Enamel Structure - Age Changes - Clinical Considerations PDF

ENAMEL- STRUCTURE AGE CHANGES CLINICAL CONSIDERATIONS Dr Sandeep Gupta Assistant Professor  CONTENTS ❖STRUCTURE ❖AGE CHANGES ❖CLINICAL CONSIDERATIONS STRUCTURES SEEN IN ENAMEL ❖Enamel Rods ❖Hunter Schreger Bands ❖Incremental Lines of Retzius...

ENAMEL- STRUCTURE AGE CHANGES CLINICAL CONSIDERATIONS Dr Sandeep Gupta Assistant Professor  CONTENTS ❖STRUCTURE ❖AGE CHANGES ❖CLINICAL CONSIDERATIONS STRUCTURES SEEN IN ENAMEL ❖Enamel Rods ❖Hunter Schreger Bands ❖Incremental Lines of Retzius ❖Perikymata ❖Enamel cuticle SURFACE STRUCTURES ❖Enamel cracks ❖Enamel Lamellae ❖Neonatal Lines ❖Enamel Spindles ❖Gnarled Enamel ❖Enamel Tufts ❖Dentinoenamel Junction ❖Odontoblastic Processes  ENAMEL Enamel rods RODS Enamel rods are the fundamental structural unit of enamel; each rod is extending from its site of origin at the dentino-enamel junction (DEJ) to the outer surface of enamel  The inter rod region surrounds each rod and its crystals are ENAMEL oriented in a direction different from those making up the RODS rod. Rods (prisms, R) and interrod enamel. (interprismatic substance, IR)  ENAMEL RODS The boundary between rod and inter rod enamel is delineated by a narrow space containing organic material known as ‘rod sheath’.  ENAMEL RODS ✓Enamel rods-clear crystalline structure- permitting light. ✓Cross section under light microscope- appear hexagonal/round/oval resemble fish scales. ✓Keyhole Or Paddle Shaped Prism In Enamel.  ENAMEL RODS In transverse section, the enamel rods have a keyhole shape A HEAD formed by the rod -commonly directed towards the incisal or occlusal aspect A TAIL formed by interrod- directed towards the cervical region of the teeth  Key hole pattern of enamel rods ENAMEL RODS formed by four each rod ameloblasts 1 contributes 3 2 to four each different rods ameloblast 4  ENAMEL RODS ✓Enamel is built from closely packed and long ribbon like crystals- Apatite crystals Length-0.05 – 1 micrometer Avg. thickness-30 nanometer Width-90 micrometer  ENAMEL RODS Calcium phosphate unit cell has a hexagonal symmetry and gives hexagonal outline to crystal.  ENAMEL RODS ✓Enamel rods- from DEJ to enamel run tortuous course. ✓Oblique direction & wavy course of rods-length of rods greater than thickness of enamel. ✓Rods in cusp region are longer than in cervical region.  STRIATIONS STRIATIONS ✓Each enamel rod built of segments separated by dark lines- gives it striated appearance ✓Segments- 4 micrometer G.S CROSS STRIATIONS OF RODS  DIRECTION OF RODS ✓Right angles to dentin surface. ✓Deciduous-cervical & central part approx. horizontal,cusp & incisal region increasingly oblique-almost vertical in cusp. ✓Permanent-similar in occlusal third,in cervical-deviate from horizontal in apical direction.  GNARLED GNARLED ENAMEL ENAMEL If the disks are cut in an oblique plane, especially near the dentin ; in the region of the cusps or incisal edges, the rod arrangement appears to be complicated—the bundles of rods seem to intertwine more irregularly. This optical appearance of enamel is called gnarled enamel G.S 40 X  GNARLED ENAMEL CLINICAL SIGNIFICANCE- The irregular twist intertwining may be associated with increased strength of enamel enabling it to withstand strong masticatory forces.  HUNTER SCHREGER BANDS ✓Originate at DE border & pass outward ending at some distance from outer enamel surface. ✓Alternate zones of slightly different permeability & different content of organic material.  HUNTER SCHREGER BANDS  INCREMENTAL LINES / STRIAE INCREMENTAL LINES / STRIAE OF RETZIUS OF RETZIUS These are the incremental growth lines in enamel representing the rhythmic deposition of enamel. STRIAE OF RETZIUS In a longitudinal sections of the tooth they are seen as a series of dark lines extending from dentinoenamel junction toward the tooth surface.  INCREMENTAL The evenly spaced striae of Retzius LINES / STRIAE OF RETZIUS represent a 6–11 day rhythm in enamel formation while other Retzius lines are suggested to be due to stress. It is estimated that about 25–30 striae do not reach the surface. A. Stria of Retzius B. Dentino-enamel junction  INCREMENTAL NEONATAL LINE LINES / STRIAE OF RETZIUS ✓Enamel of deciduous teeth develop partly before and partly after birth boundary between two portions marked by accentuated incremental line of retzius-NEONATAL LINE/RING. ✓Result of abrupt change in environment and nutrition of newborn. prenatal enamel postnatal enamel DENTINOENAMEL JUNCTION ✓Structurally unique interphase uniting two mineralized tissues with very different matrix composition and physical properties. ✓Into shallow depressions of dentin fit rounded projections of enamel ✓In sections DEJ appears as scalloped line- convexities of the scallops directed towards dentin. STRUCTURES SEEN IN ENAMEL ❖Enamel Rods ❖Hunter Schreger Bands ❖Incremental Lines of Retzius ❖Neonatal Lines ❖Perikymata ❖Enamel cuticle SURFACE STRUCTURES ❖Enamel cracks ❖Enamel Lamellae ❖Enamel Spindles ❖Enamel Tufts ❖Gnarled Enamel ❖Dentinoenamel Junction SURFACE STRUCTURES ✓Relatively structureless layer of enamel approx 30 micrometer thick. ✓No prism outlines visible ✓Apatite crystals parallel to one another & perpendicular to striae of retzius. ✓Heavily mineralised than bulk of enamel beneath it. PERIKYMATA ✓Also called IMBRICATION LINES. ✓Transverse wave like grooves, external manifestations of striae of retzius. ENAMEL CUTICLE ✓Delicate NASMYTH’S MEMBRANE – covers newly erupted crown ✓removed by mastication.  ENAMEL CUTICLE ✓Erupted enamel – covered by pellicle-precipitate of salivary proteins. ✓Reforms within hours after enamel surface is mechanically cleaned. ENAMEL LAMELLAE Enamel lamellae are thin, leaf like structures that extend from enamel surface toward the dentinoenamel junction. They may extend to and sometimes penetrate into dentin. Hypomineralised G.S 40 X  ENAMEL LAMELLAE Type A- Type B- Type C poorly calcified lamellae cracks filled with rod segments. consisting of organic restricted to degenerated matter(from enamel cells. saliva). may reach UPto reach into dentin dentin CRACKS Narrow, fissure like structures In ground sections caused by grinding of the specimen. ✓cracks (contain saliva & oral debris). ✓Extend to varying distances along surface at right angles to DEJ(from which they originate). ENAMEL TUFTS ✓Is a narrow,ribbonlike structure, Arise at DEJ & reach into enamel to about 1/3 or 1/5 of its thickness. ✓Appear as tufts of grass in G.S ✓Extend in direction of long axis of crown. ENAMEL TUFTS  ENAMEL SPINDLES ENAMEL SPINDLES The slender projections OF underlying odontoblasts that traverse the dentinoenamel junction are called enamel spindles.  ENAMEL SPINDLES ✓These hair like processes, thickened at end ✓In G.S of dried teeth – organic content of spindles disintegrates – replaced by air-spaces appear dark in transmitted light.  AGE CHANGES ATTRITION/WEAR OF OCCL/PROXIMAL CONTACT POINTS PERIKYMATA DISAPPEAR COMPLETELY COLOR- DARKER RESISTANCE TO DECAY REDUCED PERMEABILITY  AGE Attrition/wear of occl/proximal contact points –result CHANGES of mastication. Wear facets are increasingly pronounced in older people.  AGE CHANGES Generalised loss of rod ends & slow flattening of perikymata- Finally –perikymata disappear completely  AGE CHANGES CHANGE IN PERMEABILITY OF OLDER TEETH TO FLUIDS increase in the size of the crystal. Decreases the pores between them causing a reduction in permeability CLINICAL CONSIDERATIONS CLINICAL CONSIDERATIONS POSTDEVELOPMENT CAVITY PREPARATION & CARIES OF THE ENAMEL STRUCTURE LOSS CARIES ENAMEL STRUCTURES ACID ETCHING OF PREDISPOSE TEETH TO ENAMEL CARIES POSTDEVELOPMENTAL LOSS OF TOOTH STRUCTURE TOOTH WEAR- ✓ATTRITION is the loss of tooth structure caused by tooth to-tooth contact during occlusion and mastication. Some degree of attrition is physiologic. ✓ ABRASION - loss of tooth structure caused by a mechanical process. ✓ variety of patterns- depending on the cause. ✓EROSION - loss of tooth structure caused by a chemical process. ✓The acidic source - foods or drinks, vitamin C, swimming pools with poorly monitored pH. voluntary regurgitation (e.g.. psychologic problems, bulimia, occupations CARIES OF THE ENAMEL Smooth Surface Caries Pit & fissure caries Deep enamel fissures predispose teeth to carie CLINICAL CONSIDERATIONS IN CAVITY PREPARATION ✓Course of enamel rods –importance in cavity preparation. ✓Cavity prep-no unsupported enamel rods –to be left-at cavity margins- break & produce leakage-bacteria lodge-secondary caries. ENAMEL STRUCTURES PREDISPOSE TEETH TO CARIES ✓Deep enamel fissures ✓Dental lamellae  ENAMEL- pit fissure sealants coating the susceptible areas of the enamel with the so-called pit fissure sealants  more recently developed techniques in operative dentistry consists of the use of composite resins. These materials can be mechanically “bonded” directly to the enamel surface. THANK YOU