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RCPV (2014) 109 (589-590) 21-25

Resumo: De forma a investigar a prevalência de diastemas aber-tos ou oclusos e a sua associação com doenças periodontais, foram efectuadas examinações dentárias completas em dentes molares de 50 cadáveres de cabeças de cavalo. Diastemas aber-tos (mediana=2) apresentaram um maior grau de desenvolvi-mento de doenças periodontais (P<0.001) que diastemas oclusos (mediana=0); éguas (mediana=2) apresentaram mais elevado grau de desenvolvimento de doenças periodontais (P<0.01) que cavalos castrados (mediana=1); e dentes na mandíbula (media-na=2) apresentaram mais elevado grau de desenvolvimento de doenças periodontais (P<0.001) que em maxilas (mediana=1). Uma regressão logística foi ajustada aos dados recolhidos para modelar a probabilidade de diastemas abertos ou oclusos, que resultou num racio de “odds” (2.351) que favorece as éguas (em oposição a cavalos castrados) no desenvolvimento de diastemas abertos (P<0.01); as maxilas (em oposição a mandíbulas) apre-sentam também “odds” favoráveis (1.994) ao desenvolvimento de diastemas abertos (P<0.05); e grau de desenvolvimento de doenças periodontais correlaciona-se (ratio de “odds” de 2.092) com diastemas abertos (P<0.001).

Palavras-Chave: cavalos, odontologia, diastemas, doenças pe-riodontais

Abstract: To investigate the prevalence of open and closed diastemata and association with periodontal disease, thor-ough dental examinations were performed on cheek teeth of 50 cadaver horse heads. Open diastemata (median=2) have a higher degree of periodontal disease (P<0.001) than closed di-astemata (median=0); mares (median=2) have a higher degree of periodontal disease (P<0.01) than geldings (median=1); and mandible teeth (median=2) have higher degree of periodontal disease (P<0.001) than maxilla (median=1). A logistic regres-sion was fitted to the data to model the probability of devel-opment of open vs. closed diastemata, and it was found that mares have favourable odds ratio (2.351) for the development of open diastemata (P<0.01); maxilla have a favourable odds ratio (1.994) for the development of open diastemata (P<0.05); and degree of periodontal disease relates (P<0.001) with open diastemata (odds ratio of 2.092).

Key Words: equine, dentistry, diastemata, periodontal disease.

Introduction

Equine diastemata are defined as a pathological dental condition that presents as abnormal spaces between two adjacent teeth within the same dental arcade (Carmalt, 2003), and its prevalence varies (e.g. Carmalt, 2003; Ramzan and Palmer, 2011). Presence of cheek teeth diastemata is considered to be grossly under-diagnosed because of its difficult to find when examining animals in vivo (Collins and Dixon, 2005).

Cheek teeth diastemata can be congenital or acquired (Collins and Dixon, 2005). Congenital diastemata are considered a result of absent or abnormally spaced dental buds (Carmalt and Wilson, 2004) thus leading to gap formation (Carmalt, 2003). Acquired diastemata develop primary due to dental displacements, fractured crowns, tooth loss and iatrogenic interference by the premature removal of deciduous teeth (Carmalt, 2003), and also secondary as a result of dental migration (Car-malt and Wilson, 2004).

Carmalt (2003) first introduced a distinguishable classification for the two types; diastemata that, ‘re-gardless of trapping feed between adjacent teeth and contributing to the presence of halitosis, do not re-sult in any clinically discernible oral pain or gingival pathology’ can be classified as open; In comparison, closed (valve) diastema is described as the pres-ence of painful spaces between adjacent cheek teeth caused by inaccurate angulation. Open diastema should allow for the ingress and egress of feed ma-terial and valve diastemata presents as a ‘triangular shaped defect’, where feed material can only ingress (Carmalt and Wilson, 2004).

The primary development of diastemata occurs as a result of insufficient rostro-caudal angulation of the cheek teeth, whereby the dental buds with nor-mal angulation develop too far apart (Dixon, 2006). Consequently, insufficient compression occurs on

A prevalência de diastemas abertos ou oclusos em dentes molares de cavalos e a sua associação com doenças periodontais

The prevalence of open and closed diastemata in cheek teeth of horses and its association with periodontal disease

Fernando Mata*, Claire Johnson, Ashton Flavell-Irving)

Department of Animal & Land Sciences, Health & Welfare Research Group, Hartpury College, University of the West of England, Hartpury, Gloucester, GL19 3BE, UK

*Correspondência: fernando.da-mata@hartpury.ac.ukTel: +44(0)1452702345; Fax: +44(0)1452700629

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the occlusal surface of the cheek teeth thus allowing interdental spaces to open (Baker and Easley, 2005). As the horse ages the cheek teeth remain tapered in towards their apices and the reserve crown becomes progressively smaller (Dixon, 2006). Tight com-pression at the occlusal surface of the cheek teeth is maintained by progressing eruption of the angulated rostral and caudal cheek teeth (Dixon, 2006). How-ever as the horse ages and progresses into the geriat-ric category the reserve crown ultimately wears away and can no longer achieve compression, therefore, as a result diastemata develop (Dixon, 2006).

Diastemata can develop secondarily in conjunc-tion with the development of acquired cheek teeth displacements (Dixon, 2006). Dixon et al. (1999) proposed that cheek teeth displacements occur due to congenital or acquired defects. Congenitally dis-placement of caudal cheek teeth are considered to be more frequent (Dixon et al., 1999) and develop as a result of overcrowding of the dental arcades during the eruption period (Dixon and Dacre, 2005). Open diastemata can occur between the displaced and ad-jacent teeth suggesting displacements materialise due to abnormal spacing of the tooth bud, rather than overcrowding of the arcades, which, depending on breed type, can also be an occurring factor (Dixon and Dacre, 2005).

Due to the pathological nature of equine diastem-ata, feed material can become deeply impacted into the gingiva and periodontal tissues (Dixon et al., 2008). As a result of this, periodontal food pockets develop where food impaction becomes deeper and contribute to progressive stretching, inflammation and obliteration of the periodontal ligament (Dixon, 2006). The presence of impacted feed stasis and the results of its decomposition trigger the events of per-iodontal disease (Klugh, 2005).

Material and methods

Fifty cadaver heads were used in this study. These were collected from Potters abattoir, in Taunton, Somerset, United Kingdom. A convenience sampling method was implemented, as all the horses used for collection of data were the ones available for eutha-nasia during a single day at the abattoir.

Severity of present periodontal disease was graded from 0-4 by matching the clinical signs described in the periodontal grading system to the clinical signs presented in each cadaver, as proposed by Klugh (2005) (Table 1). The “diastemata prevalence” was visually identified using a torch and dental mir-ror and the “diastemata prevalence” classification (“open”, “closed”) was established using the defini-tions proposed by Carmalt (2003) (Table 2).

Due to the dichotomy nature of the variable “di-astemata prevalence” (“open”, “closed”), several generalised linear models with links belonging to the

binomial family, were adjusted and that with the best fit was chosen. The goodness of fit was evaluated via Deviance and Akaike’s Information Criterion (AIC), being the best fit achieved with a logistic regression.

Three factors (“gender”, “jaw” and “side”) and two covariates (“age” and “degree of periodontal disease”) were used to model and predict prevalence of “open” or “closed” diastemata. The levels considered for the different factors were: “gender” (“gelding”, “mare”); “jaw” (“maxilla”, “mandible”); and “side” (“right”, “left”). A backwards stepwise procedure for selection of significant variables and covariates was implemented, and those found to be significant were left in the model.

“Degree of periodontal disease” was also ana-lysed via Mann-Whitney U test for “gender” (“geld-ing”, “mare”); “jaw” (“maxilla”, “mandible”); “side” (“right”, “left”) and “diastemata prevalence” (“open”, “closed”). Age was also analysed via independent sam-ples Students t test and was correlated with “degree of periodontal disease” via Spearman’s rank correlation.

Table 1 - Stages of Periodontal Disease (Klugh, 2005)

Stage Clinical signs

0 Normal periodontium where there is no attachment loss and depth of the gingival sulcus is 5mm or less.

1Presence of gingivitis, gingiva swollen and reddened. Gin-gival sulcus is normal depth and also there is no attachment loss. Any cemental disease remains supraginginval.

2

Feed material is trapped in the interproximal space and further progression presents as a periodontal pocket packed with food stasis, attachment loss is 25% and sul-cus depth is greater than 5mm.

3Moderate periodontal disease, where further attachment loss occurs, presence of periodontal pockets is similar to stage 2 and sulcus depth is greater than 5mm.

4

Severe periodontal disease including, gingival re-cession, ulceration, edema, gross periodontal pock-eting, lysis of alveolar bone and loose teeth. In se-vere cases the cementum is decayed and the secular epithelium is necrotic with possible presence of pu-rulent discharge.

Table 2 - Classification of diastemata prevalence (Carmalt, 2003)

Diastema prevalence Clinical signs

Open

Pathological gaps between adjacent cheek teeth that interrupt the normal consistency of the oc-clusal surface. Feed material can ingress and egress.

Closed (valve)

The valve is enclosed rostrocaudally by the cheek teeth, ventrally by the gingiva and dorsally by the occlusal surface of the dental arcade. Feed materials can only ingress.

The statistical package used was the SPSS/PASW© Statistics 18. The Research was approved by the Ethics Committee of the University of the West of England (Hartpury College) (Reference: ETHICS2010/22-S).

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Results

This study shows a total of 317 diastemata recorded from the sample of 50 cadaver heads used. From these 36.9% (117/317) were recorded as “closed” diastema and 63.1% (200/317) were recorded as “open” di-astema. Also 68.8% (218/317) were observed in the maxilla and 31.2% (99/317) in the mandible. There is a prevalence of diastemata accompanied with periodontal disease (198/317, 62.5%) against 37.5% (119/317) not accompanied by periodontal disease. Figure 1 shows the distribution of diastemata through the dentition in our study and in Ramzon and Palmer (2011); the comparison of both studies show a sig-nificant difference in the distribution (Χ2=293.7, P<0.001).

The “degree of periodontal disease” is signifi-cantly different between: “mare” (median=2) and “geldings” (median=1) (Mann-Whitney U=7261, P<0.01); “open” (median=2) and “closed” (me-dian=0) (Mann-Whitney U=7568, P<0.001); and “mandible” (median=2) and “maxilla” (median=1) (Mann-Whitney U=8540, P<0.001). Age is not sig-nificantly different (Student t=1.142, P>0.05) be-tween “open” and “closed”, and also does not cor-relate with “degree of periodontal disease” (Spear-man’s ρ = 0.051, P>0.05).

For the logistic regression modelling “diastemata prevalence” the factors “jaw” (P<0.05) and “gender” (P<0.01) were found to be significant, as well as the covariate “degree of periodontal disease” (P<0.001). The full description of the equation parameters is pre-sented in table 3, where the 95% confidence intervals are also stated, together with the odds ratios. For the factor “jaw”, the level “mandible” was set as the refer-ence and as can be read in the table, “maxilla” led to a 135% increase in the odds ratio of “open” vs. “closed” diastema. Therefore, diastemata have a higher prob-ability of being open if located in the maxilla.

Figure 1 – Comparison of percentages of diastemata observed in the different interproximal positions between cheek teeth in hors-es. From the centre to the extreme: maxilla, right 1 to 5; maxilla, left 6 to 10; mandible, left 11 to 15; mandible, right, 16 to 20.

Figure 2 - Logistic curve graphing the probability of open dias-temata, as function of gender (mare, gelding), jaw (mandible, maxilla) and degree of periodontal disease.

Figure 3 - Logistic curve graphing the probability of closed diastemata, as function of gender (mare, gelding), jaw (mandi-ble, maxilla) and degree of periodontal disease. Obtained as the complementary probability of open diastemata.

Table 3 – Logistic regression equation parameters to model “prevalence of open diastema”, as function of the factors “gender” and “jaw” and the covariate “degree of periodontal disease”.

Variables in the equation β SE (β) P-value 95% CI (β) OR (eβ) 95% CI OR (eβ)

Gender Mare 0.855 0.283 < 0.01 0.301 1.409 2.351 1.798 2.905

Gelding 0

Jaw Maxilla 0.690 0.286 < 0.05 0.129 1.251 1.994 1.440 2.548

Mandible 0

Periodontal disease 0.738 0.103 < 0.001 0.536 0.940 2.092 1.538 2.646

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Relatively to the factor “gender”, the level “gelding” was treated as reference, and “mare” leads to an in-crease in 99% in the odds ratio of “open” vs. “closed” diastema. Therefore, diastemata have a higher proba-bility of being open in mares rather than geldings. Fi-nally, the covariate “degree of periodontal disease” was found to be positively related with open diastemata and therefore, the higher the degree of periodontal disease the higher the probability of finding open diastemata. Figure 2 uses the logistic regression fitted to graph the probability of finding open diastemata in dependency of the factors and covariate considered in the model; with figure 3 being its complement.

Discussion

Throughout the literature it is frequently acknow-ledged that cheek teeth diastemata are more prone to occur within the caudal aspect of the mandibular ar-cades (e.g. Dixon et al., 1999; Dixon et al., 2008; du Toit et al., 2009). Our results show the same tendency, but with regards to the type of diastemata, our study shows that within the maxilla, open diastemata (oD) has a higher prevalence (P<0.05) than within mandi-ble. The distribution of diastemata through the diffe-rent interdental spaces of cheek teeth did not show a specific pattern apart from the fact that the number of observations is higher in the mandible. The lack of agreement (P<0.001) with Ramzon and Palmer (2011) in this distribution is the illustration of lack of patterns and existence of some randomness.

Results from the current study illustrate that the ma-jority of diastemata are accompanied with periodontal disease (PD) (198/317, 62.5%), which agrees with the trends of previous studies (e.g. Dixon et al., 2008; du Toit et al., 2008; Simhofer, et al., 2008). The investi-gation of association of degree of PD with diastemata showed a positive relation between oD and degree of PD (P<0.001). Carmalt (2003) suggest that oD do not associate with discernible oral pain or gingival patho-logy, such as PD. He also suggested that closed diaste-mata (cD) is concerned with oral pain and the trapping of feed materials, thus leading to the bacterial degrada-tion of feed material and the development of gingivitis and PD. Carmalt (2003)’s suggestion is not confirmed by this study, however PD has been associated with older (>15 years) horses (Casey and Tremaine, 2010), with the same association being seen with regards to oD and aged horses by Townsend et al. (2008) and, therefore both PD and oD correlate positively with age and associate each other. The observation of Vlaminck et al. (2006) that PD is a slow progressing disease also corroborates this hypothesis, once if it is a slow pro-gress, tends to be prevalent in older animals.

Degree of PD is also shown to be higher in oD than cD (P<0.01). We observe a higher probability of fin-ding oD in the maxilla and therefore we were expec-ting the degree of PD to be higher in the maxilla, whi-

ch does not happen. The mandible has in fact a higher degree of PD than the maxilla (P<0.01), resulting from the difference between diastemata cases (much higher in mandibles, independently of type of diastemata). It can therefore be stated from these findings that the ma-xilla is less likely to contain diastemata, but those that are present have a higher probability of being open and developing PD, whereas the mandibles are more likely to have a higher quantity of diastemata with these, indi-vidually, having lower probabilities of being open and therefore developing PD.

Age has been studied as a contributing factor to the prevalence of diastemata and there is literature associa-ting age with PD and diastemata (e.g. Carmalt, 2003; Carmalt et al., 2004; du Toit et al., 2009), however in our study no relations between age, degree of periodontal di-sease and type of diastemata were established (P>0.05), which may be due to chance, as this relationship has be-come evident in several previous studies.

With regards to difference between gender it was found that mares have a higher degree of periodontal disease (P<0.01) and also higher odds (P<0.01) for oD vs. cD. This is an aspect not referred before in the literature, but it was already noted by Ramzan et al. (2009) the existence of sexual dimorphism in horse te-eth. In humans it was reported that men have higher salivary Ca than Women, and that high level of salivary Ca are positively correlated with dental health (Sewón et al., 1998).

In conclusion there is limited research relating PD with the prevalence of oD and cD. The current study brings some light into this gap, showing the higher pro-bability of development of PD in oD. With regards to gender and jaw, mares and maxilla have higher odds for development of oD than gelding and mandible. PD degree is higher in mares, oD and mandible when each variable is considered separately.

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