The diagnosis and treatment of skeletal open bite remains one of the most challenging problems for orthodontists. Recently, two studies have answered some questions regarding early treatment of skeletal open bite.
In a prospective cephalometric study, Tran et al. evaluated the effects of combining high-pull headgear (HPHG) with minimal masticatory muscle functional training on craniofacial morphology changes. Thirty-one skeletal open bite patients (average age 9.3 ± 1.3 years) were treated with fixed palatal expanders (BPE), transpalatal arches (TPA), high-pull headgear (HPHG), and mandibular lingual arches for 23 ± 4.7 months. After rapid palatal expansion (RPE), patients were randomly divided into a functional training group and a non-functional training group. Patients in the functional training group bit on occlusal pads five times a day for one minute each time. Cephalometric analysis was performed on lateral skull radiographs before and after treatment to record morphological indicators. The control group was matched by age, gender, and mandibular plane angle with the treatment group and underwent similar pre- and post-treatment cephalometric analysis. In the functional training group, maximum bite force values and electromyographic parameters of the masseter muscle were recorded before and after functional training. The linear relationship between bite force and electromyographic parameters was used to evaluate muscle strength.
The study results showed: functional muscle training helps with vertical control; using only high-pull headgear can deepen overbite and intrude maxillary molars; if combined with muscle function training, it significantly reduces ANB angle and gonial angle, causing an average anterior and superior rotation of the mandible by 2.2°; there was no significant difference in regression coefficients of maximum bite force values and electromyographic parameters before and after muscle function training; although muscle function training does not increase chewing muscle strength, it improves facial aesthetics, helping to compensate for abnormal vertical growth patterns.
In another retrospective cephalometric study, Sankey et al. evaluated a new method for early treatment of vertical skeletal dysplasia with maxillary constriction. Thirty-eight patients (average age 8.2 ± 1.2 years) participated in this study and underwent lip closure training, fixed palatal expanders (BPE), and Crozat appliances or lip bumpers for the mandible over 1.3 ± 0.3 years. The expanders here had posterior occlusal pads that remained fixed during treatment. Patients with poor masticatory muscle strength (79%) wore high-pull headgear for 12-14 hours daily. The control group was matched by age, gender, and mandibular plane angle.
The results showed: wearing HPHG did not significantly affect treatment outcomes; this treatment method significantly promotes anterior and superior growth of the condyle; it causes the mandible to rotate forward at 2.7 times the rate of the control group; after treatment, posterior face height increased, maxillary molars were relatively intruded, and the anterior movement of the pogonion, gnathion, and menton points of the mandible increased by 90-190% compared to the control group, increasing overbite and reducing overjet. This study suggests that this treatment method may be very suitable for patients with open bites caused by three-plane skeletal discrepancies.
Ten Questions Regarding Early Treatment of Open Bite
From June 13-17, 1997, the American Orthodontic Experts Committee (CDABO) held a special academic seminar on early treatment in Quebec City, Canada. During the meeting, some questions were raised, and the following are parts related to early treatment of open bite.
1. What is "early treatment"?
CDABO defines early treatment as: treatment that begins during the primary dentition or mixed dentition period, promoting dental and jawbone development before the permanent dentition erupts. Its aim is to correct malocclusion or prevent its formation, and also to reduce the need for or shorten the duration of orthodontic treatment in the permanent dentition.
2. What are the differences between dental open bite and skeletal open bite?
Dental open bite is often associated with thumb sucking or finger sucking habits, and age is an important factor related to dental open bite. Worms et al. reported that 80% of anterior open bite patients aged 7-9 years old to 10-12 years old will self-correct. When patients break bad habits, dental open bite can be corrected. Skeletal open bite often presents with compensatory excessive eruption of upper incisors and excessive alveolar height.
3. What is the relationship between tooth eruption and skeletal open bite?
According to Cangialosi's research, dental open bite is often accompanied by insufficient eruption of anterior teeth, which is due to certain factors obstructing normal eruption of incisors. Once bad habits like thumb sucking are eliminated, dental open bite tends to self-correct. Cangialosi also reported that excessive eruption of molars and incisors is more severe in skeletal open bite than in dental open bite.
4. What are the common phenotypic characteristics of skeletal open bite?
Patients with skeletal open bite often exhibit the following characteristics: short posterior lower face height, long anterior lower face height, large mandibular plane angle and gonial angle, posterior-inferiorly tilted maxilla, lingual braces. Patients usually have excessively developed alveolar height, possibly accompanied by maxillary constriction and posterior crossbite. Mandibular retrognathism with anterior open bite is often associated with bad tongue habits.
5. Advantages of early treatment for skeletal open bite?
For patients with signs of skeletal open bite, early treatment is necessary for successful correction. Early in growth and development, the facial growth pattern is established. If a skeletal open bite patient does not receive treatment until the permanent dentition stage, the opportunity to change their growth pattern is lost, leaving orthognathic surgery as the only option. Additionally, early treatment improves facial aesthetics, benefiting the child's physical and mental health.
6. Which method is most suitable for treating skeletal open bite?
Controlling vertical height is key to successfully treating skeletal open bite. Treatment should increase the anteroposterior height ratio, promote anterior-superior rotation of the mandible, and vertical growth of the condyle. Intruding molars to cause counterclockwise rotation of the mandible is a decisive step in treatment. In Tran's study, the treatment method was: using a rapid palatal expander (RPE) with occlusal pads 2-3mm greater than the resting interocclusal space, expanding at a rate of 0.25mm per day until the maxillary molars reach distal crossbite. After maintaining with RPE for three months, it is removed and replaced with a transpalatal arch (TPA) to maintain the width between the molars. A 15mm diameter palate button is placed 3mm away from the central palate mucosa. Patients must wear high-pull headgear (HPHG) for 12 hours daily, with a force of 500g per side. During treatment, the mandibular arch length is maintained with a lingual arch, inhibiting excessive eruption of molars.
7. At what age should treatment begin for skeletal open bite patients?
Children have greater growth potential and tissue remodeling possibilities than adolescents. Additionally, children are more likely to cooperate with complex treatments than teenagers. Therefore, treatment should begin when the patient is 7-8 years old and understands cooperation.
8. Can muscle functional training improve the skeletal morphology of children with skeletal open bite by enhancing muscle strength?
Currently, there is no single treatment model that effectively meets the needs of skeletal open bite treatment. Therefore, we must consider the impact of chewing muscles and their functions on the development of the stomatognathic system. Chewing muscles in skeletal open bite patients are often underdeveloped, with smaller bite forces. Tran et al.'s study results showed: using only high traction without muscle functional training has no effect on alveolar height, maintaining the position of the upper molars while increasing overbite; high traction combined with muscle functional training facilitates anterior-superior rotation of the mandible, reducing the angles of the ANB angle and gonial angle to achieve mandibular orthopedic goals. Although muscle functional training does not increase chewing muscle strength, it improves facial aesthetics, aiding in compensating for abnormal vertical growth patterns.
9. What should be the treatment outcome for skeletal open bite after treatment?
The basic treatment outcome of early treatment depends on the orthodontist's diagnosis of malocclusion causes and ability to correct malocclusions. The growth and development period is the key to successful treatment; to achieve non-surgical success, early functional orthopedic treatment must be conducted to improve vertical growth patterns.
10. Should orthodontic treatment begin for skeletal open bite patients in the mixed dentition stage?
Orthodontic treatment should begin for skeletal open bite patients in the mixed dentition stage.