COMPARISON OF DIFFERENT MAXILLARY ADVANCEMENT PROTOCOLS IN PATIENTS WITH UNILATERAL CLEFT LIP AND PALATE: A FINITE ELEMENT ANALYSIS

doi:10.21203/rs.3.rs-3328860/v1

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Research Article

COMPARISON OF DIFFERENT MAXILLARY ADVANCEMENT PROTOCOLS IN PATIENTS WITH UNILATERAL CLEFT LIP AND PALATE: A FINITE ELEMENT ANALYSIS

https://doi.org/10.21203/rs.3.rs-3328860/v1

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published 20 Apr, 2024

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Objectives

The aim of this study was to evaluate the stress distributions and possible amount of movement in the maxillofacial region resulted from different maxillary advancement protocols in patients with unilateral cleft lip and palate.

Material and Methods

A model with unilateral cleft lip and palate (CLP model) was created for finite element analysis. Three different protocols were compared: (1) usage of a face mask with elastics over a conventional acrylic plate; (2) usage of a face mask with elastics over miniplates placed in the infrazygomatic crest region; (3) usage of elastic from the menton plate placed in the mandible to the infrazygomatic plates in the maxilla.

Results

Dental effects were greater in the protocol with a face mask over a conventional acrylic plate, whereas skeletal effects were greater in maxillary protraction protocols using skeletal anchorage. The maximum amount of counterclockwise rotation of the maxilla was observed in traditional acrylic plate face mask protocol.

Conclusions

Skeletally anchored face mask caused more skeletal impact and displacement than other models. Clockwise rotation of the mandible was observed in the face mask model, while counterclockwise rotation was observed in the model with infrazygomatic plates and menton plate.

Clinical relevance:

When planning maxillary protraction treatment in patients with cleft lip and palate, it should be considered that more movement in the sagittal plane might be expected on the cleft side than the non-cleft side, and miniplate and screws on the cleft side are exposed to more stress when using infrazygomatic plates as skeletal anchorage.

Facemask

Finite element analysis

Maxillary advancement

Unilateral cleft lip and palate

In individuals with complete cleft lip and palate, maxillary growth is often compromised by the restrictive forces resulting from the lip and palate repair [1]. As a result, individuals with cleft lip and palate often show a Class III skeletal pattern associated with anterior crossbite. Over the years, the most common treatment for mild maxillary retrusion in individuals with complete cleft lip and palate has been the usage of face mask for maxillary protraction [2]. Although favorable changes has been reported with face mask treatment, limited orthopedic effects can be achieved according to the severity of maxillary retrusion in individuals with unilateral cleft lip and palate [3, 4]. In addition, it may cause side effects such as molar mesialisation and maxillary incisor proclination in the maxillary dental arch [5]. Therefore, the most accepted treatment protocol for moderate or severe maxillary retrusion is maxillary advancement with orthognathic surgery at the end of the growth period [6]. The disadvantage of this protocol is that patients with unilateral cleft lip and palate, who usually exhibit facial dysmorphology, spend their childhood and adolescence without treatment [7].

Some studies have reported that the usage of modified surgical miniplates for skeletal anchorage with face mask treatment maximizes the orthopedic effects [8–10]. More recently, De Clerk et al. [11] and Nguyen et al. [12] introduced the Bone Anchored Maxillary Protraction (BAMP) protocol, which involves the placement of modified surgical miniplates in both maxilla and mandible, and usage of class III intermaxillary elastics over these plates. In this protocol, it was argued that pure bone-anchored orthopedic forces applied with intermaxillary elastics over miniplates can increase midfacial growth of patients with maxillary retrusion and prevent unwanted vertical growth in the lower facial region, unlike the traditional face mask protocol applied over the acrylic plate.

Mars et al. [13] published a simple method for scoring treatment outcomes in patients with unilateral cleft lip and palate called the GOSLON (Great Ormond Street, London and Oslo) criterion in which the possible treatment outcomes are displayed on models and scored by experienced assessors. According to this criterion, cases with a Goslon score of 4 are at the limit that can be treated orthopedically to correct the skeletal disorder; however, orthognathic surgical treatment might be required in adulthood if facial growth is not appropriate or if early treatment cannot be performed successfully. There is lack of knowledge in the literature on the effects of traditional and skeletal maxillary advancement protocols in unilateral cleft lip and palate patients with Goslon score 4. There are limited number of finite element method studies on maxillary advancement treatment of children with cleft lip and palate, in which Goslon scores had not been mentioned [14–16]. Besides, to the best of our knowledge, no study has compared different protraction methods in cleft lip and palate patients.

The aim of this study was to evaluate the stress distributions and the amount of possible movement in the maxillofacial region caused by different maxillary advancement protocols in patients with unilateral cleft lip and palate using finite element analysis.

Institutional Review Board (IRB) of the XXX reviewed the study protocol and granted ethical approval (XXX). A cone-beam computed tomography image of an 11-year-old patient with unilateral cleft lip and palate was used for the creation of the skull model used in the study. The arrangement of the three-dimensional network structure and its transformation into a mathematically appropriate solid network structure, the creation of three-dimensional finite element analysis models and the finite element analysis process were carried out on HP workstations with INTEL Xeon E-2286 processors with a clock speed of 2.40 GHz and 64 GB ECC memory.

The .stl model was obtained from the tomography data using 3DSlicer software. Reverse engineering and three-dimensional CAD activities were carried out with ANSYS Spaceclaim software, solid models were made suitable for the analysis environment, and optimized mesh generation activities were performed with ANSYS Workbench software; LS-DYNA solver was used for the solution of the finite element models created.

The trabecular bone was obtained by taking the inner surface of the three-dimensional mandibular cortical bone with adjusted thickness as reference. Periodontal ligaments in appropriate thickness were modelled with reference to the outer surface of the teeth. Sutures were created by performing "boolean" operation between the bone segments with contact surfaces. The acrylic plate, infrazygomatic plate, face mask, menton plate and miniscrews were modelled in ANSYS Spaceclaim software based on the dimensions in the product catalogue (Fig. 1). In BAMP protocol, three titanium miniplates of 1.2 mm profile thickness were used. They were placed in the infrazygomatic crest region of the maxilla bilaterally and mandibular anterior region, and these plates were secured with 3 titanium miniscrews of 5 mm length and 2.3 mm diameter.

The acrylic plate was placed in each model to open the occlusion. Similar to the clinical conditions, acrylic parts were connected to each other with 0.043 inch stainless steel wire passing through the palatinal region (Fig. 1).

All prepared models were placed in the correct coordinates in 3D space in ANSYS Spaceclaim software and the modelling process was completed. The material properties given as elastic modulus and Poisson's ratio were defined numerically (Table 1).

Table 1

Material properties of the analysed model
	Elastic Modulus [MPa]	Poisson's Ratio
Cortical Bone	13700	0.30
Trabecular Bone	1370	0.30
Tooth	20700	0.30
Periodontal Ligament	500	0.49
Suture	10	0.49
Titanium Alloy	114000	0.3
Stainless Steel	193000	0.3
Acrylic	15	0.35

Three different mechanics were compared in the unilateral cleft lip palate model (CLP model). The first mechanic was usage of a face mask with elastics placed at a 30° angle to the occlusal plane from a conventional acrylic plate. The second mechanic was usage of a face mask with elastics placed at a 30° angle to the occlusal plane from miniplates placed in the infrazygomatic crest area. The third mechanic was usage of elastics from the menton plate placed in the mandible to the infrazygomatic plates in the maxilla (Fig. 2).

When the infrazygomatic plates and menton plates are placed in the most appropriate anatomical regions, the angle of the applied elastics was calculated as 40°.

In face mask over acrylic plate model and face mask over infrazygomatic plates model, the elastic forces were applied 500 grams per side. In the model of the elastic use over infrazygomatic and menton plates, the elastik forces were applied 250 grams per side. The models were fixed at the nodal points in the foramen magnum region by restricting all degrees of freedom to prevent movement in all three axes. A total of 3 linear static analyses were performed for 3 models under the specified force and boundary conditions. The number of elements and nodes for different analysis models are given in Table 2.

Table 2

Number of elements and nodes for different models used in the study
	Total Number of Nodes	Total Number of Elements
Acrylic plaque + Face mask	2243550	10814380
Infrazygomatic plaque + Face mask	2245054	10826364
Infrazygomatic plaque + Menton plate	2183795	10516826

In order to be able to perform analyses and obtain accurate results in the mathematical models created, the surface relations of the parts forming the model with each other must be defined in the analysis program. For this purpose, in all study models, the connection of all parts with contact between them was defined as "bonded type contact". This approach is based on the assumption that the parts move with full correlation during movement. Since the values obtained are the result of mathematical calculations without variance, statistical analyses cannot be performed. The aim was to carefully analyze and interpret the obtained values and stress distributions.

The changes occurred in the maxillary protraction models with three different anchorage methods were evaluated using Von Misses stress and displacement values. Nasomaxillary complex and alveolar bone, cleft region, nasomaxillary suture, frontomaxillary suture, frontonasal suture, zygomaticomaxillary suture, zygomaticotemporal suture, zygomaticofrontal suture, maxillary dentition, infrazygomatic plates, menton plates, miniscrews and temporomandibular region were analyzed in this study.

When a face mask was used from the acrylic plate, the Von Misses stress was seen in the alveolar bone around teeth, the lateral walls of the alveolar processes, and the pterygomaxillary suture. When a face mask was used from infrazygomatic plates, stress was observed in the lateral area of the zygomatic process, the infrazygomatic region, and the pterygomaxillary suture. The intense stress seen around the infrazygomatic plates decreased gradually while showing a peripheral distribution. When the elastics were used between infrazygomatic plates and menton plate, the areas with the highest stress were the infrazygomatic area where the plates were applied, the lateral parts of the zygomatic bone and the lateral nasal walls. Tension forces decreased by distributing from these three areas to the surrounding structures (Fig. 3).

When the displacement values were analysed in the axial plane (X-axis), expansion was observed on the cleft side in the maxillary protraction model with face mask over acrylic plate, while contraction was observed on the cleft side in other models. On the other hand, in the maxillary protraction model with elastics between infrazygomatic plate and menton plate, narrowing was observed on the non-cleft side, while expansion was observed in the models using face mask. The highest displacement in the sagittal direction (Y-axis) was observed in the model planned for maxillary protraction with a face mask on infrazygomatic plates, especially more on the cleft side. On the cleft side, it is mostly observed in the alveolar bone and in the peripheral structures surrounding the maxillary posterior teeth and gradually decreases towards the lateral nasal walls. In all models, a higher amount of movement was observed in the sagittal plane on the cleft side compared to the non-cleft side. In the vertical direction (Z axis), the maximum displacement was observed as the movement of the anterior maxillary region to the superior direction in the model in which maxillary protraction was performed with a face mask over the infrazygomatic plates. The least movement in the vertical direction was observed in the maxillary protraction model protocol involving the use of elastics between infrazygomatic plates and menton plate (Fig. 4–6).

The maximum amount of counterclockwise rotation in the maxilla as a result of protraction was observed in the face mask model using acrylic plates and the minimum amount was observed in the model using elastics between infrazygomatic plates menton plate. As a result, a clockwise rotation of the mandible was observed in the face mask model, whereas a counterclockwise rotation was observed in the model using infrazygomatic and menton plate (Fig. 7).

The findings show that in all three models, tension forces occur in the area surrounding the maxillary posterior teeth and in the pterygomaxillary suture area, while compression forces occur in the lateral walls of the nasal region.

Regarding nasomaxillary suture, Von Misses stress was observed at a minimal level from superior to inferior of the left suture in all three groups. Forces in the form of pressure on the nasomaxillary suture were more intense. When the displacement values were analysed, a displacement to the superior direction and a compression to the posterior direction were observed in the models (Fig. 3).

Regarding frontonasal suture, frontomaxillary suture and zygomaticotemporal suture Von Misses strain showed homogeneous distribution in all three groups. When the displacement values were analysed, displacement in the superior direction was found in the models, while slight displacement was observed posteriorly (Fig. 3). Von Misses strain in the zygomaticomaxillary suture was observed most in the inferior part of the sutural area and least in the superior area in all three models. When the displacement values were analysed in the zygomaticomaxillary suture, an anterior movement was observed in all three groups in the models. When Von Misses values in the zygomaticofrontal suture are analysed, it starts intensely in the sutural area and decreases in the superior and inferior directions in all three groups. When the displacement values were analysed, minor displacement was observed in all groups (Fig. 3).

When the maxillary dentition was taken into consideration, in the maxillary protraction model with a face mask over a conventional acrylic plate, Von Misses stress was concentrated in the maxillary right first premolar and left deciduous first molar teeth, respectively. A decrease in stress was observed from the posterior region to the anterior region, and reached minimal values in the incisors. At the coronal level, stress was concentrated in the mesial region of the buccal cusps of the affected teeth. When the roots were analysed, more stress was observed in the buccal root than in the palatinal root. In the other two CLP models, since skeletal anchorage was used, the stress was homogeneously distributed with minimal values in the maxillary dentition. Looking at the displacement data in the maxillary protraction model with a face mask over a conventional acrylic plate, the crowns of the teeth in the incisor region were displaced labially, and the roots palatinally when examined in the sagittal direction. In the vertical plane, there was a displacement to the superior direction in the incisors, more in the teeth adjacent to the cleft line, while it decreased towards the posterior. A similar amount of anterior displacement was observed in all teeth, and on the basis of crowns and roots, it was observed that the crowns of all teeth were displaced more anteriorly than the roots. Minor movements were observed in the skeletally supported models (Fig. 8).

Regarding the force loading on the miniplates, the Von Misses stress continued to increase starting from the neck opening into the mouth to the level where the second miniscrew was applied. The area where the force was most concentrated was the miniplate section surrounding the inferior screw and the neck of the screw. The distribution of the force in the miniscrews was heterogeneous and when the Von Misses stresses were analyzed from the inferior to the superior screw, it was observed that the values gradually decreased. However, it was observed that the miniplate and screws on the cleft side were exposed to more stress. Similarly, the Von Misses stress was concentrated mostly around the first screws of the menton plates starting from the neck opening into the mouth (Figs. 9 and 10).

When the temporomandibular region is analysed, the compression stress force is highly effective in the glenoid fossa region in the face mask over acrylic plate and face mask over infrazygomatic plates models, while it is less effective in the maxillary protraction model involving the use of elastic over infrazygomatic plates and menton plate (Fig. 11).

Finite element analysis is a computer-aided simulation frequently used especially in engineering and health fields [17]. With these simulations, an infinite number of variables are transformed into a predictable finite number of elements. In this way, the data obtained can be converted into predictable results in terms of treatment mechanics [18]. Different methods such as modelling with medical images, anatomical modelling and segmentation have been proposed to obtain the finite element model to be analysed [17]. In the modelling method which is frequently used in medical images, the tissues such as bone and dental structures should be well-separated and their mechanical properties should be well-defined to the program; because when the effects of the force are examined in the software, the three-dimensional image will react according to the mechanical properties and boundary values [17].

In order to create the most accurate physical features of the patient, the image used in our study was created using cone beam computed tomography data of a patient with Class III skeletal malocclusion and cleft lip and palate. The properties of structures such as enamel, dentin, cementum and periodontal ligament were manually entered into the analysis, where the reference values were applied by taking into account the values defined in previous studies [19, 20].

The acrylic plate, infrazygomatic plate, face mask, menton plate and miniscrews used in our study were modelled in ANSYS Spaceclaim software based on the dimensions in the product catalogue. The acrylic plate connected with a 0.043-inch wire passing through the palatinal region was applied to open the occlusion in each model. Eman et al. [21], Yang et al. [17] and Zhang et al. [22] also used bite blocks to open the occlusion in order to correct the cross-closure in the incisor region in their studies. On the contrary, Parveen et al. [15] did not use any appliance to open the occlusion in their studies. Although acrylic plates are not used in all cases where skeletal anchorage is applied, acrylic plates can be inserted in order to control unwanted movements such as undesirable expansion that may be caused by the forces transmitted to the cleft fragment and to better control the movement of the alveolar bone on the cleft side.

When the literature on the forces applied for maxillary protraction in skeletal malocclusions with Class III maxillary retrusion is examined, it is seen that forces ranging from 150 grams to 1200 grams are applied [22–24]. In the studies conducted, an average force of 500 g was applied in the methods using face masks, while an average force of 150–200 g was applied in BAMP treatments. In this study, models with facemask therapy, the elastic forces were applied 500 grams per side. In the model of the elastic use over infrazygomatic and menton plates, the elastik forces were applied 250 grams per side.

Not only the amount but also the direction of the applied force is important. Parveen et al. [15] investigated the effects of face mask application with different force vectors (+ 20°, 0° and − 20°) relative to the occlusal plane on individuals with unilateral cleft lip and palate in a finite element analysis study. According to their study, it was found that more movement was obtained in all planes in patients with a face mask applied with + 20° (inferior to the occlusal plane) compared to the other group. Although there is no general consensus in the literature regarding the angle of force application during face mask use, it is generally preferred that the applied force should pass 20° to 30° below the occlusal plane [22, 25]. In this study, the direction of the elastic force was applied to pass 30° below the occlusal plane.

The highest Von Misses stress occurred in the alveolar bone adjacent to the teeth and in the lateral walls of the alveolar processes and pterygomaxillary suture as a result of the application of force with a face mask over the acrylic plate appliance. This result is thought to be due to the fact that some of the force applied in the traditional model is transmitted to the dentition through the acrylic appliance on the maxillary teeth. In the maxillary protraction model with a face mask over the infrazygomatic plates, the maximum stress occured in the lateral area of the zygomatic process of the maxillary bone, in the infrazygomatic region and in the pterygomaxillary suture. The stress, which were especially concentrated in the area where the plates were applied, gradually decreased while showing a peripheral distribution. In protraction models applied directly over the infrazygomatic crest, a slight tensile force was observed in the alveolar bone. Since the force was applied directly to the bone region in skeletally supported maxillary protraction models, it is an expected result that the stresses were concentrated in the zygomatic process region of the maxillary bone.

When the displacement values were analyzed, the highest displacement in the sagittal direction occurred in the part of the maxilla where the plates were applied and in the pterygomaxillary suture region in the skeletally supported protraction models, while in the maxillary protraction model with a face mask over acrylic plate the highest displacement was observed in the alveolar bone and surrounding structures surrounding the maxillary posterior teeth.

When the amount of displacement in the sagittal direction was compared, it was observed that the skeletal models showed an anterior displacement especially in the maxillary basal bone, while the maxillary protraction model with a face mask over acrylic plate showed an anterior displacement in the dentition. When the amount of displacement was evaluated, it was observed that there was more change in the maxillary protraction model with a face mask over infrazygomatic plates than in the maxillary protraction model with a face mask over an acrylic plate. It was found that the least amount of displacement occurred in the model with menton plate compared to the other models. This is thought to be due to the fact that the angle of application of the force from the elastic is different from the other two models. Kamath et al. [24] investigated maxillary protraction including the use of a face mask over the infrazygomatic crest and elastic over the infrazygomatic crest and menton plate in their bone-assisted maxillary protraction study. They concluded that the most sagittal movement in the maxilla was found in the face mask group over the infrazygomatic crest. In this respect, our findings are in agreement with the findings of Kamath et al. [24].

In this study, the data of a patient who had not undergone secondary alveolar bone grafting was used. In some studies facemask therapy performed after an alveolar bone graft produced more anterior maxillary migration and less pronounced mandibular clockwise rotation than those in the ungrafted group. They found that the alveolar bone graft seemed to play a crucial role to distribute the stress more evenly between the segments [14, 22].

In the vertical direction (Z-axis), the maximum displacement was observed as the movement of the premaxillary region to the superior direction in the model with maxillary protraction with a face mask over infrazygomatic plates. The least movement in the vertical direction was observed in the maxillary protraction model protocol involving the use of elastic over infrazygomatic plates and menton plate. In the study conducted by Kim et al. [26], maxillary protraction model with miniplates resulted in superior movement of the maxilla, comparable with our findings. Zhang et al. [22] performed maxillary protraction with a face mask in patients with cleft lip and palate and showed a superior movement in the anterior part of the maxilla, comparable with our study.

Although skeletally assisted maxillary protraction therapy with a face mask cannot completely prevent palatal rotation, it uses a downward and forward force. Jahanbin et al. [27] reported that a downward angle of more than 30° is needed to prevent counterclockwise rotation of the palatal plane in patients with cleft lip and palate. They stated that when intermaxillary elastics are used in the treatment of BAMP, counterclockwise rotation occurs with class III elastics. Yan et al. [28] evaluated the three-dimensional movement of the craniomaxillary complex during maxillary protraction with bone anchorage and dental anchorage by finite element analysis. In their study, the craniomaxillary complex in the dental anchorage model was displaced anteriorly with a counterclockwise rotation and the degree of rotation gradually decreased as the angle between the force vector and the occlusal plane increased between 0° and 30°. Also, in the bone anchorage model, the craniomaxillary complex was displaced anteriorly with counterclockwise rotation and the degree of rotation gradually decreased with increasing angle from 0° to 20°. However the nasomaxillary complex rotated posteriorly with clockwise rotation when a 30° force vector was used. Similarly, in our study, there were differences in terms of elastic application between the models using face masks and the model using intermaxillary elastics. While an angle of 30 degrees was applied in the models using a face mask, an angle of 40 degrees was applied in the model where elastic was applied through miniplates. These differences affected the movements occurring in the maxilla and the degree of rotation in the maxilla. According to our findings, there was a clockwise rotation in the mandible in the models using the face mask, while there was a counterclockwise rotation in the model using elastic over miniplates. Therefore, in cleft patients with skeletal Class III malocclusion and maxillary retrusion, lower anterior facial height can be controlled by changing the direction of the applied force, regardless of which anchorage is used.

The compressive stresses on the frontonasal, frontomaxillar and nasomaxillar sutures seem to occur as a result of the tendency for counterclockwise rotation of the nasomaxillary complex.

While the face mask over acrylic plate showed mostly dentoalveolar effect, orthopaedic effect was observed more in skeletal supported models. Especially in the zygomaticomaxillary, zygomaticotemporal and zygomaticofrontal sutures in the midface region, the stress distribution was more intense than in the tooth-supported model, and an anterior displacement was also observed. Therefore, better aesthetic results can be obtained in the mid-face region with skeletally supported models. These findings in our study are similar with the study of Yang et al. [14].

When the displacement values in the maxillary dentition were analysed, the findings of our study were associated with more skeletal movement in the skeletally supported maxillary advancement models and more dental movement in the acrylic plate over face mask model, comparable with the findings of Kamath et al. [24].

When the changes occurring in miniscrews with infrazygomatic plates and menton plate were analysed, it was shown that excessive force accumulation may occur in the fixation screws used in the fixation of mini plates, especially in the screw closest to the arm in which force was applied, and this may cause loss of the fixation screw. Another important consideration is the number of fixation screws used. In the study by De Clerk et al [29], it was emphasised that the number of screws applied to the maxilla should be at least three, and three fixation screws were used in this study. If two fixation screws are used, the distribution of the force between the screws will be more critical and this will affect the effectiveness of the treatment. Additionally, it was observed that the miniplates and screws on the cleft side were subjected to more stress. This finding indicates that the risk of loss of mini screws and mini plates in that area is higher. This finding is in agreement with Jahanbin et al. [27] and Kamath et al. [24]. Kamath et al. [24] stated that the success rate could be increased with minimally invasive surgery, full compliance with postoperative instructions and good follow-up by the orthodontist.

In the light of the findings in our study, it is seen that high compression stresses occur in the glenoid fossa in the models including face mask, while less stress occurs in the maxillary protraction model including the use of elastic over infrazygomatic plates and menton plate. Stress created in the temporamandibular joint area in the early period may trigger joint disorders in the future. Mathew et al. [30] showed that the stress in the glenoid fossa decreases with the increase in the angle of the force applied for maxillary protraction with the occlusal plane in their finite element stress analysis study, which supports the findings of our study.

Although the results obtained in this study provide information about the initial stress distribution and displacement pattern in the maxillary protraction of individuals with cleft lip and palate, the actual treatment outcome may be different because the soft tissue and post-surgical scar tissue in the lip and palate were not taken into account during modelling. Therefore, further studies are needed to investigate the effects of soft tissue and postoperative scar tissue on maxillary protraction in patients with cleft lip and palate.

In the maxillary protraction model with a face mask over a conventional acrylic plate, dental effects were found to be greater, while skeletal effects were found to be greater in other models.
More movement in the sagittal plane was observed on the cleft side than the non-cleft side in all three CLP models.
In individuals with unilateral cleft lip and palate with a Goslon score of 4, the maxilla protrudes in the sagittal direction in all 3 treatment methods. The most movement is seen in face mask treatment over infrazygomatic plates.
Clockwise rotation of the mandible was observed in the face mask model, while counterclockwise rotation was observed in the model with infrazygomatic plates and menton plate.
It was observed that the miniplates and screws on the cleft side were exposed to more stress. This finding indicates that the risk of loss of mini screws and mini plates in that region is higher.
As the angle of the force applied for maxillary protraction with the occlusal plane increases, the compressive stress in the glenoid fossa decreases.

BAMP

Bone anchored maxillary protraction

GOSLON

Great ormond street, london and oslo

Acknowledgements

Not applicable

Author contributions

GA contributed the conception and design of the study, acquisition, analysis and interpretation of data; HGC contributed to the conception and design of the study, interpretation of data, and writing of the final version of the manuscript. All authors read and approved the final manuscript.

Funding

This study was granted by a scientific research project, supported by XXX University.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Institutional Review Board (IRB) of the XXX University reviewed the study protocol and granted ethical approval (IRB No: XXX).

Consent for publication

The content of the manuscript has not been published or submitted for publication elsewhere. Consent was obtained from the patient and parents.

Competing interests

The authors declare that they have no competing interests.

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No competing interests reported.

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COMPARISON OF DIFFERENT MAXILLARY ADVANCEMENT PROTOCOLS IN PATIENTS WITH UNILATERAL CLEFT LIP AND PALATE: A FINITE ELEMENT ANALYSIS

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