Dental surveying

What is a Dental Surveyor?

–        An instrument to determine the relative parallelism of two or more surfaces of the teeth and or other part of cast of the removable partial denture.

What is Surveying?

–        A procedure to locate and delineate the control of the abutment teeth and or other associated parts of the dental cast before constructing the removable partial denture.

What are the purposes of dental surveying?

1)     To determine the most desirable path of placement that will minimise or eliminate the interferences during placement and removal of removable partial denture. 

2)     To identify the proximal tooth surfaces that needed or must be parallel to the path of insertion to act as the guiding planes during placement and removal of RPD.

3)     To locate & measure the abutment teeth which will act as retention.

4)     To determine the height of contour of the abutment teeth and the undesirable undercut where it will be avoided or blocked or eliminated.

5)     To identify the suitable path of placement that permits the insertion for retainers and artificial teeth for best esthetic advantage. 

6)     To permit accurate charting of the mouth preparation to be done. 

7)     To determine the bony areas or tooth that is needed to be surgically removed or different path of insertion will be selected.

8)     To record the position of cast in relation to the path of placement for future references. 

What is the definition of Path of Insertion?

–        It is the direction of which the restoration move from initial contact with the supporting teeth to the terminal end where the denture base comes in contact with the oral tissue and the occlusal rest is seated in its place. 

What are the Surveying Tools used in surveying?

1)     Analysing Rods 

–        Used to determine the tooth and tissue undercut

2)     Carbon Markers

–        Protected in a metal sheath to prevent it from breakage

–        Used to draw the greatest circumferences of the tooth (Survey Line)

3)     Undercut Gauges

–        Comes in 3 sizes (0.1”, 0.2”, 0.3”) 

–        Used to determine the number of undercut (size of undercut)

4)     Wax Trimmer

–        To remove the excess wax after the blockage of undercuts to prevent over-contouring and to keep the wax parallel to the path of insertion.

What are the factors that determine the Path of Insertion?

1)     Guiding Planes

–        Function of the guiding planes

: to ensure the rigid part of the dentures are able to pass through the existing areas of interference.

: to control and limit the movement of RPD during insertion, removal and function.

: to ensure predictable clasp assembly function which includes retention and stabilization.

2)     Retentive Areas 

–        Retentive undercuts must be present on the abutment teeth both at horizontal tilt and at the tilt of path of placement, to prevent dislodgment of the RPD. 

–        Desirable undercuts

: has sufficient depth, suitable location, reasonable accessibilities in relation the retentive clasp chosen for the RPD design.

–        Undesirable undercuts

: all tooth and tissue undercuts that interferes with the path of insertion

: must be blocked before RPD construction. 

3)     Interferences

–        These areas include the proximal tooth undercut, palatinus and mandibularis tori, lingually and mesially inclined teeth, bony exostoses and tissue undercuts. 

–        Must be removed by

: surgery

: changing the path of placement

: relief of the denture

: construction of crowns

4)     Esthetics

–        Unfavourable survey lines usually related to #11 and #13 will affect the aesthetic due to positioning of the clasp (metal display) 

–        How to prevent this?

: change the path of insertion to minimise the display of clasps and metal components

: recontouring of the tooth  

Rules of Surveying:

1)     Undercut cannot be used or created by tilting the cast.

2)     All cast are originally surveyed with the occlusal plane parallel to the base of surveyor.

3)     The retentive tips must engage the undercuts with the undercuts which are present when the cast is surveyed in horizontal tilt. 

4)     Undesirable undercuts and areas of interference are removed during mouth preparation by recontouring the teeth or making necessary restorations. 

Contributor– Medico Umairah Zulkifli