A long-term study on the clinical effects of mechanical widening of cheek teeth diastemata for treatment of periodontitis in 202 horses (2008–2011)


  • P. M. Dixon,

    Corresponding author
    1. Department of Clinical Veterinary Studies, Royal (Dick) School of Veterinary Studies and Roslin Institute, Easter Bush Veterinary Centre, University of Edinburgh, UK
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  • S. Ceen,

    1. Department of Clinical Veterinary Studies, Royal (Dick) School of Veterinary Studies and Roslin Institute, Easter Bush Veterinary Centre, University of Edinburgh, UK
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  • T. Barnett,

    1. Department of Clinical Veterinary Studies, Royal (Dick) School of Veterinary Studies and Roslin Institute, Easter Bush Veterinary Centre, University of Edinburgh, UK
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  • J. M. O'Leary,

    1. Department of Clinical Veterinary Studies, Royal (Dick) School of Veterinary Studies and Roslin Institute, Easter Bush Veterinary Centre, University of Edinburgh, UK
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  • T. D. Parkin,

    1. School of Veterinary Medicine, Boyd Orr Centre for Population and Ecosystem Health College of Medical, Veterinary and Life Sciences, University of Glasgow, UK
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  • S. Barakzai

    1. Department of Clinical Veterinary Studies, Royal (Dick) School of Veterinary Studies and Roslin Institute, Easter Bush Veterinary Centre, University of Edinburgh, UK
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Reason for performing study

Cheek teeth diastemata are a common cause of painful periodontal disease in horses, but there is limited objective information on their treatment.


To assess the long-term response to diastema widening in clinically affected horses.

Study design

Retrospective study.


Medical records from cases of cheek teeth diastemata treated by diastema widening referred to the University of Edinburgh Equine Hospital from 2008 to 2011 were analysed.


During this period, 302 horses were diagnosed with clinically significant cheek teeth diastemata, of which 202, median age 11 years, with severe associated periodontitis were treated by widening of 674 problematic diastemata; 89.8% between mandibular cheek teeth and 10.2% between maxillary cheek teeth, with a mean of 1.5 treatments performed per case. These 202 cases showed quidding in 76.2%; weight loss in 33.2%; bitting problems in 20.1% and halitosis in 10.9%, with 5.4% being asymptomatic. Follow-up of 92% of treated cases, a mean of 20.8 months after their initial treatment, showed that 72.6% had complete remission of clinical signs that was permanent (for the duration of this study) in 50.5% and temporary in 22%. A partial response was obtained in 17.2%, no response was obtained in 4.3%, and owners were unsure of response in 5.9%. Clinical improvement was sometimes delayed, with 19% taking >4 weeks following treatment for improvement. Inappropriate sites were burred in individual teeth of 6 horses, causing iatrogenic pulpar exposure in 2 cases, but following treatment none developed clinical signs of apical infection.


Diastema widening is an effective but potentially invasive treatment for horses with cheek teeth diastemata with severe periodontitis.

Potential relevance

Diastema widening by trained personnel is suitable for advanced cases of cheek teeth diastema, but many cases require repeated treatments.


Diastema of equine cheek teeth was briefly described in some early literature [1], but over the past 15 years this has been recognised as a very common and significant equine dental disorder [2-4]. Currently, cheek teeth diastema is recognised as the main cause of oral pain and quidding in referred dental cases in the UK [5, 6]. Some degree of cheek teeth diastema is common in horses, and a recent survey in a UK first opinion equine practice showed that 49.9% of horses having dental examinations had cheek teeth diastemata, and periodontal disease was associated with 40% of these [7]. Older equids also have a high prevalence of cheek teeth diastemata, and 85% of geriatric donkeys [8] and 42% of geriatric horses [9] being affected. Equine cheek teeth diastemata have been classified as: primary diastemata (believed to be due to inadequate angulation of cheek teeth or from cheek teeth developing too far apart); secondary diastemata (e.g. caused by displaced or supernumerary teeth, or by overgrowths at the periphery of cheek teeth rows); and senile diastemata (caused by the normal tapering in of teeth in an apical direction, along with age-related loss of angulation of the 06s and 11s) [10]. Horses may have a combination of these types of diastemata. The shape of diastemata has also been classified as open or closed [11] and du Toit et al. showed the interproximal space at the occlusal surface of valve diastemata to be about 40% of their width at the gingival level, in contrast to open diastemata, which have a similar width throughout the depth of the diastema [12].

Currently, there is little consensus concerning the treatment of cheek teeth diastemata [4], which previously included extraction of adjacent teeth, or reduction of the occlusal surface of the 2 teeth adjacent to the diastema and sometimes of the opposing teeth [5]. Some operators just remove the food from diastema-related periodontal pockets, whereas others fill the emptied diastema with soft plastic or hard acrylic-based bridging materials to help prevent further food impaction. Diastema widening is also used to treat clinically significant diastemata [5, 6, 13]. The shortage of objective studies on diastema treatments has recently been noted [4], with only one peer-reviewed case series (n = 60) published to date [6].

The aims of this study were to examine a large number of affected horses having diastema widening treatment, to document the duration of clinical remission after initial treatment and to identify risk factors for failure of response to treatment.

Materials and methods

The records of all referred horses (2008–2011) diagnosed with clinically significant periodontal disease (i.e. having associated gingival retraction and periodontal pockets containing food material) caused by cheek teeth diastemata at the University of Edinburgh Equine Hospital that were treated by diastema widening were retrospectively examined. Most cases were referred following diastemata recognition by referring practitioners or because of clinical signs of severe dental disease, such as quidding. A minority of cases were referred because of paranasal sinusitis, facial swelling, impaction colic, choke or weight loss, and were diagnosed with clinically significant cheek teeth diastemata in this hospital. Cases were assigned to one of 4 groups: primary diastemata, secondary diastemata, combined primary and secondary diastemata, and senile diastemata (that included all horses aged >20 years without secondary diastemata, but also included horses aged <20 years with clinically senile teeth). The inciting causes of secondary diastema were documented, as were the number and location of diastemata widened in each case.

Diastema widening technique

Horses were restrained in stocks and sedated with romifidinea (0.04–0.12 mg/kg bwt) and butorphanolb (0.02 mg/kg bwt). Flunixin meglumine (Finadyne)c (1.1 mg/kg bwt, i.v.) was administered preoperatively. All horses received i.m. penicillin (10 mg/kg bwt) and neomycind (5 mg/kg bwt) preoperatively and phenylbutazone (Equipalazone)e (2.2 mg/kg bwt) orally for 3–7 days post operatively. Cases with deep periodontal disease were also given trimethoprim-sulfadiazine (Noridine granules)f orally for 5–7 days post operatively.

Using a full mouth speculum, headlight and dental mirror or oral endoscope, in addition to palpation of each interdental space, a variety of long-handled right-angled picks, specialised diastema forcepsg and a manualg or motorised pressurised water pickh were used to remove impacted food from diastemata. Diastemata with severe associated periodontitis were widened using motorised dental equipmenti and conical and cylindrical, solid tungsten carbide diastema burrs (Powerfloat)i. Widening was usually carried out for no longer than 5 s continuously before flushing 50–100 ml of water over the treated site using a dental syringe, and also by cleaning and cooling the diastema burr by rotating it against an underwater brush.

A previously described diastema widening technique [6] was used, taking care when widening obliquely oriented or curved diastemata (prevalent between the lower 10s −11s). Because the pulp horns are closest to the caudal aspect of the cheek teeth [14], an attempt was made to remove most dental tissue from the rostral aspect of the tooth lying caudal to the diastema, by applying a steady, caudally directed pressure on the instrument while widening left mandibular or right maxillary diastemata with this anticlockwise, rotating instrument from the lingual aspect.

Re-examinations were requested 3 months following the initial treatment and if possible, 6–12 months later. Owners were later sent a postal questionnaire that allowed them to give a graded, subjective assessment of their horse's dental signs prior to and following treatment. A complete response to treatment indicated full resolution of all clinical signs, whereas a partial response indicated some clinical improvement. Cases with complete resolution were divided into those with permanent resolution (for the duration of this study, i.e. mean follow-up of 20.8 months; range 3–48 months) and temporary resolution, where complete resolution of clinical signs occurred for a limited period, before some or all signs returned. Owners that did not respond to the written questionnaire were contacted by telephone, and where telephone contact was not possible, the referring veterinarian was contacted.

Data analyses

Two separate univariable and multivariable logistic regression models were developed using complete permanent resolution or complete resolution (permanent or temporary) of clinical signs as the dependent variables. Univariable screening for significant variables, including number and type of presenting signs, duration of clinical signs prior to treatment, horse age, diastema type (primary, secondary, combined or senile), location and number of widened diastemata, was set at P = 0.25 and variables were only included in a final multivariable model if the likelihood ratio test was P<0.05.


Of 302 cases with clinically significant cheek teeth diastemata (other horses examined during this period had cheek teeth diastemata without periodontitis), 202 were treated by diastema widening, including 57 (28%) Thoroughbreds and Thoroughbred crosses, 34 (17%) Warmbloods and Warmblood crosses, 61 (30%) ponies and pony crosses, 27 (13%) draughts and draught crosses, and 23 (13%) other breeds. These 202 horses had a mean age of 12.3 years (range 1–39 years) with primary diastema cases (n = 86) having a mean age of 10.5 years (range 2–20); secondary diastema cases (n = 71) of 9 years (range 1–27); combined primary and secondary cases (n = 21) of 10 years (range 2–22) and senile cases (n = 24) of 23 years (range 17–39).

Clinical signs included: quidding in 76.2% (154/202 cases); weight loss in 33.5% (n = 67); bitting problems in 21% (n = 42); halitosis in 11% (n = 22); buccal food pocketing in 6.5% (n = 13); bony facial swelling in 6% (n = 12); anorexia in 4.5% (n = 9); colic in 4% (8); dysmastication in 3.5% (n = 7) and choke in 1.5% (n = 3). Multiple clinical signs (mean number of signs = 1.9, range 2–5) were present in the 188 symptomatic horses. The 14 asymptomatic cases (6.9%) were diagnosed during routine dental examinations by referring veterinarians.

One hundred horses with clinical cheek teeth diastemata were not treated by diastema widening. These horses, of similar ages and breeds to the treated cases, generally had less severe periodontal disease than the diastema widened group and a lower prevalence of clinical signs, e.g. quidding in 48%, weight loss in 29.8%, bitting problems in 14.4%. However, this group also included some severe cases of secondary cheek teeth diastema that were treated by extraction of displaced cheek teeth; cases with diastema-induced oromaxillary or oronasal fistulas; severe intercurrent dental diseases and multiple senile diastemata. In some miniature horses diastema widening was not attempted because of the high risk of pulpar exposure owing to the small size of these teeth, and also to restricted access in their small oral cavities. Most of these 100 cases had removal of food from periodontal pockets, reduction of transverse overgrowths opposite the diastemata (if present), and in some cases filling the diastemata and periodontal pockets with dental impression material (Affinis)j or dental wax. Treatment data on this very heterogeneous group are not presented.

Location of diastemata

A total of 674 diastemata with associated periodontitis were widened in 202 horses, including 605 (90%) mandibular and 69 (10%) maxillary cheek teeth diastemata (Fig 1). The caudal mandibular positions were worst affected, with the Triadan 09–10 position having the highest prevalence of lesions (i.e. 24.8% of all diastemata), whereas the same maxillary position (Triadan 09–10) had the lowest prevalence of diastemata (i.e. 1.6%).

Figure 1.

Frequency of diastemata between the different Triadan positions in treated horses.

The inciting causes of diastemata in 86 cases of secondary and combined (primary and secondary) diastemata included cheek teeth displacements, with rotation in some (n = 76, 86%), prior cheek teeth extraction (n = 4), supernumerary cheek teeth (n = 3), oligodontia (n = 2) and marked dental overgrowth (n = 1).

Many cases required repeated treatments, especially when forage was reintroduced in the autumn/winter. Overall, horses had a mean of 1.5 treatments/case during this study. Primary diastema cases had a mean of 1.4 treatments (range 1–6); secondary diastema cases 1.8 treatments (range 1–7); combined diastema cases had 2 treatments (range 1–4) and senile diastemata cases had 1.1 treatments (range 1–2).

Owing to restricted visibility at the commonly affected caudal mandibular cheek teeth, and also to head and/or tongue movements that could not be adequately controlled by sedation in some horses, inappropriate sites were burred in a single caudal mandibular tooth in 6 horses. In 4 horses, dentine was damaged without causing pulpar exposure, but pulpar exposure occurred in 2 cases (Fig 2). The exposed pulp horns had calcium hydroxide paste (Preline)k inserted into them insofar as was possible (owing to poor access to a ventral site on the caudal aspect of damaged teeth) and trimethoprim-sulfonamidef was administered orally for 7 days. Neither case developed clinical signs of apical infection (follow-up 21 and 27 months).

Figure 2.

Iatrogenic exposure of 5th pulp horn of Triadan 408 due to removal of excessive dental tissue from the caudal aspect of this tooth.

Follow-up information

Follow-up information was obtained for 92.1% (186/202) of cases, a mean of 20.8 months (range 3–48 months) following the initial treatment. The postal questionnaire had a 37% (75/202) response rate and a telephone interview was subsequently completed for 41% (82/202) of cases, with similar success rates obtained by both methods. In 24 cases (12%), including 9 of 14 cases that were asymptomatic prior to the initial treatment, clinical periodontal re-evaluations were performed in this hospital and in 5 (2%) cases some information was gained from the referring veterinary surgeon.

Response to treatment

Primary diastema cases

Follow-up information was available in 77/86 (89.5%) of primary diastema cases, with 74% (57/77) showing complete resolution of clinical signs, with 51.9% (40/77) having permanent resolution (mean follow-up time of 20.8 months) after their initial treatment, while 22.1% (17/77) showed complete but temporary resolution of clinical signs for a mean duration of 8 (range 2–36) months, with some signs then recurring (Fig 3). Partial resolution of clinical signs was recorded in 14.3% (11/77) and complete absence of a favourable response in 2.6% (2/77), including one case reported to be worse following treatment. In 7 cases (9.1%) owners were unsure of response, including in 3 horses that were asymptomatic despite having significant periodontal disease prior to their initial diastema widening.

Figure 3.

Response to treatment in 186 horses affected with primary, secondary, senile and combined (primary and secondary) cheek teeth diastemata.

Secondary diastema cases

Follow-up information was available in 97.2% (69/71) of horses with secondary diastema (Fig 3), 69.6% (48/69) had complete resolution of signs, including 47.8% (33/69) with permanent resolution, and 21.7% (15/69) with temporary resolution for a mean of 8 months (range 1–24 months). Partial resolution was recorded in 21.7% (15/69) and 2.9% (2/69) had no response to treatment, with one reported to be worse following treatment. Owners were unsure of response in 5.8% (4/69) of cases, including in 2 cases that were asymptomatic prior to treatment.

Combined primary and secondary diastema

Follow-up information was available in 19/21 cases with combined primary and secondary diastemata, with complete resolution of signs recorded in 84.2% (16/19); 68.4% (13/19) had permanent resolution and 15.8% (3/19) had temporary resolution for a mean duration of 6.3 months (range 2–18 months). Partial resolution of signs was recorded in one case (5.3%). There was no response in 2 cases (10.5%), one of which was reported to be markedly anorexic for some days following treatment.

Senile diastema

Follow-up information in 21/24 cases with senile diastemata showed complete resolution of signs in 66.7% (14/21) of cases: 38.1% (8/21) had permanent resolution and 28.6% (6/14) had temporary resolution for a mean duration of 7.5 months (range 1–12 months). Partial resolution of clinical signs was recorded in 5 cases (23.8%) and 2 cases (9.5%) showed no response, but in both cases later extraction of a single loose tooth adjacent to diastemata resulted in complete resolution of signs.

Information on the length of time following treatment before clinical improvement occurred was available for 141 treated horses, with 27.7% (39/141) showing improvement immediately following treatment; 17.7% (25/141) between 1 and 3 days following treatment; 8.5% (12/141) between 3 and 7 days; 19.9% (28/141) between 7 and 14 days; 7.1% (10/141) between 14 and 28 days; 11.3% (16/141) between 28 and 56 days, 7.8% (11/141) took over 56 days following treatment to show improvement.

Recurrence of clinical signs

The clinical signs that recurred in horses (n = 73) with temporary or partial resolution of clinical signs included quidding in 84.9% (62/73), weight loss in 24.7% (18/73), halitosis in 17.8% (13/73) and bitting problems in 15.1% (11/73). Re-examination of these cases showed further periodontal food entrapment caused by drifting of teeth that caused narrowing of previously widened diastemata, as well as entrapment of food in newly developed diastemata. Transverse overgrowths were inevitably found on the cheek teeth opposite widened diastema and were removed, in addition to re-widening of diastemata or widening newly developed significant diastema.

Factors affecting clinical outcome

Multivariable logistic regression models showed no significant effect of any of the variables examined on whether complete permanent resolution or complete resolution (permanent or temporary) of clinical signs occurred following diastema widening. Therefore, no statistically significant risk factors could be identified for failure of response to treatment (defined as absence of complete permanent resolution or complete resolution [permanent or temporary] of clinical signs).

Client satisfaction

Diastemata widening treatment was felt to be worthwhile by 85.4% (134/157) of owners; 12.1% (19/157) were unsure of its value and 2.5% (4/157) felt it was not worthwhile.


Although there has been a major resurgence in research into equine dental disease over the past 2 decades [15-17], there remains a marked shortage of objective studies that prevents this discipline moving more quickly towards more desirable, evidence-based treatments. There is little consensus on what the optimal treatments are for cheek teeth diastemata [4], with as noted, only one peer-reviewed study on diastema treatment published to date [6].

This study included 90% mandibular and 10% maxillary diastemata, similar to the 87% mandibular and 13% maxillary positions in the 207 diastemata treated in the previous study [6]. The current study showed that 74% of horses with primary diastemata initially had complete remission of signs, similar to the previous study, where 72% of primary diastema cases had complete remission [6]. However, the current study followed up cases for a mean of 20.8 months, compared to 9.5 months in the former study [6], and this longer study period showed that complete remission of signs was sometimes temporary, with only 51.9% of cases still having complete remission in the longer term.

In the current study, 69.6% of cases of secondary diastemata initially showed complete remission of signs, which is higher than in the previous study, where just 48.4% of cases had full remission [6]. However, the response was temporary in 21.7% of the current cases and in the longer term a similar proportion, i.e. 47.8% of cases of secondary diastemata, had full resolution of signs. If the current study followed horses with secondary diastemata for a longer duration, it is likely that an even higher recurrence of signs would be found, because the underlying aetiology (e.g. displaced teeth) remains [6]. Inexplicably, horses with combined primary and secondary diastemata had the highest complete remission. Where complete resolution occurred in horses with senile diastemata this was often temporary.

There was no significant association between diastema type, horse age, location or number of widened diastemata and complete resolution of clinical signs following diastema treatment, indicating that diastema widening is an equally useful treatment for all categories of diastemata cases. We were therefore unable to identify any statistically significant risk factors for failure of response to treatment, and this may be due to the high success rates with this treatment and subsequent low number of overall treatment failures.

Many horses showed improvement within 3 days of diastema widening that was probably partly due to the concurrent phenylbutazone therapy. Surprisingly, many cases had a delayed response to treatment, which could be explained by the reported 2–3 months timescale for healing of some equine periodontal lesions following diastema treatment [4].

Quidding was the main sign reported before treatment, and an even higher prevalence (84.9%) of quidding was reported in horses with recurrence of signs or in horses where signs did not fully resolve. Recurrence of clinical signs was often reported when horses were re-introduced to forage in the autumn/winter. It is unclear whether this is because grass is less likely to become entrapped in diastemata than conserved forage or, in part, because quidding may not be observed when horses are grazing extensively. However, in support of the former hypothesis, diastema-affected horses at pasture rarely lose weight, in contrast to when housed and fed forage [6].

Cheek teeth diastemata can vary greatly from just the presence of single pieces of forage caught between the clinical crowns of teeth without even gingival involvement and where treatment is not needed, to cases with multiple deep periodontal pockets causing great pain during eating, or occasionally even osteomyelitis of the supporting bones, apical infection or orosinus/oronasal fistulation [10]. For diastemata associated with less severe periodontitis, food removal and temporary packing of diastemata may be of value [4], especially in younger horses, where considerable dental eruption remains that may allow compression of the occlusal aspects of teeth between the angled Triadan 06s and 11s that may later permanently close the diastemata [6]. Some authors claim that most diastemata are caused by malocclusions and so can be treated by occlusal reductions [18]; however, significant cheek teeth overgrowths were not a feature of primary cheek teeth diastemata cases in some previous studies [2, 6], nor in any primary diastema cases in this study, and were rarely identified in secondary or combined diastemata in this study.

The diastema-widening treatment described here is an invasive procedure with the potential to cause pulpar exposure, as recorded in 2 horses in this study, and also to cause thermal damage to pulp [19]. It could be argued that this technique should be reserved for cases with severe periodontitis, especially if they do not respond to more conservative treatments. In the current study, that only included referred cases with severe periodontitis that often travelled long distances, diastema widening was the treatment of choice, for logistical as well as therapeutic reasons. Despite iatrogenic pulpar exposure occurring in 2 cases, no signs of apical infection developed with >21 months' follow-up. Clinical signs of apical infection may take several years to develop in the horse and it is possible that our follow-up period in these 2 cases was not long enough. Because this was a retrospective study, we did not assess and quantitatively score periodontal pathology at individual diastemata; this would have more objectively assessed the response to treatment in re-examined horses, rather than relying on owner surveys, which can overestimate clinical success rates.

In conclusion, diastemata widening is an effective but potentially invasive treatment for treating severe periodontal disease caused by cheek teeth diastemata. The described treatment by trained personnel is suitable for advanced cases of cheek teeth diastema, but many affected horses require repeated treatments.

Authors' declaration of interests

No competing interests have been declared.

Ethical animal research

Not applicable. Retrospective study of clinical records.

Sources of funding

This research was supported by the Royal (Dick) School of Veterinary Studies.


P.M.D. contributed to study design, study execution, data collection and preparation of the manuscript. S.Z.B. contributed to study execution and preparation of the manuscript. T.B and J.O.L. contributed to study execution. S.C. contributed to data collection. T.D.P. contributed to data analysis and interpretation.

Manufacturers' addresses

  1. aBoehringer Ingleheim, Bracknell, Berkshire, UK.

  2. bFort Dodge Animal Health, Southampton, Hampshire, UK.

  3. cMSD MSD Animal Health, Milton Keynes, Buckinghamshire, UK.

  4. dIntervet UK Ltd, Milton Keynes, Bucks, Buckinghamshire, UK.

  5. eArnolds Veterinary Products Ltd, Shrewsbury, Shropshire, UK.

  6. fNorbrook Laboratories, Corby, Northamptonshire, UK.

  7. gKruuse UK Ltd, Sherburn in Elmet, North Yorkshire, UK.

  8. hEquine Blades Direct, Wedmore, Somerset UK

  9. iD & B Enterprises Inc, Calgary, Canada.

  10. jColtene Whaledent, Altstätten, Switzerland

  11. kHenry Schein, Melville, New York USA