Hygienic partial denture design

 Lately I've been watching through and reading resources by Dr. Findlay Sutton, a prosthodontist in the UK who educates about denture technique and design. One particular aspect of dentistry which I need to develop is the design of partial dentures. When my colleagues have asked me in the past to assist them with a partial denture design, my answer has bee "ask someone else, I don't know much about partial denture design." Perhaps this is an effective way of passing the buck, but it is not possible when I am facing the same task with my own patients. I can remember one particularly bad RPD design I prescribed back at uni. It was a unilateral, premolar replacement and I prescribed a full palatal coverage from molar to molar with a lingual plate covering the gingival margins of all the teeth in question. I received a fair earful from my supervisor upon seeing the product who had not actually seen the design prior to construction. This particularly careless approach to denture design hints at how poor this skill of mine actually was. I did not even know how little I knew about the subject to know how poorly I had performed.

Currently, I would say that I can avoid obvious design errors such as the one I performed at university, but the finer details of design as well as the 'why' a design choice should be made still escapes me. Findlay Sutton advocates the use of a hygienic partial denture design which prioritises low gingival coverage, irritation and improved cleansability in contrast to 'traditional' denture designs which prioritise biomechanical considerations with hygiene as an afterthought. Hygienic designs do not compromise on biomechanical retention and stability though, instead finding a way to question the dogma and produce alternative designs which are not only retentive, stable and comfortable but also kind to the periodontium. Dr. Sutton advocates designs popular in Scandinavia detailed in the 'Textbook of Removable Prosthodontics: The Scandinavian Approach by Margareta Molin Thoren and Johan Gunne'. I haven't been able to purchase a copy of this book as it is rarely available online but I will try to get a copy somehow in the future. Instead I read through an article on his website: 'Removable Partial Denture Design: A Need to Focus on Hygienic Principles?' Dr. Sutton has a generous wealth of information freely available on his website and this article is one that gives a summary of a workshop on hygienic design.

A quote I liked out of the article is one paraphrased from a German document: "If the base elements of the RPD do not contact either teeth or periodontium, it cannot cause any injuries to these structures." The aim of hygienic denture design is to create a simple design which avoids coverage of the gingival margin with denture bases, clasps, major and minor connectors avoiding contact with the gingival margin and 3mm of tissue around tooth surfaces with a minimum number of minor connectors.

Why?

-Covering the free gingiva leads to irritation of the gingival margin from movement of the prosthesis, prevention of saliva contact, increase in plaque accumulation and food impaction increasing inflammation, root caries, periodontal disease and tooth loss.

How?

-Minimise minor connectors: Minor connectors are the denture componentry that join the major connectors to the componentry such as clasps, indirect retainers and rests. As major connectors join components on one side of the arch to the other, they are generally located on the palatal or lingual of teeth. Therefore, minor connectors branching from major connectors to contact the teeth will cross the gingival margin and break hygienic principles. Minor connectors can be avoided by extending clasps, rests and framework in contact with teeth from the pontic areas.

- The pontic tooth adjacent to an abutment tooth has the potential to trap food and plaque against the abutment tooth if there is no clearance of the abutment tooth. The first pontic tooth next to an abutment area can be attached to the metal framework with no pink acrylic designed as an ovate pontic (as in the drawings above) to allow clearance from the gingival margins around the abutment teeth.

- Clasps should be placed as far away from the gingival margins as possible as gingivally approaching clasps cross the gingival margin and in shallow sulci can cause trauma to alveolar mucosa. An occlusally approaching retainer achieves this but may pose aesthetic concerns as they are more likely to be visible. the alternative suggested is a horizontally approaching arm directly from the pontic or denture base.