I would much rather do conservative restorations in composite resin—where it’s much more cost-effective and conservative, yet creates a beautiful result,” Margeas says.
In essence, bonding enables dentists to be less invasive and retain more of their teeth—and their natural tooth structure—longer. That may explain why dentists strive to bond restorations despite its cumbersome protocol, which requires multiple steps and very delicate treatment execution, Blatz says.
“If it doesn’t work, then you’re looking at failure,” Blatz cautions. “But if you do it properly and with the proper materials, we have the ability to be less invasive and help patients keep their teeth longer, so it’s obviously the way to go.”
When it comes to placing restorations, success ultimately depends upon material choice per case, our experts suggest. Therefore, it’s important to look at each case individually and choose what restorative materials are best, and then coordinate the adhesive or cement accordingly.
1. Blatz MB, Alvarez M, Sawyer K, Brindis M. How to bond zirconia: the APC concept. Compend Cont Educ Dent. 2016;37(9):611-617.
Ceramic Thickness Requirements When Supported by Dentin
In a master’s thesis completed this summer by graduate prosthodontics resident Dr. Carlota Suarez, the occlusal thicknesses of 0.3 mm, 0.5 mm, 0.8 mm, and 1.5 mm of bonded lithium disilicate onlays supported by the clinically equivalent situation of all of the enamel abraded away from a mandibular molar and therefore supported almost completely by dentin were evaluated.1 The researchers ran the specimens through 1.2 million cycles of dynamic loading in a thermal-cycled aqueous environment. Dr. Suarez demonstrated that when a dentin substrate supports the ceramic, a greater thickness of ceramic (ie, at least 0.8 mm) is required. Comparatively, when enamel supports the onlay, the ceramic thickness can be in the range of 0.3 mm to 0.5 mm.1,2
1. Suarez C. Fracture Resistance of Minimal Thickness Ceramic Partial Coverage Restorations Under Dynamic Loading. MSD Thesis, University of Washington, 2016.
2. Suarez C, Beuer F, Sorensen JA. Fracture resistance of minimal thickness ceramic partial coverage restorations under dynamic loading. J Prosthet Dent. Manuscript in preparation.
Shear Bond Strength of Adhesives to Dentin with Varying Moisture Conditions
The results of new research have demonstrated how a new class of adhesives is highly tolerant of dentin moisture conditions and can ultimately significantly reduce technique sensitivity.1,2 Last year, John A. Sorensen, DMD, PhD, FACP, professor of restorative dentistry, director of the Biomimetics Biomaterials Biophotonics Biomechanics & Technology Laboratory, and director of the Graduate Prosthodontics Program at the University of Washington School of Dentistry, and his team conducted in vitro studies measuring shear bond strength to dentin and enamel controls. They set up their tests with four different dentin moisture surface conditions after treatment with phosphoric acid: Group 1 had a layer of water; Group 2 was “moist dentin” typically considered to be the ideal dentin bonding condition; Group 3 was air-dried for 3 seconds; and Group 4 was air-dried for 10 seconds. Manufacturers’ directions were then followed for application of dentin adhesives, and then direct filling materials were placed and light-cured.
“We were very impressed with the bond strengths observed with several of the adhesives,” Sorensen says. “The adhesives tested demonstrated significant improvements in tolerance of dentin surface moisture conditions.”
The results of these bond strength tests with the same four dentin moisture surface conditions combined with cements showed that several adhesives/cements were highly tolerant of varying dentin moisture conditions. The two best systems were Adhese Universal/Variolink Esthetic (Ivoclar Vivadent; www.ivoclarvivadent.com), with dentin bond strength values of dentin moisture groups 1, 3, and 4 ranging from 82% to 99% of the ideal moist dentin; and Scotchbond™ Universal/RelyX™ Ultimate (3M; www.3M.com) ranging from 77% to 93% of moist dentin.1,2
“We also evaluated the self-etching bond strengths and found that of the four adhesives/cements evaluated, the self-etch enamel bond strengths ranged from 64.3% to 86.3% for the phosphoric-acid–etched enamel,” Sorensen says. “The self-etch dentin bond strengths ranged from 64% to 87% for the phosphoric-acid–treated moist dentin.”
This means that the new generation of adhesive/cement systems bring, first, a reduction in technique sensitivity with a considerable improvement in the tolerance of dentin moisture surface conditions, Sorensen explains. Secondly, with the improvements in the self-etching qualities of these adhesives, dentists can have a second line of defense by knowing the dentin self-etching qualities of the adhesives can correct potential procedural mistakes made during the adhesive preparation process.1,2
1. Sorensen JA, Chen Y-W. Shear bond strength of adhesives to dentin with varying moisture conditions. J Dent Res. 2016: Spec. Iss. Ab# 1342.
2. Sorensen JA, Chen Y-W. Shear bond strength of cements to dentin with varying moisture conditions. J Prosthet Dent. Manuscript in preparation.