Study models 101 trimming

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Study Models 101Kathy Malone RDH, EFDA, CDA,BS

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Trimming

3¼ “

The cut is made at a 90 degree angle to the midline of the palate

Trim the model with the longest anterior/posterior length firstUsually the maxillary arch

Trimming the Posterior Border

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Trimming the Posterior Border

You may draw a light line on the model to help with trimming.

Keep the line parallel with the wheel

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Articulate the untrimmed half with the trimmed half

• Use the trimmed half as a template.

• When the trimmed half just touches the wheel stop trimming!( You will see bubbling)

• The models will remain articulated when placed on the counter top

• Follow this guideline for the rest of the trimming cuts.

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Trimmed cut has not met the wheel. Continue until both halves meet.

Untrimmed Trimmed

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Both trimmed and untrimmed cuts meet the wheel

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Notice how the posterior cuts are even on both models when articulated

• The borders of both halves should be even on all cuts and remain articulated when placed on a counter for viewing.

5Incorrect

Correct

Trim the widest model first--Usually the maxillary arch

Maxillary Arch

Trimming the Lateral Borders

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Trimming the Lateral Borders


You may draw a light line on the model to help with trimming. The markings on the buccal cusps in this example are made dark for illustration purposes only. Dark lines will mar the final study model.

Trimmed side

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Notice how the lateral cuts are even on both models when articulated

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Keep the muccobuccal fold!!!

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This is too close!!!

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Correct Incorrect

Trim from the midline of the canine to the midline of the arch and repeat on the opposite side.

Trimming Maxillary Anterior Borders

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You may draw line on the model to help with trimming.

Use the midpalatine suture as a midline guide. The patient’s dentition midline may not be the middle.


Trimmed

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Mandibular Arch

You can initially trim this arch with a point and then remove it so the models will articulate

Trimming Mandibular Anterior Border

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Trimming Mandibular Anterior Border

• Mandibular anterior border is rounded. You may initially trim with a point utilizing the maxillary arch model to insure articulation. Remove the tip to make the rounded appearance.

Remove Point

88

Incorrect

Correct

Trim the heels at a 90 degree angle to an imaginary line from the midpoint of the canine and repeat at each side.

Trimming the Heel

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Trimming the Heel

• Notice the line drawn from the point of the canine to the back corner.

• The cut should be perpendicular to the line.

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Trimming the Heel

Trimmed Untrimmed

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Trimming away Excess Stone for Visibility

Notice the difference between the untrimmed side and trimmed side.

Use bur on lathe or buffalo knife to trim away the excess.

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The dentition must be visible. Remove excess stone with a bur on the lathe or a buffalo knife.

Stone in the way and dentition cannot be seen

Stone removed and dentition can be seen.

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Cleaning Up After Trimming• Rinse off the wheel and base plate

with sprayer.• Wipe off the countertop and

cabinets.– The stone will streak on the

countertops!

• Clean the sink.• Wipe off the bur on the lathe.• Empty lathe tray.• Clean off the lathe shield.• Sweep the floor.• Clean up any trash.

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Turning in Study ModelRemember to:

• Write the patient’s name and date of impression on both halves of the models.

• Turn model in with wax bite

• Turn in with self assessed competency/process paper

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Final Criteria for a Acceptable Study Model

• All anatomy present• Free from voids and saliva nodules• Stone evenly mixed• Bases parallel ( 0-5 degrees) to the occlusal table• Symmetrical cuts and angles as described in the presentation• Have adequate depth of muccobuccal fold• Remain articulated when laid on all sides• Complete visual access of the dentition• Tongue area flat• Names and date on each half of the model

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Study models 101 trimming

Education

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