I recently dined at one of my favorite restaurants. Following the meal, the server asked if I wanted the rest of my drink in a to-go cup. I had done that many times, so I didn’t think anything of it. For some reason, the size of the lid that came on the Styrofoam cup was just slightly too small, so it wouldn't seal or stay on correctly. To get it to fit, I had to stretch the lid slightly or wrinkle up the cup below. No matter what I tried, the top just popped back off after a few seconds.

Upper Teeth Must Be 23% Wider than Lower Teeth
Your upper and lower teeth are a set, just like a cup and lid. The upper teeth must be bigger to fit with no spacing in the upper or crowding in the lower. Years ago, an orthodontist named Dr. Bolton identified this phenomenon and determined that the upper teeth must be 23% larger than the lower ones, or they wouldn’t “fit.” When the upper and lower sets of teeth don’t match because the teeth are different sizes, the condition is known as a Bolton Discrepancy.

Narrow Upper Laterals Common Create Bolton Discrepancies
The most common cause of a Bolton discrepancy is narrow upper laterals. When upper laterals are narrower than they should be, there will either be extra space in the upper (next to the narrow teeth or between the central incisors) or crowding in the lower. The most common “fix” for a Bolton discrepancy is to make the lower anteriors slightly narrower using interproximal reduction (slenderizing or air-rotor stripping). This is the equivalent of making the cup a little smaller so the lid will fit. If the upper laterals are very narrow, the best approach is to veneer or crown the malformed teeth.

Missing Teeth Can Also Create Bolton Discrepancies
Another cause of Bolton Discrepancies is an entire missing tooth in the lower anterior. If the upper anteriors are all the correct size, but a lower incisor is missing, the “cup” is now too small, and the resulting orthodontic condition is excessive overjet (an “overbite”). This type of discrepancy can be addressed by making the upper teeth narrower or adding a tooth (a bridge or implant) or tooth structure (veneers or crowns) in the lower. Again, the goal is to adjust the overall tooth sizes so the upper is 23% wider than the lower.

A Simple Hack for Recognizing Bolton Discrepancies
Although the most accurate way to determine tooth sizes is to measure individually, a “quick and dirty” way to identify Bolton Discrepancies is to compare the sizes of the upper and lower lateral incisors. The upper laterals should be significantly wider (about 50% bigger) than the lower laterals. If they appear to be the same size or narrower, there is a good chance that the upper and lower teeth won’t fit correctly after they are aligned and all the spaces closed.

NOTE: The author, Dr. Greg Jorgensen, is a board-certified orthodontist in the private practice of orthodontics in Rio Rancho and Albuquerque, New Mexico. He was trained at BYU, Washington University in St. Louis, and the University of Iowa. Dr. Jorgensen’s 30 years of specialty practice and 10,000+ finished cases qualify him as an expert in two-phase treatment, extraction and non-extraction therapy, functional orthodontics, clear aligners (Invisalign), and multiple bracket systems (including conventional braces, Damon and other self-ligating brackets, Suresmile, and lingual braces). This blog is for informational purposes only and is designed to help consumers understand currently accepted orthodontic concepts. It is not a venue for debating alternative treatment theories. Dr. Jorgensen is licensed to diagnose and treat patients only in New Mexico. He cannot diagnose cases described in comments nor select treatment plans for readers. The opinions expressed here are protected by copyright laws and can only be used with the author’s written permission.