Bone and cortical bone thickness of mandibular buccal shelf for mini-screw insertion in adults

Abstract

Objective: To analyze the buccal bone thickness, bone depth, and cortical bone depth of the mandibular buccal shelf (MBS) to determine the most suitable sites of the MBS for mini-screw insertion.

Materials and methods: The sample included cone-beam computed tomographic (CBCT) records of 30 adult subjects (mean age 30.9 ± 7.0 years) evaluated retrospectively. All CBCT examinations were performed with the i-CAT CBCT scanner. Each exam was converted into DICOM format and processed with OsiriX Medical Imaging software. Proper view sections of the MBS were obtained for quantitative and qualitative evaluation of bone characteristics.

Results: Mesial and distal second molar root scan sections showed enough buccal bone for mini-screw insertion. The evaluation of bone depth was performed at 4 and 6 mm buccally to the cementoenamel junction. The mesial root of the mandibular second molar at 4 and 6 mm showed average bone depths of 18.51 mm and 14.14 mm, respectively. The distal root of the mandibular second molar showed average bone depths of 19.91 mm and 16.5 mm, respectively. All sites showed cortical bone depth thickness greater than 2 mm.

Conclusions: Specific sites of the MBS offer enough bone quantity and adequate bone quality for mini-screw insertion. The insertion site with the optimal anatomic characteristics is the buccal bone corresponding to the distal root of second molar, with screw insertion 4 mm buccal to the cementoenamel junction. Considering the cortical bone thickness of optimal insertion sites, pre-drilling is always recommended in order to avoid high insertion torque.

Keywords: Extra-alveolar orthodontic anchorage; Mandibular buccal shelf; Mini-implants; Mini-screw; Skeletal anchorage; Temporary anchorage devices.

Figure 1.

Software interface; reoriented reference scan lines (sagittal: yellow line; axial: violet line; and coronal: blue line) in order to best fit the direction of the long axes of the mesial root of the second left mandibular molar.

Figure 2.

The bucco-lingual thicknesses of total bone (cortical + medullary bone) and cortical bone were measured on two horizontal reference lines apically located at 6 mm (TotThick-at-6) and 11 mm from the CEJ (TotTick-at-11).

Figure 3.

The apico-coronal bone depth thicknesses of total bone (cortical + medullary bone) and coronal cortical bone were measured on two vertical reference lines buccally located at 4 mm (TotaDepth-at4 and CortDepth-at-4) and 6 mm (TotaDepth-at6 and CortDepth-at-6) from the CEJ.

Figure 4.

Occlusal drawing of left mandibular buccal shelf. A mini-screw representation was placed corresponding to the insertion site with the optimal anatomic characteristics. It is the zone of MBS adjacent to the distal root of the second molar and 4 mm buccal to the CEJ.