This is the 463rd most frequent Icelandic word.
þess
"Þess" translates to "of it" or "its" in English.
The word "þess" is part of the conjunction "vegna þess að", which translates to "because". Here, it is used to introduce the reason for the necessity to visit the dentist.
Ég þarf að fara til tannlæknis vegna þess að ég finn fyrir verk.
I need to go to the dentist because I feel pain.
Similar to the second example, "þess" is part of the phrase "þess virði", referring to the entity or effort being justified by the value or outcome.
Nám kefir mikla vinnu, en það er þess virði.
Education requires a lot of effort, but it is worth it.
In this sentence, "þess" is used within the construction "þess virði", which means "worth something". The word "þess" relates to the idea or proposition being evaluated.