Kinematic analysis of equine masticatory movements: comparison before and after routine dental treatment

The objective of this study was to compare masticatory movements before and after dental treatment using kinematic analysis. The masticatory movements of 15 adult Warmblood horses with mild dental pathology chewing standardised hay were recorded on three consecutive days before and three times after (days 7, 21, 28) dental correction. The results of the leading mandibular tracking marker, located at the caudal edge of the inter-mandibular suture, were compared statistically. Reproducibility of measurements prior to dental treatment was excellent (P<0.05). Rostrocaudal mandibular motion was significantly reduced after dental correction (9±2mm vs. 8±2mm; P=0.046). Oscillations during the power stroke were significantly reduced after dental correction (R(2)=98.3%±0.3 vs. 98.8%±0.3; P=0.050). Although significant changes were observed in individual horses, the overall results of lateral and dorsoventral mandibular motion did not reveal significant differences. In conclusion, kinematic analysis of masticatory movements provided reproducible results and may be useful to evaluate changed movement patterns following dental correction.     

Effect of rostrocaudal mobility of the mandible on feed digestibility and fecal particle size in horses

OBJECTIVE: To evaluate the effect of rostrocaudal mobility (RCM) of the mandible during extension and flexion of the atlanto-occipital joint on weight gain, feed digestibility, and fecal particle size in horses. DESIGN: Randomized controlled trial. ANIMALS: 34 pregnant mares housed in 1 barn. PROCEDURES: Horses were randomized into a treatment (n = 17) or control (17) group. All horses were sedated, and the distance between the rostral portions of the upper and lower incisor arcades was determined during extension and flexion of the atlanto-occipital joint; mandibular RCM was calculated as the difference between these values. In the treatment group, measurements were made after dental floating. Body weight was recorded 1 day before dental floating and at intervals after mandibular RCM determination for a period of 24 weeks. Feces were collected from each horse during two 5-day periods. Samples of feed and feces were analyzed to determine feed digestibility; particle size analysis was performed on dried fecal samples. RESULTS: Data obtained from each group of horses revealed that RCM of the mandible did not affect weight gain, feed digestibility, or particle size in feces; there were no differences among breeds. Controlling for age and number of dental lesions did not significantly affect results. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, RCM of the mandible did not appear to affect weight gain, feed digestibility, or fecal particle size. On the basis of these and other published data, the assumption that dental abnormalities affect digestion detrimentally in horses needs to be reevaluated.     

A COMPLEMENTARY RADIOGRAPHIC PROJECTION OF THE EQUINE TEMPOROMANDIBULAR JOINT

The complexity of the equine skull makes the temporomandibular joint a difficult area to evaluate radiographically. The goal of this study was to determine the optimal angle for a complementary radiographic projection of the equine temporomandibular joint based on a computed tomography (CT) cadaver study. CT was performed on six equine cadaver heads of horses that were euthanized for other reasons than temporomandibular joint disease. After the CT examination, 3D reconstruction of the equine skull was performed to subjectively determine the angle for a complementary radiographic projection of the temporomandibular joint. The angle was measured on the left and right temporomandibular joint of each head. Based on the measurements obtained from the CT images, a radiographic projection of the temporomandibular joint in a rostral45°ventral-caudodorsal oblique (R45°V-CdDO) direction was developed by placing the X-ray unit 30° laterally, maintaining at the same time the R45°V-CdDO angle (R45°V30°L-CdDLO). This radiographic projection was applied to all cadaver heads and on six live horses. In three of the live horses abnormal findings associated with the temporomandibular joint were detected. We conclude that this new radiographic projection of the temporomandibular joint provides superior visualization of the temporomandibular joint space and the articular surface of the mandibular condyle.     

Computed tomographic features of the temporomandibular joint in 10 Jeju horses

BackgroundThe equine temporomandibular joint (TMJ) has a complex anatomical structure that makes diagnosis of TMJ disorders difficult. Computed tomography (CT) is now available in equine medicine; hence, TMJ evaluation has become more convenient.ObjectivesThe objectives of this study were to describe the CT features of the TMJ in Jeju horses and to compare these features with those of Thoroughbreds.MethodsIn this report, the TMJs of 10 Jeju horses (mean age: 4.5 ± 1.9 yr; mean body weight: 282.6 ± 40.3 kg) and 6 Thoroughbreds (mean age: 7.3 ± 1.6 yr; mean body weight: 479.7 ± 44.0 kg) were examined using CT. After CT scanning, the Hounsfield units (HU) and height to width ratio (H:W) of the mandibular condyle were measured.ResultsThe mean H:W in Jeju horses was significantly lower than that in Thoroughbreds. The mean HU in Jeju horses was lower than that in Thoroughbreds; however, the difference was not significant. The most frequent CT finding was an irregular medial margin of the mandibular condyle in both breeds.ConclusionsIn this study, the shape of the mandibular condyle in Jeju horses was flatter than that in Thoroughbreds. This report could be useful in evaluating the TMJ in Jeju horses. Moreover, CT could be a pragmatic choice for the examination of the TMJ in horses.     

Effect of dental correction on voluntary hay intake,apparent digestibility of feed and faecal particle size in horse

Summary In nine adult Warmblood horses with mild to moderate dental findings (no signs of discomfort during chewing), voluntary hay intake before and after dental correction was examined. In a second experiment, digestibility of feed and faecal particle size were determined (3 days of total faecal collection) before and after dental correction. During both digestion trials including a 3‐day adaptation period, the amount of hay and concentrate (mixture of oats, barley and maize) was kept constant in each individual horse before and after dental correction. Voluntary hay intake in individual horses ranged from 11 to 22 g DM/kg BW/day and did not differ before and after dental treatment. Apparent digestibility of DM, energy, crude fibre and Nfe increased significantly after dental correction (energy digestibility before dental correction 46.8 ± 7.4%, after dental correction 51.5 ± 8.5%). Apparent digestibility of feed was higher in horses eating more concentrates than in those eating less concentrates. Improvement of digestibility was more marked in horses eating larger amounts of grain. There was no relationship between severity or type of dental alterations and improvement of apparent feed digestibility. Dental correction had no effect on faecal particle size.     

Arthroscopic Anatomy of the Equine Temporomandibular Joint

OBJECTIVE: To develop an arthroscopic approach to, and describe the arthroscopic anatomy of, the equine temporomandibular joint (TMJ). STUDY DESIGN: Cadaveric study, after which the technique was tested in horses. ANIMALS OR SAMPLE POPULATION: Ten cadaveric equine heads and 5 normal horses (age, 5-13 years; weight, 425-545 kg). METHODS: Specimens or horses were positioned in right lateral recumbency. After fluid distention of the TMJ, arthroscopic portals were made in the dorsal compartment over the most prominent portion of the joint outpouching (caudodorsal approach) and in rostral and intermediate locations. The joint was explored and photographed. Positional changes in the mandible were made to determine if observation of the joint could be improved. Instrument portals were created to assess the feasibility of surgical arthroscopy. Cadaveric heads were dissected to assess iatrogenic damage, whereas experimental horses were observed for postoperative complications for 30 days. RESULTS: A caudodorsal arthroscopic approach provided the best evaluation of the dorsal compartment of the TMJ. The approach allowed observation of the rostral and caudal synovial pouches and the lateral aspect of the joint including the articular disc. Examination of the medial aspect of the joint was limited to the most rostral and caudal aspects. Access to the lateral aspect of the ventral compartment of the TMJ was precluded by the position of the transverse facial artery and vein. In specimens, iatrogenic damage was minimal and limited to the articular fibrocartilage, articular disc, and penetration of the parotid salivary gland. If the latter also occurred in horses, no adverse effects were noted. In horses, mild fluid extravasation occurred and resolved within 1 day. All horses ate normally after surgery but had periarticular swelling and mild pain upon palpation of the TMJ for 2 days. CONCLUSIONS: A caudodorsal arthroscopic approach to the TMJ allowed adequate observation of the lateral aspect of the dorsal compartment of the joint. Access to the ventral compartment was precluded by the location of the transverse facial artery and vein. CLINICAL RELEVANCE: Conditions affecting the lateral and caudal aspects of the dorsal compartment of the TMJ should be visible by arthroscopy.     

Arthrocentesis of the temporomandibular joint in adult horses

OBJECTIVE: To develop a method for arthrocentesis of the temporomandibular joint in adult horses. ANIMALS: 7 equine cadaver heads and 6 clinically normal adult horses. PROCEDURE: Fluoroscopy, contrast radiography, and computed tomography were used on cadaver specimens to locate the temporomandibular joint, identify externally palpable landmarks for joint access, guide needle placement into the joint, and illustrate regional anatomy. The arthrocentesis technique was performed on 6 live healthy adult horses to determine efficacy and safety of this procedure. RESULTS: Externally palpable structures were identified as landmarks for temporomandibular arthrocentesis, including the lateral border of the condylar process of the mandible, the zygomatic process of the temporal bone, and the lateral pericapsular fat pad. Arthrocentesis was successful in all 6 joints in the live horses, and no complications developed. CONCLUSIONS AND CLINICAL RELEVANCE: The technique identified will improve the ability to examine and treat the temporomandibular joint in horses.     

Arthroscopic treatment of temporomandibular joint sepsis in a horse

OBJECTIVE: To report arthroscopic debridement and lavage of a septic temporomandibular joint (TMJ) in a horse. DESIGN: Clinical case report. ANIMALS: A 12-year-old Thoroughbred mare. METHODS: Arthroscopic investigation of the dorsal joint pouch of the right TMJ was made through a stab incision into the dorsocaudal compartment. Mechanized resection of synovium and fibrinous debris combined with copious lavage, and intra-articular and systemic antibiotic administration was used to treat the septic TMJ. RESULTS: Arthroscopic debridement and lavage of the TMJ, in combination with intra-articular and systemic antimicrobials resulted in resolution of sepsis. Eight months post-operatively, there was no clinical evidence of degenerative joint disease or ankylosis of the TMJ. CONCLUSION: TMJ sepsis is rare in horses, however, standard arthroscopic equipment can be used in the management of this condition with minimal complications. CLINICAL RELEVANCE: Arthroscopic debridement and lavage should be considered for evaluation and initial treatment of TMJ sepsis in horses.     

Temporomandibular joint cytokine profiles in the horse

It has been suggested that dental abnormalities lead to temporomandibular joint inflammation and pain that may be mitigated by regular dental care. There is considerable literature on the pathophysiology of equine joint disease including studies on cytokine profiles in diseased appendicular joints. This study examined the effects of age and dental malocclusions summarized as a dental pathology score on equine temporomandibular joint cytokine (IL-1, IL-6, IL-8, TNF alpha and TGF-beta1, -beta2, -beta3) concentrations. TGF-beta3 was not detected in any joint sample. IL-1, IL-6 and TNF alpha were not influenced by age. Foals had significantly lower concentrations of lL-8 and TGF-beta1, and higher levels of TGF-beta2 compared with older horses. Age did not effect cytokine concentration in older horses although there was a trend towards increasing 1L-8 with age. The dental pathology score increased with age in mature horses, however there was no effect of dental pathology score on cytokine concentration. There was no effect of incisor eruption, and presence or number of periodontal lesions on temporomandibular joint cytokine concentration. Our findings indicate that age but not dental pathology affected temporomandibular joint proinflammatory cytokine concentration in this population of horses.     

Electromyographic evaluation of masseter muscle activity in horses fed (i) different types of roughage and (ii) maize after different hay allocations

The aims of this study were to monitor electromyographic (EMG) activity of masseter muscle in healthy horses fed (i) different types of roughage and (ii) maize after different hay allocations. Four horses were offered the following three diets ad libitum: hay, haylage or straw/alfalfa chaff (SAC). In a second trial, four horses were fed cracked maize (CM) and hay in three different orders: (i) CM after a 12‐h overnight fast; (ii) CM immediately after restricted hay intake (0.6 kg hay/100 kg BW); or 3) CM after hay intake ad libitum. The activity of the masseter muscle was determined by EMG (IED^®), and the following were measured: amplitude (muscle action potential = MAP, maximum voltage) and duration of MAP (s). The intake of hay or haylage was associated with intense masseter muscle activity (MAP: hay, 10 ± 1.7 V; haylage, 11 ± 3.3 V; and duration of MAP: hay, 0.31 ± 0.04 s; haylage, 0.30 ± 0.04 s). Similar intense chewing was measured for SAC (MAP 13 ± 3.8 V), although duration of the chewing cycle was relatively short (0.22 ± 0.03 s, diet p < 0.05), which is possibly related to the shorter fibre length. CM was consumed rapidly, with less intense masseter muscle activity (MAP 6.0 ± 1.5 V). Hay intake before CM did not affect chewing force of CM, but duration of chewing cycle was significantly prolonged by feeding hay ad libitum before CM was fed. The consumption of hay, haylage or SAC was associated with intensive masseter muscle activity that was likely to stimulate salivary flow rate. In contrast to roughage, concentrates like CM are consumed rapidly with less intensive masseter muscle activity. This situation is associated with a low salivary flow that may have an adverse effect on gastric function.     

Mandibular condylectomy and meniscectomy for the treatment of septic temporomandibular joint arthritis in a horse

OBJECTIVE: To report use of mandibular condylectomy for treatment of advanced degenerative joint disease of the temporomandibular joint (TMJ) caused by sepsis. DESIGN: Clinical case report. ANIMALS: Two-year-old Noriker filly. METHODS: Computed tomography (CT) was used to confirm advanced degenerative joint disease of the left TMJ and for follow-up after mandibular condylectomy and removal of necrotic meniscus. RESULTS: Painful swelling (3 weeks duration) with drainage located just caudal to the left lateral canthus of the eye was associated with atrophy of the left masseter muscle, masticatory problems, and inappetence. There was incisor malocclusion with a 1.4 cm resting lateral mandibular deviation to the right and inability to open the mouth more than a few centimeters. Left mandibular condylectomy combined with meniscectomy and thorough debridement of the septic left TMJ resulted in resolution of clinical signs and complete return of function. Streptococcus zooepidemicus, intermediately resistant to penicillin and subsequently to enrofloxacin, was isolated from the wound. Regeneration of a mandibular "pseudocondyle" was evident on CT at 4 months. At 4 months and 1 year the filly had maximal mouth opening >10 cm and no malocclusion. CONCLUSION: Mandibular condylectomy can be used to facilitate management of septic TMJ arthritis. There was no radiologic or clinical evidence of TMJ ankylosis >1 year after meniscal removal. CLINICAL RELEVANCE: Mandibular condylectomy, including meniscectomy, is an acceptable treatment option for advanced TMJ septic arthritis and allowed return of normal masticatory function.     

THE EFFECT OF OBLIQUITY ON THE RADIOGRAPHIC APPEARANCE OF THE TEMPOROMANDIBULAR JOINT IN DOGS

The temporomandibular joint is formed between the condyloid process of the mandible and the mandibular fossa of the temporal bone. The basic anatomy of this joint was assessed and described in a series of skulls including dolichocephalic, mesaticephalic and brachycephalic breeds. The facial index and rotational angles were measured with the facial index providing a useful method of classifying skull types but the rotational angle being of limited use in assessment of the temporomandibular joint until normal breed values are established. Equipment was designed to allow repeatable positioning of the temporomandibular joint for radiography at a variety of lateral and long axis rotational angles relative to the central x-ray beam. The regions of the joint and anatomic features visualized in each view are demonstrated. 10 degrees rotation was required in either axis to project the joints independently of each other. Lateral rotational angles of 10 to 30 degrees in mesaticephalic and dolichocephalic breeds and 20 to 30 degrees in brachycephalics and long axis rotational views of 10 to 30 degrees depending on the region of interest were considered to be the most useful.     

Coronoidectomy as a treatment for mandibular immobility caused by fracture of the coronoid process in three horses

This report describes the history, clinical signs and treatment of three horses suffering from deviation and immobility of the mandible resulting from fracture of a coronoid process of the mandible. Deviation and immobility resulted from impingement of a callus between the temporal bone and zygomatic arch. Fracture of the coronoid process was identified by using radiography, ultrasonography, computed tomography or a combination of two or more of these imaging modalities. Osteoarthritis of the ipsilateral temporomandibular joint of two horses was identified. All horses were treated by excising the fractured coronoid process, and two were also treated by excising the diseased ipsilateral mandibular condyle. All horses were able to open their mouth more widely immediately after surgery. One horse experienced moderate post-operative haemorrhage, and all had severe shear mouth. Shear mouth was ameliorated gradually over many months by rasping dental overgrowths. Mandibular movement of all horses improved, allowing efficient mastication of feed. One horse was able to be used as a showjumper, one horse was sold at Thoroughbred yearling sales and was lost to follow-up, and one horse died from an unrelated gastrointestinal disease 10 months after mandibular coronoidectomy and condylectomy.     

Mandibular Condylectomy Technique and Results in Normal Horses

A technique of mandibular condylectomy and menisectomy is described. Unilateral condylectomy and menisectomy were performed in two horses, and two horses were treated by bilateral condylectomy and unilateral meniscectomy. Minor temporary alterations in mastication occurred following unilateral condylectomy; more severe and longer lasting abnormalities of prehension and mastication occurred following bilateral condylectomy. Malocclusion occurred in all horses following surgery but was only clinically significant in one horse that developed occlusion of the lower incisor teeth 3 mm caudal to the upper incisor teeth following bilateral condylectomy. Maximal mouth opening was normal following unilateral condylectomy and increased following bilateral condylectomy, both immediately following surgery and after 16 weeks. Maximal lateral deviation of the mandible was increased immediately following unilateral and bilateral condylectomy; 16 weeks following surgery one joint had increased, and two had normal and three had decreased maximal lateral deviations. On radiographic, gross, and histological evaluation, the condylectomy sites underwent remodelling and bony proliferation to produce "pseudo" condyles. At necropsy, 16 weeks following surgery, five of the six operated temporomandibular joints contained fibrous tissue with single or multiple cavities lined by synoviocytes. The nonoperated temporomandibular joints were normal. Functional use of the mandible was good in three horses; the fourth horse developed significant malocclusion and had satisfactory function following bilateral condylectomy.     

Anatomy of the equine temporomandibular joint: study by gross dissection, vascular injection and section

REASONS FOR PERFORMING STUDY: The minute anatomy of the temporomandibular joint (TMJ) in horses is poorly documented in the literature. OBJECTIVES: To examine in detail the anatomy of the normal equine TMJ and the relationship of the joint to adjacent structures. METHODS: The anatomy of the TMJ was examined in 12 equidae using dissections, synovial and vascular injections and frozen and plastinated sections. Relevant structures were photographed. RESULTS: Rostral and caudal compartments were identified in the dorsal and ventral synovial pouches of the TMJ. Lateral and caudal ligaments were identified and attachments of the masticatory muscles over the TMJ were documented. Direct relationships between the TMJ and components of the ear were found, and the vascular supply described. CONCLUSIONS: This joint is related to some components of the ear as in man, and has its own peripheral vascular supply. Potential relevance: A knowledge of the detailed anatomy of the equine TMJ is a prerequisite to interpreting the imaging techniques, and will enable improved diagnosis of TMJ pathologies.     

Effect of dental floating on the rostrocaudal mobility of the mandible of horses

OBJECTIVE: To evaluate the effect of dental floating on the position of the mandible relative to the maxilla (a measure of rostrocaudal mobility [RCM] of the mandible) during extension and flexion of the head of horses. DESIGN: Randomized controlled blinded trial. ANIMALS: 59 horses housed in 1 barn. PROCEDURE: Horses were formally randomized into a treatment (n = 33) or control (26) group. All horses were sedated, and the distance between rostral portions of the upper and lower incisor arcades were determined with the head fully extended and flexed at the poll (the difference in measurements represented the RCM of the mandible). The oral cavity was examined. For the treatment group, dental floating was performed, and the incisor arcade measurements were repeated. RESULTS: Dental correction resulted in a significant increase in RCM of the mandible in 31 of 33 horses. The mobility was greater in heavy horses than that detected in other breed classifications. Age and number of dental lesions did not significantly affect mobility before or after dental floating. CONCLUSIONS AND CLINICAL RELEVANCE: Dental floating increased RCM of the mandible, but measurement of this variable was not an indicator of the number or extent of dental lesions, and no specific dental abnormality appeared to significantly affect RCM of the mandible in horses. In horses, measurement of RCM of the mandible can be used as a guide to determine whether dental correction is necessary; after dental floating, it can be used to ensure that irregularities of the occlusal surface have been corrected.     

Partial mandibular condylectomy and temporal bone resection for chronic,destructive, septic arthritis of the temporomandibular joint in a horse

Sepsis of the temporomandibular joint (TMJ) of the horse is rare. This case report describes the use of radiography, ultrasonography and computed tomography to diagnose sepsis of the TMJ in a 2‐year‐old Thoroughbred filly. The mandibular condyle and temporal bone were partially resected to successfully remove necrotic tissue within and surrounding the TMJ. Sepsis resolved and the horse returned to race training. Follow‐up computed tomography examination showed generation of a mandibular ‘pseudocondyle’ at 8 months post operatively.