RETENTION AND STABILITY

WHAT IS RETENTION? IT IS THE ABILITY OF THE DENTURE TO RESIST VERTICAL TISSUE AWAY MOVEMENT.

WHAT IS STABILITY? IT IS THE QUALITY OF THE DENTURE TO BE FIRM AND STEADY, WHEN FUNCTIONAL FORCES ARE APPLIED. (RESISTANCE TO HORIZONTAL AND ROTATIONAL FORCES).

FACTORS AFFECTING RETENTION.

1- ADHESION PHYSICAL ATTRACTION BETWEEN UNLIKE MOLECULES.(DENTURE-SALIVA-MUCOSA)

2- COHESION PHYSICAL ATTRACTION BETWEEN SIMILAR MOLECULES.(SALIVARY MOLECULES)

3-INTERFACIAL SURFACE TENSION (CAPILLARY ATTRACTION). THE ATTRACTIVE FORCES BETWEEN SURFACE MOLECULES. IT IS THE RESISTANCE TO SEPARATION POSSESED BY A FILM OF LIQUID BETWEEN 2 WELL ADAPTED SURFACES.

4- ATMOSPHERIC PRESSURE WHEN YOU SEAT THE DENTURE, AIR ESCAPES FROM UNDERNEATH THE FITTING SURFACE, FORMING A PARTIAL VACCUUM BETWEEN THE MUCOSA AND THE DENTURE, RESULTING IN TRAPPED REDUCED PRESSURE. ATMOSPHERIC PRESSURE IS LARGER, THUS SEATS THE DENTURE.

5- VISCOSITY. THE RESISTANCE OF PART OF THE FLUID TO MOVE OVER ANOTHER. THE GREATER THE VICOSITY THE BETTER THE RETENTION.

6- GRAVITY. IS CONSIDERED RETENTIVE TO THE LOWER DENTURE, AND DISPLACING TO THE UPPER DENTURE.

ALL THE FACTORS WORKING TOGETHER.

1-SHAPE OF POLISHED SURFACE.

2-DENTURE FOUNDATION AREA

3-PRESENCE OF UNDERCUTS

4- DENTURE EXTENSION

5- INTIMATE CONTACT

1-RIDGE HEIGHT

2-SOFT PALATE ANATOMY

3- ARCH RELATIONSHIP

4- TONGUE SHAPE

5- VISCOSITY OF SALIVA

1- RIDGE AUGMENTATION

2- VESTIBULOPLASTY DEEPENING OF THE VESTIBULE TO GAIN RIDGE HEIGHT.

3- DENTAL IMPLANTS

1- ADHESIVES CREAMS USED AS ADHESIVE IN THE FITTING SURFACE OF THE DENTURE.

2- MICRO SUCTION DISCS

3- DENTAL IMPLANTS

SOME PATIENTS HAVE THE NEUROMUSCULAR AND PSYCOLOGICAL ABILITY, TO COPE AND USE THE DENTURE.

FOR A DENTURE TO BE STABLE IT SHOULD BE RETENTIVE FIRST.!!!!!!!

WHICH IS MORE STABLE!!!!!!!!!!!

THE FURTHER AWAY THE OCCLUSAL PLANE, FROM THE RIDGE, THE LESS THE STABILITY.

PLACING THE POSTERIOR TEETH SLIGHTLY LINGUAL TO THE CREST OF THE RIDGE, THE MORE STABLE. THE FORCES FALLING ON THE TEETH BECOMES MORE CENTRALISED. THIS IS KNOWN AS “ LEVER BALANCE”.

INCLINED PLANE ACTION

FIRST ROCKING THEN MIDLINE FRACTURE.

V- SHAPED PALATE HELPS RESIST LATERAL LOADS.

THE OCCLUSAL WIDTH IS LESS THAN THE NATURAL, THUS DECREASING THE AMOUNT OF LOAD FALLING ON THE DENTURE.

LARGE AND MEDIUM SIZED TONGUES HELP STBILIZE THE LOWER DENTURE.

THE CHEEK AND THE TONGUE SEAT THE DENTURES IN PLACE.