Prostho_Article_Lingualized Occlusion2_Layout 1 12/16/10 8:52 AM Page 78 prosthodontics feature Denture wearers have three things they desire most from their prostheses: aesthetics (a natural look), comfort Two Concepts and function. Comfort and function are directly linked with the occlusal scheme incorporated into the prosthe- in Denture ses. But what is the best scheme? Occlusal schemes are divided into two classes – Occlusion anatomic and non-anatomic. Depending on where an indi- vidual received his or her pre-doctoral training will play a significant role in the occlusal scheme a doctor selects. There is far too much material that needs to be taught and Lingualized Occlusion far too little didactic time available to permit an in-depth study of all aspects of denture occlusion in a pre-doctoral curriculum. Each school might by necessity emphasize one vs. Linear Occlusion – particular type of occlusal scheme depending on the philos- ophy and background of the school and department head. What’s the Difference? It is the responsibility of the dental school to prepare its stu- dents, first and foremost, to successfully pass their dental board examination. To that end, the student must be pro- ficient in one occlusal concept, not all. by William S. Jameson, BS, DDS, FACP, FICD In these two categories, linear and lingualized occlusal forms (Condyloform and AutoCentric Posteriors, Candulor USA, Inc.) have a history of being the most functionally efficient. In the Glossary of Prosthodontic knife on a chopping block. From a personal perspective, a Terms both are defined.1 For lingualized occlusion, “this sharp knife on a chopping block is functionally more effi- form of occlusion articulates the maxillary lingual cusps cient than a grinding, crushing type of occlusion. with the mandibular occlusal surfaces in centric working Stability of the mandibular prosthesis is directly asso- and non-working position.” More recently, the term has ciated with the lack of cusp/fossa interference in arriving changed to “lingual contact occlusion” to dispel the mis- at or exiting from centric occlusion position and the lack conception that the mandibular teeth have been moved of interference in eccentric movements. This is much lingually. The mandibular occlusal surface might be flat or harder to attain with lingualized occlusion since there is a poses a shallow central fossa into which the opposing lin- specific cusp to fossa intercuspation, whereas linear occlu- gual cusp articulates (Figs. 1a & 1b). For linear occlusion, sion has no inclines with which the blade might contact “the occlusal arrangement of artificial teeth, as viewed in when the patient closes into centric or eccentric articula- the horizontal plane, wherein the masticatory surfaces of tion. With linear occlusion, articulating forces are in a ver- the mandibular posterior artificial teeth have a straight, tical, stabilizing direction whereas tipping forces might long, narrow occlusal form resembling that of a line, usu- occur in lingualized occlusion if there are any premature ally articulating with opposing monoplane teeth (Figs. 2a contacts prior to achieving centric articulation. Instability & 2b).” In the arrangement of both, the point of occlusal of the prosthesis leads to discomfort from tissue irritation contact is over the crest of the residual ridge for mechani- and loss of residual ridge over time. cal stability. Lingualized occlusion has been likened to a In addition to differences in occlusal form, there are mortar and pestle, whereas linear occlusion resembles a differences in the principles of articulation. With linear Fig. 1a Fig. 1b Fig. 2a Fig. 2b 78 January 2011 » dentaltown.com Prostho_Article_Lingualized Occlusion2_Layout 1 12/20/10 1:17 PM Page 79 feature prosthodontics occlusion success is directly linked with noninterference Do you know? between opposing tooth surfaces. That applies to the ante- )('&)% $)%#"! )! rior component as well as the posterior component. To '%)")! facilitate this, the mandibular anterior teeth are arranged %)!!!!'#)! in centric position a half millimeter below the occlusal plane, which is determined by the incisal edges of the maxillary central incisors in the anterior and halfway up .$$ the retromolar pad on either side in the posterior (Fig. 3). $ #$"!" "$!"$!!"$ To prevent anterior contact in protrusive position, the $ $!$"$$$$ mesial one-third of the maxillary first premolar is beveled $ $$$!"$"$!$! $$ $ !$!$ """$$$$ at a 45-degree angle toward the distal contact area of the - ,+*-)('&'+,%'+$-#'"")! canine. This creates a straight edge against which the blade .$$ of the mandibular first premolar will make contact as the - +-), -'+)-"%'+-!-!)(',()- %!+$-!)",'! -$ mandible moves forward and upward, preventing anterior - '%-)'%)!-('$%-!)-!- )(-!)-!) '+ - contact. This creates a posterior, vertical force in the pre- molar area which seats rather than rotating the maxillary .$$ prosthesis on the anterior residual ridge (Fig. 4). "$ $"$ $"$$ $"$ $$!$$!$ "$$!"$$! " $!$ $ ! $ !)'+!)&)+%-* .$$ $ $""$!$!!"$ $ "!$$!$"""$"$$ - ,'+$--'&"()-%!,*'%'+,(-,'! '*)-$ $ " $!$!"""$$ Fig. 3 - -)')!-'%-+-!$-%+$)-'!!'%,%'+$- !,) .$$ $ "$$ $!$ !$ "$$$$$ $$$$"$ $$!$"$ $"$ $!$$ - -%'&) -- )-!)'+!)&)+%-' -'+' '()-,+*- &%--- .$$ $ !'*)- &% -!& -%$- ",)- $ ""$"$ " $"$! $$ - ")!,%!') --,)-,'! '*)-%'&)-$ Fig. 4 - ,+*- ,%' -",%')+%-) %)%'-*)&,+* $ .$$ $ $!"$!$$" $ $!$ One reason for the popularity of lingualized occlu- - " %-!%*+%'-%))%- )-)')!-' -$ sion can be attributed to the fact that its technical aspects - !& -%'+ - &%-,+*-+* -,'! '*) are basically the same as conventional anatomic occlu- sion. That said, the inherent anterior vertical overlap is a given. Even if the anterior teeth are arranged out of con- tact in centric articulation, with occlusal wear (porcelain Now you know! prosthetic teeth are rarely used) and posterior ridge )('&)% $)%#"! ) resorption, the mandible will move forward and upward with resulting anterior tooth contact. When this occurs, a rocking or rotational movement of the prosthesis occurs !!!% )%! %!"%)%! '!"!"! with its associated anterior hyperfunction and in one of $ !!$ !! every four patients, loss of the premaxilla.2, 3 Arranging posterior lingualized teeth is much more 1 800 232-7732 difficult than linear prosthetic teeth due to the required cusp/fossa relation. If the maxillary anterior teeth are www.preat.com continued on page 80 #$!!!" - - - -,+%,-+)-- FREE FACTS, circle 23 on card dentaltown.com « January 2011 79 Prostho_Article_Lingualized Occlusion2_Layout 1 12/16/10 8:52 AM Page 80 prosthodontics feature continued from page 79 positioned for aesthetics and phonetics, followed by the relation, a distinctive click or ringing sound is heard. If mandibular anterior and posterior teeth, the articulation by chance the occlusion is off, a dull or double-click will of the maxillary first premolar to the mandibular first pre- be heard. The operator then parts the lips and has the molar is usually problematic. If the maxillary posterior patient close slowly into a retruded position. With no teeth are arranged followed by the mandibular posterior incline planes to obstruct the view, the first point of con- teeth, the mandibular anterior teeth might have problems tact can be observed. Knowing this, the blades are marked filling the remaining space (Fig. and more accurately relieved. 5). This problem does not exist This is repeated until bilateral, with linear posterior teeth since simultaneous contact is achieved. the blade in one arch articulates With only vertical occluding anywhere on the flat surface in forces, the possibility of lateral the opposing arch (Fig. 6). shifting of the prosthesis during The final difference to con- refinement is eliminated. The sider is occlusal adjustment or patient is then instructed to bring refinement. With lingualized Fig. 5 the mandible forward into an occlusion, the first point of a end-to-end relationship and premature contact will be hid- checked for contact. The bilateral den within the occlusal fossa. fulcrum should prevent contact, Because of this, one must rely but if present, either the maxil- entirely on marking the spot lary or mandibular offenders are with articulating paper. In the reduced until only light, kissing mouth, if the first contact is on contact remains. The decision as an inclined plane, the prosthe- Fig. 6 to which teeth to reduce depends ses could shift as tissue is dis- primarily on aesthetics. placed under occlusal loading. The most accurate method would be an intraoral nee- Conclusion dle point tracing and lab remount. Some advocate The occlusal scheme chosen by the clinician will using the intraoral tracing device with gradually closing always be a personal decision based on knowledge and the marking screw until contact is made, marked and experience. This is basically the conclusion drawn by relieved. This is repeated until bilateral uniform contact attendees at The International Prosthodontic Workshop on all articulating surfaces is achieved. If the contacting on Complete Denture Occlusion4 in 1972 when they force is too great, tissue displacement could still be a stated, “At present, the choice of a posterior tooth form source of error. or arrangement for complete dentures is an empirical As defined earlier, with linear occlusion, one arch procedure. The available research fails to identify a supe- contains a bladed occlusal form and articulates with flat rior tooth form