Small breeds of dog are especially prone to dental issues and periodontal disease. New insights during puppyhood were gained by tracking a population of 61 Yorkshire terrier dogs that were sequentially acquired by the Waltham Petcare Science Institute at approximately 8 weeks of age. The average age at deciduous tooth exfoliation, average age at permanent tooth eruption and persistent deciduous teeth (PDT) incidence were determined. The extent of periodontal disease was assessed under general anaesthesia between the ages of 37 and 78 weeks together with analysis of the oral microbiota composition of dental plaque via high throughput sequencing. The study was approved by the Waltham Animal Welfare and Ethical Review Body and run under licensed authority in accordance with the UK Animals (Scientific Procedures) Act 1986.

The ages of exfoliation of deciduous teeth and eruption of permanent dentition were influenced by body weight and tooth type. These dentition changes tended to occur later in dogs ≤ 3 kg versus dogs > 5 kg. Generally, incisors were exfoliated first, followed by premolars and then canines. Yorkshire terriers had a high incidence of PDT. At a body weight of 4.5 kg, the estimated proportion of PDT was: incisors 0.86% (0.32, 2.31), canines 15.62% (7.62, 29.37) and premolars 3.57% (1.62, 7.66). PDT risk was also dependent on bodyweight, with 89.1% of canines retained in dogs ≤ 3 kg compared to 12.0% in dogs > 5 kg.

At 37 weeks of age, 98% of dogs had periodontitis with on average 29.6% (95% confidence interval; 23.6%, 36.4%) of the teeth in the mouth affected. The average percentage of teeth in the mouth with periodontitis was 2.74 (2.23, 3.37) times higher at 78 weeks of age compared to 37 weeks of age. The canine teeth had a significantly higher probability of periodontitis compared to all other tooth types at both 37 and 78 weeks of age (p<0.001).

Analysis of the microbial population of 42 subgingival plaque samples from 22 dogs (1 to 4 samples per dog) indicated that health and mild gingivitis were associated with higher relative abundance of taxa belonging to the phylum Proteobacteria (e.g., Moraxella and Pasteurellaceae). In moderate gingivitis there was increased representation of taxa belonging to the phylum Firmicutes (e.g., Peptostreptococcaceae, Lachnospiraceae, Erysipelotrichaceae and Frigovirgula) and Bacteroidetes (Porphyromonas canoris). Periodontitis was also associated with an increased representation of some taxa belonging to the phylum Firmicutes (e.g., Peptosteptococcaceae), Spirochaetea (e.g., Treponema) and Synergistetes (e.g., Synergistales).

Breeds of dog that are susceptible to PDT and developing periodontitis, such as Yorkshire terriers, require close monitoring from a young age. Veterinarians and owners need to be aware that this breed is likely to need extraction of PDT before 6 months of age and that strategies to help prevent the development of periodontal disease as soon as their adult dentition is present will be needed. Although tooth brushing is the most frequent recommendation for preventative homecare this is not always realistic, and therefore alternative ways to prevent plaque accumulation that are practical for both dogs and their owners are required.