Dentin Fracture Research Articles

Effect of carbodiimide and chlorhexidine on the bond strength longevity of resin cement to root dentine after radiation therapy.

To evaluate the effect of carbodiimide (EDC) and chlorhexidine (CHX) on the bond strength (BS) of resin cement to root dentine of teeth submitted to radiotherapy. One hundred and twenty extracted maxillary canines were selected and assigned to 2 groups (n=60): nonirradiated and irradiated (30 cycles of 2Gy, total 60Gy). Roots lengths were standardized, and canals were prepared and filled. Post spaces were then prepared, and the samples were redistributed according to dentine treatment (n=20): saline solution (SF); CHX 2%; or EDC 0.5M. After drying the post space, fibreglass posts were cemented. Cross-sectioned slices were obtained, and in half of the specimens of each subgroup (n=10), the analysis was performed immediately; the others (n=10) were stored for 10months before analyses. The most cervical slice of each third was subjected to a push-out test and failure pattern analysis (n=10), and the most apical slice submitted to the analysis of the adhesive interface by SEM (n=5). The bond strength data were submitted to anova and Tukey tests, the adhesive interface adaptation was submitted to Kruskal-Wallis and Dunn's tests, and the Chi-square test was used to evaluate the type of failure. The irradiated specimens had significantly lower bond strength (13.8±4.3) than the nonirradiated (18.1±3.1; P<0.001). For the irradiated teeth, the bond strengths were significantly lower in the SF and CHX groups (P<0.001). Also, the bond strengths reduced significantly after 10months in the SF and CHX groups (P<0.001). Cohesive failures occurred in dentine for irradiated specimens. Poorer interface adaptation, dentine fractures and microfractures were observed in irradiated specimens, and better adaptation was observed for specimens after EDC treatment. Radiotherapy was associated with lower bond strength and worse interface adaptation. Dentine treatment with EDC contributed to adhesive interface longevity during the cementation of glass fibre posts in nonirradiated and irradiated teeth.

Do hybrid arch bar screws pose a risk to the dentition?

Objective Hybrid arch bars have become popular alternatives to traditional Erich arch bars for use in craniomaxillofacial surgery. They offer the benefit of decreased time for application, reduced risk of sharps exposure to healthcare personnel, and decreased risk of compromised periodontal health. However, it has not been established if they pose a significant risk to the dentition. Damage to the teeth, such as violation of the pulpal canal or root fracture, can lead to clinically significant sequelae. The purpose of the study was to examine if the screws contact or violate the tooth structure during placement. Study Design A retrospective radiographic review of 50 patients treated with Stryker SMARTLock Hybrid Maxillomandibular fixation system at University Medical Center Hospital in New Orleans, from January 2018 to August 2018, was conducted. Postoperative axial slices of computed tomography (CT) scans were examined for screw position relative to the adjacent tooth roots. Patients were excluded if they were fully edentulous, were incarcerated, or did not have arch bars applied to both arches. Variables examined were screw violation of the periodontal ligament, gross disruption of tooth root dentin, pulpal violation, and root fracture. The location of the tooth injured with regard to the maxilla versus the mandible and the anterior, premolar, or molar dentition was also examined. Statistical analysis was performed with unpaired t test and 1-wayanalysis of variance with Tukey's post hoc test. Results Fifty patients were analyzed, for a total of 507 screws in 100 arches with 1340 teeth present. Overall, 31.49% of teeth had contact or injury with the screws, with screw violation of the periodontal ligament (7.39%), dentin (19.78%), and pulp (3.81%) and root fracture (0.45%). There was a significantly higher incidence of root fracture in the mandible (N = 5) versus maxilla (N = 1) (P Conclusions Hybrid arch bars offer many benefits to the surgeon, but there is no risk of the screw contacting or violating the tooth structure. There is an increased risk to the anterior dentition and the maxillary dentition. The mandibular teeth are also more likely to experience root fracture compared with the maxillary teeth. The hybrid arch bars should be applied with consideration to patient anatomy and tooth position to prevent injury to the tooth roots.

Assessment of Traumatic Dental Injuries of Permanent Incisors in a Group of Visually Impaired Egyptian Children and its Association with Influencing Factors

Background: prevalence of traumatic dental injuries (TDIs) among visually impaired children varies from one country to another. Different factors aside visual impairment influences the prevalence as well as the severity of such injuries. Evaluating the level of the health care provided for those children by comparing number of traumatized cases and number of treated cases would help in documenting the need for creating a special health care program for them. Aim: this study aims at assessment of traumatic dental injuries in a group of visually impaired Egyptian children and the effect of the relative factors in their prevalence. Design: A cross sectional analytic study using a questionnaire and clinical examination was conducted to assess the prevalence of TDIs of the upper and lower permanent incisors and its relevant factors in children attending two governmental schools for blind children, one school for girls and the other one for boys. Results: Among 402 blind students examined in the current study, 210 (52.2%) students were males and 192 (47.8%) were females. Prevalence of traumatic dental injuries among the study population was 9.95% (40 students). Prevalence of traumatic dental injuries among males was (11.43%) while it was (8.33%) among females, the difference was not significant. Upper central incisors had the highest frequency of trauma (72.5%) and fracture of enamel and dentine was the most frequent TDIS (57.5%). Fall was the most common cause of injury (55%) and the most frequent place of injury was at home (55%). Mean age of children at time of injury is 11.85 (±1.47) years. Only five cases (12.5%) had dental treatment and restoration of their traumatic injuries. There were significant correlations between increased overjet and/ or inadequate lip coverage and the prevalence of TDIs.Conclusions: Environmental factors proposed to influence the prevalence of TDIs were difficult to evaluate in the presence of similar conditions in both schools. The most significant oral factors in predisposing TDIs in blind children are increased overjet and inadequate lip coverage. More efforts are needed to provide better dental health care service for visually impaired children.

Prevalência de trauma dental em crianças e adolescentes atendidos no NEPTI da FOUFBA

A indissociabilidade entre ensino, pesquisa e extensão é almejável para a oferta do ensino odontológico de qualidade. O estudo teve por objetivo determinar o perfil dos pacientes atendidos no Núcleo de Extensão/Pesquisa em Trauma Dental na Faculdade de Odontologia da Universidade Federal da Bahia. A pesquisa foi realizada com 86 pacientes de ambos os sexos, com idade entre 0 e 14 anos, apresentando lesões alvéolo-dentárias. Dois indivíduos já haviam sido atendidos anteriormente, retornando com novo trauma, totalizando 88 episódios de traumatismos. Os dados foram coletados de março de 2016 a janeiro de 2018 e as variáveis avaliadas foram idade e sexo do paciente, dentes afetados, tipo, etiologia, classificação e local onde ocorreu o trauma. Dos 86 pacientes 58,1% eram meninos e 41,9% meninas, com idades variando entre 1 e 14 anos, com média de 5,5 (± 3,7) anos. Na maioria dos casos um dente foi afetado e os incisivos centrais superiores foram os mais atingidos. Nos dentes decíduos a subluxação foi o trauma mais frequente nos tecidos de suporte e a fratura coronária com exposição pulpar nos tecidos dentais. Nos dentes permanentes a avulsão foi o trauma mais frequente nos tecidos de suporte e as fraturas do esmalte e da dentina nos tecidos dentários. Foi possível caracterizar o perfil dos pacientes que foram tratados com lesões dentárias no projeto, permitindo aos cirurgiões-dentistas conhecer a população de risco da região, as principais causas e os traumas mais frequentes.

Bioactivity evaluation of calcium silicate‐based endodontic materials used for apexification

This study aims to compare the bioactivity of Biodentine, ProRoot MTA and NeoMTA Plus with regard to their element uptake (Ca, Si and Ca/P) by root canal dentine in a simulated apex (n=30 each) and evaluate the correlation between the dentine fracture resistance (n=30 each) and interfacial layer thickness. Specimens immersed in a corrected simulated body solution (c-SBF) for 1, 30 and 90days were used. In all test materials, the Ca and Si concentrations in the root dentine were found to be significantly higher, whereas the Ca/P and Si concentrations increased over time (P<0.05). The dentine fracture resistance showed a difference at only day 30. The dentine fracture resistance of Biodentine and ProRoot MTA was positively correlated with the Si and Ca/P values, and the mean interfacial layer thickness of all specimens. A high biomineralisation capacity of ProRoot MTA and Biodentine, and their positive effects on the dentine fracture resistance during the first 30days suggest that they may present more advantages than NeoMTA Plus in apexification treatment.

The effect of flowable composite lining and dentin location on microtensile bond strength and internal fracture formation.

The objective of this study was to determine the effect of flowable composite lining and dentin location on internal dentin fracture formation in the microtensile bond strength (MTBS) test using swept-source optical coherence tomography (SS-OCT). MTBS test beams (1.0×1.0 mm) were prepared from human superficial and deep dentin, which was bonded with a self-etch adhesive (Clearfil SE Bond) and hybrid composite resin (Clearfil AP-X), with or without flowable lining (Clearfil Majesty ES-Flow). We tested 4 groups according to placement technique (with vs. without flowable liner) and dentin (superficial vs. deep) locations. Cross-sectional 2D images of the bonded interface were obtained before and after the MTBS test. Internal dentin fracture after MTBT was observed as a bright zone in SS-OCT. Flowable lining significantly reduced internal fracture formation in dentin (p<0.05). Dentin location significantly influenced MTBS (p<0.05), and this was reduced by flowable lining usage.

Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography

Understanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45° and 70° to the long axis of the tubules (i.e. radial to the tusk). For the 0° sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70° test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45° test-piece showed intermediate behaviour. In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. Statement of SignificanceThis paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin.

Does dental trauma influence the social judgment and motivation to seek dental treatment by children and adolescents? Development, validation, and application of an instrument for the evaluation of traumatic dental injuries and their consequences.

One's smile clearly plays a significant role in the perception and judgment that others have of one's appearance and personality. We sought to develop and validate a questionnaire related to the social judgment of children and adolescents and to evaluate, through its application, the perceptions and judgment of children and adolescents regarding their view of different traumatic dental injuries and their consequences (TDIs-Cs) as well as the motivation to seek dental treatment. The aspects of acceptability, discriminative properties, internal consistency, test-retest reliability, and construct validity were evaluated in the developed questionnaire. A cross-sectional study was conducted involving 100 boys and girls aged 10-15years. Images of an adolescent male and female were either manipulated or not (control) to create different types of TDI-C (eg, enamel fracture, enamel and dentin fracture, crown colour change, and tooth loss/avulsion). These images were analysed by the participants, using a previously validated questionnaire with a six-positive-point and six-negative-point scale, in relation to their social physical and psychosocial characteristics. The data were analysed with the Friedman, Wilcoxon, and Mann-Whitney tests (P<0.05). The developed questionnaire presented high acceptability, strong discriminative properties, satisfactory internal consistency, and satisfactory test-retest reliability, but weak construct validity. The presence of TDI-C had a negative effect on all characteristics evaluated (P<0.001). Tooth loss had the highest level of rejection. Additionally, the presence of TDI-C had a greater negative impact on the aspects of 'starting fights', 'being given a nickname', and 'being ashamed to smile' in males than in females (P<0.05). Children and adolescents with TDI-C were judged as needing to seek dental treatment (P<0.001). The questionnaire developed showed properties of validity and reliability in its administration in a child and adolescent population. TDIs-Cs have a negative influence on the social judgment of children and adolescents.

Prevalence and etiology of dental trauma in schoolchildren aged 6 to 12 years

Aim: To investigate the prevalence and etiological factors of dental trauma in school-age children aged 6 to 12 years. Methods: A study was developed in children and adolescents between the ages of 6 and 12 of both genders enrolled in 3 municipal public schools. An oral examination of the permanent or deciduous incisors was performed, if they were still present in the oral cavity, to evaluate the presence of dental trauma, need for treatment and sequels, and the method of examination and classification of dental trauma of O'Brien. Results: The prevalence of dental trauma was 4.03% (n=29). The most verified traumas were enamel crack / enamel fracture and enamel / dentin fracture without pulp exposure. It was observed that the most affected teeth were the permanent upper central incisors and the age at which trauma was most observed was 11 years, the main etiological factor was fall from a height, in 65.3% of schoolchildren (n=19). Conclusion: The prevalence of dental trauma was 4.03%, with no statistically significant difference between genders. The permanent right upper central incisor was the most affected, occurring predominantly at home and at school. The dissemination of information about dental trauma and emergency protocols to parents and teachers need to be encouraged.

The Influence of Post System Design and Material on the Biomechanical Behavior of Teeth with Little Remaining Coronal Structure.

To evaluate the influence of different post systems on the biomechanical behavior of teeth with a severe loss of remaining coronal structure. Fifty standardized bovine teeth (n = 10 per group) were restored with: cast post-and-core (CPC), prefabricated metallic post (PFM), parallel glass-fiber post (P-FP), conical glass-fiber post (C-FP), or composite core (no post, CC). The survival rate during thermomechanical challenging (TC), the fracture strength (FS), and failure patterns (FP) were evaluated. Finite element models evaluated the stress distribution after the application of 100 N. All specimens survived TC. Similar FS was observed among post-containing groups. Groups P-FP and CC presented 100% repairable fractures. The von Mises analysis showed the maximum stresses into the root canal in groups restored with metallic posts. Glass-fiber posts and CC presented the maximum stresses at the load contact point. Glass-fiber groups showed lower stresses in the analysis of maximal contact pressure; CPC led to the highest values of contact pressure. The modified von Mises (mvM) stress in dentin did not show differences among groups. Moreover, mvM values did not reach the dentin fracture limit for any group. The type of intracanal post had a relevant influence on the biomechanical behavior of teeth with little remaining coronal structure.

Oral Health Status among Egyptian Preschool Children

Background: Oral health is a part of general health, as oral cavity is considered a gateway of the body. Health of dentition and mouth play a major role in the children’s life. Aims: this study aimed to obtain updated information of oral health statues including dental caries situation, gingival condition and traumatic injuries in Egyptian preschool children. Methods: This cross sectional study was carried out in Mansoura city on one thousand children with an age from 3 - 6 years who were attending private and public kindergarten. Children were examined for dental caries using dmft index of primary teeth. Gingival condition was assessed using PMA index (papillary, marginal, and attached gingiva). Upper and lower primary anterior teeth were assessed for signs of dental trauma: treated dental injury, enamel fracture, enamel/dentin fracture, pulp injury, and missing teeth due to trauma. Data were analyzed by Mann-Whitney, Kruskal-Wallis and Chi- square tests. Results: the prevalence of dental caries in preschool children was 61.4%, while the mean dmft was (2.930±3.281) in males and (2.332±2.852) in females. However, prevalence of gingival inflammation was 7.4%, and dental trauma was 10%. Enamel fracture was the highest followed by dentin fracture and discoloration. Conclusion: there was high prevalence of dental caries, while the prevalence of gingival inflammation and traumatic injury were low among Egyptian preschool children.

Traumatic dental injuries of the permanent incisors and its relation to malocclusion in patients attending the pedodontic clinic in College of Dentistry, Baghdad University

Dental trauma is a public health problem in young aged patients. The aim of thisstudy was to investigate the percentage and severity of dental trauma andmalocclusion and their correlation, as well as analyze the general risk factors like theeffect of age, gender, causes of the trauma and malocclusion in anterior permanentteeth.The sample of the present study include patients who came to the Pedodonticclinic in the Pedodontic and Preventive department at the College ofDentistry/Baghdad University seeking treatment of traumatized anterior permanentteeth. The traumatized teeth were examined clinically (according to Garcia-Godyclassification) and radiographically. Types of occlusion was determined according toAngle’s classification, while the over jet and overbite were recorded according to thecoding criteria described by Kinnan’s study.In all age groups, the most frequent cause of trauma was found to be falls (61.4%).Enamel and dentin fracture was the most frequently seen type of injury(38.6%) inwhich upper central incisors were the most affected teeth from dentaltrauma(47.7%).Regarding malocclusion, patients with class II malocclusion represent(71.9%) from the total sample, while those with increased over jet (26.3%) in which(66.7) of them seek treatment for two fractured teeth. However, the number of injuredteeth per child was 1.54. Increased overbite was correlated with more sever type ofdental trauma.There is a relationship between malocclusion and fractured anterior teeth in whichmalocclusion will increase the number of fractured teeth as well as the severity ofdental trauma

An analysis of crack growth in dentin at the microstructural scale.

Dentin is a biocomposite possessing complex hierarchical structure, which endows this hard tissue with excellent damage tolerance. In this study, crack growth in dentin at the microstructural scale is investigated and the synergistic effects of plastic deformation of intertubular dentin (ITD), elasticity and fracture properties of peritubular dentin (PTD), and fracture properties of PTD/ITD interface on the fracture of dentin are explored. A micromechanical model is developed, which captures the experimentally observed fracture process of dentin, i.e. occurrence of microcracking of PTD ahead of the main crack. It is found through numerical simulations that high relative stiffness and low cohesive strength of PTD increase the propensity of microcracking of PTD, whereas reduce the plastic dissipation and toughness of the microstructure of dentin. The microcracking of PTD can be also promoted by low toughness of PTD. The large friction angle and weak strain hardening of ITD could promote the microcracking of PTD, and simultaneously enhance the toughness of the microstructure of dentin. In addition, it is identified that the cohesive strength of the PTD/ITD interface plays a crucial role in dominating fracture mechanisms; low cohesive strength leads to fracture of interface and suppresses microcracking of PTD, which provides an explanation for the crack deflection along interface observed in experiments. Nevertheless, the toughness of interface has a negligible influence on the fracture of dentin.

Structural Changes in Human Teeth after Heating up to 1200&amp;amp;deg;C in Argon Atmosphere

The phase transformation of hydroxyapatite (HAP, Ca10(PO4)6(OH)2) to the beta tricalcium phosphate phase (β-TCP, β-Ca3(PO4)2) at 1100°C is well known. However, in the case of human tooth, the HAP phase transformation is still an open area. For example, the CaO phase has sometimes been reported in the set of phases that make up the teeth. In this study, physical changes of human teeth when subjected to heat treatment in inert atmosphere (argon) were studied. The results were compared with those obtained in air atmosphere, from room temperature (25°C) up to 1200°C. Morphological changes were analyzed by light and scanning electron microscopy (SEM). The HAP to β-TCP phase transformation was followed in powder samples by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Heating of teeth results in the removal of organic material and structural water before the HAP to β-TCP phase transformation, the increment in hardness and the induced crystal growth. The percentage of the phases, crystal growth and lattice parameter variations as a function of temperature was quantified by Rietveld analysis. The black color was observed in dentin heated under argon atmosphere. Differences in expansivity produce fractures in dentin at 300°C in argon and at 400°C in air. In dentin, the coexistence of the HAP and β-TCP phases was observed after 800°C in argon and after 600°C in air; in enamel it was observed at 600°C in argon compared with 400°C in air. In general, the role played by the argon atmosphere during the thermal treatment of the teeth is to retard the processes observed in air.

Chitosan in different concentrations added to a two-step etch-and-rinse adhesive system: influence on bond strength to dentin

Objective: the aim of the present study was to evaluate the influence of adding different concentrations of chitosan to an experimental two-step etch-and-rinse adhesive system on the bond strength and failure mode to dentin. Material and Methods: thirty-two flat dentin surfaces were obtained from extracted human third molars and divided into four groups (n=8) for application of the adhesive systems: AD - conventional two-step adhesive system (Adper Single Bond 2); EXP – experimental two-step etch-and-rinse adhesive system; Chi0.2% - EXP with addition of 0.2% Chitosan; Chi0.5% - EXP with addition of 0.5% Chitosan. Resin composite build-ups were made and the composite/dentin specimens were sectioned to obtain rectangular beams with a bond area of approximately 1mm2. After 24 hours, the sticks were submitted to microtensile bond strength tests in a universal test machine. The fracture pattern was evaluated under a stereoscopic loupe at 40X magnification. Results: one-way analysis of variance showed that the type of adhesive system had no significant effect on the bond strength values (p = 0.142), showing the mean bond strength values (standard deviation), in MPa, for the groups as follows: AD=20.1 (5.4); EXP=16.6 (2.3); Chi0.2%=16.1 (2.8); Chi0.5%=16.9 (2.3). In all the groups there was predominance of cohesive fractures in dentin, representing 68 to 82% of the failure modes. Conclusion: the addition of 0.2 or 0.5% of chitosan had no influence on the bond strength and failure mode of an experimental two-step etch-and-rinse adhesive system to dentin.KeywordsChitosan; Dental Adhesives; Failure Mode; Microtensile Bond Strength.

The effect of microcracking in the peritubular dentin on the fracture of dentin

Dentin is a biocomposite possessing elegant hierarchical structure, which allows it to resist fracture effectively. Despite the considerable efforts to unravel the peculiar fracture behavior of dentin, the effect of microstructural features on the fracture process is largely unknown. In this study, we explore the interaction between the primary crack with crack tip located in intertubular dentin (ITD) and microcracking of peritubular dentin (PTD) ahead of the primary crack. A micromechanical model accounting for the unique composite structure of dentin is developed, and computational simulations are performed. It is found that the microcracking of PTD located in the crack plane in front of the primary crack tip can promote the propagation of the primary crack, increasing the propensity of coalescence of primary crack and microcracks nucleating in PTD. We show that the two-layer microstructure of dentin enables reduction in driving force of primary crack, potentially enhancing fracture toughness. The high stiffness of PTD plays a critical role in reducing the driving force of primary crack and activating microcracking of PTD. It is further identified that the microcracking of PTD arranged parallel to the crack plane with an offset could contribute to the shielding of primary crack.

Influence of remaining coronal tooth structure on fracture resistance and failure mode of restored endodontically treated maxillary incisors

Statement of problemLimited information is available on the effect of an incomplete ferrule because of the varying residual axial wall heights and the volume of residual tooth structure on the fracture resistance of endodontically treated and restored maxillary incisors. PurposeThe purpose of this in vitro investigation was to examine the effect of varying residual axial wall heights, residual coronal tooth structure, and the absence of 1 proximal axial wall on the fracture resistance and failure mode of endodontically treated teeth restored with metal posts. Material and methodsSixty intact human maxillary central incisors were divided into 6 groups (n=10): no ferrule (NF), 2-mm complete ferrule (CF2), 2-mm (IF2), 3-mm (IF3), and 4-mm (IF4) incomplete ferrules missing a single interproximal wall, and a control group that had a 6-mm incomplete ferrule (IF6). Cast metal post-and-cores were placed in all experimental specimens except for controls. Control specimens received 1 interproximal cavity preparation extending to the root canal access and a composite resin restoration. Complete metal crowns were then cemented on all specimens. Completed specimens were subjected to thermocycling (6000 cycles, 5°C/55°C) followed by the immediate testing of fracture resistance. Failed specimens were sectioned buccolingually and evaluated to identify the failure mode. The data were analyzed with an analysis of variance (ANOVA) and the Student-Newman-Keuls multiple comparison test (α=.05). ResultsAn incomplete ferrule (IF2) with 1 interproximal wall missing had significantly reduced fracture resistance (697 N) compared with a complete ferrule (932 N). An increase of 3 to 4 mm of remaining wall height improved fracture resistance, from 844 N (IF3) to 853 N (IF4). Partial decementation was noticed in 8 NF and 5 IF2 specimens. IF3 and IF4 had no decementations. Radicular fractures and cracks (catastrophic failure) were observed in all IF2, IF3, and IF4, 9 CF2, and 6 NF specimens. In 7 specimens without posts (IF6, control), composite resin foundation and/or coronal dentin fracture were observed and the failure was considered repairable. ConclusionsThe results of this in vitro study indicated that specimens with a 2-mm ferrule of uniform height were more resistant to fracture than specimens with a 2-mm ferrule and 1 missing interproximal wall. An increased wall height of 3 or 4 mm was associated with a significant increase in fracture resistance and can compensate for the missing interproximal wall.

Analysis of crack interacting with the composite microstructure of dentin

Abstract Dentin possesses strong fracture resistance, which is attributed to various toughening mechanisms associated with its unique hierarchical structure. In this study, the effects of microstructural features on crack growth in dentin are analyzed. A plasticity model incorporating a local fracture criterion is used to model the mechanical behavior of intertubular dentin (ITD), and a brittle cracking model is used for the peritubular dentin (PTD). Computational simulations of fracture behavior of microstructured dentin are performed, showing that crack growth in microstructured dentin is accompanied by microcracking of PTD ahead of the primary crack, and that fracture of dentin is caused by the merging of the primary crack and microcracks nucleating in PTD. It is identified that the decrease in tubule radius and PTD thickness can lead to the development of a significant degree of microcracking in PTD, thereby enhancing toughness. We further reveal that the toughness of microstructured dentin is dependent on tubule density. The transition in fracture mechanism from multiple void interactions to crack-void interaction occurs as the tubule density decreases, which promotes toughness of dentin. In addition, the effect of the arrangement of dentin tubules is also discussed. The findings of this study provide a mechanistic insight into the region dependent fracture behavior of dentin.

Biomechanical behavior of teeth without remaining coronal structure restored with different post designs and materials

The aim of this study was to access the biomechanical behavior of teeth without remaining coronal structure when restored with posts of different materials and configurations. Fifty bovine teeth (n=10 per group) with standard dimensions were restored as follows: cast post and core (CPC), prefabricated metallic post (PFM), parallel glass-fiber post (P-FP), conical glass-fiber post (C-FP) or composite core (no post, CC). The survival rate during thermomechanical challenging (TC), the fracture strength (FS), and failure pattern (FP) were evaluated. Finite element models were realized to evaluate the stress distribution with a 100N load. All post-containing teeth survived TC, while CC had 30% of failures. CPC and C-FP had the higher fracture strength, but a high number of irreparable fractures (60%), such as PFM (70%). Von Mises analysis has shown the maximum stresses into the canal in groups restored with metallic posts, while glass-fiber posts and CC presented the maximum stresses at load contact point in the crown. CPC led to higher modified von Mises (mvM) stress in the cervical third of dentin. However, mvM values did not reach the dentin fracture limit for any group. Analysis of maximal contact pressure has shown better stress distribution along with the dentin interface in post-containing groups, especially for CPC.

Crack initiation and propagation in composite microstructure of dentin

Dentin possesses unique hierarchical structure through long-term natural selection, which imparts exceptional mechanical properties to this hard tissue. In this study, the combined effects of ductile fracture of intertubular dentin (ITD) and brittle cracking of peritubular dentin (PTD) on the crack initiation and propagation in the composite microstructure of dentin are explored. A micromechanical model accounting for the unique two-layer microstructure of dentin is developed and numerical simulations of fracture of microstructured dentin are performed. It is found that microcracking of PTD prior to the penetration of main crack into PTD and crack deflection along the interface between PTD and ITD are two major mechanisms involved in the fracture of microstructured dentin, which is in a good agreement with experimental observations. The competition between the two mechanisms is governed by PTD strength. Furthermore, we reveal that the elastic and fracture properties of PTD and strain hardening of ITD greatly affect the fracture behavior of dentin. The decrease in elastic modulus and increase in tensile strength of PTD elevate the notch tip plasticity, increasing the propensity of crack initiation at notch tip. Whereas such variations in elastic modulus and tensile strength of PTD can lead to the transition of fracture mechanism from multiple void interactions to crack-void interaction, thereby enhancing toughness of dentin. Increasing the strain hardening exponent of ITD can also give rise to the amplified toughness.