Correlation between Experimental Cyclic Fatigue Resistance and Numerical Stress Analysis for Nickel-Titanium Rotary Files

Introduction

The aim of this investigation was to study cyclic fatigue resistance of various nickel-titanium (NiTi) rotary files under various root canal curvatures by correlating cyclic fatigue fracture tests with finite-element analysis (FEA).

Methods

Four NiTi rotary instruments with different cross-sectional geometries but comparable sizes were selected for this study: ProTaper (Dentsply Maillefer, Ballaigues, Switzerland), ProFile (Dentsply Maillefer), HeroShaper (Micromega, Besançon, France), and Mtwo (VDW, Munich, Germany). The ProFile and HeroShaper files were of size 30/.06 taper, the Mtwo was of size 30/.05 taper, and the ProTaper was F3. The cyclic fatigue test was conducted in a custom-made device that simulated canals with 25°, 35°, and 45° curvature. For the FEA, the file models were meshed, and 17-mm long curved canals were modeled to have same curvatures as the cyclic fatigue tests. Numerical analysis was performed to determine the stress distributions in the NiTi instruments while they rotated in the simulated curved canals.

Results

ProTaper (the stiffest instrument) showed the least cyclic fatigue resistance and highest stress concentration for all tested curvatures, whereas Mtwo showed the best cyclic fatigue resistance. A comparison between the FEA and fatigue results showed that when stresses increased, the number of instrument rotations to fracture decreased. Maximum stresses in the instruments predicted the approximate location of the fatigue fracture.

Conclusions

The stiffer instrument had the highest stress concentration in FEA and the least number of rotations until fracture in the cyclic fatigue test. Increased curvature of the root canal generated higher stresses and shortened the lifetime of NiTi files. Finite-element stress analysis reflected cyclic fatigue fracture resistance.     

Load-bearing capacity of human incisor restored with various fiber-reinforced composite posts

Objectives

The aim of this study was to evaluate the load-bearing capacity and microstrain of incisors restored with posts of various kinds. Both prefabricated titanium posts and different fiber-reinforced composite posts were tested.

Methods

The crowns of human incisors were cut and post preparation was carried out. The roots were divided into groups: (1) prefabricated serrated titanium posts, (2) prefabricated carbon fiber-reinforced composite posts, (3) individually formed glass fiber-reinforced composite posts with the canal full of fibers, and (4) individually formed “split” glass fiber-reinforced composite posts. The posts were cemented and composite crowns were made. Intact human incisors were used as reference. All roots were embedded in acrylic resin cylinders and stored at room temperature in water. Static load was applied under a loading angle of 45° using a universal testing machine. On half of the specimens microstrain was measured with strain gages and an acoustic emission analysis was carried out. Failure mode assessment was also made.

Results

The group with titanium posts showed highest number of unfavorable failures compared to the groups with fiber-reinforced composite posts.

Significance

With fiber-reinforced composite posts the failures may more often be favorable compared to titanium posts, which clinically means repairable failures.     

The effect of different adhesive system applications on push-out bond strengths of glass fiber posts

PURPOSE

Over the past years, the adhesion of fiber posts luted with simplified adhesive systems has been a matter of great interest. The aim of this study was to assess the post retentive potential of a self-adhesive resin cement using different adhesive systems to compare the push-out bond strengths of fiber posts.

MATERIALS AND METHODS

The post spaces of 56 mandibular premolar roots were prepared and divided into 4 experimental groups and further divided into 2 subgroups according to testing time (n=7). The fiber posts (Rely X Fiber Post) were luted with a self-adhesive resin cement (RelyX Unicem) and one of the following adhesive systems: no adhesive, a total-etch adhesive resin (Single Bond), a two-step self-etch adhesive resin (Clearfil SE Bond) and a one-step self-etch adhesive resin (Clearfil S3 Bond). Each root was cut horizontally, and 1.5 mm thick six root segments were prepared. Push-out tests were performed after one week or three months (0.5 mm/min). Statistical analysis were performed with three-way ANOVA (α=.05).

RESULTS

Cervical root segments showed higher bond strength values than middle segments. Adhesive application increased the bond strength. For one week group, the total-etch adhesive resin Single Bond showed higher bond strength than the self-adhesive resin cement RelyX Unicem applied without adhesive resin at middle region. For 3 months group, the two-step self-etch adhesive resin Clearfil SE Bond showed the highest bond strength for both regions. Regarding the time considered, Clearfil SE Bond 3 months group showed higher bond strength values than one week group.

CONCLUSION

Using the adhesive resins in combination with the self-adhesive resin cement improves the bond strengths. The bond strength values of two-step self-etch adhesive resin Clearfil SE Bond improved as time passes.     

Direct contact with mineral trioxide aggregate activates and differentiates human dental pulp cells

Introduction

Mineral trioxide aggregate (MTA) is routinely used for pulp-capping procedures. However, little is known about its direct interaction with the cells or whether MTA is capable of releasing soluble factors that could help in differentiating cells. There have been no previous studies showing this aspect of MTA. Hence, the aim of this study was to determine whether direct contact of the cells with MTA was necessary to help differentiate the pulp cells into odontoblast-like cells.

Methods

Human dental pulp cells were cultured on gray MTA, either in direct contact or away from the cells on a cell culture insert, and the levels of gene expression, secretion of vascular endothelial growth factor (VEGF), and the rates of cell proliferation were analyzed.

Results

MTA when placed in direct contact with the cells promoted up-regulated the expression of important odontoblastic genes like osteocalcin and dentin sialoprotein, thereby showing that direct contact of the cells with the MTA is necessary to promote differentiation of the pulp cells into odontoblast-like cells, which in turn are responsible for dentin bridge formation. MTA also induced an increase in the secretion of VEGF when placed in direct contact with the cells.

Conclusions

Overall, our study supports the fact that direct contact of the cells with the MTA is necessary to help differentiate them into odontoblast-like cells, which in turn will lead to a successful treatment outcome.     

Influence of filling materials on the bonding interface of thin-walled roots reinforced with resin and quartz fiber posts

Introduction

A common complication during the restoration of severely destroyed teeth is the loss of coronal root dentine. The aim of this study was to evaluate the influence of different sealers on the bonding interface of weakened roots reinforced with resin and fiber posts.

Methods

Sixty extracted maxillary canines were used. The crowns were removed, and the thickness of root dentine was reduced in the experimental (n = 40) and positive control (n = 10) groups. The specimens of experimental group were assigned to four subgroups (n = 10) according to the filling material: gutta-percha + Grossmann’s sealer, gutta-percha + AH Plus (Dentsply De Trey Gmbh, Konstanz, Germany), gutta-percha + Epiphany (Pentron Clinical Technologies, Wallingford, CT), and Resilon (Resilon Research LLC, Madison, CT) + Epiphany. In the negative control group (n = 10), canals were not filled. After post space preparation, the roots were restored with composite resin light-activated through a translucent fiber post. After 24 hours, specimens were transversally sectioned into 1-mm-thick slices. Push-out test and scanning electron microscopic (SEM) analyses of different regions were performed. Data from push-out test were analyzed by using Tukey post hoc multiple comparison tests. The percentage of failure type was calculated. Data from SEM analysis were compared by Friedman and Kruskal-Wallis tests (α = 0.05).

Results

The mean bond strength was significantly higher in the negative control group as compared with the other groups (P < .05). In all groups, the most frequent type of failure was adhesive. Overall, apical and middle regions presented a lower density of resin tags than the coronal region (P < .05).

Conclusions

The push-out bond strength was not affected by sealer or region. The canal region affected significantly the resin tag morphology and density at the bonding interface.     

Retentive strength and sealing ability of new self-adhesive resin cements in fiber post luting

Objective

To assess by means of “thin-slice” push-out test, light and scanning electron microscopy, the interfacial strength and sealing ability of new self-adhesive resin cements when used to lute fiber posts into endodontically treated teeth.

Methods

RelyX Unicem 2 Automix (3M ESPE, RUA), Maxcem Elite (Kerr, ME) and seT (SDI, S) were utilized in combination with RelyX Fiber Posts (3M ESPE). In each group 5 posted roots were used for push-out testing and 5 were processed for observations of interfacial morphology and nanoleakage under light microscope and scanning electron microscope. Five to six slices were obtained from each posted root. The statistical significance of the influence on post push-out strength of luting agent, dowel space level, and between-factor interaction was assessed using Two-Way Analysis of Variance (ANOVA) and Tukey test as needed. Differences in nanoleakage scores were also statistically evaluated (Kruskal-Wallis ANOVA) (p < 0.05).

Results

Luting agent was a significant factor for post push-out strength. The interfacial strength achieved by RUA (9.3 ± 2.6 MPa) was significantly higher than that of ME (6.7 ± 2.7 MPa) and that of S (5.4 ± 3.1 MPa), which were comparable to each other. Dowel space level and between factor interaction were not statistically significant. Statistically comparable interfacial nanoleakage was observed in all the groups.

Significance

The three new self-adhesive resin cements exhibited similar sealing properties, although the post retentive ability was superior with RUA.     

Influence of connector design and material composition and veneering on the stress distribution of all-ceramic fixed dental prostheses: A finite element study

Objectives

Finite element analysis is a standard method to simulate the stress distribution in all-ceramic dental restorations in order to estimate the loading capacity of the brittle components. The hypothesis of this study was that stresses in the connector area of a veneered FDP are strongly influenced by the framework dimensions and the veneering material.

Methods

Finite element analyzes of bilayered fixed dental prostheses with three different framework-designs and three different veneering materials were conducted, applying the loads onto the veneering as well as directly onto the framework. The outer shape of the veneering ceramic remained constant for all cases.

Results

The maximum first principal stresses in the framework of the fixed dental prostheses (FDP) decreased with smaller framework dimensions when the load was applied on the veneering. By applying the load directly onto the framework of the FDP without veneering a converse tendency was found. The variation of the veneering material lead to the conclusion that stresses in the framework became higher with decreasing Young's modulus of the veneer, while the stresses in the veneer increased at the same time.

Significance

The veneering material plays a significant role for the failure of a FDP and cannot be neglected neither in testing nor in simulation. Thus the loading capacity of dental restorations can only be reasonably evaluated when the whole restoration is taken into account, including framework and veneering.     

Four-year clinical evaluation of Class II nano-hybrid resin composite restorations bonded with a one-step self-etch and a two-step etch-and-rinse adhesive

Objective

The objective of this prospective clinical trial was to evaluate the 4-year clinical performance of an ormocer-based nano-hybrid resin composite (Ceram X; Dentsply/DeTrey) in Class II restorations placed with a one-step self-etch (Xeno III; Dentsply/DeTrey) and two-step etch-and-rinse adhesive (Ivoclar Vivadent).

Methods

Seventy-eight participants received at random at least two, as similar as possible, Class II restorations of the nano-hybrid resin composite bonded with either a single step self-etch adhesive or a control 2-step etch-and-rinse adhesive. The 165 restorations were evaluated using slightly modified USPHS criteria at baseline and then yearly during 4 years.

Results

162 restorations were evaluated at 4 years. Postoperative sensitivity was observed in 6 patients (3 Xeno III, 3 Exite) between 1 and 3 weeks. Eleven failed restorations (6.8%) were observed during the follow up. Seven in the one-step self-etch adhesive group (7.7%) and four in the 2-step etch-and-rinse group (5.6%). This resulted in non-significant different annual failure rates of 1.9% and 1.4%, respectively. Fracture of restoration was the main reason for failure.

Conclusion

The ormocer-based nano-hybrid resin composite showed a good clinical performance in Class II cavities during the 4 year evaluation. No significant difference was seen in overall clinical effectiveness between the two adhesives.     

Fiber post etching with hydrogen peroxide: effect of concentration and application time

Introduction

Etching is necessary to expose the fibers and enable both mechanical and chemical bonding of the resin core to the fiber post. This study evaluated the effect of concentration and application time of hydrogen peroxide on the surface topography and bond strength of glass fiber posts to resin cores.

Methods

Fiber posts were etched with 24% or 50% hydrogen peroxide for 1, 5, or 10 min (n = 10). Posts without any treatment were used as a control. After etching, the posts were silanated and adhesive resin was applied. The posts were positioned into a mold to allow a self-cured resin core to be inserted. The post/resin assembly was serially sectioned into five beams that were subjected to a tensile bond strength test. Data were subjected to two-way ANOVA and Tukey test (α = 0.05). The surface topography was analyzed using scanning electronic microscopy.

Results

Non-etched post presents a relatively smooth surface without fiber exposure. Application of hydrogen peroxide increased the surface roughness and exposed the fibers. All experimental conditions yielded similar bond strength values that were higher than those obtained in the control group.

Conclusion

Both 24% and 50% hydrogen peroxide exposure increased the bond strength of resin to the posts, irrespective of the application time.     

Effect of chlorhexidine and ethanol on the durability of the adhesion of the fiber post relined with resin composite to the root canal

Introduction

The aim of this study was to investigate the effects of pretreatment of gel chlorhexidine and ethanol on the bond strength and durability of the adhesion of the fiber post relined with resin composite to the root dentin.

Methods

Sixty bovine incisor roots were divided into four groups: irrigation with physiologic solution (control), 5 minutes with chlorhexidine, 1 minute with ethanol, and 5 minutes with chlorhexidine followed by 1 minute with ethanol. Fiber posts relined with resin composite were cemented with RelyX ARC (3M ESPE, St Paul, MN) and a self-etching adhesive system Clearfil SE Bond (Kuraray, Kurashiki, Japan). Each group was randomly divided into three subgroups: 24 hours of water storage, 12 months of water storage, and 12 months of oil storage. All roots were sectioned transversely in the coronal, middle, and apical regions, producing 1-mm thick slices, and the push-out test was performed. Statistical analysis was performed using analysis of variance and the Tukey test for post hoc comparisons (α = 0.05).

Results

Immediate groups showed similar bond strength values with or without chlorhexidine and/or ethanol pretreatment (P > .05). A significant decrease in the bond strength in the control group was observed after 12 months of storage in water and oil (P < .05). The use of chlorhexidine- and/or ethanol-preserved bond strength in the groups stored in water and oil for 12 months (P < .05).

Conclusions

Chlorhexidine and/or ethanol pretreatment were capable of preserving the bond strength of the fiber post relined with resin composite to root dentin for 12 months.     

Numerical fatigue 3D-FE modeling of indirect composite-restored posterior teeth

Objective

In restored teeth, stresses at the tooth-restoration interface during masticatory processes may fracture the teeth or the restoration and cracks may grow and propagate. The aim was to apply numerical methodologies to simulate the behavior of a restored tooth and to evaluate fatigue lifetimes before crack failure.

Materials and methods

Using a CAD-FEM procedure and fatigue mechanic laws, the fatigue damage of a restored molar was numerically estimated. Tessellated surfaces of enamel and dentin were extracted by applying segmentation and classification algorithms, to sets of 2D image data. A user-friendly GUI, which enables selection and visualization of 3D tessellated surfaces, was developed in a MatLab^® environment. The tooth-boundary surfaces of enamel and dentin were then created by sweeping operations through cross-sections. A class II MOD cavity preparation was then added into the 3D model and tetrahedral mesh elements were generated. Fatigue simulation was performed by combining a preliminary static FEA simulation with classical fatigue mechanical laws.

Results

Regions with the shortest fatigue-life were located around the fillets of the class II MOD cavity, where the static stress was highest.

Significance

The described method can be successfully adopted to generate detailed 3D-FE models of molar teeth, with different cavities and restorative materials. This method could be quickly implemented for other dental or biomechanical applications.     

A prospective, randomized single-blind study of the anesthetic efficacy of frequency-dependent conduction blockade of the inferior alveolar nerve

Introduction

The purpose of this prospective, randomized single-blind study was to evaluate the degree of pulpal anesthesia obtained with frequency-dependent conduction blockade of the inferior alveolar nerve (IAN).

Methods

Eighty adult volunteers randomly received two IAN blocks: an IAN block followed by continuous electrical stimulation for 3 minutes of the first molar or lateral incisor for six cycles over a time period of 64 minutes; an IAN block followed by mock electrical stimulation using the same cycles. The IAN blocks were administered at two separate appointments spaced at least 1 week apart in a crossover design. An electric pulp tester was used to test for anesthesia of the first molar and lateral incisor. Anesthesia was considered successful when two consecutive 80 readings were obtained within 15 minutes, and the 80 reading was recorded through the 60th minute.

Results

The anesthetic success rate for the stimulated IAN block was 35% and 48% for the lateral incisor and first molar, respectively. For the mock stimulated IAN, success was 18% for the lateral incisor and 62% for the first molar. There was no significant difference between the two IAN block techniques.

Conclusions

We concluded that the stimulation of nerves in the presence of local anesthesia (frequency-dependent nerve block) did not statistically increase the success rate of pulpal anesthesia for an IAN block.     

The slippery slope - Critical perspectives on in vitro research methodologies

Objectives

This paper attempts to provide critical perspectives on common in vitro research methodologies, including shear bond testing, wear testing, and load-to-failure tests. Origins of interest in high-quality laboratory data is reviewed, in vitro data is categorized into property and simulation protocols, and two approaches are suggested for establishing clinical validity. It is hoped that these insights will encourage further progress toward development of in vitro tests that are validated against clinical performance and/or by producing clinically validated failure or damage mechanisms.

Materials and methods

Published shear and tensile bond data (macro and micro) is examined in light of published finite element analyses (FEA). This data is subjected to a Weibull scaling analysis to ascertain whether scaling is consistent with failure from the bonded interface or not. Wear tests results are presented in light of the damage mechanism(s) operating. Quantitative wear data is re-examined as being dependent upon contact pressure. Load-to-failure test results are re-analyzed by calculating contact stresses at failure for 119 tests from 54 publications over more than 25 years.

Results

FEA analyses and reported failure modes (adhesive, mixed, cohesive) are consistent with failure not involving interfacial “shear stresses” as calculated in published work. Weibull scaling clearly suggests failure involving external surfaces of specimens, not interfacial origins. Contact stresses (pressures) are clearly an important variable in wear testing and are not well-controlled in published work. Load-to-failure tests create damage not seen clinically due to excessively high contact stresses. Most contact stresses in the 119 tests examined were calculated to be between 1000 MPa and 5000 MPa, whereas clinical contact stresses at wear facets have been measured not to exceed 40 MPa.

Conclusions

Our community can do a much better job of designing in vitro tests that more closely simulate clinical conditions, especially when contact is involved. Journals are encouraged to thoughtfully consider a ban on publishing papers using bond tests and load-to-failure methods that are seriously flawed and have no clinical relevance.     

Influence of chlorhexidine and ethanol on the bond strength and durability of the adhesion of the fiber posts to root dentin using a total etching adhesive system

Introduction

The aim of this study was to investigate the effects of pretreatment of gel chlorhexidine (CHX) and ethanol (EtOH) on the bond strength and durability of the adhesion of the fiber post relined with resin composite to the root dentin using a total etch adhesive system.

Methods

Forty bovine incisor roots were divided into four groups after phosphoric acid etching: irrigation with physiologic solution (control), 5 minutes with CHX, 1 minute with EtOH, and 5 minutes with chlorhexidine followed by 1 minute with EtOH. Fiber posts relined with resin composite were cemented with either RelyX ARC (3M ESPE, St Paul, MN) and a total etch adhesive system Scotchbond Multi-Purpose (3M ESPE). Each group was randomly divided into two subgroups: 24 hours of storage and 12 months of storage. All roots were sectioned transversely, and the push-out test was performed. Failure modes were observed, and the bond strength means were analyzed by analysis of variance and the Tukey test (α = 0.05).

Results

CHX irrigation resulted in homogeneous bond strength values at 24 hours and 12 months of storage (P < .05). A significant bond strength decrease was noticed after 12 months of storage when irrigations were performed with physiologic solution and EtOH application only or associated with CHX (P < .05).

Conclusions

The use of CHX pretreatment could preserve the bond strength of the fiber post relined with resin composite to root dentin for 12 months. The use of EtOH and CHX followed by EtOH did not preserve the bond strength of the total etch adhesive system Scotchbond Multi-Purpose.     

Experimental and FE shear-bonding strength at core/veneer interfaces in bilayered ceramics

Objectives

To compare the bond strength of a ceramic veneer material to two different ceramic core materials using shear strength testing and finite element analysis (FEA).

Methods

15 blocks of ceramic cores were made of each of IPS e.max ZirCAD (Ivoclar-Vivadent, Schaan, Liechtenstein) (ZirCAD) and lithium disilicate IPS e.max CAD (LS). These were veneered using IPS e.max Ceram (Ceram) according to the manufacturers’ instructions. Samples were then mounted, placed inside a shear testing jig and loaded at their core/veneer interfaces with a universal testing machine. Fractured specimens were then examined fractographically at 45×. An independent t-test and a Mann-Whitney U test were used to detect differences in bond strengths and the patterns of failure between the two groups, respectively (p > 0.05). Two-dimensional plane stress FE-models were constructed and subjected to shear loading simulating the experimental conditions.

Results

Mean shear stresses (MPa) were 28.8 (9.5) for ZirCAD/Ceram and 29.1 (8.3) for LS/Ceram. Differences were not statistically significant. Fracture patterns were significantly different between the 2 groups as all ZirCAD/Ceram samples broke adhesively at their interface while LS/Ceram samples broke cohesively in the veneer or the core or had mixed adhesive/cohesive failure. Stress distributions in the FEA models were also different, corresponding to the variable fracture patterns in the 2 groups.

Significance

Although shear stresses were similar, fractographic analysis and finite element modeling suggested better bonding between the veneering ceramic and the glass-ceramic than to the zirconia cores. Improved bonding techniques are necessary to prevent clinical delamination of veneered zirconia restorations.     

Angiotensin-converting enzyme (ACE), angiotensinogen (AGT), and angiotensin II type 1 receptor (AT1R) gene polymorphisms in generalized aggressive periodontitis

Aim

Host response to periodontopathic microorganisms can be modulated by genetic factors. Accumulated evidence highlighted the role of renin-angiotensin system (RAS) in inflammatory response thus potential implication of this molecular system in the pathogenesis of periodontitis can be suggested. The present study investigated common genetic variants of molecules within the RAS family namely angiotensin-converting enzyme (ACE), angiotensinogen (AGT) and angiotensin II type 1 receptor (AT1R) in relation to generalized aggressive periodontitis (G-AgP).

Methods

DNA was obtained from peripheral blood of 103 G-AgP patients and 100 periodontally healthy subjects. ACE I/D, AGT M235T and AT1R A1166C polymorphisms were genotyped by polymerase chain reaction and restriction fragment length polymorphism method. Chi-square, ANOVA and logistic regression were used in statistical analyses.

Results

Both ACE I/D and AT1R polymorphisms were similar in G-AgP and healthy groups (p > 0.05). G-AgP subjects exhibited decreased AGT TT genotype and T allele frequency as compared to healthy subjects (p < 0.05). The same trend was also observed in the nonsmoker subgroup regarding investigated RAS polymorphisms.

Conclusions

Present findings suggest that AGT M235T TT genotype and T allele might be associated with decreased risk for G-AgP in Turkish population.     

Influence of root canal taper on its cleanliness: a scanning electron microscopic study

Introduction

Taper is a factor that determines final root canal dimensions and, consequently, the dimensions of the space for the cleaning action of irrigants. Therefore, the aim of the present study was to investigate the influence of taper on root canal cleanliness.

Methods

Root canals of 45 mandibular incisors were divided into 3 groups and prepared with GT rotary files to apical preparation size 30 and final taper 0.04, 0.06, and 0.08, respectively. Irrigation with 2.5% NaOCl was performed after each file. The final irrigation sequence was 10 mL 17% ethylenediaminetetraacetic acid, followed by 10 mL 2.5% NaOCl and 10 mL saline solution. The presence of debris and smear layer on root canal walls was evaluated under the scanning electron microscope with the use of a 4-category scale system.

Results

The presence of debris was minimal in all groups. Statistical analysis for the presence of smear layer showed no significant differences between the groups, whereas a significant difference was detected between the apical and middle thirds of each group.

Conclusions

Under the conditions of this study, root canal preparation with tapers 0.04, 0.06, or 0.08 did not affect canal cleanliness. Debris removal was almost complete for all tapers, whereas smear layer was not removed, especially from the apical part of the canals.     

A comparative mechanical and bone remodelling study of all-ceramic posterior inlay and onlay fixed partial dentures

Objectives

Comparative studies of bone remodelling and mechanical stresses between inlay and onlay fixed partial dentures (FPD) are rather limited. The purpose of this paper was to evaluate the biological consequence in posterior mandibular bone and the mechanical responses in these two different prosthetic configurations.

Methods

Three-dimensional (3D) finite element analysis (FEA) models are created to explore the mechanical responses for the inlay and onlay preparations within the same oral environment. Strain induced bone remodelling was simulated under mastication. The remodelling adopted herein relates the strain in the bone to the change of Hounsfield Unit (HU) value in proportion to the surface area density (SAD) of bony morphology, which allows directly correlating to clinical computerised tomography (CT) data.

Results

The results show that both FPD designs exhibit a similar resultant change in bone mineral density (BMD) though the onlay configuration leads to a more uniform distribution of bone density. The inlay design results in higher mechanical stresses whilst allowing preservation of healthy tooth structure.

Conclusions

This study provides an effective means to further clinical assessment and investigation into biomechanical responses and long-term restorative outcome with different FPD designs.

Clinical significance

Quantifying in vivo stress distributions associated with inlay/onlay FPDs can further supplement clinical investigations into prosthetic durability, FPD preparation techniques (i.e., taper angles, material development), consequent stress distributions and the ongoing biomechanical responses of mandibular bone.     

Recurrent Apical Periodontitis and Late Endodontic Treatment Failure Related to Coronal Leakage: A Case Report

Introduction

This article describes a case of late failure after endodontic retreatment as characterized by recurrent post-treatment apical periodontitis.

Methods

At the time of the initial treatment, the patient presented with acute apical abscess associated with a tooth with pulp necrosis caused by trauma. Four years later, the tooth was retreated because of persistent disease. The follow-up examination 28 months after retreatment showed complete healing.

Results

The patient returned 11 years and 7 months later for bleaching of the discolored tooth, and although the periodontal tissues were clinically and radiographically normal, a fracture line was observed on the mesial aspect of the pulp chamber. Extraction was indicated, but the patient only returned 5 years and 9 months later. Then a radiograph showed recurrent post-treatment apical periodontitis. The tooth was extracted, and histopathologic and histobacteriologic analyses revealed bacterial colonies along the fracture line and colonizing ramifications and accessory canals at the apical root canal system.

Conclusions

Coronal leakage can be regarded as the most reasonable explanation for resurgence of the disease. However, a predisposing overlapping condition in the form of root fracture conceivably favored the penetration of bacteria from saliva and plaque biofilm along the filled root canal.     

Thickness and microhardness of deciduous tooth enamel with known DLX3 mutation

Aim

To investigate the thickness and hardness of teeth affected by a 2-bp deletion (c.561_562delCT) in the DLX3 gene.

Methods and materials

Extracted maxillary deciduous second molar was collected from the affected individual at age 12 years 7 months. Samples were sectioned buccolingually after embedding in epoxy resin. We measured the enamel thickness and microhardness and performed an elemental analysis using an electron probe microanalyser.

Results

On average, the hardness of the enamel with a 2-bp deletion in DLX3 was about 53% of normal enamel hardness. The mutant enamel thickness was about half of the thickness of the normal control. The calcium level in the enamel with the 2-bp deletion was slightly decreased, while the magnesium level was slightly increased, in comparison to levels measured for normal teeth.

Conclusion

This study shows that enamel affected by a 2-bp deletion in DLX3 has reduced thickness as well as diminished microhardness. These data may explain the severe attrition and interdental spacing observed in affected individuals.