20A Reader's forum American Journal of Orthodontics and Dentofacial Orthopedics

Reply to Dr. Berg

First, I thank Prof. Berg for his generous comments regarding the case I presented in the April issue of the AJO/DO.

I routinely use palatal arches with auxiliary springs in the treat- ment of palatally impacted maxil- lary canines and in a fair number of cases where maxillary canines are located buccally. The decision whether to use a palatal arch when the teeth are impacted in a buccal position depends on the crown tip location and the direction of force required for optimal tooth move- ment.

In this case, a palatal arch with an auxiliary spring was positioned before surgery in case palatal force systems were required. As I explained in the case presentation, success depended on the absence of ankylosis and whether the maxil- lary canines could be moved past

the root apex of the maxillary later- al incisors. For this reason, I did not want to remove the deciduous canines before the maxillary canines had been brought down a certain distance. Consequently, because of the occlusion, it was not possible to pass an auxiliary spring across the arch.

In this case, I decided to bond before surgery, because a buccal approach was likely. The surgeon could then pass the ligature from the lingual button through the flap and hook it over the arch wire, thus reducing the amount of pain asso- ciated with initial activation.

If no brackets had been present at surgery, the surgeon would have had to fix this wire to either the lat- eral incisor or the first premolar. During initial activation, the wire from the button would be straight- ened out and consequently cut

through soft tissue, leading to patient discomfort.

In my early days as an orthodon- tist, I did use a high labial arch with auxiliary springs in a certain number of cases with buccally impacted maxillary canines. However, I found that it was difficult to control such a high labial arch in some cases and abandoned this practice many years ago.

Whenever a palatal arch with auxiliary spring can be used, I agree with Dr. Berg that initial harmoniza- tion of the impacted canines without bonded teeth is an advantage for the reason he mentions, and nor- mally I postpone bonding in such cases to a time when the impacted tooth is near eruption.

Jan ~degaard Madlaveien 9

4008 Stavanger Norway

In favor of semirapid expansion

I would like to congratulate Drs. Sandikgio-lu and Hazar I on their recent article. It is the first scientific presentation I have seen that com- pares slow, semirapid, and rapid expansion. Slow expansion is usual- ly defined as approximately one third mm per week, semirapid as 1 mm per week, and rapid is approxi- mately 3 mm per week. Although many firm opinions are expressed by clinicians to justify their preferred rate, there has been little firm evi- dence available. Critics of slow expansion dislike the pain, the tis- sue damage, and the box-shaped arch form that often results. I dis- cussed these issues in 19772 when I first recommended a simirapid rate of 1 mm per week.

Story 3 showed that rapid expan- sion was followed by poor tissue repair, as the capillary network can hardly keep up with the separation

of the suture. Many clinicians feel that in the long term, expansion relapses to an extent that renders it valueless, whereas others use it routinely in their practice. The relapse does seem highly variable, but several studies 4,5 have shown that the widening of the vault is sta- ble and it is the alveolus that tends to relapse. This would suggest that it is advantageous to separate the suture.

Sandikio-lu and Hazar appear to have had some difficulties in gain- ing cooperation with the patients who wore the semirapid appliances that were removable. I note from their figures that although the patients were asked to open at 1 mm per week, the effective rate over the 5.5 months was less than a fifth of a millimeter per week. In my clini- cal experience, that is too slow to open the suture and is not really

semirapid. This study could possibly be misleading in this respect. My own research 6 suggests that semi- rapid expansion is very stable.

I could perhaps offer the authors some advice in gaining an effective rate of 1 mm per week. First, insist that the patients wear the appliance while eating. This may be impossi- ble to start with, but children will hardly notice it in their mouth within 10 days. Second, open one eighth of a turn each day, not one quarter every other day. The periodontal membrane is approximately an eighth of a millimeter thick and so an eighth of a turn, distributed between the two sides, will only reduce it by half, not crush it. Also it is easier to remember something you do every day. Third, check the amount of opening at each visit, because if the rate of opening slows much below 1 mm per week, the suture will not separate and most of the widening

American Journal of Orthodontics and Dentofacial Orthopedics Volume 112, No 4

Reader's forum 21A

will be alveolar and liable to greater relapse. I personally use an adapted form of Crozat clasp that can be adjusted so firmly that the child needs the assistance of their parents to remove the appliance. Little is achieved by adjusting loose remov- able appliances.

One final point in favor of the semirapid rate is that it can be relied on to separate adult sutures in 75% of cases, whereas rapid expansion fails in almost the same proportion

(R. Scavo, 1986 unpublished clinical trial). This is of major significance in presurgical cases, and it is a shame that this knowledge is not more widespread.

John Mew Heathfield, Sussex, U. K.

Tel~fax 01435 862045

REFERENCES

1. Sandikqio-lu M, Hazar S. Skeletal and dental

changes after maxillary expansion in mixed dentition. Am J Orthod Dentofac Orthop 1997;111:321-7.

2. Mew JRC. Relapse following maxillary expansion. Br Dent J 1977;143:301-6.

3. Story E. Tissue response to the movement of bones. Am J Orthod 1973;64:229.

4. Labret LML. Expansion with labiolingual and removable appliances. Am J Orthod 1964;50:786-7.

5. Skiener V. Expansion of the midpalatal suture by removable plates studies by the implant method. Trans Eur Orthod Soc; 1964. p.143- 58.

6. Mew JRC. Relapse following maxillary expansion. Am J Orthod 1983;83:56-61.