tion as is a molar with the sinus "draped" over its roots. Working near the membrane with a bur is highly inadvisable, as the sharp bur would quickly punch through the membrane.

The maxillary sinus has a tendency to collect fluids. Although cilia in its lining waft fluids and particles toward the osteum maxillare for expulsion into the nasal cavity, this passageway is high on the wall (30) separating the sinus from the nose. Thus when the head is held vertically, as it usually is during working hours, the sinus must be almost full for it to drain into the nose. Even then very little fluid escapes unless the head is tilted to bring the fluid level near the opening. Some people have an accessory opening (31) lower in the wall, and they have fewer problems with sinus drainage.

The problem of collecting fluids is aggravated by the fact that the other sinuses may drain into the maxillary sinuses, and blowing the nose hard can force material to back up into the maxillary sinuses. Also, when the tissues around the osteum maxillare swell due to infection or irritation, they can close the passageway into the nose.

Fluid trapped in the sinuses with infectious agents often causes problems that should be noted by the dentist, particularly the implantologist. Pressure in the sinuses may make the patient nervous and subject to headaches. Working near an already sensitive area invites complications.

Bone resorption may have partially exposed the superior alveolar nerves, permitting direct contact with the sinus membrane. Thus irritation or pain from an infected membrane can be confused in the patient with upper teeth with pulpitis. Because the implantologist is generally working on patients with significant bone resorption, there is a good chance that the pain from sinusitis may be blamed on the presence of an implant. In the patient with teeth, sinusitis often can be differentiated from pulpitis by the extent of

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