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PubMedDate not supplied

Evolutionary integration and morphological diversification in complex morphological structures: mandible shape divergence in spiny rats (Rodentia, Echimyidae).

The rodent mandible has become a paradigm for studies on the development and evolution of complex morphological structures. We use a combination of geometric and multivariate morphometric methods in order to assess the correspondence between integration patterns and a priori biological models in the context of evolutionary shape divergence in the mandible of rodents of the family Echimyidae. The correlation of shape distances among operational taxonomic units (individuals, species, genera) in separate morphogenetic components allowed the construction of integration matrices among mandible components for data sets corresponding to varying levels of genetic divergence (intergeneric, interspecific, and intrapopulational). The integration matrices were associated with a priori biological (developmental, genetical, modular) models, and the maximum integration axes (singular warps) were compared with realized axes of maximum interspecific variation (relative warps). The integration pattern and intensity were not stable in data sets with different levels of genetic divergence, and the varying functional demands during the ecological radiation in the family were probably responsible for the differences in observed integration patterns. Developmental and genetic models were significantly associated with the interspecific integration patterns observed, suggesting a role for neutral evolution during the evolutionary divergence of mandible shape. However, directional and stabilizing selection were not discarded as processes responsible for the generation of interspecific integration. The choreography of the morphogenetic components in the mandible is highly flexible and the integrated groups of components can be reorganized depending on functional demands during evolutionary shape changes.

Animals↗
PubMed2004

Morphometric analysis of the mandible in growing rats with different masticatory functional demands: adaptation to an upper posterior bite block.

Functional appliances displace the mandible forward and/or downward, causing a stretching of the orofacial soft tissues, muscles included. The resulting forces are directly or indirectly transmitted to the underlying dento-skeletal tissues. The hypothesis underlying the present investigation was that the insertion of a bite-opening appliance influences the lateral morphology of the rat mandible during growth, and that, moreover, this influence depends on the masticatory functional demands. One-hundred and four 4-wk-old male albino rats were divided into two groups, fed a hard and soft diet, respectively. After 2 wk, half of the animals in each experimental group were fitted with upper posterior blocks, and 4 wk later they were killed. Their left hemi-mandibles were transilluminated, photographed under magnification, and digitized on screen. A total of 170 points were used to draw the lateral outline of the mandible. In addition to the inhibitory effect on the height of the dento-alveolar process, the upper bite block resulted in significant changes in the condyle inclination, the length of the coronoid process, and the occlusal plane inclination. Masticatory functional demands influenced this adaptation in an additive way. The results raise the question of whether orthodontic treatment with posterior bite blocks might have different effects on the mandible, depending on the characteristics of the orofacial soft tissues.

Adaptation, Physiological↗
PubMed2006

Mandible analysis in sex steroid-deficient rats.

The aim of this study was to evaluate, by morphologic techniques, the effects of sex steroid deficiency on mandible bone remodeling of female rats, in groups of different experimental periods and to compare the results with 90-day orquiectomized males. Female and male Wistar rats, 3 months old, were divided into experimental groups and at the end of each experimental period were killed, and mandibles were extracted. The left mandibles were prepared with rote technique bone and examined by a light microscope. Morphological analyses of the mandibles demonstrated resorption signals in the alveolar bone, after 30 days in ovariectomized females, but it was more intense 90 days after castration. The orquiectomized group exhibited some signals of resorption similar to the ovariectomized group of 60 days. Morphometric analysis of alveolar bone thickness in females after 60 days was in agreement with morphological results. However, the analysis of periodontal ligament thickness did not show any significant difference. There were variations in sexual hormone deficiency in the mandibles of males and females and they seemed to be more precocious in ovariectomized than in orquiectomized rats. It is important for a health professional to have knowledge about bone metabolism to improve the quality of life of postmenopaused and old people.

Alveolar Bone Loss↗
PubMed2000

Long-term follow-up of severely atrophic edentulous mandibles reconstructed with short Brånemark implants.

BACKGROUND: Oral implant treatment (Brånemark System) of edentulous mandibles has been presented in numerous studies. However, with regard to the severely atrophic lower jaw, no long-term follow-up studies with solely short implants are available. PURPOSE: The purpose of the present investigation was to retrospectively follow the long-term treatment outcome of patients with severely resorbed edentulous mandibles being subjected to oral implant placement with short (6-7 mm) Brånemark implants. MATERIALS AND METHODS: A total of 247 standard (7 mm long, Ø 3.75 mm) and 13 wide (6 mm long, Ø 5 mm) implants were inserted in 49 patients, all of whom exhibited severe resorption of edentate mandibles. Fixed implant-supported prostheses were manufactured for 45 patients, whereas 4 patients received overdentures. The patients were followed for a mean period of 8 years (range, 1-14 yr). RESULTS: Seventeen implants failed during the study period (cumulative implant survival rate 95.5% at 5-yr and 92.3% at 10-yr follow-up). Implant-supported constructions were worn continuously throughout the investigation by all study subjects. Marginal bone loss, measured after 1, 5, and 10 years of function, concurred with studies of Brånemark implants placed in more voluminous mandibles. No major clinical or construction complications occurred in the followed patients. CONCLUSIONS: The outcome of the present study showed that placement of short Brånemark implants without the use of bone grafting procedures for reconstruction of severely atrophic edentulous mandibles is a highly predictable treatment procedure.

Adult↗
PubMed2003

Early functional loading in the fully edentulous mandible after mandibular resection and reconstruction due to an ameloblastoma: case report.

BACKGROUND: Immediate or early functional loading of implants in fully edentulous mandibles can enhance patient comfort and the ability to masticate within a few days after implant placement. Recently there has been evidence that this method of restoring edentulous mandibles is predictable. PURPOSE: The goal of this case report is to present the treatment of a patient diagnosed with a large ameloblastoma in the mandible. After removal of the tumor and mandibular reconstruction, the patient had complete anesthesia in the right mandible, with an alveolar ridge deformity. METHODS: Two years after removal of an ameloblastoma in the right mandibluar sextant, five implants were installed between the mental foramina. One implant was installed for safety reasons in the event one of the others was lost. This implant remains buried. A denture was used as a drilling guide. Abutments were attached to the implants, and impression copings were fixed to the abutments. The denture was used for the "pickup" impression. Flaps were sutured, maintaining exposure of the abutments. In the laboratory, gold cylinders were heat cured to the tissue side of the denture. The cylinders were attached to the cast with laboratory screws. The gold cylinders were heat cured to the intaglio side of the denture. Five days after implant placement, the nonmetal reinforced acrylic denture was fixed to the implants with laboratory screws. The bridge is removed annually, and the implants are examined for mobility and periapical radiographs are taken. RESULTS: The patient has worn the prosthesis for 2.5 years without loss of implants and without breakage of the nonmetal reinforced denture. At 2.5 years the implants are stable, implant sites demonstrate stable crestal bone, and the patient is eating comfortably and without limitations. CONCLUSION: Early functional loading of implants in the edentulous mandible may offer patients the option of wearing implant-supported prosthesis immediately or shortly after implant insertion.

Acrylic Resins↗
PubMed2003

Clinical assessment and surgical implications of anatomic challenges in the anterior mandible.

BACKGROUND: The anterior mandible is generally considered a rather safe surgical area, involving few risks of damage to vital anatomic structures. Nevertheless, both neurosensory disturbances and hemorrhages have been reported after implant surgery in that particular area. PURPOSE: With the increasing demand for oral implant placement, the anatomy of the anterior mandible should receive more attention. This review will focus on the anatomic peculiarities of the anterior mandible and the related clinical implications. METHODS: The scientific evidence on the anatomic, histologic, physiologic, and clinical aspects of the neurovascularization of the anterior mandible will be reviewed. RESULTS: Surgical complications may be attributed to the existence of a mandibular incisive canal with a true neurovascular supply. Potential risks may also be related to the presence of the lingual foramen and anatomic variations, such as an anterior looping of the mental nerve. CONCLUSIONS: Preoperative radiographic planning for oral implant placement in the anterior mandible should therefore not only consider all esthetic and functional demands but should also pay particular attention to the anatomic peculiarities of this region to avoid any neurovascular complications.

Arteries↗
PubMed2004

Implant stability, tissue conditions, and patient self-evaluation after treatment with osseointegrated implants in the posterior mandible.

BACKGROUND: Implant treatment in the posterior mandible is considered challenging because of bone resorption and the presence of the inferior alveolar nerve, which may result in the use of short implants. PURPOSE: To evaluate implant stability, tissue conditions, and patient opinion after treatment with implant-supported bridges in the posterior mandible. MATERIALS AND METHODS: Thirty-four patients treated with implant-supported bridges in the posterior mandible according to a two-stage protocol were clinically and radiographically examined and interviewed after a mean functional time of 3.9 years. One hundred five Brånemark implants (Nobel Biocare AB, Gothenburg, Sweden) were placed in premolar and molar regions to support 40 bridges. Twenty-eight implants were placed anterior to the mental foramen, and 77 implants were placed posterior to the mental foramen. Bridges were supported either by two or by three implants. After 2 to 6 years, the bridges were removed to analyze the resonance frequency of the implants with the use of a special instrument (Osstell instrument, Integration Diagnostics AB, Gothenburg, Sweden), and an implant stability quotient (ISQ) was recorded for each implant. RESULTS: One implant was lost. An ISQ range of 59 to 90 (mean, 70.05) expressed stability of fully integrated implants in the posterior mandible. Significantly higher (p < .024) ISQ values were found in implants in three-implant bridges when compared with implants in two-implant bridges. There were no differences in ISQ values between molars/premolars, implant types, implant widths, implant lengths, anchoring depth, or uni- or bilateral mandibular bridges. Good mucosal health in the periimplant soft tissue and minor bone resorption around the implants were observed. Patients were generally very satisfied with the treatment outcome. CONCLUSIONS: High implant stability can be reached in the posterior mandible. The implants were more stable in three-implant bridges than in two-implant bridges. The patients were highly satisfied with the treatment, and few complications were seen.

Aged↗
PubMed2006

Immediate loading of Brånemark System Implants: a comparison between TiUnite and turned implants placed in the anterior mandible.

PURPOSE: The aim of the present study was to compare the treatment outcome of TiUnite- and turned-surfaced Brånemark System (Nobel Biocare AB, Göteborg, Sweden) implants when applying immediate loading of cross-arch designed fixed partial dentures in the anterior mandible. MATERIALS AND METHODS: Fifteen patients with edentulous mandibles participated in the study. In one half of the jaw, between the exit of the nerve-vessel bundle and the midline, one type of implant was placed and in the remaining half the other type. The implants were loaded the day of surgery via a fixed, temporary supra-construction. Ten days later, the permanent one was screw retained to the implant pillars. RESULTS: The present 18-month clinical trial failed to demonstrate any differences regarding healing and cumulative success rate of an an-oxidized implant surface (TiUnite) and a turned (turned) one when implants in the anterior mandible were exposed to functional load within 24 hours after installation. CONCLUSION: A high predictability regarding the treatment outcome for immediately loaded Brånemark implants in the anterior mandible was observed. Furthermore, no difference between the traditional turned and the an-oxidized implant surface (TiUnite) could be observed. However, it has to be stressed that all implants (irrespective of surface) were placed in the anterior mandible and also that all the patients demonstrated a high level of oral hygiene.

Aged↗
PubMedDate not supplied

Evaluation of the mandible as an alternative autogenous bone source for oral and maxillofacial reconstruction.

The objective of this study was to quantify the amount of bone graft material present in the different regions of the mandible while avoiding the inferior alveolar neurovascular bundle, mental foramen and tooth injury. The study was carried out on 16 samples of dry, cadaverous skull. The dimensions of the anterior part of ascending ramus, mandibular symphysis and mandibular body in these samples were evaluated. The osteotomy lines in the anterior part of the ascending ramus were made in front of the mandibular canal from the mandibular notch to 3 mm posterior of the root of the third molar. The osteotomy line in the mandibular body was made just medial to the external oblique ridge from the ascending ramus to approximately 3 mm posterior to the mental foramen. Vertical osteotomy lines were then made from the cut ends of the first osteotomy down to the lower border of the mandible. The osteotomy lines in the mandibular symphysis were performed on the mandible with 5-mm safety margins caudal to the expected position of the mandibular dentition, anterior to the position of the mental foramen, and cephalad to the inferior border of the mandible. It was determined that the dimensions of the anterior part of the ascending ramus were 37.60 mm x 33.17 mm x 22.48 mm x 9.15 mm, and the thickest part of the graft material was 12.23 mm. The average horizontal length of the mandibular body bone was 35.10 mm, and the average vertical length was 19.13 mm. The dimensions of the bone graft obtained from the mandibular symphysis were 45.36 mm x 10.31 mm, and the average thickness was 9.63 mm. Based on the results of this study, it is apparent that the different regions of the mandible can reliably be selected as the harvest site in a variety of oral and maxillofacial reconstructive procedures.

Bone Transplantation↗
PubMed2004

Implantology and the severely resorbed edentulous mandible.

Patients with a severely resorbed edentulous mandible often suffer from problems with the lower denture. These problems include: insufficient retention of the lower denture, intolerance to loading by the mucosa, pain, difficulties with eating and speech, loss of soft-tissue support, and altered facial appearance. These problems are a challenge for the prosthodontist and surgeon. Dental implants have been shown to provide a reliable basis for fixed and removable prostheses. This has resulted in a drastic change in the treatment concepts for management of the severely resorbed edentulous mandible. Reconstructive, pre-prosthetic surgery has changed from surgery aimed to provide a sufficient osseous and mucosal support for a conventional denture into surgery aimed to provide a sufficient bone volume enabling implants to be placed at the most optimal positions from a prosthetic point of view. The aim of this paper is to review critically the literature on procedures related to the severely resorbed edentulous mandible and dental implant treatment. The study includes the transmandibular implant, (short) endosseous implants, and reconstructive procedures such as distraction osteogenesis, augmentation of the mandibular ridge with autogenous bone, and bone substitutes followed by the placement of implants. The number of patients participating in a study, the follow-up period, the design of the study, the degree of mandibular resorption, and the survival rate of the dental implants all are considered evaluation parameters. Although numerous studies have described the outcome results of dental implants in the edentulous mandible, there have been few prospective studies designed as randomized clinical trials that compare different treatment modalities to restore the severely resorbed mandible. Therefore, it is not yet possible to select an evidence-based treatment modality. Future research has to be focused on long-term, detailed follow-up clinical trials before scientifically based decisions in treating these patients can be made. This will contribute to a higher level of care in this field.

Alveolar Bone Loss↗
PubMed1996

Quantitative radiographic changes in the mandible, femur and vertebra in lactating rats fed a low-calcium diet.

OBJECTIVE: To determine whether similar changes occur in the mandible, femur and vertebral body in generalized osteopenia. METHODS: Osteopenia was induced in the bred animal group using a low calcium diet from parturition onwards. Control groups were virgin and bred rats fed a normal diet. Rats in each group were weighed weekly, and subgroups of 12 rats in each treatment group were killed at ages 18, 24, 36 and 48 weeks. A separate reference group of 12 rats was killed at age 12 weeks, i.e. day 0 of the comparative study. The mandibles, both femurs and the first lumbar vertebrae of all rats were removed post-mortem and radiographs made for each individual bone; measurements of cortical thickness and bone widths were made from these radiographs using a computer-based video image analysis system. RESULTS: Significant differences among treatment groups were detected for each bone type; changes were sustained over the 48-week study period for the femur and vertebrae but were transient, except for alveolar bone height, in the mandible. Significant differences were found for cortical thicknesses and bone widths in the mandible, femur and vertebrae, based on the duration of the low-calcium diet. Although significant differences in the thickness of some cortices were found in the mandible, dimensional changes were small. CONCLUSIONS: Mandibular cortical width is an unreliable indicator of osteopenia in this rat model.

Analysis of Variance↗
PubMed1996

Quantitative computed tomography of trabecular bone in the mandible.

OBJECTIVE: To evaluate the potential use of quantitative computed tomography (QCT) for the assessment of bone mineral density of the edentulous mandible prior to implant placement. METHODS: Ten 2 mm thick CT slices of anterior and posterior edentulous sections from 15 mandibles were obtained perpendicular to the buccal and lingual plates. The bone mineral density, expressed as the amount of calcium hydroxyapatite (mg cm-3) of the trabecular bone, was calculated using a method that takes into account the influence of fat. RESULTS: The variation of bone mineral density between mandibles was high. Anterior sections showed higher values than posterior sections and a variation was found within sections of the same mandible. CONCLUSION: CT provides a site-related measure of the bone mineral density in the mandible and appears potentially useful as a non-invasive method to determine a parameter that may reflect bone quality prior to implant placement.

Aged↗
PubMed1998

Geographical variation of mandible size and shape in the Ryukyu wild pig (Sus scrofa riukiuanus).

We measured adult mandibles of Ryukyu wild pigs from Amami-Oshima, Kakeroma, Okinawa, Ishigaki and Iriomote Islands. The size cline was not statistically recognized among the populations of Nansei Islands. The Ishigaki population was significantly larger than Iriomote one in mandible length. Some measurement ratios indicated that the ramus is enlarged laterally and that the body of mandible is dorso-ventrally developed in Ishigaki and Iriomote populations. The Amami-Oshima mandibles were relatively smaller than those of Okinawa and Iriomote populations in length item of body of mandible. These results will contribute to the zoo-archaeology on the historical change of size and shape in the island populations, and to the evolutionary biology on the morphological adaptation of this animal.

Animals↗
PubMed2000

Changes in cortical bone mineralization in the developing mandible: a three-dimensional quantitative computed tomography study.

Quantitative computed tomography (QCT) was completed in 34 subjects between the ages of 9 and 33 years with symmetrical mandibles in order to investigate the three-dimensional cortical bone mineral density (BMD) distribution in the mandible. The number and distribution of the pixels were determined at three levels: (1) representing the entire mandibular bone; (2) the cortical bone at 60% above the baseline defined as the segmentation level (around 1050 mg/cm3) and representative of only cortical bone; and (3) the highest mineralized cortical bone (>1250 mg/cm3). The geometrical distribution of the highest mineralized areas was evaluated by three-dimensional reconstruction of the images. The total number of pixels for the entire mandible increased significantly at each time point represented at four increasing ages groups (9-11 years of age, 12-14 years of age, 15-17 years of age, and >18 years of age). The male and female subjects had a similar total number of pixels for the entire mandible before the age of 11, but the male subjects showed a significantly larger total number of mandibular pixels after that age. Comparison of the number of pixels for pure cortical bone (60% segmentation level) and the highest mineralized cortical bone indicated a significant increase with maturation with the greatest change occurring between the 13-year and 16-year age groups. However, the ratio of cortical bone/total bone increased at a more rapid rate in the male subjects and reached a plateau by the 16-year age group, showing distinct differences in mineralization of the mandible between the sexes.

Adolescent↗
PubMed2006

Comparison of rat mandible bone characteristics in F344 substrains, F344/Du and F344/N.

The characteristics of the mandible bone were compared through DXA methods between two major substrains of F344 rats, F344/DuCrlCrlj and F344/NSlc at around 60 days of age. Since these two substrains are clearly different in survival and mandible morphology, some genetic differences are supposed to exist. In contrast to a previous microsatellite analysis, clear and significant differences were detected in the body and mandible weights, the mandible bone mineral contents (BMC), bone area (AREA), bone mineral density (BMD) and bone mineral ratio (BMR), between F344/DuCrlCrlj and F344/NSlc, with the mandible molar teeth intact in the bone. Thus, care is needed in the experimental use of these substrains, as results may differ between them. The newly proposed parameter, BMR, may especially contribute to the comparison of bone characteristics among species.

Absorptiometry, Photon↗
PubMed2006

Morphometric comparison of the rat mandible in F344 substrains, F344/Du and F344/N.

The shape of the mandible was compared by morphometric methods to ascertain the genetic differences between two substrains of F344 rats, F344/DuCrlCrlj and F344/NSlc. Since these two substrains are clearly different in survival and the incidence of age associated disorders; thus, some genetic differences are suggested to be present between them. Although previous microsatellite analysis did not detect any differences between the two F344 substrains, the present study clearly detected interesting differences in the mandible morphology. At 2 months of age, the F344/Du mandible was characterized by a larger size, especially in length, than the F344/N mandible. The shape of the mandible seemed to be more variable in F344/N. This clear substrain difference suggests the importance of the substrain recognition in F344 rats, especially in experimental usage.

Animals↗
PubMed1989

[An electromyographic study of the inferior heads of the lateral pterygoid muscles during displacements of mandible].

The purpose of this study was to investigate electromyography of the inferior heads of lateral pterygoid muscles in experimental displacement of mandible, and its clinical application for reproduction and diagnosis of mandibular position. In the experiments, the mandibular position was changed in vertical and horizontal directions and muscle activity of the inferior heads was analyzed quantitatively. The results obtained were as follows: 1. Muscle activity of inferior heads was increased with amount of the displacement in anterior direction, and reached to great increase in 1.0 mm and 2.0 mm displacement of mandible. 2. No definite tendency of ipsilateral inferior heads was shown in lateral displacement of mandible. 3. Muscle activity of contralateral inferior heads in lateral displacement was increased with amount of the displacement, and 3 muscles showed great increase in 1.0-2.0 mm displacement of mandible. 4. As vertical increase was less than 2.0 mm, muscle activity of the inferior heads was decreased as to that of intercuspal contact position. 5. Muscle activity of the inferior heads in retruded position showed a little increased, but evidently as to that of intercuspal contact position. 6. Increasing patterns of muscle activities in anterior displacement were different from in contralateral displacement. 7. In anterior mandibular position an ability of presuming a mandible displacement over the limits of 1.0 mm from intercuspal contact position was suggested using muscle activity of inferior head as an index, and in lateral mandibular position that over the limits of 1.5 mm suggested.

Electromyography↗
PubMed1995

Normal age-related conversion of bone marrow in the mandible: MR imaging findings.

OBJECTIVE: The mandible is one of the most common sites for osteomyelitis and other marrow-based diseases. Therefore, knowledge of the normal patterns of marrow distribution could help evaluate marrow-based diseases. The purpose of this study was to assess the age-related normal sequence of conversion from hematopoietic to fatty marrow in the mandible as depicted on MR images. SUBJECTS AND METHODS: We prospectively reviewed T1-weighted MR images of the mandible for the distribution of hematopoietic and fatty marrow. Forty-five subjects 4 months to 25 years old with no known marrow abnormality were examined with the spin-echo technique. Marrow conversion was assessed in the condyle, ramus, angle, and body of the mandible using visual grading based on homogeneity, signal intensity, and a signal-intensity ratio determined by the intensities of the surrounding subcutaneous fat and air. RESULTS: Conversion of hematopoietic to fatty marrow occurred first in the mandibular body, followed by the angle, ramus, and finally the condyle. The marrow in the region distal to the ramus had almost fully converted to fatty marrow by the third decade of life, but the remaining regions contained some hematopoietic marrow. Further substantiating these results, the signal-intensity ratio increased up to about 90% in the angle and 70% in the ramus by the age of 10 years and then leveled off. On the other hand, the signal-intensity ratio in the condyle reached 60% by age 15 and remained unchanged for the following 10 years. CONCLUSION: The normal age-related conversion from hematopoietic to fatty marrow in the mandible follows a well-defined sequence, first seen in the mental region early in childhood, then in the body, the ramus, and finally the condyle.

Adolescent↗