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PubMed1986

Growth pattern of the mandible: some reflections.

The dynamics of the growth of bones is a complex process. The growth pattern of the mandible has been assessed by the application of various methods described for the study of the growth of bones. Some of these lend themselves primarily to basic experimental rather than clinical work. The use of any one of these methods will reveal certain information. With the use of two or more of them in combination, however, considerably more accurate information can be obtained. Since John Hunter's classical descriptions more than 200 years ago, advances in the understanding of the growth pattern of the mandible have been possible with the refinement of older methods and the development of newer ones. To date, serial cephalometric roentgenography in concert with radiopaque implants, which serve as fixed reliable markers, is the most accurate method to determine the growth pattern of the mandible. To this armamentarium, digital subtraction radiography, computerized tomography, and magnetic resonance imaging may be methods that will offer more detailed and accurate information.

Animals↗
PubMed1991

A computer-based assessment of structural and displacement asymmetries of the mandible.

The purpose of this article was to assess and quantify the different components that can lead to mandibular asymmetry in a person during or at the end of growth and to investigate the extent to which improvement can be obtained in the different situations. Three boys and 17 girls, 8 to 21 years of age, with facial asymmetry and chin deviation were selected. Posteroanterior cephalometric radiographs were taken in intercuspal position. On each radiograph, three mandibular points (menton, gonion or antegonion, and articular point) were selected to define a mandibular area. A vertical axis of reference was also determined. Computer-aided design was employed to develop two systems (A and B) to assess a symmetry degree of the mandible. With system A, the left mandibular area was rotated around the vertical axis of reference, and the degree of the superimposition between the left and right areas was plotted. With system B, the left area was rotated around an axis that ran through menton and was perpendicular to a line connecting the two articular points of the mandible. Also, in this case, the degree of superimposition between the two areas was plotted. With system A, the degree of superimposition was a function of mandibular position and mandibular symmetry. With system B, it was a function of mandibular symmetry only. Thus through comparative examination of the data, assessment of displacement asymmetry and structural asymmetry was possible. In two patients, only displacement asymmetry was present, whereas 14 patients showed various features of structural asymmetry. The patients were treated with orthopedic splints to keep the mandible in a position of symmetry. Orthodontic treatment followed so that the intercuspal position would finally coincide with the position of symmetry. Computer-aided design analysis was performed again after a mean observation period of 41.1 months. In 11 patients an improvement in symmetry was observed with both systems. The patients in whom no improvement of structural asymmetry was observed showed a relatively high degree of symmetry at the beginning or had a considerably higher age than the mean age of the whole group. The clinical implications of the data are discussed.

Adolescent↗
PubMed2006

Methods to evaluate profile preferences for the anteroposterior position of the mandible.

INTRODUCTION: Facial profile disharmonies in the anteroposterior (AP) position of the mandible are among the most frequent reasons that patients seek orthodontic treatment. Various methods are available for assessing profile preferences, and differences between them could affect treatment decisions. The purposes of this study were to compare and contrast 3 methods of evaluating profile preferences for the AP position of the mandible. METHODS: Facial profile preferences of white orthodontists (n = 28) and white (n = 56) and Japanese-American (n = 55) laypeople were evaluated. The esthetic significance of variations in the AP position of the mandible was investigated by using 3 methods: a traditional semantic differential scale, the Perceptometrics method (Health Programs Intl, Wellesley, Mass), and the implicit association test (IAT). RESULTS: Findings from the semantic differential scale show that, overall, there is a general preference among orthodontists and laypeople for an orthognathic profile (P <.001). Findings from the Perceptometrics method indicate that orthodontists consider the most pleasing profile to be more forward than do lay subjects (P <.001). The IAT results show a positive bias among all 3 groups toward orthognathic profiles and a negative bias toward profiles with mandibular retrognathism or prognathism. The IAT suggested that laypeople were more tolerant of mandibular prognathism in men than in women (P <.01), and more tolerant of mandibular retrognathia in white women than in men (P = .03). CONCLUSIONS: These results support the benefits of using both implicit and explicit methods to assess facial profile preferences.

Adult↗
PubMed2006

Relationship of bone utilization and biomechanical competence in hominoid mandibles.

This investigation explores regional variation in bone mass in the mandibles of large-bodied hominoids with respect to the masticatory biomechanical environment. Cortical area, subperiosteal area, mandibular length, maximum and minimum area moments of inertia are sampled at 7 sections along the mandibular corpus in 20 specimens each of Homo sapiens, Pan troglodytes, Pongo pygmaeus and Gorilla gorilla. The null hypothesis is that bone is utilized similarly among species, between sexes and among corpus locations in terms of economy of bone deployment (relative to subperiosteal area) and efficiency in producing structural stiffness (relative to cross-sectional moments of inertia). The alternative hypothesis is that dietary toughness and the scaling of muscular force recruitment produces an unfavourable stress environment in the mandible such that larger species (Gorilla and Pongo) use relatively more cortical bone than Pan and Homo. Three-way factorial analysis of variance (with species, sex and location as main effects) indicates significant interaction of species and location for all indices of bone economy and efficiency. Sex is significant as a main effect or interacting with location in all indices of cortical area. While allometric effects are not readily discernible in these data, the null hypothesis of a common pattern of bone utilization is decisively rejected. Human mandibles use relatively more cortical bone than those of great apes, particularly in anterior regions of the corpus. Among the apes, orangutans use very little cortical bone to achieve mechanical stiffness.

Adult↗
PubMed2006

Functional significance of strain distribution in the human mandible under masticatory load: numerical predictions.

A common feature of studies of mandibular morphology is the assumption that there is some functional relation between the form of the lower jaw and masticatory stress. It was noted that the local variation in cortical bone thickness in the mandibular corpus appears to be stereotypical among anthropoids. This occurs at sections under the molars, where the lingual cortical plate is thinner than buccal one. In this study we investigate and contrast the strain pattern along buccal and lingual surfaces of the mandibular corpus during mastication using a numerical model of a human mandible. We show that strain distribution differs in alveolar and mid-corpus segments of the mandible and that the latter develops an alternate pattern between the buccal and lingual aspects of the working and balancing sides of the jaw. We then relate the magnitude of these strains to Frost's mechanostat. Our results suggest that the cortical asymmetry of the human mandible is in fact not related to strain patterns generated during mastication.

Adult↗
PubMed2005

Intra-articular ramus ostectomy combined with costochondral grafting for the treatment of recurrent ankylosis of the mandible.

PURPOSE: This report seeks to demonstrate a technique for treating recurrent ankylosis of the mandible by creating a functional false joint at a level distal to the original joint. PATIENTS AND METHODS: This is a retrospective study involving patients treated between 1999 and 2003. Under general anaesthesia the ramus was exposed via a submandibular approach and a block of bone was removed from it inferior to the sigmoid notch. Temporary intermaxillary fixation was applied. A costochondral graft was interposed between the resected ends of bone and secured with mini-plates. Postoperatively intermaxillary fixation was maintained for 3 days after which the jaw was actively mobilized. RESULTS: The technique was used in the treatment of six patients with recurrent ankylosis of the mandible ranging in age from 9 to 38 years. Follow-up was between 1 and 4 years. All the patients had a satisfactory interincisal opening ranging from 25 to 35 mm. CONCLUSION: The technique does not require the exposure of the ankylosed joint proper but instead creates a false and functional joint at a lower level. It also permits lengthening and advancement of the mandible.

Adolescent↗
PubMed2005

The combined use of two endosteal implants and iliac crest onlay grafts in the severely atrophic mandible by a modified surgical approach.

Seventeen patients, who received an iliac crest onlay bone graft augmentation to their severely atrophic mandible with simultaneous placement of two endosteal implants by a modified surgical approach, were studied retrospectively. Follow-up ranged from 0.5 to 7.9 years after implant loading with an average follow-up of 4.3 years. Frequency of wound dehiscences and other postoperative complications, the extend of resorption of the initial graft, and the implant success rate were assessed. Two patients, who had a previous history of preprosthetic and implantological procedures at the surgical site, developed a serious wound dehiscence with loss of two implants in one patient and need for antibiotic treatment and sequestrectomy in the other patient. One implant was lost in two other patients with a negative surgical history, resulting in an implant success rate of 88.2%. The average resorption at the last follow up visit was 15% of the initial graft. Damage of the mental nerve was seen in 14.7% of nerves. Our preliminary data indicate that the procedure presented provides a reliable and predictable method for the construction of an implant-bearing overdenture in patients with a severely atrophic mandible. This one-step procedure can not be recommended for patients with a history of surgery in the anterior mandible.

Adult↗
PubMed2004

A three-dimensional computer model of the human mandible in two simulated standard trauma situations.

PURPOSE: A three-dimensional finite element model of the human mandible was developed to simulate and analyse biomechanical behaviour in two standard trauma situations. This computer-based study was made to assess the stress patterns within human mandibles generated by impact forces. MATERIAL AND METHODS: The mandibular model was generated using 7.073 nodes and 30.119 tetrahedra. A commercial finite element solver was then applied to this mesh to compute stresses generated in standard trauma situations (a blow in the symphysis region and another one to the body of the mandible). RESULTS: The results indicate that following a blow to the symphysis region, maximum stress areas were located at the symphysis, retromolar and condylar regions. In the case of a blow to the mandibular body, the maximum stress areas were located at the contralateral angle, the ipsilateral body and the ipsilateral condylar neck regions. CONCLUSION: The main application of this study was the prediction of fractures as a consequence of known forces.

Biomechanical Phenomena↗
PubMed2006

Effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on bone consolidation on distraction osteogenesis: a preliminary study in rabbit mandibles.

AIM: To examine the effectiveness of administering recombinant human bone morphogenetic protein-2 (rhBMP-2) in distraction osteogenesis. MATERIAL AND METHODS: Twenty-one mature male Japanese white rabbits underwent unilateral mandibular osteotomy. After 5 days, the osteotomized mandibles were distracted 1mm/day for 10 days. On the first day (groups A-1 [n=4] and A-2 [n=4]) or on the last day (group B [n=5]) of distraction, rhBMP-2 mixed with collagen gel was injected into the distraction zone. In control groups (groups C-1 [n=4] and C-2 [n=4]), the mandibles were distracted without rhBMP-2 injection. At the end of the distraction period (groups A-1 and C-1) and after 2 weeks of consolidation (groups A-2, B, and C-2), the distracted mandibles were harvested and examined with soft radiographs, peripheral quantitative computed tomography (pQCT), and microscopy. RESULTS: Radioopacity was more marked in the distraction zone of the groups with rhBMP-2 than in control groups. The mineral density of the cortical bone (BMD) was higher in groups B and A-2 than in group C-2. Histologically, bone formation was more advanced in groups A-2 and B than in group C-2. The cortical BMD was higher in group A-1 than in group C-1. Histologically, bone formation was more advanced in groups A-2 and B than in group C-2. CONCLUSION: These results suggest that rhBMP-2 promotes bone formation in distraction osteogenesis.

Absorptiometry, Photon↗
PubMed2005

A Neandertal mandible from the Cova del Gegant (Sitges, Barcelona, Spain).

A human mandible from the site of Cova del Gegant is described here for the first time and compared with other Middle and Upper Pleistocene representatives of the genus Homo from Europe and Southwest Asia. The specimen was recovered from sediments which also yielded Mousterian stone tools and Pleistocene fauna. The preserved morphology of the mandible, particularly in the region of the mental foramen, clearly aligns it with the Neandertals, making the Cova del Gegant the only known site in Catalonia documenting diagnostic human skeletal remains in association with Middle Paleolithic stone tools. This represents an important new addition to the human fossil record from the Iberian Peninsula and joins the Bañolas mandible in documenting the course of human evolution in the northern Mediterranean region of Spain.

Age Determination by Teeth↗
PubMed2005

Mechanical characteristics of the mandible after bilateral sagittal split ramus osteotomy: comparing 2 different fixation techniques.

PURPOSE: Using finite element (FE) computer model simulation, we compared the mechanical characteristics of the mandible after bilateral sagittal split ramus osteotomy (BSSRO) through the use of 2 different techniques to stabilize the osteotomy. MATERIALS AND METHODS: Based on the reconstructed geometry from computed tomography scans of dry adult skull with a mandibular deformity requiring surgical correction, we developed 3-dimensional FE models that simulate BSSRO with 2 different techniques to stabilize the osteotomy. Technique 1 uses 3 bicortical titanium screws. Technique 2 uses a curved titanium plate with 4 monocortical screws. Five different load cases were applied to the mandible after the simulated BSSRO with the mandible being constrained at both temporomandibular joints. To evaluate the efficacy of these 2 stabilization techniques, we compared 1) the resulting deflections at the central incisor, 2) the mechanical stresses developed in the bone in the vicinity of the stabilizing implants, and 3) the mechanical stresses developed within the screw/plating system themselves. RESULTS: Technique 1, using 3 bicortical titanium screws, leads to smaller deflections at the central incisor for all 5 load cases, suggesting higher mechanical stability. Technique 1 also leads to lower mechanical stresses in the bone and in the implanted screws, whereas technique 2 is associated with higher values in each of these quantities. CONCLUSIONS: To stabilize osteotomies after a 3-dimensional simulated BSSRO, 3 bicortical screws forming an inverted-L configuration are shown to offer more effective load transmission in the mandibular construct. This technique, when examined in an FE model, leads to higher stability with lower mechanical stresses in the bone near the bicortical screws.

Adult↗
PubMed2004

Dorsal nasal reconstruction using bone harvested from the mandible.

PURPOSE: This article describes a technique for reconstructing nasal deformities resulting from trauma. Bone harvested from the lateral ramus/body of the mandible is used to provide nasal support for major nasal deformities. PATIENTS AND METHODS: Ten patients underwent repair of their nasal deformities with an autogenous bone graft harvested from the mandible. Primary bone grafting was used to repair a nasal deformity associated with a naso-orbito-ethmoidal fracture in 8 patients. Secondarily, 2 patients underwent placement of a graft for correction of a saddle nose deformity. RESULTS: All patients achieved aesthetic results. There was maintenance of nasal projection and symmetry without displacement of the graft. None of the patients complained of an unnatural hardness of the nasal tip or dorsum. All grafts healed without evidence of infection, dehiscence, or necrosis. CONCLUSION: The lateral ramus/body of the mandible provide an excellent donor site alternative for nasal reconstruction.

Bone Transplantation↗
PubMed2004

Immediate loading of definitive implants in the edentulous mandible using a fixed provisional prosthesis: The denture conversion technique.

PURPOSE: This article presents a clinical technique for immediate implant loading in the completely edentulous mandible. MATERIALS AND METHODS: The protocol recommends the placement of 4 to 5 root-form implants in the anterior mandible between the mental foramina. Upon insertion the implants must have favorable primary stability. Abutments are added to the implants and the patient's lower denture is converted into an immediate load provisional fixed prosthesis. RESULTS: The denture conversion technique has been shown to provide predictable results for immediate implant loading in the edentulous mandible. The final prosthesis is fabricated upon integration of the implants in 3 months. CONCLUSION: The denture conversion technique offers several advantages because it may be used with most commercially available implant systems and it incorporates conventional implant components. Guidelines for patient selection, presurgical preparation, implant surgery, prosthesis fabrication, and postoperative care are reviewed.

Dental Abutments↗
PubMed2006

Mandibular remodeling after bilateral sagittal split osteotomy for prognathism of the mandible.

PURPOSE: To describe the postoperative remodeling changes in the mandible after bilateral sagittal split osteotomy to correct mandibular prognathism. PATIENTS AND METHODS: Twenty patients who underwent bilateral sagittal split osteotomy for the correction of mandibular prognathism were studied for postoperative remodeling changes within the mandible. The 6-week, 1-year, and long-term postoperative cephalometric mandibular tracings of 12 patients were superimposed using the fixation wires as the stable reference points to demonstrate the specific locations of the intrabony remodeling. RESULTS: There was a general direction of remodeling at the condylion and gonion anteriorly and superiorly, while the B point and pogonion did not show much change in remodeling. At the condylion, 60% and 40% of the cases showed significant horizontal and vertical remodeling, respectively. At the gonion, 50% and 55% of the cases showed significant horizontal and vertical remodeling, respectively. No correlation was found between the remodeling changes at condylion and gonion and the surgical movement or relapse at B point and pogonion. There was a significant correlation between the observed horizontal relapse at gonion and the horizontal remodeling changes at this point showing that the postoperative displacement of this point is a result of both positional translocation and remodeling changes. CONCLUSION: The results of this study show that there are intrabony remodeling changes that occur in the mandible after sagittal split osteotomy and that these continue for a long period of time in some patients. This remodeling occurred more in the condylar and gonial areas, while the chin remained relatively stable.

Adolescent↗
PubMed2004

Design and fabrication of custom mandible titanium tray based on rapid prototyping.

UNLABELLED: During the past few years, the combination of medical imaging and rapid manufacturing technique has proven to be a very important development. On the other hand, the conventional method has some drawbacks. For example, it takes longer time to complete an operation and it also presents some difficulty in matching the repaired contours. With advanced software and hardware, an image of an undamaged bone similar to that of the patient can be made from computerised tomography (CT); and a physical object constructed by the mirror-processed image data can be quickly fabricated with a high degree of fitting with the patient's bone. This paper presents a methodology for the design and fabrication of an individual titanium tray for the repair of mandible defects. Methods for the tray modeling using CAD system are presented: A 3D model of the bony defect is generated after the acquisition of helical CT data. An individual tray is designed using freeform surfaces geometries and fabricated by rapid prototyping (RP) technology. The results of tray filling with bone-grafting materials are then presented. RESULT: the tray is inserted into the patient mandible segment. The symmetry and reconstruction quality contour of the repaired mandible was satisfactory. Thus, the patient is able to eat normally. The bone-grafting material harvested from the anterior ilium was low. The clinical experience showed that rapid prototyping and reverse engineering software are effective methods of fabricating custom trays for mandibular reconstruction after bone loss due to a tumor.

Adult↗
PubMed2005

Critical size defect in the canine mandible.

OBJECTIVE: The purpose of this study was to determine the minimum size defect in a canine mandible that would not spontaneously heal during the dog's natural life (the critical size defect). STUDY DESIGN: Sixteen adult female mongrel dogs underwent continuity resection on both sides of the mandible to create bilateral defects. In 8 dogs, mandibular defects ranging from 5 to 20 mm were created with periosteal resection. In the other 8 dogs, mandibular defects ranging from 30 to 60 mm were created preserving the periosteum. The dogs were then killed at 6 months and the defects examined using radiographs and histologic analysis. RESULTS: When the periosteum was removed, mandibular defects greater than 15 mm failed to heal across the entire defect. However, when the periosteum was preserved, mandibular defects needed to be greater than 50 mm in order to fail to heal. CONCLUSION: The critical size defect in a canine mandible model is 15 mm when the periosteum is removed and 50 mm when the periosteum is preserved.

Animals↗
PubMed2006

Experimental evaluation of bone quality measuring speed of sound in cadaver mandibles.

OBJECTIVES: To demonstrate in vitro the feasibility of speed of sound (SOS) measurements through the mandible and to investigate the relationships between mandibular SOS, local bone mineral density (BMD), and the ratio between trabecular and cortical thicknesses (Tb.Th/Cort.Th). The long-term goal is to find a safe, simple test for bone quality in sites for dental implant placement. METHODS: Excised human mandibles (N = 23) were used for the measurement of sound transmission with two 1.6 MHz transducers. Three regions of interest (ROIs) were selected in each of the specimens, namely incisor, premolar, and molar regions. To determine short-term precision, 10 measurements (with repositioning between measures) were performed for each ROI. Local BMD and mandibular cross-sectional morphological characteristics were determined by dual x-ray absorptiometry (DXA) and computed tomography (CT). RESULTS: The coefficient of variation for SOS was found to be 1%. SOS measurements at different sites were significantly different. A significant linear relationship was found between SOS and BMD (r2 = 0.62; P < .0001), whereas a nonlinear relationship was found between SOS and Tb.Th/Cort.Th (r2 = 0.53; P < .0001). CONCLUSION: This in vitro study demonstrated the feasibility of SOS measurement through the mandible. Mandibular SOS reflects local BMD and Tb.Th/Cort.Th. In vivo studies are now required to confirm the predictive power of SOS measurement for bone quality assessment and its potential usefulness as a clinical diagnostic technique.

Absorptiometry, Photon↗
PubMed1988

Enhancement of rehabilitation by use of implantable adjuncts with vascularized bone grafts for mandible reconstruction.

Restoration of mandibular continuity after trauma or cancer by means of vascularized bone grafts, as described by Taylor and coworkers in 1979, has become an established method of oral rehabilitation. Still considered by some an endpoint in reconstruction, we have found that the judicious application of newly described dental prosthetic materials can provide the patient with improved appearance and function associated with a fully restored mandible. Twelve patients who underwent vascularized bone grafting for mandibular reconstruction had adjunctive implantation to improve either dentition or to reconstruct the temporomandibular joint. Nine patients had dental implants to restore permanent stable dentition either by placement of the mandibular bone staple plate or osseointegrated implants. Three additional patients underwent placement of metallic condylar head prostheses placed on the vascularized bone graft at the time of transfer. These patients demonstrated good mastication and an excellent incisal opening which was maintained in the late postoperative period. Vascularized bone transfer for restoration of continuity of the mandible should not be considered an endpoint in and of itself. By using implantable dental devices to restore dentition and condylar head prostheses to improve both the aesthetic result and function of the mandible to complement the vascularized osteocutaneous flap, we can bring our patients closer to the goal of total rehabilitation. The majority of these patients would otherwise never have been offered a chance at restoration of dentition. All had beneficial effects with regard to mastication and the majority also had improved speech.

Biomechanical Phenomena↗