Despite of major advances in the field of cariology, dental caries still remains a major problem affecting human population across the globe. However caries process is now well-understood; much of it has been described extensively in the dental literature. Early Enamel !"#$%& lesion appears white because the normal translucency of the enamel is lost. Even though initial enamel lesions have intact surfaces, they have a low mineral content at the surface layer when compared to sound enamel; thus showing a lower hardness value at the surface than for sound enamel tissue. '((),'(*) +hen there is acid attac on the tooth surface, the acids lowers the surface pH and diffuse through the plaue, which causes loss of minerals from the enamel and dentine. his mineral loss compromises the mechanical structure of the tooth and lead to cavitation over a long period of time. he subseuent re-minerali/ation process is nearly the reverse. +hen oral pH returns to near neutral, a *0 and 1$ 234 ions in saliva incorporate themselves into the depleted mineral layers of enamel as new apatite. he deminerali/ed /ones in the crystal lattice act as nucleation sites for new mineral deposition. '*) his cycle is fundamentally dependent upon enamel solubility and ion gradients. Essentially, the sudden drop in pH following meals produces an under saturation of those essential ions 5a *0 and 1$2 34 6 in the plaue fluid with respect to tooth mineral. his promotes the dissolution of the enamel. !t elevated pH, pH, the ionic super-satur super-saturation ation of plaue plaue shifts the euilibrium euilibrium the other way, causing a mineral deposition in the tooth. $ver the course of human life, enamel and dentin undergo unlimited cycles of de-minerali/ation and re-minerali/ation. '*) 7or many years, fluorides have been used as the agent for countering carious tooth process. However recent reviews have concluded that the decline in caries may be at an end or even in reversal, with levels increasing in some areas. '(3) hus, there is a need for developing new biomaterials which can act as an adjunct to the existing fluorides or can individually act as an agent for arresting the carious lesion and their reminerali/ation. #n the present study, we have compared the reminerali/ation potential of two different dentifrices, which are not normally the ey active ingredients in the dentifrices largely used. onsidering the importance of the surface layer in caries progression, the evaluation of changes in this region is relevant, thus &8H measurement is a suitable techniue for studying dereminerali/ation process. 8icro hardness measurement is appropriate for a material having fine microstructure, non-homogenous or prone to cracing lie enamel. &8H indentations provide a relatively simple, non-destructive and rapid method in deminerali/ation and reminerali/ation studies.
'9)
"ather than using the traditional pH-cycling method, a modified version '(:) was utili/ed in our study, in an attempt to simulate the real-life situation. his included a 3 h deminerali/ing cycle twice a day, with one * h and one intervening overnight reminerali/ing cycle, respectively. !nd to replicate early morning, midday and before bed-time tooth brushing, toothpaste was applied thrice daily. he reminerali/ing solutions used in the study were created to replicate supersaturation by apatite minerals found in saliva and were similar to those previously utili/ed by ten ate and Duijsters. ') Even though all the specimens were sectioned from different teeth, the variations among them did not yield any major effect on the progression of deminerali/ation. his was confirmed by the P -value -value obtained for all the hardness measurements 5 P < < :.:6 before the in-vitro pH cycling commenced. #t was therefore reasonable to disregard such variations when analy/ing the data after pH cycling. !fter the treatment treatment regime regime with the respective respective dentifrices, dentifrices, increase increase in mean microhardness microhardness was
observed in both groups 'able (); this is in accordance with various previous studies carried out for determining the reminerali/ation potential of =!>, '(2),'(),'(?) 11-!1, '(@),'(A),'(9) and when compared >roup ! and >roup = showed statistically significant values after pH-cycling regimen 'able *). =!> is a ceramic material consisting of amorphous sodium-calcium-phosphosilicate which is highly reactive in water and as a fine particle si/e powder can physically occlude dentinal tubules. '*:) #n the aueous environment around the tooth, i.e., saliva in the oral cavity, sodium ions from the =!> particles rapidly exchange with hydrogen cations 5in the form of H3 $ 0 6 and this brings about the release of calcium and phosphate 51$2 4 6 ions from the glass. '*() ! locali/ed, transient increase in pH occurs during the initial exposure of the material to water due to the release of sodium. his increase in pH helps to precipitate the extra calcium and phosphate ions provided by the =!> to form a calcium phosphate layer. !s these reactions continue, this layer crystalli/es into hydroxycarbonate apatite 5H!6. '*:) %nlie other calcium phosphate technologies, the ions that =!> release form H!-5a mineral that is chemically similar to natural tooth mineral6 directly, without the intermediate !1 phase. hese particles also attach to the tooth surface and continue to release ions and re-minerali/e the tooth surface after the initial application. he deposits are firmly attached and are not removed by thorough washing and brushing. hese particles have been shown, in in-vitro studies, to release ions and transform into H! for up to * wees. '**) ! study was carried out to determine the reminerali/ing effects of =!> on bleached enamel. #t concluded that =!> deposits were found on the enamel surface of all the specimens, suggesting that they may act as a reservoir of ions available for reminerali/ation at sites of possible deminerali/ation. '*3) his may explain the higher hardness values of =!> dentifrice after reminerali/ation. he present study also revealed that 11-!1 reminerali/ed enamel lesion in human enamel in-vitro . 11-!1 is calcium phosphate-based delivery systems containing high concentrations of calcium phosphate. he roles of 11-!1 has been described as - locali/ation of the !1 on the tooth surface and buffer the free calcium and phosphate ion activity, thereby helping in maintaining the role of super saturation. he 11 stabili/es the calcium and phosphate in a metastable solution facilitating high concentration of the a *0 and 1$2 34 which diffuses in the enamel lesion when 11-!1 comes in contact with the lesion. '*2) However the lower hardness values for 11-!1 may be due to its amorphous nature; which does not adhere to the enamel surface, unlie =!> gets attached to tooth, hence not reminerali/ing the tooth surface for a longer period of time to enhance its hardness. ! study investigated the enamel reminerali/ation potential of 11-!1 and =!>, showed that, after scanning electron microscope analysis it was clearly seen that although both group samples had plugs that sealed the fissures formed by deminerali/ation, =!> plug appeared to be more compact and intimately attached to the enamel surface. he deposits formed by 11-!1 were smaller and amorphous, while =!> created larger, more angular deposit. '*() his may also explain the high values of hardness for =!> as compared to 11-!1 in the current study; as =!> attaches more intimately and compactly to the tooth surface.
