Tooth Surface Research Articles

Proteome of the 2-h in vivo Formed Acquired Enamel Pellicle of Adolescents with Erosive Tooth Wear, Caries, or Sound

Introduction: Acquired pellicle (AP) acts as a membrane preventing acids from coming into direct contact with the tooth. Possibly, individuals with different dental health status present changes in its composition that could disrupt this function. Thus, the aim of this study was to compare the protein composition of the AP in adolescents with erosive tooth wear (ETW), caries, or sound. Methods: Calibrated examiners in BEWE index and ICDAS-merged Epi criteria assessed ETW and caries in a sample of 454 systemically healthy adolescents aged 12–15 years old. Thirty subjects from that sample were selected for this study: ETW group (n = 10; total BEWE ≥9 and absence of dentinal caries lesions); caries group (n = 10; total BEWE <9 and with at least one dentinal caries lesion), and sound group (n = 10; total BEWE <9 and absence of dentinal caries lesions). Two-hour-formation AP samples were taken from buccal, occlusal/incisal, palatal/lingual tooth surfaces. Protein composition was analysed by liquid chromatography-tandem mass spectrometry. Using mean reporter ion values, relative abundances of proteins were compared among the three groups to calculate for fold changes. Twofold protein increases or decreases were reported (t test, p < 0.05). Gene Ontology (GO) of included proteins was assigned. Results: Mean age of participants was 13.1 ± 1.14 years and 56.6% were females. The prevalence of ETW was of 66.6% and of dentinal caries of 33.3%. The GO analyses showed that the majority of detected proteins were stress response related. The ETW group disclosed upregulated relative abundance of antileukoprotease (2.85-fold in ETW vs. sound and 2.34-fold in ETW group vs. caries group); histatin (2.42-fold in ETW group vs. sound group and 2.20-fold in ETW group vs. caries group), and prolactin-induced protein (2.30-fold in ETW group vs. sound group and 2.06-fold in ETW group vs. caries group) (p < 0.05). Hemoglobin subunits alpha (HBA) and beta (HBB) showed decreased relative abundances in the ETW and caries groups when compared to the sound group (HBA: 0.42-fold in ETW group and 0.40-fold in caries group; HBB: 0.45-fold in ETW group and 0.38-fold in caries group; p < 0.05). Conclusion: AP from individuals with ETW showed differences when compared to other dental conditions, with relative abundance increasing of some stress response-associated proteins in ETW and a decrease in proteins related to salivary protection against acid challenges.

On gear time-varying meshing stiffness calculation considering indexing feeds and processing characteristics of gear shaping processing

Gear shaping causes processing characteristics on gear tooth surfaces (PCGTS), e.g., gear tooth surface deviation (GTSD) and processing textures (PT), which can affect gear meshing performances. Gear shaping simulation is operated to obtain PCGTS with different indexing feeds. An improved contact stiffness method of gear tooth surfaces is developed based on a wedge-shaped contact form to obtain tooth contact stiffness with PT caused by gear shaping. An improved time-varying meshing stiffness (TVMS) method for gears manufactured by gear shaping is developed to calculate TVMS of gears with GTSD and PT under different indexing feed conditions. Effectiveness of the improved TVMS method is validated using the finite element method. Analysis results of the proposed contact stiffness method of gear tooth surfaces indicate that PT caused by gear shaping can aggravate fluctuations of gear tooth contact stress. Analysis results of the proposed TVMS method for gears also indicate that GTSD of gear tooth surfaces caused by gear shaping can reduce their TVMS. The proposed TVMS method of gears can effectively analyze TVMS of gear tooth surfaces via gear shaping and evaluate processing settings of gear shaping to improve gear meshing performances.

Effect of Listerine and Chlorhexidine mouthwashes with antidiscoloration system on the colour change of CAD/CAM conventional and novel lithium disilicate ceramics

Background It has been reported that using mouthwashes can discolour the surface of teeth. Their effect on the stainability of newly introduced lithium disilicate ceramics is, however, unknown. Objective: The purpose of this in vitro study was to investigate how mouth washes affected the color change of new and conventional lithium disilicate (LS2) ceramics that were finished using various techniques. Materials and Methods A total of 56 ceramic slices were produced from conventional LS2 (E Max CAD, Ivoclar) and a novel virgilite based LS2 (Cerec Tessera, Dentsply Sirona). According to the finishing method, the specimens were divided into glazed and polished subgroups. Each subgroup was further subdivided into two based on immersion in chlorhexidine (CHXD) or Listerine (LIST) mouth washes. A handheld spectrophotometer was used to measure the color attributes, and color differences (ΔE00) were then counted using specific equation. Data were analyzed using ANOVA and Tukey’s post-hoc tests. Results Significant differences in color change (ΔE00) values were observed between conventional and novel LS2 ceramics, as well as between different finishing methods and mouth-rinse solutions. Chlorhexidine induced higher color differences than Listerine, with average ΔE00 values of 0.959 and 0.885, respectively (p &lt; 0.001). The polished specimens generally exhibited higher ΔE00 values than the glazed specimens, with average values of 1.071 and 0.792 for conventional LS2, and 0.836 and 0.786 for novel LS2 (p &lt; 0.001). However, most color changes did not exceed the perceptibility and acceptability thresholds. Conclusion Using CHXD and LIST mouth washes affected the color change of polished or glazed conventional and novel lithium disilicate ceramics. In general, the stainability of polished specimens was higher than that of glazed ones. There was more discoloration on specimens immersed in CHXD than those immersed in LIST. Bangladesh Journal of Medical Science Vol. 23 No. 04 October’24 Page : 1178-1184

Novel orthodontic adhesives with antibacterial, mineralization and fluorescence properties for enamel demineralization prevention

Enamel demineralization is one of the most common adverse effects of fixed orthodontic treatment, mainly because the appliances affect oral hygiene maintenance, potentially leading to plaque accumulation and oral flora dysbiosis. Adhesives are essential for fixed orthodontic treatment, but excessive adhesives on tooth surfaces might be stained aesthetically and serve as additional sites for plaque accumulation. Some research gaps exist for simultaneously addressing orthodontic enamel demineralization and proper adhesive removal. In this study, novel multifunctional orthodontic adhesives (MFOAs) were developed using amino-silane functionalized zinc oxide quantum dots (AF-ZnOQDS) with fluorescence property, antibacterial agent dimethylaminohexadecyl methacrylate (DMAHDM), and mineralizing material 45S5 bioactive glass (BG-45S5) as the modifiers. The three were incorporated into Transbond XT adhesive at different mass fractions and relevant properties were evaluated in vitro and in vivo. The results indicated that the MFOA-3 with 3 wt% AF-ZnOQDS, 5 wt% DMAHDM, and 7.5 wt% BG-45S5 possessed long-term antibacterial ability, dual-mineralization activity, and strong fluorescence properties. It had clinically acceptable physicochemical properties and good biocompatibility, providing a desirable anti-demineralization effect. Therefore, MFOA-3 provides a new strategy to solve the two major challenges of enamel demineralization and proper removal of adhesives during fixed orthodontics, and thus has great value in clinical application.

Multi-objective optimization of helical gear transmission geometric parameters using MOPSO

Abstract Helical gears are widely used in mechanical devices, but insufficient tooth strength can easily lead to premature failure, which is an urgent problem to be solved. To overcome this challenge, this paper introduces a multi-objective particle swarm optimization algorithm, which comprehensively considers the comprehensive effects of modification coefficient, number of teeth, and modulus on the performance of helical gears. By constructing a mathematical model with the geometric parameters of helical gears as the core design variables, aiming to minimize the difference between the maximum bending stress of helical gear roots and the contact stress on the tooth surface, we have achieved optimization of gear performance. Using MATLAB for algorithm programming, the established model was efficiently optimized and solved. After optimization, the bending strength difference and tooth surface bearing capacity of the gear pair have been significantly improved, ensuring the stability and reliability of the operation of the high-pressure sleeve disassembly transmission device.

Poly-ether-ether-ketone (PEEK) versus dead-soft coaxial bonded retainers: a randomized clinical trial. Part 1. Stability, retainer failure, and participant satisfaction.

Poly-ether-ether-ketone (PEEK) was introduced in dentistry as an alternative to metal alloys. To assess the effectiveness of PEEK-fixed retainers in preserving the stability of mandibular anterior and participant satisfaction as compared to the Dead-soft coaxial fixed retainer (DSC). A single-centre, two-arm parallel groups randomized clinical trial. The patients treated with pre-adjusted orthodontic appliances who have a Little's Irregularity Index (LII) ≤ 0.5mm have been enrolled in the trial. PEEK retainers were prepared to round 0.8mm wire by computer-aided design and manufacturing, and the DSC wire was carefully adapted to the lingual surface of the lower anterior teeth. The primary outcome was the stability of lower anterior teeth as assessed by LII, while the secondary outcomes were changes in occlusal parameters, retainer failure, and patient satisfaction. The data were collected at the debonding stage (T0), 1 month (T1), 3 months (T3), and 6 months (T6) after starting the trial, except for patient's satisfaction, which was recorded using an electronic form at T1 and T6. Single blinding of participants. A total of 46 participants with an age range of 12-28 years old were randomly allocated to the two groups (n = 23 in each). Only one participant dropped out; therefore, 45 participants were analysed. The DSC group showed a significant increase in LII at T3. Both retainer groups had comparable occlusal measurements, failure frequency, and survival time, with no significant difference. The patients in the DSC group reported a statistically significant perception of change in the position of their teeth compared to those in the PEEK group. No harmful effects have been reported. Limited follow-up duration and the inability to blind the operator due to the nature of the intervention. After 6-month retention, the PEEK retainer was equally effective to DSC retainers in maintaining the teeth alignment, with no significant differences regarding the failure frequency, survival rate, and general patient satisfaction. https://register.clinicaltrials.gov. (NCT05557136).

ОПРЕДЕЛЕНИЕ ТЕМПЕРАТУРЫ ЗУБЬЕВ ПИЛЫ ДЛЯ ТЕРМОФРИКЦИОННОГО РЕЗАНИЯ МЕТОДОМ КОМПЬЮТЕРНОГО МОДЕЛИРОВАНИЯ

In this study, the results of computer 3D modeling of the thermal friction process occurring between the teeth of a saw blade made of 50XGFA steel and a billet made of 45 steel are considered. The models were created using the SIMULIA/Abaqus software package to analyze temperature changes on the contacting surfaces of teeth and plates under plastic deformation conditions. As part of the work, various loads on the teeth and their effect on temperature parameters, heat generation and physical properties of materials are analyzed. As a result of the simulation, it was found that the optimal load for the teeth at plate temperatures from 400 to 600 ° C is 3.1 kN. This mode prevents excessive heating of the teeth, since their surface temperature does not exceed 650 ° C after passing 250 mm, the critical length of the contact zone during batch cutting.

OPTIMIZATION AND IMPROVEMENT OF CARIES TREATMENT IN THE FIELD OF PERMANENT TEETH FISSURES IN CHILDREN

Dental caries is the most common dental disease in children. The problem of timely diagnosis, prevention and adequate treatment of this pathology occupies one of the leading places in pediatric therapeutic dentistry. However, before applying the sealant, the dentist faces the difficult task of assessing the condition of the fissure, diagnosing a possible latent carious lesion, and choosing adequate tactics for therapeutic and preventive measures. Fissure caries occupies the first place in the structure of carious lesions of the teeth. Based on this, the problem of prevention and treatment of fissure caries is extremely urgent. It has been established that fissure caries occurs immediately after teething. The high incidence of fissure caries is associated with the features of the anatomical structure of the fissures, the accumulation of food residues and the formation of aggressive dental plaque in the natural recesses of the tooth and a longer period of hypomineralization compared with smooth tooth surfaces. There is a direct relationship between the initial level of mineralization of the enamel of fissure teeth and the risk of fissure caries.

Silane and acid etch cross contamination of dentin and composite reduced µ-tensile bond strength.

To investigate whether acid etch contamination of silane-treated composite influenced repair bond strength and whether silane contamination on dentin influenced composite bond strength to dentin. Forty composite blocks stored in water for 4 weeks were divided into four groups. Specimens in groups 1-3 were coated with Bis-Silane and contaminated with acid etch + water spray (group 1) or water spray (group 2). Group 3 was not contaminated. Group 4 was untreated. The occlusal third of 60 third molars was cut off, ground flat, and divided into three groups. After etching, the surfaces in groups A and B were contaminated with Bis-silane. The contaminated surfaces in group A were re-etched.Each composite repair group and composite-dentin group was divided into two subgroups receiving Adper Scotchbond 1 XT or Clearfil SE Bond 2 adhesives followed by a composite build up. After ageing for 3 months, specimens were sectioned into 1.1 mm × 1.1 mm rods for tensile testing and strength calculated at fracture. The fracture was examined using microscope. Bis-Silane surface treatment increased the repair bond strength. Contamination with acid reduced the strength of the repair bond. Similar results were obtained for both adhesives. Tooth surface contamination with silane reduced the bond strength between dentin and composite. Additional acid etching or water spray on silane contaminated dentin did not influence the weakened bond strength. Most fractures were adhesive type. Silane contamination on etched dentin and acid etch contamination on silanized composite surfaces significantly reduced tensile bond strength.

Sensitivity analysis and compensation for tooth surface deviation of spiral bevel gear machine tool

To analyze the quantitative mapping relationship between the geometric errors of the five-axis CNC machine tool and the tooth surface deviation of spiral bevel gears, and identify the key geometric errors that affect the machining deviation of the spiral bevel gear tooth surface, a sensitivity analysis method for tooth surface machining deviation of spiral bevel gear based on screw theory and EFAST method is proposed. Firstly, the machining model of the spiral bevel gear tooth surface based on the five-axis CNC machine tool is established. Then, the geometric error transfer model of the machine tool is established based on the screw theory. Combined with the EFAST global sensitivity analysis method, the key geometric errors that affect tooth surface deviation are identified. Finally, the reliability and effectiveness tests are performed by comparing the results to the local sensitivity analysis method and simulating compensation for the key geometric errors. The result of compensation shows that the tooth surface deviation is reduced significantly according to global sensitivity analysis. The feasibility of applying sensitivity analysis to control the tooth surface deviation of spiral bevel gears has been demonstrated.

Impact of Xylitol chewing gum on levels of oral Streptococcus mutans. A systematic review

Objectives. This systematic review evaluates the effectiveness of xylitol in combating Streptococcus mutans, a key bacterium associated with dental caries. Methods. We performed a search across Scopus, Open Grey, PubMed, Science Direct, and EBSCO databases. After screening and excluding articles that did not meet our predefined inclusion criteria, we selected seven out of the eighty-nine initially identified articles. Data extraction was carried out in three stages: identification, screening, and assessment of eligibility. Results. Among the studies included in this review, six were randomized clinical trials, and one was a before-and-after comparison. Most of these studies indicate that xylitol chewing gum may effectively reduce S. mutans counts, potentially lowering the risk of dental caries. Conclusion. The reviewed studies show that xylitol chewing gum positively affects both the quality and quantity of S. mutans. It inhibits S. mutans adhesion to tooth surfaces, reduces the production of sticky substances, and alters the bacteria's morphology. Consequently, this leads to improvements in plaque index, gingival index, and DMFT scores.

ANALYSIS OF THE QUALITY OF THE RESTORED GEAR TOOTH OF LARGE-MODULE GEARS

This study examines the quality of a gear tooth surface fragment restored through electric arc welding. Visual inspection revealed a defect-free, dense surface. Macrostructure examination displayed uniformity and absence of cracks in the metal sample. The high hardness (HRC-36.61) of the weld deposit is crucial for wear resistance, while the base metal, with lower hardness (HRC-29.09), ensures ductility and impact toughness. Martensitic and residual austenitic structures in the weld deposit indicate deformation-resistant properties, with austenite providing good ductility and martensite contributing to high hardness and strength, making the material resistant to wear and deformation under dynamic loads. Thin lens-like martensitic plates and a reed-like structure suggest unique formation characteristics during electroslag welding’s oxidizing-reducing reactions. Microstructure analysis revealed a finer structure in the weld deposit compared to the base metal. The base metal exhibited a ferrite-pearlite structure typical of many steels, unchanged after welding. The weld deposit showed elevated carbon (0.70 %) and manganese (1.38 %) concentrations, typical for weld deposits, influencing mechanical properties. Elements like manganese and molybdenum enhance wear resistance, while the presence of chromium (0.42 %) and nickel (0.12 %) improves corrosion resistance, crucial in aggressive environments. Keywords: large-module gears, tooth wear, electro slag surfacing, hardness, analysis

Evaluation of Etching Time Effect on Shear Bond Strength of Orthodontic Brackets Bonded with Self-Adhesive Composite: An in-Vitro Study

Introduction: Precise acid etching of the tooth surface is a significant factor in the strength of the bracket bond. The current study aimed to determine the effect of different application times of acid etching on the shear bond strength of metallic orthodontic brackets under controlled laboratory conditions. Methods: Sixty intact premolar teeth were selected for this in-vitro study. The samples were divided into four groups based on the different acid etching times: 20, 25, 30, and 35 seconds. The teeth surfaces were etched with 37% phosphoric acid according to the specified times, and brackets were bonded to the enamel surface using GC Ortho connect composite. Shear bond strength values of the brackets was measured using a Universal Testing Machine. The amount of Adhesive Remnant Index was also observed using a stereomicroscope. Additionally, the surface roughness of the tooth enamel after bracket bonding was examined using SEM. The results related to shear bond strength were analyzed with one-way ANOVA statistical test and using SPSS version 16 software. The non-parametric Kruskal Wallis (Wallis-Kruskal) test was also used to check the frequency of ARI index. Results: The highest shear bond strength was observed at 25 seconds, and the lowest at 30 seconds. However, there was no significant difference in the shear bond strength of brackets was observed among the four groups (p=0.186). The highest ARI score was observed at 35 seconds, and the lowest at 20 seconds. No statistically significant difference was observed in the ARI scores in different groups. SEM images revealed that the enamel surface porosity was highest at 20 seconds. Conclusion: The results indicate that the shear bond strength and ARI at different acid etching times do not significantly differ. Therefore, orthodontic bracket bonding can be performed with less acid etching time.

Does body surface area of children affect the oral health?

To evaluate relationship between oral health and body surface area among children. The observational, cross-sectional study was conducted from January to February /2022 after approval from the ethics review committee of the College of Dentistry, University of Baghdad, Baghdad, Iraq, and comprised children of either gender aged 6-8 years who were randomly selected from primary schools in the city. Body surface area was calculated geometrically using different formulas, and the DuBois formula was used to make the intervals. The estimated body surface area values were broadly divided into four intervals: 0.8-0.9, >0.9-1.0, >1.0-1.1, >1.1. Dental caries was examined using the World Health Organisation criteria related to decayed, missed and filled teeth and surfaces for primary and permanent teeth. Dental plaque and gingival health status were measured using plaque and gingival indices. Data was analysed using SPSS 22. There were 240 subjects. There was no significant difference in terms of mean body surface area intervals of decayed, missed and filled teeth and surfaces for primary and permanent teeth (p>0.05). The mean values of gingival index showed significant differences across body surface area intervals (p<0.05). Mean plaque index values showed no significant differences (p>0.05). No relationship between body surface area and caries experience of primary and permanent teeth was found. However, increasing the body surface area increased gingival inflammation.

In vitro early proximal caries detection using trilateral short-wave infrared reflection at 1050 and 1550 nm.

This in vitro study evaluated the diagnostic potential of short-wave infrared reflection (SWIRR) at 1050 and 1550 nm for proximal caries detection from the occlusal, buccal and lingual surfaces of posterior teeth under clinically relevant conditions. Bitewing radiography (BWR) was the alternative index test and micro-computed tomography (μCT) the reference standard. 250 proximal surfaces of extracted human teeth were examined using SWIRR at 1050 and 1550 nm and BWR. SWIRR, BWR and μCT findings were evaluated twice by two trained examiners. SWIRR images were evaluated from occlusal and trilateral (occlusal, buccal and lingual combined) views. Sensitivity, specificity and AUC were calculated. Reliability assessment was performed using κ statistics. SWIRR (1050 nm) showed sensitivity of 0.44 for occlusal and 0.55 for trilateral assessment, paired with specificity of 0.96 and 0.90, whereas SWIRR (1550 nm) showed sensitivity of 0.73 and 0.85 paired with specificity of 0.76 and 0.59. Compared to occlusal view, trilateral SWIRR view revealed ≈10% higher sensitivity and lower specificity. BWR revealed lowest sensitivity (0.30) and highest specificity (0.99). Over-and underestimation of caries demonstrated opposite trends: from 1050-1550 nm, overestimation of trilateral SWIRR increased (0.08-0.29), while underestimation decreased (0.15-0.06). Trilateral SWIRR has higher sensitivity and lower specificity for proximal caries, than occlusal SWIRR. 1050 nm are more suitable for trilateral SWIRR and 1550 nm for occlusal examinations. A combination of SWIRR at 1050 and 1550 nm may exhibit a balanced sensitivity and specificity for proximal caries.

Reliability of the Assessment of Tooth Wear Severity on Dental Hard Tissues and Dental Restorations, Using the TWES 2.0, by Nonexperts.

Tooth wear is a multifactorial process resulting in the loss of dental hard tissues. For its assessment, the tooth wear evaluation system (TWES) 2.0 has been published. Previous studies on the TWES involved well-trained practitioners, rather than nonexperts. The first aim of this study was to investigate the reliability of the assessment of tooth wear severity on dental hard tissues, using the TWES 2.0, by nonexperts. The second aim was to investigate the reliability of assessment of wear severity on dental restorations, using a third scale. Forty-seven dental students evaluated at least 9 of 14 possible patient cases on dental casts and intraoral photographs. Cohen's kappa (agreement with sample solution) and Fleiss' kappa (Inter-rater reliability) were calculated. The agreements of the operators' ratings compared to the sample-solution resulted in Cohen's kappa between 0.02 and 0.9. The agreements were 0.34 for occlusal; 0.43 for vestibular; 0.57 for oral surfaces. Inter-rater reliability (Fleiss' kappa) was 0.35 for occlusal, 0.17 for vestibular and 0.24 for oral assessment. The inter-rater reliability of the ratings on tooth surfaces with restorations was lower with 0.21 (occlusal), 0.14 (vestibular) and 0.39 (oral). The agreement on different restorations differed tremendously. The ability to correctly assess the cases varied considerably between individual examiners. Within the limits of this study, assessment of restorations was slightly more challenging compared to natural teeth, particularly in occlusal regions or when the restorative material is gold. Subsequent studies should address whether enhanced training and improved definition of tooth wear grades result in higher reliability scores.

Impact of FokI (rs2228570) and BglI (rs739837) polymorphisms in VDR gene on permanent tooth eruption: A cross-sectional study

IntroductionGenetic polymorphisms who disturb the mineral homeostasis during tooth development and eruption are candidate to clarify the molecular mechanisms involved in changes in the tooth eruption chronology. In this study, we evaluate whether the FokI (rs2228570) and BglI (rs739837) polymorphisms in the Vitamin D receptor (VDR) gene are associated with changes in the chronology of eruption of permanent teeth. Material & methodThis cross-sectional study randomly included 353 biologically unrelated children, both sexes, without systemic impairment or syndromes and history of trauma during the primary dentition. One operator perform the oral clinical examination. The tooth was considered erupted if there was a visible minimum of any tooth surface emerging from the mucosa. Genomic DNA was extracted from buccal epithelial cells from saliva samples. Genotyping was performed by Real-Time Polymerase Chain Reactions using TaqMan® technology. The average of the total number of erupted permanent teeth between the genotypes was compared by the Mann-Whitney test and multivariate Generalized Linear Models (GLM) (α = 5 %). β values with Confidence Interval (CI) 95 % were calculated. ResultsThe heterozygous adenine-guanine genotype of the FokI significantly decreases the number of erupted permanent teeth (β = −1.15; CI 95 % = −2.22 to −0.07; p = 0.036). In the stratified analysis for maxillary and mandibular teeth, this genotype was associated with a decrease in the number of erupted maxillary permanent teeth (β = −0.65; CI 95 % = −1.22 to −0.09; p = 0.023). BglI was not associated with permanent teeth eruption. ConclusionThe FokI, but not BglI, in the VDR may delay the eruption of permanent teeth.

Mathematical model and generation analysis for crossed helical gear system

Purpose Crossed helical gears have point contact and their surfaces are subject to high surface stress. Contact stress and root tooth stress are the most common sources of failure in crossed helical gear. This paper aims to study the load-carrying capacity and performance of crossed helical gear teeth with different gear tooth profiles. To overcome defects and reduce the sensitivity to small shaft angle changes. The combined tooth profile is designed to reduce the bending stresses, contact stresses and tooth deflection, and prevent pinion failure in the gearbox. Design/methodology/approach The principle of the method is a line contact is introduced instead of a point contact between two teeth in mesh with each other. The tooth surface of the helical gear is designed and cut by a modified tool. Higher normal pressure angles like 25° and 35° are used. The modified involute is accomplished to eliminate interference between the teeth. Engineering software packages have been applied to generate all crossed helical gears gear profiles. The modification is compounding curves consisting of an epicycloid-involute-hypocycloid gear teeth profile generated by the cutter modified. Findings The stresses in the crossed helical gear teeth profile were reduced by increasing the normal pressure angle values. Using a 35° pressure angle the enhancement percentage in contact stress and teeth fillet region will be about 29.345% and 15.421%, respectively. The best enhancement in a gear’s resistance is the epicycloid-involute-hypocycloid gear teeth profile. The enhancement was 32.610% and 18.588%. The skew in line of action in skewed helical gear will be sensitive when the crossing angles are small. Their teeth surface tends to be easily worn out; however, the wearing process will be reduced by using a proposed gear teeth profile. Practical implications The gear teeth to be modified are cut by a shaper process. The modifying rack cutter of this study can be used as a reference for creating a different helical gears sample. The helical teeth surface is modified to become an envelope of the other. This makes an original point contact change into a line contact. The epicycloid-involute-hypocycloid gear teeth profile is preferred for a higher contact ratio and a large load capacity. This work explicitly introduces a new method of kinematic consideration to improve the load capacity of crossed helical gear. Originality/value This paper showed some novel results by the unique shape of the rack-cutter designed to generate different helical angles and different gear positions. In the future, it will make valuable contributions to the further development of the dynamic performance of a crossed helical gear system through the study in the field of using asymmetric teeth profiles of helical gears with tip relief as the manner to enhance the crossed helical gear performance. Investigation of crossed helical gear by applying a predesigned parabolic function of transmission error enables the absorption of linear discontinuous functions caused by misalignment.

Synergistic effects of bacteria, enzymes, and cyclic mechanical stresses on the bond strength of composite restorations

Predicting how tooth and dental material bonds perform in the mouth requires a deep understanding of degrading factors. Yet, this understanding is incomplete, leading to significant uncertainties in designing and evaluating new dental adhesives. The durability of dental bonding interfaces in the oral microenvironment is compromised by bacterial acids, salivary enzymes, and masticatory fatigue. These factors degrade the bond between dental resins and tooth surfaces, making the strength of these bonds difficult to predict. Traditionally studied separately, a combined kinetic analysis of these interactions could enhance our understanding and improvement of dental adhesive durability. To address this issue, we developed and validated an original model to evaluate the bond strength of dental restorations using realistic environments that consider the different mechanical, chemical, and biological degradative challenges working simultaneously: bacteria, salivary esterases, and cyclic loading. We herein describe a comprehensive investigation on dissociating the factors that degrade the bond strength of dental restorations. Our results showed that cariogenic bacteria are the number one factor contributing to the degradation of the bonded interface, followed by cyclic loading and salivary esterases. When tested in combinatorial mode, negative and positive synergies towards the degradation of the interface were observed. Masticatory loads (i.e., cycling loading) enhanced the lactic acid bacterial production and the area occupied by the biofilm at the bonding interface, resulting in more damage at the interface and a reduction of 73 % in bond strength compared to no-degraded samples. Salivary enzymes also produced bond degradation caused by changes in the chemical composition of the resin/adhesive. However, the degradation rates are slowed compared to the bacteria and cyclic loading. These results demonstrate that our synergetic model could guide the design of new dental adhesives for biological applications without laborious trial-and-error experimentation.

A novel time-varying mesh stiffness model for orthogonal face gear drives considering EHL

PurposeThis study aims to research the time-varying mesh stiffness (TVMS) model for orthogonal face gear drives considering elastohydrodynamic lubrication (EHL) and provide a theoretical basis for understanding the dynamic characteristics of face gear drives.Design/methodology/approachConsidering EHL, a novel model is proposed to calculate the TVMS of orthogonal face gears using the deformation compatibility condition. First, the tooth surface equations of orthogonal face gears are derived according to the tooth surface generation principle. Then, the oil film thickness on the tooth surface of face gears is obtained by solving the governing equations of EHL. Furthermore, the proposed model is used to calculate the TVMS of face gears along the mesh cycle and is verified. Finally, the effects of module, tooth number of shaper cutter and pressure angle on mesh stiffness are analyzed.FindingsThe results indicate that when the contact ratio is greater than 1 and less than or equal to 2, the TVMS of face gears exhibits a phenomenon of double-single tooth alternating meshing where sudden changes occur. As the module increases, the overall mesh stiffness of face gears increases, and the magnitude of the sudden change at the moment of single-double tooth alternating meshing gradually increases. As the tooth number of shaper cutter and pressure angle increase, so does the TVMS of face gears. When the effect of oil film is considered, the calculated TVMS of face gears slightly increases overall and the increase in average oil film thickness leads to a rise in the TVMS. This study provides a theoretical basis for understanding the dynamic characteristics of face gear drives.Originality/valueThis study’s originality and value lie in its comprehensive approach, which includes conducting analysis based on loaded tooth contact, considering the influence of elastohydrodynamic lubrication, proposing a novel analytical–finite–element model, calculating TVMS of face gears, verifying the proposed model and analyzing the effects of typical structural parameters and oil film thickness.