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PubMedDate not supplied

Hexachlorobenzene-induced incisor degeneration in Sprague-Dawley rats.

Hexachlorobenzene (HCB) was administered to female Sprague-Dawley rats in a 13-week toxicity study conducted for the National Toxicology Program (NTP). Groups of 10 rats were treated by gavage with 0.0, 0.03, 0.1, 0.3, 1.0, 3.0, 10, or 25 mg/kg HCB in corn oil 5 days/week for 13 weeks. Dose-dependent, region-specific, maxillary incisor degeneration was observed in animals given HCB at doses of 1.0 mg/kg/day and higher. Treatment with 1.0 mg/kg/day resulted in focal mesenchymal cell vacuolation and focal osteodentin formation within the pulp. Lesions were restricted to a short linear region subjacent to the odontoblast layer along the lateral aspect of the incisor at the level of the dentin-enamel interface. When observed in both incisors, lesions were bilaterally symmetric. Treatment with 3.0 mg/kg/day resulted in lateral and medial pulp lesions and focal odontoblast degeneration with dentin niche formation along the lateral incisor margin in some animals. Treatment with 10 mg/kg/day resulted in a higher incidence of lateral dentin niches and a low incidence of medial dentin niches. In animals treated with 25 mg/kg/day, a high incidence of bilaterally symmetric, lateral and medial, dentin niches were observed. The morphology and distribution of HCB-induced incisor lesions in rats are consistent with injury to a selective population of preodontoblasts.

Administration, Oral↗
PubMed2002

Apoptosis in the connective tissues of the periodontal ligament and gingivae of rat incisor and molar teeth at various stages of development.

Apoptosis in the periodontal connective tissues was studied using the TUNEL technique, supported by electron microscopy. For 16 rats (aged 3, 8, or 104 weeks), nuclear fragmentation was assessed using the TUNEL technique (for 4 of the animals aged 8 weeks, incisor eruption was experimentally increased by trimming of teeth to the gingival margin--unimpeded eruption). A further 8 rats (aged 8 and 104 weeks) were employed for electron microscopy. For the incisor, prior to aging, and regardless of eruptive behavior (i.e., for both impeded and unimpeded incisors), there was little evidence of apoptosis in the periodontal ligament or gingival connective tissues. For the molar, apoptosis was also not usually detected when the teeth were erupting or in the mature, erupted state. In the aged animals, however, there was a marked increase in apoptosis (as assessed by the TUNEL technique) within the periodontal ligament and gingivae of both the molars and incisors (where eruption rates also increased). Nevertheless, electron microscopy indicated that significant numbers of apoptotic cells were only in the incisor periodontium. These findings are not consistent with the view that the periodontal fibroblasts provide a component of the force(s) responsible for eruption.

Aging↗
PubMed2002

FGF10 maintains stem cell population during mouse incisor development.

Mouse incisors have a cervical loop that gives rise to dental epithelium in the apical region of the tooth germ, in contrast to molars. In a study of formation of the stem-cell compartment, we focused on expression patterns of fibroblast growth factor (Fgf) 10 and Fgf3 in developing mice incisors. At E14, Fgf10 and Fgf3 were coexpressed in the dental papilla. After E16 mesenchymal cells underlying cervical loop expressed Fgf10 but not Fgf3. To illustrate the role of FGF10, we analyzed incisor development of Fgf10-deficient mice. The germs of FGF10-null mice proceeded to cap stage normally. However, at a later stage, the cervical loop was not formed. Functional disorder of FGF10 by a neutralizing anti-FGF10 antibody induced apoptosis in the cervical loop of incisor explants. Recombinant FGF10 rescued the cervical loop from apoptosis. These results show that FGF10 maintains the stem-cell compartment in the developing incisor tooth germ.

Animals↗
PubMed1993

A T.E.M. stereological analysis of blood vessels and nerves in marmoset periodontal ligament following endodontics and magnetic incisor extrusion.

Maxillary incisor fracture is a common dental injury. It is frequently treated by endodontic therapy, orthodontic extrusion, and a retention period. The aim of the study was to mimic this regime and stereologically quantify the vascular and neural reconstitution of the periodontal ligament (PDL). Ten marmosets (Callithrix jacchus) had the right maxillary incisor crown removed, root canal treatment, and magnetic incisor root extrusion of 1.2 mm. After incisor retention for 9 weeks, the animals were perfusion fixed for electron microscopy. The incisor PDL was sectioned at 250 micron intervals from the cervical to apical region and recorded for stereological evaluation. Further evaluations were conducted with a two-way analysis of covariance using program 3V of the BMDP-81 statistical software package. The total luminal PDL vascular volume was statistically unchanged. An increased occurred in the mean number of venous capillaries from 0.07 +/- 0.3 to 0.17 +/- 0.3 per 560 microns 2 of PDL (P < 0.05). Vessel wall and luminal volume of post-capillary-sized venules decreased from 1.64 to 1.03 per cent, and 5.32 to 3.04 per cent (P < 0.05), respectively. Mean luminal and abluminal diameters for post-capillary-sized venules were reduced (P < 0.05). Myelinated and unmyelinated axons showed no significant change in volume (Vv), length (Lv), or surface (Sv) densities. Axon number/unit, PDL area, and mean diameters demonstrated no statistical differences. Since the PDL demonstrated almost complete morphological re-establishment of the microvascular and axon systems, it is considered that this clinical treatment is a justifiable rationale.

Analysis of Variance↗
PubMed1995

An investigation of the association between overjet size, lip coverage, and traumatic injury to maxillary incisors.

This study investigated the association between overjet size and lip coverage when assessing the likelihood of traumatic injury to maxillary incisors. Eleven-hundred-and-thirty-seven 11- and 12-year-olds were examined in school for traumatic injury to their maxillary incisors. The size of overjet and the adequacy of lip coverage of the maxillary incisors was assessed for each child. One-hundred-and-sixty-seven (15 per cent) had experienced traumatic injury to their maxillary incisors. Both increased overjet and inadequate lip coverage of the maxillary incisors were found to be significant risk factors. However, inadequate lip coverage was the single most important independent predictor of traumatic injury (P < 0.001), with a relative odds ratio of 2.62. The results suggest that much of the predictive value of increased overjet may be explained by inadequate lip coverage.

Chi-Square Distribution↗
PubMed1998

The relationship between irregularity of the incisor teeth, plaque, and gingivitis: a study in a group of schoolchildren aged 11-14 years.

The relationship between irregularity of teeth and periodontal disease was investigated in 201 children aged 11-14 years. The upper and lower incisor teeth were assessed for spacing, labio-lingual displacement, and mesiodistal overlap at each of the six contact areas. Plaque and gingivitis were assessed at six sites on each of the four upper and four lower incisor teeth. There was evidence for a direct relationship between the number of contact areas with tooth displacement combined with overlap and the number of sites with gingival redness (R = 0.25, P < 0.001), bleeding (R = 0.18, P < 0.01), and profuse bleeding (R = 0.25, P < 0.001). There was no evidence for a relationship between labio-lingual displacement alone and gingivitis. One-hundred-and-twenty-eight subjects without tooth displacement combined with incisor overlap had, respectively, 34, 15, and 35 per cent fewer sites with redness (P < 0.01), bleeding (P < 0.05), or profuse bleeding (P < 0.01) than the 73 subjects with overlap. The statistical significance of these differences was unaffected by covariate adjustment to take account of the effect on gingivitis of variation in the number of sites with plaque. There was no evidence of a relationship between incisor overlap and amount of plaque in these subjects. The results indicate that overlapping of incisor teeth is directly related to gingivitis and this relationship cannot be explained simply by an effect on oral hygiene.

Adolescent↗
PubMed1999

Morphological changes in periodontal mechanoreceptors of mouse maxillary incisors after the experimental induction of anterior crossbite: a light and electron microscopic observation using immunohistochemistry for PGP 9.5.

Ruffini nerve endings (mechanoreceptors) in the periodontal ligament (PDL) of mouse incisors were examined to elucidate whether experimentally-induced crossbites cause any changes or abnormalities in their morphology and distribution. Anterior guiding planes were attached to the mandibular incisors of 3-week-old C3H/HeSlc mice. At 3 days and 1, 2, 4, 6, and 8 weeks post-attachment of the appliance, the mice were sacrificed by perfusion fixation. Frozen sagittal cryostat sections of the decalcified maxillary incisors were processed for immunohistochemistry of protein gene product 9.5, followed by histochemical determination of tartrate-resistant acid phosphatase activity to reveal sites of alveolar bone resorption. Despite the absence of bone resorption within the lingual PDL of control mice, distinct resorption sites were seen in the respective regions of the experimental animals. Unlike the controls, many Ruffini endings showing vague and swollen contours, with unusually long and pedunculated micro-projections were observed in the affected lingual PDL of the incisors in the experimental animals with short-term anterior crossbite induction. Club-shaped nerve terminations with few, if any, micro-projections were observed in the lingual PDL of experimental animals with long-term induction, as well as in aged control mouse incisors. Differences in the distribution of Ruffini endings were also observed. These results indicate that changing the direction of the force applied to the PDL results in rapid and prolonged changes in the morphology of Ruffini-like mechanoreceptors.

Acid Phosphatase↗
PubMed2005

A jig for measuring incisor inclination.

The aim of this study was to design and construct a jig for measuring the inclination of the upper incisors to the maxillary plane and of the lower incisors to the mandibular plane. After several prototypes had been tested, the required properties for a successful jig were identified and a simple inexpensive device was produced. Measurements obtained when using the jig on 51 subjects were compared with cephalometric values by means of regression analysis. This revealed that measurements obtained using the jig against the upper and then the lower incisor crowns could be converted to cephalometric incisor angulations with 96 per cent accuracy to 10 degrees, by adding 23 and 3 degrees, respectively. The jig was accurate to 5 degrees on 69 per cent of occasions for the upper teeth. The 5 degrees accuracy with the lower incisors was only 27 per cent, although over a 6 degree range it improved to 78 per cent. For upper and lower tooth measurements combined, the jig was accurate to within 6 degrees on 75 per cent of occasions.

Cephalometry↗
PubMed2005

An approach to maintain orthodontic alignment of lower incisors without the use of retainers.

The purpose of this investigation was to examine the long-term stability of orthodontic alignment of lower incisors without the use of retainers. The study sample comprised 56 patients treated according to a protocol that included over-correction of rotated teeth at an early stage of treatment and systematic enamel reduction (stripping) of the approximal surfaces in the mandibular anterior region, both during treatment and follow-up. Care was also taken to maintain dental arch form and to avoid lateral expansion of the lower dental arch and proclination of the incisors. Dental study casts were obtained pre-treatment, at the end of treatment, and 3 years post-treatment. Alignment of the mandibular incisors was recorded using Little's irregularity index. The inter-canine distance and the sum of the mesio-distal widths of the mandibular incisors and canines were also measured. The total amount of enamel removed from the approximal surfaces of the lower anterior teeth ranged from 0.3 to 5.0 mm (mean 1.9 mm). The mean increase in irregularity index score of 0.6 from post-treatment to 3 years follow-up indicated good stability. In 45 per cent of the patients the change in score during this period was less than 0.5, indicating that the treatment approach presented may be considered an alternative strategy to placement of lower retainers to safeguard the stability of alignment of mandibular incisors.

Cephalometry↗
PubMed2002

Response of the incisor tooth to 2,3,7,8-tetrachlorodibenzo-p-dioxin in a dioxin-resistant and a dioxin-sensitive rat strain.

Dioxins are ubiquitous environmental pollutants that afflict developing teeth. To find out if the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the continuously erupting rat incisor is associated with the sensitivity to TCDD acute lethality and to see the histological basis for any macroscopic findings, we exposed 25 resistant Han/Wistar (Kuopio; H/W) and 20 sensitive Long-Evans (Turku/AB; L-E) female rats to total doses of 0.17, 1.7, 17, and 170 (only H/W rats) micro g/kg TCDD. Each dose group comprised five animals. The treatment was started when the rats were 10 weeks old and continued for 20 weeks. The exposure time covered two life cycles of the incisor. Stereomicroscopic examination of the dissected mandibles showed color defects and pulpal perforation of the lower incisors at 17 and 170 micro g/kg TCDD. Tissue sections revealed odontoblastic and pulpal cell death and the consequent arrest of dentin formation at the incisal tooth end at the same doses. H/W rat incisors were affected closer to the germinative tooth end at 170 than at 17 micro g/kg TCDD, resulting in a larger perforation. In accordance with the enamel discoloration, the postsecretory enamel organ underwent, albeit inconsistently, precocious squamous metaplasia with pronounced proliferation. Thus, both the mesenchymal and, to a lesser extent, epithelial elements of the forming tooth were affected dose-dependently at relatively high doses of TCDD. Similar responses in both strains implied that the impaired formation of the incisor tooth, at least of its mesenchymal elements, is not associated with the differential resistance of H/W and L-E rats to TCDD acute lethality.

Animals↗
PubMed2006

Clinical performance of resin-bonded composite strip crowns in primary incisors: a retrospective study.

AIM: The purpose of this study was to assess retrospectively the longevity of resin-bonded composite strip crowns placed in primary maxillary incisors. DESIGN: Records for 200 out of 387 children, aged 22-48 months, treated in a private paediatric dental practice and who presented for follow-up after at least 24 months were included in the study. The parameters recorded at baseline and/or at follow-up were: habits, the number and location of the decayed surfaces, colour, texture, and chipping of the restoration. Radiographic evaluation of the restorations, the quality of the margins, and the presence of pulpal and/or periapical pathoses were recorded. RESULTS: More than 80% of the restorations were judged to be successful at the final follow-up examination. Only the number of carious surfaces of the tooth at baseline influenced the treatment outcome. The failure rate was higher in central incisors with four affected surfaces (P = 0.005), and in lateral incisors with four carious surfaces (P = 0.0003), than in those presenting one or two carious surfaces in both central and lateral incisors (P = 0.002). CONCLUSION: The high success rate of resin-bonded composite strip crowns with a 2-year follow-up seen in this study suggests that this treatment modality is an aesthetic and satisfactory means of restoring carious primary incisors in young children. The retention rate is lower in teeth with decay in three or more surfaces, particularly in children with a high caries risk.

Child, Preschool↗
PubMed2004

Socio-economic burden of permanent incisor replantation on children and parents.

This study describes the socio-economic burden and attitudes of children and their parents following replantation of avulsed incisors. Records of 80 patients with 99 avulsion injuries treated in a teaching hospital clinic from 1988 to 1999 were reviewed. Mean age at time of injury was 10.6 years (range = 6.6-17.7 years). Complete records for a minimum of 1 year were obtained for 43 patients with 60 replanted incisors. Mean treatment procedures provided during the first year included 5.5 diagnostic periapical radiographs, 1.9 occlusal radiographs, 1.3 pulpectomies, and 2.7 pulp medicament applications. The mean estimated treatment cost and direct time (dentist) for first-year post-trauma management was 1465 dollars CAD and 7.2 h, respectively. Treatment costs were significantly higher during the first year post-trauma for patients who had their incisors extracted (P = 0.04), but there was no significant difference in direct treatment time between the two groups (P = 0.19). Twenty-one patient-parent pairs were surveyed for a number of qualitative factors. Ninety per cent of patients and 86% of parents reported that school and work time was lost. Even after having gone through the painful experience of replantation, the demands of recall, and in some cases, extraction, the majority of patients (67%) and parents (81%) stated that they would have still made the same (replantation) decision. Patient and parent responses were not statistically different (P = 0.453). Almost half the parents stated they would be willing to pay over 2000 dollars CAD to save an incisor. Patients rated retention of an incisor as significantly more important than infraocclusion. This is the first study to quantify the treatment burden of replantation of avulsion injuries exclusively in the pediatric population. This study describes the socio-economic burden and responsibilities of patient/parent and dentist and their role in informed consent.

Absenteeism↗
PubMed1992

Treatment of crown fractured incisors with laminate veneer restorations. An experimental study.

A method is described by which crown fractured incisors are restored with cast ceramic (Dicor) laminate veneers after initial treatment with either reattachment of the original crown fragment with a dentin bonding agent, with a composite resin build-up or no treatment (i.e. the veneer alone is used to restore the incisal edge). In order to elucidate the effect of the fragment/composite-tooth bonding interface on fracture strength of the restored teeth, the fracture strengths of the various treatment groups were compared to that of intact teeth supplied with Dicor laminate veneers. In an experimental investigation using central and lateral incisors from sheep, it was found that fracture strength (16.6 +/- 4.2 MPa) equal to that of intact incisors (16.1 +/- 2.6 MPa) could be achieved using laminate veneers made of porcelain on fractured teeth whose crown fragments were reattached using a dentin bonding agent (5). In the present investigation, using the same experimental model but using cast ceramic (Dicor) laminate veneers, the fracture strength of the restored incisors was significantly increased (21.0 +/- 3.7 MPa), exceeding that of intact teeth. The fracture strength of intact teeth was also exceeded in veneered incisors which were initially restored with a conventional composite resin build-up (20.2 +/- 5.6 MPa). However, the greatest fracture strength (28.2 +/- 8.9 MPa) was achieved when a Dicor laminate veneer alone was used to restore the fractured incisal edge.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Treatment of intruded permanent incisors: a multidisciplinary approach.

The case presented is a report of a healthy 11-year-old boy, who fell down and traumatized his four maxillary incisors. Both central incisors were deeply intruded with concomitant uncomplicated crown fractures, and both lateral incisors suffered concussion. The intruded teeth were repositioned using a removable orthodontic appliance and were endodontically treated 3 weeks after trauma. Tooth 11 became ankylosed 3 months post trauma, and tooth 21 was extruded to its original position after 5 months. Five months post-trauma, teeth 12 and 22 underwent necrosis and were endodontically treated. In addition, tooth 22 presented an external inflammatory root resorption that was arrested by calcium hydroxide paste after 3 months. A crown-lengthening procedure was performed on tooth 11 10 months post-trauma, exposing the clinical crown to a better condition for restoration. All 4 incisors were restored with a composite material, and the incisal edges of the central incisors were shaped at the same level. Two months after the crown lengthening procedure, spontaneous eruption occurred on tooth 11, that had been ankylosed. The restored incisal edge of tooth 11 was reduced to the same level of tooth 21. The patient is under periodical examination till a definitive orthodontic treatment can be performed.

Ankylosis↗
PubMed1997

Multiple dens invaginatus affecting maxillary lateral incisors and a supernumerary tooth.

Dens invaginatus is a developmental variation resulting from an alteration in the normal growth pattern of the dental papilla of a tooth. This anomaly occurs predominantly in maxillary permanent lateral incisors. Multiple occurrence in maxillary incisor teeth in the same patient has frequently been reported, and examination of bilateral teeth for the anomaly is often carried out routinely. This paper reports an unusual case of multiple invaginations, including dens invaginatus affecting maxillary lateral incisors and a supernumerary tooth and minor invaginations of the upper canines. Moreover, the case illustrates the importance of examining all the teeth in patients who present with dens invaginatus and palatal pits in incisors and canines. The possibility that the supernumerary tooth had resulted from gemination of the lateral incisor tooth germ is discussed.

Dens in Dente↗
PubMed2006

Long-term effect of different treatment modalities for traumatized primary incisors presenting dark coronal discoloration with no other signs of injury.

The aim was to compare the long-term outcomes of root canal treatment with that of follow-up-only in traumatized primary incisors in which dark discoloration is the only sign of injury. Root canal treatment was performed in 48 dark discolored asymptomatic primary incisors following trauma. Twenty-five of them [root canal treatment (RCT) group] were followed till eruption of their permanent successors. Ninety-seven dark discolored asymptomatic primary incisors were left untreated and invited for periodic clinical and radiographic examination. Of these, 28 [follow-up (FU) group] were followed till eruption of their permanent successors. The parameters examined included early extraction of the traumatized primary incisor, early or delayed eruption of the permanent successors, ectopic eruption of the permanent successor and signs of enamel hypopcalcification or hypoplasia in the permanent successor. Chi-square test was used for statistical analysis. Seven of 25 (28%) of the RCT group and 32% (nine of 28) of the FU group required early extraction. Five of 25 (20%) of the RCT group and 21% (six of 28) of the FU group showed early or delayed eruption of the permanent successors. Sixteen of 25 (64%) of the RCT group and 79% (22 of 28) of the FU group showed ectopic eruption of the permanent successors. Enamel hypopcalcification or hypoplasia in the permanent successors was equally found (36%) in both groups (nine of 25 in the RCT group and 10 of 28 in the FU group). None of differences was statistically significant. Root canal treatment of primary incisors that had change their color into a dark-gray hue following trauma with no other clinical or radiographic symptom is not necessary as it does not result in better outcomes in the primary teeth and their permanent successors.

Chi-Square Distribution↗
PubMed2006

Fluoride intake levels in relation to fluorosis development in permanent maxillary central incisors and first molars.

Gaps remain in our knowledge about the levels of fluoride intake that cause dental fluorosis. The purpose of this study was to report the fluorosis prevalence by levels of estimated fluoride intake in an effort to understand the importance of different levels of daily fluoride intake. As part of the longitudinal Iowa Fluoride Study, subjects were followed from birth to 36 months with questionnaires every 3-4 months to gather information on fluoride intake from various sources. Daily fluoride intake in mg per kg body weight (BW) was estimated from water, beverages and selected foods, fluoride supplements and dentifrice. Six hundred and twenty-eight subjects were examined for fluorosis on permanent incisors and first molars at about age 9 by two calibrated examiners using the Fluorosis Risk Index categories. Fluorosis prevalence rates were determined separately for maxillary central incisors and first molars by levels of estimated fluoride intake. There were significant positive associations between fluorosis prevalence and levels of fluoride intake. Cumulatively from birth to 36 months, average daily intake of 0.04 mg F/kg BW or less carried relatively low risk for fluorosis (12.9% for maxillary central incisors, 6.8% for first molars). Average daily intake of 0.04-0.06 mg F/kg BW showed a significantly elevated risk for fluorosis (23.0% for maxillary central incisors, 14.5% for first molars), while fluorosis risk was even higher for average intake above 0.06 mg F/kg BW (38.0% for maxillary central incisors, 32.4% for first molars). The study suggests that fluorosis prevalence is related to elevated fluoride intake when averaged over the first 3 years of life, but is even more strongly related to fluoride intake that is elevated for all of the first 3 years of life.

Adult↗
PubMed1990

Incisor microwear and diet in three species of Colobus.

Examination of incisor microwear in three species of Colobus revealed that the predominantly folivorous C. badius more closely resembles C. satanas, a seed predator/folivore, than C. guereza, another predominantly folivorous species. This demonstrates that species of the same broad dietary category can have very different patterns of incisor microwear, indicative of differences in food procurement behavior and/or the physical properties of dietary items for some portion of the diet. Conversely, species of different categories can have microwear patterns that, superficially at least, are quite similar. The dissimilarity in incisor microwear between C. badius and C. guereza is mirrored to a certain extent in molar microwear, although the differences are not nearly so great on the molars. The differences between C. badius and C. guereza may involve different food items in the major, folivorous portions of their diets, or they may relate to differences in the very minor fruit and bark components. The similar microwear patterns of C. badius and C. satanas demonstrate that incisor microwear by itself is unreliable for assigning fossil species to broad dietary categories. Incisor microwear can be used to infer finer dietary distinctions in fossil species for which dietary category has been determined by other means.

Animals↗