Cementum and root surface debridement
E-facilitator:
Sophie

Learning outcomes
Provide an overview of the histological structure of cementum.
Present a poster on the clinical implications of debriding root surfaces with hand instruments and the considerations that need to be accounted for in your instrumentation technique.






Histological Structure of Cementum
What is Cementum?
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The Histological Structure of a Tooth

Cementum is the thin layer of calcified tissue covering the dentine of root. It is one of the four tissues that support the tooth in the jaw ( the periodotium), the others being the alveolar bone, the periodontal ligament and the ginginvae. Cementum varies in thickness at different level of the tooth . It is thickest at the root apex and in the interadicular area of multirooted teeth, and thinnest in the cervically.is pale yellow with a dull surface. It is softer then dentine and preameability varies with age and the type of cementum, the cellular variety being more premeable. In genral cementum is more premeabile then dentine.The relative softness of cementum , combind with its thinness cervically, means that it is readily removed by abrasion when gingival recession exposes the root surface to the oral environment and the Loss of cementum in such area exposes dentine.Cementum is part of periodotum that attaches the teeth to the alveolar bone via periodontal ligament.It is rich in collagen fiber and embeded in organic matrix(Berkovitz B.K.B. at el 2005)


How is Cementum formed?
When dental follicle cells come in contact with dentine, they differentiate into cementoblasts and begin to lay down cementum.The fisrt cementum is formed pre-reuptively. While post emergence, continuously deposited throughout life and this allow for continueal reattachment of the periodental ligament fibers.Cementoblasts which are typical protine secreting cells initially secerte an organic matrix consisting of intrinsic collagen fibers and ground substance.The cementoblasts may not recede after laying down cementum, but rather can become incorporated into the cementum similar to ostecytes. This matrix minerlises the same way as the dentine with deposition of matrix vesicles containing apatite crystals.


Composition and Structure of Cementum
Cementum has many features in common with bone, but does not contain any blood vessels or lymph vessles. Mature cementum is a very hard connective tissue that, by weight, contains approximately 65% mineralised material, 23% organic material and 12% water. Cementum forms in a crystalline structure, containing various forms of calcium. The main formation of calcium found in cementum is calcium hydroxyapatite (Ca10(PO4)6(OH)2), similar to that found in enamel and dentine. The calcium hydroxyapatite in cementum, however, most closely resembles the composition of that found in bone. Cementum is thickets at the tooth’s apex and in the interradicular areas of multi-rooted teeth (50 to 200 micrometers) and thinnest at the CEJ at the cervix of the tooth (10 to 50 micrometers) (Bath-Balogh & Fehrenbach 2006).Cementum is avascular and has no innervation


Different Types of Cementum
classification of cementum is based on the presence or absence of cell- cellular and acellular cementum. Acellular which is also called primary cementum is the initial layer of cementum deposited on the intermediate cementum and formed in a slower rate. As the name indicates acellular contains no embdded cememtocytes. It covers the root adjacent to the dentine and has many layers covering the cervical one third near the CEJ.
whereas cellular cementum is found mainly in the apical area overlying the acellular cementum.
Cellular cementum which is also called secondary cementum consists of the last layrs of cementum deposited over the aceelular cementum,mostly at the apical one third of the root.Cellular is formed a lot faster amd has many embedded cementocytes and its peripheries are cementoblasts in the periodontal ligament, which allows for the future production of more cellular cementum when needed.



Functions of Cementum and the Periodontium
The cementum around the surface of a tooth root has various functions. These include acting as a seal to the tubules in root dentine to prevent damage or sensitivity to the dentine and more importantly, to provide attachment for the periodontal fibre groups. Along with the gingiva, periodontal ligament and alveolar bone, cementum forms the periodontium or attachment apparatus of the tooth. Changes in cementum with cementocytes allow for limited adaptation of the teeth to changes in the alveolus, root lengthening in respose to occlusal wear, and reparative function.


Changes in Cementum Related to Age

Being unable to regenerate, acellular cementum does not grow or repar itself with age. However, with age cementum may be lost due to exposure in conjunction with erosion and abrasion.

The Cementum-Enamel Junction

There are three pattern arrangement of cementum and enamel may be seen.
Pattern 1 where the cementum overlaps the enamel for a short distance which may cause some difficulty discerning the DEJ from calculus around the cervix.
Pattern 2 where the cementum , and the enamel meet at the end joint, presenting no problem for the clinician and the patient.
Pattern 3 where the cementum and enamel fail to meet and the dentene is exposed and the patient may experience hypersensivity.
A combination of all forms of junction is fund on all teeth. There is a variation in the percentage of the different junctions present on each tooth.

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Clinical Situations Involving Cementum
There are cementicles which are calcified bodies of cementum could be found either attached to the cementum root surface or lying free in the periodontal ligament .Cementicles are formed from the apposition of cementum around cellular debris in the PDL, possibly as a result of trama to sharpey's fibers. It can cause problem during periodontal treatment.
There are also symmertrical spheres of cementum attached to the cemental root surface similar to enamel pears called cemental spurs.Cemental spurs can result from irregular deposition of cementum on the root. cemental spurs could interfere with periodontal treatment and also can cause problem in differentiation from calculus.
Gingival recession and subsequent root surface exposure allow cementum which is a thin layer to be removed easily from the root surface this results in exposure of dentinal tubules . This causes dentinal hypersensivitivity which is a short, sharp painful reaction that can occure when the area of exposed dentine is subjected to mechanical, thermal or chemical stimulus.Instrumentation of root surface s also can result in dentinal hypersentisivity. The posibility of creating dental hypersensivity emphasis the importance of conservation of cementum during instrumentation.
Hypercementosis (HC) refers to abnormally large cellular cementum deposits on the apical third of one or more teeth. Such deposits form bulbous enlargements on the roots may interfere with dental extractions. The cause of this anomaly is not known.
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Radiographic appearance of maxillary posterior teeth with evidence of hypercementosis (HC).





Clinical Implications of Debriding Root Surfaces

When debriding the root surface of teeth, protection of cementum is a goal of periodontal debridement. It is now clear that cementum removal is not necessary on most root surface.As in the past it was thought that bacterial products were firmly held in the cementum of periodontally involved teeth and that the only way to remove these bacterial products was to remove the cementum from the root surface. It is now known that the bacterial products can be removed from the root surfaces by using modern ultrasonic instruments or very light instrumentation strokes with hand- activated instruments (Nield- Gehrig 2004).
Cementum spurs, often occurring around the CEJ, can cause problems in the removal of calculus. It can often be difficult to differentiate between cementum and calculus, and so during calculus removal some cementum may also be broken away. This may result in the surface not being smooth or exposing dentine, increasing the risks of decay and sensitivity. When calculus forms on the tooth surface is creates niches for the accumulation of bacteria and debris. This poses the potential risk of tooth demineralisation as a result of this accumulation, as the bacteria 'eat away' at the tooth surface. Debridement is a preventative periodontal treatment procedure involving the complete removal of calculus from the tooth surface. This is done with the use of special scaling instrumentation that is run along the tooth surface, removing the overlying calculus. Subgingival calculus on the root surface attaches to the cementum irregularities or in areas of cementum resorption occuring in nodular, ledge, smooth veneer and other forms. Since the cementum at the cervical third of the tooth is very thin, it is possible for this to be removed during the removal on calculus if the wrong technique or pressure is applied with the instrumentation (Harris & Garcia-Godoy 2004). This consequently will expose the underlying dentine and cause increased sensitivity. Since the cementum at the cervical third is acellular, if it is removed it will not regenrate. This may also lead to the loss of periodontal attachment, gingival recession or, if the root surface is not smooth, further ecological niches for the accumulation of bacteria (Bath-Balogh & Fehrenbach 2006).


References

Nield-Gehrig J s 2004, Fundamentals of periodontal Instrumentation & Advanced Root Istrumentation, fifth edition, Lippincott Williams & Wilkins, USA.
Provenza D V 1986, Oral Histology, Inheritance and development, Lea & Febiger,USA
Bath-Balogh M, Fehrenbach M 2006, Dental Embryology, Histology and Anatomy, 2nd Edn., Elsevier Saunders, Missouri
Harris N, Garcia-Godoy F 2004, Primary Preventitive Dentistry, 6th Edn., Pearson, New Jersey
Wilkins E 2005, Clinical Practice of the Dental Hygienist, 9th Edn., Lipincott Williams & Wilkins, Baltimore
Berkovitz B K B, Holland G R,Moxham B J 2005,Oral Anatomy, Histology and Embryology, third edition, Mosby international limited
Simon H 2006, http://www.lifespan.org/adam/indepthreports/10/000024.html, Periodontal Disease, Lifespan