Table 1.

Effect of amino acids on oral health.

Amino Acid	Effect on Oral Health	Material	References
Alanine	Alanine and histidine form citrulline. A higher concentration of citrulline in saliva is correlated with periodontitis.	Human	[105]
Arginine	Arginine improves calcium absorption by the formation of soluble complexes with calcium that maintain calcium in an absorbent form, which is important for enamel maturation. Higher concentration saliva in Stage III Grade C generalised periodontitis.	Human	[105]
L-Arginine	L-Arginine monohydrochloride in saliva inhibits bacterial coaggregation in the oral cavity by decreasing the viscosity of extracellular polymeric substances produced by bacteria and altering cellular metabolism resulting in biofilm dispersion and reducing antibiotic tolerance.	Human	[102]
Aspartic acid	Adult age estimation is based on aspartic acid racemisation in dentine.	Human	[106]
Cysteine	Toxic to oral Streptococci through inhibiting an enzymatic step in the valine-leucine biosynthetic pathway.	Human	[107]
	Reduces bacterial biofilm adherence and biofilm biomass.	A multi-species plaque-derived biofilm model	[108]
N-Acetyl-L-cysteine (from L-cysteine)	Reduces pain and hypersensitivity of teeth. Protects gingivae from white lesions and oral mucosal inflammation after using bleaching agents.	Human	[109]
	As mouthwash, it treats and prevents gingivitis	Human	[110]
Glutamic acid	Higher in Stage III Grade C generalised periodontitis.	Human	[105]
Glutamine	Topical administration to patients receiving stomatoxic chemotherapy resulted in 20% decrease in moderate and severe oral mucositis.	Human	[111]
Glycine	Glycine supplement reduced dental caries development by 65.7% through the changes in the fatty acid composition of the tooth and a reduction in growth rate (no effect on the retention of either calcium or phosphorus by dietary glycine).	Rodent (rat)	[112]
	Glycine is an integral part of collagen that is an intrinsic component of the tooth structure. Reduced level of saliva glycine has been associated with collagen degradation. Hence, higher salivary glycine has been associated with reduced risk of dental caries and periodontitis through reduced collagen degradation and decreased collagenase activity, leading to less inflammation in gingiva.	Human	[113,114]
Histidine †	Reduces the risk of dental caries. Lack of histidine and its derivatives in saliva results in chelation, i.e., formation of metal complexes with amino acids, leading to initial lesion and secondary to destruction of the organic matrix by the action of proteolytic bacteria.	Human	[103]
Isoleucine †	Found in carious dentine	Human	[115]
Leucine †	Repaired carious enamel.	Human	[116]
	Leucine-rich amelogenin peptide regulates receptor activator of NF-kappa B ligand (RANKL) expression in cementoblast/periodontal ligament cells.	Rodent (mouse)	[117]
Lysine †	Important for the integrity of dentally attached epithelium to act as a barrier to microbial products.	Lysine decarboxylas extracted on Eikenella corrodens bacterial cell surface	[118]
Methionine †	Methionine reduces the adverse effect of fluorides on soft tissue, and this has been found to be optimal for the prevention of the adverse effects of chronic fluoride intoxication together with vitamin E in drinking water.	Rodent (rat)	[119]
Phenylalanine †	May inhibit dental caries development. In bacteria, phenylalanine is converted to phenylpropionate or phenylacetate, resulting in alkali environment which is an essential factor in maintaining plaque pH homeostasis.	Human	[120]
Proline	Salivary proline-rich glycoprotein regulates the oral calcium homeostasis by controlling the supersaturated state of saliva with respect to calcium phosphate salts, countering the plaque acidity, formation of dental pellicle, and influencing the composition of plaque.	Human	[121]
	Moreover, this prevents the adherence of oral microorganisms inhibiting their growth and neutralises acids from biofilms protecting from dental caries.	Human	[122]
Serine and threonine †	Interact with host cytoplasmic phosphoproteins, facilitating internalisation of bacteria.	Primary cultures of human gingival epithelial cells	[123,124]
Tryptophan †	Tryptophan metabolites generated from oral supplementation of tryptophan promote regulatory T-cell (Treg) differentiation and suppress proinflammatory T-helper cell (Th)1 and Th17 phenotypes.	Rodent (mice)	[125]
	Higher saliva tryptophan level was observed in Stage III Grade B generalised periodontitis.	Human	[105]
Tyrosine	Potential biomarker of oral lichen planus (lower levels). Tyrosine is suggested to be involved in the antioxidative defence.	Human	[126]
Valine †	Detected in sound dentine compared to carious dentine.	Human	[115]
Homocysteine ‡	Associated with high narrow palate, mandibular prognathia (protruding lower jaw), crowding and early eruption of teeth and short dental roots.	Human	[127]

^† Essential amino acids, ^‡ is an AA but not present in the diet and not included in 21AAs.