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Kinematic analysis of equine masticatory movements: Comparison before and after routine dental treatment
The Veterinary Journal 190 (2011) 49–54
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The Veterinary Journal journal homepage: www.elsevier.com/locate/tvjl
Kinematic analysis of equine masticatory movements: Comparison before and after routine dental treatment Hubert Simhofer a,⇑, Melanie Niederl a, Claudine Anen a, Astrid Rijkenhuizen a, Christian Peham b a b
Clinic for Large Animal Surgery and Orthopaedics, Dept. IV, University for Veterinary Medicine, Vienna, Austria Movement Science Group, Dept. IV, University for Veterinary Medicine, Vienna, Austria
a r t i c l e
i n f o
Article history: Accepted 19 September 2010
Keywords: Horse Mastication Kinematic analysis Dentistry Dental correction
a b s t r a c t The objective of this study was to compare masticatory movements before and after dental treatment using kinematic analysis. The masticatory movements of 15 adult Warmblood horses with mild dental pathology chewing standardised hay were recorded on three consecutive days before and three times after (days 7, 21, 28) dental correction. The results of the leading mandibular tracking marker, located at the caudal edge of the inter-mandibular suture, were compared statistically. Reproducibility of measurements prior to dental treatment was excellent (P < 0.05). Rostrocaudal mandibular motion was significantly reduced after dental correction (9 ± 2 mm vs. 8 ± 2 mm; P = 0.046). Oscillations during the power stroke were significantly reduced after dental correction (R2 = 98.3% ± 0.3 vs. 98.8% ± 0.3; P = 0.050). Although significant changes were observed in individual horses, the overall results of lateral and dorsoventral mandibular motion did not reveal significant differences. In conclusion, kinematic analysis of masticatory movements provided reproducible results and may be useful to evaluate changed movement patterns following dental correction. Ó 2010 Elsevier Ltd. All rights reserved.
Introduction The first attempts to analyse masticatory movements scientifically were performed by Leue (1941, 1944) who constructed a socalled ‘molograph’, a mechanical device that provided two-dimensional (2D) recording of masticatory movements. Half a century later, Collinson (1994) examined the masticatory movements of horses using video analysis. Other techniques, such as magnetometry (Plesh et al., 1993), were less satisfactory since they were either overly elaborate or contained biological risks, such as the radionuclide-tracking method (Salomon and Waysenson, 1979). Chewing is a complex three-dimensional (3D) movement consisting of repeated mandibular movements that are specified and limited by the paired temporomandibular joints (TMJ). A masticatory cycle consists of three phases, the opening-, the closing- and the power stroke (Collinson, 1994; Baker, 1999, 2002). Using kinematic analysis, the exact 3D movements of the equine TMJs have been described by Bonin et al. (2006, 2007). During the opening stroke, the mandible is moved in a ventro-rostro-lateral direction until the point of maximal ventral excursion is reached. In the closing stroke, the mandible is then moved to the opposite side in a dorso-caudo-lateral direction until the cheek teeth of one side make contact.
In the power stroke, the occlusal surfaces of the mandibular teeth shear over those of their maxillary counterparts in a laterodorsal direction. The power stroke ends at the most dorsal point of the masticatory cycle. Masticatory movements are directed either in a clockwise or counter-clockwise direction (Collinson, 1994; Baker, 1999, 2002; Bonin et al., 2007). The effects of dental correction on rostrocaudal mandibular mobility (Carmalt et al., 2003) and on the effectiveness of mastication and digestion (Gatta et al., 1995; Krusic et al., 1995; Ralston et al., 2001; Carmalt et al., 2004) have been evaluated in clinical studies. The objectives of the current study were to test the repeatability of kinematic analysis of masticatory movements in horses and to examine the effects of dental correction on equine mastication. Materials and methods Animals The study, which was approved by the ethics commission of the University for Veterinary Medicine Vienna, was performed in 15 adult Warmblood horses (10 geldings, 5 mares) aged 8–19 years with a complete permanent dentition. All animals were in good body condition and displayed un-changed food uptake and mastication. All animals belonged to the University for Veterinary Medicine Vienna. Preparations, experimental setup
⇑ Corresponding author. Tel.: +43 1 25077 6642; fax: +43 1 25077 5393. E-mail address: [email protected] (H. Simhofer). 1090-0233/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2010.09.014
A complete, standardised examination of the oral cavity including inspection, palpation and endoscopic examination (Simhofer et al., 2008) was performed 1 week before the first measurement. To undertake this examination, the horses
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H. Simhofer et al. / The Veterinary Journal 190 (2011) 49–54
were sedated with detomidine hydrochloride (Domosedan, Pfizer, 0.02 mg/kg bodyweight [BW], intravenously [IV]) and butorphanol (Butomidor, Richter, 0.01 mg/kg BW, IV). The mouth was opened using a full mouth speculum. All findings were recorded using a standard computer protocol (Dental Consult, VUW). No signs of moderate or severe dental disease were detected in any of the horses. However, mild pathological changes, such as sharp enamel points or ridges (<3 mm estimated height [EH]), rostral or caudal focal dental overgrowths (hooks, ramps, <3 mm EH), unilateral or bilateral wave mouth formation (<3 mm EH), exaggerated transverse ridges (<3 mm EH), dental displacement (<2 mm, estimated) or slightly rotated teeth (<10°, estimated) were diagnosed in all animals. The skin over defined marker locations (Fig. 1) was shaved (2 cm2) and 10 spherical marker balls of 10 and 20 mm diameter were glued to the horse’s skin using cyanoacrylate glue. Masticatory movements were recorded using six high speed video cameras (sample rate 120 Hz, Motion Analysis Systems) arranged in a circle around a treadmill, which served as feedlot. Camera positions in different altitudes enabled constant surveillance of the horse’s heads during food uptake (Fig. 2). Prior to each measurement, the system was calibrated using a two-step procedure (Pribanic et al., 2007). One week before the trial period, the diet of all horses was changed to hay of standardised quality (hay analysis: Institute for Applied Botany, VUW) from a single distributor. During this period, the animals were fed on the treadmill to minimise
Fig. 1. Marker locations: marker 1 was located median at the border between the nasal and frontal bones; marker 2 on the midline at the level of the nasoincisival notch; markers 3 and 4 were placed bilateral at the temporal bones dorsal to the TMJ; markers 5 and 6 were glued to the rostral edge of the right and left facial crest; markers 7 and 8 were attached to the right and left mandible 1 cm rostral to the notch for facial vessels; marker 9 was located at the caudal edge of the intermandibular suture and marker 10 finally resembled an additional marker fixed to an extension on marker 1 to define a segment coordinate system.
bias by new surroundings. The animals were taken to the study site in pairs (experimental and companion) and fed simultaneously from the ground to further minimise stress during data collection times. Within a 7-day period, three measurements were performed on consecutive days in each horse under identical conditions and hay of standard quality (approximately 0.5 kg) was presented. Recording commenced 2 min after the initiation of food uptake when the animals had settled down and focused on mastication. After completion of these initial measurements, all animals were subjected to dental treatment. Subsequently three recordings of masticatory movements were performed in each horse on days 7, 21 and 28 after dental treatment under identical conditions, as described above.
Fig. 3. Coordinate system on the head and directions of movements: X-axis: rostrocaudal movement; Y-axis: latero-lateral movements; Z-axis: dorsoventral movements.
Fig. 2. Camera setup: cameras 1 and 6 were elevated to 130 cm and located behind the horse. Another pair of cameras (2 and 4) was positioned 160 cm above ground at right angles with the horse’s head; cameras 3 and 4 were placed in front of the horse recording masticatory movements from an altitude of 185 cm.
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H. Simhofer et al. / The Veterinary Journal 190 (2011) 49–54 Dental treatment Dental treatments were performed in standing, sedated (detomidine hydrochloride, 0.015 mg/kg BW, IV; butorphanol tartrate, 0.02 mg/kg BW, IV) animals. Focal dental overgrowths (sharp enamel points, hooks, ramps) of the cheek teeth were removed and mild wave mouth formations and any exaggerated transverse ridges were corrected using powered rotating tools (Swiss float, Eisenhut-Vet AG) and hand rasps. No corrective procedures were performed on the incisor teeth. To prevent methodical bias, all animals were treated by the same veterinarian (HS).
Data processing, statistical analysis Tracking of raw data was performed using EVA 6.0 software. In order to isolate the masticatory movements, transformation of coordinates was performed using MatLab 7.0.1 software. The movement was transformed in the segmental coordinate system (Fig. 3). Thus, rostrocaudal movements could be depicted on the X-axis, transverse (lateral) locomotion on the Y-axis, opening (ventral) – and closing (dorsal) motion on the Z-axis of a 3D coordinate system. Selected chewing cycles were displayed graphically and the chewing frequency was calculated. For further analysis, a minimum of 15 complete chewing cycles was isolated. The initial point of a single cycle was defined as the minimal value (i.e., the point of maximal ventral mandibular excursion) of marker 9, at which the cycles were separated (Fig. 4). To enable comparison of individual cycles, they were normalised to 100% using MatLab 7.0.1. The mean durations of the masticatory cycles were calculated. Additionally, the maximum ranges of rostrocaudal, lateral and dorsoventral mandibular translations were measured. Lateral mandibular excursion was calculated by subtracting the minimum value from the maximum of each respective chewing cycle. The distance of the dorsoventral and rostrocaudal mandibular movements was calculated by subtraction of the maximal and minimal values of the same marker on the respective (X- and Z-) axes. Mean values of at least 15 isolated chewing cycles (five per day of measurement) were generated and the differences were calculated. Mean values and standard deviation were calculated and displayed. Testing for normality of distribution was performed using the KolmogorovSmirnov test. Subsequently, the mean values of all measurements prior to dental treatment were analysed using ANOVA for repeated measures, as were the results post treatment. Results of the measurements before and after dental treatments
were summated in two groups and the mean values of the respective groups were subjected to a paired t-test. The individual results of all horses were compared and analysed for significant differences using the program SPSS 12.0 with statistical difference accepted at P 6 0.05.
Analysis of the ‘power stroke’ The term power stroke refers to the final phase of the masticatory cycle in which food was crushed between the cheek teeth. The moment of contact between maxillary and mandibular cheek teeth was defined as the initial point of each power stroke. According to definition, the end of the power stroke was reached at the most dorsal point of the masticatory cycle. Data of each power stroke was isolated, a trend line was generated and linear regression (R2) was calculated. The results were screened for normal distribution (Kolmogorov–Smirnov test) and statistic analysis (multivariate ANOVA for repeated measures) was performed.
Results Description of masticatory movements Mastication is a 3D movement which can be displayed in three 2D planes (Figs. 5a–c) to be fully understood. A dorsal view was obtained when the movements of marker 9 in relation to the stationary skull markers along the X- and Y-axis were displayed (Fig. 5a).
Fig. 5b. Frontal view of the same horse’s chewing cycle as shown in Fig 5a. Dorsoventral and lateral movements of marker 9 are displayed.
Fig. 4. Dotted lines indicate points of separation of a single masticatory cycle. Xaxis: time; Y-axis: distance (cm).
Fig. 5c. Lateral view of the chewing cycle depicted in Figs. 5a and 5b. Dorsoventral and rostrocaudal movements of marker 9 are displayed.
Table 1 Comparison of mandibular movements before dental correction (in mm). Direction of movements (marker 9) Fig. 5a. Dorsal view of a representative chewing cycle of horse 2 (mean values of 15 chewing cycles, first measurement after dental treatment). Rostrocaudal and lateral movements of marker 9 are displayed.
Trial 1 Trial 2 Trial 3 Mean
Rostrocaudal mandibular movement (X-axis) 9 ± 2 Lateral mandibular movement (Y-axis) 59 ± 7 Dorsoventral mandibular movement (Z-axis) 45 ± 4
9±2 61 ± 7 45 ± 5
9±2 56 ± 7 45 ± 5
9±2 59 ± 6 45 ± 5
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H. Simhofer et al. / The Veterinary Journal 190 (2011) 49–54
Visualisation of mandibular translocation on the Y- and Z-axis created a frontal (as if standing before the horse) view of the horse’s masticatory movement (Fig. 5b). A lateral view of a masticatory cycle was obtained by transposition along the X- and Z-axis (Fig. 5c).
Masticatory movements before and after dental treatment: comparison of groups
The average duration of a masticatory cycle was 0.70 ± 0.04 s prior to dental treatment and 0.69 ± 0.04 s after dental treatment, which equated to a chewing frequency of 1.4 Hz. The duration of masticatory movements did not change significantly (P = 0.115) after dental treatment.
Mean values and standard deviations for each measurement in each direction of movement are shown in Table 2. The comparison of masticatory movements before and after dental treatment revealed that rostrocaudal mandibular motion (mean before: 9 ± 2 mm) was significantly reduced after dental correction (8 ± 2 mm; P = 0.046). Mean mediolateral mandibular excursion, lateral excursion and dorsoventral mandibular movements, on the contrary, did not change significantly after routine dental correction.
Reproducibility of measurements before dental treatment
Analysis of individual results
The data sets of the three kinematic measurements of each horse before dental correction were used to evaluate the repeatability of the kinematic system. The ranges of lateral and dorsoventral mandibular movement depended on the distance of the respective tracking marker’s position to the point of rotation to the TMJ. The presented data was based on results from marker 9 (caudal end of the inter-mandibular suture). The results of rostrocaudal, mediolateral, total lateral and dorsoventral mandibular motion are shown in Table 1. Statistical analysis revealed no significant differences for the three ranges of motion in all three trials, which suggested that reproducible results could be obtained using kinematic analysis of masticatory movements under standardised conditions.
The results of all individuals before and after dental treatment are displayed in Table 3. Rostrocaudal mandibular movement (Xaxis) varied between 7 and 10 mm both before and after dental treatment. A reduced motion in this direction was observed in 9/ 15 horses. Three horses displayed an increased range of rostrocaudal motion after dental treatment, while three other animals had no change in the motion range. Lateral mandibular excursion ranged from 48 to 68 mm before and from 53 to 71 mm after dental treatment. It increased in 11/ 15 animals and decreased in the remaining four. A significant increase of motion range was found in seven horses and a significant decrease in one individual. Dorsoventral mandibular movements were reduced in 11/15 horses (significant in nine individuals). An increased range of motion was found in three animals with one horse displaying a significant increase. Un-changed results were obtained of one horse.
Duration of masticatory cycles
Table 2 Comparison of mean values of mandibular movements before and after dental correction. Significant changes are indicated (*). Direction of movements (marker 9)
Before dental treatment (mm)
After dental treatment (mm)
Direction of mastication
Mean rostrocaudal mandibular movement (X-axis) Mean lateral mandibular movement (Y-axis) Mean dorsoventral mandibular movement (Z-axis)
9 ± 2*
8 ± 2*
59 ± 6
62 ± 6
45 ± 4
43 ± 4
The direction of chewing changed between measurements for 14/15 horses. Only one horse consistently chewed on the left side (counter-clockwise). During 45 measurements prior to dental treatment, 30 horses (67%) were chewing on the left side (counter-clockwise) and 15 (33%) on the right (clockwise) (chi2: P = 0.053). After dental treatment, this 2:1 ratio changed significantly in favour of the left side with 35 horses (78%) chewing left and 10 (22%) on the right side (chi2: P = 0.0001).
Table 3 Comparison of individual results before and after dental treatment (in mm). Significant changes are indicated (*).
1: WB, g, 14 years 2: Trotter, g, 16 years 3: Trotter, g, 13 years 4: WB, g, 9 years 5: WB, g, 9 years 6: WB, m, 14 years 7: Trotter, m, 6 years 8: WB, g, 15 years 9: WB, g, 16 years 10: WB, g, 15 years 11: WB, g, 15 years 12: Polo, m, 10 years 13: WB, g, 15 years 14: Hafl, m, 5 years 15: Hafl, m, 8 years
Rostrocaudal excursion, Xaxis
Lateral excursion, Y-axis
Dorsoventral excursion, Zaxis
Before
After
Before
After
Before
After
10 ± 2 7±1
9±2 7±2
48 ± 9 68 ± 4
53 ± 3* 65 ± 5
37 ± 3 43 ± 3
44 ± 2* 43 ± 2
8±2
7±2
57 ± 3
62 ± 5*
42 ± 2
40 ± 1*
7±2 9±2 8±2 8±2
9 ± 0.5 8±2 8±4 7±2
58 ± 5 52 ± 5 63 ± 10 65 ± 7
65 ± 9* 60 ± 9* 67 ± 10 71 ± 10
46 ± 2 44 ± 2 43 ± 4 42 ± 2
44 ± 3* 43 ± 2* 41 ± 2* 42 ± 2
9±2 11 ± 2 11 ± 3 8±2 8±2
9±2 13 ± 3 9±2 7±2 6±2
53 ± 6 50 ± 4 68 ± 7 62 ± 6 54 ± 9
59 ± 5* 59 ± 6* 62 ± 9* 69 ± 8* 56 ± 9
51 ± 2 47 ± 3 54 ± 2 49 ± 2 40 ± 3
49 ± 1* 48 ± 2 48 ± 4* 45 ± 2* 40 ± 2
9±3 8±2 13 ± 5
8±2 9±2 10 ± 3
64 ± 6 57 ± 4 61 ± 7
60 ± 4 58 ± 7 56 ± 4
48 ± 2 41 ± 2 45 ± 2
50 ± 4 37 ± 3* 41 ± 3*
WB, Warmblood; Polo, polo pony; Hafl, Haflinger; g, gelding; m, mare.
Analysis of the power stroke Mandibular movements during the power stroke while masticating hay appeared to be significantly ‘smoothened’ after dental treatment. Prior to dental correction linear regression (R2) was 98.3% ± 0.3, after dental treatment a value of 98.8% ± 0.3 was calculated (P = 0.050). Discussion The main advantage of kinematic analysis over other techniques (Leue, 1941, 1944; Salomon and Waysenson, 1979; Plesh et al., 1993) used for measurement of masticatory movements is that it provided quantitative data (Bonin et al., 2006, 2007). Bonin et al. (2007) also hypothesised that kinematic analysis could be utilised to evaluate the range of motion of the TMJ before and after dental procedures in individual animals and in horses with TMJ disease. The aim of this study was to test this hitherto unproven hypothesis. The extent of lateral mandibular excursion and chewing frequency largely depends on the type of food eaten (Leue, 1941; Bonin et al., 2007). Consequently, the present study used
H. Simhofer et al. / The Veterinary Journal 190 (2011) 49–54
standardised hay to compare mandibular movements before and after dental treatment. The comparison of motion ranges of three measurements of individual horses performed on consecutive days before floating revealed constant ranges of motion in all animals, as previously described by Leue (1941), Baker (2002) and Collinson (1994), although differences in motion range were observed between individuals. The majority of horses (14/15; 93%) in this study changed the chewing direction with only one animal consistently masticating on the left side, which differed from the report of Collinson (1994). Interestingly, the trend to chew on the left side (counterclockwise) significantly increased after dental correction in this study. The distribution of markers on the horse’s heads was an important factor for accurate measurement (Bonin et al., 2006) and pilot studies showed that the main tracking marker should be located at the caudal end of the inter-mandibular suture. The thin layer of subcutaneous soft tissue at this site minimised skin displacement compared to other locations. Skin displacement was a major source of potential systematic error in kinematic studies (Van Weeren et al., 1990; Bonin et al., 2006, 2007) and no correction algorithms for skin displacement on the equine head were available (Bonin et al., 2006). Placement of the main tracking marker as described above eliminated the need for a virtual midline marker, as described by Bonin et al. (2006, 2007). The positioning of markers may also significantly influence the results of translational movements (Bonin et al., 2007). For example, we measured a mean lateral translation of 50 mm (53 mm after dental treatment) with a marker placed caudal to the level of the incisors, which was greater than reported (45 mm) when the marker was at the level of the incisors (Collinson, 1994; Baker, 2002) or fourth premolar (19.9 mm; Bonin et al., 2006, 2007). However, the mean rostrocaudal translation of 9.0 mm (8.0 mm after treatment) in the current study was comparable to one earlier study (9.8 mm; Bonin et al., 2006), yet higher than a further study (6.1 mm; Bonin et al., 2007), the latter of which was consistent with clinical measurements (Carmalt and Allen, 2006; Carmalt et al., 2006). Dorsoventral mandibular movement (45 mm before and 43 mm after treatment) was wider than reported previously (Bonin et al., 2006, 2007). However, the different marker positions in the respective studies and the varying distances of the markers to the temporomandibular joints made a direct comparison impossible. Furthermore, the frequency of mastication while chewing hay was slightly higher in the current study (1.4 Hz) than described elsewhere (1.2 Hz; Bonin et al., 2007). Variable factors, including the composition of food, size and breed of the horse and individual chewing patterns have a significant influence on mandibular excursions (Leue, 1944; Baker, 2002; Collinson, 1994; Bonin et al., 2006, 2007). We also observed considerable variation of movement ranges and patterns, similar to that reported previously (Baker, 2002). While excessive focal dental overgrowths and periodontal disease are painful conditions which might severely compromise mastication (Dixon and Dacre, 2005), the presence of less severe overgrowths might simply impede normal mandibular kinematics. The current study found that reduction of focal dental overgrowths on equine cheek teeth changed masticatory movements, although the horses used did not react uniformly to routine dental treatment, so the assumption that the reduction of focal dental overgrowths would result in larger lateral excursions could not be verified. Indeed, 4/11 horses displayed reduced lateral excursions, which may have related to the fact that horses display a variety of different mastication patterns prior to any dental correction (Leue, 1941; Baker, 2002). Rasping teeth inevitably resulted in the smoothening of certain parts of the masticatory surface, which may have forced some
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horses, at least temporarily, to adapt their mastication to a more vertically orientated pattern (Bonin et al., 2007). More comprehensive studies are therefore required to determine the basic patterns of mastication, which were first described by Leue (1944). Furthermore, some equine dental practitioners suggest that dental correction will increase the rostrocaudal movement of the mandible (Carmalt and Allen, 2006; Carmalt et al., 2006), although this approach reduced rostrocaudal mandibular movement in 9/15 animals in the current study. A possible explanation might be that the ridges of the cheek teeth, after being reduced, do not need to be ‘brought into position’ to match the corresponding grooves in the opposing dental row during the power stroke. It should therefore be considered that some horses may not need to move the mandible as much rostrally after dental correction while chewing and that an increased range of motion does not necessarily indicate improved mastication (Carmalt et al., 2006). Moreover, the type and extent of dental treatment will depend in underlying pathology, so variability of the resulting masticatory movements after dental treatment could be expected. It is therefore difficult to interpret the changed masticatory movements induced by dental therapy. Further studies combining kinematic analysis with quantitative measurements of chewing forces (Staszyk et al., 2006; Huthmann et al., 2009) might provide a greater understanding of mastication and the individual reactions of individual horses to dental therapy. Conclusions It has been demonstrated that kinematic analysis of equine masticatory movements provides reproducible results. This method was also found suitable for the evaluation of changed masticatory movement patterns following dental correction. Conflict of interest statement None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper. Acknowledgements The authors want to thank James Carmalt and Edmund Hainisch for proof reading and valuable suggestions. References Baker, G.J., 1999. Dental physiology. In: Baker, G.J., Easley, J. (Eds.), Equine Dentistry. W.B. Saunders, London, pp. 29–34. Baker, G.J., 2002. Equine temporomandibular joints (TMJ): morphology, function and clinical disease. In: Proceedings of the 48th Annual Convention of the American Association of Equine Practitioners, pp. 442–447. Bonin, S.J., Clayton, H.M., Lanovaz, J.L., Johnson, T.J., 2006. Kinematics of the equine temporomandibular joint. American Journal of Veterinary Research 67, 423– 428. Bonin, S.J., Clayton, H.M., Lanovatz, J.L., Johnston, T., 2007. Comparison of mandibular motion in horses chewing hay and pellets. Equine Veterinary Journal 39, 258–262. Carmalt, J.L., Allen, A.L., 2006. The effect of rostro-caudal mobility of the mandible on feed digestibility and fecal particle size in the horse. Journal of the American Veterinary Medical Association 229, 1275–1278. Carmalt, J.L., Townsend, H.G.G., Allen, A.L., 2003. Effect of dental floating on the rostrocaudal mobility of the mandible of horses. Journal of the American Veterinary Association 223, 666–669. Carmalt, J.L., Townsend, H.G.G., Janszen, E.D., Cymbaluk, N.F., 2004. Effect of dental floating on weight gain, body condition score, feed digestibility, and fecal particle size in pregnant mares. Journal of the American Veterinary Association 225, 1889–1893. Carmalt, J.L., Carmalt, K.P., Barber, S.M., 2006. The effect of occlusal equilibration on sport horse performance (dressage). Journal of Veterinary Dentistry 23, 226– 230.
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Collinson, M., 1994. Food Processing and Digestibility in Horses (Equus caballus). BSc Thesis, Monash University. Dixon, P.M., Dacre, I.T., 2005. A review of equine dental disorders. The Veterinary Journal 169, 165–187. Gatta, D., Krusic, L., Casini, L., Colombani, B., 1995. Influence of corrected teeth on digestibility of two types of diets in pregnant mares. In: Proceedings of the 14th Equine Nutrition and Physiology Symposium, Ontario, California, January 19– 21, pp. 326–331 Huthmann, S., Staszyk, C., Jacob, H.G., Rohn, K., Gasse, H., 2009. Biomechanical evaluation of the equine masticatory action: calculation of the masticatory forces occurring on the cheek tooth battery. Journal of Biomechanics 42, 67– 70. Krusic, L., Easley, J., Pagan, J., 1995. Influence of corrected teeth on daily food consumption and glucose availability in horses. In: Proceedings of the 1st Symposium on Horse Diseases, Radenci, Slovenia, 23rd–24th March, pp. 53– 68. Leue, G., 1941. Beziehung zwischen Zahnanomalien und Verdauungsstörungen beim Pferd unter Heranziehnung von Kaubildern. Doctoral Thesis, Tierärztliche Hochschule Hannover.
Leue, P., 1944. Längs- und Querlüfter der Mahlflächen beim Zubeißen unter Pferden. Berliner und Münchener Tierärztliche Wochenschrift und Wiener Tierärztliche Monatsschrift 4, 123–125. Plesh, O., Bishop, B., McCall Jr., W.D., 1993. Kinematics of jaw movements during chewing at different frequencies. Journal of Biomechanics 26, 243–250. Pribanic, T., Sturm, P., Cifrek, M., 2007. Calibration of 3D kinematic systems using orthogonality constraints. Machine Vision and Applications 18, 367–381. Ralston, S.L., Foster, D.L., Divers, T., Hintz, H.F., 2001. Effect of dental correction on feed digestibility in horses. Equine Veterinary Journal 33, 390–393. Salomon, J.A., Waysenson, B.D., 1979. Computer-monitored radionuclide tracking of three-dimensional mandibular movements. Part I: theoretical approach. Journal of Prosthetic Dentistry 41, 340–344. Simhofer, H., Griss, R., Zetner, K., 2008. The use of oral endoscopy for detection of cheek teeth abnormalities in 300 horses. The Veterinary Journal 178, 396–404. Staszyk, C., Lehmann, F., Bienert, A., Ludwig, K., Gasse, H., 2006. Measurement of masticatory forces in the horse. Pferdeheilkunde 22, 12–16. Van Weeren, P.R., van den Bogert, A.J., Barneveld, A., 1990. A quantitative analysis of skin displacement in the trotting horse. Equine Veterinary Journal Suppl. 9, 101–109.
Contents lists available at ScienceDirect
The Veterinary Journal journal homepage: www.elsevier.com/locate/tvjl
Kinematic analysis of equine masticatory movements: Comparison before and after routine dental treatment Hubert Simhofer a,⇑, Melanie Niederl a, Claudine Anen a, Astrid Rijkenhuizen a, Christian Peham b a b
Clinic for Large Animal Surgery and Orthopaedics, Dept. IV, University for Veterinary Medicine, Vienna, Austria Movement Science Group, Dept. IV, University for Veterinary Medicine, Vienna, Austria
a r t i c l e
i n f o
Article history: Accepted 19 September 2010
Keywords: Horse Mastication Kinematic analysis Dentistry Dental correction
a b s t r a c t The objective of this study was to compare masticatory movements before and after dental treatment using kinematic analysis. The masticatory movements of 15 adult Warmblood horses with mild dental pathology chewing standardised hay were recorded on three consecutive days before and three times after (days 7, 21, 28) dental correction. The results of the leading mandibular tracking marker, located at the caudal edge of the inter-mandibular suture, were compared statistically. Reproducibility of measurements prior to dental treatment was excellent (P < 0.05). Rostrocaudal mandibular motion was significantly reduced after dental correction (9 ± 2 mm vs. 8 ± 2 mm; P = 0.046). Oscillations during the power stroke were significantly reduced after dental correction (R2 = 98.3% ± 0.3 vs. 98.8% ± 0.3; P = 0.050). Although significant changes were observed in individual horses, the overall results of lateral and dorsoventral mandibular motion did not reveal significant differences. In conclusion, kinematic analysis of masticatory movements provided reproducible results and may be useful to evaluate changed movement patterns following dental correction. Ó 2010 Elsevier Ltd. All rights reserved.
Introduction The first attempts to analyse masticatory movements scientifically were performed by Leue (1941, 1944) who constructed a socalled ‘molograph’, a mechanical device that provided two-dimensional (2D) recording of masticatory movements. Half a century later, Collinson (1994) examined the masticatory movements of horses using video analysis. Other techniques, such as magnetometry (Plesh et al., 1993), were less satisfactory since they were either overly elaborate or contained biological risks, such as the radionuclide-tracking method (Salomon and Waysenson, 1979). Chewing is a complex three-dimensional (3D) movement consisting of repeated mandibular movements that are specified and limited by the paired temporomandibular joints (TMJ). A masticatory cycle consists of three phases, the opening-, the closing- and the power stroke (Collinson, 1994; Baker, 1999, 2002). Using kinematic analysis, the exact 3D movements of the equine TMJs have been described by Bonin et al. (2006, 2007). During the opening stroke, the mandible is moved in a ventro-rostro-lateral direction until the point of maximal ventral excursion is reached. In the closing stroke, the mandible is then moved to the opposite side in a dorso-caudo-lateral direction until the cheek teeth of one side make contact.
In the power stroke, the occlusal surfaces of the mandibular teeth shear over those of their maxillary counterparts in a laterodorsal direction. The power stroke ends at the most dorsal point of the masticatory cycle. Masticatory movements are directed either in a clockwise or counter-clockwise direction (Collinson, 1994; Baker, 1999, 2002; Bonin et al., 2007). The effects of dental correction on rostrocaudal mandibular mobility (Carmalt et al., 2003) and on the effectiveness of mastication and digestion (Gatta et al., 1995; Krusic et al., 1995; Ralston et al., 2001; Carmalt et al., 2004) have been evaluated in clinical studies. The objectives of the current study were to test the repeatability of kinematic analysis of masticatory movements in horses and to examine the effects of dental correction on equine mastication. Materials and methods Animals The study, which was approved by the ethics commission of the University for Veterinary Medicine Vienna, was performed in 15 adult Warmblood horses (10 geldings, 5 mares) aged 8–19 years with a complete permanent dentition. All animals were in good body condition and displayed un-changed food uptake and mastication. All animals belonged to the University for Veterinary Medicine Vienna. Preparations, experimental setup
⇑ Corresponding author. Tel.: +43 1 25077 6642; fax: +43 1 25077 5393. E-mail address: [email protected] (H. Simhofer). 1090-0233/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2010.09.014
A complete, standardised examination of the oral cavity including inspection, palpation and endoscopic examination (Simhofer et al., 2008) was performed 1 week before the first measurement. To undertake this examination, the horses
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were sedated with detomidine hydrochloride (Domosedan, Pfizer, 0.02 mg/kg bodyweight [BW], intravenously [IV]) and butorphanol (Butomidor, Richter, 0.01 mg/kg BW, IV). The mouth was opened using a full mouth speculum. All findings were recorded using a standard computer protocol (Dental Consult, VUW). No signs of moderate or severe dental disease were detected in any of the horses. However, mild pathological changes, such as sharp enamel points or ridges (<3 mm estimated height [EH]), rostral or caudal focal dental overgrowths (hooks, ramps, <3 mm EH), unilateral or bilateral wave mouth formation (<3 mm EH), exaggerated transverse ridges (<3 mm EH), dental displacement (<2 mm, estimated) or slightly rotated teeth (<10°, estimated) were diagnosed in all animals. The skin over defined marker locations (Fig. 1) was shaved (2 cm2) and 10 spherical marker balls of 10 and 20 mm diameter were glued to the horse’s skin using cyanoacrylate glue. Masticatory movements were recorded using six high speed video cameras (sample rate 120 Hz, Motion Analysis Systems) arranged in a circle around a treadmill, which served as feedlot. Camera positions in different altitudes enabled constant surveillance of the horse’s heads during food uptake (Fig. 2). Prior to each measurement, the system was calibrated using a two-step procedure (Pribanic et al., 2007). One week before the trial period, the diet of all horses was changed to hay of standardised quality (hay analysis: Institute for Applied Botany, VUW) from a single distributor. During this period, the animals were fed on the treadmill to minimise
Fig. 1. Marker locations: marker 1 was located median at the border between the nasal and frontal bones; marker 2 on the midline at the level of the nasoincisival notch; markers 3 and 4 were placed bilateral at the temporal bones dorsal to the TMJ; markers 5 and 6 were glued to the rostral edge of the right and left facial crest; markers 7 and 8 were attached to the right and left mandible 1 cm rostral to the notch for facial vessels; marker 9 was located at the caudal edge of the intermandibular suture and marker 10 finally resembled an additional marker fixed to an extension on marker 1 to define a segment coordinate system.
bias by new surroundings. The animals were taken to the study site in pairs (experimental and companion) and fed simultaneously from the ground to further minimise stress during data collection times. Within a 7-day period, three measurements were performed on consecutive days in each horse under identical conditions and hay of standard quality (approximately 0.5 kg) was presented. Recording commenced 2 min after the initiation of food uptake when the animals had settled down and focused on mastication. After completion of these initial measurements, all animals were subjected to dental treatment. Subsequently three recordings of masticatory movements were performed in each horse on days 7, 21 and 28 after dental treatment under identical conditions, as described above.
Fig. 3. Coordinate system on the head and directions of movements: X-axis: rostrocaudal movement; Y-axis: latero-lateral movements; Z-axis: dorsoventral movements.
Fig. 2. Camera setup: cameras 1 and 6 were elevated to 130 cm and located behind the horse. Another pair of cameras (2 and 4) was positioned 160 cm above ground at right angles with the horse’s head; cameras 3 and 4 were placed in front of the horse recording masticatory movements from an altitude of 185 cm.
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H. Simhofer et al. / The Veterinary Journal 190 (2011) 49–54 Dental treatment Dental treatments were performed in standing, sedated (detomidine hydrochloride, 0.015 mg/kg BW, IV; butorphanol tartrate, 0.02 mg/kg BW, IV) animals. Focal dental overgrowths (sharp enamel points, hooks, ramps) of the cheek teeth were removed and mild wave mouth formations and any exaggerated transverse ridges were corrected using powered rotating tools (Swiss float, Eisenhut-Vet AG) and hand rasps. No corrective procedures were performed on the incisor teeth. To prevent methodical bias, all animals were treated by the same veterinarian (HS).
Data processing, statistical analysis Tracking of raw data was performed using EVA 6.0 software. In order to isolate the masticatory movements, transformation of coordinates was performed using MatLab 7.0.1 software. The movement was transformed in the segmental coordinate system (Fig. 3). Thus, rostrocaudal movements could be depicted on the X-axis, transverse (lateral) locomotion on the Y-axis, opening (ventral) – and closing (dorsal) motion on the Z-axis of a 3D coordinate system. Selected chewing cycles were displayed graphically and the chewing frequency was calculated. For further analysis, a minimum of 15 complete chewing cycles was isolated. The initial point of a single cycle was defined as the minimal value (i.e., the point of maximal ventral mandibular excursion) of marker 9, at which the cycles were separated (Fig. 4). To enable comparison of individual cycles, they were normalised to 100% using MatLab 7.0.1. The mean durations of the masticatory cycles were calculated. Additionally, the maximum ranges of rostrocaudal, lateral and dorsoventral mandibular translations were measured. Lateral mandibular excursion was calculated by subtracting the minimum value from the maximum of each respective chewing cycle. The distance of the dorsoventral and rostrocaudal mandibular movements was calculated by subtraction of the maximal and minimal values of the same marker on the respective (X- and Z-) axes. Mean values of at least 15 isolated chewing cycles (five per day of measurement) were generated and the differences were calculated. Mean values and standard deviation were calculated and displayed. Testing for normality of distribution was performed using the KolmogorovSmirnov test. Subsequently, the mean values of all measurements prior to dental treatment were analysed using ANOVA for repeated measures, as were the results post treatment. Results of the measurements before and after dental treatments
were summated in two groups and the mean values of the respective groups were subjected to a paired t-test. The individual results of all horses were compared and analysed for significant differences using the program SPSS 12.0 with statistical difference accepted at P 6 0.05.
Analysis of the ‘power stroke’ The term power stroke refers to the final phase of the masticatory cycle in which food was crushed between the cheek teeth. The moment of contact between maxillary and mandibular cheek teeth was defined as the initial point of each power stroke. According to definition, the end of the power stroke was reached at the most dorsal point of the masticatory cycle. Data of each power stroke was isolated, a trend line was generated and linear regression (R2) was calculated. The results were screened for normal distribution (Kolmogorov–Smirnov test) and statistic analysis (multivariate ANOVA for repeated measures) was performed.
Results Description of masticatory movements Mastication is a 3D movement which can be displayed in three 2D planes (Figs. 5a–c) to be fully understood. A dorsal view was obtained when the movements of marker 9 in relation to the stationary skull markers along the X- and Y-axis were displayed (Fig. 5a).
Fig. 5b. Frontal view of the same horse’s chewing cycle as shown in Fig 5a. Dorsoventral and lateral movements of marker 9 are displayed.
Fig. 4. Dotted lines indicate points of separation of a single masticatory cycle. Xaxis: time; Y-axis: distance (cm).
Fig. 5c. Lateral view of the chewing cycle depicted in Figs. 5a and 5b. Dorsoventral and rostrocaudal movements of marker 9 are displayed.
Table 1 Comparison of mandibular movements before dental correction (in mm). Direction of movements (marker 9) Fig. 5a. Dorsal view of a representative chewing cycle of horse 2 (mean values of 15 chewing cycles, first measurement after dental treatment). Rostrocaudal and lateral movements of marker 9 are displayed.
Trial 1 Trial 2 Trial 3 Mean
Rostrocaudal mandibular movement (X-axis) 9 ± 2 Lateral mandibular movement (Y-axis) 59 ± 7 Dorsoventral mandibular movement (Z-axis) 45 ± 4
9±2 61 ± 7 45 ± 5
9±2 56 ± 7 45 ± 5
9±2 59 ± 6 45 ± 5
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Visualisation of mandibular translocation on the Y- and Z-axis created a frontal (as if standing before the horse) view of the horse’s masticatory movement (Fig. 5b). A lateral view of a masticatory cycle was obtained by transposition along the X- and Z-axis (Fig. 5c).
Masticatory movements before and after dental treatment: comparison of groups
The average duration of a masticatory cycle was 0.70 ± 0.04 s prior to dental treatment and 0.69 ± 0.04 s after dental treatment, which equated to a chewing frequency of 1.4 Hz. The duration of masticatory movements did not change significantly (P = 0.115) after dental treatment.
Mean values and standard deviations for each measurement in each direction of movement are shown in Table 2. The comparison of masticatory movements before and after dental treatment revealed that rostrocaudal mandibular motion (mean before: 9 ± 2 mm) was significantly reduced after dental correction (8 ± 2 mm; P = 0.046). Mean mediolateral mandibular excursion, lateral excursion and dorsoventral mandibular movements, on the contrary, did not change significantly after routine dental correction.
Reproducibility of measurements before dental treatment
Analysis of individual results
The data sets of the three kinematic measurements of each horse before dental correction were used to evaluate the repeatability of the kinematic system. The ranges of lateral and dorsoventral mandibular movement depended on the distance of the respective tracking marker’s position to the point of rotation to the TMJ. The presented data was based on results from marker 9 (caudal end of the inter-mandibular suture). The results of rostrocaudal, mediolateral, total lateral and dorsoventral mandibular motion are shown in Table 1. Statistical analysis revealed no significant differences for the three ranges of motion in all three trials, which suggested that reproducible results could be obtained using kinematic analysis of masticatory movements under standardised conditions.
The results of all individuals before and after dental treatment are displayed in Table 3. Rostrocaudal mandibular movement (Xaxis) varied between 7 and 10 mm both before and after dental treatment. A reduced motion in this direction was observed in 9/ 15 horses. Three horses displayed an increased range of rostrocaudal motion after dental treatment, while three other animals had no change in the motion range. Lateral mandibular excursion ranged from 48 to 68 mm before and from 53 to 71 mm after dental treatment. It increased in 11/ 15 animals and decreased in the remaining four. A significant increase of motion range was found in seven horses and a significant decrease in one individual. Dorsoventral mandibular movements were reduced in 11/15 horses (significant in nine individuals). An increased range of motion was found in three animals with one horse displaying a significant increase. Un-changed results were obtained of one horse.
Duration of masticatory cycles
Table 2 Comparison of mean values of mandibular movements before and after dental correction. Significant changes are indicated (*). Direction of movements (marker 9)
Before dental treatment (mm)
After dental treatment (mm)
Direction of mastication
Mean rostrocaudal mandibular movement (X-axis) Mean lateral mandibular movement (Y-axis) Mean dorsoventral mandibular movement (Z-axis)
9 ± 2*
8 ± 2*
59 ± 6
62 ± 6
45 ± 4
43 ± 4
The direction of chewing changed between measurements for 14/15 horses. Only one horse consistently chewed on the left side (counter-clockwise). During 45 measurements prior to dental treatment, 30 horses (67%) were chewing on the left side (counter-clockwise) and 15 (33%) on the right (clockwise) (chi2: P = 0.053). After dental treatment, this 2:1 ratio changed significantly in favour of the left side with 35 horses (78%) chewing left and 10 (22%) on the right side (chi2: P = 0.0001).
Table 3 Comparison of individual results before and after dental treatment (in mm). Significant changes are indicated (*).
1: WB, g, 14 years 2: Trotter, g, 16 years 3: Trotter, g, 13 years 4: WB, g, 9 years 5: WB, g, 9 years 6: WB, m, 14 years 7: Trotter, m, 6 years 8: WB, g, 15 years 9: WB, g, 16 years 10: WB, g, 15 years 11: WB, g, 15 years 12: Polo, m, 10 years 13: WB, g, 15 years 14: Hafl, m, 5 years 15: Hafl, m, 8 years
Rostrocaudal excursion, Xaxis
Lateral excursion, Y-axis
Dorsoventral excursion, Zaxis
Before
After
Before
After
Before
After
10 ± 2 7±1
9±2 7±2
48 ± 9 68 ± 4
53 ± 3* 65 ± 5
37 ± 3 43 ± 3
44 ± 2* 43 ± 2
8±2
7±2
57 ± 3
62 ± 5*
42 ± 2
40 ± 1*
7±2 9±2 8±2 8±2
9 ± 0.5 8±2 8±4 7±2
58 ± 5 52 ± 5 63 ± 10 65 ± 7
65 ± 9* 60 ± 9* 67 ± 10 71 ± 10
46 ± 2 44 ± 2 43 ± 4 42 ± 2
44 ± 3* 43 ± 2* 41 ± 2* 42 ± 2
9±2 11 ± 2 11 ± 3 8±2 8±2
9±2 13 ± 3 9±2 7±2 6±2
53 ± 6 50 ± 4 68 ± 7 62 ± 6 54 ± 9
59 ± 5* 59 ± 6* 62 ± 9* 69 ± 8* 56 ± 9
51 ± 2 47 ± 3 54 ± 2 49 ± 2 40 ± 3
49 ± 1* 48 ± 2 48 ± 4* 45 ± 2* 40 ± 2
9±3 8±2 13 ± 5
8±2 9±2 10 ± 3
64 ± 6 57 ± 4 61 ± 7
60 ± 4 58 ± 7 56 ± 4
48 ± 2 41 ± 2 45 ± 2
50 ± 4 37 ± 3* 41 ± 3*
WB, Warmblood; Polo, polo pony; Hafl, Haflinger; g, gelding; m, mare.
Analysis of the power stroke Mandibular movements during the power stroke while masticating hay appeared to be significantly ‘smoothened’ after dental treatment. Prior to dental correction linear regression (R2) was 98.3% ± 0.3, after dental treatment a value of 98.8% ± 0.3 was calculated (P = 0.050). Discussion The main advantage of kinematic analysis over other techniques (Leue, 1941, 1944; Salomon and Waysenson, 1979; Plesh et al., 1993) used for measurement of masticatory movements is that it provided quantitative data (Bonin et al., 2006, 2007). Bonin et al. (2007) also hypothesised that kinematic analysis could be utilised to evaluate the range of motion of the TMJ before and after dental procedures in individual animals and in horses with TMJ disease. The aim of this study was to test this hitherto unproven hypothesis. The extent of lateral mandibular excursion and chewing frequency largely depends on the type of food eaten (Leue, 1941; Bonin et al., 2007). Consequently, the present study used
H. Simhofer et al. / The Veterinary Journal 190 (2011) 49–54
standardised hay to compare mandibular movements before and after dental treatment. The comparison of motion ranges of three measurements of individual horses performed on consecutive days before floating revealed constant ranges of motion in all animals, as previously described by Leue (1941), Baker (2002) and Collinson (1994), although differences in motion range were observed between individuals. The majority of horses (14/15; 93%) in this study changed the chewing direction with only one animal consistently masticating on the left side, which differed from the report of Collinson (1994). Interestingly, the trend to chew on the left side (counterclockwise) significantly increased after dental correction in this study. The distribution of markers on the horse’s heads was an important factor for accurate measurement (Bonin et al., 2006) and pilot studies showed that the main tracking marker should be located at the caudal end of the inter-mandibular suture. The thin layer of subcutaneous soft tissue at this site minimised skin displacement compared to other locations. Skin displacement was a major source of potential systematic error in kinematic studies (Van Weeren et al., 1990; Bonin et al., 2006, 2007) and no correction algorithms for skin displacement on the equine head were available (Bonin et al., 2006). Placement of the main tracking marker as described above eliminated the need for a virtual midline marker, as described by Bonin et al. (2006, 2007). The positioning of markers may also significantly influence the results of translational movements (Bonin et al., 2007). For example, we measured a mean lateral translation of 50 mm (53 mm after dental treatment) with a marker placed caudal to the level of the incisors, which was greater than reported (45 mm) when the marker was at the level of the incisors (Collinson, 1994; Baker, 2002) or fourth premolar (19.9 mm; Bonin et al., 2006, 2007). However, the mean rostrocaudal translation of 9.0 mm (8.0 mm after treatment) in the current study was comparable to one earlier study (9.8 mm; Bonin et al., 2006), yet higher than a further study (6.1 mm; Bonin et al., 2007), the latter of which was consistent with clinical measurements (Carmalt and Allen, 2006; Carmalt et al., 2006). Dorsoventral mandibular movement (45 mm before and 43 mm after treatment) was wider than reported previously (Bonin et al., 2006, 2007). However, the different marker positions in the respective studies and the varying distances of the markers to the temporomandibular joints made a direct comparison impossible. Furthermore, the frequency of mastication while chewing hay was slightly higher in the current study (1.4 Hz) than described elsewhere (1.2 Hz; Bonin et al., 2007). Variable factors, including the composition of food, size and breed of the horse and individual chewing patterns have a significant influence on mandibular excursions (Leue, 1944; Baker, 2002; Collinson, 1994; Bonin et al., 2006, 2007). We also observed considerable variation of movement ranges and patterns, similar to that reported previously (Baker, 2002). While excessive focal dental overgrowths and periodontal disease are painful conditions which might severely compromise mastication (Dixon and Dacre, 2005), the presence of less severe overgrowths might simply impede normal mandibular kinematics. The current study found that reduction of focal dental overgrowths on equine cheek teeth changed masticatory movements, although the horses used did not react uniformly to routine dental treatment, so the assumption that the reduction of focal dental overgrowths would result in larger lateral excursions could not be verified. Indeed, 4/11 horses displayed reduced lateral excursions, which may have related to the fact that horses display a variety of different mastication patterns prior to any dental correction (Leue, 1941; Baker, 2002). Rasping teeth inevitably resulted in the smoothening of certain parts of the masticatory surface, which may have forced some
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horses, at least temporarily, to adapt their mastication to a more vertically orientated pattern (Bonin et al., 2007). More comprehensive studies are therefore required to determine the basic patterns of mastication, which were first described by Leue (1944). Furthermore, some equine dental practitioners suggest that dental correction will increase the rostrocaudal movement of the mandible (Carmalt and Allen, 2006; Carmalt et al., 2006), although this approach reduced rostrocaudal mandibular movement in 9/15 animals in the current study. A possible explanation might be that the ridges of the cheek teeth, after being reduced, do not need to be ‘brought into position’ to match the corresponding grooves in the opposing dental row during the power stroke. It should therefore be considered that some horses may not need to move the mandible as much rostrally after dental correction while chewing and that an increased range of motion does not necessarily indicate improved mastication (Carmalt et al., 2006). Moreover, the type and extent of dental treatment will depend in underlying pathology, so variability of the resulting masticatory movements after dental treatment could be expected. It is therefore difficult to interpret the changed masticatory movements induced by dental therapy. Further studies combining kinematic analysis with quantitative measurements of chewing forces (Staszyk et al., 2006; Huthmann et al., 2009) might provide a greater understanding of mastication and the individual reactions of individual horses to dental therapy. Conclusions It has been demonstrated that kinematic analysis of equine masticatory movements provides reproducible results. This method was also found suitable for the evaluation of changed masticatory movement patterns following dental correction. Conflict of interest statement None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper. Acknowledgements The authors want to thank James Carmalt and Edmund Hainisch for proof reading and valuable suggestions. References Baker, G.J., 1999. Dental physiology. In: Baker, G.J., Easley, J. (Eds.), Equine Dentistry. W.B. Saunders, London, pp. 29–34. Baker, G.J., 2002. Equine temporomandibular joints (TMJ): morphology, function and clinical disease. In: Proceedings of the 48th Annual Convention of the American Association of Equine Practitioners, pp. 442–447. Bonin, S.J., Clayton, H.M., Lanovaz, J.L., Johnson, T.J., 2006. Kinematics of the equine temporomandibular joint. American Journal of Veterinary Research 67, 423– 428. Bonin, S.J., Clayton, H.M., Lanovatz, J.L., Johnston, T., 2007. Comparison of mandibular motion in horses chewing hay and pellets. Equine Veterinary Journal 39, 258–262. Carmalt, J.L., Allen, A.L., 2006. The effect of rostro-caudal mobility of the mandible on feed digestibility and fecal particle size in the horse. Journal of the American Veterinary Medical Association 229, 1275–1278. Carmalt, J.L., Townsend, H.G.G., Allen, A.L., 2003. Effect of dental floating on the rostrocaudal mobility of the mandible of horses. Journal of the American Veterinary Association 223, 666–669. Carmalt, J.L., Townsend, H.G.G., Janszen, E.D., Cymbaluk, N.F., 2004. Effect of dental floating on weight gain, body condition score, feed digestibility, and fecal particle size in pregnant mares. Journal of the American Veterinary Association 225, 1889–1893. Carmalt, J.L., Carmalt, K.P., Barber, S.M., 2006. The effect of occlusal equilibration on sport horse performance (dressage). Journal of Veterinary Dentistry 23, 226– 230.
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