prostho sheet # 3 - Reham kelano

The surveyor consists mainly from:
-Base
-vertical arm
-horizontal arm: this arm could be continuous or it could be formed of two arms joined together by a joint, it also could be movable around the vertical arm or fixed in its place
-vertical spindle: which holds the tools used in surveying through something called a tool holder



-Dental surveyor table: which is used to hold the diagnostic cast in its place, this table can be adjusted to different tilts by the usage of a knob called “universal joint mechanism”, and it also can be either fixed to the base or removable.



Surveying tools:
1-analyzing rod : first tool used to study the undercuts , there will be a wedge shaped space between the rod and the tooth below the survey line and this is the undercut area !

2-carbon markers: we draw by its SIDE the survey line and its tip should be very close to the gingival margin and drawing on it, this will give us a better 3 dimensional view of the undercut areas, we should never draw the survey line under any circumstances using the tip of the carbon marker cause this will give us a false survey line and will definitely result in a false undercut area.
It’s been widely accepted by dentists that the zero tilt is drawn using a carbon marker and the alternative tilt is done by using a colored marker
~ Carbon markers should be beveled before used!


3-undercut gauge: as the name implies this gauge determines the undercuts in certain tooth or teeth, these undercuts are important as we said because we’ll gain retention once the chromium alloys gets into it!
The three gauges in the picture above from left to right are
.01 , .02 and .03 of an inch which is equal to 0.25 , 0.5 and 0.75 mm respectively
The 1st one is suitable for chromium type RPDs while the 2nd is more suitable for gold alloys RPDs and the last one is suitable for RPDs made of stainless steel this one provides the maximum elasticity to go into these undercuts providing retention so its superior from this aspect to both chromium and gold RPDs

4-wax trimmer








The uses of a surveyor:
-survey the diagnostic cast:
we need to look carefully to the outlines of our saddles in these diagnostic casts, we don’t restore everything, like missing 8s and sometimes even missing 7s sometimes we restore them, other times we don’t.
-survey the master cast
-determination of the path of insertion and removal of the RPD on both the diagnostic and the master cast
This path of insertion will and should engage some undercuts from those of the zero tilt so that the whole RPD will resist dislodgment during chewing of any sticky foodstuff because these forces are perpendicular to the occlusal plane while the path of insertion and removal is not!
This path also provides retention to the RPD, it could also enhance esthetics and it could spare the dentist from doing too much preparation inside the mouth thus conserving the tooth structure, and we usually construct this path so that we minimize interferences between the teeth, so for example if the anterior teeth were tilted lingually, it would make sense to construct an RPD that would go with this tilt (parallel to this tilts) instead of being perpendicular which would probably result in interferences
-determination for the need to recontour the abutment teeth:
Sometimes we do certain adjustments on the survey line if we see that it’s too high or too low or not continuous ….etc this is done by using the wax trimmer
-drawing of a survey line:
This line is drawn on the abutment teeth by using a carbon marker which is vertical relative to the base of the surveyor, this line will divide the tooth surface into 3 main areas; those which are above the survey line “non-undercut areas”, those which are under the survey line “undercut areas” and the survey line itself, its really important to determine the undercut and the non-undercut areas at the zero tilt, because once again these undercut areas will provide retention and resistance against displacing forces by any sticky material that is stuffed between the jaws because it will stick to both jaws and will eventually-if no proper retention is obtained- dislodge the prosthesis ,the direction of these dislodging forces is perpendicular to the occlusal plane
The magnitude of the dislodging forces differs according to the type of the sticky foodstuff used or consumed!
If these forces exceed the retention provided by the retentive arms for example, then displacement of the RPD will occur!

Note: it’s important to know that we do two tilts, one is the zero tilt and the other tilt is the one that is parallel to the path of insertion and removal which could be anterior tilt,posterior tilt or any combination of them all, the direction of which is the same as that of the analyzing rod in relation to the tilted cast! So the analyzing rod is like an arrow that would be pointing to the path of insertion and removal
Also when we draw the two lines that represent the two tilts, it’s important to always remember that those areas below the 1st line are the undercut areas and not the ones below the colored or the 2nd line !

• PRECISION ATTACHMENT: are attachments for retention between the partial denture and the tooth, these attachments should be parallel to each other

-Tripodization which means, we make a certain tilt and mark it so that we can go back to it whenever we want to!

• Survey line should be drawn not only on teeth but also on the tissues, because the RPDs flanges may interfere with them so its important that we take this point into consideration
• Having more than one path of insertion is not acceptable,this happenes when we’ve got spaces between the tooth and the RPD, which will allow different ways for insertion and removal
• Providing guiding planes of 2-4 mm on abutment teeth will assure you that you’ll have one path of insertion and removal which is the ideal case! Less than 2 mm is not efficient.
• If all the rules apply, but we have the path of insertion in the same direction as the dislodging forces then this is highly unstable and will be displaced with any minimal forces because there are no undercuts that provide retention in this case! So the dislodgment path and the insertion path should not coincide.

So after this we should be able to define the Reasons for choosing another tilt during surveying which are:
1- To achieve better esthetics
2- To obtain more retention
3- Avoid anatomical interferences
4- Conserve tooth structure

Things that the alternative tilt will NOT provide:
1- Retention of the clasps assembly
2- Will not make the RPD easier to be handled by the patient


 If we have an anterior edentulous saddle in front of the teeth, we will need a tilt that will be parallel to it and not perpendicular because it would be highly anesthetic resulting in bulging of the lips

That’s all for today
Good luck 
Reham Kilano
3rd Lecture
1/3/11