Ibrahim Sevki BayrakdarIsmail Gumussoy

Ozkan MilogluYasin Yasa

COMPARATIVE EVALUATION OF THE RAPID PALATAL EXPANSION ZONE USING ULTRASONOGRAPHY AND

CONVENTIONAL RADIOGRAPHYDepartment of Oral Diagnosis and Dentomaxillofacial Radiology, ERZURUM

Rapid palatal expansion (RPE) was first introduced in the

1860s by Angell for the treatment of maxillary constriction. It

later became a conventional orthodontic treatment. RPE is

used in orthodontic practice to correct posterior crossbite and

dental crowding and to facilitate correction of Angle Class II

and Class III malocclusions. The overall objective of RPE is to

widen the maxilla by separating the midpalatal suture and the

circummaxillary sutural system.

Oral radiographs and computed tomography (CT) are

commonly used methods to assess the palatal expansion

zone. However, Sumer et al. indicated that ultrasonography

(US) might be a useful and accurate method to evaluate bone

fill in the midpalatal suture in patients undergoing surgically

assisted RPE. In the orthopedic literature, US has been shown

to be accurate and reliable for the evaluation of distraction

osteogenesis wounds in long bones. Studies also showed that

US was useful for the evaluation of mandibles treated with

distraction osteogenesis.

The purpose of this study was to assess the accuracy of US

in evaluating the sutural opening in a series of patients

undergoing RPE, verifying the reliability of the method against

those of oral radiographic findings.

The study sample consisted of 29 nonsurgical patients (mean age,

13.9 years; range, 11-20 years; 12 males, 17 females) with mixed or

permanent dentition who underwent RPE therapy as part of

comprehensive orthodontic treatment. Subjects with craniofacial

anomalies that would have required any type of surgical intervention

were not included in the study. Individuals with prior orthodontic

treatment history, such as phase I treatment, were also excluded from

the sample. Each patient had a 2-banded Haas appliance, which was

supported by the bilateral maxillary first molars, with extension of the

expansion arms along the gingiva of the premolars.

Methods and materials

2-banded Haas appliance

Maxillary expansion started at the beginning of the orthodontic

treatment for all the patients, and the appliance was activated by one

turn per day until the maxillary constriction was corrected. Depending

on the amount of expansion, the activation period ranged from 21 to 25

days. All evaluations, including occlusal radiographs and US

examinations, were performed immediately after appliance practice

(T1), 10 turns (T2), and 20 turns (T3) during the expansion period. In

total, 87 US images and 87 occlusal radiographies of 29 patients were

evaluated.

Maxillary occlusal radiographs were taken using a Belmont Photo X-II

dental X-ray machine, set at 60 kVp and 7 mA with an exposure time of

0.50 s. Vista scan phosphor plate system was used. To ensure

standardization of the occlusal radiographs of the maxillary region, the

patient sat upright, with the sagittal plane perpendicular to the floor

and the occlusal plane horizontal. The receptor was placed with the long

dimension perpendicular to the sagittal plane, crosswise in the mouth.

The central ray was directed at a vertical angulation of +65 degrees

and a horizontal angulation of 0 degrees, the bridge of the nose just

below the nasion, and toward the middle of the receptor. The central ray

entered the patient’s face through the bridge of the nose.

Radiographic examination

technique

Radiographic examination technique

Two experienced radiologists performed the US examinations.

Sonograms were obtained in the axial planes using an Applio 300

(Toshiba, Tokyo, Japan) 8 MHz linear array transducer. The ultrasound

probe was positioned outside the mouth on the skin overlying the

midpalatal suture, and the US beam was oriented perpendicular to

the bone surface. A real-time survey was then performed of the

midpalatal suture, producing axial slices.

Ultrasound scanning technique

Ultrasound scanning technique

The radiographs revealed a normal anatomical structure at the

beginning of the treatment prior to expansion of the midpalatal sutural

opening. As the midpalatal suture was opened, the radiographic image

showed a larger radiolucid area, parallel to the suture or triangular

shaped, with its base toward the anterior region of the face.

Radiological evaluation

Using US, the surfaces of the bone segments were easily identified,

and assessments in the expansion zone could be performed accurately

during the active phase of expansion. The area was characterized by a

nonhomogeneous and hyperechoic, sharply demarcated zone. A real-

time US survey of the sutural expansion was performed in all 29 patients.

The duration of the study was approximately 3 min.

Ultrasonography evaluation

Pre-expansion, the median palatin suture appears on occlusal

radiographs as a thin radiolucent line in the midline between the two

portions of the premaxilla. It extends from the alveolar crest between

the central incisors superiorly through the anterior nasal spin and

continues posteriorly between the maxillary palatin processes to the

posterior aspect of the hard palate. The suture is limited by two

parallel radiopaque borders of thin cortical bone on each side of the

maxilla. US cannot be used to evaluate the sutural opening at this

stage due to the presence of intact and thick vestibular cortical bone,

which reflects ultrasound beams, making it impossible for the beams

to penetrate the bone structure.

AT THE BEGINNING OF THE TREATMENT (T1)

During the RPE period, as patients turn the screw, the midpalatal

suture is opened and appears on occlusal radiographs as a thick

radiolucent line in the midline between the two portions of the maxilla.

The thickness of the radiolucent line increases over time. Likewise, on

the US examination, this structure appears as a hyperechoic line

because the ultrasound beam is not reflected and can easily penetrate

the expansion gap.

AT THE 10th DAY OF TREATMENT (T2)

AT THE 20th DAY OF TREATMENT (T3)

The US and occclusal radiography findings were

comparable with regard to the assessment of the sutural

opening at the beginning, 10th, and 20th days of the

expansion period.

In the current study, US was used to assess the midpalatal suture in

patients undergoing RPE. To the best of our knowledge, there are no

published quantitative or semiquantitative sonographic comparisons of

sutural expansion with oral radiographies and US in RPE patients. US was

used in one study of three surgically assisted RPE patients, where it

proved accurate in the measurement of the gap across the osteotomy and

in the evaluation of callus formation. In that study, which is similar to our

evaluation, callus formation was examined after expansion. In contrast,

we compared US findings of midpalatal sutural expansion during the

active RPE period with those of radiographic examinations.

US is an easy-to-use, inexpensive tool that can provide accurate

information on midpalatal sutural expansion in patients undergoing RPE.

In the present study, the accuracy of US was as high as that of

radiography in the determination of sutural expansion. A major

advantage of US is that it is a real-time imaging tool with no ionizing

radiation.

Conclusion

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