Intraoral approach using CAD/CAM technology for the Dingman method: a case description

Introduction

Orthognathic surgery is performed to correct the position and shape of the upper and lower jaw bones and improve occlusion and speech in patients with jaw deformities. In Japan, orthognathic surgery has been covered by insurance since April 1990, and patients with various oral conditions visit Department of Oral and Maxillofacial Surgery, Tokyo Dental College Suidobashi Hospital (our hospital) for surgical orthodontic treatment (1).

With the recent introduction of digital technology, several reports have been published on the use of three-dimensional (3D) simulations for safe performance of intraoral surgical procedures, from surgical planning to treatment (2-8). Although, the Dingman method is usually performed via an extraoral approach (9). Historically, Dingman [1944] described a mandibular body osteotomy—typically via an extraoral approach—with low infection risk due to the lack of intraoral–extraoral communication. Over the subsequent decades, intraoral sagittal split ramus osteotomy (SSRO), developed by Obwegeser and modified by Dal Pont, Hunsuck, and Epker, supplanted the Dingman approach due to broader bone contact and rigid fixation (10-13). We applied an intraoral approach Dingman method using computer-aided design (CAD)/computer-aided milling (CAM) technology, as first part of the surgical orthodontic treatment of a patient with acromegaly with an excessive overjet on the premise that a mandibular setback will ultimately be performed via SSRO.

Herein, we report our experience. This case is reported in accordance with the CARE checklist. Because only a single case is presented, the PROCESS guidance for case series was not applied; however, relevant PROCESS items were cross‑checked to enhance transparency.

Case presentation

A 37-year-old man, who had previously undergone endoscopic transnasal resection of a growth hormone-producing pituitary adenoma, presented to our hospital with chewing difficulty. His medical history included otitis media, sinusitis, pituitary adenoma, and acromegaly. Extraoral examination revealed a concave facial profile, and mandibular deviation to the right was observed in the frontal view (Figure 1A-1C). Intraoral examination revealed Angle class 3 malocclusion on both sides, with an overjet of 30 mm and overbite of +4 mm. The midline of the maxillary dentition was deviated to the left by approximately 3 mm from the facial midline (Figure 1D-1F). Furthermore, a standard cephalogram demonstrated an ANB angle of 17°, labial inclination of the maxillary anterior teeth, and lingual inclination of the mandibular anterior teeth. Based on these findings, the patient was diagnosed with an arched bite accompanied by acromegaly and jaw deformities (maxillary retrusion, mandibular prognathism, and facial asymmetry). Preoperative orthodontic treatment was initiated following the extraction of the ankylosed maxillary second and third molars on both sides (Figure 2A-2C). The maxillary second and third molars were removed to facilitate orthodontic decompensation, avoid posterior interferences after mandibular setback, and harmonize arch coordination in anticipation of staged mandibular surgery. No temporomandibular joint (TMJ) pain, clicking, or limitation was noted; maximum interincisal opening remained within normal limits.

Figure 1 Facial photographs (A-C) and intraoral photographs (D-F). These images were published with the patient’s consent.

Figure 2 Panoramic radiograph (A) after preoperative orthodontic correction; frontal view (B) and lateral cephalograms (C).

Treatment plan

Comparison of the preorthodontic and simulated postorthodontic models indicated that considerable amount of posterior movement of the mandible was required. Thus, treatment with maxillary osteoplasty alone was challenging. Hence, a staged surgical treatment plan was developed. The first stage involved a Le Fort I osteotomy to correct the maxillary occlusal plane and move the maxilla forward by 5 mm (Figure 3). The second stage involved the Dingman method for the mandible, and the third step involved SSRO to achieve normal occlusion after bony union was confirmed. The bilateral mandibular first molars were selected for extraction during the Dingman procedure because the left mandibular first molar had difficulty erupting and to improve the excessive overjet. Furthermore, we decided to use an intraoral approach using an osteotomy device and ultrasonic cutting instrument.

Figure 3 3D virtual simulation showing (A) maxillary advancement/occlusal plane correction (Le Fort I), (B) intraoral Dingman osteotomy plan with posterior translation of the tooth‑bearing segment using the first‑molar extraction space, and (C) anticipated minor step between mandibular segments after fixation. 3D, three-dimensional.

Bilateral mandibular first molars were extracted because the left first molar had eruption and movement difficulty and because symmetric extraction provided a controlled bony gap equal to the molar’s mesiodistal width, permitting posterior translation of the distal segment while reducing the risk of root-canal interference and facilitating intercuspation during the final SSRO stage.

Given the extreme overjet and the need to correct the maxillary occlusal plane, a staged strategy was adopted: stage 1 (Le Fort I osteotomy) to level/advance the maxilla; stage 2, an intraoral Dingman mandibular body osteotomy to posteriorly reposition the tooth‑bearing segment using the extraction space and avoid excessive ramus manipulation; and stage 3, SSRO to finalize occlusion after consolidation. In this patient, the required setback magnitude and acromegaly‑related mandibular morphology favored a staged approach: an intraoral Dingman osteotomy to posteriorly translate the tooth‑bearing segment using the extraction gap, followed by SSRO to finalize occlusion after consolidation.

Guide design dimensions (at the first‑molar region). The osteotomy‑guide slot width was set to the measured mesiodistal diameter of the first molar, enabling equivalent posterior translation. The buccal cortical window was designed at its center to allow safe piezo access while maintaining ≥2 mm clearance from the mandibular canal and ≥1.5 mm from adjacent roots.

The devices to be used in the Dingman method were fabricated in collaboration with the Fabrication Laboratory Tokyo Dental College (FabLab TDC), which opened at Tokyo Dental College in 2013 (3). The FabLab TDC is equipped with surgical simulation software, inkjet 3D printers, optical scanners, and other equipment, and outputs 3D data from computed tomography (CT) scans and other sources. Two osteotomy devices were designed and fabricated for this procedure. CT was performed with a slice thickness of 0.6 mm (Somatom Definition AS, Munich, Germany) after completion of the preoperative orthodontic treatment, and a 3D model of the mandible was reconstructed using the scan data. Because of the difficulty in accurately reproducing the dentition owing to the effects of orthodontic brackets and prostheses, an optical impression (Trios; 3Shape, Copenhagen, Denmark) was made and converted to the STL data format. Based on the mandibular data reconstructed from the CT and optical-impression data, virtual surgical planning was performed using CAD software (Magics, Materialize, Leuven, Belgium). For the mandibular osteotomy site, the position of the mandibular canal was determined, and two surgical guides were fabricated: one for osteotomy that reached the lower border of the mandible and maintained the mesiodistal distance between the bilateral mandibular first molars, and the other for buccal cortical bone osteotomy that clearly indicated the inferior alveolar nerve (IAN) position during surgery (Figure 4A-4D). Magics CAD software (Materialize) was used to set the mandibular canal to white and the bone to clear (Figure 5A-5C), thereby creating a 3D model of the mandibular bone after movement. Prior to surgery, the fixation plate was adapted to the model (Figure 5D).

Figure 4 Osteotomy device design data and devices manufactured using a 3D printer. Osteotomy device design (A); IAN position guide indicating the mandibular canal (B); stereolithographic osteotomy guide fabricated using a 3D printer (C); IAN protection retractor model fabricated using a 3D printer (D). 3D, three-dimensional; IAN, inferior alveolar nerve.

Figure 5 Steps leading up to pre-bending of the intraoperative fixation plate. Inferior alveolar nerve and first molar are color-coded (A). Simulation of the transection of the first molar and bone equivalent to the mesiodistal diameter. The distal bone fragment is moved backwards to the ideal position (B,C). Model with prebent fixation plate printed using a 3D printer, with particular attention paid to the positions of the tooth roots and nerve (D).

In the surgical procedure, the bone was precisely and safely excised using a fabricated cutting guide, and subsequent bone fixation was performed (Figure 6A-6E). The necessity for an extraoral incision was eliminated. A CAD/CAM mandibular osteotomy guide was seated and secured with occlusal rests; verification windows permitted visual confirmation. A buccal cortical window was created using an ultrasonic instrument under continuous irrigation, following the second (IAN‑position) guide. The IAN was gently mobilized and protected with a smooth‑edged IAN protection retractor placed according to the guide’s canal indicator. Osteotomy was then completed through the guide slot with intermittent cutting and frequent visual confirmation via the verification windows, avoiding sustained traction on the nerve. No direct damage to the IAN was observed, and the paralysis resolved one year after the surgical procedure. A subsequent analysis of postoperative radiographs indicated that the patient had made significant progress (Figure 7A-7C). A small step between proximal and distal segments was anticipated on simulation; this was clinically unapparent and required no secondary contouring. Should palpability or esthetic concern arise, minor recontouring at plate removal can be considered. A subsequent analysis of the superimposition of preoperative planning and postoperative CT data revealed that the anterior segment demonstrated 97.5% accuracy (Figure 8A,8B).

Figure 6 Intraoperative photographs. A mucoperiosteal flap was elevated (A). The osteotomy guide was seated and secured with buccal monocortical screws; osteotomy was performed through the guide slot (B,C). The buccal cortical window was created, and the IAN was gently mobilized and protected with a smooth‑edged IAN protection retractor (D). Two pre-bent metal plates were used on each side for fixation (E). IAN, inferior alveolar nerve.

Figure 7 Panoramic radiograph (A) after operation; frontal view (B) and lateral cephalograms (C).

Figure 8 Accuracy analysis by ICP (GOM Inspect). (A) Color-mapped surface deviation between the preoperative plan and 3‑month postoperative CT (green within ±2 mm). (B) Histogram/cumulative plot; 97.5% of anterior-segment surface points were within ≤2 mm of the plan. CT, computed tomography; ICP, iterative closest point.

Postoperative outcomes (12 months): the patient achieved markedly improved masticatory efficiency and facial appearance. No TMJ pain, clicking, or limitation was noted; maximum interincisal opening remained within normal limits. Neurosensory function in the lower lip area was clinically normal based on light‑touch and two‑point discrimination testing.

All procedures were in accordance with institutional and national research committee standards and the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Since the first mandibular setback surgery for mandibular prognathism was performed by Hullihen in 1849 (14), numerous other surgical procedures have been described. Recently, owing to improvements in imaging technology, instruments, and tools, surgical procedures such as SSRO, intraoral vertical ramus osteotomy, and intraoral inverted ‘L’ osteotomy have been established (15-17). However, depending on the severity of jaw deformation, treatment using these procedures alone may not be feasible. The Dingman procedure, which was selected in this case, is a partial bone resection method that was first described in 1944 (9). It is a two-stage procedure usually performed in the mandibular premolar region intra- and extraorally. The procedure has the following advantages: (I) reduced surgical invasion; (II) low incidence of nerve damage and negligible postoperative paralysis; (III) owing to the absence of communication between the inside and outside of the mouth during surgery, the risk of infection is small; and (IV) it is suitable for selected cases. Moreover, in cases where a significant amount of posterior mandibular movement is necessary, such as in our patient, and where the mandible is lowered in two stages, this method allows only the dental arch to be moved posteriorly without manipulating the ramus. However, the disadvantages of this procedure are (I) extraoral scarring; (II) few teeth are sacrificed; and (III) intermaxillary fixation (IMF) is required for a relatively long period owing to the small bone contact surface.

In this case, an intraoral approach was performed, and the osteotomies were performed in the mandibular first-molar regions. Thus, mandibular canal invasion was anticipated. Therefore, surgical guides for the osteotomies were fabricated before the procedure. The FabLab TDC team engages in a multitude of fundamental research endeavors that are subsequently applied in clinical practice (3-8).

In the field of oral and maxillofacial surgery, 3D devices have been used in clinical practice since 2016 to virtually perform surgical procedures with high accuracy. Currently, they are widely used in surgeries such as Le Fort I osteotomy (6) and genioplasty (7). In 2021, Koyachi et al. (6) used CAD/CAM and magnetic resonance technologies to validate the precision of maxillary positioning during Le Fort I osteotomy. A high degree of reproducibility (90.3%) was demonstrated by superimposing the plan onto the preoperative plan in three dimensions. In this case, a 3D surgical simulation was performed in advance with our accumulated technology to date, a 3D model was generated, and a surgical guide was prepared to enable the safe performance of the Dingman method, which had previously been performed via an extraoral approach.

Our intraoral guided Dingman technique aligns with current computer‑aided orthognathic workflows, which integrate cone‑beam computed tomography (CBCT) and intraoral scans to create a composite skull for virtual planning and CAD/CAM guide fabrication. Reported accuracy of digitally planned orthognathic procedures is high, with 3D iterative closest point (ICP)‑based analyses frequently employing a 2 mm clinical threshold; our 97.5% anterior‑segment accuracy is consistent with these data.

Traditional (extraoral) Dingman drawbacks include a cutaneous scar, sacrifice of teeth at the osteotomy site, and relatively prolonged IMF due to limited bone contact. In our intraoral, guided modification, visible scarring is avoided, but tooth extraction and careful IAN mobilization are required. A small step between proximal and distal segments was anticipated on simulation; it was clinically unapparent and required no secondary contouring. Minor recontouring can be considered at plate removal if symptomatic. Compared with the traditional extraoral Dingman approach, the intraoral execution avoids visible scarring while maintaining the historically low infection risk related to the lack of intraoral-extraoral communication. However, it necessitates tooth extraction and careful IAN mobilization, and it offers less bone contact than bilateral sagittal split osteotomy (BSSO)—therefore staging and rigid fixation plus orthodontic finishing are critical. Relative to BSSO, this staged approach may reduce unfavorable ramus splits in very large setbacks.

Conclusions

In the present case, we selected the Dingman method as a step in the comprehensive treatment of a patient with skeletal mandibular prognathism and excessive overjet. Surgery was performed safely and accurately via an intraoral approach with the assistance of a surgical guide prepared after preoperative computerized surgical simulation.

Acknowledgments

None.

Footnote

Funding: This study was supported by Tokyo Dental College, Well-being Project.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1348/coif). K.S. reports this study was supported by Tokyo Dental College, Well-being Project. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures were in accordance with institutional and national research committee standards and the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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