Bite and balance in the archer: Ishigami 1992 study

A single archer, a 22-year-old student on his university archery team, was measured on a platform that records body sway while he shot with and without a clear resin bite splint. The splint raised the bite by 2, 5 or 10 mm, measured at the incisors. The reference was his own normal variability: nine measurements without the splint, taken over three days, show how much the values change by themselves from one trial to the next.

With 2 and 5 mm the changes stayed within that range, although one of the indices tended to fall as the minutes went by. With 10 mm the sway area and the length of the centre of gravity's path dropped below the range as early as 5 minutes after the splint went in, and after 15 minutes so did the third index, which describes how readily the centre of gravity returns towards its mean position. The largest reduction in area came at 30 minutes, and in that condition the amplitude of sway, both sideways and front to back, in the second before the shot was also smaller than without the splint.

The authors conclude that for this archer a 10 mm splint, put in about half an hour before shooting, might make the aiming posture steadier, and they allow that each archer may respond differently.

The splint was made from impressions of the dental arches, mounted on an articulator, adjusted in centric relation and then refined in the mouth, in three thicknesses (2, 5 and 10 mm at the edge of the left central incisor). Without the splint the archer kept his teeth lightly clenched, as is usual when aiming; with it he clenched on the splint. The platform met the Japanese JIS standard and fed a computer, sampling at 20 Hz.

Each recording lasted 10 seconds and covered a whole shot, from set-up through the draw, aiming, release and follow-through: the authors chose 10 seconds because this archer took that long per arrow on average, and the rules at the time allowed two and a half minutes for three arrows. He shot with his eyes open, in competition clothing and equipment, with his feet parallel, but with the target about a metre beyond the arrow point, so in a laboratory rather than on a field.

Measurements were taken three times before the splint went in and then at 2.5, 5, 15, 30 and 60 minutes, for each thickness. The indices were the area covered by the centre of gravity, the length of its path and its convergence towards the mean position, expressed as a percentage of the mean without the splint; for the second before the shot the authors looked at the maximum amplitude of the sideways and front-to-back traces.

This is one archer, measured in a single series of sessions, and the result applies to him: the authors themselves say more participants are needed. There is no condition with a splint that does not raise the bite and no blinded comparison, so the effect of thickness cannot be separated from that of having something in the mouth, clenching differently or getting used to the session. The 10 mm values fall as the minutes pass, and growing familiarity with the platform may play a part too; the reference range comes from nine measurements over three days, not from trials alternated with those using the splint.

The target was a metre away, so the visual task, and probably the mental demand, were not those of a real shot: the authors themselves think vision weighed heavily on these results. Finally, no scores were recorded. The study measures body sway, not where the arrow goes, and the idea that a steadier platform reading means better shots remains a hypothesis.

For anyone who shoots, the study offers little that can be used directly. It shows that in one archer a very thick splint, 10 mm, far more than a thin mouthguard, changed the body sway recorded by the platform, while 2 and 5 mm did not move it beyond his normal variability. It does not say whether the group on the target changes, whether the finding holds for other archers, or how the splint compares with simply keeping the teeth lightly clenched for the same length of time.

One point is worth keeping in mind: here the body needed minutes, not seconds, to settle, and the largest effect came after half an hour. A splint is a dental device all the same, and this single-person study is not enough to regard it as an aid to aiming.