Orthodontists’ preferences regarding the difference of bracket bonding height between the maxillary incisors

ABSTRACT Introduction: The vertical position of orthodontic brackets in maxillary incisors may influence the incisal step between the anterior teeth and thereby interfere with the smile esthetics. Even so, esthetic standards have been modified over time and consistently required technical adjustments. Objective: This study analyzed orthodontists’ preferences regarding the difference of bracket bonding height between the maxillary central incisors (MCI) and maxillary lateral incisors (MLI), and further determined whether the orthodontist sex, age and time of specialization have association to their choices. Methods: This study collected data through an electronic form. Study participants analyzed a clinical case in which they indicated their preference for bracket bonding height. The placement height options ranged from 3.0 mm to 5.5 mm from the incisal edge, with 0.5-mm intervals, or at the clinical crown center (CCC). The difference in the bonding height between the MCI and MLI was analyzed, considering the formation of incisal steps between these teeth. Results: Participants indicated that the difference in bracket bonding height between the MCI and MLI should be as follows: 0 mm (3.9%); 0.5 mm (78.3%); 1 mm (7.6%); 1.5 mm (0.2%); and CCC (9.9%). There was no statistically significant correlation between the choice for bracket bonding height and sex, age and time since specialization. Conclusion: Most participating orthodontists choose the 0.5-mm difference in bracket placement height between the MCI and MLI. The variables sex, age and time since specialization did not influence this choice.


INTRODUCTION
An appropriate positioning of orthodontic accessories is required for alignment and leveling of dental arches, which is a basic precept of orthodontic intervention. Hence, minor variations in the positioning of orthodontic brackets and other accessories may jeopardize the efficacy of the orthodontic treatment. [1][2][3] The bonding height of anterior brackets has a high impact not only on establishing overbite and mandibular function, but also on the vertical position of the incisors, which ultimately reflects on aspects such as youthfulness, sensuality and smile esthetics. [4][5][6][7][8][9] The demand for esthetic treatments has increased greatly the last decades. 7,10 Orthodontists should be aware that the correct placement of brackets may vary in each patient, which should be accounted for in the orthodontic and esthetic planning. [11][12][13][14] Several orthodontic prescriptions have been suggested over the years, with some variation of protocols and techniques regarding bracket bonding heights. Most authors propose that orthodontists should keep a difference between 0.0 mm and 0.5 mm in the bonding height of orthodontic brackets between the maxillary central incisors (MCI) and lateral incisors (MLI), which may affect the step between these teeth and the smile arc. 11, 13 Nascimento MHA, Brandão KMN, Menezes CC, Machado AW, Santamaria-Jr M -Orthodontists' preferences regarding the difference of bracket bonding height between the maxillary incisors 5 Studies analyzing the esthetic perception of incisal steps between the MCI and MLI and their influence on the smile arc have shown that orthodontists frequently fail to follow the recommended bracket bonding heights prescribed in the literature. [6][7][8]13 However, orthodontists' preferences regarding the difference of bracket bonding height between the MCI and MLI remain unknown.
Despite the variations in tooth anatomy, most orthodontic prescriptions are based on population averages, have disregarded the smile arc, are relatively old, and have not been adapted to current esthetic requirements. 13 Thus, the present study aimed to analyze the difference in bracket bonding heights between the MCI and MLI, which is responsible for the central-to-lateral incisal step at the end of the alignment and leveling phase. Furthermore, the variables sex, age and time since specialization were checked for an association with orthodontists' preferences, and the results obtained herein were compared against the esthetic standards reported in the literature. The study participants were asked to evaluate clinical parameters -facial photographs (frontal, smile and right-side profile), intraoral photographs (frontal, right-side and left-side lateral, and occlusal) and a photograph indicating the length and width of the MCI clinical crown (Fig 1). The clinical parameters presented a female patient with Angle Class I malocclusion, absence of crossbite, 30% overbite, absence of significant dental asymmetries, and slight mandibular crowding. The patient had 3-mm passive exposure of the MCI, 0-mm smile gingival exposure when smiling, and a nice smile arc, as normal clinical parameters. 10,[15][16][17][18][19] In the intraoral photographs, the size of the incisors was adjusted for an 80% width/height ratio. This adjustment aimed to avoid bias while determining the bracket placement height, with a potential need for gingival recontour or increment of incisal edges. In addition, one of the sides was mirrored to avoid asymmetries. 20 All adjustments were carried out using Adobe Photoshop (version CS5; Adobe Systems, San Jose, California, USA).
This study was based on previous researches, in which it was found that the 2-mm central-to-lateral incisal step was considered aesthetic 6

RESULTS
The sample characteristics are presented in

DISCUSSION
The central-to-lateral incisal step can be formed in the fixed orthodontic therapy by placing brackets at different heights or by making intrusion and extrusion bends. While studies on the esthetic preferences of orthodontists have been recently published, [6][7][8]13 there are no population-based studies addressing orthodontists' preferences in the difference of bracket bonding height between the maxillary incisors, as analyzed herein.  The orthodontists who place the orthodontic brackets at the CCC level commonly do so in all teeth. While they are not necessarily looking for a more esthetic relationship between the MCI and MLI, this could create a step of approximately 0.8 mm and 0.9 mm for males and females, respectively, considering the average size of the maxillary anterior teeth. 22 Therefore, this specific parameter is closer to the esthetic values described in the literature. 6,8,21 It is worth noting this would be beneficial only for teeth with an average anatomical proportion.
The clinical parameters example used in this study was of a female patient. Some authors point out that females should have a greater step in the maxillary incisors and, consequently, a more pronounced smile arc, 6,8,23 which could lead to a bonding height preference with a step greater than what was found.
Considering that orthodontists tend to prefer the 1.0-to-2.0-mm step between the MCI and MLI, 6,8,21 there seems to be inconsistency between such esthetic preference and their bracket bonding height choice. Extrusion or intrusion bending of incisors, or bracket rebonding for this purpose, require contention of orthodontic movements for better stability, particularly prior to removal of the fixed orthodontic appliance. Thus, the execution of rebonding or bending procedures near the removal of the orthodontic appliance may cause relapses and major esthetic losses. 24,25 Anterior and laterality guides should also be checked while changing the steps between the incisors. 6,26 The present study showed the variables sex, age and time since specialization training were not significantly associated with the orthodontists' preferences in the difference of bracket Nascimento MHA, Brandão KMN, Menezes CC, Machado AW, Santamaria-Jr M -Orthodontists' preferences regarding the difference of bracket bonding height between the maxillary incisors 16 bonding height between the maxillary incisors. So, this study rejects the hypothesis that younger or recently graduated professionals would be more likely to adopt a bracket placement height consistent with current esthetic standards.
In this research, the number of forms submission to the orthodontists was large, however there was a small return compared to the total, although safe statistical calculations were possible. This is a difficulty common to surveys that carry out data collections through questionnaires. So, this study did not aim to indicate the best bracket placement height for maxillary anterior teeth, but only to compare orthodontists' preferences with what has been recommended in the literature for esthetic design for central-to-lateral incisal step, in this studied population. Variations in the sample, dental anatomy, or statistical modeling are likely to occur, which makes it inappropriate to generalize the measurements obtained herein. Further studies are needed to better understand the relationship between orthodontists' preferences regarding bracket bonding heights and the current esthetic standards of maxillary anterior teeth vertical positioning.