Radiographic characterization of the maxillary septum and septal bullae in horses: An ex vivo study.

The anatomical variations of the maxillary septum and the septal bullae can generate challenges during the interpretation of radiographs of the horses' heads and make it difficult to accurately identify the sites affected in sinus disorders. The description of the radiographic appearance of these structures is currently scarce in the scientific literature. This work aims to describe the anatomical and radiographic characteristics of the maxillary septum and maxillary septal bullae in horses. Six chemically preserved equine cadaver heads were used which, after being submitted to the maxillary osseous flap, the maxillary septum and its respective bullae were identified. Radiographic examinations before and after contrast impregnation on these structures were performed. The positioning of the maxillary septum varied between the anatomical specimens and between the sides of the same specimen. The 30° oblique dorsoventral lateral and lateral projections allowed the identification of the maxillary septum and septal bullae. However, the bullae remained superimposed on the dental arches in the dorsoventral projections with the mandible in a neutral position or with the mandible displaced. The oblique offset radiographic positioning was suggested and proved effective for the examination of the maxillary septal bullae, where the mandible was displaced to the side of the bullae to be examined, and the radiographic beam inclined in the same direction. The maxillary septum and its bullae could be properly identified in a macroscopic way after the osseous flap and the contrasted radiographic examination allowed its adequate interpretation. Variations in size and position are considered normal for the equine species.

Equine Sinus Surgery.

The anatomy of the equine paranasal sinuses is critical to understand to assess the extent of the disease process, the optimal surgical approach, and the ability to drain through the normal nasomaxillary pathway. By following established anatomic landmarks, direct sinus access can be used to further explore the sinus compartments, remove compromised cheek teeth, remove any purulent debris or feed contamination, and establish drainage. Many complications can be avoided or minimized by thoroughly evaluating all sinus compartments and critically assessing the ability of the sinus to drain.

Equine Nasal Endoscopy: Treating Bullae Disease and Sinus Disease.

The nasal conchal bullae (dorsal and ventral) are separate, air-filled structures within their respective dorsal and ventral nasal conchae. Computed tomography scans have assisted with the increasing diagnosis of empyema of the nasal conchae. This condition is usually associated with dental or sinus disease. Drainage of affected bullae is considered critical for resolution of clinical signs. The ventral conchal bullae can be easily viewed with a standard 10 mm diameter flexible endoscopy via the middle nasal meatus. This approach can also be used for fenestration of the bullae, using a diode laser, equine laryngeal forceps, or bipolar vessel sealing device.

Ultrasonographic assessment of normal jugular veins in Standardbred horses.

BACKGROUND: Ultrasonography (US) is the recommended imaging technique to evaluate jugular veins. This prospective randomized clinical study was designed to collect a series of B-mode US measurements of manually distended jugular veins in healthy Italian Standardbreds and to find possible correlations between ultrasound measurements and animal morphometric characteristics. Forty-two horses, eight males and 34 females (range 3-22 years; bodyweight 494.4 ± 41.7 kg), were included in the study. The diameters and wall thicknesses of both jugular veins were measured at three different sites of the neck. The differences in ultrasound measurements based on scans, age, gender, side, and site of the neck were evaluated by ANOVA or by the Kruskal-Wallis test. The effects of the morphometric measures on each ultrasound parameter were evaluated by MANOVA (P < 0.05). RESULTS: The ultrasound measurements did not differ significantly between the three different sites or between genders; hence, they were pooled together in the results. On the transverse scan, the mean dorsoventral and lateromedial diameters were 1.58 ± 0.23 and 2.20 ± 0.25 cm, respectively; the mean superficial and deep wall thicknesses (SWT and DWT) were 0.07 ± 0.01 and 0.08 ± 0.01 cm, respectively. On the longitudinal scan, the mean dorsoventral diameter was 1.59 ± 0.26 cm, and the SWT and DWT were both 0.08 ± 0.01 cm. Neck length, from the caudal edge of the mandible to the thoracic inlet, was related to the dorsoventral diameter in both longitudinal and transverse scan and to the SWT and DWT in transverse scan, whereas height at the withers (measured with tape) and estimated weight were related to the wall thickness. Dividing the subjects into groups by age in years ("young" 3-7, "mature" 8-14, "old" > 14), differences were found for the lateromedial diameter in the transverse scan and the SWT on the longitudinal scan. The main limitation of this study was that only one operator performed the measurements. CONCLUSION: The US measurements of the jugular veins and their relationship with morphometric measures reported in this manuscript might be considered as guidelines both for early diagnosis and monitoring jugular vein abnormalities in healthy Italian Standardbred horses.

Evaluation of the equine mental foramen block: cadaveric and in vivo injectate diffusion.

OBJECTIVE: To describe injectate diffusion for two equine mental foramen block techniques. STUDY DESIGN: Descriptive anatomic study. ANIMALS: A total of 12 equine heads and three live horses. METHODS: Equine heads were longitudinally sectioned to create 24 hemi-heads for testing two mental foramen block techniques (T1 and T2) and two injectate volumes (3 and 5 mL) of mixed dye and contrast medium. T1 needles were directed rostrocaudally into the mental foramen for 3 cm, and T2 needles were directed dorsolaterally to ventromedially into the foramen for 1 cm. Hemi-heads were randomly assigned one injection technique and volume. Radiographs evaluated needle tip positioning, distance traveled by injectate and injectate diffusion pattern. Specimens were dissected to measure the length of circumferential nerve staining. The more effective technique was tested in three live horses and evaluated via computed tomography. Summary statistics described results. RESULTS: Neither injection technique nor injectate volume had a significant impact on circumferential nerve staining. Circumferential nerve staining, median (range), was 15 (0-33) mm for T1 and 10 (0-42) mm for T2. Injectate diffusion patterns revealed that injectate was more likely to thread alongside the inferior alveolar nerve for T1 (9/12) and bolus around the rostral inferior alveolar nerve for T2 (9/12). Bolus diffusion patterns were associated with increased circumferential nerve staining ≥1 cm (9/24) when compared with thread patterns (6/24). Diffusion of injectate within the mandibular canal was greater with 5 than 3 mL. In vivo testing of T2 with 5 mL injectate resulted in decreased incidence of circumferential nerve staining ≥1 cm [median (range) 5 (0-14) mm]. CONCLUSION AND CLINICAL RELEVANCE: T2 created an injection diffusion pattern more likely to result in circumferential nerve staining ≥1 cm, but the low incidence of in vivo circumferential nerve staining ≥1 cm suggests that block efficacy may vary.

Anatomic analysis of the equine mental foramen and rostral mandibular canal using computed tomography.

OBJECTIVES: To characterize the anatomy of the mental foramen and determine associations with age, weight, sex and breed. STUDY DESIGN: Retrospective descriptive study. ANIMALS: Forty-one horses, 0.6-25.2 years and weighing 136-820 kg. METHODS: Computed tomography (CT) studies of equine heads performed over 5 years were evaluated in multiplanar and three-dimensional reconstruction. Measurements obtained were positioning of the foramen along the mandible, foramen height and width, foramen-canal angulation and rostral canal mineralization. Exploratory statistical analyses investigated associations between measurements and age, weight, sex and breed. RESULTS: Evaluation of 41 CT studies revealed foramen positioning was one-third of the horizontal distance of the incisor-premolar space from the second premolar and one-third of the vertical distance in the mandible from the dorsal surface of interproximal space at the level of the foramen. Age was negatively correlated to horizontal positioning [r = -0.42; 95% confidence intervals (CI), -0.64 to -0.13]. Mean foramen width was 6.4 (range, 2.3-17.1) mm and height 5.6 (range, 2.1-10.3) mm. Age and foramen height (r = 0.32; 95% CI, 0.01 to 0.57) and width (r = 0.30; 95% CI, -0.01 to 0.30) were positively correlated. Thoroughbred and Warmblood/Draft horses had increased foramina heights compared with Quarter horses [analysis of variance (anova)p = 0.02]. Males had wider foramina (95% CI, -2.66 to 0.07). Angulation of the foramen-canal was mean ± standard deviation 68.3 ± 12.8° (range, 37.9-105.6°) transverse plane, 28.3 ± 4.1° (range, 18.2-39.0°) saggital plane and 41.4 ± 8.45° (range, 22.2-58.6°) dorsal plane. Older horses had decreased mineralization of the rostral canal (anova, left p = 0.015, right p = 0.025). CONCLUSIONS: The size, shape, positioning and angulation of the mental foramen varies. Mineralization of the canal is decreased in older horses. CLINICAL RELEVANCE: This study improves understanding of mental foramen anatomy and complications with needle placement.

Comparison of computed tomography and high-field (3.0 T) magnetic resonance imaging of age-related variances in selected equine maxillary cheek teeth and adjacent tissues.

BACKGROUND: Modern imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) have the advantage of producing images without superimposition. Whilst CT is a well-established technique for dental diagnostics, MRI examinations are rarely used for the evaluation of dental diseases in horses. Regarding equine endodontic therapies which are increasingly implemented, MRI could help to portray changes of the periodontal ligament and display gross pulpar anatomy. Knowledge of age-related changes is essential for diagnosis, as cheek teeth and surrounding structures alter with increasing age. The aim of the present study was to highlight the advantages of CT and MRI regarding age-related changes in selected equine cheek teeth and their adjacent structures. RESULTS: The CT and MRI appearances of the maxillary 08 s and 09 s and adjacent structures were described by evaluation of post-mortem examinations of nine horses of different ages (Group A: <6 years, B: 6-15 years, C: ≥16 years). Most of the tissues selected were imaged accurately with MRI and CT. Magnetic resonance imaging gives an excellent depiction of soft endo- and periodontal units, and CT of hard dental and bony tissues. Negative correlation between dental age and pulpar sizes was found: 71.3% of the changes in pulp dimensions can be explained by teeth aging. Pulpar sizes ranged from 14.3 to 1.3 mm and were significantly smaller in older horses (p < 0.05). A common pulp chamber was present in 33% of the teeth with a mean dental age of 2.25 years. Ninety-four percent of the 08 and 09 alveoli of all groups were in direct contact with the maxillary sinus. An age-related regression was found (R2 = 0.88) for the distance between alveoli and the infraorbital canal. CONCLUSIONS: The present study provides information about the dental and periodontal age-related morphology and its visibility using different imaging techniques. These results aid in evaluating diagnostic images and in deciding which is the superior imaging modality for clinical cases.

Occlusal Angles of Equine Incisors.

The angulation of equine incisors is frequently used as a parameter for dental corrections. However, the term incisor angle is only vaguely defined, and no studies exist presenting a series of reliable measurements in individual incisors of multiple horses. The aim of this study was to establish an exact method to determine incisor angles and to test whether clinically accessible landmarks (facial crest and bars) are suitable to estimate incisor angles. Eighteen horses were used to create 3-dimensional (3D) reconstructions of the skulls from computed tomography (CT) data sets. Reference planes (median and transverse plane) were calculated using defined anatomical landmarks. Subsequently, occlusal planes for incisors and for incisor quadrants were calculated. Occlusal table angles were measured in relation to the reference planes. For each incisor, sagittal and transverse angles were measured. Mean values of individual incisor angles ranged from 3.5° to 6.8° (transverse angle) and from 32.6° to 44.9° (sagittal angle). No significant differences were detected in mean between the left and the right side when teeth in same Triadan positions were compared. However, in individual horses, marked differences between the left and the right side of the jaws occurred. Mandibular incisors showed significantly steeper sagittal angles than maxillary incisors. Furthermore, angles of opposing incisors were correlated with each other. The facial crest and the upper jaw bars featured a curved shape and were therefore of limited use to estimate the angulation of the upper incisors. In contrast, the lower jaw bars were suitable to determine the angulations of lower incisors.

COMPUTED TOMOGRAPHIC APPEARANCE OF THE TEMPOROMANDIBULAR JOINT IN 1018 ASYMPTOMATIC HORSES: A MULTI-INSTITUTION STUDY.

Published descriptions of nonseptic arthritis of the equine temporomandibular joint (TMJ) are rare and large studies investigating variations in the TMJ for asymptomatic horses are lacking. The objectives of this cross-sectional, retrospective, multi-institutional study were to describe anatomical variations in the TMJ detected using computed tomography (CT) in an equid population asymptomatic for TMJ disease and determine whether these variations were associated with patient signalment, reason for CT examination, or CT slice width. Medical records at eight hospitals were searched for horses that had head/neck CT scans and no clinical signs of TMJ disease. Age, breed, sex, clinical presentation, and CT slice width data were recorded. Alterations in CT contour and density of the mandibular condyles, mandibular fossae, and TMJ intra-articular discs were described for each horse. Generalized logistic regression was used to test associations between anatomical variations and horse age. A total of 1018 horses were sampled. Anatomical variations were found in TMJ CT images for 40% of horses and 29% of joints. These were dichotomous with regard to age. Horses <1 year old commonly had alterations in the shape and density of the mandibular condyle. Older horses commonly had spherical hypodensities within the mandibular condyles consistent with bone cysts; and hyperdense regions of the intra-articular disc consistent with dystrophic mineralization. Findings indicated that TMJ anatomic variations were common in CT images of younger and older horses asymptomatic for TMJ disease. Future studies are needed to more definitively characterize these CT variations using gross pathology and histopathology.

3 tesla magnetic resonance imaging of the occipitoatlantoaxial region in the normal horse.

The aim of this study was to describe the appearance of the ligamentous structures of the occipitoatlantoaxial (OAA) region in the normal horse by 3 tesla (3T) magnetic resonance imaging (MRI). The MRI images of the longitudinal odontoid ligament, tectorial membrane, dorsal and ventral atlantoaxial ligaments, dorsal atlantooccipital membrane with its reinforcing ligaments, and the lateral atlantooccipital ligaments of 10 horse cadavers were evaluated. All ligaments and membranes were identified in all planes, except for the lateral atlantooccipital ligament in the sagittal plane due to its cranioventrolateral course. All were iso to mildly hypointense to musculature of the neck in T1W with the exception of the tectorial membrane that was moderately hypointense; moderately hypointense in PD-SPIR, and markedly hypointense (isointense to cortical bone) in T2W. The PD-SPIR was the best sequence to identify all ligaments and membranes from their cranial and caudal attachments. The longitudinal odontoid ligament, ventral atlantoaxial ligament, and reinforcing bands of the dorsal atlantooccipital membrane presented a characteristic striped heterogeneous signal behavior thought to be due to fibrocartilaginous content. The remaining ligaments and membranes showed homogeneous signal intensity. Special anatomical features in this species such as the fan-shaped longitudinal odontoid ligament, absence of the transverse ligament and presence of the ventral atlantoaxial ligament were documented. Ligamentous structures that stabilize the equine OAA region were described with MRI in this study and these findings could serve as an anatomic reference for those cases where instability of this region is suspected.

Three-dimensional anatomy of equine incisors: tooth length, enamel cover and age related changes.

BACKGROUND: Equine incisors are subjected to continuous occlusal wear causing multiple, age related changes of the extragingival crown. It is assumed that the occlusal wear is compensated by continued tooth elongation at the apical ends of the teeth. In this study, µCT-datasets offered the opportunity to analyze the three-dimensional appearance of the extra- and intraalveolar parts of the enamel containing dental crown as well as of the enamel-free dental root. Multiple morphometric measurements elucidated age related, morphological changes within the intraalveolar part of the incisors. RESULTS: Equine incisors possess a unique enamel cover displaying large indentations on the mesial and distal sides. After eruption tooth elongation at the apical end outbalances occlusal wear for two to four years resulting in increasing incisor length in this period of time. Remarkably, this maximum length is maintained for about ten years, up to a tooth age of 13 to 15 years post eruption. Variances in the total length of individual teeth are related to different Triadan positions (central-, middle- and corner incisors) as well as to the upper and lower arcades. CONCLUSION: Equine incisors are able to fully compensate occlusal wear for a limited period of time. However, after this ability ceases, it is expected that a diminished intraalveolar tooth length will cause massive changes in periodontal biomechanics. The time point of these morphodynamic and biomechanical changes (13 to 15 years post eruption) occurs in coincidence with the onset of a recently described destructive disease of equine incisor (equine odontoclastic tooth resorption and hypercementosis) in aged horses. However, further biomechanical, cell biological and microbiological investigations are needed to elucidate a correlation between age related changes of incisor morphology and this disease.

Oral examination and charting: setting the basis for evidence-based medicine in the oral examination of equids.

The oral examination is performed in equids to assess and monitor oral health status, provide diagnoses, and determine efficacy of treatments. While there is currently insufficient scientific material of adequate quality to enable evidence-based medicine in equine dentistry, this by no means negates the clinician's responsibility to provide oral health care in a scientific and ethical manner. To do so requires that the clinician be knowledgable and skilled in dentistry and general medicine, that each case upholds the principles of scientific method, and that data is gathered and appraised in an objective, precise, consistent, uniform, and reliable manner.

The gold standard of dental care: the juvenile horse.

Postpartum evaluation of the foal's head and mouth are performed to detect craniofacial malformations and other congenital defects. Detailed oral examination and diagnostic imaging can provide diagnostic and prognostic information about congenital abnormalities of the mouth or skull. Important abnormalities of foals include wry nose, cleft palate, overbite (parrot mouth), and underbite (monkey mouth, sow mouth). Tumors and cysts can be detected in young horses. In juvenile horses, primary dental care procedures include oral examination, management of sharp enamel points, management of deciduous teeth, and management of wolf teeth. Facial or jaw swellings are also important considerations.

Advances in equine dental radiology.

Although diagnostic images can be obtained with traditional rare-earth film-screen combinations, digital radiography (DR) has enhanced the ability of the general practitioner to obtain diagnostic radiographs of the equine head. With the widespread availability of DR in equine practices, the practitioner can more readily learn the correct positioning for the various projections of the equine head that are used to evaluate the dentition and sinuses. Digital systems provide rapid processing of the image, enabling the practitioner to correct positioning errors and retake the image without significant delay.

A fresh look at the anatomy and physiology of equine mastication.

There have been many significant and interesting developments in equine dental anatomy during the past 20 years that are of major clinical significance in better understanding the physiology of equine mastication, the etiopathogenesis of some dental disorders, and their safe treatment. The many recent significant developments include descriptions of the enamel infolding of cheek teeth and of infundibular anatomy, including the frequent absence of cementum infilling in many infundibulae, which can lead to infundibular caries. Many important developments in equine dental anatomy are summarized in this article.

Examination of the depth of the equine hard palate.

Equine behavioral problems and loss of optimum performance have been associated with musculoskeletal injury and, more recently, dental disease. Injuries to a horse's tongue and bars of the mandible due to bitting have been documented. However, another point of contact of the bit, the hard palate, has thus far been virtually ignored. The objective of the study was to determine if there was a significant range associated with the depth of the equine hard palate and if this range was associated with a certain breed, age, or sex of the horse. Oral examinations were performed on 52 horses and a measurement of the hard palate was taken. The study group was comprised of 27 mares, 24 geldings and 1 stallion. They were further divided into the age groups: 3-5 years (3), > 5-10 years (18), > 10-15 years (19), and > 15 years (12). Lastly, the groups were divided into the following breed categories: Quarter Horse, Thoroughbred, and Other. Analyses revealed that palate depth has a broad range that is not associated with any breed, age, or sex. Normal reference ranges were established for the data and suggests that the hard palate should be considered and measured when choosing a bit. Further research is necessary to determine which bits are best suited for each palate depth.

Isolation and characterization of multipotent mesenchymal stromal cells from the gingiva and the periodontal ligament of the horse.

BACKGROUND: The equine periodontium provides tooth support and lifelong tooth eruption on a remarkable scale. These functions require continuous tissue remodeling. It is assumed that multipotent mesenchymal stromal cells (MSC) reside in the periodontal ligament (PDL) and play a crucial role in regulating physiological periodontal tissue regeneration. The aim of this study was to isolate and characterize equine periodontal MSC. Tissue samples were obtained from four healthy horses. Primary cell populations were harvested and cultured from the gingiva, from three horizontal levels of the PDL (apical, midtooth and subgingival) and for comparison purposes from the subcutis (masseteric region). Colony-forming cells were grown on uncoated culture dishes and typical in vitro characteristics of non-human MSC, i.e. self-renewal capacity, population doubling time, expression of stemness markers and trilineage differentiation were analyzed. RESULTS: Colony-forming cell populations from all locations showed expression of the stemness markers CD90 and CD105. In vitro self-renewal capacity was demonstrated by colony-forming unit fibroblast (CFU-F) assays. CFU-efficiency was highest in cell populations from the apical and from the mid-tooth PDL. Population doubling time was highest in subcutaneous cells. All investigated cell populations possessed trilineage differentiation potential into osteogenic, adipogenic and chondrogenic lineages. CONCLUSIONS: Due to the demonstrated in vitro characteristics cells were referred to as equine subcutaneous MSC (eSc-MSC), equine gingival MSC (eG-MSC) and equine periodontal MSC (eP-MSC). According to different PDL levels, eP-MSC were further specified as eP-MSC from the apical PDL (eP-MSCap), eP-MSC from the mid-tooth PDL (eP-MSCm) and eP-MSC from the subgingival PDL (eP-MSCsg). Considering current concepts of cell-based regenerative therapies in horses, eP-MSC might be promising candidates for future clinical applications in equine orthopedic and periodontal diseases.

Endoscopic anatomy of the cervical vertebral canal in the horse: a cadaver study.

REASON FOR PERFORMING STUDY: Localisation of spinal cord compression in horses with cervical vertebral stenotic myelopathy is inexact. Vertebral canal endoscopy has been used in man to localise spinal cord lesions and has the potential to become a useful diagnostic technique in horses. OBJECTIVE: To establish a surgical approach via the atlanto-occipital space to the cervical vertebral canal in equine cadavers and describe the endoscopic anatomy of the cervical epidural and subarachnoid spaces. METHODS: The cadavers of 25 mature horses were used to assess 3 surgical methods to approach the cervical vertebral canal, including 2 minimally invasive and one open technique. Once the approach had been made, a flexible videoendoscope was inserted into the epidural space (epiduroscopy) or the subarachnoid space (myeloscopy) and advanced caudally until the intervertebral space between C7 and T1 was reached. RESULTS: The epidural and subarachnoid spaces could not be accessed reliably using the minimally invasive techniques. Furthermore, damage to the nervous tissues was a frequent complication with these procedures. The open approach allowed successful insertion of the videoendoscope into the epidural and subarachnoid spaces in all horses and no inadvertent damage was observed. Anatomical structures that could be seen in the epidural space included the dura mater, nerve roots, fat and the ventral internal vertebral venous plexus. In the subarachnoid space, the spinal cord, nerve roots, blood vessels, denticulate ligaments and external branch of the accessory nerve were seen. CONCLUSIONS: Using the open approach, epiduroscopy and myeloscopy over the entire length of the cervical vertebral canal are possible in the mature horse. POTENTIAL RELEVANCE: Cervical vertebral canal endoscopy may become a valuable tool to localise the site of spinal cord injury in horses with cervical vertebral stenotic myelopathy and could aid in the diagnosis of other diseases of the cervical spinal cord.

Evolution of Old World Equus and origin of the zebra-ass clade.

Evolution of the genus Equus has been a matter of long debate with a multitude of hypotheses. Currently, there is no consensus on either the taxonomic content nor phylogeny of Equus. Some hypotheses segregate Equus species into three genera, Plesippus, Allohippus and Equus. Also, the evolutionary role of European Pleistocene Equus stenonis in the origin of the zebra-ass clade has been debated. Studies based on skull, mandible and dental morphology suggest an evolutionary relationship between North American Pliocene E. simplicidens and European and African Pleistocene Equus. In this contribution, we assess the validity of the genera Plesippus, Allohippus and Equus by cladistic analysis combined with morphological and morphometrical comparison of cranial anatomy. Our cladistic analysis, based on cranial and postcranial elements (30 taxa, 129 characters), supports the monophyly of Equus, denies the recognition of Plesippus and Allohippus and supports the derivation of Equus grevyi and members of the zebra-ass clade from European stenonine horses. We define the following evolutionary steps directly relevant to the phylogeny of extant zebras and asses: E. simplicidens-E. stenonis-E. koobiforensis-E. grevyi -zebra-ass clade. The North American Pliocene species Equus simplicidens represents the ancestral stock of Old World Pleistocene Equus and the zebra-ass clade. Our phylogenetic results uphold the most recent genomic outputs which indicate an age of 4.0-4.5 Ma for the origin and monophyly of Equus.

Anatomical studies of maxillary cheek teeth infundibula in clinically normal horses.

REASONS FOR PERFORMING STUDY: Although clinical disorders of equine maxillary cheek teeth (CT) infundibula are common, anatomical knowledge of these structures is poor. HYPOTHESIS: Anatomical examinations of sectioned CT infundibula will better define their shapes and sizes and allow identification of infundibular cemental variations and changes. MATERIAL AND METHODS: Cheek teeth were extracted post mortem from 33 horses, aged 3-30 years, without a clinical history of dental disease. The CT were sectioned longitudinally in the bucco-palatal plane through the widest aspects of both infundibula. The infundibular surfaces were then assessed morphologically, including by measurements of areas of cemental variations and changes. Specimens from selected teeth were examined histologically. RESULTS: Infundibular length and infundibular surface area, and infundibular length as a proportion of dental crown length progressively decreased with age, e.g. infundibular length was up to 89 mm after eruption to 2 mm in one older horse. Triadan 06 and 09 positions had significantly shorter CT and therefore infundibula, than the other 4 Triadan positions. Only 11.7% of infundibula were filled completely with normal appearing cementum, 8.2% of infundibula (especially the 09 position) had complete cemental caries; 22.6% of infundibula had areas with cemental hypoplasia and the remaining 57.5% of infundibulae had a variety of other cemental appearances, including the presence of central defects, localised occlusal caries and cemental discolourations. Histology showed the presence of an apical blood supply to infundibular cement in younger horses. CONCLUSIONS: Anatomical variations of CT infundibular cement are very common and some changes, such as areas of localised cemental hypoplasia, may predispose to the development of infundibular caries. POTENTIAL RELEVANCE: This more complete description and quantification of CT infundibular anatomy should allow more rational assessment and treatment of equine CT infundibular disorders.