Abstract
Dareshuri horses are the predominant breed in Fars Province, Iran. Although disorders affecting their maxillary cheek teeth and maxillary sinuses are relatively common, limited fundamental data are available on the dimensions and relationships of these structures at different ages. Given the significant anatomical changes in the heads of young horses as they mature, this study aimed to evaluate age-related changes in the position and anatomical relationships of individual maxillary cheek teeth within the rostral and caudal maxillary sinuses (RMS and CMS, respectively), as well as changes in the lengths and heights of individual sinus compartments during their growth. Radiographs were performed on 29 heads of live, healthy horses aged between 4 months and 5 years and were analyzed using the EConsole1 Radiography Viewer software (V.3, 2017, DRTECH Europe GmbH, Schwalbach am Taunus, Germany). Statistical analyses revealed that the only significant change throughout the study was an increase in the length of the CMS (4.075 ± 0.99 cm; SE), which was more significant in horses up to three years old. At less than 1 year old, the only tooth present in the maxillary sinus was M1. At 1–2 years old, M2 was observed entering the maxillary compartments; PM4 entered the RMS at 2–3 years old, and M3 entered the CMS at 3–4 years old. Eventually at 4–5 years old, PM3, M1, and M2 were present in the RMS, and M2 and M3 were present in the CMS. This information should be of value in the diagnosis and treatment of Dareshuri maxillofacial disorders and used as a reference for further anatomical investigations.
Keywords: cheek teeth, Dareshuri horses, head/skull radiography, maxillary sinus
The Dareshuri horse is an indigenous Iranian breed known for its endurance, adaptability, and historical significance in the region [2, 17, 36]. This breed is not only a cultural and historical asset to Iran but also plays a vital role in local economies, especially in rural and nomadic communities where it is used for transportation, labor, and traditional events [14]. Despite its importance, research on the unique anatomical and developmental characteristics of the Dareshuri horse is limited, particularly in relation to its maxillary sinus and dental structures. Based on the authors’ professional experience in Iran, especially in Fars Province, dental problems affecting the maxillary sinus are a common issue in this breed (although there is no published data on this). Understanding the specific anatomical features of this breed can improve veterinary care, helping to preserve the health and longevity of the horses of this breed, which are an important part of Iran’s heritage and cultural practices.
The paranasal sinuses of horses consist of six pairs of sinuses: the frontal and dorsal conchal (commonly known as the concho-frontal sinus), ventral conchal, sphenopalatine sinus, and rostral and caudal maxillary sinuses, which are known as the RMS and CMS, respectively [19, 44]. Diseases of the equine paranasal sinuses are of special interest in equine medicine, as primary and secondary sinusitis are common and widespread conditions. These diseases may result from trauma, dental diseases, or space-occupying lesions [1, 9, 18, 31, 42]. The maxillary sinus is the largest part of the paranasal sinuses in the horse, and it plays an integral role in respiratory function and is one of the most frequently affected parts in sinusitis [3, 8, 32]. Given that dental root infection is the cause of secondary sinusitis; and that the growth of the equine cheek teeth is part of a very dynamic system in which their spatial positions change and move forward (mesial drift) concurrently with skull growth and maxillary sinus enlargement [20, 21, 26, 40], understanding the positional relationship between the maxillary sinus compartments and the embedded parts of the teeth would assist in diagnosing and treating related diseases in horses [20, 34]. Previous studies have shown that the maxillary sinuses of horses under 5 years old are primarily filled with the apices of Triadan 08–11 (or PM4 and M1–M3) [15, 40, 44]. As the reserve crowns of cheek teeth shorten with age, the maxillary sinus consequently enlarges, and its rostral limit approaches the infraorbital foramen [19].
There are several variations in the positional relationships between the caudal cheek teeth and maxillary sinus at different ages, and it is important to note which teeth occupy the sinus space. Thus, this study was designed to evaluate these relationships across different age groups [21, 26, 27, 40]. By focusing on the Dareshuri horse, the research aims to provide new insights that could lead to improved diagnostic and treatment approaches tailored specifically to this breed, ultimately enhancing equine veterinary and dentistry care in Iran.
The objectives of this study were to evaluate the changes of the maxillary sinus diameters and their relationships with age, and to determine the location of the root of each cheek tooth within the maxillary sinus compartments and their morphometric changes at various stages of growth in Dareshuri horses using the plain radiography technique. This research not only fills an important gap in the scientific understanding of this native breed but also contributes to the broader field of equine anatomy and dentistry in Iran. Additionally, data of this study can be compared with data from other breeds to identify potential breed-specific characteristics.
Material and Methods
This study was approved (approval number: 9730084) by the Animal Ethical Committee of Shiraz University, Shiraz, Iran.
A total of 29 horses (14 females and 15 males), aged between less than 6 months and 5 years, were included in the study. Each horse was examined for craniofacial abnormalities (e.g., wry nose, brachygnathism, and prognathism) and dental abnormalities such as fractured teeth, supernumerary teeth, cheek teeth caries, and diastema. Horses with any of these abnormalities were excluded from the study. The ages of the horses were confirmed based on the birth dates recorded on their ID cards. The horses were divided into five age groups: less than 1 year old (group A, n=7), 1–2 years old (group B, n=5), 2–3 years old (group C, n=5), 3–4 years old (group D, n=6), and 4–5 years old (group E, n=6). The number of cases involved, divided by gender, is shown in Table 1.
Table 1. Comparison of the mean diameters of maxillary sinus compartments among the study groups.
| Group | Gender | Range of age (months) | Rostral maxillary sinus (cm) ± SE | Caudal maxillary sinus (cm) ± SE | |||
|---|---|---|---|---|---|---|---|
| Male | Female | Length | Height | Length | Height | ||
| A | 3 | 4 | 4–12 | 4.48 ± 0.35 | 4.68 ± 0.24 | 3.74 ± 0.21 | 5.27 ± 0.67 |
| B | 3 | 2 | 12–24 | 5.21 ± 0.73 | 4.86 ± 0.34 | 5.62 ± 0.84 | 5.01 ± 0.34 |
| C | 3 | 2 | 24–36 | 5.57 ± 0.51 | 4.89 ± 0.28 | 7.02 ± 1.26 | 5.41 ± 0.33 |
| D | 3 | 3 | 36–48 | 5.57 ± 0.70 | 5.36 ± 0.74 | 6.88 ± 0.72 | 6.21 ± 0.63 |
| E | 3 | 3 | 48–60 | 6.45 ± 0.43 | 5.48 ± 0.27 | 7.81 ± 0.66 | 6.52 ± 0.58 |
Radiographic examination
Radiographic examinations were performed using right laterolateral projection (Fig. 1). Radiographs were obtained using 17 × 17-inch computed radiography cassettes (DRTECH flat-panel veterinary system model EVS 43534W, with TRUVIEW® ART, Advanced Reverse Filtering Technology, a pixel size 140 µm, and a pixel resolution of 2,048 × 1,536 (3.1 million pixels); DRTECH, Seongnam, South Korea) and a digital X-ray radiography machine. The imaging parameters were set at 80 kVp and 15 mA for adult horses, and at 75 kVp for foals less than 1 year old (group A) [4, 5]. In order to prevent motion artifacts, foals were sedated by intravenous injection of diazepam (0.1–0.25 mg/kg) or xylazine (0.2–0.5 mg/kg) before image acquisition; adults were sedated with xylazine (0.3–1 mg/kg) [11].
Fig. 1.
Examples of radiographs from each study group.
To reduce measurement errors, all horse heads were positioned in full contact with the radiography cassettes, and the x-ray machine was set a fixed distance of 30 centimeters from the head.
Image parameters
The following measurements were obtained from laterolateral projection radiographs:
Measurements related to the maxillary sinus
1. Length and height of the RMS and CMS
Specific criteria were applied to evaluate these parameters: The frontonasal bone was considered a reference line. A line parallel to the frontonasal bone, indicating the longest length, was measured to determine the length of each compartment of the maxillary sinus. Measurement was conducted separately for each compartment. A second line, perpendicular to the first, was drawn to indicate the maximum possible height of the compartments (Fig. 2).
Fig. 2.
Right laterolateral radiograph of the skull of a 20-month-old (group B) Dareshuri horse indicating the maxillary sinus measurement method.
The nasofrontal bone served as a reference line (red line), and two lines parallel to it, indicating the longest lengths of the RMS and CMS, were considered and measured as the lengths of each compartment (green lines). The heights of each compartment were measured considering two lines (yellow lines) prependicular to the previous lines as indicating the highest height of each compartment. Please note that the lines are depicted for schematic purposes to simply explain the measurement method. For the actual evaluation in the current study, all measurements were conducted by using the Econsole1 Radiography Viewer software, (V.3, 2017, DRTECH Europe GmbH, Schwalbach am Taunus, Germany).
Measurements related to the maxillary cheek teeth
1. Position of maxillary cheek teeth within the RMS and CMS: The position of each maxillary cheek tooth within the RMS and CMS was determined across the different age groups of Dareshuri horses (Fig. 3).
Fig. 3.
Right laterolateral radiograph of the skull of a 20-month-old (group B) Dareshuri horse indicating the maxillary cheek teeth measurement method.
The border of the maxillary sinus was determined by the yellow line, and that of the maxillary septum was determined by the green line. The teeth located in the maxillary sinus are the M1 and M2 in the RMS and CMS, respectively. The long axis of each tooth served as the reference line (black line) for these measurements. The longest length of each tooth within the maxillary region was measured parallel to this line at various points (blue lines), and the mean of these measurements was calculated to determine the average length of the tooth in each compartment. Please note that these lines are depicted for schematic purposes to simply explain the measurement method. For the actual evaluation in the current study, all measurements were conducted by using the Econsole1 Radiography Viewer software, (V.3, 2017, DRTECH Europe GmbH, Schwalbach am Taunus, Germany).
2. Length of the reserve crowns in the maxillary sinus: The mean length of the reserve crowns present in the rostral and caudal maxillary sinus was measured by measuring along the long axis of each tooth. To clarify, the long axis of each tooth was utilized as the reference line for these measurements. The longest length of each tooth within the maxillary region was measured at various points parallel to this line, and the mean of these measurements was calculated to determine the average length of the tooth (Fig. 3).
Image analysis
All images were assessed by a diagnostic imaging specialist, and all desired parameters were measured using the EConsole1 Radiography Viewer software (V.3, 2017; DRTECH Europe GmbH, Schwalbach am Taunus, Germany).
Statistical analysis
Statistical analyses were performed using the IBM SPSS Statistics software (version 22, 2013, 64-bit edition, IBM Corp, Armonk, NY, USA), including normality assessment of the measurements related to the maxillary sinus compartments. A one-way ANOVA was used to evaluate the changes in each group, followed by the Scheffé test for pairwise group comparisons. Correlations between age and the diameters (length and height) of the maxillary sinus were evaluated by means of Pearson’s correlation coefficient. Significance probabilities were based on a null hypothesis of no difference, and the critical probability was taken to be P<0.05. Confidence intervals were calculated for all estimates, with a confidence level of 95%.
The GraphPad Prism v.8 software (GraphPad Software, Inc., San Diego, CA, USA) was used for creating the graphs.
Results
Changes in the diameters of maxillary sinus compartments
Based on the data in Table 1, the mean length and height of the RMS in group A (4 months to 1 year old) were 4.48 cm (SE=0.35) and 4.68 cm (SE=0.24), respectively, while the mean length and height of the CMS were 3.74 cm (SE =0.21) and 5.27 cm (SE=0.67) respectively.
At the age of 1 to 2 years (group B), the lengths of the CMS and RMS had increased by 1.88 cm (SE=1.05) and 0.73 cm (SE=0.77), respectively, compared with the length in group A. At this age, there was no significant change in the heights of the sinuses, with an increase of only 0.18 cm (SE=0.60) and decrease of 0.26 (SE=0.81) in the RMS and CMS, respectively, as compared with the preceding age group.
At the age of 2 to 3 years (group C), the lengths of the RMS and CMS had increased by 0.35 cm (SE=0.83) and 1.39 cm (SE=1.13), respectively, compared with the preceding age group. However, the increases in the heights of the sinuses remained insignificant, measuring just 0.02 cm (SE=0.65) in the RMS and 0.40 cm (SE=0.87) in the CMS.
At the age of 3 to 4 years (group D), there was no significant increase in the length of either the RMS or CMS, whereas the increase in the heights of the RMS and CMS were 0.47 (SE=0.62) and 0.79 (SE=0.84), respectively.
At the age of 4 to 5 years (group E), there was an increase in the lengths of the RMS and CMS, with them increasing by 0.87 cm (SE=0.86) and 0.93 cm (SE=1.03), respectively. Additionally, the heights of the RMS and CMS increased as much as 0.11 cm (SE=0.59) and 0.31 cm (SE=0.80), respectively.
Overall, these results suggest that the changes in the lengths of the maxillary sinus throughout the study were only statistically significant in the CMS (Fig. 4), which increased by 4.06 cm (SE=0.99, P=0.01). Although an increase was observed in the RMS (1.96 cm, SE=0.73), it was not statistically significant. It is worth noting that the most substantial increase in the lengths of both parts occurred up to the age of 3 years, with increases of approximately 1.08 cm (SE=0.77) in the RMS and 3.27 cm (SE=0.07) in the CMS.
Fig. 4.
Assessment of diameter changes (cm) with age (months) among the different study groups.
On the other hand, the change in height in both sections of the maxillary sinus was not statistically significant; however, it was observed that the total increase in the height of the CMS (1.24 cm, SE=0.77) was greater than that of the RMS (0.80 cm, SE=0.57). The greatest increase in height for both parts occurred between the ages of 2 and 4 years, with the RMS increasing by 0.59 (SE=0.62) and the CMS increasing by 1.107 cm (SE=0.84).
Considering the genders of the cases involved in the study, some differences were observed among males, particularly in CMS Length. However, the results of one-way ANOVA conducted with the IBM SPSS Statistics software (Version 22, 2013, 64-bit edition, IBM Corp., Armonk, NY, USA) indicated no statistically significant differences between genders throughout the study (Table 2).
Table 2. Comparison of measurements of the maxillary sinus between the genders of the involved horses.
| Measured factor | Mean ± SE | Sig | |
|---|---|---|---|
| Male | Female | ||
| RMS length | 5.50 ± 0.40 | 5.35 ± 0.33 | 0.78 |
| RMS height | 4.89 ± 0.29 | 5.22 ± 0.23 | 0.38 |
| CMS length | 6.74 ± 0.64 | 5.46 ± 0.48 | 0.13 |
| CMS height | 5.88 ± 0.42 | 5.51 ± 0.30 | 0.49 |
Although some differences were observed between males and females, particularly in CMS length, the results of one-way ANOVA performed using the IBM SPSS Statistics software (version 22, 2013, −64-bit edition, IBM Corp., Armonk, NY, USA) indicated no significant difference between genders throughout the study. This test was conducted based on a null hypothesis of no difference and a critical probability of statistical significance (Sig)<0.05. RMS, rostral maxillary sinus; CMS, caudal maxillary sinus.
Correlation between age and maxillary sinus growth
The data in this study, as shown in Fig. 5, followed a normal distribution. Pearson’s correlation test revealed a significant positive correlation between age and growth of the CMS length (r=0.665, P<0.001). Moreover, RMS length and CMS height showed positive correlations with age (r=0.481, P=0.008, for RMS length; r=0.414, P=0.025, for CMS height). In contrast, the RMS height was the only parameter which did not exhibit any correlation with age (r=0.265, P=0.164).
Fig. 5.
Scatter plot with linear regression lines (lines) and confidence intervals (dotted lines), showing the correlation between age (months) and diameters (cm) for different study parameters of the maxillary sinus.
Changes in tooth position in relation to changes in the diameter of the maxillary sinus compartments
According to the data presented in Table 3, the overall findings of this study indicate that, in the age range of less than 1 year (group A), the only reserve crown present in the maxillary sinus was M1 (Triadan 09), which was located in both the RMS and CMS. Between the ages of 1 to 2 years (group B), in addition to M1 (Triadan 09), the reserve crown of M2 (Triadan 10), which normally begins to form at this age, was observed in both parts of the maxillary sinus. In the 2- to 3-year-old group (group C) in addition to M1 (Triadan 09), PM4 (Triadan 08), which was forming in the skull at this age, had entered the RMS in 3 out of 5 cases. At this age, with a greater increase in the length of the CMS compared to RMS —about 1.39 cm (SE=1.13) compared to group B — M2 (Triadan 10) was observed to have entered the CMS in all cases (it was not present in the RMS). M1 (Triadan 09) was still present in the CMS in 3 out of 5 cases. M3 (Triadan 10), which could be seen forming in some cases, had not yet entered the sinus in any of the cases. In group D (3–4 years old), similar to the previous group, PM4 and M1were observed in RMS, the only notable change compared with the preceding age group was the appearance of M2 (Triadan 10) in 4 out of 6 cases. In the CMS, M3 (Triadan 11) was observed to be entering the compartment in 5 out of 6 cases. M2 (Triadan 10) was seen in all cases, and M1 (Triadan 09) could still be seen in one case in the CMS. In group E (4–5 years old), the positions of the reserve crowns were uniform across all cases, with PM4 (Triadan 08) and M1 (Triadan 09) present in all cases in the RMS, M2 (Triadan 10) observed in 4 out of 6 cases in the RMS, and M2 (Triadan 10) and M3 (Triadan 11) observed in the CMS.
Table 3. Locations and mean lengths of teeth in the maxillary sinus in the different study groups.
| Sinuses | RMS | CMS | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Teeth Groups | PM4 (08) | M1 (09) | M2 (10) | M3 | PM4 | M1 (09) | M2 (10) | M3 (11) | ||||||
| Length (cm) ± SE |
N | Length (cm) ± SE |
N | Length (cm) ± SE |
N | Length (cm) ± SE |
N | Length (cm) ± SE |
N | Length (cm) ± SE |
N | |||
| A | ND | 0/7 | 2.44 ± 0.34 | 7/7 | ND | 0/7 | ND | ND | 2.01 ± 0.40 | 7/7 | ND | 0/7 | ND | 0/7 |
| B | ND | 0/5 | 2.71 ± 0.44 | 5/5 | 3.0 ± 0.02 | 2/5 | ND | ND | 2.45 ± 0.81 | 2/5 | 3.5 ± 0.52 | 4/5 | ND | 0/5 |
| C | 1.71 ± 0.07 | 3/5 | 3.1 ± 0.25 | 5/5 | ND | 0/5 | ND | ND | 3.76 ± 0.14 | 3/5 | 3.9 ± 0.18 | 5/5 | ND | 0/5 |
| D | 1.59 ± 0.13 | 3/6 | 3.09 ± 0.09 | 6/6 | 3.5 ± 0.30 | 4/6 | ND | ND | 3.81 | 1/5 | 4.0 ± 0.21 | 6/6 | 1.16 ± 0.14 | 5/6 |
| E | 2.35 ± 0.50 | 6/6 | 2.98 ± 0.48 | 6/6 | 3.0 ± 0.64 | 4/6 | ND | ND | ND | 0/5 | 2.8 ± 0.49 | 4/5 | 2.09 ± 0.34 | 6/6 |
RMS, rostral maxillary sinus; CMS, caudal maxillary sinus; N, number; ND, not determined.
Discussion
The anatomy of the paranasal sinuses in horses has been extensively studied, with research focusing on adult horses [8, 15, 19, 20] as well as foals [4, 32]. Various methods, including CT images [16, 23, 25, 27,28,29,30, 32, 37,38,39, 44] and 3D digital models [6, 14, 21, 31, 32, 39, 41, 42], have been used to measure the volume of these sinuses. According to previous studies by Nickels et al. [32], Hillmann [19], and Baratt [4], enlargement of the sinuses continues until around 5 years of age as the head matures. Based on this finding, the current study was designed to evaluate age-related changes in the maxillary sinus, focusing on individuals ranging in age from less than 1 year to 5 years.
A recent investigation on Warmblood horses done by Borowska et al. [6] proved that the maxillary sinus is the largest paranasal sinus in adult horses, as the CMS has the largest volume among the paranasal sinus compartments [7, 27], followed by the FS [7], and the middle conchal sinus (MCS) has the smallest volume [7]. Furthermore Bahar et al. [3] reported that the FS is the largest sinus and that the MCS is the smallest sinus in Arabian foals, but these findings were not based on any morphometric data. Their findings also indicated, however, that the maxillary sinus showed the most significant volumetric changes up to 5 years of age in this breed [4]. While there is abundant information on the diameters of the maxillary sinus and their changes with aging in various studies and textbooks [4, 6, 26, 27, 32, 35], no morphometric studies have, to the best of authors’ knowledge, focused on changes in the diameters of maxillary sinuses in the Dareshuri breed in relation to age.
Changes in maxillary sinus diameters and their correlations with age
Studies done by Brinkschulte et al. and Liuti et al. on Thoroughbred and Warmblood horses revealed a significant positive correlation between head volume and the volume of each individual sinus compartment, which is compatible with previous results [7, 27]. It was also documented that the growth in head size, which is the consequence of maturation, would influence the growth of the sinus compartments in younger horses [27]. In two different studies conducted by Borowska et al. and Brinkschulte et al., significant age-related increases in the volumes of the sinus compartments, particularly in the CMS and RMS were proved in Warmblood horses [6, 7]. Additionally, these authors and other researchers have found that the majority of age-related variations in volume in Warmblood and Thoroughbred breeds occur in the RMS, ventral conchal sinus (VCS), and CMS compartments, all of which house dental alveoli and, therefore, tend to expand in volume with dental eruption [7, 19, 27]. Similar results were reported for Arabian horses in one study that compared the volume of sinus compartments between foals and proved that there were threefold and six-fold increases in the volumes of the RMS and CMS, respectively, with aging, indicating that the most significant volumetric change is found in the CMS [16].
The results of the current study conducted on the Dareshuri horse align with those of previous studies on other breeds, as the most notable age-related differences in sinus volume were observed in the length of the CMS. It is noteworthy that the greatest increases in the lengths of both the RMS and CMS occurred up to the age of 3 years in this breed, while the most significant increases in heights were observed between 2 to 4 years of age (this result was the novelty of the current study). Furthermore, the growth in the sinus diameter correlated positively with age and CMS length, showing the most significant correlation.
In contrast, a study conducted on Shetland ponies reported differing results, as no age-related correlation was found with sinus volume. This discrepancy may be attributed to the age range of the horses, which were over 6 years old, included in the study and the absence of young, growing ponies in the sample population [24].
These differences may reflect the breed-specific variations in craniofacial morphology among Warmbloods, Thoroughbred, Arabian, Dareshuri horses, and Shetland ponies. Alternatively, they could be attributed to variations in the timing of skeletal maturation or the age ranges of the horses included in the studies. For instance, the Warmblood horses in the studies of Brinkschulte et al. and Borowska et al. ranged from 2 to 25 years old, and the Thoroughbred horses in the study by Liuti et al. were within the age range of 1 to more than 15 years of age. Moreover, the Arabian horses were foals in one study but were adults in another study, and the Shetland ponies were more than 6 years old [3, 5, 7, 27]. In contrast, this study focused on horses aged 1 to 5 years, as previous studies have documented that the most significant growth changes in the skull occur within this age range. Furthermore, to the best of the author’s knowledge, no prior studies have been conducted on the Dareshuri horse.
Changes of the positions of cheek teeth reserve crowns
According to equine dentistry textbooks, the location of the tooth root apices and the volume of the tooth roots contained within the sinus are important anatomical considerations for both diagnostic and treatment purposes [12, 13, 22, 33, 43]. Several studies have documented the age-related rostral drift of maxillary cheek teeth during maturation [19, 27]. In general, it is believed that the maxillary sinus in young horses (<5 years) is filled with the tooth roots of the four caudal cheek teeth (Triadan 08–11). In horses older than 5 years, the apical portions of 1/208 and 1/209 lie within the RMS, while 1/210 and 1/211 lie within the CMS. By the age of 10 years, the RMS no longer contains the apices of the 1/208 [12, 13, 22, 43]. However, there is limited information on the positional changes of these teeth during maturation, especially from less than 1 year to 5 years of age. This gap in knowledge prompted the current study, which investigated these changes during the maturation of Dareshuri horses.
According to Dixon et al., it is generally accepted that in young adult Thoroughbred horses, the alveoli of maxillary Triadan 06–07, 08–09, and 10–11 are located in the maxillary bone, RMS/VCS, and CMS, respectively [10]. Moreover, a study by Liuti et al. comparing three different age groups of Thoroughbred horses, 1 to 6 years, 6 to 15 years, and more than 15 years of age, revealed that the mean length of the reserve crowns varied significantly with age. The findings of the study by Liuti et al. align with those of the previously mentioned study by Dixon et al., confirming that teeth 06 and 07 do not contact any sinus compartments but that all 08s are located within the RMS (either partially or fully). Furthermore, most 09s are entirely situated within the RMS, while Triadan 10 exhibits variability, as these teeth can be found in either the RMS or CMS. In contrast, all 11s are consistently located in the CMS. Yet, there is an absence of objective information regarding the exact intra-sinus disposition of their alveoli [27].
To the best of the authors’ knowledge, no study has yet evaluated these changes (specifically the positions and lengths of the reserve crowns) in horses ranging from under 1 year to 5 years of age, particularly in the Dareshuri breed. Therefore, the findings regarding the teeth positions in Dareshuri horses differ from those of previous studies, which may be attributed to the age range of the cases involved in this study or to breed variations. However, further investigations involving similar age ranges in other breeds (e.g., Warmbloods or Thoroughbreds) are necessary to compare and confirm these observations.
According to the current study, the apex of PM4 (Triadan 08) was first observed entering the RMS at the ages of 2–3 years old and was fully positioned in the RMS in all cases starting in the 4–5-year-old age group, and it was not seen in the CMS in any of the study cases. Notably, this tooth enters the RMS earlier in the Dareshuri horse than in the Arabian foal [3]. The reserve crowns of Triadan 09 (M1) were consistently positioned in the RMS in all cases throughout the study. They were present in the CMS in all cases for the age group under 1 year old, but in the last group (4–5 years old), it was no longer observed in the CMS. Triadan 10 (M2) was absent in the RMS in the under 1-year- (group A) and 2–3-year-old (group C) age groups but appeared in some cases in other groups: 1–2 years (2/5 cases), 3–4 years (4/6 cases), and 4–5 years (4/6 cases). In contrast, it was first present in the CMS at the age of 1 year, and it remained fully positioned there in all subsequent age groups. Triadan 11 (M3) was never found in the RMS in any of the cases, and it first appeared in the CMS at 3 years of age and was fully positioned in this compartment in all cases in the 4–5-year-old age group.
These patterns of maxillary cheek teeth disposition are consistent with the concept of rostral drift of the cheek teeth, which has been documented in different breeds in previous studies conducted on Thoroughbreds [12, 19, 27].
Clinical relevance
This study provides valuable information about the Dareshuri breed, particularly regarding the dimensions of the maxillary sinus. In addition to offering anatomical insights, this knowledge will assist Iranian equine practitioners in enhancing their understanding of maxillary sinus morphology to better plan potential surgical interventions, such as sinusotomy or sinus flap procedures. It may also be helpful in reducing the risk of surgical complications by refining surgical approaches, including the identification of appropriate trephination sites for the Dareshuri horse (by having estimates of the diameters of maxillary sinus compartments at different ages in this breed). Additionally, by understanding the length of the cheek teeth reserve crowns present within the maxillary sinus, the risk of the occurrence of inadvertent damage to these structures during trephination and other surgical intervention will be reduced. Furthermore, understanding the positions of teeth is essential for diagnosis and treatment of both dental and paranasal sinus diseases. For instance, infection in maxillary cheek teeth can potentially lead to secondary sinusitis. Therefore, knowledge of dental positioning within the maxillary sinus is crucial for conducting thorough dental examinations, as it provides information about the probable cheek tooth causing secondary sinusitis and information for assessing the likelihood of dental disease as an underlying cause of sinus-related conditions.
Suggestion and Errors
This study has a few limitations that should be addressed in future research. Firstly, all the horses were evaluated using digital radiographs. While the CT scan is considered the gold standard for assessing such structures, the lack of CT scan facilities for horses in Iran necessitated the use of conventional methods, including DR radiography and radiograph image processing software (EConsole1), for measurements and further evaluation. Future studies should aim to incorporate CT scanning to improve accuracy and reliability. The second limitation was the small sample size. To address these limitations, it is suggested that future studies include a larger sample size, employ CT scans for more precise imaging, and track the horses individually throughout their lives to monitor changes in the maxillary sinus structure over time. Such longitudinal studies would provide more comprehensive data, including the correlation between the rostral and caudal maxillary sinus diameters and age. This would contribute valuable insights into the development of these structures over the life course of the horse.
Acknowledgments
The authors gratefully acknowledge Dr. Younes Kamali, assistant professor of the Department of Anatomy, Mashhad University (Mashhad, Iran) for suggesting the idea of performing this research, as well as the assistance of the technicians at the Department of Surgery, School of Veterinary Medicine, Shiraz University, particularly Mr. Moslem Rezaei and Mr. Mohsen Nowrouzi for their invaluable contribution in performing the radiography. Their support was crucial in carrying out this study.
References
- 1.Allen J.R., Barbee D.D., Boulton C.R., Major M.D., Crisman M.V., Murnane R.D. 1987. Brain abscess in a horse: diagnosis by computed tomography and successful surgical treatment. Equine Vet. J. 19: 552–555. [DOI] [PubMed] [Google Scholar]
- 2.Arefnejad B., Zeinalabedini M., Talebi R., Mardi M., Ghaffari M.R., Vahidi M.F., Nekouei M.K., Szmatoła T., Salekdeh G.H. 2024. Unveiling the population genetic structure of Iranian horses breeds by whole-genome resequencing analysis. Mamm. Genome 35: 201–227. [DOI] [PubMed] [Google Scholar]
- 3.Bahar S., Bolat D., Dayan M.O., Paksoy Y. 2014. Two- and three-dimensional anatomy of paranasal sinuses in Arabian foals. J. Vet. Med. Sci. 76: 37–44. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Baratt R.M. 2020. Dental radiography and radiographic signs of equine dental disease. Vet. Clin. North Am. Equine Pract. 36: 445–476. [DOI] [PubMed] [Google Scholar]
- 5.Barrett M.F., Easley J.T. 2013. Acquisition and interpretation of radiographs of the equine skull. Equine Vet. Educ. 25: 643–652. [Google Scholar]
- 6.Borowska M., Lipowicz P., Daunoravičienė K., Turek B., Jasiński T., Pauk J., Domino M. 2024. Three-dimensional segmentation of equine paranasal sinuses in multidetector computed tomography datasets: preliminary morphometric assessment assisted with clustering analysis. Sensors (Basel) 24: 3538. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Brinkschulte M., Bienert-Zeit A., Lüpke M., Hellige M., Staszyk C., Ohnesorge B. 2013. Using semi-automated segmentation of computed tomography datasets for three-dimensional visualization and volume measurements of equine paranasal sinuses. Vet. Radiol. Ultrasound 54: 582–590. [DOI] [PubMed] [Google Scholar]
- 8.Brinkschulte M., Bienert-Zeit A., Lüpke M., Hellige M., Ohnesorge B., Staszyk C. 2014. The sinonasal communication in the horse: examinations using computerized three-dimensional reformatted renderings of computed-tomography datasets. BMC Vet. Res. 10: 72. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Cudd T.A., Mayhew I.G., Cottrill C.M. 1989. Agenesis of the corpus callosum with cerebellar vermian hypoplasia in a foal resembling the Dandy-Walker syndrome: pre-mortem diagnosis by clinical evaluation and CT scanning. Equine Vet. J. 21: 378–381. [DOI] [PubMed] [Google Scholar]
- 10.Dixon P.M., Hawkes C., Townsend N. 2008. Complications of equine oral surgery. Vet. Clin. North Am. Equine Pract. 24: 499–514, vii. [DOI] [PubMed] [Google Scholar]
- 11.Doherty T., Valverde A., Reed R.A. (eds.) 2006. Manual of Equine Anesthesia and Analgesia. pp. 275–281. Blackwell Publishing, Oxford. [Google Scholar]
- 12.Easley J., Dixon P., Du Toit N. (eds.) 2022. Equine Dentistry and Maxillofacial Surgery. Cambridge Scholars Publishing, Cambridge. [Google Scholar]
- 13.Easley J., Dixon P.M., Schumacher J. (eds.) 2010. Equine Dentistry-E-Book: Equine Dentistry-E-Book. Elsevier Health Sciences. [Google Scholar]
- 14.Fotovati A. 2000. Persian horse breeds from ancient time to present and their rules in development of world horse breeds. Asian-Australas. J. Anim. Sci. 13: 401. [Google Scholar]
- 15.Freeman D.E. 2003. Sinus disease. Vet. Clin. North Am. Equine Pract. 19: 209–243, viii. [DOI] [PubMed] [Google Scholar]
- 16.Goodarzi N., Zehtabvar O., Tohidifar M. 2021. Applied anatomy of the skull in the Arabian horse: a computed tomographic, cross-sectional, volumetric and morphometric study. Vet. Med. Sci. 7: 2225–2233. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Hedayat Evrigh N., Khalkhali Evrigh R., Seyedsharifi R., Omri M. 2019. Genetic diversity in paternal line of Iranian horses using partial sequencing of chromosome Y. Pizhuhishhayi Ulumi Damii Iran 11: 389–398. [Google Scholar]
- 18.Henninger W., Frame E.M., Willmann M., Simhofer H., Malleczek D., Kneissl S.M., Mayrhofer E. 2003. CT features of alveolitis and sinusitis in horses. Vet. Radiol. Ultrasound 44: 269–276. [DOI] [PubMed] [Google Scholar]
- 19.Hillmann D.J. 1975. Skull. pp. 318–348. In: Sisson and Grossman’s the Anatomy of the Domestic Animals. 5th ed. (Getty R, ed.), WB Saunders, Philadelphia. [Google Scholar]
- 20.Huthmann S., Gasse H., Jacob H.G., Rohn K., Staszyk C. 2008. Biomechanical evaluation of equine masticatory action: position and curvature of equine cheek teeth and age-related changes. Anat. Rec. (Hoboken) 291: 565–570. [DOI] [PubMed] [Google Scholar]
- 21.Johnson T.J., Porter C.M. 2006. Dental overgrowths and acquired displacement of cheek teeth. In: American Association of Equine Practitioners-Equine Dentistry Focus Meeting, Ed: AAEP American Association of Equine Practitioners, Indianapolis (Vol. 65). [Google Scholar]
- 22.Klugh D.O. 2010. Principles of Equine Dentistry. CRC Press, Boca Raton. [Google Scholar]
- 23.Kraft S.L., Gavin P. 2001. Physical principles and technical considerations for equine computed tomography and magnetic resonance imaging. Vet. Clin. North Am. Equine Pract. 17: 115–130, vii. [DOI] [PubMed] [Google Scholar]
- 24.Köhler L., Schulz-Kornas E., Vervuert I., Gittel C., Winter K., Berner D., Gerlach K. 2021. Volumetric measurements of paranasal sinuses and examination of sinonasal communication in healthy Shetland ponies: anatomical and morphometric characteristics using computed tomography. BMC Vet. Res. 17: 41. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Kunkel M. E., Moral A. I., Tingelhoff K., Bootz F., Wahl F. 2009. Validity of paranasal CT image reconstruction for finite element models in otorhinolaryngology. pp. 273–286. In: Advances in Computational Vision and Medical Image Processing: Methods and Applications. Springer, Dordrecht. [Google Scholar]
- 26.Liuti T., Daniel C.R., Dixon P.M., Reardon R.J.M. 2022. Studies on age-related changes in equine cheek teeth angulation and dental drift. Front. Vet. Sci. 8: 804061. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Liuti T., Reardon R., Dixon P.M. 2017. Computed tomographic assessment of equine maxillary cheek teeth anatomical relationships, and paranasal sinus volumes. Vet. Rec. 181: 452. [DOI] [PubMed] [Google Scholar]
- 28.Manso‐Díaz G., García‐López J.M., Maranda L., Taeymans O. 2015. The role of head computed tomography in equine practice. Equine Vet. Educ. 27: 136–145. [Google Scholar]
- 29.Manso‐Díaz G., Taeymans O., García‐López J.M., Weller R. 2021. Application and indications of magnetic resonance imaging and computed tomography of the equine head. Equine Vet. Educ. 33: 31–46. [Google Scholar]
- 30.McKlveen T.L., Jones J.C., Sponenberg D.P., Scarratt K., Ward D.L., Aardema C.H., Jr 2003. Assessment of the accuracy of computed tomography for measurement of normal equine pituitary glands. Am. J. Vet. Res. 64: 1387–1394. [DOI] [PubMed] [Google Scholar]
- 31.Morrow K.L., Park R.D., Spurgeon T.L., Stashak T.S., Arceneaux B. 2000. Computed tomographic imaging of the equine head. Vet. Radiol. Ultrasound 41: 491–497. [DOI] [PubMed] [Google Scholar]
- 32.Nickels F.A. 2011. Nasal passages and paranasal sinuses. pp. 557–568. In: Equine Surgery, 4. (Auer, J.A., and Stick, J.A. eds.), Elsevier Saunders, St. Louis. [Google Scholar]
- 33.Pease A. P. 2017. The equine head. p. 230. In: Textbook of Veterinary Diagnostic Radiology. E-Book. [Google Scholar]
- 34.Probst A., Henninger W., Willmann M. 2005. Communications of normal nasal and paranasal cavities in computed tomography of horses. Vet. Radiol. Ultrasound 46: 44–48. [DOI] [PubMed] [Google Scholar]
- 35.Puchalski S.M. 2012. Advances in equine computed tomography and use of contrast media. Vet. Clin. North Am. Equine Pract. 28: 563–581. [DOI] [PubMed] [Google Scholar]
- 36.Salek Ardestani S., Zandi M.B., Vahedi S.M., Janssens S. 2022. Population structure and genomic footprints of selection in five major Iranian horse breeds. Anim. Genet. 53: 627–639. [DOI] [PubMed] [Google Scholar]
- 37.Smallwood J.E., Wood B.C., Taylor W.E., Tate L.P., Jr 2002. Anatomic reference for computed tomography of the head of the foal. Vet. Radiol. Ultrasound 43: 99–117. [DOI] [PubMed] [Google Scholar]
- 38.Solano M., Brawer R.S. 2004. CT of the equine head: technical considerations, anatomical guide, and selected diseases. Clin. Tech. Equine Pract. 3: 374–388. [Google Scholar]
- 39.Stewart H.L., Siewerdsen J.H., Nelson B.B., Kawcak C.E. 2021. Use of cone-beam computed tomography for advanced imaging of the equine patient. Equine Vet. J. 53: 872–885. [DOI] [PubMed] [Google Scholar]
- 40.Stieger-Vanegas S.M., Hanna A.L. 2022. The role of computed tomography in imaging non-neurologic disorders of the head in equine patients. Front. Vet. Sci. 9: 798216. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 41.Tingelhoff K., Moral A.I., Kunkel M.E., Rilk M., Wagner I., Eichhorn K.G., Wahl F.M., Bootz F. 2007. Comparison between manual and semi-automatic segmentation of nasal cavity and paranasal sinuses from CT images. Annu. Int. Conf. IEEE Eng. Med. Biol. Soc. 2007: 5505–5508. [DOI] [PubMed] [Google Scholar]
- 42.Tremaine W.H., Dixon P.M. 2001. A long-term study of 277 cases of equine sinonasal disease. Part 1: details of horses, historical, clinical and ancillary diagnostic findings. Equine Vet. J. 33: 274–282. [DOI] [PubMed] [Google Scholar]
- 43.Tutt C. 2011. Equine dentistry: routine examination and floating. Equipment required. Companion Anim. 16: 4–10. [Google Scholar]
- 44.Waguespack R.W., Taintor J. 2011. Paranasal sinus disease in horses. Compend. Contin. Educ. Vet. 33: E2. [PubMed] [Google Scholar]