**5.3. Mesiodistal angulation of maxillary incisors**

It has been mentioned in the literature that there is a greater stability of extraction space closure if the roots end up parallel, because when the roots also follow, the roots are also accompanied, a compression is generated in the place, causing ischemia and consequent destruction of the fibers transseptals. Subsequently, new fibers are formed and configured according to the new tooth position [33, 43].

Mulligan [45] stated that divergent roots are more conducive to keeping the space closed. He believes that when the roots are parallel, the vector of functional forces goes through the long axis of the tooth. However, when the roots are divergent, there is a space between the force vector and the tooth resistance center. This creates a moment that favors the approach of the crowns. The author also added that each patient has a moment of stability. And if within a period of up to 6 weeks without orthodontic treatment, the space remains closed, the ideal moment has been reached. But if there is a recurrence of the diastema, it would be necessary to further diverge the roots.

According to Reitan [37], the stability of the tooth position is greatly influenced by the direction in which the tooth was moved. The vestibular and lingual inclination of teeth has great chances of relapse. However, the mesial and distal movements, with a period of containment, are stable movements, except in cases of extrabuccal force for Class II correction.

Morais et al. reported no association between relapse of interincisor diastema and root parallelism. While midline diastema relapse occurred in 60% of the sample, lateral diastemas closure remained stable after treatment. Only initial diastema width and overjet relapse showed association with relapse of midline diastema [46].

#### **5.4. Retention**

**5.2. Relation between periodontium and recurrence of diastema**

as a primary factor in the relapse of dental positions.

them incisively distally to the initial position [25, 42].

ment had a positive effect on the stability of the retraction.

and increase the stability of space closure.

median diastema recurrence.

104 Current Approaches in Orthodontics

transseptal areas.

It is believed that alveolar bone played the most important role in reopening orthodontically closed spaces [36]. However, several authors [15, 42] consider supra-alveolar gingival tissues

Transseptal fibers are part of the supra-alveolar fibers group of the periodontal ligament and are composed mainly of collagen fibers. They are firmly inserted into the cementum, close to the cementum-enamel junction, and are responsible for holding together the adjacent teeth. They do not have elastic fibers, but their elastic characteristic is due to their structural form of tiny springs, which form as the fibers mature [25]. It is believed that their role in medial diastema recurrence is due to this elastic property, pressing the incisors mesially and pulling

When they examined microscopically the interdental papilla of patients with median diastema, Campbell, Moore, and Matthews [42] observed that the insertion fibers of the brake had continuity with the gingival fibers of that area. The authors also verified an excess of accumulated and compressed gingival tissue in this area after the orthodontic closure of the space, which would act to reopen the spaces. In conclusion, it was suggested that the fibrous network of interincisive supra-alveolar tissues may be one of the main factors responsible for

Similar situation, where a compression of gingival tissues was observed in orthodontically closed dental extraction sites, had already been observed by Edwards [15] and Parker [43]. In the aforementioned study, Edwards [15] noticed that the transseptal fibers, especially those near the alveolar ridge, reorganized and appeared normal after 10–14 days with retention of space closure. The author suggested that this was caused by the heavy forces applied during the final closure of space and by the approximation of the roots (parallelism), causing ischemia at the site and subsequent destruction of the compressed transseptal fibers. These, in turn, would be completely replaced by new fibers. Ten Cate et al. [44] have mentioned that it would be possible to remodel the transseptal fibers by a process called fibroblastic activity, where the fibroblasts are able to synthesize and degrade the collagen simultaneously, controlling its remodeling in the periodontal ligament and in the deeper

In addition, Parker's findings [43] demonstrated that transseptal fibers within 60 days did not readapt to the new tooth position and were responsible for the reopening of the space. In this study, the effect of transseptal fibers on the stability of space closure was histologically evaluated, where the first permanent molar was extracted and the second premolar was retracted. In addition, the authors observed that the parallelism of the roots at the end of the closure increased stability and concluded that the fibrotomy of these fibers together with the contain-

Bell [36] believed that the interdental septum was responsible for the instability of diastema closure and advocated subapical osteotomy in the space to be closed to facilitate movement In a study by Edwards [15], a recurrence rate of 88% was found in patients with abnormal labial frenulums who used retention for 16–22 months. In another similar group, but with a retention time of 8–10 months, this proportion was similar, 91% of cases with reopening of diastema. This may suggest that, in patients with abnormal labial frenulum, stability is not influenced by retention time, but rather by labial frenulum surgery.

Depending on the type of initial malocclusion, the use of retention throughout life is recommended [38].

Fixed retention is often cited as the only satisfactory method to promote stability at the closure of the previous diastema [32, 47]. However, the commonly available fixed retention present undesirable characteristics for long-term use, since they restrict access to gingival tissues, making their hygiene difficult. Currently, there is a type of fixed retention through small magnets attached to the lingual surface of the incisors, in previously diastematic areas [48].

Removable retention is not considered a good choice in cases of interincisive diastema because, soon after removal, the teeth already begin to move away [32, 45]. In addition, prolonged use of this retainer category would generate back-and-forth movements, which are potentially damaging.
