Orthodontic correction of overjet/overbite ('parrot mouth') in 73 foals (1999-2013)

Comparison of Computed Tomography Assisted 3D Cephalometric Measurements in Straight Egyptian Arabian and Thoroughbred Horses

Dental malocclusions are commonly encountered in horses. The objective of this study was to report the normal cephalometric values from skull computed tomography (CT) scans of adult Straight Egyptian Arabian (SEAR) and thoroughbred (TB) horses and to compare differences in the measurements between the two breeds. Standing skull CTs were performed on 29 clinically normal adult horses (15 SEAR; 14 TB) and cephalometric measurements were taken. All 9 cephalometric measurements, as well as the interincisal angle, were found to be significantly greater in TB than SEAR (P < 0.05). TB were found to have significantly greater facial line: mandibular length (FL/ML) ratios compared to SEAR (P = 0.002) whereas for the maxillary cheek teeth length: ethmoidal line ratio (Mxa/EtL), SEAR were found to have significantly greater values than TB (P = 0.0007). SEAR cephalometric measurements, as well as certain ratios, differ significantly from TB and could have an impact on the development of dental malocclusions in this breed. Further investigation is needed to ascertain whether these cephalometric differences between the two breeds predispose the SEAR to the development of dental malocclusions.

The use of the geometric morphometric method to illustrate shape difference in the skulls of different-aged horses

The geometric morphometrics method (GMM) is a technique to study scale and shape relationships of structures using Cartesian geometric coordinates rather than linear, areal (of area), or volumetric variables. GMM has been of great value in many biological studies, but does not appear to have been used to examine equine skulls.

In this exploratory study, twenty-nine normal equine heads of three different age groups: <5 years old (N = 9), 6–15 years old (N = 10) and > 16 years old (N = 10) were examined.

Computed tomography (CT) bone window DICOM images were reconstructed into isosurfaces (3-dimensional contoured surfaces), onto which landmarks were added using Stratovan Checkpoint® software. Data from 29 landmarks were analysed using MorphoJ analysis, which applies a Procrustes fit, prior to reducing data dimensionality through principal component (PC) analysis. PCs with and without allometry were considered. Allometric shape described by PC1 accounted for 27% of variance. Loading pertaining to: the pterygoid process, bilaterally; caudal aspect of hard palate; tip of nasal bone; ethmoid sinuses, bilaterally; caudal aspect of the ventral conchal bulla, bilaterally and caudal aspect of the vomer bone suggest that these anatomical structures are predictive of age group. When allometric effects (shape variation explained by size) were removed, PC1 was unable to distinguish horses by age group. Allometric shape differences could distinguish the youngest versus the two older age groups. The potential applications of GMM in equine diagnostic imaging are wide ranging and include the investigation of changes in the equine skull with respect to genetics and characterisation of conformation-related diseases affecting the teeth, jaws and sinonasal compartments.

Cephalometric Study of the Overjet Development in Warmblood Foals

Class II malocclusion is the most frequently occurring congenital malocclusion in horses. Radiographic cephalometric procedures adopted from human dentistry were used to study the development of overjet in a population of 650 Warmblood foals. Thirteen foals were diagnosed with measurable overjet at the beginning of the study. The malocclusion in nine foals resolved spontaneously and four foals without overjet at 2 weeks of age developed the condition during the first year of life. A cephalostat used in human orthodontics to immobilize the patient's head while being radiographed was replaced by a researcher-made head-holding device, whose size was based on the results of a pilot study. Laterolateral digital radiographs of each foal's head (cephalograms) were taken at five time points until the age of 12 months. Thirteen cephalometric points were identified and nine distances were measured on each radiograph. Additionally, the angle between the long axis of the upper and lower incisors was evaluated. Cephalometric measurements proved to be useful to identify foals that showed spontaneous regression of the malocclusion over the study time between 9 and 16 weeks of age.

Treatment of class 2 malocclusion by corrective osteotomy using two short locking compression plates

Objective

To describe a symphyseal osteotomy stabilised with two short locking compression plates (LCPs) for treatment of class 2 malocclusions.

Study design

Case series.

Methods

Five horses (age range 8 months to 5¾ years) with overjets and/or overbites ranging from 6 to 32 mm and from 0 to 60 mm, respectively, were treated by osteotomy through the caudal third of the mandibular symphysis, cranial to the interdental space. After cranial distraction and ventral rotation of the rostral part of the mandible, two short (5/6 hole), bent 3.5 mm LCPs were applied ventro‐laterally and secured with two or three locking screws on each side of the osteotomy. In one case, the osteotomy gap was filled with bone marrow.

Results

Final outcome was good to excellent. Two cases needed a second corrective surgery, one because of non‐occlusion of the cheek teeth and another because of abaxial deviation of the rostral portion of the mandible. In three cases with a persistent fistula, LCPs were removed after bridging; drainage resolved and wounds healed. The time to bridging of the osteotomy gap ranged from 2 to 6.5 months. The procedure is technically challenging. It is important that the incisors are well aligned, which proved to be difficult when there was an abnormal maxillary incisor arcade. Incisors should not make contact when LCPs are fixed. The cheek teeth, however, should have good occlusion after positioning and fixation of the LCPs. Endodontic treatment of open incisor pulp cavities may be helpful.

Main limitations

The study population was small and relatively heterogeneous in severity. A larger population with more severe cases might have allowed for a more definitive assessment of the value of the technique for clinical practice.

Conclusions

This technique can be used to achieve a good correction for class 2 malocclusions. The approach provides adequate stability with smaller implants than other published techniques that require transection of both rami. The technique is less invasive and preserves the roots of the incisors and cheek teeth, as well as the mandibular canal.

Study of the relationship between overjet development and some skull bone measurements in Warmblood foals

Overjet is defined as the projection of the maxillary incisors labial to their antagonists in a horizontal direction. This malocclusion in horses can lead to incorrect dental wear and is aesthetically undesirable. Whether lengthening of the maxilla or shortening of the mandible causes the condition has not yet been determined. Therefore, a measurement technique was developed to investigate the correlations between skull bone measurements in overjet-affected individuals. The position of the incisors in 650 Warmblood foals born in a private German stud was examined at two weeks of age, revealing the prevalence of overjet to be 2 per cent. Five measurements were made on each foal's head and comparisons with a second set of measurements that were made later in the foals first year showed a change in the presence or degree of overjet over time. Nine of 13 foals diagnosed with measurable overjet at the beginning of the study resolved spontaneously. Thirteen foals had no evidence of overjet at birth, of which four developed the condition during the first year of life. The methods used for measuring longitudinal changes in different skull bones and for the assessment of malocclusion in foals affected with overjet were considered effective.