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PubMed1978

Solitary maxillary central incisor and normal stature.

Two children, one boy and one girl, each with solitary maxillary deciduous and permanent central incisors, normal height, and normal plasma growth hormone levels, are reported. Review of the literature reveals fourteen reports of patients with a similar dental anomaly. Of these, three are normal in height. The height and growth rate of patients with a single maxillary central incisor should be evaluated prior to growth hormone evaluation; such investigation should be undertaken only if the height is two standard deviations below the mean or if there is evidence of plateauing of linear growth.

Abnormalities, Multiple↗
PubMed1981

The relationship between crown size and the incidence of bifid root canals in mandibular incisor teeth.

From an initial sample of 729 extracted mandibular incisor teeth a final sample of 286 (172 central and 114 lateral incisors) was used to determine if any relationship existed between crown size, expressed as the M-D/F-L index, and the presence of bifid canals within the root of the tooth. The M-D/F-L index was calculated for each tooth and was matched against the presence of bifid canals as determined from radiographs of the lateral aspect of the teeth. The results indicate that bifid canals occur more frequently in teeth with the smaller M-D/F-L index and from regression equations, which had a high coefficient of correlation, the indications are that the incidence of bifid canals among the teeth with the lowest M-D/F-L index could be as high as 70 percent.

Dental Pulp Cavity↗
PubMed1981

Endodontic access to maxillary lateral incisors.

One hundred thirty-one maxillary lateral incisors were radiographed from a mesiodistal vantage point. Projections of the buccal and lingual walls onto the incisal showed that 16 percent opened to the buccal of the incisal edge; 32.9 percent were buccal and inclusive of the incisal edge, 43.5 percent were buccal and lingual to the incisal edge, 6.9 percent were inclusive of the lingual to the incisal edge, and 0.8 percent were entirely to the lingual of the incisal edge. Theoretically, the highest success rate that could be achieved for that portion of endodontic therapy that depends upon canal débridement would be gained by having the occlusal access opening in the most direct path to the long axis of the root canal. In this study it has been shown that, for maxillary lateral incisors, that path would necessitate that out occlusal opening be made inclusive of and slightly buccal to the incisal edge.

Debridement↗
PubMed1983

Dilaceration of permanent upper lateral incisors: frequency, direction, and endodontic treatment implications.

A sample of 480 extracted permanent upper lateral incisors was visually examined and the direction of dilaceration was recorded. It was found that 52.1 percent of the roots of these teeth were distolabially dilacerated. Analysis of radiographs of another sample of 442 endodontically treated teeth revealed that distolabial dilaceration occurred in 52 percent of the cases. It is proposed that oversight of the distolabial direction of root dilaceration of upper lateral incisors can be a contributing factor in the failure of endodontic treatment of these teeth.

Humans↗
PubMed1989

Scanning electron microscopic investigation of maxillary lateral incisors with a radicular lingual groove.

Fourteen human lateral incisors with a radicular lingual groove were observed under the scanning electron microscope to explore the communications between the groove and the pulp cavity. Observations showed that accessory foramina could be found not only in the groove, but also in the corresponding wall of the pulp cavity and a cross section. A complete lack of closure of the calcified tissues along the groove, allowing for direct connection of the pulp and the periodontium, was not found in these specimens. Therefore, it is suggested that accessory canals are the main way of communication between the pulp and the periodontium of the incisors with a radicular lingual groove. Because the accessory canals could be found either in the crown part or in the root part of the groove, infectious materials may get into the pulp cavity when there are pathologic conditions either through accessory foramina in the crown part or through accessory foramina exposed by localized periodontitis around the groove.

Dental Pulp Cavity↗
PubMed1982

Osteoclasts with ruffled borders from above the tip of the erupting incisors of osteopetrotic mice and rats.

Electron microscopy of the bone above the incisor of 10-day-old microphthalmic mice (mi) and incisors absent rats (ia) demonstrated that in both osteopetrotic mutants, osteoclasts indistinguishable from normal and with well-developed ruffled borders were present. Study of the same region in younger and older animals showed the type of abnormal osteoclast typical of the respective mutant strain.

Animals↗
PubMed1987

Effect of maxillary incisor angulation and inclination on arch length.

This article discusses the quantitative effects of angulation of incisors on dental arch length. The incisors are approximated mathematically to rectangular shapes, which enables the authors to calculate the change in arch length when teeth are tipped and to describe graphically the effect of other influencing parameters. The authors demonstrate that the height and the width of a tooth crown can enhance or diminish the effect of angulation on arch length. In addition to angulation, dental arch length is also influenced by torque. A mathematic formula has been derived and the results are demonstrated numerically and graphically. The authors show that vertical positioning of the brackets plays an important role because torquing is a rotational movement around the center of the bracket slot. Hence, in calculating the effect of torque on dental arch length, one must consider different angles and axes than those discussed by Andrews.4 The interaction between angulation and inclination and its influence on dental arch length has been investigated. It has been found to cause little change in arch length.

Cephalometry↗
PubMed1992

The orthodontic management of congenitally absent maxillary lateral incisors and second premolars: a case report.

The orthodontic management of congenitally missing maxillary lateral incisors and second premolars is the subject of this case report. The primary orthodontic consideration was the maintenance of facial esthetics in a 12-year-old boy while consolidating, aligning, and coordinating the dental arches. The maxillary canines were orthodontically positioned in the lateral incisor spaces. The maxillary posterior teeth, including the deciduous second molars, were protracted to esthetic positions where they could function without interferences. The stability of the occlusion depends on the longevity of the maxillary deciduous second molar roots, which did not resorb during active tooth movement.

Anodontia↗
PubMed2004

Effects of pregnancy and lactation on the microhardness of rat incisor dentine and enamel.

Pregnancy and lactation affect the rate of maternal dentine apposition and mineralization in the rat. In this study we have measured the effects of pregnancy and lactation on the degree of mineralization of dentine and enamel by using the microhardness method in rat incisors. At incisal sections, pregnant and lactation group enamel values were increased compared to that of a control group; the pregnancy and post-lactation period dentine values decreased slightly compared to the control group. At neck sections, pregnant and lactation group enamel values were decreased compared to that of the control group; the pregnancy and post-lactation period dentine values were also decreased slightly compared to the control group. At the post-lactation period neck section dentine mineralization was decreased compared with the incisal section. As a result, enamel and dentine layers of rat incisors are affected to varying degrees by these changes in mineralization levels during the maternal period.

Animals↗
PubMed2004

Measurement of bite force variables related to human discrimination of left-right hardness differences of silicone rubber samples placed between the incisors.

This study was designed to examine human subjects' ability to discriminate between spatially different bite pressures. We measured actual bite pressure distribution when subjects simultaneously bit two silicone rubber samples with different hardnesses using their right and left incisors. They were instructed to compare the hardness of these two rubber samples and indicate which was harder (right or left). The correct-answer rates were statistically significant at P < 0.05 for all pairs of different right and left silicone rubber hardnesses. Simultaneous bite measurements using a multiple-point sheet sensor demonstrated that the bite force, active pressure and maximum pressure point were greater for the harder silicone rubber sample. The difference between the left and right was statistically significant (P < 0.05) for all pairs with different silicone rubber hardnesses. We demonstrated for the first time that subjects could perceive and discriminate between spatially different bite pressures during a single bite with incisors. Differences of the bite force, pressure and the maximum pressure point between the right and left silicone samples should be sensory cues for spatial hardness discrimination.

Adult↗
PubMed2006

Effect of turpentine-induced fever during the enamel formation of rat incisor.

OBJECTIVE: Some epidemiological studies have indicated that diseases resulting in prolonged and sustained fever, such as exanthemata, respiratory infections and otitis media in infantile period or childhood are likely to have a marked deleterious effect on enamel formation, but the relationship between fever and enamel defects is unknown. The purpose of the present study was to induce a persistent high fever and examine the effects on the developing tooth enamel. METHODS: Twenty male Wistar rats weighting 140+/-10 g were used in this study. For the experimental group, a dose of 2.3 ml/kg steam-distilled turpentine was subcutaneously injected into both hind limbs five times at 12h intervals. Control rats received 2.3 ml/kg of sterile saline into the same injection site. The rectal temperatures of animals were measured at the febrile period. After constant periods, the animals were sacrificed, and the mandibular incisors were examined by contact microradiography (CMR) and histological observation. RESULTS: The febrile state lasted for 57 h and the average temperature rose 1.51 degrees C higher than that of the control group. The ground sections, semi-thin and ultra-thin sections of mandibular incisors were prepared and the enamel was observed. The microradiographs showed a radiolucent line along with the incremental line in the enamel. Moreover, microscopic examination indicated disorientation of enamel prism and crystal-free area within this radiolucent lesion. CONCLUSIONS: Persistent high fever pattern was established firmly by the turpentine injections and the process of enamel formation was influenced by the febrile period.

Amelogenesis↗
PubMed2006

Isolation and partial sequencing of cDNA clones from rat incisor after Nd:YAG laser irradiation in root canal.

OBJECTIVE: The purpose of this study was to identify the genes expressed in odontoblast-like cells and related to osteodentin production of pulp cells in vivo during the repair process. METHODS: A pulsed Nd:YAG laser was irradiated in mandibular incisors of rats at 2 W and 20 pulses/s for 5 s. We constructed a unidirectional cDNA library from the non-calcified portion of irradiated incisors, sequenced cDNA clones and classified their sequences by homology search through the GenBank database. RESULTS: Of the sequences determined, 26% represented sequences of new genes that were not related to any previously reported gene. 65.5% of the clones strongly matched genes and proteins in the databases. Among them, sequences found more than once were amelogenin, ameloblastin, amelin, collagen alpha1 type 1, osteonectin, nestin, enamelin and osteocalcin. Sequences detected only once were transforming growth factor beta-1 (TGF-beta1), growth hormone receptor (Ghr), glypican, enamelysin (Mmp20), amelin 2, integral membrane protein 2B, amelogenin precursor (Ame1), splicing factor 3b, insuline-like growth factor binding protein 5. CONCLUSION: This library reflects the gene expression during the dentin repair process in vivo including the odontoblast-like cell specific gene expression and osteodentin-production. Using this library, we indicate the candidate genes which might be related to odontoblast-differentiation and formation of osteodentin.

Animals↗
PubMed2006

Requirement of proper occlusal force for morphological maturation of neural components of periodontal Ruffini endings of the rat incisor.

The present study examined the effect of reduced occlusal force on morphological maturation of periodontal Ruffini endings, primary mechanoreceptors in the periodontal ligament, of the rat incisor. The reduction of occlusal force was induced by grinding the cutting edges of unilateral incisors of the rat from postnatal day 14 (PN14d), when periodontal Ruffini endings are immature. Under normal development, the axon terminals of Ruffini endings gradually ramified with the passage of time, and showed ruffled outlines having numerous dot-like structures around PN28d. When the mechanical stimulation was reduced, appearance of dot-like structures at the axon terminals delayed. Quantitative analysis elucidated that the percentages of immunoreactive areas for protein gene product 9.5, a marker protein of neural elements, at ground side were significantly smaller than those at non-ground side 14 days following the initial grinding. The distribution and morphology of terminal Schwann cells was not apparently affected. The present results indicate that the proper mechanical stimulation to the ligament contributes to the morphological maturation of the periodontal Ruffini endings.

Animals↗
PubMed2006

Morphometric study of length and grooves of maxillary lateral incisor roots.

OBJECTIVE: Root grooves are considered a risk factor for periodontal disease. The purpose of this study was to measure the length of the root of maxillary lateral incisors (MLI), as well as the width and depth of the concavities of their proximal surfaces, and also to determine the prevalence of palato-gingival grooves. METHODS: the width and depth of root concavities, as well as root length were evaluated in 73 MLI. All teeth were measured using a digital contour measuring instrument for the root grooves and a caliper for evaluating root length. RESULTS: After statistical analysis (p<0.05) it was possible to confirm: the mean root length on its mesial surface was (15.47+/-1.72 mm), on its distal surface (14.99+/-1.70 mm), on its buccal surface (13.10+/-1.69 mm) and on its lingual surface (12.71+/-1.53 mm); concavities were present in 100% of the samples; concavities were found 2mm, coronally from the CEJ, at the CEJ, and apically up to 8mm; the concavities were wider than deeper; on the mesial surface, the greatest width was (1.05 mm) and the greatest depth was (0.06 mm) both at the CEJ; 5) on the distal surface the greatest width was (0.73 mm) at 6mm apically from the CEJ and the greatest depth was (0.003 mm); the palato-gingival groove was observed in 9.58% of the samples. CONCLUSIONS: The mesial surface of the maxillary lateral incisor is the longest. The root concavities on the proximal surfaces are present in 100%. One must get acquainted to the morphological variations of roots to enhance diagnosis and treatment.

Humans↗
PubMed2004

FGF-2 potently induces both proliferation and DSP expression in collagen type I gel cultures of adult incisor immature pulp cells.

We investigated the effects of both cytokines and extracellular matrices on the proliferation and differentiation of immature adult rat incisor dental pulp cells. These immature cells, which have a high-proliferative potency in vitro and do not express mRNAs for dentin non-collagenous proteins such as dentin sialoprotein (DSP), bone sialoprotein (BSP), and osteocalcin, exist in the root regions of adult rat incisors. Fibroblast growth factor-2 (FGF-2) stimulated the proliferation of these immature cells and the subsequent production of mineralized calcium was induced by beta-glycerophosphate treatment. Additionally, FGF-2 dramatically induced the expression of DSP and BSP mRNAs, but only in collagen type I gel cultures, whereas neither plate-coated collagen type I nor fibronectin, laminin or collagen type IV cultures could produce this effect and generate sufficient physiological levels of these transcripts. Although bone morphogenetic protein-4 could not induce the proliferation of immature dental pulp cells nor upregulate DSP mRNA expression, it had a synergistic effect upon DSP transcript levels in conjunction with FGF-2. These results suggest that both the presence of FGF-2 and the three-dimensional formation of immature dental pulp cells in collagen type I gel cultures are essential for both DSP expression and odontoblast differentiation. These observations provide valuable information concerning the study of the commitment and differentiation of odontoblast lineages, and also provide a basis for the rational design of cytokine and extracellular matrix based compounds for regenerative therapies in new dental treatments.

Animals↗
PubMed2004

Relation in color of three regions of vital human incisors.

OBJECTIVES: For an adequate color reproduction, it is very valuable to quantify the color distribution in human teeth accurately. The aim of this study was to determine the color relation between three tooth segments (cervical, middle and incisal) in vital upper central incisors, using digital photography. METHODS: Digital recordings of 64 upper right central incisors were made using a standardized head-camera setup. The L*a*b* values of three regions were attained from the standardized digital images using software. RESULTS: There were statistically significant linear correlations for L* and b* between the three tooth segments (all r's > or = 0.60; p < 0.001). The correlation coefficient for a* was lower compared to L* and b* values. The L* and b* values of cervical and incisal tooth segment could be calculated from L* and b* values of middle tooth segment. SIGNIFICANCE: These results show the potency for color mapping of a whole tooth surface by extrapolation of color values of only one part of the surface.

Adult↗
PubMed2005

3D FEA of cemented steel, glass and carbon posts in a maxillary incisor.

OBJECTIVES: A comparative study on the stress distribution in the dentine and cement layer of an endodontically treated maxillary incisor has been carried out by using Finite Element Analysis (FEA). The role of post and cement rigidity on reliability of endodontic restorations is discussed. METHODS: A 3D FEM model (13,272 elements and 15,152 nodes) of a central maxillary incisor is presented. A chewing static force of 10 N was applied at 125 degree angle with the tooth longitudinal axis at the palatal surface of the crown. Steel, carbon and glass fiber posts have been considered. The differences in occlusal load transfer ability when steel, carbon and glass posts, fixed to root canal using luting cements of different elastic moduli (7.0 and 18.7 GPa) are discussed. RESULTS AND SIGNIFICANCE: The more stiff systems (steel and carbon posts) have been evaluated to work against the natural function of the tooth. Maximum Von Mises equivalent stress values ranging from 7.5 (steel) to 5.4 and 3.6 MPa (respectively, for carbon posts fixed with high and low cement moduli) and to 2.2 MPa (either for glass posts fixed with high and low cement moduli) have been observed under a static masticatory load of 10 N. A very stiff post works against the natural function of the tooth creating zones of tension and shear both in the dentine and at the interfaces of the luting cement and the post. Stresses in static loading do not reach material (dentine and cement) failure limits, however, they significantly differ leading to different abilities of the restored systems to sustain fatigue loading. The influence of the cement layer elasticity in redistributing the stresses has been observed to be less relevant as the post flexibility is increased.

Bite Force↗
PubMed2005

Influence of tooth preparation design on the stress distribution in maxillary central incisors restored by means of alumina porcelain veneers: a 3D-finite element analysis.

AIM: The present study aimed at providing 3D-FEA engineering tools for the understanding of the influence of tooth preparation design on the stress distribution and localization of critical sites in maxillary central incisors restored by means of alumina porcelain veneers under functional loading. METHODS: A 3D-FEM model of a maxillary central incisor is presented. An arbitrary chewing static force of 10 N was applied with an angulation of 60 and 125 degrees to the tooth longitudinal axis at the palatal surface of the crown. The model was considered to be restored by means of alumina porcelain veneers with different tooth preparation designs. The differences in occlusal load transfer ability of the two restorative systems are discussed. RESULTS: The maximum Von Mises equivalent stress values were observed in the window restorative system for both 125 and 60 degrees load angulations. When the chamfer with palatal overlap preparation was simulated, the stress distributed uniformly in the cement layer, whereas in the window preparation the stress mainly occurred in the incisal area of the cement layer. SIGNIFICANCE: When restoring a tooth by means of porcelain veneers, the chamfer with palatal overlap preparation better restores the natural stress distribution under load than the window technique.

Aluminum Oxide↗