Chantha K. Jayawardena

Histochemical localization of cholinesterase activity in the dental epithelium of guinea pig teeth

Cholinesterase is known for its remarkable diversity in distribution and function. An association of this enzyme with proliferative and morpho-differentiating tissues has been reported in several species. Here we report on the first evidence of the presence of cholinesterase in the enamel organ of continuously erupting incisors and molars of the guinea pig. Frozen sections of the incisors and molars of the guinea pig were incubated for histochemical demonstration of cholinesterase activity by means of the thiocholine method as described by Karnovsky and Root. The cholinesterase activity was observed in several types of cells of the dental epithelium; cells forming the basal portion of the enamel organ, outer enamel epithelium and maturation stage ameloblasts of both the incisors and molars. In the crown analogue side, the outer enamel epithelial cells gained strong reactions for cholinesterase and maintained the reaction throughout the secretory and maturation stages of amelogenesis. In contrast, cholinesterase reactions were lacking in the inner enamel epithelium, pre-ameloblasts, and secretory ameloblasts. In the early stage of enamel maturation, ameloblasts began to show positive reactions for cholinesterase, which was upregulated in the incisal direction. Although both tooth types showed similar reactive patterns for cholinesterase at the growing ends, maturation ameloblasts depicted a different pattern of staining displaying the reactions only sporadically in molars. These data indicate the role of cholinesterase in the enamel organ in tooth morphogenesis and function of guinea pig teeth.

Association of Learning Approaches With Academic Performance of Sri Lankan First-Year Dental Students

Background: Primarily deep approach (DA) and surface approach (SA) to learning have been distinguished among students. Purpose: We aimed to determine the learning approaches and their association with the academic performance of a batch of 1st-year Sri Lankan dental students. Methods: Learning scores of students were calculated using the revised two-factor study process (R-SPQ-2F) questionnaire and they were correlated with the academic performance of students. Results: The 80.65% of students showed a greater DA score than SA score. Mean values of students’ DA and SA scores were 31.79 ± 6.1 and 22.74 ± 5.5, respectively. A positive statistically significant correlation (r = .3, p < .05) was observed only between DA score and marks of Short Answer Questions in anatomy. Conclusions: This sample of students uses both deep and surface learning approaches with more preference to DA than SA. The correlation between learning approaches and academic performance was inconsistent.

Distribution pattern of cholinesterase enzymes in human tooth germs.

The two distinct molecular forms of cholinesterase (ChE) are acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Our previous studies have reported that ChE is involved in tooth development. However, further experiments are needed to understand the precise action of ChE in tooth development. This study aimed to localise types of ChE in human tooth germs, and identify their distribution pattern. ChE were localised in frozen sections of jaws which were prepared from dead fetuses, neonates and stillborns who were free from visible abnormalities by Karnovsky and Root method. AChE was identified in the inner and outer enamel epithelia including the cervical loop region, stratum intermedium and preameloblasts of tooth germs at bell stage. Secretory ameloblasts were free from staining. The bud and cap stages of permanent tooth germs showed AChE activity on the lingual aspect and top surface of the epithelial ingrowths, respectively. BuChE activity was localised in the degenerating dental lamina. Our study reported the first evidence of localisation of ChE in human tooth development and identified the possible molecular form of ChE in tooth germs as AChE. Also, our results have provided strong evidence to speculate the action of AChE is on the cells of enamel organ during tooth development.

Regional distribution of interglobular dentine in human teeth

Interglobular dentine (IGD) is an area of poorly mineralized dentine matrix. It has been reported that there is an association between the retraction of odontoblast processes (OP) and the formation of IGD. A variation of the extent of OP has been described depending on the region of the tooth and age. This study aimed to find out the regional distribution of IGD in human teeth to observe any association between the extent of OP and the pattern of distribution of IGD. Ground sections were prepared from 52 extracted permanent teeth and the presence of IGD was observed in different regions of the crown and the root. The highest occurrence of IGD was found in the cervical and middle thirds followed by intercuspal, and coronal third in the crown. Statistical analysis of data depicted that the occurrence of IGD differed according to the region of the tooth. In roots, the highest occurrence of IGD was seen in the cervical third followed by the middle third. Previous reports have shown that OP extend up to the dentine-enamel junction in the coronal region and to the inner one-third of the cervical region. The varied pattern of distribution of IGD in the crown and root observed in our results corresponds to the above findings. Therefore, it is reasonable to surmise that there is an association between the distribution of IGD and the extent of OP. This allows us to confer that IGD tends to form in areas where OP do not extend to the dentine-enamel junction.