Mechanical Properties Prof. Dr. Manal A. El-Ebiary Hello Mechanical Properties Prof. Dr. Manal A. El-Ebiary

Prof. Dr. Manal A. El Ebiary Dental Bio- Materials Department Faculty of Dentistry Tanta & MUST Universities

Elastic Impression Materials Aqueous elastic impression materials (Hydrocolloids) Non-aqueous elastic impression materials (rubber bases)

Elastic Impression Materials

Aqueous Hydrocolloid impression Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

( change in temperature) Hydrocolloid Reversible Agar ( change in temperature) Irreversible Alginate (Chemical reaction) Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Suspension Solution Colloid Hydro- colloid Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloids Solvent and Solute Colloids Solution single phase, which means a homogenous mixture, where the solute exists as small molecules or ions in the solvent. Emulsion heterogeneous two-phase system, a dispersed phase of particles of at least sufficient size to be seen microscopically, dispersed in a medium. Colloids

HYDROCOLLOIDS Colloids between these two extremes. heterogeneous two-phase system, like suspension particle size of the dispersed phase is smaller. hydrocolloids when the dispersion medium is water. Colloids may exist in the sol and gel state.

sol = viscous liquid sol → gel (agglomeration of the molecules of dispersed phase, to form fibrils or chains of molecule), in a network pattern, called brush heap structure. Agglomeration of the molecules of the dispersed phase to form chains of molecules in a network pattern,

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Brush heap Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Sol Gel 1- Reduction in temperature e.g. (reversible as in agar) 2- Chemical reaction e.g. (irreversible as in alginate)

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Sol Viscous liquid Gel jelly like structure Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

General properties of hydrocolloids

1. Gel strength: The strength or toughness of a gel depends on: a. The concentration of the fibrils: The greater the concentration, the stronger the material. b. The concentration of fillers: Which are inert powders added to a gel to render it less flexible. c. In reversible gels: The lower the temperature, the stronger the gel and vice versa.

2. Dimensional changes after setting: The loss of water is termed synersis and occurs also by evaporation. The uptake of water is called imbibition synersis and imbibition of the gel should be avoided as the former causes shrinkage, and the latter results in swelling and expansion.

Storage media, such as: 2% potassium sulfate or 100% relative humidity, reduce the dimensional changes. The best results are obtained with 100% relative humidity (storage in 100% relative humidity results in minimum amount of shrinkage). Hydrocolloid impression must be poured within a short time after removal from the mouth

3. Disinfection: → Disinfection should be relatively rapid to prevent dimensional changes. Disinfectant is sprayed on the exposed surface.

The impression should not be soaked in the disinfectant The impression should not be soaked in the disinfectant. Immediately wrap the impression in a disinfectant soaked paper towel and place it in a sealed plastic bag for 10 minutes. Finally remove the wrapped impression from the bag, unwrap, rinse thoroughly, shake off the excess water and pour the model with stone.

4. Compatibility with gypsum: [Gypsum cast may be too soft]: This may be due to the presence of the water on the surface of the hydrocolloid which affects the setting and surface properties of the gypsum cast Or due to the chemical composition of some hydrocolloids which retard the setting of gypsum products.

This disadvantage can be overcome by two ways: 1- By immersing the impression in a solution containing an accelerator for the setting of gypsum products, before pouring the impression with the gypsum. 2- By incorporating a plaster hardener or accelerator in the hydrocolloid material by the manufacturer. 3- The cast should not be left too long in contact with the impression. The set stone absorbs water from the water-filled impression. The result is a chalky surface with poor details.

Reversible hydrocolloid Agar Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Application Full mouth impression Quadrate impression Duplicating material Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary It is supplied as a sealed container to prevent evaporation of water Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Composition Agar 13% it is polysaccharides from seaweeds Borax to increase gel strength and increase viscosity but it retards the setting reaction of gypsum products Potassium sulfate to counteract the retarding effect of borax Water 83% as a dispersion medium filler to control strength , viscosity , rigidity Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Manipulation Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Cooling (43C) Heating (100 C) Agar Sol Agar Gel Hysteresis Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Hysteresis The liquefaction temp. and gelation temp. are different Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Sequence during manipulation Heating in boiling water for 10 minutes to obtain fluid materials Stored at 65 C Conditioning or tempering at 46 C to cool the material to be compatible with oral tissue Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Removal of the impression by sharp snap removal to avoid inaccuracy to from viscoelastic nature of the material Pouring the impression immediately .however possible storage in 100% humidity if needed Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Properties Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Accuracy Flow :- sufficiently fluid to record fine details Dimensional stability ( Evaporation - syneresis - imbibition ) Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Elasticity :- it is a viscoelastic materials , elastic recovery 98.8% Then rapidly removal is necessary to avoid deformation or distortion Compatibility with gypsum product avoid soft surface of stone model Retention with tray :- by using perforated tray Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Mechanical properties :- agar thickness = 4:6 mm to increase tear strength Difficult technique and time consuming Cannot electroplated due to imbibition Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Irreversible hydrocolloid Alginate Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Application The most widely used materials Full mouth impression Quadrate impression Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Composition Potassium alginate or sodium alginate, To react with Ca ion to give Ca alginate gel Calcium sulfate ,to release Ca ion to react with alginate Trisodium phosphate to delay gel formation ( retarder) Filler e.g. Diatomaceous earth to strength the gel Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Setting reaction Retardation step Gelation step Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Manipulation Shack well Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Factors affecting setting time Temperature Ratio Type Mixing rate Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Slower or faster setting can be achieved, by using cooler or warmer water respectively. Reduction of the powder ratio leads to increases the setting time, but it reduces the strength and accuracy of the alginate. Type of alginate Fast setting = l: 2 min. Regular setting =2:4 min. Increase mixing time leads to decrease setting time. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Properties Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Accuracy Flow :- high flow to record fine details Dimensional stability ( Evaporation - syneresis - imbibition ) Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Compatibility with gypsum products Impression Tray Hydrocolloid impression Gypsum model Gypsum products are generally cast into an impression that could contain bacterial or viral contaminants. Impressions are disinfected but the process is not sufficiently consistent to guarantee that there is not risk to laboratory technicians. Some gypsum products contain disinfectants. Lab technicians routinely wear gloves to protect themselves from persistent bacteria such as Hepatitis C. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Impression Tray VERY FAST (SNAP) RAPID removal of an elastomeric impression material leads to the least chance for plastic deformation if the procedure involves rapid elastic deformation. Remove the impression with a SNAP. [CLICK] This creates a rapid loading rate. Remember that all polymers are very STRAIN RATE SENSITIVE. [CLICK] If the stress is applied quickly, then all the energy is stored elastically and the material will not undergo plastic deformation. This is particularly important in the region of the greatest deformations (e.g., the margins) [CLICK] Fast removal rates [CLICK] guaranteet that loads (see the blue dotted line) only generate elastic deformations. Slow removal rates [CLICK] would actually cause plastic deformation and distort the impression in critical areas. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Elasticity :- it is a viscoelastic materials , elastic recovery 97.3% Flexibility It is the most flexible of all elastic impression materials then easy removed from mouth Retention with tray :- by using perforated tray Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Mechanical properties :- thickness = 4:6 mm to increase tear strength and rapid removal increase tear strength and decrease deformation Cannot electroplated due to imbibition Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary Goodbye Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary