# Bonding Failures of Lingual Orthodontic Brackets:
## 4 Discussion  
Incognito(tm) customized brackets have an extended gold alloy base and are metal-casted. However, instead of fully customized brackets, some practitioners prefer to use standard lingual brackets and a straightwire archive, instead of the \"mushroom-shaped\" robot-bended lingual archive offered by the Incognito(tm) system. This implies that the brackets are placed more gingivally than usual, that the amines' brackets are rotated 10-15 deg, and that some brackets are placed at an increased distance from the tooth surface [12]. This is performed on a digital setup derived from the malocclusion model: the brackets are digitally placed on each tooth on an ideal continuous arch. At this point, acrylic transfer jigs can be 3D-printed and used to place any commercial standard bracket, according to the individual preferences of the practitioner, on the malocclusion model at the exact planned position. The KommonBase system, with its extended bonding base, allows for single tooth bonding in presence of severely crowded teeth, or for rebonding in case of debonding [11]. Understanding the risk of bracket bonding failure with such techniques is of great importance, since bracket debondings have an impact on overall treatment time [17]. The overall failure rate for both types of lingual brackets (7.6%) was only slightly higher than the failure rate reported for labial straightwire brackets (5.7%) [18]. The present finding is in accordance with other studies that found similar failure rates between lingual and labial brackets [10,19]. The increased bonding surface and enamel sandblasting performed before lingual brackets bonding could suggest a decreased failure rate, although a systematic review with meta-analysis confirmed that enamel sandblasting does not provide an advantage in terms of bonding strength [20]. Moreover, [PERSON] et al. observed a significant effect of bracket's base surface area on bonding strength up to an area of 6.82 mm\({}^{2}\), beyond which it seems pointless to increase [21]. Because, however, conventional labial brackets and different types of lingual brackets can have a base area larger than this anyway (ranging from 9 mm\({}^{2}\) to 35 mm\({}^{2}\)[22]), this can further explain the similar failure rate observed in the present study. Posterior teeth were more prone to failure than incisors and canines, both in the upper and in the lower jaws. A similar result has been reported by many authors [19,23,24,25] and could be attributed to an increased occlusal force in the posterior area, although some contrasting findings are also present [26,27]. Never the less, this trend is similar for labial brackets [17]. Observing 150 patients over seven months, [PERSON] et al. reported a failure rate of 6.4% for labial brackets, also reporting an increased failure rate for conditions like increased overbite, adolescents, lower arch, posterior teeth, and rounded NiTi wires [28]. Similarly, in a retrospective study on labial brackets, [PERSON] et al. reported a failure risk 7.7 times higher for posterior teeth, and a risk increased by 1.15 times for every 1 mm increase in overbite [29]. The greatest number of debondings was observed during the earliest phase of treatment, within three to six months from the start of treatment (Figure 1). As bonding strength is not time-dependent [30], immediate failures can be ascribed to occlusal interferences or procedural mistakes, whilst debondings that happen later on can be attributed to the patient's compliance, dietary habits or other factors. In addition, because only first time failures were considered, it is also possible that fewer failures in the long term were observed because the brackets most prone to failure were already debonded at that time. Regarding the comparison of failure rates between the groups, no significant difference was observed. In a previous randomized clinical trial [4], the failure rate over a 12-month period for the Incognito and the Harmony lingual systems ranged from 1.9% to 5.5% with