A study of holographic interferometry on the initial reaction of maxillofacial complex during protraction

Three-dimensional zygomatic changes after rapid maxillary expansion in growing patients

PURPOSE

To assess the effects of rapid maxillary expansion (RME) treatment on the zygomatic bone complex (ZBC).

METHODS

In this single-center retrospective study, pre- and posttreatment cone-beam computed tomography (CBCT) images of 38 patients treated with RME were analyzed to investigate changes in the coordinates of the ZBC landmarks. At the start of treatment (T0), the patients' mean age was 11.1 ± 3.8 years (range 8.3-14.9 years). Cohen's d test was used to evaluate statistical differences.

RESULTS

There were statistically significant differences between T0 and T1 (P < 0.01) in the measurement values for the maxillary transverse width (ΔT: 3.18 ± 2.58, d: 1.23), frontozygomatic sutures (ΔT: 1.09 ± 0.56, d: 0.43), lowest point of the zygomaticomaxillary sutures (ΔT: 3.16 ± 1.78, d: 0.78), frontomaxillary angular parameter (right side ΔT: 2.81 ± 1.63, d: 1.73; left side ΔT: 2.52 ± 1.20, d: 2.10), frontozygomatic angular parameter (right side ΔT: 2.81 ± 1.63 d: 1.07; left side ΔT: 2.21 ± 2.79, d: 0.61), anterior intermaxillary distance (ΔT: 2.11 ± 1.42, d: 0.99), interzygomaticotemporal distance (ΔT: 2.00 ± 2.42, d: 0.99), and zygomatic angular parameter (right side ΔT: 2.06 ± 1.29, d: 1.6; left side ΔT: 2.02 ± 1.86, d: 1.09).

CONCLUSIONS

After RME in growing patients, the zygomatic bone showed pyramidal expansion in the coronal plane and parallel palatal expansion in the axial plane. In addition, significant lateral relocation of the zygomatic bone occurred. The zygomatic bone tended to rotate outward in conjunction with the maxilla, with a typical center of rotation close to the superior side of the frontozygomatic suture. These results shed light on the patterns of skeletal expansion in the zygomatic bone associated with RME in growing patients.

A New Methodology for the Digital Planning of Micro-Implant-Supported Maxillary Skeletal Expansion

INTRODUCTION

Miniscrew-assisted rapid palatal expansion (MARPE) appliances utilize the skeletal anchorage to expand the maxilla. One type of MARPE device is the Maxillary Skeletal Expander (MSE), which presents four micro-implants with bicortical engagement of the palatal vault and nasal floor. MSE positioning is traditionally planned using dental stone models and 2D headfilms. This approach presents some critical issues, such as the inability to identify the MSE position relative to skeletal structures, and the potential risk of damaging anatomical structures.

METHODS

A novel methodology has been developed to plan MSE position using the digital model of dental arches and cone-beam computed tomography (CBCT). A virtual model of MSE appliance with the four micro-implants was created. After virtual planning, a positioning guide is virtually designed, 3D printed, and utilized to model and weld the MSE supporting arms to the molar bands. The expansion device is then cemented in the patient oral cavity and micro-implants inserted. A clinical case of a 12.9-year-old female patient presenting a Class III malocclusion with transverse and sagittal maxillary deficiency is reported.

RESULTS

The midpalatal suture was opened with a split of 3.06 mm and 2.8 mm at the anterior and posterior nasal spine, respectively. After facemask therapy, the sagittal skeletal relationship was improved, as shown by the increase in ANB, A-Na perpendicular and Wits cephalometric parameters, and the mandibular plane rotated 1.6° clockwise.

CONCLUSION

The proposed digital methodology represents an advancement in the planning of MSE positioning, compared to the traditional approach. By evaluating the bone morphology of the palate and midface on patient CBCT, the placement of MSE is improved regarding the biomechanics of maxillary expansion and the bone thickness at micro-implants insertion sites. In the present case report, the digital planning was associated with a positive outcome of maxillary expansion and protraction in safety conditions.

Three-dimensional changes of the zygomaticomaxillary complex after mini-implant assisted rapid maxillary expansion

INTRODUCTION

The aim of this study was to investigate 3-dimensional changes of the zygomaticomaxillary complex (ZMC) after mini-implant assisted rapid maxillary expansion (MARME).

METHODS

A total of 15 pairs of cone-beam computed tomography 3-dimensional images taken before expansion (T0) and after expansion (T1) were analyzed by measuring changes in the coordinates of the landmarks of the ZMC.

RESULTS

Changes in the x coordinates of the landmarks showed significant expansion (P <0.01) and greater expansion at the lower than upper portion of the ZMC (P <0.05) in the transverse dimension. All y coordinates of the landmarks except the jugal point (J) showed forward displacement (P <0.05), and the z coordinates of ANS, PNS, Alare, A, and ectocanine showed downward displacement (P <0.01) in the sagittal and vertical dimensions. Also, z coordinates of the landmarks that were closer to the midsagittal plane and in a more posterior portion of the ZMC displaced further downward (P <0.05). SNA and ANB angles increased (P <0.05 and P <0.001, respectively) and the SNB angle decreased (P <0.01). There was a significant correlation between changes in the x coordinates of the ectomolare and ectocanine and the amount of expansion measured from the center of resistance of the maxillary first molars (CR6; P <0.05). There was no significant correlation between the amount of CR6 expansion and changes in y and z coordinates of the landmarks.

CONCLUSIONS

3-Dimensional changes of the ZMC after MARME showed expansion in a pyramidal shape from the coronal view, downward and forward displacement from the sagittal view, and parallel palatal expansion from the axial view. These findings might be useful for understanding skeletal expansion patterns using MARME.

Deformation of the zygomaticomaxillary and nasofrontal sutures during bone-anchored maxillary protraction and reverse-pull headgear treatments: An ex-vivo study

INTRODUCTION

Bone-anchored maxillary protraction (BAMP) is an emerging treatment that involves applying a protraction load to the maxillary bone. Although it is believed that such an approach results in better sutural separation, this has not been investigated. This study aimed to assess and compare the deformation of 1 circumaxillary suture (zygomaticomaxillary suture [ZMS]) and 1 facial suture (nasofrontal suture [NFS]) during BAMP and reverse-pull headgear (RPHG) treatment.

METHODS

The study was performed ex vivo on 15 pig heads. Miniplates were placed in the maxillary bone and the body of the mandible. A molar tube was bonded to the maxillary first molars. Six single-element strain gauges and 3 differential variable reluctance transducers were installed across the ZMS and NFS bilaterally. Each head underwent BAMP and RPHG unilaterally and bilaterally.

RESULTS

In unilateral experiments, both BAMP and RPHG resulted in tension on the ipsilateral ZMS and NFS and compression on the contralateral side, with higher magnitude in the BAMP group. In bilateral experiments, both modalities resulted in tension at the ZMS, with higher magnitude in the BAMP group. Deformation of the NFS was different between the 2 groups: tension in majority of the BAMP and compression in most of the RPHG heads.

CONCLUSIONS

Our study shows a higher magnitude of sutural separation in BAMP than in RPHG. The pattern of sutural deformation is consistent with a forward displacement of the midface in BAMP compared with an upward and backward rotation in the RPHG. Rotation of the maxilla was also present in some of the subjects who underwent BAMP.

Effect of Long-Term Use of Facemask With Miniplate on Maxillary Protraction in Patients With Cleft Lip and Palate

The purpose of this retrospective study was to investigate the effect of a long-term use of facemask with miniplate (FM-MP) on maxillary protraction in cleft lip and palate (CLP) patients. The subjects were 21 CLP patients (16 unilateral CLP and 5 bilateral CLP patients), who were treated with identical lip and palate surgical method and FM-MP therapy performed by single surgeon and single orthodontist. Lateral cephalogram was taken before (T1; mean age, 11.1 years) and after maxillary protraction (T2; mean age, 16.9 years). The mean duration of FM-MP was 68.0 months. After 17 cephalometric variables were measured, statistical analysis was performed. During T1-T2, the maxilla showed significant forward movement (ΔA-vertical reference plane, 4.8 mm, P < 0.001; ΔSNA, 1.9 degree, P < 0.001; ΔA-N perp, 1.9 mm, P < 0.05), although the mandible exhibited a forward growth (ΔSNB, 1.2 degree, P < 0.05). Despite downward movement of the posterior maxilla with counterclockwise rotation (Δpalatal plane angle, -1.5 degree, P < 0.05), the mandible did not exhibit clockwise rotation but counterclockwise rotation (ΔSN to mandibular plane angle, -1.4 degree, ΔBjork sum, -1.4 degree, Δocclusal plane to SN plane angle, -1.5 degree, ΔFMA, -1.0 degree, all P < 0.05) and showed decrease in Gonial angle (-1.2 degree, P < 0.01). Although there was labioversion of the maxillary incisor (ΔU1 to SN, 4.1 degree, P < 0.05), the mandibular incisor did not exhibit significant linguoversion (ΔIMPA, -1.3 degree, P > 0.05). Long-term use of FM-MP is effective on maxillary protraction in adolescent CLP patients without clockwise rotation of the mandible, the main drawback of conventional facemask with tooth-borne anchorage.

Effect of maxillary protraction with alternating rapid palatal expansion and constriction vs expansion alone in maxillary retrusive patients: a single-center, randomized controlled trial

INTRODUCTION

The objective of this randomized controlled trial was to investigate the effects of facemask protraction combined with alternating rapid palatal expansion and constriction (RPE/C) vs rapid palatal expansion (RPE) alone in the early treatment of maxillary retrusive patients.

METHODS

Patients with a midface deficiency were recruited and randomly allocated into either the control group (RPE) or the intervention group (RPE/C). Eligibility criteria included the following: age 7 to 13 years old, Class III malocclusion, anterior crossbite, ANB less than 0°, Wits appraisal less than -2 mm, A-Np less than 0 mm, and no cleft of lip or palate. The primary outcome was the degree of maxillary forward movement after treatment. The secondary outcomes were the changes of the other cephalometric variables after treatment and the treatment time. Simple randomization was carried out using a random number table at the beginning of the study. Envelopes containing the grouping information were used to ensure allocation concealment from the researchers. Blinding was applicable for cephalometric analysis only. Hyrax palatal expanders and facemask maxillary protraction were used in all patients. Patients in the RPE group were treated with rapid palatal expansion for 1 week. Patients in the RPE/C group were treated with RPE/C for 7 weeks. The expansion or constriction rate was 1 mm per day. Cephalometric analysis with traditional cephalometric measurements and an x-y coordinate system were used to compare the pretreatment and posttreatment cephalometric radiographs. Independent t tests were used to compare the data between the 2 groups.

RESULTS

A total of 44 patients were randomized to either the RPE group or the RPE/C group in a 1:1 ratio. One subject in the RPE group was lost to follow-up during the treatment. Per-protocol analysis was used. All the other 43 patients reached the treatment completion criteria and were analyzed (RPE group: n = 21; RPE/C group: n = 22). The average protraction time was 10.84 months in the RPE group, which was significantly longer than that in the RPE/C group (9.06 months) (effect size [ES], 1.78 [95% CI, 0.15, 3.42; P = 0.033]). Maxillary forward movement increased by 3.04 mm in the RPE/C group, which was significantly greater than that in the RPE group (2.11 mm) (ES, -0.93 [95% CI, -1.65, -0.20; P = 0.013]). The counterclockwise rotation of the palatal plane was 1.73° in the RPE/C group, which was significantly greater than that in the RPE group (0.83°) (ES, 0.90 [95% CI, 0.08, 1.73; P = 0.033]). The degree of mandibular downward and backward rotation was significantly smaller in the RPE/C group (P <0.05). No serious harm was observed during treatment and research.

CONCLUSIONS

Facemask maxillary protraction with RPE/C might positively affect the forward movement of the maxilla compared with facemask protraction with RPE alone in the early treatment of maxillary retrusive patients. Although the differences between the groups were statistically significant for forward movement of the maxilla and rotation of the palatal and mandibular planes, these may not be clinically relevant, since the differences were less than 1 mm and 1°, respectively.

REGISTRATION

This trial was not registered.

PROTOCOL

The protocol was not published before trial commencement.

FUNDING

This research was supported by Peking University Research Fund. No conflict of interest is declared.

An alternative clinical approach to achieve greater anterior than posterior maxillary expansion in cleft lip and palate patients

Cleft lip and palate patients commonly present maxillary constriction, particularly in the anterior region. The aim of this case report was to describe an alternative clinical approach that used a smaller Hyrax screw unconventionally positioned to achieve greater anterior than posterior expansion in patients with complete unilateral cleft lip and palate. The idea presented here is to take advantage of a reduced dimension screw to position it anteriorly. When only anterior expansion was needed (patient 1), the appliance was soldered to the first premolar bands and associated to a transpalatal arch cemented to the first molars. However, when overall expansion was required (patient 2), the screw was positioned anteriorly, but soldered to the first molar bands. Intercanine, premolar, and first molar widths were measured on dental casts with a digital caliper. Pre-expansion and postexpansion radiographs and tomographies were also evaluated. A significant anterior expansion and no intermolar width increase were registered in the first patient. Although patient 2 also presented a greater anterior than posterior expansion, a noteworthy expansion occurred at the molar region. The alternative approach to expand the maxilla in cleft patients reported here caused greater anterior than posterior expansion when the Mini-Hyrax was associated to a transpalatal arch, and its reduced dimension also minimized discomfort and facilitated hygiene.

An Analysis of the Stress Induced in the Periodontal Ligament during Extrusion and Rotation Movements: A Finite Element Method Linear Study Part I

BACKGROUND

Orthodontic tooth movement occurs due to various biomechanical changes in the periodontium. Forces within the optimal range yield maximum tooth movement with minimum deleterious effects. Among various types of tooth movements, extrusion and rotational movements are seen to be associated with the least amount of root resorption and have not been studied in detail. Therefore in this study, the stress patterns in the periodontal ligament (PDL) were evaluated with extrusion and rotational movements using the finite element method FEM.

MATERIALS AND METHODS

A three-dimensional (3D) FEM model of the maxillary incisors was generated using SOLIDWORKS modeling software. Stresses in the PDL were evaluated with extrusive and rotational movements by a 3D FEM using ANSYS software with linear material properties.

RESULTS

It was observed that with the application of extrusive load, the tensile stresses were seen at the apex, whereas the compressive stress was distributed at the cervical margin. With the application of rotational movements, maximum compressive stress was distributed at the apex and cervical third, whereas the tensile stress was distributed on cervical third of the PDL on the lingual surface.

CONCLUSION

For extrusive movements, stress values over the periodontal ligament was within the range of optimal stress value as proposed by Lee, with a given force system by Profitt as optimum forces for orthodontic tooth movement using linear properties. During rotation there are stresses concentrated at the apex, hence due to the concentration of the compressive forces at the apex a clinician must avoid placing heavy stresses during tooth movement.

The effects of micro-implant assisted rapid palatal expansion (MARPE) on the nasomaxillary complex--a finite element method (FEM) analysis

Background

Orthodontic palatal expansion appliances have been widely used with satisfactory and, most often, predictable clinical results. Recently, clinicians have successfully utilized micro-implants with palatal expander designs to work as anchors to the palate to achieve more efficient skeletal expansion and to decrease undesired dental effects. The purpose of the study was to use finite element method (FEM) to determine the stress distribution and displacement within the craniofacial complex when simulated conventional and micro-implant-assisted rapid palatal expansion (MARPE) expansion forces are applied to the maxilla. The simulated stress distribution produced within the palate and maxillary buttresses in addition to the displacement and rotation of the maxilla could then be analyzed to determine if micro-implants aid in skeletal expansion.

Methods

A three-dimensional (3D) mesh model of the cranium with associated maxillary sutures was developed using computed tomography (CT) images and Mimics modeling software. To compare transverse expansion stresses in rapid palatal expansion (RPE) and MARPE, expansion forces were distributed to differing points on the maxilla and evaluated with ANSYS simulation software.

Results

The stresses distributed from forces applied to the maxillary teeth are distributed mainly along the trajectories of the three maxillary buttresses. In comparison, the MARPE showed tension and compression directed to the palate, while showing less rotation, and tipping of the maxillary complex. In addition, the conventional hyrax displayed a rotation of the maxilla around the teeth as opposed to the midpalatal suture of the MARPE. This data suggests that the MARPE causes the maxilla to bend laterally, while preventing unwanted rotation of the complex.

Conclusions

In conclusion, the MARPE may be beneficial for hyperdivergent patients, or those that have already experienced closure of the midpalatal suture, who require palatal expansion and would worsen from buccal tipping of the teeth or maxillary complex.

Comparative evaluation of maxillary protraction with or without skeletal anchorage

INTRODUCTION

The aim of this prospective clinical study was to evaluate the skeletal, dentoalveolar, and soft-tissue effects of maxillary protraction with miniplates compared with conventional facemask therapy and an untreated Class III control group.

METHODS

Forty-five subjects who were in prepubertal or pubertal skeletal growth periods were included in the study and divided into 3 groups of 15 patients each. All subjects had skeletal and dental Class III malocclusions with maxillary deficiency, vertically normal growth pattern, anterior crossbite, Angle Class III molar relationship, normal or increased overbite, and retrusive nasomaxillary complex. Before maxillary protraction, rapid maxillary expansion with a bonded appliance was performed in both treatment groups. In the first group (MP+FM), consisting of 5 girls and 10 boys (mean age, 10.91 years), facemasks were applied from 2 titanium miniplates surgically placed laterally to the apertura piriformis regions of the maxilla. The second group (FM) of 7 girls and 8 boys (mean age, 10.31 years) received maxillary protraction therapy with conventional facemasks applied from hooks of the rapid maxillary expansion appliance. The third group of 8 girls and 7 boys (mean age, 10.05 years) was the untreated control group. Lateral cephalometric films were obtained at the beginning and end of treatment or observation in all groups and analyzed according to a structural superimposition method. Measurements were evaulated statistically with Wilcoxon and Kruskal-Wallis tests.

RESULTS

Treatment periods were 6.78 and 9.45 months in the MP+FM and FM groups, respectively, and the observation period in the control group was 7.59 months. The differences were significant between the 3 groups (P <0.05) and the MP+FM and FM groups (P <0.001). The maxilla moved forward for 2.3 mm in the MP+FM group and 1.83 mm in the FM group with maxillary protraction. The difference was significant between 2 groups (P <0.001). The protraction rates were 0.45 mm per month in the MP+FM group and 0.24 mm per month in the FM group (P <0.001). The maxilla showed anterior rotation after facemask therapy in the FM group (P <0.01); there was no significant rotation in the MP+FM group. Posterior rotation of the mandible and increased facial height were more evident in the FM group compared with the MP+FM group (P <0.01). Both the maxilla and the mandible moved forward significantly in the control group. Protrusion and mesialization of the maxillary teeth in the FM group were eliminated in the MP+FM group. The maxillomandibular relationships and the soft-tissue profile were improved remarkably in both treatment groups.

CONCLUSIONS

The undesired effects of conventional facemask therapy were reduced or eliminated with miniplate anchorage, and efficient maxillary protraction was achieved in a shorter treatment period.

Phase-shifting real-time holographic interferometry applied to load transmission evaluation in dried human skull

Phase-shifting real-time holography with photorefractive Bi(12)SiO(20) crystal as holographic recording medium applied to load transmission evaluation and tension dissipation on a dried human skull under loading is presented. The applied loading stands as a simulation of isolated contraction (SIC) of some masticatories muscles. The four-frames phase-shifting technique and the unwrapping branch-cut technique were used to obtain the phase map. The quantitative results show the feasibility of the employed system in the study of microdisplacements in the skull structure provided by SIC.

Pilot study evaluating the effects of a cervical headgear on the C-axis: the growth axis of the dentomaxillary complex

The C-axis, a growth vector for the dentomaxillary complex, is a means of quantifying complex maxillary growth in the sagittal plane through 3 key cephalometric measurements. This pilot study examined the effect of a cervical headgear, worn 8 to 10 hours per day, on the growth axis. The mean velocity of C-axis length increase in normally growing boys in the age range studied is 1.14 mm per year. In normally growing girls, the C-axis length increase is nonlinear, varying from a mean of 1.67 mm per year at age 9 and to 0.78 mm per year at 13.5 years of age. The cervical headgear reduced the C-axis length increases by 73.7% in boys and 61.1% in girls. The growth axis vector angle theta; was not clinically affected in either sex, but the palatal plane angle alpha became more acute in both sexes, rather than becoming more obtuse as it does in normally growing adolescents. Additional research should be undertaken to determine the effects on the C-axis by other cervical headgears having different lines of action relative to the center of resistance of the dentomaxillary complex, as well as occipital-pull and straight distal-pull headgear.

Extraoral appliances: a twenty-first century update

With the locations of the centers of resistance of the dentomaxillary complex having recently been defined, and with the newly acquired knowledge of the critical interplay between part-time extraoral and full-time intraoral force systems, the basic designs of all types of extraoral appliances are discussed in depth. Armed with this information, the clinician can improve the efficiency of all extraoral appliances to obtain better dentomaxillary-complex growth control and negate or enhance appliance-induced intraoral force systems.

Evaluation of the modified maxillary protractor applied to Class III malocclusion with retruded maxilla in early mixed dentition

The purpose of this study was to evaluate the effects of orthodontic treatment with a maxillary protraction bow appliance on anterior crossbite patients with Class III malocclusion in the mixed dentition. The 29 patients treated with a maxillary protraction bow appliance (11 boys, 18 girls) were compared with 25 matched, untreated controls with anterior crossbite (10 boys, 15 girls). The mean age before treatment was 8 years 7 months (range, 6 years 3 months to 11 years 6 months). The mean treatment period to achieve a normal overjet was 10.2 months (range, 5 to 18 months). Fifty-nine cephalometric angular and linear parameters were compared between the treated group and the untreated controls using the analysis of variance and the paired t test to evaluate the effect of gender and the maxillary protraction bow appliance treatment. Skeletal and dentoalveolar advancement of the maxilla and retrusion of the mandible contributed significantly to the improvement of Class III malocclusion in the treated group. These results suggest that a maxillary protraction bow appliance is effective for correcting anterior crossbite with a retruded maxilla in the early mixed dentition.

The biomechanics of rapid maxillary sutural expansion

Micro-displacements (fringe patterns) in the bones of the craniofacial complex as seen through laser holography during midpalatal sutural expansion with the Hyrax appliance are used to define the centers of rotation of the maxillary halves in both the frontal and occlusal views. Biomechanical analyses of the maxillary expansion force system are concomitant with the holographic findings and strongly suggest that the stainless steel wires joining the teeth to any expansion device be of the largest diameter possible. In addition, in the case of the Hyrax expansion device, it is recommended that the manufacturer increase the diameter of the activating screw as well as those of the 2 adjacent wire guides. And, importantly, the use of acrylic as a structural member to join the teeth to a sutural expansion device should be avoided if tipping of the maxillary halves is to be minimized, as the acrylic lacks sufficient rigidity.

The relationship of arch length to alterations in dental arch width

An accurate method is presented for forecasting alterations in arch length related to various width increases in each dental arch. It is based on combined beta and hyperbolic cosine functions which express the expanded dental arches with correlation coefficients of r = 0.98, between measured data and representations of the dental arch. When the midpalatal suture is expanded, canine width and molar width alterations are not equal because the line of action of the expanding force is anterior to the center of resistance of the dentomaxillary complex. Therefore, canine to molar width ratio alterations of 1:1, 1.25:1, and 1.5:1 are examined, and simple linear functions are presented for purposes of predicting changes in arch length.

The effects of a modified protraction headgear on maxilla

Protraction headgears are commonly used in the treatment of Class III malocclusion characterized by maxillary retrognathism. The upward and forward rotation of the maxilla during protraction is a major unwanted side effect. The aim of this study was to eliminate the upward and forward rotation of maxilla while protracting. Seventeen patients with Class III malocclusion as a result of maxillary retrognathism were treated for 3 months; their average age was 12.81 years. A full coverage acrylic cap splint-type rapid maxillary expansion appliance was cemented and activated twice a day for 5 days. After sutural separation, a maxillary modified protraction headgear was worn and 750 g of force was applied. Wilcoxon signed rank test was carried out to evaluate 42 parameters measured on cephalometric radiographs. The maxilla was displaced anteriorly by downward and backward rotation. The mandible was displaced downward and backward due to anterior elongation of the maxilla. Extrusion and lingual tipping of the upper incisors and intrusion of upper molars and downward and backward rotation of functional occlusal plane were observed. The aim of our study was achieved, which was to avoid upward and forward rotation while protracting the maxilla. In conclusion, maxillary modified protraction headgear (MMPH) can be used effectively in Class III patients with retrognathic maxilla and anterior open bite tendency.

Biomechanical considerations in distraction of the osteotomized dentomaxillary complex

The completely osteotomized dentomaxillary complex is essentially a free body constrained only by its soft tissue attachments. Therefore the line of action and point of application of any protractive force(s) used during distraction osteogenesis must be considered relative to its center of mass. This is in contrast to the nonsurgically separated dentomaxillary complex, which is a constrained body, and therefore the application of protractive force(s) must be considered relative to its center of resistance. These two centers are not coincident. With knowledge of the location of the center of mass, predictable protraction of the dentomaxillary complex can be achieved. In this study, the center of mass of an adult maxillary specimen osteotomized to emulate a Le Fort I osteotomy was determined. Protractive force(s) through the center of mass will produce linear advancement along its line of action. Protractive movement of the dentomaxillary complex can be adjusted downward and forward or upward and forward by locating the protractive force(s) line of action superior or inferior to the center of mass. A cleft patient is described wherein the surgically separated dentomaxillary complex is protracted downward and forward with a force vector superior to its approximate center of mass. This results in a predictable increase in overbite and overjet with negligible mandibular rotation.