3. Reparative cementum
When root surfaces undergo external resorption, i.e. resorption mediated by cells in the gingiva or periodontal ligament, the damage may be limited in time and extent. Such damage is often followed by a reparative phase, with new cementum deposited over the previously resorbed surface. In the early phase of repair, reparative cementum is typically composed of cellular, intrinsic fiber cementum. Because it lacks Sharpey's fibers, this type of cementum does not contribute to tooth anchorage. New anchorage can be provided by extrinsic or mixed fiber cementum that forms over the layer of intrinsic fiber cementum.
Fig.
98: Cellular, intrinsic fiber cementum (CIFC) is typically observed in areas of
cementum repair, following an episode of external root resorption. Unlike bone,
which undergoes alternating episodes of resorption and deposition during normal
remodeling, cementum does not remodel. Therefore, cementum resorption is generally
considered an abnormal process. An exception would be the resorption that takes
place during the shedding of the primary dentition. Since intrinsic fiber cementum
does not contain Sharpey's fibers, it does not contribute to tooth anchorage.
Fig. 99: Area of cementum repair. A layer of cellular, mixed fiber cementum
(CMFC) secreted by cementoblasts (CB) over the cellular, intrinsic fiber cementum layer
provides new anchorage por periodontal ligament fibers. A reversal line (RL) at the
junction of the new cementum and the dentin (D) delineates the extent of the external
resorptive lesion.
Fig. 100: Transmission electron micrograph of the junction between an old (OC)
and a new (NC) cementum layer. The moderately electron -dense granular layer (SL) at
the interface between the two cementum layers most likely represents a smear layer produced by mechanical instrumentation
during a previous treatment procedure. Treatment of the instrumented root with acid
or a chelating agent can remove the smear layer.
Demineralization of specimens containing areas of cementum repair often produces split artifacts when the smear layer has not been removed. However, these splits are not readily evident in non-demineralized specimens. Whether the presence of a smear layer under new cementum has any clinical relevance is not clear.
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