Denture Midterm: Gypsum Products Overview

Denture Midterm

• Gypsum products are calcium sulfate dihydrate (CaSO₄⋅2H₂O)

Types of Gypsum Products

• Type 1 (Impression Plaster): Used for taking impressions, crucial for its rigidity and non-undercut design. It is used as a luting agent and requires heating to release three water molecules, transforming into calcium sulfate hemihydrate (CaSO₄⋅½H₂O), a process which is exothermic (releases heat). Water is driven off as steam, forming beta hemihydrate.

• Type 2 (Model Plaster): Used for preliminary casts, requiring rough particles for structure.

• Types 3 and 4 (Dental Stone): These types of stone include modifiers to control setting time and expansion. Color is achieved through the addition of calcium chloride. A smoother crystal structure distinguishes them from plaster. These are ideal for master casts for removable prosthodontics (dentures, implants), and orthodontic applications.

• Type 5 (Die Stone): Used for creating casts and models for dentures, implants and inlays.

• C and B Models: These are specific models used in the dental industry.

• Implant Models: Special models created for implant work.

Impression Plaster Type 1

• Used to take impressions, must be free of undercuts for accurate results.

• Acts as a sealing agent in intraoral gothic arch pin tracing techniques.

• Requires a conversion of calcium sulfate dihydrate to calcium sulfate hemihydrate.

• This process is exothermic, meaning it releases heat, and results in a steam release during the conversion.

Dental Stone

• Dental stone types 3 and 4 include modifiers to adjust setting times and expansion.

• Color is distinguished from plaster by additives

• Dehydration in calcium chloride solutions results in smoother crystals.

• Used for master casts, fabrication of dentures, implants, and orthodontic appliances.

Dental Gypsum Type 5

• Used for die stones
• High strength
• Very fine particle size
• May include a binder additive to increase strength to withstand turbulent materials

Accelerators

• Potassium Sulfate

• Sodium Chloride (a pinch of salt)

• Warm water

Retardants

• Borax
• Sodium Citrate
• Increase water
• Food (Sodium Chloride)

Impression Materials

• Alginate: A preliminary impression material.
• Polyvinyl siloxane (PVS): A final impression material.
• Bite registration: Impression material for recording the bite.

Handling Alginate

• Disinfect impressions
• Wrap impressions in moist paper towel

Bite Registration

• Special material: Used for registering vertical dimensions.
• Extremely rigid and known as "blue mousse".
• Used by clinicians to record patients' vertical dimensions for denture fabrication.

Terminology (Edentulous Landmarks)

• Maxillary
• Residual Ridge (Alveolar Ridge) - area of the upper jaw where teeth were
• Mid Palatine Raphe (Midline) - line from incisive papilla to bisect the palatine fovea.
• Incisive Papilla - a small bump at the anterior of the ridge.
• Rugae - a bumpy area on the palate.
• Maxillary Tuberosity - a rounded dome of bone.
• Hamular Notch - a groove across the posterior of the maxilla, distal to the tuberosity
• Palatine Fovea - two depressions on either side of the raphe
• Frenum - muscle attachments (ridge to facial tissue and buccal/labial)

Sulcus

• Deepest line of a groove situated on the buccal and labial areas.

Posterior Palatal Seal Area (Vibrating Line)

• Junction of the hard and soft palate, where the maxillary denture ends

Mandibular

• Frenum

• Ridge attached to the lingual and labial areas

Retromolar Pads

• Pear or triangular shapes on the posterior of the ridge.

Buccal Shelf

• Almost flat area located buccally from the ridge.

Retromylohyoid Ridge

• Irregular bony ridge on the mandibular lingual surface.

Setting Up Technique

• Arranging artificial teeth within the arch.
• Wax-up simulating tissue and palatal areas.
• Employing occlusal rims for reference.
• Midline establishment using opposing arches.

Canine Line

• Fabricated through occlusal rims.
• Provides guidance for tooth shade and selection.

Mould Selections

• Size and shape of teeth.

• Overjet and overbite

• Axis of teeth

• Length of teeth

Other Important Details

• Setting expansion - Between 0.1%–0.3%
• If underwater, significant expansion may occur (hygroscopic expansion)
• Preliminary impressions for stock trays (Preliminary models)
• Final impressions for custom trays (Final models)
• First premolars, then second, then first molars
• Long axis placement is perpendicular to the plane of occlusion.
• Cusp placement in proper fossae (concavities).
• Mesial buccal cusps of the first molar are in the buccal groove of the lower 6, and second molar are in the buccal groove of the lower 7.
• Steps for denture fabrication: de-articulate, invest, wax elimination, packing, polymerization, de-flask, trim, polish, deliver.

Loss of Tooth Cause

• Mesial drift
• Bone resorption of alveolar ridge.
• Resorption is immediate but slows to become gradual.
• Shrinking and changes in jaw structure.
• Maxilla and mandible shapes are altered.
• Gum disease and pockets.
• Misalignment and overeruption of teeth
• Loss of vertical dimension.

Further Considerations

• Various measurements and procedures
• Bite registration (centric occlusion, point of contact, position of mandibular condyle)
• Vertical dimension of rest
• Ridge of acrylic, high lip lines, low lip lines, cuspid lines, the custom tray, measurements (length, width, thickness)

This quiz covers the essential types of gypsum products used in denture crafting and their specific applications. Learn about the various types, including Impression Plaster, Model Plaster, and Dental Stone, along with their chemical properties and uses in dental procedures. Ideal for students preparing for their denture midterm examination.