DENTAL ABNORMALITIES OF EIGHT WILD QINLING GIANT PANDAS (AILUROPODA MELANOLEUCA QINLINGENSIS), SHAANXI PROVINCE, CHINA Open Access

Dental health, especially in wild animals, is important for survival. Without proper treatment, dental abnormalities may lead to oral pain, difficulty foraging or hunting, and anorexia (Wallach and Boever 1983; Bellows 2004; Holmstrom et al. 2004). Secondary complications, such as malnutrition; gastrointestinal, cardiovascular, and renal diseases, isolation from feeding territory, and other systemic disorders can be fatal (Wallach and Boever 1983; Stromquist et al. 2009; Jin et al. 2012). Although dentistry is well practiced in veterinary science, most research and practice are focused on companion and domestic animals. Systematic studies on wild giant pandas (Ailuropoda melanoleuca) are rare (Wenker et al. 1999; Hu 2001; Stromquist et al. 2009; Jin et al. 2012).

Two subspecies of giant panda, Ailuropoda melanoleuca qinlingensis and Ailuropoda melanoleuca sichuanensis, are recognized on the basis of cranial features, color patterns, and genetics (Wan et al. 2003, 2005). The Qinling subspecies, A. m. qinlingensis, lives only in the Qinling Mountains in Shaanxi Province and has seven regional populations, totaling 273 pandas (Lu et al. 2001; Liu et al. 2002, 2009; Hu and Wei, 2004; Feng et al. 2009). The panda population in these mountains has a unique distribution pattern and evolutionary history. They are different from the mainstream population of A. m. sichuanensis in morphology and molecular biology (Lu et al. 2001; Loucks et al. 2003; Wan et al. 2003, 2005; Liu et al. 2009). Nonetheless, the habits and diet of Qinling pandas are similar to the pandas in Sichuan. They are territorial, solitary animals in the wild (Schaller et al. 1985; Tang 1992). The average lifespan of a wild giant panda is about 20 yr, compared with 25–30 yr for captive giant pandas (Hu 2001; Jin et al., 2012). They primarily spend their lives roaming and feeding in bamboo forests. The diet is 95–99% bamboo and occasionally other vegetation or carcasses of small animals (Schaller et al. 1985, 1989; Tang 1992; Hu 2001). Because bamboo is poor in nutrients, giant pandas must eat large amounts and different kinds of bamboo to fulfill essential nutrient requirements. They spend about 14 h/d consuming 12–38 kg of bamboo (Reid et al. 1989; Schaller et al. 1989; Tang 1992; Loucks et al. 2003).

A normal adult giant panda has 42 teeth, including incisors (I), canines (C), premolars (P), and molars (M) with a dental formula of 2 (I 3/3, C 1/1, P 4/4, M 2/3; Huang 1993). Captive Sichuan giant pandas at Beijing Zoo have a high prevalence of dental caries, tooth wear, and tooth loss (Jin et al. 2012).

Here, we report a systematic dental case study of wild Qinling giant pandas. We evaluated the complete dental and periodontal status of wild Qinling giant pandas, compared results with captive giant pandas and other bear (Ursidae) species, and reveal the importance of dental health for giant panda survival in the wild.

This is a joint research project lead by the China National Foping Nature Reserve and China Agriculture University, Department of Veterinary Medicine, approved by the China National Foping Nature Reserve Committee. From November 2010 to April 2014, eight wild adult Qinling giant pandas (six males and two females) were tracked at the China National Foping Nature Reserve (33°33′to 33°46′N, 107°41′to 107°55′E) in Shaanxi Province as a routine procedure to assess this endangered species’ health status and to check the GPS device and battery. Dental inspection is added as a comprehensive examination for assessing the health of the pandas. Seven of these animals were tracked by using their original GPS collars (custom made by Zhongke Xintong Information and Technology Co., Ltd., Shenzhen, China). One animal’s collar was lost, and the panda was tracked and recollared. Three (pandas 1, 5, and 8) were tracked and examined again in 2014. All animals were immobilized for routine physical examinations, blood and fecal sample collections, GPS collar fitting, or collar check and battery change. Pistol systems (Dan-Inject, Børkop, Denmark) were used for remote drug delivery for immobilization. We used 3-mL darts with 2.0×40-mm, plain needles to inject a mixture of dexmedetomidine and zolazepam-tiletamine intramuscularly into the lateral hip region. The anesthetic formulation was 8 μg/kg dexmedetomidine (Dexdomitor, Orion Cooperation and Orion Pharm, Espoo, Finland) and 2 mg/kg zolazepam-tiletamine (Zoletil 100 Injectable Anesthetic/Sedative for Dogs, Cats, Zoo, and Wild animals, Virbac Australia Pty. Ltd., New South Wales, Australia; Mainka and He 1993; Jin et al. 2012; Reed et al. 2012). The anesthetic protocol was derived from previous anesthetic data, experience, and the animals’ body condition. The duration of anesthesia was approximately 60 min, allowing for physical examinations, sample collecting, dental examination, and dental radiology. The general health status of all pandas is summarized in Table 1.

Y.J. conducted all dental examinations and radiology. Results were recorded on a dental examination chart modified for giant pandas (see Appendix). Three categories with nine indices were evaluated for each tooth and graded accordingly. The first category was oral hygiene, which includes the plaque index (PI) and calculus index (CI). The second was tooth abnormalities, which includes the tooth fracture index (Fr), tooth wear index (W), caries index, discoloration, tooth absence, supernumerary, and pulp exposure (PE). The third category was the surrounding periodontal structures, which includes gingival index, periodontal index, mobility index (M), and furcation involvement index. For a detailed index system for evaluation and grading, see Appendix.

The overall occlusion was evaluated and recorded. Periodontal pocket depth was measured with a dental explorer probe (Jorvet-937cn-Explorer/Probe 23/12, Jorgensen Laboratories Inc., Loveland, Colorado, USA; Bellows 2004; Holmstrom et al. 2004), and the deepest single site was recorded. A dental decay was defined as a discolored area of the tooth surface in which a dental probe could be inserted and when removed had slight resistance (Harvey 1985; Bellows 2004; Holmstrom et al. 2004; Stromquist et al. 2009). A decayed tooth has a rough and coarse inner surface of the cavity. Tooth wear was classified according to the progressive loss in the overall surface of the tooth in all planes (mainly, the occlusal, lingual, and buccal), which results in a smooth and fine surface. Teeth were defined as absent when all tooth structures, including crown and root, were absent during oral exam and on dental radiographs (Harvey 1985; Bellows 2004; Holmstrom et al. 2004; Stromquist et al. 2009). Dental plaque was evaluated by applying a thin layer of plaque disclosing agent (iC Plaque; iM3 Pty. Ltd. Australia, Lane Cove, New South Wales, Australia) on the tooth surface and graded accordingly (Fig. 1A). Oral pH was measured by using a portable pH meter (FiveGo pH Meter, Mettler-Toledo Inc., Columbus, Ohio, USA). The pH measurements were taken three times, and the average was recorded. The Appendix shows all indices inspected and the grading scales used. The tooth numbering system used is the modified Triadan system (Floyd 1991).

Dental radiology was performed on all teeth by using a portable intraoral dental radiology machine (ADX4000 Digital Radiography System, Dexcowin Co., Ltd., Seoul, Korea). The sensor of the portable digital x-ray machine is small; so several small images were needed for a complete x-ray image of one tooth. All teeth and periodontal structures were evaluated (Fig. 1B), and findings were compared with the dental examination findings. Statistical analysis was done by using Statistical Product and Service Solutions (SPSS China, Shanghai, China) for correlations between all indexes, age, and sex.

The estimated age for study animals ranged 5–20 yr at the time of examination. Ages were estimated based on the time of collar fitting, dental condition, animal’s appearance, health status, and individual history. All animals bred naturally in the wild. One male (panda 4) had massive intestinal ulcers that caused severe malnutrition and died soon after examination. All six male pandas had scar tissue on the facial and neck area, probably due to fighting during mating season.

Pandas 1, 5, and 8 were tracked and examined again in 2014. Panda 5 had a nursing juvenile and had lost significant weight since the 2011 examination. Panda 8 had severe health problems (Table 1) and died 8 d after return to the reservation base. Postmortem examination revealed death was due to peritonitis and septicemia. Existing health problems and general condition for other pandas are summarized in Table 1.

We examined 303 teeth. The average pH value was 8.4. Panda 5 had a base narrow occlusion causing severe wear on the lingual side of all mandibular canines and incisors (Fig. 1C). Panda 1 had a complicated fracture on tooth 304 (Fig. 1D). Panda 6 had a fractured maxilla due to trauma (Fig. 1E). Existing health problems and general comments are summarized in Table 1.

Various degrees of plaque and calculus were found in all pandas; 78.9% of teeth (I = 265) had plaque. Canines, premolars, and molars were the most affected (100% of 32 canine; 79.7% of 102 premolars; 100% of 80 molars). Incisors were the least affected. (PI1, n = 34; PI2, n = 17). Most teeth had PI2 (n = 125); 48.5% of teeth had calculus (n = 163). Molars were most affected (88%; CI1, n = 60; CI2, n = 10). No teeth were graded CI3. No statistical correlation was found between plaque and calculus prevalence. Detailed dental examination results of 2011 are summarized in Table 2.

All animals had oligodontia, and 10% of teeth were absent (n = 33). Absent teeth include 101, 103, 201, 301, 303, 401, 105, 106, 205, 206, 305, 306, 405, and 406. First premolars were the most frequently absent teeth (n = 18). No supernumerary teeth were found. Seven of eight pandas had tooth discoloration. Incisors were the most affected (20%, n = 19).

Six pandas (five males and a female) had tooth fractures. All fractures occurred on incisors and canines (n = 32 and n = 21), and canines had the highest prevalence (66%), with grade Fr1 being the most common (n = 13). Of incisors, 33% were fractured (n = 32). No statistical correlations were found between fracture, tooth discoloration, and PE, but all Fr3 and Fr4 teeth showed discoloration and visible pulpitis.

No pandas had tooth caries during 2010 to 2011.

All pandas had different degrees of tooth wear, involving 88.1% of teeth (n = 296). Incisors were the most worn: 20% of incisors were graded W1 (n = 17), 41% (n = 35) were graded W2, and 37% (n = 31) were graded W3 (Fig. 1F). Canines and premolars were the least worn. Tooth wear for all animals was charted. Radiology indicated tooth wear patterns for each panda were relatively symmetrical (Fig. 1G).

Six pandas (all males) had mild gingivitis affecting the incisors, canines, and premolars (n = 17, n = 4, and n = 11). All animals had normal periodontal pocket depth (0–2 mm), and no teeth showed any mobility. Only one panda had mild periodontitis on 201. No furcation involvement was found.

When pandas 1, 5, and 8 were reexamined in 2014, all had increased severity of tooth discoloration. Pandas 1 and 8 had additional tooth loss and fracture; pandas 5 and 8 had caries in the grooves of the molar occlusal surface but with no advancement in periodontal pocket depth. The periodontal pocket depths were advanced to 3 mm in panda 1. Panda 5 had more severely worn mandibular canines due to base narrow occlusion, and a tooth mobility of M1 on 205. Only panda 8 showed furcation involvement on 407. Comparison of dental abnormality findings are summarized in Table 3.

Dental radiology findings were consistent with the dental examination results. No unerupted teeth were detected, and little evidence of periodontal diseases was found. Radiographic changes were consistent with pulpitis and apical periodontitis on canines, premolars, and molars. One furcation involvement on tooth 407 was evident (Fig. 1H). Damage of the enamel caused by tooth wear was found on all severely damaged teeth, including incisors, canines, premolars, and molars. Radiographic evidence of tooth decay was found on five molar teeth between two animals in 2014.

In this systematic study of dental abnormalities of wild Qinling giant pandas, we found that all pandas had various degrees of dental abnormalities. Dental attrition due to tooth wear was the most common abnormality. Tooth fractures were also common, with canines and incisors being the most fractured teeth. Maxillary and mandibular fractures were also found, but tooth caries were rare. Periodontal disease was not found, but calculus and plaque varied with pandas and progressed over time. Oligodontia was also common.

Dental health is important for panda survival in the wild. Although, no statistical correlation between dental health and mortality was found (likely due to the small sample size), both pandas that died during the study had poor dental condition, systemic health problems, and malnutrition before death. Poor dental health could cause anorexia, which would result in decreased bamboo intake and cause malnutrition and weakness. A weak wild panda will lose in territorial fights and be forced to live in areas with low bamboo density. With limited bamboo resources, the animal would have to eat tough bamboo stems to survive. Ingested bamboo fragments with sharp edges could cause ulcers or perforation of the digestive tract, causing gastrointestinal disorders and other systematic problems and, finally, lead to death. Thus, deteriorating dental health in wild giant pandas could be life-threatening.

Despite its taxonomic classification as a carnivore, wild giant pandas are primarily herbivorous, with a diet consisting of 95–99% bamboo (Reid and Jinchu 1991; Tang 1992; Huang 1993). However, they retain the digestive system of a carnivore, and thus derive little energy and little protein from the consumption of bamboo (Hu 2001; Wan et al. 2003). Because the diet is low in nutrition, it is important for a wild giant panda to keep its digestive tract full. An average wild giant panda eats 9–14 kg of bamboo shoots for at least 14 h a day (Reid et al. 1989; Reid and Jinchu 1991; Tang 1992). Constant chewing and extensive use of the teeth result in severe tooth wear (Fig. 1F). Tooth wear in most wild pandas was symmetrical, indicating that tooth wear may be mostly mechanical, and wild giant pandas alternate the usage of their teeth, resulting in a symmetrical chewing pattern (Fig. 1G).

Tooth fracture and mandibular and maxillary bone fractures were common in wild pandas. The uniquely shaped canine teeth were the most fractured, followed by incisors. Although they prefer tender bamboo shoots and leaves, death and regeneration of bamboo or a harsh season means pandas in the wild may have to eat tough stems (Johnson et al. 1988; Reid et al. 1989; Reid and Jinchu 1991; Liu et al. 2002), causing trauma to their teeth. During mating season, males fight for mates and better territories (Schaller et al. 1985; Hu 2001). We observed that when they fight, they bite their opponent’s neck and face, locking teeth and throwing their heads back and forth. Such behavior can result in canine tooth fracture and maxilla or mandibular fractures (Fig. 1D, E).

When compared with captive panda in Beijing Zoo and other bear species, the wild giant panda’s diet contains more bamboo and less sugar (Manville 1990; Tang 1992; Hu 2001; Holmstrom et al. 2004; Zhang 2004; Stromquist et al. 2009; Jin et al. 2012). They are also younger than average age during examination, with more alkaline saliva similar to Swedish brown bears (Ursus arctos; Stromquist et al. 2009). Moreover, all captive giant pandas at the Beijing Zoo were Sichuan pandas, with smaller skulls and smaller teeth that have deeper and more uneven grooves (Wan et al. 2005; Liu et al. 2009; Jin et al. 2012); they also do not fight for mates or territory. These anatomic, dietary, behavioral, and physiologic differences may explain the wild Qinling pandas’ fewer dental caries, greater tooth wear, and more severe tooth fractures compared with captive giant pandas and some other bear species. Similar to the captive panda study by Jin et al. (2012), all wild Qinling pandas had different degrees of dental plaque and mild to moderate calculus, with increasing severity with age. Serious periodontal disease was not found, because the flavonoid compound in bamboo can act as an antiseptic and antioxidant; the bamboo fibers also can brush the tooth surface preventing the formation of plaque and calculus (Tang 1992; Sato et al. 1996; Williams et al. 2004; Zhang 2004; Jin et al. 2012). Oligodontia was common in wild giant pandas as in captive giant pandas, with first premolars being the most frequently missing teeth (Jin et al. 2012). Further research is needed to determine the reason for the absence of the first premolar.

Limitations of this study include the small sample size of wild Qinling giant pandas. Dental plaque samples were not collected owing to equipment and legislative constrains. We could not achieve long-term follow up on all eight wild giant pandas. Our findings may have important clinical application, but they cannot elucidate all patterns and epidemiology of dental and periodontal diseases in the wild panda population. Further studies are needed to compare the oral microbial flora of wild and captive giant pandas and to investigate the relation of dental abnormalities in terms of giant panda behavior, chewing patterns, and chances of survival in the wild.

We thank Amy S. Kapatkin for help in preparation of the paper.