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A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics by Dr. Chad Foster

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Categories: Orthodontics;
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics   

by Chad Foster, DDS, MS, editorial director

Orthopedic maxillary expansion with a rapid palatal expander (RPE) has long been an effective tool in orthodontics. While there are a variety of scenarios where an RPE is indicated, the most common is a mixed-dentition patient with a unilateral or bilateral posterior crossbite. In these situations where the maxillary arch is narrow/constricted relative to the mandibular arch, an RPE alone is very effective in correcting the maxillary transverse deficiency.

There are times, however, where the maxilla is clearly narrow/constricted but there is no posterior crossbite. Often these cases show a true maxillary transverse deficiency paired with a matching/compensated lower arch that shows posterior teeth in excessive lingual inclination. This malocclusion has been previously termed “bimaxillary transverse constriction.” In such cases I have found that effective use of an RPE alone can be challenging. As the RPE expands the maxilla, sometimes the mandibular first molars naturally expand/upright (or “track”) with the expanding maxillary molars as you would hope, but many times they don’t. When they don’t track well, the amount of maxillary expansion is limited. Expanding the maxillary arch in this scenario poses a risk of relative overexpansion of the maxillary molars into a buccal crossbite (Brodie/scissor) position. Effectively, in these bimaxillary transverse constriction cases, mandibular dental expansion via uprighting of the excessively lingually inclined lower first molars can be the rate-limiting step in proper maxillary expansion.

There are different orthodontic strategies aimed at dental expansion of the mandibular posterior teeth in these types of mixed dentition patients. Schwarz expanders, expanded lower lingual holding arches, and two-by-four limited braces with archwire expansion are some common approaches. About seven years ago, I started using a different approach that I’ve found to be simple, inexpensive and effective in influencing uprighting/expansion of the lower first molars in these cases.

Case 1
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics



Case 2
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics
A Voice in the Arena: RPE, Caplin Hooks and Nighttime Elastics


The use of Caplin hooks
For mixed-dentition cases where maxillary expansion is indicated, where there is no posterior crossbite and where the lower molars show a high degree of lingual inclination, in addition to standard use of an RPE, I will bond Caplin hooks to the lingual surface of the lower first molars and instruct the patient to (at night only) wear 3/16-inch, 6-ounce elastics from the buccal hooks on the upper first molar RPE bands to the Caplin hooks on the lingual of the lower first molars. In doing so, I almost never run into issues with the lower molars failing to “track” with the expanding upper molars. Case 1 is an example of this. (The Caplin hooks on the lingual of the L6s are difficult to see in the “after” photos because they’re hidden a bit by the tongue.) A few tips are warranted:
  • Parents can be frustrated if the Caplin hooks are debonding and causing unforeseen extra visits to rebond. Bonding the hooks on the lingual surface of the lower first molars is challenging because of the difficulty in isolating that area from saliva contamination, particularly in a squirmy young mixed-dentition patient. For that reason, this bonding procedure is best done with four hands (an assistant helping).
  • I like to maximize the total area of the bonding surface, so I will etch and prime the whole lingual surface of the lower molars and flow composite over a large surface of the enamel, over and beyond the base of the Caplin hook mesiodistally. Case 2 shows an initial case setup just before expansion; notice the elastics in buccal photos. Just make sure the composite does not cover the hook portion of the Caplin hook. Also make sure the composite does not extend at all occlusally above the lingual surface, which could lead to the upper molars contacting it when chewing and causing debonding of the composite and the hook.
When expansion is complete, I like to section the mesial lingual arms of the RPE, flow composite into the turning component to prevent spontaneous back-turning, and remove the Caplin hooks. The lower molars that have expanded/uprighted require no supplementary retention at that point because their buccal cusps are functionally retained within the cusps of the upper molars. I typically aim to maintain the sectioned RPE for 12 months after the last turn. Another tip for high-angle or dolichofacial patients who could be sensitive to the vertical component of the nighttime crossbite elastics is to flow the composite from the lingual of the lower first molars up and across their whole occlusal surface. The now heavier vertical force of occlusion on these lower molars will act to mitigate the unwanted vertical/eruptive influence of the elastics.


Conservative Phase I treatment
I am very conservative with Phase I treatment and was honored to share some of my thoughts on that subject at the 2023 AAO Annual Session in Chicago with a lecture titled “Wants vs. Needs: Conservative Early Treatment Strategies.” My preference is not to do Phase I at all but when it is needed, I try to make use of the most conservative means possible. More than 80% of my mixed-dentition exam patients will receive no treatment at all, 10%–15% will receive some type of simple appliance-only treatment, and less than 5% will have what I consider to be true Phase I treatment involving appliances plus limited braces.

Expansion in mixed dentition is a controversial topic, particularly lately in the online forums. I want to express clearly that I am strongly opposed to the idea that every kid who comes in the door needs an expander, that expansion is a cure-all for any and all airway issues, that expansion in 3-year-olds is great idea, or any other such quackery. However, I am also strongly opposed to defining and treating maxillary transverse deficiency only when it happens to be accompanied by a posterior crossbite. In cases of bimaxillary transverse constriction, I hope you will find this technique as simple and effective as I have!

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