Orris

In spacer design what kind of spacer given in mandibular knife edge ridge in prosthodontics

Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Searching the Web

spacer design knife edge ridge mandibular complete denture prosthodontics

Reading Web Page

https://www.walshmedicalmedia.com/open-access/a-clinical-rev…

Reading Web Page

https://www.ijmacr.com/asset/images/uploads/17195790693973.p…

Searching the Web

knife edge mandibular ridge "no spacer" OR "spacer not given" complete denture impression technique

Here is a thorough answer compiled from multiple peer-reviewed prosthodontic sources:

Spacer Design for Mandibular Knife-Edge Ridge

What is a Knife-Edge Ridge?

A knife-edge ridge is a form of residual alveolar ridge caused by rapid buccolingual (lateral) resorption of both the buccal and lingual cortical plates, leaving a sharp, narrow, blade-like crest. It is especially common in the mandibular anterior region (prevalence reported as high as 89% in the mandibular edentulous arch) and is a frequent finding in long-term denture wearers.

Spacer Given for Mandibular Knife-Edge Ridge

For the mandibular knife-edge ridge, the general principle is:
No spacer (or minimal/no relief wax) is given over the knife-edge ridge crest.
The rationale is based on the selective pressure impression technique:
  • The knife-edge ridge crest is sharp, narrow, and covered by thin, non-resilient, pressure-sensitive mucosa. It cannot bear occlusal loading.
  • Placing a spacer would create additional pressure against this thin mucosa during function, accelerating bone resorption and causing pain.
  • Instead, the buccal shelf (oblique ridge area / external oblique ridge area) is the primary stress-bearing area of the mandible, and impression pressure is directed there.

Spacer Placement Rules - Mandibular Arch (Summary)

AreaSpacer Given?Reason
Knife-edge ridge crestNo spacer / no reliefPressure-sensitive; thin overlying mucosa
Residual alveolar ridge (general)1 mm base-plate waxTo provide space for impression material
Buccal shelfNo spacer (exposed)Primary stress-bearing area; acts as tissue stop/stopper
Retromolar padNo spacer (exposed)Stress-bearing area; acts as guiding stop
Anterior ridge (canine region)Tissue stops cut through spacerFor proper seating of custom tray

Specific Spacer Designs by Various Authors (Mandibular Arch)

  1. Boucher (1951) - Selective pressure technique: 1 mm baseplate wax over the mandibular ridge except the buccal shelf area and retromolar pad (both left exposed as stress-bearing areas). No spacer used if metallic oxide paste (ZOE) is the final impression material.
  2. Bernard & Levin - 2 mm baseplate wax over residual alveolar ridges excluding the buccal shelf area; 8-10 relief holes over the ridge crest.
  3. Morrow, Rudd & Rhoads - Full coverage spacer (one layer baseplate wax), 2 mm short of vestibular depth; 2 tissue stops at canine region bilaterally; relief holes at crest of mandibular ridge.
  4. Miscellaneous (selective pressure) - 1 mm baseplate wax over the entire alveolar ridge except the retromolar pad; 2 tissue stops at canine region.
  5. T-spacer / Partial spacer (mandible) - Used when the anterior mandibular ridge is atrophic, resorbed, or knife-edge/flabby. The spacer covers only the anterior residual alveolar ridge; the posterior and buccal shelf areas are left exposed as stress-bearing stoppers. This is based on selective pressure technique.

For Knife-Edge Ridge Specifically: Modified Impression Approach

When the knife-edge ridge is present:
  • Minimum pressure impression technique is preferred (not selective pressure, not mucocompressive).
  • The crest of the knife-edge ridge receives no spacer and no pressure - it must be recorded in its undisplaced (resting) state.
  • A partial/T-spacer may be used anteriorly to avoid loading the sharp crest while still recording the buccal and lingual sulci.
  • Final impression materials of choice: light-body polyvinyl siloxane (PVS) or zinc oxide eugenol (ZOE) paste - both low-viscosity, minimal pressure materials.
  • Some authors recommend a perforated custom tray over the knife-edge ridge crest with a fluid impression material (low-viscosity elastomer or ZOE paste) so pressure dissipates through the perforations.

Key Principle (DeVan's Concept Applied)

"Preserve what remains rather than restore what is lost." The knife-edge ridge must be recorded with minimal or no pressure (no spacer over the crest = tray contacts the ridge, reducing impression material bulk and pressure). Directing forces away from the ridge crest and toward the buccal shelf preserves the remaining bone.
Sources: Jain AR & Dhanraj M, A Clinical Review of Spacer Design for Conventional Complete Denture, Biol Med (Aligarh) 8:307, 2016; Verma S et al., Spacer Designs for Impressions in Conventional Complete Dentures, IJMACR 2024; Sikri A et al., Prosthodontic Management of Knife-Edge Ridge, DJIGIMS 2022; IPS Kerala JPID Vol 7 Issue 1.
This is a shared conversation. Sign in to Orris to start your own chat.