Powered by Blogger.
RSS

MICROSTOMIA

10:19 PM |


MICROSTOMIA

INTRODUCTION

Microstomia is a chronic reduction in the dimensions of the oral aperture and although it is not classified by any particular size criteria, it is defined by its effects on function or appearance.

CAUSES


  • ·         systemic conditions or autoimmune diseases affecting the connective tissues (such as scleroderma)
  • ·          oro-facial syndromes.{ Freeman-Sheldon (whistling face) syndrome, Burton skeletal dyslpasia,Plummer-Vinson syndrome, Treacher collins syndrome}
  • ·          post-surgical scarring following peri-oral procedures
  • ·          following trauma( particularly electrical or chemical burn injuries)
  • ·         head and neck radiation,
  • ·          fibrosis of masticatory muscles
  • Prosthetic rehabilitation of microstomia patients presents difficulties at all stages, right from the preliminary impressions to insertion of prostheses.

A patient who has significant chronic mandibular hypomobility and reduced oral aperture following surgery and chemoradiotherapy for an intra-oral squamous cell carcinoma



IMPRESSION TECHNIQUES

  • ·         the use of stock impression trays of each half of the mouth for sectional impressions with heavy and light body silicone impression materials,
  • ·          flexible impression trays made with silicone putty.
  • ·          modeling plastic impression compound has also been described to make sectional impressions of edentulous arches.              ( mechanisms to connect sectional custom trays include hinges, plastic building blocks, orthodontic expansion screws or locking levers)

  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments0
Posted by Neeta

ROLE OF PATH OF INSERTION IN RPD

9:09 AM |



DEFINATION
  •        Path of insertion and withdrawal is the direction in which the prosthesis moves in relation to the support system when it is seated in or removed from the mouth, guided by the contact of its rigid parts with the abutment.
  •       Path in which the prosthesis is
     Placed/removed
                      
                              - GPT  2005
                                                                                               
                                               
PATH OF INSERTION AS PER KENNEDYS CLASSIFICATION
  • Tooth bounded edentulous space (Kennedy class III) - single path of insertion
  •   In Kennedy class II modification cases- single path of insertion, guided by the modification space
  •   Free ended saddles (Kennedy class I and II cases) – multiple path of insertion
  •   Additional guiding planes on the lingual surfaces of other teeth may be developed to control the path of insertion
SINGLE PATH OF INSERTION

SINGLE PATH OF INSERTION

MULTIPLE PATH OF INSERTION

  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments1
Posted by Neeta

SINGLE AND ROTATIONAL PATH OF INSERTION

9:06 AM |

SINGLE PATH OF INSERTION
  •  Equalizes retention on all abutment teeth retentive arms  oppose each other on opposite sides of the arch
q  Provides bracing and cross arch stabilization of teeth
q  Directs forces along the long axes of the tooth
q  Allows partial denture to be placed and removed without encountering interferences
q  Minimizes torquing forces of the partial denture
q  Provides frictional retention from contact of the parallel surfaces of the teeth 

ROTATIONAL PATH OF INSERTION
q  Permits one portion of the framework to be seated first , followed by the remainder of the framework
q  Suitable for tooth bounded edentulous spaces especially for anterior edentulous spaces

Advantages
q  Requires minimal number of clasps
q  reduces tooth coverage
q  decreases plaque accumulation
q  Esthetics improved
q  Clasps are eliminated
q  Closer adaptation around the defects by acrylic
q  Abutment tooth preparation is minimal

  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments0
Posted by Neeta

KEYSTONES OF PARTIAL DENTURE

9:01 AM |

KEYSTONES OF PARTIAL DENTURE

  • GUIDING PLANE
  • RETENTIVE AREAS
  • INTERFERENCES
  • ESTHETICS
                                                                PATH OF INSERTION 
DESIGN OF THE PROSTHESIS

  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments0
Posted by Neeta

GUIDING PLANE

8:58 AM |


GUIDING PLANE
q  Two of more parallel vertical surfaces of abutment teeth
q  Control & limit movement of RPD
q  Initial contacts for RPD
q  Guide surfaces
q  May occur naturally
q  May have to be prepared
q  By minimal shaping of the enamel(>0.5mm)
q  By building appropriate surface into a cast metal restoration
q  Are prepared where rigid components contact the abutment
q  Proximal plates
q  Bracing arm
q  Rigid portion of the retentive arm
Effectiveness of Guideplanes
           Most effective when:
q  Parallel to each other
q  Directly opposing each other
q  More than one common axial surfaces
q  Prepared on several teeth
q  Cover a large surface area
q  Class I & II – use short guide planes
q  Class III & IV – use long guide planes

  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments0
Posted by Neeta

GUIDING PLANE...........

8:56 AM |


GUIDING PLANE.............
Function of Guiding Planes
q  Retention and stability
q  Intimate frictional contact of the prosthesis against these surfaces
q  Limit the possibilities that exist for dislodgement
q  Stabilization of abutment teeth
q  Reciprocation
q  Lowering the height of contour
If some degree of parallelism does not exist during placement and removal, trauma to the teeth and the supporting structures and strain on the denture parts is inevitable
q  Should be
q  Like an area on a cylindrical object
q  Continuous and unbounded by line angles(line angles weakens the clasp assembly)
q  1 ⁄ 2 the width of the distance between the tips of adjacent buccal and lingual cusps
q  1 ⁄ 3rd the buccal lingual width of the tooth

  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments0
Posted by Neeta

RETENTIVE AREAS

8:07 AM |


RETENTIVE AREAS
  •   RETENTION         -
            is the property of the clasp that resists dislodgement of the prosthesis from the tooth in an occlusal direction.
Retentive area…..
  • It is this infrabulge area or the undercut area that is used for the placement of the retentive clasp component
  •  3 dimensions –
    •   Mesiodistal dimension
    •  Occlusogingival dimenson
    •   Buccolingual dimenson
  • Clasp is retentive when
    •   Positioned on the surface of the tooth that is cervical to the greatest circumference of the tooth
    •   Resists distortion that is required for the clasp arm to escape from the area beneath the bulge of the tooth
  •   PATH OF DISPLACEMENT
            is the direction in which the denture tends to be displaced in function. This is at right angles to the occlusal plane
q  Retentive undercuts must be present on the abutment teeth when the cast displays a horizontal tilt.
q  Changing the tilt to produce undercut is just an illusion
q  Only when the undercut is verified on the horizontal survey , the tilt can then be changed to optimize the undercut on any tooth.
q  If retentive undercuts are not present they should be created
q  By recontouring of enamel
q  Cast restorations


  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments1
Posted by Neeta

RETENTIVE AREAS....

8:02 AM |

Retentive Areas........

q  Amount of desirable undercut …
q  0.01 inch-at the mesiobuccal distolingual line angle
                                 - gingival 3rd of the clinical crown
                                - when the cast chrome alloy is used for framework
                                                                                               
q  I bar design is used when the undercut is more on the center of the facial surface
q  If large molars or if gold is to be used instead of chrome , slightly deeper undercut is necessary
                           0.015 inches
q  If wrought wire combination is used
                          0.020inches (Coz of greater flexibility of the wrought wire )
q  Ideally, retentive clasps should be bilaterally opposed.
q  Similar retentive areas should exist on all principal abutment teeth
                                THE AMOUNT OF RETENTION SHOULD ALWAYS BE THE MINIMUM NECESSARY TO RESIST A REASONABLE DISLODGING FORCE

  • Digg
  • Del.icio.us
  • StumbleUpon
  • Reddit
  • RSS
Read User's Comments0
Posted by Neeta
Subscribe to: Posts (Atom)