How do you decide where to position posterior teeth when constructing a complete removable denture prosthesis for an edentulous patient? Do you delegate the decision to the dental laboratory? Do you start at lingualized occlusion and adapt or refine the patient's contours to customize the outcome? Or do you focus on the anatomic features of the supporting structures and the patient's perceived range of adaptability?
Data collected from the clinical appointments leading to an evaluation of the trial setup forms the basis of denture occlusion. Conventional or digital impression techniques capture the supporting tissues, and the wax rim identifies tooth position and records the relationship between the maxilla and the mandible.
While thinking through occlusal design options, the considerations involved in the patient's anatomic presentation and their neuromuscular coordination provides information helpful to customizing the outcome.
The Cuspal Inclination of Posterior Teeth
Traditionally, selecting denture teeth is based on the dimensions and contours of anterior maxillary teeth (#6 -11 or #1-3 through #2-3). Denture tooth manufacturers provide decision-tree guidance, which identifies the lower anterior teeth to match while accounting for the restorative space and the relationship to the opposing teeth. The size and proportion of the posterior teeth are selected based on the cuspal inclination of the premolars and molars.
Flat plane, zero degree, or monoplane posterior teeth represent one end of the continuum of options. The middle of the continuum includes varying degrees of cuspal inclines considered to be shallower than natural teeth, including 5-degrees, 10-degrees, 15-degrees, and even 22-degrees, as options for semi-anatomic teeth. The other end of the continuum includes teeth designed to match anatomic contours with cuspal inclines around 33-degrees.
After identifying the vertical dimension of occlusion with contoured wax rims, a patient with a significant amount of bone presents with a limited volume of restorative space compared to a long-standing edentulous patient who presents with a significant distance between the maxilla and mandible.
Deciding where to position the posterior teeth is based on the potential stability of the denture's base. A high degree of stability provided by excellent supporting structures lends well to anatomic teeth with steeper cuspal inclines. On the other hand, patients with minimal residual ridge anatomy and a large distance between the maxilla and mandible can be a destabilizing force on a denture's base.
The advantage of working with cuspal inclines built into posterior denture teeth is the opportunity to construct a balanced occlusion, i.e., contact on both the working side (chewing side) and the nonworking side (balancing side) during the “power stroke” when food is being pulverized.
Working with the contours of the teeth helps stabilize the removable dentures during functional chewing movement. Balanced occlusion provides an opportunity to re-position the dentures while speaking. For example, if the lower denture is beginning to come loose, the patient can quickly close together to re-position and continue their interaction.
The Flexibility of Lingualized Occlusion
Lingualized occlusion is a popular recommendation for edentulous patients working with complete dentures. The flexibility inherent in lingualized occlusion provides for variations to include balanced occlusion concepts and elements of monoplane occlusal design.
The key feature of lingualized occlusion emphasizes the palatal cusp of the maxillary premolars and molars where the cusps contact the central groove of the opposing lower posterior teeth.
Available options include:
- Cusped teeth opposing flat plane lower posteriors
- Cusped teeth opposing lower posteriors with shallower cuspal inclines
- Cusped teeth opposing lower posteriors with identical cuspal inclines
Balanced occlusion is possible in options two and three while setting the teeth with a compensating curve to mimic the curve of Spee and the curve of Wilson. The primary advantage of working with opposing lower posteriors designed with flat plane or 0-degree cuspal inclinations is the convenience of adjusting the completed dentures after insertion.
The goal of lingualized occlusion is to eliminate lateral interferences created by the palatal inclines of the maxillary buccal cusps. When working with upper and lower posterior denture teeth with identical cuspal inclination, the maxillary posteriors are rotated - cervical aspect is positioned toward the palate and the cusp tip is positioned toward the buccal mucosa. Introducing shallower cuspal inclines for the mandibular posterior teeth preserves the goal of minimizing contact of the palatal inclines of the maxillary posteriors during working movements and lowers the difficulty level required of post-insertion adjustments.
The technical component of posterior denture occlusion design rests in creating a balancing side contact. Why would that be important? Because the stability of a moveable complete denture prosthesis rests on a pressure-sensitive and dynamic supporting base of soft tissue.
Protecting the anterior teeth becomes more important with restorative treatment that includes dental implants designed to increase the retention and stability of the intended prosthesis.
Creating contact on the articulator with the intention of extending the range of bilateral simultaneous posterior contact to include the “power stroke” segment of an excursive movement involves management of the coupled contours in the posterior. The denture setup on the left side (Fig. 2) demonstrates the contact between the palatal cusp of the maxillary molar and the lingual half of the opposing lower posterior tooth. The diagrams on the right side (Fig. 2) demonstrate options to modify the way the upper and lower teeth come together on the working side to create contact on the balancing side.
Matching the Patient's Mandibular Movement
Grinding away the lingual cuspal inclines provides the opportunity to customize the lower posterior teeth to match the patient's mandibular movement. The condylar inclination is identified with a protrusive record at the wax-rim appointment. This information is transferred to an adjustable articulator as the condylar element is modified.
Working with flatter cusp angles for the opposing posterior denture teeth minimizes the amount of material available for adjustment, which results in a decreased ability to customize the occlusal contacts for the patient. For a patient with a steep condylar inclination, cross-arch balance using lower posterior teeth with flatter cusp angles will require the incorporation of a compensating curve in the denture tooth setup.
Rotating both the maxillary and the mandibular teeth based on condylar inclination information transferred to an articulator preserves the opportunity for cross-arch balance. It also preserves the next-level denture occlusion with balance across the buccal and palatal halves of the posterior teeth and cross-arch balance.
A loose definition of lingualized occlusion is a blend of several philosophies in the design of posterior denture tooth contact both in the fully seated condylar position and in the initial functional eccentric movements of the mandible. Working through the concept of lingualized occlusion provides a foundation for other design options for edentulous patients looking for complete removable dentures. The design features and the considerations involved in the patient's anatomic presentation as well as their neuromuscular coordination provide information helpful in customizing the best outcome for the patient.
Douglas G. Benting, D.D.S., M.S., F.A.C.P. is a member of Spear Resident Faculty.