According to studies, baking soda (sodium bicarbonate) is one of the safest abrasives used as a dentifrice (powder or paste used for cleaning teeth). You are more likely to run the risk of enamel abrasion with incorrect brushing techniques or the use of a hard bristled brush.
Abrasives Are Necessary for Cleaning Power
Though toothpastes contain a variety of ingredients that work to keep the dentition healthy such as ingredients to fight cavities, plaque, gingivitis, tartar, halitosis, sensitivity, and teeth whitening agents, a European study concluded that most of the cleaning achieved from a toothpaste is through abrasion. 
The cleaning agents in toothpaste can work by either chemical or mechanical means. A chemical cleaning agent, for example, would be hydrogen peroxide, whereas a mechanical cleaning agent would be an abrasive such as calcium pyrophosphate. Sodium bicarbonate, or baking soda, is both a chemical and mechanical cleaning agent 
The addition of abrasives to oral hygiene routines does more than remove stains for whiter teeth. Abrasives such as baking soda have also been shown to remove plaque accumulation to help prevent gum disease. 
Baking Soda the Best of Its Category
There are three common categories of abrasives that are most often added to toothpastes to boost their cleaning power—phosphates, carbonates, and silicas.  It is important that a toothpaste should contain enough abrasives to remove and help prevent staining without it being overly abrasive to result in loss of tooth structure. This is where baking soda leads the pack. 
The Radioactive Dentin Abrasion (RDA) measures how abrasive a toothpaste is. The FDA sets the limit at 250, considering anything lower to be safe while still being effective. Most abrasives that are added to toothpastes have an RDA of 70-110. Baking soda has the lowest RDA of all abrasive additives at an RDA of 30-40. 
Why Baking Soda Is Still Effective Even Though It Is Less Abrasive
Baking soda works to remove stains from teeth through both mechanical and chemical actions. This means more cleaning power with the least abrasion.
A University of Rochester study found that when 100 adults used 52% and 65% sodium bicarbonate for six months, 50% realized a reduction in plaque, 70% a reduction in gingival inflammation, and 60% reduction in staining.  When compared to calcium phosphate, a common toothpaste additive, baking soda mean ration of abrasion to cleaning power was 10:1 compared to 1:7 for the calcium pyrophosphate. 
Additional Benefits of Baking Soda for Teeth
For most people, the biggest culprit of enamel erosion is not found in the particular teeth cleaning method chosen, but in the acidic foods they choose to eat. Foods that are acidic such as fruit juices, colas, and wine all weigh heavily on tooth erosion. But here again is an additional benefit of baking soda. Brushing with baking soda will help to neutralize acids in mouth. In fact, baking soda helps to neutralize enamel eroding acids so well that swishing with sodium bicarbonate is commonly recommended for patients with acid reflux, undergoing chemotherapy, or have morning sickness due to pregnancy.
The chemical reaction of baking soda with saliva has also been shown to positively change the oral microflora inducing beneficial effects on plaque and surface stain accumulation. 
Dentifrice Recommendations Should Be Patient Specific
Something that is beneficial to some may not be beneficial to others. For example, if you already have erosion of the dentition, you need to be very careful in the care and maintenance of your teeth to avoid increasing the risk of further abrasion. Your dentist is your best guide to choosing the optimal cleaning method for your teeth. 
 Advances in Dental Research; Wülknitz P.
Cleaning power and abrasivity of European toothpastes
1997; Volume: 11; Pages: 576-579
  Dr. John Hefferren, Dr. Na Li
Dentifrice Abrasives: Heroes or Villains
Fiona M. Collins, BDS, MBA, MA
Reflections on Dentifrice Ingredients, Benefits and Recommendations
Dr. Fiona M. Collins, MBA, MA
Treatment Options for Tooth Discoloration and Remineralization
 Compendium in Continuing Education in Dentistry; Zambon JJ, Mather ML, Gonzales Y
A microbiological and clinical study of the safety and efficacy of baking soda dentifrices
1998; 18:(Suppl. No. 21) 539–544
5 Things You Didn’t Know about Your Teeth