# A Modified Hyrax-Type Expander Is Effective for Distal Bodily Movement of the Maximally First Molar
## 4 Treatment Alternatives  
For the treatment of the ectopically erupted maxillary canine, the first possible option was to extract the maxillary canine to improve the space shortage. The advantages of this method are that it would allow for early improvement of the space shortage and eliminate the need for traction on the canine. However, the maxillary canines have longer roots and may remain and function for a longer period of time compared with other tooth types [18], so this option was considered disadvantageous both esthetically and functionally.  
The second possible option was extraction of the maxillary left first premolar. This method would be effective for gaining traction space for the maxillary left canine but would be disadvantageous in that the removal of the maxillary left first premolar may cause deviation of the maxillary midline, which was aligned with the facial midline. Furthermore, it may also cause lingual inclination of the maxillary anterior teeth, whose axis was normal at the initial examination. Another disadvantage is that this option would result in an occlusal relationship with one fewer tooth than the normal dentition.  
For the third option, we focused on the presence of the maxillary left third molar and examined the feasibility of extracting the second molar and distally moving the first molar to create space for the eruption of the left canine. In this method, after distal movement of the first molar, the second premolar and first premolar would be moved distally in sequence, and the canine would be aligned after the traction space has been secured, which may require a longer treatment period than other treatment methods. On the other hand, the advantage of this method is that the third molar could be aligned into the maxillary arch to obtain occlusal alignment without reducing the number of teeth.  
After being informed of the expected results and the advantages and disadvantages of each treatment option, the patient and his guardians chose the third option.  
For this method, we also considered the use of a unilateral first molar distal movement appliance with a screw implanted into the bone as an anchorage source, which is a common practice nowadays. However, because there were concerns about the stability of the implanted screw due to the young age of the patient (14 years), and because the patient refused to have the screw implanted, we decided to proceed with treatment using an appliance that was less surgically invasive. Although fixed maxillary molar distal movement appliances such as the pendulum and Greenfield molar distalizer appliances  
Figure 5: Orthodontic occlusal guidance appliance. (**A**) Intraoral photographs. Abutment bands (*); resin button (a); lingual arch (b); canine traction hook (c). (**B**) Lateral cephalogram. Expansion screw (dotted line); expansion screw placement plane (a); maxillary first molar (U6) occlusal surface (b).  
are commonly used, these appliances have been reported to cause distal inclination of the maxillary first molar while it is being moved distally [19,20]. Therefore, in the present case, we devised a maxillary molar distal movement appliance that would allow for distal bodily movement of the maxillary molar without distal inclination and used it for treatment.