Background
This study presents an assessment of the 3-dimensional (3D) morphologic and volumetric changes in the mandible and condyle after the use of a novel intraoral bone-anchored maxillary protraction (BAMP) device, specifically personalized with 3D-printed titanium plates, in adolescents with skeletal Class III malocclusion. Through the integration of a medical-industrial collaborative approach in the design and fabrication of patient-specific implants, the aim of this research is to establish an innovative treatment model that enhances the efficacy and precision of orthopedic interventions.
Methods
This retrospective cohort study included 33 patients aged 11-13 years who were divided into a treatment group (TG; n = 15) that received BAMP and an untreated control group (CG; n = 18). Pretreatment and posttreatment cone-beam computed tomography scans were analyzed via MIMICS software (Materialise, Leuven, Belgium: http://biomedical.materialise.com/mimics ) for 3D reconstruction and morphometric evaluation of the condylar volume, surface area, diameter, mandibular ramus dimensions, and axial angle.
Results
The TG exhibited a significant reduction in condylar anteroposterior diameter (0.16 ± 0.09 mm compared with 1.86 ± 1.05 mm in the CG; P = 0.001; 95% confidence interval [CI] = 0.1574-0.1654 mm) and a significant increase in condylar mediolateral diameter (2.02 ± 1.06 mm compared with 0.64 ± 1.08 mm in the CG; P = 0.001; 95% CI = 1.6214-2.7692 mm). The increase in condylar surface area in the TG was smaller than that in the CG (70.51 ± 88.30 mm 2 compared with 196.83 ± 259.50 mm 2 in the CG; P = 0.042; 95% CI =–390.2642 to 2937.8041 mm 2). In addition, there was a notable decrease in the mandibular axial angle within the TG (–3.61° ± 3.25° compared with 0.19° ± 1.84° in the CG; P = 0.001; 95% CI =–5.1079° to 0.1478°). No statistically significant differences were observed in the variations of condylar volume ( P = 0.182), condylar height ( P = 0.627), mandibular ramus volume ( P = 0.301), and mandibular ramus height ( P = 0.611).
Conclusions
BAMP facilitated the directional remodeling of condylar growth and mandibular morphology, promoting mediolateral expansion and counterclockwise rotation. These findings indicate the potential of BAMP to influence the progression of skeletal Class III malocclusion. However, several limitations exist: the technology is still in clinical trials, limiting its scope, sample size, and follow-up duration for assessing long-term outcomes. The impact on long-term mandibular growth is unclear. Larger studies with longer follow-ups and multicenter efforts are needed to determine BAMP’s long-term efficacy and clinical limitations.
Highlights
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A new 3D evaluation of mandibular and condylar changes using a custom 3D-printed titanium BAMP device in adolescents with skeletal Class III malocclusion presents an innovative personalized implant design, providing a precise method for managing complex skeletal malocclusions.
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The BAMP device may have the potential to regulate condylar growth, reducing anteroposterior expansion (0.16 vs 1.86 mm in controls) and enhancing mediolateral growth (2.02 vs 0.64 mm in controls).
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Counterclockwise mandibular rotation was observed, with the BAMP group showing a significant decrease in the mandibular axial angle (−3.61° vs 0.19° mm in controls), indicating a positive skeletal change tendency for patients with hyperdivergent Class III malocclusion.
Class III malocclusion is prevalent in orthodontic clinics, affecting 14.94% of Chinese children during primary dentition, 9.65% during mixed dentition, and 14.98% during early permanent dentition. It typically presents as maxillary retraction or mandibular protrusion. The condition often worsens over time, so early intervention is crucial to minimize the need for subsequent orthognathic surgery. , Maxillary protraction is a common treatment during tooth replacement, in which orthodontic appliances are used to stimulate forward maxillary development and improve the facial structure. During maxillary protraction, orthodontic forces are transmitted primarily to the maxilla by supporting teeth, leading to inevitable dental changes, such as inclination or movement of maxillary molars and crowding of anterior teeth. These changes, coupled with insufficient tooth replacement or eruption, can hinder the retention of orthodontic appliances, especially in patients with skeletal Class III malocclusion with multiple congenitally missing teeth, making traditional treatments challenging. Consequently, research has focused on minimizing these issues and enhancing maxillary growth by developing stable intraoral braces that directly target the maxilla.
Recent advancements in osteogenic anchorage have led to the development of a novel technique, known as bone-anchored maxillary protraction (BAMP), which uses bone as the primary support for traction in addressing dental issues. In a study by Liang et al, anterior osteogenic anchorage traction was compared with conventional dental anchorage in the maxillary canine region. The results indicated that osteogenic traction more effectively facilitated maxillary bone growth and advancement, while also mitigating the labial tilt of maxillary incisors, the lingual tilt of mandibular incisors, the elongation of maxillary first molars, and the rotational shifts of both maxillary and mandibular planes. Furthermore, Kim et al conducted a clinical trial with a limited sample size using a customized BAMP device. After a 2-year treatment period, the ANB angle improved from–4.56° to–1.09°, and the Wits appraisal angle improved from–7.52 to–3.26 mm. Indicators of both sagittal and vertical growth exhibited a trend toward normalization, with minimal discrepancies observed between the preoperative simulations and the actual surgical outcomes.
The aforementioned research indicates that BAMP can more effectively promote maxillary bone development while reducing adverse forces on the intraoral dentition. However, wearing a facial frame, which is esthetically unappealing, is necessary, and 25%-33% of patients experience recurrence during puberty, requiring some severe cases to undergo orthognathic surgery owing to continued mandible overgrowth. , Therefore, there remains a need to develop a more sophisticated intraoral bone anchorage device for anterior traction, that can apply sustained force to the maxilla to achieve long-term growth modification. This approach would enhance esthetic outcomes without compromising the patient’s social interactions. Research on personalized orthodontic devices and bone remodeling, which uses 3-dimensional (3D) printing and computer-aided design/computer-aided manufacturing technology, is on the rise. This growth, propelled by advancements in additive manufacturing and personalized treatment concepts, suggests that the production of more compact and sophisticated intraoral devices will soon overcome existing technical challenges.
Nonetheless, current research on the modifications of the mandible and condyle under BAMP is limited and remains a subject of debate. Huang et al conducted a review of the directional growth and morphologic alterations of the mandible after conventional anterior traction treatment. Their observations indicate that the counterforce exerted by the chin strap results in the superior and posterior migration of the mandibular condyle, whereas the mandible itself demonstrates a propensity for downward and clockwise rotation. Whether the effects of BAMP on mandibular growth and morphology differ from those of conventional anterior traction therapy warrants further investigation.
Cone-beam computed tomography (CBCT) has recently achieved widespread recognition for its use in the 3D evaluation of dental structures and their surrounding anatomic features. This imaging modality is considered particularly valuable for examination, diagnosis, treatment planning, and the assessment of clinical outcomes. This research project aims to investigate mandibular remodeling by employing an innovative intraoral bone anchorage device in patients with skeletal Class III malocclusion, using CBCT 3D reconstruction for analysis. Furthermore, in this study, customized 3D-printed titanium plates were developed through medical-industrial collaboration, with the objective of establishing a new treatment paradigm. The hypothesis of this study is that prolonged traction using personalized titanium plates can effectively facilitate mandibular growth remodeling.
Material and methods
Participants were recruited from the Department of Orthodontics at the Hospital of Stomatology, Hebei Medical University (ethics review number: [2023]0201), as well as from the Nankai University Stomatological Hospital (Tianjin Stomatological Hospital, ethics review number: PH 2024-Q-002). We defined the patient population, the interventions and comparators, the outcomes of clinical interest, and the design of the study ( Fig 1 ).
Flow chart of the study participant selection and grouping processes.
Participants were included in the study if they met the following criteria: (1) informed consent was obtained from the patients’s family; (2) aged 11-13 years; (3) presented with maxillary retraction and mandibular protrusion; (4) facial concavity; (5) cervical vertebral maturation stage 2 and 3; (6) ANB angle (the angle formed by A [subspinale], N [nasion], and B [supramental]) <0°; (7) anteroposterior dysplasia indicator (the angle formed by NP [nasion-pogonion]-FH [Frankfort horizontal plane], AB-NP, palatal plane [anterior nasal spine–posterior nasal spine]-FH) >86°; (8) in the intercuspal position, anterior crossbite could not be repositioned to align with the opposing teeth’s edges; (9) MP-SN angle (the angle formed by the mandibular plane [MP] and the anterior cranial base plane [sella-nasion, SN]) ≥37°; and (10) the chin did not exhibit significant tilt, with the horizontal linear deviation of the chin point from the median sagittal plane in the resting position measuring less than 2 mm.
The exclusion criteria for participants were as follows: (1) the presence of functional or dental anticuspation in which anterior teeth can be repositioned to the opposite edge; (2) known metal allergies; (3) the presence of mental illness that impairs self-care or cooperation with treatment; (4) the presence of systemic diseases, such as hematologic or cardiac conditions, that preclude tolerance of treatment; (5) a history of facial trauma; (6) previous orthodontic treatment; and (7) unilateral condylar hypertrophy, tumors, or genetic conditions that may lead to asymmetrical facial development.
After the application of the aforementioned screening criteria, a total of 33 patients were included in the study, as detailed in Table Ⅰ . Among these patients, 15 patients (comprising 9 males and 6 females) with skeletal Class III malocclusion composed the treatment group (TG) and underwent intervention via a personalized, 3D-printed titanium plate BAMP. The control group (CG) consisted of 18 patients (8 males and 10 females) with skeletal Class III malocclusion. These control participants were matched to the TG based on age, sex, and duration of observation.
Table I
Baseline for the TG and the CG
| TG | CG | P value | X 2 | ||
|---|---|---|---|---|---|
| T1 | Sex distributions (male/female), n (%) | 9 (60.00)/6 (40.00) | 8 (44.44)/10 (55.56) | 0.614 | 0.254 |
| Year | 11.91 ± 1.36 | 10.53 ± 1.85 | 0.121 | ||
| Growth stage | CVS Ⅱ-Ⅲ | CVS Ⅱ-Ⅲ | |||
| Dental stage | Mixed dentition or permanent dentition | Mixed dentition or permanent dentition | |||
| T1-T2 | Duration (y) | 3.00 ± 0.77 | 2.69 ± 0.60 | 0.497 | |
| T2 | Year | 14.91 ± 1.69 | 13.22 ± 2.36 | 0.137 | |
| Growth stage | CVS Ⅲ-Ⅴ | CVS Ⅲ-Ⅴ | |||
| Dental stage | Permanent dentition | Permanent dentition |
Note. P values were determined via an independent-samples t test.
Comprehensive informed consent was obtained from both the patients and their guardians. Preoperative CBCT scans (T1) were routinely acquired, and the resulting data were used to design and fabricate personalized titanium plates and surgical guides through 3D reconstruction technology. The tissue-facing surface of the personalized titanium plate was precisely contoured to match the bone surface at the implantation site, ensuring optimal stability. The titanium plate was implanted under local anesthesia, with the procedure guided by a surgical guide, and a retractor hook was positioned in the vestibule of the mouth. The mandibular titanium plate arm was bent at an angle of 120° in the posterior and superior directions. The maxillary titanium plate arm is designed with flexibility, allowing the final line of traction to pass 5-10 mm anteriorly and superiorly above the center of the condyle ( Fig 2 , A-D ). Intermandibular traction was applied between the ipsilateral maxillary and mandibular titanium plate hooks 2-3 weeks postoperatively, with a resting force of 250-350 g on each side, which was maintained for 22 hours per day ( Fig 2 , E-F ). During each follow-up appointment, force measurements were conducted using a spring dynamometer at centric occlusion. The dimensions and quantity of elastic bands were promptly adjusted to ensure that the forces remain within the appropriate range. Patients were instructed to document their daily rubber band usage on a designated chart, which was reviewed at each subsequent appointment. In instances in which the recorded wearing time was deemed insufficient, timely educational interventions were provided to the patient. Follow-up assessments were performed every 6 weeks throughout the treatment duration, during which the stability of the titanium plates and the condition of the surrounding mucosa were evaluated for any signs of loosening or abnormalities. During this period, each patient underwent maxillary arch width adjustment using bonded expanders until bilateral posterior coverage reached a minimum of 3 mm. Subsequently, fixed appliances were employed to achieve alignment of the entire dentition. Given the ongoing growth and development, no interceptive extractions were planned during this phase of treatment. Should phased extraction orthodontics become necessary, it will be discussed with the patient and their parents after the completion of this treatment phase and the study. Customized titanium plates served as temporary skeletal anchorage devices to facilitate tooth movement, highlighting a significant advantage of this innovative orthodontic system. Importantly, no additional implant-supported anchorage was required. Continuous intermaxillary traction was enabled by the titanium plates throughout the treatment period.
Customized titanium plate implantation surgery and intraoral and facial photographs: A, Right maxillary titanium plate implantation; B, Left maxillary titanium plate implantation; C, Right mandibular titanium plate implantation; D, Left mandibular titanium plate implantation; E, Intraoral photographs; F, Facial photographs.
The CG comprised patients who elected to postpone early orthodontic treatment because of personal considerations, such as academic or financial constraints, or health-related factors rendering titanium plate implantation surgery temporarily inadvisable. Comprehensive informed consent was obtained from both the patients and their guardians, addressing the potential risks associated with future orthognathic surgical interventions, and they agreed to participate in regular follow-up assessments. The observation period for the CG was defined as follows: it commenced when patients were temporarily unable to undergo early orthodontic treatment for the aforementioned reasons or when they voluntarily chose to defer treatment. The observation period concluded when patients met the criteria for treatment or consented to proceed with treatment.
Before the commencement of the observation period, a CBCT scan (T1) was performed for all patients. During the observation period, we conducted regular evaluations of each patient’s condition at follow-up appointments and provided them with information regarding the necessity of treatment. The observation period concluded when patients either met the criteria for treatment or provided informed consent to proceed with treatment. Patients and their guardians were given the option to choose between subsequent conventional adhesive anterior traction treatment and BAMP therapy. Baseline characteristics, including growth stage, chronological age, dental age, and severity of skeletal malocclusion, were consistently maintained across both the treatment and CGs, with no statistically significant differences observed. This consistency effectively minimized selection bias from both research and clinical perspectives. From a financial standpoint, our hospital offered appropriate fee reductions for patients experiencing economic hardship through supplementary policies and research funding. All patients and their guardians maintained accurate medical records and signed informed consent forms.
Outcomes
For patients who underwent BAMP, when an anterior tooth overbite exceeding 3 mm and a Class I molar relationship were observed during treatment, improvements in the concave profile were noted. Lateral cephalometric radiographs were obtained to assess the achievement of ANB and other sagittal skeletal relationship measurements approaching the Class I normal range. It is recommended to continue maintaining BAMP intermaxillary traction for an additional 3 months. Once complete dental alignment and a relatively stable occlusal relationship of the cuspids were achieved, a CBCT (T2) scan was conducted again. At the same time, this phase of treatment and research has been concluded. The orthodontic brackets were subsequently removed, and the retention phase commenced. The mean treatment interval between T1 and T2 was 3.00 ± 0.77 years.
In the CG, the observation period concluded once the patients’ oral conditions met the criteria for initiating treatment or when consent to commence treatment was obtained from the patients and their guardians. Afterward, a CBCT (T2) scan was conducted. The mean observation interval between T1 and T2 was 2.69 ± 0.60 years. Patients were then given the option to choose between conventional maxillary protraction therapy and BAMP therapy for their subsequent treatment.
A CBCT device (KaVo 3D eXam, Charlotte, NC) was employed using specific scanning parameters, which included a single 360° rotational scan as the projection angle, an energy setting of 120 kV, a current of 5 mA, a slice thickness of 0.3 mm, a scanning field measuring 17 × 23 cm, and a scanning duration of 17.8 seconds (zoom: 51.88%, window level: 1400, and window width: 5000). The field of view encompassed the region from the hairline to the soft tissue point below the chin. A mirror was positioned opposite the CBCT unit to facilitate proper alignment. Each patient was instructed to maintain a stable, natural head position while looking straight ahead during the CBCT imaging process.
The CBCT data were subsequently transformed into quantitative computed tomography (QCT) images, calibrated linearly based on Hounsfield Units (HU). This calibration used the CBCT images of a bone mineral density calibration phantom, employing the attenuation coefficient of the implanted titanium plate as a reference standard. The raw image data were processed using MIMICS (Materialise, Leuven, Belgium: http://biomedical.materialise.com/mimics ) to achieve 3D reconstruction of the dental and maxillary craniofacial structures. A comprehensive description of this procedure is provided in the subsequent section.
Each sample was standardized to a consistent head position for each scan: (1) the orbital-auricular plane, also known as the Frankfort horizontal plane, was defined by aligning the horizontal plane to pass through both bilateral external auditory canals (PoR and PoL) and the superior margin of the right infraorbital points (OrR); (2) the median sagittal plane was established perpendicular to the orbital-auricular plane, passing through the nasion point (N), the basion point (Ba), and the anterior nasal spine point (ANS); (3) the nasion-coronal plane was determined by passing through the nasion point and being perpendicular to the aforementioned 2 planes; and (4) the origin of the 3D coordinate system was set at the nasion point (N).
Using the patient’s CBCT 3D simulation, a virtual surgical plan was developed, accompanied by the design of customized titanium plates and surgical guides. This product employs metal powder 3D printing technology, ensuring that the chemical composition of the metal powder adheres to the specifications outlined in GB/T 13810-2017, the National Standard of the People’s Republic of China for processed materials of titanium and titanium alloys used in surgical implants. For comprehensive information on manufacturers and declarations of interest, kindly consult the Acknowledgments section. The titanium plate produced through additive manufacturing has been subjected to a series of biological evaluations, demonstrating exceptional biocompatibility.
The average thickness of the titanium plate was 0.9 ± 0.05 mm, with internal hole diameters ranging from 1.5 mm, a hole taper of 45°, and a variable number of holes ranging 2-6. In accordance with the design specifications, the implant nail (model: MA102Y1.5∗5) must be strategically positioned to circumvent critical anatomic structures, including the tooth root and maxillary sinus. The mandibular titanium plate is situated between the roots of the mandibular lateral incisors and mandibular canines. In contrast, the design of the maxillary titanium plate is more adaptable, with the fixed plate being partially located at the zygomatic alveolar ridge. Intermaxillary traction is applied between the traction hooks of the maxillary and mandibular titanium plates, with a plumb line for the extension of the traction force line positioned over the condylar centroid ( Fig 3 , A-D ). The distance between the condylar centroid and the plumbing foot ranged 5-10 mm ( Fig 3 , E ). The production of guide plates necessitates the incorporation of digital intraoral scanning technology to create dental models in the standard tessellation language format, using an intraoral scanner (iTero; Align Technology, Santa Clara, Calif). Patents have been granted for personalized titanium plates and guide plates. Comprehensive product specifications are available in the patent documents, identified by patent numbers ZL 2022 2 1205186.0 and ZL 2022 2 1715585.1.
Titanium plate design: A, Maxillary titanium plate; B, Mandibular titanium plate; C, Maxillary guide plate; D, Mandibular guide plate; E, Digital design and force vector geometry ( dashed line , the force extension lines for the traction of the maxillomandibular titanium plate).
The reconstructions were performed via QCT images, which were represented as 12-bit pixel maps, providing 4096 gray scale values per pixel to depict the x-ray attenuation coefficients of the tissues. Each mandibular CBCT dataset analyzed in this study comprised 400-500 slices, with an interslice spacing of 0.3 mm, resulting in a voxel volume of approximately 0.027 mm 3. These QCT images were subsequently imported into MIMICS (Materialise) for the initial creation of 3D geometries.
Within the MIMICS (Materialise) program, the images were initially scaled to the Hounsfield scale, with the attenuation coefficient of tissue fluid set to 0. The Hounsfield scale employs a minimum pixel value of–1024 to represent gas attenuation. Pixel values, estimated in HU, ranged 150-250 HU for the bone trabeculae and from 251-2100 HU for the bone cortex.
To maintain scientific rigor, consistent pixel thresholds ranging 226-2042 HU were applied during threshold segmentation of the dataset, and the reconstruction process used QCT data calibrated with the previously mentioned quantitative bone mineral density model, in conjunction with titanium plates of standardized density serving as reference points. This approach ensured consistent attenuation characteristics across all datasets, thereby maintaining uniformity in the final density representation of cortical bone within the mandible. As a result, the measured skeletal geometric volumes exhibited uniformity in surface depth, facilitating statistically valid comparative analysis. This process of image segmentation delineated a highlighted region, indicating the selected image. The bones within this region were subsequently reconstructed via threshold segmentation, and a 3D virtual model was generated.
This model was refined via established voxel-based MIMICS (Materialise) algorithmic techniques, in which a uniform depth of smoothing was applied to the skeletal surfaces reconstructed from each CBCT dataset. Redundant data at the sides and surrounding tissues on the x-, y-, and z-axes were removed.
The criteria for establishing the coordinate origin and reference plane for the reconstructed 3D mandible image are as previously outlined. The measurement marker points used in this process included the following ( Table Ⅱ ): (a) the point of the mandibular angle; (b) the medial turning point of the mandibular ascending ramus; (c) the lateral turning point of the mandibular ascending ramus; (d) the most concave point of the sigmoid notch; (e) the apex of the condyle; (f) the highest point of the ascending mandibular branch; (g) the most anterior point of the condylar process; (h) the most posterior point of the condylar process; (i) the lateral-most point of the condylar process; and (j) the medial-most point of the condylar process.
Table II
Measurement marker points and measurement items
| Marker points | Anatomic definition |
|---|---|
| a | The point of the mandibular angle |
| b | The medial turning point of the mandibular ascending ramus |
| c | The lateral turning point of the mandibular ascending ramus |
| d | The most concave point of the sigmoid notch |
| e | The apex of the condyle |
| f | The highest point of the ascending mandibular branch |
| g | The anterior-most point of the condylar process |
| h | The posterior-most point of the condylar process |
| i | The lateral-most point of the condylar process |
| j | The medial-most point of the condylar process |
| Items | |
| 1 | Condylar volume (mm 3) |
| 2 | Condylar surface area (mm 2) |
| 3 | Mandibular ramus volume (mm 3) |
| 4 | Mandibular ramus height (mm) |
| 5 | Condylar height (mm) |
| 6 | Mandibular axial angle (°) |
| 7 | Condylar mediolateral diameter (mm) |
| 8 | Condylar anteroposterior diameter (mm) |
The measurements included the following: (1) condylar volume (cubic millimeters); (2) condylar surface area (square millimeters); (3) mandibular ramus volume (cubic millimeters); (4) mandibular ramus height (millimeters); (5) condylar height (millimeters); (6) mandibular axial angle (°); (7) condylar mediolateral diameter (millimeters); and (8) condylar anteroposterior diameter (millimeters). Calculate the mean of the bilateral values for each CBCT to obtain the final result.
Segmentation planes and marker points of the mandible are shown in Figure 4 . Plane A is aligned parallel to the Frankfort horizontal plane and is positioned at point d. Plane B is defined by the intersection of 3 key landmarks: points a, b, and c. The mandible is segmented along these planes to separate the condylar and ascending mandibular portions from the mandibular body, as illustrated in Figure 4 . The condylar volume (1), mandibular ramus volume (3), and condylar surface area (2) were subsequently measured. Line A is constructed from point e to point a, intersecting plane A at point f. The segment from point f to point a represents the mandibular ramus height (4), whereas the segment from point e to point f represents the condylar height (5).
