"The Ferrule Effect"

Many a times in our practice we come across cases where it becomes hard to react, imagine a patient comes to your office with a post core and the crown in his hand.. What would you do?? make a new more retentive post or do you use a cement which would have a greater tensile strength??
Most of the time we fail to check for a proper "ferrule".

A ferrule effect is defined as the envelopment of the tooth structure by a crown.
According to studies it is shown that 1.5mm of tooth structure is sufficient enough to ensure the transmission of masticatory forces to both the post and tooth. A tooth broken at the gum line offers no form of resistance to transversal forces and thus the post has to take the entire load, in this there is a high chance for the cementation to fail.

When the tooth fractures at the gum line it is important to gain a 1.5mm ferrule by bringing the marginal finishing line of the future restoration more apically. In theory, the marginal finishing line of the crown should be no less than 2 mm from the bony ridge, as there is a risk that it could
lead to an inflammatory response that is commonly known as violation of biological width.
(Biological width is a 1 mm attachment of connective tissue; a 1 mm attachment of epithelial tissue; and a 0.7 mm sulcus depth.)

To obtain an adequate ferrule effect for teeth that are fractured at the gingival level the following can be done

• Gingivectomy
• Osteoectomy
• Orthodontic extrusion

Thus when a post is in position, and receiving lateral forces, the ferrule ensures the dentine is under compression (which it is good at).If the was no ferrule, the dentine would be under tension (which it is poor at), and would fracture. The ferrule effect comes not from the post or core, but from the crown ringing the dentine. Ideally, the ferrule would go down as far as the post.


Dentine prepared to receive ferrule



Post and core done




Crown here provides the ferrule effect. The lateral forces transmitted from the crown to the post cause compression of dentin coronally.

Shade selection in dental practice

Shade selection is one of the most crucial aspect in the field of aesthetic dentistry. Be it a composite build up or ceramic crowns the essence of a success depends on a lot many factors of which shade selection is one of the prime. Shade matching is a much more complicated task than it may look like and is one where there is a high margin of error. This article deals with the problems faced in shade matching and a few ways to a more perfectible esthetic restorations.

The most common error which occurs in matching of a shade is the light condition. Tooth color matching is usually done under different light sources without paying attention to the compatibility of light conditions in dental practice and laboratory. It happens that a dentist matches the color in daylight, while a dental technician,who has different color vision besides, produces the restoration under incandescent light source. Light conditions for tooth shade matching procedure should be standardized and compatible with light conditions in dental laboratory.

Ideal light source for dentistry should have the following characteristics:

a) to be color corrected, i.e. to have a full visible spectra range

b)to have enough intensity to eliminate ambient light, but not to be so strong to “wash” the color and to mask the color differences. The task to ambient light ratio should not succeed 3:1.

c)to be diffuse and pleasant for the eye, enabling it to percept the color without fatigue

d)to be standard, that is not to change its quality and quantity depending on time of the day or season and should not change from place to place.

In color matching procedure, it is necessary to pay attention to viewing geometry and the background and the surrounding. Perception distance, patient's clothes, make up, color of the uniform, equipment, furniture, walls and ceiling of a dental practice are also factors of importance. According to all of this, it is obvious that there are many different factors on which proper color matching depends. Their variability should be reduced to the minimal.

Standard shade matching procedure is well known The tooth color is matched in daylight, using
the shade guide. But this has an incomplete and insufficient information, if added that daylight is not constant itself and the color temperature ratio varies 1:20 depending on the time of the day and meteorological factors, the confusion is complete.
It is important that color selection is done when the patient is first seated in the dental chair because by the end of the appointment, when the patient has held the mouth open with a cotton roll for most of the time dehydration has occurred, altering chroma and value. The teeth will take more than 24 hours to regain their normal characteristics of colour. Along with this , by the end of the appointment the clinician's eyes are fatigued resulting in a lesser ability for adequate shade matching.
For a successful shade natching the patient′s mouth should be leveled with the dentist′s eyes and the Samples from the shade guide should be applied parallel with the tooth whose color is being matched, not in front of it (it will appear lighter), and not behind it (it will appear darker).
Most of the dentist's use a single shade guide for shade matching, though a few studies state that a combination of using two shade guides improve the shade matching capabilities.
It is adviced to match the hue value and chroma seperately and the clinician should not look at the tooth for more than 5 sec. it is also suggested that the clinician should look at a blue surface for a minute after this, which improves the perception of yellow colour.

To improve the communication between dental practice and laboratory, it is suggested that
diagrams, i.e. schemes, should be used. A facial view of the clinical crown is used to indicate the position of the various shades, while a proximal view will tell the technician how the body
and enamel porcelains should be layered. Photographs or slides can be very useful for showing shade gradation and characterization. Photographs can not however, accurately represent
color, but the photograph should show the shade guide in the field and be correctly positioned as a reference point.

The above stated are a few basics for a more successful shade matching, even though with more sophisticated digital shade matching systems, taking a proper shade is much more easier these days but even these should not be the only method for shade taking rather these should be adjuvant to the traditional shade matching system.