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On-line version ISSN 2176-9451
Dental Press J. Orthod. vol.16 no.5 Maringá Sept./Oct. 2011
Leopoldino Capelozza FilhoI; Alberto ConsolaroII; Mauricio de Almeida CardosoI; Danilo Furquim SiqueiraI
IPhD Professor, Graduate and Postgraduate
Program of Specialization and Master's Degree in Orthodontics at Sagrado Coração
University - Bauru/USC
IIFull Professor of Oral Pathology, FOB-USP. Full Professor Postgraduate Program, FORP-USP
INTRODUCTION: The management of unerupted
teeth has always been considered as a challenging procedure in orthodontic practice.
Within this perspective, the search for effectiveness in the procedures adopted
for the management of unerupted teeth is essential, which explains the purpose
of the present paper. When enamel drilling is performed, a natural structure
is transfixed, which may be restored with composite material and may dispense
from risky procedures such as bonding attachment technique and lasso wire technique.
OBJECTIVE: The present paper aims to present protocols for enamel drilling for canine traction (EDCT), specifically for maxillary canines, the most frequent teeth showing tooth position anomalies. In this paper, clinical cases with different degrees of complexities were illustrated, and, based upon the literature review and the 30 years of expertise with high rate of clinical success, advantages and disadvantages are discussed comparing EDCT and accessory bonding for canine traction (ABCT).
Keywords: Canine impaction. Tooth traction. Segmented arch mechanics.
The most frequent absence of teeth in the dental arch involves permanent canines, if third molars are not taken into account.21,28,36 In random samples, the frequency of unerupted canines ranges from 1.5 to 2% in the maxilla, and 0.3% in the mandible10,20,22,23,26,30,35 Conversely, frequency is high (23.5%) in samples previously selected for orthodontic treatment.3,24,37 In female patients the unerupted canines (1.17%) are twice as frequent as in males (0.51%)2 and occur palatally two to three times more often than buccally.1,33
Although hereditary33 factors seem to play a role in the pathogenesis of unerupted teeth, especially in palatal occurrences, the exact causes are still unknown.34 Among the factors most often associated with unerupted teeth are discrepancies between tooth size and arch length, abnormal position of the tooth germ or tooth, prolonged retention or early loss of deciduous teeth, the occurrence of cystic or neoplastic formation and iatrogenic causes.2,4 Although unfounded, other etiologies are sometimes mentioned, such as systemic causes.
The diagnosis and treatment of unerupted teeth requires competent general practitioners, pediatric dentists, oral and maxillofacial surgeons, periodontists and orthodontists, as well as patient compliance.31,36 Prognosis for the use of tooth traction should be considered with serious reservation, or at least rather limited at first because the chance of failure can never be ruled out as it depends on many variables.38 Parents or legal guardians should be made keenly aware of the odds to avert false expectations.
Conventional radiographic techniques have always presented limitations in locating unerupted maxillary canines, especially panoramic X-rays, which require additional radiographs such as periapical X-rays by the Clark technique10 or occlusal maxillary radiographs. These techniques were limited and could only spot unerupted canines buccally or palatally, but the relationship between canines and adjacent teeth was not addressed and the potential loss of the root structure of lateral incisors (which are most commonly affected teeth in these situations) was totally unknown. Orthodontic planning was thereby curtailed since it was only possible to assess these variables and the integrity of the lateral incisor root during the surgical procedure performed in order to access the unerupted canine. Common sense, caution and periodic controls were a necessary support to ensure that procedures based on this limited diagnostic came to fruition.
Cone beam computed tomography (CBCT) made the diagnosis of anomalies in the position of maxillary canine, also called dysgenesis, much more effective. CBCT's various slice planes and the resulting 3D reconstructions, viewable from virtually every angle, allows today's professionals to plan orthodontic traction of maxillary canines with greater accuracy and refinement. This allows surgeons to deal with canines, their dental follicle, cervical region and adjacent teeth with the aid of detailed planning, which ultimately reduce the risks of unintended outcomes. In other words, technological advances in imaging have increased the chances of orthodontic traction being accomplished more safely and accurately. It also eliminates the possibility of preexisting processes such as external cervical resorption, aveolodental ankylosis and replacement resorption in the teeth to be submitted to traction.17 When the imaging diagnosis reproduces more faithfully the actual position, the prognosis tends to be more precise and the treatment plan can be tailored to the individual.
With the purpose of individualizing the mechanics in terms of the direction of orthodontic traction forces, it was, and still is, adequate that orthodontists be invited to watch the surgery in order to view the exact position of the unerupted canine. As a result, traction would be planned and all such details noted in the patient's records. When the orthodontist was not present during surgery, it was requested that information was described in an official referral to enable safer traction. Maintaining this hypothesis, the surgeon must have enough orthodontic knowledge to guide the orthodontist on how best to perform the movement.
Early identification of non-eruption of the canine may reduce the need for complex and expensive orthodontic treatment. It is important that general practitioners and pediatric dentists be vigilant when monitoring eruption in children in the mixed dentition stage, not just by taking care of oral health, but also by identifying potential disruptions in this process. Ectopic eruption and impaction of maxillary permanent canines are frequent issues in orthodontic practice. In addition to being regarded as real challenges for the orthodontist, these two oral conditions can significantly lengthen total treatment time11 as well as increase treatment complexity.8
In planning treatment of an unerupted canine, one is advised to assess the thickness of the dental follicle, bearing it in mind when creating space to accommodate this tooth in the dental arch, aiming at either normal canine eruption or its orthodontic traction. The space required for the physiological eruption of an unerupted canine is, in theory, 1.5 times the mesiodistal size of the canine crown, a necessary condition for eruption to occur without orthodontic assistance.12,15
In patients with unerupted canines, the corresponding deciduous teeth are usually found in the arch and their mesiodistal dimension is much smaller than that of the permanent canine. Creating space in the analogous arch for the mesiodistal dimension of the unerupted canine is a daunting task and often impossible to achieve, especially if the goal is to increase space by 50%.12 It is usually impractical, from a mechanical point of view, to wait for a physiological eruption, and this is precisely why traction is indicated. Monitoring the patient and the risky relations of this tooth with the neighboring teeth will determine the appropriate moment for this approach.
When the patient's face and the transverse dimensions of the upper arch can support it, orthopedic maxillary expansion seems unquestionable with this protocol - a sine qua non condition for a real increase in bone mass by adding bone to the midpalatal suture - creating space and enabling a better eruption pathway. The goal is a real bone gain by placing bone in the region of the midpalatal suture and increasing the perimeter of the arch. This creates favorable conditions for the canine to find eruption space and redirect its pathway, often avoiding surgical approaches and orthodontic traction. This is only possible within a follow-up perspective with growth monitoring and assisted eruption, where these problems are diagnosed at an early stage, enabling an interceptive procedure and subsequent follow-up to assess progress.
According to the literature, several therapeutic treatment options are available for patients affected by this anomaly, namely: Absence of immediate treatment and long-term monitoring, self-transplantation of the canines, extraction of unerupted canines and closing of spaces with restorative treatment, extraction of unerupted canines and closing of spaces with orthodontic treatment, and finally, surgical exposure of unerupted canines and use of orthodontic forces to bring the tooth into occlusion.2,4,31,32,35
When canine traction is indicated, the surgical approach is performed and the tooth prepared for this procedure by tying the tooth, bonding a fixed orthodontic appliance or drilling the crown enamel. This is one of the procedures that can be performed in orthodontic treatment to position teeth in the dental arch without compromising normal esthetics and function.19 There is consensus indicating that the canine should never be tied with wire because of the inherent difficulty posed by this procedure and because it causes cervical resorption as the steel ligature is placed along the cementoenamel junction (CEJ). Historically, the first protocols used in the traction of unerupted maxillary canines consisted in binding the neck of the tooth with steel wire. The force and displacement of the orthodontic wire on the neck of the tooth would expose the dentin gaps in the CEJ, adding to the constant inflammation that resulted from the continuous trauma.17
Accessory Bonding for Canine Traction (ABCT) and Enamel Drilling for Canine Traction (EDCT) are the most common procedures. ABCT is perhaps the technique of choice of most dentists as it prevents erosion of tooth structure. Contrary to the choice of most orthodontic colleagues, the authors of this article never performed the ABCT procedure for reasons that will be presented in this paper, and have always applied the EDCT procedure for this purpose. This technique was successfully applied over thirty years of orthodontic practice and now boasts a caseload with 100% successful cases, which justifies its disclosure to the scientific community. In addition to this outstanding accomplishment, it should be emphasized that not a single canine ever required further treatment, which was the main reason for always choosing this option. Over time, a protocol for this procedure was formulated and is presented below. The EDCT technique can be adopted in all cases with no restriction because drilling can be performed in different areas of the crown of the unerupted canine, according to how one needs to move this tooth.
In light of the above, the aim of this paper is to create protocols for EDCT technique, specifically for maxillary canines since these teeth are more often affected by position anomalies, also called dysgeneses. By describing the advantages and disadvantages of EDCT compared with the ABCT technique, illustrated through case studies of different levels of complexity, the primary intention is to create a concise methodology, based on the literature and filtered through clinical experience of over thirty years performing EDCT with a high success rate.
ADVANTAGES AND DISADVANTAGES OF ENAMEL DRILLING FOR CANINE TRACTION (EDCT): COMPARATIVE ANALYSIS
Decreased risk of a new surgical procedure
The risk of a new surgical procedure to access the unerupted canine may occur in the ABCT technique due to immediate bond failure of the accessory after delivery of the traction force. This bond failure may be caused by excessive force and/or contamination during the process of bonding the orthodontic accessory. Considering that most patients eligible for traction are children, management may prove more difficult, with increased risk of this occurrence while exposing them to a new surgical procedure, a risk that could certainly be avoided. Therefore, the authors' preference for EDCT - despite the biological cost involved (wear of enamel, a structure that is not replaced by the body) - considerably reduces the possibility of reopening for new access to the unerupted canine, since when this tooth is tied the risk is virtually nonexistent.
Less tissue manipulation
The dental follicle (DF) is the essential and fundamental structure in tooth eruption. The epithelial structures of the dental follicle - such as the reduced epithelium of the enamel organ and the islands/cords of epithelial remnants of the dental lamina - constantly release epidermal growth factor (EGF) in the connective tissue (CT). This mediator, along with other EGF-activated mediators, induces pericoronal bone resorption, an essential phenomenon in the occurrence of tooth eruption.
The cementoenamel junction lies between enamel and cementum. It is therefore reasonable to assert that the DF in the cervical region overlies the line formed by the neighboring relationship between enamel and cementum. The CEJ has gaps along the cervical circumference of all human teeth in which the tubules are open and exposed to inorganic and organic components, but especially proteins. This cervical region is a sensitive tooth structure due to the fragile junction between enamel and cementum.16,17
During surgical removal of the DF in the cervical region the dentin gaps present in all human teeth, including deciduous teeth, are inevitably exposed to connective tissue after the flap is folded back over the tooth. The exposure of these dentin proteins, defined as sequestered antigens, can induce, over weeks or months, an immunological process of elimination that is clinically known as External Cervical Resorption (ECR). This process may occur during orthodontic traction or after the tooth has reached the occlusal plane.16,17 In many such cases a belated detection tends to be the rule. ECR is defined as a slow, painless, insidious process that does not compromise pulp tissues. In more advanced cases, it can lead to gingival inflammation and pulpitis secondary to bacterial contamination. One way to prevent this occurrence is to leave at least 2 mm of soft tissue from the DF attached to the cervical region.16,17
The ABCT technique requires greater exposure of the crown and hence greater need to remove osseous tissue and manipulate the DF, implying a higher risk of trauma to the ECJ. This region should be handled only when absolutely necessary.16,17 When this occurs, the chances of external resorption in this region after the traction procedure are increased, which causes loss of structure of the tooth under traction. This effect can be further compounded by excessive or extensive application of acids and other products used to etch the tooth enamel. Over-application can drain these products into the cervical region, where fixation of the DF to the ECJ occurs, chemically affecting cells and tissues, exposing and even increasing dentinal gaps and releasing the sequestered antigens into the adjacent tissue after the surgical wound has healed.16,17
The surgical procedure must be well planned and carried out with precision, without exaggerated forces and repetitive handling of the instruments used in the procedure.19 Surgical instruments should not be anchored or fixed to the cervical region of the upper canines because chisels and tips of surgical instruments such as forceps can mechanically damage the follicle and periodontal tissues in the cervical region and expose or increase the exposure of the dentin at ECJ, a starting point for ECR.16,17
When drilling is the procedure performed to access the unerupted canine, only a small portion of the tooth crown requires exposure, and only enough to allow the procedure to be performed. This portion of the crown may be the tip of the cusp or any of the proximal surfaces, depending on the anatomical features of the canine, which displays an enamel bridge along the entire crown with sufficient strength to withstand anchorage and traction.
After performing the surgical procedure a wound is formed from damaged epithelium and exposed connective tissue over the enamel. The reduced epithelium of the enamel organ tends to proliferate rapidly, covering once again the enamel and the ligature wire placed in the perforation over a period of hours or days. The underlying connective tissue starts forming again from the granulation tissue that grows temporarily in the area. Thus, the enamel is not exposed to the connective tissue until the tooth reaches the oral environment.16,17
Shorter surgery time
The EDCT technique eliminates the need for conventional steps of regular bonding, which involves etching, moisture control, adhesive application and bonding of orthodontic accessory. Performing all these steps in an environment with total moisture control requires more time in the trans-surgical phase, considering the difficulty of this procedure, which is carried out through surgical exposure of the canine in an open field. In addition, the surgical procedure must be performed by a competent oral and maxillofacial surgeon, although these professionals, more often than not, have little experience in bonding orthodontic accessories. The EDCT technique eliminates all the steps listed above, which results in shorter surgical time, less bleeding and therefore less postoperative edema.
Application of force in the long axis of the tooth with a better established magnitude
The EDCT technique allows the application of force directly to the long axis of the tooth under traction, resulting in increased control over traction direction. When an accessory is bonded to the buccal or lingual surface of an unerupted canine and traction force is applied, the direction of the resultant force should be observed in order to avoid undesired movement.
Moreover, the presence of a bulky body such as a bracket or button on the surface of the canine in an area subjected to a repair process after access surgery probably restricts canine movement making it difficult to determine the amount of force to be applied. Admittedly, the ideal force must be small in magnitude, ranging from a minimum amount of around 35 to 60 grams, when traction copies an eruption movement, to greater forces, required when the canine needs to undergo translatory forces in order to avert obstacles in its eruption pathway. In either case, determining an adequate force is rendered more difficult if restrictive factors, such as the ones mentioned above, establish undefined magnitude decreases in the force available to perform the movement of traction.
Risk of enamel fracture
The EDCT technique requires care to prevent the enamel from fracturing when twisting the ligature wire. Stronger ligatures are often used for this purpose, i.e., so that the risk of fracture and consequent need for reopening are minimized. Twisting the ligature without considering basic precautions, as inserting the explorer probe tip between the ligature and the canine, can cause enamel fracture and require new drilling, further increasing the biological cost of the procedure.
Potential pulp damage
Canine drilling should be performed perpendicular to the long axis of the tooth with a small diameter (¼") high speed spherical carbide bur and copious irrigation. This is important to prevent the bur from reaching the pulp chamber, thereby causing irreversible pulpitis or even requiring endodontic treatment. The competence and experience of a professional surgeon is of paramount importance to avoid such damage.
Some patients report sensitivity after drilling, and during traction a direct friction between ligature and tooth structure may cause minor discomfort, which should be considered normal as it is quite tolerable. Normally, when the canine emerges in the oral cavity the patient is referred to a specialist in Esthetic Dentistry and the perforation is restored, minimizing sensitivity. Be it as it may, throughout the many years of experience that underpin the protocol presented in this paper, complaints have never been greater than reported and biological damage has never been observed.
When the EDCT technique is performed, the hole drilled during the procedure should be filled by means of esthetic restoration following the emergence of the unerupted canine in the oral cavity. Given the ongoing advances in dental restorative materials and assuming that this procedure is performed by a competent professional - by drilling a big enough hole as to allow the passage of a folded ligature wire - it is unreasonable to suspect that drilling might impair esthetics. As stated earlier, a spherical ¼" diameter carbide bur should suffice.
Greater professional experience
The EDCT procedure requires an experienced, insightful surgeon to determine the actual position of the unerupted canine since this drilling, as previously stated, should be performed perpendicular to the long axis of the tooth, despite the reduced need for removal of osseous tissue and manipulation of the DF. The cases that require greater attention are those with severe impaction because the procedure - which involves a flap in an open field, as well as the presence of bleeding - is usually performed in children or adolescents, with little if any collaboration, under local anesthesia, protocol usually adopted by the authors' surgical team.
ADVANTAGES AND DISADVANTAGES OF ACCESSORY BONDING FOR CANINE TRACTION (ABCT): COMPARATIVE ANALYSIS
Lower biological cost
Since the ABCT procedure does not require drilling of the unerupted canine crown, it entails a lower biological cost compared to the EDCT technique, i.e., canine structure is fully preserved. It is worth mentioning that this biological cost is decreased as long as care is exercised in washing the canine crown after etching so as not to allow the acid to remain in the DF when the ABCT technique is performed.
Lower risk of pulp damage
When the ABCT procedure is performed, drilling of the unerupted canine crown is not necessary and therefore the risks related to pulp damage are minimized or virtually eliminated. The risk of pulp damage is related to a poorly executed EDCT technique, i.e., when drilling is not performed perpendicular to the long axis of the unerupted canine.
Increased manipulation of the dental follicle (DF)
It should be noted that the ABCT technique requires exposure of the unerupted canine crown so as to create a surface large enough to bond the attachment used for traction. Therefore, the need to remove osseous tissue is greater as is the manipulation of the DF during the surgical procedure. Whenever these tissues are over-manipulated the biological costs are higher, as well as the risks of ECR occurring after traction of the unerupted canine.
Longer surgery time
The ABCT technique requires more surgical time because besides the usual procedures there is the need to perform the steps of a conventional bonding procedure, which involves etching, moisture control, primer application and bonding of orthodontic accessory, while at the same time striving to control bleeding so that the risk of a bond failure is minimized during the traction movement. All these steps increase trans-surgical time, causing discomfort to the patient due to a longer procedure and more bleeding during surgery and, consequently, more postoperative edema.
Forces induced to perform traction of unerupted canines should be directed, whenever possible, using the long axis of the tooth as reference. Typically, the bonding of a bracket or lingual button to the mesial region of the clinical crown of an unerupted canine does not allow the traction force to make the tooth copy the eruption movement. Since the bonding of this accessory, which will receive the wire and the traction forces are routinely performed in less than ideal positions, resulting from unfavorable technical conditions and the need to restrict tissue manipulation, canine displacement can follow undesired pathways. This may present risks for the adjacent teeth and require more extensive movements for the proper positioning of the canine after its emergence in the oral cavity (Fig 1).
Even in this context of inadequate movement of the canine, an additional difficulty lies in defining the level of force, which should be at the same time light and suitable for the traction movement. In other words, copying the eruption movement or predicting the type of displacement that the canine will perform during eruption caused by orthodontic traction, seems to be very important and made difficult when the ABCT technique is adopted.
CLINICAL CASES THAT ILLUSTRATE THE ENAMEL DRILLING FOR CANINE TRACTION (EDCT) TECHNIQUE
In this topic, the EDCT surgical technique will be demonstrated through case studies that disclose different levels of complexity, which will be discussed in the captions of each figure.
CLINICAL CASE 1
CLINICAL CASE 2
CLINICAL CASE 3
ENAMEL DRILLING FOR CANINE TRACTION (EDCT) TECHNIQUE: STEP BY STEP
The EDCT technique has always been the first therapeutic option embraced by the authors' team. This procedure has been performed as a protocol for canine traction for over 30 years. This surgical technique involving drilling of the crown of the unerupted canine (EDCT) was first carried out in the mid-80s by Prof. Dr. Reinaldo Mazzottini in patients with cleft lip and palate at the HRAC-USP/Bauru hospital, Brazil, and later performed in patients in the authors' private practice.
The surgical technique involves exposing the canine crown enough to bore a small hole in it with a small diameter (¼") spherical carbide bur. Drilling should be performed with extreme care so as not to encroach on the pulp chamber.31 The diameter should be sufficient as to allow the passage of a folded ligature wire (0.30 mm / 0.12-in). The drill should bore a hole into the crown of the unerupted canine always perpendicularly to the long axis in order to prevent the bur from approaching the dental pulp. This orientation is not always easy in view of the position of the canine, and requires an experienced surgeon.
Another crucial point is that after passing the folded ligature through the hole in the crown, attention should be paid when twisting the ligature wire. An instrument - most commonly an explorer probe - must always be interposed between the ligature wire and the tooth enamel in order to avoid enamel fracture, which might prompt the need to repeat the drilling.
In this topic, the EDCT surgical technique will be shown step by step using a patient with an indication for traction of teeth #13 and #23, where access and preparation for traction on both unerupted canines was performed in the same surgical procedure.
CLINICAL CASE 4
Orthodontic traction is intended to redirect the eruption pathway and assist or even replace the eruption force of the unerupted tooth.12 It consists of an extrusive tooth movement and, as such, is determined by the periodontal ligament and its cells.18 Although it is a safe and effective procedure in clinical practice it should only be performed based on biological and up-to-date scientific knowledge. When performed with controlled forces and movement, the pulp is not affected and the odontoblasts remain unscathed and do not cause internal resorption.7,13
When the pathway of an unerupted tooth compresses the vessels of the periodontal ligament of adjacent teeth - with or without orthodontic traction - cementoblasts die on the spot and the root is resorbed to give rise to the follicle and its moving crown. By redirecting the eruption pathway of the unerupted maxillary canine and/or the growth vectors involved in the process, tooth root resorption will cease in neighboring teeth and the surface will be repaired with new cementum and cementoblasts. Extraction of the unerupted tooth triggers a process of regression and re-covering of the resorbed area by new cementoblasts, with deposition of a new layer of cementoblasts and reattachment of periodontal fibers.14,15
Thus, it is advisable to increase the space between the teeth in the upper arch so that the unerupted tooth can lodge itself in the area enclosing the DF and its crown. For the purpose of having a measurable parameter, it is recommended that the mesiodistal distance from the canine crown be calculated and the result multiplied by 1.5. This is not always possible from a clinical point of view, but the use of this criterion and measurement represents a starting point for decision making relevant to each case.14,15 Often, this space cannot be obtained. An alternative that might prevent this inconvenience is to divert the eruption pathway of the canine undergoing traction to a site outside the region of conflict with the roots of adjacent teeth. In canines retained on the palate side, this procedure can be performed, whereas canines retained on the buccal side can hardly benefit from this maneuver. The deciding factor in rendering this procedure practicable is the extensive area of attached gingiva provided by the palate, in contrast to a scarcity of attached gingiva on the buccal side.
Since the DF is comprised of soft tissues, it may be physically compressed between the canine crown and the roots of the lateral incisor and first premolar, but performing this maneuver during traction may result in the lateral resorption of these roots. The opening of space or, as seen above, a temporary change in the eruption pathway eliminates compression of the periodontal ligament of adjacent teeth while cementoblasts and cementum re-cover the roots of these teeth. The DF of the unerupted tooth is farthest from the root surface and its mediators no longer act as enhancers of dental resorption, but rather only stimulate pericoronal bone resorption to enable the eruption to take place in the desired pathway. By moving an unerupted canine through orthodontic traction, whenever possible, the dental follicle is also moved away, which is usually sufficient to stop root resorption and repair the surface.14,15
The mechanics of choice for unerupted canine traction should be fully tailored to suit each individual. Thus, straight wire mechanics, admittedly ineffective in this regard, should be avoided for this purpose. Whenever segmented mechanics is employed to enable the mechanical traction of an unerupted canine, movement control becomes much more efficient, with greater control over side effects and reduced need for appliance activation.29
These factors together greatly reduce the risk of resorption of the teeth adjacent to the unerupted canine by completely individualizing the direction of traction. This resorption is certainly one of the orthodontists' greatest fears in carrying out this procedure, which often leads them not to generate these forces for fear of resorption, especially in the lateral incisors. Clinicians with no experience in these movements often discontinue the process for fear of not being able to observe the intraosseous canine, with negative impact on the movement of traction.
The traction force should be continuous and measurable. The amount of force indicated for anterior teeth, according to Graber and Vanarsdal,25 should be between 35 and 60 grams, similar to the movement of the erupting canine. It should be slow and continuous to allow adjacent tissues to accompany the movement, avoiding interruptions during this process. This amount of force must be measured using a quality tension gauge, with enough sensitivity to measure small amounts of force, such as reported above.
Furthermore, inducing stronger forces can partially damage or tear and rupture the apical neurovascular bundle that enters the root canal, causing calcium metamorphosis of the pulp and aseptic pulp necrosis, respectively.18,19 The induced tooth movement resulting from traction of the unerupted maxillary canines - an extrusive movement - must have forces that are delivered and dissipated slowly, consistent with normal biological tissue. Connective and epithelial tissues are constantly remodeling, which gives them remarkable ability to adapt to new functional demands.16,17
Sometimes, depending on the original position of the canine and the pathway set for its traction, the force required could be greater than that used only to trigger the movement of the unerupted tooth, which copies the movement of eruption. Translation (bodily) movements are often needed, and considering the range of movement, forces of greater magnitude may be necessary. They must be defined in line with those that would be necessary for it to move with the erupted tooth in its socket.
To obtain low-intensity, continuous forces, technological advances now allow orthodontists to work with good quality resilient wires with moderate formability, which enables the placement of first, second and third order bends. Beta-titanium or titanium-molybdenum (TMA) wires feature half the stiffness and hence double the resilience when compared to steel wires of the same cross section. Moreover, these wires preserve activation for a longer period of time. Frequent activations are no longer necessary and continuous forces are maintained. In addition, one should work with the greatest possible distance between molar tube and canine in order to increase the cantilever and decrease forces.27
In orthodontic traction the bundles of periodontal fibers, which are usually inclined toward the apex - from the fascicular bone toward the cementum - are stretched in the occlusal direction and reverse this inclination. Compression of vessels and cells will be small but sufficient to generate mediators that promote bone resorption in the periodontal surface and reattachment of Sharpey's fibers in new positions. In the apical region during orthodontic traction, fiber stretching occurs nearly parallel to the long axis of the tooth and the amount of mediators released by the cells amid fibers and extracellular matrix fibers tends to be slightly higher than normal: Apposition due to new bone formation will be almost immediate.16
When the TMA wire is inserted into the auxiliary tube of the first permanent molar and the other end is inserted more occlusally in relation to the unerupted canine, this force has an extrusive component that causes a reaction in the anchorage molars, i.e., a mesial angulation movement of the crown and distal movement of the root, with a tendency toward mesial intrusion. The canine moves occlusally and tends toward lingual inclination of the crown and buccal inclination of the root as a result of the buccal force relative to the center of resistance of the canine.29
In an attempt to minimize side effects during the movement of traction of the canine, the use of an efficient anchorage system is indicated. In such cases, one should opt to use a welded transpalatal bar with large diameter wires (1.0 to 1.2 mm). Adapted bars should be avoided in these situations because there is some slack between the lingual tube and the palatal bar, which minimizes the control of side effects by allowing greater movement of the anchorage molars.
Even with the use of palatal bars fabricated with large diameter wires, the side effects are never fully controlled, but minimized. Whenever possible, one should band first molars with triple tubes to perform traction supported on the auxiliary first molar tubes, so that the anchorage is enhanced by including these teeth in the upper leveling, with the large caliber leveling arch passing through the main tube.
In cases where maxillary expansion is indicated, a Haas-type expander offers an excellent anchorage choice in view of the ruggedness of these expansion appliances. The segmented arches used in traction can be anchored on the tubes welded to the first molar bands or on the acrylic portion of the expander.
Clinical experience, cost-effectiveness analysis and the level of risk involved in the traction of unerupted permanent canines led the authors to conclude that the EDCT protocol is more suitable than the ABCT protocol.
The authors would like to thank Professor. Dr. Reinaldo Mazzottini, surgeon in charge of performing the EDCT procedure in the clinical cases illustrated in this article and Prof. Dr. Daniela Garib for contributing the ABCT clinical case in the lower arch. Gratitude is also due to Dr. Evandro Borgo for assembling the tomographic slices and 3D reconstructions.
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Contact address Submitted: August 16, 2011
Leopoldino Capelozza Filho
Rua Padre João, nº 14-71
CEP: 17.012-020 - Bauru/SP, Brazil
Revised and accepted: August 30, 2011
Submitted: August 16, 2011