CAD - COMPLETE DENTURES: retention and stability & problems and solutions

Question 1

Define retention.

Answer 1

It is the resistance to vertical forces directed away from the mucosa. (what keeps a denture from coming out).

Question 2

What is denture stability?

Answer 2

Where the denture remains in place during function (eating, speaking, swallowing).

Question 3

Retention can be achieved through suction and close adaption of denture to tissues. What happens if air/fluid gets between the soft tissues and denture?

Answer 3

Seal is broken which causes the denture to drop.

Question 4

What factors can aid retention?

Answer 4

• Border seal (peripheral seal & Post Dam)
• Saliva (adhesion/cohesion & seal)
• Patient control (muscular forces & neutral zone)
• Accessory retention (over dentures, implants and denture fixatives)

Question 5

What is the benefit of a border seal in complete dentures?

Answer 5

Prevents air / food / water getting underneath the denture and displacing it from the tissues.

Prevents the loss of retention.

Question 6

How is an effective border seal achieved?

Answer 6

The gap must be as small as possible, whilst allowing movement of the soft tissues.

Question 7

What is the ‘Post Dam’ feature of upper complete dentures?

Answer 7

Raised edge at the posterior border of the denture that creates an air tight seal against air/fluid between the denture and palatal mucosa.

Placed over the hard palate and extended for a larger surface area.

Question 8

What are the two methods for creating a Post Dam?

Answer 8

Clinically: use a mucocompressive material along the back edge of the impression tray.

Technically: the technician creates a small groove in the plaster at the back edge of the intended denture.

Question 9

What considerations should be made after the denture fit when a post dam is used in the denture design?

Answer 9

Can leave an imprint in the mucosa and cause ulceration. Check at denture review if smoothing is required.

Question 10

How is an effective border seal achieved at the impression stage?

Answer 10

1. Use a non – perforated tray.
2. Use green / pink stick to compress the post dam area and record the functional width of the sulcus in the tuberosity region (upper posterior area).
3. Ensure retention on the tray before continuing with impression by pulling down vertically.

Question 11

Patients who suffer from _______ may have difficulties with retention of upper dentures

Answer 11

Xerostomia

Note: this may be associated with drugs, radiotherapy, rheumatoid arthritis, Sjogren’s syndrome.

Question 12

What is the role of saliva in creating a border seal?

Answer 12

A thin film of saliva between the mucosa and denture creates a border seal through weak intermolecular forces of attraction via adhesion and cohesion; which prevents air/food from getting under the denture.

Question 13

How can you check if a patient has xerostomia?

Answer 13

• Wipe gloved finger along the inside of cheek.
• Challocombe Scale

Question 14

How is retention achieved through muscular forces?

Answer 14

Muscles keep the seal intact and push the denture into place.

e.g. the tongue - the action of biting can cause the denture to fall down, so tongue helps push denture up.

Question 15

Which condition may cause loss of muscular control that lead to problems with denture retention?

Answer 15

Parkinson’s disease
Stroke (facial paralysis)
Motor neurone disease

Question 15

Which condition may cause loss of muscular control that lead to problems with denture retention?

Answer 15

Parkinson’s disease
Stroke (facial paralysis)
Motor neurone disease

Question 16

What are the adv / disadvantages of implant retained overdentures?

Answer 16

Adv: treatment option for the treatment of atrophic mandible.

Disadv: requires adequate bone, expensive.

Question 17

What product can be recommended to patients to aid retention of dentures?

Answer 17

Denture fixative.

Question 18

What are the benefits of implant treatment?

Answer 18

• Maintains bone
• Gives support and provides positive retention.
• Higher degree of patient satisfaction
• Improved bite force
• Improved chewing ability

Question 19

How do denture fixatives work?

Answer 19

Acts by making saliva more viscous.

Increases feeling of security for patients.

Improves seal, max. bite force and QoL.

*Use sparingly - increases plaque. If needing to use daily - see dentist.

Question 20

What are the risks of fixatives containing zinc?

Answer 20

Zinc overdoses reported.
Numbness and tingling of arms and legs.
Problems with walking and balance.

Note: advise patients to opt for zinc free versions.

Question 21

What are the effects of denture instability?

Answer 21

Pain - denture rubbing every time it moves out of place. Extra pressure exerted to keep the denture in place (clenching together to prevent denture falling out).

Looseness

Inability to chew - denture moving, causing pain.

Denture moving during speech

Social/psychological effects.

Question 22

What are the associated factors of denture looseness with unstable dentures?

Answer 22

Denture moving breaks the border seal.

Lack of muscular control

Lack of saliva to create seal

Displacement by muscles (neutral zone)

Question 23

What are the social/psychological impacts of unstable dentures?

Answer 23

Avoids social occasions

Self-conscious

Altered food choices

Poorer QoL

Question 24

What causes the loss of stability?

Answer 24

Premature occlusal contacts

Teeth not in correct position in relation to the ridge

Interferences on lateral movements

Changes in support area under the denture

Question 25

What is the difference between balanced occlusion and balanced articulation?

Answer 25

Balanced occlusion – teeth meet evenly on both sides at the same time when the patient closes.

Balanced articulation – during lateral movements the contacts are shared across as many teeth as possible. No cuspal interferences when jaw is moved side to side.

Question 26

What happens if there is a premature contact with a patients dentures?

Answer 26

Patient will bite prematurely on one side.

Air enters under the denture at the top, causing denture to fall out.

Question 27

Upon examination, it may looks as though dentures fit well but premature contacts cause patients problems when they eat. List these problems and how premature contacts can be detected clinically.

Answer 27

Premature contacts cause problems such as pain, soreness and ulceration on review.

Flange may be over-extended or occlusion causing too much pressure on one side.

Difficult to detect. But, clinically you can hold the lower denture in place whilst patient is closing together – feel for tactile pressure through fingers - which side hitting first? *difficult to tell with articulating paper – blue marks both sides.

Question 28

A poorly designed denture with poor occlusion and over-extended flanges may cause _________.

Answer 28

Ulcers, which in time can cause soft tissue hyperplasia. This is a reaction to continued trauma.

Question 29

For maximum support on chewing, how should teeth be positioned on a denture?

Answer 29

Palatal cusp of upper teeth, and the central fossa of lower teeth should be directly over the ridge.

Question 29

Give examples of some design considerations of lower dentures that can aid stabilisation.

Answer 29

Leaving off the 7s can provide the tongue with more space to stabilise the lower denture.

Making teeth narrower can reduce tongue cramping

The occlusal plane should be lower than the tongue.

Question 30

What is the neutral zone in lower dentures?

Answer 30

The area where the outward forces from the tongue are neutralized or nullified by the forces of the lips and cheeks acting inward during functional movements.

The position of the denture where it is least displaced by movement of muscles of the facial expression and the tongue

Question 31

What would happen if lower teeth are not placed over the ridge?

Answer 31

Denture will be displaced by the mentalist muscle, especially when the ridge is flat.

*Lower anteriors need to be placed straight over the ridge.

Question 32

What is the curve of Wilson (Monson) in denture occlusion?

Answer 32

The curve of Wilson is the across arch curvature or posterior occlusal plane.

Arc of the curve, which is concave for mandibular teeth and convex for maxillary teeth are defined by a line drawn from left mandibular first molar to right mandibular first molar.

*Teeth sit on a curve. Due to jaw sliding down at an angle (due to articular eminence)-> movement of condyle.

Question 33

What is the Christensen’s phenomenon in denture occlusion?

Answer 33

Localised gaps that appear between the rows of teeth during lateral or protrusive movements while partial functional contacts are maintained.

Creates a premature contact anteriorly

Question 34

What is the Curve of Spee?

Answer 34

Defined as the curvature of the mandibular occlusal plane beginning at the tip of the lower canine and following the buccal cusps of the posterior teeth, continuing to the terminal molar.

As teeth protrude, all teeth stay in contact (curves up at back).

Upper teeth should curve upwards and out

Question 35

Which articulator would you use if you are only interested in getting the restoration correct in ICP? [with good canine guidance]

Answer 35

Simple hinge

Question 36

Which articulator would you use if you want to ensure that lateral and protrusive excursions will not create unwanted interferences?

Answer 36

Semi-adjustable

Question 37

Which articulator would you use if you are making a denture? [conformative]

Answer 37

Average value

*Can replicate ICP, opening and closing by rotation & translation, lateral movements.

Question 38

Changes to the support area such as loss of bone / flabby ridge can lead to mobile tissues – if support area is mobile, how will this affect the denture?

Answer 38

Can cause denture instability.

*After extraction, bone resorption occurs. 0.1mm on average lost yearly over time.

Question 39

What is the aim of primary impressions? What do we need to record for upper and lowers?

Answer 39

To define the denture support area.

For uppers, record whole of palate, maxillary tuberosities, alveolar ridge, and any prominent frenal attachments.

For lowers, record up to the entire ridge, buccal shelf on each side, any prominent frenal attachments, retromolar pads and papilla.

Question 40

What is the aim for secondary impressions?

Answer 40

To record the entire functional denture-bearing area to ensure maximum support, retention, and stability for the denture during use.

Question 41

What are the requirements for a special tray?

Answer 41

Handle needs to be positioned correctly – if it is horizontal, it doesn’t allow for border moulding.
Need to fully extend to retromolar pads for lowers.
Need to conform to shape of primary imp.

Question 42

For a resorbed ridge with no bony undercut which tray do you need? For a bony undercut which tray do you need?

Answer 42

Resorbed ridge with no bony undercut – close fitting tray
Bony undercut – spaced tray (3mm for alginate; 1.5mm for elastomers/Si).

Question 43

What is the normal naso-labial angle for a class 1 incisal relationship?

Answer 43

Naso-labial angle should be 90-110 degrees for Class I incisal relationship.

Question 44

What is an alma gauge used for?

Answer 44

Used to find the dimensions for the current denture
This allows us to produce identical wax rims when recording the occlusion
Acts by recording the vertical height, proclination & position of anterior teeth
This reduces the time at the max rim stage (minimal adjustment needed)

Question 45

What is the purpose of recording occlusion for complete dentures?

Answer 45

Want to try and achieve bilateral simultaneous contacted in retruded contact position at the correct OVD.

Question 46

What is a copy denture? What are the different options available?

Answer 46

COPY DENTURE – a denture that’s a duplication with or without modifications of a pts. Existing denture.

Option One
Occlusion is recorded when trying in the acrylic base with wax teeth and sealed with Blu- mousse.
New imps. are then recorded when the dentures have been made (light-boded Si wash) using a closed mouth technique.

Option Two
Take imps. first and get dentures fitting properly.
Record occlusion.