this lecture covers the section related to stress bearing areas, peripheral seal and different impression techniques

1. DENTURE BEARING AREA
AND IMPRESSION
TECHNIQUES
ASSISTANT PROFESSOR
DR. SHOAIB RAHIM
BDS, FCPS
DEPARTMENT OF PROSTHODONTICS

2. DENTURE BEARING AREA

3. ANATOMY OF SUPPORTING STRUCTURES
• Surface area of dentate mandible and maxilla
45cm2
• Surface area of edentulous mandible is
14cm2(12.25) and maxilla 24cm2(22.96)

4. FORM AND SIZE OF ARCHES
• The original size and arch form before extractions
• The severity of periodontal disease
• Amount of alveoloplasty at the time of tooth extraction
• Forces developed by the surrounding musculature
• Forces accruing from the wearing of dental prostheses
• The relative length of time different parts of the jaws have been edentulous
• Unknown genetic predisposition to bone resorption

5. MUCOUS MEMBRANE
• Composed of mucosa and submucosa
• Submucosa formed by connective tissue that
varies in character from dense to loose areolar
tissue
• Attachment of mucous membrane to bone
through submucosa and periosteum
• Thin submucosal layer results in soft tissues to be
less resilient
• Loose attachment of submucosa to periosteum
or inflammation or edematous results in easily
displaceable tissue

6. MUCOUS MEMBRANE
• Well fitting dentures increase the amount of
keratinization
• Stimulation of mucosa of residual ridge through
toothbrush physiotherapy increases keratinization
• Removing dentures from mouth at night, for 6 to 8
hours, allows keratinization to increase and the signs of
inflammation to reduce

7. RESIDUAL RIDGE
• Shape and size of residual alveolar ridge dependent on anatomic
contour of patient’s dentate arch
• After dental extraction, width and height of residual alveolar ridge
change
• Maxillary anterior alveolar ridge is proclined, the resorption of
ridge creates a smaller maxillary prosthetic base
• Mandibular dentition is positioned lingual to basal bone;
resorption of residual ridge creates denture-bearing area that is in
more buccal position with flatter and wider base

8. DENTURE BEARING AREA
• Stress bearing areas
• Peripheral seal
• Relief areas

9. STRESS BEARING AREA
MAXILLA
Primary
• Firm tuberosities
• Hard palate on either side of palatal raphe
Secondary
• Alveolar ridge
• Rugae
MANDIBLE
Primary
• Buccal shelves
• Retromolar pads
Secondary
• Alveolar ridge

10. RELIEF AREAS
• Secondary stress bearing areas
• Palatal torus
• Median palatal raphe
• Mandibular tori
• Retromylohyoid ridge
• Undercuts or sharp boney prominence on ridges

11. MAXILLA
• Palate covered by soft tissue of varying thickness
• Extremely thin submucosa in medial palatal suture area
• Anterolaterally the submucosa contains adipose tissue
• Posterolaterally it contains minor salivary gland tissue

12. MAXILLA
• Incisive foramen is located beneath the incisive papilla
• It lies nearer to the crest of the ridge as resorption
progresses
• Tuberosities are dense fibrous connective tissues with
minimal compressibility
• Torus palatinus is hard bony enlargement that occurs
in the midline

13. MAXILLARY PERIPHERAL BORDERTISSUES AND CONTOURS
• Labial vestibule
• Right and left buccal vestibules
• Vibrating line

14. MAXILLARY PERIPHERAL BORDERTISSUES AND CONTOURS
• Buccal vestibule lies opposite the tuberosity and extends
from the buccal frenum to the hamular notch
• Size of buccal vestibule varies with the contraction of
buccinator muscle, position of the mandible, and amount
of bone lost from the maxilla
• The size and shape of the distal end of the buccal flange
of the denture must be adjusted to the ramus and the
coronoid process of the mandible and to the masseter
muscle
• Distal to the buccal frenum and palpable superior to the
vestibule is the root of the zygoma

15. MAXILLARY PERIPHERAL BORDERTISSUES AND CONTOURS
• Hamular notch forms the distal limit of the buccal
vestibule
• Palpated with a mouth mirror orT-shaped burnisher
• Consists of thick submucosa made up of loose
areolar tissue
• Pterygomandibular raphe, covered by mucosa,
extends from the hamulus inferiorly into the
retromolar pad
• Tissues in the notch should be displaced by the
posterior palatal border of the denture to achieve a
posterior palatal seal

16. MAXILLARY PERIPHERAL BORDERTISSUES AND CONTOURS
• Vibrating line marks the beginning of motion in the
soft palate
• It usually passes 1 to 2 mm anterior to the fovea
palatinae
• Made up of the aponeurosis and muscle fibers of
the tensor veli palatini muscles, glandular tissue,
and mucosa, all of which can be displaced with the
denture

17. MANDIBLE
• Buccal shelf is the area between the mandibular
buccal frenum and the anterior edge of the
masseter muscle
• Medially it is bound by the crest of the ridge
• Laterally by the boney external oblique ridge
• Distally by the retromolar pad
• Buccal shelf does not resorb because of its
muscle attachments on the posterior and lateral
borders

18. MANDIBLE
• Mylohyoid ridge is a boney prominence along
the lingual aspect of the mandible
• Mental foramen and genial tubercles require
relief

19. MANDIBULAR PERIPHERAL BORDERTISSUES AND
CONTOURS

20. MANDIBULAR PERIPHERAL BORDERTISSUES AND
CONTOURS

21. MANDIBULAR PERIPHERAL BORDERTISSUES AND
CONTOURS
Retromolar pad
• Triangular pad of tissue
• Anterior portion is keratinized
• The posterior aspect is composed of thin,
nonkeratinized epithelium; loose connective tissue;
glandular tissue; fibers of temporalis tendon and
buccinator and superior constrictor muscles; and
the pterygomandibular raphe
• Underlying bone is dense cortical
Anterior
portion:
keratinized
Medially:
PMR & SC
Laterally:
Buccinator
Posteriorly:
Temporalis

22. MANDIBULAR PERIPHERAL BORDERTISSUES AND
CONTOURS

23. IMPRESSION TRAYS

24. PRINCIPLES OF IMPRESSION
To make an ideal impression, the following concepts should be adhered to, irrespective of the
selected technique:
• The tissues of the mouth must be healthy
• The impression should extend to include the entire basal seat within the limits of function
of the supporting and limiting tissues
• If redundant tissue or boney projections of the ridge cannot be surgically removed, space
for them must be created within the denture
• Proper space for the selected impression material should be provided within a properly
fitting impression tray

25. PRINCIPLES OF IMPRESSION
• A guiding mechanism should be provided for correct positioning of the impression tray in
the mouth
• A physiological type of border molding procedure should be performed by the dentist or by
the patient under the guidance of the dentist
• The external shape of the impression must be similar to the external form of the complete
denture

26. THEORIES OF IMPRESSION
Based on pressure:
• Muco-static impression
• Muco-compressive/ Muco-Displacive impression
• Selective pressure impression
Based on position of mouth:
• Open mouth
• Closed mouth
Based on tissue manipulation:
• Hand manipulation
• Function movements

27. MUCOSTATIC
• Minimum pressure on tissues/mucosa
• Utilizes the concept of interfacial surface tension
• Retention is optimal
• Disadvantages:
• Uneven pressure/support
• Relatively short flanges

28. MUCOCOMPRESSIVE
• Mucosa/ tissues recorded under pressure
• Advantages:
• Occlusal load evenly spread
• Good retention during function
• Disadvantages:
• Increased bone resorption
• Excessive pressure on lining mucosa
• Compromised/reduced retention during rest

29. SELECTIVE PRESSURE
• Combines principles of muco-static and muco-compressive impressions
• Based on the knowledge of anatomy and physiology of oral structures
• Denture supporting area divided into different zones
• Disadvantage:
• Impossible to record different areas with varying pressure

30. IMPRESSION MATERIALS
• Non elastic impression materials
• Elastic impression materials
• Hydrocolloids
• Elastomers

31. NON ELASTIC IMPRESSION MATERIALS
• Impression plaster
• Zinc oxide eugenol (ZOE)
• Impression Compound

32. IMPRESSION PLASTER
• Used as muco-static impression material
• Used in patients with displaceable tissues
• Can be as an occlusal registration material

33. ZINC OXIDE EUGENOL
• Dimensionally stable with negligible shrinkage (<0.1%)
• Accurate impression with good surface details because of low viscosity
• May fracture in undercut area
• Does not adhere with set plaster or stone
• Can be removed by immersing in warm water
• Setting reaction can be accelerated by presence of water, high humidity or heat
• Non eugenol pastes are available to avoid burning sensation
• Disinfected by immersion in a 2% alkaline glutaraldehyde solution

34. ZINC OXIDE EUGENOL
• Mainly used for final impressions of edentulous ridges with minor or no undercuts
• As a wash impression with other impression materials, such as impression compound
• As an occlusal registration material
• As a temporary liner material for dentures
• As a surgical dressing
• As a pressure indication paste

35. IMPRESSION COMPOUND
• Available in the form of cakes (red) and sticks (green, grey or red)
• Reversible impression material
• The material is softened by heat over a flame or in a temperature-controlled water bath to
the required softening temperature
• When direct flame is used, such as when using compound sticks, the material should be
moved over the flame in such a manner that it will not be allowed to boil or ignite so that the
constituents are volatilized
• When the material is placed in a water bath, prolonged immersion or overheating can result
in low molecular weight ingredients leaching out from the compound, resulting in increased
brittleness and/or grainy mass

36. IMPRESSION COMPOUND
• Type I (Lower Fusing Material)
Cakes: As an impression material for completely edentulous patients, the material is softened
by heat, inserted into the tray, and placed against the tissues before it cools to a rigid mass
Sticks: As a border molding material for the custom tray, the material is used before making
the final impression
• Type II (Higher Fusing Material)
Used as a tray adaptation material, which requires more viscous properties. It is used for
making a primary impression of the soft tissues and then used as a tray to support a thin layer
of a second impression material, such as ZOE paste, hydrocolloids, or nonaqueous elastomers

37. IMPORTANT CONSIDERATIONS FOR PROPER USE OF
IMPRESSION COMPOUND
• Material has a very low thermal conductivity = adequate time is needed to attain thorough
heating and cooling
• Incorporation of water as a result of wet kneading results in excessive flow of the material
at mouth temperature, producing distortion as the impression is removed from the mouth
• Tray used for the impression must be strong and rigid
• Does not record fine details
• Cast should be poured as soon as possible, at least within the first hour, to minimize any
distortion
• Disinfected by immersion in sodium hypochlorite, iodophors, or phenolic glutaraldehydes

38. ELASTIC IMPRESSION MATERIALS
• Hydrocolloids:
• Agar (reversible)
• Alginate (irreversible)
• Elastomers
• Poly sulphide
• Silicones
• Condensation silicone
• Addition silicone
• Poly ether

39. AGAR
• One of the most accurate impression materials for
recording fine details because of their low viscosity
and great degree of recovery
• For making agar impressions, the gel is liquefied by
placement in boiling water
• The impression tray is maintained in position,
allowing the fluid mix to intimately capture all
anatomical details
• Disinfected by immersion in sodium hypochlorite,
iodophors, and glutaraldehyde

40. ALGINATE
• Ease of manipulation without the need for expensive equipment
• Material of choice for making preliminary impressions for edentulous patients
• Because of its high viscosity and its ability to displace tissues it is not recommended for use
as a final impression material
• Dustless alginates are produced by the incorporation of glycerin into the alginate powder
which prevents the constant inhalation of alginate dust
• To control infection and microbial contamination, disinfectant materials, such as
chlorhexidine acetate or quaternary ammonium, are added to the alginate powder

41. COMMON ERRORS
ENCOUNTERED WHEN MAKING
ALGINATE IMPRESSIONS
PROBLEM
• Inadequate working or setting time
• Distortion
• Tearing
REASON
• High water temperature; incomplete
spatulation; low water/powder ratio;
improper storage of the alginate powder
• Movement of the tray during gelation;
premature removal of the tray; no snap
quick removal of the tray; delay in pouring
the cast
• Impression removed before it sets; slow
rate of removal of the impression from
the mouth; thin mix used; presence of
deep undercuts; inadequate material in
the tray

42. COMMON ERRORS
ENCOUNTERED WHEN MAKING
ALGINATE IMPRESSIONS
PROBLEM
• Loss of detail
• Consistency
• Dimensional changes
• Porosity
• Poor stone surface
REASON
• Premature tray removal from the mouth
• Incorrect water/powder ratio; inadequate
mixing; hot water used for mixing
• Delay in pouring the impression
• Air entrapped in the mix during
spatulation
• Delay in separating the cast from the
impression

43. ELASTOMERS
• Indicated for making accurate final impressions
• Trays may be border molded with a wax spacer in place
• Tray adhesives are required
• Border molding can be carried out using modeling
compound sticks, or using a medium-to-high viscosity
elastomeric material
• All types of elastomers undergo shrinkage upon
polymerization, and those with reaction by-products

44. IMPRESSION PROCEDURE

45. PRIMARY IMPRESSION
• Recorded in stock tray with:
• High viscosityAlginate
• Silicone putty
• Impression compound

46. SECONDARY IMPRESSION
• Recorded in custom tray either with 1-2mm wax spacer or relief holes
• Can also be recorded in the form of wash impression
• Impression can be recorded with:
• Impression plaster
• ZOE
• Elastomers
• Alginate

47. SECONDARY IMPRESSION

48. MAXILLARY AND MANDIBULAR BORDER MOLDING

49. MAXILLARY AND MANDIBULAR BORDER MOLDING

50. POSTERIOR PALATAL SEAL
Identification:
• Locating anatomy on the model
• Observing tissue color difference
• Mirror probing to assess tissue resilience
• Patient tolerance
• Observing soft palate movement

51. POSTERIOR PALATAL SEAL
• Consists of anterior and posterior vibrating lines
Functions:
• Provide retention
• Serves as barrier and prevents food accumulation beneath denture
• Compensates for polymerization shrinkage

52. TECHNIQUES FOR RECORDING POSTERIOR PALATAL SEAL
• Arbitrary techniques:
• Conventional technique (Winkler's technique)
• Boucher’s technique
• Physiologic techniques:
• Fluid wax technique
• Stick compound technique
• Extended palatal technique

53. CONVENTIONALTECHNIQUE
• Locate hamular notch and vibrating line
• Mark with indelible pencil
• Transfer the mark to impression tray or baseplate
• Scrap the cast according to the marked area up to 1-1.5mm deep

54. BOUCHER’STECHNIQUE
• Locate hamular notch and vibrating line
• Mark with indelible pencil
• Transfer the mark to impression tray or baseplate
• Scrap the cast according to the marked area in the form of “V-shaped” notch up to 1-
1.5mm deep and 1.5mm wide

55. FLUID WAXTECHNIQUE
• Final impression recorded with ZOE or impression plaster
• Posterior palatal seal area marked with indelible pencil and transferred to the impression
• Impression/moth temperature wax is painted on to the marked area
• Impression placed back in patient’s mouth

56. STICK COMPOUND TECHNIQUE
• Done at the time of final impression appointment
• Green stick is applied on the tray in area of vibrating line
• Impression tray is trimmed distal to it

57. EXTENDED PALATALTECHNIQUE
• Introduced by Silverman
• Posterior border is extended 8.2mm distally
• Not widely used

58. POSTERIOR PALATAL SEAL PROBLEMS
• Over extension
• Under extension
• Over damming
• Under damming

59. BOXING
• To preserve the functional width and depth of the sulcus
• Can be done by using Rope and Boxing wax
• Kept 2-3mm away from the border
• Height of the boxing wax should be 10-15mm above the impression
• Can also be done by using a mixture of plaster and pumice in equal quantity
• Kept 2-3mm away from the border

60. IMPRESSIONVARIATIONS

61. RESORBED RIDGE
• Recorded using admix impression technique
• Consists of 3 parts impression compound and 7 parts green stick
• Removes the soft tissue folds and smoothens the tissue over them

62. UNEMPLOYED RIDGE
• Presence of a thin mobile thread-like ridge which is essentially fibrous in nature
• Ridge becomes non supporting because of previous denture use history
• Utilize the concept of selective pressure impression technique

63. FLABBY RIDGE

64. DIABETIC/ HYPERTENSIVE/ XEROSTOMIC PATIENT
• Muco-static impression technique
• Mid Day and short appointments
• Impression recorded with alginate in a well spaced impression tray
• In case of xerostomia patient maybe advised to rinse before placing the impression in the
patient’s mouth

65. PARKINSONIAN PATIENT
• If on medication then the patient will report with xerostomia/ reduced salivary flow
• If not on medication then pooling of saliva maybe observed
• Use of hydrophilic and fast setting impression material
• Utilization of suction before and during impression recording procedure
• May use para sympatholytic at the time of impression making

66. GAGGING
• Counselling
• Modelling
• Distraction
• Topical local anesthetic
• Mixing of local anesthetic in the impression
• Systemic desensitization (marble technique, tooth brush technique or training bases)
• Medications (Anti emetic)
• Sedation/ General anesthesia
• CAD CAM
• No treatment

67. THANKYOU