shammasm, complete dentures, intro to dentures, 3rd year

1. CUSTOM IMPRESSION
TRAYS AND
CONSTRUCTION OF
MASTER CASTS

2. Learning outcomes
1. Define custom trays and list the
materials for making custom tray.
2. Explain the procedure for making a
custom tray.
3. Define border molding and list the
materials for doing border molding.
4. Define final impressions and list the
materials for making final impressions
and master casts.

3. Patient Visit #2
Visit 2
Clinical
procedure
Lab.
procedure
Evaluation of custom
impression trays
Border molding
Beading & Boxing
& Pouring
the casts
Master casts
Final impression Record Bases
Occlusal Rims

4.  Custom tray: an
individualized impression tray
made from a cast recovered
from a preliminary impression.
 It is used in making a final
impression.

5. Why Use Custom Trays?
Custom trays provide
anatomically correct extension of
denture impressions.
Allow homogeneous thickness of
impression material.
Provide accuracy.

6. Requirements of a custom tray
a) stability in air and in a moist
environment,
b) volume stability over time,
c) moisture resistance,
d) rigidity,
e) adhesion of the impression material in
the tray and
f) even thickness of impression material.

7. Materials Used for Custom Trays
1. The chemically-cured (CC)
acrylic resin custom tray materials
2. Visible Light-Cured (VLC) resin
custom tray materials

8. The chemically-cured (CC) acrylic resin
custom tray materials have some
disadvantages:
Polymerization shrinkage
A time interval must be allowed between
the fabrication and the use of these custom
trays
The hazardous effects caused by the
monomer (methyl methacrylate) include
dermatologic reactions

9. VLC resin is:
less hazardous,
reduces preparation time,
easy to use and
has good handling properties.

10. Identify Denture Extensions
Mark the anticipated final
extension of the denture in
pencil on the cast
Method of fabrication of a
custom tray

12. Mark Tray Extensions
 Mark the tray extension in
pencil about two mm shorter
than the first pencil line except
in posterior palatal seal area.

14. Mark spacer outline
 Mark the spacer outline 2 mm
short of the tray outline. Also
mark the tissue stops in canine
(2) and molar (2) region. Spacer
in the posterior palatal seal
should be bow shaped.

16. Why Spacer?
 The spacer provides room for the
impression material
 It also minimizes the pressure
that could distort the mucosa.

17. Tissue Stops:
 1. To orient the tray
 2. For uniform thickness of the
impression material

18. Block-out undercuts
 Block-out under cuts with
modelling wax.
 To avoid breakage of cast or the
tray

19.  undercut: the contour of a
cross-sectional portion of a
residual ridge or dental arch
that prevents the insertion of a
dental prosthesis

20. Separating media
 Sodium alginate +
calcium sulfate =
insoluble calcium
alginate

21.  Apply separating media on the
cast so that acrylic resin does not
stick to the cast.
Applying separating media

22. Adapt Baseplate Wax to
Spacer Line on Cast

23. Adapt Baseplate Wax to
Spacer Line on Cast

24. Adapt Baseplate Wax to Spacer Line on
Cast

25. Mixing acrylic
 The accepted polymer-to-
monomer ratio is 3:l by
volume.

26.  When monomer and polymer
are mixed in the proper
proportions, a workable mass
is produced. Upon standing,
the resultant mass passes
through five distinct stages.

27. Tray Resin
Manipulation
Check Consistency Sandy Stage
Stringy
Stage
Dough
Stage
Mixing
Completed Tray

28.  These stages may be described
as:
 (1) sandy,
 (2) stringy,
 (3) dough,
 (4) rubbery, or elastic, and
 (5) stiff

29. Adapting Tray Material in Dough
Stage

30. Handle Design

31. Handle Design
 Functions of handle:
 1. Supports the lip while making
impression.
 2. Tray handles are particularly
helpful when loading, placing and
orientating custom trays in the
mouth.

32. Handle Design and placement

33. Handle Dimensions
 3-4 mm thick
 8-10 mm long
 8-10 mm wide

34. Finger rests
Finger rests
 Finger rests help in holding the
tray in position when making
the final impression.

35. Functions of finger rests
Stabilize tray in mouth
Equal distribution of pressure
Reduces pressure applied to
tissues

36. • The finger rests (arrow) should
not impinge upon the tongue
space and not extend above the
occlusal plane and are placed
near the 2nd
premolar/1st
molar
teeth.

37. Trimming the Tray

38. Tray periphery should be 2 -3 mm
thick. The edges should be rounded.
The rest of the tray should be about
2 mm in thickness.

39. Border Molding

40. Border molding - Maxillary

41. Border molding - Mandibular

42.  Border molding: the shaping of
the border areas of an impression
material by functional or manual
manipulation of the soft tissue
adjacent to the borders to
duplicate the contour and size of
the vestibule.

43. MATERIALS USED FOR BORDER
MOLDING
1. Low fusing compound
2. Putty consistency of elastomeric
impression materials

44. Wax Spacer Removal
 After border molding, remove wax
spacer
 Do not dislodge border molding

45. Final Impression: the
impression that represents the
completion of the registration of the
surface or object.
 also called master impression
 Secondary impression ------ not a
good term

46. MATERIALS USED FOR FINAL
IMPRESSION
1. Zinc Oxide Eugenol Impression
Paste
2. Elastomeric Impression
Materials (medium body and
light body)

47. Definitive Cast: a replica of the
residual ridge areas, and/or other
parts of the dental arch used to
fabricate a prosthesis;
 also called final cast or master casts

48. Materials used for making final
casts:
Alpha hemihydrate (dental stone)

49. Methods of pouring casts
 1. Inversion method (for preliminary
casts)
 2. Beading and boxing method (for
master casts)
 A. Wax boxing method
 B. Plaster of paris and pumice
boxing method

50. Wax boxing method

51. Beading

52. Land area
Land area

53. Land
area
Land Area: the portion of a dental
cast that extends beyond the
impression’s replica surface laterally.

54. Boxing an impression:
 The enclosure (box) of an
impression to produce the
desired size and form of the
base of the cast and to
preserve desired details.

55. Boxing an impression

56. Advantages of beading and
boxing
 Superior hardness of cast surface
 Provides land area
 Preserves borders of the
impression
 Minimizes trimming

58. Pouring of casts
 Once beading and boxing is done
pour cast with dental stone (100 gm
of stone to 28-30 ml of water) and
allow it to set for about an hour.

59. Retrieving of casts
 After the cast has set, place the tray
with cast in hot water to soften the
low fusing compound and carefully
separate the cast from the
impression.

60. Plaster and pumice boxing
method

61. The method we will use is the 1:1
plaster/pumice mixture. Equal parts of
plaster and pumice are mixed together
dry, then enough water is added for the
mix to become smooth and creamy.
H2O
Plaster
Pumice

62. Plaster and pumice boxing method

63. Boxing and Pouring an Impression

64. Trimming the master casts

65. Master Casts for Complete
Dentures
 It is on these casts that dentures
are made.

66. Outline of Bases for Trimmed
Casts
 Follow the contour of the
ridges, with rounded angles
Mandibular Maxillary

67. Completed Master Cast
Land
(2-3 mm )
Base (15-17 mm thick)
Depth of vestibule
(2-3 mm)

68. The base for this cast was insufficient and
eventually it fractured necessitating
remaking of the impression
Trimming the Master Cast

69. Trimmed Model

70. Indexing the master cast
 Indexing is done to accurately
remount the cast on an
articulator.

71. For laboratory remounting of
dentures

72.  Two types of indexing:
1.Groove indexing method
2.Notch indexing method

73. 1. Groove indexing method
 In this method, V- shaped
grooves are made on the cast for
indexing.

74. 2. Notch indexing method
 In this method, 3 notches are
placed at the edges of the cast at
its thickest portion.