Surveying in partial dentures Flashcards
what is a dental surveyor and its purpose?
a paralleling instrument used to identify, analyse and mark the **maximum contours **of a tooth and tissues of dental casts
what are the areas under the maximum contours called?
undercuts
what is the primary objective of surveying?
establish a suitable path of insertion that will utilise guide surfaces to provide long term retention
what is the common path of displacement?
a single, defined direction in which a removable partial denture is designed to be inserted and removed from the mouth - 90 degrees to the occlusal plane which is taken to be horizontal
what is tripoding and why is it useful?
- once a cast is in place on the table of a surveyor with the occlusal plane in a horizontal position
- three vertical lines are drawn on the cast on different sizes
- these lines orientate the cast on the tripoding table and records the decided path of displacement
- the cast can be removed and replaced with the recorded paths intact
why may you need to alter the path of insertion?
- with the common path of displacement, there are tooth and soft tissue undercuts which result in spaces and bad aesthetics
- with an altered path of insertion, tilting the cast to the guide surfaces on the tooth and soft tissue can eliminate spaces, resulting in better aesthetics and improvements in retention
what is the analysing rod? what does it do?
- analysing rod ‘eyeballs’ the undercuts
- enables a path of insertion and removal to be chosen
- table can be tilten to provide retention (guide surfaces of teeth), improve appearance (closing gaps) or eliminate interference (tooth or ridge undercuts preventing satisfactory path of insertion)
what is a graphite marker? what does it do?
- graphite rod with a chiseled edge
- the long side is used against the cast surface and the tip is lined up with the gingival margin
- chisel shape enables it to go inter-proximally between teeth
what is the survey line? what does it indicate?
- the survey line is drawn by the graphite marker on the tooth or soft tissue surface
- it indicates the extent of an undercut which must be used or eliminated by blocking out to create a uniform path of insertion/removal
what are undercut gauges? what are they used for?
- undercut gauges mark the position of the undercut area with a fine pencil point
- different types of undercut gauge relate to different metals used
- 0.25mm - cast CoCr
- 0.5mm - cast gold alloy
- 0.75mm - wrought stainless steel
describe the overall surveying procedure
- place cast on survey table with the occlusion in the horizontal plane (path of displacement)
- tripod this position
- use the analysing rod to eyeball the cast before marking it
- decide the path of insertion and removal and tripod the position
- use a graphite marker to mark soft and hard tissue undercuts (common path of displacement and altered path of insertion - two colours)
- use a 0.25mm undercut gauge to determine undercut position for retention
