A New Method for Trimming Orthodontic Study Model

Trimming study models has a set of requirements, these requirements vary from one laboratory to another.

Scriber and Divider

Traditionally, scribers are used to trim the base of the upper which is parallel to the occlusal plane. However, scribers are heavy and expansive. A cheap metallic divider with one hand based with plaster can be used. The height of the scribing hand can be adjusted by the set screw. The effect is similar to a scriber but it is handier.

Set Squares and Ortho Trimmer

Sides of the study model are trimmed with the help of set squares or a trimmer with trimming angle, or by eye estimation.

Set squares are difficult to make and should have already abandoned by most users.

Orthodontic trimmer is a good choice but sometimes it is not available in some laboratories.

Eye estimation may produce undesired effect.

Template Method

Here I would introduce another method; the template method.

Advantages of using this method is that the templates are easier to make, the trimming process is faster, and accurate result can be obtained.

A set of 3 – 4 different sizes of template with the preformed angle.

The templates should be made from transparent acrylic with midline is scribed onto the template.

Template Is Attached on the Upper Model

2 rolls of Blue tack or plasticine are attached on sides of the template. This facilities the position template onto the upper model.

Adjust the position of the template so that the template is symmetrical aligned with upper model and with 8mm from the base of the model. A smaller template should be used.

Trim the Posterior Border of the Upper Model

With the help of a symmetroscope, the posterior border of the upper model is trimmed until the model is symmetrical (median suture in line with the center of the symmetroscope).

Trim the Sides of the Upper Model

The anterior, lateral and heel sides aretrimmed based on the sides of the template. Make sure that the anterior sides meet at the midline. Check the symmetry with an accurate Symmetroscope. Fine adjustments can be made.

Symmetry can also be checked by putting the model with the base facing the Symmetroscope.

Trim the lower model against the upper.

Trim Lower Model and Check for Discrepancy

Lower anterior edge is trimmed by rotating the model from one side to the other.

Check the sizes of the upper and lower models by putting the base against each other. If there are discrepancies in size. This indicates that the trimming plate is not perpendicular to the platform.

Template Is Attached in This Instructable

The symmetroscope pattern is attached and can also be used for making the templates