Summary
Context/objective: Reliable bracket adhesion is essential, both for functional reasons and to protect the patient’s smile. This study aims to introduce a new bracket placement guide based on smile arc protection. This is why the table is titled Guide to Position Smile-Arc (GPS-A).
Content/methods: Two tables based on the authors’ clinical experience, one for the maxilla and the other for the mandible. These tables are designed to guide bracket placement in order to get or preserve the most aesthetically-pleasing smile arc. As an introduction to the new table, we present the limitation of other commonly-used tables (Alexander and MBTTM).
Results: Detailed instructions to use the table. Indications are given for adjustments of dental morphology to perform ahead of time.
Conclusions/implications: A summary of the benefits of using this guide is given. The clinical table is an easy and reliable reference guide for practitioners to bond the brackets in such a way to yield pleasant smiles and functional occlusions.
Introduction
The aesthetics of the face and smile are some of the patient’s essential features. Thanks to recent progress in orthodontic technology, it is possible to not only produce excellent occlusion, but also to improve the patient’s appearance and fulfil their requests. Planning treatment while taking into account facial aesthetics to preserve the smile arc is to be done at the same time as planning the strategy for perfect occlusion. The functional purpose of orthodontics is always to produce protective occlusion, in which the front teeth protect the back teeth from interference during lateral or protrusive movements, and the back teeth likewise protect the front teeth by providing sufficient contact when the mouth is closed.
The smile arc, in a frontal view, is defined as the relationship between the curvature of the incisal edges of maxillary anterior teeth (incisors and canines) and the curvature formed by the lower lip when smiling. The ideal smile arc occurs when the upper incisal line has a parallel curvature to that formed by the lower lip when smiling. This parallel relationship is described as “consonant”. In a flat, or non-consonant smile, the maxillary incisal line is flattened in relation to the curvature of the lower lip when smiling.
According to Frush and Fisher3, a sharper curvature of the maxillary incisal edges between the two canines is more attractive and gives the person a more youthful appearance than if they had a flattened smile. This is why a smile arc is a desirable feature even for people who have a flat lower lip when smiling. The goal should be the ideal positioning of the canines relative to one another and functional anterior occlusion.
Precisely positioning the brackets is essential to finish the treatment with excellent occlusion and an attractive smile. Additionally, the most common reason for delays and treatment difficulties is incorrectly bonded brackets. When some teeth are extremely poorly positioned, it is not always possible to place the bracket in the ideal position at the first visit, but it is recommended to attempt to do so anyway in order to avoid the need to reposition it and to use a compensatory arc later on during treatment.
Historically, the bracket bonding method taught in dental universities is ill-suited for optimising aesthetics.
If one assumes that all patients have central maxillary incisors located 4.5 mm above the incisal edges, lateral incisors at 4 mm and canines at 5 mm, and the orthodontist fails to take into account the relationship between incisal edges and the lower lip, the aesthetic criteria will not be met.
Personalised placement of the braces is just as important as a personalised treatment plan.
Dr Tom Pitts has developed a Smile Arc Protection (SAP) protocol with bracket positions that consistently produce beautiful smiles. Dr Tomàs Castellanos has quantified this aesthetic positioning by measuring tooth length. It could be said to be a “Tom-Tom” protocol.
Bracket bonding represents a challenge for many orthodontists.
This problem can be mitigated by using a suitable ruler and tables, whether for direct or indirect bonding.
The Alexander technique5 is based on premolar height (X in the Vari-Simplex bracket height table) (Figure 1) to position the brackets of the entire arc.
For instance, if the normal slot height of a premolar bracket is 4.5 mm from the occlusal cusp, the other heights given in this table would be 5.0 mm for a canine, 4.0 mm for a lateral incisor and 4.5 mm for the central incisors.
The MBT™ table (Figure 2) offers another commonly used guide for bracket bonding. It provides the average positions for maxillary arc brackets: 4.5 for the first premolar (X – 0.5 mm), 5.0 mm for a canine (X), 4.5 mm for a lateral incisor (X – 0.5 mm) and 5.0 mm for a central incisor (X)6.
These bracket placement techniques, along with others that are based on known tables and braces, provide precision and reproducibility. Unfortunately, placing brackets with such height differentials tends to flatten the smile arc.
A flattening of the smile arc can occur through several mechanisms during orthodontic treatment. In particular, the normal alignment of the maxillary and mandibular dental arcs can lead to lower curvature of the maxillary incisors relative to the curvature of the lower lip.
Ackerman, et al.,4 assessed the smile arcs of patients, some of whom were treated in their own practices and some who were treated elsewhere. Nearly 40% of the patients they had treated showed visible changes in the smile arc, with flattening in 32% of cases. In the SAP treatment group, 13% had smile arc changes, but flattening only occurred in 5% of cases. This article introduces a new table to guide bracket bonding based on smile arc. This is why the table is titled Guide to Position Smile-Arc (SAP) (Images 1 and 2).
Suggested table for vertical bracket placement
Rationale
The tables in Figures 3 and 4 is based on a large number of clinical studies, measurements on plaster castings and digital models of patients treated by the teams of Dr
Tom Pitts and Dr Tomàs Castellanos.
Its versatility and efficacy will be further explored in successful case studies using this table.
The table makes it easy to vertically place the brackets in a position that produces suitable smile arcs and mutually-protective occlusions.
It accounts for occlusal morphology, such as articular eminence inclination, which is more vertical in dolichocephalic patients than in mesocephalic or brachycephalic patients.
In dolichocephalic patients, the molar cusps are higher than in brachycephalic patients, and the fossa are deeper; the clinical crowns of anterior teeth also have greater cervicoincisal height.
All of these characteristics indicate that a larger overbite is needed to disocclude the posterior teeth in the eccentric movements of dolichocephalic subjects.
On the other hand, people with narrower faces, a flatter TMJ eminence, and anterior teeth with shorter clinical crowns, require less overbite to disocclude the posterior teeth in eccentric movements.
Similarly, when considering the relationship between smile arc and incisor profile, clinicians must extrude maxillary incisors in the case of a flat smile or maintain the incisal smile arc when it is aesthetically pleasing.
For a functional occlusion and aesthetic smile arc, it is necessary to maintain a divergence between the occlusogingival placement of the slot and occlusive cusps or the incisal edges, from the second buccal tube to the central maxillary incisor.
The divergence is also important when considering that the differential in millimetres between the slot height and the central incisor, and the height in millimetres of the second buccal tube can be used to get an idea of the overbite rate at the end of treatment.
It also affects the incline of the occlusal plane.
The final overbite when the maxillary incisors cover the mandibular ones too much, or if there is openbite, also depends on the elastic bands, lingual buttons, mini-screws and other auxiliary items that may affect the bracket’s torque.
Of course, mini-screws can also be used to improve the position of the maxillary incisor by intrusion of the mandibular incisors, when necessary.
The transition point between the anterior and posterior dental segments further establishes the smile arc. Therefore, the position of the entire dental arch should be planned based on this reference point.
When the maxillary incisors are more extruded in order to improve the smile arc and enamel presentation, more coverage can be produced by increasing the overbite.
To avoid this effect, the table introduces compensation in the position of the canine to canine mandibular bracket slots.
How to use the table (Figures 3 and 4)
Before using the table, some patients require tooth reshaping to get the ideal morphology of each tooth.
This enameloplasty procedure is based on a plaster model study and only removes the minimal amount of dental enamel needed.
The enameloplasty is performed on pronounced marginal ridges of the lingual surfaces, on the incisor angles and ridges, and on irregular vestibular surfaces.
Irregular vestibular surfaces are a barrier to optimal bracket placement, which influences rotation and torque control1.
In most cases, the canines need to be reshaped in order to improve their role in the smile arc.
This procedure does not interfere with their functional role for disocclusion.
The gingival margins are very important for anterior aesthetics.
Clinicians occasionally must do an initial gingivoplasty with laser, electrosurgery or another similar technique.
It is important to bring the right morphology, but clinicians should not reshape all hard and soft tissue, since leaving small offsets until the end of treatment leaves open the possibility of final detailing when the teeth are in the best position possible.
When teeth have fractures or an abnormal amount of wear, they need to be reconstructed before bracket placement for ideal dental anatomy.
Clinicians must discuss this with the patient, since dental restoration may be needed in the future.
If the maxillary molars have high and pronounced cusps, they require reshaping to avoid interference or early contact.
The same applies to the lingual cusps of premolars.
After achieving the ideal dental morphology, bracket bonding height in the maxillary arc is selected as follows:
Measure the length of the crown of the maxillary canine, from the end of the cusp to the gingival margin (after reconstruction, reshaping or gingivoplasty).
Find this measurement in the columns of the Smile Arc Protection (SAP) table, and choose the adjacent number in the row (Figure 6).
The numbers in this row give the positions of each bracket.
Use this method to select the heights for the mandibular brackets:
a) Measure the length of the crown of the mandibular canine, from the end of the cusp to the gingival margin (after reconstruction, reshaping or gingivoplasty).
b) Find this measurement in the columns of the Smile Arc Protection (SAP) table, and choose the adjacent number in the row.
These numbers provide the position to bond each of the brackets of the mandibular zone (Figure 7).
Orthodontists can generally use this technique for adequate occlusion and an attractive smile.
Specific considerations
The second maxillary molars must always be in intrusion.
Their tubes are always positioned to place these teeth in slight intrusion in order to get a negative crown inclination and avoid functional interference.
The offset between the maxillary incisors and the lateral maxillary incisor must be kept between 0.5 and 1 mm in order to allow the mandibular canine to move during protrusive excursions and also to improve smile arc.
Longer incisors need a greater height differential.
To account for this, the table includes two additional options.
For the mandibular molars, it is important to maintain an occlusal plane that provides adequate junction with the antagonist teeth.
Personalisation of the table for cases treated with premolar extraction.
The effective mechanisms currently available, combined with the use of mini-screws and passive self-ligating systems for tooth shifting towards the molar extraction site have made treatment by premolar extraction less common. But when the orthodontist decides that extraction is the best option for the patient, the table can be personalised. To do so, the anterior segment is managed as normally indicated in the SAP table, only the offset between the premolar and canine will be 0.5 mm in every case, and the offset between the premolar and the molar will be 1 mm in every case in order to avoid the interference of inadequate levels in these segments.
Use of the ruler for the vertical placement of each bracket.
The positioning ruler to measure bracket bonding height is placed slightly differently depending on the segment of the dental arch being considered.
For the incisors, canines and premolars, we suggest using the calibrator placed at 90° from the tangent of the median zone.
For the molars, it is suggested to place it parallel to the occlusal surface of each molar (trace an imaginary line between the buccal and lingual cusps of each molar).
Benefits from using this table.
Reducing positioning errors, which are avoided thanks to improved precision.
Reproducibility and predictability for bracket bonding.
Convenient and standardised bonding procedure.
Avoiding repositioning brackets and/or introducing excessive corrective wires.
Reducing time in chair and patient discomfort.
Shortening the treatment by several months is an effective way to motivate patients.
Providing better torque level control.
Orthodontists can generally use this technique for adequate occlusion and an attractive smile.
REFERENCES
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elastics protocol for smile arc protection. Clin Impres. 2009;17(1):1-11. - Sarver D, Ackerman MB.
Dynamic smile visualization and
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for smile capture. Am J Orthod Dentofacial Orthop. 2003;124(1):4-12. - Frush JP, Fisher RD.
The dynesthetic interpretation of the dentogenic
concept. J Prosthet Dent. 1958;8:558-581. - Ackerman JL, Ackerman MB, Brensinger CM, Landis JR.
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morphometric analysis of the posed smile. Clin Orthod Res.
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Principles of the Alexander Discipline. Chicago, IL: Quintessence;
2008:59. - McLaughlin R, Bennett J, Trevisi H. Systemized Orthodontic Treatment
Mechanics. Philadelphia, PA: Mosby; 2001:60-65. - Echeverri E, Sencherman G. Neurofisiología de la oclusión.
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Editorial Monserrate; 1991:175–189. - Sarver DM.
The importance of incisor positioning in the esthetic smile:
the smile arc. Am J Orthod Dentofacial Orthop. 2001;120(2):98-111.