Preparation Design eMax

PREPARATION DESIGN PRINCIPLES

Research indicates that brittle restorative materials, like dental ceramic, are best when under compression. Thus, a ceramic onlay with an even thickness of 1mm to 2.5 mm, passively seated over the shallow concavity or saucer, come in full compression under masticatory forces. This principle does apply to any ceramic material. A toned object of uniform thickness can rest on another flat surface and support a given load on top of it without breaking. In a similar fashion, a restoration fabricated utilizing the design and principles discussed, can perform withstanding forces exerted upon it.

             

  Standard “G.V.Black” preparation techniques supply the necessary mechanical retention to get a posterior restoration for conventional cementation; however, the all-ceramic bonded restoration will depend on chemical bonding for preservation, which eliminates the requirement of residual cuspal outline for mechanical retention. Many dentists resist the concept of lacking a retentive element on a restoration, leaving the preparation with enough convexities to generate excessive tension on the ceramic once it bonded.

              

A rise in firing stresses is assigned to the cooling of ceramic material, which is another possible challenge with uneven thickness in an all-ceramic restoration. Thin areas cool more rapidly than thicker areas (uneven contraction), creating stresses inside restoration. Occasionally these stresses stay in the restoration, but aren't readily seen until much later- after the restoration was in patient’s mouth for some time. While conceptually acceptable, such preparations can be left with sharp angles and undercuts. Even if the final restorations may have a suitable thickness, the inside will continue to be under tensile stress. Additionally, small undercuts left on the preparation will have to be blocked in the laboratory, producing a layer of bonding resin that is thicker than required.

             

  Fragile materials, such as dental ceramics, are subject to disastrous failure under the right conditions. Consistent fractures or “chipping” of a ceramic restoration may have more regarding the quality and handling of the material by both dentist and dental ceramist. Passive flaws and inclusions may also end in failures, and are pretty much controlled during the fabrication process. Strength in delicate materials is a bit more of conditional material property, and flaws that affect strength can be introduced in the course of fabrication process or through grinding, when the restoration is adjusted during seating by the dentist. Longevity of the restoration depends upon each of these factors.

Preparation Guidelines
For preparation guidelines please refer to our IPS Empress Esthetic/IPS e.max Prep Guide.

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