Decrease In Fracture Resistance Research Articles

Restorations of Endodontically Treated Teeth

Endodontically treated teeth are fragile compared to vital teeth. The reason for the decrease in fracture resistance and hardness is related to the deterioration of the structural integrity as a result of caries, trauma and cavity preparation. Restorations in endodontically treated teeth are applied considering the remaining tooth structure and functional status. For many years, post core systems that require additional preparation in the root canal, as well as the loss of most of the coronal tooth structures, are used for the final restoration of endodontically treated teeth. Endocrowns are monoblock restorations that attach to the pulp chamber and its walls, providing macro-mechanical and cementation with micro-mechanics, thus requiring no additional preparation. The first study written on ceramic endocrown was published in 1995. In this study, it is defined as a ceramic monoblock production technique for the restoration of endodontically treated teeth. This procedure was later named "endocrown" in 1999.

Influence of Thermal and Mechanical Load Cycling on Fracture Resistance of Premolars Filled with Calcium Silicate Sealer

The aim of this study was to evaluate the aging effect of thermomechanical cyclic load on fracture resistance of lower premolars obturated with AH Plus and BioRoot RCS root canal sealers. Forty-eight single-rooted premolars teeth were instrumented with REVO-S files up to SU/0.06 taper. The teeth were randomly assigned into 2 main groups (n = 24) according to the selected two root canal sealers (AH Plus or BioRoot RCS). All teeth were obturated using matching gutta-percha. Each main group were further divided into 3 subgroups (A, B and C) (n = 8). Group A acted as the negative control group (non-Thermomechanical aging). Whereas Group B and C were subjected first to thermal variations in a thermal cycling machine (7500 and 15,000 thermal cycles), then two different dynamic loading periods namely 3 × 105 and 6 × 105 in a masticatory simulator with a nominal load of 5 kg at 1.2 Hz which simulate approximately 1 ½ and 3 years of clinical function respectively. The roots were decoronated and fracture resistance were measured using a universal testing machine. After thermal-mechanical aging, BioRoot RCS showed significantly higher fracture resistance (p < 0.05) than AH Plus. As the thermal-mechanical cycles increased both AH Plus and BioRoot RCS exhibited a significant decrease in fracture resistance (p < 0.05). It could be concluded that thermomechanical aging had a significant impact on the outcome of the fracture resistance of AH Plus and BioRoot RCS.

Comparative Evaluation of Fracture Resistance of Endodontically Treated Teeth Instrumented With K3XF Rotary Files Using Different Tapers.

To compare the effect of different tapers of the K3XF file system on the fracture resistance of endodontically treated mandibular premolars obturated with a three-dimensional (3-D) obturation system. For the study, 80 freshly extracted human mandibular premolars with single well-developed roots without any curvatures were taken and the tooth roots were wrapped in a single layer of aluminum foil, and they were placed vertically in a plastic mold filled with self-curing acrylic resin. The access was opened, and working lengths were determined. The canals were instrumented keeping an apical size of #30 by different taper rotary files: Group 1: un-instrumented (control group), Group 2: 30/.04, Group 3: 30/.06, Group 4: 30/.08 K3XF file system, and teeth were obturated using a 3-D obturation system, and access cavities were filled using composite. Both experimental and control groups were subjected to fracture load using a conical steel tip (0.5mm) attached to a universal testing machine to record force applied in newton until root fracture. Root canal instrumented groups showed lower fracture resistance than the uninstrumented group. Hence it could be concluded that endodontic instrumentation with increased taper rotary instruments caused a decrease in fracture resistance of the teeth, and biomechanical preparation of root canal system with rotary or reciprocating instruments caused a significant decrease in fracture resistance of endodontically treated teeth (ETT), thereby decreasing their prognosis and long-term survival.

Performance of thin blast-loaded steel plates after ballistic impact from small-arms projectiles

It is known from real blast-load events that the combined effect of fragment impact and blast loading is more severe than the effect of the blast loading alone. The present study investigates this effect by comparing the blast response of thin steel plates pre-damaged by either ballistic impacts or idealized pre-cut circular holes under similar blast loading conditions. The ballistic impacts were performed with a rifle, firing 7.62 mm APM2 projectiles, and the subsequent blast loading was applied in a shock tube facility. During the blast tests, pressure measurements and two high-speed cameras were used to record the dynamic response of the target plates and allowed for a reliable experimental procedure. To investigate the strength-ductility trade-off dilemma of the material during extreme loading, three different steels with different levels of strength and ductility were used in the tests. Numerical simulations were conducted in an attempt to obtain more insight into the fracture characteristics of the plates.For similar loading conditions and material, the target plates exposed to ballistic impact showed a reduced resistance to fracture during blast loading compared with target plates containing pre-formed circular holes. As for the effect of material strength and ductility, the global deformation decreased, while the localization of plasticity increased, with an increased material strength. The fracture resistance was also observed to decrease with increased material strength. The numerical models were able to capture the main trends observed in the physical tests, i.e., a decrease in fracture resistance with initial ballistic impact, and a reduction in fracture resistance with increased material strength. The numerically predicted crack paths also showed a strong dependence upon the initial cracks caused by the petals from the ballistic impacts.

Degradation response of mode I and mode III fracture resistance of sandstone under wetting–drying cycles with an acidic solution

The edge notched disk bend samples were adopted to investigate the degradation response of mode I and mode III fracture resistance of green sandstone under wetting–drying cycles in an acidic solution. Meanwhile, the degradation damage mechanism was clarified by observing the variations of the microstructures of the rock. The results indicated that the mode I and mode III fracture resistance reduced with increasing wetting–drying cycle times, which were decreased respectively by 34.3% and 36.8% after undergoing 10 cycles. Fracture toughness ratio KIIIC/KIC was slightly reduced with increasing cycle times, and the degradation damage on mode I fracture resistance was less than that of mode III. The major reason for the decrease in fracture resistance was the irreversible physical–chemical damage accumulation and the changes in microstructure characteristics during cyclic wetting–drying procedure.

Fracture Load and Fracture Patterns of Monolithic Three-Unit Anterior Fixed Dental Prostheses after In Vitro Artificial Aging-A Comparison between Color-Gradient and Strength-Gradient Multilayer Zirconia Materials with Varying Yttria Content.

(1) Background: Due to advantages such as avoidance of chipping, pulp-friendly tooth preparation and cost reduction, zirconia is increasingly being used monolithically without veneering. Nevertheless, to enable good aesthetics, various multilayer systems have been developed. The aim of this study was to investigate the impact of different zirconia multilayer strategies and yttria levels on fracture load, fracture pattern, stress distribution and surface roughness. (2) Methods: Monolithic three-unit anterior FDPs were made from three different color-gradient zirconia multilayer materials with different yttria levels corresponding to varying strength and degrees of translucency grades (Katana HTML, STML, UTML, Kuraray) and one strength-gradient zirconia multilayer material (Katana YML, Kuraray) and artificially aged in a chewing simulator (1.2 × 106 load cycles, 50 N, 2 × 3000 thermocycles, 5–55 °C). Analyses of fracture load, fracture pattern, fracture surfaces, stress distribution and roughness were performed after the fracture load test. Shapiro–Wilk, Kruskal–Wallis, Mann–Whitney U-tests and one-way ANOVA were used (p < 0.05). (3) Results: Fracture loads of the high strength color-gradient material HTML and the strength-gradient material YML were comparable after 5 years of aging (p = 0.645). Increasing yttria levels resulted in a decrease in fracture resistance of 42–57% (p < 0.05). Surface roughness of different zirconia generations is comparable after polishing and aging. (4) Conclusions: Color-gradient multilayer zirconia materials and new strength-gradient zirconia materials with similar yttria levels in the basal layers show comparable mechanical properties and are suitable for anterior FDPs.

Hydrogen-assisted fracture resistance of pipeline welds in gaseous hydrogen

Fracture resistance of pipeline welds from a range of strength grades and welding techniques was measured in air and 21 MPa hydrogen gas, including electric resistance weld of X52, friction stir weld of X100 and gas metal arc welds (GMAW) of X52, X65 and X100. Welds exhibited a decrease in fracture resistance in hydrogen compared to complementary tests in air. A general trend was observed that fracture resistance in 21 MPa hydrogen gas decreased with increasing yield strength. To accommodate material constraints, two different fracture coupon geometries were used in this study, which were shown to yield similar fracture resistance values in air and 21 MPa hydrogen gas; values using different coupons resulted in less than 15% difference. In addition, fracture coupons were removed from controlled locations in select welds to examine the potential influence of orientation and residual stress. The two orientations examined in the X100 GMAW exhibited negligible differences in fracture resistance in air and, similarly, negligible differences in hydrogen. Residual stress exhibited a modest influence on fracture resistance; however, a consistent trend was not observed between tests in air and hydrogen, suggesting further studies are necessary to better understand the influence of residual stress. A comparison of welds and base metals tested in hydrogen gas showed similar susceptibility to hydrogen-assisted fracture. The overall dominant factor in determining the susceptibility to fracture resistance in hydrogen is the yield strength.

Evaluating the mechanical response of novel synthetic femurs for representing osteoporotic bone

Osteoporosis is a disease prevalent in older adults, characterized by high porosity in bone and subsequent decrease in fracture resistance. This demographic is also the population that most frequently receives devices such as hip implants. However, high porosity complicates surgery and reduces the fixation and effectiveness of orthopaedic devices, which are typically designed using cadaveric specimens from the general population. Synthetic bones are also used in the design of such devices but need to represent the properties of the patient population. Thus, the mechanical response of two iterations of novel synthetic femurs were evaluated for their ability to represent osteoporotic cadaveric specimens and were tested and compared against cadaveric specimens across four loading modes. The first iteration had reduced density and wall thickness compared to standard models and was typically too rigid or too stiff to be a feasible alternative to cadaveric specimens. The second iteration, with similarly reduced wall thickness and further reduced density, was quite representative, with no statistical differences identified against the cadaveric specimens in any loading mode, except in screw pullout. Such a model can provide a foundation for the development of orthopaedic devices better suited to osteoporotic bone, potentially improving surgical outcomes, reducing medical expense, and improving quality of life for patients.

The age-related decrease in material properties of BALB/c mouse long bones involves alterations to the extracellular matrix.

One possibility for the disproportionate increase in fracture risk with aging relative to the decrease in bone mass is an accumulation of changes to the bone matrix which deleteriously affect fracture resistance. In order to effectively develop new targets for osteoporosis, a preclinical model of the age-related loss in fracture resistance needs to be established beyond known age-related decreases in bone mineral density and bone volume fraction. To that end, we examined long bones of male and female BALB/c mice at 6-mo. and 20-mo. of age and assessed whether material and matrix properties of cortical bone significantly differed between the age groups. The second moment of area of the diaphysis (minimum and maximum principals for femur and radius, respectively) as measured by ex vivo micro-computed tomography (μCT) was higher at 20-mo. than at 6-mo. for both males and females, but ultimate moment as measured by three-point bending tests did not decrease with age. Cortical thickness was lower with age for males, but higher for old females. Partially accounting for differences in structure, material estimates of yield, ultimate stress, and toughness (left femur) were 12.6%, 11.1%, and 40.9% lower, respectively, with age for both sexes. The ability of the cortical bone to resist crack growth (right femur) was also 18.1% less for the old than for the young adult mice. These decreases in material properties were not due to changes in intracortical porosity as pore number decreased with age. Rather, age-related alterations in the matrix were observed for both sexes: enzymatic and non-enzymatic crosslinks by high performance liquid chromatography increased (femur), volume fraction of bound water by 1H-nuclear magnetic resonance relaxometry decreased (femur), cortical tissue mineral density by μCT increased (femur and radius), and an Amide I sub-peak ratio I1670/I1640 by Raman spectroscopy increased (tibia). Overall, there are multiple matrix changes to potentially target that could prevent the age-related decrease in fracture resistance observed in BALB/c mouse.

Inhibiting the osteocyte-specific protein sclerostin increases bone mass and fracture resistance in multiple myeloma

AbstractMultiple myeloma (MM) is a plasma cell cancer that develops in the skeleton causing profound bone destruction and fractures. The bone disease is mediated by increased osteoclastic bone resorption and suppressed bone formation. Bisphosphonates used for treatment inhibit bone resorption and prevent bone loss but fail to influence bone formation and do not replace lost bone, so patients continue to fracture. Stimulating bone formation to increase bone mass and fracture resistance is a priority; however, targeting tumor-derived modulators of bone formation has had limited success. Sclerostin is an osteocyte-specific Wnt antagonist that inhibits bone formation. We hypothesized that inhibiting sclerostin would prevent development of bone disease and increase resistance to fracture in MM. Sclerostin was expressed in osteocytes from bones from naive and myeloma-bearing mice. In contrast, sclerostin was not expressed by plasma cells from 630 patients with myeloma or 54 myeloma cell lines. Mice injected with 5TGM1-eGFP, 5T2MM, or MM1.S myeloma cells demonstrated significant bone loss, which was associated with a decrease in fracture resistance in the vertebrae. Treatment with anti-sclerostin antibody increased osteoblast numbers and bone formation rate but did not inhibit bone resorption or reduce tumor burden. Treatment with anti-sclerostin antibody prevented myeloma-induced bone loss, reduced osteolytic bone lesions, and increased fracture resistance. Treatment with anti-sclerostin antibody and zoledronic acid combined increased bone mass and fracture resistance when compared with treatment with zoledronic acid alone. This study defines a therapeutic strategy superior to the current standard of care that will reduce fractures for patients with MM.

Fracture resistance of endodontically treated teeth restored with a bulkfill flowable material and a resin composite.

To determine and compare the fracture resistance of endodontically treated teeth restored with a bulk fill flowable material (SDR) and a traditional resin composite. Thirty maxillary and 30 mandibular first molars were selected based on similar dimensions. After cleaning, shaping and filling of the root canals and adhesive procedures, specimens were assigned to 3 subgroups for each tooth type (n=10): Group A: control group, including intact teeth; Group B: access cavities were restored with a traditional resin composite (EsthetX; Dentsply-Italy, Rome, Italy); Group C: access cavities were restored with a bulk fill flowable composite (SDR; Dentsply-Italy), except 1.5 mm layer of the occlusal surface that was restored with the same resin composite as Group B. The specimens were subjected to compressive force in a material static-testing machine until fracture occurred, the maximum fracture load of the specimens was measured (N) and the type of fracture was recorded as favorable or unfavorable. Data were statistically analyzed with one-way analysis of variance (ANOVA) and Bonferroni tests (P<0.05). No statistically significant differences were found among groups (P<0.05). Fracture resistance of endodontically treated teeth restored with a traditional resin composite and with a bulk fill flowable composite (SDR) was similar in both maxillary and mandibular molars and showed no significant decrease in fracture resistance compared to intact specimens. No significant difference was observed in the mechanical fracture resistance of endodontically treated molars restored with traditional resin composite restorations compared to bulk fill flowable composite restorations.

Fracture resistance of weakened bovine teeth after long-term use of calcium hydroxide.

In some parts of the world, revascularization may not be the most feasible treatment option for necrotic immature teeth. Therefore, apexification remains the most widely utilized treatment option for these cases. This study aimed to evaluate the fracture resistance of weakened bovine tooth roots treated with various irrigant solutions as well as long-term application of calcium hydroxide intracanal medication (ICM). One hundred seventy bovine teeth were randomly divided into three experimental groups (n = 50) and two control groups (n = 10). Group SS was irrigated with physiologic solution; group CHX was treated with 2% chlorhexidine gel and group NaOCl was irrigated with 1% sodium hypochlorite. After instrumentation, root canals were dressed with calcium hydroxide and evaluated at different periods (15, 60, 90, 180, and 360 days). The specimens were loaded at a 45° angle to measure fracture resistance through the use of an EMIC test machine. A decrease in fracture resistance was observed during the time of ICM dressing. The highest values of fracture resistance were observed in group SS with 15 days of ICM, not differing from the control group. Irrigation with NaOCl associated with ICM for 15 days presented the lowest fracture resistance; however, a statistically significant difference was not observed when compared with SS and CHX in the same time period. In longer periods of exposure to ICM (180 and 360 days), root canals irrigated with NaOCl and CHX showed significantly lower fracture resistance than SS (P < 0.05). Apexification with periodic changes of calcium hydroxide medicament leads to weakness of the teeth independent of the irrigation solution used.

Effect of three calcium hydroxide formulations on fracture resistance of dentin over time.

The long-term use of calcium hydroxide has been discouraged throughout the recent decade due to a proposed decrease in fracture resistance of dentin. This weakening has grave implications when used on immature teeth with thin dentinal walls in procedures such as apexogenesis. The purpose of this study was to identify the effects of three commercial calcium hydroxide formulations (Vitapex, Ultracal XS and Pulpdent) on the fracture resistance of dentin in relation to time. Two-hundred and forty deciduous lamb incisors were collected, cleaned and shaped, and filled with one of the three calcium hydroxide formulations and one negative saline control. At one, three, and 6 months, these teeth were fractured on an Instron machine to determine fracture resistance. No statistical differences were observed among any of the experimental groups, nor between any of the experimental groups and negative control groups. Based on our findings, there appears insufficient evidence to support that either Vitapex, Ultracal XS, or Pulpdent will cause a decrease in fracture resistance of dentin within a 6-month period.

In vitro evaluation of the effect of post system and length on the fracture resistance of endodontically treated human anterior teeth

The aim of this study was to evaluate the effect of post system and length on the fracture resistance of endodontically treated human anterior teeth. Seventy-five extracted human incisors were endodontically treated, out of which 60 were decoronated 2mm above the cementoenamel junction and divided into two experimental groups based on the type of post system to be used: glass fiber post (GFP) and Ribbond fiber post groups (RFP). Endodontically treated human anterior teeth in which no post was placed served as control group. Each group was divided into two subgroups according to the length of post space: 5 and 10mm and all the samples were restored with metal crowns. The fracture resistance was measured by applying loads at an angle of 130° to the long axis of teeth in an Instron universal testing machine. The results revealed that GFP group at 10-mm post space length showed the significantly highest fracture resistance (740.2133N) among all groups and subgroups. Decrease in post length resulted in the decrease in fracture resistance in GFP group (425.1867N), whereas in group RFP 5-mm subgroup (299.6200N) showed significantly higher fracture resistance than 10-mm subgroup (216.9300N) but lesser than the control (437.8733N) in both the subgroups. Glass fiber posts efficiently increase the fracture resistance of an endodontically treated tooth but the determination of optimal post length is also essential. The present investigation highlights the significance of using glass fiber posts in the restoration of endodontically treated teeth. Endodontically treated teeth restored with glass fiber posts showed increased fracture strength and favorable mode of fracture, and are therefore highly recommended to achieve better clinical outcomes.

Comparative Evaluation of Resistance Failure in Nonprecious Metal-Ceramic Restoration at the Incisal Edge with Varying Thickness under Different Application of Load: An in vitro Study

To determine the resistance failure value of nonprecious metal-ceramic restorations at the incisal edge with varying thickness under different application of load. An Ivorian central incisor was prepared to receive metal-ceramic crown, which was further duplicated, invested, casted and 72 metal dies were fabricated in Co-Cr alloy. Metal dies were relieved with die spacer, lubricated and wax patterns were prepared for metal copings, which were further invested and casted and 72 metal copings were fabricated. The ceramic materials were used for the study viz. Vita/VMK, IPSd SIGN, and superporcelain. Ceramic built-up was carried out according to manufacturer instructions. Incisal ceramic built-up was carried out with increasing thickness from 2.00 to 2.5 and 3.00 mm. A total of 72 samples, prepared for the study, were divided into two groups, i.e. group I (36 samples) and group II (36 samples), as per the direction of application of load. The samples were mounted on acrylic block (6 samples/block). A total 12 acrylic blocks were prepared. All the samples were tested using universal testing machine (MTS/USA). The load was applied with crosshead speed of 5 mm/min. Fracture resistance was found to be highest for the 2.00 mm and lowest for 3.00 mm incisal ceramic thickness samples regardless of the ceramic material in both groups. There was a gradual decrease in fracture resistance as the incisal ceramic thickness increased from 2.00 to 3.00 mm in all samples. Fracture resistance was marginally higher for incisal ceramic build-up of 3 mm thickness on group II metal copings than on group I copings. Fracture resistance was highest for IPSd SIGN followed by that of Vita/VMK-95 and superporcelain. A 3.00 mm incisal ceramic thickness offered greater fracture resistance in comparison to lower values of incisal thickness; IPSd SIGN offered greatest fracture resistance followed by that of Vita/VMK-95 and superporcelain.

Influence of Veneering Materials on the Marginal Fit and Fracture Resistance of an Alumina Core System

This study was undertaken to assess the influence of three-veneering materials on the marginal fit, fracture resistance, and failure pattern of In-Ceram alumina crowns. Forty In-Ceram cores were constructed and divided into four groups of ten each. Ten alumina cores were left unveneered, forming the first group for core testing, while the other 30 copings were divided into three groups depending on the veneering material used. The vertical marginal gaps of the alumina copings were measured before and after veneer placement at 16 sites using an optical microscope. The specimens were then loaded to fracture at a crosshead speed of 1 mm/min. Fractured specimens were examined, and the fracture patterns of the crowns were recorded. Selected specimens were examined using scanning electron microscope. Data were presented as means and standard deviation values. One-way ANOVA was used to compare between mean gap areas and fracture resistance of the three materials. Duncan's post hoc test was used for pairwise comparison between the means when ANOVA test was significant. Vitadur-N-veneered crowns showed statistically the highest mean vertical gaps, while no significant difference was evident between the marginal fits of Vitadur-α- and VM7-veneered crowns. Regarding the strength, a statistically significant decrease in fracture resistance of the cores was evident after veneering with Vitadur-N; however, no significant change in mean fracture resistance value of Vitadur-α- and VM7-veneered crowns was evident compared to the alumina cores. VM7-veneered crowns showed the highest fracture resistance values. Vitadur-N-veneered crowns showed the highest mean vertical gaps and the lowest mean fracture resistance values of the tested groups, while VM7-veneered crowns combined the highest fracture resistance values and clinically acceptable margins. The best interface quality and finest ceramic texture were evident in case of VM7 material.

Mechanical Properties of Highly Filled Latex-Based Polystyrene/Laponite Nanocomposites

Nanocomposite films containing up to 50 wt. % laponite have been prepared from emulsion polymerized polystyrene (PS)/laponite latexes with the laponite attached to the PS particle surfaces. Below Tg, the observed stiffness increases are accounted for by classical models for mechanical reinforcement, but these severely underestimate the stiffness above Tg. An alternative model has therefore been proposed, in which the laponite and PS with reduced mobility form a cellular network, consistent with TEM observations. This cellular network is also argued to play an important role in the decrease in fracture resistance at high laponite contents, through decreases in matrix ductility and breakdown of the laponite stacks.

Crack tip opening angle measurement through a girth weld in an X100 steel pipeline section*

ABSTRACTCrack tip opening angle (CTOA) is becoming one of the most accepted methods for characterizing fully plastic fracture. It provides a measure of the resistance to fracture for a material in cases where there is a large degree of stable‐tearing crack extension during the fracture process. Our current pipeline research uses the CTOA test as an alternative, or addition, to the CTOD (crack tip opening displacement) and the fracture energy characterization provided by the J‐integral approach. A test technique was developed for measurement of CTOA that uses a modified double cantilever beam (MDCB) specimen. A digital camera and image analysis software were used to record the progression of the crack tip and to estimate the CTOA. In this article, CTOA data on crack growth orientations perpendicular to pipeline girth welds are presented. The CTOA for X100 high strength bainitic gas pipeline steel is reported. Two different specimen gauge sections, 3 mm and 8 mm, were used and the effect of the specimen thickness on the CTOA is discussed. The results show a change in the CTOA as the crack grows into the heat affected zone (HAZ). A slight improvement in the fracture resistance is measured, and through the weld, a slight decrease in fracture resistance is observed.

Comparison of fracture resistance in root canals of immature sheep teeth after filling with calcium hydroxide or MTA

Thirty immature sheep incisor teeth were tested for their fracture resistance after various treatment modalities using calcium hydroxide (CH) or a mineral trioxide aggregate material (MTA) as a root filling. The incisors, having approximately 80% of their root growth completed, were removed from jaws of slaughtered sheep and divided into four experimental groups. The pulps were extirpated from all the teeth through the open apexes. (a) Saline group: the teeth were preserved in saline for 100 days at 6 degrees C. (b) CH group: the root canals were filled with CH and sealed apically with IRM and stored as above. (c) MTA group: the canals were filled with MTA and stored as above. (d) CH+MTA group: the canals were filled with CH and sealed with IRM. After 30 days, the CH was replaced with MTA and stored as above. At the end of the 100-day storage period, all teeth were embedded in plaster of Paris and tested for fracture strength at the cervical area in an Instron testing machine. The results showed a decrease in fracture resistance (a) of the incisors with CH in the root canals after 100 days of storage, compared to (b) teeth stored in intracanal saline and (c) teeth with 30 days of CH and then filled with MTA, and (d) those filled with MTA in the canals. In conclusion, when CH was kept in the canals of immature sheep teeth for only 30 days followed by root filling with MTA there was no significant decrease in strength of the root within an observation period of 100 days. This finding may be of importance in the decision of treatment plans for teeth with pulp necrosis and immature root formation.

アパタイトセラミックスの生体活性機能による微細構造変化と破壊特性

Biocompatible materials, such as bioactive ceramics and bioactive glasses can be effective in the repair of bone defects during orthopaedics surgery. These materials have been found by observation to exhibit varying degrees of osteoconductive behavior. The hydroxyapatite ceramics and bioactive glass ceramics was known as a highly bioactive ceramics, and replacements of lost bone. However, it is to be inferior to a fracture characteristic in a weak point of apatite ceramics. In the present study, surface structural changes of apatite ceramics with the bioactive function and mechanical property in simulated body fluid were investigated. Sub-micrometer hydroxyapatite ceramics powder was used as starting materials for making hydroxyapatite ceramics. Pressure less sintering was preformed at 1300°C in O2 atmosphere using the pre-sintered bodies. Fracture resistance (KQ) was evaluated by ASTM E399-90 method. And also, fracture resistance tests were performed using compact tension specimens. It has been confirmed by SEM observation, thin-film X-ray diffraction matter and FT-IR reflection spectroscopy that the apatite layer can be reproduced on the surface of the hydroxyapatite ceramic even in a cellular simulated body fluid with in concentrations nearly equal to those of human blood plasma. As a result, corrosion degradation of hydroxyapatite ceramics were preferentially recognized on hydroxyapatite particle after short time immersion into simulated body fluid. The general tendency of drastic decrease in fracture resistance was recognized in these materials. The fracture resistance of the specimen was found to decrease with increasing corrosion degradation, especially after 3 weeks immersion in simulated body fluid. This remarkable degradation in fracture resistance is considered to be caused by crack propagation through corroded pit. However, the specimens after 4 weeks immersion into simulated body fluid showed improved fracture resistance compared with those of corroded hydroxyapatite ceramics. There improvements in fracture resistance may be brought about through the mechanics was shown to induce the apatite layer formation on it's surface in some areas between 4 and 8 weeks by simulated body fluid.