CEMENTUM

CEMENTUM: is a specialized hard layer of calcified mesenchymal tissues which forms the outer covering of the anatomical root. Begins at cervical portion of the tooth at the cementoenameljunction & continues to the apex.

Function

• Furnishes a medium for the attachment of collagen fibers that bind the tooth to surrounding structures.

• Serves as major reparative tissue for root surface.

DistrbutionI. It varies in thickness at different levels of the root. It is

thickest at the root apex and in the interradicular areas of multirooted teeth, and thinnest cervically.

II. The thickness cervically is 10-50µm, and apically, 50-200µm. It is contiguous with the periodontal ligament on its outer surface and is firmly adherent to dentine on its deep surface.

III. As cementum is slowly formed throughout life, this allows for continual reattachment of the periodontal ligament fibers.

IV. It is deposited throughout life and there is always a thin layer of uncalcified matrix on its surface.

Physical CharacteristicsI. Hardness is less than that of dentin and bone.

II. Light yellow in color, It’s lighter in color than dentin but more darker than enamel.

III. Can be distinguished from enamel by its lack of luster & its darker hue.

IV. Permeable to a variety of materials, Its permeability decreases with age.

V. Avascular receive nutrient from the surrounding periodontal space and not innervated.

Chemical Composion

I. Contains 45% to 50% inorganic substances mainly calicum, hydroxyapatite, phosphate & fluride.

II. 50% to 55% organic material & water.

III. Organic portion consists primarily of type I collagen & proteoglycans.

IV. Cementum has the highest fluoride content of all the mineralized tissues.

Cementogenesis

Cementum develops from the activity of esenchymal cells of dental follicle after fragmentation of the epithelial root sheath.

After formation of dentin, loss of continuity occurs in the epithelial root sheath.

This allows adjacent cells of the investing layer of the dental follicle to come to lie on surface of root dentin & these are induced to differentiate into cementoblasts.

Structure

I. Cells

II. Matrix

III. Mineralized fibers

Cellular components of cementumCementocytes

I. Soon after Hertwig’s sheath breaks up, undifferentiated mesenchymal cells from adjacent connective tissue of the dental sac differentiate into cementoblasts.

II. The spaces that the cementocytes accupy in the tissue are called lacunae, and the channels that their processes extend along are the canaliculi, adjacent canaliculi are often connected.

III. They are preferentially orientated towards the periodontal ligament to get their chief source of nutrition.

IV. Some unmineralized matrix may be seen in perilacunaspace.

Cementoblast

I. Line up along the cemental surface in the PDL which responsible for replacement of cementum if tooth is injured.

II. Synthesize collagen & proteoglycans which make up the organic matrix of cementum.

III. Have numerous mitochondria, a well-formed golgiapparatus, & large amounts of granular endoplasmic reticulum.

Cementocyte near cementumsuface

FibersThe fibrous matrix consist both:

Sharpey's fibres(Extrinsic fibers ): are the terminal ends of principal fibres of the periodontal ligament, that insert into the cementum and into the periosteum of the alveolar bone,it’sperpendicular or oblique to the root surface.

Intrinsic fibers: It’s non periodontal collagen fibers made up by cementoblast and all of these fibers run parallel to the DCJ.

Sharpey's fibres

Classification of cementumCellular cementumAcellular cementum

I. Covers the apical third and interradicular.

II. Formed after the tooth reaches the occlusal plane.

III. It contains embededcementocytes.

IV. Thickness is in the range of 100-1000 µm

V. Lesser number of Sharpy’sfibers.

VI. Main function is adaptation. VII. Formed at faster rate.VIII.Deposited over the acellularcementum.

I. Covers the cervical third of the root.

II. Formed before the tooth reaches the occlusal plane.

III. Does not contain embedded cementocytes.

IV. Thickness is in the range of 30-230 µm

V. Abundance of sharpey’s fibers.VI. Main function is anchorage.VII.Formed at slow rate.VIII.First layer of cementum.

Acellular cementum

Cellular cementum

Cementodentinal Junction

Smooth in permanent teeth, But Scalloped in deciduous teeth.

Dentin is separated from cementum by a zone known as the intermediate cementum layer.

This layer is predominantly seen in apical two-thirds of roots of molars & premolars.

Cementodentinal Junction

Cementoenamel Junction

In 60% of the teeth, cementum overlaps the cervical end of enamel for a short distance.

In 30% of all teeth, cementum meets the cervical end of enamel in a relatively sharp line.

In 10% of the teeth, enamel & cementum do not meet.

Relationship between cementum & enamel at the CEJ

DevelopmentalAnomalies

&Clinical

Considerations

Enamel pearls

Occur if epithelial sheath fails to be displaced from the dentin surface, the IEE may become differentiated into ameloblasts and produce an enamel droplet (or pearl) on the root surface.

This usually occurs in close proximity to the cervical region.

may become exposed and act like calculus to favor plaque retention and promote periodontal disease.

Enamel pearls

HypercementosisIs an abnormal thickening of cementum.

May be diffuse or circumscribed.

May affect all teeth of the dentition, be confined to a single tooth, or even affect only parts of one tooth.

If the overgrowth improves the functional qualities of the cementum, it is termed cementum hypertrophy.

If the overgrowth occurs in non-functional teeth or if it is not correlated with increased function, its termed cementumhyperplasia.

Extensive hyperplasia of cementum is occasionally associated with chronic periapical inflammation.

Hyperplasia of cementum in non-functioning teeth is characterized by a reduction in the number of Sharpey’s fibers embedded in the root.

may complicate the extraction of affected teeth.

appear on radiograph as radiopaque mass at the root apex.

Hypercementosis

Cementicles

Small, globular masses of cementum.

found in approximately 35% of human roots.

They are not always attached to the cementum surface but may be located free in the periodontal ligament.

It may result from microtrauma & aging.

They are more common in the apical and middle third of the root and in root furcation areas.

May interfere with periodontal treatment.

Free Cementicles

Attached Cementicles On SurfuseOf Cementum

Enamel projections

Occur if amelogenesis is not turned off, continued amelogenesis may produce enamel projections on the root surface.

Most commonly extending into molar bifurcations.

May favor the development of periodontal disease in affected bifurcations.

Enamel projections

Cementum exposureGingival recession

Gum recession is not directly linked with age but generally it is a more common condition in adults over the age of 40.

Causes: poor plaque control, abrasion due to “hard” tooth brushing habits, mouth trauma and occlusion.

problems associated: tooth sensitivity, cemental caries risk, periodontal disease, esthetic problems.

Bone loss also occurs with gingival recession, giving less support to the teeth.

Gingival recession

Clinical Concederation

1. Anchoring function: it mediates the attachment of the tooth to the gingival connective tissue, as well as to the periodontal ligament and, hence, the alveolar bone.

2. Protective function: as it is less susceptible to resorption than bone.

This allows pressure induced movement of the tooth through bone, as in orthodontics, while minimizing resorptive damage to the tooth.

Causes Of Cemental Resorption

Trauma from Occlusion .

Deficiency of Ca .

Cyst & Tumors Deficiency of Vit. A & D.

Periapical Pathology .

Hypothyroidism .

Excessive orthodontic forces .

3. Reparative function: New cementum formation is a key process during therapeutic procedures aimed at gaining new attachment, as it mediates new attachment of the tooth to the periodontal ligament and bone.

While it is possible for bone to fuse directly with the dentin and cementum of the tooth through ankylosis, this is considered an undesirable process, as it results in progressive resorption of the tooth structure because of ongoing osteoclastic (odontoclastic) activity.

4. Regular Cementum deposition at the root apex, helps to replenish the lost tooth height due to occlusal wear.

Aging Of Cementum

Surface become rough and irrigular.

Cemental Resorption.

Permeability Decreases.

More Cemental deposition is greater in the apical zone, which may lead to closure of the apical foramen.

The lacunae of cellular cementum appear empty (loss of cementocytes).