Search Results (36)

Dental enamel exhibits a unique combination of high hardness and high toughness. This outstanding mechanical property is closely tied to its multi-scale hierarchical structure. In this study, rat tooth enamel was selected as the research object, the different structural layers and mechanical properties of tooth enamel were investigated and characterized experimentally. The multi-scale mechanical models with different structural layers were developed and analyzed using numerical simulations. The research results indicate that, regarding the load-bearing mechanism, the outer layer of tooth enamel consists of hydroxyapatite crystal bundles arranged in parallel and inclined orientations, and this structural feature enables it to exhibit excellent elastic modulus and resistance to deformation, while the inner layer with cross-arranged crystal bundles shows different mechanical response characteristics. In terms of crack propagation behavior, the outer layer is more prone to crack initiation due to the consistency of crystal orientation, and the cracks tend to extend in a straight line, while the unique cross arrangement of crystals in the inner layer can effectively inhibit crack propagation by inducing crack deflection and branching mechanisms, thus demonstrating more excellent fracture toughness. This “outer hard and inner flexible” gradient structure design elucidates the synergistic mechanism between crystal orientation and crack propagation behavior in tooth enamel, offering significant design insights for biomimetic composite materials. Full article

Bamboo fiber is a prime green fiber due to its renewability, biodegradability, and high specific strength. Bamboo-fiber-reinforced epoxy (BFRE) composites have seen extensive use and shown great promise for natural biofiber-reinforced friction materials. Inspired by the decussated fiber alignment of bovine enamel, this study investigated how fiber orientation influences the tribological properties of BFRE composites. Specifically, the proportion of fibers oriented vertically to the surface was varied at seven levels: 0%, 25%, 33%, 50%, 67%, 75%, and 100%. The tribological performance was assessed through wear reciprocating testing and microscopic morphological characterization techniques. Results indicate that the bio-inspired fiber decussation can reduce the wear loss of the BFRE composites. Among all bio-inspired BFRE composites, BFRE composites with 67% vertical fibers achieve the best wear resistance. The vertical fibers in the BFRE composites can withstand pressure to provide a “compression–rebound” effect, while the parallel fibers can resist shear stress. The decussated structure inhibits crack initiation and propagation during wear and promotes transfer film formation, reducing wear loss. The findings expand understanding of the correlation between the bovine-tooth-like decussated structure and its tribological mechanisms, thereby offering essential guidance for the biomimetic design of high-performance BFRE composites for friction material application. Full article

Alkyd resins are among the most common coatings used for exterior wood joinery. In Romania, solvent-borne alkyd coatings are widely used to finish wood. The study aims to compare the performance after 7 years of outdoor exposure of two types of alkyd coatings, a semi-transparent brown stain with micronized pigments (Alk1) and an opaque white enamel (Alk2), applied directly on wood or wood pre-treated with three types of resins: acryl-polyurethane (R1), epoxy (R2), and alkyd-polyurethane (R3). Fir (Abies alba) wood served as the substrate. Cracking, coating adhesion, and biological degradation were periodically assessed through visual inspection and microscopy. Additionally, a cross-cut test was performed, and the loss of coating on the directly exposed upper faces was measured using ImageJ. The results indicated that resin pretreatments somewhat reduced cracking but negatively affected coating adhesion after long-term exposure. All samples pretreated with resins and coated with Alk1 lost more than 50% (up to 78%) of the original finishing film by the end of the test. In comparison, coated control samples lost less than 50%. The Alk2 coating exhibited a film loss between 2% and 12%, compared to an average loss of 9% for the coated control. Overall, samples pretreated with alkyd-polyurethane resin (R3) and coated with alkyd enamel (Alk2) demonstrated the best performance in terms of cracking, adhesion, and discoloration. Full article

Background/Objectives: Dental cavity preparation is a critical procedure in restorative dentistry that involves the removal of decayed tissue while preserving a healthy tooth structure. Excessive stress during tooth preparation leads to enamel cracking, dentin damage, and long term compressive pulp health. This study employed finite element analysis (FEA) to investigate the stress distribution in dental structures during cavity preparation using round diamond burs of varying diameters and depths of cut (DOC). Methods: A three-dimensional human maxillary first molar was generated from computed tomography (CT) scan data using 3D Slicer, Fusion 360, and ANSYS Space Claim 2024 R-2. Finite element analysis (FEA) was conducted using ANSYS Workbench 2024. Round diamond burs with diameters of 1, 2, and 3 mm were modeled. Cutting simulations were performed for DOC of 1 mm and 2 mm. The burs were treated as rigid bodies, whereas the dental structures were modeled as deformable bodies using the Cowper–Symonds model. Results: The simulations revealed that larger bur diameters and deeper cuts led to higher stress magnitudes, particularly in the enamel and dentin. The maximum von Mises stress was reached at 136.98 MPa, and dentin 140.33 MPa. Smaller burs (≤2 mm) and lower depths of cut (≤1 mm) produced lower stress values and were optimal for minimizing dental structural damage. Pulpal stress remained low but showed an increasing trend with increased DOC and bur size. Conclusions: This study provides clinically relevant guidance for reducing mechanical damage during cavity preparation by recommending the use of smaller burs and controlled cutting depths. The originality of this study lies in its integration of CT-based anatomy with dynamic FEA modeling, enabling a realistic simulation of tool–tissue interaction in dentistry. These insights can inform bur selection, cutting protocols, and future experimental validations. Full article

Multi-principal element alloys (MPEAs) exhibit distinct characteristics compared to conventional single-principal element-based metallic materials, primarily due to their unique design, resulting in intricate microstructural features. Currently, a comprehensive understanding of the fabrication processes, compositional design, and microstructural influence on the tribological and corrosion behavior of multi-component alloys remains limited. While the hardness of MPEAs generally correlates positively with wear resistance, with higher hardness typically associated with improved wear resistance and reduced wear rates, quantitative relationships between these properties are not well established. In this study, the Al₁₀Cr₁₇Fe₂₀NiV₄ alloy was selected as a model system. A homogeneous Al₁₀Cr₁₇Fe₂₀NiV₄ alloy was successfully synthesized via mechanical alloying followed by spark plasma sintering (SPS). To further investigate the correlation between hardness and wear rate, varying concentrations of alumina nanoparticles were incorporated into the alloy matrix as a reinforcing phase. The results revealed that the Al₁₀Cr₁₇Fe₂₀NiV₄ alloy exhibited a single-phase face-centered cubic (FCC) structure, which was maintained with the addition of alumina nanoparticles. The hardness of the Al₁₀Cr₁₇Fe₂₀NiV₄ alloy without nano-alumina was 727 HV, with a corresponding wear rate of 2.9 × 10⁻⁴ mm³·N⁻¹·m⁻¹. The incorporation of nano-alumina increased the hardness to 823 HV, and significantly reduced the wear rate to 1.6 × 10⁻⁴ mm³·N⁻¹·m⁻¹, representing a 45% reduction. The Al₂O₃ nanoparticles effectively mitigated alloy wear through crack passivation and matrix strengthening; however, excessive addition reversed this effect due to the agglomeration-induced brittleness and thermal mismatch. The quantitative relationship between hardness (HV) and wear rate (W) was determined as W = 2348 e^(−0.006HV). Such carefully bounded empirical relationships, as demonstrated in studies of cold-formed materials and dental enamel, remain valuable tools in applied research when accompanied by explicit scope limitations. Full article

(1) The aim of this in vitro study was to investigate the handling of proximal-cervical undermined enamel margins on the adhesive performance of differently fabricated and differently cemented ceramic inlays and partial crowns (2) Methods: 192 extracted third molars received MOD (n = 96) and partial crown (n = 96) preparations. A mesial 2 × 2 × 4 mm cervical groove was created in dentin to simulate a deeper (dentin) caries excavation. This dentin groove was either left (G/groove), filled with composite (F/filling), or completely removed (D/dentin). Distal proximal boxes did not receive a groove and served as controls within the same tooth. Labside (e.max Press) restorations additionally went through a temporary phase. Labside and chairside (e.max CAD) inlays and partial crowns were then adhesively luted with Syntac/Variolink Esthetic (SV) or Adhese Universal/Variolink Esthetic (AV). Initially, and again after thermomechanical loading (TML: 1 million cycles at 50 N, 25,000 thermocycles at 5 °C/55 °C), specimens were molded and the resulting 24 groups of epoxy replicas (n = 8) were gold-sputtered and examined for marginal gaps using scanning electron microscopy (200× magnification). Light microscopy (10× magnification) was used to measure proximal cervical crack propagation in adjacent enamel. (3) Results: Regardless of the adhesive system, D groups generally showed significantly lower marginal quality (79–88%; p < 0.05), with the universal adhesive performing better than the multi-step adhesive system (p < 0.05). Subgroups G and F were similar in marginal quality (94–98%; p > 0.05) and not worse than the controls (p > 0.05) regardless of the adhesive system, but showed less cracking in F than in G (p < 0.05). In general, fewer cracks were observed in chairside CAD/CAM restorations than in laboratory-fabricated restorations (p < 0.05). Partial crowns showed better marginal quality (96–98%) and less cracking than inlays (p < 0.05). (4) Conclusions: If the dentin level is lower than the enamel level in ceramic preparations after caries excavation in the proximal box, the resulting undermined enamel should not be removed. In terms of enamel integrity, partial crowns outperformed inlays. Full article

Marginal enamel fractures (MEF) are a common clinical concern in dentistry, particularly in anterior teeth. These fractures occur at the enamel margins and their etiopathogenesis involves a complex interplay of mechanical, chemical, and biological factors. The ongoing research focuses on an overview of MEF to improve the knowledge about this condition. Understanding the multifaceted nature of MEF is crucial for devising effective preventive and therapeutic strategies in contemporary restorative dentistry. Indeed, mechanical stresses, such as occlusal forces and parafunctional habits are primary contributors for MEF. Additionally, it can happen at the enamel-restoration interface due to expansion and contraction of restorative materials. Chemical degradation, including acid erosion and the breakdown of adhesive bonds, further exacerbates the vulnerability of enamel. Biological factors, such as enamel composition and the presence of micro-cracks also play a role in the development of MEF. Clinical management of MEF involves subtractive or additive techniques, repairing or replacing the compromised tooth structure using techniques to ensure the integration with the natural enamel. Full article

Despite the rise in popularity of ceramic braces for adults, the risk of enamel microcracks (EMCs) upon removal remains a significant drawback for both dental professionals and patients. Our study aimed to assess the effects of thermocycling, pre-curing, and co-curing techniques with different bonding agents on the enamel surface of teeth after the removal of ceramic brackets. We also examined the incidence, quantity, length, and direction of EMCs on tooth surfaces. Additionally, the adhesive remnant index (ARI) scores and orthodontic bracket bond failure modes were evaluated and compared. The study divided 40 extracted upper canine teeth into ten groups for further analysis. Two groups had intact enamel as the negative control, while the remaining groups had orthodontic ceramic brackets bonded using different bonding agents and curing techniques. Thermocycling was performed in five groups, and ARI was assessed after debonding. The study findings were statistically significant (p < 0.05) in demonstrating the impact of curing techniques on EMCs and debonding outcomes. Seventh-generation bonding agents resulted in complete adhesive removal (ARI = 0). The microcracks’ incidence, number, and length showed insignificant results. Differences in ARI between thermocycler and non-thermocycler samples were insignificant. Both co-curing and pre-curing techniques yielded comparable ARI results. This study highlights the importance of using advanced bonding agents to minimize enamel damage during ceramic bracket debonding. Full article

Enamel microcracks (EMCs) arising during the removal of metal orthodontic brackets represent a considerable challenge in dentistry. This in vitro study aims to explore the impacts of thermocycling, the types of orthodontic bonding agent, and curing techniques on the enamel surface of the tooth structure following the debonding of orthodontic metal brackets. It also examines the incidence, number, length, and direction of EMCs on the buccal surface of the tooth. Additionally, the study compares adhesive remnant index (ARI) scores and bracket failure post-debonding. Forty extracted human maxillary canines were divided into ten groups, including intact enamel negative controls (groups 1, 2) and groups (3–8) with metal brackets bonded using two different bonding agents and curing techniques. Following bonding, half of the groups underwent thermocycling testing. EMCs, ARI scores, and bracket failure modes were evaluated. The formation, length, and direction of cracks did not significantly differ among groups, regardless of experimental conditions. Thermocycling had no significant effect on ARI scores or bracket failure modes. However, significant variations were observed among curing technique groups, with seventh-generation bonding agents demonstrating potential effectiveness in achieving complete adhesive removal. The study underscores the importance of considering bonding agent systems and curing protocols to optimize bond outcomes and minimize the risk of metal bracket failure in orthodontic treatment. Full article

Aim: The objective of this study was to explore the effects of fixed orthodontic appliances on enamel structure by assessing microfractures, surface roughness, and alterations in color. Methods: This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A systematic search of online databases was conducted using the keywords ‘enamel’ AND ‘orthodontic debonding’. Eligibility criteria included both in vivo and ex vivo clinical trials conducted on human teeth. Results and Discussion: A total of 14 relevant papers were analyzed. Various instruments and techniques were utilized across different studies to assess surface roughness, color change, and surface fractures. Conclusions: The findings of this study suggest that ceramic brackets may lead to an increase in enamel fractures, particularly during bracket removal. The surface roughness of enamel exhibits variability depending on the adhesive substance and polishing methods used post-removal. Fixed orthodontic appliances could induce changes in enamel color, which may be alleviated by the use of nano-hydroxyapatite or specific polishing techniques. Further research is necessary to identify effective strategies for managing these color changes and improving the overall outcomes of fixed orthodontic treatment. Full article

High-speed rubber cup polishing can exacerbate tooth surface damage, especially when preexisting conditions such as early caries or cracks exist. This study aimed to quantify the extent of damage to sound teeth based on rotating rubber cup speed and assess the damage in relation to the tooth surface condition. Using a rubber cup, 36 sound teeth were polished at 100, 3000, and 10,000 rpm, and 24 teeth with early carious lesions and 24 cracked teeth were polished at 3000 and 10,000 rpm. Polishing was performed using a rubber cup and prophylaxis paste, applying an on–off method (3.0 N force for 3 s). Damage depth was quantified using a surface profilometer and examined using scanning electron microscopy. Polishing at 10,000 rpm caused significantly more damage to sound teeth than polishing at lower speeds (depth increase: 71.45 ± 15.12 µm at 100 rpm; 61.91 ± 17.82 µm at 3000 rpm; p < 0.001). Teeth with early carious lesions or cracks demonstrated more damage after polishing than sound teeth (p < 0.05). Therefore, the rotational speed of the rubber cup has a critical impact on the extent of enamel damage. Higher speeds can increase the damage depth in both sound and damaged tooth surfaces. Full article

(1) Background: A widespread problem in oral health is cavities produced by cariogenic bacteria that consume fermentable carbohydrates and lower pH to 5.5–6.5, thus extracting Ca²⁺ and phosphate ions (PO₄³⁻) from teeth. Dental restorative materials based on polymers are used to fill the gaps in damaged teeth, but their properties are different from those of dental enamel. Therefore, a question is raised about the similarity between dental composites and natural teeth in terms of density and hardness. (2) Methods: We have used Raman spectroscopy and density and microhardness measurements to compare physical characteristics of several restorative dental composites at different polymerization intervals. (3) Results: XRVHerculite^®, Optishade^®, and VertiseFlow^® showed the very different characteristics of the physical properties following four polymerization intervals. Of the three composites, OptiShade showed the highest polymerization rate. (4) Conclusions: Only fully polymerized composites can be used in teeth restoring, because incomplete polymerization would result in cracks, pitting, and lead finally to failure. Full article

This study systematically reviews the literature to evaluate the potential relationships between oral/perioral piercing and consequent oral complications in the corresponding society. The second objective was determining public/professional sectors’ awareness of the subject. This research followed PRISMA and Cochrane guidelines for conducting systematic reviews and searching scientific databases, including PubMed, Scopus, Cochrane, and Google Scholar, until April 2023. Cross-sectional, cohort, and case–control studies in English were deemed eligible. The methodological quality of the included studies was assessed using proper quality assessment guidelines. Of the 965 initial articles retrieved, 34 were considered suitable for qualitative synthesis after screening procedures and removing duplicates and irrelevant records. There appears to be an imbalance between the general public’s low and dentists’ high awareness. This draws attention to the shortage of professional and societal knowledge-sharing and education initiatives. Women were more than twice as likely as men to have oral piercings. Piercing usage had a low incidence among a cohort of students with a mean age of 16. Merely circumstantial evidence has indicated a plausible correlation between oral and perioral piercings and the emergence of secondary bacterial and fungal colonization, particularly periodontopathogenic bacteria and Candida albicans. Furthermore, several adverse consequences have been observed linked to various piercings—such as lip and tongue piercings. These include caries, gingivitis/periodontitis, dental fractures, enamel chipping/cracks, plaque buildup, bone loss, bleeding, inflammation, and swelling. Given the risks involved and the complications that might impair oral health, the prevalence of oral piercings is alarming. As a result, public health authorities need to firmly support initiatives to raise awareness of the risks associated with oral/perioral piercings. For piercers to enhance their expertise in this field, professional training is necessary because there is a shortage of knowledge on the possible adverse effects of piercings. Full article

Deformation behavior of the composite “eggshell–polymer plomb” was examined under bending. Hen eggs were taken as a biological material for experiments. It was shown that a viscoelastic polymer coating does not change the type of deformation behavior of the composite, given that the eggshell continued to be brittle despite its mechanical characteristics varying widely for a brittle solid. Joint “polymer plomb–eggshell” never cracked under bending and hence exhibited a high cohesion strength under the stresses applied in these experiments. It seems that the composite “eggshell—polymer plomb” could substitute for the composite “tooth enamel–polymer plomb” under elaboration of novel restorative materials for dentistry, namely, for examination of their mechanical properties, including cohesive strength. Full article

Non-carious cervical lesions (NCCLs) represent a form of tooth wear, characterized by the irreversible loss of dental hard tissues at the enamel–cement junction, without the involvement of caries and dental trauma. The aim of this study was to highlight the morphological elements of NCCLs via their stereomicroscopic examination and to confirm the role of this examination in the diagnosis of early lesions. In addition, the association between the morphological aspects identified during the stereomicroscopic examination of NCCLs and their etiological factors was determined. For this study, extracted teeth with NCCLs were examined with a stereomicroscope. The morphological aspects of NCCLs were evaluated at magnifications up to 75×. In wedge-shaped NCCLs, the stereomicroscopic examination allowed the identification and measurement of scratches, furrows and cracks. In saucer-shaped NCCLs, the stereomicroscopic examination highlighted the smooth appearance of the walls. The presented study highlighted the role of stereomicroscopic examination in the assessment of NCCL morphology and in their early diagnosis. The study confirmed, in particular, the role of occlusal overloads and tooth brushing in determining the morphology of NCCLs. Full article