Date post: | 14-Jul-2015 |
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Retentional factors
Retentional factors
1. Clinical anatomical features
2. Physical features
3. Retention aids
Functional stability= denture usage
Stability during fonation:
The denture does not move disturbingly from the mucosal-bony base during fonation ,mouth opening and closing, swallowing, articulation in connection with fonation
Stability during mastication:
The denture does not move disturbingly from the mucosal-bony base during mastication and articulation in connection with mastication
1. Clinical anatomy features
I. The size of the mucosal bony base that is suitable for bearing mastication forces
II. The height of the edentulous alveolar ridge
III. Retential areas
IV. Neuromuscular forces
The useable place which can bear the masticatory pressure
Alveolar process is the edentulous alveolar ridge after losing natural teeth.
In case of severe resorption the body of the mandibule is covered by the base of the denture.
The height of the alveolar process will inhibit the horizontal displacement of the denture.
The useable place which can bear the masticatory pressure
Upper arch: 3937 mm2 Lower arch: 1770 mm2 It is approximately equal with the polished
surface of the baseplate This area play an important role in keeping
denture in place
The size of the mucosal bony base, that is suitable for the retention of the denture, influence:
Effectiveness of the physical forcesMastication force that loads the mucosal bony
base (24-25 N)
1. Clinical anatomy features
III. Retentional areas on the upper jaw:
Maxillary tuberHigh and curved
quadrangular shaped ridge
Undercut area between the buccal frenules in the vestibule
1. Clinical anatomy features
III. Retentional areas on the lower jaw:
Lingual fossa
1. Clinical anatomy features
III. Retentional areas on the lower jaw:
Edentulous ridge: totally preserved high ridge
1. Clinical anatomy featuresIV. Neuromuscular forces:
The surrounding muscles and active and passive muscle functions have the most important stabilizing effect
The oral mucosa (bucca, lips, tongue) and the underlying musculature touch and load the polished surface of the denture with various forces during mastication (20-30 N)
2. Physical forces
1. Capillary pressure2. Ventill effect (inner/outter)3. Gravity4. Masticatory pressure
I. Capillary pressure (upper/lower):
Surface tension of the saliva between the denture baseplate and the mucosa
Adhesion: connecting force between unlike molecules (mucosa-saliva)
Cohesion: connecting force between alike molecules (saliva-saliva)
If the saliva film is thinner, the force of retention will be better
Lack or overproduction of saliva affect negatively for retention
II. Ventill effect (upper/lower):
Seal the border of the denture
Vacuum is created under the denture base
Inner ventill effect:The border of the denture is
sinked into the mobile mucosa
Outter ventill effect:Connection between the
mucosal surface of the denture and the buccalmucosa
III. Gravity (lower)
Casted metal base Casted metal arteficial teethMax.:32-35 gThe excessive loading cause atrophy
Masticatory pressure:Natural dentition: 120-140 KpaEdentulous: 20-30 Kpa
IV. Masticatory pressure:
The denture stability by masticatory forces depends on the occlusal pattern of the arteficial posterior teeth:
Anatomical arteficial posterior teeth:Different OV widthAngle between the slope of the cusp and
horizontal plane is different (20-45 degree)Material can be ceramic or acrilicIt has always shifter effectIt cause horizontal displacement of the
denture
2. Physical forces
Non-anatomical arteficial posterior teeth:It has stabilizing effect
Mechanical occlusal-surfaced molar: the occlusal surface is non-anatomicalthe vestibular, oral and approximal surfaces are
anatomical
Mechanical molar: it is not compare of the natural teeth
French-type artifical posterior teeth
It was used on older people in abrasive teeth
Myerson-type
Normal artificial teeth has flat, shallow fissure
Transversal cutterMarginal cutter
2. Conclusion of physical forces
Prosthetic function is more important than cosmetic ones in the posterior region:
Stabilization of the dentureProtection of the mucosal bony baseBetter mastication
3. Retention aidDenture fixative:
Unfavourable situations
Nervus system disorders
Surgical or congenital defects
Shortening initial learning period
Retention aidMicrovalves, denture adhesives (Corega)Suction disc (don’t use it)Denture spring (don’t use it)Grooves cut into the palate of the master cast