Trimming (Shaping) Casts Dr. Pauline Hayes Garrett Department of Endodontics, Prosthodontics, and Restorative Dentistry University of Maryland, Baltimore

Objective The object of cast trimming is to produce a symmetrical base for the occluded casts of your patient. This is especially important for orthodontic treatment planning and should carry over into all disciplines of dentistry for treatment planning. Your finished study casts will be part of your patient’s permanent records and as such should have a professional appearance for discussing treatment with your patient and colleagues. The following description of trimming casts will be tailored to your Operative Dentistry typodont. Instructions for “orthodontic” trimming will be presented by the orthodontic faculty.

The cast base should be ~1/2” thick! Adult maxillary casts should measure approximately 1-1/2 inches, and adult mandibular casts should measure approximately 1-1/4 inches, with 1/3 being the base, 1/3 showing tissue and anatomic structures and 1/3 showing the teeth. IF YOU ARE NOT SURE ABOUT THE QUALITY OF YOUR CASTS, ASK YOUR LABORATORY INSTRUCTOR TO EVALUATE THEM BEFORE YOU TRIM THEM.

Cast Trimmer The electric powered cast trimmer is used to remove excess stone and produce a flat, symmetrical base. It is a revolving abrasive wheel that must be kept lubricated and clean during use by a constant stream of water bathing the wheel. If operated dry, it will become clogged with particles of stone.

1st Step Place the cast on its base, and trim away excess at the posterior aspect of the cast which duplicates the base of the typodont as recorded in the impression.

Step 2 Next determine if the base of the cast is parallel to the occlusal (biting) surfaces of the posterior teeth. If it is not, place the cast on the posterior end trimmed in Step 2, and press the base against the wheel to parallel it to the teeth.

Place the cast back on its base and trim the remaining periphery to the area on the cast which duplicates the base of the typodont as recorded in the impression. The casts should be rinsed with clean water and left to dry for at least 12 hours. Do not store the casts in an occluded position, as the teeth may wear or fracture especially when the casts are wet.

After drying, small blebs or imperfections in the surfaces of the stone may be scraped away with a laboratory knife or wax spatula. Large blebs or imperfections usually require making a new set of impressions and casts.

Some time you need to do it over!