Porcelain veneers have hairline cracks on them a week after placement. Any suggestions? (photos)

My dentist placed eight porcelain veneers on my upper front teeth a week ago. Now four of them have hairline cracks on them. Why can it be so? I don't grind my teeth during the night. I have not had any trauma or eaten anything hard. We controlled my teeth well for paracontact. Can veneers itself be with defects? Or can it be a problem of wrong placement?