Susan Herring

University of Washington Seattle | UW

Objective: Botulinum neurotoxins (BoNT) are used in masticatory muscles for pain relief, unloading of the mandible, and cosmetic facial contouring. Treatment is often repeated every few months as function returns. This study assessed masticatory function and musculoskeletal structure after multiple BoNT treatment of the rabbit masseter. Design:...

Cranial sutures are complex soft tissue structures whose mechanics are often studied due to their link with bone growth in the skull. Researchers will often use a cross-sectional two-dimensional slice to define suture geometry when studying morphometry and/or mechanical response to loading. However, using a single cross section neglects the full su...

Botulinum neurotoxins (BoNTs) are paralytic agents used to treat a variety of conditions in jaw muscles. Although their effect is considered temporary, there are reports of persistent functional changes. Using rabbits that received BoNT injection in one masseter muscle, the recovery of neuromuscular connection was investigated using nerve stimulati...

Mobility is a fundamental characteristic of mammalian teeth, and has been widely used to determine individual tooth prognosis. However, the direction and extent of tooth movement under functional loads are unknown. This study investigated maxillary molar mobility, alveolar bending, and periodontal space (PDL) fluid pressure during mastication and m...

Objective To compare the morphology and mechanical function of sutures in normal pigs and minipigs to those of Yucatan minipigs, a natural model for midfacial hypoplasia. Setting and Sample Population Research took place at the Department of Orthodontics at the University of Washington and used varying sample sizes of normal‐snouted pigs and Yucat...

Objective To evaluate cone-beam computed tomography (CBCT) image quality via cephalometric measurement variability while reducing radiation exposure by altering the radiographic technique. Materials and Methods A human cadaver was imaged using a Morita Accuitomo 170 CBCT machine at various technique parameters: tube voltages of 60, 70, 80, and 90...

The development of the mandibular symphysis in late fetal and postnatal pigs, Sus scrofa dom. (n = 17), was studied as a model for the early fusing symphysis of anthropoid primates, including humans. The suture‐like ligaments occurring in species that retain a mobile symphysis are not present in the pig. Instead, cartilage is the predominant tissue...

Introduction: Current craniofacial growth modification devices use static forces, but cyclic forces are believed by some to be more effective. The latter have not been evaluated in large animal models, and it is not known how such forces are transmitted to distant parts of the skull. In this study, we aimed to (1) develop a portable loading system...

In addition to conveying the forces of attaching muscles and ligaments to the zygomatic and temporal bones, the arch periosteum is responsible for lateral apposition and medial resorption during the growth period. In this contribution, we describe the vasculature of the zygomatic arch in young pigs (Sus scrofa dom.) in order to understand the relat...

Background: In recent years large bibliographic databases have made much of the published literature of biology available for searches. However, the capabilities of the search engines integrated into these databases for text-based bibliographic searches are limited. To enable searches that deliver the results expected by comparative anatomists, an...

Introduction: Temporary paralysis of the masseter muscle caused by botulinum toxin is a common treatment for temporomandibular disorders, bruxism, and muscle hypertrophy. Loss of masseter force is associated with decreased mandibular mineral density. Our objectives were (1) to establish whether bone loss at the mandibular condyle is regionally spe...

Like humans, domestic pigs are omnivorous and thus are a common model for human masticatory function. Prior attempts to characterize food-tooth interactions and jaw movements associated with mastication have been limited to aspects of the oral apparatus that are visible externally (with videography) and/or to 2D movements of oral structures (with m...

Pigs respond to direct administration of botulinum neurotoxins (BoNTs), although they are resistant to botulism. The human masseter is frequently targeted for BoNT therapy. We aimed to understand how BoNT affects chewing by injecting porcine masseters. One masseter of minipigs was injected with BoNT serotype A or B at doses comparable to those used...

The growth of the nasal septal cartilage is believed to be a driving force of midfacial growth. Cellular proliferation is an important contributor to growth of the cartilage, but this factor has been rarely investigated. The current study was undertaken to assess the proliferation and cellular density in the septal cartilage of fast-growing juvenil...

The expanding nasal septal cartilage is believed to create a force that powers midfacial growth. In addition, the nasal septum is postulated to act as a mechanical strut that prevents the structural collapse of the face under masticatory loads. Both roles imply that the septum is subject to complex biomechanical loads during growth and mastication....

Introduction: The nasal septum is thought to be a primary growth cartilage for the midface and, as such, has been implicated in syndromes involving midfacial hypoplasia. However, this internal structure is difficult to study directly. The aims of this study were to provide direct, continuous measurements of the growth of the nasal septal cartilage...

Botulinum neurotoxins are responsible for the paralytic food poisoning, botulism. Commercial formulations such as botulinum neurotoxin type A are increasingly used for various conditions, including cosmetic recontouring of the lower face by injection of the large masseter muscles. The paralysis of a major muscle of mastication lowers occlusal force...

Introduction:The nasal septal cartilage (NSC) is thought to be a driving force of midfacial growth. However, it is not clear whether the NSC expands uniformly. Previous reports suggest that interstitial growth and cellular proliferation in the NSC varies by region, but results are not consistent. Objectives: To measure the interstitial growth and...

Introduction: Loading history affects periodontal ligament (PDL) and alveolar bone morphology. Previous literature shows that force can increase the complexity of the tooth-bone interface whereas soft diets lead to thinning of the PDL space and disorganization of PDL fibers. Weakening of jaw muscles is a treatment for severe bruxism, and reduction...

Objective: The 7 serotypes of botulinum toxin vary in effectiveness. This project investigated how botulinum toxin Type-A (BTX/A) and Type-B (BTX/B) differentially affect the physiology and anatomy of the pig masseter muscle(MA). Method: BTX/A (100 units, n=3; 200 units, n=1), BTX/B (5,000 units, n=3), or an equivalent volume of 0.9% saline (n=2)...

Objective: To investigate short- and long-term effects of botulinum toxin Type A (BTX/A) on the neuromuscular responses of the masseter muscle (MA). Method: Of 15 rabbits, 5 were untreated (control), and 10 received 10 units of BTX/A injected into one MA. The treated rabbits were examined 4 weeks (short-term) or 12 weeks (long-term) after the inj...

Objectives: Paralysis of the masseters using botulinum toxin (BTX) is a common treatment for cosmetic reduction of the masseters, muscle spasm, bruxism, and pain. In a previous study, rabbit masseters injected with BTX functionally recovered, but remained significantly lighter than uninjected muscles 12 weeks after injection. The goal of this study...

Objective: The mechanism for tooth extraction induced residual alveolar ridge reduction (RRR) during adolescence is poorly understood. This study investigated the alveolar bone morphology, growth, resorption and functional loading at normal and extraction sites using an adolescent pig model. Design: Sixteen 3-month-old pigs were divided into two...

The skull does not bear body weight, causing speculation that craniofacial bones are not dependent on loading for their maintenance, unlike limb bones. The relative ease of changing alveolar bone using orthodontic forces seems to belie this notion, as do experiments modifying sutural and condylar growth using applied loads. Nevertheless, these may...

Paralysis of the masticatory muscles using botulinum toxin (BTX) is a common treatment for cosmetic reduction of the masseters as well as for conditions involving muscle spasm and pain. The effects of this treatment on mastication have not been evaluated, and claims that the treatment unloads the jaw joint and mandible have not been validated. If B...

The tooth– bone interface consists of the cementumcovered root, the periodontal soft tissues, and the bony alveolar socket. Each of these structures is a complex of cellular and matricial constituents, variably arranged and geometrically irregular. The three major components ...

Although the FEED database focuses on muscle activity patterns, it is equally suitable for other physiological recording and especially for synthesizing different types of information. The present contribution addresses the interaction between muscle activity and ligamentary stretch during mastication. The postorbital ligament is the thickened edge...

Objective: To evaluate functional loading and bone quality of the mandible following injection of botulinum neurotoxin type A (BoNT/A) in the masseter. Methods: Forty adult female New Zealand white rabbits received injection of either BoNT/A or saline into one masseter muscle. Animals were terminated at 4 and 12 weeks. In a terminal procedure, gage...

Objective: To evaluate masticatory muscle function after paralysis of one masseter using botulinum neurotoxin type A (BoNT/A) and during the course of recovery. Methods: Forty adult female New Zealand rabbits were injected either with BoNT/A (n=20) or saline (n=20) in one masseter. Electromyographic activity (EMG) was recorded during mastication be...

The size and the shape of craniofacial bones results from periosteal activity, which can be either appositional or resorptive. The periosteum is often used as a source of graft material for osteogenesis, but differences in cellular makeup and proliferative capacity may render resorptive regions unsuitable for transplant. This study was undertaken t...

Orthodontic relapse is a common and significant problem. Few risk factors have been identified, and the role of bone has only recently been investigated. The purpose of this study was to examine the influence of alveolar bone volume and tooth volume on dental relapse. The sample was chosen from the postretention database at the Department of Orthod...

Non-healing fractures can result from trauma, disease, or age-related bone loss. While many treatments focus on restoring bone volume, few try to recapitulate bone organization. However, the native architecture of bone is optimized to provide its necessary mechanical properties. Hyaluronic acid (HA) hydrogel scaffold systems with tunable degradatio...

This study investigated the role of occlusion in the development of biomechanical properties of alveolar bone in the miniature pig, Sus scrofa. The hypothesis tested was that the tissues supporting an occluding tooth would show greater stiffness and less strain than that of a non-occluding tooth. Maxillary teeth opposing the erupting lower first mo...

The buccinator muscle forms the lateral wall of the oral cavity. It is presumed to aid mastication by maintaining bolus position. Such a function would involve thickening the cheek, possibly compressing the alveolar bone and contributing to malocclusions. However, neither buccinator deformation nor its effect on pressure has been demonstrated. Our...

The purpose of this study was to investigate the effects of reduced masticatory function on midline suture growth and morphology in growing pigs. 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, Univers...

The cartilaginous nasal septum plays a major role in structural integrity and growth of the face, but its internal location has made physiologic study difficult. By surgically implanting transducers in 10 miniature pigs (Sus scrofa), we recorded in vivo strains generated in the nasal septum during mastication and masseter stimulation. The goals wer...

Alveolar bone supports teeth during chewing through a ligamentous interface with tooth roots. Although tooth loads are presumed to direct the development and adaptation of these tissues, strain distribution in the alveolar bone at different stages of tooth eruption and periodontal development is unknown. This study investigates the biomechanical ef...

Objectives: To study the effects of location, orientation and loading speed on the compressive mechanical properties of porcine nasal septal cartilage. Methods: Porcine nasal septa were extracted from freshly slaughtered specimens (N=23) and frozen in phosphate-buffered saline. Specimens were thawed and six samples were cut from each specimen, tw...

Surgical periosteal injury and masticatory loading are likely factors affecting the healing of a mandibular DO site. This study is aimed to characterize the healing features of an early-phase mandibular DO site and assess the effects of these factors. Eighteen 3-6-month-old miniature pigs received a right mandibular osteotomy and were distracted fo...

In this study, we investigated orthodontic space closure of premolar extraction sites with miniplate anchorage compared with conventional tooth-borne anchorage in 8 adult beagle dogs. A split-mouth design with all 4 quadrants was used. Four premolars were extracted to create adequate space for premolar retraction. Retraction was performed with nick...

In addition to their role in skull growth, sutures are sites of flexibility between the more rigid bones. Depending on the suture, predominant loading during life may be either tensile or compressive. Loads are transmitted across sutures via collagenous fibers and a fluid-rich extracellular matrix and can be quasi-static (growth of neighboring tiss...

Mandibular periosteum moves in the direction of new apposition. This displacement, usually termed "migration," is thought to involve the fibrous layer of periosteum, with the deeper osteogenic layer remaining at its original location except for its blood vessels. To assess whether periosteal displacement includes cells as well as matrix and whether...

Loading of temporomandibular tissues during mandibular distraction may cause changes in condylar growth and cartilage thickness. This study examines the effects of distraction on the condyle in a large animal model by explicitly measuring growth and in vivo loading. Unilateral mandibular distraction was carried out on 20 growing minipigs divided in...

Bone growth at the cranial sutures relies on proliferation of osteogenic progenitor cells and/or differentiation of osteoblasts. The current study was undertaken to assess these events in relation to suture growth and fusion. A total of 21 pigs, divided into three age groups (0.5-1.5 months, 3-4 months and 5-7 months), were used for immunohistochem...

Micromovement at a fracture or distraction osteogenesis (DO) site may play a significant role in bone formation and healing. Mastication is an important physiological process that can cause substantial micromovement at a mandibular disjunction. The purpose of this study is to characterize and quantify the micromovement caused by mastication. Eighte...

Masticatory muscles are anatomically and functionally complex in all mammals, but relative sizes, orientation of action lines, and fascial subdivisions vary greatly among different species in association with their particular patterns of occlusion and jaw movement. The most common contraction pattern for moving the jaw laterally involves a force co...

Modulation of force during mammalian mastication provides insight into force modulation in rhythmic, cyclic behaviors. This study uses in vivo bone strain data from the mandibular corpus to test two hypotheses regarding bite force modulation during rhythmic mastication in mammals: (1) that bite force is modulated by varying the duration of force pr...

The nasofrontal suture links the nasal complex with the braincase and is subject to compressive strain during mastication and (theoretically) tensile strain during growth of nasal soft tissues. The suture's ability to transmit compressive and tensile loads therefore affects both cranioskeletal stress distribution and growth. This study investigated...

This article summarizes the views expressed at the third session of the workshop "Tissue Engineering--The Next Generation," which was devoted to the engineering of complex tissue structures. Antonios Mikos described the engineering of complex oral and craniofacial tissues as a "guided interplay" between biomaterial scaffolds, growth factors, and lo...

Dental relapse of the mandibular incisors after orthodontic treatment is a common problem, and few risk factors have been identified. The purpose of this case-control study was to evaluate whether the amount or the structure of mandibular bone affects the potential for postorthodontic mandibular incisor relapse. The subject sample was selected from...

Endochondral ossification at the caudal junctions of the cartilaginous nasal septum, in combination with interstitial expansion of the septum, is thought to displace the facial skeleton away from the neurocranium. However, the rate of endochondral ossification has not been measured or related to rates of septal enlargement. This study examined endo...

Domestication of vertebrates is based on the understanding of the needs of animals in their natural environment and the success of this domestication throughout human history is largely dependent on the knowledge of their feeding behaviour. The aim of this volume is to provide advanced students and researchers with a review of current knowledge of...

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 dyna...

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...

Fixation at the osteotomy site for mandibular distraction osteogenesis (DO) is probably not rigid, especially during mastication. Micromotion may affect the course of DO. This study aimed to measure the mobility of the fresh distractor-fixed osteotomy site in response to mastication and masticatory muscle stimulation. Twenty-eight domestic pigs, 6...

The purpose of this investigation was to determine if the mechanical environment of the mandible is changed by osteotomy and fixation, as assessed by the measurement of bone strain on the condylar neck and mandibular corpus. Immediately following unilateral mandibular osteotomy and distractor placement, strain gauges were attached directly to the c...

Hydrogel scaffolds releasing angiogenic and osteoinductive molecules were used to induce bone growth in a bone defect model. Optical coherence tomography was utilized to characterize morphological changes during the temporal progression of bone regeneration.

At the time of weaning, infant animals have little experience with hard food, and thus their skulls are not likely to be epigenetically adapted for the loads imposed by mastication. We examined bone strain in the zygomatic arch of 4-week-old weanling piglets. Functional strains in piglets differed from those previously reported for older pigs in th...

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...

Direct measurement of temporomandibular joint (TMJ) tissue deformation requires animal experimentation. Most of the available data pertain to the mechanical strain on the bone surfaces around the joint. However, bone is rarely the first joint tissue to show injury, being affected after damage to collagenous tissues such as the disc or capsule. Caps...

The orbicularis oris and buccinator muscles of mammals form an important subset of the facial musculature, the perioral muscles. In many taxa, these muscles form a robust muscular hydrostat capable of highly manipulative fine motor movements, likely accompanied by a specialized pattern of innervation. We conducted a retrograde nerve-tracing study o...

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 we...

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 muscl...

Cranial bones and sutures are mechanically loaded during mastication. Their response to masticatory strain, however, is largely unknown, especially in the context of age change. Using strain gages, this study investigated masticatory strain in the posterior interfrontal and the anterior interparietal sutures and their adjacent bones in 3- and 7-mon...

The TMJ is unique to mammals, but among different mammalian groups its morphology and function vary enormously. Practicality dictates that animal models will not be the closest mimics of the human condition. Currently, the most used species are rats, rabbits, pigs, and ruminant ungulates. Each has distinctive TMJ adaptations. Except for pigs, it is...

In this study, we examined the effects of mandibular distraction osteogenesis on the morphology and the microdensity of the rat condyle. Materials and Methods: One hundred twenty-nine rats were allocated to 4 experimental groups (n = 32 or 33). Each received unilateral mandibular ramus osteotomy and distraction device placement. After a 3-day laten...

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...

The rostrum is a large diameter, thin-walled tubular structure that receives loads from the teeth. The rostrum can be conceptualized both as a rigid structure and as an assemblage of several bones that interface at sutures. Using miniature pigs, we measured in vivo strains in rostral bones and sutures to gain a better understanding of how the rostr...

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...

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....

Movement is an important aspect of the biomechanics of the temporomandibular joint (TMJ). To track the relative movements of TMJ components, radio-opaque markers were implanted in the left squamosal bone, mandible and retrodiscal tissue of miniature pigs. Medial-lateral (ML) and dorsal-ventral (DV) fluoroscopic records were made 8-10 weeks later du...

The mechanical environment is a regulator of growth and adaptation of the musculoskeletal system, including joints. Although pigs (Sus scrofa) are used frequently as models for temporomandibular joint (TMJ) dysfunction, no systematic description of microanatomy exists for this species. We injected the thymidine analog 5-bromo-2'-deoxyuridine (BrdU)...

Intraoral splints are a commonly used dental treatment for a variety of conditions. Because such splints alter the condyle-disc-fossa relationship, they probably change the loading status of the temporomandibular joint (TMJ), including the TMJ disc. Collagen, a major constituent of the disc, acts to resist tensile loading, and it is presumed that t...

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...

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 prolife...

'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 s...

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 per...

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...

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...

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...