Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multi-faceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.

Calcium isotopic patterns in enamel reflect different nursing behaviors among South African early hominins

Nursing is pivotal in the social and biological evolution of hominins, but to date, early-life behavior among hominin lineages is a matter of debate. The calcium isotopic compositions (δ^44/42Ca) of tooth enamel can provide dietary information on this period. Here, we measure the δ^44/42Ca values in spatially located microsized regions in tooth enamel of 37 South African hominins to reconstruct early-life dietary-specific variability in Australopithecus africanus, Paranthropus robustus, and early Homo. Very low δ^44/42Ca values (<-1.4‰), indicative of milk consumption, are measured in early Homo but not in A. africanus and P. robustus. In these latter taxa, transitional or adult nonmilk foods must have been provided in substantial quantities relative to breast milk rapidly after birth. The results suggest that early Homo have continued a predominantly breast milk-based nursing period for longer than A. africanus and P. robustus and have consequently more prolonged interbirth interval.

Modelling of stress distribution and fracture in dental occlusal fissures

The aim of this study was to investigate the fracture behaviour of fissural dental enamel under simulated occlusal load in relation to various interacting factors including fissure morphology, cuspal angle and the underlying material properties of enamel. Extended finite element method (XFEM) was adopted here to analyse the fracture load and crack length in tooth models with different cusp angles (ranging from 50° to 70° in 2.5° intervals), fissural morphologies (namely U shape, V shape, IK shape, I shape and Inverted-Y shape) and enamel material properties (constant versus graded). The analysis results showed that fissures with larger curved morphology, such as U shape and IK shape, exhibit higher resistance to fracture under simulated occlusal load irrespective of cusp angle and enamel properties. Increased cusp angle (i.e. lower cusp steepness), also significantly enhanced the fracture resistance of fissural enamel, particularly for the IK and Inverted-Y shape fissures. Overall, the outcomes of this study explain how the interplay of compositional and structural features of enamel in the fissural area contribute to the resistance of the human tooth against masticatory forces. These findings may provide significant indicators for clinicians and technicians in designing/fabricating extra-coronal dental restorations and correcting the cuspal inclinations and contacts during clinical occlusal adjustment.

Effect of Two Remineralizing Agents on Initial Caries-like Lesions in Young Permanent Teeth: An in Vitro Study

AIM

To compare the effect of nano-hydroxyapatite (9000 ppm F) and casein phosphopeptide-amorphous calcium phosphate fluoride (900 ppm F) pastes on initial enamel carious lesions of young permanent teeth.

MATERIALS AND METHODS

Sixty extracted young premolars with a standardized window on enamel were immersed in a demineralizing solution for 48 hours to produce subsurface enamel lesions. They were divided into three groups according to remineralizing agents (n = 20) group I: nano-hydroxyapatite paste; group II: casein phosphopeptide-amorphous calcium phosphate fluoride paste; and group III: control (without an agent). The enamel surface microhardness (SMH) was measured at baseline, after the incipient enamel lesion, and after treatment. Additional twenty young premolars were selected and prepared as mentioned above for surface morphology evaluation by scanning electron microscope (SEM).

RESULTS

No significant difference was found in mean surface microhardness in teeth treated with nano-hydroxyapatite paste and those treated with casein phosphopeptide-amorphous calcium phosphate fluoride p = 0.26. SEM showed improvement in surface defects of demineralized enamel in the two test groups.

CONCLUSION

Nano-hydroxyapatite and casein phosphopeptide-amorphous calcium phosphate fluoride pastes were effec -tive in rehardening the initial enamel caries lesions in young permanent teeth.

CLINICAL SIGNIFICANCE

The best strategy for caries management is to focus on the methods of improving the reminer-alization process with the aid of the remineralizing agents. The current study compared the remineralizing effect of two remineralizing agents. Within the limitations of the study, both remineralizing agents were effective for remineralization of early caries-like lesions.

[Electronic probe analysis of enamel remineralization effect of casein phosphopeptide-amorphous calcium phosphate promoted by different concentrations of fluorine]

Objective: To evaluate the remineralization effect and mechanism of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) with different concentrations of fluorine on demineralized enamel using electronic probe. Methods: Extracted premolar teeth for orthodontic purpose were immersed into lactic acid gel to prepare artificial white spot lesions (10 teeth in each group). Then the specimens were randomly assigned to three groups: Control group, with 5% of the CPP-ACP+deionized water; Group A with 5% CPP-ACP+500 mg/L F(-) and Group B with 5% CPP-ACP+900 mg/L F(-). The teeth in each group were soaked in different solutions for 4 days and then were measured using electron probe tester. The changes of contents among the three groups were compared. Results: No statistically significant difference in the percentage of fluorine was found in the control group before and after treatment (P=0.06), and the difference in the percentage of fluorine quality in the other two groups was statistically significant (P<0.05). Statistically significant difference was found between calcium oxide and phosphorus peroxide in the three groups before and after mineralization (P<0.05). The percentage change of fluorine mass in group B [(0.107±0.035)%] was significantly greater than that in group A [(0.057±0.038)%] (P<0.05), while fluorine mass in group A was significantly greater than that in control group [(0.013±0.019)%] (P<0.05). In group A and group B, the change in quality of calcium oxide and phosphorus peroxide was significantly greater than that in control group (P<0.05), while no significant difference was found between group A and group B (P>0.05). Conclusions: The addition of fluorine in CPP-ACP increased the transport and penetration of calcium, phosphorus and fluorine on enamel surface.

Impact of a simplified in situ protocol on enamel loss after erosive challenge

This study investigated the effect of the period of use and location of intraoral appliances on enamel surface loss. This randomized, single blind in situ study was conducted in 2 crossover phases based on the period of use, in which maxillary and mandibular appliances were simultaneously worn. Bovine enamel blocks (n = 120) were randomly divided among the studied groups by surface hardness. In each phase, fifteen volunteers used one maxillary appliance and two mandibular appliances for 5 days. Erosive challenge was performed 4X/day by immersion in 0.01 M HCL for 2 minutes. In the continuous phase, the intraoral appliances were worn for 20 hours. In the intermittent phase the appliances were worn for 8 hours and 30 minutes. Enamel loss was determined profilometrically. The discomfort of use of the appliances were evaluated in a questionnaire. Data were analyzed by two-way ANOVA/Tukey’s test and chi-square test (p<0.05). The maxillary appliance promoted higher enamel loss compared to the mandibular one (p<0.001). Intermittent use of appliances resulted in similar enamel loss to the continuous one (p = 0.686). All volunteers preferred to use the maxillary appliance in an intermittent regimen. The intermittent use of maxillary appliance is a simplified reliable protocol appropriated for in situ erosion studies in enamel.

A Review of Enamel Remineralisation Potential of Calcium- and Phosphate-based Remineralisation Systems

PURPOSE

Along with calcium and phosphate ions, fluoride ions promote remineralisation of noncavitated carious lesions to form fluorapatite. However, the supply of calcium and phosphate ions from saliva may not be adequate for effective remineralisation in patients with high caries risk. Therefore, an additional supply of calcium and phosphate ions is mandatory to enhance effective remineralisation with fluoride ions. Several calcium- and phosphate-based remineralisation agents are available for clinical use. However, the nature of the incorporated calcium and phosphate ions and the method of their stabilisation are not similar. Therefore, this review summarises research findings on the enamel remineralisation potential of calcium- and phosphate-based remineralisation agents.

MATERIALS AND METHODS

Appropriate key words were used and the Pubmed electronic database was searched to retrieve articles. Screening through titles and abstracts identified relevant articles. Full text review of the identified relevant articles was performed and the significant findings were summarised and presented in this review.

RESULTS

Several studies including laboratory-based studies, in situ and randomised controlled clinical trials showed casein phosphopeptide amorphous calcium phosphate (CPP-ACP)-containing remineralisation agents to have superior remineralisation potential compared to other forms of calcium- and phosphate-based remineralisation agents, such as functionalised tri-calcium phosphate (fTCP) and amorphous calcium phosphate (ACP).

CONCLUSIONS

More long-term clinical studies are necessary to compare the enamel remineralisation potential of calcium- and phosphate-based agents that contain fTCP and ACP with those containing CPP-ACP. Additional well-designed randomised controlled clinical trials are also necessary to justify long-term clinical supplemental use of products containing CPP-ACP.

The compression dome concept: the restorative implications

Evidence now supports the concept that the enamel on a tooth acts like a compression dome, much like the dome of a cathedral. With an overlying enamel compression dome, the underlying dentin is protected from damaging tensile forces. Disruption of a compression system leads to significant shifts in load pathways. The clinical restorative implications are significant and far-reaching. Cutting the wrong areas of a tooth exposes the underlying dentin to tensile forces that exceed natural design parameters. These forces lead to crack propagation, causing flexural pain and eventual fracture and loss of tooth structure. Improved understanding of the microanatomy of tooth structure and where it is safe to cut teeth has led to a revolution in dentistry that is known by several names, including microdentistry, minimally invasive dentistry, biomimetic dentistry, and bioemulation dentistry. These treatment concepts have developed due to a coalescence of principles of tooth microanatomy, material science, adhesive dentistry, and reinforcing techniques that, when applied together, will allow dentists to repair a compromised compression dome so that it more closely replicates the structure of the healthy tooth.

Enamel biorhythms of humans and great apes: the Havers-Halberg Oscillation hypothesis reconsidered

The Havers-Halberg Oscillation (HHO) hypothesis links evidence for the timing of a biorhythm retained in permanent tooth enamel (Retzius periodicity) to adult body mass and life history traits across mammals. Potentially, these links provide a way to access life history of fossil species from teeth. Recently we assessed intra-specific predictions of the HHO on human children. We reported Retzius periodicity (RP) corresponded with enamel thickness, and cusp formation time, when calculated from isolated deciduous teeth. We proposed the biorhythm might not remain constant within an individual. Here, we test our findings. RP is compared between deciduous second and permanent first molars within the maxillae of four human children. Following this, we report the first RPs for deciduous teeth from modern great apes (n = 4), and compare these with new data for permanent teeth (n = 18) from these species, as well as with previously published values. We also explore RP in teeth that retain hypoplastic defects. Results show RP changed within the maxilla of each child, from thinner to thicker enameled molars, and from one side of a hypoplastic defect to the other. When considered alongside correlations between RP and cusp formation time, these observations provide further evidence that RP is associated with enamel growth processes and does not always remain constant within an individual. RP of 5 days for great ape deciduous teeth lay below the lowermost range of those from permanent teeth of modern orangutan and gorilla, and within the lowermost range of RPs from chimpanzee permanent teeth. Our data suggest associations between RP and enamel growth processes of humans might extend to great apes. These findings provide a new framework from which to develop the HHO hypothesis, which can incorporate enamel growth along with other physiological systems. Applications of the HHO to fossil teeth should avoid transferring RP between deciduous and permanent enamel, or including hypoplastic teeth.

Influence of trace elements on dental enamel properties: A review

Dental enamel, an avascular, irreparable, outermost and protective layer of the human clinical crown has a potential to withstand the physico-chemical effects and forces. These properties are being regulated by a unique association among elements occurring in the crystallites setup of human dental enamel. Calcium and phosphate are the major components (hydroxyapatite) in addition to some trace elements which have a profound effect on enamel. The current review was planned to determine the aptitude of various trace elements to substitute and their influence on human dental enamel in terms of physical and chemical properties.

Does Layering Minimize Shrinkage Stresses in Composite Restorations?

Polymerization shrinkage of resin composites may impair restoration longevity. It is hypothesized that layering, rather than bulk, techniques result in less stress in the tooth-restoration complex. The aim of this study was to compare shrinkage stresses for different restorative techniques used for cusp-replacing restorations with direct resin composite. In a 3-D FE model, the dynamic process of shrinkage during polymerization was simulated. Time-dependent parameters (shrinkage, apparent viscosity, Young’s modulus, Poisson ratio, and resulting creep), which change during the polymerization process, were implemented. Six different restorative procedures were simulated: a chemically cured bulk technique, a light-cured bulk technique, and 4 light-cured layering techniques. When polymerization shrinkage is considered, a chemically cured composite shows the least resulting stress. The differences seen among various layering build-up techniques were smaller than expected. The results indicate that the stress-bearing locations are the interface and the cervical part of the remaining cusp.

Chemical and Structural Information from the Enamel of a Troodon Tooth Leading to an Understanding of Diet and Environment

Synchrotron micro X-ray fluorescence (XRF) spectroscopy with two-dimensional element mapping, micro X-ray diffraction (XRD), electron spin resonance spectroscopy (ESR) and atomic force microscopy (AFM) were used to investigate the chemical and structural nature of the enamel of a tooth from Troodon, a small theropod dinosaur. These methods show that the crystallites in the Troodon tooth are submicron-sized carbonated calcium hydroxyapatite, which are semi-randomly oriented with a preferred orientation of (002) towards the surface of the tooth. Transition metal ions are distributed in the voids between crystallite clusters. Comparison of the ESR spectra indicates that the Troodon tooth had less exposure to UV than a fossilized crocodile tooth.

Investigation of Intra- and Inter-individual Variations of Mineralisation in Healthy Permanent Human Enamel by Raman Spectroscopy

PURPOSE

To systematically examine mineralisation of healthy human enamel using Raman spectroscopy and provide an understanding of baseline variations that may be inherent in the healthy enamel from individual to individual as well as variations within a tooth.

MATERIALS AND METHODS

Human teeth were obtained in compliance with the NIH guidelines. The teeth were collected fresh within the date of the extraction and kept moist at all times with wet tissue paper without any additional disinfecting treatment. The samples were individually wrapped in wet tissue paper and stored in a -20°C freezer. Prior to Raman analysis, the specimens were thawed at room temperature for 30 min. A Raman microscope was employed with a 10X objective used to focus the laser light (785 nm). Raman spectroscopy scores were validated by microcomputed tomography (μCT) on the two teeth which had the highest and lowest mineralisation found in the Raman scans.

RESULTS

Mineralisation levels varied substantially between individuals. The highest Raman-based mineralisation intensity was about 5-fold greater than the lowest mineralisation score. Incisor mineralisation also varied dramatically depending on different sites on the tooth.

CONCLUSIONS

Clinically applicable non-invasive techniques such as Raman spectroscopy that can quantify mineral content, such as Raman spectroscopy, may help answer whether or not mineralisation is associated with caries risk.

Tooth enamel properties and morphology after microabrasion: an in situ study

AIM

This study evaluated the effect of saliva on enamel after microabrasion with different microabrasive compounds under in situ conditions.

METHODS

Enamel/dentin blocks (16 mm² ) from bovine incisors were divided into nine groups (n = 19): one control group (no treatment), four groups treated with microabrasion using 35% phosphoric acid (H₃ PO₄ ) + pumice, and the last four groups treated with microabrasion using 6.6% hydrochloric acid (HCl) + silica. The treated groups were subdivided according to the in situ regimen: without salivary exposure, 1 h, 24 h, or 7 days of saliva exposure. Surface microhardness (SMH) and cross-sectional microhardness (CSMH) were tested. Scanning electron microscopy (SEM) was used to evaluate enamel morphology. Microhardness data were tested by analysis of variance, and Tukey's and Dunnett's tests (α = 0.05).

RESULTS

The SMH analysis revealed that all the microabrasion-treated groups presented significantly-reduced SMH values when compared to the control group (P < 0.05). Treatment with HCl + silica was more prone to the effect of saliva than H₃ PO₄ + pumice, even for CSMH analysis, once the superficial layers reached the same microhardness of that of the control group (P > 0.05). These results were confirmed by SEM, which demonstrated the mineral recovery effect over time.

CONCLUSION

Saliva was effective in promoting the rehardening of enamel after microabrasion, mainly for the surfaces treated with HCl + silica.

The role of organic proteins on the crack growth resistance of human enamel

With only 1% protein by weight, tooth enamel is the most highly mineralized tissue in mammals. The focus of this study was to evaluate contributions of the proteins on the fracture resistance of this unique structural material. Sections of enamel were obtained from the cusps of human molars and the crack growth resistance was quantified using a conventional fracture mechanics approach with complementary finite element analysis. In selected specimens the proteins were extracted using a potassium hydroxide treatment. Removal of the proteins resulted in approximately 40% decrease in the fracture toughness with respect to the fully proteinized control. The loss of organic content was most detrimental to the extrinsic toughening mechanisms, causing over 80% reduction in their contribution to the total energy to fracture. This degradation occurred by embrittlement of the unbroken bridging ligaments and consequent reduction in the crack closure stress. Although the organic content of tooth enamel is very small, it is essential to crack growth toughening by facilitating the formation of unbroken ligaments and in fortifying their potency. Replicating functions of the organic content will be critical to the successful development of bio-inspired materials that are designed for fracture resistance.

A Systematic Study on Tooth Enamel Microstructures of Lambdopsalis bulla (Multituberculate, Mammalia)--Implications for Multituberculate Biology and Phylogeny

Tooth enamel microstructure is a reliable and widely used indicator of dietary interpretations and data for phylogenetic reconstruction, if all levels of variability are investigated. It is usually difficult to have a thorough examination at all levels of enamel structures for any mammals, especially for the early mammals, which are commonly represented by sparse specimens. Because of the random preservation of specimens, enamel microstructures from different teeth in various species are often compared. There are few examples that convincingly show intraspecific variation of tooth enamel microstructure in full dentition of a species, including multituberculates. Here we present a systematic survey of tooth enamel microstructures of Lambdopsalis bulla, a taeniolabidoid multituberculate from the Late Paleocene Nomogen Formation, Inner Mongolia. We examined enamel structures at all hierarchical levels. The samples are treated differently in section orientations and acid preparation and examined using different imaging methods. The results show that, except for preparation artifacts, the crystallites, enamel types, Schmelzmuster and dentition types of Lambdopsalis are relatively consistent in all permanent teeth, but the prism type, including the prism shape, size and density, may vary in different portions of a single tooth or among different teeth of an individual animal. The most common Schmelzmuster of the permanent teeth in Lambdopsalis is a combination of radial enamel in the inner and middle layers, aprismatic enamel in the outer layer, and irregular decussations in tooth crown area with great curvature. The prism seam is another comparably stable characteristic that may be a useful feature for multituberculate taxonomy. The systematic documentation of enamel structures in Lambdopsalis may be generalized for the enamel microstructure study, and thus for taxonomy and phylogenetic reconstruction, of multituberculates and even informative for the enamel study of other early mammals.

Modifying the biomechanical response of mouthguards with hard inserts: A finite element study

PURPOSE

To investigate the influence of a high elastic modulus material insert on the stress, shock absorption and displacement of mouthguards.

METHODS

Finite element models of a human maxillary central incisor with and without mouthguard were created based on cross-sectional CT-tomography. The mouthguard models had four designs: without insert, and middle, external, or palatal hard insert. The hard inserts had a relatively high elastic modulus when compared to the elastic modulus of ethylene vinyl acetate (EVA): 15 GPa versus 18 MPa. A non-linear dynamic impact analysis was performed in which a heavy rigid object hit the model at 1 m/s. Strain and stress (von Mises and critical modified von Mises) distributions and shock absorption during impact were calculated as well as the mouthguard displacement.

RESULTS

The model without mouthguard had the highest stress values at the enamel and dentin structures in the tooth crown during the impact. It was concluded that the use of a mouthguard promoted lower stress and strain values in the teeth during impact. Hard insertion in the middle and palatal side of the mouthguard improved biomechanical response by lowering stress and strain on the teeth and lowering mouthguard displacement.

[Periodontal health during pregnancy and the dental health of the child]

Several studies have shown an association between local/systemic infections and preterm-low birth weight (PTLBW), and it might be an important part of the etiology. Oral Infections such as periodontitis may act as a distant reservoir of microbes, microbial products and inflammatory mediators. These might influence pregnancy and contribute to restriction of fetal growth and induction of early labor and PTB. Enamel formation of the primary teeth begins at 11-14 weeks of fetal life and is completed by the end of 3rd postnatal month. The initial phase consists of matrix formation, followed by calcification in utero. Since enamel is a stable structure, defects involving its matrix secretion and/or maturation of primary teeth can act as a permanent record of insults occurring pre- or perinatally. Any stressful event during pregnancy and birth may lead to metabolic changes in the formation of the enamel, resulting in clinically enamel defects. Severe infections occurring during amelogenesis may be associated with enamel hypoplasia. Babies born after maternal complications during pregnancy or babies who experience a traumatic birth must be considered to be at risk of developing Early Childhood Caries - ECC when exposed to excessive bottle nursing. Therefore oral healthcare should be kept during pregnancy.

Influence of structural hierarchy on the fracture behaviour of tooth enamel

Tooth enamel has the critical role of enabling the mastication of food and also of protecting the underlying vital dentin and pulp structure. Unlike most vital tissue, enamel has no ability to repair or remodel and as such has had to develop robust damage tolerance to withstand contact fatigue events throughout the lifetime of a species. To achieve such behaviour, enamel has evolved a complex hierarchical structure that varies slightly between different species. The major component of enamel is apatite in the form of crystallite fibres with a nanometre-sized diameter that extend from the dentin-enamel junction to the oral surface. These crystallites are bound together by proteins and peptides into a range of hierarchical structures from micrometre diameter prisms to 50-100 μm diameter bundles of prisms known as Hunter-Schreger bands. As a consequence of such complex structural organization, the damage tolerance of enamel increases through various toughening mechanisms in the hierarchy but at the expense of fracture strength. This review critically evaluates the role of hierarchy on the development of the R-curve and the stress-strain behaviour. It attempts to identify and quantify the multiple mechanisms responsible for this behaviour as well as their impact on damage tolerance.

Electrical Pulp Testing: Sources of Error

INTRODUCTION

Accurate identification and assessment of an inflamed or necrotic tooth is essentialfor endodontic treatment. The purpose of this research was to investigate possible sources of error associated with the use of the electric pulp tester (EPT).

METHODS

Forty-six intact teeth (23 tooth pairs) in 22 patients were evaluated in vivo. For the tooth pairs, one tooth had to have been previously endodontically treated and restored with a class II amalgam restoration. The restoration was required to have proximal contact with a class II amalgam of another vital posterior tooth. EPT was performed on pulpless and vital teeth for experimental groups (enamel, restoration, contacting, or isolated).

RESULTS

The highest rate of false positive responses (82%) was found in the pulpless restored contacting group, suggesting that EPT impulses are able to travel through proximal metallic contacts and stimulate teeth distant from the EPT probe. All vital tooth groups had a high rate of positive responses with no significant diferences.

CONCLUSIONS

If a tested tooth contains an interproximal restoration contacting adjacent restorations or the gingival, the teeth must be isolated (rubber dam) and the EPT probe should be placed in a region suspected to have uninterrupted tubule paths to the pulp.

[Physiological changes in the morphology of the main structural enamel unit - hydroxyapatite crystal - during its life span (in vitro study)]

The in vitro study by means of complex laboratory techniques including X-ray faze analysis, infrared spectroscopy, scanning electron and atomic force microscopy defined age-related physiological mineralization process as a shift of the structural enamel unit - nanocrystalline hydroxyapatite crystals - TO microcrystal phase. Relevant anatomical sites with age-dependent enamel optical characteristics corresponding to certain ratio of hydroxyapatite phases and the compliance of their color characteristics to composites enamel layers were revealed.

[The possibility of increasing the tooth enamel caries in children and adolescents through an integrated remineralizes fluoropolymer coatings with tricalcium phosphate]

In the survey we conducted a prospective cohort oral 138 children and adolescents living in the same environmental conditions. To study the effect of the complex representation remineralizes fluorine-containing tricalcium phosphate coating for the prevention of caries-the process in childhood, all surveyed were divided into 3 groups with high, medium and low enough average caries based on clinical and laboratory examination. The authors found a 7-fold the efficiency of preventive measures in the group with sufficient average caries and 5 times the efficiency in the group with low average caries in relation to subgroups where remineralizes-present fluorine-containing coating with tricalcium phosphate is not applicable. Furthermore, it was found that the accumulation of fluorine occurs only in a surface layer of the enamel within 100 micrometers.

Dynamic finite element analysis and moving particle simulation of human enamel on a microscale

BACKGROUND

The study of biomechanics of deformation and fracture of hard biological tissues involving organic matrix remains a challenge as variations in mechanical properties and fracture mode may have time-dependency. Finite element analysis (FEA) has been widely used but the shortcomings of FEA such as the long computation time owing to re-meshing in simulating fracture mechanics have warranted the development of alternative computational methods with higher throughput. The aim of this study was to compare dynamic two-dimensional FEA and moving particle simulation (MPS) when assuming a plane strain condition in the modeling of human enamel on a reduced scale.

METHODS

Two-dimensional models with the same geometry were developed for MPS and FEA and tested in tension generated with a single step of displacement. The displacement, velocity, pressure, and stress levels were compared and Spearman׳s rank-correlation coefficients R were calculated (p<0.001).

RESULTS

The MPS and FEA were significantly correlated for displacement, velocity, pressure, and Y-stress.

CONCLUSIONS

The MPS may be further developed as an alternative approach without mesh generation to simulate deformation and fracture phenomena of dental and potentially other hard tissues with complex microstructure.

Finite element analysis of different restorative materials in primary teeth restorations

AIM

The purpose of this finite element analysis (FEA) study is to evaluate and compare the stress distributions at the primary molars and restorative materials according to the material used.

MATERIALS AND METHODS

A total of 12 3D models of Class II cavities in primary molars plus one control model were analysed. Study design: Three-dimensional FEA was used to compare stress distribution on enamel, dentin and restoration surfaces of cavities.

STATISTICS

Stresses occurring under occlusal forces were compared with the von Mises criterion.

RESULTS

The highest von Mises stress values at the enamel and restoration of restored tooth 84 were computed. On the basis of these results, all materials were ranked on enamel stress as: flowable composite resin (FCR)> compomer > resin modified glass ionomer cement (RMGIC) > giomer composite resin (GCR) > hybrid composite resin (HCR) > amalgam. Moreover, ranking of materials on restoration stress was FCR < compomer < RMGIC < GCR < amalgam < HCR.

CONCLUSION

A restorative material with appropriate elasticity module, able to balance stress concentrations, should be used to increase the survival rate of both the hard tissue of the tooth and the restoration material.

Comparative study of the measurement of enamel demineralization and remineralization using transverse microradiography and electron probe microanalysis

Transverse microradiography (TMR) and electron probe microanalysis (EPMA) are commonly used for characterizing dental tissues. TMR utilizes an approximately monochromatic X-ray beam to determine the mass attenuation of the sample, which is converted to volume percent mineral (vol%min). An EPMA stimulates the emission of characteristic X-rays from a variable volume of sample (dependent on density) to provide compositional information. The aim of this study was to compare the assessment of sound, demineralized, and remineralized enamel using both techniques. Human enamel samples were demineralized and a part of each was subsequently remineralized. The same line profile through each demineralized lesion was analyzed using TMR and EPMA to determine vol%min and wt% elemental composition and atomic concentration ratio information, respectively. The vol%min and wt% values determined by each technique were significantly correlated but the absolute values were not similar. This was attributable to the complex ultrastructural composition, the variable density of the samples analyzed, and the nonlinear interaction of the EPMA-generated X-rays. EPMA remains an important technique for obtaining atomic ratio information, but its limitations in determining absolute mineral content indicate that it should not be used in place of TMR for determining the mineral density of dental hard tissues.

Assessment of Er:YAG laser for cavity preparation in primary and permanent teeth: a scanning electron microscopy and thermographic study

PURPOSE

Most studies of cavity preparation using Er:YAG lasers have employed permanent teeth. This study's purpose was to compare the cutting efficiency of an Er:YAG laser versus diamond burs in primary and permanent teeth in order to measure thermal effects on the pulp and evaluate lased surfaces using scanning electron microscopy (SEM).

METHODS

A total of 80 primary and permanent teeth were used. Crater depths and mass loss were measured after delivering laser pulses at varying energies onto sound or carious enamel or dentin using the Key-3 laser. Control samples were cut using diamond burs in an air turbine handpiece. Thermal changes were measured using miniature thermocouples placed into the pulp chamber. Lased surfaces were evaluated using SEM.

RESULTS

Laser ablation crater-like defects were deeper in dentin than enamel at the same pulse energy. Greater ablation rates for dentin and enamel and significantly more efficient removal of carious tooth structure by laser was present in primary teeth. Temperature rises in the pulp did not exceed the 5.5 degrees Celsius threshold in any teeth during laser ablation.

CONCLUSIONS

The Er:YAG laser is an efficient device for cavity preparations in primary teeth, with no unacceptable increases in temperature detected in this model.

Influence of self-made saliva substitutes on tribological characteristics of human enamel

This paper describes the results of tests on the influence of human saliva and its substitutes on tribological characteristics of friction pairs. Each pair consists of enamel and one of the following materials: ceramics, the Meridian B2 dental composite, the GK dental amalgam, and Ti-6Al-4V titanium alloy. The saliva substitutes used were prepared using pyrophosphates, xanthan gum, and mucins dissolved in a saline buffer. The results of the tribological tests show that the values of the parameters under investigation (coefficient of friction and linear wear) were different from each other. Some similarity was observed between the evaluated level of wear characteristics after the friction process in the environment of human saliva and that in the environment of one of the mucins tested. Microscopic observations of the surfaces of the enamel samples after friction revealed varied forms of tribological wear.

Thermal response of a dental tissue induced by femtosecond laser pulses

This paper reports a theoretical and experimental study for thermal transport in a thin slice of human tooth induced by a 120 fs, 800 nm pulse laser at a repetition rate of 1 kHz. The surface reflectivity of enamel and the convection heat transfer coefficient were determined using an inverse heat transfer analysis. Instead of a fully three-dimensional modeling, two simplified two-dimensional (2D) planar and axisymmetric heat conduction models were proposed to simulate the temperature fields. The temperature responses obtained from the 2D planar and axisymmetric model agree well with the experimental measurements. On the other hand, the one-dimensional (1D) result significantly differs from the 2D axisymmetric one, suggesting that care should be taken when a 1D thermal model is considered for estimating temperature response.

Opportunistic feeding strategy for the earliest old world hypsodont equids: evidence from stable isotope and dental wear proxies

Background

The equid Hippotherium primigenium, with moderately hypsodont cheek teeth, rapidly dispersed through Eurasia in the early late Miocene. This dispersal of hipparions into the Old World represents a major faunal event during the Neogene. The reasons for this fast dispersal of H. primigenium within Europe are still unclear. Based on its hypsodonty, a high specialization in grazing is assumed although the feeding ecology of the earliest European hipparionines within a pure C₃ plant ecosystem remains to be investigated.

Methodology/Principal Findings

A multi-proxy approach, combining carbon and oxygen isotopes from enamel as well as dental meso- and microwear analyses of cheek teeth, was used to characterize the diet of the earliest European H. primigenium populations from four early Late Miocene localities in Germany (Eppelsheim, Höwenegg), Switzerland (Charmoille), and France (Soblay). Enamel δ¹³C values indicate a pure C₃ plant diet with small (<1.4‰) seasonal variations for all four H. primigenium populations. Dental wear and carbon isotope compositions are compatible with dietary differences. Except for the Höwenegg hipparionines, dental microwear data indicate a browse-dominated diet. By contrast, the tooth mesowear patterns of all populations range from low to high abrasion suggesting a wide spectrum of food resources.

Conclusions/Significance

Combined dental wear and stable isotope analysis enables refined palaeodietary reconstructions in C₃ ecosystems. Different H. primigenium populations in Europe had a large spectrum of feeding habits with a high browsing component. The combination of specialized phenotypes such as hypsodont cheek teeth with a wide spectrum of diet illustrates a new example of the Liem’s paradox. This dietary flexibility associated with the capability to exploit abrasive food such as grasses probably contributed to the rapid dispersal of hipparionines from North America into Eurasia and the fast replacement of the brachydont equid Anchitherium by the hypsodont H. primigenium in Europe.

How the tooth got its stripes: patterning via strain-cued motility

We hypothesize that a population of migrating cells can form patterns when changes in local strains owing to relative cell motions induce changes in cell motility. That the mechanism originates in competing rates of motion distinguishes it from mechanisms involving strain energy gradients, e.g. those generated by surface energy effects or eigenstrains among cells, and diffusion-reaction mechanisms involving chemical signalling factors. The theory is tested by its ability to reproduce the morphological characteristics of enamel in the mouse incisor. Dental enamel is formed during amelogenesis by a population of ameloblasts that move about laterally within an expanding curved sheet, subject to continuously evolving spatial and temporal gradients in strain. Discrete-cell simulations of this process compute the changing strain environment of all cells and predict cell trajectories by invoking simple rules for the motion of an individual cell in response to its strain environment. The rules balance a tendency for cells to enhance relative sliding motion against a tendency to maintain uniform cell-cell separation. The simulations account for observed waviness in the enamel microstructure, the speed and shape of the 'commencement front' that separates domains of migrating secretory-stage ameloblasts from those that are not yet migrating, the initiation and sustainment of layered, fracture-resistant decussation patterns (cross-plied microstructure) and the transition from decussating inner enamel to non-decussating outer enamel. All these characteristics can be correctly predicted with the use of a single scalar adjustable parameter.

Shear bond strength and fracture analysis of human vs. bovine teeth

Purpose

To evaluate if bovine enamel and dentin are appropriate substitutes for the respective human hard tooth tissues to test shear bond strength (SBS) and fracture analysis.

Materials and Methods

80 sound and caries-free human erupted third molars and 80 freshly extracted bovine permanent central incisors (10 specimens for each group) were used to investigate enamel and dentine adhesion of one 2-step self-etch (SE) and one 3-step etch and rinse (E&R) product. To test SBS the buccal or labial areas were ground plane to obtain appropriate enamel or dentine areas. SE and E&R were applied and SBS was measured prior to and after 500 thermocycles between +5 and +55°C. Fracture analysis was performed for all debonded areas.

Results

ANOVA revealed significant differences of enamel and dentin SBS prior to and after thermocycling for both of the adhesives. SBS- of E&R-bonded human enamel increased after thermocycling but SE-bonded did not. Bovine enamel SE-bonded showed higher SBS after TC but E&R-bonded had lower SBS. No differences were found for human dentin SE- or E&R-bonded prior to or after thermocycling but bovine dentin SE-bonded increased whereas bovine dentine E&R-bonded decreased. Considering the totalized and adhesive failures, fracture analysis did not show significances between the adhesives or the respective tooth tissues prior to or after thermocycling.

Conclusion

Although SBS was different on human and bovine teeth, no differences were found for fracture analysis. This indicates that solely conducted SBS on bovine substrate are not sufficient to judge the perfomance of adhesives, thus bovine teeth are questionnable as a substrate for shear bond testing.

Osteopetrosis, osteopetrorickets and hypophosphatemic rickets differentially affect dentin and enamel mineralization

Osteopetrosis (OP) is an inherited disorder of defective bone resorption, which can be accompanied by impaired skeletal mineralization, a phenotype termed osteopetrorickets (OPR). Since individuals with dysfunctional osteoclasts often develop osteomyelitis of the jaw, we have analyzed, if dentin and enamel mineralization are differentially affected in OP and OPR. Therefore, we have applied non-decalcified histology and quantitative backscattered electron imaging (qBEI) to compare the dental phenotypes of Src(-/-), oc/oc and Hyp(-/0) mice, which serve as models for OP, OPR and hypophosphatemic rickets, respectively. While both, Src(-/-) and oc/oc mice, were characterized by defects of molar root formation, only oc/oc mice displayed a severe defect of dentin mineralization, similar to Hyp(-/0) mice. Most importantly, while enamel thickness was not affected in either mouse model, the calcium content within the enamel phase was significantly reduced in oc/oc, but not in Src(-/-) or Hyp(-/0) mice. Taken together, these data demonstrate that dentin and enamel mineralization are differentially affected in Src(-/-) and oc/oc mice. Moreover, since defects of dental mineralization may trigger premature tooth decay and thereby osteomyelitis of the jaw, they further underscore the importance of discriminating between OP and OPR in the respective individuals.

Characterization of tooth structure and the dentin-enamel zone based on the Stokes-Mueller calculation

This is the first study of dentin-enamel zone (DEZ) identification with tooth structure characterization based on the optical Stokes-Mueller measurement. Stokes vectors of a cross-sectional tooth slice were measured using various polarization inputs. The direction of the DEZ is different in enamel and dentin structures; therefore, the Stokes profiles can specifically characterize the structures based on the DEZ. This optical method, using polarimetry, provides a useful tool for characterizing tooth.

Hierarchical flexural strength of enamel: transition from brittle to damage-tolerant behaviour

Hard, biological materials are generally hierarchically structured from the nano- to the macro-scale in a somewhat self-similar manner consisting of mineral units surrounded by a soft protein shell. Considerable efforts are underway to mimic such materials because of their structurally optimized mechanical functionality of being hard and stiff as well as damage-tolerant. However, it is unclear how different hierarchical levels interact to achieve this performance. In this study, we consider dental enamel as a representative, biological hierarchical structure and determine its flexural strength and elastic modulus at three levels of hierarchy using focused ion beam (FIB) prepared cantilevers of micrometre size. The results are compared and analysed using a theoretical model proposed by Jäger and Fratzl and developed by Gao and co-workers. Both properties decrease with increasing hierarchical dimension along with a switch in mechanical behaviour from linear-elastic to elastic-inelastic. We found Gao's model matched the results very well.

The role of enamel proteins in protecting mature human enamel against acidic environments: a double layer force spectroscopy study

Characterisation of the electrostatic properties of dental enamel is important for understanding the interfacial processes that occur on a tooth surface and how these relate to the natural ability of our teeth to withstand chemical attack from the acids in many soft drinks. Whereas, the role of the mineral component of the tooth enamel in providing this resistance to acid erosion has been studied extensively, the influence of proteins that are also present within the structure is not well understood. In this paper, we report for the first time the use of double-layer force spectroscopy to directly measure electrostatic forces on as received and hydrazine-treated (deproteinated) enamel surfaces in solutions with different pH to determine how the enamel proteins influence acid erosion surface potential and surface charge of human dental enamel. The deproteination of the treated samples was confirmed by the loss of the amide bands (~1,300-1,700 cm(-1)) in the FTIR spectrum of the sample. The force characteristics observed were found to agree with the theory of electrical double layer interaction under the assumption of constant potential and allowed the surface charge per unit area to be determined for the two enamel surfaces. The values and, importantly, the sign of these adsorbed surface charges indicates that the protein content of dental enamel contributes significantly to the electrostatic double layer formation near the tooth surface and in doing so can buffer the apatite crystals against acid attack. Moreover, the electrostatic interactions within this layer are a driving factor for the mineral transfer from the tooth surface and the initial salivary pellicle formation.

The role of property gradients on the mechanical behavior of human enamel

In this study, the mechanical design principles of human enamel were evaluated using a hybrid experimental and computational approach. Nanoindentation was applied to evaluate the load-depth response of human enamel, and Vickers indentations were used to assess the damage behavior. An elastic-plastic numerical model was then developed to analyze the stress and strain distribution about the indentations, and to characterize energy dissipation about indents in three locations including inner, middle and outer enamel. Results confirm that enamel exhibits a gradient in its mechanical behavior. Outer enamel has a limited potential for energy dissipation by inelastic deformation, indicating that the ability of outer enamel to resist fracture is low. While inner enamel, the region close Dentin Enamel Junction (DEJ), possesses less resistance to penetration deformation, it has a much higher capacity to dissipate energy by inelastic deformation than outer enamel. The computational simulations identified that the gradients in mechanical properties of human enamel promote resistance to penetration, energy dissipation and mitigation of fracture, all critical performance requirements of human teeth.

Abrasive, silica phytoliths and the evolution of thick molar enamel in primates, with implications for the diet of Paranthropus boisei

BACKGROUND

Primates--including fossil species of apes and hominins--show variation in their degree of molar enamel thickness, a trait long thought to reflect a diet of hard or tough foods. The early hominins demonstrated molar enamel thickness of moderate to extreme degrees, which suggested to most researchers that they ate hard foods obtained on or near the ground, such as nuts, seeds, tubers, and roots. We propose an alternative hypothesis--that the amount of phytoliths in foods correlates with the evolution of thick molar enamel in primates, although this effect is constrained by a species' degree of folivory.

METHODOLOGY/PRINCIPAL FINDINGS

From a combination of dietary data and evidence for the levels of phytoliths in plant families in the literature, we calculated the percentage of plant foods rich in phytoliths in the diets of twelve extant primates with wide variation in their molar enamel thickness. Additional dietary data from the literature provided the percentage of each primate's diet made up of plants and of leaves. A statistical analysis of these variables showed that the amount of abrasive silica phytoliths in the diets of our sample primates correlated positively with the thickness of their molar enamel, constrained by the amount of leaves in their diet (R(2) = 0.875; p<.0006).

CONCLUSIONS/SIGNIFICANCE

The need to resist abrasion from phytoliths appears to be a key selective force behind the evolution of thick molar enamel in primates. The extreme molar enamel thickness of the teeth of the East African hominin Paranthropus boisei, long thought to suggest a diet comprising predominantly hard objects, instead appears to indicate a diet with plants high in abrasive silica phytoliths.

Development of fluorapatite cement for dental enamel defects repair

In order to restore the badly carious lesion of human dental enamel, a crystalline paste of fluoride substituted apatite cement was synthesized by using the mixture of tetracalcium phosphate (TTCP), dicalcium phosphate anhydrous (DCPA) and ammonium fluoride. The apatite cement paste could be directly filled into the enamel defects (cavities) to repair damaged dental enamel. The results indicated that the hardened cement was fluorapatite [Ca(10)(PO(4))(6)F(2), FA] with calcium to phosphorus atom molar ratio (Ca/P) of 1.67 and Ca/F ratio of 5. The solubility of FA cement in Tris-HCl solution (pH = 5) was slightly lower than the natural enamel, indicating the FA cement was much insensitive to the weakly acidic solutions. The FA cement was tightly combined with the enamel surface, and there was no obvious difference of the hardness between the FA cement and natural enamel. The extracts of FA cement caused no cytotoxicity on L929 cells, which satisfied the relevant criterion on dental biomaterials, revealing good cytocompatibility. In addition, the results showed that the FA cement had good mechanical strength, hydrophilicity, and anti-bacterial adhesion properties. The study suggested that using FA cement was simple and promising approach to effectively and conveniently restore enamel defects.

Pseudogenization of the tooth gene enamelysin (MMP20) in the common ancestor of extant baleen whales

Whales in the suborder Mysticeti are filter feeders that use baleen to sift zooplankton and small fish from ocean waters. Adult mysticetes lack teeth, although tooth buds are present in foetal stages. Cladistic analyses suggest that functional teeth were lost in the common ancestor of crown-group Mysticeti. DNA sequences for the tooth-specific genes, ameloblastin (AMBN), enamelin (ENAM) and amelogenin (AMEL), have frameshift mutations and/or stop codons in this taxon, but none of these molecular cavities are shared by all extant mysticetes. Here, we provide the first evidence for pseudogenization of a tooth gene, enamelysin (MMP20), in the common ancestor of living baleen whales. Specifically, pseudogenization resulted from the insertion of a CHR-2 SINE retroposon in exon 2 of MMP20. Genomic and palaeontological data now provide congruent support for the loss of enamel-capped teeth on the common ancestral branch of crown-group mysticetes. The new data for MMP20 also document a polymorphic stop codon in exon 2 of the pygmy sperm whale (Kogia breviceps), which has enamel-less teeth. These results, in conjunction with the evidence for pseudogenization of MMP20 in Hoffmann's two-toed sloth (Choloepus hoffmanni), another enamel-less species, support the hypothesis that the only unique, non-overlapping function of the MMP20 gene is in enamel formation.

Anticaries potential of commercial fluoride rinses as determined by fluoridation and remineralization efficiency

OBJECTIVE

The objective of this work was to compare the anticaries potential of several currently marketed fluoride-containing mouthrinse products using two in vitro approaches: 1) fluoride uptake studies of demineralized human enamel samples after exposure to rinse products; and 2) microhardness studies of sound enamel samples after exposure to the rinse products and demineralizing agents.

METHODS

Four currently marketed rinse products, formulated at 100 ppm F, were evaluated in fluoride uptake studies relative to a negative (water) rinse control (Study 1). The same rinse products were evaluated in microhardness studies (Study 2) against a positive control, ACT Anticavity rinse, which is formulated with 225 ppm F and carries the ADA Seal of Acceptance as an effective anticavity mouthrinse. Test products included ACT Total Care rinse (pH = 6.34), Listerine Total Care rinse (pH = 3.57), Crest Pro-Health for Me rinse (pH = 3.33), and Crest Pro-Health Complete rinse (pH = 3.43).

RESULTS

Study 1-Samples treated with any of the fluoride-containing rinses showed significantly higher (p < 0.05) levels of fluoride uptake than the negative (water) control. Two of the products (Crest Pro-Health for Me and Crest Pro-Health Complete) showed significantly higher (p < 0.05) levels of fluoride uptake into demineralized enamel than the other marketed rinses (Listerine Total Care and ACT Total Care). Study 2-Samples treated with the same two rinse products (Crest Pro-Health For Me and Crest Pro-Health Complete) showed significantly lower mineral loss than the other rinse products, as well as the positive control.

CONCLUSION

Results of these in vitro studies indicate that the Crest mouthrinse products evaluated here are capable of providing significantly better fluoridation of demineralized enamel, as well as significantly better protection against the initiation and progression of demineralization, compared to the other marketed fluoride-containing mouthrinse products tested.

The mechanical anisotropy on a longitudinal section of human enamel studied by nanoindentation

Nanoindentation has been widely used for probing the mechanical properties of tooth, especially for characterizing its complex hierarchical structures. Previous studies have confirmed the anisotropic mechanical behaviors caused by the alternated orientations of enamel rods and the alignment of fibril-like hydroxyapatite crystals, but the longitudinal section of enamel, which was composed of parallel-arranged rods, was regarded as a homogeneous continuum as always. In this study, nanoindentation combined with SEM was carried out with the indenter rotating on the longitudinal section of enamel to evaluate the relativity between the nano-mechanical properties and the orientation of indentation impressions. It has been shown that the enamel presented different elastic modulus and hardness with different angles of indenter on its longitudinal section, and its anisotropy was also confirmed by the remarkable asymmetric morphologies of impressions. We observed that the parallel arrangement of crystal fibrils and enamel rods might trigger the expansion of the micro-cracks in preferred orientation, and result in scalene triangle indentation impressions, altering contact areas as well as inconsistent mechanical behaviors. Consequently, it is considered that the longitudinal sections of enamel should be modeled as anisotropic.

Dental enamel: genes define biomechanics

Regulated gene expression assembles an extracellular proteinaceous matrix to control biomineralization and the resultant biomechanical function of tooth enamel. The importance of the dominant enamel matrix protein, amelogenin (Amel); a minor transiently expressed protein, dentin sialoprotein (Dsp); an electrogenic sodium bicarbonate cotransporter (NBCe1); the timely removal of the proteinaceous matrix by a serine protease, Kallikrein-4 (Klk4); and the late-stage expression of Amelotin (Amtn) on enamel biomechanical function were demonstrated and measured using mouse models.

Effect of 10% sodium ascorbate and 10% alpha-tocopherol in different formulations on the shear bond strength of enamel and dentin submitted to a home-use bleaching treatment

This in vitro study assessed the shear bond strength of human enamel and dentin submitted to a bleaching treatment with 10% carbamide peroxide and treatment with antioxidant agents containing 10% alpha-tocopherol and 10% sodium ascorbate formulated in solution and gel. Sixty human dental enamel slabs (E) and 60 human dental dentin slabs (D) were randomly divided into six groups (n = 10). Groups E1 and D1 were negative control groups and the bleaching agent was not applied. The bleaching agent was applied daily for two-hours on the dental slabs of all the other groups and, during the remaining 22 hours, the specimens were stored in an artificial saliva solution for a total of 14 days. Groups E2 and D2 were positive control groups and they only received application of the bleaching agents. Antioxidant agents were applied in Groups E3 and D3 (10% sodium ascorbate solution), E4 and D4 (10% alpha-tocopherol solution), E5 and D5 (10% sodium ascorbate gel) and E6 and D6 (10% alpha-tocopherol gel) for two hours. Cylinders were made with microhybrid resin composite and a total-etch adhesive system for shear bond strength tests. These tests were performed in a universal testing machine at a speed of 0.5 mm/minute to obtain the values in MPa. ANOVA (p > 0.05) showed no significant differences among groups E4, E5, E6 and E1. However, groups E3, E5 and E6 presented statistically similar values to group E2. The Kruskal-Wallis test showed no significant differences among D1 and all the other experimental groups; the same values occurred with D2, which did not differ from the experimental groups. Antioxidant treatment with 10% alpha-tocopherol solution was the only effective agent to revert the oxidizing effects of the bleaching treatment on enamel.