Tooth borne dentures Flashcards
Primary imps
- required for
- tray selection
Using ‘off the peg’ impression trays
Needed for planning, design, construction of special trays
Tray selection - should be 4mm between flange of tray and buccal surfaces of teeth
Articulators are used to…
To position the maxillary and mandibular casts in a particular relationship
Articulator designs
Different designs available
- hinge articulator
- average value (movement) articulator
- Arcon (semi adjustable)
- non-arcon (semi adjustable)
- fully adjustable
Semi-adjustable articulators
Produce a simulation of anatomical relationships and movements, good occlusal function
What is needed as well as an articulator
Facebow and occlusal records
Surveying
Parallelometer Identifies parallel surfaces and points of maximum contour Clinician should survey cast Helps decide pre-prosthetic treatment Several attachments
Surveying - analysing rod
Place against teeth & ridges
Identify undercut areas and parallel surfaces
Doesn’t mark cast
Surveying - graphite marker
Moved round teeth and ridges
Marks position of maximum convexity (survey line) separating non-undercut from undercut area
Tip of marker should be level with gingival margin
If not, false survey line produced
Undercut gauge
Measure extent of undercut
0.25mm, 0.50mm, 0.75mm
Allows correct positioning of retentive clasp arms
Trimming knife
To eliminate unwanted undercuts on master cast
Wax added and excess removed
Gives surface parallel to path of insertion
Duplicate cast made
Guide planes
2 or more parallel axial surfaces Limit path of insertion Improve stability Can occur naturally on teeth Trimming knife can be used to prepare guide planes on wax patterns
Path of insertion
The path followed by a denture from its first contact with teeth until fully seated
Coincides with path of withdrawal
May or may not coincide with path of displacement
May be single path or multiple paths of insertion
4 stages of surveying procedure
Preliminary visual assessment – eyeballing cast
Initial Survey
Analysis
Final Survey
Initial survey
Cast positioned in occlusal plane horizontal
Identify undercuts that could provide retention
Analysis of horizontal plane or tilted cast
Need to consider
- appearance
- interference
- retention
A system of design
Saddles Support Retention Bracing and reciprocation Connector Indirect retention Review of completed design
What are saddles and what are they made from
The part of the denture that rests on covers the edentulous areas and carries the artificial teeth and gingiva
Acrylic or framework of metal overlaid by acrylic
Concerns about saddles
Design of occlusal surface Base extension Design of polished surface Material for impression surface Junction between saddle and abutment tooth
Design of occlusal surface of saddles
Important to position artificial teeth to produce even contact in intercuspal position & occlusal balance
Material for the impression surface (saddles)
Metal or acrylic
Acrylic – can add to, advantage with bone resorption in distal extension saddle
What is support in relation to an RPD
Resistance to vertical forces directed towards the mucosa
Planning support is dependent on
Root area of abutment teeth
Extent of the saddles
Expected forces on the saddles
Components for tooth support
Occlusal rests
Cingulum rests
Incisal rests
Overdenture abutment teeth
Other functions of rests
Distribution of horizontal force
Maintaining components in correct position
Protecting the denture/abutment tooth junction
Providing indirect retention
Reciprocation
Preventing over eruption
Improving occlusal contact
Retention is
Components which resist displacement of denture
Retention is achieved by
Using clasps which engage undercuts
Muscular control
Physical forces from coverage of mucosa by denture
Path of insertion
Categories of clasps
Occlusally approaching Gingivally approaching I bar clasp Other variations -ring clasp (occlusally approaching) -L or T shaped (gingivally approaching)
RPI system
Combination of occlusal rest (R), distal guide plane (P) and gingivally approaching I bar (I)
Used mainly with mandibular distal extension saddles
Connectors
Major and minor
Join together the components of a denture
Minor – join the small components e.g. rests, clasps to saddles or major connectors
Keep number to minimum to keep design simple.
Major – links saddles and unifies structure of denture
Also provides bracing and support by distributing functional loads widely to teeth and mucosa (maxillary)
Also provides indirect retention by contacting surfaces and palatal coverage
Upper jaw connectors are dependent on
Function Anatomical constraints Hygiene Rigidity Patient acceptability
Upper jaw connector types
Palatal plate Ring connector (skeletal)
Low jaw connectors
Constraint – small distance between lingual gingival margin and functional depth of floor of mouth
Connects components, indirect retention and guide planes
If gingival recession occurred, even less room for connector
Problems with oral hygiene and rigidity
Indirect retention
Resistance to rotation about clasp axis by acting on the opposite side to the displacing force
Roles and responsibilities of the dentist in relation to RPDs
Assess patient Modify oral environment -tooth preparation -perio tx -ortho/ oral surgery Design partial denture Pass all relevant information to technician Monitor denture in changing oral environment
Roles and responsibilities of the technician in relation to RPDs
Support and advise dentist during design phase
Construct denture using prescribed design to actual denture
Getting the information from clinic to laboratory
Study models Written description of design Design drawn on models Photographs Discussions
Classification of the partially edentulous case
By support used by the RPD -tooth borne -mucosa borne -tooth and mucosa borne By the edentulous area: Kennedy classifications
Kennedy class I
Bilateral edentulous areas located distal to the remaining natural teeth
Often known as free-end saddles
Kennedy class II
A unilateral edentulous area located posterior to the remaining natural teeth
Kennedy class III
A unilateral edentulous area with natural teeth remaining anterior and posterior to it
A bounded saddle
Kennedy class IV
A single edentulous area located anterior to the remaining natural teeth
Kennedy classification - modifications + example
In class I, II, and III (not IV) any additional bounded edentulous areas are stated to be modifications E.g. class III modification 2 (2 extra edentulous areas) *Always use most posterior edentulous area as the main classification*
Saddle definition
The part of denture that sits on the edentulous ridge on which the denture teeth are placed
Support definition
Component that resists vertical force down onto the mucosa
-rests (occlusal and cingulum) and saddle areas in free end saddle cases
How is retention achieved
Use clasps that engage undercuts on tooth surface; use polished surface of saddle areas (like complete dentures)
Clasps may approach undercut area from occlusal or gingival direction depending on depth and position of undercut
Bracing and reciprocation are used to
Support teeth and retain the denture
- horizontal forces occur during chewing due to tooth-tooth contacts and muscular force
- dentures may be moved antero-posteriorly or laterally
- can cause tooth, periodontal and mucosal trauma
How is bracing achieved
Bracing teeth to resist the forces is done by clasp arms and plates
Bracing on the ridges or palate is done by major connectors and flanges
Reciprocation aids
Retention
How is reciprocation achieved?
A bracing clasp arm or plate in contact with a tooth opposite a retentive part of the clasp can improve retention of the clasp by holding the tooth firm as the denture is pulled in a vertical direction
Indirect retention
component part of the denture that resists displacement of denture away from mucosa in a pivoting movement around a fulcrum Especially important in Kennedy class I and IV situations
Indirect retention is provided by
Clasps, rests, connectors correctly positioned on the opposite side of the fulcrum of movement
Minor connectors join
the small components of the denture to the saddles or major connector
The major connector links
the saddle areas and so joins all parts together
-provides support and often indirect retention
Examples of connectors
Plates, bars of different designs
Planning a bilateral free end saddle (Kennedy Class I) case
Bilateral free end saddle- most problematic
Unstable situation unless carefully planned
Support is provided by mucosa of edentulous area (saddle) and last tooth.
Last tooth provides greater support as is firmer.
Use occlusal rests to support denture on teeth
Need clasps to retain denture
Denture teeth can be pulled posteriorly – potentially damaging to last tooth
Protect teeth by bracing them and improve effectiveness of retentive clasps by reciprocation
No teeth posterior to saddle so denture can tip in an occlusal direction pivoting on last tooth in arch – poor retention, need to consider indirect retention
Connect the components together considering space available (connectors)
One small problem – we don’t know where to place the clasps or the best path of insertion of the denture etc as we do not know the depth of undercuts
We cannot locate positions for bracing and reciprocation
or indirect retention
We need to survey the model
Then using all the information complete the design
Working imps (2.)
Obtained after denture designed and tooth preparation completed
Special tray – accurate impression, functional depth, width of sulci
Uniformly spaced – optimum elastic recovery
Cold cure or light cured acrylic resin
Spacer – depends which impression material using
Borders 2mm short of sulcus depth
Stops (2. imps)
On internal surface, maintain spacing for impression material
Allow tray to be placed in same position each time
Can request lab to make stops in tray or make own using green stick
3 point location
Check tray extension – trim back if over extended, add greenstick if under extended
Lingual border moulding – raise tongue to contact upper lip, touch each corner of mouth
Taking the secondary impression
Choice of material
Preparation of mouth – block off open interdental spaces; remove saliva
Seat impression, border moulding, hold in position
Inspect of accuracy
-rounded borders, no air blows, no tray showing
-retake if not happy
Can use indelible pencil to mark 3mm away from the border
Trim cast once pencil mark on die stone reached
Jaw registration
Record jaw relationship – ICP or RCP
Mount models on articulator in exactly same position as in mouth
Position artificial teeth correctly
Different categories of jaw registration
Stable intercuspal position
Occlusal stop
Unacceptable intercuspal position
Absence of occlusal contact
Occlusal rims
Can be on shellac bases, acrylic resin or metal framework
Try in mouth and check for stability
If poor – retake impression
Adjustment of occlusal rims
Mid-incisal point 10mm in front of incisive papilla
Anterior inferior border to incisal level – adjacent teeth and lip line
Interpupillary line
May need to trim rim to accommodate natural teeth, esp maxillary anteriors
Posterior occlusal plane
Opposing natural teeth determine position
Maxillary rim –parallel to alar-tragal line
Correct B-L position of teeth
Buccal side of rim just contact cheek mucosa when mouth half open
Adjust mandibular block until even contact with maxillary block
Adjust mandibular rims until teeth in neutral zone
Rim encroaching on tongue
Jaw relationship may be determined by intercuspation of remaining teeth
If not assess resting vertical dimension
Adequate freeway space
Record jaw relation in RCP when guidance lost
Final registration if acceptable occlusal stop
Further 1mm of wax removed
Recording medium placed between rims
Final registration if no occlusal stop
Close pt in RCP and maintain while recording medium setting
Metal backing usually required for
artificial maxillary anterior teeth when opposing natural teeth
Metal try in
No teeth or wax rims
Check correct design as prescribed
Check on cast
Try in mouth using correct path of insertion
Do NOT force into place , may not be able to remove it
Look to see what is stopping seating
Look at cast – abrasions
Clinical examination
Gentle rocking – fulcrum
Once seated, assess stability
Assess all components
If unsatisfactory – new impression
Check stability of casting with finger pressure
Kennedy Class I and II will rock unless stop to support mesh present
Fully tooth-supported frameworks should
Carefully remove any sharp edges at gingival margins
Care adjusting around connectors – will create gap not rock.
Check metal framework does not interfere with occlusion
Patients viewpoint
Visual assessment
Articulating paper
Shimstock
Selective grinding to eliminate
Tooth try in
Examine on cast first
Check position of any posterior teeth with natural teeth
Aesthetics of anterior teeth – harmonise with natural teeth
Even intercuspation, balanced occlusion and articulation – guided by natural teeth
Seat in mouth along planned path of insertion – inspect fit, positioning of all components, flange extension, aesthetics
Functional movements of lips, cheeks, tongue should not displace denture
Assess relationship of artificial teeth to soft tissues
Check vertical and horizontal relationships
If natural teeth create occlusal stop, check artificial teeth in even contact with them
If no occlusal stop, check even contact in RCP
Flange thickness
Mesial and distal borders:
-thin to blend with mucosa
-avoids food packing
Lateral borders of anterior flange should be thinned and terminate over convexities of roots of adjacent teeth
Allows restoration of papilla
Poor appearance due to:
-gum margin lower than natural teeth
Borders should extend to full depth of sulcus recorded on cast
Occlusal forces distributed as widely as possible
Adjacent musculature reinforce retention and stability
Aesthetics
Shade, mould, arrangement
Harmonise with natural teeth
Incisal edges of natural anterior teeth follow curve formed by lower lip when smiling
Any characterisation requests by patient?
Insertion of completed denture
Polished surfaces - borders rounded and smooth
Fitting surface – no sharp edges, ridges or acrylic pearls
Seat in mouth along planned path of insertion and withdrawal
Problems with seating – acrylic in undercuts
Flange – will blanch if interference present, common with prominent alveolar ridges
Once seated check fit of all components
Denture should be retentive and stable
Assess occlusion
Heavy tooth contact – ‘target marking’
Light centre surrounded by ring of ink
Other marks (paper taking up the space) – less distinct and lack lighter centre
Also can use shimstock
BULL rule
Instructions to patient
Verbal and written Any expected difficulties and limitations Importance of muscular control Path of insertion and removal Denture and oral hygiene
Review
Any damage to oral tissues? dentures functional? Any adjustment required?
1st review after a week
Common complaints: loose; pain; both
Errors in occlusion
-diffuse mucosal damage
-lack of even contact – uneven loading
-lateral and protrusive interferences – displace denture and damage tissues
-facial discomfort; tenderness in muscles of mastication
Errors in impression surface
Other factors e.g. ridge morphology
MUST assess occlusion!!
Over extension – visual; pressure indicator paste
Processing errors – acrylic pearls
Plaque and denture control
Reassess oral and denture hygiene
Reinforce and modify as necessary
Disclosing solution for denture
Denture maintenance
Regular inspections – caries, plaque accumulation, gingivitis
Continued alveolar resorption esp lower distal extension saddles progressively reduces mucosal support for dentures
Rebases
Repairs and additions to dentures
Denture and angular stomatitis
