Creating highly esthetic posterior restorations that conform to the existing occlusal scheme for routine dental patients is highly challenging.
Oftentimes, clinicians take the time and effort to sculpt beautiful occlusal anatomy, only to take a burr and reduce it to a concave grey mass during the occlusal adjustment phase. So, how do we create a “wow” restoration without significant post-placement occlusal adjustment?
“Form ever follows function, that is the Law” - Louis Henry Sullivan (The Tall Office Building Artistically Considered, 1896)
Louis Henry Sullivan was perhaps America’s first truly modern architect. He pioneered the concept of the skyscraper in the Midwest and argued that a building’s exterior design (the form) should reflect the activities (the function) going on inside the walls.
This concept is much the same for teeth. If the function (occlusal scheme and functional pathways) is considered then the form (morphology — for example cuspal position, cuspal incline angle and fissure position) will be automatically correct. In this way, esthetics are created almost as a byproduct of occlusal control.
This is very similar to the concept of the DeVreugd occlusal compass, whereby the anatomy of the occluding surfaces of the teeth is built with heavy reference to the functional pathways in dynamic occlusion. Each color on the compass references as the pathways of the cusp tips travel back to centric (during chewing) and outwards from centric (during parafunction). Keeping these areas free of contact ensures an adjustment-free restoration.
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This sequence shows the build-up protocol for an upper first molar tooth. The tooth is isolated, prepared and a dentin-bonding agent applied and the cusps are placed in the following sequence.
The operator always begins opposite the largest cusp. The largest cusp is the mesiopalatal (MP), therefore we begin with the mesiobuccal (MB). One of the critical landmarks is the mid-buccal fissure, which defines the position of the compass point (occluding point in CR/MIP) and the blue movement (laterotrusion). A very rough guide for ideal placement of the mid-buccal fissure should be a right angle to the theoretical line drawn between mesiobuccal and distobuccal cusp tips (Figures 1 and 2).
The MB cusp is placed (Figure 3) copying the cuspal inclines of adjacent teeth by aligning them to an explorer and then transferring to the tooth you are working on (Figures 4 and 5).
The tip of the MB cusp extends roughly to a line approximating that of the midpoints of the mesial and distal marginal ridges. This is estimated and visualized with the same explorer (Figure 6). Prior to polymerization, a small depression is placed adjacent to the mid-buccal fissure with an instrument such as a posterior occlusal carver, this creates a pathway for the yellow lateroprotrusive movement, which is forwards and outwards.
After polymerization, the distobuccal cusp is placed while maintaining the position of the mid-buccal fissure, therefore creating the blue laterotrusive movement, which is outwards. Prior to polymerization, the posterior occlusal carver is used to create a depression just to the distal of the mid-buccal fissure, allowing the lateroresutrusive or side-shift movement, which is outward and backward. The working side movements are thus complete (Figure 7).
The mesiopalatal cusp is then modeled with reference to non-working side movements and a small depression is placed on the cusp to allow the green mediotrusive movement out from the compass point. A finger-like projection is created from the mesial marginal ridge into the compass point to allow clear protrusive pathways (Figure 8).
Finally, the distopalatal cusp is placed to complete the build-out. Ensure that the palatal fissure runs distally to recreate the transverse ridge (Figure 9).
If this protocol is followed, only minor occlusal adjustments should be required after placement. The restoration is then polished.
Jason Smithson, BDS (Lond), DipRestDentRCS (Eng), is a member of Spear Resident Faculty.
Sullivan LH “The Tall Office Building Artistically Considered”. Lippincotts Magazine, March 1896
DeVreugd RT “The Occlusal Compass Concept: A Practical Approach to Posterior Tooth Morphology” QDT 1997; 20: 75.