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Prosthodontics > partials > Flashcards

partials Flashcards

1
Q

which material of partial dentures to avoid in bad perio patients

A

avoid cobalt chromium, do acrylic

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2
Q

What are the main steps in partial denture production

A
  1. Initial assessment.
  2. Primary impressions with alginate and/or compound
    [3. Lab make model cast and reg blocks
  3. Primary reg (only needed if no stable occlusal contacts. Reproduce natural tooth contacts. Blue mousse) ]
  4. Lab articulate study casts
  5. Design denture and Survey. Pick suitable design. Finalise design and fill in design sheet
  6. Discuss with patient the design. Do any tooth modifications. Request special tray
  7. Secondary impression
  8. Lab make master cast and cast metal framework
  9. Try-in framework
  10. Secondary reg (on framework)
  11. Try-in
  12. Insert
  13. Review
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3
Q

Reasons for partial dentures

A

-Replace missing teeth, preserve remaining dentition
-improves speech, eating (nutrition), biting, occlusal stability, aesthetics, maintain vertical dimension, maintain space to prevent tooth drifting, Psychological and social impact. Prevent over eruption
-Can aid the stabilisation phase (as may not be possible for low BPE and no caries)
-Prevent resorption as there will now be a stimuli.
-Transitional denture to allow teeth to be added to it and transition to complete denture
-the patient must want them, don’t force them, unless you believe they really will benefit from them

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4
Q

Risks/ consequences of partial dentures

A

-plaque retentive= increased risk of perio, caries
-tooth modifications and loss of tooth tissue
-trauma from denture components to soft and hard tissues - abrasion, mucosal trauma
-reduced patient tolerance
-allergic reaction
-increased mobility in abutment teeth

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5
Q

Information to gather at initial patient assessment. Patient factors affecting partial denture success

A

-History: identify main concern, previous denture wear, expectations, dissatisfactions
-Examination: assess oral health, current denture, risk factors for oral disease. OHA [charting, BPE, RAG, ridge anatomy, occlusion, arc of closure, interdental and interocclusal spaces]
-further investigations: radiographs, sensibility testing
-assess factors that may affect success: expectations, age, dexterity, cognitive capacity (consent), mobility to attend appointments,, muscular control for inserting denture, nutrition, oral hygiene, anatomy, degree of stabilisation, motivation, OH
-assess their need, consider alternatives (do nothing, bridge, implant), identify risks and benefits, recognise limitations, consider materials. Prepare the patient by giving OHI, diet analysis, scaling, eliminating BOP, pockets, extract poor prognosis teeth, restorations

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6
Q

How to take a primary impression for a partial denture. Things to consider

A

-as usual consider tray size, your position, the trays position
-you want to capture the full denture bearing area: sulcus depths, retromolar pad, maxillary tuberosity, occlusal aspects of teeth
-want 3-5mm between tray and occlusal plane
-use dentate trays

-use alginate, and supportive compound may be needed in areas with large spaces to carry alginate into these difficult to reach areas
-use compound if gap is wider than 2 thumb widths. Place compound in tray in these saddle areas, about half way up the tray. Put into mouth, shouldn’t touch teeth or tissues. Then Pour alginate over the full tray and take impression

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7
Q

What are the steps in denture design, before surveying

A
  1. Cross out teeth that are missing but not to be replaced [black]
  2. Saddles - hatch [black]
  3. Rests at end of saddles, on abutment teeth [red]
  4. Clasps - retentive and reciprocator component. Clasp either side of midline, 1 anterior 1 posterior, max of 2, each clasp must have a rest [green]
  5. Indirect retention - draw line between clasps and ensure retention perpendicular to line to prevent see-saw movement
  6. Major connectors [black]
  7. Bracing
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8
Q

Explain the Kennedy classification

A

Class I: Bilateral free end saddles
Class II: Unilateral free end saddle
Class III: no free end saddles, bounded saddle(s)
Class IV: anterior saddle that crosses midline

Each class apart from IV has modifications depending on the further edentulous spaces
Mod 1: 1 space
Mod 2: 2 spaces
Mod 3: 3 spaces
Mod 4: 4 spaces

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9
Q

Factors that affect the different design options and placement of clasps

A

-mobile teeth
-aesthetics
-position of undercuts
-health of PDL
-size of tooth- insufficient clasp length
-occlusion
-shape of sulcus - insufficient depth

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10
Q

Function of the saddle

A

Part which sits over the alveolar ridge and carries the artificial teeth.
Prescribing a saddle does not always mean prescribing the replacement of teeth
A large saddle will provide a lot of support and bracing especially in a class 1 or 2 denture

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11
Q

Functions of rests

A

-sit on occlusal, cingulum (and occasionally incisal surfaces) of natural teeth, adjacent to saddle
-Support – resistance to vertical forces directed towards the mucosa. Allow teeth to take some load
-Maintaining position of components i.e. clasps
-Providing Indirect retention
-Protection of the junction between denture and abutment tooth.
-deflect food away from saddle-abutment junction

1 rest will support 1 and a half teeth, so can take one off of a small saddle

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12
Q

Function of clasps. What are the 2 components

A

A mechanical means to help retain a partial denture by engaging undercuts on the tooth surface.
They are referred to as ‘direct retainers’. Resists dislodging forces

-they have retentive and reciprocation elements
-retentive part=terminal 1/3 only provides retention, sitting in the undercut. flexible, thinned, tapered. The remainder of the clasp sits in non-undercut. Sits passively
-reciprocator= reciprocates the retentive component to resist tooth movement. Doesn’t sit in undercut.

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13
Q

the different types of clasps and reciprocation

A

-clasp arm, circumferential, 3-armed
-I bar = gingivally approaching used on premolars or incisors. They are longer so allow flexibility, but require sufficient sulcus depth. They improve aesthetics on incisors

-reciprocation may take the form of a rigid connector, if it extends right up the the gingival margin
type used usually depends on position of undercut

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14
Q

how long do the clasp arms need to be in molars/ premolars. What materials are used for clasps

A

-CoCr is a fairly rigid material and Clasps need flexibility, therefore:
-Clasp arms need to be 12-15mm in length
-Some premolars may have insufficient length so either change clasp design of change the material (acrylic denture can have gold or stainless steel, CoCr can have gold)

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15
Q

What factors affect retention of a clasp

A

-length (longer is more retentive)
-elasticity of alloy
-depth of undercut engaged
-cross section/thickness of clasp

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16
Q

What is a major connector and the different types. How many mm does it need to clear gingival tissues

A

-connects the parts of the prosthesis on one side of the arch to the other
-Where possible avoid coverage of gingival tissues (min 4mm clearance)
-if lots of teeth missing then want lots of support on palate
-can reciprocate with connector in anterior teeth

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17
Q

Function of the minor connector

A
  • join the major connector to other parts of the denture, additionally they may have a ‘bracing’ and ‘stabilising’ effect.
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18
Q

What is indirect retention in partial dentures. What it is provided by. How to assess it when designing

A

-Resistance to rotational or tipping displacement around the clasping axis
-Provided by: Rests, Connectors, saddles
-stops see-saw movement

-Draw axis between clasp tips, check if retentive factors on either side, perpendicular to axis. Prevents see-saw motion. Want it to be balanced

19
Q

What are bracing forces

A

Resistance to horizontal (lateral) forces from parts of the denture resting against vertical surfaces on teeth and residual ridge

20
Q

How to use the surveyor

A

-assessing undercuts, guide planes, dead spaces, path of insertion
-place cast on model table. Make it flat so natural line of insertion
-marking undercuts by marking most bulbous part- marker at level of gingival margin around tooth. Everything below the line is undercut. look for tissue undercuts too
-get undercut gauge and find the undercut. See how low down the bit that sticks out goes until the shank rests agains the tooth. If survey line is too low and undercut too low then may need to add composite, or if survey line too high then remove enamel.
-Mark where you want clasp. may need tooth adjustments to allow flat guide planes
-mark side of cast to show how it was surveyed (line of insertion for path of natural displacement)

-if changing pattern of insertion (due to big undercuts that would cause big triangles and poor retention) then carry out secondary survey with different colour and mark side of cast again

21
Q

How much undercut do you want

A

usually 0.25mm
But for circumferential and I bars they are more flexible so 0.5mm

22
Q

Reasons for changing the path of insertion for a partial denture

A

If big tissue undercut and undercuts neck to saddle on the abutment teeth
1. Improves aesthetics -less bulky labially as it can engage into tissue undercut
2. gets rid of black triangles at guide planes
3. improves retention as more surface area against tissues in the undercut, at guide planes
4. Minimises interferences

23
Q

What are guide planes

A

mesial and distal proximal surfaces next to saddle
minor adjustments to flatten surface reduce the undercut for a definite path of insertion and more surface area in contact to aid retention. Also removes black triangles. And allow for a definitive path of insertion

24
Q

Why tooth modifications may be required for a partial denture

A

-if an undercut is too high for a clasped tooth (survey Line sits too high so clasp would be too high) then the past of the tooth where the clasp wouldn’t be in undercut is drilled to lower it
-too low undercut, then composite added to improve it

-guide planes on mesial/distal proximal surfaces of teeth next to the saddle, can be changed to improve aesthetics and retention
-undercuts may be really big which create black triangles, and also decrease retention as there is decreased surface area in contact
-drilling some enamel can flatten the proximal surface and improve aesthetics, retention and enable a definite path of insertion
-teeth on either side of saddle must be mutually parallel when making changes

-areas where rest seats may need drilling to evenly distribute the load (only if benefits outweigh risks eg. may damage existing restoration)

-may need to cut enamel if there is no space for clasp to occlude onto

25
Q

Special tray requirements. A major difference between it for partial and completes

A

Rigid and strong
Cover the entire denture bearing area
Border extensions should be 2mm short of the sulcus and muscle attachments for greenstick
Peripheral edge of the tray should be smooth and rounded and of an even width (2-3mm)
Handle should be angulated so as not to interfere with the lip

Perforations are required (unlike for complete dentures) allowing escape for excess impression material helping to prevent the build-up of hydrostatic pressure.

26
Q

What makes an occlusion stable and unstable

A

-stable= maintained contacts, no parafunction, no symtpoms
-unstable= loss of contacts, tilting, drifting, overeruption, may manifest after many years

27
Q

Reasons for a cobalt chromium and acrylic partial denture

A

-CoCr= gets support from hard and soft tissues. Best option in most cases as best support and stability. Not used in bad cases of perio
-Acrylic=gets support only from soft tissues. Would be used if inadequate support from remaining teeth or if the denture is to be provided as an immediate denture. More porous so candida infection more likely.

28
Q

Why support and stability of free end saddle dentures are not great(class I and II) Techniques to improve this

A

-Indirect retention is often a problem with free-end saddles due to no support posteriorly,
-indirect retention is ultimately determined by the type of major connector and whether rest elements can be placed onto the anterior teeth
-when vertical load is applied excess leverage is applied to abutment tooth distally, causing mobility, bone loss, denture instability
-retromolar region is spongey so more rapid resorption in this area and more saddle rotation. Discomfort
-Therefore:
- cover as much surface area as possible to distribute functional forces widely
-the Alternative cast technique
-RPI system
-stress breakers

29
Q

Name types of lower and upper major connectors. What factors to consider when choosing

A

-upper= plate, horseshoe, posterior bar, skeletal
-lower= lingual plate (most common), lingual bar, sublingual bar, dental bar, labial bar

-consider aesthetics, tooth spacing, frenal attachments, interferences, clinical crown height, sulcus depth, prognosis of remaining teeth, how easy it is to keep clean, how tolerable, how rigid, if it provides indirect retention or bracing

30
Q

Flexible dentures pros and cons

A

[Such as Valplast, Sunflex - You will see patients who have had these provided]

-no visible clasps, and the denture clicks into place under divergent undercuts

-but have the potential to be more damaging than even pure acrylic dentures, because the load is not shared between hard and soft tissues, only soft tissues, and they allow differential loading.

-We need some good evidence to show this

31
Q

What is the alternative cast technique for free end saddle dentures

A

-provides a more stable denture for the Class 1 & 2 lower cases, due to their poor posterior support and indirect retention
-using special tray to record mucocompressive impression
-metal framework made on master model, acrylic saddle is added to saddle to act as special tray, impression taken using ZOE, lab alters cast by cutting away the free end saddle and seating framework onto model and boxing in the wax then adding plaster then removing wax and framework to reveal new model which is now mucostatic over the teeth and mucocompressive over the free-end saddle
-want to maximise coverage, shorten and narrow occlusal table

32
Q

What is the RPI system for lower free end saddles

A

-prevents excess distal pulling of abutment tooth
-it is a clasp assembly consisting of:
1. Rest moved mesial- allows more even distribution of load
2. Distal guide Plate - cutting last standing tooth so thin metal minor connector sits close to the abutment tooth. Prevents rotation and limits vertical displacement
3. I bar clasp - no undue stress on abutment

minor connector carrying mesial rest seat acts as reciprocation along with distal plate. Lingual bar preferred to lingual plate

33
Q

Use of diagnostic index for anterior flanges

A

-used in cases with anterior flange, with lack of vertical height, lack of horizontal overlap
-after secondary impression, instead of asking for framework to be fabricated, request for wax try in for planning purposes
-Lack of space means thin acrylic and risks of denture teeth shearing off. So metal backings can be incorporated into the palatal/lingual denture teeth to help protect them as it is stronger and can be made in thin section

34
Q

Factors influencing support for a free end saddle

A

Length of saddle (longer=more movement, more damaging)
Compressibility of tissues (more compressible=more movement)
Extent of coverage of the denture base
The impression technique and accuracy
The accuracy and fit of the denture base
The occlusal forces applied

35
Q

Difference between stress breakers and rigid design

A

-stress breaking clasps= Avoids rotation of the denture due to compressible tissue and causing damage to tooth. Saddle component able to move more than tooth supported component. More load transmitted to ridge tissues. More even load distribution. Use flexible clasp or change rest/clasp relationship. But more complex, costly, less tolerable, needs greater plaque control
-Rigid design= easier to design, more amendable to good plaque control,

36
Q

How the lab produces a Cobalt Crome framework, after tooth modifications, major impression, design

A

-Pour master model
-Place primary model on surveyor, find the chosen POI, lock off surveyor and remove
-Swap major model to surveyor, carry out survey and prepare in order to duplicate and create a refractory model
-prep the model: wax used to relieve and block out unfavourable undercuts. Spacer applied to saddle. Ledge created for accurate position of clasp tip
-create refractory model using agar gel. Investment poured into mould.
-framework is waxed up incrementally onto model
-wax pattern sprued and invested
-casting via lost wax technique
-de-vested, trimmed, electrobrightened
-finished and polished

37
Q

Reason for gingival approaching clasps

A

for incisors and premolars
gives more length than an occlusal approaching clasp on smaller teeth
aesthetically pleasing, hidden by the length

38
Q

Pros and cons of a lingual bar and lingual plate

A

-Plate-most common. Good bracing, indirect retention, rigidity, tolerance
-Bar -better for hygiene purposes. But need sufficient sulus depth, poorer indirect retention and bracing, possible less rigid, possibly less tolerated

39
Q

How much sulcus depth do you need for a lingual bar

A

-can be rigid if sufficient thickness. Needs clearance of 6-7mm from gingival margin to base of lingual sulcus. As the bar is around 3mm deep, and 3mm from margin

40
Q

when might backings on anterior teeth be needed

A

When a patient has a very close vertical or horizontal overbite and when excursions either fracture teeth or wears the incisor edge

41
Q

Reasons for an acrylic partial denture

A

temporary, immediate (inserted after extraction), transitional (will eventually need completes/ will need future teeth additions), poor tooth prognosis/ bad perio, stabalisation phase (improve function, aesthetics, occlusal stability), ease patients to edentulous state

42
Q

The clinical and lab stages of transitional immediate acrylic partial dentures

A

-Patient assessment and primary impressions
-Cast poured, record blocks made if no bilateral anterior and posterior contacts
-Preliminary registration
-Articulate study casts with reg
-Survey and design
-special tray made
-Tooth mods
-Major impressions: request major cast and reg blocks
-Articulate, prepare model – block out undercuts which interfere with the POI, set up trial dentures
-Registration: temporary base of light cured acrylic resin with wire (which won’t fit perfectly until made into permanent acrylic resin)
-try-in
-insert

43
Q

Can clasps be added to acrylic partial dentures

A

-Stainless steel clasps often added at later stages as don’t sit well in wax. They are not accompanied by rests and can distort easily and fail to engage the tooth properly
-Or cobalt chrome rests and clasps can be added if there is adequate support from dentition. But can causes stresses and fracture within the acrylic

Prosthodontics (2 decks)

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