Components Of Appliances Research Articles

Controlling Three-Phase Induction Motor with an Internet of Things (IoT) Smart Industrial Panel

Abstract: With the transition from manual to auto systems, technology has been advancing globally. The smart control panel is the subject of this study. The electrical components of appliances can be inductive, resistive, or capacitive. The majority of inductive devices are motors. a three-stage There are many uses for induction motors in the global power system because of its many benefits, including low starting power, low maintenance cost, and widespread use. This paper discusses fault analysis in induction motors using MATLAB/SIMULINK, providing optimal protection combining traditional and IoT for both automatic and manual methods, and making it fully controllable according to the requirements of protection engineers for various loads. This is important for the economy and the motors' longevity, as it ensures that they operate optimally with the best smart protection techniques. In this setup, the control elements include a molded-case circuit breaker for safety, a temperature and vibration sensor with an Internet of Things (IoT) based remote data collecting method for automatic protection, and a selector switch for human control and automatic operation.

Metal Artifact Reduction by Using MARS System of a CBCT Unit with Different Components of Fixed Orthodontic Appliances: An In vitro CBCT Analysis

Introduction During Cone beam computed tomography (CBCT) imaging in the head and neck region of patients who are undergoing fixed orthodontic treatment, the different components of fixed orthodontic appliances can produce various metal artifacts which may degrade the diagnostic image quality in the region of interest. Therefore, the metal artifact reduction software (MARS) system can be used in most CBCT units to reduce the amount of artifacts generated from various fixed orthodontic appliance components including skeletal anchorage devices. Aims and Objectives The main purpose of this study was to quantitatively evaluate the effectiveness of MARS system of a CBCT unit in reducing the amount of artifacts generated by various fixed orthodontic appliance components during CBCT imaging. Materials and Methods Four dental arch shaped phantoms that were fabricated along with different fixed orthodontic appliance components (metal bracket, molar band, transpalatal arch, mini-implant) underwent CBCT scanning without and with the MARS setting option. After using the MARS system of a CBCT unit, the reduction in the amount of artifacts that were generated by various fixed orthodontic appliance component was calculated by using Google Colab software that utilized Python code and OpenCV system to generate a binary mask image. The resulting mask image highlights the areas where artifacts are detected, allowing for further analysis or visual inspection. The contours found within the mask image represent the boundaries of the artifact regions. Results After calculating the percentage decrease in artifact area for each component of fixed orthodontic appliance, one-way analysis of variance (ANOVA) test was performed to compare the percentage decrease in artifact area for each component of fixed orthodontic appliances. *P-values are calculated using one-way analysis of variance ( p < 0.05). The percentage decrease in artifact area for different components of fixed orthodontic appliance ranged from 39.67% to 48.58%. The stainless steel bracket showed the significant artifact area reduction with a mean percentage decrease of 48.58% as compared to other components. Conclusion The effect of MARS system in reducing the amount of metal artifacts generated varied according to the component type of fixed orthodontic appliance and, MARS system was more efficient for stainless steel brackets as compared to other components. CBCT imaging of head and neck region can be carried out without taking off the orthodontic appliances by applying MARS system which can significantly decrease the artifact area.

Repair and recycling of PCBs and their components based on obsolescence index: a domestic electrical appliances case study.

Population expansion and improving living standards, particularly in developed nations, have led to an increase in the usage of domestic electrical equipment, worldwide energy consumption, and CO2 emissions per capita. To limit the usage of non-reusable components and the amount of garbage that must be transferred at the end of a product's life cycle, longer-lasting electrical domestic appliances are a pillar of the circular economy. In recent years, the complexity of printed circuit boards (PCBs) used in the manufacture of modern electrical devices has increased, leading to an increase in device failures. This study focuses on the maintenance and recycling of domestic electrical appliance components and printed circuit boards. The proposed methodology for PCB repair is defined as a sequential quadratic programming (SQP) problem implemented in MATLAB environment and successfully tested to a variety of domestic appliances such as refrigerator, dishwasher and washing machine. The possibility of recycling metal parts of electronic components, which were replaced after PCBs' repair was also studied. Metals' percentage concentration of PCB electronic components for three customer's budgets considering metals and valuable metals recovery as given from the corresponding average metal recovery and calculated from different recycling procedures presented in the literature. The results of the proposed procedure in terms of valuable metals gave 38.4078ppm of silver. We also compared the suggested procedure with other works in terms of environmental perspective considering four measures, namely the gross energy requirement (GER), the global warming potential (GWP), the acidification potential (AP), and the solid waste burden (SWB). In terms of economic perspective and considering the existence of silver (Ag) in the electronic components, the recommended method gave comparable amount of money. Finally, a comparison of different recycling works from a technical viewpoint is also conducted. Moreover, a reparability index of domestic electrical appliances is introduced to further quantify the results of the proposed algorithm.

Relationships between House Characteristics and Exposures to Metal(loid)s and Synthetic Organic Contaminants Evaluated Using Settled Indoor Dust.

This study investigates associations between house characteristics and chemical contaminants in house dust, collected under the nationally representative Canadian House Dust Study (2007–2010). Vacuum samples (<80 µm fraction) were analysed for over 200 synthetic organic compounds and metal(loid)s. Spearman rank correlations between contaminant concentrations in dust and presence of children and pets, types of flooring, heating styles and other characteristics suggested a number of indoor sources, pointing to future research directions. Numerous synthetic organics were significantly associated with reported use of room deodorizers and with the presence of cats in the home. Hardwood flooring, which is a manufactured wood product, emerged as a source of metal(loid)s, phthalates, organophosphate flame retardants/plasticizers, and obsolete organochlorine pesticides such as ∑DDT (but not halogenated flame retardants). Many metal(loid)s were significantly correlated with flame-retardant compounds used in building materials and heating systems. Components of heating appliances and heat distribution systems appeared to contribute heat-resistant chemicals and alloys to settled dust. Carpets displayed a dual role as both a source and repository of dust-borne contaminants. Contaminant loadings (<80 µm fraction) were significantly elevated in heavily carpeted homes, particularly those located near industry. Depending on the chemical (and its source), the results show that increased dust mass loading may enrich or dilute chemical concentrations in dust. Research is needed to improve the characterisation of hidden indoor sources such as flame retardants used in building materials and heating systems, or undisclosed ingredients used in common household products, such as air fresheners and products used for companion animals.

The Effect of Thymus Vulgaris Essential Oil and Chlorhexidine on Candida Albicans Accumulated on Removable Orthodontic Appliance: A Clinical Trial.

Orthodontic removable appliances can facilitate the accumulation of certain microorganisms and microbial plaque on tooth surfaces and appliance components. Since long-term use of chemical agents is not recommended, an alternative option would be medicinal plants for disinfection of the oral cavity. The aim of this study was to assess the efficacy of thymus vulgaris (T. vulgaris) essential oil to decrease the count of candida albicans (C. albicans) accumulated on removal orthodontic appliances. In this 2-arm parallel controlled clinical trial, forty-four patients whose removable orthodontic appliances were contaminated with C. albicans were randomly divided into two groups by electronic random sampling. In the first group, T. vulgaris essential oil spray and in the second group, 0.2% chlorhexidine (CHX) spray was applied to the appliances. Thereafter, the C. albicans colony count was measured at baseline (T0) and at 2 (T1) and 5 (T2) days after the intervention. Microbial samples were collected by a sterile swab from 3 spots on the internal surface of orthodontic appliances. The Friedman test was used for within-group comparisons and the Mann Whitney test was employed to compare the efficacy of T. vulgaris essential oil with CHX. The results of this study revealed that continuous use of 2%T. vulgaris essential oil or 0.2% CHX significantly decreased the colony count of C. albicans on removable orthodontic appliances; Howevere, no significant difference was noted in the efficacy of 2% T. vulgaris essential oil and 0.2% CHX in decreasing the C. albicans colony count. T. vulgaris essential oil and CHX have favorable antimicrobial activity against C. albicans. Moreover, 2% T. vulgaris essential oil can be considered as an alternative to 0.2% CHX to eliminate fungal contamination of orthodontic appliances.

MotorBeat

More and more home appliances are now connected to the Internet, thus enabling various smart home applications. However, a critical problem that may impede the further development of smart home is overlooked: Small appliances account for the majority of home appliances, but they receive little attention and most of them are cut off from the Internet. To fill this gap, we propose MotorBeat, an acoustic communication approach that connects small appliances to a smart speaker. Our key idea is to exploit direct current (DC) motors, which are common components of small appliances, to transmit acoustic messages. We design a novel scheme named Variable Pulse Width Modulation (V-PWM) to drive DC motors. MotorBeat achieves the following 3C goals: (1) Comfortable to hear, (2) Compatible with multiple motor modes, and (3) Concurrent transmission. We implement MotorBeat with commercial devices and evaluate its performance on three small appliances and ten DC motors. The results show that the communication range can be up to 10 m.

ORTHODONTIC FORCE DIFFERENCE ON ACTIVE COMPONENTS ACTIVATION OF REMOVABLE ORTHODONTIC APPLIANCES (PERBEDAAN BESAR GAYA ORTODONTI PADA AKTIVASI KOMPONEN AKTIF PERANTI ORTODONTI LEPASAN)

Orthodontic treatment is performed by moving the malposition teeth into a good position in the dental arch with a removable or fixed orthodontic appliance. In this regard, the removable orthodontic appliance has an active component to transmit the orthodontic force that will result in orthodontic tooth movement. The orthodontic force used must be optimal in the sense of being able to produce tooth movement without causing side effects that endanger the periodontal tissue. It is necessary to activate the active components of the appliance, which in orthodontic treatment can be done several times until the desired tooth position is achieved. This study aims to explain the differences in orthodontic force in activating active components of removable orthodontic appliances. The research method was an experimental laboratory. A total of 24 removable orthodontic appliances used in this study were divided into two groups. The first group has a Z spring or single cantilever spring active component, and the other group has a labial bow. Each active component is activated by opening the loop by 1mm, 1.5mm, and 2mm, and in each activation, the magnitude of the force generated is measured using a tension gauge. Data analyzed by Mann Whitney (p&lt;0.05). The result showed different activations carried out in this study resulted in significantly different forces with p=0.029. The force generated in each activation increases as the loop opening increases. Based on that results, it can be concluded that there is a significant difference in the force magnitude generated by the activation of the removable orthodontic appliance active component.

Artificial intelligence and 3D printing technology in orthodontics: future and scope

&lt;abstract&gt; &lt;p&gt;New digital technologies, like in other fields, have revolutionized the health care field and orthodontic practice in the 21&lt;sup&gt;st&lt;/sup&gt; century. They can assist the health care professionals in working more efficiently by saving time and improving patient care. Recent advances in artificial intelligence (AI) and 3D printing technology are useful for improving diagnosis and treatment planning, creating algorithms and manufacturing customized orthodontic appliances. AI accomplishes the task of human beings with the help of machines and technology. In orthodontics, AI-based models have been used for diagnosis, treatment planning, clinical decision-making and prognosis prediction. It minimizes the required workforce and speeds up the diagnosis and treatment procedure. In addition, the 3D printing technology is used to fabricate study models, clear aligner models, surgical guides for inserting mini-implants, clear aligners, lingual appliances, wires components for removable appliances and occlusal splints. This paper is a review of the future and scope of AI and 3D printing technology in orthodontics.&lt;/p&gt; &lt;/abstract&gt;

The effect of live demonstration and flipped classroom with continuous formative assessment on dental students\u2019 orthodontic wire-bending performance

BackgroundWire-bending skills is commonly taught through live demonstrations (LD) though flipped classroom (FC) method has gained popularity. Continuous formative assessment promotes personalised learning via closely monitored progress, with the identification of students’ strengths and weaknesses. This study aims to evaluate the effects of LD and FC teaching methods, supplemented with continuous formative assessment, on dental students’ learning of wire-bending skills for six types of removable orthodontic appliance components. A deeper understanding of the relative effectiveness between LD and FC teaching methods can help identify the most appropriate method to achieve student learning objectives, which is especially important given the current Covid-19 pandemic.MethodsForty third-year undergraduate dental students were randomly assigned into FC (n = 20) or LD (n = 20) cohort. Each student attended six teaching sessions, each to teach students’ competency in fabricating one type of wire component, for a total competency in fabricating six wire components over the course of six teaching sessions. Either LD or FC teaching methods were used. After each session, wire assignments had to be submitted. Wire assignments were then evaluated using a blinded wire-bending assessment protocol. As part of their formative assessment, the assessment results were distributed to students, lecturers, and technicians before the next session. After the first session (T0) and at the end of all six sessions (T1), students completed a self-reported questionnaire.ResultsThe mean wire-bending scores for FC were significantly higher than LD for two of the six assignments, namely the Adams clasp (p < 0.01) and Z-spring (p = 0.03). Scores for both LD and FC increased significantly over time, which may be attributed to formative assessment. There was no statistically significant correlation between wire-bending scores and video usage. Students were satisfied with both teaching methods, according to T0 and T1 questionnaires.ConclusionsBoth LD and FC are equally effective in transferring practical orthodontic wire-bending skills and well-received by students. Continuous formative assessment may have enhanced students’ learning of orthodontic wire-bending skills. Further studies with control group are recommended to investigate the effect of formative assessment on teaching practical dental skills.

Ductile Response of Basalt Fibre Reinforced Concrete Beams

This paper presents the effects of adding basalt fibres on reinforced concrete beams. The fibre volume fraction Vf ranges from 0.0 to 2.0 %. First crack load, service load, yield &amp; ultimate load and their corresponding deflections were noted. The ductility response of BFRC beams were evaluated. The results show that 1.5% by volume of basalt fibre improves the overall performances. The maximum increase in deflection and energy ductility was found to be 34 % and 39% respectively when compared to that of reference beam. The increasing application of basalt is noticed as an insulating material in the construction and automotive industry and less hazardous than asbestos fiber. Basalt fabrics are produce d for the structural, electro-technical purposes. Structural applications include electromagnetic shielding structures, various components of automobiles, aircraft, ships and household appliances.

Hardness and toughness evaluation of developed Al metal matrix composite using stir casting method

Composite materials have many unique properties which mostly conventional materials usually do not comprise. One of these properties is the better volume to weight ratio which is very useful for designing of components of aircrafts, automobiles, domestic appliances and electronic devices. However some challenges occur in development of homogenous metal matrix composites because of different phases of matrix material and reinforcement materials. In this study, three different aluminium based metal matrix composites have been developed by varying the percentage of matrix (Al6063) and reinforcement (flyash and Al2O3) materials by using stir casting method and after that the hardness and toughness have been determined. Stir casting method has been used because of its low cost setup and portability. Result shows that the contribution of Al2O3 particles plays an important role in increasing the hardness of composite material.

A performance model of a multiprocessor computer appliance of a real-time control system

The article proposes a performance model of a multiprocessor computer appliance in a real-time control system, built using the mathematical apparatus of queuing theory, and different from existing similar models in that they take into account the possibility of failure and recovery of the hardware components of computer appliances. This article also explores the possibility of optimizing technical and economic characteristics using the proposed model. Due to optimization problem characteristics we should conclude that such optimization may be performed by evolutionary algorithms.

Pain perception of orthodontic treatment - A cross-sectional study.

Objectives:The objectives were to evaluate the intensity of pain perceived 24 hours following insertion of fixed orthodontic appliance components i-e separators, bands and brackets.Methods:This cross-sectional study conducted at a Dental College in Karachi (July 2017-March 2018) investigated the amount of pain perceived during different stages of fixed orthodontic treatment. The inclusion criteria were healthy individuals without systemic disease, age 13-26 years, fixed orthodontic treatment candidates having healthy permanent first molars. The exclusion criteria were missing permanent first molars, patients requiring brass wire separators instead of elastomeric separators and molar tubes instead of bands, ongoing or previous periodontal disease and syndromic patients. Pain intensity was assessed in ninety eight patients using a Numeric Rating scale (NRS) at baseline (T0) before insertion, and 24 hours after insertion (T1) of a component. This procedure was repeated six times, twice each for separators, bands and brackets. Scoring was done on the NRS from 0 to 10 where 0 indicated no pain and 10 indicated worst pain possible.Results:A significant difference in perceived pain was found between baseline and after 24 hours of placement of all components (P-value 0.000). Odds ratio indicated that males were at a greater risk to feel pain than females at baseline and after 24 hours of insertion of all components. Mann-Whitney U test showed that the most painful components at baseline were bands (Mean value=0.56) and after 24 hours were brackets (Mean value 6.25).Conclusions:Significant increase in pain was noted 24 hours after insertion of separators, bands and brackets. The most painful components were bands at baseline and brackets after 24 hours of insertion. There were no significant variations in pain perception based on age. However, males perceived higher pain than females both at baseline and after 24 hours.

Novel Switched Reluctance Machines for Domestic Appliances

Switched reluctance motors (SRM) are the core components of household appliances, which directly affect the performance and quality of household appliances. We have studied the application of switched reluctance motors in the home appliance industry. The 12/8-pole three-phase switched reluctance motor with a new rotor structure was proposed for the performance of SRM and the performance is simulated by MATLAB tools. Besides, the control principle and the operating equations of the switched reluctance motor are also introduced and deduced in detail. For the further work, although the 12/8 pole switched reluctance motor can effectively reduce the torque ripple, it cannot be completely eliminated. Therefore, the next step should continue to explore ways to reduce torque ripple.

Comparison of virtual and physical dimensions in AM resin dental devices and fit of devices with conventionally produced base plates

PurposeThe purpose of this study is to develop and apply clinically relevant methods of analysing the accuracy of dental appliances fabricated using additive manufacture (AM) compared to the computer-aided design (CAD) geometry. The study also compared fit between conventionally laboratory-fabricated and AM-produced base plates.Design/methodology/approachThe techniques were applied to two types of dental devices where AM fabrication methods could foreseeably be used as an alternative to laboratory production. “L” and cubic shapes of defined dimensions and spatial locations were positioned on the devices which were fabricated using AM. For assessing the dimensions, the “L” and cubic shapes were then measured on the physical builds ten times and compared to the CAD model. To assess the fit of AM and lab-produced devices, three upper and three lower conventionally fabricated acrylic base plates were compared to three upper and three lower plates. Silicone impression material was allowed to set between the casts and the base plates which filled any discrepancy between the two surfaces. The thickness of this silicone media was measured ten times at five different points on each base plate type and the results compared.FindingsThe results indicated that the evaluated CAD/AM technique is able to produce dental appliance components that are consistent with tolerance levels that would be expected with conventional methods of baseplate design. This research demonstrated that a fully CAD/AM methodology represents a potentially viable alternative to conventional lab-based methods for two types of dental appliances.Originality/valueThis work is original. The authors do not believe any previous papers similar to the one submitted have been published.

Corrosion resistance of fixed orthodontic appliance components in Ringer's solution

Corrosion resistance of fixed orthodontic appliance components in Ringer's solution

The influence of artificial salivary pH on nickel ion release and the surface morphology of stainless steel bracket-nickel-titanium archwire combinations

Background: In the oral cavity, orthodontic appliances come into contact with saliva which may cause corrosion capable of changing their surface morphology due to the release of metal ions. Surface roughness can influence the effectiveness of tooth movement. One of the ions possibly released when body fluid comes into contact with brackets and archwire is nickel ion (Ni). Ni, one of the most popular components of orthodontic appliances, is, however, a toxic element that could potentially increase the likelihood of health problems such as allergic responses during treatment. Purpose: The purpose of this study was to investigate the effect of different artificial salivary pH on the ions released and the surface morphology of stainless steel (SS) brackets-nickel-titanium (NiTi) and archwire combinations. Methods: Brackets and archwires were analyzed by an Energy Dispersive X-Ray Detector System (EDX) to determine their composition, while NiTi archwire compound was examined by means of X-ray Diffraction (XRD). The immersion test was performed at artificial salivary pH levels of 4.2; 6.5; and 7.6 at 37°C for 28 days. Ni ion release measurement was performed using an Atomic Absorption Spectroscopy (AAS). Surface morphology was analyzed by means of a Scanning Electron Microscopy (SEM). Results: The chemical composition of all orthodontic appliances contained Ni element. In addition, XRD was depicted phases not only NiTi but also Ni, Titanium, Silicon and Zinc Oleate. The immersion test showed that the highest release of Ni ions occured at a pH of 4.2, with no significant difference at various levels of pH (p=.092). There were surface morphology changes in the orthodontic appliances. It was revealed that at a pH of 4.2, the surfaces of orthodontic appliances become unhomogenous and rough compared to those at other pH concentrations. Conclusion: The reduction of pH in the artificial saliva increases the amount of released Ni ions, as well as causing changes to the surface morphology of brackets and archwires.

Rinsing effect of 60% bay leaf (Syzygium polyanthum wight) aqueous decoction in inhibiting the accumulation of dental plaque during fixed orthodontic treatment

Background: Fixed orthodontic appliance patients have a high risk to increasing plaque accumulation in tooth surface due to the presence of fixed appliance components. Using mouthwash with antibacterial agent from herbal material can control dental plaque accumulation. Bay leaf (BL) contains active compounds such as essential oil, tannin and flavonoid that have been known as an antibacterial agent. Purpose: The purpose of this study was to determine the effect of rinsing with 60% of BL aqueous decoction to the accumulation of dental plaque in fixed orthodontic appliance patients. Method: This research was an experimental clinical research with pretest and post-test control group design conducted on 20 subjects with age ranged between 18-25 years old. All subjects were undergoing the last stage (finishing) of fixed active orthodontic treatment. The subjects were instructed to rinse with 60% of BL aqueous decoction and 0.2% chlorhexidine as a control. Wash out period that needed between rinsing with 60% of BL aqueous decoction and rinsing with 0.2% chlorhexidine was 7 days. Each mouthwash used routinely for 7 days with same duration and intensity. Plaque scoring was measured before and after each treatment using Orthodontic Plaque Index (OPI). Result: One-way Anova test showed that there was a significant difference in the plaque index before and after treatment between the group of rinsing with 60% of BL aqueous decoction and group of rinsing with chlorhexidine (p&lt;0.05). Conclusion: Rinsing with 60% BL aqueous decoction can decrease the accumulation of dental plaque in fixed orthodontic appliance patients.

Effects of three different mouthwashes on the surface characteristics of nickel-titanium and Stainless steel archwires in orthodontics

Introduction: Patients are recommended regular using of mouthwashes to control dental caries or periodontal diseases since orthodontic treatment may have detrimental effects on the tooth structures. However, chemical agents may potentially damage metal components of orthodontic appliances. The aim of this study was to evaluate the influence of three mouthwashes on the surface characteristics of nickel–titanium (NiTi) and Stainless steel (SS) arch wires. Methods and Materials: 15 pieces of 0.016 inch NiTi and 15 pieces of 0.016-inch SS wires were randomly assigned into 5 groups including 2 controls (as- and artificial saliva) and 3 experimental groups. The samples in all groups were stored in artificial saliva in an incubator at 37˚C for one month, after that, the test groups were immersed in Chlorhexidine 0.12%, Hydrogen peroxide 0.12% and Persica mouth washes for 30 min, 1.5 h and 1.5 h, respectively. Then, the samples were washed by distilled water and returned to artificial saliva for more than two months. Surface topography changes and the number of corrosion holes were characterized via a scanning electron microscope (SEM).Two way ANOVA and Tukey tests were used to compare groups. Results: SEM photographs of the present study showed significant corrosion rate among as- received group and Persica (p=0.04), Chlorhexidine (p=0.02), and artificial saliva group (p=0.008) in NiTi wires, but there was no significant difference in the surface topography between any of the groups in SS wires. Conclusion: Alterations in surface of NiTi wires were significantly more than SS wires. Although not significant, 0.12% Chlorhexidine and Peroxide showed higher pitting view on SS and NiTi wires, respectively compared to other mouthwashes

Cytomorphometric Analysis on the Effects of Components of Orthodontic Appliances on the Epithelial Cells of the Buccal Mucosa.

Aim:The aim of the present study was to evaluate the effect of fixed orthodontic appliances on the epithelial cells of buccal mucosa in patients undergoing orthodontic treatment.Materials and Methods:The study group included 30 healthy patients who were advised orthodontic treatment. Applying sterile cement spatula, scrapping of exfoliated buccal epithelial cells was performed from the middle part of the inner cheeks before starting the orthodontic treatment and at 1st week, 2nd week, 1 month, and 45 days after the treatment, followed by smearing and staining with Papanicolaou stain. Light microscope was used to score micronuclei, and independent two-tailed t-test was used for statistical analysis.Results:Micronuclei were assessed during the various stages of treatment and were recorded accordingly. At 1 week, there was increase in micronuclei number compared to before starting the treatment (day 0) and at 15th day; 30th day showed decrease in number compared to 1 week but increase compared to day 0. The results of day 45 were almost equal to day 0 with a significant P value (P < 0.001).Conclusion:Fixed orthodontic appliances induce increased micronuclei frequency, especially in the first weeks of treatment, however, these genotoxic effects tend to approach baseline levels in later period.