Investigating the Effectiveness of Low-Level Laser in Reducing Root Resorption of the Upper Incisors During Intrusion Movement Using Mini-Implants in Adult Patients With Deep Overbite: A Randomized Controlled Clinical Trial

Abstract

Background: Deep bite is a common characteristic of malocclusion, and many methods are used to treat it, including mini-implants used for the intrusion of the upper incisors. Orthodontically induced inflammatory root resorption (OIIRR) is an inevitable and unexpected side effect of orthodontic therapy. However, resorption of the root could be affected by the type of tooth movement, such as intrusion. Several studies have indicated the effectiveness of low-level laser therapy (LLLT) in accelerating orthodontic movement, but studies that have evaluated the role of this laser in reducing the risk of OIIRR have been limited. This trial aimed to investigate the effectiveness of LLLT in reducing the resorption of the roots of the upper incisors during their intrusion in the context of deep bite correction.

Materials and methods: Thirty patients (13 males, 17 females; mean age 22.4±3.37 years) with deep overbite were recruited and allocated to the laser or the control groups. Mini-implants were inserted between the roots of the upper central incisors and the lateral incisors from the labial aspect at the gingival-mucosal junction on both sides with a force of 40 g on each side through an NiTi coil spring. A low-level laser (Ga-Al-As) with 808 nm wavelength in a continuous mode, with the parameters 250 milliwatt power output, 4 Joules/point energy density, and 16 seconds irradiation per point, was applied to the root of each of the upper incisors. The laser was applied on the first day of the upper incisor intrusion (T1), then on days 3, 7, and 14 of the first month. In the second month, the laser was applied every 15 days, adjusting the spring strength every four weeks until the end of the intrusion stage (T2), which was determined by reaching a normal overbite. As for patients in the control group, the strength of the nickel-titanium springs was adjusted every four weeks to the required strength of 40 g on each end until reaching a normal overbite.

Results: There was a volumetric decrease in both groups' upper central and lateral incisors roots, and this decrease was statistically significant (P<0.001). However, the difference between the two groups was not statistically significant in each central and lateral incisor volume root (P=0.345 and 0.263 for U1 and U2, respectively). Also, both groups had a linear decrease in upper central and lateral incisors roots, which was statistically significant (P<0.001). At the same time, the difference between the two groups was not statistically significant in each central and lateral incisor root length (P=0.343 and 0.461 for U1 and U2, respectively).

Conclusion: The low-level laser irradiation using the current protocol did not significantly affect the amount of root resorption induced by incisor intrusion in the experimental group compared to the control group.

Keywords: adult patients; cone beam computed tomography – cbct; deep bite; intrusion; low-level laser; mini-implants; overbite; root resorption; upper incisor intrusion; volumetric analysis.

Figure 1. CONSORT flow diagram of patients' recruitment, follow-up, and entry into data analysis

CONSORT: Consolidated Standards of Reporting Trials; LLLT: low-level laser therapy.

Figure 2. The soldered hooks were placed between the central and lateral incisors on each side.

Figure 3. Coil springs were extended between the mini-implants' heads and the soldered hooks.

Figure 4. Laser irradiation in the experimental group. A: The blue dots indicate the areas of irradiation on the vestibular surface of the tooth. B: The blue dots indicate the areas of irradiation on the palatal surface of the tooth.

Figure 5. The software used to view and manipulate the DICOM files from CBCT Images. This software is also used to construct the roots of the upper incisor teeth. A: Orientation of the axes in the three dimensions. B: Determination of the appropriate intensity for each patient individually through the "Threshold" window. C: Once the 3D models of the upper incisors' roots were constructed, their volumes could be calculated

DICOM: Digital Imaging and Communication in Medicine; CBCT: cone-beam computed tomography.

Figure 6. Calculating the root length on CBCT images in the sagittal view. A: Orientation of the two axes (i.e., the frontal and the axial) on the sagittal view. B: Measuring the distance between the two parallel yellow lines to determine the root length

CBCT: cone-beam computed tomography.