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Use Present Perfect - Active or Passive

1. Numerous analyses of the microbial make-up of plaque in subjects of different caries experience (to reveal) a correlation between the presence of Streptococci mutans and caries.

2. When an adjacent tooth (to extract) for other reasons, direct access is possible.

3. From the middle of the 17th century, gutta percha (to recommend) for all sorts of uses.

4. It (to use) in dentistry for over 130 years, as a temporary restorative, an impression material, or as a root canal filling material.

1 Numerous analyses of the microbial make-up of plaque in subjects of different caries experience have revealed a correlation between the presence of Streptococci mutans and caries.2. When an adjacent tooth has been extracted for other reasons, direct access is possible.3. From the middle of the 17th century, gutta percha has been recommended for all sorts of uses.4. It has been used in dentistry for over 130 years, as a temporary restorative, an impression material, or as a root canal filling material.