Edited by: Carsten Staszyk, Justus Liebig Universität Gießen, Germany
Reviewed by: Derek Cissell, University of California, Davis, United States; Kevin S. Stepaniuk, Columbia River Veterinary Specialists, United States
Specialty section: This article was submitted to Veterinary Dentistry and Oromaxillofacial Surgery, a section of the journal Frontiers in Veterinary Science
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Equine cheek teeth disorders, especially pulpar/apical infections, can have very serious consequences due to the frequent extension of infection to the supporting bones and/or adjacent paranasal sinuses. Limited studies have assessed the accuracy of computed tomographic (CT) imaging in the diagnosis of these disorders, and no study has directly compared imaging and pathological findings of the alveoli of diseased equine cheek teeth.
To validate the accuracy of CT and radiographic imaging of cheek teeth disorders by comparing CT and radiographic imaging, gross and histological findings in abnormal cheek teeth and their alveoli extracted from equine cadaver heads.
Fifty-four cadaver heads from horses with unknown histories that had died or been euthanized on humane grounds obtained from a rendering plant had radiography, CT imaging, and gross pathological examinations performed. Based on imaging and gross examination findings, 30 abnormal cheek teeth (26 maxillary and 4 mandibular) identified in 26 heads were extracted along with their dental alveoli where possible, and further CT imaging, gross, and histological examinations were performed. Eight maxillary cheek teeth (including four with attached alveolar bone) from these heads, that were normal on gross and CT examinations, were used as controls.
Gross pathological and histological examinations indicated that 28/30 teeth, including two supernumerary teeth, had pulpar/apical infection, including pulpar and apical changes. A further supernumerary and a dysplastic tooth were also identified. Abnormal calcified tissue architecture was present in all three supernumerary and in the dysplastic tooth. CT imaging strongly indicated the presence of pulpar/apical infection in 27 of the 28 (96.4%) pulpar/apically infected teeth, including the presence of intrapulpar gas (
No history or breed-related information was available on these cases.
There was a 96.4% correlation between a CT diagnosis and confirmative pathological findings in 28 apically infected teeth confirming the accuracy of CT imaging in diagnosing equine pulpar/apical infections. There was also excellent correlation between CT and histological alveolar bone findings.
Equine cheek teeth disorders, especially bacterial pulpar infection that lead to apical infections (hereafter termed
Currently, radiography is the main imaging technique used to diagnose equine dental disease, but it is frequently inaccurate in early cases of cheek teeth apical infections (
Computed tomography (
Several studies (
This study was approved by the Ethical Review Committee of The Royal (Dick) School of Veterinary Studies and Roslin Institute, The University of Edinburgh on the 16th February 2012. The heads of 54 horses, similar in size to Thoroughbred heads, were obtained from a rendering plant between October 2012 and March 2013. They originated from horses with unknown histories that had died or were euthanized on humane grounds due to disease. The heads were resected at the level of the atlas and then frozen, usually on the day of death.
After they were thawed, six computed radiographic projections were obtained from each head to allow examination of the cheek teeth (Agfa CR 25 digitizer NX8000 HP7900 Raid Server, Agfa Healthcare UK Ltd., Brentford, Middlesex, UK) including: lateral, dorsoventral, two latero 45° dorsal–lateroventral oblique of the maxillary arcades, and two latero 45° ventral–laterodorsal oblique of the mandibular arcades.
Transverse CT images of the heads, positioned on their mandibles, were then acquired with a multislice CT scanner (Siemens, Volume Zoom, Germany) in a helical scan mode using a 512 × 512 matrix, 120 kV, 300 mA, focal spot 1.2, at a slice thickness of 3 and 1.5 mm; images were saved in DICOM format. Radiographic and CT images were evaluated by two observers using dedicated software Osirix® (
To compare the head sizes in this study population with head sizes of a known breed, CT images of 12 Thoroughbreds of known age [0–5 years old (
Head “length” (i.e., distance from the caudal aspect of the orbit to the nasoincisive notch) was measured from CT sagittal reconstructions; head “width” (width of the hard palate at the level of Triadan 06) was measured from CT dorsal reconstructions, and head “height” (distance from the hard palate to the dorsal aspect of the maxillary bone at the level of the orbit) was measured using CT sagittal reconstructions. These three measurements were multiplied together to produce a measurement of head “volume” (
CT evaluation included the assessment of the pulp horns including for the presence of gas-attenuating structures. To accurately identify the presence of gas, a point-shape region of interest (ROI) tool was placed in a consistent manner over the gas-attenuating structures within the pulp horn, and the HU value was generated as shown in Figure
Each extracted abnormal and control tooth was photographed on all sides and grossly examined, before being transversely sectioned into four equal parts, i.e., occlusal, two mid-crown and apical aspects, using a 1 mm thick lapidary blade. A 5 mm thick section was cut from each of the above portions, then visually examined and photographed on both sides. These thin sections were fixed in formalin before decalcification, histological processing, and examination.
The dental sections were decalcified and embedded in paraffin wax, and 4 µm thick sections were cut and stained with hematoxylin and eosin as described (
A paired
Since gross pathological and histological changes are the gold standard for confirming the presence of dental disease, the pathological findings are presented first here, in contrast to the sequence of the actual study where imaging was initially performed.
Thirty abnormal cheek teeth were identified including 26 maxillary teeth: Triadan 06 (
Alveolar bone surrounding the dental reserve crown and apex remained intact around 21 teeth (all with apical infection) but became detached from the other 9 teeth during extraction or histological processing. Gross examination of the external aspects of the dental alveoli was unrewarding due to iatrogenic chisel damage from the extraction process.
Gross pulpar abnormalities including discolored, absent, or necrotic pulp were present in 23 of 28 teeth (81.5%), all which were later histologically confirmed to have pulpar/apical disease (see
Gross dentinal changes, mainly the presence of circumpulpar dentinal staining and irregular dentinal–pulpar margins, were grossly identified around 1 or more pulp horns in 18/28 teeth (64.3%) (Figures
Generalized periodontal thickening or fibrous soft tissue swellings of the periapical region were grossly identified in 25/28 teeth (89.3%) with apical infection. Limited, subgingival periodontal changes were visible in one dysplastic tooth without endodontic disease, likely due to malformation of the junction between the periodontal ligament and the alveolar bone.
Proliferative calcified apical changes, including thickened, irregularly shaped roots and/or more generalized apical hypercementosis, were grossly identified in 24/28 teeth (85.7%) with apical infection. Limited peripheral cemental destructive changes were present near the gingival margin in the dysplastic cheek tooth.
Gross and deep caries with discolored enamel (grade 2 caries) was identified in the infundibulae of 7/26 maxillary cheek teeth (26.9%), with as noted a pulpar–infundibular connection in one tooth.
In summary, of the 28 teeth later confirmed histologically to have pulpar/apical infection, 23 had gross pulpar abnormalities, 26 had apical calcified tissue changes, and 26 had periapical periodontal changes. Gross changes in external shape and of internal architecture (on cut section) were present in all three supernumerary (two with intercurrent apical infection and one endodontically normal) and the dysplastic tooth. Limited periodontal and peripheral cemental thickening were present in the dysplastic tooth. No gross changes were identified in the eight control teeth.
In the four control maxillary cheek teeth with attached alveolar bone, the peripheral cemental profile was smooth histologically and supported by a band of well-vascularized periodontal ligament of uniform thickness, in turn bordered more peripherally by anastomosing trabeculae of alveolar bone. The main bony trabeculae were oriented parallel to the circumference of the tooth and were interspersed with marrow fat (Figures
Histological transverse section of normal alveolar bone. HE. Note the smoothly outlined peripheral cemental profile (*) that is bordered more peripherally by anastomosing trabeculae of alveolar bone. The main bony trabeculae are oriented parallel to the profile of the circumference of the tooth (^) and are interspersed with marrow fat. No osteoclastic activity is apparent.
Histological transverse section of normal alveolar bone. HE. Note the alveolar bony trabeculae oriented parallel to the profile of the circumference of the tooth (*) and interspersed with marrow fat. No osteoclastic activity is apparent. Note the normal pulp stroma with blood vessels (^).
The 21 apically infected teeth with attached dental alveolus had changes in the alveolar bone that were not present in the control teeth. For the purposes of this study, these changes were regarded as abnormal. The changes were marked in 16 teeth and less severe in five. They were characterized by multifocal disruption of the normal trabecular pattern of the alveolar bone, which was usually associated with expansion/thickening of the periodontal ligament. Entrapped within this stroma were variably sized, irregular islands of disorganized alveolar bone, many of which had scalloped profiles associated with numerous osteoclasts occupying Howship’s lacunae (Figures
Histological transverse section of the apex of Triadan 110 including of distorted alveolar bone. HE. There is focal disruption and disorganization of the normal trabecular pattern of the alveolar bone with thickening of the surrounding periodontal ligament. The thickened periodontal ligament and disorganized islands of alveolar bone form a protruding “tongue” that focally displaces the peripheral cementum.
In the alveolar bone of the five teeth with milder changes, there was mild scalloping of the alveolar bone, mild osteoclast activity, and slightly increased thickening of the periodontal ligament. In three of these five cases, there was slight sclerosis of the periapical alveolar bone on both radiographic and CT imaging.
In addition to the aforementioned thickening of the periodontal ligament associated with alveolar bone changes in all 21 alveoli, further histological abnormalities were noted in the periodontal ligament that remained attached to 18/28 apically infected teeth (64.3%). These changes included the presence of hemorrhage/fibrin (
Pulpar changes were histologically present in all 28 teeth diagnosed with pulpar/apical infection, and such histological evidence was the main criterion for diagnosing these teeth with pulpar/apical infection. These changes involved 96 of the 152 pulps (mean 3.6 affected pulps/tooth, range 1–5) in the 28 teeth, with every pulp diseased in 3/28 teeth.
Histological pulpar abnormalities included what we termed “faded pulp” in 20/28 (71.4%) teeth. This feature was characterized by a pulp stroma that was much paler than that of normal viable pulps, with loss of nuclear detail in stromal fibroblasts, loss of normal vasculature and, sometimes, the accumulation of loose dentinal debris at the pulp periphery (
Histological changes were present in dentine surrounding infected pulps in 7/28 (25%) infected teeth, including dentinal lysis at the pulp periphery (
Histological abnormalities were present in the peripheral periapical cementum in 15/28 apically infected teeth, including cemental lysis and caries-like destruction (
Histological infundibular changes were found in 9/26 (34.6%) maxillary cheek teeth including the accumulation of plant material, bacteria, debris, and carious infundibular cementum.
The final pathological diagnoses were apical infection (
No pulpar or periapical abnormalities were detected in one supernumerary tooth, the dysplastic tooth, or the eight control teeth. In addition, one tooth with pulpar discoloration and histological evidence of neutrophil/bacterial pulpar infiltration did not have any CT imaging evidence of apical infection.
The main CT findings in the 28 teeth diagnosed with apical infection included: gas within pulps (
In all 16 teeth with severe histological alveolar bone changes, perialveolar bone changes were visible on CT, but only 4 of these 16 cases had identifiable periapical alveolar changes radiographically.
Following extraction, CT imaging of the 28 teeth diagnosed with apical infection at 0.5 mm slice thickness also showed convincing evidence of apical infection on CT imaging in 27/28 teeth, including the presence of intrapulpar gas in 17/27 teeth (2 teeth with gas in pulps on pre-extraction CTs sustained iatrogenic fractures to the roots of the affected pulp horns during extraction with exposure of the affected pulp and loss of intrapulpar gas); increased pulpar volume in 7/27 teeth and irregular pulp horn margins in 14/27 teeth [total of 21/28 (75%) with pulpar changes]. Pre- and post-extraction CT imaging changes in infundibulae and roots were similar.
Radiographic abnormalities strongly indicative of apical infection were found in 14 of the 28 apically infected teeth (50%), including root blunting (clubbing) (
Liuti et al. (
A significant amount of dental imaging information is also gained from assessment of the periodontal ligament and alveolus of a suspect tooth. In clinical cases, the periodontal ligaments can only be pathologically examined in areas that (very variably) remain attached to the extracted tooth. In addition, some periodontal pathological changes, such as hemorrhage and fibrin, may be iatrogenic due to the
Alveolar bone cannot be pathologically examined in clinical cases, so it is not possible to compare imaging and pathological alveolar bone findings in such cases. The use of diseased teeth from fresh cadaver heads in this study allowed most of the periodontal ligament to be removed along with adjacent alveolar bone in 70% (21/30) of teeth. This facilitated pathological assessment of alveolar bone when present and, as noted, allowed a more complete assessment of the periodontal ligaments that additionally, were free of iatrogenic extraction-related inflammatory changes.
Alveolar bone was histologically abnormal around all 21 apically infected teeth where it remained attached. Changes included extensive osteoclastic activity and marked disruption of the trabecular alveolar bone with its replacement by a collagenous stroma, the latter leading to apparent thickening of the periodontal membranes on CT imaging.
Normal alveolar bone constantly remodels to accommodate the changing size and shape of erupting brachydont teeth (
Buhler et al. (
Radiographically, alveolar bone sclerosis has been described as an imaging feature dental apical infection (
Apically infected teeth always have one or more infected pulps (that precedes the periodontal infection) (
Other CT changes associated with apical infection, including clubbing (hypercementosis), fragmentation, and/or lysis of roots, were present in 27/28 (96.4%) of the cases. Changes to the apical calcified tissues (mainly increased deposition of cementum around roots) were more obvious grossly and were present in 26/28 (92.8%) teeth while histological changes (including erosion, necrosis, and biofilm/plaque deposition) were present in 15/28 (53.6%). This discrepancy between gross and histological findings may be due to loss of some roots during decalcification and histological processing (
Casey et al. showed that CT and pathological findings in formalin-preserved, apically infected cheek teeth correspond well with respect to mineralized dental tissue changes or the presence of food material in the pulp canals (
The production of gas by anaerobic bacteria, such as
With severe (grade 3) infundibular caries with subsequent erosion of cementum, enamel and dentine, and pulpar invasion, or with infundibular caries-related sagittal fractures and subsequent apical infection (
Casey et al. (
It is possible that the prolonged storage of teeth by Casey et al. (
Using the HU values from CT images is an established methodology to identify small gas cavities in tissue; vacuum phenomenon in the intervertebral disks has been described on CT as an accumulation of gas (principally nitrogen) in the vertebral column with a range of density between −900 and −980 HU (
None of the infected teeth had advanced gross destructive changes or extensive proliferative cemental apical deposits, i.e., all appeared to be low-grade chronic pulpar/apical infections and this may explain the poor sensitivity of radiography in diagnosing these infections at this early stage. In a similar study (
Radiography detected changes including tooth root clubbing (52%) and periapical sclerosis (29.6%) in teeth with histologically confirmed apical infection. Overall, radiography detected changes that were considered sufficient to recommend extraction in 14/28 (50%) of the current cases, similar to the findings of Liuti et al. (
Infundibular caries can cause midline sagittal fractures of affected teeth (
Apically infected teeth have by definition, changes in their periodontal ligaments, especially around the apex, and periodontal lesions were grossly identified in 89% (25/28) of apically infected teeth in this study. However, periodontal lesions were histologically detectable in only 64.2% (18/28) of these 28 teeth. The absence of this finding in the other 10 teeth is likely due to failure to capture localized periapical periodontal lesions in sections, loss of apical tissues during histological preparation or possibly due to the pulpitis not extending to the periapical periodontal tissues in some very early pulpar infections. There was a good correlation in this study between the histological findings and radiographic, CT and gross periodontal findings. However, it can be difficult to differentiate grossly between preexisting changes and extraction-induced changes in the periodontal ligament. In this study, this was not of concern because the alveolar bone and periodontal ligament were removed with the tooth after death.
Inflammatory cells were only present in a small number of periodontal tissues from these teeth and they mainly had a perivascular distribution, suggesting hematogenous origin rather than direct extension from an apical lesion. Gross examination excluded a descending periodontal route of infection for the two infected supernumerary teeth. Such a route can come into play in some supernumerary/dysplastic teeth that are not well seated into their alveoli (
In this study, pulp stones were found both free in the pulp and embedded in the secondary dentine, both in abnormal (16/30) and control teeth (4/8) similar to the findings of Liuti et al. (
This study has shown an inexplicably high prevalence (51.9%) of pulpar/apical infection in 54 heads obtained from a rendering plant. Unfortunately, no clinical histories were available for any of these cases, and this extraordinarily high prevalence of dental disease may be a reflection of the study population. These were all ill horses that had died from disease or were euthanized on humane grounds. It would appear that none was euthanized on the grounds of old age since the mean age was 12 years (5–20 years). No heads contained evidence of significant decomposition and, in all 26 horses with the 28 apically infected teeth, just 4.5% (28/627) of the cheek teeth had imaging or gross pathological evidence of apical infection. In addition, in 89% (25/28) of the apically infected teeth, some pulp horns were grossly and histologically normal, thus confirming that postmortem changes did not cause the observed pathological changes.
The true prevalence of clinical equine cheek teeth endodontic/periapical disease in the general equine population is unknown but, as adjudged by the caseload of this equine hospital, cases with external signs of apical infection such as mandibular or maxillary swellings, sinus tracts or dental sinusitis, it is likely to be less than 2%. However, occlusal pulpar exposure (indicating some prior pulpar insult) is sometimes clinically apparent in teeth without clinical signs of apical infection. In addition, some cheek teeth with “idiopathic fractures” (
Changes highly indicative of apical infection were identified on CT imaging in 96.4% and radiographically in 50% of pathologically confirmed apically infected cheek teeth. Alveolar bone changes were histologically present in all 21 examined alveoli, and all 16 alveoli with marked alveolar bone changes had detectable CT alveolar changes. This study confirms the superior accuracy of CT compared with radiography in detecting equine cheek tooth apical infection and showed excellent correlation between both dental and alveolar CT imaging and pathological findings.
This study was approved by the Ethical Review Committee of The Royal (Dick) School of Veterinary Studies, Roslin Institute, The University of Edinburgh on the 16th February 2012.
TL contributed to study design and execution, data analysis and interpretation, and manuscript preparation. SS contributed to study execution and interpretation and manuscript preparation. PD contributed to study design and execution, data analysis, and manuscript preparation. All the authors approved the final manuscript.
The authors declare that the research was conducted in the absence of any commercial or financial relationship that could be constructed as a potential conflict of interest.
The authors would like to thank Mr. Neil McIntyre and Craig Pennycook for their technical assistance.