A simplified procedure for survey and design of diagnostic casts

DENTAL DANIEL

TECHNOLOGY

H. GEHL,

A simpbfied diagnostic

Section

p

editor

ure for

swvey

and

design

of

casts

Arthur M. LaVere, D.D.S.,* and Angelo 1. Freda, C.D.T.** University of the Pacific School of Dentistry, San Francisco,

Calif.

P

reservation of abutment teeth and supporting structures of the oral cavity depends on accurate and knowledgeable survey and design. The diagnostic cast(s) to be used in the determination of a removable partial denture design must be a true reproduction of the dental arches. The burden for the success of a removable partial denture lies with the dentist, where it rightfully belongs. Only the dentist has the knowledge and information concerning the patient’s oral cavity to design a removable prosthesis so that it will function to its utmost effectiveness. Given proper direction by the dentist, the dental laboratory technician will be able to render a better service to the dental profession. T o plan, survey, and design a removable partial denture which will provide proper retention, support, stabilization, and esthetics, the dental surveyor must be utilized as an adjunctive tool in the treatment plan. DENTAL

SURVEYOR

The surveyor is not a complex instrument, and though there are several types available, each has three main components. These are: ( 1) a horizontal base, (2) a vertical spindle, and (3) a movable table with a tilt top permitting anterior, posterior, and lateral movement of a mounted cast. The surveyor aids in determining parallelism, heights of contour of a tooth, and undesirable tissue prominences. By tilting the mounted cast, the most favorable path of insertion and removal for the prosthesis can be ascertained. There are some misunderstandings concerning the surveying procedure. Claims are made that tilting can create undercuts when, in fact, on a particular tooth, they may be nonexistent. Another generalization is that anterior tilts should be used for *Professor and Chairman, Department of Removable Prosthodontics. **Department of Removable Prosthodontics. 680

Survey

and

Fig. 1, A and B. The mandibular cast is locked in position posterior tilt is determined by the contact of the analyzing the abutment teeth. This area denotes the guide planes.

design

of diagnostic

casts

681

on the survey table. The anterorod at the height of contour of

anterior extension-base partial dentures and posterior tilts for distal-extension partial dentures. This article will attempt to clarify much of the mystique which surrounds what is basically an uncomplicated procedure by presenting material in a simplistic format. SURVEYING

THE DIAGNOSTIC

CAST

Factors that determine the path of insertion are1 : ( 1) guiding planes (proximal tooth surfaces that are parallel to one another), (2) retentive areas (those that lie below the height of contour), (3) interferences (tooth or tissue which might be abraded on insertion and removal), and (4) esthetics (a design which will display the least metal and base material and allow for proper placement of teeth). Locating the path of insertion. Place the cast on the tilt-top table and adjust to a 0 degree tilt, with the occlusal plane parallel to the base of the surveyor. This tilt is considered to be most favorable, because many patients seat a partial denture with the biting force of an occlusal load and it is easier for the dentist to make the necessary mouth preparations. Locating the guiding planes. ( 1) Place the analyzing rod in the surveyor spindle. (2) Move the tilt-top table, with the cast in position slightly anteroposteriorly, until the spindle contacts the occlusal one third of the proximal surfaces of the proposed abutment teeth (Fig. 1). When anterior teeth are missing, guide planes on either side of the edentulous space must be given precedence. Locating the retentive ureas. (1) Slightly tilt the table from the recommended 0 degree position to a lateral direction for determining presence of undercuts. An attempt is made to equalize the amounts of undercuts on the abutment teeth, to place clasp tips for maximal esthetics, and to determine whether or not one or more

682

LaVere

J. I’rosthrt. Dent. June, 1973

and Freda

Fig. 2, A and B. The mandibular cast is locked in position tilt is determined by the contacting of the analyzing rod abutment tooth. This area will denote whether a true undercllt of

the

abutment

teeth

must

be

prepared

for

on the survey at the gingival exists.

(Fig.

a restoration

table in the most favorable position. Locating the survey lines and tripoding the cast. (1)

table. The one third

2j.

(2)

lateral of the

Lock

the

adjustable with

a carbon

marker.

(2)

Mark

teeth and tissue prominences. means

of

three

widely

(3)

separated

the

height

Record dots

of with

plane. This makes possible the maintenance and it is known as tripoding the cast.

OUTLINING

RESTS AND

GUIDE

contour

on

the cast position

made

same

Replace

the

the

the analyzing tentative

for future

carbon

of the original

marker

abutment

orientation fixed

by in

the

path of insertion,

PLANES

Outline the mesial or distal rests and the type of retainer (circumferential, or wrought wire) based upon individual philosophies. Guide planes are adjacent to edentulous spaces in most instances. MINOR

rod

bar, made

CONNECTORS

Outline the minor connectors on the cast. To avoid gingival impingement, minor connectors should not have beaded peripheries. Instead, they should be afforded relief as they cross the gingival margin. Where more than one vertical minor connector is used, at least a 5 mm. space between them is necessary. If a distal-extension base is to be used, an indirect retainer should be utilized to prevent movement of the partial denture in an occlusal direction. MAJOR

CONNECTORS

Outline the major connectors on the cast. Based on the support and rigidity needed for preservation of tissues, the type of major connector is selected. Other considerations for the selection of major connectors may include the opposing occlusion, type

Survey

and

design

of

diagnostic

casts

683

of tissue and ridges, and amount of bracing required. Major connectors in the maxillary arch are kept at least 6 mm. away from gingival margins, and in the mandibular arch, the connector is kept at least 3 mm. from the gingival margins. RETENTION

MESH

FOR DENTURE

BASE

RESIN

Draw the retention mesh for the denture base resin on the cast. Wide-open straptype retention is preferred because of the ease in the packing of the denture base resin. Cross loops are placed so as not to interfere with artificial tooth position and to reduce fracture of the denture base. Stagger external and internal finish lines so as not to weaken the metal in those areas. Finish lines are developed to allow resin and metal to terminate in a butt joint. EXTENT

OF DENTURE

BASE

RESIN

Draw the correct extent of the denture base on the cast. Extension-base dentures should extend to include anatomic landmarks similar to a complete denture. Example: The base should extend into the hamular notch for a maxillary distalextension removable partial denture and cover the pear-shaped pad for a mandibular distal-extension removable partial denture. DRAWING

THE CLASPS

Draw the final clasp design on the cast based on personal philosophy. A clasp must provide support, bracing, retention, and reciprocation and must engage more than 180 degrees of the abutment tooth. It must also be passive when in final position on the tooth. SUMMARY The procedure described for survey and design of diagnostic casts is applicable to either dental arch. It is presented in a sequential manner, is not complex, and will produce uniformly acceptable results. The following steps should be followed: ( 1) locate a path by tilting the cast; (2) mark the survey lines and tripod the cast; (3) outline the rests and guide planes; (4) draw minor connectors; (5) draw major connectors; (6) draw retention mesh for acrylic resin; (7) draw acrylic resin base extension; and (8) draw direct retainers (clasps). References 1.

McCracken,

2.

pany. LaVere, A. M., and Krol, Removable Partial Denture,

W. L.:

UNIVERSITY SCHOOL

2155 SAN

OF THE

Partial

Denture

PACIFIC

DENTISTRY WEBSTER ST. CALIF.

St. Louis,

1964,

A. J.: Selection of a Major Connector J. PROSTHET. DENT. 30: 102-105, 1973.

OF

FRANCISCO,

Construction,

94115

The for

C. V. Mosby the

Com-

Extension-Base