Limits of orthodontic therapy
Orthodontic treatment entails movement and adaptations of dental and dentoalveolar structures and the adaptation of neuromuscular and soft tissue structures around them. The new teeth positions acquired must be balanced with the functional needs of the stomatognathic system, which has primary functions of mastication, speech, deglutition and respiration. The goals of orthodontic treatment and/or combined orthognathic surgery are to provide functional and aesthetically acceptable occlusion, which is in harmony with the functions of the stomatognathic system.
Orthodontic tooth movement
Orthodontic tooth movements can be more realistically carried out about correction of inclinations, labiolingual movements, corrections of rotations and some intrusion. Extrusion of teeth is predictable and relatively simpler to perform than an intrusion. After movement into the newly acquired positions, the teeth should retain their roots surrounded by healthy alveolar bone and gingiva. Biologically, there can only be a limited labial movement of the anterior teeth. A greater range of palatal movement of maxillary teeth is possible but for limits of palatal contours and proximity of the incisive canal (IC). Similarly, maxillary teeth can only be expanded buccally to a limited extent within the limits of the buccal plates of the alveolar bone.
The limited alveolar bone mass around incisors limits tooth movements in the anterior segment of the mandibular arch. Expansion of the mandibular arch beyond adaptation to expanding maxillary arch is not an orthodontic reality. These boundaries have been quantified and graphically re-parented as the envelope of tooth movements. In growing children, treatment with dentofacial orthopaedics combined with orthodontic treatment brings about a more extensive range of jaw movements. For example, correction of large overjet can be achieved with the forward positioning of the mandible and retraction of maxillary anterior teeth. These observations have been tabulated ( Table 8.1 ) and graphically represented in Figs 8.1.i and 8.1.ii. With current innovative methods of anchorage control supported with implants and possibilities of skeletal expansion in the maxilla and en masse movement of the whole arch, the existing limitations are not fully expressed in the envelope. These are later given in the chapter under 3D evaluation and envelope of discrepancy.
TABLE 8.1
Limits of orthodontic, orthopaedic, and surgical movements in three planes of space (in mm)
Source: Modified from Proffit WR, Ackerman JL. Diagnosis and treatment planning. In: Graber TM, Swain BF (eds). Orthodontics: Current Concepts and Techniques, St. Louis, Mosby, (1985).
| MAXILLA | MANDIBLE | |||||||
|---|---|---|---|---|---|---|---|---|
| Orthodontics | Orthopaedics | Orthognathic surgery | Orthodontics | Orthopaedics | Orthognathic surgery | |||
| Anterior segment | Sagittal | Labial movement | 2 | 5 | 10 | 5 | 10 | 12 |
| Palatal movement | 7 | 12 | 15 | 3 | 5 | 25 | ||
| Vertical | Intrusion | 2 | 5 | 15 | 4 | 6 | 10 | |
| Extrusion | 4 | 6 | 10 | 2 | 5 | 15 | ||
| Posterior segment | Vertical | Intrusion | 3 | 4 | 10 | 3 | 4 | 10 |
| Extrusion | 2 | 3 | 10 | 2 | 4 | 10 | ||
| Transverse | Buccal movement | 3 | 4 | 7 | 2 | 4 | 5 | |
| Palatal movement | 2 | 3 | 4 | 1 | 2 | 3 | ||
Limits and boundaries of orthodontic treatment.
Figure 8.1.i Limits and boundaries of orthodontic treatment in the maxilla.
Figure 8.1.ii Limits and boundaries of orthodontic treatment in the mandible. With current innovative methods of anchorage control supported by mini implants and possibilities of skeletal expansion, the existing limitations of the maxilla and en-masse movement of the whole arch are much greater. Some of these aspects are represented in Figs 8.2 and 8.3 .
Implants and skeletal anchorage supported orthodontics
Introducing miniscrew implants and skeletal anchorage systems (SASs) in orthodontic armamentariums has expanded the possibilities of orthodontic tooth movements, especially in treating complex malocclusion. The temporary anchorage devices (TADs) can provide absolute anchorage, allowing maximum retraction possible in the extraction spaces. Implant-supported and other SASs can facilitate complex dental movements, impossible with conventional orthodontics. Distal movement of the entire arch and intrusion of molars were considered impossible and can be achieved with implant-supported biomechanics. In some borderline adult cases for orthognathic surgery with severe class I bimaxillary protrusion and class II skeletal malocclusion can be managed with TAD-supported anchorage as non-surgical cases. The appended case study is an excellent example of successful treatment in an adult class II case. ( Fig. 8.2 ).
Orthodontic treatment in an adult with skeletal class II malocclusion, severe crowding and successful outcome.
Figure 8.2.i Pre-treatment photos of an adult female with class II malocclusion, significant lip protrusion, and crowding was treated using implant-supported anchorage to correct a gummy smile. Pre-treatment cephalometric analysis revealed a large ANB angle of 9.5 degrees, suggesting surgery may improve the patient’s retruded chin and gummy smile. However, after a thorough discussion with the patient, she avoided surgery; therefore, management was solely orthodontic.
Superimposition of the lateral cephalometric radiographs before and after treatment showed that the maxillary first molars and central incisors were intruded and distalised. Despite the significant movement of the maxillary teeth, no root resorption was observed after treatment.
Post-treatment profile and occlusion after approximately three years of active treatment. A good class I occlusion and balanced facial appearance were observed. The treatment was completed in two phases. During the first phase, a sectional arch was used to achieve distal movement and intrusion of the lateral teeth. During the second phase, a full-sized archwire was used to achieve levelling of the entire maxillary dentition and intrusion of the anterior teeth. Facial appearance and occlusion remained good after three years of retention.
Research studies have been done to quantify dental movements in three dimensions of space. These are summarised as follows ( Table 8.2 ). A recent systematic review suggested mini-implants supported biomechanics caused superior anchorage control by providing less molar mesialisation along with the intrusion of the molars and incisors.
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En masse distalisation of maxillary buccal segments
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En masse distalisation of a maxillary arch up to 4 mm with a SAS in adult patients was achieved combined with simultaneous traction of the first and second molars.
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Incisor retraction and intrusion
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Incisor retraction at the incisor edge has been reported at 8.2+2.4 mm at the maxillary incisor edge. Using the structural superimposition method, one study reported 5.77 mm of maxillary retraction and 5.43 mm of mandibular incisor retraction in class I bimaxillary cases.
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Intrusion of buccal segments: maxillary molars
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In adult patients with severe open bite, absolute intrusion of the molars can be achieved supported with miniscrews as an anchorage device by 2.3 mm.
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In experimental studies on adult female beagles with fully erupted dentition, second premolars were intruded on an average extent of 1.8 mm after 4 months and 4.2 mm after 7 months using an anchored device.
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Intrusion of mandibular buccal segments: mandibular molars
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Sugawara reported successful treatment of nine adult open bite patients with SAS. The mandibular first molar had an average intrusion of 1.7 mm while the second molar had an average intrusion of 2.8 mm.
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Experimental studies on dogs showed that mandibular molars could be intruded by 3.4 mm over 7 months.
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The active intrusion of buccal segments allows anti clockwise rotation of the mandible and thereby helps in closing the open bite in vertical growers and adults.
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Maxillary skeletal expansion assisted with implants (non surgical)
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An umbrella review reported that skeletal transverse maxillary expansion width increased by 2.33 mm.
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TABLE 8.2
Temporary anchorage device supported orthodontic tooth movements
| S.no. | Type of dental movement | Maximum movement mm | Experiment design | Author/year |
|---|---|---|---|---|
| 1 | Incisor retraction and intrusion |
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|
Liou EJ, Chang PM, 2010 |
|
|
Monga N, Kharbanda OP, 2016 | ||
| 2 | En masse distalisation of maxillary buccal segments | 4 mm simultaneous traction of the first and second molars | Case Study. Adult patient | Tanaka et al., 2008 |
| 3 | Intrusion of buccal segments: maxillary molars. | 2.3 mm intrusion of maxillary molars. | Thirty adults (15 for non-implant treatment and 15 for implant-anchored treatment). | Deguchi et al. 2011 |
|
Adult Beagles dogs. 6 Females. Had fully erupted dentition. | Daimaruya T, Takahashi I, 2003 | ||
| 4 | Intrusion of buccal segments: mandibular molars | First molars 1.7 mm second molars |
|
Sugawara et al, 2002 |
| Mandibular molars 3.4 mm | Using SAS in dogs showed that mandibular molars could be intruded by 3.4 mm on average over 7 months | Daimaruya T, Nagasaka H, 2001 | ||
| 5 | Miniscrew assisted rapid maxillary expansion MARPE non-surgical | Skeletal maxillary expansion in transverse dimensions increased by 2.33 mm | An Umbrella Review. | Ventura et al. 2022 |
|
Systematic Review and Meta-Analysis | Kapetanovic‘ A., Theodorou C.I 2021 |
IMW , Inter-molar width; ICW , inter-canine width; IPM , inter-premolar width.
Limits of dentofacial orthopaedic treatment
Dentofacial orthopaedic treatment in growing children has been shown to generate more substantial changes compared to orthodontics alone. Its unique ability to improve sagittal repositioning of the mandible results in alterations in oral cavity volume, skeletal bases, and dentoalveolar structures. This treatment modality can improve facial aesthetics, functional occlusion, and overall oral health. Generally, overjet up to 12–15 mm is correctable with dentofacial orthopaedic appliance. The corrected overjet is often an outcome of a combination of retroclination of maxillary incisors, some proclination of mandibular incisors and an acquired forward position of the mandible.
Although there are no definite guidelines based on negative overjet for the maxillary protraction or camouflage treatment of class III malocclusion, cases with normal mandible and deficient maxilla are more suited for protraction. A familial type of severe class III malocclusion may not respond to conventional dentofacial orthopaedic treatment, even though it is diagnosed and intercepted early. In these cases, diligent observations and diagnosis would be needed to ascertain if the malocclusion is interfered with in growing age or if it should be treated later with orthognathic surgery.
Orthognathic surgery
Malocclusions beyond the possibilities of treatment with orthodontics alone and patients beyond the age for possible dentoskeletal orthopaedic growth modifications can be managed with a combined approach of orthognathic surgery and orthodontics.
The nature of malocclusion, the magnitude of the problem and the complexity of the skeletal and dental relationships are the basis of a treatment plan and detriments if the deformity can benefit from orthodontics alone or would require a combination of jaw surgery and orthodontics.
Orthognathic surgery of the facial skeleton permits repositioning the maxilla and mandible in all three dimensions of space. However, there are biological limits to such changes, which have been classically summarised by Proffit and Ackerman ( Figs 8.1.i and 8.1.ii ). In the opinion of orthodontists, the maximum limits with orthodontic treatment were a positive overjet of up to 8 mm, a negative overjet of 4 mm or less, and a transverse discrepancy of up to 3 mm.
The amounts of changes possible in three planes of space have been quantified for both maxilla and mandible and orthodontics alone or orthodontics with orthognathic surgery.
Distraction osteogenesis
Research studies on biological principles and technological advances in the development of multiplanar devices of distraction osteogenesis now allow a more extended range of lengthening procedures, such as maxillary protraction, more so in cleft patients and mandibular lengthening in patients with TMJ ankylosis where orthognathic surgery has limitations. The multi-planar distraction devices allow tailoring on lengthening in several vectors. Complex malocclusions can be successfully treated with modern distraction appliances, supported by 3D virtual model visualisation and an interdisciplinary approach.
Table 8.1 summaries limits of orthodontic treatment, dentofacial orthopaedics and orthognathic surgery. The values shown in the table are extreme limits of movements, and it is not necessary that these treatment effects are always possible or would be stable in the future. Generally, the range of possible movements in vertical and sagittal directions is greater for both the mandible and maxilla. In contrast, movement possibilities in a transverse plane, that is expansion and constriction, are minimal, more so in the mandible.
3D evaluation and envelope of discrepancy
With the latest advancements in 3D imaging technology, such as low radiation cone beam computed tomography (CBCT), researchers and clinicians are studying the relationship between the IC and the contour of the palate with respect to the roots of maxillary incisors. Clinicians can now know how these factors can affect or limit the extent of orthodontic tooth movement. The IC and its relationship with maxillary incisor roots have been investigated for root resorption during the midline correction, the extent of incisor root retraction and the possibilities of IC remodelling in growing subjects with orthodontic tooth movement.
In the case of maxillary molars, two aspects are critical for buccal segment roots and their anatomical relationship with the maxillary sinus (MS). The MS relations with roots of the maxillary molar may affect intrusion, bodily movement for space closure and large mesial movement of the maxillary second/third molar with roots traversing through the sinus.
Incisive canal and incisor root morphology and orthodontic tooth movement
The IC is a tubular structure on the palatal side of the maxillary anterior teeth that connects the nasal and oral cavity. The IC is surrounded by thick cortical bone and contains blood vessels and nerves coursing through it. Therefore, caution must be exercised when moving the anterior maxillary teeth palatally. This is because contact between the root and cortical bone can lead to root resorption or the arrest of root migration.
To leverage this, we must be familiar with the 3D position of the maxillary anterior tooth root in relation to the IC to avoid possible iatrogenic root resorption.
Matsumura et al. used CBCT images to quantitatively analyse the positional relationship between the maxillary incisor root, anterior alveolar bone, and the IC. They found three significant anatomical points of concern to orthodontists.
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Maxillary incisor inclination was significantly correlated with the maxillary alveolar bone and IC inclination.
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Maxillary incisor root and IC were closest to each other at the oral aperture level.
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The maximum cross-sectional area of the IC was observed at the maxillary incisor root apex level.
The IC can affect the root resorption while attempting to treat midline shift. In a case study by Imamura et al. where treatment was instituted to correct the maxillary midline shift to the left by 5.5 mm, significant root resorption was found in the maxillary right central incisor root. In contrast, no root resorption was found in the contralateral incisor root despite a similar pattern of tooth movement in the bilateral maxillary central incisors ( Figs 8.3.i–8.3.iv ). Differences in 3D positioning, including contact between the incisal roots and the IC, may be responsible for the different root resorption patterns. Panoramic and posteroanterior (PA) cephalometric radiographs showed a sufficient parallel shift of the incisor roots with tilting of the maxillary incisors to the right after treatment due to the space gained in the maxillary left lateral incisors and shifting the maxillary midline to the right ( Figs 8.3.v–8.3.vii ).
