Convenience of vestibular surfaces of lower canines for accepting retention elements of removable partial denture

Abstract

Lower canines often appear as abutment teeth of partially edentulous dental arch. Crown contours of these teeth are mostly inconvenient for placing clasps. The convex vestibular surfaces with sufficient undercuts for placing retention elements are obligatory on lower canines but it is not common case. Aim of this paper was to confirm a high frequency of inexistence of buccomesial and buccodistal undercuts of the lower canines. Measuring of buccomesial and buccodistal undercuts on abutment lower canines was preformed on 50 diagnostic casts of lower jaw, belonging to Kennedy class I, where the canine was a border of shortened dental arch. For this procedure paralelometar Unit „Degussa" with a special measuring device was used. The undercut depth could be read directly within a range of 0-1.0 mm. Results show that unprepared lower canines have poor possibilities for retention removable partial denture with clasps. Our positive clinical experiences in recontouring vestibular surfaces of the abutment teeth point to two methods of making an artificial undercut: non-invasive (making an artificial undercut using composite materials) and invasive (using modified fixed restorations). Considering fact that vestibular surfaces of lower canines as abutment teeth are in most cases without undercuts, recontouring of this surfaces in almost all occasions is necessity. If vestibular undercuts don't exist, non-invasive techniques should always have advantiges to invasive techniques. The vestibular surfaces of abutment teeth might be recontoured by using non-invasive techniques with minimal destruction of integrity of teeth. Lately, the composite materials are used for forming artificial undercut.

Donji očnjaci ce često pojavljuju kao retencioni zubi kod krezubih bolesnika sa skraćenim zubnim nizom. Oblik krune ovih zuba često nije pogodan za postavljanje livenih kukica, jer vestibularne površine ovih zuba uglavnom ne pokazuju dovoljnu podminiranost. Cilj ovog rada je da se utvrdi učestalost nepostojanja bukomezijalne i bukodistalne podminiranosti na donjim očnjacima. Merenje bukomezijalne i bukodistalne podminiranosti na donjim očnjacima obavljeno je na 50 radnih modela donje vilice klase Kenedi I, kod kojih su očnjaci predstavljali granicu skraćenog zubnog niza. Za ovu proceduru korišćen je paralelometar Unit „Degussa" sa mikroanalizatorom, koji poseduje mogućnost merenja dubine podminiranosti od 0 do 1,0 mm. Rezultati pokazuju da nepripremljeni donji očnjaci imaju male mogućnosti za retenciju parcijalne skeletirane proteze livenim kukicama. Imajući u vidu činjenicu da vestibularne površine donjih očnjaka često ne pokazuju dovoljnu vestibularnu podminiranost, preoblikovanje ovih površina je u tom slučaju neophodno.