Key words: anterior tooth grinding, anterior tooth protrusion, asymmetrical dental arch, crossbite, lip closure insufficiency, nasolabial angle, premolar extraction, restricted nasal breathing, ridge size < dental arch length, skeletal transverse discrepancy, transverse dental arch discrepancy, transverse dental arch discrepancy > 5 mm, two-stage intervention
If orthodontic palatal expansion of the small maxilla is no longer possible due to advanced skeletal growth, surgical intervention is necessary. Transverse maxillary distraction is indicated when the apical base of the maxilla is too small for a crowding-free insertion of the teeth into the dental arch while avoiding extractions (alveolar ridge size < dental arch length). A typical symptom may be anterior tooth crowding. In such cases of narrow maxillary arches, narrow nasal entrances are commonly noticeable. Restricted nasal breathing is often a functional symptom, which leads to mouth breathing and, as a consequence, an open mouth.
Narrow maxillary arches with anterior crowding in relation to the mandibular arch are cited as a criterion for bony crowding of the maxilla. If, on the other hand, the anterior teeth are not crowded, posterior teeth that are almost parallel to each other may indicate a transverse crowding of the posterior maxilla that requires surgical correction. In both cases, unilateral or bilateral crossbites and edge-to-edge bites are common. Asymmetrical dental arches may also be an indication for transverse maxillary distraction if an asymmetrical formation or positional relationship of both hemimaxillae originating in the skull base/occiput has occurred. Surgical expansion is necessary to subsequently orthodontically coordinate the dental arch to the antagonistic dental arch.
Further considerations for the indication result from the orthodontic pretreatments during skeletal growth: Situation models are not always sufficient for diagnostics if the attention of the person treating first is preferentially focused on the coordination of the dentition. An additional anterior cephalometric radiograph is necessary to detect a transverse dental arch discrepancy with a narrow maxillary base.
Transverse maxillary distraction is also indicated if there is transverse overextension as a result of orthodontic arch shaping. This allows the maxillary base to be expanded palatally and the posterior segments to be straightened.
Maxillary anterior tooth crowding can be resolved by premolar extractions before or during the skeletal growth spurt in the course of orthodontic treatment. This reduces the outstanding 3D bony growth of the maxilla. This can lead to a steep position of the maxillary anterior teeth and a steep anterior guidance angle, with possible functional problems as a result. Furthermore, a reduction of the upper lip prominence and an increase of the nasolabial angle results. The alternative of transverse maxillary distraction alone can help avoid these esthetic disadvantages and preserve the native length of the dental arch.
Anterior crowding in the maxilla and mandible (dental arch length deficit with too narrow apical base) based on too narrow apical bone bases may indicate simultaneous transverse maxillary distraction and transverse mandibular distraction (dental arch = alveolar ridge).
If, in addition to a severe malocclusion, a transverse dental arch discrepancy is present, eg with a slight crossbite/ edge-to-edge bite (< 5 mm in the molar region) in the maxilla, this can also be corrected by simultaneous maxillary multisegmentation during maxillomandibular osteotomy.
If the 5-mm distance is exceeded, two-stage surgical correction is more likely to be successful out of concern for transverse bony stability: first transverse maxillary distraction and 1 year later Le Fort I osteotomy, and if necessary maxillomandibular osteotomy.
15.2 Transverse maxillary distraction planning and distraction options
Key words: clinical planning, model operation, radiologic planning
The operation is planned, clinically, radiologically, and on the basis of a model operation.
Clinically, the completeness and intramaxillary symmetry or asymmetry of the maxillary arch, the tooth position within the dentition, the occlusal mismatch with the mandibular teeth, and the lack of width to the mandibular alveolar process can be determined.
The panoramic radiograph is essential for the general overview of jawbones and teeth and specifically for the evaluation of whether there is sufficient interdental space for the osteotomy. Anterior cephalometric radiography provides a complementary diagnostic aspect in the posterior alveolar process, which is clinically more difficult to see. Ricketts analysis can be used to compare the posterior transverse arch and alveolar process width of the narrow maxillary arch with the wider mandibular arch. With DVT or CT scans all bony or dental structures of the maxilla including the extent of the sinus recessions can be evaluated. A simulation of the extent of distraction, the vector of distraction, and the final occlusal result can be performed as well. The palatal placement of implants or screws for distractor fixation without damaging the dental roots can also be planned three dimensionally.
The alternative conventional model surgery with plaster casts allows the simulation of the result as well; however, the internal structures like dental roots, bone thickness, and sinus extent remain hidden.
15.2.2 Distraction options
Key words: asymmetrical maxillary expansion, maxillary expansion anterior < posterior, maxillary expansion anterior > posterior, parallel transverse maxillary distraction
If the distance to the transverse maxillary expansion is the same in the anterior and posterior arch region, a parallel expansion of the small maxilla can be performed with a unidirectional distractor:
Bone-supported Rapid Palatal Expander (RPE; KLS Martin)
Tooth-, bone-, or hybrid-supported hyrax screw (eg, Dentalline, Forestadent, Dentaurum).
Implant-fixed Hyrax screw Brölex (Forestadent) (see section 15.6 and Fig 15-7).
If there is intramaxillary asymmetry, the distraction direction is also determined in the model operation to achieve symmetrically aligned maxillary partial arches at the end of the distraction, which can be orthodontically shaped into a symmetrical dental arch:
Asymmetrical fixed bone-supported RPE (eg, KLS Martin)
If a larger transverse expansion is required in the anterior region than in the molar region during this model operation in order to establish a neutral occlusion to the mandible, then transverse distraction must be performed individually: anterior > posterior. The same applies to narrow maxillae with regular anterior position but narrow posterior regions. In this case, individual distraction is also required, but vice versa, mainly in the posterior maxillary region:
Tooth-, bone- or hybrid-supported Maxpander (Medicon).
15.3 Distractor screws and anchoring methods
15.3.1 Distractor types
The medical technology market has led to an almost unmanageable supply of distractors. In the following remarks, the distractor screws preferred by the authors in the last three decades are discussed.
The Hyrax screw is a uniaxial expansion screw with two guide rails, which allows unidirectional parallel distraction of both parts of the maxilla. It can be tooth-, bone-, implant-, or hybrid-fixed. As a rule, the distraction distance is up to 12 mm (eg, Dentalline, Dentaurum, Forestadent). In individual cases it can be used for transverse widening of asymmetrical maxillas (Fig 15-1).
Screw-in-screw (RPE, Transpalatal Distractor)
By rotating an internally threaded cylinder around a screw in which another counter-threaded screw is fixed, both screws can be rotated out of the cylinder. The screw ends fix mobile bone bearing surfaces with sharp metal tips, which can be pressed into the lateral palatal walls and fixed with short monocortical screws. Distraction is unidirectional. Special attention must be paid to educating the patient to activate the screw. The maximum distraction distance depends on the cylinder length, which is available in different sizes (eg, RPE, KLS Martin; Transpalatal Distractor [TPD], Synthes).
Fan-type expansion screw (Ragno)
The fan-type expansion screw (Ragno screw, Leone) opens two metal rods hinged at the apex against each other in an angular manner. It allows an angular distraction of both parts of the maxilla and is usually anchored to the teeth. In the case of a preferably anteriorly intended transverse expansion, the apex of the fan screw should lie far posteriorly in the palate in order to achieve the desired expansion of the hemimaxillae with both pairs of distraction arms directed anteriorly. If the apex lies palatally further anterior and already at the level of the posterior distraction arm pair, transverse compression of the posterior anchor teeth occurs during activation. This also applies to the opposite application of the fan-type expansion screw (Leone).
Double expansion screw (Maxpander)
The double expansion screw consists of two expansion screws that are connected in parallel via a median-transverse sliding axis. The respective distraction arm pair associated with an expansion screw can be tooth-, bone-, or hybrid-fixed via ball-and-socket joints or dental ligament fixation modules. This enables individual biaxial transverse maxillary distraction, eg anterior > posterior or vice versa or biaxial up to 13 mm (Maxpander, Medicon).
15.3.2 Anchoring methods
Key words: dental fabrication necessary, instability of the maxillary expansion, long treatment time, necessity for abutment teeth, no previous periodontal disease, preoperative insertion by orthodontist
Tooth-supported distractors have the advantage of being inserted preoperatively without surgical measures. However, the dental technical fabrication of the appliance is carried out beforehand after taking a maxillary impression. Four abutment teeth are required for anchorage. If these are not available, a combination with a bone anchor is conceivable. There is the disadvantage of long lever arms with eccentric fixation to the teeth, far from the palatal distraction gap. The risk of transverse recurrence is also increased because the palatal distraction gap narrows due to postoperative scar constriction. Tooth-supported distractors are not indicated in cases of periodontal disease. The treatment time is long because complete orthodontic follow-up cannot begin until the retention period of 6 months has ended due to tooth fixation. This method is still widespread in Germany because of historical and actuarial reasons.
Bone-supported unidirectional distractors
Key words: any tooth status, post-bleeding, regardless of previous periodontal disease, risk of dislocation of the jaw halves, risk of fracture of the palatal bone lamella, short treatment time and orthodontist starts after distraction end, technically demanding with activation problems
Bone-supported unidirectional distractors (screw-in-screw) have the advantage of a short overall treatment time. The preoperative insertion of the multiband appliance saves the patient the arduous insertion after the end of the distraction phase. Orthodontic arch shaping can begin early at the end of distraction and quickly eliminates distraction-related dislocations of the two halves of the maxilla. Intraoperatively, dummies are used to select the appropriate size of RPE or TPD distractors depending on the existing palatal width. The appliance is attached bilaterally palatally of the distraction gap, has practically no lever arms, and acts directly and stably. Palatal root damage can be avoided after opening the access by precise inspection of the palatal bone surface. A disadvantage is occasional technical difficulties with spontaneous resetting of the screw. Intensive instruction of the patient performing the activation, their relatives, and the orthodontist are necessary. Rare occurrences are fracture of the thin palatal bone lamella or postoperative bleeding in the distraction phase. They can be successfully treated by changing to a tooth-supported distractor or by resetting the screw and compressing the wound.
Key words: fracture prevention palatal, high stability due to anterior bone anchorage, necessity for a dental anchor, short treatment time and orthodontist starts after distraction end, unilateral combination with bone anchor if necessary
Hybrid-supported distractors (anterior palatal bony, posterior dental fixed) combine most of the advantages of tooth-supported and bone-supported distractors. The orthodontic treatment can start at the end of the distraction, since only one disturbing dental band is available per molar region. If an anchor tooth is missing, a screw implant can be used as a substitute. There is no palatal secondary bleeding. There is high transverse stability due to the anterior bone anchorage, no stress on the thin palatal bone, and no risk of tooth root damage. The Benefit System with Hyrax Screw (Dentalline) and the Maxpander System with double expansion screw (Medicon) are available as distraction systems.
15.4 Surgical procedure
Key words: anchoring screws, impression taking and model fabrication, laser fixation, local anesthesia, model screws, prebending the distraction arms
Case 1 (Fig 15-2) is used as an example of transverse maxillary distraction with a palatal bone-fixed double extension screw (Maxpander, Medicon).