Evaluation of Different RPD design considerations from a clinical perspective Flashcards
Q: What is evidencebased dentistry?
A: an approach to oral health care that requires the judicious integration of:
- Systematic assessments of clinically relevant scientific evidence, relating to the patients oral and medical condition and history, together with the
- Dentists clinical expertise and
- The patients treatment needs and preferences
Why is scientific evidence limited in Removable Prosthodontics?
- Too many variables!
- Difficult and/or unethical to design robust clinical trials 3. Declining interest
- One of the most ‘technical’ specialties in dentistry
- A lot of good quality research remains unpublished…
Saddles:
Bounded edentulous areas should not be restored with a unilateral denture:
Aggre? Disaggree?
Agree: 50% Disagree: 37% Neutral: 13%
- Risk of swallowing or inhalation
- Length of the saddle: shorter saddles more likely to be suitable for unilateral RPD
- Unilateral dentures do not distribute the loads as widely as conventional RPDs
Saddles:
Spaced mesh retention for the acrylic base should be
used for free-end saddles:
Agree? Disagree?
Agree: 94% Disagree: 6% Neutral: 0%
- This facilitates adjustments and modifications, such as relining of the saddle
- This is likely to be required in free-end saddles
Tissue stop:
A tissue stop should be included beneath the metal retention latticework in free-end saddles
Saddles:
A tissue stop should be included beneath the metal retention latticework in free-end saddle:
Agree? Disagree?
Agree: 64% Disagree: 30% Neutral: 6%
- This stabilizes the mesh during final processing of the acrylic
- Otherwise some flexing of the mesh may occur in the flask towards the tissues
- If the altered cast technique is used the tissue stop will no longer contact the crest of the ridge in the modified cast
Saddles:
Anterior bounded saddles should be closely adapted to the guide surfaces of the abutment teeth (closed design) for aesthetics and retention:
Agree? Disagree?
Agree: 100% Disagree: 0% Neutral: 0%
- More natural appearance; avoid black triangles
- Carefully select POI
- Proximal undercuts can be engaged by acrylic to assist retention
- Posterior tilt when surveying – beware of creating undercuts distally of the last abutment teeth!
Saddles:
Anterior bounded saddles should have an ‘open face’ (gum-fitted) design if there is no labial resorption of the ridge.
Agree? Disagree?
Agree: 50% Disagree: 31% Neutral: 19%
- Significantly better appearance (initially)
- If ridge resorption occurs, unsightly gaps will appear
- Indicated for smaller saddles, immediate transitional RPDs and overdentures
Saddles
Mandibular free-end saddles should carry artificial teeth with reduced width occlusally.
Agree? Disagree?
Agree: 88% Neutral: 12% Disagree: 0%
- Support deficit particularly in the mandible
- Reduce occlusal loads transferred to the mucosa
- Reduced number of artificial teeth also welcome
- Less force is required for a small occlusal table to penetrate the bolus
- Also: increased space for the tongue
Occlusal rests:
The support axis for a saddle should be placed as close to the line of the dental arch as possible.
Agree? Disagree?
Agree: 94% Disagree: 6% Neutral: 0%
- Support axis: an imaginary line passing through the rests supporting a saddle
- Axial loading of the abutments and stability of the saddle
Occlusal rests:
When there is a unilateral saddle at least one additional rest should be placed on the opposite side of the arch
Agree? Disagree?
Agree: 94% Disagree: 6% Neutral: 0%
- Cross arch support prevents rotation around the long axis of the saddle in the direction of the rest
- Addition of a clasp resists rotation in the opposite direction
Occlusal rests:
Rests should not be placed on the maxillary lateral incisorsor on the mandibular incisors.
Agree? Disagree?
Disagree: 53% Agree: 35% Neutral: 12%
- Small roots, reduced total area of periodontal ligament
- Majority of Prosthodontists felt that if these teeth are periodontally sound they can be used to support RPDs
- Difficulty: preparation of adequate rest seat without penetrating the enamel
Occlusal rests:
Rests should be placed in prepared rest seats.
Agree? Disagree?
Agree: 88% Disagree : 12% Neutral: 0%
- Avoid occlusal interference
- Produce favourable tooth surface for support with axial loading
- Reduce prominence of the rest
- Clearly indicate to the technician the location of the rest
Occlusal rests:
If the abutment teeth are periodontally sound, rests supporting a bounded saddle should be placed immediately adjacent to the saddle.
Agree? Disagree?
Agree: 94% Neutral: 6% Disagree: 0%
- Efficient support
- Simpler design; avoiding need for minor connectors to carry rests to more distant sites
- Help prevent food trapping between abutment tooth and denture teeth
Occlusal rests:
If an abutment tooth has lost a moderate amount of periodontal support, rests supporting a bounded saddle should be placed non adjacently on the abutment tooth and on the next tooth.
Agree? Disagree?
Agree: 64% Disagree: 18% Neutral: 18%
- Share the occlusal load between 2 teeth
- However: complicates the design
- If no active periodontal disease: abutment should be treated as healthy tooth
Occlusal rests:
If an abutment tooth has lost a moderate amount of periodontal support, a rest supporting a bounded saddle should be placed on the nearest suitable site on the next tooth.
Agree? Disagree?
Agree: 70% Disagree: 24% Neutral: 6%
- Contingency planning: if the abutment is lost, the RPD will still function optimally
- Contra-argument: if this abutment cannot offer support for an RPD it could be extracted prior to construction of the RPD
Occlusal rests:
A rest for a free-end saddle should be placed mesially on the abutment tooth if this is periodontally and coronally sound.
Agree? Disagree?
Agree: 94% Neutral: 6% Disagree: 0%
- Avoid distal tilting of the abutment tooth
- More even distribution of loads in the edentulous area
- However: no evidence of distal tilting of the last abutment tooth
- More relevant in the mandible
Occlusal rests:
A rest for a free-end saddle should be placed mesially on the tooth anterior to the abutment tooth if the latter has a poor prognosis.
Agree? Disagree?
Agree: 76% Disagree: 12% Neutral: 12%
- If the tooth is lost, the saddle can be extended mesially and still be supported by a rest placed mesially on the last abutment tooth
- It could be argued that such an abutment tooth should be extracted prior to construction of the RPD
Clasp design:
An occlusally approaching clasp which is supported by a rest should not approach closer than 1mm to the gingival margin.
Agree? Disagree?
Agree: 88% Disagree: 12% Neutral: 0%
- Otherwise the clasp may cause irritation of the gingivae
- If the clasp is not supported by a rest, the distance between clasp tip and
- gingival margin should be greater than 1mm
Clasp design:
Occlusally approaching clasps should have only the terminal 1/3rd of the retentive arm entering the undercut.
Agree? Disagree?
Agree: 100% Disagree: 0% Neutral: 0%
- If the clasp arm crosses the survey line prematurely it may deform permanently in function; apply excessive force on the abutment tooth; or it may be difficult or impossible to place and remove the RPD
Clasp design:
An occlusally approaching clasp cast in cobalt chromium alloy should engage a 0.25mm undercut.
Agree? Disagree?
Agree: 88% Disagree: 6% Neutral: 6%
- If the undercut is less than 0.25mm resulting retention may be unpredictable
- If the undercut is bigger than 0.25mm there is a risk of permanent deformation of the clasp
Clasp design:
A retentive clasp cast in cobalt chromium alloy should be at least 15mm in length.
Agree? Disagree?
Agree: 58% Disagree: 24% Neutral: 18%
- This length allows flexing by 0.25mm without permanent deformation
- Can be achieved with occlusally approaching clasps on molars and gingivally approaching clasps on any tooth
Clasp design:
A retentive clasp made by wrought wire should engage a 0.5mm undercut.
Agree? Disagree?
Agree: 94% Disagree: 6% Neutral: 0%
- Stainless steel and gold wire clasps are more flexible
- Increased proportional limit allows engaging a deeper undercut
Mandibular connectors:
A bar-type connector is preferred to a lingual plate.
Agree? Disagree?
Agree: 94% Disagree: 6% Neutral: 0%
- Bar connectors do not cover gingival margins, therefore are more hygienic
- Also do not impinge on the gingivae, as a poorly supported lingual plate may do
Mandibular connectors:
A sublingual bar is preferred to a lingual bar.
Disagree? Agree?
Disagree: 52% Agree: 24% Neutral: 24%
- Sublingual bar is more rigid at the horizontal plane
- It may be used in a shallower lingual sulcus
- It is located lower in the sulcus and therefore may be less obtrusiveto the tongue
- However, the experts seem to disagree!
Mandibular connectors:
The upper border of a bar connector should not be placed closer than 3mm to the gingival margins.
Agree? Disagree?
Agree: 94% Disagree: 6% Neutral: 0%
- Widely accepted as the minimum clearance required
Mandibular connectors:
A lingual bar connector requires a minimum depth of lingual sulcus of 7mm.
Agree? Disagree?
Agree: 82% Disagree: 18% Neutral: 0%
- 3mm minimum gingival clearance
- 4mm minimum bar height
Mandibular connectors:
A sublingual bar connector requires a minimum depth of lingual sulcus of 5mm.
Agree? Disagree?
Agree: 81% Neutral: 13% Disagree: 6%
- 3mm minimum gingival clearance
- 2mm minimum bar height
Mandibular connectors:
If the lingual sulcus depth is less than 5mm a lingual plate is indicated.
Agree? Disagree?
Agree: 53% Neutral: 29% Disagree: 18%
- Too shallow for lingual or sublingual bar
- Healthiest alternative: dental bar
- Lingual plate indicated if the anterior teeth are not suitable for a dental bar
Mandibular connectors:
A lingual plate requires support at either end by a rest in a positive rest seat.
Agree? Disagree?
Agree: 100% Disagree: 0% Neutral: 0%
- Otherwise it may ‘sink’ towards the tissues under occlusal loads and traumatize the gingivae
- Also may transfer horizontal forces to the anterior teeth if unsupported
Maxillary connectors:
A maxillary major connector should uncover the anterior hard palate if possible.
Agree? Disagree?
Agree: 100% Disagree: 0% Neutral: 0%
- Anterior palate: highly innervated
- Avoid interference with speech
- Increase enjoyment of food
- Improve tolerance
Maxillary connectors:
Maxillary minor connectors should cross the gingival margins at right angles.
Agree? Disagree?
Agree: 88% Neutral: 12% Disagree: 0%
- More hygienic design, prevent food trapping
Maxillary connectors:
If there is a palatine torus it should be avoided by using an anterior plate, posterior plate or ring design depending on its location.
Agree? Disagree?
Agree: 88% Disagree: 12% Neutral: 0%
- Avoid discomfort from compression of thin mucosa against torus
- Avoid tolerance problems caused by the thickness of the major connector added to the prominence of the torus
