Infection Control & Safety
Describe two laboratory rules that reduce cross-contamination risk in the dental laboratory
No eating, drinking, or smoking in the lab; wear personal protective equipment (PPE) when working in the laboratory.
List the five types of gypsum products named in the document.
Impression Plaster (Type I), Model Plaster (Type II), Dental Stone (Type III), Die Stone (Type IV), High-Strength Stone (Type V).
Give two primary criteria a custom impression tray must meet
Must be sufficiently rigid; must fit and adapt well to the arch.
What is the purpose of a model trimmer in the dental lab?
Used to trim study models.
Name three natural or plant-derived waxes listed in the text.
Beeswax (animal), Carnauba (plant), Candelilla (plant). (Paraffin and ceresin are mineral; gum dammar and rosin are plant-derived.)
A lab tech sustains a small cut while adjusting a plaster model. According to the document, what must they do immediately?
Report all accidents to the dentist immediately.
Which gypsum type is described as strongest and requiring the least water for mixing?
High-Strength Stone (Type V).
Where should the outline of a tray extend on the cast?
Over the attached gingiva to the mucogingival junction and 2–3 mm beyond the last tooth in the quadrant.
Name two uses of the dental lathe as listed in the document.
To trim and polish custom trays, provisional coverage, dentures, and indirect restorations; attachments include abrasive grinding wheel or rag wheel.
Identify the three general classifications of dental waxes.
Pattern waxes, Processing waxes, Impression waxes.
Explain why following manufacturer’s instructions for equipment operation is listed under laboratory safety and give one example of a possible consequence if ignored.
Manufacturer instructions ensure safe, correct operation and prevent hazards (chemical exposure, mechanical injury). Ignoring them could cause equipment misuse leading to accidents or improper processing (e.g., overheating, monomer exposure).
Compare the crystal properties and resulting strength between model plaster (Type II) and dental stone (Type III).
Model plaster crystals are irregular and very porous, require more water, producing weaker models. Dental stone crystals are more uniform and less porous, producing stronger, denser casts.
Describe the purpose of a spacer and name two materials that can be used to create it
Spacer creates room in the tray for impression material. Materials: baseplate wax, folded moist paper towel, or a commercial nonstick molding material.
Match equipment to function: Vacuum Former, Vibrator, Articulator.
Vacuum Former — create custom trays (bleaching trays, mouth guards); Vibrator — remove air bubbles from dental stone; Articulator — holds maxillary and mandibular models to reproduce mandibular relation to maxilla.
Differentiate inlay wax, casting wax, and baseplate wax by primary clinical use.
Inlay wax — hard/brittle, pattern for indirect restoration; Casting wax — used for single-tooth restorations and partial denture metal portions; Baseplate wax — record occlusal rims, set denture teeth, denture wax-up.
Identify three administrative or behavioral controls from the text that complement PPE to maintain a safe dental laboratory.
Keep cosmetics away from the area; keep hair pulled back; clean the work area before and after every procedure.
Explain how powder-to-water ratio affects working time and final model strength. Include what happens with too little vs. too much water.
Too little water makes mix hard to mix with shorter working time; too much water makes it thin, longer setting time and much weaker final model. Accurate measurement is essential: water by volume, powder by weight.
Explain the function of spacer stops and how placement differs for edentulous vs. prepared-teeth impressions.
Spacer stops prevent over-seating of the tray, ensuring adequate impression material thickness. Edentulous trays require at least four stops on the crest of the alveolar ridge (first/second molar area). Trays for prepared teeth have stops placed near—but not on—the prepared teeth.
Describe the role of a facebow and articulator together in laboratory procedures.
Facebow records spatial relationship of maxilla to some cranial reference and transfers that relationship to the articulator, which then holds maxillary and mandibular models in positions that reproduce mandibular movements relative to the maxilla.
For which clinical tasks is sticky wax useful, and what property makes it suited to these tasks?
Useful in creation of wax patterns or joining acrylic resin because it becomes very tacky when heated, allowing pieces to adhere temporarily; composed of beeswax and resin.
Propose a short laboratory protocol (3–4 steps) for disinfecting a custom impression tray after finishing, consistent with the guidance in the document.
Rinse tray to remove debris; follow manufacturer’s disinfectant instructions to immerse/spray and contact for required time; rinse if required by product directions; allow to dry and store/label per clinic protocol.
For a crown/bridge die requiring dimensional accuracy, which gypsum product is recommended and why? Include any alternate name given in the document.
Die Stone (Type IV), also known as densite or improved dental stone, recommended for its strength, hardness, and dimensional accuracy for creating dies for wax pattern fabrication.
Create a stepwise summary (4–6 steps) of producing a vacuum-formed thermoplastic custom tray from cast to finishing, using terms from the text.
Outline tray margins; place spacer over outlined area and add stops by cutting holes; paint separating medium; form thermoplastic over the cast using vacuum former; remove tray, remove spacer and clean tissue side with a stiff brush after final set; smooth outer edges, rinse and disinfect per manufacturer’s instructions.
For trimming and finishing models intended for patient records, explain the anatomic:art portion proportion and why a wax bite registration is used during trimming.
Anatomic portion should be two-thirds of trimmed cast; art portion one-third. Wax bite registration is used to articulate casts accurately during trimming to preserve occlusal relationships and proper geometry.
Compare acrylic resin tray materials vs. premixed light-cured tray materials in terms of advantages / disadvantages described in the document.
Acrylic resin trays: advantage — strong and easily adaptable; disadvantage — liquid monomer is volatile and hazardous. Light-cured premixed tray materials: advantage — do not contain methylmethacrylate monomer and provide excellent adaptation for dentulous/edentulous/partially edentulous situations.