Testing Teeth Visibility in Toothbrushing Scenes | Comparing 6 Prompt Expressions

Key Findings

• showing teeth and grinning are the most reliable for exposing teeth. Both achieved visible upper teeth in 3 out of 3 images
• showing teeth maintains the toothbrushing action while showing teeth. The toothbrush stays near the mouth, preserving the scene’s coherence
• grinning produces the highest teeth exposure but the toothbrush tends to drift away from the mouth. The result looks more like “smiling while holding a toothbrush” than “brushing teeth”
• biting toothbrush produced nearly identical results to the control. The biting action didn’t lead to teeth exposure
• The control (brushing teeth alone) shows virtually no teeth. The toothbrush covers the mouth by default

Experiment Design

Base Prompt (Fixed)

1girl, 32yo japanese actress, topless, upper body, bathroom mirror, morning sunlight, holding toothbrush, [condition variable]

upper body frames the shot closer to the face, making teeth visibility easier to evaluate.

Conditions

Note: A04 replaces holding toothbrush, brushing teeth with biting toothbrush — this is an action change, not a tag addition.

Results by Condition

A00: Control (brushing teeth)

seed 1	seed 2	seed 3

Observation: 0 out of 3 images show visible teeth. The toothbrush covers the mouth area in all cases, with the mouth in a closed or nearly closed position. The bathroom mirror composition is consistently reproduced across all seeds.

A01: open mouth

seed 1	seed 2	seed 3
		NSFW - クリックで表示

Observation: 2 out of 3 images (s2, s3) show upper teeth. The mouth opening is noticeably wider than the control, with teeth visible through or beside the toothbrush. s3 shows the widest mouth opening with the clearest teeth visibility.

A02: showing teeth

seed 1	seed 2	seed 3

Observation: 3 out of 3 images show clearly visible upper teeth. The expression shifts toward a smile with raised mouth corners, exposing the teeth. The toothbrush remains near the mouth, maintaining coherence as a toothbrushing scene.

A03: visible teeth

seed 1	seed 2	seed 3

Observation: 2 out of 3 images (s1, s2) show slightly visible teeth, but not as clearly as A02. s3 has a more closed mouth with poor teeth visibility. Despite being a similar expression to showing teeth, visible teeth does not reliably guide teeth exposure.

A04: biting toothbrush

seed 1	seed 2	seed 3

Observation: 0 to 1 out of 3 images show faintly visible teeth. Results are nearly identical to the control. The biting action implies closing the mouth around the toothbrush, which works against teeth exposure.

A05: grinning

seed 1	seed 2	seed 3
		NSFW - クリックで表示

Observation: 3 out of 3 images show clearly visible upper teeth. Ties with A02 for the highest teeth visibility. However, the toothbrush tends to be held away from the mouth, making the composition look more like “smiling while holding a toothbrush” than actively brushing.

Comparison Summary

Practical Takeaways

• Use showing teeth for the best balance of teeth visibility and toothbrushing coherence. It achieves both goals simultaneously
• grinning maximizes teeth exposure but sacrifices the brushing action. Better suited for “smiling with a toothbrush” compositions
• visible teeth and showing teeth look like similar expressions but produce different results. showing teeth is consistently more effective
• biting toothbrush has no effect on teeth exposure. The biting action closes the mouth rather than opening it
• topless, upper body, bathroom mirror, morning sunlight produces a stable morning bathroom scene. The mirror composition was reliably reproduced across all conditions

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