## 3 Results  
At the macroscopic level, all 12 teeth collected from OI patients showed abnormal, yellow/brownish or opalescent grey discolorations. Teeth from healthy donors showed no signs of pathological changes at the macroscopic level.  
The structural and ultrastructural features of the enamel and dentin in sound primary teeth and teeth from patients affected by OI were assayed. Two investigators independently observed and described the images. They had no previous knowledge of whether the observed samples were harvested from healthy or OI donors.  
In teeth from healthy donors, SEM analysis presented enamel with rare micropores and abundant prisms with an undulated and sinuous trend (Figure 1C,D). Enamel from patients with OI, on the contrary, showed an irregular trend of the enamel prisms (Figure 2C) and the crystals of hydroxyapatite were found to be unpacked (Figure 2D) in all teeth subjected to observation.  
In the dentin, SEM examination of the surface confirmed the presence of compact collagen fibers (Figure 1B). The intertubular tissue was observed to be stably packed (Figure 1A), while in pathological dentin, it had lower surface density compared with the control (Figure 2A,B).  
Morphological studies showed clear differences between normal dentin and dentin found in OI patients. Semithin section analysis of the normal dentin displayed a regular organization of tubules (Figure 3A), whereas dentin in OI patients showed dysplastic and irregular dental tubules  
Figure 1: SEM analysis of enamel and dentin from healthy donors. (**A**): Intertubular tissue; (**B**): Collagen fibers; (**C,D**): Enamel with rare micropores and abundant prisms.  
Figure 2: SEM analysis of enamel and dentin from OI patients. (**A,B**): Intertubular tissue and collagen fibers; (**C**): Enamel prisms; (**D**): Unpacked crystals of hydroxyapatite.  
(Figure 3B,C). In addition, the dentin in OI children presented tubules without odontoblastic process, but with large collagen fibers that entirely cross the tubule (Figure 3C). This particular characteristic was mainly evident in TEM analysis (Figure 4D,E).  
In dentin from healthy donors, TEM analysis showed normal morphological features as well as compacted collagen with a fibrillar scaffold and regular odontoblastic process residues. One was embedded in a dense network of collagen fibers highlighted by contrast of the grids with tannic acid (Figure 4A-C).  
On the contrary, dentin from patients affected by OI showed areas lacking dentin tubules; in most tubules, odontoblastic processes were absent (Figure 4D), and the tubular area presented collagen bundles and unusual and characteristic collagen circles (Figure 4E,F). The dentinal tissue was observed to be of low density; in fact, collagen was lax, unorganized, and unpacked (Figure 4F). Large interfibrillar free spaces were evident (Figure 4F). In dentin tubules, some necrotic aspects could also be identified  
Figure 4: TEM analysis of dentin from healthy and OI donors. (**A–C**): Compacted collagen with a fibrillar scaffold and regular odontoblastic process in healthy donors; (**D**): Absence of odontoblastic process in dentin tubules in OI patients; (**E,F**): Unusual collagen circles with unorganized and unpacked collagen in OI patients.  
Figure 3: Morphological analysis of dentin from healthy and OI donors. (**A**): Dentin from healthy donors; (**B,C**): Dentin from OI donors without odontoblastic process.  
(Figure 4F). Overall, the above described changes related to dentin were seen in all teeth collected from OI patients.