How to avoid root canal therapy?

Simplest generic reply - Don't go for Root Canal Therapy. The tooth becomes dead after RCT as its blood and nerve supply has been permanently removed. The body recognizes it as a dead part and tries to dispose of it via decomposition.

Root cause of cavities is lack of nutrition in modern day diet and lack of cleanliness of mouth which allows bacteria to play their game on the teeth.

• Take raw plant food. Take lots of fruits and vegetables. Our ancestors did not use tooth brush or tooth paste and still had long lived teeth because they ate natural food. Tooth brush was introduced in early 1900 to the world.
• Take raw and cooked vegetables, especially green leafy vegetables.
• Take sprouted nuts, seeds and beans only.
• Eliminate ALL processed foods, packaged food and fast food. Strictly avoid white sugar, white rice, flour products and grains. 
• Eliminate phytic acid by avoiding grains, nuts and beans. You may consume them by sprouting  but not otherwise as people do generally. Phytic acid deprives teeth of minerals.
• Take raw dairy foods. If raw dairy food is not available, say good bye to pasteurized milk.
• Take food two times a day.
• Take relevant food supplements with your meals for fat soluble vitamins (A, D, E and K, especially vitamin D).
• Take food supplements for minerals (calcium, magnesium, phosphorus).
• Saliva is the best defense for teeth. It contains minerals that naturally strengthen teeth by cleansing them of common germs. Saliva keeps the mouth in slightly alkaline state which avoids cavities.
• Your saliva keeps your mouth in a neutral or slightly alkaline state.
• Brush and floss your teeth after every meal. Brush, Floss, Rinse, Repeat twice a day.
• Keep your body healthy with exercise and good life style.
• Use mineralizing toothpaste.
• Do not use any toothpaste with glycerin, it counteracts remineralization.
• Do oil pulling. Oil pulling is swishing coconut oil in-between your teeth for 20 miniutes or a minimum of 5-10 minutes. Spit it out when you are done and swish your teeth with water for few seconds. If 20 minutes look too much, you may do it while taking shower, reading a book, checking social media on internet or some other time when you do not have to speak. Do it daily or 3-5 times a week,  preferably first thing in the morning. This is a simple oral detoxification procedure that can cure many diseases such as tooth decay, gingivitis, headaches, diabetes.