Age-related morphometry of equine incisors

In the present study the age-related morphological characteristics of 948 equine incisors were investigated. After extraction, total incisival length and root length were measured at the vestibular side of the teeth. Equine incisors reach their maximal length 2-3 years after eruption. Notwithstanding severe occlusal wear, this maximal length is maintained during most of the horses' life due to prolonged root formation. Root formation, at the rate of 2.5 mm per year, starts at the age of 5-6 years and continues until the age of 17. As the root of the incisor develops, its apical foramen narrows and changes position. In young horses the apical foramen is situated at the apex of the tooth, whereas in older individuals it is located at the mesial, distal, or lingual side of the tooth at a distance of 5-15 mm from the dental apex. In horses aged over 20 years apical foramina are still present. Radiographic imaging is a good method with which to obtain reliable information concerning the total incisival length and the size and position of the apical foramen.     

A study of the thickness of cheek teeth subocclusal secondary dentine in horses of different ages

Reasons for performing study: There is limited knowledge on the thickness of subocclusal secondary dentine in equine cheek teeth (CT). Hypotheses: Subocclusal secondary dentine is of consistent thickness above different pulp horns in individual horses and its thickness increases with age. Methods: 408 permanent CT were extracted post mortem from 17 horses aged 4–30 years, with no history of dental disease. The CT were sectioned longitudinally in the medio‐lateral (bucco‐palatal/lingual) plane through each pulp horn, and the thickness of the secondary dentine overlying each pulp horn was measured directly. Results: The subocclusal thickness of secondary dentine above the pulp horns of CT varied from a mean thickness (above all pulp horns) of 12.8 mm (range 5–33 mm) in a 4‐year‐old to 7.5 mm (range 2–24 mm) in a 16‐year‐old horse. There was wide variation in the depth of subocclusal secondary dentine above different pulp horns, even within the same CT. In contrast to expectations, occlusal secondary dentine thickness did not increase with age. There were no significant differences in occlusal secondary dentine thickness between rostral and caudal, or medial and lateral aspects of the CT, or between contralateral CT. Mandibular CT had significantly thicker subocclusal secondary dentine than maxillary CT. Pink coloured secondary dentine was sometimes found 1–3 mm occlusal to the pulp horn in sectioned CT and this was likely caused by artefactual blood staining from the underlying pulp during sectioning. Conclusions: The thickness of subocclusal secondary dentine varies greatly between individual pulp horns, teeth and individual horses and can be as low as 2 mm over individual pulp horns. Potential relevance: Due to the great variation in the thickness of subocclusal secondary dentine between horses, and even between pulp horns in individual CT, there is a risk of exposure or thermal damage to pulp and thus of apical infection, even with modest therapeutic reductions of CT occlusal overgrowths. In the light of these findings, great care should be taken when reducing equine CT overgrowths and larger dental overgrowths should be reduced in stages.     

The prevalence of secondary dentinal lesions in cheek teeth from horses with clinical signs of pulpitis compared to controls

Reasons for performing study: With the advent of detailed oral examination in horses using dental mirrors and rigid endoscopy, secondary dentinal lesions are observed more frequently. More information regarding the association of secondary dentinal defects with apical dental disease would improve the sensitivity of oral examination as a diagnostic aid for pulpitis. Objectives: To assess prevalence and severity of secondary dentinal defects observed on examination of occlusal surfaces of cheek teeth (CT) from horses showing clinical signs of pulpitis compared to asymptomatic controls. Methods: Records from all cases of equine CT exodontia at the University of Bristol over a 4 year period were examined. Case selection criteria included the presence of clinical signs of pulpitis, an intact extracted tooth and availability of a complete history and follow up. Cases where coronal fracture or periodontal pocketing featured were excluded. CT from cadavers with no history of dental disease served as normal controls. Triadan positions and eruption ages of control teeth were matched with those of teeth extracted from cases. CT from selected cases and control teeth were examined occlusally. Secondary dentinal defects were identified and graded. Prevalence of occlusal lesions in CT with pulpitis and controls was compared. Results: From the records of 120 horses where exodontia was performed, 40 cases matched selection criteria. Twenty‐three mandibular and 21 maxillary CT were extracted from cases. The controls consisted of 60 mandibular and 60 maxillary CT from 7 cadaver skulls. Secondary dentinal defects were significantly over‐represented in CT extracted from cases of pulpitis (P<0.001). Of diseased mandibular CT, 56.5% had defects compared to none of the controls. Of diseased maxillary CT, 57% had defects compared with 1.6% of controls. Multiple defective secondary dentinal areas and severe lesions were more prevalent in diseased mandibular CT compared with diseased maxillary CT. Conclusions and practical significance: Careful examination of occlusal secondary dentine is an essential component in investigation of suspected pulpitis in equine CT.     

Pathological studies of cheek teeth apical infections in the horse. 1: Normal endodontic anatomy and dentinal structure of equine cheek teeth

Morphological examinations were performed on 100 normal equine cheek teeth (CT) of 1–12 years dental age (i.e. time since eruption), using gross examination, dissection microscopy, computerised axial tomography, and decalcified and undecalcified histology. The CT in Triadan 07–10 positions consistently had five pulp horns, but the 06 CT had an additional pulp horn more rostrally. Mandibular and maxillary Triadan 11s had six and seven pulp horns, respectively. Sections of CT taken 2–6 mm below the occlusal surface (variation due to normal undulating occlusal surface) showed the presence of pulp in up to 50% of individual maxillary CT pulp horns, and in up to 25% of individual mandibular CT pulp horns. The histological appearances of primary and secondary dentine were described and it is proposed that the type of dentine present most centrally in every pulp chamber examined, currently termed tertiary dentine, should be re-classified as irregular secondary dentine, and that the term tertiary dentine be reserved for the focal areas of dentine laid down following insult to dentine or pulp.     

The distribution of intratubular dentine in equine incisors: a scanning electron microscopic study

The distribution of intratubular (peritubular) dentine was studied by scanning electron microscopy in 12 equine incisor teeth. High levels of intratubular dentine were found in the peripheral regions of the dentine. In these areas, a marked asymmetry occurred, as intratubular dentine was predominantly deposited onto the side of the dentinal tubular walls nearest to the dentino-enamel junction. The quantity and asymmetry of intratubular dentine were reduced towards the centre of the tooth. The significance of these variations in the amount and distribution of intratubular dentine between the different dentinal regions is discussed.     

An anatomical study to evaluate the risk of pulpar exposure during mechanical widening of equine cheek teeth diastemata and 'bit seating'

Reasons for performing study: Cheek teeth (CT) diastemata are a major equine dental disorder that can be treated by mechanically widening the diastemata. There is limited anatomical knowledge of the spatial relationships of the individual pulps to the adjacent interproximal surfaces; on the risks of exposing the 6th pulp horn when performing the clinically unproven ‘bit seating’ procedure on Triadan 06s. Objectives: To describe the anatomical relationships between the occlusal and interproximal surfaces of CT and the adjacent pulp horns; and between the 6th pulp horn and the occlusal and rostral surfaces of Triadan 06s. Methods: The CT from 30 skulls of horses subjected to euthanasia for non‐dental reasons were sectioned to expose the rostrally and caudally situated pulp horns to allow the anatomical relationships between the pulp horns and the occlusal and interproximal aspects of the CT to be assessed. Results: Pulp horns were mean ± s.d. of 5.74 ± 1.45 (range 1.3–10.8 mm) from the nearest interproximal surface, with 5.3% of pulp horns being <3.5 mm from the interproximal surface. In contrast to expectations, pulps tended to became closer to the interproximal surface (and also to the occlusal surface) with increasing age. Teeth with physiologically tall clinical crowns, and also those in the Triadan 09 position had pulps that were closer to the interproximal surfaces than the remaining CT. The more caudally situated pulp horns, i.e. in particular, the 4th maxillary and 5th mandibular pulp horns were closer to the interproximal surfaces than the remaining pulp horns and these pulp horns also had the thinnest sub‐occlusal secondary dentine. Pulps that were close to the interproximal surface were also found to be close to the occlusal surface of the CT. Conclusions and potential relevance: While diastema widening is theoretically safe between the majority of CT, a small proportion of pulp horns are only 1.3 mm from an interproximal surface and others lie just 1.6 mm beneath the occlusal surface, and such pulps are at risk of pulpar exposure and to thermal injury during this procedure. The risk of pulpar exposure increases when dental tissue is removed from the caudal aspects of CT.     

Pathological studies of cheek teeth apical infections in the horse: 5. Aetiopathological findings in 57 apically infected maxillary cheek teeth and histological and ultrastructural findings

Examination of 57 apically infected maxillary cheek teeth (CT) showed one or more viable pulps and minimal apical calcified tissue changes present in recently infected CT. With chronic infections, pulps were necrotic or absent, pulp horns were filled with food if occlusal pulpar exposure was present, and gross caries of dentine was occasionally present. With chronic infections, the apical changes varied from gross destructive changes in some teeth, to extensive proliferative calcified apical changes in others. Infundibular caries was believed to cause apical infection in just 16% of infected (maxillary) CT, anachoretic infection in 51%, periodontal spread in 12%, fractures and fissures in 9%, dysplasia in 5% and miscellaneous or undiagnosed causes in 7%.Histology showed viable pulp and absence of circumpulpar dentinal changes in some recently infected CT, but chronically infected teeth had loss of predentine and progressive destruction of the circumpulpar secondary, and even primary dentine, with bacteria identified within the dentinal tubules surrounding infected pulps. Tertiary dentine deposition was rarely detected. Scanning and transmission electron microscopy confirmed these histological findings and showed extensive destructive changes, especially to the dentinal architecture surrounding the pulp chambers of some infected teeth.     

A study of sub-occlusal secondary dentine thickness in overgrown equine cheek teeth

The presence of cheek tooth loss or defects, with subsequent overgrowth of the opposing teeth, is common in horses. Little is known about the factors that control the deposition of sub-occlusal secondary dentine (SO2D) in normal equine teeth, but these are likely to include stimulation of the occlusal surface. There appears to be no information on the possible alterations to this process when teeth develop overgrowths and, consequently, of the net effect on SO2D thickness caused by reduced stimulation of the occlusal surface and of absent/reduced normal occlusal wear (attrition). Knowledge of the likely thickness of SO2D in overgrown teeth may help reduce the risks of pulp horn exposure or thermal damage during therapeutic reduction of overgrowths. This study utilised 24 permanent cheek teeth (CT) with overgrowths (mean overgrowth height: 9.5 mm; range, 3.4-17.9 mm), and 18 control CT obtained from 15 horses of different breeds and ages. The thickness of SO2D was measured above 94 matched pulp horns in control and overgrown CT and showed a mean value of 12.14 mm (range 1.87-36.02 mm) in overgrown teeth and of 10.25 mm (range 2.64-17.26 mm) in controls. There was no significant difference between SO2D thickness in overgrown (mean 11.38 mm) and control (11.41 mm) mandibular CT, but SO2D was significantly thicker in overgrown (mean 12.57 mm) as compared to control maxillary (9.41 mm) CT. A comparison of SO2D thickness above the 94 matched pulp horns in overgrown and control teeth showed that 49% (46/94) of pulps in overgrown teeth had less SO2D overlying them than had control teeth. Of major clinical relevance was that the height of dental overgrowths was greater than SO2D thickness over one or more pulp horns in 14/24 overgrown teeth. Consequently, reduction of these overgrown teeth to the level of adjacent normal-height teeth would cause occlusal pulp exposure in 58% of teeth, in addition to possible thermal damage to additional pulp horns. It was concluded that equine CT overgrowths should be gradually reduced, by a few millimetres at a time, over a prolonged period.     

Observations of the cheek tooth occlusal angle in the horse

The angle of occlusion was evaluated in 230 mandibular cheek teeth from 21 horses. There was no significant relationship between horse condition (sedated, anesthetized, dead) and measurement of mean cheek tooth occlusal angle. Cheek tooth occlusal angle was not significantly affected by the position of the tooth in the mandibular arcade or tooth age. The measurement of individual mandibular cheek tooth occlusal angles was predictive for occlusal angle of the entire mouth. Multiple variations of the incisor separation angle technique were predictive of cheek tooth molar occlusal angle for the measured arcade and the entire mouth but was significantly different contralaterally, suggesting that the single tooth method may be preferred. However, despite the limitations of the relatively simple incisor separation angle technique, it may provide the equine veterinary dentist a rapid method of assessing cheek tooth occlusal angle to ensure proper dental floating methods and outcomes.     

Donkey dental anatomy. Part 2: Histological and scanning electron microscopic examinations

Ten normal cheek teeth (CT) were extracted at post mortem from donkeys that died or were euthanased for humane reasons. Decalcified histology was performed on three sections (sub-occlusal, mid-tooth and pre-apical) of each tooth, and undecalcified histology undertaken on sub-occlusal sections of the same teeth. The normal histological anatomy of primary, regular and irregular secondary dentine was found to be similar to that of the horse, with no tertiary dentine present. Undecalcified histology demonstrated the normal enamel histology, including the presence of enamel spindles. Scanning electron microscopy was performed on mid-tooth sections of five maxillary CT, five mandibular CT and two incisors. The ultrastructural anatomy of primary and secondary dentine, and equine enamel types-1, -2 and -3 (as described in horses) were identified in donkey teeth. Histological and ultrastructural donkey dental anatomy was found to be very similar to equine dental anatomy with only a few quantitative differences observed.     

Occlusal fissures of the equine cheek tooth: Prevalence,location and association with disease in 91 horses referred for dental investigation

Reason for performing study: Fissures of the occlusal surface of the equine cheek tooth are poorly understood and their association with dental disease is unknown. Objective: To describe the prevalence and location of occlusal fissures in the cheek teeth (CT) of a group of horses referred for dental investigation/treatment, and determine association with intercurrent dental disease. Methods: Digital video recordings of oral endoscopic examinations for all horses referred to the Rossdales Equine Hospital for dental investigation from November 2006 to June 2009 were reviewed. Location of occlusal fissures in relation to both Triadan tooth position and pulpar secondary dentine was recorded; direction of fissure and concurrent involvement of enamel was also documented. The CT location considered at the time of examination to be the primary site/s of disease was correlated with presence of fissures on these teeth. Results: 91 cases meeting the inclusion criteria were identified. Occlusal fissures were documented in 58.2% (53/91) cases, with a total of 227 CT being affected. Fissures were most prevalent mid‐arcade. The majority (92.1%) of fissures in maxillary CT were associated with the caudal palatal pulp horn. Fissures in mandibular CT were predominantly associated with the buccal pulp horns (95.7%). There was no significant difference in the median number of CT with fissures in relation to gender. There was no correlation between age (r²= 0.01) of horse and number of CT with fissures. A significantly greater number of CT with multiple occlusal fissures was found in mandibular compared to maxillary arcades. No correlation was found between presence of fissures and location of individual CT considered to be primarily responsible for presentation. Conclusions: Occlusal fissures in this group of animals were common and not correlated to primary site of dental disease. Potential relevance: In horses subjected to dental investigation, occlusal fissures of the cheek teeth should not be considered an indicator of tooth compromise. Location and direction of fissure propagation in most cases is inconsistent with occlusal fissures being causally implicated in slab fractures of cheek teeth, although site predilection may indicate a possible association with masticatory forces.     

Pathological studies of cheek teeth apical infections in the horse: 2. Quantitative measurements in normal equine dentine

Measurements of primary, regular and irregular secondary dentine and pulp dimensions were made on transverse, sub-occlusal and mid-tooth sections, of 40 maxillary and 42 mandibular control equine cheek teeth (CT) of different ages. Maxillary and mandibular CT primary dentine in different age groups had a mean thickness of 922–1065 μm and 1099–1179 μm, respectively, on the lateral aspects, and 1574–2035 μm and 1155–1330 μm, respectively, on the medial aspects of pulp horns. Surprisingly, some increase in thickness was found in some mandibular CT primary enamel in the first few years following eruption.Regular secondary dentine thickness increased with age, for example at mid-tooth level in mandibular CT from 124 μm at 3 years dental age to 290 μm at >7 years dental age on the lateral aspect of pulp horns, and from 166 μm to 509 μm on the medial aspects of pulp horns, indicating a deposition rate of 0.5–10 μm/day. This type of dentine was thicker sub-occlusally than in the mid-tooth region. Maxillary dentinal dimensions showed a similar age-related increase in thickness. Maxillary CT dentine was significantly thicker (72% in primary, 43% in regular secondary dentine) on the medial compared to the lateral aspects of pulp horns, but mandibular CT dentine was just 15% and 14% thicker in primary and regular secondary dentine thickness, respectively, on the their medial as compared to their lateral aspects. Dentinal and pulp dimensions varied between individual pulp horns, Triadan tooth position, and dental age, with complex interactions between these variables for some parameters.     

Pathological studies of cheek teeth apical infections in the horse: 3. Quantitative measurements of dentine in apically infected cheek teeth

Histological measurements of dimensions of primary, regular secondary and irregular secondary dentine, pulp diameter and assessment of the levels of predentine, resting lines and enlarged areas of intertubular dentine were performed in apically infected mandibular and maxillary cheek teeth (CT). These examinations showed significantly reduced regular and irregular secondary dentine thickness in diseased as compared to control CT, with 21/26 infected maxillary CT and 15/18 infected mandibular CT having reduced regular secondary dentine (varying between 27.4% and 89.1% reduced secondary dentine levels compared to age and site matched control CT values). As a result of decreased dentinal deposition, significantly wider pulp horns were present in diseased compared to control CT.No significant differences were found between diseased and control primary dentine thickness in maxillary CT, and minor differences in mandibular CT were not believed to be clinically significant. The significantly reduced presence of predentine and of intertubular dentine and the increased presence of resting lines in diseased compared to control CT confirms that long-term disruption of normal dentine deposition had occurred in many infected CT.     

Morphology of the Dentin Structure of Sloths Bradypus tridactylus: A Light and Scanning Electron Microscopy Investigation

The aim of this study was to describe the dentine morphology of sloths (Bradypus tridactylus). The sloth teeth were removed and prepared for light microscopy (LM) and scanning electron microscopy analyses (SEM). LM revealed two patterns of tubular dentins: an outer with dentinary tubules over the all tooth length and one in the inner part with larger diameter and more spaced tubules, when compared to those present in the outer dentine. These findings were confirmed by SEM, which revealed a tubular pattern in the outer dentine like in humans. The inner dentine displayed pared grouped tubules that were characterized as vascular channels. It can be concluded that this sloth species present two types of dentins: an inner dentin (ortodentin) and an outer dentin characterized as a vascular dentin. This suggests a partial evolutive/adaptive process of this dental tissue, as compared to other mammalian species.     

Extraction techniques for equine incisor and canine teeth

Extraction of equine incisor and canine teeth is a vital part of equine dentistry. Although dental pathology involving the incisor and canine teeth is less common, the practitioner should be prepared to diagnose conditions and develop a treatment plan. Depending on the pathology revealed via oral examination and intraoral radiographs, the treatment plan may include either simple (nonsurgical) or surgical extraction of an incisor or canine tooth. Technique and instrumentation refinement over the last 20 years has led to more precise extraction procedures with reduced secondary trauma to healthy tissues. As a result, incisor and canine extraction procedures are more predictable in execution and quality, with minimal complications.     

Morphological features of the seminiferous epithelium in cat (Felis catus, L. 1758) testes

The aim of the present study was to assess the changes in the germinal epithelium in cats of different ages. Routine histological staining was applied to perform morphological and stereological examinations. The animals were divided into five groups according to age: under 8 months (n=28), 8-12 months (n=30), 12-36 months (n=33), 3-6 years (n=14) and older than 6 years (n=13). The appearance of the gonads of the males in the first group varied the most. The seminiferous tubules of the youngest cats consisted of a monolayer of supporting cells and a few spermatogonia. No tubular lumina were present, and the diameters of the seminiferous tubules reached 132.5 microm. We noted the typical arrangement of gametogenic cells with a tubule diameter of 191.83 microm in the second group. We observed multilayer germinal epithelia with the most significant production of gametes and a seminiferous tubule diameter of 202.61 microm in the third group. The diameters of the seminiferous tubules of the forth and fifth groups were 193.38 microm and 191.84 microm, respectively. The obtained data revealed that the most intensive morphological diversification of the seminiferous epithelium in cats occurs at about 7-8 months of age. The diameters of seminiferous tubules were highest in the third group of cats, and the activity of spermatogenesis of this group, expressed as the number of sperm per 10 mm(2), was also the most distinctive. The spermatogenesis process was most evident in cats between 12 and 36 months of age, which was also when the sperm concentration was highest per estimated surface.     

Xenografting of bovine secondary follicles into ovariectomized female severe combined immunodeficient mice

Xenografting of ovarian tissue into immunodeficient mice has been used as a model to study the dynamics of follicular development and provides an alternative method for the production of mature oocytes. In a previous experiment, we demonstrated that xenografted bovine secondary follicles developed to the antral stage in severe combined immunodeficient (SCID) mice. In the present study, we examined the development of bovine secondary follicles (140-190 microm in diameter) grafted into ovariectomized mice in comparison with intact female mice as a control. At 4 weeks after grafting, several antral follicles ranging from 350 to 550 microm (457.6 +/- 50.8 microm) in diameter were found in the control mice, while a single large (larger than 2.5 mm) antral follicle and other small follicles were observed in every ovariectomized mouse. At 6 weeks after grafting, the mean diameter of morphologically normal follicles had further increased in the control group (591.8 +/- 132.0 microm). In ovariectomized mice, however, the mean diameter of follicles decreased (4 weeks: 864.2 +/- 988.2 microm; 6 weeks: 496.5 +/- 137.6 microm), since the single large antral follicle observed at 4 weeks had degenerated by 6 weeks. In control mice, more than 70% of follicles were morphologically normal and formed an antrum, and most of the follicles contained morphologically normal oocytes which grew to 122.5 +/- 2.2 microm. In ovariectomized mice, morphologically normal oocytes also grew larger than before grafting, but their survival rate was significantly lower than that in control mice. These results suggest that ovariectomy of host mice alters the developmental pattern of xenografted bovine secondary follicles to accelerate a single follicle to develop in the graft.     

Tubular contents of equine dentin: a scanning electron microscopic study

The dentinal tubules of 20 permanent equine incisors were investigated by scanning electron microscopy. Occlusal surfaces and longitudinal fracture planes of both etched and undecalcified teeth were examined. Three different types of structure were observed inside the dentinal tubular lumen. Odontoblastic processes could only be visualized in the circumpulpal parts of the tubules. The more peripheral parts were empty or housed cylindrical structures that probably correspond to the laminae limitantes. Collagen fibres were frequently observed in the tubular lumina and were most numerous in the circumpulpal parts of the tubules.     

Comparison of the microhardness of enamel, primary and regular secondary dentine of the incisors of donkeys and horses

The microhardness of the enamel, primary dentine and regular secondary dentine of seven donkey and six horse incisors was determined with a Knoop indenter at the subocclusal and mid-tooth level. The mean microhardnesses of the donkey incisor enamel, primary dentine and secondary dentine were 264.6 63.00 and 53.6 Knoop Hardness Number, respectively. There was no significant difference between the microhardness of the enamel and primary dentine on the incisors of the donkeys and horses, but the microhardness of the regular secondary dentine of the donkeys' incisors at the mid-tooth level was slightly but significantly less than that of the horses. There was also a difference in the microhardness of the secondary dentine between the subocclusal and mid-tooth levels in both donkey and horse incisors.     

Measurement of clinical crown length of incisor and premolar teeth in clinically healthy rabbits

The clinical crown length of rabbit teeth has not been well documented. The aim of this study was to determine the clinical crown length of incisor and cheek teeth, and the periodontal probing depth in young healthy rabbits without clinical signs of dental disease. Two groups of 20 male rabbits were measured, the first in 2007 and the second in 2008/2009. The measurements were taken with rabbits under general anesthesia using a periodontal probe. The average crown length (mm) of the mandibular third and fourth premolar, and maxillary second premolar teeth was 3.1 +/- 0.4, 2.6 +/- 0.4, and 1.5 +/- 0.4, respectively. The periodontal probing depth for the cheek teeth in the maxilla and the mandible was very similar (0.5 - 1.0-mm). There was a minor difference in the average crown length (mm) of the mandibular (6.4 +/- 0.6) and maxillary (6.1 +/- 0.9) incisor teeth. The periodontal probing depth (mm) was different when comparing maxillary (2.2 +/- 0.4) and mandibular (5.1 +/- 0.8) incisor teeth. The divergence in tooth length in individual rabbits and between the two groups was minimal. Measuring the crown length of the rostral cheek and incisor teeth with a periodontalprobe is easy to do in the rabbit and should be integrated into the clinical examination. The measurement results of this study can be used as a reference when trimming teeth.