Assessment of Dental Abnormalities by Full-Mouth Radiography in Small Breed Dogs
This study was performed to evaluate full-mouth radiographic findings to determine the prevalence of dental abnormalities and analyze the relationship between dental abnormalities and age in small breed dogs. Sixteen predetermined categories of abnormal radiographic findings were evaluated in 233 small breed dogs. In total, 9,786 possible permanent teeth could be evaluated. Of those, 8,308 teeth were evaluated and abnormal radiographic findings were found in 2,458 teeth (29.6%). The most common teeth with abnormal radiographic findings were the mandibular first molars (74.5% on the left and 63.9% on the right) and the maxillary fourth premolars (40.5% on the left and 38.2% on the right). Bone loss of any type (15.8%) was the most commonly detected radiographic abnormal finding among the 16 categories. Dental conditions with a genetic predisposition were frequently occurred in the mandibular premolar teeth. Shih tzu frequently had unerupted teeth and dentigerous cysts. Among the teeth with abnormal radiographic findings, 4.5%, 19.8%, and 5.3% were considered incidental, additional, and important, respectively. Findings that were only detected on radiographs, which were not noted on routine oral examination, were more common in older dogs. Full-mouth radiographic evaluation should be performed to obtain important information for making accurate diagnoses.
Introduction
Veterinary dentistry has evolved to maintain appropriate oral health care for pets. The oral cavity is considered a window to the body because oral manifestations accompany many systemic diseases, such as autoimmune skin diseases, chronic kidney diseases, and canine distemper virus infection. Further, oral pathology especially periodontitis, can induce systemic disease, including valvular disease, endocarditis, or systemic bacteremia. The gold standard of veterinary oral health care involves clinical oral examination, radiography, dental prophylaxis, and treatment.1
Dental radiology is an essential diagnostic modality. A large number of veterinary patients do not show signs of either discomfort or pain until loss of function has developed; therefore, many oral problems could be missed in the early stages and worsen before owners are aware that any oral problems exist. Dental radiography helps detect hidden pathologic conditions that lie underneath the gingival margin.2,3 Periodontal disease, endodontic disease, caries, resorptive lesions, fractures, and neoplastic conditions require radiographs for a more accurate diagnosis.4 One previous study suggests that dental radiography provides additional, clinically useful information of dental diseases in 72% of dogs.5 Radiography is particularly important when endodontic therapy is performed and for assisting posttreatment monitoring.1–3 Fractures and progressive oral problems require periodic radiographic assessment because the healing process may not progress satisfactorily.1
The routine use of full-mouth radiography is recommended due to high sensitivity of detecting dental diseases compared with selective radiography.5 Currently, full-mouth radiography is well established in veterinary medicine.5,6 Numerous studies have been performed to evaluate the diagnostic value of full-mouth radiography, but sparse investigations regarding dental abnormalities in association with each tooth have been reported.7,8 In addition, no previous studies regarding dental abnormalities in a large population of small breed dogs have been reported. Therefore, the purpose of this study is to evaluate 16 predetermined categories of radiographic abnormal findings using full-mouth radiography and to estimate the incidence of each abnormal finding in a large population of small breed dogs.
Materials and Methods
In total, 233 small breed dogs (< 8 kg) referred for dental evaluation and treatment between Nov 2008 and Jun 2010 were included in this study. Dogs were separated into 4 groups based on age. Group I included dogs ≤ 4 yr, group II included dogs 5–8 yr, group III included dogs 9–12 yr, and group IV included dogs ≥ 13 yr. General anesthesia was induced for all radiographic examinations. The radiographs were obtained using a standard, wall-mounted dental radiography unita and a direct digital imaging system with a No. 2 sensorb. To take full-mouth radiographs, a standardized system in positioning, views, and technique was used (Table 1).5,6 All dental radiographs were evaluated by the same veterinary clinician (C-G.K.) with a standard approach under the same conditions.
C, canine; I, incisor; M, molar; P, premolar.
Abnormal radiographic findings for each of the existing teeth were evaluated using the following 16 predetermined categories: vertical bone loss, horizontal bone loss, combined bone loss, furcation exposure, periodontal-endodontic lesion, periapical radiolucency, abnormally wide pulp cavity, root fracture, tooth resorption, ankylosis, retained root, root dilaceration, fused roots, embedded tooth, dentigerous cyst, and dens invaginatus. Missing teeth were classified as truly missing, not truly missing, and congenitally missing. Not truly missing teeth were defined as teeth missed on oral examination, though detected on dental radiographs. Those teeth included retained roots, embedded teeth, and teeth associated dentigerous cysts. Congenitally missing teeth were defined as missing teeth on oral and radiographic examinations in dogs < 4 yr of age without a history of oral disease and dental treatment.
Teeth included in those categories were recorded by clinical importance (i.e., incidental radiographic findings, additional radiographic findings, and important radiographic findings). Incidental radiographic findings were defined as findings with no clinical importance, such as fused roots and root dilaceration without furcation exposure. Additional radiographic findings were defined as findings providing additional diagnostic information to the expected radiographic findings, such as bone loss, root dilaceration with furcation exposure, and furcation exposure. Important radiographic findings were defined as findings with clinical importance, such as retained root, periodontal-endodontic lesion, periapical radiolucency, abnormally wide pulp cavity, root fracture, tooth resorption, ankylosis, embedded tooth, dentigerous cyst, and dens invaginatus. In this study, stages of tooth resorption and periodontal-endodontic lesion were not classified based on the radiographic results.
Statistical Analysis
The occurrence rates of radiographic abnormal findings by each tooth were calculated separately, and the prevalence was calculated based on the existing teeth for each tooth type. The differences in prevalence of radiographic findings between the age groups were tested using Pearson's χ2 test. A two-sided P value < 0.05 was considered statistically significance. All statistical analysis was performed using a commercial software system.c
Results
A total of 233 dogs, including a total of 11 small breeds, were evaluated. The most common breeds were Maltese (31.8%), Yorkshire terriers (22.7%), and shih tzu (15.4%). Among the age groups, group II (54.9%) was the most common, followed by group I (20.6%), group III (16.3%), and group IV (8.2%). The age of dogs ranged from 6 mo to 18 yr (mean age, 6.6 yr). Mean age of each group was 2.0 yr (group I), 6.0 yr (group II), 10.4 yr (group III), and 14.2 yr (group IV).
The mean number of views needed to complete a full-mouth radiographic survey in this study was 10.8 (2,550 views in 233 dogs). There was no difference in the number of views between the brachycephalic (10.19 in shih tzu) and mesaticephalic breeds (10.41 in Maltese and 10.28 in Yorkshire terriers). Overall, 9,786 possible permanent teeth could be evaluated. The number of existing and missing teeth was 8,308 (84.9%) and 1,478 (15.1%), respectively. Among the existing teeth, the number of abnormal and normal teeth on dental radiographs were 2,458 (29.6%) and 5850 (70.4%), respectively.
The prevalence of radiographic normal (no clinical value) and abnormal findings (incidental findings, 4.5%; additional findings, 19.8%; important findings, 5.3%) were 70.4% and 29.6%, respectively. The distribution of radiographic abnormal findings according to the age groups was also assessed (Figure 1). The percentage of no clinical value decreased with age (P < 0.05), and the percentage of radiographic incidental findings decreased with increasing age. The percentage of radiographic additional and important findings increased with age (P < 0.05, respectively).
Citation: Journal of the American Animal Hospital Association 49, 1; 10.5326/JAAHA-MS-5830
Among the 16 different categories, the most commonly observed findings were bone loss (Table 2). With increasing age, the frequency of detected abnormal radiographic signs consistent with periodontitis (such as bone loss, furcation exposure, or tooth resorption) was increased. Tables 3A and B show the prevalence of 16 radiographic abnormal findings by tooth. The occurrence rate of radiographic abnormal signs was high in the mandibular first molar and maxillary fourth premolar teeth. In contrast, the canine, first premolar, and last molar teeth had relatively lower rates of abnormal radiographic signs compared with other teeth.
Number of existing teeth in each age group.
Group I, ≤ 4 yr; Group II, 5–8 yr; Group III, 9–12 yr; Group IV, ≥ 13 yr.
C, canine; I, incisor; M, molar; P, premolar.
C, canine; I, incisor; M, molar; P, premolar.
The occurrence rate of each of the 16 predetermined radiographic abnormalities was analyzed by single tooth. For the incisors, abnormally wide pulp cavity was observed most commonly in the right maxillary second incisors and the mandibular first incisor had a significantly high incidence of root fracture. In the case of the premolar teeth, tooth resorption occurred more frequently than in the other types of teeth, but fused roots were not observed. The left maxillary premolar teeth had a higher rate of furcation exposure. In particular, the maxillary first premolar teeth had a higher incidence of retained roots, whereas the left maxillary second premolars had a higher incidence of periodontal-endodontic lesions than the other types of teeth. In both the maxillary and mandibular first premolars, congenitally missing teeth were generally observed. Interestingly, the mandibular first premolar teeth of shih tzu were the only type of teeth where dentigerous cysts were detected. In the molars, maxillary first and second molars had a higher incidence of vertical bone loss and periapical radiolucency than the other types of teeth. The mandibular first molars were the only type of teeth where dens invaginatus was observed and those teeth commonly had root dilacerations. Fused roots were most commonly observed in the mandibular second molars.
The maxillary and mandibular first premolars and mandibular second and third molars were most frequently missing. Further, the maxillary and mandibular first premolars and mandibular second and third molars were most frequently congenitally missing (Figure 2). The overall prevalence of not truly missing teeth was 6.3%. Among the three categories of not truly missing teeth, the prevalence of retained roots increased with age (P < 0.05), and the prevalence of embedded teeth decreased with age (P < 0.05). Teeth associated with dentigerous cysts were rarely observed (Figure 3).
Citation: Journal of the American Animal Hospital Association 49, 1; 10.5326/JAAHA-MS-5830
Citation: Journal of the American Animal Hospital Association 49, 1; 10.5326/JAAHA-MS-5830
Discussion
This study used a digital imaging system and a No. 2 sensor to take full-mouth radiographs. An average of 10.8 views needed to complete a full-mouth radiographic survey for small breed dogs. That number of views was slightly more than the 9.3 views reported in a previous study using standard dental radiographic film (No. 0, 2, and 4).6
Although there may have been some breed difference according to skull type, there was no difference in the number of views between the brachycephalic and mesaticephalic breeds. One previous study demonstrated that the number of views needed for full-mouth radiography was associated with the size of the dog.5 Time needed to take each view was 1 min, and the total time required to take a full view was 10–12 min. Time is an important factor to consider for decreasing the cost and anesthetic risk during full-mouth radiography.5
In an analysis of the abnormal findings in each tooth, 29.6% of teeth showed radiographic abnormal findings. Among the teeth with abnormal radiographic findings, 84.8% of the teeth showing radiographic evidence of dental disease provided additional and important findings. The prevalence of abnormal radiographic findings in each tooth in this study was significantly lower than previously reported (72.0%).5 The cause of this difference may be attributed to the different assessment method. The previous study assessed the incidence of abnormal radiographic findings by individual dog. For example, one dog with only a few teeth showing radiographic evidence of dental disease was included in the group showing either additional or important findings. In contrast, the current study assessed the incidence of abnormal radiographic findings by individual tooth. As a result, most of the teeth belonged to either the no clinical value or incidental findings and only a few teeth belonged to either the additional or important findings groups. For instance, a dog with only a few teeth showing radiographic evidence of dental disease was included in the group showing either additional or important findings. Most of the teeth belonged to either the no clinical value group or incidental findings and only a few teeth belonged to the additional or important findings. Therefore, assessment of full-mouth radiographic abnormalities by individual tooth can provide a more accurate assessment of the overall dental condition.
Among the predetermined 16 categories, bone loss (including vertical, horizontal, and combined bone loss) was the most common finding, which affected more than half of the teeth. Similarly, another study reported that bone loss was the most commonly observed radiographic finding.5
Periapical radiolucency on radiographs is generally associated with endodontic disease. That lesion appears as a radiolucency surrounding the root apex with a loss of lamina dura in the immediate area, resulting in osteoclastic bone resorption.9 Verstraete et al. (1998) reported that radiographs of the maxillary first and second molars in dogs obtained using the standard bisecting angle technique are difficult to evaluate.5 The maxillary molar teeth could be superimposed easily on the occlusal and crown enamel, and the mesiobuccal and distobuccal roots of the maxillary molar teeth could mimic the short roots.10 Therefore, furcation exposure could not be detected by intraoral dental radiography except for in a few maxillary molar teeth. Cases with deep periodontal pockets at the maxillary molar tooth roots may show periapical radiolucency on the intraoral dental radiographs. Therefore, the high incidence of periapical radiolucency of the maxillary molar teeth was likely primarily caused by periodontitis rather than endodontic disease. Those results show that periodontal probing combined with intraoral dental radiography is essential for examining the extent of periodontal disease and furcation exposure of the maxillary molar teeth.
In this study, all embedded teeth and dentigerous cysts were observed in the mandibular first premolar teeth. Niemiec (2010) reported that the maxillary canine and first premolars were observed most commonly as unerupted teeth.11 Embedded teeth are unerupted teeth due to a lack of an eruptive force.12 The most common cause is the presence of an overlying structure (bone, soft tissue, or tooth) that interferes with normal eruption. That condition is observed most often in brachycephalic and small breed dogs.11 In brachycephalic breeds, teeth are often unerupted because there is insufficient space for all the teeth in the oral cavity conformationally.13 In the current study, shih tzu had a high frequency of embedded teeth, attributable to the anatomic characteristic of brachycephalic breeds.
Root fractures and retained roots are generally caused by a tooth injury.9 In the current study, the frequency of root fracture was highest in both mandibular first incisors. That finding is considered to be due to a lack of supporting bone and tissue around the mandibular incisor teeth root compared with the maxillary first incisors. Therefore, mandibular incisor teeth root are easily fractured by external forces.14 In contrast, teeth with retained roots were commonly detected in the maxillary first premolars. In such cases, the tooth may be sheared off below the alveolar margin as a result of the injury, with the root remaining undetected. Often, the root is not detected until it becomes infected and/or inflamed.15 Root dilacerations are relatively common in both the mandibular premolars and molars, but fused roots were observed only in the mandibular second, third, and fourth premolars as well as the second molars.
Dental radiography should be used in areas missing teeth to differentiate between congenital defects and acquired dental pathologies. Acquired dental pathologies, such as retained roots, impacted or imbedded tooth, cyst formation, tooth extraction (due to fracture, severe periodontitis, etc.) can result in missing teeth. In the current study, acquired missing teeth were most commonly observed in the first premolars and second and third molars. That result suggests that the first premolars and second and third molars may be the most common site of severe dental pathologies requiring dental extraction. In contrast, congenital missing teeth were most commonly observed in the right mandibular first premolars. That result is similar to a previous study.16
In the analysis of not truly missing teeth, an embedded tooth occurs as a result of congenital or developmental condition at young age. Retained roots resulting from acquired tooth damage or fracture showed an age-related increase tendency. In addition, the correlation between the incidence of embedded teeth and dentigerous cysts, embedded teeth might transform into dentigerous cysts with increasing age. Therefore, any missing teeth noted during an oral examination should prompt a thorough, full-mouth radiographic examination to determine either any clinically invisible or underestimated dental condition(s) in dogs.
Conclusion
An assessment of the clinical value of full-mouth radiography suggests that the diagnostic yield of full-mouth radiography is high, and full-mouth radiographic evaluation should be performed together with a clinical dental examination to obtain additional information for an accurate diagnosis. This study showed that alveolar bone loss was the most commonly observed finding, and small breed dogs were susceptible to periodontal disease. This analysis of the prevalence of radiographic dental abnormalities (analyzed by individual tooth) using full-mouth radiography can help veterinarians better diagnose tooth abnormalities in small breed dogs.
Distribution of full-mouth radiographic findings according to age in 233 small breed dogs. A: Group I (≤ 4 yr); B: Group II (5–8 yr); C: Group III (9–12 yr); and D: Group IV (≥ 13 yr).
Prevalence of total and congenital missing teeth in 233 small breed dogs. Lmand, left mandibular; Lmax, left maxillary; Rmand, right mandibular; Rmax, right maxillary.
Prevalence of not truly missing teeth according to age in 233 small breed dogs. Group I (≤ 4 yr); Group II (5–8 yr); Group III (9–12 yr); and Group IV (≥ 13 yr).
Contributor Notes
