Mastication : Incision Guidances

– C-   INCISION VS PROTRUSION MOVEMENT

Incision mov

 

 

Fig. C20: The incision movement, that split and introduce the food bolus in the mouth, is in centripetal orientation. The elevator muscles with retropulsive action are responsibles for itt (deep masseter, medium and posterior temporal, see figure C5).

Fig. C21a: Young woman, twenty years old, in class 1 relationship, with an optimal mastication.

Incis-pro Sand

 

 

 

Fig. C21: Protrusion (upper) and incision (lower).Compared movements are on the movie. They are different. Incision guides are more marked (pictures are copied from the movie).

Important: During protrusion movement, only anterior guidances are generally recorded, when during incision, posterior balanced contacts, going with anterior leading guides are revealed on marking papers.
If you first test, a protrusion movement till incisors edge to edge, and then an incision movement, with pressure of elevator muscles, you can be aware of this reality

Incision

Which movement ask to a patient, when checking and balancing anterior teeth?
The movement of incision is in centripetal orientation (fig. C20, 21). The usual protrusion movement asked to a patient to check occlusion is in opposite orientation, with a different muscular recruitment (see figure C5). During simulation of protrusive movement, only anterior leading guides are revealed on colored paper, while during incision, anterior leading guides, are accompanied by bilateral, balanced rear guides, that are not dominant.
This rear accompaniment of the anterior teeth is working early, in class 1, with an overbite and incisor angle in the normality (Slavicek 1983).

When a deep incisor overbite is present, with a closed incisor angle, like in class II division 2, the posterior subsidiaries incision guides appear late and occur in the close area of MIO.
In open bites, the only guides are posteriors. There is a posterior incision.

In young adults, these posterior guides, are often present, but generally thin. They become more prominent with age and occlusal wear . They follow, in a personalized way, the progressive degradation of the initial optimal model.

Incis conc pal  Palatal concavity

Fig. C22: Only incision guides are in touch with the whole palatal concavity, of the maxillar incisors, when protrusion guides seem to “fly over”.

About palatal anatomy of maxillary incisors.
The presence of a well marked palatal concavity in maxillary incisors finds its functional significance, when in cycle-out, the edge of lower incisors pass transversely across these palatal concavities in a slightly anterior situation (see vidéo C14). They therefore have a functional equilibrium relationship with the undisputed volume of the molar cycle output tables. But they have not any significance for incision and protrusion movements.

prot post  Incis post

Fig. C23 The difference of muscular recruitment slightly changes  the mandibular position: on upper figure  depressors= no rear contacts, on lower figure, elevators= rear accompanying guides

Bibliography

  • Gaudy, J.F.; Hadida, A.; Brunel, G.; Tavernier, J.C.  Les muscles masticateurs possédant une insertion capsulo- méniscale au niveau de l’articulation temporo-mandibulaire. Inf. Dent., 1992, 39 : 3517-3522
  • Lauret J.F., Le Gall M.G. The function of mastication: A key determinant of dental occlusion.  Pract. Periodont. Aesth. Dent. 1996; 8:807-818.
  • Le Gall M.G.  “What Occlusion for the Implant prosthesis”   Impl. Dent. 1997; 1: 50-51  (AAIP International  Conference: “Implant Prosthodontics: Practical Techniques for the Implant Team” Atlanta (Georgia)  Nov 8-10 1996
  • Le Gall M.G., Lauret J.F.  The Function of Mastication: Implications for Occlusal Therapy. Pract. Perio. Aest. Dent  1998; 10 (2): 225-229
  • Le Gall M. G., Lauret J. F. (†).  Book : 3rd edition enriched (2002, reprinted 2004, 2008, 2011) “The occlusal function: clinical implications“ (French edition only) Editions CDP.2011 Paris  www.editionscdp.fr/
  • Slavicek R. Les principes de l’occlusion  Rev d’ODF 1983(17) IV: 449-490