Trimming Diagnostic Cast Mr. Caputo Unit #1 Lesson #11

Today’s Class Driving Question: How does a model trimmer shape a dental model? Learning Intentions: We will be able to describe various methods of constructing custom trays and demonstrate creating a light-cured custom tray. Anchor: What is the difference between dental plaster, dental stone, and die stone?

Factors That Affect the Setting Time Water temperature the cooler the water used, the longer the material will take to set spatulation Water-to-powder ratio when a high proportion of water is used, setting time is delayed and crushing strength is lowered, creating a weak model unusable for laboratory procedures Time and speed of spatulation rapid spatulation accelerates setting time

Pour Methods Two-step pour method: anatomic part is poured and allowed to set and then base portion is created separately using a spatula to form a flat patty Boxed pour method: boxing wax or model base former is used to create border for the base of the model Inverted pour method: both the anatomic portion and base of the model are completed with one mix

Tray with Teeth on Top Base

Trimming Dental Models Soak in water for at least 30 min before trimming Trim maxillary model first and then occlude the mandibular model with the maxillary model Model should be placed on model trimmer working table to assess whether it is parallel Always use eye protection when using model trimmer

Marking of the Model Pencil is used to mark trimming landmarks at the posterior, canine eminence, and between the central incisors

Trimming the Posterior of the Maxillary Model

Trimming the Model Base

Trimming of Models Insert the Figure found in Procedure 37-2 on pg. 590 that has the caption “Place the models together to cut the posterior”

Models Should Balance Together

Ideal Models Clearly define three maxillary and three mandibular frenula Should stand together on all sides without separating Visible tuberosity and retromolar pads Should have a ½-inch base, clear and clean vestibule, level teeth Should present well with clean lines, without bubbles, and with all teeth visible when viewed from the facial

Examination of Model Sitting on Counter

Considerations When Designing Custom Impression Trays Material from which the tray will be made Desired extension of the tray into peripheral and posterior areas Thickness of any spacer to be placed on the cast Location of any tissue Position and form of a handle if used

Custom Tray Design Wax or tin foil may be used and adapted to the model before custom tray construction Perforations may be placed in the tray Tissue stops may be placed

Custom Tray Design Tray must extend past the maxillary tuberosities on upper arch and retromolar pads on lower arch Lingual extension on mandibular custom tray should cover mylohyoid ridge Tray handles are helpful when loading, placing, and orienting the custom tray

Homework #4 Explain how you would train a dental worker in infection control.