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