Mirror image

Sept. 1, 2006
One of the most basic tools in dentistry is the dental mouth mirror. Without a dental mirror, it would be very difficult to see many locations in the oral cavity.

One of the most basic tools in dentistry is the dental mouth mirror. Without a dental mirror, it would be very difficult to see many locations in the oral cavity. Imagine the awkward positions a hygienist would need to assume to evaluate the lingual surfaces of the maxillary anterior teeth or the most posterior of the maxillary molars. To help with this, the mirror has evolved from strictly metal to disposables and molded types.

The mirror often becomes an extension of one’s fingers, and allows dental professionals to retract tongues and tissues comfortably to allow for better access during exams. Effectively using the mirror allows a clear view of the working site without impinging on the nearby tissues or pinching the lip, which is painful for the patient. Another advantage of the mirror is that it becomes an indirect light source when it reflects from overhead lighting onto the mirror’s surface. When light reaches the mirror, it is not absorbed but directed back to the tissues and through the teeth. This is called transillumination. Craze lines within teeth can be viewed more easily with the mirror, as well as calculus deposits, which appear densely opaque when light is blocked by the buildup.

How do mouth mirrors work?

There are different types of mirrors. Some offer concave magnification, while others are flat, and can be back or front reflecting. A flat mirror may produce a false or double image. The front reflecting or front surface mirrors are smooth, so the photons bounce off at the same angle they hit or reflect. The light is not magnified, so there are no double images. The image is not magnified because the mirror is not concave. Conversely, a light source reflects off a mirror at an angle equal to its angle of incidence. When a light beam strikes a mouth mirror at a specific angle from vertical, it reflects from the point of incidence at the same or equal angle from vertical in the opposite direction. More simply stated, all mirrors work on the principle of reflective light. Particles of light, or light photons, strike a mirror surface and reflect and enter the eyes to form an image.

When light hits a curved or concave mirror, images become magnified. Generally, the working end of the mirror curves away from the clinician so that the image viewed closely will appear enlarged and objects far away will appear upside down. A “mirror image” is a backward image to our taught eye. The beam of light alters its direction, yet remains parallel. These are virtual images that are the same size as the original object.

You may remember instructors in hygiene school saying you will be able to train your eyes to read these reverse images. You’ve probably noticed the side view mirror on your car says, “Objects may be closer than they appear.” But the driver’s side mirror does not say this. The passenger’s side mirror is curved so the driver’s vision may span a broader rear distance. Because of the curve on the passenger mirror, visual distortion causes vehicles to appear closer. In contrast, the driver’s side mirror is flat because cars to the left are closer to the driver and there is no distortion.

Dental mirrors and handles are made of different materials. Metal mirrors are common and may have round threaded heads fitted to a socket-handle (which are replacable when scratched) or have working ends which are weld-mounted and not removable. Another choice is the double-sided mirror which has a front and back mounted mirror and allows for multiple views and retraction. Molded and disposable mirrors offer clinicians some advantages in that they are lightweight and can be easily manipulated, which reduces stress and wrist fatigue.

There are several mouth mirrors available. Dux Dental/Clive Craig offers an autoclavable front surface, rhodium-plated mirror in a variety of colors. A front reflecting surface mirror means the glass is on top. Rhodium-plated refers to the evaporation of rhodium on the surface, which avoids distortion of images. Rhodium offers sharpness, a bright reflective surface, and a distinct reflected image.

In contrast, some mirrors may be back surface type mirrors, which is the same as a regular mirror. These mirrors have a protective (waterproof) coating on one side and glass on the other, which provides an optimal reflection. An example of a back surface mirror is the fiberglass mirror by Formadent. This is reusable, available in size four black resin, and appropriate for air polishing. Denticator offers a teal-colored, size four dental mirror with a second surface or back surface reflection.

Another type of mirror is the crystal mouth mirror by the Zirc company. It is comprised of 40 different layers of oxides, which offer clarity and a high degree of color accuracy. The resin handles have incorporated antibacterial protection called Microban®, which will not wear from use. Microban® is an antimicrobial agent that deters the growth of bacteria. It permeates the cell walls of thin-walled microorganisms and disturbs metabolic function. Also, the soft-grip antimicrobial handle is ergonomic.

For a uniquely shaped mirror, try the disposable Flecta mirror from Pulpdent. This elongated mirror is double-sided and good for retracting, because it offers a large oval surface. It is ideal for dispensing with home-care instruction because it offers patients a better view of their teeth between recare visits.

Mouth mirrors are in the dental armamentarium with a range of uses from reflecting light to retraction of tissues. Areas of the mouth that are difficult to light need a mouth mirror to reflect light onto the surfaces. Mirrors help prevent injury during tongue and cheek retraction. Antibacterial protection in nonmetal handles is a nice benefit. Most dental professionals enjoy the advantages of quality mirrors for clear images.

The author did not receive compensation for products mentioned. To learn more about dental mirrors, visit the Web at www.duxdental.com, www.formadent.com, www.denticator.com, www.zirc.com, and www.pulpdent.com.

Karen Kaiser, RDH, graduated from St. Louis’ Forest Park dental hygiene program in 1994 and currently practices at the Center for Contemporary Dentistry in Columbia, Ill. She has written several articles for RDH and other publications, sits on dental hygiene panels, and is an evaluator for Clinical Research Associates. She can be contacted at [email protected].