When replacing a missing back tooth, there are several main factors to consider other than aesthetics, as you’ll need a fake tooth that’s strong, functional and durable to support you daily:

• Functionality: As your back teeth bear most of the chewing load, back tooth replacements must be strong enough to withstand higher biting forces. Strong, durable materials like titanium or zirconia, or preferably, metal-ceramic options. 
• Stability: Back tooth replacements, bearing a lot of chewing forces, need to stay securely in place, for example, when eating, to maintain your comfort too. Fixed solutions like implants and bridges will hold the advantage over removable options here.
• Durability: As molars endure significant pressure, the longevity of your restoration and materials is an important factor, as removable options might wear faster or require more frequent adjustments. 
• Preservation: A priority in the back of the mouth should be to preserve the bone in the jaw to keep other teeth and gums healthy. In this case, implants are the only option because they are the only restoration that replaces the tooth root and thus maintains jawbone density.