Traumatic tooth shortening in commercial piglets: Effects on gross tooth pathology and mRNA markers of inflammation and pain.

Aim of Investigations The aim of the study was to characterise the long-term effects (1-6 weeks) of two methods of tooth resection (clipping and grinding) on tooth pathology and markers of inflammation and pain in commercial piglets. The experiments are part of a project aimed at assessing the effects of the management practice of tooth resection on piglet welfare. Methods Forty-eight female piglets from 8 replicates (litters) were assigned to one of three treatments (SHAM, CLIP, GRIND). Tooth integrity was scored post-mortem at 1 or 6 weeks after tooth treatment (n=8/treatment/time-period). Dental pulp was extracted from 384 teeth (8/pig) - pooled and processed at pig level - to quantify changes in mRNA transcript expression of C-X-C motif chemokine ligand 8 (CXCL8) and calcitonin related polypeptide beta (CALCB) as neuropeptide markers of inflammation and pain using reverse transcription quantitative PCR. Data were analysed using the statistical package R Studio. The statistical tests used to analyse CALCB and CXCL8 were ANOVA and Kruskal-Wallis respectively. Results All CLIP and GRIND piglets exhibited pulp exposure. Mean percentage numbers of needle teeth with exposed pulp were 0. 8%, 65. 8%, and 85. 8% in SHAM, GRIND, and CLIP piglets respectively. In resected teeth, CXCL8 gene expression was found to be significantly increased by both methods of tooth resection (p<0. 001) at both time periods (mean fold-changes relative to SHAM were 333-fold and 483-fold at 1 week and 330-fold and 558-fold at 6 weeks for GRIND and CLIP treatments respectively) indicating a prolonged localised inflammatory state in the tooth pulp induced by both methods of tooth resection. In resected teeth, expression of CALCB was found to be significantly downregulated (p<0. 001) in week 1 (mean fold changes relative to SHAM were 0. 55-fold for GRIND (p<0. 05) and 0. 29-fold for CLIP (p<0. 001)), with the CLIP downregulation being significantly greater than that of GRIND (p<0. 05). By week 6, this downregulation was reduced to a tendency for GRIND (0. 41-fold change relative to SHAM, p=0. 06), whereas CLIP downregulation remained significant (0. 13-fold change relative to SHAM, p<0. 001) and significantly greater than for GRIND (p<0. 05). These findings indicate an effect of tooth resection on CALCB expression within the tooth pulp that is stronger and longer lasting when clipping is used as opposed to grinding. Conclusions Tooth resection by both clipping and grinding induces a prolonged localised inflammatory state lasting up to 6 weeks after injury as evidenced by increased mRNA expression of the pro-inflammatory cytokine CXCL8 within the injured tooth pulp. The two treatments differentially reduced CALCB expression in the injured tooth pulp suggesting both methods may have implications for dental pain in piglets. Tooth grinding had less of an effect than clipping on CALCB expression within the tooth pulp which lasted up to 1 week after tooth resection but was attenuated by 6 weeks post-injury. Tooth clipping has a greater impact on CALCB mRNA expression which was still present at 6 weeks after tooth resection. CALCB is a potent vasodilator and neurotransmitter associated with pain processing and peripheral sensitization. Down-regulation of CALCB expression may be associated with greater tooth damage activating descending pain modulation in response to injury to dental pulp afferent innervation, although this has yet to be confirmed or otherwise in this study. In summary the findings of this study suggest that tooth clipping and tooth grinding in piglets has differential and detrimental effects on tooth integrity which have implications for sustained inflammatory tooth pain in piglets up to 6 weeks after tooth resection injury. Conflicts of Interest The authors have no conflicts of interest Source of Financial Support for the Project SRUC Research Excellence Academic Development Fund - Investigating behavioural and neural/cellular consequences of tooth resection in commercial piglets: implications for welfare