Topic
Squamosal bone
About: Squamosal bone is a research topic. Over the lifetime, 19 publications have been published within this topic receiving 445 citations.
Papers
TL;DR: Paleorhinus, the most primitive phytosaur genus, has external nares well forward of the antorbital fenestrae, the posttemporal arch at level of the skull roof, a slender rostrum without crests, homodont dentition, a low quadrate, and no trace of a posterior squamosal process as discussed by the authors.
Abstract: The long-snouted, crocodile-like, amphibious reptiles of the Late Triassic known as phytosaurs are assigned to 5 genera on the basis of cranial characters. The most primitive genus, Paleorhinus, has external nares well forward of the antorbital fenestrae, the posttemporal arch at level of the skull roof, a slender rostrum without crests, homodont dentition, a low quadrate, and no trace of a posterior squamosal process. Mystriosuchus, which has highly specialized posterior nares, tall quadrate, and depressed posttemporal bar, retains the primitive form of the squamosal, homodont dentition, and slender (much longer) rostrum of Paleorhinus from which it may be derived through Francosuchus (the European subgenus of Paleorhinus). The remaining phytosaur genera are characterized by rounded processes of the squamosal bone projecting well behind the occipital surface of the skull, and by the development of heterodont dentition and generally more robust skulls. Angistorhinus, the most primitive member of this lineage, retains a primitive posttemporal arch at the level of the skull deck, but is advanced over Paleorhinus in its posteriorly placed external nares. Its rostrum is slender and lacks crests; the dentition is only slightly differentiated. Phytosaurus and Rutiodon, the more specialized members of this group, have depressed posttemporal arches and tall quadrates. Rostra of Rutiodon vary from slender and uncrested in small skulls to moderately robust with high dorsal crests in the posterior half in the largest individuals; teeth vary from moderately to strongly heterodont. The squamosal processes are slender and show progressive phyletic elongation. The ratio of rostral to postrostral length varies inversely with size. Phytosaurus skulls are characterized by massive rostra with continuous dorsal crests and have a relatively constant rostral ratio independent of size; the squamosal processes are short and deep; dentition is strongly heterodont; considerable evidence suggests that the dorsal armor plates differed from other phytosaurs.
75 citations
TL;DR: Using young miniature swine, for the first time recorded strains from both the medial and lateral aspects of the squamosal bone during mastication and masseter muscle stimulation to explain why partial removal of the masseter had little effect on the growth of the zygomatic flange.
Abstract: Despite a number of previous biomechanical studies on the zygomatic arch, unanswered questions remain about its three-dimensional loading and growth. Using young miniature swine, we have for the first time recorded strains from both the medial and lateral aspects of the squamosal bone during mastication and masseter muscle stimulation. Strains from the zygomatic bone flange and zygomatic arch growth data were also obtained from the same animals. A second study on a younger group of animals examined the growth of the zygomatic flange following partial removal of the masseter. Strain data indicated that the squamosal bone is bent out-of-plane and that this pattern of loading is quite different from that of the adjacent zygomatic bone, which experiences much lower strains with little evidence of out-of-plane bending. Surprisingly, strains were higher in the zygomatic flange during contralateral chews and contralateral masseter stimulations than during ipsilateral chews/stimulations. These strains proved to arise from movement of the condyle, explaining why partial removal of the masseter had little effect on the growth of the flange. Other growth results indicated an approximately threefold greater rate of subperiosteal deposition on the lateral surface of the squamosal bone than on the zygomatic bone. This difference in growth rate is attributed to the presence of sutures that contribute to the lateral displacement of the zygomatic bone but not the squamosal bone. This explanation does not exclude the possibility that the rapid apposition on the lateral squamosal surface is regulated by the high surface strains that result from out-of-plane bending.
63 citations
Journal Article•
TL;DR: Both osseous and ligamentous components of the TMJ are strained during mastication, and the latter are more deformed on the balancing side.
Abstract: Aims An animal study of functional biomechanics was undertaken to understand normal loading of the temporomandibular joint (TMJ) and to provide insight into the pathogenesis of TMJ disorders. Methods Bone strain and ligamentous deformation were measured during mastication in 26 10-month-old minipigs. Half the subjects had undergone a surgical disruption of the left lateral capsular and disc attachments to the condyle 5 to 6 weeks previously. Rosette strain gauges were bonded to the left lateral surfaces of the squamosal bone near the TMJ, the condylar neck, and the mandibular corpus below the molar region. Differential variable reluctance transducers (DVRTs) were placed bilaterally in the lateral capsular tissue of the joints. Bone strains, ligamentous deformations, and the electromyographic activities of the masseters and lateral pterygoids were recorded during natural mastication. Results In all animals on both working and balancing sides, mastication caused bone strains that were dominated by tension in the squamosal bone site and by compression in the other sites. Measurements from the DVRT revealed elongation of the lateral capsular tissue in the last phase of the power stroke and shortening in the initial phase of opening, which was almost simultaneous with the development of bone strain. Strain in the capsule ranged from 3 to 25%, with the strain of the balancing side exceeding that of the working side. The surgical disruption did not alter chewing side preference or bone strain, but a tendency toward more extensive ligamentous deformation on the intact side was observed. Furthermore, the ratio of masseter to lateral pterygoid activity was smaller on the disrupted side and larger on the intact side, in comparison to control pigs. Conclusion Both osseous and ligamentous components of the TMJ are strained during mastication, and the latter are more deformed on the balancing side. Disruption of the lateral attachment had little effect on strain in the osseous components but appeared to increase strain in the capsule and to modify the balance of masticatory muscle activity.
55 citations
TL;DR: Both strains and pressures in the jaw joint varied according to specific muscle activity, and surgical disruption enhanced both pressure changes and bone strains under either muscle contraction but their overall patterns were not altered.
52 citations
TL;DR: The prenatal development of the mandibular joint in mice was studied in fetuses at 15 to 20 days insemination age and the future condylar process of the Mandible can be recognized in its relationship to the external pterygoid muscle, inferior alveolar nerve, and Meckel's cartilage.
Abstract: The prenatal development of the mandibular joint in mice was studied in fetuses at 15 to 20 days insemination age. The ramus of the mandible can be delineated as early as the fifteenth day by distinct differences in the degree of condensation of mesenchyme at the site of the future joint. The future condylar process of the mandible can be recognized in its relationship to the external pterygoid muscle, inferior alveolar nerve, Meckel's cartilage, pre-cartilaginous alisphenoid process of the future basisphenoid bone, and the anlage of the squamosal bone with its zygomatic process.
Differentiation is rapid through the twentieth day of gestation at which time the following major elements of the joint can be recognized: a fibrous intra-articular disc continuous with the tendon of the external pterygoid muscle; a vascular synovial mesenchyme with upper and lower synovial spaces; an ossified squamosal bone with a fibrous joint lining; and a well developed condylar process with good representation of differentiating cells in the zones of chondrification and ossification.
Among the elements not yet evident, however, are (1) hemopoietic marrow in the condyle, (2) a constricted neck at the base of the condyle, and (3) a fibrous capsule or capsular ligament.
45 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2018 | 1 |
| 2014 | 1 |
| 2012 | 1 |
| 2003 | 1 |
| 2000 | 3 |
| 1997 | 1 |