Definitive impressions and ridge resorption

Question 1

Bone changes (alveolar resorption)

Answer 1

1. Magnitude
2. Site and pattern
3. Time relations
4. Influencing factors
5. Problems

Question 2

Magnitude

Answer 2

Approx x4 as much resorption of mandible as maxilla (inconvenient)

Question 3

Site and pattern: mandibular resorption

Answer 3

Residual ridge further lingual anteriorly, further buccal posteriorly - in at the front and out at the back
--> class II pxs overbite would be heightened due to resorption
Need to make teeth on top of strongest point of ridge

Question 4

Site and pattern: maxillary resorption

Answer 4

Residual ridge is displaced palatally in all cases

Can put teeth roughly where they were before

Question 5

Time relations

Answer 5

Main amount of bone loss over the first year
Immediate dentures will become loose
Shrinkage slows down and becomes less significant after 4-5 years

Question 6

Influencing factors

Answer 6

Systemic: osteoporosis
Local: retained roots preserve alveolar bone, as do biocompatible implants
-careful of caries on retained roots
Denture induced: some evidence that denture wearing contributes to resorption (if only wearing denture on uppers)

Question 7

Problems

Answer 7

Denture insecurity
-ill-fitting dentures (no flange, immediate dentures)
-outside the neutral zone
Occlusal problems: cross-bite
Pain:
-mucosa traumatised by compression against sharp, resorbed bony ridges (irregular resorption)
-relative movement of mental foramina will result on p on nerve as it exits
Appearance: lack of support of soft tissues (angular cheilitis - distance between rest & bite becomes bigger_

Question 8

The molar crossbite

Answer 8

When buccal cusps of upper molars sit inside of buccal cusps of lower molars
-in edentulous pxs often due to palatal resorption of upper arch & buccal change of lower ridge due to resorptive pattern

Question 9

Requirements of working impressions

Answer 9

Ridge without undercuts (or minimal undercuts)
-rigid impression material in close fitting special tray
Ridge with large undercuts
-elastic impression material in spaced special tray
-often young edentulous pxs

Question 10

What is an undercut?

Answer 10

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

Question 11

Choice of secondary impression materials: ZnO Eugenol

Answer 11

• Mucostatic
• Technique is mucocompressive if used with non-spaced non-perforated tray
• Sometimes used with one spacer
• Can be used with two spacers and wide perforations in mild flabby areas - relatively mucostatic
• Cheap, easy to modify and accurate

Question 12

Mucostatic

Answer 12

Runny material in spaced tray

Not going to cause any pressure or force to ridges

Question 13

Minimal undercuts (ZnO eugenol)

Answer 13

Tray fits tissues closely, extended just short of final periphery of where the denture is to be extended to.
1-2mm short of the deepest part of the sulcus

Question 14

What prevents distortion with bigger undercuts

Answer 14

Constraining tray

Elastic material: alginate or silicone

Question 15

Thickness of alginate for secondary impressions

Answer 15

3mm thickness

Otherwise losing accuracy

Question 16

The use of tissue stops (ZnO egenol, silicone, alginate)

Answer 16

All impression materials work at an optimum thickness
ZnO needs no tissue stop
Silicone requires 1.5mm tissue stop
Alginate requires 3mm tissue stop
-ask lab to create these for you
-aimm for relatively non-compressive areas
-stops tray showing through if exciessive pressure is placed

Question 17

If you forget tissue stop

Answer 17

There is always ribbon wax or greenstick

Question 18

Clinical technique

Answer 18

1. Tray adjustment
2. Record impression
3. Correct impression
4. Technical detail

Question 19

Tray adjustment

Answer 19

Ensure marked lines are clearly visible and all frenal attachments have full relief
In case of underextension: corrected by addition of light-cure composite ‘green stick’

Question 20

Where should the tray extend to?

Answer 20

1-2mm away from deepest part of sulcus

Question 21

Recording impression

Answer 21

On lower, px should stick tongue up & out and move it side to side
Let it set before border moulding
Make sure upper is in line with labial frenum (oo ah noises, open wide, move side to side)
Finger rests sometimes made to prevent fingers distorting periphery (even amount of p on both sides - in premolar region)

Question 22

Correct impression

Answer 22

The impression must be corrected wherever tray penetrates
Materials:
-posterior with ZoE compressionally
-anterior silicone body mucostatically

Question 23

The flabby/ fibrous ridge

Answer 23

• Ridge becomes displaceable due to fibrous tissue deposition
• Most frequently seen in upper molar region
• Can occur when natural teeth oppose and edentulous ridge
• Causes instability of denture due to lack of underlying bone

Question 24

Window box

Answer 24

For implants and flabby ridges

Inject silicone in there or use wax

Question 25

Use of the Alma Gauge

Answer 25

Horizontal reading - how far ahead upper incisors are in front of incisive papilla
Vertical reading - for height of denture (can adjust to make you see more teeth)

Question 26

Instructions to lab

Answer 26

• Please make upper and lower wax registration rims
• Alma gauge readings of old upper denture using incisive as fixed point V12 H7 - adjust where indicated
• If no dentures to use as a guide then ask for 22mm upper x 18mm lower (big person)

Question 27

Technical detail

Answer 27

The completed impression is beaded by technician 2-3mm short of deepest part of sulcus
This ensures margin of final denture will be extended to precise extent of functional record