The prevalence, location, and size of enamel pearls on human molars

abstract — Of 8,854 extracted molars in Norwegians, 201 teeth contained a total of 219 macroscopically detectable enamel pearls. The uncertainty in tooth determination had a limited effect upon the prevalence figures. Maxillary molars showed a higher prevalence than mandibular molars. The highest prevalence, 4.6%, was found on maxillary third molars. With few exceptions, the pearls were located in the bifurcation area or in the furrow between incompletely separated roots. The mean pearl diameter was 0.96 mm, and the mean distance to the cemento-enamel junction 2.8 mm. The relationship between enamel pearls and cervical enamel projections is discussed. It is suggested that simple enamel pearls and cervical enamel projections are of a similar nature and origin. The enamel of composite enamel pearls is probably initiated in a different way.     

Cervical enamel projections in Chinese first permanent molars.

Cervical enamel projections in relation to molar furcations may act as predisposing factors in periodontal attachment loss. Limited data are available documenting these features in Chinese teeth. The purpose of this study was to determine the prevalence and distribution in a sample of first permanent molars from Hong Kong Chinese. Three hundred and sixty-two extracted first molars (194 maxillary, 168 mandibular) were selected from the Prince Philip Dental Hospital tooth collection and examined using a dissection microscope for identification and classification. Cervical enamel projections were identified in 59 per cent of maxillary and 79 per cent of mandibular first molars. Buccal aspects were more frequently involved. Forty-nine per cent were Grade III (extending to the furcation area); over one-half were particularly slender while 18 per cent were discontinuous. A modification to the classification system is proposed in order to delineate these features in future studies.     

Exaggerated abrasion/erosion of human dental enamel surfaces: a case report

An atypical, rapidly proceeding abrasion/erosion of the labial enamel surfaces of the maxillary and mandibular incisors and canines in a 27-yr-old man is reported. Ultrastructural examination of a replica of the teeth showed a practically structureless enamel surface both at the initial examination and after 12 months. However, at the end of the period, minor areas of dentin tubules became visible, indicating that a substantial loss of the tooth substance had taken place. The patient's occupation involved daily environmental contact with proteolytic enzymes. In vitro study of enamel exposed to one of the actual proteolytic enzymes showed dissolution of enamel substance, and it cannot be excluded that enzymatic decomposition of the organic enamel matrix is a contributing cause of the observed exaggerated loss of tooth substance.     

Scanning electron microscopy of fluorideinduced disturbances on the enamel surface of rat molars

Abstract — Rats were given a single high dose of fluoride at the age of 5 days and killed after 24 h, 10 or 15 days. The maxillary Erst molars were prepared for scanning electron microscopic examination. It was concluded that a single dose of fluoride, preferentially affecting ameloblasts with a high secretory activity, leads to the formation of subameloblastic cysts and enamel hypoplasias covered with granular deposits.     

Effects of phosphonoformic and phosphonoacetic acids on developing enamel of rat molars

Abstract – The effect of a single subcutaneous injection of different dosages of phosphonoformic or phosphonoacetic acid on the developing dental tissues of the rat molar was studied. The substances were injected at different rat ages and effects on the developing teeth were analyzed by means of histochemistry of frozen sections and scanning electron microscopy. Molars of rats injected at the age of 10 or 15 days showed no pathologic changes. Administration of phosphonoacetic acid in a dosage of 10 or 20 mg P/kg b.w. had no demonstrable effect on the dental tissues in any of the animals. Phosphonoformic or phosphonoacetic acid in a dosage of 10 or 30 mg P/kg b.w. respectively induced subameloblastic cysts 24 h after injection to 4–7-day-old rats. The cysts were mainly localized on the mesial sides of the cusps under ameloblasts in the late secretory stage. Calcified depositions were seen in the ameloblastic layer lining the cystic cavities. A thin zone, the staining of which indicated a high mineral content, was seen in. the outermost enamel layer under the cysts, A few days later, enamel hypoplasias were seen in areas previously occupied by cysts. A lightly stained line was observed in the enamel matrix demarcating the amount of enamel matrix formed before and after the injection. Hypoplastic lesions were also noted in the enamel surface of newly erupted molars. These findings suggest that the two injected monophosphonates can induce pathologic changes in the developing enamel organ and hypoplasias in the enamel.     

Demineralization of human enamel

abstract — The aim of the present paper is to demonstrate that enamel can be dissolved in two, chemically distinct ways. Each of six premolars were exposed to 8 ml of a pH 5.0 buffer. The ionic activity products for Ca₅(PO₄)₃OH, Ca₅(PO₄)₃F, CaHPO₄, CaF₂andCa₄H(PO₄)₃ were determined. It was found that the liquid phase initially was unsaturated with respect to all solid phases and that hydroxyapatite and fluorapatite were dissolving coincidently. Four hours after initiation of the experiments the liquid phase was supersaturated with respect to fluorapatite while still unsaturated with respect to hydroxyapatite, which resulted in a formation of fluorapatite in the enamel and a dissolution of hydroxyapatite from the enamel, the net result being a loss of mineral.     

The effect of mechanical trauma on the tooth germ of rat molars at various developmental stages: a histopathological study

Abstract— Intrusive trauma was experimentally applied to the tooth germ at different developmental stages in the rat first molar. The tooth germ at the earliest (postnatal day 1, initiating stage of enamel matrix formation) and the latest (postnatal day 10, calcifying stage of preformed enamcl matrix) developmental stages studied showed localized enamel hypoplasia as a direct sequela of trauma. Thc tooth germs in which enamel matrix was rapidly thickening (postnatal days 3, 5, 7) and had not yet started to calcify showed the most intense and extensive injuries to the formation and structural organization of both enamel and dentin. As for indirect effects secondary to trauma, tooth germ dislocation was observed chiefly in tooth germs at the same developmental stages, frequently resulting in ankylosis. The present experimental model may be helpful for clarifying thc histogenesis of traumatic changes in the developing tooth germ.     

The ultrastructure of fluorosed human dental enamel

abstract — More than 80 specimens of enamel from 20 ground sections of eight teeth showing severe dental fluorosis have been examined in the transmission electron microscope. The study has shown that the prisms have normal size and form, but are surrounded by large periprismatic gaps. The individual crystals commonly appear in cross sections as regular, flattened hexagons with an average width of 91 nm and average thickness of 45 nm. Particularly in the tail regions and at prism peripheries, extensive intercrystalline spaces were found. The crystal lattice demonstrated a spacing of 0.82 nm. Demineralization of thin sections with PTA showed a preferential dissolution of the crystal centers. Based on the ultra-structural observations it is proposed that the hypomineralized regions of fluorosed enamel are produced by an arrest of enamel maturation, possibly due to toxic damage to the ameloblasts in the absorptive or maturative phase of their life cycle.     

A three-dimensional analysis of enamel distribution patterns in human permanent first molars

The morphology of the enamel cap and the thickness of the enamel of human molars are regarded as closely related to function. Previously, enamel thickness has been studied in specific sections only, not the distribution patterns of the entire crown. Here, the three-dimensional distribution pattern of the enamel of human permanent first molars was examined with a newly developed system. A distinctive pattern of enamel thickness common to all the individuals examined was found, regardless of the variation in absolute enamel thickness among individuals. It was confirmed that the lingual faces of upper molars and the buccal faces of lower molars have thicker enamel than the other crown faces. Moreover, in lower molars, enamel was significantly thicker at the hypoconid than at the protoconid crown face. The distal face tended to exhibit thicker enamel than either mesial or lingual faces, owing to the thicker hypoconulid enamel. It is suggested that the gradients of thickness within a molar are not necessarily manifested according to direction, but are the result of cusp-specific patterning. The distribution of enamel in the occlusal fovea was found to correspond to the morphology of the outer enamel surface, with the exception of the distinctly thin enamel at and near the tip of the mesiobuccal cusps in both upper and lower molars. The thickness of the enamel in that region might therefore be related to developmental timing or the topography of the enamel–dentine junction, rather than to functional demand. When viewed from a whole-crown, three-dimensional perspective, enamel thickness patterns are in part, but not entirely, explained as an adaptation to functional demand.     

Human and bovine enamel erosion under 'single-drink' conditions

Tooth-surface pH is lowered, during drinking, to a value close to the pH of the drink itself. After the drink is swallowed, the pH rises to baseline values but this process can take several minutes. Few techniques can quantify enamel erosion at timescales representative of single drinks. The objective of this study was to compare human and bovine erosion over acid-exposure times of 2 s to 1 h. Human and bovine enamel softening was compared in vitro using nanoindentation (2-60 s of exposure to acid) and tissue loss was compared using optical profilometry (1-60 min of exposure to acid). Nanoindentation revealed statistically significant softening after 2 s (human) and 5 s (bovine); there were no significant differences in hardness reduction for the two tissues at any time-point. Profilometry demonstrated statistically significant tissue loss after 20 min (human) and 10 min (bovine); bovine tissue loss progressed 30% faster than human tissue loss. These results support the use of bovine enamel as a substitute for human enamel in erosion studies, with the understanding that for moderate exposure times bovine enamel erodes 30% faster than human enamel. Nanoindentation can be used to detect enamel dissolution at timescales comparable to the oral dwell-time of a single 'mouthful' of a beverage.     

Studies on root enamel (I). Some historical notes on cervical enamel projections

This is the first in a series of papers dealing with root enamel. An historical study of cervical enamel projections revealed that they were described as early as the 1st half of the 19th century, while numerous more detailed studies employing microscopy were published in the 1920s. The possible association of cervical enamel extensions and furcation involvements, which had been credited to Masters and Hoskins, was found to be clearly stated by Watson and Woods.     

Three-dimensional study of human dental fissure enamel by synchrotron X-ray microtomography

The three-dimensional morphology of human tooth fissures and the quantification of mineral distribution in fissure enamel are pertinent to the development and diagnosis of caries. Synchrotron X-ray microtomography was used to measure linear attenuation coefficients (at 25 keV) at high spatial resolution with a volume-imaging element (cubic voxel) of 4.9 × 4.9 × 4.9  µ m³ in a block from a human premolar that included part of a stained fissure. From the linear attenuation coefficient, the mineral concentration, expressed as g_HAp cm⁻³ (where HAp is stoichiometric hydroxyapatite), was calculated. The mean mineral concentration in bulk enamel was 2.84 g_HAp cm⁻³. Well-defined regions (1.5–2.6 g_HAp cm⁻³), extending up to ≈ 130  µ m from the base of some narrower lengths of the fissure and up to ≈ 50  µ m deep from the fissure surface, were attributed to hypomineralization. Other regions of low mineral concentration, some (1.4–2.3 g_HAp cm⁻³) lying within the expected course of the fissure base and some (2.2–2.7 g_HAp cm⁻³) deep to the pit, were also considered to be of developmental origin. However, a diffuse distribution of low mineral concentrations (2.2–2.7 g_HAp cm⁻³) in the pit walls was attributed primarily to demineralization from caries. The fissure contained heterogeneous material (≤ 0.5 g_HAp cm⁻³) exhibiting partial mineralization.     

不同增稠载体的过氧化脲漂白剂对釉质表面形态的影响

目的:研究不同载体和浓度的过氧化脲(carbamide peroxide,CP)漂白剂对釉质表面形态的影响。方法:分别以Carbopol、PVP、Poloxamer为凝胶增稠载体,配制含100g/L、150g/L和200g/LCP的CP漂白剂(pH6.5)和不含CP的凝胶制剂,利用近期拔除的离体前牙牙冠分组观察CP漂白剂对釉质表面形态的影响。结果:以Carbopol,PVP或Poloxamer作为增稠载体的漂白剂,随着CP浓度的增高,釉质表面从轻度溶解、脱矿,蜂窝状改变,直至正常釉质层消失,"鱼鳞状"的釉柱结构清晰可辨。其中以Poloxamer为增稠载体的漂白剂较之更甚。结论:以Carbopol,PVP或Poloxamer作为增稠载体的漂白剂,随着CP浓度的增高,釉质表面出现不同程度的形貌改变。     

A comparison of the erosive susceptibility of cuspal and cervical enamel using an ultrasonic technique

The aim of this study was to compare the erosive susceptibility of cuspal and cervical enamel from human premolar and molar teeth. Small blocks of cervical and cuspal enamel were immersed in either orange juice or Coca-Cola at 37 degrees C and the surface enamel loss was measured by surfometry at 1, 2, 3 and 4 h. Additionally, once-hourly enamel loss was measured, specimens were placed in an ultrasonic bath containing water and ultrasonicated for 5 s to determine the degree of surface demineralization. A further set of enamel specimens were prepared that had 100 microm of the enamel surface removed. This was done to remove the hypermineralized surface enamel layer. Surface enamel loss in orange juice at 4 h, following ultrasonication, ranged from 13.2 to 16.9 microm. The surface enamel loss in Coca-Cola at 4 h, following ultrasonication, ranged from 21.7 to 27.5 microm. Subsurface enamel loss in orange juice at 4 h, following ultrasonication, ranged from 10.7 to 16.1 microm. The subsurface enamel loss in Coca-Cola for 4 h, following ultrasonication, ranged from 36.8 to 37.2 microm. Overall, little difference was found in the erosive susceptibility of cervical and cuspal enamel to the effects of orange juice or Coca-Cola.     

A scanning electron microscopic and microradiographic study of pits in fluorosed human enamel

Abstract— The aim of the present study has been to correlate the surface appearance of pitted, fluorosed enamel in the scanning electron microscope (SEM) with the microradiographic features of the underlying tissue. Intact enamel surfaces of severely fluorosed teeth appeared similar to that of normal enamel. In the unabraded surfaces discrete pits were sharply demarcated from the surrounding intact enamel surface leaving steep walls of parallel running rods. The microradiographic appearance of sections made through pits indicated that focal loss of surface enamel occurred corresponding to the inner highly hypomineralized part of the fluorotic subsurface lesion. The abrupt wall formation and the finding that the striae of Retzius never changed direction along the margins of the lesions indicated that pits in fluorosed enamel may be secondarily produced defects rather than true hypoplasias. Further evidence of the posteruptive origin of the defects was derived from the observation that enamel lamellae occasionally formed part of the lateral border. The relatively higher degree of radiopacity observed in the tissue surrounding the pit indicates a posteruptively acquired deposition of minerals in the exposed porous enamel.     

Root and canal morphology of Thai maxillary molars

AIM: To investigate the root and canal morphology of 268 maxillary permanent molars collected from an indigenous Thai population. METHODOLOGY: The cleaned teeth were accessed, the pulp dissolved by sodium hypochlorite under ultrasonication, and the pulp system injected with Indian ink. The teeth were rendered clear by demineralization and immersion in methyl salicylate. The following observations were made: (i) number of roots and their morphology; (ii) number of root canals per root; (iii) root-canal configuration in each root using Vertucci's classification with additional modifications; and (iv) presence and location of lateral canals and intercanal communications. RESULTS: All the maxillary first and second molars had three separate roots. Only, half (51%) of the maxillary third molars had three separate roots; the other half had fused or conical roots. The majority of the distobuccal (98.1-100%) and palatal (100%) roots had type I canals. Over half of the mesiobuccal roots of first (65%) and second (55%) molars had two canals. The most common (44.2%) canal configuration in mesiobuccal roots of first molars was type IV (two canals, two foramina). A variety of canal types were found in the mesiobuccal roots of second molars. Maxillary third molars showed the greatest diversity of canal morphology. There was an increase in the prevalence of lateral canals towards the apical part of the roots and intercanal communications were present in 16% of each of first, second and third Thai maxillary molars. CONCLUSIONS: The mesiobuccal roots of Thai maxillary molars possessed a variety of canal system types. Over 50% of the first molars had a second mesiobuccal canal. The palatal and distobuccal canals mainly had type I canals. Only, a small proportion (7.3-13.3%) of the roots exhibited lateral canals which were the most common in the apical third     

Uncoated specimen of human enamel obeerved in the scanning electron microscope

Abstract – A1-mm-thick section of human premolar was acid etched and observed uncoated in the SEM at accelerating voltages of 3, 5, 10 and 15 k v . Prisms and interprismatic substance were easily distinguishable. Low-voltage operation (3 and 5 k v ) gave the best results. Specimen charging was detectable at 5 k v and caused reduced image quality at 10 and 15 k v . Application of silver paste did not reduce charging appreciably. Prolonged observation at high magnification (x 10 000) resulted in contamination of the specimen with consequent charging and reduced resolution. Dental enamel seems to be a material which is well suited when uncoated for obervation in the SEM. This may be due both to the high content of the relatively heavy atom calcium, giving good secondary electron emission, and possibly to a certain degree of conductivity caused by diffusible icons.