The prevalence of secondary dentinal lesions in cheek teeth from horses with clinical signs of pulpitis compared to controls



Reasons for performing study: With the advent of detailed oral examination in horses using dental mirrors and rigid endoscopy, secondary dentinal lesions are observed more frequently. More information regarding the association of secondary dentinal defects with apical dental disease would improve the sensitivity of oral examination as a diagnostic aid for pulpitis.

Objectives: To assess prevalence and severity of secondary dentinal defects observed on examination of occlusal surfaces of cheek teeth (CT) from horses showing clinical signs of pulpitis compared to asymptomatic controls.

Methods: Records from all cases of equine CT exodontia at the University of Bristol over a 4 year period were examined. Case selection criteria included the presence of clinical signs of pulpitis, an intact extracted tooth and availability of a complete history and follow up. Cases where coronal fracture or periodontal pocketing featured were excluded. CT from cadavers with no history of dental disease served as normal controls. Triadan positions and eruption ages of control teeth were matched with those of teeth extracted from cases. CT from selected cases and control teeth were examined occlusally. Secondary dentinal defects were identified and graded. Prevalence of occlusal lesions in CT with pulpitis and controls was compared.

Results: From the records of 120 horses where exodontia was performed, 40 cases matched selection criteria. Twenty-three mandibular and 21 maxillary CT were extracted from cases. The controls consisted of 60 mandibular and 60 maxillary CT from 7 cadaver skulls. Secondary dentinal defects were significantly over-represented in CT extracted from cases of pulpitis (P<0.001). Of diseased mandibular CT, 56.5% had defects compared to none of the controls. Of diseased maxillary CT, 57% had defects compared with 1.6% of controls. Multiple defective secondary dentinal areas and severe lesions were more prevalent in diseased mandibular CT compared with diseased maxillary CT.

Conclusions and practical significance: Careful examination of occlusal secondary dentine is an essential component in investigation of suspected pulpitis in equine CT.


Clinical signs of pulpitis are a common reason for referral of horses to equine hospitals for dental investigation (Dixon et al. 2000). The identification of the afflicted tooth can be challenging, particularly in cases where pulpitis is not associated with a dental fracture or periodontal disease. With the advent of detailed occlusal examination with a dental mirror or an oral endoscope, more accurate observation of occlusal changes is possible (Tremaine 2005; Johnson and Porter 2006; Simhofer et al. 2008a). This potentially valuable diagnostic aid is accessible to equine clinicians.

Radiography is the most popular diagnostic technique for investigation of disorders affecting the equine head (Barakzai 2006) and is considered an essential adjunct to equine dental evaluations (Dixon 1997). However, as a solitary diagnostic aid, conventional dental radiography has been shown to have limited sensitivity and specificity, particularly in the case of caudal maxillary CT (Gibbs and Lane 1987; Weller et al. 2001; Barakzai et al. 2006). Other imaging modalities such as computed tomography and scintigraphy have shown promise with regard to the diagnosis of pulpitis (Tietje et al. 1996; Weller et al. 2001; Henninger et al. 2003) but are currently used less widely for this purpose. Hence, extra information from occlusal findings would be a welcome addition to the diagnostic armoury.

Exodontia remains the most effective treatment for pulpitis that is refractory to antibiotic therapy (Dixon et al. 2000; Tremaine 2004). While greater numbers of extractions are being performed per os with lower complication rates than retrograde techniques (Tremaine 1997; Dixon et al. 2000), exodontia is not a benign procedure. Many short- and long-term complications have been reported, particularly where repulsion is employed as a technique (Prichard et al. 1992; Lane 1997; Dixon et al. 2000; Vlaminck 2007; Townsend et al. 2008). Hence, identification of the correct tooth for extraction is imperative. Accurate diagnosis could be facilitated by more information regarding the clinical relevance of occlusal findings.

Management of pulpitis with apicectomy and endodontic treatment has been described (Baker and Kirkland 1992; Boswell et al. 2001; Simhofer et al. 2008b). This treatment has had limited success due to lack of information available about the anatomy andpathology involved, late detection and technical limitations. More sensitive diagnostics and accurate detection of the affected tooth at an earlier stage in the disease process, combined with a better understanding of the pathology involved, could promote earlier and more effective conservative treatment of pulpitis.

The aetiology of pulpitis has been described previously (Dixon et al. 2000; Dacre 2005) as ‘primary’, (no gross intraoral pathology or obvious route for infection) or ‘secondary’ (due to periodontal disease or coronal fracture). In cases where there is no gross dental pathology detected on oral examination (previously described as ‘primary’), the diagnosis of the affected tooth is more challenging. It is in these cases that validation of the prevalence and significance of occlusal pathological findings would be most useful.

Previous studies have described occlusal dentinal defects and the nature of the cause and effect relationship between dentinal defects and pulp disease has been speculated but is currently not confirmed (Becker 1962; Wafa 1988; Dacre 2004; Dacre et al. 2008a,b; du Toit et al. 2008a; van den Enden and Dixon 2008). A microscopic and ultrastructural study of normal equine CT concluded that, under normal conditions, a pulp chamber would never become exposed at the occlusal surface (Kilic et al. 1997). Becker (1962) proposed pulpar exposure to be secondary to disturbances in nutrition or inflammation of the pulp.

It is hypothesised that there is increased prevalence of secondary dentinal defects in teeth with pulpitis compared with what was previously reported. The objective of this study was to assess the prevalence and severity of secondary dentinal defects observed occlusally in CT extracted from horses showing clinical signs of pulpitis compared to matched controls and subsequently to clarify the clinical relevance of such lesions.

Materials and methods

Case selection

Clinical records of horses in which extraction of CT was performed at the University of Bristol Veterinary Hospital between 2003 and 2007 were reviewed. Case selection criteria included presence of clinical signs of pulpitis (i.e. bony swelling of the mandible or maxilla, external or oral draining tracts or unilateral nasal discharge), availability of a complete history and follow-up and a grossly intact extracted tooth (i.e. excluding teeth damaged iatrogenically during extraction by repulsion techniques). Cases where coronal fracture or periodontal pocketing featured were excluded. Diagnostic modalities used for identifying the affected tooth included radiography, oral examination, upper respiratory endoscopy and scintigraphy. The extracted teeth were preserved in 10% formalin.


Cheek teeth to serve as controls were obtained from cadavers that had been subjected to euthanasia due to nondental problems. The cadaver skulls were disarticulated. Rows of mandibular and maxillary cheek teeth were excised from the remainder of the skull with a band saw as described by Dacre (2004) and preserved in 10% formalin. Triadan positions and dental ages for the diseased teeth and controls were calculated. Dental ages were calculated as described by Dacre (2004), Dacre et al. (2008a), van den Enden and Dixon (2008) and Windley et al. (2009a); i.e. the emergence time of the CT (Martin 2002) subtracted from the horse's age as calculated from the year of birth recorded on their passports. Teeth of Triadan position 11 were excluded from the controls due to the different endodontic anatomy of these teeth (Dacre 2004; Dacre et al. 2008a; Windley et al. 2009a) and as there were no diseased teeth from this position. Dental ages and Triadan positions (either 06 or 07–10) of controls were matched with those of the diseased teeth. For every diseased tooth, at least one matched control was provided.

Secondary dentinal assessment

The occlusal surfaces the extracted diseased teeth and controls were photographed and examined for the presence of secondary dentinal fissures by the first author using a fine dental probe and a 23 gauge needle. Secondary dentinal defects were graded in order of severity (1, 2 or 3, Fig 1, Table 3) The location of the affected secondary dentinal areas was also recorded. The secondary dentinal areas were assigned names according to their anatomical position. These names, and also the numbering system for the pulp horns as described by Dacre (2004), Dacre et al. (2008a) and du Toit et al. (2008b) are depicted in Figures 2 and o2 (see supporting information). In cases where multiple secondary dentinal areas were affected, the prevalences of the various possible combinations of affected areas were recorded.

Figure 1.

Grading system for secondary dentinal lesions. (a) Grade 0; Smooth secondary dentinal surface, no irregularities. (b) Grade 1. Irregular secondary dentinal area but cannot advance 23 gauge needle. (c) Grade 2. Needle can be advanced partially (e.g. 2–3 mm) to gain purchase in dentine. (d) Grade 3. Needle can be advanced through secondary dentine further than 2–3 mm with minimal resistance.

Table 3. The grading system used for describing occlusal secondary dentine (see also Fig 1)
0Smooth surface, no irregularities.
1Irregular area but cannot advance 23 gauge needle.
2Needle (23 gauge) can be advanced partially (2–3 mm) to gain purchase in dentine.
3Needle (23 gauge) can be advanced through dentine further than 2–3 mm with minimal resistance.
Figure 2.

Occlusal anatomy of (a) mandibular cheek tooth (CT) of Triadan 07–10, and (b) maxillary CT of Triadan positions 07–10. The locations of the dark-staining secondary dentinal areas are assigned names related to their anatomical location for the purposes of this paper. The endodontic numbering systems of Dacre 2005 ( ) and du Toit et al. 2008b (*) are also illustrated. See Fig o1 (supporting information) for occlusal anatomy for teeth of Triadan 06 position.

Repeatability of the grading system was confirmed by blinded thrice repeated occlusal examinitions. The prevalence of occlusal secondary dentinal lesions in diseased and control teeth was compared using Fisher's exact test. Statistical significance was set at P<0.05.


Selected cases

Records from 120 horses which underwent CT exodontia were reviewed. Of these, 93 cases showed clinical signs of pulpitis. Of these 93 cases, 63 were cases where there was no coronal fracture or periodontal pocketing associated with the affected tooth, 15 had coronal fractures, 9 had periodontal disease (periodontal pocketing was due to supernumerary teeth in 2 cases, displaced teeth in 4 cases and primary diastemata in 2 cases), and 6 horses had unerupted impacted teeth. Of the 63 horses with no coronal fractures or periodontal pocketing, 40 horses had 44 CT extracted intact with a complete history and follow up available. These 44 CT consisted of 23 mandibular CT from 20 horses and 21 maxillary CT from 20 horses.

Median dental ages of the 23 mandibular and 21 maxillary CT from selected cases were 4 and 7 years, respectively, range 0–13 years and 2.5–16 years. Clinical details of the selected cases are summarised in Table 1.

Table 1. Clinical details of 41 cases of cheek tooth (n = 44) pulpitis
 No. casesNo. teethAge median (range) yearsEruption age median (range) yearsExternal swellingExternal discharging tractNasal dischargeQuiddingBitting problems
Rostral maxillary CT111295112301
(Triadan 06, 07 and 08)  (6–16)(3–13)92%17%25%0%8%
Caudal maxillary CT99141320800
(Triadan 09–11)  (3.5–17)(2.5–16)22%0%88%0%0%
Mandibular CT2023742212009

Thirty-eight (86%) of the 44 diseased teeth from selected cases were extracted per os. There were no teeth of Triadan positions 10 or 11 among the diseased teeth from selected cases. Triadan position 08 was most commonly represented amongst the diseased mandibular CT, consisting of 9 (39%) of 23 CT from selected cases. Triadan positions 07 and 09 were the most commonly represented amongst the diseased maxillary CT, each consisting of 9 (43%) of 21 CT from selected cases (Table 2).

Table 2. Extraction methods employed and Triadan positions of cheek teeth (CT) extracted from selected cases
 No. teethPO extractionRepulsionBuccotomyTriadan 06Triadan 07Triadan 08Triadan 09
Maxillary CT2120102919
Mandibular CT2318326593


Control teeth consisted of 60 maxillary and 60 mandibular CT from 7 cadaver skulls. The median emergence age was 5.5 years (range 0–16 years) for the mandibular controls and 8.5 years (range 0–16 years) for maxillary controls (Charts o1 and o2, see supporting information).

Secondary dentinal findings

Secondary dentinal defects were significantly over-represented in diseased teeth (P<0.001).

Mandibular CT:

Of the 23 diseased mandibular teeth, 13 (56.5%) had defects compared to none of 60 controls (Table 4). The rostral buccal (RB) and caudal buccal (CB) areas were most commonly defective, each being affected in 8 out of 23 (35%) diseased mandibular teeth (Table o1 see supporting information). Eight (35%) mandibular CT had more severe lesions (Grade 3).

Table 4. Secondary dentinal defects observed upon occlusal examination of diseased cheek teeth (CT) and normal controls
 No. teethSecondary dentinal defects present>1 area defective secondary dentineTeeth with Grade 3 (severe) secondary dentinal defects
Diseased mandibular CT231398
Normal mandibular controls60000
Diseased maxillary CT211251
Normal maxillary controls60100

Nine of 23 (39%) diseased mandibular teeth had multiple secondary dentinal areas affected. These consisted of one tooth of Triadan 06 position which had all 6 secondary dentinal areas affected and 8 CT of Triadan positions 07–09. The mean number of affected dentinal areas in these 8 CT was 2.75 areas (range 2–4). The combinations of caudal lingual (CL) + CB and RB + CB were most common. Both of these combinations were manifest in 4 (50%) of the 8 affected CT of Triadan positions 07–09 (Fig o2 see supporting information).

Thin fissure lines were noted in 2 diseased mandibular CT. In both cases the fissures were evident on the buccal aspect of the tooth in the longitudinal plane. They travelled through the RB and CB secondary dentinal areas, both of which were defective (Fig o3 see supporting information).

Maxillary CT:

Of the 21 diseased maxillary teeth, 12 (57%) had defects compared to 1 (1.6%) of 60 controls (Table 4). The single affected control (with a dental age of 14 years) had a Grade 1 dentinal defect in one area of secondary dentine. The CB secondary dentinal area was most commonly defective, being affected in 6 out of 21 (28.5%) diseased maxillary CT (Table o1 see supporting information). Two (10%) diseased maxillary CT had Grade 3 defects.

Of the diseased maxillary teeth, 5 (24%) had multiple areas of defective secondary dentine. The average number of affected areas was 2.4 (range 2–3). In these 5 CT with multiple defective areas, the combination of RB + CB areas was the most common combination, being manifest in 3 out of 5 (60%) teeth.

Sensitivity and specificity

As a test for pulpitis in equine CT under these conditions, careful examination of secondary dentinal defects had a sensitivity of 54.5% and a specificity of 98.9%.


Clinical external signs of pulpitis (e.g. bony swellings, discharging tracts and nasal discharge) reflect an advanced disease state. These signs were included as the selection criteria in this study as are, at present, the primary means by which we identify horses with pulpitis. Earlier diagnosis of pulpitis during a routine dental examination could facilitate more prompt and less invasive treatment. The findings of this study endorse the examination of occlusal secondary dentine as a valuable aid for earlier diagnosis of pulpitis.

The provision of age matched controls allowed direct comparison of secondary dentine in diseased and healthy teeth whilst accounting for possible occlusal variations with age. It is known that attrition stimulates deposition of dentine, with secondary and tertiary dentine being progressively laid down after emergence in human teeth (Pashley and Liewehr 2006; Nanci 2008). Estimated dental rather than actual ages were used in this study in order to allow for the staggered emergence times of equine cheek teeth. There is variability in the emergence times of equine CT (Ramzan et al. 2009), which is a limitation of using estimated dental ages. Comparisons would be more accurate by providing age matched cadaver skulls for each of the 44 diseased teeth. The use of control teeth from only 7 horses may limit the significance of conclusions of the prevalence of defects in cases vs. controls based on this sample size, although the matching of each specimen with at least one tooth matched for location and dental age was a practical compromise for the purposes of this study. There are apparently no other studies, that have directly compared the occlusal surfaces of cases with pulpitis with matched controls. Knowledge of the range of normal, as well as abnormal findings gives clearer insight into the clinical relevance of occlusal findings.

In contrast to the cases, the control teeth were examined intact in their respective mandibles and maxillae, for practical reasons as was performed by other authors (Dacre 2004). Hence the controls were readily identifiable to the investigator, precluding the possibility of a blinded study. However, the teeth from cases included in the study were extracted (2003–2007) by the second author, assisted by the first author in some cases (since 2007). Occlusal lesions were recorded from the preserved specimens by the first author, without influence from the second author, although the observer did have access to case records. Although this does not constitute a blinded study, a sufficient degree of interinvestigator independence as well as intrainvestigator repeatability was achieved to enable the observations to be robust.

The aetiopathogenesis of pulpitis, especially in teeth with no obvious external cause, remains unclear. By restricting the study to teeth with no obvious external cause of pulpitis findings from this most intriguing group can contribute to understanding of the cause of this disease. The representation of Triadan positions in the diseased teeth in this study was similar to that in case series of apically infected CT (Dixon et al. 2000). The over-representation of mandibular Triadan position 08 and maxillary 07s may indicate a role of transient impaction during emergence in the aetiology of pulpitis in these teeth as previously proposed by Crabill and Schumacher (1998). The over-representation of maxillary CT from Triadan position 09 (Table 2) and the older median estimated dental age of these teeth (Table 1) could indicate a different aetiology of pulpitis in these teeth compared with the rostral maxillary (Triadan 06-08) and mandibular CT.

The lower prevalence of secondary dentinal defects in the controls in this study compared with the other studies of CT from equids with no history of dental disease (Wafa 1988; du Toit 2008a) may reflect the lower median emergence ages (5.5 years for mandibular CT and 8.5 for maxillary CT) of the control teeth in this study. Hence, this study indicates that secondary dentinal defects are a significant finding in the relatively younger age-group of horses in which pulpitis is prevalent.

It has been proposed, that if pulpar insult or death occurs, the production of secondary dentine by the odontoblasts ceases or is reduced (Dacre 2004; Dacre et al. 2008d). However, in human teeth, odontoblasts affected with milder injury can survive and be up-regulated to secrete a reactionary type of tertiary dentine at the pulp dentine interface (Smith 2008). In a study in donkey teeth, a single pulp horn with occlusal exposure had vital pulp present more apically (du Toit et al. 2008a). Hence, much remains to be ascertained regarding equine dentinogenesis. Dacre et al. (2008d) found histological evidence of slower deposition of secondary dentine in diseased equine CT. Occlusal pulpar exposure in 34% of 41 mandibular CT and 23% of 57 maxillary CT with pulpitis was recently reported (Dacre et al. 2008b,c). In another recent study 35% of 54 teeth with comparable selection criteria to this study had pulpar exposure, with a further 10% of 79 apically infected CT in the study having ‘occlusal pitting’ (van den Enden and Dixon 2008). There is a higher prevalence of secondary dentinal defects in the present study (57% of mandibular and maxillary CT) compared with the prevalence of pulpar exposure reported by the above studies. This could be due to a contrast in methodology. Our study documented minor occlusal secondary dentinal defects, whereas the other studies concentrated on severe secondary dentinal lesions where pulpar exposure was evident. ‘Occlusal pitting’, reported by van den Enden and Dixon (2008), could correspond with lesion described as a Grade 1 secondary dentinal defect in our study and ‘pulpar exposure’, could correspond with a Grade 3 defect.

The prevalence of 35% of Grade 3 lesions in diseased mandibular CT in this study is the similar to the prevalence of occlusal exposure reported by the studies of van den Enden and Dixon (2008) and Dacre et al. (2008b,c). The difference between the prevalence of severe dentinal lesions (Grade 3) between maxillary (10%) and mandibular (35%) CT in our study contrasts with the findings of other studies (Dacre 2008b,c; van den Enden and Dixon 2008). However, Becker (1962) also commented on this difference in the prevalence of lesions between mandibular and maxillary CT where pulpar exposure was also reported to occur mainly in mandibular CT.

Multiple defective secondary dentinal areas were evident in 24% of diseased maxillary and 39% of diseased mandibular CT in this study. This suggests that lesions in these teeth are a result of odontoblast compromise rather than a primary cause of pulpitis. The studies of (Kilic et al. 1997; Dacre 2004; Dacre et al. 2008b,c,d; van den Enden and Dixon 2008) made a similar proposition. It has yet to be proven whether defective secondary dentine is a causal factor of pulpitis or whether it is consistently a consequence of pulpitis due to another reason (e.g. anachoresis).

There are no significant similarities in the prevalence of secondary dentinal defects in particular dentinal areas in this study and the study of van den Enden and Dixon (2008). Studies of normal endodontic anatomy by Dacre et al. (2008a) and Windley et al. (2009a) found the CL and CB pulp horns to communicate in closest proximity to the occlusal surface of mandibular CT of Triadan positions 07–10. The high prevalence of the combination of CL and CB areas being concurrently defective in this study (55% of 8 mandibular CT of Triadan position 07–10 with multiple defects) could be associated with this anatomical feature. The above anatomical studies also reported a higher prevalence of communications between all pulp horns in maxillary CT compared with mandibular teeth. The number of maxillary CT in this study with multiple defects (n = 5) was too small to conclude any possible association with endodontic anatomy.

Dentinal defects were noted clinically in only 2 mandibular teeth in a retrospective study of 162 horses with apically infected teeth (Dixon et al. 2000). However, the authors noted that such lesions could be missed on a cursory examination. Wafa (1988) also noted the importance of occlusal examination as part of the clinical examination. With modern sedatives and better equipment, such as dental mirrors, and fine dental probes, a more thorough occlusal examination is facilitated in the standing horse (Tremaine 2005; Johnson and Porter 2006; Simhofer et al. 2008a; Ramzan 2009). Subtle occlusal lesions may therefore be detected more easily under these conditions, providing useful diagnostic information. In this study, the grading system for dentinal lesions was based upon the depth that a 23 gauge needle could be advanced through a dentinal lesion. In the clinical situation, this system could be replicated by using a fine dental probe.

An early study reported that with radiographs alone, the afflicted tooth could only be identified in half of cases involving the caudal maxillary CT (Gibbs and Lane 1987). More recent studies found sensitivities of 52 and 69%, respectively, and specificities of 95 and 70% for radiography in the investigation of dental disorders (Weller et al. 2001; Barakazai et al. 2006). Scintigraphy has been shown to complement radiographic examination of dental structures. A combination of these 2 diagnostic modalities had a sensitivity of 97.7% and a specificity of 100% in the diagnosis of dental disease (Weller et al. 2001). The reliability of radiography could also be potentiated with a detailed occlusal examination.

Thin fissure lines were noted going through the buccal secondary dentinal areas of 2 diseased mandibular CT in this study were also noted in 3 of 79 CT with pulpitis in a similar study (van den Enden and Dixon 2008). In that study, the affected teeth were also mandibular CT, and in 2 of the 3 cases, the fissure line travelled through the two buccal pulp horns. Dacre et al. (2007) and Dixon et al. (2006) reported buccal slab fractures involving the buccal pulp horns to be the most prevalent idiopathic fractures in mandibular CT. It is possible that such fissure lines may progress to become slab fractures.

The present study examines the prevalence of dentinal lesions in extracted diseased teeth from clinically symptomatic horses. The careful examination of occlusal surfaces in clinical cases can be interpreted, in light of the findings, to demonstrate the probability of pulpitis where lesions are detected. Further studies are required to confirm the role of secondary dentinal defects in the aetiopathogenesis of apical disease.


This study was generously funded by the Horse Trust. We would like to thank Professor William Browne for statistical advice and also the pathology technicians and photographers at the Department of Clinical Veterinary Science in the University of Bristol for their assistance with this study.

Author contributions Both authors contributed to all aspects of this paper.