BONDING BRACKET TO A CERAMIC CROWN - UNDERSTANDING MADE EASY

Daniel Ziskind,  Dr. M.D., Israel

www.lingualnews.com Vol. 2 No 1, May 2004 

Ceramic material is considered to produce the most aesthetically pleasing result in the replacement of a lost, damaged or unattractive enamel surface. Consequently the demand for ceramic prosthetic restorations such as crowns has been increasing. These types of crowns present a special challenge in adult orthodontics. This is because of the difficulty in bonding attachments to this surface.

In the mid 1960s, McLean and Hughes developed a core material based on reinforcement of  feldspathic glass with alumina, (content of ~85%) commonly referred to as alumina.. The construction of a conventional porcelain crown involves three stages: Compacting, Firing and Glazing. The porcelain powder is mixed with water and made into a paste. This paste is applied to the metal core. The dental porcelains are mixtures of feldspar and quartz. The lack of strength and toughness of the early porcelain necessitated its support by a stronger substructure such as metal, or developing a stronger ceramic material.

In the 1980s the glass-infiltrated high strength ceramic cores were developed, for example In-Ceram®, Vita Zahnfabrik, Bad Säckingen, Germany ( www.vita-zahnfabrik.com). In the 1990s the all-alumina core was introduced. For example Techceram®, Techceram Ltd, ( www.techceram.com) ; Procera All Ceram®, Nobel Biocare, ( www.nobelbiocare.com/global/en/Products/Procera/default.htm).

Hot-pressing of glass ceramic based on a SiO2–Li2O system (Empress II®, Ivoclar-Vivadent, Schaan, Liechtenstein (www.ivoclarvivadent.com ) provides better strength and superior esthetic results. In Figure 1, an old crown tooth 22 with fractured margin (A), was replaced by an Empress II® crown (B)*.

Fig 1: An old crown tooth 21 with fractured margin (A), was replaced by an Empress II® crown (B)*.

The use of an acrylic-based bonding material as a method of delivering orthodontic attachments to the above mentioned ceramics is a relatively complex procedure involving several steps and four layers (Figure 2). The ceramic surface should be conditioned prior to the bonding procedure. Grinding the surface with diamond burs also improves the bonding slightly since mechanical retention based on the ceramic surface topography is critical for the success of the bracket retention.

Fig 2:  Delivering orthodontic attachments to ceramics is a procedure involving several steps and four layers

Three different surface conditioning methods can be used (1) hydrofluoric acid etching, (2) airborne particle abrasion, (3) tribochemical silica coating. (Rocatec®) (Figure 3).  Chemical etching the surface is the most common practice in conditioning, however, not all ceramics can be chemically etched (Figure 4). Therefore an alternative technique should be used. It is important to match the adequate conditioning procedure to the type of ceramic crown available. The following experiments tested the effect of the conditioning methods on different ceramic materials. When considering attachments to a ceramic crown surface, it is important to distinguish between its inner and outer surface.

Fig 3: Three different surface conditioning methods can be used (1) hydrofluoric acid etching, (2) airborne particle abrasion, (3) tribochemical silica coating

Fig 4: Types of dental ceramics

The effect of three different surface conditioning methods on the bond strength of Bis-GMA based luting cement to six commercial dental ceramics was tested. It was found that bond strengths of the luting cement tested on the dental ceramics following different surface conditioning methods varied in accordance with the ceramic types.

Hydrofluoric acid gel was effective mostly on the ceramics whose structure is glass matrix based. Roughening the ceramic surfaces with air particle abrasion provided higher bond strengths for high-alumina ceramics and the values increased more significantly after silica coating/silanization. (1). Another study emphasized  that surface treatment is important for resin adhesion to ceramic and suggested that silane treatment was the main factor responsible for resin bonding to ceramic. (2). When bonding to pure alumina ceramic or Zirconia ceramic (YPSZ), a durable bond strength was achieved only by using a composite resin containing an adhesive phosphate monomer after air abrading the ceramic surface. It was also shown that tribochemical silica coating of YPSZ did not result in a durable resin bond as it does on glass-infiltrated alumina ceramic (3, 4).

References:
1. Effect of surface conditioning methods on the bond strength of luting cement to ceramics. Ozcan M, Vallittu PK. Dent Mater. 2003 Dec;19(8):725-31.

2. Effect of different ceramic surface treatments on resin microtensile bond strength. Filho AM, Vieira LC, Araujo E, Monteiro Junior S. J Prosthodont. 2004 Mar;13(1):28-35.

3. Resin bond strength to densely sintered alumina ceramic. Friederich R, Kern M.
Int J Prosthodont. 2002 Jul-Aug;15(4):333-8.

4. Bonding to zirconia ceramic: adhesion methods and their durability. Kern M, Wegner SM. Dent Mater. 1998 Jan;14(1):64-71.

*Ardent Dental laboratory, Mr. O. Asulin CDT & Mr. S. Rosenblum CDT Jerusalem, Israel
* Mr. Avinoam Akabi,Mbt Eichut Dental laboratory, Jerusalem, Israel.

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Adult and Lingual Orthodontics
EDITORS:
Dr. Silvia Geron D.M.D., M.Sc
Dr. Rafi Romano D.M.D., M.Sc
Dr. Pablo Echarri D.M.D., M.Sc