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Gypsum Products used in Dentistry

Introduction Gypsum products used in dentistry are based on calcium sulphate hemihydrate (CaSO 4.2H20) The current ISO Standard or !ental Gypsum "roducts identi ies i#e types o material as ollo$% Type & !ental plaster' impression Type 2 !ental plaster' model Type ( !ental stone' die' model Type 4 !ental stone' die' hi)h stren)th' lo$ e*pansion Type + !ental stone' die' hi)h stren)th' hi)h e*pansion Composition !ental plasters(plaster o "aris)% !ental plaster is produced by a process ,no$n as calcinations. "laster remains the most important model material or many dental restorations. -s the precision o it o restorations and orthodontic appliances depends on the .uality o the dental plaster/stone' they must comply $ith the hi)h .uality demanded in dental technolo)y.

Dental stone

Manipulation and setting characteristics "laster and stone are mi*ed $ith $ater to produce a $or,able mi*. Hydration o the hemihydrate then occurs producin) the )ypsum model or die. Water/powder ratios for gypsum model and die materials.

Water (ml) Powder(g) W/P ratio

(ml/g) Plaster Stone 50-60 20-35 100 100 100 0.55 0.30 0.1 6

Theoretical 1 .6 ratio

0or hand mi*in) a clean' scratch ree rubber or plastic bo$l ha#in) a top diameter o about &(0 mm is normally recommended. !le"i#le $i"ing %owls

The material should be used as soon as possible a ter mi*in) since its #iscosity increases to the sta)e $here the material is un$or,able $ithin a e$ minutes. The settin) reaction is e*othermic' the ma*imum temperature beib) reached durin) the sta)e $hen inal hardenin) occurs. Control of setting times: 0actor $hich control the settin)s o )ypsum products can be di#ided into those controlled by manu actures and those controlled by the operator. The manu acture can control the concentration o nucleatin) a)ents in the hemihydrated po$der Operator controls temperature and 1/" ratio and mi*in) time. Properties of the set material The stren)th )ypsum depends' primary' on the porosity o the set material and the time or $hich the materials is allo$ed to dry out a ter settin)s. Since stone is al$ays mi*ed $ith at a lo$er 1/" ratio than plaster it is less porous and conse.uently much stron)er and harder. (1hen porous increased' stren)th decreased). The ability o dental )ypsum products to reproduce sur ace details o hard or so t tissues either directly or rom impression is central to their suitability as model or die materials. This ability is 2ud)ed by measurin) the e*tent to $hich accurately machined lines in a bloc, o stainless steel can be reproduced in a sample o the material. Applications When strength , hardness and accuracy are required dental stones are normally used in preference to dental plaster. The stone materials are less likely to be damaged during the playing down . Thus , these materials are used when any work is to be carried out on the model or die as would be the case when constructing a denture on a model or a cast alloy crown on a die. When mechanical properties and accuracy are not of primary importance the cheaper dental plaster is used. Ad antages and disad antages Ad antages Ine*pensi#e and easy to use -ccuracy and dimensional stability Disad antages: 3echanical properties are not ideal.
Occlusal (Bite) Adjustment

This procedure ma,es corrections to the bite associated $ith loose' shi tin) teeth or teeth that are bitin) too hard. 4alancin) and e#enly distributin) the bitin) and che$in) orces on a tooth reduces the looseness and relie#es e*cessi#e pressures on the supportin) )um and bone structures. This painless procedure ma,es corrections to the bite by means o a dental drill usin) a ine stone' not at all li,e the one or drillin) out ca#ities 1e o ten use the T5Scan Computer54ased Occlusal -nalysis to e#aluate i e*tensi#e ad2ustment is needed. 1e record &00 pro)ressi#e bite re)istrations per minute o#er a 4 to 6 sec time rame as $e ha#e you bite and hold' bite and slide le t' bite and slide ri)ht and inally bite and slide your teeth or$ard. - ine red/blue mylar ilm is usually placed bet$een the teeth to mar, $here the teeth are touchin)7 the incorrect mar,in)s are then )round o by a ine inishin) bur and repolishin) $ith rubber points $ith impre)nated diamond paste. What are some of the !IG"! that may #ustify an occlusal ad#ustment: $oose or shifting teeth: sometimes one si)n is increased spacin) bet$een the upper ront teeth. Occasionally' you may eel that your teeth do not hit correctly. Grinding or clenching of your teeth: this habit (usually stress 5related) can cause an une#enly distributed and e*cessi#e bitin) orce on se#eral o your teeth and subse.uently on the bone support $hich holds the teeth in your 2a$. %eadache may sometimes accompany the )rindin) or clenchin) o your teeth. The headache in most o these cases $ill occur in the temporal re)ions o your head (lateral to the eyes. PAI": One or more teeth may hurt upon eatin) or bitin) do$n normally. This is usually caused by the eruption o a tooth beyond the normal plane o the bite' such that only one or t$o teeth contact prematurely. !ensiti ity to temperature (sometimes hot' but mostly cold). -)ain this is due to the premature contact bet$een one or more teeth. 1ith the ,no$led)e that one can bite $ith a orce o up to 200 pounds per s.uare inch' the ner#e $ithin the tooth )ets irritated and hypersensiti#e. 1hat are some additional modes o therapy alon) $ith an occlusal ad2ustment% Construction or abrication o a %awley &ite Plane . This is especially indicated $hen teeth are #ery loose and to resol#e headaches associated $ith )rindin) o the teeth. !plinting: I one or more teeth are #ery loose such that unctionin) (che$in)) becomes di icult' the loose teeth can be 8tied8 to the ad2acent stron)er teeth by means o a splint. - material called 9ibbond ($hich is a :e#lar material) is placed 2ust underneath the sur aces o the teeth that are to be splinted and subse.uently sealed $ith a composite illin) material. This techni.ue is not considered permanent in that o#er time it can detach' but it is o ten cost5e ecti#e until an alternate solution can be ound. Medication: 3uscle rela*ers or anti5in lammatory medications can be used i the 2a$ muscles are ti)ht' esp. durin) the ni)ht or $hen $a,enin) up rom sleep.