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MDENT210 > Dentures > Flashcards

Dentures Flashcards

1
Q

What percentage of the population are denture wearers?

A

15%

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2
Q

Where should the upper denture finish?

A

1-2mm before the fovae palatine

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3
Q

What sort of landmarks to look for in the upper arch?

A

Midline raphe, Hamular notch, sulcus and fraena, incisive papilla

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4
Q

What sort of landmarks to look for in the Lower arch?

A

retromolar pad, external oblique ridge (outer) and mylohyoid ridge (inner), lingual gingival remnant (rare)

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5
Q

What is the average distance from the tip of the incisors to the bac of the incisive papilla?

A

12 1/2 mm

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6
Q

What issues can arise with the mental nerve and dentures?

A

When teeth is lost, bone shrinks away and the mental foramen with mental nerve gets closer to the surface - can get pressurised by denture above it so patients get numbness/ sharp pains in this region

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7
Q

Why do impression materials need to be rigid?

A

impressions have to be sent to the lab and need to retain their shape (alginate prone to shape change due to water changes)

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8
Q

What does greenstick allow you to do?

A

It allows you to increase the length of a stock tray to make it more suitable for a patient’s mouth e.g. extending the trays over the retromolar pads or post-dam regions

can also use inside a poorly fitting tray to customise to an extent where a satisfactory primary impression can be made

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9
Q

What is the purpose of primary impressions?

A

record anatomy and permit primary models to be cast

To allow construction of special trays to record working impressions

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10
Q

What is border moulding?

A

pulling down the lips and cheeks to simulate what happens during chewing/speaking etc whilst taking the impression

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11
Q

How long should you disinfect the impression for?

A

10 minutes

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12
Q

How can you alter the properties of alginate?

A

more water = more running and vice verse

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13
Q

What happens to site and pattern in mandibular resorption?

A

Ridge is pushed further lingual anteriorly (in at the front) and further buccal posteriorly (out at the back)

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14
Q

What happens to site and pattern in maxillary resorption?

A

Residual ridge is displaced palatally in all cases

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15
Q

What are the influencing factors of bone resorption? (systemic, local, denture induced)

A

Systemic - osteoporosis
Local - retained roots preserve alveolar bone as do biocompatible implants
Denture induced - some evidence that denture wearing contributes to resorption

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16
Q

What is the molar crossbite?

A

When the buccal cusps of the upper molars sit inside of the buccal cusps of the lower molars

In edentulous patients this is often due to the buccal resorption of the upper arch and the buccal change of the lower ridge due to the resorptive pattern

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17
Q

How does irregular resorption cause pain?

A

Caused as mucosa is sandwiched between sharp bony spicules and denture

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18
Q

What is angular cheilitis?

A

inflammation of one or both corners of the mouth. Often the corners are red with skin breakdown and crusting. It can also be itchy or painful. The condition can last for days to years.

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19
Q

How are the requirements of ridges with and without undercuts different?

A

Ridge without undercuts (or minimal) - rigid impression material in close fitting special tray

Ridge with large undercuts - elastic impression material in spaced special tray

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20
Q

What are the properties of ZnO?

A
  • Mucostatic - minimal force going through mucosa, recording mucosa at rest - runny material whereas silicone putty is mucocompressive - forces tissues down
  • technique is mucocompressive if used with non spaced non perforated tray (close-fitting tray), mucostatic in areas where it isn’t as close-fitting
  • Sometimes used with one spacer - fine, bumpy ridge, zno wants to be thickened up around these areas
  • Can be used with two spacers and wide perforations in mild flabby areas – relatively mucostatic at the front of the mouth but mucocompressive at the back of the mouth
    Cheap, easy to modify and accurate
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21
Q

Why are tissue stops used?

A

All impression materials work at an optimum thickness

  • ZnO needs no tissue stop
  • Silicone requires a 1.5mm tissue stop
  • Alginate requires a 3mm tissue stop
  • stops the tray showing through if excessive pressure is placed
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22
Q

Where should the tray extend to?

A

Extension of tray should be 1-2mm away from the deepest part of sulcus

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23
Q

Why are finger rests made sometimes?

A

To prevent the fingers distorting the periphery

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24
Q

How is the impression corrected wherever the tray penetrates?

A

Use of handpiece and bur to trim away where tray shows through

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25
Q

How is an impression of a flabby ridge taken?

A
  • upper anterior region mainly
  • ## natural teeth oppose an edentulous ridge
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26
Q

What does the alma gauge measure?

A

The vertical and horizontal height relative to position of anterior central incisors

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27
Q

What are the average vertical and horizontal heights?

A

22mm upper

18mm lower

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28
Q

What is resting face height?

A

Height from nose to chin when all muscles in face relaxed, jaw slightly open but lips put together

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29
Q

What is occlusal face height?

A

Height from nose to chin when teeth are brought together, lips still closed

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30
Q

What is the freeway space?

A

The difference between RFH AND OFH

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31
Q

How are OFH and FWS related?

A

Increasing OFH reduces FWS - INVERSLEY PROPORTIONAL

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32
Q

What is the ideal freeway space?

A

2-4mm

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33
Q

What is the intercuspal position/ centric occlusion

A

occlusal position of the mandible in which the cusps of the teeth of both arches fully interpose themselves with the cusps of the teeth of the opposing arch

teeth fully meet

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34
Q

What is central relation/ retruded position?

retruded contact position - first contact within the rotational movement of the condyle sliding down the fossa when the mouth opens

A

the mandibular jaw position in which the head of the condyle is situated as far posteriorly and superiorly as it possibly can within the mandibular fossa/glenoid fossa

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35
Q

What is retruded contact position?

A

The first teeth/tooth that meets when the head of the condyle first makes rotational movement?

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36
Q

Why do denture patients need RCP as a reference point?

A

Only reliable starting point for occlusion due to being edentulous

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37
Q

What are foxes plane guide?

A

See whether dentures are parallel in 2 planes - intrapupillary plane and alatragal plane

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38
Q

What do the dividers do?

A

measure distance between nose and chin

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39
Q

What are the 3 key measurements at the registration rims stage?

A

The OFH with old dentures in
The RFH with the patients most comfortable denture in
Then determine what you want the OFH to be when the new dentures are made

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40
Q

Why is the OFH of the old set of dentures important?

A

OFH of old dentures is much easier to measure than RFH as patient has something to bite against that is reproducible

Patients struggle to adapt to large changes in OFH

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41
Q

How to relax the patient to find RFH?

A

Ask patient to touch their lips together very gently whilst staring at a distant object

1,2,3, - lips touch on 3
Gentle imperceptible blowng
Say mmm
Look away and wait until patient relaxed

  • measure with the patient wearing only one denture
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42
Q

Where do you mark the incisal plane of the registration rim?

A

Parallel to the interpupillary line and approx level of upper lip

Mark posterior occlusal plane parallel to alar of nose/tragus of ear

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43
Q

What can be added to improve lip support to the wax blocks?

A

Extra wax

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44
Q

How to adjust the lower block?

A

Guide patient to RCP
tongue to back of mouth
Trim lower block until meeting evenly in retruded position at the predetermined OFH

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45
Q

Why do we use finger rests on registration block?

A

Secure hold of the mandible and prevent the registration block from moving during the process

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46
Q

Why do we use occlusal notches on both blocks?

A

They allow silicone to seal the blocks together in a unique position and allow the technicians to reattach the blocks in the correct position if they come apart

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47
Q

What should you check at the try in phase?

A 
Aesthetics
The OVD/OFH
Occlusion in relation to ICP and RCP - ICP = RCP
The border extensions
The border thickness 
Neutral zone issues
Tongue space
Mark post dam and lower border extensions
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48
Q

What is a class 2 div 2 occlusion?

A

Anterior incisors slightly retroclined

Lateral incicsors slightly proclined

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49
Q

How can you get more teeth to contact in occlusion?

A

Take tip off canine

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50
Q

What is a post dam?

A

Raised part at the back of the dentures - need to map this for retention of denture
Bigger the patient = deeper the post dam
- compressibility different indifferent areas - edges of hard palate are more compressible

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51
Q

How to mark the post dam?

A

Get patient to say aah
See where the vibrating line is - mark visually
Palpate anteriorly to this with a ball/pear burnished to see which tissues are compressed
Consider 2 post dams - retching
Ask lab to make it as thin as possible

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52
Q

What sort of faults can arise with dentures?

A

Patient related
Laboratory related
Clinical related

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53
Q

What sort of patient related faults with dentures can arise?

A

Systemic disease - Parkinson’s, dyskinesia, hormonal

Local pathology - atrophy, fibrous replacement, undercuts, anomalies

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54
Q

What is a torus palatinus?

A

Solid lump of bone in the palate

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55
Q

What lab related faults can arise?

A

Technical errors - investment tooth movement, processing - flash of acrylic, post dam
- damage to the model

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56
Q

What clinician related faults can arise with dentures?

A

Impression defects

Registration errors

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57
Q

What is the placement technique for correcting clinican related faults for dentures?

A 
Inspect fitting surface 
Insert - correct faults
Check occlusion - correct faults
Fitting surface - remove pressure spots
Security - correct faults
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58
Q

What is the fitting surface? I

A

Anything in direct contact with the tissues

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59
Q

What is the polished surface?

A

The outer labial part of the denture

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60
Q

What rule is used to adjust the lateral excursions with a bur?

A

BULL rule - for articulation - adjust buccal uppers and lingual lowers only

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61
Q

What is the main reason for getting denture stomatitis?

A

Keeping dentures in at night

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62
Q

What are the important points about the denture try in stage?

A

get patient to sign in the notes that aesthetics are acceptable

  • get opinion of significant other person
  • mark borders and extensions of periphery
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63
Q

What are the two compensation curves introduced for occlusal balance?

A

The antero-posterior curve - curve of spee

a lateral curve - curve of monson

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64
Q

What is balanced occlusion?

A

This relates to the first point of contact when the patient occludes in centric relation – view as a static position
As many teeth as possible should contact evenly in this position

ICP must equal RCP

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65
Q

What is the antero-posterior curve called?

A

curve of Spee

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66
Q

What does the antero-posterior curve maintain?

A

Mesio-distal contact between teeth

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67
Q

What is the lateral curve called?

A

Curve of Monson

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68
Q

How much should the teeth of the denture be showing when at rest?

A

1/2 or 2/3 of incisors but be careful of patients opinion of old dentures

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69
Q

How would you fix an error in vertical jaw relations?

A

If small, can make changes at articulator pin and request re-try

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70
Q

How would you correct an error in antero-posterior alignment of the top and bottom dentures?

A

Remove teeth where not aligned and place wax block to re-register the bite, then replace teeth in correct position

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71
Q

How would you guide the patient’s lower jaw into ICP?

A

Take firm control of lower jaw - index fingers buccal to the lower 456 region and thumbs under the chin

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72
Q

How would you check for overextensions of the denture?

A

Check cheek traction and see if denture is coming up when cheeks and lips are moved around it, trim away where extended

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73
Q

What is a common problem with the lower anterior tooth position?

A

Lower anteriors are often too far forward and have to be moved back

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74
Q

What is a common problem with the lower posterior teeth?

A

May be too far lingually so not enough space for tongue

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75
Q

Why are 7’s usually not placed in dentures?

A

Need good space for buccal fat pads (cheeks), dentures can often be misaligned and misplaced with 7’s present

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76
Q

What is the post dam?

A

back part of denture (where hard palate and soft palate)has shrinkage - no air seal to hard palate so suction reduced

post dam is the raised bit on the back

Back of denture needs to be pressed on hard palate

77
Q

Why do we need to mark the post dam?

A

Technician has no idea as to the compressibility of the mouth

every patient is different - bigger the patient- deeper the post dam

compressibility is different in different areas

inadequate post dam leads to poor posterior seal

78
Q

How do we mark the post dam?

A

Get the patient to say aaaaaaaahhhhhh

see where the vibrating line is (where midline raphe is tethered into)

palpate anteriorly to this with a ball or pear burnisher to see which tissues are compressible

consider marking more than one post dam if retching or poor tolerance is expected.

Ask the lab to keep the acrylic between the two post dams as thin as possible

79
Q

Where should the distal margin of the maxillary denture finish?

A

1-2mm anterior to foveae palatini

need to see 2 little dots when denture has tried in - cut forward

80
Q

Where is the palate always more compressible?

A

Lateral sides of palate

81
Q

What would you use to cut the post dam?

A

Ash 3- 693

scribe to the required depth with ash knife or large bur in a straight handpiece

82
Q

What other markings are useful for the lab technician?

A

Retromolar extensions
width of frenal relief
Buccal extensions around the external oblique regions (mark where the lower denture should finish - 1/2 to 2/3 back onto the retromolar pad)

83
Q

What problems can be encountered at review stage? (SPAINC)

A 
Speech
Pain
Appearance
Insecurity 
Nausea 
Chewing
84
Q

Where can pain mostly be experienced?

A

Periphery of denture bearing tissues
Centrally on denture bearing tissues - bulky prominences on ridge
Cheek/lip biting - too far buccal or too far lingual
Numbness

85
Q

What are common ulcer sites from dentures? (M, H, P, F, G)

A 
Mylohyoid region
Hamular notch 
Post dam - junction of hard and soft palate 
Around frenal attachments 
Genial tubercles - atrophic mandible
86
Q

How would you adjust a denture at review stage?

A 
Pick up technique 
Dry surfaces
Mark with ZnO2 or Dycal paste 
Transfer to denture 
Adjust denture accordingly
87
Q

How to adjust an area causing an ulcer?

A

Apply cream to the ulcer (ZnO2, Dycal paste)
Insert denture
Ulcer area picks up on the denture when removed
Adjust with bur

88
Q

How would you stop the denture impacting the mental nerve region in a severely resorped mandible?

A

Cut hollows in the areas of the denture that would impact the mental nerve region

89
Q

How would you stop the tongue being trapped by the dentures?

A

Cut the posterior tooth in half to make more space for the tongue

90
Q

How would you correct freeway space at the review stage?

A

Have to start again and remake dentures

91
Q

What can cause insecurity when speaking?

A

Muscle interference at periphery

Muscle interference of polished surfaces

92
Q

What causes insecurity when eating?

A

Occlusal interference

Poor ridge form

93
Q

How would you fix underextensions of the denture?

A

Self curing acrylic

Apply to specific areas and insert in patient’s mouth to get exact shape of area

94
Q

How would you solve an occlusal fault?

A

Pre-centric check record - insert dentures with wax on the periphery to register the bite, dentures then re-articulated

  • makes sure retruded and intercuspal positions match again (ICP = RCP)
95
Q

What can affect speech with a denture in?

A

Tooth position
Shape of base
Lack of FWS

96
Q

How can speech be improved?

A

Ridge of acrylic on upper anterior lingual surface adjusted - with ridge removed, speech is improved
Palatal cusps of 4’s can be too bulky compared to the old set
Tongue cramping

97
Q

What can cause nausea from a denture?

A 
Insecurity - post dam deficient 
Thick posterior margin
Intolerance
Dropping on to posterior tongue 
general intolerance of the denture
98
Q

How can you manage nausea patients?

A

Use a training denture

99
Q

What can cause TMJ or facial muscle pain?

A 
Nearly always FWS or occlusal problem
Patient might sleep with dentures in
Check for general redness on the ridges (FWS problem - remake dentures)
Palpate ridges for general redness 
Often no discernible ulcers
100
Q

Where can pain mostly be experienced?

A

Periphery of denture bearing tissues
Centrally on denture bearing tissues - bulky prominences on ridge
Cheek/lip biting - too far buccal or too far lingual
Numbness

101
Q

What are common ulcer sites from dentures?

A 
Mylohyoid region
Hamular notch 
Post dam - junction of hard and soft palate 
Around frenal attachments 
Genial tubercles - atrophic mandible
102
Q

How would you adjust a denture at review stage?

A 
Pick up technique 
Dry surfaces
Mark with ZnO2 or Dycal paste 
Transfer to denture 
Adjust denture accordingly
103
Q

How to adjust an area causing an ulcer?

A

Apply cream to the ulcer
Insert denture
Ulcer area picks up on the denture when removed
Adjust with bur

104
Q

How would you stop the denture impacting the mental nerve region in a severely resorped mandible?

A

Cut hollows in the areas of the denture that would impact the mental nerve region

105
Q

How would you stop the tongue being trapped by the dentures?

A

Cut the posterior tooth in half to make more space for the tongue

106
Q

How would you correct freeway space at the review stage?

A

Have to start again and remake dentures

107
Q

What can cause insecurity when speaking?

A

Muscle interference at periphery

Muscle interference of polished surfaces

108
Q

What causes insecurity when eating?

A

Occlusal interference

Poor ridge form

109
Q

How would you fix underextensions of the denture?

A

Self curing acrylic

Apply to specific areas and insert in patient’s mouth to get exact shape of area

110
Q

How would you solve an occlusal fault?

A

Pre-centric check record - insert dentures with wax on the periphery to register the bite

111
Q

What can affect speech with a denture in?

A

Tooth position
Shape of base
Lack of FWS

112
Q

How can speech be improved?

A

Ridge of upper anterior lingual surface adjusted
Palatal cusps of 4’s can be too bulky compared to the old set
Tongue cramping

113
Q

What can cause nausea from a denture?

A

Insecurity - post dam deficient
Thick posterior margin
Intolerance
Dropping on to posterior tongue

114
Q

How can you manage nausea patients?

A

Use a training denture

115
Q

What can cause TMJ or facial muscle pain?

A 
Nearly always FWS or occlusal problem
Patient might sleep with dentures in
Check for general redness on the ridges (FWS problem - remake dentures)
Palpate ridges for general redness 
Often no discernible ulcers
116
Q

What is a summary of the first 4 stages in making a denture?

A

Record the shape of the ridges
Record the inter-ridge relationships
Make a wax template
Convert the template to a denture

117
Q

What are the 7 stages of denture making?

A 
Construction
Primary Impressions
Secondary or Definitive Impressions
Registration
Wax Try in

Provision
Denture Fit
Post-fit Review
6-12 months post-fit Review

118
Q

What are the 2 categories of relevant anatomical structures to dentures?

A

Those making the denture periphery - the maxilla and the mandible

Those marking the site of the teeth - the maxilla

119
Q

What does the hamular notch mark?

A

The distal edge of the maxillary denture where tendon of tensor palatine expands into soft palate

120
Q

What do the sulcus and fraena mark?

A

Marks functional extent of the denture

121
Q

What does the retromolar pad mark?

A

Distal extent of mandibular denture

122
Q

What does the mylohyoid ridge and and external oblique ridge mark?

A

Medial and lateral limits of bony support

123
Q

What does the lingual gingival remnant and incisive papilla indicate?

A

Indicates the lingual margin of posterior teeth and labial surfaces of anterior teeth

124
Q

What 2 muscle insertions are important landmarks for dentures?

A

Insertion of mentalis

Insertion of genioglossus

125
Q

List some points of information you would give to gain the full and valid consent of dentures?

A

Diagnosis – what the current problem is
Prognosis – chance of success of the new dentures
Can the patients desires and wishes be realistically achieved?
The number of visits needed and what treatment will be carried out
Proposed changes, benefits and risks
Ask the patient if they understand, and ask if they have any questions
Clearly document in the clinical notes that this has been carried out

126
Q

What should you tell or ask the patient on subsequent denture visits?

A

Diagnosis – what the current problem is
Prognosis – chance of success of the new dentures
Can the patients desires and wishes be realistically achieved?
The number of visits needed and what treatment will be carried out
Proposed changes, benefits and risks
Ask the patient if they understand, and ask if they have any questions
Clearly document in the clinical notes that this has been carried out

127
Q

What are the 4 requirements of a denture impression material?

A

Accuracy
Resolution
Dimensional Stability
Rigid or elastic

128
Q

What are the ideal properties of a denture impression material? and what are the practical problems?

A

Simple technique, cheap to use, bonds to tray
Viscous during placement
Elastic when set

Viscoelastic when set
Unstable with time

129
Q

Why is a bonding agent applied to the tray?

A

Mechanical retention via perforations insufficient by itself.

130
Q

Why is the impression material made in a stiff mix?

A

Stiff, viscous mix serves to displace soft tissues from denture-bearing area

131
Q

Where do you stand in relation to the patient when taking impressions?

A

For upper impression – stand behind the patients right shoulder and their maxilla should be at your elbow height
For lower impression – stand in front of the patient and the mandible should be at your elbow height

132
Q

What is the angle of the chair for an upper impression?

A

60 degrees

133
Q

Where do you first put the maxillary tray when inserting?

A

Hover the tray , pull back the upper lip then place the tray in the labial sulcus first – the midline labial frenum is your key landmark.
Then tip the tray upwards posteriorly until alginate can be seen just beyond the distal aspect of the tray

134
Q

How can you adjust the primary impression?

A

Remove overextensions
Remove obstacles to peripheral flow
Relieve fraena

135
Q

Where do you mark the periphery of the primary impression for the lab?

A

Mark periphery 2mm inside the maximum depth of the impression
This will confirm the extent of the special tray

-indelible pencil

136
Q

Where does the ridge resorb in the maxilla?

A

Residual ridge is displaced palatally in all cases

137
Q

What is the most common material and tray used for the working/definitive impressions?

A

Close fitting tray with zinc oxide eugenol (rigid material) - CCDH

138
Q

What do you do if you have a ridge with some undercuts for the working impression?

A

Change the spacing around the undercuts rather than changing to a complete elastic impression material - silicone can’t define the borders as well as zinc oxide

139
Q

What is an undercut?

A

the contour of a cross-section of a residual ridge of dental arch that would prevent the placement of a denture or other prosthesis

140
Q

Which materials require a spacer if used for the working impression?

A

Silcione/alginate (elastic materials) - alginate should also have perforations in the tray

Zno doesn’t

141
Q

What is the width of the spacer for alginate?

A

3mm

too little or too much - alginate will distort

142
Q

How many tissue stops are used for the working impression usually?

A

3 different points on the tray

- stops tray showing through if excessive pressure placed

143
Q

Where is the most common place for underextensions on the working impression?

A

disto-lingual of the lower

144
Q

Why does a flabby ridge cause instability of the denture?

A

Due to lack of underlying bone

145
Q

Why are the finger rests placed in the premolar region?

A

Most stable place

146
Q

What does the horizontal and vertical height of an alma gauge tell you?

A

horizontal - how many mm the tip of the incisors are forward from the incisive papilla

vertical - the length from the tip of the incisors to the incisive papilla

147
Q

What do you record the jaw relationship for dentures?

A

retruded position + (RFH - 3mm)

148
Q

Why might it be useful for the patient to wear one denture when measuring RFH?

A

If they are very overclosed without them in, will help to have one in and measure natural height

149
Q

What does notching of the registration rims allow?

A

Accurate mutual location of the rims together for the technicians - seal in unique position

150
Q

How do dentures achieve balanced articulation?

A

They have multiple contacts on both sides of the denture in lateral and protrusive movements which stops the dentures from tipping - opposite to dentate patients

151
Q

Which curve maintains mesio-distal contact?

A

antero-posterior curve - curve of spee

152
Q

Which is the balancing curve between the working and translating condyles?

A

Curve of Monson

153
Q

What other markings other than the post dam need to be scribed for the technician?

A

Retromolar extensions
Width of frenal relief
Buccal extensions around the external oblique regions
Mark where the lower denture should finish – ½ to 2/3 back onto the retromolar pad

154
Q

What are the main approx 10 things to check for when the patient comes in for the try in phase?

A

check upper for:
intra pupillary plane
ala-tragal plane
colour, shade, appearance, lip support

lower:
lower tooth position correct
anterior teeth position

upper meet lower denture at predetermined height
does icp=rcp

155
Q

What paste can be used to remove pressure spots on the fitting surface?

A

PSI paste?

156
Q

What could be a causing a loss of security anteriorly?

A

insufficient fraenal relief

157
Q

What is denture stomatitis?

A

a common condition where mild inflammation and redness of the oral mucous membrane occurs beneath a denture. In about 90% of cases, Candida species are involved, which are normally a harmless component of the oral microbiota in many people. Denture-related stomatitis is the most common form of oral candidiasis (a yeast infection of the mouth).

158
Q

What is central pain often due to?

A

Bony ridges

159
Q

What is cheek biting often due to?

A

Lack of space for buccal fat pads between upper and lower denture

160
Q

What is tongue biting often due to?

A

Lack of FWS

or lower dentures too far in lingually

161
Q

What can cause an insecure upper denture?

A

Lack of peripheral seal usually at the distal margin

162
Q

What type of error is chewing usually?

A

Occlusal error
Locked occlusion

corrected by pre-centric check record

163
Q

What are the ideal properties for a denture base material?

A 
Biocompatible
Aesthetic
Hygienic (Resistant to bacterial contamination)
Dimensionally stable
High Strength, stiffness, hardness and toughness
High thermal conductivity
Low density
Cost

Ease of:
Processing
Repair/adjust
Reproduction of surface detail

Radiopacity

164
Q

what materials are used in denture base materials (6)?

A 
Polymethyl methacrylate (PMMA)
Polyetheretherketone (PEEK) 
Nylon: flexible dentures (Valplast)
Polyamide (Bredent)
Cobalt Chrome alloy
Titanium
165
Q

What is PMMA?

A

Poly (methyl methacrylate)
Plastic

Organic polymer : Long chain molecule of repeated units of methyl methacrylate

Thermoplastic Tg ranges from 85 -165C

166
Q

What initiator is used to start the process of free radical polymerisation of PMMA?

A

Benzyl peroxide

This molecule readily splits into two, each fragment having one unpaired electron.
These fragments attack the C=C bond starting the polymerisation.

167
Q

What cross linking agent is used between PMMA polymer chains to increase its mechanical and physical properties?

A

Diethylene glycol dimethacrylate

168
Q

What sort of processing problems can occur with dentures bases?

A

Porosity - Volatisation of monomer during curing if the temperature is raised too quickly.
This is because the reaction is exothermic and the monomer has a relatively low boiling point

Polymerisation shrinkage - Can result in the denture not contacting the hard palate or porosity
- polymer heated too quickly

Processing strains
These may arise due to dissimilar materials being used (e.g.ceramic teeth or CoCr components)
Also if the polymer is cooled too quickly

169
Q

How can porosity of a denture base be avoided?

A

Use a slow heating cycle when curing and keep under pressure

170
Q

How can polymerisation shrinkage of the denture base be minimised?

A

Use polymer beads to reduce the necessary polymerisation to a minimum
Keep denture under pressure and use a slow cool when curing
Incorporate a post dam on to the denture to compensate

171
Q

What alternative processing routes are there to make a denture base?

A

‘Injection molding’ of acrylic dough
Injection molding of acrylic above Tg
Milling from block

172
Q

What is injection moulding?

A

Heat material to above to above Tg
Squeeze into mould using high pressure
works for PMMA, Polyamide, PEEK

173
Q

What is the composition of PMMA?

A 
Powder
Polymethyl methacrylate granules
Initiator
Pigments, Dyes & Opacifiers
Plasticisers
Synthetic fibres (nylon)

Liquid
Methyl methacrylate monomer
Inhibitor (hydroquinone)
Cross linking agent

174
Q

What is cold cure/auto cure used for?

A

Mainly used for repairs or attaching teeth to a CoCr RPD

175
Q

Why does cold cure have more porosity?

A

Has a lower molecular weight so more porosity which is less dense, soft, weaker and is prone to discolouration.

176
Q

What does high impact PMMA contain a co-polymer of?

A

butadiene and styrene

Results in a dispersion of rubber inclusions.

177
Q

What materials can denture teeth be made out of?

A

Acrylic
Highly crossed linked acrylic
Composite
Ceramic

178
Q

Why may denture wearers get irritant contact dermatitis?

A

usually associated with the release of residual monomer

Delayed hypersensitivity (Type IV)

179
Q

Why do dentures need relining?

A

Carried out when denture becomes ill-fitting due to bone resorbtion.

180
Q

What do you usally reline a denture with?

A

conventional PMMA.

Cold cure resin may be used if this is to be a temporary measure or the procedure is being carried out on an RPD

181
Q

How is a denture relined?

A

Remove undercuts & periphery chairside
Take an impression (ZOE or Silicone)
Send to lab, Model is cast
Vertical dimension recorded (articulator or reline jig)
Impression material replaced with wax
Usual processing to replace wax with acrylic

182
Q

What are the issues with Tokuso chairside reline material?

A

Remove too soon – distortion
Remove too late – exothermic reaction
Residual monomer
Colour retention

183
Q

Why may soft liners be used?

A

It absorbs shock between the hard base of your denture and your gums. Soft liners can be used when creating new dentures or retrofitted into existing dentures. Processed soft liners provide comfort and relief for individuals with receded and flattened gum tissues that don’t respond well to the stress of dentures.

184
Q

What are the requirements of a soft liner?

A 
Low elastic modulus
Retain low elastic modulus
High resilience
Good adhesion to denture base
High tear strength
Biocompatible
Antibacterial
Dimensionally stable
Good surface wettability
185
Q

What materials can be used for a soft liner?

A

Plasticised Heat cured acrylic
e.g Coe Super Soft

Silicone rubber
Cold Cured - e.g Flexibase, TSR
Heat cured - e.g. Molloplast-B

Silicone/Acrylic co-polymer
e.g. Flexor

186
Q

What are the differences between silicone based and acrylate based soft liners?

A

Silicone based:

Highly resilient
Retain softness
Weak bond to acrylic
Susceptible to growth of candida
Poor tear strength
No permanent deformation
Poor wettability
Needs regular replacement

Acrylate based:

Not as resilient as silicones
Go hard with time 
Resistant to bacterial growth
Excellent bond to acrylic
Acceptable tear strength
Susceptible to creep
Good wettability
needs regular replacement
187
Q

What are tissue conditioners?

A

These are temporary linings that allow traumatised tissue to recover before carrying out definitive treatments

Tissue conditioning is an effort to restore the health of the tissues of the denture foundation area before master impressions are made by relining the dentures with temporary denture reliners.

188
Q

What is the composition of tissue conditioners (visco gel)?

A

Polyethylmethacrylate (low Tg)
Butyl phthalyl glycolate (plasticiser)
Ethyl alcohol (solvent)

MDENT210 (7 decks)

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