Basic sciences

Understanding the basics of science is mandatory to sail through the vast ocean. This section tries to give the possible basic knowledge in managing dental problems.


1. Why human dentition is known as diphylodont?

Because human dentition has two sets of teeth eruption during the cycle from childhood to adult.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and science of Operative Dentistry.Mosby publications;2002;15

2. Why Canines are the strong and stable abutment teeth for prosthetic work?

Because they have the stocky anatomic crown form and they possess the longest root.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.Swift JR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;15

3. Why Enamel cannot withstand masticatory forces without Dentin?

Even though Enamel is the hardest substance of the human body, it is very brittle with a high elastic modulus and low tensile strength. Since dentin is more elastic and a compressive tissue, it acts as a cushion for enamel. Enamel rods which do not have support of the dentin (unsupported enamel) will easily get fractured even with little force from hand instruments. Hence during cavity preparation all the unsupported enamel should be removed.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.Swift JR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;17

4. Why some patients experience sensitivity during tooth preparation in Enamel?

Because of the presence of Enamel Spindles which are odontoblastic processes that cross over the dentino-enamel junction into the enamel. These serve as pain receptors leading to higher sensitivity in enamel in some patients.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Strudevant's Art and Science of Operative Dentistry.Mosby publications;2002;19

5. Why is dentin considered as a living tissue?

Dentin is formed by dentinoblasts, whose cell body is present in the pulp after formation of dentin. The cell body extends their cytoplasmic processes into the dentinal tubules in the mineralized dentin. These processes have the ability to react and respond to the physiologic and pathologic stimuli. Hence it is considered as a living tissue.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;22

6. Why does the patient complain of sensitivity/pain while cutting dentin during operative procedures?

The most accepted theory for dentinal pain/hypersensitivity is Branstrom's Hydrodynamic theory. The dentinal tubules are composed of odontoblastic process and dentinal fluid. Near the pupal end, mechanoreceptor nerve endings are entangled with the odontoblastic cell body and extend inside the dentinal tubules. Operative procedures like cutting, drying, pressure changes, osmotic shifts or change in temperature will cause movement of dentinal fluid inside the tubules. These small rapid fluid movements lead to deformation of odontoblastic process along with mechano receptors giving rise to pain and sensitivity.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;26-27

7. Why does pulpal pain linger even after the removal of stimuli in certain instances?

The normal intrapulpal pressure is about 10mm of Hg.There is a rise in the intrapuplal pressure in inflammed tooth and when an external stimulus is applied to such a tooth, the intrapulpal pressure rises further leading to compression of free nerve endings , causing pain. When the stimulus is removed, it will take few moments for the intrapulpal pressure to return back to normal depending upon the status of inflammation. Hence in all inflammed pulp, pain lingers even after the removal of stimuli. It is usually observed that if the pain lingers for 10-15 seconds after the removal of stimuli, the pulp is at a reversible state of inflammation. And if it lingers for more than 15 seconds, it denotes that the pulp is in irreversible state of inflammation and endodontic intervention or extraction is indicated.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;30-31

8. Why is it important to know which stimuli provokes pulpal pain?

The stimuli which usually provoke pulpal pain are sweets ,cold and heat. The sweet and cold causes pain by means of hydrodynamic phenomenon whereas hot stimuli elicits pain by vascular phenomenon.The sugar causes changes in the osmotic gradient and cold dries the open dentinal tubules, thereby leading to deformation of mechanoreceptors present at the pulpal end of the dentinal tubules. This causes sharp pain, which is essentially of dentin origin. Hence pain from cold & sweets indicate that there is remaining intact open dentinal tubules present to elicit such a response. On the other hand, hot stimuli leads to vasodilatation of blood vessels, leading to extravasation of serus fluid. As the result ,edema occurs causing rise in the intrapulpal pressure, which compreses the free nerve endings present in the pulp causing sharp pulpal pain. Thus pain from hot stimuli indicate that the pulp is already in the inflammed status.

9. Why pulpal pain is spontaneous in certain instances?

Inflammed pulp leads to increased intrapulpal pressure resulting in compression of free nerve endings and pain. During the initial stages of inflammation, the raised intrapulpal pressure is not sufficient to provoke pain by itself and requires an external stimuli. As the inflammation progresses towards irreversible status, it leads to pulpal necrosis and formation of isolated area of microabscess. These microabscesses will continue to expand with progression of inflammation and will coalace over a period of time. The external stimuli of even lesser intensity will provoke pain and the pain may linger for longer duration confirming the advanced stage of inflammation. If left unattended, the coalaced abscess may break leading to sudden rise in intrapulpal pressure sufficient enough to cause pain by itself without any external stimuli. Hence in advanced stages of inflammation, pulpal pain will be spontaneous indicating the irreversible nature of pulpal pathosis.

Ref: Endodontic therapy, Franklin S Wiene,Mosby,4th edn,1989

10. Why should restorations reproduce the contour of the tooth precisely?

Normal buccal and lingual contour of the tooth surface helps in deflecting the food in such a way that they gently stimulate the investing tissue underneath. Improper location and degree of facial and lingual convexities in restorations, like undercontouring will cause trauma to the investing tissue. Over contouring on the otherhand will lead to increased plaque retention and gingival inflammation. The proximal height of contour provides the contact and supports the interdental tissue. Failure to reproduce in the restoration will lead to food impaction and damage to the supportive tissue.

Ref: Theodore.M.Roberson,Harald.O.Heymann,Edward.J.SwiftJR.Sturdevant's Art and Science of Operative Dentistry.Mosby publications;2002;32-33

11. Why pulpal pain is always diffused?

Pulp contains only free nerve endings for pain transmission. Propioceptive receptors, which are required for sense of localization is not present in the pulp. Hence pulpal pain will always be diffused.

Ref: Endodontic therapy, Franklin S Wiene,Mosby,4th edn,1989

12. Why percussion test is important to assess the pulpal pathosis?

Propioceptive receptors are present only in periodontium. The localization of pain to stimulus is possible only when the pathosis/inflammation from pulp extends to periapical region involving periodontium. Hence positive percussion test indicate the apical periodontitis is present. Pain of pulpal origin with negative percussion test indicates that the inflammation is restricted to pulp.

Ref: Endodontic therapy, Franklin S Wiene,Mosby,4th edn,1989