The diffuse value of the teeth (and possibly eyewhites, if I recall correctly) does need adjusting from the default value in the shader.

You wrote that you changed the gamma value on every texture except the neck.

Firstly, this suggests that you went into each of the figure's materials and did that. No no! All you do is go into the VSS prop materials, change it there (in six shaders), and Synchronise.
(Edited to add: after changing the Prop shaders, its a good idea to save this new non-GC version to your Props library).

Secondly, what gamma value did you set?

Thirdly, I would advise using bagginsbill's Lightmeter (new version) to check the 'real' diffuse and specular light levels in your scene.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)