How Symmetrical Are Bony Orbits in Humans?

PURPOSE: Establishing the symmetry of intraindividual orbital volumes is crucial for radiologic assessment, preoperative planning, and postoperative outcome evaluation. However, no reliable method exists to measure orbital volume because of problems in defining the bony boundaries of the orbit. Therefore, the purpose of this study was to propose a new approach to analyze human orbits and determine its application for quantifying bony symmetry in a cohort of patients. PATIENTS AND METHODS: Computed tomography scans of 93 patients were retrospectively collected from our institutional database. The intraindividual volume difference was quantified using a surface model derived from manual segmentations. The average shape of the orbit was calculated iteratively and nonrigidly registered to both orbits of all patients. After registration, the surface reconstructions of all orbits had an identical mesh topology and vertices at corresponding anatomic locations. The volume difference was calculated locally based on the relative position of the vertices at equivalent locations in the left orbit and right orbit. This approach was used to quantify the volume difference between the left and right orbits for all patients. Interobserver sensitivity was assessed in 5 randomly chosen patients and was measured independently by 3 specialists. RESULTS: An average difference of 600 ± 500 µL between the volumes of the left and right orbits was found, representing a difference of 2.1%. Although the difference in volume was small, the volumes were significantly different (P = .039). The largest asymmetries were found in the roof and floor area. CONCLUSIONS: The method proposed to measure the difference in volume between the left and right orbits is automated and does not rely on a closed orbital volume, which provides more objective volume measurements. With the help of modern computed tomography techniques and the coherent point drift method, it was possible to show that the intraindividual volume difference in the orbits is approximately 2%, not 7 to 8% as often cited in the literature.

What Is the Incidence of Implant Malpositioning and Revision Surgery After Orbital Repair?

PURPOSE: Postoperative radiographic examinations are the gold standard in maxillofacial surgery, except in orbital reconstruction. Therefore, the purpose of this study was to estimate the frequency of implant malposition and revision operation after orbital repair. MATERIALS AND METHODS: This retrospective cohort study was conducted in a level I trauma center at the University Hospital in Bern, Switzerland. To assess the incidence of malpositioning, a qualitative analysis of postoperative computed tomography scans, as well as comparative volumetric measurements of the orbits, was conducted. Furthermore, the incidence of and reason for secondary revision procedures were evaluated. RESULTS: From September 2008 to December 2015, a total of 71 emergency patients (73 implants) were treated at the Department of Cranio-Maxillofacial Surgery with a titanium mesh (48 male patients; mean age, 56 years). The implant position was rated as poor in 17 cases (23%) by the qualitative analysis. The volumetric assessment showed no significant results. Revision intervention was needed in 12 patients (17%) because of an unsuccessful treatment outcome causing relevant clinical symptoms. CONCLUSIONS: Patients with large orbital defects who require surgical treatment with a titanium mesh are at risk of implant malposition. Because in this study, poor positioning of the implant is the main reason for surgical revision, we postulate that a postoperative radiographic control should be obtained routinely. Only then can long-term sequelae due to inadequate reconstruction be avoided.

Clinical evaluation of the iterative metal artefact reduction algorithm for post-operative CT examination after maxillofacial surgery.

OBJECTIVES: Metal artefacts present challenges to both radiologists and clinicians during post-operative imaging. Such artefacts reduce the diagnostic effectiveness of CT scans and mask findings that could be vital for patient management. Thus, a powerful artefact reduction tool is necessary when imaging patients with metal implants. Our aim was to test the recently introduced iterative metal artefact reduction (iMAR) algorithm in patients with maxillofacial implants. METHODS: Images from 17 patients with diverse maxillofacial metal implants who had undergone CT scans were qualitatively and quantitatively analyzed before and after metal artefact reduction with iMAR. RESULTS: After iMAR application, images exhibited decreased artefacts and improved image quality, leading to detection of lesions that were previously masked by artefacts. The application of iMAR did not affect image quality in regions distant from the metal implants. CONCLUSIONS: The application of iMAR to CT examinations of patients with maxillofacial metal implants leads to artefact reduction, improvement of image quality and increased diagnostic utility. Routine implementation of iMAR during imaging of patients with metal hardware implants could add diagnostic value to their CT examinations.

Biomechanical evaluation of different angle-stable locking plate systems for mandibular surgery.

PURPOSE: To compare the initial stability and stability after fatigue of three different locking systems (Synthes(®), Stryker(®) and Medartis(®)) for mandibular fixation and reconstruction. METHOD: Standard mandible locking plates with identical profile height (1,5 mm), comparable length and screws with identical diameter (2,0 mm) were used. Plates were fixed with six screws according a preparation protocol. Four point bending tests were then performed using artificial bone material to compare their initial stability and failure limit under realistic loading conditions. Loading of the plates was performed using of a servo hydraulic driven testing machine. The stiffness of the implant/bone construct was calculated using a linear regression on the experimental data included in a range of applied moment between 2 Nm and 6 Nm. RESULTS: No statistical difference in the elastic stiffness was visible between the three types of plate. However, differences were observed between the systems concerning the maximal load supported. The Stryker and Synthes systems were able to support a significantly higher moment. CONCLUSION: For clinical application all systems show good and reliable results. Practical aspects such as handling, possible angulation of screw fixation, possibility of screw/plate removal, etc. may favour one or the other plating system.

The role of postoperative prophylactic antibiotics in the treatment of facial fractures: a randomised, double-blind, placebo-controlled pilot clinical study. Part 3: Le Fort and zygomatic fractures in 94 patients.

The aim of this study was to evaluate the difference between the effect of a 5-day and a 1-day postoperative course of antibiotics on the incidence of infection after midfacial fractures. A total of 98 patients with displaced Le Fort or zygomatic fractures that required operation were randomly assigned into 2 groups, both of which were given amoxicillin/clavulanic acid 1.2g intravenously every 8h from the time of admission until 24h postoperatively. The 5-day group was then given amoxicillin/clavulanic acid 625 mg orally 8-hourly for another 4 days. The 1-day group was given placebo orally at the same time points. Patients were followed up 1, 2, 4, 6, and 12 weeks, and 6 months, postoperatively. The development of an infection of the wound was the primary end point. Ninety-four of the 98 patients completed the study. Two of the 45 patients in the 5-day group (4%) and 2/49 in the 1-day group (4%) developed postoperative wound infections. One in each group had a purulent infection, while the others had only wound breakdown. Two patients of the 5-day group and one in the 1-day group developed rashes on the trunk. There were no significant differences in the incidence of infection or side effects between the groups. In midfacial fractures a 1-day course of antibiotics postoperatively is as effective in preventing infective complications as a 5-day regimen.

The role of postoperative prophylactic antibiotics in the treatment of facial fractures: a randomized, double-blind, placebo-controlled pilot clinical study. Part 2: Mandibular fractures in 59 patients.

The aim of this study was to evaluate the difference between a 5-day and a 1-day postoperative course of antibiotic on the incidence of infection after mandibular fractures involving the alveolus. Sixty-two patients with fractures of the mandible involving the dentoalveolar region were randomly assigned to 2 groups, both of which were given amoxicillin/clavulanic acid 1.2 g intravenously every 8 h from admission until 24 h postoperatively. The 5-day group were then given amoxicillin/clavulanic acid 625 mg orally every 8 h for another 4 days. The 1-day group was given an oral placebo at the same intervals. Follow-up appointments were 1, 2, 4, 6, 12 weeks and 6 months postoperatively. Development of an infection was the primary end point. Fifty-nine of the 62 patients completed this study. Six of the 30 patients in the 5-day group (20%) and 6 out of the 29 in the 1-day group (21%) developed local wound infections. Three of the 6 in the 1-day group developed purulent discharge and swelling. One patient in the 5-day group developed a rash on the trunk. There were no significant differences in the incidence of infection or side effects between the groups. In fractures of the mandible involving the alveolus, a 1-day postoperative course of antibiotic is as effective in preventing infective complications as a 5-day regimen.

The role of postoperative prophylactic antibiotics in the treatment of facial fractures: a randomised, double-blind, placebo-controlled pilot clinical study. Part 1: orbital fractures in 62 patients.

The aim of this study was to evaluate the difference between the effects of a 5-day and a 1-day course of antibiotics on the incidence of postoperative infection after displaced fractures of the orbit. A total of 62 patients with orbital blow-out fractures were randomly assigned to two groups, both of which were given amoxicillin/clavulanic acid 1.2g intravenously every 8h from the time of admission to 24h postoperatively. The 5-day group were then given amoxicillin/clavulanic acid 625 mg orally every 8h for 4 further days. The 1-day group were given placebo orally at the same time intervals. Follow up appointments were 1, 2, 4, 6, and 12 weeks, and 6 months, postoperatively. An infection in the orbital region was the primary end point. Sixty of the 62 patients completed the study. Two of the 29 patients in the 5-day group (6.8%) and 1/31 patients in the 1-day group (3.2%) developed local infections. In the 5-day group 1 patient developed diarrhoea. In the 1-day group 1 patient developed a rash on the trunk. There were no significant differences in the incidence of infection or side effects between the groups. We conclude that in displaced orbital fractures a postoperative 1-day course of antibiotics is as effective in preventing infective complications as a 5-day regimen.

Low-profile titanium mesh in the use of orbital reconstruction: A pilot study.

OBJECTIVES/HYPOTHESIS: The purpose of this study was to share our clinical experience in the use and accuracy of a newly designed, low-profile titanium mesh (Modus OPS 1.5; Medartis, Basel, Switzerland) for primary internal orbital reconstruction. STUDY DESIGN: Observational study. METHODS: This study was conducted at the Department of Cranio-Maxillofacial Surgery at the University Hospital of Bern, Switzerland, starting November 2008. Patients were included who had a defect size of ≥2 cm(2) or fractures of more than one wall. The operations were performed within 14 days after trauma. To repair the orbital fracture, a newly designed titanium mesh was applied. The technical innovation in regard to these plates is the low-profile height of 0.25 mm along the border and 0.2 mm in the mesh area. Two different sizes of two different types of mesh are available for reconstruction. Preoperative computed tomography (CT) scans were obtained to assess the fracture size and location. A maxillofacial surgeon performed pre- and postoperative assessments (at 2 weeks, 12 weeks, and 6 months). Ophthalmologic assessments were performed preoperatively and 6 months after the operation. Postoperative CT scans were obtained within 12 weeks after the operation and the orbital volumes analyzed by a radiologist. RESULTS: Twenty-seven patients underwent surgery (11 female; average age, 55.2 years). Final postoperative ophthalmologic follow-up was obtained at a mean of 8.8 months (range, 4.0-20.1 months). Twenty-five patients (93%) had a successful treatment outcome without complications. In two patients, the plate was buckled in the posterior edge region and had to be replaced. Surgical revision was performed within 3 weeks after the first procedure. These patients showed good clinical and radiologic outcome after the second procedure. At the final assessment, none of the patients had experienced diplopia. Three patients showed slight enophthalmos (2-mm side difference), however, without any subjective functional or aesthetic concerns. According to the literature, an average orbital volume difference of up to 1.95 cm(3) is normal. In our study, radiologic volume assessment showed a side difference of ≥2 cm(3) in four patients, of which one patient presented with a clinically detectable enophthalmos. CONCLUSIONS: The newly designed, thin titanium mesh is a reliable and safe implant for the repair of orbital defects. Owing to insufficient intraoperative control, two plates showed buckling at the posterior border, which made a repair necessary. Awareness of this problem may avoid such complications in the future. However, it would seem reasonable to improve the stability of the mesh by increasing the profile height, to minimize potential complications.

Incidence, aetiology and pattern of mandibular fractures in central Switzerland.

PURPOSE: The two major causative factors for mandibular fractures, as stated in the literature, are either interpersonal violence or motor vehicle accidents. The purpose of this study was to describe epidemiological trends of mandibular fractures in Switzerland. A special emphasis was directed towards the potential impact of socio-economic standards on the mechanism and pattern of mandible fractures. PATIENTS AND METHODS: A database of patients aged over 16 years who had been diagnosed with a mandibular fracture between January 2000 and December 2007 at the University Hospital of Bern, Switzerland's largest Cranio-Maxillofacial-Surgery Centre, was retrospectively reviewed. Patients' data including gender, age, mechanism of accident, fracture site and associated injuries were analysed and compared with previously published data. RESULTS: There were a total of 420 patients with 707 mandibular fractures. The two most common causes of injury were road traffic accidents (28%) and various types of sports injuries (21%). A total of 13% of the patients were under the influence of alcohol or drugs at admission. Fractures were predominantly situated in the condyle/subcondyle (43%) and in the symphysis/parasymphysis region (35%). Occurrences of fractures in the angle and in the body were low, at 12% and 7% respectively. CONCLUSION: In contrast to other highly developed countries, sports- and leisure-related accidents outnumbered motor vehicle accidents and altercations. The data presented here supports the assumption of a correlation of trauma cause and fracture pattern.

Osteoporosis and bisphosphonates-related osteonecrosis of the jaw: not just a sporadic coincidence--a multi-centre study.

INTRODUCTION: Bisphosphonates (BPs) are powerful drugs that inhibit bone metabolism. Adverse side effects are rare but potentially severe such as bisphosphonate-related osteonecrosis of the jaw (BRONJ). To date, research has primarily focused on the development and progression of BRONJ in cancer patients with bone metastasis, who have received high dosages of BPs intravenously. However, a potential dilemma may arise from a far larger cohort, namely the millions of osteoporosis patients on long-term oral BP therapy. PATIENTS AND METHODS: This current study assessed 470 cases of BRONJ diagnosed between 2004 and 2008 at eleven different European clinical centres and has resulted in the identification of a considerable cohort of osteoporosis patients suffering from BRONJ. Each patient was clinically examined and a detailed medical history was raised. RESULTS: In total, 37/470 cases (7.8%) were associated with oral BP therapy due to osteoporosis. The majority (57%) of affected individuals did not have any risk factors for BRONJ as defined by the American Association of Oral and Maxillofacial Surgery. The average duration of BP intake of patients without risk factors was longer and the respective patients were older compared to patients with risk factors, but no statistical significant difference was found. In 78% of patients the duration of oral BP therapy exceeded 3 years prior to BRONJ diagnosis. DISCUSSION: The results from this study suggest that the relative frequency of osteoporosis patients on oral BPs suffering from BRONJ is higher than previously reported. There is an urgent need to substantiate epidemiological characteristics of BRONJ in large cohorts of individuals.

Repair of orbital floor fractures using bioresorbable poly-L/DL-lactide plates.

OBJECTIVE: To assess the long-term clinical and radiologic findings after insertion of a bioresorbable polylactide plates P(L/DL)LA 70/30 implant (PolyMax) in the repair of orbital floor and wall defects, with special focus on stability and clinical signs of foreign-body reaction. METHODS: Forty-six patients who had orbital blowout fractures with at least 1.5-cm(2) bone defects in 1 or 2 walls were included in this retrospective study. Each defect was reconstructed within 2 weeks of injury using a triangle form plate of polylactide. Computed tomography (CT) was performed before the operation and 1 year postoperatively. In 17 patients, additional CT was performed within 2 to 3 years postoperatively. Clinical assessments were performed preoperatively and at 3-, 6-, and 12-month intervals postoperatively. RESULTS: None of the patients showed clinical foreign-body reactions. There was no evidence of infection. Diplopia was seen in 6 patients 3 months postoperatively but normalized in 5 patients at 6 months. Mild enophthalmos was seen in 2 patients postoperatively at 1 year. No sagging of the reconstructed area was found on CT. CONCLUSIONS: The P(L/DL)LA 70/30 implant is a well-tolerated, reliable material in orbital repair of relatively large defects. The bioresorbable plate leaves a stable bridge of healed bone or soft tissue after complete degradation.

Bone and cartilage wedge technique in posttraumatic enophthalmos treatment.

OBJECTIVE: To evaluate a new surgical method, using calvarial bone graft combined with a wedge of irradiated homologous costal cartilage, for the revision repair of posttraumatic enophthalmos. METHODS: This retrospective study was performed from January 1, 2003, through December 31, 2007. Eight patients were diagnosed as having unilateral posttraumatic enophthalmos. All the patients had previously undergone insufficient primary repair of their orbital fractures. In the revision surgery a calvarial bone graft was placed in the area of the defect using a transconjunctival approach. In combination with this technique, a wedge of irradiated rib cartilage was placed on the bone graft behind the globe. Patients were assessed preoperatively and postoperatively by ophthalmologists and maxillofacial surgeons. Standard follow-up examinations were performed at 2 and 4 weeks and at 3 and 6 months after surgery. Computed tomographic scans were obtained preoperatively and postoperatively from all patients. RESULTS: For all 8 corrected orbits, favorable cosmetic results were obtained regarding the position of the globe. The mean preoperative Hertel exophthalmometer showed a difference of 3.1 mm and 0.7 mm postoperatively. Improvement of ocular motility and reduction of diplopia were achieved in only 1 patient; in the others, motility and diplopia remained unchanged. No postoperative complications were observed. CONCLUSION: The bone and cartilage wedge technique seems to be a useful surgical technique for the cosmetic correction of posttraumatic enophthalmos.

Computer-assisted design and manufacture of implants in the late reconstruction of extensive orbital fractures.

OBJECTIVE: To evaluate the use of computer-assisted designed and manufactured (CAD/CAM) orbital wall and floor implants for late reconstruction of extensive orbital fractures. METHODS: We performed a retrospective data review on 29 patients treated for extensive orbital fractures from January 1, 1997, through December 31, 2007, at the University College London Hospitals. The use of a CAD/CAM technique based on cross-sectional computed tomographic scans, generating an accurate stereolithographic model, enabled surgeons and technicians to plan and create the best dimension and position of the implant. Sheet titanium was then pressed to shape from a design outlined on a counterdie of the new reconstructed model. RESULTS: Twenty-nine patients with late enophthalmos due to complex orbital fractures underwent successful reconstruction surgery. Enophthalmos was corrected in all patients. Diplopia was improved in 14 patients, and extraocular movement was improved in 13. CONCLUSIONS: The CAD/CAM implants represent a financially viable method for secondary reconstruction of the orbit. This method enables the surgeon to plan the operation in detail, facilitates the surgical procedure, and can help to improve the outcome.

Dental injuries in association with facial fractures.

PURPOSE: The aim of the study was to investigate the association between dental injuries and facial fractures. MATERIALS AND METHODS: We performed a prospective study of 273 patients examined at a level 1 trauma center in Switzerland from September 2005 until August 2006 who had facial fractures. Medical history and clinical and radiologic examination findings were recorded to evaluate demographics, etiology, presentation, and type of facial fracture, as well as its relationship to dental injury site and type. RESULTS: In 273 patients with dentition, we recorded 339 different facial fractures. Of these patients, 130 (47.5%) sustained a fracture in the non-tooth-bearing region, 44 (16%) had a fractured maxilla, and 65 (24%) had a fractured mandible. Among 224 patients with dentition who had a facial fracture in only 1 compartment, 140 injured teeth were found in 50 patients. Of 122 patients with an injury limited to the non-tooth-bearing facial skeleton, 12 sustained dental trauma (10%). In patients with fractures limited to the maxilla (n = 41), 6 patients had dental injuries (14.5%). In patients with fractures to the mandible (n = 61), 24 sustained dental injuries (39%). When we compared the type of tooth lesion and the location, simple crown fractures prevailed in both jaws. Patients with a fracture of the mandible were most likely to have a dental injury (39.3%). The highest incidence of dental lesions was found in the maxilla in combination with fractures of the lower jaw (39%). This incidence was even higher than the incidence of dental lesions in the lower jaw in combination with fractures of the mandible (24%). CONCLUSIONS: Knowledge of the association of dental injuries and maxillofacial fractures is a basic tool for their prevention. Our study showed that in cases of trauma with mandibular fracture, the teeth in the upper jaw might be at higher risk than the teeth in the lower jaw. Further larger-scale studies on this topic could clarify this finding and may provide suggestions for the amelioration of safety devices (such as modified bicycle helmets).

Impact of educational posters on the lay knowledge of school teachers regarding emergency management of dental injuries.

The purpose of this study was to investigate the knowledge of school teachers about the emergency management of dental trauma, after an educational poster campaign. A total of 1000 questionnaires were sent to 100 schools in the area where the poster had been distributed. This was compared to another 100 schools (1000 questionnaires) in an area, Where the poster had not been distributed. The questionnaire surveyed demographic data, basic knowledge of emergency management of tooth fracture, luxation and avulsion injuries. A total of 511 questionnaires were returned (25.5%) and analyzed. Results showed differences between the two assessed areas. Teachers, who worked in the area with poster distribution, had better knowledge in handling tooth injuries. For the management of tooth fractures the portion of teachers, who knew the correct handling procedure, was 78.9% (area with poster campaign) vs 72.1% (area with no poster campaign), for the management of tooth luxation it was 87% vs 84% and for the management of tooth avulsion it was 71% vs 54%. In the area with the poster campaign 49% (n = 90 out of 185) of the teachers stated to have gained some knowledge about this topic beforehand. Out of these, 75 teachers (75/90 = 83%), had gained their information from the educational poster. Out of the 75 teachers, who had seen a poster on this topic, 68 (68/75 = 91%) would have managed such an emergency correctly. The present study shows the positive effect of educational poster campaigns. It therefore should encourage professionals in this field to embark on similar projects.

Aneurysmal bone cyst of the tuberculum articulare of the temporomandibular joint: a case report.

A case is presented of a 14-year-old boy with aneurysmal bone cyst of the tuberculum articulare of the temporomandibular joint (TMJ). This disease rarely involves the skull, and involvement of temporal bone is even more rare. To our knowledge, only 22 cases have been reported in the literature. This is the first case of aneurysmal bone cyst of the tuberculum articulare of the TMJ described in the literature.

Effects of epidermal growth factor on the invasion activity of the oral cancer cell lines HSC3 and SAS.

Epidermal growth factor (EGF) is excreted in a high concentration in human saliva and modulates the growth and differentiation of various cancer cells. To elucidate the molecular mechanisms by which EGF affects oral cancer growth and invasion, we analyzed the Matrigel invasion activity of the cultured oral cancer cell line. Cells grown under the influence of EGF were subjected to Matrigel invasion assays and cells grown in the absence of EGF were used as controls. Gelatin-zymography and Northern blot analyses quantified the invasiveness and tumorigenicity. Chloramphenicol acetyltransferase assay (CAT assay) determined the EGF stimulation of matrix metalloproteinase (MMP) expression. EGF increased the number of cells penetrating a Matrigel membrane. Gelatin-zymography and Northern blot analysis revealed that MMP9 and Ets1 expressions correlated with EGF but MMP2 was not changed. a transient transfection assay revealed that EGF increased the promoter activities of the MMP9 genes in HSC3 and SAS cells. These results suggest that EGF increases the invasion activity of oral cancer cells partly by increasing MMP9.

Orbital manifestation of whipple's disease: an atypical case.

BACKGROUND: Whipple's disease is a systemic disorder caused by an infection with a gram-positive bacillus, Tropheryma whipplei. Almost every organ system can be affected in Whipple's disease, resulting in varying clinical symptoms. CASE REPORT: As far as we are aware, this report of a 61-year-old male is the first presenting with a periorbital manifestation of the disease, with severe exophthalmos and optic nerve involvement, leading to rapid visual loss. This emergency case was successfully treated by a surgical orbital decompression combined with systemic use of antibiotics and steroids. CONCLUSION: Whipple's disease can affect the periorbital tissues and the optic nerve, causing massive exophthalmos and serious transient visual loss. In such a case surgical decompression of the affected orbit combined with antibiotics and steroids is a recommended valid treatment option.

Soft tissue profile changes following mandibular advancement and setback surgery an average of 12 years postoperatively.

PURPOSE: The aim of this study was to assess long-term changes in position of soft tissue landmarks following mandibular advancement and setback surgery. MATERIALS AND METHODS: Twenty-seven patients (14 women, 13 men; mean age, 36 years) who had undergone either mandibular advancement (15 patients) or setback surgery (12 patients), were available for a long-term follow-up an average of 12 years postoperatively. In all of these cases, lateral cephalometric radiographs taken immediately before operation, at 1 week, 14 months, and 12 years postoperatively, were studied. RESULTS: During the 14 months postoperatively, soft tissue chin and mentolabial fold followed its underlying hard tissue in all patients. A continuous skeletal relapse was observable 12 years after mandibular advancement, but soft tissue chin moved more in an anterior direction. After mandibular setback, soft and hard tissue landmarks remained almost unchanged. Over the entire observation period, a thickening of soft tissue at pogonion was generally seen, and particularly a thickening of the whole chin in the setback group. All patients showed a significant lengthening and thinning of the upper lip. In all except 2 males, the patient's body weight increased markedly. CONCLUSION: In contrast to the immediate postoperative stage, soft tissue changes observed an average of 12 years after the primary operation do not directly follow the movements of the underlying skeletal structure. The soft tissue profile changes observed over such a long term seem to be influenced not only by the underlying skeletal structure but also by other factors such as weight gain and aging process.