Introduction

Orthodontic movements and gingival recession (GR) have always been a clinical concern. Wennstrom et al. (1996), about tooth movement within the arch, stated that: “a more lingual positioning of the tooth results in an increase of the gingival height on the facial aspect with a coronal migration of the soft tissue margin. The opposite will occur when changing to a more facial position in the alveolar process.” When the tissue is apical to the cement–enamel junction (CEJ), it is called GR. Some unpublished data are suggesting that there is a higher incidence of GR in patients orthodontically treated for transverse discrepancy (Graber et al., 2005). On the other hand, other studies failed to correlate expanding movement and vestibular recessions. Bassarelli et al. studied stone models before and after treatment and found no higher incidence of increased length of clinical crown (Bassarelli et al., 2005). One other study, from the same group, concluded that even in the case of proclination of mandibular incisors there was no correlation between orthodontic treatment and developing vestibular recession. Anyway, they included a thin biotype as a predictor of GR in proclination of mandibular incisors (Melsen and Allais, 2005). In both studies, the analysis was performed right at the end of orthodontic treatment, thus limiting the possibility to intercept a late manifestation of apical migration of the gingival margin. One possible theory is, in fact, that orthodontics per se is not creating a recession but it may create a marginal bone resorption if the tooth is moved outside the bony envelope of the alveolar process (Wennstrom, 1996). This may be observed, for example, in untreated patients with crowding. In these cases, the discrepancy between mesiodistal teeth’s size and the space available may force some of the teeth outside the bony alveolar housing. Staufer and Landmeser showed that in cases of more than 5 mm of crowding, GR of more than 3.5 mm was 12 times more likely to occur (Staufer and Landmeser, 2004). This may not be irreversible as previously thought. In a recent case report, a nonsurgical correction of multiple recessions “was accomplished by orthodontically moving teeth more into alveolar bone and by taking more careful oral hygiene measures” (Northway, 2013) (Figures 7.1–7.5).

This is confirming the importance of achieving proper 3D positioning of the roots inside the bony alveolar housing after orthodontic treatment. GR may eventually become evident only if an inflammatory process (traumatic and/or infective) starts the disruption of the gingival attachment. We, therefore, may expect to visualize the incidence of recessions only sometime after treatment (Figure 7.6a–c).

A more recent study evaluated the long‐term development of labial GRs during orthodontic treatment and retention phase (Renkema et al., 2013). In this retrospective case‐control study on stone models, the percentage of subjects with recessions was consistently higher in cases than controls. The presence of GR was scored (yes or no) on plaster models of 100 orthodontic patients (cases) and 120 controls at the age of 12 (T12), 15 (T15), 18 (T18), and 21 (T21) years. In the treated group, T12 reflected the start of orthodontic treatment and T15 – the end of active treatment and the start of retention phase with bonded retainers. Overall, the odds ratio to have recessions for orthodontic patients as compared to controls is 4.48 (p < 0.001; 95% CI: 2.61–7.70). In particular, the lower incisors seem to be more at risk: “Our results suggest that lower incisors are particularly vulnerable to the development of recessions in orthodontic patients. For example, 31% of the cases and 16.7% of the controls demonstrated at least 1 recession site at T21 (in all the teeth except lower incisors, ratio – 2 : 1), whereas 13% cases and 1.7% controls had at least 1 lower incisor with a recession at T21 (ratio – 8 : 1).” They concluded that “orthodontic treatment and/or the retention phase may be risk factors for the development of labial gingival recessions, while mandibular incisors seem to be the most vulnerable to the development of gingival recessions.”

A systematic review reported a potential association between orthodontic proclination outside the envelope of bone and a higher occurrence or severity of GR (Joss‐Vassalli et al., 2010). Orthodontists routinely compare the length of the dental arch perimeter to the mesiodistal dimension of teeth. Depending on the difference between these two measurements a decision is made to either strategically extract or interproximally strip teeth in order to allow for a realignment of the dentition.

From the periodontal perspective, however, space analysis does not evaluate the buccolingual (sagittal) dimension of the teeth or the alveolar bone perimeter compared to the roots dimension.

Some authors propose individual clinical reference points to establish the maximum possible arch expansion. Richman, examining 72 teeth from 25 consecutively treated patients with facial clinical GR of more than 3 mm, pointed out that conventional orthodontic space analysis does not evaluate the buccolingual dimension of the tooth associated with the alveolar bone present at that level (Richman, 2011). The authors using cone‐beam computed tomography (CBCT) showed that although all of the teeth were periodontally healthy, they all had significantly prominent facial tooth contours and associated alveolar bone dehiscences. A radiographic supporting bone index (RSBI) was proposed, which is the sagittal difference between the alveolar bone width measured 2–3 mm apical to the CEJ, and the width of the tooth measured at that level, as an aid to evaluate eventual risk of periodontal damage after orthodontic treatment (Figure 7.6d–z).

Radiographic Evaluation of Orthodontic Side Effects

Most studies on alveolar bone changes in patients who have undergone orthodontic treatment have used bitewing and/or periapical radiography, thus restricting the assessments to proximal bone surfaces (Hollender et al., 1980; Bondemark, 1998; Janson et al., 2003). Low doses, high‐quality CBCT in office is now becoming more easily available, offering the possibilities of evaluating bone changes in every dimension (Fuhrmann, 1996). During orthodontic tooth movement, teeth may be repositioned beyond the bony alveolar housing with resultant dehiscence and fenestration formation (Sarikaya et al., 2002).

Lund et al. using CBCT investigated in 152 patients the distance between the CEJ and the marginal bone crest (MBC) at buccal, lingual, mesial, and distal surfaces from central incisors to first molars in adolescents before (baseline) and after extractive orthodontic treatment (study endpoint) (Lund et al., 2012). Patients with Class I malocclusion, crowding, and an over‐jet of 5 mm were examined with a CBCT unit using a 60 by 60‐mm field of view and a 0.125‐mm voxel size. Lingual surfaces, followed by buccal surfaces, showed the largest changes. Eighty‐four percent of lingual surfaces of mandibular central incisors exhibited a bone‐height decrease of >2 mm (Figure 7.7).

They concluded that “while some differences may be explained by reasons other than the orthodontic treatment per se, it seems likely that loss of marginal bone height, at least in the short‐term, can be a side effect of extractive orthodontic treatment for a specific type of malocclusion, where retraction of teeth in anterior jaw regions causes remodeling of the alveolar bone.” Same results were demosted in 10 years follow‐up study (Westerlund et al., 2017): “The results demonstrated a significantly lower marginal bone level on the buccal side of the mandibular front teeth in the orthodontically treated patients compared with the orthodontically untreated group.”

Garib et al. also showed a correlation between rapid palatal expansion and thinning of the vestibular plate up to almost 1 mm (Garib et al., 2006). This confirmed what was already stated before the advent of periodontally accelerated osteogenic orthodontics (PAOO^®): the buccal plate of the alveolus may be considered inviolable and any movement beyond that line might cause bony dehiscence and eventually a GR (Engelking and Zachrisson, 1982). PAOO^® revolutionary modifies this vision and the concept can be stretched to the point that, according to Williams and Murphy, “the alveolar “envelope” or limits of alveolar housing may be more malleable than previously believed and can be virtually defined by the position of the roots” (William and Murphy, 2008) (Figure 7.8a–g).

Research Experience

Orthodontic therapy could potentially lead to GR in cases where the teeth are moved outside the envelope of bone. The purpose of this case series was to test the applicability of corticotomy with concomitant guided bone regeneration procedure (GBR) to regenerate bone in the direction of movement outside the original bony housing.

Material and Methods

Ten adult patients (60 anterior teeth), in good general health (7 females and 3 males, between the ages of 18–41, mean 26.6 ± 8.2), were enrolled in the study all‐presenting with severe anterior crowding. Orthodontic therapy in all the investigated sites was associated with selective surgical corticotomies and simultaneous GBR procedures. CBCT examinations were performed before starting orthodontic treatment (T0) and at the end of treatment (T1). All exams were made using a 9000 3D CBCT (Carestream Health, United States) unit, equipped with a flat‐panel detector. The exposed volume was 50 mm by 30 mm (voxel size = 0.679 μ to 0.2 mm, depending on a “stitching” of three consecutive volumes was performed to represent the entire jaw), encompassing the teeth in the jaw where the corticotomy was to be carried out. Exposure parameters were: 70 kV, 8–10 mA (based on the subject’s size), and a single 360° 24–72 seconds exposure time comprising a range of 235 to 468 projections. CBCT was performed to evaluate the thickness of bone and the 3D positioning of the roots in the alveolar ridge before treatment.

Preoperative and postoperative data were analyzed with a dicom viewer (Slicer^® https://www.slicer.org/) that allows superimposition of different CBCT exams. Slicer recognizes landmarks in the analysis and highlights volumetric differences. Following CBCT superimposition, reconstructions were made for each individual tooth, and preoperative and postoperative images were obtained. Measurements were then analyzed with an open‐source image‐processing program designed for scientific multidimensional images (J Image, https://imagej.net/Welcome). The known dimension of the brackets (2 mm) was used as reference point (Figure 7.4). Once the dimension was calibrated, the measurements were calculated for both pre and postoperative slices (Figure 7.5). The long axis of the tooth was then determined by joining the apex and the incised edge. A line was then traced perpendicular to the long axis passing through the CEJ to determine the length of the root, as described by Lund et al. (2010). The root was then divided in two with another line perpendicular to the long axis passing through the midpoint. This line also divides the buccal plate into two halves, coronal and apical. For two reasons only the coronal part of the buccal plate was calculated: (i) bone is anatomically thinner at the crestal margin and more prone to resorption during orthodontic movement (proclination); (ii) coronal osseous augmentation is more challenging due to tensions which develop in the flap during healing, possibly displacing grafted materials apically. For these reasons together with the greater clinical relevance, only the coronal half of the buccal plate was considered for this analysis (Figure 7.10a, b).

Posttreatment measurements were made and the difference between pre and posttreatment values represented the change in alveolar thickness following surgery and tooth movement. Statistical test analysis was conducted using the commercial package SPSS. Student t‐test for the difference of group means was applied with a P value of <0.05 (Figure 7.9a–c).

Results

The study sample included 10 adult patients in whom a total of 60 teeth were orthodontically repositioned outside of their native bony envelope following corticotomy. The average follow‐up time was 7 months (range 6–9 months).

The average thickness changes of the coronal buccal plate, were indirectly determined by the software Slicer^®, which analyzed the coronal osseous area of the pre and post‐op CBCTs. The average area was found to be 0.58 ± 0.22 mm² at T0 and 1.76 ± 0.4 mm² at T1, with a statistically significant difference at P < 0.05.

Further subdivision of the results based on tooth type (canine‐lateral‐central) is summarized and presented in the Tables 7.1–7.3.