Dietary consistency and the midline sutures in growing pigs.

OBJECTIVES: The purpose of this study was to investigate the effects of reduced masticatory function on midline suture growth and morphology in growing pigs. SETTING AND SAMPLE POPULATION: The sample was 20 pigs separated into two dietary groups and raised at the Department of Anthropology, Harvard University. Midline suture specimens were analyzed at the Department of Orthodontics, University of Washington. MATERIALS AND METHODS: Ten farm pigs and 10 minipigs, all male, were randomly assigned to hard (n = 9) and soft-diet (n = 11) groups. Fluorochromic mineral labels were administered to document bone apposition, and the animals were killed after 12 weeks. Undecalcified sections of the interfrontal, interparietal, internasal, and intermaxillary sutures were evaluated for bone quantity and sutural thickness, interdigitation ratio and growth rate. RESULTS: Soft-diet pigs were characterized by a slower rate of weight gain and less bone than their hard-diet counterparts. Even after correction for weight gain, soft-diet pigs had reduced suture growth rate and thickness. However, no difference in interdigitation ratio was detected between dietary groups. CONCLUSIONS: Restriction to a soft diet reduces midline suture growth and bone apposition in the growing pig.

Dynamic mechanics in the pig mandibular symphysis.

During mastication, various biomechanical events occur at the mammalian jaw symphysis. Previously, these events have been studied in the static environment, or by direct recording of surface bone strains. Thus far, however, it has not been possible to demonstrate directly the forces and torques passing through the symphysis in association with dynamically changing muscle tensions. Therefore, we modified a previously published dynamic pig jaw model to predict the forces and torques at the symphysis, and related these to simulated masticatory muscle tensions, and bite, joint and food bolus forces. An artificial rigid joint was modelled at the symphysis, allowing measurements of the tri-axial forces and torques passing through it. The model successfully confirmed three previously postulated loading patterns at the symphysis. Dorsoventral shear occurred when the lower teeth hit the artificial food bolus. It was associated with balancing-side jaw adductor forces, and reaction forces from the working-side bite point. Medial transverse bending occurred during jaw opening, and was associated with bilateral tensions in the lateral pterygoid. Lateral transverse bending (wishboning) occurred at the late stage of the power stroke, and was associated with the actions of the deep and superficial masseters. The largest predicted force was dorsoventral shear force, and the largest torque was a 'wishboning' torque about the superoinferior axis. We suggest that dynamic modelling offers a new and powerful method for studying jaw biomechanics, especially when the parameters involved are difficult or impossible to measure in vivo.

Condylar mineralization following mandibular distraction in rats.

The impact of mandibular distraction on condyles is poorly understood. To examine how condylar mineralization is affected, we performed distraction in 128 one-month-old rapidly and 126 three-month-old slowly growing rats. The rate of distraction was 0.0 mm (sham), 0.2 mm (slow), 0.4 mm (moderate), or 0.6 mm (rapid). From 7 to 9 rats from each rate (n = 29-32) were killed at 4 time periods (D6, D10, D24, and D38) following osteotomy. Calcein and alizarin were injected 6 and 3 days, respectively, prior to death. Methacrylate-embedded sagittal condylar sections were examined under epifluorescence, and mineral apposition rates were measured. Results indicated that: (1) rapidly growing rats showed higher mineral apposition rates (p < 0.01-0.001) than did slowly growing rats; (2) mineral apposition rates were lower in distracted sides at all times in rapidly growing rats (p < 0.05-0.01), while this side-dependency was seen only at D24 in slowly growing rats (p < 0.05); and (3) distraction rates had little effect on mineral apposition rates. Thus, mandibular distraction decreases condylar mineral apposition rates, but only in rapidly growing rats, which is related to surgery and its functional consequences, not to the distraction rate.

Bone--special problems of the craniofacial region.

PROBLEMS: The craniofacial region presents special problems for tissue engineering. First, the stresses and strains that engineered tissues will encounter are mostly unknown. Second, if tissue engineering is to be useful in ameliorating craniofacial anomalies, it will have to mimic the growth activity of the native tissues. These problems are interrelated in that bone growth responds to loading conditions. METHODS: Our work uses miniature technology to measure skull deformation during function in the miniature pig. Growth is quantified in the same animals by labeling replicating cells with bromodeoxyuridine and newly mineralized bone with fluorochromes. The mandibular condyle and the cranial sutures are both candidate areas for tissue engineering, and craniofacial periosteum is a promising graft material. RESULTS: The condyle is compressed by the reaction load at the temporomandibular joint (TMJ). Cell divisions in the perichondrium are negatively correlated with bone strain. Craniofacial sutures deform during function much more than adjacent bones, and strains can be either tensile or compressive. In contrast to expectation, functional tension is not correlated with sutural growth rate. However, functional strain does predict sutural morphology, with compressed sutures showing complex interdigitation. Periosteum shows striking differences between resorptive and appositional surfaces. The resorptive medial side of the zygomatic arch is under pressure during function. Tensile strain perpendicular to the surface is probably greater on the temporal than on the zygomatic bone, thus correlating with more rapid periosteal apposition on the temporal. CONCLUSION: Engineered implants may be more likely to succeed if their architecture suits the strain environment in which they will function.

Enamel microstructure and microstrain in the fracture of human and pig molar cusps.

The role of microstructure in enamel strain and breakage was investigated in human molar cusps and those of the pig, Sus scrofa. Rosette strain gauges were affixed to cusp surfaces (buccal human M3, n=15, and lingual pig M1, n=13), and a compressive load was applied to individual cusps using an MTS materials testing machine. Load and strain data were recorded simultaneously until cusp fracture, and these data were used to estimate enamel stresses, principal strains, and stiffness. Fractured and polished enamel fragments were examined in multiple planes using scanning electron microscopy (SEM). Human cusp enamel showed greater stiffness than pig enamel (P=0.02), and tensile stress at yield was higher (17.9 N/mm2 in humans versus 8.9 N/mm2 in pigs, P=0.06). SEM revealed enamel rod decussation in both human and pig enamel; however, only pig enamel showed a decussation plane between rod and inter-rod crystallites. Human inter-rod enamel was densely packed between rods, whereas in pig enamel, inter-rod enamel formed partitions between rows of enamel rods. Overall, human enamel structure enabled molar cusps to withstand horizontal tensile stress during both elastic and plastic phases of compressive loading. In contrast, pig cusp enamel was less resistant to horizontal tensile stresses, but appeared to fortify the enamel against crack propagation in multiple directions. These structural and biomechanical differences in cusp enamel are likely to reflect species-level differences in occlusal function.

Time series analysis of jaw muscle contraction and tissue deformation during mastication in miniature pigs.

Masticatory muscle contraction causes both jaw movement and tissue deformation during function. Natural chewing data from 25 adult miniature pigs were studied by means of time series analysis. The data set included simultaneous recordings of electromyography (EMG) from bilateral masseter (MA), zygomaticomandibularis (ZM) and lateral pterygoid muscles, bone surface strains from the left squamosal bone (SQ), condylar neck (CD) and mandibular corpus (MD), and linear deformation of the capsule of the jaw joint measured bilaterally using differential variable reluctance transducers. Pairwise comparisons were examined by calculating the cross-correlation functions. Jaw-adductor muscle activity of MA and ZM was found to be highly cross-correlated with CD and SQ strains and weakly with MD strain. No muscle's activity was strongly linked to capsular deformation of the jaw joint, nor were bone strains and capsular deformation tightly linked. Homologous muscle pairs showed the greatest synchronization of signals, but the signals themselves were not significantly more correlated than those of non-homologous muscle pairs. These results suggested that bone strains and capsular deformation are driven by different mechanical regimes. Muscle contraction and ensuing reaction forces are probably responsible for bone strains, whereas capsular deformation is more likely a product of movement.

The effects of intraoral splints on the masticatory system of pigs.

While evidence exists to support the effectiveness of splints on conditions involving the masticatory musculature, few research projects have examined the results of long-term splint wear. The purpose of this study was to examine the function of the masticatory system over a 2-month time period of splint wear. Young adult female miniature pigs were divided into three groups: a control (C) group that wore no intraoral splint, a control splint (CS) group that wore a splint increasing bite height, and a protrusive splint (PS) group that wore a splint increasing bite height and moving the mandible anteriorly. Splints were worn constantly. Fine-wire needle EMG was performed prior to splint delivery and at 1 and 2 months post-splint delivery. Bilateral superficial masseters and zygomaticomandibularis (ZM, equivalent to deep masseter) muscles were monitored during normal feeding. Absolute EMG output, percentage output, and cycle timing were unaffected by chronic splint wear. However, chewing coordination was significantly changed in the splinted groups in both sessions post-splint delivery relative to baseline readings and to the C group (P < 0.005). Trends indicate that the coordination of the PS group was more greatly altered than that of the CS group.

Modelling the masticatory biomechanics of a pig.

The relationships between muscle tensions, jaw motions, bite and joint forces, and craniofacial morphology are not fully understood. Three-dimensional (3-D) computer models are able to combine anatomical and functional data to examine these complex relationships. In this paper we describe the construction of a 3-D dynamic model using the anatomical (skeletal and muscle form) and the functional (muscle activation patterns) features of an individual pig. It is hypothesized that the model would produce functional jaw movements similar to those recordable in vivo. Anatomical data were obtained by CT scanning (skeletal elements) and MR imaging (muscles). Functional data (muscle activities) of the same animal were obtained during chewing by bipolar intramuscular electrodes in six masticatory muscles and combined with previously published EMG data. The model was driven by the functional data to predict the jaw motions and forces within the masticatory system. The study showed that it is feasible to reconstruct the complex 3-D gross anatomy of an individual's masticatory system in vivo. Anatomical data derived from the 3-D reconstructions were in agreement with published standards. The model produced jaw motions, alternating in chewing side, typical for the pig. The amplitude of the jaw excursions and the timing of the different phases within the chewing cycle were also in agreement with previously published data. Condylar motions and forces were within expected ranges. The study indicates that key parameters of the pig's chewing cycle can be simulated by combining general biomechanical principles, individual-specific data and a dynamic modelling approach frequently used in mechanical engineering.

Mechanical properties of the periosteum in the pig, Sus scrofa.

The fibrous periosteum forms an intermediary between muscle and ligament forces and the underlying osteoblastic tissue, thus the mechanical properties of the periosteum are critical to understanding osteogenic stimuli. Regional and directional variation in periosteal properties may contribute to the biomechanical regulation of growth in some bones. Periostea of the pig mandibular body, zygomatic arch and metacarpal were loaded to failure under continuous tension. Each tissue type was tested in both the long-axis and transverse orientation. Stiffness, peak stress and peak strain were compared between orientations and among regions. Within the zygomatic periosteum there was little indication of regional difference, and neither zygomatic nor mandibular periosteum showed directional differences. The metacarpal periosteum showed a directional effect only in peak strain, which was greater longitudinally than transversely. There were striking differences, however, among the periostea of the three bones. The zygomatic arch periosteum was the stiffest tissue (91.7+/-30.5 MPa) and showed the highest strength (12.3+/-4.6 MPa). The metacarpal periosteum demonstrated slightly lower stiffness and strength (84.7+/-35.1 and 11.3+/-5.3 MPa), and peak strains in zygomatic and metacarpal periostea were similarly high (17.7+/-3.7 and 17.9+/-3.7 MPa, respectively). The periosteum of the mandibular body was the most deformable tissue (63.0+/-25.4 MPa), with the lowest-peak strain (15.6+/-3.0 MPa) and the least strength (8.2+/-4.1 MPa). These results correspond with those of previous work in long bones, in that periosteum interfacing with ligament or muscle (e.g. zygomatic, metacarpal) demonstrates greater stiffness and strength than periosteum adjacent to loose connective tissue (e.g. mandibular body). Therefore, the degree to which the periosteal tissue serves as a functional interface between bone and muscle is reflected in the different failure properties of periostea from different bones. The structural fortification of the zygomatic arch periosteum relative to other periosteal tissues suggests a role for the periosteum in stabilizing the zygomatic arch-muscle functional complex. On the other hand, the similar failure properties of zygomatic and squamosal periostea from the zygomatic arch mean that the differential growth of these bones cannot be attributed to mechanical stimuli intrinsic to the periosteal tissue.

Jaw muscles and the skull in mammals: the biomechanics of mastication.

Among non-mammalian vertebrates, rigid skulls with tight sutural junctions are associated with high levels of cranial loading. The rigid skulls of mammals presumably act to resist the stresses of mastication. The pig, Sus scrofa, is a generalized ungulate with a diet rich in resistant foods. This report synthesizes previous work using strain gages bonded to the bones and sutures of the braincase, zygomatic arch, jaw joint, and mandible with new studies on the maxilla. Strains were recorded during unrestrained mastication and/or in anesthetized pigs during muscle stimulation. Bone strains were 100-1000 micro epsilon, except in the braincase, but sutural strains were higher, regardless of region. Strain regimes were specific to different regions, indicating that theoretical treatment of the skull as a unitary structure is probably incorrect. Muscle contraction, especially the masseter, caused strain patterns by four mechanisms: (1) direct loading of muscle attachment areas; (2) a compressive reaction force at the jaw joint; (3) bite force loading on the snout and mandible; and (4) movement causing new points of contact between mandible and cranium. Some expected patterns of loading were not seen. Most notably, strains did not differ for right and left chewing, perhaps because pigs have bilateral occlusion and masseter activity.

Loading of the temporomandibular joint: anatomical and in vivo evidence from the bones.

'Loading of the TMJ' is usually understood to mean a compressive force applied to the articular surfaces of the jaw joint. Theoretical models of jaw mechanics can be manipulated to support either the presence or the absence of loading, depending on the assumed contraction patterns of the muscles and the assumed occlusion. This paper synthesizes a series of studies on jaw joint function using pigs as substitutes for humans. Bone strain (deformation) was directly measured on the lateral surfaces of the condylar neck and the squamosal (equivalent to the human temporal) bone. Chewing strains indicate that loading does occur and is not light. The peak strains on the condyle are indeed primarily compressive, but the situation is dynamic. Small tensile strains can occur during chewing, and protrusive splints may decrease the strain resulting from muscle stimulation. The squamosal bone is even more surprising, in that the major strain is tensile. The most likely explanation for this finding is that the squamosal bone is bent under the load. Thus, the two elements of the TMJ are deformed in different ways by the same movements and muscle activities. Internal bony architecture reflects these differences. The condyle is filled with fine, vertically oriented bony trabeculae. The articular eminence has thick cortices and trabeculae oriented approximately transversely. In conclusion, the TMJ is loaded, but the situation is complex. The largest forces seen by the condyle are compressive, and they arise from muscle contraction. These same forces serve to bend the squamosal bone.

Mass properties of the pig mandible.

Specification of mass properties is an essential step in the modeling of jaw dynamics, but obtaining them can be difficult. Here, we used three-dimensional computed tomography (CT) to estimate jaw mass, mean bone density, anatomical locations of the mass and geometric centers, and moments of inertia in the pig jaw. High-resolution CT scans were performed at one-mm slice intervals on specimens submerged in water. The mean estimated jaw mass was 12% greater than the mean wet weight, and 33% more than the mean dry weight. Putative bone marrow accounted for an extra 13% of mass. There was a positive correlation between estimated mean bone density and age. The mass center was consistently in the midline, near the last molar. The mean distance between the mass center and geometric center was small, especially when bone marrow was taken into account (0.58 +/- 0.21 mm), suggesting that mass distribution in the pig jaw is almost symmetrical with respect to its geometric center. The largest moment of inertia occurred around each mandible's supero-inferior axis, and the smallest around its antero-posterior axis. Bone marrow contributed an extra 9% to the moments of inertia in all three axes. Linear relationships were found between the actual mass and a mass descriptor (product of the bounding volume and mean bone density), and between the moments of inertia and moments of inertia descriptors (products of the mass descriptor and two orthogonal dimensions forming the bounding box). The study suggests that imaging modalities revealing three-dimensional jaw shape may be adequate for estimating the bone mass properties in pigs.

The fracture behaviour of human and pig molar cusps.

Masticatory efficiency depends upon the ability of the molar cusps to apply concentrated bite forces to food particles and simultaneously to withstand the dental stresses that may cause enamel fracture. This study investigated how low-crowned molar cusps in omnivorous mammals, specifically humans, Homo sapiens, and pigs, Sus scrofa, resist fracture under compressive load. A uniaxial compressive load was applied to individual molar cusps with a materials testing machine. The progressive loading and deformation of the cusps were recorded for interrupted and continuous tests. In interrupted tests, the appearance of progressive cusp fracture was recorded. Stiffness and fracture stresses were calculated from continuous test results. Pig cusps responded to both interrupted and continuous loads with greater deformation; progressive crumbling of the cusp tip resulted in new occlusal contacts on enamel lophs. Conversely, human cusps showed minimal breakage before failure. Continuous compressive tests demonstrated the greater stiffness of human cusps, as well as the capacity to sustain higher cusp tip stresses. The greater stiffness and high fracture resistance of human cusps may be attributed to the thickness of enamel. Test results reflected fundamentally different means of crown stress management that correspond with phylogenetic differences in masticatory function.

Osteoprotegerin, a crucial regulator of bone metabolism, also regulates B cell development and function.

Osteoprotegerin (OPG) is a CD40-regulated gene in B cells and dendritic cells (DCs). We investigated the role of OPG in the immune system by generating opg(-/-) mice. Like its role as a regulator of bone metabolism, OPG also influences processes in the immune system, notably in B cell development. Ex vivo, opg(-/-) pro-B cells have enhanced proliferation to IL-7, and in opg(-/-) spleen, there is an accumulation of type 1 transitional B cells. Furthermore, opg(-/-) bone marrow-derived DCs are more effective in stimulating allogeneic T cells than control DCs. When challenged with a T-dependent Ag, opg(-/-) mice had a compromised ability to sustain an IgG3 Ag-specific response. Thus, in the immune system, OPG regulates B cell maturation and development of efficient Ab responses.

Thromboelastograph assay for measuring the mechanical strength of fibrin sealant clots.

In order to provide sustained hemostasis or tissue sealing, fibrin sealants must generate adhesive clots with mechanical properties capable of resisting forces, such as shear, that might break or tear the clot. Commercial preparations of fibrin sealants should generate clots of adequate and consistent mechanical strength. The mechanical strength of fibrin sealants is often measured as bonding strength in in vivo or ex vivo animal wound models. These tests can be useful predictors of clinical efficacy. However, these, as well as many in vitro tensile strength tests for fibrin sealant, tend to be laboratory specific and require extensive reagent preparation time and analyst training. The thromboelastograph has historically been used to screen for plasma protein and platelet disorders that lead to defective clot formation. The authors have developed a simple in vitro test, using a standard thromboelastograph that can provide reliable, reproducible information on the rheology of clots generated by fibrin sealant preparations. Using this method, the shear strength of fibrin sealant clots was measured and shown to correlate with the fibrinogen, but not the thrombin, concentration in the sealant. Shear strength was also shown to correlate with the sealant concentration of the fibrin cross-linking proenzyme, factor XIII. Sealants containing lysine, which can act as an alternate substrate for factor XIII enzyme and prevent efficient fibrin chain cross-linking, were shown by this method to generate clots of substantially reduced shear strength. The method distinguished between thrombin-catalyzed clot formation and other fibrinogen clotting mechanisms as evidenced by the significantly lower shear strength associated with batroxobin-generated fibrin clots.

Ontogeny of histochemical fiber types and muscle function in the masseter muscle of miniature swine.

In this study of masticatory maturation, the ontogeny of the histochemical fiber type composition of musculus masseter is examined in the omnivorous miniature swine (Sus scrofa). Fiber type characteristics are interpreted by comparison with electromyography (EMG) recorded during feeding behavior. Similar to locomotion studies, the results suggest a correspondence between the composition and arrangement of motor units and their recruitment pattern. Serial sections of masseter muscles from 10 minipigs, ranging from 2 weeks to slightly over 1 year of age, were stained for myosin adenosine triphosphatase (mATPase) activity to distinguish slow-twitch from fast-twitch fibers, and for nicotinamide adenosine dehydrogenase-tetrazolium reductase to assess the aerobic capacity of the same fibers. Although maintaining a uniformly high aerobic capacity throughout ontogeny and in adult animals, a transition is observed in the relative proportions of fast- and slow-twitch fibers. The primarily fast-twitch neonatal pig masseter eventually comprises approximately 25-30% slow-twitch fibers in adults, with a higher predominance of slow fibers in the deep (vs. superficial) and anterior (vs. posterior) regions of the muscle. Furthermore, while individual fibers of adult masseters generally stain for either alkaline- or acid-stable mATPase activity, a substantial proportion of cells in developing animals exhibits the presence of both isozymes. EMG results indicate functional heterogeneity within the masseter of adult pigs. During chewing, when pig chow is replaced by cracked corn, EMG activity in the deep portion of the muscle either decreases or increases slightly. In the superficial portion, however, muscle amplitudes become dramatically higher for corn, surpassing levels generated for chewing the less obdurate chow. These results are consistent with a behavioral transition from neonatal suckling to sustained mastication of foods of more complex textures eaten by adult pigs. The relationship between these fiber type and EMG results for pig masseter corresponds to those pertaining to motor unit recruitment in the extensor muscles of locomotion. Implications of this work for the evolutionary morphology of mastication also are discussed.

Strain in the braincase and its sutures during function.

The skull is distinguished from other parts of the skeleton by its composite construction. The sutures between bony elements provide for interstitial growth of the cranium, but at the same time they alter the transmission of stress and strain through the skull. Strain gages were bonded to the frontal and parietal bones of miniature pigs and across the interfrontal, interparietal and coronal sutures. Strains were recorded 1) during natural mastication in conjunction with electromyographic activity from the jaw muscles and 2) during stimulation of various cranial muscles in anesthetized animals. Vault sutures exhibited vastly higher strains than did the adjoining bones. Further, bone strain primarily reflected torsion of the braincase set up by asymmetrical muscle contraction; the tensile axis alternated between +45 degrees and -45 degrees depending on which diagonal masseter/temporalis pair was most active. However, suture strains were not related to overall torsion but instead were responses to local muscle actions. Only the coronal suture showed significant strain (tension) during jaw opening; this was caused by the contraction of neck muscles. All sutures showed strain during jaw closing, but polarity depended on the pattern of muscle usage. For example, masseter contraction tensed the coronal suture and the anterior part of the interfrontal suture, whereas the temporalis caused compression in these locations. Peak tensile strains were larger than peak compressive strains. Histology suggested that the skull is bent at the sutures, with the ectocranial surface tensed and the endocranial surface predominantly compressed. Collectively, these results indicate that skulls with patent sutures should be analyzed as complexes of independent parts rather than solid structures.

Three-dimensional loading and growth of the zygomatic arch.

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.

Effects of intraoral splint wear on proteoglycans in the temporomandibular joint disc.

Intraoral splints are a common dental treatment for dysfunctions of the temporomandibular joint (TMJ), but their effects on the structures of the joint, specifically the disc, have not been well investigated. This study examined proteoglycans (PGs) of the TMJ disc of the miniature pig and tested for alterations resulting from intraoral splint wear. Sixteen female pigs were divided into three groups: control (C), control splint (CS), and protrusive splint (PS). Splinted groups received chrome-cobalt ramp splints which were worn continuously for 2 months. PG content within various disc locations was determined by colorimeteric assay. PG synthesis and type were examined by labeling with (35)S-sulfate and SDS-PAGE analysis. Average water content of the disc was 77.1%, which places it at the high end of the normal range for collagenous biomaterials (60-80%). PGs migrating to the positions typical of aggrecan, biglycan, and decorin on SDS-PAGE were present in all locations of all groups. The highest content and synthesis of PGs were always found in the intermediate band of the disc regardless of group (P < 0.05), supporting the notion that this band encounters heavy compressive loading during function. The joints of animals from both splinted groups showed a high frequency of gross pathology. Biglycan synthesis was increased in both splinted groups (P < 0.05). Newly synthesized biglycan had a shorter migration distance in the intermediate bands of the CS group, suggesting increased hydrodynamic size. These findings suggest that intraoral splint wear may cause disc damage or remodeling.