What instruments are needed for hand mixing?
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A clean rubber bowl, a clean plaster spatula, a clean plaster knife, and an automatic vibrator.
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What instruments are needed for hand mixing?
A clean rubber bowl, a clean plaster spatula, a clean plaster knife, and an automatic vibrator.
What is flasking in the context of dental models?
Flasking is the process of enclosing a model in investment material to create a mold.
What is the primary application of Thermo-plastic Vacuum Adapted Resin?
It is used in dental applications, particularly for creating dental prosthetics.
What are the two main categories of impression trays?
Stock trays and custom trays.
How does laser powder-bed fusion work?
It adds successive layers of metal powder and uses a laser to melt each layer into place.
What process is used to adapt Thermo-plastic Vacuum Adapted Resin?
It is adapted using a vacuum process.
What does investment refer to in the context of gypsum applications?
It refers to the process of encasing a dental model for casting.
What is the importance of pouring impressions immediately?
To prevent shrinkage and ensure accuracy.
What characteristics do different dental materials have?
Resistance to discoloration and deterioration, and a beautiful finish.
What is the most common material used for preliminary impressions?
Alginate.
What is the importance of the W/P ratio in the procedure?
It determines the required amount of cast material and distilled water for mixing.
What is the result of heating Gypsum under pressure?
The powder particles are regular and less porous (α hemihydrate, or dental stone).
What is one application of gypsum in the dental field?
Impression material.
What are the types of stock trays?
Metallic (sterilizable and reusable) and disposable (for convenience).
What types of stock trays are available for dentulous and edentulous patients?
Dentulous tray and edentulous tray.
What are the two parts of the cast composed of?
Anatomical part and base portion.
What is recommended for the surface of elastomer impressions like silicone rubber or poly-sulphide?
Coat with a wetting agent such as Aurofilm to lower surface tension.
What material is commonly used to fabricate custom trays?
Self-cured Poly Methyl Methacrylate (PMMA).
What type of movement does a Simple Hinge Articulator allow?
Only hinge rotational movement; opening and closing.
What additional motions does an Average Value Articulator permit?
Horizontal as well as vertical motion.
What is the purpose of a final or master impression?
To get a detailed negative imprint of the arch for a master or working model.
What is the W/P ratio for Type I Impression Plaster?
100g : 60ml.
What is the first step in the thermo-plastic vacuum adapted resin procedure?
Outline the periphery.
Name a disinfectant commonly used in infection control.
Sodium hypochlorite, Iodophors, or Chlorine dioxide.
What is a plaster index used for in dentistry?
It is used for making plaster indices.
What is the purpose of mounting models in an articulator?
To simulate jaw movements and occlusion.
What thickness of cast material is prepared on a flat plate during the Two Stages Technique?
2 to 3 cm thick.
What types of records are required for centric relation?
Centric relation record, protrusive records, and lateral record.
What methods can be used for fixing a model to an articulator?
Plaster, magnet, retentive pin, screw mounting plate, and special shape of mounting plaster.
What should be done if the alginate impression dried before cast separation?
Soak in water for 5 minutes.
How are materials chosen for dental milling?
According to their purpose.
What type of wire is recommended for reinforcing the shellac tray?
At least 1.5mm stainless steel round wire.
What does a Semi-adjustable Articulator simulate?
Condylar pathway using average or mechanical equivalents.
What is the water to powder ratio for Impression Plaster (Plaster of Paris)?
60 ml of water to 100 g of powder.
What is the purpose of heating the thermo-plastic resin sheet?
To soften the sheet gradually.
What is the purpose of an impression tray?
To transport the impression material to the mouth, confine the material to the surfaces being recorded, and control and support the impression material during taking and setting.
What should be done to the unsupported area of a Zinc-Oxide Eugenol impression?
It should be kept away from the heat source.
How should alginate impressions be covered before pouring?
With wet napkins to avoid shrinkage.
What are the different arch types for impression trays?
Full arch and partial arch (quarter, anterior, posterior).
What type of record is used for a non-adjustable articulator?
1 or 2 records.
What is flasking in dental applications?
It is the process of enclosing a model in a flask for processing.
What should be ensured before separating the cast from the impression?
No part of the tray should be connected to the gypsum.
What is a dental articulator?
A mechanical device that represents the temporomandibular joint (TMJ) and jaw members, allowing maxillary and mandibular casts to be attached to simulate upper and lower jaw movements.
What method is used to mix the cast material?
Mechanical mixing method.
What is a characteristic of the Average Value Articulator regarding TMJ?
It does not orient the motion of TMJ.
How should the cast material be mixed?
By mechanical mixing to avoid air bubbles.
What is a preliminary or study model?
A model obtained by pouring the preliminary impression.
What is the W/P ratio for Type II Model Plaster?
100g : 30ml.
What is done after blocking out the undercut?
Duplicate the cast.
What is the disadvantage of the Single Stage Technique?
The cast material might not stick to the inner surface of the inverted impression, affecting dimensional accuracy.
How should an impression be preserved to maintain its integrity?
It should be suspended in a tray holder or supported in a tray stand, avoiding unnecessary touching or displacing.
What are the two available sets for Model Plaster?
Fast and regular sets.
Why is a color pigment added to Impression Plaster?
To distinguish it from cast/model materials.
What system does a dental milling machine use?
A CAD/CAM system.
What is the first step in the boxing technique for crown and bridge?
Use beading wax to stick around the periphery for sufficient depth of sulcus.
What is the purpose of wrapping a wax strip around the beading wax?
To form a box for pouring the cast material.
How should the cast material and distilled water be measured?
According to the recommended water-to-powder (W/P) ratio.
What are spaced perforated trays used for?
They allow for the impression material to flow through the perforations.
What does the ability to adjust distances between the condyles in a fully-adjustable articulator allow?
It allows for full simulation of the condylar structures.
What is a cast or model in dentistry?
The positive likeness or duplication of the patient’s oral situation, such as the arch or group of teeth.
How does gypsum material compare in terms of ease of use?
Gypsum materials are known for their ease of use.
What characterizes a non-adjustable articulator?
It can accept a single static registration, has no mandibular movement except opening and closing, and is commonly called a 'Hinge Articulator'.
What is the first step in preparing the cast for assembly?
Trim the cast to a suitable size to facilitate assembly and future flasking.
What are the two types of Semi-adjustable Articulators?
Arcon and Non-Arcon.
What are the two common types of impression materials?
Rigid impression materials and elastic impression materials.
What is the first step in preparing models for mounting on a Fixed Condylar Path Articulator?
Preparation before mounting the upper cast onto the mounting platform.
What adjustment should be made for parallelism of the arms?
Adjust the screw and increase the distance if the cast is too large.
What are the components of special design for impression trays?
What is Type III gypsum material according to ADA Specification #25?
Dental Stone.
What is the purpose of placing the rubber bowl on the vibrator during hand mixing?
To remove large air bubbles from the mixture.
What should coincide with the midline of the platform during mounting?
The median suture line of the upper cast.
What is the recommended thickness for the handle of the tray?
3 - 4 mm thick.
What is the minimum thickness for the thinnest part of the cast?
At least 1 cm thick.
What type of material is Thermo-plastic Vacuum Adapted Resin?
It is a type of thermoplastic material.
What is the first step in the Two Stages Technique procedure?
Measuring materials, mixing the cast material, and pouring the impression up to the pencil mark.
What is created on the surface of the cast material in the Two Stages Technique?
Mechanical locks.
What is the disk-shaped dental material called?
A 'disc'.
Name some types of disk materials used in dental milling.
Non-metallic zirconia, ceramic, wax, PMMA (acrylic resin), titanium, and cobalt.
What is a close fitted special tray?
A type of special tray that fits closely to the patient's dental arch.
What is a disadvantage of the Two Stages Technique?
It is time-consuming.
What should be checked if bite rims are used before mounting?
Correct fitting to ensure accurate articulation.
Why should care be taken when removing the tray and impression material?
To avoid breaking teeth, particularly for single standing teeth.
What is the classification of dental articulators?
Class I: Non Adjustable, Class II: Average Value, Class III: Semi Adjustable, Class IV: Fully Adjustable.
What technique is used to pour the cast material into the impression?
Pour a small amount at one end and use a vibrator to allow it to run over the impression.
What is the purpose of duplicating a model with agar in the heat-cured acrylic procedure?
To create a working model for the tray.
What is done after packing the flask with clear denture base material?
Polymerize the resin with the recommended curing cycle.
What undesirable outcome can result from a preliminary impression?
Over extension due to excessive impression material pushing the cheek out, creating a false record of the sulcus.
What material is used to block undesirable undercut areas?
Lead bead.
What is the recommended W/P ratio for hand mixing stone powder?
Usually 300g of powder for one impression including base.
What is a benefit of gypsum materials in terms of cost?
They are inexpensive.
What is the recommended outline level for non-critical areas in tray fabrication?
Down to the gingival level.
Why is it important for special trays to cover all required oral tissues?
To provide accurate anatomical extension.
What are Type IV and Type V gypsum materials used for?
Die Stone, Low Expansion (Type IV) and Die Stone, High Expansion (Type V).
How long should the mixture be spatulated during hand mixing?
About 45 seconds.
What happens if too much water is added to the gypsum mix?
It results in a thin mix.
What is the setting time for Zinc-Oxide Eugenol paste after insertion into the mouth?
3 to 4 minutes.
What is a plaster index used for?
It is used for mounting models in an articulator.
What does the composition of investment typically include?
A mixture of various materials designed for mold-making.
What should be done to avoid drying shrinkage in irreversible hydrocolloid or agar impressions?
Wrap or cover with wet napkins.
What are custom or special trays used for?
They are specially designed and fabricated for individual patients.
What is the first step in the shellac tray procedure?
Outline the tray.
What material is recommended as a spacer when using shellac?
A mixture of plaster and pumice or wet non-asbestos casting lining material.
What features can be adjusted in a fully-adjustable articulator?
Condylar width, angle, condylar post angle, and incisive angle.
What must be cleared from the tray before removing it?
Excess stone.
What are some applications of dental articulators?
Diagnosis of occlusal relationships, diagnostic waxing, artificial teeth setting, treatment planning, and fabrication of dental appliances like dentures, crowns, and bridges.
What is an advantage of the boxing technique?
Can control the form of the cast easily and has higher density and strength.
What is required to secure silicone material onto the tray?
Adhesive/glue.
What is the time for recovery of the rubber impression material?
At least half an hour.
What are the different types of rubber impression materials based on viscosity?
Light, regular, and heavy-body.
What contributes to the strength of gypsum products?
Porosity and the shape of particles.
What should the periphery or extension of special trays be like?
Accurate.
What must be ensured regarding the impression material on the tray?
It must be firmly secured.
What is the purpose of providing suitable space for impression material in special trays?
To achieve the best result in capturing details.
What feature allows for easy adjustments to special trays?
Easy chair-side modification.
What is the periphery extension coverage for edentulous patients?
Normally down to the deepest part of the sulcus, 1mm above the sulcus.
What is done after the resin sheet is adapted to the model?
Trim the excess material and add S.S. wire or acrylic handle.
What temperature range does impression compound soften in a water bath?
From 55 to 70 °C.
How do special trays minimize tissue distortion?
By providing a stable and accurate impression environment.
What technological advancement is mentioned in relation to trays and articulators?
3D Printed Trays & Articulator.
Why is impression compound not suitable for detailed impressions?
It cannot copy the detail of oral tissue and is affected by heat.
What is the length of the handle for partial cases?
25mm long.
How can you separate impression plaster from the cast?
By tapping gently on the impression plaster surface with an instrument like Lecorn.
What is the next step after removing the mounted upper cast from the articulator?
Accurately and firmly articulate it with the lower cast.
What should be done after the plaster sets?
Trim the excess plaster with a Stanley knife or model trimmer, then smoothen with sandpaper.
What is a recommended method for infection control during mixing?
Spray rather than immerse.
How is gypsum used in constructing dental models?
It is used to create models and dies.
What are the types of dental articulators mentioned?
Fully adjustable, semi-adjustable, and non-adjustable.
What shape is the dental material cut into?
The shape of a tooth.
Why is shellac seldom used for making special trays?
It is brittle, thermo-plastic, dimensionally unstable, and can clog burs during adjustment.
What is the main characteristic of the Arcon type articulator?
The condylar tracks are on the upper arm and the condylar head is on the lower arm, resembling the TMJ.
How does the Non-Arcon type articulator differ from the Arcon type?
In the Non-Arcon type, the condylar tracks are on the lower member and the condylar heads are on the upper arm, reversing the TMJ.
How long should the separating medium be immersed in water?
15 minutes.
What are the common features of dental articulators?
They consist of upper and lower arms to which maxillary and mandibular casts are attached, with a movable joint mechanism representing the temporomandibular joint.
What is a two-part tray?
A sectional tray that consists of two parts for easier handling.
How is the rubber impression material supplied?
In pastes (Base & Catalyst).
What is a disadvantage of the boxing technique?
It is time-consuming to make the 'box'.
What types of relations can a Semi-adjustable Articulator accept?
Both centric and eccentric relation.
Why is gypsum considered inert?
Because it is harmless.
How does the strength of Model Plaster compare to Dental Stone?
Model Plaster produces a weak cast compared to Dental Stone.
What is a requirement for an accurate impression?
A rigid tray covering all required surface details.
What are rigid impression materials used for?
They are used for impressions of areas without undercuts, such as edentulous cases.
What is the purpose of the stopper in tray fabrication?
To keep the tray at an optimum distance from the oral tissue for the best properties of impression materials.
What is a key characteristic of Impression Plaster regarding its stability?
It is dimensionally stable but easily broken.
What happens in over areas of an impression?
Large amount of contraction occurs.
How should the upper and lower casts be held in place?
Using sticky wax and toothpicks.
How does the water to powder ratio affect gypsum materials?
It affects setting time, working time, expansion, strength, and accuracy.
What should be applied to the upper retentive pin and arm before mounting?
Vaseline.
What is the primary use of impression compound in clinical settings?
To modify the contour and border of the tray.
What is the length of the handle for edentulous cases?
12mm long.
What tool can be used to remove the tray from impression plaster?
A plaster knife, by inserting it between the tray and impression material.
What should be marked on the mounting plaster?
Necessary data/measurements such as vertical dimension, date, and articulator number.
How long should the cast be immersed in water?
10 minutes.
What is the recommended mixing ratio used for?
To mix the tray material.
What should be marked onto the mounting plaster?
The necessary data/readings.
What is the purpose of investment in dental procedures?
It is a mixture of materials used to make a mold.
What type of 3D printer is described in the text?
Laser powder-bed fusion type.
What is a dental milling machine used for?
To process prosthetics such as fillings and crowns to replace missing teeth.
What is the best practice for pouring alginate impressions?
To pour the impression immediately.
How should the anatomical part impression be poured?
Using a vibrator.
Can the base portion be poured with or without a vibrator?
Yes, it can be poured with or without a vibrator.
What is the first step in the Single Stage Technique Procedure?
Rinse the impression with running water to remove dirt and saliva, then blow away excess water.
What is the first step in preparing for mounting on a simple hinge articulator?
Remove occlusal interference on the upper and lower casts.
What type of rubber is commonly used for master impressions?
Poly-sulfide Rubber/Silicone Rubber.
What is the purpose of a bleaching tray?
To hold bleaching agents against the teeth for whitening.
What features can be adjusted in a Semi-adjustable Articulator?
Adjustable condylar guidance and adjustable incisal guide table.
What allows gypsum materials to accurately reproduce fine detail?
Their accurate reproduction capabilities.
How much plaster is typically used for one model with a base?
Around 300g.
What is a key requirement for special trays in dentistry?
They must be dimensionally stable and rigid.
What is an advantage of the Single Stage Technique?
It is fast, making it suitable for diagnostic casts.
What is the diameter of the perforation in the trays?
About 2mm.
What happens in thin areas of an impression?
Small contraction occurs.
What should be done if there is distortion of the impression material from the tray?
Check the accuracy of the impression; questionable impressions should be discarded by the dentist.
What property of gypsum materials helps them resist wear?
Abrasion resistance.
Where should perforations not be made on the trays?
On stoppers and handles.
What should the surface of special trays be like?
Clean, smooth, and without sharp edges.
What should be done to the land area of the cast if necessary?
Trim down the land area.
What is one material used for special trays?
Self-cured Poly Methyl Methacrylate (PMMA).
What should the occlusal plane be?
Horizontal.
What is the purpose of applying a separating medium?
To prevent adhesion between the tray material and the cast.
At what angle should the handle be positioned for edentulous cases?
About 5 to 15 degrees to the vertical.
What should you do to soften impression compound?
Immerse the impression and cast into hot water.
What is hygroscopic expansion in gypsum?
It occurs when gypsum soaked during setting, causing water to fill pores and increase volume.
How does increasing the water-to-powder ratio affect setting time?
It retards setting, resulting in a weaker and inaccurate model.
What is the recommended method for mixing gypsum to avoid air bubbles?
Mixing in one direction.
What can act as retarders in the setting reaction of gypsum?
Blood, saliva, and alginate.
What is the purpose of the laser in laser powder-bed fusion?
To melt each layer of metal powder into place on the part being created.
How many records are needed for a fully adjustable articulator?
Five records.
What should be done if the models are too dry before merging with the base cast material?
Soak them in water.
What is done after inverting the impression in the Two Stages Technique?
Put it onto the cast material on the flat plate and trim the excess with a plaster knife.
What is the advantage of the Two Stages Technique compared to the single stage technique?
Higher density and strength, resulting in more accuracy.
What should be drawn around the periphery of the tray?
A predict line using an indelible pencil, about 3mm above the periphery.
What is Type I gypsum material according to ADA Specification #25?
Impression Plaster.
What technique is used to pour the mixed cast material into the impression?
Use a vibrator to allow the cast material to run over the impression without trapping air bubbles.
What is the first step in the heat-cured acrylic tray procedure?
Outline the periphery.
What is a spaced non-perforated tray?
A tray that has space for impression material but no perforations.
What is a master/working model used for?
It is used to fabricate dental appliances and is obtained from the impression using a custom tray.
What is a preliminary impression?
An impression using a stock tray to get the first negative imprint of the arch for a study model.
Where is the duplicated cast placed during the procedure?
On the center of the pressure forming machine (e.g., Dufomat).
What are some trimming considerations in dental applications?
Proportion of base to anatomical part, parallelism, use of bite registration, outer border of cast, and shaping of anterior part of upper and lower arches.
How do special trays enhance the retention of impression materials?
By improving the grip of the impression material onto the tray.
Where should the center line be located when mounting the upper cast?
On the incisor mark on the platform or the incisal pin of the articulator should point to the center line.
What is the first step in the hand mixing procedure?
Measure the stone powder and distilled water according to the recommended W/P ratio.
How is the softened resin sheet applied to the model?
By pressure and vacuum adaptation.
What must be added to separate the impression material from the stone?
A separating medium, such as water glass.
What is the significance of good color contrast in gypsum materials?
It aids in visual differentiation and detail recognition.
What is important about the water/powder ratio when mixing mounting plaster?
It must be correct.
What instruments are needed for mechanical mixing?
A clean plaster spatula, a mechanical mixing vessel/jar, a mechanical vibrator, and a vacuum mixer.
What is the initial setting time for gypsum?
8 to 10 minutes.
What is a property of special tray materials regarding manipulation?
They should allow easy laboratory manipulation.
What technique is used to remove air bubbles during mechanical mixing?
Using a vacuum mixer.
What causes setting expansion in gypsum?
Crystal growth during setting.
What is a seldom-used material for special trays?
Shellac.
How can you remove the tray with compound from the cast?
By lifting the handle of the tray.
What is the layering requirement for a partial perforated tray?
One layer of sheet wax on teeth (5mm away from gingival) and one layer covering both teeth and oral tissue.
What is the recommended mixing time for plaster using a vacuum mixer?
45 seconds to 1 minute.
What is one key property of gypsum materials?
Dimensional accuracy.
What is Type II gypsum material used for?
Diagnostic cast, mounting of stone cast, art portion of working cast, flasking procedure for full acrylic dentures.
What is used to block out the undercut in the thermo-plastic resin procedure?
Wax.
What is done with the remaining cast material after filling the impression?
Place it onto a flat plate with a height of 2 to 3 cm and larger area than the impression size.
What type of impression material is Impression Plaster classified as?
Mucostatic impression material.
What is one advantage of using a special tray in dental impressions?
Compatible with selected impression material.
What causes distortion in an impression?
If the tray does not fit well or if the impression material is not uniform in thickness.
What advancements in technology are mentioned for improving dental treatments?
Intra-oral scanners, digital impressions, 3D printing, and milling.
What is the separation distance between each perforation?
Around 5mm.
How do intra-oral scanners benefit dental treatments?
They provide direct information of oral tissue for milling prostheses or sending digital information to dental laboratories.
When should an impression be poured?
As soon as possible after the impression material recovers from its memory.
What is the purpose of Zinc-Oxide Eugenol (ZOE) paste?
Used for non-undercut situations such as edentulous cases, relining, or rebasing partial denture cases.
What is the first step in the Auto Polymerizing Resin procedure?
Outline the tray.
What is the periphery extension requirement for crown and bridge cases?
1-2mm below the gingival and 3-4mm in the crown/bridge area.
What is important about the Water/Powder ratio when mixing mounting plaster?
It must be correct.
What should be done a day or more ahead of tray use?
Make trays, as acrylic undergoes polymerization shrinkage for 24 hours.
How should impression plaster be stored to avoid drying shrinkage?
It should be kept in a plastic bag.
What type of resin is adapted for thermo-plastic vacuum/pressure?
Thermo-plastic Vacuum/Pressure Adapted Resin.
What are some examples of elastic impression materials?
Alginate, Silicone Rubber, Polysulphide Rubber, Elastomers.
Where is the finger press used in edentulous cases?
On the crest of the ridge near the second premolar/first molar region.
When should the cast be separated from the impression?
After 1 hour.
What should be done with excess tray material?
Cut it with scissors or a scalpel.
What happens when the water-to-powder ratio is decreased?
It shortens the setting time but makes the mix difficult to manipulate and can include bubbles.
What is a characteristic feature of Dental Stone, high strength (Type IV)?
It is often colored pink and is stronger than Type III stone.
How does the strength of different types of gypsum products rank?
Type I < Type II < Type III < Type IV.
What is used to make the spacer and block undercuts in the heat-cured acrylic procedure?
Wax.
What additives can be used to regulate the setting time of Impression Plaster?
Accelerators like potassium sulphate or retarders like borax.
What is a working cast/model?
A duplicate of the master model on which all steps in fabricating the dental appliance will be done.
What tool is used to remove surface beads that avoid normal articulation in dental applications?
Acrylic cutter.
What is the purpose of making an index on the base of the cast?
For the split cast technique.
What should be done to an impression before disinfection?
Remove saliva and dirt by rinsing under running water, then soak in disinfectant.
What is necessary for the impression materials in special trays?
They should provide correct space and uniform thickness.
What should the impression be free of to ensure accuracy?
Saliva and air bubbles.
What is the golden rule for proportioning water to powder ratio in gypsum?
Manufacturer instructions should always be followed.
What is important for securing impression materials in special trays?
Good adhesion.
How far above the sulcus should the periphery extension be for dentulous patients?
1 to 2mm above the deepest part of the sulcus.
What is the final step in the thermo-plastic vacuum adapted resin procedure?
Polish.
What should be done after applying plaster to the base of the lower cast?
Place the center line of the upper cast on the center line of the articulator.
What is water glass composed of?
Sodium oxide (Na2O) and silica (SiO2).
Name another material used for special trays.
Light-cured Acrylic Resin.
What is a desirable characteristic of special tray materials in terms of safety?
They should be non-toxic and non-irritating.
What are the three techniques for pouring casts?
Single Stage Technique, Two Stages Technique, and Boxing-In Technique.
What is the spacer requirement for an edentulous/complete tray?
One layer of sheet wax, no need to block undercut unless too severe.
What type of tray is required for Alginate impressions?
A perforated spaced tray.
What should the base of the cast be trimmed to provide?
A flat base with the stone teeth/ridge standing horizontally.
How does spatulation affect gypsum setting?
Rapid and prolonged spatulation accelerates setting and increases setting expansion.
What are accelerators and retarders in gypsum manipulation?
Chemicals added to alter gypsum solubility and setting time; accelerators speed it up, while retarders slow it down.
What distinguishes High Strength, High Expansion Dental Stone (Type V)?
It is the most costly of all gypsum materials and has the lowest W/P ratio with higher compressive strength.
What is an impression in dentistry?
A negative imprint from which a positive reproduction of the arch can be made in the form of casts/models.
What is the only relation represented by a non-adjustable articulator?
Centric occlusion.
What should be removed if they interfere with the bite?
Any beads.
What type of tray is used for master impressions with Impression Plaster?
Spaced non-perforated tray.
How does the amount of water mixed with gypsum powder affect its strength?
Higher porosity requires more water, leading to a weaker cast.
What is the process of creating a cast using gypsum?
An impression (negative replica) is poured into gypsum to make a cast (positive replica).
Name a few examples of rigid impression materials.
Impression plaster, impression compound, and zinc-oxide eugenol paste.
How should the upper cast be positioned on the mounting platform?
The upper cast must be firmly placed with the occlusal plane touching the platform.
How thick should the tray periphery be?
2 - 3 mm thick and rounded.
What is a specific design consideration for special trays?
Design for different oral situations, such as Oral and Maxillofacial Surgery (OMFS).
How is Zinc-Oxide Eugenol paste prepared?
Equal lengths of Base and Hardener are mixed on a paper pad for approximately 45 seconds.
How long should the handle of the tray be?
2 - 3 cm long.
What must be relieved in all special trays?
All frenum.
What type of tray is used with Zinc-Oxide Eugenol paste?
A close fit special tray.
What is the first step in the general procedure for making special trays?
Outline the periphery/extension of the tray.
What precautions should be taken when handling impression materials?
Keep them away from heat sources and handle with care.
How can setting expansion be decreased?
By adding accelerators like Potassium Sulphate or retarders like Borax.
What thickness should the tray material be pressed into?
2.5 mm uniform sheet.
What shape should the sheet be cut for the lower cast?
U shape.
How long do most gypsum products take to be ready for use?
30 minutes.
What is the water-to-powder (W/P) ratio for Dental Stone (Type III)?
100g: 30ml.
What is the primary use of Dental Stone, high strength (Type IV)?
Fabricating wax patterns of cast restorations (crown & bridge), implants, and precision attachments.
How should gypsum be stored to prevent setting issues?
In an airtight, dry area to avoid moisture exposure.
What should be applied to the arms for separation?
A thin layer of Vaseline.
How far should the perforation be from the border of the trays?
At least 4mm away.
What is the impact of technological advancements on dental treatments?
They make treatments more efficient, accurate, and less invasive, improving patient outcomes and technician efficiency.
How long can irreversible hydrocolloid materials be stored without significant distortion?
Up to 1 hour in a zip-lock plastic bag.
What are the normal dimensions of the handle for trays?
12mm wide, 4mm thick.
What design features should special trays have?
Suitable handle and special designs in correct position and shape.
What is the first step in the mechanical mixing procedure?
Measure the stone powder and water.
What is the final setting time for gypsum?
Reached when the materials can be safely handled and the exothermic reaction is over.
What should be ensured when pressing the upper arm onto the plaster?
Sufficient plaster should cover the locking pin.
What should be applied to the cast and spacer before preparing the tray material?
A separating medium.
What is the final step in the tray-making procedure?
Final polishing and cleansing of the tray.
When is the gypsum material considered ready?
When compressive strength reaches 80% of the strength attained after 1 hour.
What is Dental Stone (Type III) primarily used for?
Making full or partial denture models, orthodontic models, and flasking procedures for partial acrylic dentures.
How wide should the sulcus area be in relation to its height?
Double the height of the sulcus.
What must be applied to the surface of impression plaster before pouring stone?
A separating material such as water glass.
How can you disengage impression plaster from the cast?
Immerse the impression with cast into hot water to swell the starch.
What should be done with the plaster before lowering the upper arm?
Place a small amount of plaster onto the base of the upper cast.
What is a significant drawback of impression compound regarding heat?
It is brittle and should be kept away from heat sources.
What characterizes a close fitted tray?
It has no spacer and needs to block undercuts.
How should the handle be positioned for partial cases?
Nearly extend horizontally or with a bit upward.
What is the spacer requirement for a spaced non-perforated tray?
Two layers of sheet wax.
What is the purpose of wetting the model before trimming?
To make trimming easier.
What is the purpose of the light curing machine?
To polymerize the tray material.
What is the W/P ratio for Dental Stone, high strength (Type IV)?
100g: (specific amount not provided).
What is the primary application of Plaster (Type II)?
Diagnostic models, mounting, and flasking.
What is applied to the cast according to the impression material used?
Suitable layers of spacer.
What is the purpose of the spacer in special trays?
To provide room for impression material and determine tissue displacement due to pressure.
What are the properties of elastic impression materials?
They show flexibility and elastic properties when set, suitable for taking impressions with undercut areas.
What is a cost-related requirement for special tray materials?
They should be inexpensive.
What is the recommended water to powder ratio for Alginate?
Usually 1:1 as recommended by the manufacturer.
What is the recommended action if you have difficulty removing alginate from the cast?
Cut away the alginate that came out from the perforation, then section and remove it.
How do you soften zinc-oxide eugenol for removal?
Immerse the impression and cast into hot water.
How does the strength of Dental Stone (Type III) compare to plaster?
It is stronger than plaster.
Why is higher expansion needed in Type V dental stone?
To compensate for the solidification contraction of some alloys used as base metals for dental casting.
What is the purpose of the finger press during impression taking?
For resting fingers and even the impression material.
What is the layering requirement for a conservation/partial non-perforated tray?
Two layers of sheet wax covering teeth and all other tissues, 1-2mm away from gingival and 3-4mm for crown and bridge area.
What is added to the tray for handling?
The handle and finger press.
What is done to finalize the shape of the tray?
Adapt the sheet material onto the cast and mold the shape.
What effect does increasing water temperature have on gypsum setting?
It speeds up setting and increases setting expansion, shortening the working time.
How is Alginate secured onto the inner surface of the tray?
Glue or adhesive is applied.
What instruments are used for hand mixing gypsum?
Rubber bowl and plaster spatula.
What is the recommended width for the land area of the cast?
3 to 4 mm.
Why is it important to keep relevant equipment clean when working with gypsum?
To avoid unwanted acceleration of setting due to set gypsum.
What are some examples of accelerators for gypsum?
Potassium sulfate and set gypsum (slurry water).
What is the primary application of Die Stone (Type IV & V)?
Working models for crown and bridge works.
What are the two main mixing methods mentioned in Chapter 2?
Hand Spatulation and Mechanical Spatulation.
What is Gypsum primarily used for?
It is the main composition in many forms of plaster and stone.
What is the chemical name of Gypsum?
Calcium Sulfate Hemihydrate.
What is the chemical formula for Gypsum?
CaSO4*1/2H2O.
What type of reaction occurs during the chemical properties of Gypsum?
Exothermic reaction.
What happens to Gypsum when heated at atmospheric pressure at 120°C?
The powder particles become porous and irregular (β hemihydrate, plaster).
