The Study Design

This study involved 10 different combinations of framework materials and veneer ceramics. There were five zirconia, two alumina, and three PFM combinations. To mimic clinical reality, 116 dentists with a variety of backgrounds and abilities were asked to participate. Each dentist invited at least two patients in need of a 3-unit posterior prosthesis, including a molar pontic, to participate. Each CAD/CAM manufacturer selected two dental laboratories in the United States to fabricate 16 each of the restoration type. The companies could not use in-house labs for the study. The test products were randomly assigned to the dentist/patient combination, and the cases were randomly assigned to each manufacturer’s two laboratories. The dentist/patient and laboratory were blinded to each other using a coding system, which allowed the lab to know which incoming cases were part of the study. All patients are recalled yearly for evaluation of their prosthesis, both clinically and scientifically. Scanning electron microscope, clinical images, and special high-resolution gold-sputtered dies provide the major sources of the data and documentation of the condition of each prosthesis at each yearly recall.

Study conclusion:

At two years, zirconia and metal frameworks performed equally well with no breaks. Alumina had a 26% breakage, which indicates a high risk in posterior multi-unit restorations. Veneer ceramics pressed to zirconia and metal had significantly fewer defects than layered ceramics. At this point, veneer ceramics designed for zirconia need close clinical observation with an eye to improvement in formulation and handling.

Labs participating in the study:

Bay View Laboratory, Chesapeake, Va.

Da Vinci Dental Studies, West Hill, Calif.

Lord's Dental Studio, DePere, Wis.

Nakanishi Dental Laboratory, Bellevue, Wash.

Arrowhead Dental Laboratory, Sandy, Utah

Fort Washington, Fort Washington, Penn.

Blue West Dental Laboratory, El Dorado Hills, Calif.

Jason Kim Dental Laboratory, Great Neck, NY.

Dental Crafters, Marshfield, Wis.

Stanely Okon Dental Laboratory, Laguna Woods, Calif.

Esthetic Dental Arts, Albuquerque, NM.

Dental South, Gainesville, Ga.

Glidewell Laboratories, Newport Beach, Calif.