**4. Characteristics of ceramic bracket bases**

Several retention mechanisms were developed for the attachment of ceramic bracket bases to the adhesive. These are chemical retention, mechanical retention, and a combination of both methods [21, 28]. The first developed method was the chemical retention method. This method, now obsolete, used a coating of glass on the flat ceramic bracket base and then a silane coupler to achieve a chemical bond between the glass-coated bracket base and the adhesive. The silane molecule is a bifunctional molecule; that is, one end reacted with the glass coating on the bracket base, while the other end reacted with the adhesive [11, 29]. It was pointed out that the chemical retention mechanism produced very strong bonds that harmed the tooth surface in the form of cracks and enamel tear-outs during debracketing [4, 7, 11, 29–32].

Almost three decades ago, Ghafari and Chen [33] compared the performance of chemical retention ceramic brackets to silane-treated grooved base ceramic brackets (a combination of chemical and mechanical retention). They [33] concluded that mechanical retention might reduce the negative side effects of debracketing by favoring failure within the adhesive, thus protecting the integrity of the enamel surface, i.e., the health of the tooth, as well as the integrity of the ceramic bracket.

brackets. The flaming procedure yielded a bond strength that was similar to that of new ceramic brackets. However, flaming affected the esthetics of these brackets, i.e., these brackets ended up faded and dark. Er:YAG lasers completely removed the adhesive remnants from the ceramic bracket bases without damaging the base structure. Furthermore, the shear bond strength of Er:YAG laser "recycled" brackets was similar to that of new brackets. It was

Ceramic Brackets Revisited

13

http://dx.doi.org/10.5772/intechopen.79638

Yassaei et al. [44] also concluded that the Er:YAG laser presents an efficient way for "recycling" ceramic brackets. These researchers used polycrystalline ceramic brackets with a dovetailed

Debonding usually refers to the removal of orthodontic brackets and the residual adhesives

Ceramic brackets lack flexibility. In other words, the rigid ceramic and the rigid enamel have little ability to dissipate stress when exposed to debracketing forces at the end of treatment.

Several approaches aiming to minimize the side effects associated with the debracketing of ceramic brackets exist. These are the conventional (mechanical), ultrasonic, electrothermal,

Three mechanical debracketing techniques have been described. These are lift-off, wrenching, and delamination [46]. The first technique uses a lift-off debracketing instrument (LODI). This pistol-grip plier is placed over the bracket, and a debracketing force is applied to the tie-wings of the bracket. It has been pointed out that the LODI cannot be used with ceramic brackets due to their brittleness [39]. The wrenching technique uses a special tool that produces a wrenching or torsional force at the base of the bracket [46]. This approach, providing a rotational

The delamination technique was the first technique introduced and is still reported to be the most widely accepted ceramic bracket removal technique [11, 15]. This technique involves the application of a slow squeezing force with the sharp blades of the debracketing pliers placed on the enamel surface and within the adhesive, thereby producing a wedging effect

It has been stated that such a force—produced by a slow, gradual compression—would seem to offer the best chance for inducing crack propagation within the adhesive, leading to a cohesive failure, thus minimizing the risk of enamel damage as well as the risk of bracket fracture. A cohesive bond failure is a failure through a single material, where cohesive forces between

Thus, bracket fracture and/or enamel damage may occur during debracketing [2, 11].

from the tooth enamel at the end of fixed appliance treatment [45].

shear force, can be likened to the turning of a door knob.

the same atomic species are present [2, 11, 21, 46].

pointed out that the laser method may be preferred over other "recycling" methods.

base in their in vitro study.

and laser techniques [11, 21].

**6.1. Mechanical debracketing**

(**Figure 5**).

**6. Debonding of ceramic brackets**

The reports about iatrogenic tooth damage during debracketing impelled manufacturers to make changes in the base designs of ceramic brackets, relying more on mechanical retention for bond strength. In fact, the majority of ceramic brackets available today are purely mechanically retained brackets [4, 30, 34]. Mechanical retention is achieved by creating undercuts or grooves in the base of the bracket. These undercuts make a mechanical interlock with the adhesive bonding agent possible [28].

Currently, many different mechanical base designs are available, such as microcrystalline base design with a stress concentrator, button-structured base design, ball-base design with gingival ball reduction, dovetail base design, laser-structured base design, and "portal" bonding base design [4, 15, 35, 36].

An additional, interesting base design is the application of a thin layer of polymer onto the ceramic bracket base [19]. Thus, bonding takes place between the enamel and the flexible polymer mesh base. Encouraging in vitro results concerning the enamel surface after debracketing were obtained [30, 37, 38].

At this point, only two published clinical studies [14, 39] with a purely mechanical retention mechanism were encountered. There is a need for clinical studies, particularly randomized clinical studies, i.e., the gold standard for evaluating clinical procedures.
