A dynamic method for assessing the occlusal reduction of preparations

TIPS FROM OUR READERS

A dynamic method for assessing the occlusal reduction of preparations R. Saravanamuttu, B.D.S., M.Sc.* Guy’s Hospital, London, England

During the preparation of teeth for cast restorations it is important that sufficient occlusal reduction of tooth structure is performed to accommodate the restorative material of choice. It is often difficult to directly assessthe amount of reduction that exists in centric and eccentric occlusal positions of the mandible. Clinical estimation of interocclusal space in the range of 0 to 2 mm is extremely difficult on buccal and lingual cusp inclines. The lack of space for the restorative material may only become apparent when the mounted working casts are examined on an articulator. It will then be necessary to recall the patient for repreparation of the teeth and the making of new impressions. Some dentists overcome this problem by overpreparing the teeth, thus ensuring adequate space. This

approach, however, is needlessly destructive of tooth structure and will reduce the retention of the preparation. Others use a wax interocclusal record, which is removed from the preparation and measured directly. Removal risks distortion of the wax

*Senior Registrar in Restorative Dentistry.

Fig. 3. Functionally

generated

paths on wax.

Fig. 1. Prepared teeth.

Fig. 4. A and B, Direct measurement

at specific points

of preparations.

116

JANUARY

1988

VOLUME

59

NUMBER

1

TIPS FROM

OUR READERS

and it is often difficult to locate the specific regions of the preparation on the wax imprint. The following technique may be useful in overcoming these problems. 1. Prepare the tooth as usual. 2. Dry the prepared tooth surfaces (Fig. 1). 3. Place a piece of soft ribbon wax on the dry preparation(s) ensuring adequate contact on the adjacent tooth surfaces (Fig.

2). 4. Wet the opposing teeth. 5. Manipulal:e the teeth into centric and eccentric closures (Fig. 3). 6. Separate the teeth stabilizing the wax digitally to avoid dislodgment.

7. Insert a graduated periodontal probe into the soft wax (without removing from preparation) in all regions of potential contact and read the thickness of interocclusal space for the restoration (Fig. 4). This procedure may be repeated until optimal space exists for the restoration of choice. Reprint requests to: DR. R. SARAVANAMUTTU GUY’S HOSPITAL DEPARTMENTOF RESTORATIVEDENTISTRY LONDON SE1 9RT ENGLAND

Use of a paralleling post for cast orientation when fabricating removable partial denture abutment crowns Donald A. Curtis, D.M.D.,* Thomas A. Curtis, D.D.S.,** and John B. Holmes, M.A., D.D.S.*** University of California, San Francisco, School of Dentistry, San Francisco, Calif.

Casts are often sent to the dental laboratory with a work authorization for making crowns with guiding planes and undercuts suitable for a removable partial denture (RPD). Rarely is a path of placement provided by the dentist and rarely do the guiding planes or contours in the completed crown conform exactly to expectations. Communications with the dental laboratory is improved by

*Assistant Professor, Department of Restorative Dentistry. **Professor and Director, Graduate Prosthodontics. ***Clinical Professor and Chairman, Removable Prosthodontics.

Fig. 2. Proper wax contour dental technician.

Fig. 1. A small hole is placed in dental cast allowing placement of a rod parallel to analyzing rod of surveyor.

THE JOURNAL

OF PROSTHETIC

DENTISTRY

can be easily verified

Fig. 3. Path of placement and parallelism planes are verified by dentist.

by

of guiding