Secondary Dentin Formation Mechanism: The Effect of Attrition

Microscopy Research and Technique, 2004

serial microtomographic imaging; tooth development; deciduous molar ABSTRACT Dental morphogenesis and cellular differentiation are expressed in the fully formed tooth by the topography of the dentin-enamel junction and outer enamel surface. These boundaries can be differentiated using a variety of imaging systems. In this study, we used serial microCT imaging to provide accurate 3D reconstructions of developing lower human second deciduous molars. These were used to quantify the volume of enamel and dentin of individual cusps in relation to basal crown height. As growth and differentiation proceed apically, the spatial orientation of cusp tips and their bases were used to estimate their order of initiation and coalescence. We found that the order of coalescence differed from the order of initiation. We also found that dentin cusp height and volume as well as rate and quantity of enamel apposition varied along mesio-distal and bucco-lingual axes, and were independent of order of initiation and duration of growth. These results demonstrate that the potential for variation in crown size and form is maintained throughout development. We propose that the microCT model developed in this study constitutes a new approach for the investigation of developmental variation and its contribution to phylogenetic variation expressed in crown form and size.

Annals of Anatomy - Anatomischer Anzeiger, 2008

Cementum distribution was studied on transversely sectioned roots of 33 threerooted maxillary and 33 two-rooted mandibular permanent molars. The roots were sectioned at a level midway between furcation and apical region. Cementum thickness was measured at the midpoint of each of the four root surfaces and at a site exhibiting maximal cementum thickness. A reflected light microscope was used. Midpoint cementum thickness ranged between 5 and 800 mm in maxillary molars and between 5 and 700 mm in mandibular molars. Maximal cementum thickness ranged between 25 and 1140 mm in maxillary molars and between 20 and 700 mm in mandibular molars. The results indicate that cementum tends to accumulate along interradicular surfaces of multirooted molars. In addition, a tendency was noted for more cementum to occur orally than vestibularly in roots of mandibular molars as well as in buccal roots of maxillary molars. Furthermore, this study indicates that cementum accumulates in root concavities (developmental depressions), although the exact mechanism still awaits a clear explanation. Previous studies have suggested that tensile forces stimulate cementum apposition. It may be assumed, however, that masticatory function and continuing eruption of the teeth exert no discernible effect on cementum thickness in the examined region of the root. In conclusion, the observed cementum distribution could be attributed to at least two factors: one is buccal drift and the second may be the effect of root concavities. From a clinical viewpoint, the established pattern of cementum distribution in multirooted molars should be considered in endodontic and periodontal treatment.

Journal of Anatomy, 2014

Tooth crown patterning is governed by the growth and folding of the inner enamel epithelium (IEE) and the following enamel deposition forms outer enamel surface (OES). We hypothesized that overall dental crown shape and covariation structure are determined by processes that configurate shape at the enamel-dentine junction (EDJ), the developmental vestige of IEE. This this hypothesis was tested by comparing patterns of morphological variation between EDJ and OES in human permanent maxillary first molar (UM1) and deciduous second molar (um2). Using geometric morphometric methods, we described morphological variation and covariation between EDJ and OES, and evaluated the strength of two components of phenotypic variability, canalization and morphological integration, in addition to the relevant evolutionary flexibility, i.e. the ability to respond to selective pressure. The strength of covariation between EDJ and OES was greater in um2 than in UM1, and the way that multiple traits covary between EDJ and OES was different between these teeth. The variability analyses showed that EDJ had less shape variation and a higher level of morphological integration than OES, which indicated that canalization and morphological integration acted as developmental constraints. These tendencies were greater in UM1 than in um2. On the other hand, EDJ and OES had a comparable level of evolvability in these teeth. Amelogenesis could play a significant role in tooth shape and covariation structure, and its influence was not constant among teeth, which may be responsible for the differences in the rate and/or period of enamel formation.

Annali di Stomatologia, 2013

Objectives. The aims of this study were to conduct a morphometric analysis on the buccal furcation grooves in freshly extracted bifurcated maxillary first premolars (MFPs) and to correlate all anatomical measurements using microcomputed tomography. Materials and Methods. Twenty-three human MFPs with bifurcated canals were selected for this study. The specimens were analyzed with microcomputed tomography. The length, the beginning, and the ending of the grooves were measured. The minimum cross-sectional canal wall thickness in the grooves was located, and the width of the dentin thickness was calculated. All measurements were recorded and statistically analyzed. Results. The concavity of the grooves begins before the bifurcation site in 9/23 samples and after the bifurcation in 56.5% of samples. The groove length varied between 1.1-9 mm; the cross-sectional area with minimum palatal dentin thickness was 0.78±0.14 mm, which was located at a mean distance of 7.1 mm from the cementoenamel junction (CEJ) and 1.38 mm from the furcation. Conclusions. The presence of the furcation grooves in the palatal aspects of the buccal roots of the MFPs was 100%. The length, depth, location, and width of the dentin thickness of the grooves varied in relation to tooth length, bifurcation, and CEJ. These parameters should be taken into consideration before any endodontic or restorative procedures are performed. Reducing dentin width too vigorously by intracanal instrumentation can predispose to vertical root fractures or perforations; if a post cannot be avoided, it should not extend 6.5 mm from the CEJ.

Introduction: Cervical preflaring is an important step of the canal system instrumentation, but can lead to excessive enlargement or root perforation. Objective: Evaluate the remaining dentin thickness in the mandibular molars of mesial roots using cone beam computed tomography: Gates-Glidden (crown-down); Gates-Glidden (step-back); LA Axxess and Easy Pro-Design. Material and method: Were selected 40 lower molars mesial roots, which were scanned in a cone beam CT scanner before and after preparation. Were obtained five sections of the CT images with an interval of 1 mm from the furcation, and measured the thickness variation between the root canal to the root external portion in analysis software. Result: The evaluation of the different levels showed no significance within the same group for the Gates-Glidden group. On the other hand, were observed difference for LA Axxess (p=0.002) and Easy Pro-Design (p=0.005). In the intergroup analysis, were observed difference in all levels, especially for Gates-Glidden in the ascendant order (ANOVA and Tukey). Conclusion: Within the limitations of these study, is possible to conclude that the protocol with greater wear in the cervical risk area was the Gates-Glidden in step-back sequence, as the other groups were equivalent (p>0.05).

Journal of Natural Science, Biology and Medicine, 2015

Background: Predentin, the unmineralized organic matrix is important in maintaining the integrity of dentin. It is usually thick where active dentinogenesis occurs. A wide variation in its thickness is reported. Hence, we determined the variation in predentin thickness at various sites of different age groups. Materials and Methods: 60 freshly extracted teeth (maxillary and mandibular first premolars) were divided into three groups with 20 teeth in each as, Group 1-teeth with incomplete root formation (age <16 years), Group 2-teeth with complete root formation (aged between 16 and 30 years), Group 3-teeth of patients aged above 30 years. The teeth were fixed, decalcified and sections of 6 µ thickness were obtained, and stained with hematoxylin and eosin. The distance between the odontoblastic cell layers of the pulp to the border line of the dentin was considered for the measurement of the predentin thickness. A total of nine sites were considered for each specimen. Results: The present study revealed varied mean predentin thickness at all nine sites in all three age groups. Maximum and minimum thickness was observed at the apex and pulp floor respectively in all three groups. There was a statistical significant difference in predentin thickness between groups 1 and 3 and 2 and 3. Conclusion: The predentin thickness in the first group gradually increased toward the growing end near the apex, while it was relatively constant in the second group and increased overall thickness at all the sites in the third group. A notable finding was a linear increase with age in width of the predentin and the thickness vary as a function of odontoblastic activity during different stages of tooth development.

Non-carious cervical lesions (NCCL) are characterized by the loss of dental hard tissue at the cement-enamel junction (CEJ). This type of cervical tooth loss, the so-called abfraction, can be associated with cuspal flexure, due to malocclusal loads causing the tooth to laterally bend. Exceeding stresses are therefore generated in the cervical region of the tooth that cause disruption of the bonds between the hydroxyapatite crystals, leading to crack formation and eventual loss of enamel and the underlying dentine. The aim of this study was to perform stress analyses of the first maxillary human premolar. An accurate model based on CT images of both the tooth and the periodontal ligament was employed. The threedimensional finite element model was used to investigate the stress distributions and to compare the changes occurring between normal and malocclusion. The risk of failure at the CEJ and to crack initiation at the dentin-enamel junction was also estimated.

International Journal of Oral Science, 2013

The present investigation assessed the effect of acid etching on marginal adaptation of white-and gray-colored mineral trioxide aggregate (MTA) to apical dentin using microcomputed tomography (micro-CT) and scanning electron microscopy (SEM). Sixty-four extracted single-rooted human maxillary teeth were used. Following root-end resection and apical preparation, the teeth were equally divided into four groups according to the following root end filling materials: (i) white-colored MTA (WMTA), (ii) etched WMTA (EWMTA), (iii) gray-colored MTA (GMTA) and (iv) etched GMTA (EGMTA). After 48 h, the interface between root-end filling materials and the dentinal walls was assessed using micro-CT and SEM. Data were statistically analyzed using the Kruskal-Wallis and Dunn tests. Micro-CT analysis revealed gap volumes between the apical cavity dentin walls and EGMTA, GMTA, EWMTA and WMTA of (0.007 160.004) mm 3 , (0.05360.002) mm 3 , (0.003 660.001) mm 3 and (0.005 960.002) mm 3 respectively. SEM analysis revealed gap sizes for EGMTA, WMTA, EWMTA and GMTA to be (492.3613.8) mm, (594.5617.12) mm, (543.1615.33) mm and (910.7626.2) mm respectively. A significant difference in gap size between root end preparations filled with GMTA and EGMTA was found (P,0.05). No significance difference in gap size between WMTA and EWMTA were found in either SEM or micro-CT analysis. In conclusion, pre-etching of apical dentin can provide a better seal for GMTA but not for WMTA.

Introduction: Proximal enamel thickness (PET) at the mesial and distal contact areas of the complete permanent dentition has not been previously reported. Anatomic investigation of PET is essential for interproximal reduction treatment. Our objectives were to measure the PETs of the complete maxillary and mandibular dentitions at the contact areas, to compare the PETs of adjacent teeth, and to evaluate the vertical position of each contact area. Methods: We evaluated 720 extracted teeth; of these, 109 intact teeth were selected. The mesial and distal contact areas were demarcated, and each tooth was embedded in transparent epoxy resin. Blocks were prepared so that the 2 demarcated contact areas were exposed, and 6 measurements were taken and statistically analyzed. Results: Both jaws showed the same PET pattern characterized by 5 features: PET increased progressively from incisor (0.63 mm) to first molar (1.48 mm). Per tooth, mesial and distal PET did not differ. Total maxillary (26.86 mm) and mandibular (24.52 mm) PETs were similar. Paired PETs at the interproximal interface were similar, with the exception of the lateral incisor-canine interfaces. From incisor to first molar, the contact area becomes located farther gingivally. Conclusions: The existing guideline of maximal 0.5-mm interproximal reduction per 2 adjacent teeth should be kept in the anterior region and could be increased to 1 mm in the posterior region, when an equal amount is removed. (Am J Orthod Dentofacial Orthop 2015;147:435-44)

Journal of the Mechanical Behavior of Biomedical Materials, 2014

Objectives: The objective of this study was to evaluate age related changes in physical (structure/mechanical properties) and chemical (elemental/inorganic mineral content) properties of cementum layers interfacing dentin. Methods: Human mandibular molars (N¼ 43) were collected and sorted by age (younger ¼ 19-39, middle ¼40-60, older ¼ 61-81 years). The structures of primary and secondary cementum (PC, SC) types were evaluated using light and atomic force microscopy (AFM) techniques. Chemical composition of cementum layers were characterized through gravimetric analysis by estimating ash weight and concentrations of Ca, Mn, and Zn trace elements in the analytes through inductively coupled plasma mass spectroscopy. The hardness of PC and SC was determined using microindentation and site-specific reduced elastic modulus properties were determined using nanoindentation techniques. Results: PC contained fibrous 1-3 mm wide hygroscopic radial PDL-inserts. SC illustrated PC-like structure adjacent to a multilayered architecture composing of regions that contained mineral dominant lamellae. The width of the cementum dentin junction (CDJ) decreased as measured from the cementum enamel junction (CEJ) to the tooth apex (49-21 mm), and significantly decreased with age (44-23 mm; po0.05). The inorganic ratio defined as the ratio of post-burn to pre-burn weight increased with age within primary cementum (PC) and secondary cementum (SC). Cementum showed an increase in hardness with age (PC (0.40-0.46 GPa), SC (0.37-0.43 GPa)), while dentin showed a decreasing trend (coronal dentin (0.70-0.72 GPa); apical dentin (0.63-0.73 GPa)). Significance: The observed physicochemical changes are indicative of increased mineralization of cementum and CDJ over time. Changes in tissue properties of teeth can