Discussion 130

SEM imaging is a frequently used method to identify the morphological alteration of teeth. For SEM imaging, the enamel had to be etched and in this study 37% phosphoric acid was used.

The control teeth sample examined under SEM showed the typical appearance of enamel rod structure after being etched. From the image of the control teeth, it showed a distinctive etching pattern either Type I or II where the prism core was dissolved and leaving the enamel rod peripheries intact and peripheral region of the prism are dissolved preferentially and leaving the prism cores intact respectively (Mahoney et al., 2004a). The enamel rod orientation was continuous and direct without any interruption. HSB were present at the middle third of region of the enamel layer.

9.4.1 SEM for MIH teeth

In hypomineralised enamel, the typical enamel-etching pattern is absence and the enamel rod boundaries were not clearly demarcated (Mahoney et al., 2004a). In the MIH group, generally the enamel rods appear unorganised with interruption of the rods direction. Most of the affected enamel as described earlier was covered by a featureless and structureless layer (Jalevik et al., 2005). It is possible that etching a less organised enamel structure may not result in classic etch pattern. The reason may be due to poor acid solubility in less mineralized enamel, possibly due to the low mineral content and higher organic matrix as exhibited in the Raman spectra where the carbonate content increased in the hypomineralised enamel.

These findings are in line with a previous study where porous enamel contained higher carbon concentrations (Jalevik et al., 2005, Fagrell et al., 2010). Enamel in teeth affected by MIH exhibited disorganised enamel rods, a porous structure and loosely packed crystallites (Jalevik et al., 2005, Fagrell, 2011). However, carbonate substitution in hydroxyapatite crystallite is known to increase acid solubility of the mineral and should work in an opposite way (Weatherell, 1975). It is thought that the increased carbon depends on the amount of remaining organic matrix, as it has been suggested that protein might reduce the access of inorganic ions to crystallites (Robinson et al., 1971).

Hypomineralised enamel demonstrated an 8-21 fold higher protein content that might limit the action of the acid to the hydroxyapatite (Farah et al., 2010b). Consequently, the longer time required for enamel dissolution after etching may have some effect on bonding between restoration/adhesive and the affected first permanent molar enamel. The basic enamel structure with enamel rods and inter rod zones was found in porous part of enamel as well as in the normal part but the packing of the hydroxyapatite crystals seemed to be looser and poorly organized in the porous part. When the clinical and histological appearance of MIH was compared with normal enamel in a polarisation microscope analyses, yellow ⁄ brown enamel opacities were shown to be more porous than lighter opacities (Da Costa-Silva et al. 2011).

In this study, the SEM appearance between white/cream, yellow/brown or PEB type of defect showed similar features in term of porosity, unorganised enamel rods and amorphous appearance due to the presence of the structureless layer. Most of the MIH teeth had been restored with different restorative materials. From the image at high magnification, it showed formation of a gap between the restorative material and the enamel, which could lead to micro leakage and failure of the restoration.

It is important for a dentist to choose the most suitable type of restoration depending on the severity of the tooth condition. Fissure sealant is a good choice of treatment for the mild cases where the enamel appears to be in good quality and clinically and also radiographically is caries free. In moderate cases, where the enamel and dentine is involved, composite restoration is the treatment of choice. However, for the teeth with PEB where breakdown possibility is high, the treatment is either restoration or extraction. If they choose to have restoration, stainless steel crown is the best option to prevent further enamel breakdown (Daly and Waldron, 2009).

Placement of the restorative material on a defective and brittle enamel as shown in this study is not helpful. It is proved from the SEM images that a gap was present between the tooth and the restoration that maybe due to continuous enamel breakdown as the FPM is subjected to the heavy occlusal load everyday. Hence, stainless steel crown can protect the tooth from further damage.

9.4.2 SEM for AI Teeth

In primary AI tooth, the SEM image is similar to the normal enamel microstructure with well-organised enamel prism and typical pattern of acid demineralisation.

It was a totally different finding in the permanent AI teeth. Those teeth diagnosed with hypocalcified type of AI showed a different layer in the enamel, which represented the level of mineralization. Macroscopically, the cut surfaces of the enamel indicated two layers of enamel. When these teeth were examined under SEM the outer layer appeared lighter than the inner layer. Apparently, the outer layer was more mineralized than the inner layer of the enamel. This finding resembled in the previous literature where the mineralization process starts at the incisal edge towards the cervical margin, following the growth of the tooth crown (Robinson et al., 1995). After demineralization with phosphoric acid, the outer layer of the enamel disclosed the pattern of etched enamel. However, the prisms appeared very porous and unorganized. The individual crystal also seemed to be fused to each other and that in normal teeth the crystal can be visualized clearly. It is supported by the previous study, which described the condition as ‘glass like’ appearance (Shore et al., 2010).

The inner layer of the enamel appeared denser when viewed at lower magnification. The finding was similar with the MIH group where the enamel prism was obscured by a structureless layer and probably due to the high organic matrix content that prevented the demineralization process by acid etching.

In a previous study, they found type I and type II etching pattern in hypomineralised AI after being etched with 35% phosphoric acid for 30 second (Sanchez-Quevedo et al., 2006). However, in this study, both patterns were not noted, which could be due to the difference in the dissection of the tooth sample. The enamel rod in hypomineralised AI have also been described as decussated pattern, superimposed filamentous pattern or

arcade-shaped outlined because these features were also present in normal developing human enamel and though to persist in immature morphological pattern as in AI (Sanchez-Quevedo et al., 2001).

In the hypoplastic type of AI, the enamel appeared thin with an irregular surface. The enamel was insufficient in quantity as well as quality. The enamel rods in hypoplastic AI have abnormal morphology and are irregular in their course. The enamel showed poorly organized rods and difficulty to establish the boundaries between each enamel rod compared to the unaffected enamel (Shore et al., 2010, Wright et al., 1991). Both studies focused on local and smooth hypoplastic AI respectively. In this study the hypoplastic AI teeth were as classified as rough hypoplastic, which can be seen from the low magnification, which showed the irregular, rough and variations of thickness. Porosity and ‘glass-like’ appearance were also present throughout the enamel thickness.

CHAPTER 10

SYNOPSIS