy systems and the paraxial method will yield conclusive results significantly more often than the coaxial method. In the event of inconclusive results, malignancy will exist often enough to warrant follow-up.     

Evaluation of chemically-induced pore surface modifications on rock cores

Chemical modification of pore surface properties due to active components of crude oils could significantly affect production processes. Specific chemical treatments can prevent surface alteration, protecting pores from deposition of heavy oils components. Both relaxation times analysis and nuclear magnetic resonance (NMR) imaging technique are a valuable method for nondestructive monitoring of solid/liquid interface alteration especially if applied to heterogeneous rock cores, which are impossible to study using conventional methods (e.g., Amott tests and dynamic angle contact). In our work, we examined carbonate core plugs subjected to aging treatments in crude oil. Relaxation times measurement, revealing modifications of fluid/surface interactions and imaging, was applied in characterise heterogeneous systems and reveal fluid distribution changes. Nuclear magnetic resonance results were compared with a special microscopy technique (Cryo-SEM) that allows observation of fluids at the pore level, providing a better understanding of the processes involved.     

Using Scanning Lasers to Determine the Thickness of Concrete Pavement

Due to limited budgets and reduced inspection staff, state departments of transportation are in need of innovative approaches for providing more efficient quality assurance on concrete paving projects. In Iowa, the current technique is to take core samples of the pavement, which is a labor intensive, destructive process. Due to these limitations, a limited number of cores are used to estimate the pavement thickness. Any method that can reduce or eliminate cores and increase the statistical accuracy of the thickness estimate will be beneficial. One method, which uses a laser to scan the surface of the base prior to paving and then to scan the surface after paving can determine the thickness at any point. Also, scanning lasers provide thorough data coverage that can be used to calculate thickness variance accurately and identify any areas where the thickness is below tolerance. The laser scanning methodology for this study involved the following: (1) investigating characteristics of the paving process; (2) using a laser scanner on three different sites; (3) processing the data to create clean surface models; (4) performing statistical analyses to determine thickness variability; and (5) summarizing the results.     

Postoperative complications after Mainz pouch construction--with emphasis on measures to deal with narrowing of the duct aperture

Cutaneous sinus tracts in the face and neck region are often dental in origin. The purpose of this study was to characterize the clinical features and treatment of 37 consecutive cases of odontogenic cutaneous sinus tracts, collected and reviewed in a 15-year period. More than half of the patients (21 cases, 57%) were referred from medical doctors, particularly plastic surgeons and dermatologists. The sinus tracts were associated with caries (26 cases), incomplete endodontic treatment (7), crown fracture (2), vertical root fracture (1) and impacted mandibular third molar (1). They occurred most often in adolescents and adults (30 cases, 81%). The most common causative teeth were mandibular teeth (34 teeth, 85%). The chin, submental, and cheek areas were the most common sites of sinus tracts (30 cases, 81%). The majority of causative teeth (32 teeth, 80%) were treated endodontically. All fistulas healed uneventfully after proper dental treatment, without cosmetic surgery. In 63% (20 cases) of the recorded cases, complete resolution occurred within 8 weeks. Half of the patients had had fistulas for more than 6 months before receiving dental treatment, demonstrating that delays in proper diagnosis and treatment were common. As most patients suffered from unnecessary medication or surgery due to the delay of dental treatment, early dental consultation and treatment is important. Conventional endodontic treatment should be the treatment of choice if the tooth is salvageable. The increasing incidence of incomplete endodontic treatment in association with the occurrence of sinus tracts indicates that standardized endodontic therapy should be emphasized for prevention.     

The effect of serrations on carbon fibre posts-retention within the root canal, core retention, and post rigidity

The retention in root canals of serrated carbon fibre Composiposts and stainless steel Paraposts was tested under tensile load. Twenty unrestored human roots were endodontically prepared and root filled. Two groups of 10 roots received 1.4-mm Composiposts or 1.25-mm Paraposts luted with a resin cement. The specimens were then embedded in acrylic resin and mounted in an Instron machine. The tensile force (kg) required to dislodge the posts was recorded and analysed with Student's test. The results revealed that there was no significant difference in the retention of either post (P > .05). The rigidty of 10 1.4-mm serrated Composiposts was tested in a three-point bend test in an Instron machine, and the retention of composite cores to 10 of these posts under tensile force was also tested. The results from these tests were compared to previous data from the authors' laboratory and revealed that the serrations significantly reduced the rigidity of the post (P < .001) and increased the retention of a core material (P < .001).     

Assembly and analysis of conical models for the HIV-1 core

The genome of the human immunodeficiency virus (HIV) is packaged within an unusual conical core particle located at the center of the infectious virion. The core is composed of a complex of the NC (nucleocapsid) protein and genomic RNA, surrounded by a shell of the CA (capsid) protein. A method was developed for assembling cones in vitro using pure recombinant HIV-1 CA-NC fusion proteins and RNA templates. These synthetic cores are capped at both ends and appear similar in size and morphology to authentic viral cores. It is proposed that both viral and synthetic cores are organized on conical hexagonal lattices, which by Euler's theorem requires quantization of their cone angles. Electron microscopic analyses revealed that the cone angles of synthetic cores were indeed quantized into the five allowed angles. The viral core and most synthetic cones exhibited cone angles of approximately 19 degrees (the narrowest of the allowed angles). These observations suggest that the core of HIV is organized on the principles of a fullerene cone, in analogy to structures recently observed for elemental carbon.     

Changes in Thy-1 antigen immunoreactivity in the rat retina during pre- and postnatal development

This paper reports the findings of a survey of a group of general dental practitioners (GDPs) from one region of the United Kingdom. The practitioners were asked to complete a questionnaire investigating their approach to the restoration of root-filled teeth. A high response rate was achieved and the replies indicated that most practitioners restore teeth within 1 month of completing the root filling. Nonprecious cast alloys cores were popular as was amalgam for core build-ups. Most practitioners opted for a post which was two-thirds the length of the root and zinc phosphate was the most popular luting material. Almost one-quarter of respondents believed that a root is strengthened by a post retained restoration and a similar number have never attended a postgraduate meeting on the subject of the restoration of root-filled teeth.     

Mechanics of Composite Sinusoidal Honeycomb Cores

Lightweight and heavy-duty fiber-reinforced polymer (FRP) composite honeycomb sandwich structures have been increasingly used in civil infrastructure. Unique cellular core configurations, such as sinusoidal core, have been applied in sandwich construction. Due to specific core geometry, the solutions for core effective stiffness properties are not readily available. This paper presents a mechanics of materials approach to evaluate the effective stiffness properties of sinusoidal cores. In particular, the internal forces of a curved wall in a unit cell are expressed in terms of resultant forces, and based on the energy method and principle of equivalence analysis, the in-plane stiffness properties of sinusoidal cores are derived. Both finite-element modeling and experimental testing are carried out to verify the accuracy of the proposed analytical formulation. To illustrate the present analytical approach as an efficient tool in optimal analysis and size selection of sinusoidal cores, several design plots are provided and discussed. The simplified analysis and formulation presented for sinusoidal cores can be used in design application of FRP honeycomb sandwich and optimization of efficient cellular core structures.     

Mechanistic Model for Self-Healing of Core Cracks in Earth Dams

This paper describes a mechanistic model developed to understand the self-healing mechanism of two types of cracks in impervious cores of earth dams; Type A core cracks which extend from the interior of the core to the downstream filter, and Type B core cracks which extend from the upstream face of the core to the downstream filter. The base soil-crack-filter system is idealized using a four-element one-dimensional continuum to consider various processes in the core and the filter. The model is numerically implemented to predict self-healing in the idealized domain. The model predictions are validated using results from experimental investigations. A parametric study conducted with the model indicates two conditions essential to foster self-healing: a nominal erosion of the base soil, and a seepage velocity in the filter that is less than its critical seepage velocity. This study suggests that the mechanism leading to different rates of self-healing is the interplay of several parameters, viz, characteristics of base soils and filters, geometrical features of cracks, hydraulic conditions, etc. Application of the one-dimensional mechanistic model to a three-dimensional field-scale scenario is demonstrated.     

Endoesthetics. Part 1: Intra-radicular rehabilitation

The flared canal, whether due to age, carious extension, pulpal pathology or endodontic access, presents a restorative management problem. Intra-radicular rehabilitation prior to post fabrication and/or cementation, increases the chance for operative success. This is the first in a series of articles that introduces the concept of esthetic considerations in post-endodontic restorative therapy.