principle of surveying Flashcards
paralleling instrument used in RPD fabrication
dental survey
dental surveyor functions
-survey diagnostic case
-contour wax patterns
-contour ceramic and cast restorations
-place attachments requiring parallelism
-survey master cast
what are the 7 objectives of surveying diagnostic cast
- determine the most acceptable path of insertion
- identify proximal tooth surfaces that can function as guiding planes
- locate and measure areas of teeth that may be used for retention
- determine if soft or bony areas of interferences (undercuts) exist
- determine most suitable path of insertion to satisfy esthetics
- delineate height of contour on abutment teeth
- record cast position to selected path of insertion (tripod cast)
diagnostic cast survey procedures:
- path of insertion determined
- mark height of contour/survey line
- measure/mark retentive undercut
- tripod cast
this is based on guiding planes, retentive undercut, interferences, esthetics
path of insertion determined
the direction in which the RPD is inserted and removed from the abutment teeth
path of insertion
patient is unable to open mouth sufficiently to accommodate when
there is an exaggerated tilt to path of insertion
path of insertion 4 factors
- guiding planes
- retentive undercuts
- interferences
- esthetics
parallel, flattened surfaces at proximal or axial surfaces of teeth
guiding planes
contacts minor connectors aka guiding plates
guiding planes
the greater number of guiding planes, the
path of insertion is more specific
guiding planes increase
RPD stability and retention
the guiding planes are identified by tilting cast in
tilting cast in anterior-posterior direction until max parallelism of proximal surfaces
what is used to identify potential surfaces that can be converted to guiding planes by selective grinding in occlusal 1/3 to 1/2
analyzing rods
the final orientation for guiding planes is rarely > ______ degrees from horizontal
10-15 degrees
RPD mechanical retention provided by ____ that engages retentive undercut
clasp
this resist RPD dislodging forces
clasp that engages retentive undercuts
where do undercut area lies
between survey line and gingival margin
line encircling a tooth that designates its greatest diameter at a selected position determined by a dental surveyor
survey line
what will be changed if the axial inclination is changed
survey line
portion of tooth above height of contour
suprabulge area
portion of tooth below height of contour in relation to path of insertion
infrabluge area
what area is the retentive undercut within
infrabulge
where is the retentive clasp tip found
in infrabulge
(contact tooth below survey line)
where ideally is the retentive undercut within
within gingival 1/3 at least 1mm from gingival margin
how should cast tilt to equally distribute retentive undercut to abutments
not vary far from horizontal
illusion of undercut due to excessive cast tile
-will not exist clinically
-awkward path of insertion and pt unable to place RPD
false undercut
what are the typical interference areas
-lingually-inclined mand teeth
-buccally-inclined max teeth
-bony buccal exotoses, tori
-height of contour toot high, clasp would be placed too high
-tissue undercut area of bar clasp
locate and eliminate interferences such as teeth, soft tissue, and exostoses when
after tilt of cast/change path of insertion
maintain cast tilt, eliminate by surgery or recontouring of teeth
if there is inadequate space for natural tooth width, do what
recontour proximal surfaces to restore lost dimension
this indicates survery line of abutment teeth at chosen path of insertion
side of carbon marker
(tip of marker will produce incorrect survey line)
where is the survey line located
junction of middle and gingival 1/3
where retentive clasp located?
reciprocal clasp located?
retentive: proximal 2/3 of retentive about survey line and tip in infrabulge or gingival 1/3
reciprocal: middle 1/3 above survey line
if the survey line at the chosen path of insertion is too near occlusal surface, what does this mean
the clasp is too high on the tooth which can interfere with occlusion, increase leverage on tooth, and tooth recontoured to lower survey line
if the survey line at chosen path of insertion is too low:
no undercuts exist, survey line is at/near gingival margin, cannot use enameoplasty to change, requires surveyed crown!!
amount of undercut varies depending on clasp type:
0.01 for Cr-Co or Ni-Cr cast clasp
0.02 or 0.03 for wrought wire clasp
if inadequate retentive undercut
- enameoplasty to create undercut (dimple)
- addition of composite at site to create undercut
-surveyed crown
records tilt of cast at chosen path of insertion
so can reestablish path of insertion
tripod cast
what are the 2 methods of tripoding casts
- adjust height of vertical arm: marker touches 3 widely separate tissue surface areas in one plane
then circle each tripod mark - UMKC method
draw vertical lines parallel to analyzing rod on 3 sides of cast (lines widely separated)
after surveying is complete what are applied to design RPD
mechanical and biologic principles
RPD is then drawn on diagnostic cast
color code for RPD design
blue:
metal framework
wrought wire clasp
red:
indicate retentive undercut
indicate tooth modification areas
guiding planes, survey line reposition, rest seat areas
black:
survey line
tripod marks
soft tissue undercuts
what do you do after mouth preparations are complete
impressions for master cast
resurvey master cast:
-align guiding planes
-mark retentive undercuts
-mark survey line
-tripod cast
