DEN 135- CH 47
LABORATORY MATERIALS
CHAPTER 47
Page 1: Laboratory Materials Overview
General introduction to laboratory materials relevant to dental procedures.
LEARNING OBJECTIVES LESSON 47.1: LABORATORY EQUIPMENT AND DENTAL MODELS
Key Objectives:
Pronounce, define, and spell key terms related to dental materials.
Discuss safety precautions followed in the dental laboratory.
List types of equipment found in a dental laboratory and describe their uses.
Discuss dental models, including:
The role of dental models in dentistry.
Gypsum products and their role in making dental models.
The three methods of pouring dental models.
INTRODUCTION
Definition: Procedures conducted in the dental laboratory occur away from the patient treatment area, emphasizing laboratory functions.
USES OF THE DENTAL LABORATORY
Main Functions:
Making models from preliminary impressions.
Trimming and finishing diagnostic models.
Preparing custom trays.
Polishing.
Providing provisional coverage.
Creating partial or full dentures.
Fabricating indirect restorations.
SAFETY IN THE DENTAL LABORATORY
Importance: Follow safety precautions and infection control procedures due to contamination from items brought into the laboratory.
Emphasized that exposure control is crucial, similar to patient interaction.
LABORATORY RULES
General Guidelines:
No eating, drinking, or smoking allowed in the laboratory.
Cosmetics must be kept away.
Personal protective equipment (PPE) must be worn.
Hair should be kept pulled back.
Report all accidents to the dentist immediately.
Follow manufacturer’s instructions for equipment operation.
Clean the workspace before and after each procedure.
TYPES OF SAFETY IN THE DENTAL LABORATORY
Categories of Safety:
Physical Safety: Knowledge of fire extinguisher locations and fire escape routes.
Chemical Safety: Careful handling of corrosive, toxic, and carcinogenic substances.
Biohazards: Awareness that items may harbor blood and saliva which can be infective.
DENTAL LABORATORY EQUIPMENT OVERVIEW
Page Sections Overview:
Equipment Includes:
Bulk bins for dental stone.
Lab pans.
Heat sources.
Model trimmer.
Vacuum former.
Vibrating table.
Laboratory handpiece.
Sandblaster.
Articulator.
Face bow.
Dental lathe.
Specialized spatulas and bowls.
DENTAL MODELS
Definition:
Three-dimensional reproductions of the teeth and surrounding soft tissue in a patient’s maxillary and mandibular arches, also known as study casts.
USES OF DENTAL MODELS
Applications:
Diagnose fixed or removable prosthetic devices.
Diagnose orthodontic treatment needs.
Provide visual presentations of dental treatment.
Produce custom trays.
Create orthodontic appliances.
Fabricate provisional coverage.
Make mouth guards.
GYPSUM PRODUCTS
Role: Used extensively for making dental models; several characteristics and properties influence the selection of gypsum.
CHEMICAL PROPERTIES OF GYPSUM
Composition:
Mined mineral, primarily dihydrate form of calcium sulfate in its unrefined state.
Converted into a powdered hemihydrate for use in dental models.
SETTING REACTIONS OF GYPSUM
Process:
Mixing gypsum powder with water results in hemihydrate crystals dissolving to form nucleation clusters.
As crystals grow during setting, they intermesh, creating a solid mass.
PHYSICAL FORMS OF GYPSUM
Types of Gypsum Products: Five forms typically used in pouring study models:
Impression Plaster (Type I)
Model Plaster (Type II)
Dental Stone (Type III)
Die Stone (Type IV)
High Strength Stone (Type V)
Differences arise in size, shape, and porosity of hemihydrate crystals.
IMPRESSION PLASTER (TYPE I) AND MODEL PLASTER (TYPE II)
Description:
Commonly referred to as plaster of Paris, white in color.
Used for preliminary impression casts, producing diagnostic models.
Characterized by irregular shapes and high porosity, requiring a larger amount of water for mixing (weakest of study model forms).
DENTAL STONE (TYPE III)
Characteristics:
Typically yellow; provides more durability when required.
Crystals are uniform and less porous than plaster, resulting in stronger, denser models than those made from plaster.
DIE STONE (TYPE IV)
Properties:
Also known as densite or improved dental stone; strong, hard, and dimensionally accurate.
Ideal for creating dies for wax patterns in crown and bridge fabrication.
HIGH-STRENGTH STONE (TYPE V)
Attributes:
Strongest form; minimum expansion; smooth, dense crystals.
Requires the least water for mixing; used with alloys that exhibit more casting shrinkage.
Not recommended for inlays and onlays due to tight casting fit.
RECOMMENDED POWDER/WATER RATIOS FOR GYPSUM PRODUCTS
Significance: Ratio affects setting time and strength.
Model Plaster (100g): 45-50 mL water.
Dental Stone (100g): 30-32 mL water.
Die Stone (100g): 19-24 mL water.
POWDER-TO-WATER RATIO
Effects of Ratios:
Too little water leads to difficult mixing and shorter working time.
Excess water results in a thin mix that sets slower and results in weaker models.
Measurement methods:
Water measured by volume; powder measured by weight.
POURING DENTAL MODELS (SLIDE 1 OF 2)
Model Components:
Anatomic portion: emerges from the alginate impression.
Art portion: forms the base of the cast.
Pouring Methods:
Double-pour method.
Box-and-pour method.
Inverted-pour method.
POURING DENTAL MODELS (SLIDE 2 OF 2)
Detailed Methods:
Double-pour method: Anatomic portion is poured first, followed by an art portion.
Box-and-pour method: Impression enclosed in box and poured as a single unit.
Inverted-pour method: Large batch mixed and both portions poured simultaneously.
TRIMMING AND FINISHING DENTAL MODELS
Professional Appearance: Required for case presentation or patient records; involves trimming models to geometric standards.
Articulation: Wax bite registration used for articulating casts during trimming.
ANATOMIC AND ART PORTIONS
Distribution:
Anatomic portion includes teeth, oral mucosa, muscle attachments (two-thirds of cast).
Art portion forms the base, making up one-third of the overall cast.
POLISHING A PLASTER MODEL
Method:
Slurry of gypsum mixed to fill voids.
Model soaked in soapy solution for 24 hours, dried, then polished either by cloth or gloss spray.
LEARNING OBJECTIVES LESSON 47.2: CUSTOM IMPRESSION TRAYS AND DENTAL WAXES
Objectives:
Describe the three types of custom impression trays and their uses.
Identify the types of dental waxes and describe their dental applications.
CRITERIA FOR CREATING CUSTOM IMPRESSION TRAYS
Ensure the Tray:
Sufficiently rigid and securely fitting the arch.
Adapted well for edentulous or partially edentulous arches.
Maintains even distribution of impression material.
Maxillary tray covers teeth and hard palate; extends slightly beyond gingival margin.
Mandibular tray covers teeth and extends beyond the gingival margin.
GUIDELINES AND TERMINOLOGY FOR CREATING A CUSTOM IMPRESSION TRAY
Key Elements:
Undercuts: Fill with wax or molding material (causes: air bubbles, shape of the arch, carious lesions, etc.).
Outlining the tray: Designates the impression area; outlines should extend over the attached gingiva to 2-3 mm beyond the last tooth.
Spacer: Creates room for impression material.
Spacer stops: Allow adequate impression material around preparations.
Separating Medium: Aids in easy removal of the completed tray from the cast.
Handle: Enhances placement/removal ease; positioned near the midline and parallel to occlusal surfaces.
Spacer Removal: Post-formation, remove wigs and clean the tissue side of the tray.
FINISHING
Attention to Detail:
Rough inner surfaces may not need smoothing but edges must be softened to prevent injury to oral tissues.
Use laboratory knife or lathe as needed.