1. THE TRIAL DENTURE BASE
Rola M. Shadid, BDS, MSc

2. Trial Denture Assessment on Articulator
Impression surface examination
Fit
Extension
Polished surface examination
Position of lower teeth
position of upper teeth
inclination of polished surface
Occlusal surface

3. Impression surface examination
Fit
The bases of the trial dentures should be accurately adapted to the casts so there will be no movement when finger pressure is applied to occlusal surfaces.
The impression surface should be checked for any sharp projections, roughness, or excessive undercuts.
Extension
The border regions of the dentures should be shaped to conform to the depth and width of the sulci on casts.
In the upper jaw the base should be extended posteriorly to the post-dam cut in the cast, and in the lower jaw over the retromolar pad.

4. Polished surface examination
Position of lower teeth
The teeth on a lower denture should be positioned to conform to the crest of the mandibular ridges. If there are gross discrepancies between the position of the teeth and the ridge, the teeth may not be in the neutral zone, and could become the cause of instability in the mouth.
Position of upper teeth
The position of the anterior teeth should be checked in relation to the incisive papilla,and the posterior teeth according to guidelines in the previous lecture.
Inclination of polished surface
The buccal and lingual aspects of the polished surfaces must converge occlusally; so that pressure from the surrounding muscles of the cheeks, lips and tongue contributes to retention rather than displacement., the exception to this is the upper anterior area where the labial surface of the flange faces upwards and outwards.

5. Example of position of lower teeth
Occlusal view of two lower dentures: (a) the teeth follow the crest of the ridge; (b) marked discrepancies between the position of the teeth and the crest of the ridge are present, suggesting that the teeth will not be in the neutral zone. a b

6. Occlusal surface examination
There should normally be bilateral even contact in the intercuspal position. Opposing cusped teeth should interdigitate accurately.

7. Trial Denture Assessment in the Mouth

8. Trial denture assessment in the mouth
The denture should be assessed individually for:
Physical retention
Stability
Extension of denture bases
Relationship to the neutral zone
The dentures should then be assessed together for:
OVD
CR position
Esthetics
Phonetics
Establishment of the posterior palatal seal

9. Don’t Overlook Problems
Difficult/impossible to change after processing
May require removal, resetting & re-processing
Procedures more costly & time consuming

10. Physical retention
If the prognosis for the retention in the upper jaw is good, dislodgment may be difficult.
In lower denture retention is poor because of the relatively small denture bearing area and the difficulty in obtaining efficient border seal.

11. Physical retention
If the physical retention of an upper trial denture is not as good as would be expected from the anatomical conditions existing in a particular patient, the cause should be identified and, if found to be a fault in the denture, must be corrected. Denture faults may include absence of a border seal resulting from:
• Under-extension
• Inadequate width of flange
• Ineffective seal at the posterior border
• Poor fit of the denture base.

12. Stability
Movement of denture more than 2 mm suggests lack of stability of the denture.
This could be due to:
Lack of fit of the denture
Displaceability or unfavorable shape of the denture bearing area

13. Extension of denture bases
The accuracy with which the denture borders conform to the depth and width of the sulci must be determined.
The all-important posterior extension of the dentures over the retromolar pad in the lower jaw and to the post dam seal area in the upper jaw must be checked.
If marked overextension of the denture flanges is present, stretching of tissues will occur when the dentures are inserted and their elastic recoil will cause denture dislodgment

14. Overextension of denture bases
if the denture is displaced immediately after being seated, over-extension should be suspected. A small degree of over-extension may cause dislodgement of the denture when the dentist gently manipulates the lips and cheeks or when the patient raises the tongue.

15. Overextension of denture bases
The exact location of such an error can only be determined by carrying out a careful examination inside the mouth.

16. Overextension of denture bases
When over-extension is present in areas where the visibility is good, displacement of the sulcus tissues will be seen as the denture is seated. However, in the lingual pouches, visibility is poor, so the dentist will have to make an assessment based on the behavior of the lower denture as the tongue is moved.

17. Overextension of denture bases
In the lingual pouches, overextension can be assessed according to denture behavior during tongue movement
When the lower denture is inserted, it should remain in place when the mouth is half open and the tongue is positioned so that its tip lies just behind the lower anterior teeth.

18. Correction of over-extension
Correction of over-extension is by reducing the depth of the offending flange. If this is not carried out, the finished dentures will traumatize the mucosa in that area and will be unstable because of the large displacing forces exerted by the soft tissues.

19. Under-extension of denture bases
The presence of under-extension is determined primarily by intra-oral examination, when the depth of the sulcus will be seen to be greater than that of the denture flange.
In the case of the upper denture, however, a preliminary indication of under-extension will
be given by the existence of poor physical retention.
Correction of any under-extension will usually entail taking a new impression in the trial denture

20. Neutral zone
The positioning of teeth in the neutral zone is of particular importance in the case of the lower denture
When the lower denture is inserted, it should remain in place when the mouth is half open and the tongue is positioned so that its tip lies just behind the lower anterior teeth.

21. Neutral zone
If displacement of the denture does occur, the cause must be identified and the denture modified to correct the instability.
An area where this difficulty commonly arises is the lower anterior region where the lip may exert excessive pressure

22. Neutral zone
Correction of this type of fault should be carried out at the chairside so that the effect of the alterations can be assessed in the patient’s mouth.
The offending teeth may be reset in the correct relationship to the soft tissues or they may be removed and replaced with a wax rim which is shaped with a wax knife until a stable denture is produced.
The dental technician is then asked to reset the teeth in the position indicated by the rim.

23. Neutral zone
When the tongue is relaxed, it should be able to rest on the occlusal surfaces of the teeth – a situation which favors retention of the lower denture

24. Assessment of the occlusal vertical dimension

25. Verify OVD & Interocclusal Distance
Same techniques used previously
Critical to measure & feel 2-4 mm of interocclusal distance
No tooth contacts during closest speaking space

26. Changing OVD
Effects:
Occlusion
Facial esthetics

27. As mandible moves downward (opening or increasing OVD)
Incisal edge moves back
Increases overjet
Helpful Angles Class III
Problem Angles Class II

28. Vertical Dimension Alterations
One or both arches may require change
Made by the laboratory
May require resetting of all teeth in at least one arch
Height of both anterior & posterior teeth must be in harmony

29. Vertical Dimension Alterations
If only posterior teeth are changed
Undesired effect on:
Overbite relationships
Esthetics
Balancing contacts
Assess how changes will affect overall appearance

30. Assessment of CR Position

31. If a relatively large occlusal discrepancy is present, the dentist will be able to see this without any difficulty. However, the existence of smaller faults may be deduced from evidence such as slight tipping or lateral movement of the dentures as they occlude.
The dentist must approach the problem with negative attitude.

32. Methods of occlusal assessment
Visual (touch & slide method)
Patient perception
The patient should be asked if the dentures are contacting evenly. Many patients are able to detect occlusal unevenness which is so slight that it could be overlooked by the dentist.

33. Touch & Slide Method

34. 1. Guide the mandible into CR
The patient is guided into centric relation by a thumb placed on the anteroinferior portion of the chin and the index fingers bilaterally on the buccal flanges of the lower trial denture.
As tooth contact approaches, the dentist's index fingers should rise off the buccal flanges, pressure on the buccal flanges or stretching the lip with index fingers will create the risk of posteriorly displacing the lower trial denture, then the patient closes tightly.

35. 2. The patient closes slowly so that the dentist can observe the initial occlusal contact.
3. The final occlusal relationship is not so reliable, as an uneven occlusion may have been masked by compression of the mucosa beneath the denture, tipping of the denture or posturing of the mandible.

36. 4. The ideal occlusal contact is that at first contact, even maximum intercuspation at CR without denture shifting or instability & without pain; and all the teeth that occluded uniformly on articulator must have equally uniform contacts in the mouth

37. 5.Errors in occlusion may prevent intercuspation of some teeth when the first contact is made.
6. Further closure will allow the teeth to slide into CO as tipping of the denture or deviation of the mandible will occur

38. What is your management if you found that CR not coincide with CO?
You need to register new CR, mount on articulator according to new CR, and then reset teeth according to this new CR
This is done either by removing the posterior teeth from the lower occlusion rim and both occlusion rims are placed in the mouth and a new centric relation record is taken; OR register new CR by applying bite registration material on occlusal surfaces of lower teeth.

39. Removing the posterior teeth from the lower occlusion rim
To register the new centric relation, the posterior teeth are removed from the lower occlusion rim and both occlusion rims are placed in the mouth and a new centric relation record is taken, the closure is stopped when the anterior teeth have the same vertical overlap as they had before the posterior teeth are removed thus the vertical relation of the two jaws will not be changed *
Once it is determined that the centric relation record is incorrect, the vertical overlap of the anterior teeth is carefully noted , this is important because the amount of vertical overlap will be guide to the amount of closure permitted when the new centric relation record is made.

40. Apply Minimal Registration Material on Lower Occlusals
Improves record accuracy
Less resistance during closure
Reduces chance of deflection when checking record ✔ ✘ ✘ ✔

41. Small Amount of Registration Material
Opposing cusps should not penetrate
Cuspal indentations improve accuracy compared to flat wax rim

42. Accurate Mounting Teeth interdigitate perfectly
No space around the cusps
Mandibular cast removed from mounting ring
Mounting plaster ground thinner
Cast remounted, using the new record

43. Evaluation of the Esthetics

44. Esthetics Check: Amount of incisal display
Harmony of the maxillary teeth with the smile line*
Accuracy of the midline
The smile line: the curvature of the lower lip when a person smiles. The curvature of the incisal edges of lower incisors should be harmonious with smiling line.

45. Esthetics
During a normal smile, incisal and middle thirds of maxillary anterior teeth are visible in almost all patients and the cervical third in approximately half the patients.
The incisal third of the mandibular teeth will be visible in most patients.
The lower lip is a better guide for the vertical orientation of anterior teeth than the upper lips. In most patients the incisal edges of the natural lower canines and the cusp tips of the lower first premolars are even with the lower lip at the corners of the mouth when the mouth is slightly open.

46. When the teeth are above the lip at the corners of the mouth, any one or a combination of the followings may exist:
the plane of occlusion may be too high
the vertical overlap of the anterior teeth may be too much
When the lower teeth are below the lip at the corners of the mouth, the opposite situations may exist

47. Esthetics This figure shows reverse smile line
The fig. shows the midline is slanting to one side
The dental midline should coincide with the midline of the face

48. Esthetics Check Angle of the occlusal plane
The errors in location and inclination of occlusal plane can cause serious esthetic problems, in addition to functional problems and problems of stability. (The figure shows errors in occlusal plane)

49. Esthetics Check Proper soft tissue profile, contours Lip support
Display of the vermilion border
Correct nasolabial angle

50. Esthetics Ask patients for their opinion prior to voicing your opinion
Avoids biasing the patient
May be helpful to have family or friend attend the wax try-in

51. Esthetics If you or the patient have reservations about appearance
Resolve prior to final processing
Never attempt to persuade a patient out of a concern
Problems will be yours later, if the patient does not like the appearance

52. Evaluation of the Phonetics

53. Phonetics Easier to assess Teeth have replaced bulky rims
Crowded tongue space can adversely affect phonetics

54. If have not worn dentures for extended period
Phonetics
If have not worn dentures for extended period or
Dramatic changes (Contour, Tooth Position, Vertical Dimension):
Allow the patient to read a out loud for 5-10 minutes to assess phonetics and comfort

55. Lisping Non-uniform overjet of the anterior teeth
Diastemas between teeth
Palatal contours
Diamond-shaped openings between incisors

56. Bilabial sounds (p, b, m) Causes of defect in these sounds:
Insufficient support of lips by teeth or denture base
Anteroposterior position of anteriors & thickness of labial flange
Incorrect OVD

57. Labiodental (fricative) sounds (f,v)
F & v are made between the upper incisors and the the posterior one third of the lower lip
Affected by the anteroposterior position of upper anteriors and their length
If upper anteriors short, v sound will be more like an f
If upper anteriors long, f sound will be more like v

58. Linguoalveolar sounds (t,z,s,d,v,L,ch,sh)*
Valve formed by contact of tip of tongue with the most anterior part of palate or lingual side of anterior teeth (linguoalveolar)
The upper and lower incisors should approach end to end but not touch.
Affected by the length of the upper & lower anterior teeth (including their vertical overlap)
Also affected by horizontal overlap of anteriors ¶
*(t,z,s,ch,sh) are called sibilant sounds
¶ If teeth are too far lingual the t will sound like d.
If teeth are too far anterior or the palate of denture base is too thick in rugae area, d will sound more like t.

59. Linguoalveolar sounds
Incisors should approach end to end relationship

60. “S” sound
The “s” sound is the most interesting one because it is influenced by the teeth and palatal part of maxillary prosthesis. Clinical experience suggests that s & t can cause most problems in a prosthodontic context.

61. “S” sound
The tip of tongue is placed far forward, coming close but never touching the upper anteriors (touch rugae area)
A small sagittal groove is formed in the upper front part of the tongue for air to escape between the tongue & alveolus
The tongue dorsum is flat
Mandible will move forward and downward, with the teeth almost in contact

62. “S” sound Whistle on “S” sound “S” sound sounds as “sh” or “th”
Causes……
Management……..

63. Denture Base Contours Affect phonetics, comfort and retention
Should not be slightly convex in shape
Convex
Concave

64. Denture Base Contours
Ensure that the denture base is not unduly thick or thin
Excess bulk will impair comfort
Feel between index finger & thumb
Base that is too thin will be weakened
Should not be able to see through

65. It was concluded that malformation of the palatal parts of the denture influenced speech production more than differences in OVD did.

66. Establishment of the posterior palatal seal

67. CONVENTIONAL APPROACH
After assessing all the previous parameters there are certain instructions given to the patients:-
To rinse with an astringent mouth wash that is remove to stringy saliva that might prevent clear transfer marking. There are steps to be followed

68. 2. Location of pterygo maxillary notch is done by moving the T burnisher posterior to the maxillary tuberosity until it drops into the pterygo maxillary notch. This is necessary as there are times when small depression in the residual ridge may resemble pterygo maxillary notch. 3. Identification of posterior vibrating line by asking the patient to say “AH” in a normal unexaggerated fashion.

69. 4. Identification of the anterior vibration line
4. Identification of the anterior vibration line. This is done by asking the patient to say “AH” with short vigorous bursts (Valsalva Maneuver can also be used)

70. PROCEDURE
A line is placed with an indelible pencil through the pterygomaxillary notch & extended 3-4 mm antero-laterally to the tuberosity approximating the mucogingival junction. The same is done on the opposite side. This complete the outlining of pterygomaxillary seal

71. The posterior vibrating line is marked with an indelible pencil by connecting the line through the pterygomaxillary seal with line just drown demarcating the post palatal seal
The resin or shellac denture base is inserted into the mouth & seated firmly to transfer the marks from the mouth.
Denture bases are then returned to master casts to transfer the markings to the master casts.

72. The base is trimmed until the posterior vibration line so that it decides the posterior extent of the denture border.

73. (A) A T burnisher is used to palpate for the hamular process.
(B) Palpating for the pterygomaxillary notch

74. Demarcation of anterior & posterior vibrating lines in the patient mouth
Transferring these lines to denture base

75. The shape of post palatal seal is like the cupid bow, because of the projection of the posterior nasal spine.
Kingsley scraper is used to score the cast, the deepest areas are located on either side of midline, one third the distance anteriorly from the posterior vibrating line. It is usually scraped to a depth of approximately mm .

76. The tissue covering the medial palatal raphe cannot withstand the same compressive force as the tissue lateral to it; so it is scraped to depth of approximately mm within the outline of cupid bow.
The scraping tapers to a feather edge as it approaches the anterior vibrating line.
Failure to taper the posterior seal leads to tissue irritation.

77. Finally………..

78. Patient Input Use open ended questions
“How do you like the appearance?”,
rather than
“Don’t the new dentures look great?”

79. Patient Input If the patient sounds unconvinced ask more questions
Do not rush this step to save time!

80. References
Basker’s Prosthetic Treatment of the Edentulous Patient. Fourth edition.Chapter 13
Boucher's Prosthodontics Treatment for Edentulous Patients. Twelfth Edition. Chapter 19
Complete Denture Prosthodontics, 1st Edition, 2006 by John Joy Manappallil, Chapter 17
Dalhousie coninual education