Tuesday, October 7, 2008

A Material Selection –Which Ceramic to Choose?

by Yugo Hatai RDT
Smile by Yugo Pty Ltd, Sydney Australia

The field of dental ceramic materials has rapidly changed over the past decade. Traditional PFM restorations have shifted towards metal free restorations, making it essential for both the laboratory technician and dentist to understand when to choose the right ceramic materials. Which materials to choose is basically based on the amount of room the clinician prepares for the final restoration, the patient’s existing dental condition and the matching prepared tooth stump shade.

At the diagnostic wax up stage, technicians can actually prepare the model the way the clinician would ideally prepare the tooth to achieve the required result. They can in turn pass that pre treatment information onto clinician. This type of communication helps both technicians and dentists to be on the same page prior to the final impression taking, thus avoiding the back and forth syndrome.

There are roughly four different type of materials available in the metal free market today.

A. Pressables (i.e; e.max, Empress 1and 2 and esthetic veneers) E.max is recommended over the other Empress systems for aesthetics and strength when layered. E.max can be either cemented or bonded depending on the particular condition. E.max is useful to fabricate in veneers, crowns, bridges, inlays/onlays or can be pressed over Zirconia for greater strength. When layered, necessary support is required to enhance the ratio of coping to layered porcelain to increase the longevity of the restorations. The thicker the un-layered coping, the greater the strength with a slight sacrifice in aesthetics.

B. Zirconia (i.e; Lava, Procera) Copings can be made either by CAD/CAM milling or by in-house milling machines. This is the strongest material in the metal free category. Higher ceramic skills are required to achieve life-like restorations compare to other metal free materials due to their lack of translucency. Extra support in coping design is required (i.e; marginal ridges, functional cusp, or where the layered porcelain exceeds more than 2mm) to maximize the longevity of the restorations. Thickness of Zirconia can be determined with radiographic analysis similar to PFMs. making it the most suitable material to mask the metal and discolored stump/cores. Generally 1.5-2.0 mm is required for adequate tooth preparation depth. Zirconia can be used for crowns, bridges, cantilever pontics Maryland bridges, and implant abutments.

C. Alumina (i.e: Procera) Alumina is stronger than pressables, but known to be weaker than Zirconia. It has high aesthetic characteristics compared to Zirconia in general due to the light transmission, however, the needs of Alumina have been reduced since Zirconia was introduced due to the lack of strength (700MPa) compare to Zirconia (over 1000Mpa). Alumina can be used for crowns, bridges and procera laminate (veneers).

D. Feldspathic (porcelain laminate veneer (PLV)) Feldspathic porcelain is the oldest system in metal free technology. It is a technique sensitive material compare to others, however aesthetically pleasing. I personally recommend this system when working on a single anterior tooth with conservative preparation bonded to enamel or when clinician wants to preserve tooth structure. The major difference between pressables and feldspathic porcelain is first the strength; in general, pressables are stronger, due to their density and secondly the control in color; any complicated shade is achievable with Porcelain Laminate Veneer (PLV).

Clinical Suggestions

The following table is a quick easy reference guide to help the dentist communicate with his/her lab the clinical concerns when choosing a particular ceramic material.

Click over the chart to enlarge

It is essential for clinician to make sure there is no sharp corners when preparing the teeth. With the final shade photo for the color match, it is recommended to take a photo of the matching tooth with a shade guide at the beginning of tooth preparation rather than at the end of the visit to avoid color changes from tooth dehydration.

Technical Point of View…

If heavy metal cores and or severely discolored tooth preparations are anticipated, the dentist can be advised to prepare the tooth more aggressively. This should be discussed with the lab technician prior to tooth preparation or at the diagnostic wax up planning stage in order to allow adequate room for the lab technician to achieve the desired result.

When using Zirconia Bridges, the gingival surface of the pontic should be pure polished Zirconia without layered porcelain to maximize the strength. Preparations with subgingival margins requesting Zirconia do not need to have porcelain margins.

When using pressbles, the functional cusps and any occlusal contacts should not be layered to maintain maximum strength. The Zirconia surface must be highly polished when coming in contact with opposing teeth to prevent wear. The contacting and gliding surface of the cuspid should be supported either with unlayered pressables or polished Zirconia backing.

Dentist should always provide a stump shade on all cases. The technician prefers extra information to successfully design and fabricate the case in order to prevent reprepping and remakes. By providing the proper information to the lab, guess work can be avoided to achieve a better result.

It is important that dentist and lab technician are on the same page at each stage of treatment. We are a team trying to achieve the same goal!

Correspondence to: Yugo Hatai

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