Agenesis of maxillary lateral incisors: diagnosis and treatment options

ABSTRACT Introduction: There are different possibilities of orthodontic planning for cases with congenital absence of maxillary lateral incisors. This subject divides the opinion of orthodontists and oral rehabilitation clinicians, due to the advantages and disadvantages of each treatment option, which may involve opening spaces for future implants and/or prosthetic restorations, or closing the spaces by positioning the maxillary canines in the place of lateral incisors. The correct diagnosis and careful evaluation of each patient allow to determine the best therapeutic approach. This paper discusses the main topics to be considered when planning these cases. Objectives: To evaluate the main aspects related to orthodontic treatment planning in cases of congenital absence of maxillary lateral incisors, to aid the decision-making, with clinical and scientific basis.


INTRODUCTION
The hypodontia of one or more permanent teeth is one of the most common developmental anomalies in humans. A tooth is defined as congenitally absent when it has not erupted into the oral cavity, has not been extracted or accidentally lost, and is not visible on radiographic examination. 1 The etiopathogenesis is not fully understood, yet there is evidence of environmental and inherited causes or even the interaction between them.
Hypodontia occurs mainly in Caucasian patients and women.
The third molars are the most affected, followed by mandibular second premolars, maxillary lateral incisors and maxillary second premolars. 2 There are different possibilities of orthodontic treatment for cases with congenital unilateral or bilateral absence of the maxillary lateral incisors. This subject divides the opinion of orthodontists and oral rehabilitators, due to the advantages and disadvantages of each treatment option, which may include opening spaces for future implants and/or prosthetic restorations, or closing spaces by positioning the maxillary canines in the place of lateral incisors.
Regardless of the treatment chosen, the main objective of the orthodontist is to achieve a satisfactory and stable esthetic and functional result, with long-term stability. Many challenges are involved in this process, and a careful assessment must be done before decision making.
Factors as patient age, type of malocclusion, relationship of anterior teeth, facial profile, size, shape and shade of canines, as well as smile line height, should be considered.
The main criteria to be observed and considered in the diagnosis and planning of cases with congenital absence of maxillary lateral incisors will be discussed below.

PATIENT AGE
This is a relevant and maybe the main factor in decision making. Currently, orthodontists commonly receive patients with absence of maxillary lateral incisors at a very young age, with esthetic complaint (Fig 1). Usually, the permanent canines have erupted in a more mesial position, filling part of the lateral incisors space, which already simplifies the orthodontic closure of spaces.
The psychological pressure that this patient may undergo due to impaired esthetics is also a matter of concern for parents and orthodontists. This fact influences the decision for orthodontic space closure, since the patient will be able to spend the remaining adolescence period with the treatment already completed, with the natural dentition and without esthetic problems (Fig 2). 3 Schroeder DK, Schroeder MA, Vasconcellos V Agenesis of maxillary lateral incisors: diagnosis and treatment options  This approach allows maintenance of dental and periodontal architecture in their natural state, with better response to changes over time.
The option of opening spaces for implants at an early age must consider the risk of loss of alveolar bone height and thickness, since the implants can only be placed after growth completion.
The need for provisional prostheses until implant placement causes a waiting period, which is a reason for frequent patient dissatisfaction. Combined to this, there is possibility of inclination of roots of teeth adjacent to the space, requiring retreatment in the future. 4 In young patients, it is not possible to predict the tissue response around the implants. For this reason, when planning includes space opening, Zachrisson et al. 5 suggested the posterior regions, preferably in premolars region.
One disadvantage of this type of approach is the possible reopening of spaces after treatment completion. To avoid this, it is recommended to use a fixed retainer bonded on the palatal aspect of maxillary anterior teeth, after restorative esthetic recontouring of the anterior teeth. Concerning adult patients (Fig 3), decision-making should be based mainly on the anteroposterior relationship of teeth, smile line height and patient profile. If there is no significant facial and dentoalveolar growth, the orthodontist may provide excellent results in shorter treatment periods (Fig 4).

INITIAL MALOCCLUSION AND PROFILE
Several authors agree that the ideal dentofacial patterns for space closure involve patients with Angle Class II malocclusion, balanced profile and absence of crowding in the mandibular arch. 6,7 Mesial movement of the maxillary teeth can affect the axial

SMILE ANALYSIS
Patients who expose their gingiva when smiling may be harmed by replacing missing teeth with endosseous implants. Even with an excellent post-implant esthetic result, it may not be maintained over time. Over the years, the gingival and incisal margins tend to become uneven, leaving the implanted units in infraocclusion, since they do not follow the passive eruption process of adjacent teeth. This fact can interfere, less or more significantly, in the long-term smile esthetics. 6 Implant placement in esthetic areas is a procedure that depends on the operator's sensitivity, with little condition to predict the biological and technical complications that involve the procedure.
Deficiency of interdental papillae, gingival discoloration and, over the years, loss of bone height accompanied by increased probing depth can impair the outcome of orthodontic/rehabilitative treatment. 6,9,10 Conversely, adult patients with a low smile height, i.e., without any gingival exposure, may benefit from the option of implants replacing the maxillary lateral incisors (Fig 6).

PERIODONTAL, OCCLUSAL AND JOINT HEALTH
The periodontal status and aspects that influence the temporomandibular joints are other concerns that should be addressed. Some retrospective studies 11,12 have shown that the periodontal health of patients treated with space closure According to Amm et al. 8 , the presence or absence of a canine occlusion key did not show correlation with occlusal function or signs and symptoms of temporomandibular disorder. This was also mentioned by Rosa et al. 19 in a ten- year longitudinal follow-up study that reported on patients with maxillary lateral incisors agenesis treated with canine replacement. All had healthy and stable periodontal tissues, without attachment loss in the bone crests. 19 In a systematic review conducted by Silveira et al. 13 15 The systematic review performed by Abduo et al. 16 demonstrates that there is no gold standard between the two types of disocclusion for all patients. According to the authors, both situations are equally acceptable. Also, they point out that young people tend to have canine guidances, and older individuals tend to present lateral group function, since the occlusion is dynamic, adaptable and subject to changes over time. 16,17,18 Another question refers to the ability of first premolars to withstand the occlusal forces that ideally occur on the canines, without mobility. In the studies by Rosa et al. 19 , Nordquist et al. 11 and Robertsson et al. 12 , no statistically significant differences were found in the insertion of first premolars, showing that they can play an adequate functional occlusion in group disocclusions, without periodontal damage (Figs. 9, 10, 11 and 14).   More attention should still be dedicated to patients with unilateral agenesis, since there are commonly significant differences in size, shape and color between the lateral incisor and the canine on the opposite side. The lack of symmetry is perceived not only by dentists, but also by lay people. 21 To make the dental arch more symmetrical, the need and possibility of mesiodistal increase of the present lateral incisor must be assessed. 11,23,[24][25][26][27] FINISHING According to some authors, the option of orthodontic space closure represents the most conservative solution. When the case planning includes the participation of restorative specialties, the treatment result usually presents excellent esthetic and functional results (Figs. 12, 13, 14 and 15). 9,10,23,24 Restorative esthetic finishing resources involve the re-shaping of canines to improve the harmony and function. 3 Another tooth to be evaluated at completion of treatment with space closure is the maxillary first premolar, which is usually shorter and narrower than the canine. Such discrepancies should be compensated with restorative and periodontal procedures, and the patients should be aware of this demand since the planning is discussed. It is common to find the need to also   Regardless of the plan chosen for each patient, the orthodontist needs to know how to work together with other specialties to achieve optimal results. In situations where the orthodontist decides to close the maxillary spaces, the participation of restorative dentistry and periodontics is nearly mandatory. 25,26,27 Some orthodontic finishing details should be addressed when Another aspect that should be foreseen when planning these cases is the possibility of appearance of tooth-size discrepancy, which can affect the quality of intercuspation of these cases. This aspect should be reviewed during the orthodontic finalization phase, and possible mesiodistal adjustments should be performed. 11,30 Ideally, occlusion with balanced group function should be achieved, with distributed occlusal loads and, if necessary, performing an occlusal adjustment for better balance of masticatory forces. 19 In cases with space opening, a bridge can be bonded to adjacent teeth until the implant is placed (Fig 4). There is also an indication to use a removable plate to complement the retention. It should This statement leads us to reflect on our clinical approach.
There is a polarization of radical opinions. Ideally, the orthodontist should have absolute knowledge of the advantages and disadvantages of both treatment options and know how to consider them during diagnosis and planning. All considerations must be exposed to the patient and their caretakers, who must decide on the path to be followed.
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