Chapter 1: Material Structure and Binary Alloy Systemsyar 2604
This is an introduction to material structure and periodic table system. This topic also describes microstructure of the metals and alloys solidification.
Chapter 1: Material Structure and Binary Alloy Systemsyar 2604
This is an introduction to material structure and periodic table system. This topic also describes microstructure of the metals and alloys solidification.
Structure of matter /certified fixed orthodontic courses by Indian dental aca...Indian dental academy
The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.
Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078
structure_of_matter general classes and principles of adhesion.pptAryaKrishnan59
Structure of Matter:
Matter consists of atoms, which are the fundamental building blocks. Here are some key points:
Atoms: These are indivisible and indestructible particles. Each element has identical atoms in terms of mass and properties.
Compounds: Formed by combining different kinds of atoms.
Chemical Reactions: Involve rearrangements of atoms.
Principles of Adhesion in Dentistry:
Adhesion plays a crucial role in dental treatments. It involves the attachment and binding of one substance to another. Here’s what you need to know:
Bonding System Functions:
Resistance to Separation: Prevents the adherend substrate (e.g., enamel, dentin, metal, composite, ceramic) from separating from restorative or cementing materials.
Stress Distribution: Distributes stress along bonded interfaces.
Interface Sealing: Achieved via adhesive bonding between materials1.
Mechanisms of Adhesion:
Chemical Adhesion: Involves molecular or atomic attraction between contacting surfaces.
Mechanical Adhesion: Results from structural interlocking.
Combination: Adhesion can occur through both chemical and mechanical mechanisms23.
Requirements for Good Adhesion:
Wetting: Sufficient wetting of the adhesive.
Low Viscosity: Allows proper flow and penetration.
Surface Texture: Rough surface texture of the adherend.
High Surface Energy: Promotes effective bonding4.
In summary, understanding the structure of matter and principles of adhesion is essential for successful dental procedures
Structure of matter /cosmetic dentistry course by Indian dental academyIndian dental academy
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
It's very good for SPM students . You have to learn the ionic bond thoroughly. If you understand well you can explain it vividly. For other chemistry notes can email me puterizamrud@gmail.com or facebook Pusat Tuisyen Zamrud .
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
Recomendações da OMS sobre cuidados maternos e neonatais para uma experiência pós-natal positiva.
Em consonância com os ODS – Objetivos do Desenvolvimento Sustentável e a Estratégia Global para a Saúde das Mulheres, Crianças e Adolescentes, e aplicando uma abordagem baseada nos direitos humanos, os esforços de cuidados pós-natais devem expandir-se para além da cobertura e da simples sobrevivência, de modo a incluir cuidados de qualidade.
Estas diretrizes visam melhorar a qualidade dos cuidados pós-natais essenciais e de rotina prestados às mulheres e aos recém-nascidos, com o objetivo final de melhorar a saúde e o bem-estar materno e neonatal.
Uma “experiência pós-natal positiva” é um resultado importante para todas as mulheres que dão à luz e para os seus recém-nascidos, estabelecendo as bases para a melhoria da saúde e do bem-estar a curto e longo prazo. Uma experiência pós-natal positiva é definida como aquela em que as mulheres, pessoas que gestam, os recém-nascidos, os casais, os pais, os cuidadores e as famílias recebem informação consistente, garantia e apoio de profissionais de saúde motivados; e onde um sistema de saúde flexível e com recursos reconheça as necessidades das mulheres e dos bebês e respeite o seu contexto cultural.
Estas diretrizes consolidadas apresentam algumas recomendações novas e já bem fundamentadas sobre cuidados pós-natais de rotina para mulheres e neonatos que recebem cuidados no pós-parto em unidades de saúde ou na comunidade, independentemente dos recursos disponíveis.
É fornecido um conjunto abrangente de recomendações para cuidados durante o período puerperal, com ênfase nos cuidados essenciais que todas as mulheres e recém-nascidos devem receber, e com a devida atenção à qualidade dos cuidados; isto é, a entrega e a experiência do cuidado recebido. Estas diretrizes atualizam e ampliam as recomendações da OMS de 2014 sobre cuidados pós-natais da mãe e do recém-nascido e complementam as atuais diretrizes da OMS sobre a gestão de complicações pós-natais.
O estabelecimento da amamentação e o manejo das principais intercorrências é contemplada.
Recomendamos muito.
Vamos discutir essas recomendações no nosso curso de pós-graduação em Aleitamento no Instituto Ciclos.
Esta publicação só está disponível em inglês até o momento.
Prof. Marcus Renato de Carvalho
www.agostodourado.com
The prostate is an exocrine gland of the male mammalian reproductive system
It is a walnut-sized gland that forms part of the male reproductive system and is located in front of the rectum and just below the urinary bladder
Function is to store and secrete a clear, slightly alkaline fluid that constitutes 10-30% of the volume of the seminal fluid that along with the spermatozoa, constitutes semen
A healthy human prostate measures (4cm-vertical, by 3cm-horizontal, 2cm ant-post ).
It surrounds the urethra just below the urinary bladder. It has anterior, median, posterior and two lateral lobes
It’s work is regulated by androgens which are responsible for male sex characteristics
Generalised disease of the prostate due to hormonal derangement which leads to non malignant enlargement of the gland (increase in the number of epithelial cells and stromal tissue)to cause compression of the urethra leading to symptoms (LUTS
Acute scrotum is a general term referring to an emergency condition affecting the contents or the wall of the scrotum.
There are a number of conditions that present acutely, predominantly with pain and/or swelling
A careful and detailed history and examination, and in some cases, investigations allow differentiation between these diagnoses. A prompt diagnosis is essential as the patient may require urgent surgical intervention
Testicular torsion refers to twisting of the spermatic cord, causing ischaemia of the testicle.
Testicular torsion results from inadequate fixation of the testis to the tunica vaginalis producing ischemia from reduced arterial inflow and venous outflow obstruction.
The prevalence of testicular torsion in adult patients hospitalized with acute scrotal pain is approximately 25 to 50 percent
New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-5) integrates alcohol abuse and alcohol dependence into a single
disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
from mild to severe. A diagnosis of AUD requires that at least two of
the 11 DSM-5 behaviors be present within a 12-month period (mild
AUD: 2–3 criteria; moderate AUD: 4–5 criteria; severe AUD: 6–11 criteria).
The four main behavioral effects of AUD are impaired control over
drinking, negative social consequences, risky use, and altered physiological
effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
New Directions in Targeted Therapeutic Approaches for Older Adults With Mantl...i3 Health
i3 Health is pleased to make the speaker slides from this activity available for use as a non-accredited self-study or teaching resource.
This slide deck presented by Dr. Kami Maddocks, Professor-Clinical in the Division of Hematology and
Associate Division Director for Ambulatory Operations
The Ohio State University Comprehensive Cancer Center, will provide insight into new directions in targeted therapeutic approaches for older adults with mantle cell lymphoma.
STATEMENT OF NEED
Mantle cell lymphoma (MCL) is a rare, aggressive B-cell non-Hodgkin lymphoma (NHL) accounting for 5% to 7% of all lymphomas. Its prognosis ranges from indolent disease that does not require treatment for years to very aggressive disease, which is associated with poor survival (Silkenstedt et al, 2021). Typically, MCL is diagnosed at advanced stage and in older patients who cannot tolerate intensive therapy (NCCN, 2022). Although recent advances have slightly increased remission rates, recurrence and relapse remain very common, leading to a median overall survival between 3 and 6 years (LLS, 2021). Though there are several effective options, progress is still needed towards establishing an accepted frontline approach for MCL (Castellino et al, 2022). Treatment selection and management of MCL are complicated by the heterogeneity of prognosis, advanced age and comorbidities of patients, and lack of an established standard approach for treatment, making it vital that clinicians be familiar with the latest research and advances in this area. In this activity chaired by Michael Wang, MD, Professor in the Department of Lymphoma & Myeloma at MD Anderson Cancer Center, expert faculty will discuss prognostic factors informing treatment, the promising results of recent trials in new therapeutic approaches, and the implications of treatment resistance in therapeutic selection for MCL.
Target Audience
Hematology/oncology fellows, attending faculty, and other health care professionals involved in the treatment of patients with mantle cell lymphoma (MCL).
Learning Objectives
1.) Identify clinical and biological prognostic factors that can guide treatment decision making for older adults with MCL
2.) Evaluate emerging data on targeted therapeutic approaches for treatment-naive and relapsed/refractory MCL and their applicability to older adults
3.) Assess mechanisms of resistance to targeted therapies for MCL and their implications for treatment selection
Report Back from SGO 2024: What’s the Latest in Cervical Cancer?bkling
Are you curious about what’s new in cervical cancer research or unsure what the findings mean? Join Dr. Emily Ko, a gynecologic oncologist at Penn Medicine, to learn about the latest updates from the Society of Gynecologic Oncology (SGO) 2024 Annual Meeting on Women’s Cancer. Dr. Ko will discuss what the research presented at the conference means for you and answer your questions about the new developments.
Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
Selleck adjusted his fitness routine as he aged to suit his body's needs. Today, his workouts focus on maintaining flexibility, strength, and cardiovascular health. He incorporates low-impact exercises such as swimming, walking, and light weightlifting. This balanced approach helps him stay fit without putting undue strain on his joints and muscles.
Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
micro teaching on communication m.sc nursing.pdfAnurag Sharma
Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
Flu Vaccine Alert in Bangalore Karnatakaaddon Scans
As flu season approaches, health officials in Bangalore, Karnataka, are urging residents to get their flu vaccinations. The seasonal flu, while common, can lead to severe health complications, particularly for vulnerable populations such as young children, the elderly, and those with underlying health conditions.
Dr. Vidisha Kumari, a leading epidemiologist in Bangalore, emphasizes the importance of getting vaccinated. "The flu vaccine is our best defense against the influenza virus. It not only protects individuals but also helps prevent the spread of the virus in our communities," he says.
This year, the flu season is expected to coincide with a potential increase in other respiratory illnesses. The Karnataka Health Department has launched an awareness campaign highlighting the significance of flu vaccinations. They have set up multiple vaccination centers across Bangalore, making it convenient for residents to receive their shots.
To encourage widespread vaccination, the government is also collaborating with local schools, workplaces, and community centers to facilitate vaccination drives. Special attention is being given to ensuring that the vaccine is accessible to all, including marginalized communities who may have limited access to healthcare.
Residents are reminded that the flu vaccine is safe and effective. Common side effects are mild and may include soreness at the injection site, mild fever, or muscle aches. These side effects are generally short-lived and far less severe than the flu itself.
Healthcare providers are also stressing the importance of continuing COVID-19 precautions. Wearing masks, practicing good hand hygiene, and maintaining social distancing are still crucial, especially in crowded places.
Protect yourself and your loved ones by getting vaccinated. Together, we can help keep Bangalore healthy and safe this flu season. For more information on vaccination centers and schedules, residents can visit the Karnataka Health Department’s official website or follow their social media pages.
Stay informed, stay safe, and get your flu shot today!
Lung Cancer: Artificial Intelligence, Synergetics, Complex System Analysis, S...Oleg Kshivets
RESULTS: Overall life span (LS) was 2252.1±1742.5 days and cumulative 5-year survival (5YS) reached 73.2%, 10 years – 64.8%, 20 years – 42.5%. 513 LCP lived more than 5 years (LS=3124.6±1525.6 days), 148 LCP – more than 10 years (LS=5054.4±1504.1 days).199 LCP died because of LC (LS=562.7±374.5 days). 5YS of LCP after bi/lobectomies was significantly superior in comparison with LCP after pneumonectomies (78.1% vs.63.7%, P=0.00001 by log-rank test). AT significantly improved 5YS (66.3% vs. 34.8%) (P=0.00000 by log-rank test) only for LCP with N1-2. Cox modeling displayed that 5YS of LCP significantly depended on: phase transition (PT) early-invasive LC in terms of synergetics, PT N0—N12, cell ratio factors (ratio between cancer cells- CC and blood cells subpopulations), G1-3, histology, glucose, AT, blood cell circuit, prothrombin index, heparin tolerance, recalcification time (P=0.000-0.038). Neural networks, genetic algorithm selection and bootstrap simulation revealed relationships between 5YS and PT early-invasive LC (rank=1), PT N0—N12 (rank=2), thrombocytes/CC (3), erythrocytes/CC (4), eosinophils/CC (5), healthy cells/CC (6), lymphocytes/CC (7), segmented neutrophils/CC (8), stick neutrophils/CC (9), monocytes/CC (10); leucocytes/CC (11). Correct prediction of 5YS was 100% by neural networks computing (area under ROC curve=1.0; error=0.0).
CONCLUSIONS: 5YS of LCP after radical procedures significantly depended on: 1) PT early-invasive cancer; 2) PT N0--N12; 3) cell ratio factors; 4) blood cell circuit; 5) biochemical factors; 6) hemostasis system; 7) AT; 8) LC characteristics; 9) LC cell dynamics; 10) surgery type: lobectomy/pneumonectomy; 11) anthropometric data. Optimal diagnosis and treatment strategies for LC are: 1) screening and early detection of LC; 2) availability of experienced thoracic surgeons because of complexity of radical procedures; 3) aggressive en block surgery and adequate lymph node dissection for completeness; 4) precise prediction; 5) adjuvant chemoimmunoradiotherapy for LCP with unfavorable prognosis.
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
1. Prepared by:
Mahmoud Kanan Mohsin
MSc Candidate, Orthodontics
Hawler Medical University
Supervised by:
Dr. Bayan A. Hassan
BDS, MSc, PhD
Hawler Medical University
2. Has many definitions, but the most
common is that it is any substance which has
mass and occupies space.
3. Is a unit of matter, the smallest unit of
an element, having all the characteristics of
that element and consisting of a
dense, central, positively charged nucleus
surrounded by a system of electrons.
4. An atom itself is made up of three tiny kinds
of particles called subatomic particles;
1. Protons
2. Neutrons
3. Electrons
5.
6. 1) All matter is made of atoms, atoms are
indivisible and indestructible.
2) All atoms of a given element are identical in
mass and properties.
3) Compounds are formed by a combination of
two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of
atoms.
7. An ion is an atom or molecule in which
the total number of electrons is not equal to
the total number of protons, giving the atom
a net positive or negative electrical charge. If
a neutral atom loses one or more electrons, it
has a net positive charge and is known as a
cation. If an atom gains electrons, it has a net
negative charge and is known as an anion.
8. Is an electrically neutral group of two or
more atoms held together by chemical bonds.
Molecules are distinguished from ions by
their lack of electrical charge.
9. An alloy is a mixture or metallic solid solution
composed of two or more elements, e.g.
Amalgam, Bronze, gold alloy,…ect.
10. Is an attraction between atoms that
allows the formation of chemical substances
that contain two or more atoms.
11. Description of the structure of atoms
proposed (1911) by the British physicist
Ernest Rutherford. The model described the
atom as a tiny, dense, positively charged core
called a nucleus, in which nearly all the mass
is concentrated, around which the
light, negative constituents, called
electrons, circulate at some distance, much
like planets revolving around the Sun.
12.
13. Primary Bond
A bond that forms between atoms and
that involves the exchanging or sharing of
electrons.
Secondary Bond
A bond that involves attraction between
molecules. Unlike primary bonding, there is
no transfer or sharing of electrons.
14. :
The forces that hold atoms together are
called cohesive forces. These interatomic
bonds may be classified as primary or
secondary. The strength of these bonds and
their ability to form after breakage determine
the physical properties of material.
15. Interatomic
Bonding
Primary Secondary
Metalic Covalent Van der Hydrogen
Ionic Bonds
Bonds Bonds Waals Forces Bonds
16. Interatomic primary bonding may be of three
different types:
1. Ionic Bonds:
Result from the mutual attraction of positive and
negative charges.
The classic example is sodium chloride (Na+Cl-).
In dentistry, ionic bonding exists in certain
crystalline phases of some dental materials, such
as gypsum and phosphate based cement .
17.
18.
19.
20. In many chemical compounds, two valence
electrons shared by adjacent atoms.
The hydrogen molecule H2, is an example of
covalent bonding.
Covalent bonding occur in many organic
compounds, such as dental resin, in which the
compound link to form the backbone structure of
hydrocarbon chains. The carbon atom has four
valence electrons and can be stabilized by
combining with hydrogen.
24. It is the attraction force between positive
metal ions and the delocalized (freely
moving) electrons, gathered in an electron
cloud.
These free electrons are responsible for the
high electric and thermal conductivities of
metals also for their ability to deform
plastically.
Found only in metals.
25.
26.
27.
28. In contrast with primary bonds, secondary
bonds don’t share electrons. Instead, charge
variations among molecules or atomic groups
induce polar forces that attract the molecules.
29. Bonds between hydrogen atom and atoms of the
most electronegative elements (N, O, F) are called
hydrogen bonds.
When a water molecule intermingle with other
water molecules, the hydrogen (positive) portion
of one molecule is attached to the oxygen
(negative) portion of its neighboring molecule
and hydrogen bridges are formed. Polarity of this
nature is important in accounting for the
intermolecular reaction in many organic
compounds, such as the absorption of water by
synthetic dental resins.
30.
31.
32. Van der Waals Forces form the basis of a dipole
attraction. E.g. in a symmetric molecule, such as
an inert gas, the electron field constantly
fluctuates.
Normally, the electrons of the atoms are
distributed equally around the nucleus and
produce an electrostatic field around the atom.
However this field may fluctuate so that its
charge becomes momentarily positive and
negative. A fluctuating dipole is thus created that
will attract other similar dipoles. Such interatomic
forces are quite weak .
33.
34.
35.
36. In general, materials can be subdivided into
two categories according to their atomic
arrangement. In crystalline materials there is
a three-dimensional periodic pattern of the
atoms, whereas no such long range
periodicity is present in noncrystalline
materials, which possess only short-range
atomic order.
37. Atoms are bonded to each other by either
primary or secondary forces. In the solid
state, they combine in a manner that ensures
minimal internal energy. For example, sodium
and chlorine share one electron. In the solid
state, however, the atoms do not simply form
only pairs; all of the positively charged
sodium ions attract all of the negatively
charged chlorine ions. The result is that they
form a regularly spaced configuration known
as a space lattice or crystal.
38. A space lattice can be defined as any
arrangement of atom in space in which every
atom is situated similarly to every other atom.
Space lattices may be the result of primary or
secondary bonds
39. There are 14 possible lattice types or forms, but
many of the metals used in dentistry belong to
the cubic system; that is, the atoms crystallize in
cubic arrangements. All dental amalgams, cast
alloys, wrought metals, gold foil are crystalline.
Some pure ceramics, such as aluminia and
zirconia core ceramics, are entirely crystalline.
Other ceramics, such as porcelains, consists of
noncrystalline glass matrix and crystalline
inclusions that provide desired
properties, including color, opacity, and increase
in thermal expansion
coefficients, radiopacity, strength, fracture
toughness .
40.
41.
42.
43. Structures other than crystalline forms can occur in the
solid state. For example,waxes may solidify as amorphous
materials so that the molecules are distributed at random..
A resin based composite consists of resin matrix, filler
particles and an organic coupling agent that bond the filler
particles to the resin matrix. In some cases, the filler
particles are made from radiopaque glasses that are
nancrystalline.
Composites have a noncrystalline matrix and may or may
not contain crystalline filler particles.
The structural arrangements of the noncrystalline solids
don’t represent such low internal energies as do crystalline
arrangements of the same atoms and molecules.
Noncrystalline solids do not have a definite melting
temperature, but rather they gradually soften as the
temperature is raised 6.
44.
45. It’s appropriate to first consider the pure
metals, which have the simplest composition and
atomic arrangement, metals always have
crystalline structures. There are seven crystal
systems
(cubic, tetragonal, orthorhombic, rhombohedral
[trigonal] hexagonal, monoclinic, and triclinic).
Space lattice is a geometric construct wherein
each point has identical surroundings. Crystal
structures of real materials are based upon space
lattices, where there is a single atom or a group
of atoms at each space lattice point.
46. Its most convenient to visualize the crystal
structures of metals in term of their cubic
cells, where a unit cell is the smallest portion
that can be repeated in three dimensions to
produce the crystal structure.
47.
48. Ceramics, which consists of more than one atomic species, can
have crystalline or noncrystalline structures, depending upon the
materials and sometimes the mode of preparation.
Important ceramics for orthodontic application are aluminum
oxide (alumina) and zirconium oxide (zirconia), which are used
as bracket materials.
Other ceramics are found in the powder portion of cements.
Silicon dioxide (silica) is important filler in composite restorative
resins. The crystal structure of aluminum oxide is illustrative of
the principles involved with ceramics having substantial ionic
bonding character. The crystal structure consists of nearly
hexagonal close packed (hcp) arrangement of the larger oxygen
anions (O2), with the smaller aluminum cations (Al3+) located in
two- thirds of the octahedral interstitial sites in the hexagonal
close packed (hcp) structure .
49.
50. A wide variety of polymeric materials are used in
orthodontics: polyurethane elastomers for tooth
movement, adhesive resins for bonding brackets
to tooth structure, polycarbonate
brackets, elastomeric impression materials and
polycarbonate brackets. All of these polymeric
materials are based on macromolecules with
varying compositions, molecular weight and
degrees of cross linking. The polymers have
predominantly noncrystalline structures without
long range periodicity.
Schematic polymer structure of alginate
impression material.
51.
52. http://physics.about.com/
http://www.universetoday.com/
http://www.iun.edu/~cpanhd/C101webnotes/co
mposition/dalton.html
http://en.wikipedia.org/
http://www.britannica.com/EBchecked/topic/514
258/Rutherford-atomic-model
Phillips’ Science of Dental Materials, Kenneth J.
Anusavice, Eleventh Edition
Orthodontic Materials, William A. Brantley