diff --git a/frontend/src/components/ui/treatment/FdiToothChart.tsx b/frontend/src/components/ui/treatment/FdiToothChart.tsx
index d61b1b3..eba19a3 100644
--- a/frontend/src/components/ui/treatment/FdiToothChart.tsx
+++ b/frontend/src/components/ui/treatment/FdiToothChart.tsx
@@ -24,6 +24,12 @@ const TOOTH_NUMBER_GAP = 'mt-1';
 const REALISTIC_NUMBER_GAP = '2mm';
 /** Tight interproximal gap between tooth columns. */
 const TOOTH_GAP = 'gap-x-px';
+/**
+ * Centers a mark on the inline-end edge of a tooth column (between this tooth
+ * and the next in flex order). Logical `end` + 0-width flex stays correct in LTR and RTL.
+ */
+const EDGE_MARK_ANCHOR =
+  'absolute inset-y-0 end-0 z-10 w-0 flex items-center justify-center';
 
 function quadrantMirrored(fdi: FdiToothId): boolean {
   const q = fdi[0];
@@ -285,40 +291,42 @@ export function FdiToothChart({
                 />
               ) : null}
               {renderEdge ? (
-                linkInteractive ? (
-                  <button
-                    type="button"
-                    disabled={isDisabled}
-                    title={linked ? t('toothUnlinkHint') : t('toothLinkHint')}
-                    aria-label={
-                      linked
-                        ? t('toothUnlinkAria', { a: fdi, b: next! })
-                        : t('toothLinkAria', { a: fdi, b: next! })
-                    }
-                    aria-pressed={linked}
-                    onClick={(e) => {
-                      e.preventDefault();
-                      e.stopPropagation();
-                      onToggleLink?.(fdi, next!);
-                    }}
-                    className={`
-                      absolute right-0 z-10 translate-x-1/2 h-3.5 w-3.5 rounded-full border-2 transition-colors
-                      focus:outline-none focus-visible:ring-2 focus-visible:ring-primary/50
-                      ${
+                <div className={EDGE_MARK_ANCHOR}>
+                  {linkInteractive ? (
+                    <button
+                      type="button"
+                      disabled={isDisabled}
+                      title={linked ? t('toothUnlinkHint') : t('toothLinkHint')}
+                      aria-label={
                         linked
-                          ? 'border-primary bg-primary shadow-sm'
-                          : 'border-primary bg-background-secondary hover:bg-primary/15'
+                          ? t('toothUnlinkAria', { a: fdi, b: next! })
+                          : t('toothLinkAria', { a: fdi, b: next! })
                       }
-                      ${isDisabled ? 'opacity-50 cursor-not-allowed' : 'cursor-pointer'}
-                    `}
-                  />
-                ) : (
-                  <span
-                    className="absolute right-0 z-10 translate-x-1/2 h-2.5 w-2.5 rounded-full bg-primary shadow-sm"
-                    title={t('toothConnectedHint')}
-                    aria-hidden
-                  />
-                )
+                      aria-pressed={linked}
+                      onClick={(e) => {
+                        e.preventDefault();
+                        e.stopPropagation();
+                        onToggleLink?.(fdi, next!);
+                      }}
+                      className={`
+                        h-3.5 w-3.5 shrink-0 rounded-full border-2 transition-colors
+                        focus:outline-none focus-visible:ring-2 focus-visible:ring-primary/50
+                        ${
+                          linked
+                            ? 'border-primary bg-primary shadow-sm'
+                            : 'border-primary bg-background-secondary hover:bg-primary/15'
+                        }
+                        ${isDisabled ? 'opacity-50 cursor-not-allowed' : 'cursor-pointer'}
+                      `}
+                    />
+                  ) : (
+                    <span
+                      className="h-2.5 w-2.5 shrink-0 rounded-full bg-primary shadow-sm"
+                      title={t('toothConnectedHint')}
+                      aria-hidden
+                    />
+                  )}
+                </div>
               ) : null}
             </div>
           );