The effect on bond strength of surface treatments on conventional and Procera™ porcelain

The ability to successfully bond full coverage porcelain restorations to the tooth has is often necessary to improve retention and resistance to fracture. A new sintered aluminum oxide porcelain core, Procera™ (NobelBiocare- Goteborg Sweden) promises to provide esthetic, well fitting and strong cores for porcelain placement. Little is known about the ideal surface preparation of this porcelain for cementation utilizing resin cements. Objectives: This study is designed to determine the ideal surface preparation for this porcelain compared to a conventional feldspathic porcelain. Methods: 40 porcelain specimens (20- Procera^TM(P), 20-Noritake EX-3^TM(N)(Nagoya, Japan)) were prepared and randomly assigned to one of four surface treatment groups; untreated control (C), etch with 50% hydrofluoric acid (H), air abrasion with 50µm aluminum oxide (A) and air abrasion/HF acid treatment (HA). All porcelain surfaces were treated with silane primer and the bonded with Scotchbond Mutipurpose^TM (3M Espe St. Paul MN) and a 1.7mm column of RelyX^TM ARC resin cement (3M Espe St. Paul MN) as per manufacturer's instructions. Specimens were stored for one week and then thermocycled 960 times (5°-55°C). Specimens were subjected to a shear force on an Instron 1123 (Canton, MA) and the load at failure recorded. Mean (±s.d.) were calculated, reported in MPa and statistically analyzed for significance utilizing a univariate analysis and Tukey multiple comparisons test. Results: Mean values PC 2.2±0.65, PH 2.86±0.75, PA 4.0±0.79, PHA 2.2±0.29, NC 2.8±0.68, NH 4.6±0.63, NA 4.3±0.0.58 and NHA 3.68±0.57. There was no statistical difference between PC/NC, PA/NA, PH/NH, PHA/NHA but PA/NA were significantly stronger than either C and PHA. Though not reaching significance of P<0.05 PHA was weaker than PA. Conclusion: Proper surface preparation of the Procera porcelain can improve the bond of the resin cement to the porcelain surface. It appears that Procera ^TM should not be etched with HF acid and all porcelains should be air-abraded with aluminum-oxide prior cementation.