Tooth preparation for RPD does not receive the same attention and detail as tooth preparation for fixed restoration. There has been so much written about the type of burs used and how to achieve the ideal preparation for fixed restoration. But when it comes to tooth preparation for RPD, most of the materials are focused on how to prepare for the rest seats. While that is a very important element of mouth preparation for RPDs, I find that very little is written about the minor enamelplasty that is often necessary to prepare the dentition for a cast removable partial denture. Enamelplasty may be necessary on the proximal surfaces to create guide surfaces or on buccal and lingual/palatal surfaces to idealize the locations of the height of contour so that the placement of the retentive and bracing clasp arms can be made on the middle third without interferences. These areas of modification can often be identified at the initial stage of surveying by identifying the suitable path of insertion.
However, the challenge I see in dental students is the struggle to visualize intra-orally and to successfully perform and confirm the necessary enameplasty. The inability between what should be done and what is actually done can prevent someone from fabricating a well designed cast RPD.
There has been some material written about transferring the path of insertion by use of preparation guides or other extra-oral and intra-oral paralleling devices. Many of these are not readily available now and require time to prepare.
For me, I just use any readily available periodontal probe or endodontic condenser as an intra-oral surveying rod. I look at the surveyor and observe how the surveying rod touches three easily identified surfaces on the model. These can be any teeth buccal or proximal surfaces that are not part of the preparation. Then I orient my periodontal probe to lean against these pre-identified surfaces in the mouth the very same way how the surveying rod is aligned against these surfaces on the model. I make a mental note of the orientation of the probe and then without changing the orientation of the probe, I move it along to other tooth surfaces where enamelplasty is indicated to evaluate if I have performed the required tooth modification.
This is a very inexpensive way to evaluate tooth preparation. It is, however, subject to human error as you can change the orientation of the probe while moving it to different parts of the mouth. But I always have the ability to go to my reference surfaces to recheck the orientation of my probe. This has been my intra-oral surveyor for many years. You can use endodontic condensers or an instrument shaped with paralleling sides to help navigate the oral cavity to evaluate contours and undercuts. I hope this tip can help you make better RPDs. Do you have a better way to evaluate contours and undercuts without expensive tools? Please do share!
Thanks for reading.