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fracturas 1
Quiz by Nicole Andrea Díaz Cortés
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Rischio sismico: il 18 aprile 1906 san francisco in california fu scossa per 60 interminabili secondi da un terremoto di magnitudo 7,8 la città riportò danni pari al nono grado della scala mcs ma in alcune zone gli effetti provocati dal sisma furono addirittura dell'undicesimo grado tre persone su quattro rimasero senza casa crollarono oltre 25 mila edifici ma di questi solo il 10 per cento fu distrutto dal terremoto la maggior parte dei palazzi fu consumata dagli incendi divampati dalle tubature del gas divelte dalle scosse telluriche la città a bruciò per quattro giorni e quattro notti e per i due anni successivi molti furono costretti a vivere negli accampamenti il terremoto fu causato da una frattura propagatasi lungo un tratto della grande faglia di san andreas che nel suo percorso attraversa la california meridionale quella di san andreas è una faglia trasform e che si muove perciò con un movimento trascorrente i due lembi della faglia si muovono in direzioni opposte e sono in continua deformazione quella mattina si aprì una frattura lunga 430 chilometri che fece slittare i due lati della faglia fino a 6 metri in direzioni opposte si stima che almeno tremila persone persero la vita e il danno economico fu calcolato in 524 milioni di dollari allora il disastro fu inevitabile ma oggi è possibile ridurre il rischio sismico che grava su una città e sui suoi abitanti il rischio sismico di un'area dipende da tre parametri la pericolosità sismica la vulnerabilità e i costi la loro combinazione fornisce il valore complessivo del rischio più sono alti i valori di ciascun parametro maggiore è il rischio sismico quindi per ridurre il rischio bisogna ridurre al minimo l'impatto di pericolosità vulnerabilità e costi vediamo se si può e come si fa la pericolosità sismica indica con quale probabilità un territorio può risentire degli effetti di un terremoto le carte che descrivono la pericolosità sismica possono essere più o meno dettagliate e prendere in analisi il mondo intero o una regione come l'europa o un singolo paese a ogni valore si associa un colore e le zone tendenti al rosso sono generalmente le aree più pericolose purtroppo non esiste alcun modo per intervenire sulla pericolosità sismica perché questa dipende da forze geodinamiche fuori dal nostro controllo quindi per abbassare il rischio sismico di una zona possiamo intervenire solo riducendo la vulnerabilità del territorio e i costi da sostenere in caso di terremoto la vulnerabilità tiene conto della possibilità che le persone muoiono che i mezzi di soccorso non riescano a raggiungere le aree colpite e che gli edifici siano danneggiati o distrutti più la vulnerabilità è alta più sono alti i costi che la società deve sostenere in termini di perdita di vite umane danni agli edifici interventi per la ricostruzione e danno sociale per le attività colpite dal sisma quindi se abbassiamo la vulnerabilità si riducono automaticamente anche i costi e il rischio sismico complessivamente diminuisce a vantaggio di tutta la società la chiave di volta quindi è ridurre la vulnerabilità come eseguendo studi geologici e geofisici per la zona azione sismica del territorio usando tecniche di edilizia anti sismica sia per le nuove costruzioni che per le ristrutturazioni di vecchi edifici e naturalmente educando le persone per prevenire comportamenti sconsiderati in caso di terremoto per operare nei primi due campi occorrono anni di studio e formazione ora ci concentriamo invece su cosa occorre fare in caso di terremoto le esperienze di chi ha vissuto un terremoto di grande intensità e quelle di chi ha prestato i primi soccorsi sono servite a stabilire le norme di comportamento da seguire in caso di terremoto se viene sorpreso da un terremoto per prima cosa cerca riparo sotto una trave portante o se non puoi raggiungerla riparati sotto un tavolo o una sedia durante il terremoto non precipitarti a scendere le scale perché sono la parte più debole dell'edificio e possono crollare non prendere l'ascensore che può bloccarsi o precipitare e non correre in strada dove tegole e cornicioni e intonaco potrebbero colpirti in testa appena finisce la scossa chiudi il gas e stacca la corrente per evitare possibili incendi lascia l'edificio solo a scossa terminata ma prima di uscire ricordati di indossare le scarpe sempre senza potresti ferirti con vetri rotti e calcinacci poi raggiungi un posto all'aperto lontano da edifici e da linee elettriche infine evita di prendere l'automobile se non è necessario le strade infatti devono rimanere libere per consentire il passaggio dei mezzi di soccorso non sottovalutare questi consigli perché essere tutti preparati può fare la differenzaMake mcq quiz with 4 option in which one is correct -'10 Basis of Material Science • .....;;;";;;"~~;;,,;;,,,,;.;.,,;;,,,;,,;.;,.,------------ 6. Temporary materials: Some materials are meant to be placed in the oral cavity for a short period of time for different reasons. • Temporary crowns: While a permanent crown is prepared in the dental laboratory, the patient must wait for few days before it can be fabricated and cemented into place. Does patient experience any problems during this time period? If the tooth is vital (the pulp is alive), the patient is likely to experience pain and sensitivity while eating and drinking, also it looks unesthetic. What can be done to solve this problem? A temporary crown is placed before the patient leaves the clinic. It is constructed and luted in the same appointment in which the crown preparation is done. Temporary crowns are not very strong or esthetic but they serve adequately till the permanent crown is ready to be cemented. • Temporary restorations: Sometimes it is difficult to decide immediately the best line of treatment for a particular tooth. The exact condition of the pulp may not be obvious to the dentist from the patient's symptoms. A dentist removes all or part of the decay and then places a temporary restoration to have time to observe the behaviour of the pulp or to give the pilip time to heal before deciding the further treatment required. Classification based on Location of Fabrication 4,9 Materials can be classified based on the location of fabrication into: • Direct restorative materials. • Indirect restorative materials Direct restorative materials: They include those materials which are used to restore cavity preparations directly in the oral cavity (Box 1.5). Box 1.5: Examples of direct restorative materials Amalgam, composites, glass ionomer and other materials, which set by chemical reactions in the mouth. Indirect restorative materials: It includes those restorations which must be fabricated outside the mouth, indirectly on a cast/ model/ die, because their processing condition would harm oral tissues. Materials used in the construction of such prosthesis are called indirect restorative materials (Box 1.6). Box 1.6: Examples of indirect restorative materials Gold inlays, crowns of metal, ceramic and polymers, which are processed at elevated temperatures. Some indirect composite restorations can be processed under specific wavelength of light, e.g. Ceramage. Classification based on Longevity of Use 1. Permanent restorations: These restorations are not planned to be replaced for a particular time period. Though they are referred to as permanent, actually they are not, e.g. fillings, crowns, bridges and dentures do not last forever (Fig. 1.5). 2. Temporary restorations: These restorations are planned to be replaced in a short period of time, such as few days to weeks. For ~ Permanent C/) c c -.2 0 c- :;::; Cll co Interim ~ Q; 0 .8ll::1iJ C/) o~ Cll a:: c:=:J Temporary Time period Fig. 1.5: Diagram depicting the time period of use of a restoration. (Arrow in permanent restoration depicts that such restorations are not planned to be replaced for a long period of time.) Introducton to Dental Materials Dental materials Box 1.7: Characteristics of metals 1. High thermal and electrical conductivity 2. Ductility (pure metals are very soft and they can be bent without breaking) 3. Opacity (they do not transmit light) 4. Luster (they have a surface that strongly reflects light and appears bright and shiny) 5. They tend to dissolve to some extent in water or other aqueous solutions, producing cations. 6. All metals are white (actually gray) except for gold, which is yellow, and copper, which is reddish. 7. All metals are solid at room temperature except mercury, which is liquid at room temperature and is used with silver alloys as amalgam. 8. All metals have high melting temperatures because of high strength of the metallic bond that holds the atoms together. 3. Polymers 4. Composites Composites are mixtures of two or more of the first three classes in which the different components remain distinct from one another in the final structure. A common example is composite resin. Fig. 1.7a: Three-dimensional structure of iron (metal) Metals Metals are the oldest of the three classes of materials that have been used as dental materials. Metals are characterized by metallic bonds (Box 1.7) which will be discussed in the next chapter. Metals solidify with their atoms in a regular or crystalline arrangement (see Chapter 2), often in the form of a cube (Fig. 1.7a). example, temporary fillings done in a tooth during root canal treatment, which have to be replaced within 2-4 days during subsequent visits. They are used to protect the tooth and provide function till the final restoration is done. 3. Interim restoration: At times, dental treatment requires "long-term" definite temporary restorations or "interim" restorations. For examle, a 7-year-old child, met with trauma and fractured one of his central incisors. A large composite build- up may serve his immediate requirement until the root formation is completed and a permanent crown is placed. 5 Classification based on the Chemical Nature of the Material These are the atoms that make up a material and the way they are bonded together determine the properties of that materiaLS Weak bonds make for weak materials and vice versa (Table 1.4). Materials can be classified into different categories based on their primary atomic bonds (Fig. 1.6): 1. Metals 2. Ceramics Fig. 1.6: Classification of dental materials based on chemical nature 12 Basis of Material Science Box 1.9: Benefits of ceramics in dentistry 1. Many ceramic oxides are used as pigmenting agents. These oxides produce good range of colors. Due to this characteristic, we are able to match almost any tooth color with good esthetic results. 2. They are inert, i.e. not chemically reactive. This quality provides ceramics with good bio- compatibility. 3. Ceramic materials are translucent, like natural teeth. This translucency gives the ceramic crown a more natural appearance than any other dental material. Fig. 1.7b: Internal arrangement of tetrahedral structure of ceramic (silica) four large oxygen atoms surround smaller silicon atom Ceramics A ceramic is a compound formed by the union of a metallic and a non-metallic element (Box 1.8). Most of these materials are oxides, formed by the union of oxygen with metals such as silicon, aluminum, calcium and magnesium (Fig.1.7b). Ceramics may be simple or complex. Examples of simple ceramics are alumina and silica. Examples of complex ceramics are feldspar (potassium aluminum silicate) and kaolin (hydrated aluminum silicate). Ceramics may be crystalline or non- crystalline (i.e. amorphous). Porcelain is a specific type of ceramic used extensively in dentistry (Box 1.9). Box 1.8: Characteristics of ceramics 1. High melting points. 2. Brittleness, which means they cannot be bent or deformed (no sliding) to any extent without actually cracking and breaking. 3. They are poor conductor of heat and electricity. 4. They are chemically inert. 5. They have excellent esthetic result in terms of matching natural teeth. Fig. 1.8: Stucture of synthetic polymer Polymers They are the latest addition (early to mid- 1900s) to dental materials. Most of the polymers are nowadays synthesized by humans. Polymers are giant, long-chain organic molecules (Fig. 1.8). Polymers are characterized by covalent bonds within each molecule, giving them tremendous strength in a single direction. Try to break a nylon rope by pulling it! They are poor conductors of heat and electri- city. Most polymers have a structure containing thousands of carbon atoms linked together like beads on a string. Others, such as silicone polymers are formed with silicon-oxygen bonds. Introducton to Dental Materials Table 1.4: Characteristics of different materials 13 Characteristics Bond Properties Crystal structure Metals Metallic bonding High strength and hardness, high electrical and thermal conductivity BCC, FCC, or HCP unit cells Ceramics Ionic or covalent bonding, or both High hardness and stiffness, electrically insulating, refractory, and chemically inert Crystalline or amorphous Polymers Covalent bonding Low sensitivity, high electrical resistivity, and low thermal conductivity, strength and stiffness vary widely Amorphous and crystalline Composites Composites are combinations of any of the basic ceramic, metallic and polymeric materials (Box 1.10). Each material that makes up composites is called a phase. Their properties tend to be somewhere between those of their basic constituents and are used to enhance their performance, longevity and handling chracterstics. Box 1.10: Types of composites in dentistry 1. Ceramic - metallic composite: Tungsten carbide bur. 2. Metal - polymer composite: Die materials in dental laboratory. 3. Ceramic - polymer composite: Enamel, dentin, bone and restorative composites. A composite is a kind of "combination" of materials, which compliment each other. The properties lacking in one material are compensated by those of the other material. For example, restorative composite has two phases, namely resin and fillers. Teeth and bones are examples of natural composites. Enamel is a composite of hydroxyapatite (which is a ceramic material) and protein (which is a polymer). EVALUATION OF DENTAL MATERIALS Most manufacturers of dental materials maintain a quality assurance programme (As per international standard like ADA specifications) and materials are thoroughly tested before being released into the market for dental practitioner (Fig. 1.9). Laboratory Evaluations Most ADA/ ANSI specifications involve laboratory tests. The tests performed as per these specifications are useful but they all are performed in vitro, (carried out in the laboratory away from the clinical conditions) which have a lot of limitations in clinical practice.lO Clinical Notes 1. For example, most of the direct restorative materials are tested for their compressive strength but ultimately the material is subjected to a combination of compressive, tensile and shear stresses, which may decide the final success or failure of the material under masticatory load. 2. Similarly upper dentures mostly fracture along the midline because of bending. Hence a bending or transverse strength ~B-a-s-is-o-f-M-a-t-e-ria-I-S~c-ie-n-c-e-------------- ---------. test is far more meaningful for denture base materials than a compression test. Clinical Trials The majority of new materials are subjected to extensive clinical trials normally in co-operation with a dental college or hospital departments prior to their release. CONCLUSION As the number of available materials is going up, it is important that the dentist remains more aware about new products so that their judgement about the selection of material remains successful. Materials which have not been thoroughly evaluated should be avoided, specially with clinical dentistry falling under Consumer Protection Act (CPA). I Research and development I iI Manufacturer/analysis Ideal requirements for clinical use: Thermal, optical, mechanical, chemical, biological Available materials and their properties are evaluated Launch of new I product Choice and selection of material by the dentist Critical assessment based on clinical performance I I H feedback to IBone Structure, Formation, & Fracture Rehabilitación de personas con fracturasHand fractures & dislocationsTypes of fracturesWeekly Quiz 20 - Hand FracturesBone growth and remodeling New bone development is balanced with bone resorption Haversian systems are continually being replaced Bone is resorbed from one area and added to another to meet changing stresses placed on it (e.g., weight, posture, fractures) Normal growth dependent on sufficient proteins, minerals, vitamins (A, C, D) and influenced by hormones (growth, thyroid, estrogen/testosterone) Bone is capable of repair because it contains osteoprogenitor cells in the periosteum, endosteum, and bone marrow and is very well vascularized Metabolic role of bone (contains 99% of body’s total calcium in crystals) Transfer calcium from crystals to interstitial fluid and into blood Hormonal Parathyroid - stimulates osteoblasts to secrete osteoclast-stimulating factor thus promoting resorption Calcitonin - inhibits osteoclast activity