Evaluation of neurosensory alterations via clinical neurosensory tests following anterior maxillary osteotomy (Bell technique)

Abstract

Neurosensory deficits are the most common complication following orthognathic surgery. Le Fort I and sagittal split ramus osteotomies have been widely studied but there is a lack of data about the neurosensory alterations resulting from anterior maxillary osteotomy (AMO). This paper evaluates the neurosensory alterations in cutaneous regions including lower eyelid, cheek, nose, upper lip and vestibular and palatal mucosal areas using simple clinical tests following AMO performed with Bell’s incision so patients can be properly informed about the extent of sensory loss and its rate of recovery following AMO. Twenty-four sides of 12 patients (eight females; four males) with a mean age of 14.20 ± 1.86 years (range 12–17 years) were examined. Pin prick sensation, light touch sensation, static and dynamic two-point discrimination tests were used. Following AMO, vestibular mucosa, upper lip, nose and cheek were the most commonly affected sites. No alterations were detected in lower eyelid and palatal mucosa. The neurosensory deficits in cheek, nose and upper lip resolved 10 days after surgery. The vestibular mucosa showed normal sensation on day 30. In conclusion, following AMO, neurosensory alterations can occur, but it will resolve spontaneously in 30 days.

Anterior maxillary osteotomy (AMO) is a versatile procedure in the management of a variety of deformities of the anterior maxilla. AMO was first described by Cohn–Stock in 1921. Recently, AMO has become an effective component of maxillary distraction for the advancement of the anterior segment of the maxilla to create room to unravel a crowded upper arch or to align an impacted tooth into the arch. The technique described by Block and Brister in 1994 using a tooth-borne device is used in the treatment of atrophic maxillas, maxillary clefts, impacted and/or ankylosed teeth and dental crowding.

Neurosensory deficits have been reported to be the most common problem following orthognathic surgical procedures and there are numerous studies addressing neurosensory alterations resulting from orthognathic surgery. Le Fort I and sagittal split ramus osteotomies are the most commonly used orthognathic surgery interventions and have been the subjects of most evaluations. Neurosensory alterations following AMO are mostly overlooked. It has been suggested that neurosensory deficits following AMO occur but usually resolve spontaneously 6–12 months after surgery. The incidence and recovery from neurosensory alterations following AMO has not been studied analytically.

From the anatomical point of view, after the maxillary nerve enters the orbit through the infraorbital groove (infraorbital nerve), the middle and anterior superior alveolar nerves branch off to supply the anterior vestibular and palatal mucosal areas. After emerging through the infraorbital foramen, the infraorbital nerve sends out palpebral, nasal and labial branches to supply the skin of the lower eyelid, lateral surface of the external nose and upper lip, including skin, mucous membrane and vestibular mucosa. In AMO, a horizontal osteotomy line is made 5 mm superior to the apices of the maxillary teeth, from the piriform rim to the predetermined distraction site. The lateral nasal wall is incised from the piriform rim using a small osteotome. A vertical inter-dental osteotomy was made through the buccal cortex at the predetermined site and deepened by a sagittal saw, extending medially from the buccal alveolus to the palatal bone. Similarly, buccal maxillary, lateral nasal bone, inter-dental, and palatal osteotomies were made on the opposite side. The nasal septum was exposed and transected at its base by a septal osteotome. The anterior maxilla was then downfractured and mobilized. High cut osteotomies, the pressure of retractor on infraorbital nerve during surgery and downfracturing of the anterior segment could result in neurosensory deficits following surgery.

The aim of this paper is to evaluate the neurosensory alterations following AMO in cutaneous regions including the lower eyelid, cheek, nose, upper lip and vestibular and palatal mucosal areas using simple clinical tests. This information can then be used to inform patients about the healing process following AMO operations.

Material and methods

This study was prospective and carried out after institutional approval had been obtained from the Ethics Committee of Gulhane Military Medical Academy. Twenty-four sides (left and right) of 12 patients (eight females and four males) with a mean age of 14.20 ± 1.86 years (range 12–17 years), who presented with dental crowding, malocclusion and/or maxillary hypoplasia were evaluated. All patients were treated with anterior segmental distraction osteogenesis performed following an anterior segmental osteotomy, using conventional osteotomy techniques.

The surgery was carried out under general anaesthesia via oroendotracheal intubation. Local anaesthesia with 2% adrenaline was used to avoid excessive bleeding. An incision, approximately 5 mm above the attached gingiva in the buccal vestibule running from one first bicuspid to the other, was made and the mucoperiosteum was reflected to expose the piriform rim and part of the lateral maxillary wall as described by Bell. The nasal mucosa was gently reflected to expose the anterior part of the nasal floor. The bone cuts were marked using a small round burr and completed with an osteotome. The lateral nasal wall was incised from the piriform rim using a small osteotome. A vertical inter-dental osteotomy was made through the buccal cortex at the predetermined site and deepened, extending medially from the buccal alveolus to the palatal bone. Care was taken not to perforate the palatal mucosa. The nasal septum was transected at its base by a septal osteotome. The anterior maxilla was downfractured and mobilized ( Fig. 1 ). The wounds were allowed to heal for 7 days, after that, the distraction was begun.

Fig. 1
Mobilisation of the anterior segment of the maxilla.

A tooth-borne distraction device described by Bengi et al. was used ( Fig. 2 ). The screws were activated three times a day, resulting in an advancement of 0.75 mm. When the desired advancement was achieved, the distraction was continued for another 3 days to create some over-advancement. The distractors were removed after 8 weeks of consolidation and the orthodontic treatment began immediately.

Fig. 2
Custom made tooth-borne distraction device.

Neurosensory tests

Clinical neurosensory testing was performed on all patients preoperatively and at days 5, 7, 10, 30 and 60 postoperatively. The same person performed all tests, which were carried out in a calm room with the patient relaxed and comfortable, eyelids closed, in a semi-sitting position, after explaining and performing the different tests used on the hand (free from any sensory disturbance). Reference points were determined over the lower eyelid, cheek, nose, upper lip ( Fig. 3 ) and vestibular, palatal mucosal areas ( Fig. 4 ). Right and left sides were examined separately and patients were given a few minutes’ break between the different tests.

Fig. 3
Cutaneous sites examined: (a) lower eyelid; (b) cheek; (c) nose; (d) upper lip.

Fig. 4
Mucosal areas examined: (a) vestibular; (b) palatal.

Light touch sensation

Myelinated A beta fibres were examined by light touch sensation test. Monofilaments using 20 mm long nylon monofilament suture material (Ethicon, Inc., Johnson & Johnson, Somerville, NJ, USA) of four different diameters (3-0, 4-0, 5-0, and 6-0), mounted perpendicularly at the extremities of 10 cm long stainless steel handles were used for examination. A categorical grading spreadsheet of 4 to 0 (with 4 being the maximum) according to the patient’s positive reply to the monofilament calibre knowing that, preoperatively, all patients responded positively to the 6-0 monofilament diameter ( Table 1 ).

Table 1
Scores for patients’ postoperative responses to the monofilament calibres. Scored according to a grading spreadsheet of 4 to 0 (4 being maximum).
Postoperative response to monofilament calibre Scores
Positive to 6-0 monofilament 4
Positive to 5-0 monofilament 3
Positive to 4-0 monofilament 2
Positive to 3-0 monofilament 1
Negative response 0

Adopted from Geha et al.

Pin-prick sensation

The small myelinated A delta and C fibres, which convey pain stimuli were evaluated with a pin-prick sensation test. It was performed using the tip of a dental probe applied very slightly to the different areas. An appropriate response was determined as the perception of the tip of the probe as a sharp pain. Only positive or negative responses were recorded and scored 1 and 0, respectively.

Static two-point discrimination test

The slowly adapting myelinated A beta fibres were examined using a static two-point discrimination test. Two-point discrimination devices such as ‘MacKinnon–Dellon Disk-Criminator and Aesthesiometer’ were conducted according to the standards described for hand surgery. The devices are useful in the evaluation of the cutaneous neurosensory deficiencies of the maxillofacial region, but considering the shape and the size of the ‘MacKinnon–Dellon Disk-Criminator and Aesthesiometer’, the evaluation of the neurosensory alterations of the mucosal areas, especially for posterior and palatal regions, is not easy. In order to overcome this problem, the authors produced a simple device by using a colour ordered shade guide. Drill holes were prepared and blunt tipped 0.8 mm stainless steel wires were placed by using fast curing acrylic resin on the lateral surfaces of the acrylic teeth. The wires were spaced in parallel at varying intervals, measured in mm, with increasing distances between 1 and 10 mm on each tooth. Additionally, each tooth was marked with a number determining the distance between the wires ( Fig. 5 ).

Fig. 5
Application of the two-point discrimination device.

The test was performed with the single probe applied randomly to minimize the risks of weakly representative responses attributable to sensory memorisation. As it is preferable to perform the test a few times before assigning a value in millimetres, the authors retained a value when at least 7 of 10 responses were the same.

An ordinal scoring spreadsheet was used to eliminate threshold differences between patients, giving a maximal score of 5 according to the loss in millimetres compared with the patient’s preoperative results in two-point discrimination ( Table 2 ).

Table 2
Differences between the patient’s preoperative and postoperative replies were scored according to the loss in millimetres in static and dynamic two-point discrimination tests.
Difference between preoperative and postoperative values Scores
No difference 5
1–2 mm 4
2–3 mm 3
3–4 mm 2
5–6 mm 1
≥6 mm 0

Adopted from Geha et al.

Moving two-point discrimination test

The rapidly adapting A beta fibre receptor mechanism was examined and performed in the same way as static two-point discrimination, with the probes being moved between 1 and 2 cm along the areas to be tested. The scoring spreadsheet had the same format with the static two-point discrimination.

Global sensitivity score

Inspired from the study of Geha et al., light touch sensation and pin-prick sensation were considered qualitative tests and added together into a variable named qualitative sensitivity, scored between 0 and 5 separately on each side. Static and moving two-point discrimination were considered quantitative tests and combined together into a variable named quantitative sensitivity, with a total score varying between 0 and 10 for each side.

A global sensitivity score for each side was computed by addition of the previous two scores, its maximal value thus being 15. According to this computed score, each tested side was classified as having normal, subnormal, intermediate, or reduced sensation ( Table 3 ).

Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Evaluation of neurosensory alterations via clinical neurosensory tests following anterior maxillary osteotomy (Bell technique)
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