EQUINE DENTAL SINUSITIS
four of these horses, minor alveolar sequestrae causing delayed alveolar healing was found to be the reason for therapeutic fail- ure. The treatment of all four horses turned out to be success- ful subsequently to removal of these alveolar sequestrae, that is, still without the use of AB or sinus lavage. This result underlines the mechanical nature of these sequestrums as a complication to dental extraction itself (Christiansen et al., 2023 ). Due to the ret- rospective nature of this study, the exact causes of therapeutic failure following initial treatment in the remaining 19 horses were not available. Nevertheless, 10 of these 19 horses were admin- istered AB of which four horses turned out to be successful. In other cases, where both initial treatment and subsequent medical treatment failed, presence of liquid/inspissated exudate and/or bone sequestrae within the sinuses combined with impaired sino- nasal drainage, have been reported to be the main reason for non- response to these treatments (Dixon et al., 2012b , 2021 ). In such cases, trephination and sinus flap surgery have become effective ways of removing exudates from the sinuses (Dixon et al., 2021 ; Perkins et al., 2009 ; Quinn et al., 2005 ). A study by Tremaine and Dixon ( 2001b ) describes how 78% (39/50) of horses with dental sinusitis ended up being successful when repulsion was performed in all cases by means of sinusotomy, combined with lavage and AB for several days. In another study by Dixon et al. ( 2012a ), 82% (28/34) of dental sinusitis cases were reported as fully cured when sinus flap surgery and sinus lavage were performed in, respec- tively, 55% (22/40) and 78% (31/40) of the horses. In the present study, a total of 88.1% (52/59) of horses ended up being success- ful with sinus surgery (sinus trephination) performed in only 12% (7/59) of the horses. Considering that the same overall success rate can be achieved when using AB and invasive sinus lavage in only a subset of cases, makes it worth considering if the use of these invasive procedures should be limited to selected cases. The decision to perform sinus surgery and/or lavage initially should be based on principles of minimising both trauma to the horse, hos- pitalisation time and costs to the owner, while at the same time considering the severity/chronicity of disease and thus the need for additional invasive surgery. Moreover, other studies have sug- gested that minimally invasive transnasal approaches appear to be promising and cheaper alternatives to invasive procedures such as trephination and sinus flap surgery, which was also the case in the present study, where transnasal lavage was successfully used in three horses (Jehle et al., 2022 ; Kolos et al., 2020 ; Morello & Parente, 2010 ).
Other findings
Other variables with potential effect on the probability of suc- cess after initial treatment were tested by univariate analysis. None of the variables breed ( p = 0.59), tooth ( p = 0.31) and ex- traction method ( p = 0.64) were neither found to have a signifi- cant effect on the probability of AB administration nor on the probability of success after initial treatment. Despite the lack
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of significance related to extraction method, the findings in the study by Christiansen et al.
( 2023 ) indicate that horses sub-
jected to MTE still may be candidates for perioperative AB to decrease the risk of postoperative complications. From a clinical perspective, duration of clinical signs prior to admission may in- fluence the therapeutic outcome in horses with dental sinusitis. Previous studies have indicated that the presence of inspissated pus within the sinuses is commonly involved in chronical cases of dental-related sinusitis, particularly in older horses (Easley & Freeman, 2013 ). However, in this study, neither age ( p = 0.68) nor duration of clinical signs ( p = 1) were found to have any significant association with the probability of success after initial treatment. Also, prior AB administration ( p = 1) was not significantly associ- ated with the probability for success after initial treatment in this study. Prior AB administration in the days leading up to dental ex- traction potentially creates a bias in the outcome of some horses not receiving peri-operative AB during extraction. However, since the majority of horses in this study are referral cases, the specific time of prior AB administration is not known. In addition, a study by Gergeleit et al. ( 2018 ) suggests that prior AB therapy is likely to cause alterations in the microbiological composition in cases of sinusitis. The potential selection of resistant bacteria may influ- ence the effect of perioperative AB. Presently, the above circum- stances, therefore, make any conclusions on the impact of prior AB administration impossible.
Main limitations
The main limitation of this study is the retrospective design in terms of data collection from clinical records as well as follow- up information. Attempts were made to ensure retrieval of any missing information by sending written questionnaires to owners with a potential risk of recall bias, due to the inability of owners to accurately recall information in some cases regarding course of disease and treatment. Preferably, both unsuccessful and suc- cessful horses should have been admitted for follow-up examina- tion by the same veterinarian from HTK, to ensure validity of the outcomes. Another limitation of a retrospective study can be lack of uniformity, both in terms of diagnostic procedures and treat- ments. To ensure the accuracy of the diagnosis and increase the reproducibility of this study, the ideal would have been to per- form the same diagnostic steps for all horses. However, due to the availability of diagnostic tools in the study, this has not been possible to do. The limited number of individuals in some of the groups related
to the variables ‘Breed’, ‘Tooth’ and ‘Extraction method’, moreover, is a limitation of this study. Therefore, any significant potential con- founding or interaction effects, if any, cannot be identified in the results. It would require a larger number of individuals in each group to properly identify any potential effect of these variables on the probability of receiving AB or probability of success after initial treatment.
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