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Orthodontic Study Model

Dr. Heba A. Mohammad

MAHSA University

Introduction

• Study model is an accurate plasterreproductions of the teeth and their surroundingsoft tissues.

• Orthodontic study models are essentialdiagnostic records, which help to study theocclusion and dentition from all threedimensions.

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Ideal Requirements of Orthodontic

Study Models

1. Models should accurately reproduce the teethand their surrounding soft tissues.

2. Models are to be trimmed so that they aresymmetrical so that an asymmetrical arch formcan be readily recognized.

3. Models are to be trimmed in such a way that thedental occlusion shows by setting the models ontheir backs.

4. Models are to be trimmed such that theyreplicate the measurements and anglesproposed for trimming them.

5. Models are to have clean, smooth, bubble-freesurfaces with sharp angles where the cutsmeet.

6. The finished models should have a glossyfinish.

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Benefit of Study Model

1. They are invaluable in planning treatment as they are the

only three dimensional records of the patient's dentition.

2. Occlusion can be visualized from the lingual aspect.

3. They provide a permanent record of the intermaxillary

relationships and the occlusion at the start of therapy; this is

necessary for medicolegal considerations.

4. They are a visual aid for the dentist as he monitors changes

taking place during tooth movement.

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5. Help motivate the patient, as the patient can visualize the

treatment progress.

6. They are needed for comparison at the end of treatment

and act as a reference for post-treatment changes.

7. In case the patient has to be transferred to another

clinician, study models are an important record.

Parts of The Study Models

The study models can be divided into two

parts:

�The anatomic portion

�The artistic portion

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Anatomic Portion

� is that part which is the actual impression of the dental

arch and its surrounding soft tissue structures.

� This is the part must be preserved when trimming the

model.

Artistic Portion

�The stone base supporting the anatomic portion (the base of the model) .

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Study Model Fabrication and Trimming

Preliminary procedures in the fabrication of

study models are:• Remove any obviously excessive bulk on the periphery of

the models.

• Remove any nodules that may be present on the

occluding surfaces of the teeth.

• Remove any extensions in the posterior areas that

prevent occluding of the models

• Using the wax bite to occlude the models.

Steps in Art Portion Fabrication

1. The base of the lower model is trimmed parallel to the occlusal plane.

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2. Trim the back of the lower model perpendicularto the base

• This is done on a near symmetrical

model by measuring the distance from

the distal of the first molars or second

molar to the back of the model on both

the left and right sides

3. The back is trimmed so that it is 90° to the base of the model.

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4. The posterior surface should not be trimmedtoo close to the posterior aspect of themandibular teeth as the hamular notch of theupper model governs the distance, this surfaceshould be from the teeth.

5. To trim the back of the upper model, occludethe models utilizing the wax bite.

– maintains the correct interrelationship.

– prevent fracturing of the teeth

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• Carefully trim the posterior surface of the occluded

models so that the upper model matches that of the

lower model.

6. The back of the upper and lower models shouldbe 90° to the base of the lower model.

�Trim the posterior surfaces of both models until you

are just posterior to the hamular notch which should

be several millimeters posterior to the last tooth.

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7. Trim the base of the upper model so that it isparallel to the base of the lower model

• Trim until the top base is flat, but leave

several millimeters of extra height.

• The occlusal plane should be centered

between the top of the maxillary model

and the base of the mandibular model

The Lower Model

1. Make the buccal cuts on the edge of the vestibule at 60°

angle to back of the model.

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2. The anterior segment of the lower arch istrimmed into a curve, which should follow thearc of a circle

• The finished model should havethis curve trimmed to within 5 to6 mm of the anterior teeth.

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3. The heels of the lower model are cut atapproximately 115° to the back of the model

�The floor of the mouth should be leveled andsmoothed to form a flat surface.

�The ideal set of models will have the art portionrepresenting approximately 1/3rd of the totalheight and the anatomic portion approximately2/3rd of the height.

1/3 rd

2/3 rd

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The Upper Model

1. Make the buccal cuts to the edge of thevestibule at an angle of 60° to the back of themodel.

2. Make the anterior cuts so that the ends are atthe midline and approximately in the caninearea.

� Approximately 5 to 6 mm from

the labial surface of the anterior

teeth.

� Both sides of equal length and

their intersection on the midline.

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3. The heels of the upper model are formed byoccluding both the models and finishing themsuch that they are flush with the heels of thelower models at 115°.

– The heels of the upper model may not be the same

length as those of the lower model.

4. The finished height of the occluded modelsshould be 7 cm.

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Finishing the Models

• The surface must be made smooth, flat and at right

angles to the bases of the models.

• The finishing process should not change the dimensions

or any of the angulations of the models.

Carborandum Stone Technique

1. The model is rubbed over the stone with aneven pressure under a stream of water until asmooth surface results.

2. The model is set aside to dry for 48 hours ordried overnight in an orthodontic oven.

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3. The model should be labeled on the backs of

both the upper and lower models :

� patient's name

� patient's date of birth

� Registration No.

� Doctor Name

� Impression date

Glazing of Model

1. put on the models by immersing them in a commercial

gloss.

2. The models are allowed to remain in this solution for

one-half hour.

3. Holding each arch under cold water, the models are

polished and soap solution removed by buffing with

cotton.

4. The models are set on their occlusal surfaces to dry for

another twelve hours, then buffed with a very light but

rapid motion using cotton.

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Thank You