Dental material Lecture #5 Dr. Hanan Al-Zraikat Dispensing

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Dental material

• Lecture 5
• Dr. Hanan Al-Zraikat

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Dispensing Compositionpolysulfides

• Supplied in two tubes as base and catalyst, equal
  lengths are mixed giving a homologus color .
  Light body (more flowable material called wash
  impression to provide better or more accurate
  representation of intraoral structures), regular
  body, heavy body (viscous material), so different
  viscosities
• Chemical composition of base
• 80 low-molecular-weight organic polymer
  containing mercaptan reactive groups (-SH), and
  20 reinforcing agents titanium dioxide, silica,
  zinc sulfide
• Chemical composition of catalyst (to make it
  stronger)
• Lead dioxide or copper hydroxide

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Setting reaction

• Mercaptan lead dioxide
  polysulfideH2O
• H2O comes out as a by-product so it is sensitive
  to moisture temperature.
• The reaction is sensitive to temperature and
  moisture so increase in any will accelerate the
  setting (shorter setting time).
• Also sensitive to correct mixing ratio

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The red or the brown is the catalyst but the
white is the base
Mixed together to get a homologous color
Load the material into a tray, we use special
trays by taking a primary impression for the pt
with alginate then we make the special tray with
acrylic material then we take the impression by
polysulfide.
Manipulation and dispensing
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Uses

• Crown and bridge impressions as when we are
  making crowns or bridges we need to prepare the
  teeth so that the crown or the bridge will fit on
  the top, and this preparation need to be very
  accurate as we are dealing with small structure
  and we need an accurate material.
• Partial and complete denture impressions
• Clinical considerations when used
• Used with custom trays (special for special pt)
• Allow 2mm thickness
• Use tray adhesive (like spray to prevent the
  separation of the impression from the tray)
• Dry field (as it is a hydrophobic material)

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Properties of clinical interest

• Setting time 8-14 minutes this is one of the
  problem that we dont use it very much as it is
  annoying for the pt to put the impression inside
  the pt mouth for more than 10 min.
• Higher tear strength than hydrocolloids
• Accuracy improves if impression is poured within
  30 minutes as water can be produced changing its
  shape.
• very unpleasant taste and odor this is another
  reason why we dont use if often.
• Messy (orange solvent to remove stains)
• Can be irritant to oral mucosa
• For all these reasons, Polysulfides have been
  largely replaced by other rubber materials

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Silicon rubbersilicon condensation or addition
refers to the type of the polymerization, as
small monomers polymerized and linked together by
rxn called free radical rxn- in addition rxn at
the end there is no by product no alcohol no
water by product- so more accurate.In
condensation rxn it is associated with the
production of water or alcohol as a by product.
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Classification according to polymerization rxn
Condensation silicon
Addition silicon
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Condensation silicon

• Developed as alternative to Polysulfides
• Has more desirable qualities in comparison
• Easy mix easy to use
• Better taste and odorless so much more used
  friendly much comfortable for the pt
• Shorter setting time (5-7 minutes)

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Dispensing Composition

• Two pastes, base and catalyst.
• Comes as different viscosities light, medium, or
  heavy viscosity
• Base dimethylsiloxane filler -to make it
  stronger- (silica)
• Catalyst suspension of stannous octoate alkyl
  silicate

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Setting rxn

• Condensation reaction that produces ethyl alcohol
  as by product. The alcohol evaporates which
  causes dimensional instability change its shape.
• The material continues to contract with time, so
  needs to be poured within minutes so we maintain
  the shape with the accuracy that we want as we
  prevent alcohol evaporation prevent shrinking
  of the material (deformation).

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Addition silicon (PVS)

• Desirable clinical qualities
• Dimensional stability as there is no by product
• Accuracy
• Clean
• Easy to mix
• No foul odor or taste
• However, they are among the most expensive,
  otherwise it gives us excellent results.

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Dispensing composition

• Light, regular and heavy viscosities and also
  putty (the wash or the light material will be
  supported by the putty material as wash material
  shape can be changed easily)
• Dispensed as cartridge with 2 chambers (pastes),
  or two putty- system
• Base low-molecular-weight silicon with vinyl
  groups (paste system), or low-molecular-weight
  silicon with silane hydrogens (putty) silica
  filler
• Catalyst chloroplatinic acid

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Setting rxn

• Polymerization rxn of chain lengthening and
  cross-linking with reactive vinyl groups,
  producing a stable silicon rubber.
• No ethyl-alcohol by product
• Some addition silicons produce hydrogen as by
  product, manufacturers incorporated palladium
  powder (to avoid any dimensional changes that
  might happen you need to either immediately pour
  the material or by adding this powder) that
  absorbs hydrogen
• setting time 3-7 minutes very acceptable to the
  pt

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Impression making techniques

• Putty/wash technique
• One step they put the putty material in the tray
  immediately again they put the wash material on
  top of it take the impression take the
  impression in one step (used a lot when we do
  crowns or bridges)
• Two step firstly take impression with the putty,
  they take it out and remove some of it to make a
  space for the wash material, they put the wash
  re-place the tray again.
• Pros and cons for each technique and possible
  solution

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Clinical use

• Crown and bridge work as it is very accurate and
  easy to use.
• Bite registration needed when you are
  constructing the impression like crown or bridge,
  you need to know how the teeth occlude together
  relationship between the upper lower teeth- so
  the restoration will not be too high (rapid
  setting 1-2 minutes)
• but usually in our clinics we gonna use wax
  (wax shaped as an arch and placed in pt mouth)
• Indirect composite inlays it is the opposite of
  the mechanical retention the upper part smaller
  than the lower-but in inlays the upper part
  should be wider as the filling is not gonna be
  directly placed, it is going to be constructed
  outside on a model or cast then it will be
  placed in pt mouth so it is called indirect.
• You drill a cavity, take an impression by
  alginate, usually the record material not gypsum
  but in silicon, so we have a model made of
  silicon material. One of the teeth on the model
  you will find the cavity where you place the
  composite allow it to set, take it out put it
  in pt mouth.
• (silicon die technique)tv

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Polyethers

• Also used for crown and bridge work since they
  are very accurate and also more hydrophilic than
  other silicons
• Another different is that this material is more
  rigid so if we have undercuts, it is not
  recommended that we use it (if we have undercuts
  inside our oral cavity we need something flexible
  so that we can take it out easily, but if we use
  a rigid material we will not be able to take the
  tray out. as the material will stuck inside.

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Dispensing composition

• it is available in a form of 2 cartilages as we
  use a gun to press the material out (the material
  will flow out when we start pushing and go out to
  be mixed in the tube come out mechanically
  mixed so much accurate than human mixing) or in
  the form of 2 base system that should be mixed
  together.
• Dispensing same as other rubber materials (2
  tubes)
• In addition its supplied in pouches of base and
  catalyst placed in mechanical mixer (machine uses
  the base the catalyst as when we turn it on the
  material comes out you can immediately place it
  in the tray also for polyether)
• Composition
• Base low- molecular-weight polyether with cation
  reactive group
• Catalyst aromatic sulfonic acid
• clinical tip mix well to avoid irritation from
  unmixed catalyst.

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Properties

• Stiff, difficult to remove from undercuts
• Short working and setting times
• Setting time 3-5 minutes
• Sensitive to moisture and temperature
• More hydrophilic (must not be stored in water or
  disinfectant)
• very accurate you can leave it for few days re
  use it as the impression will not be affected
  will stay ok very accurate.

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Inelastic impression materials

• Impression compound
• Based on resin when you heat It, it becomes soft
  and once you place it in the tray and in the pt
  mouth at 37 degree the material will harden and
  we can soften it again a re-use it.
• softens with heat, hardens in the mouth.
• Cakes (sheets) and sticks
• Clinical uses
• Sheets
• Primary impression in metal trays as it is not
  very accurate should be poured immediately to
  prevent dimensional changes
• To make custom trays
• Sticks are used for border molding

Green stick
Metallic tray as we need it to be rigid
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Composition properties

• Thermoplastic (heated at high T cools at lower
  T) resin and waxes
• Fillers to reduce flow
• Plasticizers (make it less rigid allows a little
  flexibility)
• Organic acids or oils
• Pigments
• Properties
• Softened at 60C, remains plastic (so there is
  some flexibility and we can shaped it in the oral
  cavity) at 45C, firm at 37C
• Heated in water not by flame
• Should be poured ASAP to avoid distortion
• Used in edentulous pt when we are making complete
  dentures for pt without teeth, so we dont use it
  if there are teeth in the oral cavity.

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Other impression materials

• Impression plaster seldom used
• Composed of plaster gypsum (Ca hemihydrae)
• Used for primary impression (high PL)
• Scored with a knife in the mouth then removed and
  reassembled in the lab (distortion?)
• Wash impression
• Easy to use
• Inexpensive
• Very messy
• Give dry sensation to the mouth.
• As it is rigid it cant be removed easily from the
  mouth, you may need to break it into pieces take
  it out then stick the pieces together (might
  lead to inaccuracy).

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ZNO eugenol

• Secondary impression for complete dentures, or
  wash impression (mucostatic impression), its
  viscosity is low so it can easily flow we use
  it to edentulous pt.
• 2 tube paste system, different colors
• Zinc oxide (80) and fillers, eugenol (15) with
  oils, resin, fillers. In addition to chemical
  accelerator (zinc acetate), to shorten the
  setting time.
• Dispensed in 2 equal lengths and mixed to
  homogenous color forming zinc eugenolate
• Initial set3-6 minutes, final set10 minutes
• To accelerate (shorten the setting time) the
  setting, a drop of water or zinc acetate is
  added.

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Properties

• Brittle (not flexible), so not suitable for areas
  with undercut
• Flows readily
• Accurate
• Eugenol can be irritant (burning sensation)
• Once set, dimensionally stable

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Impression wax

• Clinical uses
• Preliminary impression for edentulous patients
• Bite registration
• Baseplate wax used to be used for provisional
  crown and bridge work
• Melted to correct voids in gypsum casts

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Disinfection of impressions

• After you take the impression you will give the
  impression to the technician so what if the pt
  has hepatitis B or AIDs or Flu. You always have
  to expect that your pt has a disease.
• The disinfectant should be compatible with the
  impression materials.
• After taking the impression, it should be souped
  into a solution (some distortion as material
  could desorbs the solution cause dimensional
  changes. ) or rinsed with water (to remove the
  blood or debris), excess water shaken off, and
  disinfectant sprayed (2 disadvantages 1- the
  spray may not reach every single part of the
  impression 2- the spray may get into your eyes or
  nose) or impression immersed in disinfectant
• Protective gloves should be worn
• Rinse after disinfection is complete

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Disinfecting casts

• Maybe necessary if impression was not properly
  disinfected, or if immersion of impression
  adversely affects the impression
• If the impression is not disinfected or comes
  from a source you are not sure about the dr.
  disinfection, Casts should be set and stored for
  24 hours before disinfection.
• Solution used Na hypochlorite, iodophors.

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Sterilizing trays

• Trays should be properly sterilized before use
• Disposable trays are recommended if appropriate
• Sterilization can be achieved by heated steam,
  dry heat, chemical vapors

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Reference dental materials, clinical
applications for dental assistants and dental
hygienists
Just want to say to every one take care about
your business as it is too hard to follow all the
mistakes and to know every thing about every one,
special if you are full of mistakes So try to
work on yourself Hanan Al-Khatib