Orthodontic materials by almuzian ok ok


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Orthodontic materials by almuzian ok ok

  1. 1. Dr. Mohammed Almuzian, University of Glasgow 2012 1 Orthodontic materials BONDING • McCol 1998 found the bracket base surface areas up to 7 mm2 are adequate for retention of fixed orthodontic appliances. • SEP 10mpc bishara 2001 • Reynold showed that the clinically required bonding is 6-8mpc • Bracket must resist a displacement force of at least 5-15 Kg for clinical success. Modern direct bonding attachments a. a mesh b. particles adhered to the bracket base (spheres, rods or similar) c. grooves or undercuts placed in the surface of the b d. Secondary surface enhancements may be: • surface roughening • flame spray coating of particles on the primary retention surface or deposition of a chemically activatable material (such as Silicon oxide) on the primary retention surface • other chemical or electrical etching Preparation of the enamel surface for bonding Surface cleaning • There is no evidence to provide support for the practice of pumice prophylaxis before etching in order to obtain adequate bond strength for conventional etching because the aim of using pumice is to remove the acquired pellicle which would be removed anyway by the etchant Barry, 1995 • Self-etching primers do require prophylaxis (Burgess et al, 2006) • Some recommend pre-etching the surface for 5 second with 37% phosphoric acid before using SEP. Fitzgeland 2011.
  2. 2. Dr. Mohammed Almuzian, University of Glasgow 2012 2 Moisture control • One of the pre-requisites for successful bonding is a dry bonding field. The use of atropine sulphate (600 mcg tablet over 12 years of age) is one way of reducing salivary flow. The patient is given a 600 microgram tablet of atropine sulphate to take one hour before bonding as a TTO drug (to take out) to dry up salivary secretions. • Contra-indications are: pregnancy, glaucoma, and severe asthma. Wearers of contact lenses should be asked to remove them and not replace them until the following day. Children under the age of 12 years are not given atropine. • There was no statistically significant effect on the observed bond failure rates. Ponduri et al (2007) Enamel etching  The use of 37% phosphoric acid with a 30 second etch time has been confirmed as a sensible routine choice for routine orthodontic bonding (Gardner and Hobson 2001)  With 30%-40% phosphoric acid: 10-30 µm of surface enamel is lost, depth of penetration of resin tags reaches 50 µm. μm; at debonding, up to 56 μm of enamel may be removed during the debonding and polishing process (Bishara 2000).  Because of the enamel loss that occurs when etching enamel with phosphoric acid, some recommend the use of maleic acid and polyacrylic acid. Polyacrylic acid produces slight etching of the enamel surface and but in addition, calcium sulphate dihydrate crystals are formed which bond securely to the enamel surface but 30% lower bond strength than that achieved with phosphoric acid (Bishara 2000).  An aqueous solution of 10% maleic acid produces an etching pattern that leads to statistically significantly higher shear bond strengths. McCol 1998  Erickson compared the use of 10% maleic acid to 37% phosphoric acid and reported that the resulting bond strengths were essentially similar but malic acid produce less penetration of the enamel.  Bin Abdullah and rock 1996 should that 15 sec is the best  Wang (1991) showed there to be no significant difference in bond strength between etching for 15, 30, 60 and 90 seconds; etching for longer than 90 seconds resulted in lower bond strengths.
  3. 3. Dr. Mohammed Almuzian, University of Glasgow 2012 3 Etching pattern Silverstone et al. (1975) and Galil, 1979  type 1 etching pattern, prism core material was preferentially removed leaving the prism peripheres relatively intact.  type 2 etching pattern, the reverse pattern was observed. The peripheral regions of prisms were removed preferentially, leaving prism cores remaining relatively unaffected.  type 3 etching pattern, there was a more random pattern, areas of which corresponded to types 1 and 2 damage together with regions in which the pattern of etching could not be related to prism morphology.  Type 4 no prism removed but only minor roughness superficially  Type 5 smooth surface Sealants • Sealants are unfilled resins (methyle metha acrylate monomer. • It is hypothesised that sealants protect etched enamel and increase bond strength because they form a protective layer over the etched enamel and allow increased penetration of the unfilled resin into the resin tags respectively. • But much concern had been raised regarding its toxciogenicity related to Bisphenol A • Some practitioners advocate precuring the primer but Osterle et al (2004) found no advantage (or disadvantage) in doing this. • Some practitioner advocate bonding without the use of resin to reduce the risk of occupational exposure to liquid resin and its unpolymerized components. In addition, another advantage of not applying liquid resin is that it saves a step and therefore saves time . However Bazagani et al 2014 showed that in the resin group, the incidence of retainer failure was 4% and occurred at the composite-wire interface; in the nonresin group, the incidence was 27% and occurred at the enamel-composite interface. The incidences of calculus accumulation and discoloration adjacent to the composite pads were 27% and 69% (P  =  0.03 and P < .001) higher in the nonresin group, respectively.
  4. 4. Dr. Mohammed Almuzian, University of Glasgow 2012 4 Self-etching primer Mechanism of action:  The phosphate group on the methacrylated phosphoric acid ester dissolves the calcium and removes it from the hydroxyapatite.  It is important to do the agitation in order to remove the dissolved calcium and allow the unused phosphorous ion to be in contact with the enamel surface.  It is important to do gentle air blowing (dispersion) to evaporate the solvent.  However, rather than being rinsed away, the calcium forms a complex with the phosphate group and is incorporated into the network when the primer polymerizes (agitation process). Evidences for the bond strength of SEP • Aljoubouri 2003, SEP per patient was significantly quicker than with the two-stage system. There was no statistically or clinically significant difference in the bond failure rate per patient between the two groups. • Ireland 2003 show less bond strength of SEP but within clinical uses. • Bishara 1998, It is of interest to note that there was a tendency to have less residual adhesive remaining on the tooth when an SEP was used than when phosphoric and maleic acids were used. This might be of advantage to the clinician because it will require less time to clean the teeth after debonding. • Zaher 2012 found that moderate evidence exists that shorter resin tag penetration produces less change in enamel colour following clean-up and polishing. Since resin impregnation in the enamel structure cannot be reversed by debonding and cleaning procedures, enamel colour alteration may occur by direct absorption of food colorants and products arising from the corrosion of the orthodontic appliance or may be the change in the refractive index of the region, modifying the diffusely reflected light component. Self-etch primers produce less resin penetration and these systems may produce less iatrogenic colour change in enamel following orthodontic treatment • Fleming, Johal et al. 2012 in their systematic review found that
  5. 5. Dr. Mohammed Almuzian, University of Glasgow 2012 5 1. Weak but statistically insignificant evidence suggests that the odds of attachment failures differ between SEP and AE orthodontic bonding techniques over a minimum period of 12 months. 2. Use of 1-step bonding techniques is likely to result in a modest time saving compared with 2-stage techniques. 3. Additional high-quality randomized controlled trials investigating the overall course of treatment are required to analyze the effect of bonding modality on demineralization around fixed appliances. 4. In the absence of clear evidence to favor either system, the choice of bonding modality remains at the discretion of each operator. • Hu 2013 Cochrane reviw Only five of the studies provided usable evidence for this review and the combined results did not enable a conclusion to be made about whether or not there is a difference in bond failure between SEPs and conventional etching. There was also no usable evidence to suggest whether SEPs or conventional etchants lead to less decay around the etching site, or are associated with fewer costs or better participant satisfaction. There was also no usable evidence to enable conclusions to be drawn about which was the best SEP, acid, concentration or etching time. Advantages of SEP 1. Less time 23 second per bracket 2. Less discomfort to pt because it doesn’t require rinsing 3. Less enamel removed by etch 4. Less decalcification 5. less discoloration Zaher 2012 6. Less bonding materials as a remnant left after deboning Bishara 1998 Disadvantage of SEP • Expensive • Low bond strength • Difficult to judge bec of no classical chalky appearance • Since it is colourless then it might be washed out and irritate the gingivae • Tech sensitive
  6. 6. Dr. Mohammed Almuzian, University of Glasgow 2012 6 • teeth should be pumiced before The bonding materials The bonding materials used in orthodontics are: 1. Diacrylates 2. Cyanoacrylates 3. Glass ionomer cements 4. Glass polyalkenoate cements 5. Resin-modified glass ionomer cements 6. Compomers (polyacid-modified resin composites) 7. Glass polyphosphonate cements Diacrylates 1. Composite introduced by Bowen 1962 2. They are most commonly based on the aromatic dimethacrylate monomer Bis-GMA and are referred to as composites or composite resins if they also contain filler particles. 3. The term composite applies only to those resin based materials that contain at least 50% of filler by mass. 4. The filler particles consist of glass beads or rods, aluminium silicate, barium, strontium and borosilicate glasses. This filler content can vary greatly, forming in the order of 50 - 80% by weight of the material. 5. Fillers reduce the polymerisation shrinkage and coefficient of thermal expansion of the material as well as improving abrasion resistance, provide radipopacity and easy of handling 1. Chemically cured Diacrylates Chemically cured diacrylate bonding agents are presented in one of two forms. • Twin paste
  7. 7. Dr. Mohammed Almuzian, University of Glasgow 2012 7 • No-mix 2. Light cured • The use of a light cured diacrylate for bonding metal orthodontic brackets was first described by Tavas and Watts (1979). • It is important the light has a wavelength of approximately 440-480nm for photoinitiation to take place. • Light curing times commonly vary between 10 seconds per inter-space (totalling 20 seconds per tooth) for halogen lamps to as little as 3 seconds per tooth for plasma arc lamps (Pettemerides et al. 2002). Advantages • Extended working time • It is much easier to clean up • The ability to immediately cure a single bracket may reduce the chance of moisture contamination • Pre-coated metal and ceramic brackets are available, so-called Adhesive Pre Coat brackets (APC - 3M Unitek). It provide less composite flash and better cross infection control and fast. Bishara 1997 found pre-coated ceramic better than uncoated and vise vesa in metal • (O’Brien 1989). Found no difference bet chemical and light cure bonding. Disadvantages When bonding a whole arch with a conventional light source, extra time is required. This disadvantage has been significantly reduced by the introduction of high speed curing lights 3. Dual cured 1. The polymerisation of the material is brought about as follows: • by chemical cure in four minutes • by conventional light cure in 30 seconds • the material can be “tacked” with a 10 second light cure and then allowed to cure chemically. 2. The system is a paste/paste adhesive and utilizes a light or chemically cured sealant.
  8. 8. Dr. Mohammed Almuzian, University of Glasgow 2012 8 The advantages • Dual cure adhesive can be quickly tacked with the light and then left to fully set chemically • If the operator fails to cure with the light for a sufficient time for a complete cure, this does not matter with a dual cure adhesive which is therefore less technique sensitive than light cure materials • The use of dual cure adhesives has been evaluated by Smith and Shivapuja (1993) and gave similar bond strengths to chemically cured and light cured materials. The disadvantages • Mixing of two pastes is required and this requires time, • Lower bond strength will result if the material is starting to set when applied. • They are not commonly used in orthodontics, since the bond-line thickness of the adhesive in orthodontics is so small as not to pose a problem of residual polymer. Cyanoacrylates (superglues) • Cyanoacrylates were first developed by Eastman Kodak in the 1950's • Cyanoacrylates can cure very rapidly when in contact with only the smallest amounts of moisture, • This polymerization process occurs in approximately five seconds and is therefore a disadvantage in direct bonding. However this is a useful characteristic for indirect bonding. • Klocke et al (2003) investigated the use of cyanoacrylates in indirect bonding and again significantly lower bond strengths were found with the cyanoacrylate than with a conventional indirect bonding adhesive Glass ionomer cements (Glass polyalkenoate cements) These cements were first introduced in 1972 (Wilson and Kent 1972) and are also commonly known as glass ionomer cements. : 1. Liquid - an aqueous solution of an organic acid, such as poly(acrylic), poly(maleic) acid. 2. Powder - consists of ion-leachable glasses, namely calcium-alumino-fluoro-silicate glasses.  The use of glass ionomer cements for bonding has been suggested for some time.
  9. 9. Dr. Mohammed Almuzian, University of Glasgow 2012 9  The bond strength issues are a particular problem and several authors have reported higher bond failure rates with glass ionomer cements (50.9%, 20%) than with composites (7.8%, 5%) (Fricker 992, Miguel et al 1995). Advantages 1. Ease of bracket and adhesive removal 2. Longer working time 3. their greater compressive and tensile strengths, 4. The possibility of eliminating etching 5. The possibility of being able to bond in a wet environment 6. Sustained fluoride release because it has hydrogyle group which take fluoride and release when the Ph of mouth drop. 7. Less decalcification because of fluoride release. 8. Their ability to chelate via an acid-base reaction with both enamel and dentine and to form ionic bonds with stainless steel. 9. Glass ionomer cements bond to enamel by the interaction of polyacrylic acid with the hydroxyapatite of the enamel. Not only is surface hydroxyapatite dissolved through interaction with such acid solution, but polyacrylic acid also remains absorbed to the hydroxyapatite. Disadvantages 1. The bond strength is less than that of composite. Recommended the use of a conditioning agent of 10% polyacrylic acid prior to bonding to increase its bonding
  10. 10. Dr. Mohammed Almuzian, University of Glasgow 2012 10 2. Glass ionomer cements do not reach their maximum strength for 24 hours Glass polyphosphonate cements Containing Aluminino-silicate glass, poly (vinyl-phosphoric acid) and tartaric acid. The claimed advantages of glass polyphosphonates over conventional glass polyalkenoate cements are 1. A rapid set, 2. A high compressive strength, 3. A low solubility. A study by Clark et al (2003) show similar failure rate to conventional GIC. Resin-modified glass ionomer cement  These cements became available in the early 1990's and differ from the glass polyalkenoate cements in that they also possess a resin component, namely HEMA (hydroxyethyl methacrylate). This can form up to 15% of the cement and can be chemically or light activated.  This resin will set by photochemical polymerisation independly of the GIC reaction setting, which is acid base and it increase the strength of the cement.  In addition to the chemical bonding of RMGICs, resin monomers penetrate surface irregularities to produce a micromechanical interlock (bond) after polymerization to form the resin tags. Demke 2001.  An alternative to the diacrylates as bonding agents, although like the glass polyalkenoate they can also be used as band cements.  When used for direct bonding, reported clinical bond failure rates have been found to be comparable with those seen using diacrylate bonding agents (Ireland 2001) Modified composite or Compomers (polyacid-modified resin composites) • These differ from resin-modified glass polyalkenoate cements principally in the ratio of the resin component, which is in the order of 30-50% (Gladys et al. 1997).
  11. 11. Dr. Mohammed Almuzian, University of Glasgow 2012 11 • Clinical bond failure rates of brackets bonded using compomer have been found to be comparable to those seen with diacrylate bonding agents, • The compomer may have the additional advantage of reducing the risk of in treatment decalcification (Millett et al. 2002). • Gillgrass et al 2001 compared chemically cured glass ionomer cement with light- cured compomer (band-lock) found GIC better than band lock in bond failure but Ireland 2001 found no difference • It is used in case when conevtional etching pattern can not be achieved as in amelogenisis imperfect or fluorosis cases. Chromatic adhesives It is recognized that if the excess adhesive is not removed, it increases the amount of plaque and can act as a mechanical irritation to the gingiva, and, therefore, potentially increase the incidence of white spot lesions. Armstrong et al (2007) no advantages. Thermochromatic This is an adhesive which is: 1. dark blue when dispensed 2. turns tooth coloured above 32°C (10 second cure time) 3. reverts to a dark blue colour below 32°C to allow complete removal with the coolant system at debonding stage (and is therefore a two-way colour change adhesive Antibacterial adhesives Another useful characteristic of an adhesive might be to give it antibacterial properties to reduce demineralisation around the bracket pad by using what is called MDPB. Additional information • Cochrane review to compare different bonding materials by Mandal 2009 , It is difficult to draw any conclusions from this review; however, suggestions are made for methods of improving future research involving orthodontic adhesives.
  12. 12. Dr. Mohammed Almuzian, University of Glasgow 2012 12 Banding Cements There are four types of orthodontic cement available today:  Zinc phosphate cements.  Polycarboxylate cement (chemcical bond to tooth by replacing Ca ions)  Glass ionomer cements  Resin modified glass ionomer cements  Poly acid modified composite resins (compomer) From Demke 2001, • Durning 1989 compared bet zinc phosphate and GIC and found failure rate and decal less in GIC , same result by Stirrups from Glasgow in 1991. • Cochrane review by Millett 2008, There is insufficient evidence to determine the most effective adhesive for attaching orthodontic bands to molar teeth in patients with full arch fixed orthodontic appliances. • Cochrane review by Millet 2011, the failure of molar tubes bonded with either a chemically- cured or light-cured adhesive was considerably higher than that of molar bands cemented with glass ionomer cement. One trial indicated that there was less decalcification with molar bands cemented with glass ionomer cement than with bonded molar tubes cemented with a light-cured adhesive.
  13. 13. Dr. Mohammed Almuzian, University of Glasgow 2012 13 Bonding to deciduous teeth enamel A recommended procedure for conditioning deciduous teeth is to sandblast with 50-micromm aluminum oxide for 3 seconds to remove some outermost aprismatic enamel and then etch for 30 seconds with the Ultraetch 35% phosphoric acid gel. The failure rate with this procedure for the authors is less than 5%. (Zachrisson ) Bonding to fluorosed enamel Noble et al (2008) • Used strong acid (40% phosphoric acid) for longer time 60 second • Alternatives micro abrasion of the enamel surface with etching in order to provide enough • Used compomer and he thought to assist roughness of the enamel surface to ensure reliable bonding. • Use band instead. Disadvantages of microabrasion 1. Damage to the enamel surface 2. A recommendation to use rubber dam 3. The problem of confining the powder to the area to be etched 4. Patient ingestion of the abrasive powder 5. Potential allergy to the abrasive powder (aluminium oxide or silicon carbide) Bonding to bleached surfaces • Bleached teeth have a 25% reduction in bond strength to composite. • This may be because the enamel surface is oxygen rich and that this prevents polymerisation of the composite. • If patients are self-bleaching, then it is advised that no bleaching takes place within a three- week period prior to the fitting of appliances. • Lai et al (2002) have shown experimentally that treatment with sodium ascorbate reverses the negative effects of bleaching on enamel. Bonding to non-tooth structures Methods of optimizing the bond strength between metal brackets and non-enamel surfaces.
  14. 14. Dr. Mohammed Almuzian, University of Glasgow 2012 14 1. Mechanical preparation (provides mechanical bond for metals & porcelain) • Retention cavity • Microetching BY chemicals, electrical, sandblasting or laser • Tin plating 2. Chemical preparation (provides mechanical bond for porcelain) • 9.6% Hydrofluoric acid (HF) – for 2-4 minutes • 4% Acidulated fluorophosphate (AFP) – for 2 minutes • 37% Phosphoric acid – for 1 minute 3. Surface treatment (provides chemical bond for metals & porcelain) • Silane coupling agents • Primers/intermediate resins • Adhesive bonding/luting resins Intraoral Sandblasting 1. utilizes aluminium oxide powder 50Micron 2. Increase bond strengths by creating a retentive surface with microscopic undercuts (Zachrisson et al., 1993). 3. It also has other applications including the removal of composite from loose brackets and from tooth surfaces as well as increasing the retentiveness of stainless steel bands (Millet et al., 1995 & Miller et al., 1996). 4. removing composite from tooth surfaces (requires different abrasive)
  15. 15. Dr. Mohammed Almuzian, University of Glasgow 2012 15 Tin Plating 1. Tin is deposited either electrolytically using a unit such as MicroTin or manually by rubbing Adlloy solution on to the metal surface. 2. This produces a uniform whitish coating of 0.2μ which when exceeds 0.5μ results in reduced bond strength. Bonding to Porcelain Zachrisson in 1993 recommend: 1. Sandblasting with 50-μ Al2O3 for 2-4 seconds 2. Application of 2-3 coats of silane coupling agent 3. Application of intermediate resin eg All-Bond 2 4. Bonding with a highly filled bisGMA resin eg Concise Bourke et al in 1999 recommend:  37% phosphoric acid for 60 seconds. Phosphoric acid does not etch porcelain like hydrofluoric acid. Instead, it neutralizes the alkaline adsorbed water layer present of all porcelain restorations in the mouth. This enhances the chemical activity of any silane agent applied subsequently (Wolf et al., 1993)  Silane coupling agent  Intermediate adhesive (unfilled light-cured resin)  Composite resin Bishara et al 2005 recommended:  Sandblasting  HF acid etching. The hydrofluoric acid differentially dissolves the glass and crystalline phases of porcelain surface to increase the surface area available for bonding  Silane coupling agent. The silane reacts with the hydrofluoric acid to form silanol which is a chemically reactive compound that adsorbs to porcelain surface and lowers its wettability  Composite
  16. 16. Dr. Mohammed Almuzian, University of Glasgow 2012 16 Bonding to gold Büyükyilmaz et al in 1995 recommend: • Sandblasting • Metal adhesive like 4-META metal adhesive. • Intermediate application resin. • Composite resin • Tin plating can improve the bond strengths only marginally. This procedure is not FDA approved (potential toxicity) and therefore is not recommended for orthodontic practice Bonding to amalgam Zachrisson et al., 1993 recommend: • There is usually enough enamel around buccal amalgam fillings to bond a bracket to, with a failure rate of 3 • The recommended method is: • Sandblasting for 2-4 seconds from a distance of 1cm • 4-META metal adhesive • The use of an intermediate primer with short curing time like Reliance Metal Primer • Alternatively, the intermediate application of a primer like All-Bond 2 Primers A+B. Recent technologies More recently, laser might be an alternative method for conditioning porcelain surfaces. Factors that influenced clinicians to use bonded molars over banded molars included the following Millet 2012  Easier to involve partially erupted teeth (89%),  Quicker to place than molar bands (72%)  Separators were not required (70%).  Easier to monitor decalcification (55%) and for less risk of gingival inflammation (69%).
  17. 17. Dr. Mohammed Almuzian, University of Glasgow 2012 17 Bracket materials 1. Metal (SS, CrCo,NiTi) 2. Ceramic 3. Polycarbonate (very weak and creep under force) 4. Polyurethane Another classification  0.018*0.028  0.022*0.028  0.022*0.030 for easy placement of piggy back Technique of manufacturing the brackets • Milling: Originally, stainless steel appliances were made from cold drawn stainless steel strip with the slot milled into them • Casting: investment casting to make the brackets • MIM: A new technique called Metal Injection Moulding (MIM) was found to be ideal for producing orthodontic brackets and tubes. In details Stainless steel bracket 1. Stainless steel bracket (Iron 71, Nickle 8, Cr 18, carbon) 2. Construction: Castable, Milled, Metal injection moulding Titanium • Used in allergic pt to nickel. It is more wettable than SS so it bond better to bonding materials.
  18. 18. Dr. Mohammed Almuzian, University of Glasgow 2012 18 • Titanium: covered by layer of Ti to reduce friction CrCo. • Less nickel sensitivity and less release of nickel • Harder than stainless steel. • Less friction than stainless steel brackets. Aesthetic and ceramic bracket (see the relevant notes) Lingual bracket (see the lingual appliance notes) Invisalign (see the clear aligner appliance notes) Aesthetic wire in orthodontics (see adults orthodontics notes) HG tubes 1. 0.045 or 0.051 inch round 2. Either occ for easy control and cleanseness 3. Or gingival to be close to the centre of rotation Welding 1. Welding is the joining of two metals by melting and fusing the base metals being joined with or without the use of a filler material. 2. Welding normally takes place at between 800°C and 1635°C. 3. A welded joint is typically as strong as or stronger than the two base metals being joined. 4. Classified into • Resistance welding is the co-ordinated application of electric current and mechanical pressure to create a coalescent bond; • Laser welding (YAG lasers ) is commonly used by orthodontic manufacturers
  19. 19. Dr. Mohammed Almuzian, University of Glasgow 2012 19 Soldering 1. Soldering is a group of joining processes by heating them to a suitable temperature and using a filler material with a liquidus 2. Less than 450°C. 3. The filler material is evenly distributed between the two closely approximated surfaces to be joined by capillary attraction. 4. A low silver content solder is sufficient for orthodontic soldering (typically is 43% silver, 37% copper 20% zinc). 5. Flux is required to keep the solder and soldered pieces covered to prevent oxidation (Borax) Solders for orthodontic purposes require the following properties 1. The melting point of the solder must be about 50°C less than the melting point of the two metals to be joined. 2. The solder should have a good bonding for the metals to be joined 3. The solder should not corrode or tarnish within the mouth Arch wire materials
  20. 20. Dr. Mohammed Almuzian, University of Glasgow 2012 20 Stress described as Force/Area and determined by Pascals (N/m2). The stress is quantified as the internal force generated by the material which is equal in magnitude and opposite in reaction to a given force. There are different types of stress described. 1. compressive 2. tensile 3. shearing 4. flexural Strain Described as the change in length of a material relative to its original length after an applied force. It may recover or remain deformed. Proportional or Elastic Limit This is the maximum value of stress before permanent deformation occurs. Yield strength: This is the value of stress at which 0.1% deformation occur. Ultimate strength: This is the value of stress at which permanent deformation occur Failure point: This is the value of stress at which breakage occur. Strength: The ability of a material to resist stress without fracture. The stress at the point of fracture determines the strength of the material.
  21. 21. Dr. Mohammed Almuzian, University of Glasgow 2012 21 Modulus of Elasticity: Calculated on the slope of the stress/strain diagram (the red one) i.e. defined as stress/strain. This can also be expressed as the rigidity of the material, with a high modulus indicating an increased rigidity. Range (or minimum elastic radius) : Describes the amount a wire can be displaced(on the diagram described as linear amount on horizontal direction) without permanent deformation. Springback: Describes the amount a wire can be displaced with only 0.1% deformation (on the diagram described as linear amount on horizontal direction). Resilience: This is the amount of energy absorbed before plastic deformation occurs. On a stress/strain diagram it is described as the area under the slope up until the elastic limit. Ductility or formability: The amount of energy absorbed before failure of fracture of an orthodontic wire (area under the slop from yield point to failure point). Toughness : The amount of energy a material can absorb before fracturing.(in the diagram is the area under the curve from failure point. It is equal to Resilience + Ductility). A material with low toughness is described as being brittle. The toughness of a material can be illustrated as the area under a stress/strain diagram. Work hardening or steel hardening: it is a process of repeated application of force that pass the yield strength but less than the ultimate strength. This will cause a repeated deformation of 0.1%. as a result the distance between the yield strength point and the failure point will be decreased on the stress strain curve which means that the ductility or the formability will be reduced leading to fracture. The crystal will be stressed in this situation. Annealing is the process of reducing the crystal stress and improve the ductility again. The ideal orthodontic wire would have the following properties: 1. Low modulus of elasticity (low stiffness) 2. Friction free 3. High strength 4. High toughness (low brittleness)
  22. 22. Dr. Mohammed Almuzian, University of Glasgow 2012 22 5. High range 6. High springback 7. High resiliency 8. High formability 9. Weldable 10. Solderable 11. Low cost 12. Biocompatible 13. Aesthetic 14. Shape memory 15. Super elasticity Amount of force=distance of defelction*radius of wire4 /Length of wire3 The behaviour of an arch wire The behaviour of an archwire depends upon: 1) The composition of the wire. 2) The diameter of the wire. 3) The length and configuration of the interbracket span. 4) The width of the brackets. 5) The friction between the wire and the bracket channel.
  23. 23. Dr. Mohammed Almuzian, University of Glasgow 2012 23 Classification • Material- as mentioned above • Morphology- round, rectangular, hybrid, arch form • Coated or non coated –ion implantation, spray coating, sleeving • Properties- as described previously Gold or Precious Metals, Kusy 2000  Largely of historical significance.  Angle used it routinely.  Popular until the mid 50’ and obsolete on the introduction of stainless steel in the 1970’s.  Gold is too soft although  Incorporation of platinum and paladium into gold may still be useful (Proffit 1993) Stainless Steel  Austenitic form  18 % chromium (anticorrosion)  8% nickel (increase ductibility)  iron 70% and carbon (to increase strength) .
  24. 24. Dr. Mohammed Almuzian, University of Glasgow 2012 24 Properties: 1. Corrosion/rust resistant. 2. High strength 3. High stiffness 4. Soldering , Possible - therefore auxillaries such as archwire hooks can be incorporated 5. Friction is low. This is very advantageous for sliding mechanics. Heat treatment of SS The SS wire is constructed by cold drawing. After each drawing to minimize the diameter, the wire crystal become elongated and tempered. So heat 800 degree is used after each drawing or annealing except after the last drawing to relieve stress incorporated on bending of the wire. The ductility of the wire increases at the expense of the ultimate tensile strength. Stainless steel may vary in 1. Composition 2. Degree of work hardening- hard, spring hard and extra spring hard 3. Packaged form- straight or coiled 4. Arch form  Bonwill-Hawley  Catenary Curve  Trifocal ellipse of Brader arch form 5. Cross sectional shape  Round  Square  Rectangular 6. Multistrands wire  Co-axial- central stainless steel wire  twisted around  Twistflex wire- 3 SS wires twisted together combining many thin wires will increase the strength but decrease the springiness. 7. Cross sectional diameter
  25. 25. Dr. Mohammed Almuzian, University of Glasgow 2012 25 Cobalt Chromium e.g. Elgiloy (40% Cr, 20% Co, 15% Nickle, 15% Iron, 7% magnisium and carbon) Has the advantage over stainless steel that it is softer and therefore more formable, but can be hardened by heat treatment 480 degree afterwards and thus increasing its strength. Properties: 1. Smaller spring back than SS unless heat treated 2. Good formability 3. High modulus of elasticity 4. Greater resistance to fatigue/distortion 5. Larger friction than SS 6. Risk of annealing when soldering leading to a loss in yield strength Nickel Titanium  In the late 1960s the Office of the Navy was studying new types of alloys that exhibited shape memory effect (SME) (Buehler & Wiley, 1962).  A nickel titanium alloy was called Nitinol, an acronym of Nickel-Titanium Naval Ordinance Laboratory. Nickel titanium archwires have now been used in orthodontics since the 1970s.  The composition is 52% Ni, 43% Ti, 3% Co. Essentially there are 3 types of commercially available (Kusy, 1997): Three types of nickel titanium, Kusy 1997, 2000 1. Martensitic stabilised alloy (eg. Unitek's original Nitinol) non-elastic Effect 2. Austenitic Active Alloy (eg. Nitinol Superelastic) Pseudoelastic Effect 3. Martensitic Active Alloy (eg. Neo-Sentalloy) Thermoelastic Effect  Austenitic phase: high temperature metallurgical phase with hexagonal crystal  Martensitic phase: low temperature metallurgical phase with cubical crystal
  26. 26. Dr. Mohammed Almuzian, University of Glasgow 2012 26  Shape memory effect is the ability of a wire to return to its original shape when the temperature elevated. It is a feature of martensitic active NiTi alloy.  R structure a metastable rhombohedral structured intermediate phase between austenite and martensite (Khier et al 1991). The R structure always seems to be present in an austenite to martensite transformation but not always in the reverse transformation (Bradley et al 1996).  Superelasticity the martensite-austenite phase transformations, generated by mechanical stress or heat, which result in a segment of the loading curve for nickel titanium alloys in which stress is independent of applied strain (or the force per unit deflection is constan). It only exists when both phases of the alloy are present. Tonner and Waters (1994) showed that the superelastic wires have to be deflected at least 2 mm before exhibiting plateau behaviour  Pseudoelastic effect defined as change in the alloy phase from austenistic (hexagonal crystal structure) to martenistic (cuboid crystal structure ) when force leading to higher resiliency, then when force relived the change in the opposite way start to occur. Since austenite has a higher elastic modulus, on loading, the slope of the graph starts with a slope three times that of martensitic stabilised alloy;  Thermoelasticity the thermal analogue of pseudoelasticity in which the martensitic phase transformation occurs from austenite as the temperature increase. The phase transformation can be reversed by decreasing the temperature to its original value (pseudo- shearing). Bishara et al (1995) have produced a useful list of the ideal properties of thermoelastic archwires. These are: 1. Highly ductile at room temperature 2. Instantaneous activation at mouth temperature 3. Ability to develop forces that will produce tooth movement 4. Once fully activated, the wire is not further activated by the heat of the mouth 5. A narrow temperature transition range such that the wire is highly ductile at room temperature and highly active at mouth temperature  Hysteresis The genius-like characteristic of this transition from the austenitic to martensitic form is that the unloading curve is different to that of the loading curve displaying reduced and constant levels of stress present over a large area of strain. To clarify in orthodontic terms, this allows a low but constant force to be applied on teeth once the wires
  27. 27. Dr. Mohammed Almuzian, University of Glasgow 2012 27 have been ligatured into the brackets, despite the presence of considerable irregularities in the patients’ archform. In material science this known as hysteresis; that being the force to activate is not the same as the force which is delivered. The change in crystaline structure can be brought about by either: a) Stress, as in the pseudoelastic effect in the Austenitic Active Alloy. b) Heat, as in the thermoelastic effect in the Martensitic Active Alloy where the transition temperature is between room and mouth temperatures. Conventional alloy (Martensitic stable)  This alloy is a stabilised martensitic alloy.  The archwire remains in the martensitic phase under clinical conditions despite changes in stress and temperature. Properties 1. Low stiffness (1/6th of that of SS) 2. No super elastic properties 3. Greater springback than SS. 4. Friction higher than SS but lower than TMA 5. Cannot be weltered or soldered (Kusy, 1997) 6. Can recycle with no appreciable loss of properties Austenitic active (pseudoelastic) The second generation pseudoelastic NiTi alloys were introduced by 1. Burstone et al., (1985) as Chinese NiTi 2. Miura et al., (1986) as Japanese NiTi. Copper NiTi 1. This is an austenitic active wire whose copper additions increase reduce the hyetserisis 2. The latest alloy to utilise pseudo elasticity is 27˚C Superelastic copper NiTi (if the TTR is 35 or 41 , the wire will be considered as thermoelastic NITI).
  28. 28. Dr. Mohammed Almuzian, University of Glasgow 2012 28 3. This contains 5 to 6 % copper and 0.2 to 0.5% chromium. 4. These benefits occur at the expense of raising its phase transition temperature to above that of the oral cavity. To compensate for this 0.5% chromium returns the transition temperature to 27%. Thermoelastic nitinol (Martensitic active) This Niti wire not only undergoes the stress induced phase transformation of its crystal structure, but also demonstrates a change in crystal structure with a change in temperature. The temperature at which a temperature transition occurs referred to as the temperature transition range (TTR). Below the TTR the wire is in the martensitic phase with a low modulus of elasticity and it can therefore be deformed (strained) easily. As the wire rises towards mouth temperature, the wire begins its transition and return to its original shape and stiffness. Heat activated nickel titanium not used in: 1. OB reduction 2. OJ reduction 3. Torque control 4. With laceback to control severely tipped canine 5. OCS to gain space for blocked teeth It is important to remember that: 1. Thermoelasticity makes archwires easier to tie in 2. Then after wire ligation and temperature elevation, the wire will behave like active austenitic. 3. The stress will induce superelasticity where the austenitic phase transform to martensitic phase 4. The shape memory occurs when martensitic phase transform to the austenitic phases. Temperature Transformation 27oC 1. Superelastic, Not thermally active during clinical use. 2. Recommended for use in patients who have
  29. 29. Dr. Mohammed Almuzian, University of Glasgow 2012 29  Average / High pain threshold.  Normal periodontal health.  Where rapid movement required Temperature Transformation 35oC  Low pain threshold.  Reduced periodontal health.  Low forces required. Temperature Transformation 40oC  Sensitive pain.  Compromised perio health.  Slow tooth movement required.  As initial rectangular archwire. Graded thermoelastic NiTi That produced different force level in different section of the AW (anteriorly the force is less than posteriorly) Titanium- molybdenum alloy (Beta Titanium) TMA 1. Described as a cross between Ni-Ti and Stainless steel, Beta Titanium was marketed as TMA and contained titanium (79%), molybdenum (11%), Zinc (6%), Strantium (4%). 2. It had very good strength but produced twice the force of NiTi and 1/3 of stainless steel, therefore not compromising anchorage and also could be deflected double the distance. 3. good torque control 4. good corrosion resistance 5. the ability to withstand soldering. 6. One of the major disavdantages of using TMA is its high frictional characteristics due largely to its ability to cold weld to stainless steel brackets, therefore rendering it unusable when teeth have to be moved a considerable distance. 7. Currently experiments involving the implantation of ions into the wire in order to reduce the frictional resistance are under way.
  30. 30. Dr. Mohammed Almuzian, University of Glasgow 2012 30 Titanium-niobium 1. Have 60% of the stiffness of TMA and are easy to bend. 2. Recommended as finishing wires Mulitstrand Wire 1. The philosophy behind it’s manufacture is to provide a material which retains the flexibility of the individual strand but with an accumulative strength. 2. Kusy and Dilley (1984) compared 0.0175 triple stranded stainless steel twistflex with 0.010 stainless steel wire and 0.016 Nitinol. it’s strength was 25% greater than that of 0.010 stainless steel, but did not posses the same range of action as Nitinol. 3. Tidy (1989) suggested high notching. 4. The latest Cochrane review showed that there no difference between different type of AW in the alignment stage except a little significant better difference when coaxial NiTi is used (Wang 2013) Facts about superelastic wires  There is little published work on the effectiveness of superelastic nickel-titanium wires. O'Brien et al (1990) showed no significant difference in contact point alignment between Nitinol and Titanol archwires over a five-week period.  Superelasticity starts after significant deflection only, but at the same time this deflection will increase the TTR above mouth temperature making the wire non superelastic hhhhhh  Dual dimension archwires normally have a rectangular section in the anterior region and round wire posteriorly. Wonder Wire (Wonder Wire Corporation) was the first archwire to have this feature but the company no longer seems to be in business; Clinical requirements of the orthodontic wires LEVELING AND ALIGNING The appropriate wire for this stage has to exhibit good springiness, low stiffness, good spring back
  31. 31. Dr. Mohammed Almuzian, University of Glasgow 2012 31 1. Gold 2. Looped stainless steel 3. Elgiloy 4. Multi-strand stainless steel wires 5. Nickel titanium alloy wires • Major drawbacks of using low rigidity AW like NiTi include cost, and also the introduction of unfavourable forces on teeth adjacent to grossly maligned units. This is also known as the rollercoaster effect and a common presentation is the intrusion of an upper lateral incisor adjacent to a buccally placed and partially erupted canine which is being extruded. This can be avoided by the use of lighter forces, for example avoiding full engagement of the wire in the bracket Retraction of teeth along a base archwire The base arch, normally .018 or .017 x .025" stainless steel, has to exhibit good stiffness and strength to resist distortion during the movement of teeth along the wire Overbite control The ideal properties include: 1. High strength- to prevent loss of arch form and bite opening curves 2. High stiffness- to provide sufficient force to initially open the bite and maintain the overbite reduction 3. Good formability- to allow increased and reverse curves to be placed 4. High resilience Commonly used archwires include: Rocking chair NiTi 0.019x0.025 or SS 0.019x0.025 or 0.021x0.025. If a Rickets utility arch is to be used then a Co-Cr wire. Space closure and overjet reduction The ideal properties include a) High stiffness to prevent archwire flexing causing in tipping of the teeth into extraction spaces
  32. 32. Dr. Mohammed Almuzian, University of Glasgow 2012 32 b) High strength to maintain the arch form c) High formability to allow closing loops if desired and torque d) By this stage, three dimensional control is required and the base arch is a rectangular .019 x.025" stainless steel. e) Overbite control, is brought about by the base arch itself. Space closure is accomplished with auxiliaries.  Various forms of elastic traction, closing modules, powerchain, elastic bands.  Niti closing coil springs have been shown to produce more rapid and consistent space closure (Samuels, 1993). Torque control a) The base arch for the final stage of treatment is .019 x .025 SS b) When individual torque is needed, eg. if 2 or 3 have palatal roots, a wire is needed which can produce a much lower force over a longer range such as.019 x .025 TMA. The downside is the loss of overbite control. Archwire sequence guide The general concept is to think in terms of three main wires, around which other wires are used as intermediate 'stepping stones' between the main wires or to achieve specific objectives. Four main wires: 1) .014 or .016 nickel titanium aligning arch, either active austenitic or active martensitic depending on the degree of malalignment. It is easier to fully engage martensitic wire as it is softer at room temperature. 2) .018 round stainless steel base arch for sliding individual teeth mesio-distally, usually to close labial segment spacing or to retract canines. 3) .017 x .025 SS or .018 x .025 Niti to initiate correction of torque differential in adjacent teeth. Early use of rectangular (.018 x .025) or square (.020 x .020) Niti is particularly applicable where bracket selection has been customised. 4) .019 x .025 stainless steel final base arch for overbite control, torque and space closure.
  33. 33. Dr. Mohammed Almuzian, University of Glasgow 2012 33 Intermediate 'Stepping stone' wires: From 1) to 2) - If starting with .014 Niti, a .018 Niti or .016 Steel wire may be necessary for 4 to 6 weeks. - If starting with .016 Niti, there may be no need for a stepping stone wire. Mandall et al (2009) have undertaken a randomised clinical trial on archwire sequences which measured time taken to get into an 0.019” x 0.025” working archwire, discomfort and root resorption. The archwire sequences were: 1. 0.016” NiTi, 0.018” × 0.025” NiTi and 0.019” × 0.025” stainless steel 2. 0.016” NiTi, 0.016” stainless steel, 0.020” stainless steel and 0.019” × 0.025” stainless steel 3. 0.016” × 0.022” CuNiTi, 0.019” × 0.025” CuNiTi and 0.019” × 0.025” stainless steel The authors found no difference in discomfort or amount of root resorption There is no difference between multistrand and NiTi at initial stage. West 1995 There is no difference between NiTi and superelastic NITINOL O’Brien 1990 There is some evidence to suggest there is no difference between the speed of tooth alignment or pain experienced by patients when using one initial aligning arch wire over another except the coaxial NiTi AW. Wang 2013
  34. 34. Dr. Mohammed Almuzian, University of Glasgow 2012 34
  35. 35. Dr. Mohammed Almuzian, University of Glasgow 2012 35
  36. 36. Dr. Mohammed Almuzian, University of Glasgow 2012 36 Impression materials , Doubleday 1998 Impression materials is defined as the negative replica of the entire mouth including hard tissues and soft tissues of the mouth, made in a plastic material, which relatively sets while still in contacts with the tooth and tissues Impression materials are used 1. To construct SM which is helpful in:  treatment planning,  fabrication of fixed or removable prostheses  post-treatment records  Silicon impression materials are often used when taking impression of neonates with orofacial cleft. 2. Transferring orthodontic bracket using the indirect bonding technique. 3. Occlusal registration. Alginate 1. Alginate is classified as an irreversible hydrocolloid material, Advantages  low cost,  easy manipulation,  comfort to the patient,  hydrophilicity 2. Alginate impressions are not dimensionally stable prone to distortion caused by expansion associated with imbibition (absorption of moisture) or shrinkage due to moisture loss (syneresis), which is leading to decreased dimensional accuracy over time. 3. Pouring as soon as possible but no longer than 30 minutes (Powers 2006) Chemical reaction 1. sodium or sodium alginates (soluble alginates), 2. calcium sulphate as reactor, 3. a fluoride as accelerator 4. sodium phosphate as a retarder
  37. 37. Dr. Mohammed Almuzian, University of Glasgow 2012 37 5. mint or vanilla flavours to their alginates. 6. Chlorhexidine into the alginate powder in an attempt to limit cross infection. 7. Some manufacturers include colour pH change Na Alginate+CaSO4 Ca Alginate+Na2SO4 Silicone impression materials  Silicones are more stable than alginate and can poured 48 hours  There are two types of silicone impression materials Condensation cured and Addition cured. Condensation cured silicones 1. are also known as polysiloxanes as they have alternating atom of oxygen and silicon. 2. Condensation cured silicones are two component systems with  Base past containing silicone polymer plus filler  Accelerator past containing cross linking agent plus an activator Addition cured silicones 1. known as polyvinylsiloxanes. 2. They are generally presented as two putties that are mixed together by hand which are easier and cleaner than condensation cure putties. 3. It is recommended not to wear latex gloves when mixing the putty or alternatively to use vinyl gloves as the latex powder inhibits the set of addition silicones. 4. Addition cured silicones are the most accurate and stable up to seven days if kept dry. 5. The setting time of silicones is temperature dependent. Storing the materials in the refrigerator can increase working time by quarter. 6. Special extra hard addition cured silicones have been developed for use as bit registration materials. Impression compound 1. Impression compound is mixture of natural resins (e.g. shellac, waxes), fillers (e.g. talc) and lubricants (e.g. stearic acid). 2. It is thermoplastic, softens when heated and hardens when cooled.
  38. 38. Dr. Mohammed Almuzian, University of Glasgow 2012 38 3. It is useful for taking impression of neonates, as it does not tear and can be removed before fully set in case of emergency.. Decontamination of impression materials and prosthetic and orthodontic appliances 1. immediately on removal from the mouth, the impression or appliance should be rinsed under running water to remove saliva, blood and debris 2. continue the process until it is visibly clean. 3. If an appliance is grossly contaminated, it should be cleaned in an ultrasonic bath containing detergent and then rinsed 4. the impression or appliance should be disinfected according to the manufacturer's recommendations. 5. Generic materials such as sodium hypochlorite (household bleach) may no longer be suitable for disinfecting impressions unless specifically recommended by the manufacturer 6. disinfectants should not be sprayed onto the surface of the impression; it lessens the effectiveness and creates an inhalation risk. 7. Immersion of the impression is recommended 8. the impression or appliance should be rinsed again in water before sending to the laboratory accompanied by a confirmation that it has been disinfected. 9. Products that are suitable for the disinfection of impressions or appliances are CE marked to demonstrate conformity to European Directives. The manufacturer's recommendations for the dilution of the disinfectant and immersion time must be followed. 10. Preforma 2% containing quaternary ammonium for 10 min is a good way for disinfection. Acrylic used in removable/functional appliance construction  The polymer used to make removable and functional appliances is based on methyl methacrylate.  Methyl methacrylate monomer, which is a liquid at room temperature, can undergo polymerisation to form poly (methyl methacrylate) or PMMA. This initiator must in turn be activated by one of the following: 1. Electromagnetic radiation e.g. ultra-violet or visible light usually in the range of 440-480nm. 2. Heat.
  39. 39. Dr. Mohammed Almuzian, University of Glasgow 2012 39 3. Chemicals e.g. tertiary aromatic amine In the cold cure resin, 10 minutes. 45°C, 2 - 3 bar.. Hot cure, 72°C, 16 hours, 3000 bar. Elastic materials Structures 1. Elastomerics amourphous polymer 2. Elastomer is a general term that encompasses materials that, after substantial deformation, rapidly return to their original dimensions. They are either natural or synthetic rubber. 3. At rest, a random geometric pattern of folded linear molecular chains exists. On extension or distortion, these molecular chains unfold in an ordered linear fashion. This is called stress induced crystallization. 4. Primary bond maintain the bond between the chain after release of the extension forces. 5. If the primary bonds are broken, the elastic limit has been exceeded and permanent deformation occur. 6. Synthetic polymers are very sensitive to the effects of free radical generating systems like ozone and ultraviolet light. The exposure to free radicals results in a decrease in the flexibility and tensile strength of the polymer. Manufacturers have added antioxidants and antiozonates to retard these effects and extend the shelf life of elastomerics Advantages 1. inexpensive, 2. can be placed by the pt 3. the prescription of the use can be changed over the time between activation 4. relatively hygienic, 5. easily applied 6. Require little or no patient cooperation.
  40. 40. Dr. Mohammed Almuzian, University of Glasgow 2012 40 7. They are used to generate light continuous forces for canine retraction, diastema closure, rotational correction, and arch constriction 8. Isotrop feature which mean the elastic gives the same force in all direction. NB: the elastic should be stretched 3 time of its diameter Disadvantages 1. permanently stain, 2. suffer a breakdown of internal bonds that leads to permanent deformation 3. stress relaxation, resulting in a gradual loss of effectiveness Elastomerics physical properties 1. Viscoelasticity 2. Stress-relaxation 3. Prestretching effects, 4. Hysteresis
  41. 41. Dr. Mohammed Almuzian, University of Glasgow 2012 41 5. Hysteresis loss Viscoelasticity Material behaviour under different level of temperature  Viscoelasticity if the material is cooled, the motion of the molecules within the material is reduced and it behaves like a glassy solid.  Above a temperature, known as the glass transition temperature (GTT), the material behaves more like a viscous rubber.  As the temperature continues to rise even further, the motion between the molecules can increase to such an extent that it will behave more like a viscous liquid .  Stress-relaxation 1. As the name suggests this is the decrease in stress that occurs with time when an elastomer is subjected to constant strain. 2. Bishara 1974 showe that PCE loss half of its force after 24 h and the remaining force stay for 4 weeks so he recommend over extension of the PCE. 3. Baty 1994 found  More consistent force if PCE manufactured by stamping rather than injection moulding  The initial force delivered depend on the company and so the force should be measured by guage however the degradation is same for all types.  Short PCe produce more force which stays longer than long PCE.  Gray PCE bec of their filler maintain and produce higher force than clear type.
  42. 42. Dr. Mohammed Almuzian, University of Glasgow 2012 42 Prestretching effects, recommended Prestretching the elastic chains a third of their original length to prestress the molecular polymeric bonds and improve the strength. But there is no clinical difference Hysteresis This is the loss of mechanical energy seen between the loading and unloading curves for an elastomer on a stress-strain curve. Therefore the force applied by an elastomeric chain or thread used to move tooth will be less than the force applied to stretch the elastic in the first instance. Hysteresis loss With repeated loading and unloading, energy will be repeatedly lost at each cycle. This might occur when a patient is wearing intermaxillary elastics where the elastic bands will undergo loading and unloading as the patient repeatedly opens and closes their mouth during the day. Reuse of orthodontic materials from bos The reuse of orthodontic materials involves several possible problems: 1. Patient’s attitude Patients and parents may be unhappy at the thought that the appliance in question is “second- hand” 2. Device performance It is conceivable that the performance of a particular component may be affected by reuse. For instance, the mechanical behaviour of a superelastic archwire could be different 3. Cross-infection control in the case of bands that have been tried in for size but not actually used, it was thought that the lumen of any attached tubes might not be adequately sterilised by autoclaving. Recent evidence suggests that this concern is unfounded and that previously tried in bands can be adequately sterilised using a bench top autoclave1.
  43. 43. Dr. Mohammed Almuzian, University of Glasgow 2012 43  All medical devices (except custom-made devices or those used in clinical trials) must have a mark of conformity (CE) stamped on the device or the packaging.  Dental laboratories making custom appliances must register with the MDA unless their products are used entirely “in-house”. Magnet in orthodontic Noar 1999 Biological effect: it can produce corrosional by product but this can be eliminated by putting the magnet in SS sheath. It has negligible side effect on the adjacent tissue. Application in orthodontics 1. Intrusion of teeth (active vertical corrector) for treatment of AOB 2. Impacted teeth 3. Sliding of teeth and space closure and opening 4. Retainer of diastema 5. Slow Maxillary expansion 6. Distalization of molars 7. Functional appliance for cl2 high angle case Light cure machine Four types A. Halogen: Conventional curing lights use halogen bulbs filtered to produce blue light. They cure adhesive under metal brackets in 20-30 seconds. Halogen lights have disadvantages: • Halogen bulbs have a life of about 50 hours • The bulb, reflector and filter degrade over time • Halogen bulbs generate significant heat
  44. 44. Dr. Mohammed Almuzian, University of Glasgow 2012 44 B. LED (light emitting Diod) Advantages 4. Lifetimes of 10,000 hours 5. Undergo little light degradation during their life. 6. No filters are required to produce blue light, 7. LEDs are robust and require little power. 8. No heat generation C. Plasma Arc D. Laser Dunn and Taloumis (2002) compared the shear bond strength of orthodontic brackets bonded to teeth with conventional halogen-based light-curing units and commercially available LED curing units. They studied two LED lights (Lumalite LumaCure and Centrix VersaLux) and two halogen lights (Demetron Optilux 501 and Demetron ProLite). The study involved bonding orthodontic brackets with Transbond XT to extracted third molar teeth and then measuring the sear bond strength of the brackets using an Instron testing machine. No significant difference in bond strength was found between the four lights; Fleming 2013 no difference between the types of light