The dental cavities of equine cheek teeth: three-dimensional reconstructions based on high resolution micro-computed tomography

Micro-CT and histological examination of accessory canals in 34 equine cheek teeth

Accessory canals and apical deltas have been extensively studied in human dentistry. Their clinical role as a difficult to clean reservoir for bacteria during endodontic treatments has been well described. Many papers describe in detail the pulp anatomy of equine dentition but little attention has been given to their apical ramifications. The goal of this paper is to describe the presence and anatomy of these accessory canals and apical deltas in healthy equine cheek teeth and discuss their possible relevance in the light of equine endodontics. To accomplish this, 15 maxillary and 19 mandibular healthy cheek teeth were collected ranging from Triadan 06 s to 11 s with eruption ages from 4 to 9 years. Their root anatomy was documented in detail based on micro computed tomography images. A subset of 3 teeth also underwent histological examination. Accessory canals were found in all but two teeth examined. Up to 44 accessory canals per tooth have been found with locations ranging from the root furcation down to the apex of the root and with highly variable diameters. Apical deltas in different stages of development were found in 84% of the roots. The presence of accessory canals identified on microCT images could be confirmed using histological examination although some of them were obliterated by reparative dentin. Accessory canals can be found in most equine cheek teeth and add complexity to their endodontic anatomy. This could have important implications for their treatment in case of pulp pathology. In humans, failure to remove bacterial biofilm from such canals has been associated with failure of endodontic treatment. Research on diseased equine teeth is required to gain a better understanding of their clinical relevance in horses.

An application of the density standard and scaled-pixel-counting protocol to assess the radiodensity of equine incisor teeth affected by resorption and hypercementosis: preliminary advancement in dental radiography

BACKGROUND

Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) syndrome is a dental disease where the radiographic signs may be quantified using radiographic texture features. This study aimed to implement the scaled-pixel-counting protocol to quantify and compare the image structure of teeth and the density standard in order to improve the identification of the radiographic signs of tooth resorption and hypercementosis using the EOTRH syndrome model.

METHODS AND RESULTS

A detailed examination of the oral cavity was performed in 80 horses and maxillary incisor teeth were evaluated radiographically, including an assessment of the density standard. On each of the radiographs, pixel brightness (PB) was extracted for each of the ten steps of the density standard (S1-S10). Then, each evaluated incisor tooth was assigned to one of 0-3 EOTRH grade-related groups and annotated using region of interest (ROI). For each ROI, the number of pixels (NP) from each range was calculated. The linear relation between an original X-ray beam attenuation and PB was confirmed for the density standard. The NP values increased with the number of steps of the density standard as well as with EOTRH degrees. Similar accuracy of the EOTRH grade differentiation was noted for data pairs EOTRH 0-3 and EOTRH 0-1, allowing for the differentiation of both late and early radiographic signs of EOTRH.

CONCLUSION

The scaled-pixel-counting protocol based on the use of density standard has been successfully implemented for the differentiation of radiographic signs of EOTRH degrees.

A histological description of alpaca (Vicugna pacos) cheek teeth: Findings and anatomical variations in macroscopically normal molars

Scientific literature on veterinary dentistry in alpacas has historically focused on the description of tooth root abscesses. However, recent studies have shown a variety of other, sometimes preceding dental conditions to be widespread in this species. To allow the development and finetuning of treatment strategies in this species, a more thorough understanding of the underlying etiopathogenesis of dental disease is required. Histological studies focusing on normal dental and surrounding tissues might serve as a basis for this purpose. Nine teeth, extracted from seven alpacas were collected. All samples were retrieved from animals that died or were euthanized for non-dental reasons. Histological sections were prepared at three different levels in each tooth and examined using light microscopy focusing on the assessment of pulp tissue, dentin, cementum, periodontal tissues and the apical region. The histological appearance of the investigated dental tissues in alpacas showed great similarities with other hypsodont species. However, a rather rare type of dentin called “vasodentin” could be identified in all examined cheek teeth. Another species-specific finding was the extremely close proximity of varying neighboring tooth roots that seemed to be responsible for inducing massive resorptive lesions. The results of this study might contribute to a better understanding of the etiopathogenesis of some dental diseases in the alpaca.

The Equine Dental Pulp: Histomorphometric Analysis of the Equine Dental Pulp in Incisors and Cheek Teeth

To maintain a healthy and functional status, equine hypsodont teeth have to produce lifelong large amounts of subocclusal dentin to prevent occlusal pulp exposure, which is caused by occlusal wear. To examine the cyto- and histological components that guarantee the lifelong high productivity of equine pulp, a limited number of ten incisors and ten cheek teeth from seven adult horses (aged 5 to 24 years) and five foals were sampled for preliminary histomorphometric and histomorphological evaluations. Independently of age, the equine dental pulp featured constant layers of predentin and odontoblastic cells, as well as soft connective tissue, composed of a cellular fibrous matrix, in which blood vessels and nerve fibers were embedded. As a result of the progressive deposition of newly formed dentin, the layer of dentin became thicker with age, and the size of the pulp chamber decreased. In contrast to the brachydont teeth, the morphological characteristics of the odontoblastic layer and the width of the predentin layer did not change with age. Therefore, it is assumed that the equine pulp tissue retained their juvenile status, which explains its unchanged ability to produce high amounts of subocclusal dentin. These preliminary, but clinically significant, findings are worthy of further investigation in order to identify strategies for equine-specific endodontic therapies.

Clinical insights into the three-dimensional anatomy of cheek teeth in alpacas based on micro-computed tomography - Part 2: Maxillary cheek teeth

BACKGROUND

Scientific knowledge regarding alpaca dentistry is relatively limited despite its clinical implications. The present gap in available supportive data leads to limited treatment options for dental pathology in alpacas in comparison to other species. The main goal of this study was to gain novel insights into the general and pulp morphology of maxillary cheek teeth to allow development of more advanced treatment strategies in the future. Also, the risk of causing pulp exposure when floating maxillary cheek teeth was of particular interest. Concurent research focusing on the anatomy of mandibular cheek teeth has been performed accordingly. The results obtained in mandibular teeth are expected to be non-extrapolatable because of the structural differences between mandibular and maxillary teeth.

RESULTS

Pulp morphology of maxillary cheek teeth showed great variation. A common pulp chamber was identified in 46/83 (55.4%) teeth with a mean dental age of 2 years and 7 months (± 2 years and 5 months). Pulpal segmentation was more commonly observed in teeth of increasing age. Full columnar segmentation was seen in 33/69 teeth (47.8%), whereas within-column segmentation was observed in 36/83 teeth (43.4%). Age and degree of segmentation of the pulpal tissue varied greatly according to Triadan position. Physical contact between roots of adjacent teeth was found in the majority of examined molars (range 82-94%) which resulted in morphological adaptations at the level of the root tips. The measured sub-occlusal dentinal thickness was as low as 0.46 mm above pulp horn 2 in a 14 years and 11 months old Triadan 09, emphasizing the risk of pulp exposure attributed to dental floating.

CONCLUSION

This study offers an objective description of age-dependent maxillary cheek teeth pulp morphology in alpacas. Current findings are of great value to provide a basis for the development of tooth-saving techniques as a treatment for dental disease in this species. Observed physical contact between the roots of different examined molars may be a facilitating factor in the spread of apical infection in chronically diseased cases. Finally, a conservative approach regarding dental floating is recommended in order to avoid iatrogenic damage to pulp tissue.

The facultative human oral pathogen Prevotella histicola in equine cheek tooth apical/ periapical infection: a case report

BACKGROUND

Prevotella histicola is a facultative oral pathogen that under certain conditions causes pathologies such as caries and periodontitis in humans. Prevotella spp. also colonize the oral cavity of horses and can cause disease, but P. histicola has not yet been identified.

CASE PRESENTATION

A 12-year-old Tinker mare was referred to the clinic for persistent, malodorous purulent nasal discharge and quidding. Conservative antibiotic (penicillin), antiphlogistic (meloxicam), and mucolytic (dembrexine-hydrochloride) treatment prior to referral was unsuccessful and symptoms worsened. Oral examination, radiography, sino-/ rhinoscopy, and standing computed tomography revealed severe apical/ periapical infection of the upper cheek tooth 209 with accompanying unilateral sinonasal inflammation and conchal necrosis. The tooth exhibited extensive subocclusal mesial infundibular cemental hypoplasia and caries, and an occlusal fissure fracture. After mechanical debridement and thermoplastic resin filling of the spacious subocclusal carious infundibular lesion, the tooth was extracted intraorally. The sinusitis and conchal necrosis were treated transendoscopically. Selective bacteriological swab cultures of affected tooth roots and subsequent matrix-assisted laser desorption ionization-time of flight mass spectrometry showed an infection with the obligate anaerobic, Gram-negative bacterium P. histicola. Surgical intervention and adapted antibiotic therapy led to normal healing without complications.

CONCLUSIONS

This study provides the first documented case of dental infection in a horse caused by P. histicola at once indicating necessity of more sufficient microbiological diagnostics and targeted antibiotic treatment in equine dental practice. This finding is also conducive to understand species-specific Prevotella diversity and cross-species distribution.

Clinical insights into the three-dimensional anatomy of cheek teeth in alpacas based on micro-computed tomography. Part 1: mandibular cheek teeth

BACKGROUND

Despite dental disease being a common health concern in alpacas, important dental pathology including apical infection, remains poorly understood. Treatment options are limited compared to veterinary dentistry techniques in other species. The primary goal of this study was to increase understanding of the external and internal anatomy of mandibular cheek teeth to enable the development of tooth sparing techniques in this species. Also, an objective evaluation of the sub-occlusal dentinal thickness in normal mandibular cheek teeth is warranted to understand the risks associated with reduction of overgrown teeth.

RESULTS

Overall pulp anatomy was variably characterized by the presence of a common pulp chamber in younger teeth, and segmentation of pulp cavities into multiple separate pulp entities within the same tooth with increasing age. A common pulp chamber was identified in 55.3% (26/47) of teeth with a mean dental age of 1 year and 11 months (± 1 year and 8 months). Columnar segmentation was recorded in the remaining teeth with a mean dental age of 6 years and 5 months (± 3 years and 11 months). Age of segmentation of the common pulp chamber into multiple separate pulp entities shows wide variation and is dependent of the specific Triadan position. The present study illustrates the presence of disto-mesial root contacts between adjacent tooth roots, often leading to morphological adaptations, most frequently observed between Triadan 09-10s (80%) and 10-11s (67%). The measured sub-occlusal dentinal thickness was as low as 1.11 mm over some pulp horns. The sub-occlusal dentinal thickness was lower than 2, 3, and 4 mm in 13.1, 38.1 and 61.4% of performed measurements, respectively.

CONCLUSION

This study provides detailed information on age-dependent mandibular cheek teeth anatomy in alpacas, which may support the use and development of advanced dental treatments in this species such as endodontics and tooth sectioning techniques. Apical morphological adaptations caused by disto-mesial root contact between adjacent mandibular cheek teeth are clearly illustrated. The limited amount of sub-occlusal secondary dentin warrants a cautious approach with regards to dental floating in alpacas.

Fracture Resistance of Equine Cheek Teeth With and Without Occlusal Fissures: A Standardized ex vivo Model

Background:Ex vivo fracture models are frequently used in human dentistry to provide insights in the fracture mechanisms of teeth. Equine cheek teeth fractures are an important dental pathology, but there has been no research performed to examine the fracture resistance ex vivo.

Objective: To evaluate the fracture resistance of equine cheek teeth and identify anatomical predictors that might influence fracture resistance in healthy teeth. It was further evaluated if the presence of a fissure caused a decrease in fracture resistance.

Study design:Ex vivo experimental design.

Methods: Individual cheek teeth were subjected to a compression load in a universal testing machine until fracture occurred. Testing was performed in two study groups. A first group of healthy cheek teeth was tested to examine anatomical predictors on fracture resistance. A second group comprised cheek teeth with occlusal fissures and an equal number of age- and size-matched fissure-free teeth as controls. The effect of possible predictors on fracture resistance was investigated by regression analysis.

Results: In the first group, fracture resistance was significantly influenced by the location on the tooth where testing was performed in both maxillary (p < 0.001) and mandibular teeth (p < 0.001). Additional significantly associated factors were Triadan number in mandibular (p = 0.009) and the mesiodistal length of the occlusal surface of maxillary teeth (p = 0.01). Experimentally induced crown fractures that extended below the simulated bone level were more frequently associated with pulp horn exposure (p < 0.001). In the second group, significant lower fracture loads were recorded in teeth with fissures (mandibular p = 0.006; maxillary p < 0.001), compared to fissure-free teeth.

Main limitations: This ex vivo model does not imitate the in vivo masticatory forces and lacks the shock-absorbing properties of the periodontal ligament.

Conclusions: The methodology used in this study provides an ex vivo experimental set-up to test fracture resistance of equine cheek teeth enabling evidence-based research to examine the potentially weakening effects of tooth pathology and its treatments. Crown resistance to fracture differed along the occlusal surface of healthy equine cheek teeth, and the presence of fissures further decreased fracture resistance.

Recent developments in equine dentistry

Equine dentistry is a rapidly developing clinical specialty. It has benefitted from key advances in anatomical and physiological research, development of equipment and instrumentation, utilisation of standing sedation and anaesthesia protocols, a change towards minimally invasive surgical techniques, and the introduction of restorative and endodontic techniques translated from techniques used in human and canine dentistry. Anatomical research has provided further insight into the endodontic system of incisors and cheek teeth and how it changes throughout development with age. Studies of the periodontium have demonstrated a rich vascular supply and repair capacity. Routine dental visits are increasingly being performed utilising sedation and clinical instruments for routine examinations. Equipment has become more efficient, battery-operated and miniaturised giving benefits to both equine dental maintenance work and advanced techniques, assisting the transition to minimally invasive techniques, and the development of endodontic and restorative dentistry. Diagnosis has also benefitted from advances in equipment such as patient-side digital radiography systems, high definition oroscopy, and small diameter flexible fibrescopes that are capable of visualising inside a pulp canal. Dental units combining endodontic high- and low-speed drills, suction and air or water flush are becoming increasingly used and adapted for equine use. Sedative combinations and standing anaesthesia protocols have meant that revisions of traditional techniques, as well as novel techniques, can be performed with almost no requirement for general anaesthesia. Equine dentistry can only continue to advance in this way if there is early identification of dental disease through clinical oral examinations, leading to a system based on prophylaxis, as in human dentistry. This necessitates a change in attitude of the public and industry in general to a proactive approach, with early intervention based on examination and diagnostic findings of practitioners and not necessarily based on the clinical signs displayed by the patient.

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.

Uneven distribution of enamel, dentine and cementum in cheek teeth of domestic horses (Equus caballus): A micro computed tomography study

Background

Hypsodont equine cheek teeth possess large dental crowns, resting partly in the bony alveolus. Over a horse’s life cheek teeth erupt continuously to compensate for occlusal wear of 3–4 mm per year. Parts of the crown initially resting in the bony alveolus become progressively exposed at the occlusal surface with time. Hitherto, it is unclear whether the typical structure of the equine occlusal surface, composed of a complex arrangement of enamel, dentin and cementum, remains constant or undergoes structural changes with age. Therefore, we tested the hypothesis that the occlusal surface composition does not remain constant by a quantitative analysis of the dental substances at multiple levels along the dental crown of equine cheek teeth.

Methods

Micro-computed tomography scans of 20 upper cheek teeth and 16 lower cheek teeth from 19 domestic horses were morphologically analysed using imaging and measurement software. Area for individual dental substances was measured at different levels from the apex to the occlusal surface. The data was statistically analysed to detect changes in the area of individual substance along the dental crown. The area of peripheral cementum was measured separately for levels inside and outside the bony alveolus.

Results

In both, upper and lower cheek teeth, enamel area decreased in an apical direction, while dentine area increased. Peripheral Cementum increased dramatically in the occlusal/coronal extra-alveolar position.

Conclusion

With increasing age the occlusal surface content of dentine increases while the content of enamel decreases. These changes are considered relevant for the detailed explanation of forage disruption in horses as well as for the recommendation of concepts in equine dentistry.

Intra-pulp temperature increase of equine cheek teeth during treatment with motorized grinding systems: influence of grinding head position and rotational speed

BACKGROUND

In equine practice, teeth corrections by means of motorized grinding systems are standard procedure. The heat resulting from that treatment may cause irreparable damage to the dental pulp. It has been shown that a 5.5°C temperature rise may cause severe destruction in pulp cells. Hence, the capability to continuously form secondary dentine is lost, and may lead, due to equine-typical occlusal tooth abrasion, to an opening of the pulp cavity.To obtain reliable data on the intra-pulp increase in temperature during corrective treatments, equine cheek teeth (CT) were modified in a way (occlusal surface smoothed, apical parts detached, pulp horns standardized) that had been qualified in own former published studies. All parameters influencing the grinding process were standardized (force applied, initial temperatures, dimensions of pulp horns, positioning of grinding disk, rotational speed). During grinding experiments, imitating real dental treatments, the time span for an intra-pulp temperature increase of 5.5°C was determined.

RESULTS

The minimum time recorded for an intra-pulp temperature increase of 5.5°C was 38 s in mandibular CT (buccal grinding, 12,000 rpm) and 70 s in maxillary CT (flat occlusal grinding, 12,000 rpm). The data obtained showed that doubling the rotational speed of the disk results in halving the time span after which the critical intra-pulp temperature increase in maxillary CT is reached. For mandibular CT, the time span even drops by two thirds.

CONCLUSION

The use of standardized hypsodont CT enabled comparative studies of intra-pulp heating during the grinding of occlusal tooth surfaces using different tools and techniques. The anatomical structure of the natural vital hypsodont tooth must be kept in mind, so that the findings of this study do not create a deceptive sense of security with regard to the time-dependent heating of the native pulp.

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.