Precision and Semi-Precision Partial Dentures (Avoiding Conventional Partial Denture Clasps)

By Brian J. Gray, DDS, MAGD, FICOI

Precision and semi-precision partial dentures, like conventional partial dentures, replace missing natural teeth with artificial teeth. However, the means by which they are retained in the mouth is different than a conventional clasp prosthesis. To better understand these partial denture types, it is best to first review the basics of conventional partial denture clasps.

How Conventional Partial Denture Clasps Function

Most partial dentures are usually kept in place by clasps. These are thin finger-like projections of special resilient metal alloy, or, in certain cases, plastic or plastic-like materials.

• Clasps rest on and around certain remaining natural teeth so that their ends extend into narrow areas below a gentler bulge on the tooth. Sometimes it is necessary to shape a tooth or make a crown for a tooth or teeth in order to develop the right amount and relationship of undercut and bulge for retention.
• When a partial denture is placed in the mouth, clasps gently spring over a tooth bulge and rest in a relaxed state within an undercut.
• A partial denture is held in place during normal eating, speaking, and other activities because clasps resist springing back over tooth bulges.
• Clasp resistance to removal is not great enough to prevent a person from comfortably removing their partial denture whenever they choose.

The Problem With Conventional Clasps

Despite numerous successful conventional clasp designs, they do have some drawbacks.

• Clasps may at times become visible. Often, this is unavoidable and usually is not objectionable. However, for some individuals, the show of clasps is simply not acceptable because of personal circumstances and compromised appearance.
• Certain partial dentures may function better with retentive means other than conventional clasps.
• Remaining natural tooth structures may be inadequate to accommodate conventional clasps. Therefore, a crown or crowns may need to be fabricated to correct these deficiencies.

Semi-Precision and Precision Partial Dentures -- Viable Alternatives

Alternatives to conventional clasp partial dentures fall into two categories, both of which have no clasps to show.

• Semi-precision partial dentures are retained in the mouth by means of mechanical interlocking components. A specially-shaped extension of the partial denture fits into or onto a complementary receiving area or projection of a natural tooth that has been crowned. The components fit snugly and consist of a semi-rigid metal-to-other-surface interface, which may also be metal or some other resilient material such as nylon.
• Precision partial dentures are similar to the semi-precision type except that the mechanical interlocking components are manufactured to extremely high tolerances and are held together by precise alignment and a rigid metal-to-metal frictional interface of components.

Advantages of Semi-Precision and Precision Partial Dentures

• A cosmetically-enhanced partial denture as compared to conventional partial dentures
• No show of metal clasps
• Blends in with the conformity of remaining natural teeth
• Functions with a more even pressure on remaining natural teeth than conventional partial dentures

Disadvantages of Semi-Precision and Precision Partial Dentures

• More costly to fabricate
• Usually some natural teeth need to be crowned
• More difficult to fabricate and adjust
• Some components may need periodic replacement

Which Type of Partial Denture Is Best?

Every patient has unique oral health needs that are best determined by a licensed dentist after a thorough examination.