Dentin is composed of approximately what percent inorganic material?

• A. 70% inorganic
• B. 20% organic
• C. 10% aqueous
• D. 40% water

Answer: (A)

Dentin's structure is a mineralized tissue where the dominant phase is inorganic mineral. By weight, roughly seven-tenths of dentin is mineral content, about 70%, primarily hydroxyapatite crystals that form a rigid scaffold within the organic matrix. The remaining portion consists of around 20% organic material, mainly type I collagen and non-collagenous proteins, plus about 10% water that fills spaces and influences diffusion through dentin tubules. Because the inorganic portion makes up the largest share, describing dentin as about 70% inorganic accurately reflects its composition. The other suggested percentages correspond to the other components (organic around one-fifth, water around one-tenth) and do not describe the overall mineral content as accurately. For contrast, enamel contains an even higher inorganic fraction, around 95%, explaining its greater hardness, while dentin remains more resilient due to its organic matrix and water content.