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Incisor and mandibular condylar movements of young adult females during maximum protrusion and lateratrusion of the jaw.

This study evaluated the correlations between condylar translation and incisor movements during maximum protrusion and lateratrusion. The sample was 27 adult females (23--35 years old), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements [linear distances (LD) and curvilinear pathways (CP)] were recorded in three dimensions for 20 s with an optoelectric (Optotrak) jaw-tracking system while each participant performed multiple maximum protrusive and lateratrusive cycles. Masticatory analysis and multilevel statistical programs computed the three-dimensional movements of the incisors and condylar hinge axis during protrusion and lateratrusion. CP of the incisor point averaged 12.0 mm (9.3 mm LD) during protrusion, 13.0 mm (11.5 mm LD) during right excursion and 12.3 mm (11.0 mm LD) during left excursion. CP of the condyles averaged 11.9--12.9 (9.2--9.5 LD) mm during protrusion. During lateratrusion the contralateral condyles moved anteroinferiorly 11.6--14.1 mm (9.5--10.2 mm LD); the ipsilateral condyles moved posterolaterally 5.8-6.8 mm (2.3--2.5 mm LD). The left condyles demonstrated more movement than the right condyles during protrusion and than the contralateral condyles during laterotrusion. Relative variation, as measured by the coefficient of variation, was greater for the movements of the ipsilateral than contralateral condyles. Incisor movements were only moderately related to condylar movements between individuals and between replicates; LDs showed stronger correlations than CPs; and correlations were stronger for lateratrusion than protrusion. While incisor and condylar movements were not affected by repeated protrusion, incisor CP (approx. 0.2 mm/cycle) and LD (approx. 0.1 mm/cycle) increased significantly with repeated excursive movements to the left and right. It was concluded that (1) incisor protrusion and lateratrusion provide moderately reliable measures of condylar translation; (2) the linear distances that the incisors move during lateratrusion provide the best measure of contralateral condylar translation; and (3) condylar movements are not affected by repeated protrusion or lateratrusion.

Adult↗

Maxillary incisor impaction and its relationship to canine displacement.

This study aimed to examine the eruption status of unerupted maxillary permanent canines in patients who also had an impacted central incisor. Seventy-five unilateral cases of the incisor anomaly were retrospectively examined. Using the initial panoramic films, we assessed the positions of the ipsilateral and contralateral canines and the lateral incisors and the timing (eruption progress) of the canines. The final position of the canines was evaluated from patient records and progress photographs. The data showed a significant increase in prevalence and severity of displaced canines in the ipsilateral side (41.3%) compared with the contralateral side (4.7%). Palatally displaced canines occurred in 9.5%, buccally displaced canines in 30.2%, and canine-lateral incisor transposition in 1.6% of the patients. Half of the buccally displaced canines in the ipsilateral side were pseudotransposed with the adjacent lateral incisor. The eruption timing of ipsilateral undisplaced canines was either similar or delayed, relative to the contralateral tooth, but never accelerated. The ipsilateral lateral incisor was strongly angulated because of a more distally located apex (5 mm) rather than a mesially tipped crown. The ipsilateral canine was relatively more superiorly positioned (undererupted). Patients who had trauma had a significantly higher prevalence and severity of canine displacement and more distally displaced lateral incisor apices. Initial height of incisor impaction did not influence the results. These data provide evidence of a significant environmental influence of an impacted maxillary central incisor in delaying and altering the eruption path of the ipsilateral maxillary canine.

Adolescent↗

Effect of unilateral superior cervical ganglionectomy on mandibular incisor eruption rate in rats.

To assess the effect of sympathectomy on rat tooth eruption, the effect of a unilateral superior cervical ganglionectomy (SCGx) on eruption rate of ipsi- and contralateral lower incisors was examined. Two experiments were performed. In a first experiment, the eruption rate of ipsilaterally denervated incisors was similar to that of contralaterally innervated incisors, when assessed for up to 28 days after surgery. In a second experiment, under conditions of unilateral unimpeded eruption of incisors performed ipsilaterally or contralaterally to a unilateral SCGx, a significantly lower eruption rate of denervated incisors at the impeded eruption side, and a significantly higher eruption rate of denervated incisors at the unimpeded side were observed, when computed every 2 days. Significant differences in individual Student's t tests at every time interval occurred mainly during the first and the last week of examination. When average daily eruption rate was computed in weekly intervals, a significant interaction between SCGx and the side of impeded or unimpeded eruption was found in a factorial ANOVA, that is, for each of the 4 weeks of examination, sympathetically denervated incisors showed lower eruption rates at the impeded eruption side, and higher eruption rates at the unimpeded side. These results indicate that incisor eruption is not modified by a local sympathetic denervation unless the contralateral lower rat incisor is cut out of occlusion.

Animals↗

Reversed palatal perforation by upper incisors in ageing blind mole-rats (Spalax ehrenbergi).

Blind mole-rats (Spalax ehrenbergi) are fossorial solitary rodents that present striking morphological, physiological and behavioural adaptations to the subterranean environment in which they live. Previous studies have shown that mole-rats are specialised in tooth-digging. The rapid eruption-rate of their incisors has evolved to compensate for their excessive wear by excavation. Males use their incisors more than females for digging and fighting, and their rate of incisor eruption is significantly more rapid than in females. Since mole-rats use their incisors for digging throughout the year, we suggest that continuous mechanical pressure on their oral tissues concentrated at the apical sites of the upper incisors leads to cell and tissue fatigue. We provide evidence for 5 stages of palatal perforation by the upper incisors at their apical sites, with maximum perforation characterising aged males. Interspecies comparisons with 7 other fossorial and semi-fossorial rodent species, and with beavers, which expose their incisors to enormous mechanical pressure, revealed that this palatal perforation is unique to the male mole-rat. We suggest that while the fast eruption rate of incisors in the mole-rat compensates for the rapid wear resulting from digging, evolutionary adaptation to continuous tooth-digging is still ongoing, since the physical pressure of digging at the apical sites of the upper incisors leads to tissue destruction, breakage of the palatal bone and possibly to death, as a result of maxillary inflammation.

Aging↗

Assessing incisor inclination: a non-invasive technique.

A method of recording incisor inclination is described using the Tooth inclination Protractor (TIP). This instrument was used to record incisor inclination on dental casts. The scores were related to traditionally determined inclinations for the upper incisor to maxillary plane and the lower incisor to mandibular plane from the lateral cephalometric radiograph. The TIP scores were closely related to the upper incisor to maxillary plane angle and lower incisor to mandibular plane angle. There was a systematic bias between the TIP and radiographically determined assessments. The TIP under-scored the lateral cephalometrically determined maxillary incisor inclination by 10.46 degrees and consistently over-scored the lower mandibular incisor angulation by 2.57 degrees. The TIP is a reliable and valid measure for assessing left and right maxillary and mandibular crown inclinations, and may also be used to record changes of incisor inclination during treatment.

Bias↗

Assessment of open and incomplete bite correction by incisor overlap and optical density of polyvinyl siloxane bite registration.

Open bite (OB) is a generalized term, which could incorporate subgroups that react differently to vertical correction. The objectives of the present study were to detect vertical treatment changes in incomplete bite (IB: inter-incisor overlap with no lower incisor contact with teeth or palate) and OB (no inter-incisor overlap) groups compared with a complete bite (CB: inter-incisor overlap with full lower incisor contact with teeth or palate) control group, to evaluate treatment response of the central and lateral incisors, and to study the vertico-sagittal interaction. Dental casts were taken at three time points, pre-treatment, post-treatment, and after one year of retention, from 54 Class II patients (22 males and 32 females with a mean age of 11 years 6 months) divided into three groups: CB (n = 21), IB (n = 18) and OB (n = 15). Measurements included incisor overlap (mm) and optical density (OD/mm2) of occlusal bite registration made of polyvinl siloxane. Both CB and IB groups demonstrated post-retention bite opening. However, bite opening in the CB group was three times greater than that in the IB group (e.g. lower lateral = -1.42 mm, 118 OD/mm2 versus -0.40 mm, 107 OD/mm2). Conversely, the OB group showed a significant (P < 0.001) bite closure (e.g. lower lateral = 1.30 mm, -377 OD/mm2). Overjet changes affected OD measurements, causing diversity in OD and millimetric measurements of the lateral incisors in the IB group. In conclusion, the OB group demonstrated a significant stable vertical correction; a post-treatment non-contact inter-incisor relationship was determined by a vertico-sagittal relapse; and full compensation of an IB was not possible.

Child↗

FGF10 maintains stem cell compartment in developing mouse incisors.

Mouse incisors are regenerative tissues that grow continuously throughout life. The renewal of dental epithelium-producing enamel matrix and/or induction of dentin formation by mesenchymal cells is performed by stem cells that reside in cervical loop of the incisor apex. However, little is known about the mechanisms of stem cell compartment formation. Recently, a mouse incisor was used as a model to show that fibroblast growth factor (FGF) 10 regulates mitogenesis and fate decision of adult stem cells. To further illustrate the role of FGF10 in the formation of the stem cell compartment during tooth organogenesis, we have analyzed incisor development in Fgf10-deficient mice and have examined the effects of neutralizing anti-FGF10 antibody on the developing incisors in organ cultures. The incisor germs of FGF10-null mice proceeded to cap stage normally. However, at a later stage, the cervical loop was not formed. We found that the absence of the cervical loop was due to a divergence in Fgf10 and Fgf3 expression patterns at E16. Furthermore, we estimated the growth of dental epithelium from incisor explants of FGF10-null mice by organ culture. The dental epithelium of FGF10-null mice showed limited growth, although the epithelium of wild-type mice appeared to grow normally. In other experiments, a functional disorder of FGF10, caused by a neutralizing anti-FGF10 antibody, induced apoptosis in the cervical loop of developing mouse incisor cultures. However, recombinant human FGF10 protein rescued the cervical loop from apoptosis. Taken together, these results suggest that FGF10 is a survival factor that maintains the stem cell population in developing incisor germs.

Animals↗

The relationship between eruption and length of mandibular incisors in young rats.

BACKGROUND: Rat incisor teeth exhibit continuous growth, hence they have frequently been used to study the eruption process. The aim of our study was to investigate changes in the eruption rate of impeded and unimpeded rat incisors and to determine if any relationship existed between eruption rate and length of the clinical crown. MATERIAL/METHODS: An image analysis technique was used to measure the length of the mandibular incisors of 23 young female Sprague-Dawley rats, aged 7 to 8 weeks. Over a four-week period, the mandibular right incisors of the 11 rats in the experimental group were shortened every two or three days. Another group of 12 rats served as the control. RESULTS: The mean unimpeded eruption rate was 1.0+/-0.1 mm/day, while the impeded eruption rate was 0.6+/-0.1 mm/day. On day 2, the eruption rate of the unimpeded mandibular incisors accelerated to 163.9% when compared to the controls. The impeded mandibular incisors increased in length by 8.8% and 12.1% for the experimental and control groups respectively. An inverse relationship was identified between the eruption rate and the length of clinical crown of the impeded mandibular incisors, while the unimpeded eruption rate was unrelated to the length difference between the left and right incisors if the length difference exceeded 0.5 mm after accelerated eruption. CONCLUSIONS: It was found that the mandibular incisors of young rats need to be shortened every two days in order to study unimpeded tooth eruption, and the shorter the tooth is cut the higher the rate of eruption.

Animals↗

Conservative treatment for malaligned permanent mandibular incisors in the early mixed dentition.

When mandibular permanent incisors erupt lingually to the corresponding primary tooth, the lingually erupted permanent incisor should be allowed to correct itself. This self correction will usually occur by eight years of age. If the primary incisor is still present at eight years of age, it should be considered overretained. Extraction is indicated. No primary mandibular central incisors are indicated for extraction, when the mandibular permanent central incisors initially erupt malaligned. In addition, if there is an apparent lack of space for the unerupted mandibular lateral incisor after the permanent central incisors have erupted, wait for the permanent lateral incisor to erupt fully. This waiting period allows for maximum intercanine width to occur. Other factors can allow for further improvement of the malaligned mandibular permanent incisors.

Child↗

[The vector analysis of the anteroposterior relationship among the apical bases and the incisors].

Using the lateral cephalometric radiographs, the points A, B, maxillary incisor tip (U) and mandibular incisor tip (L) were projected onto the Frankfort horizontal plane and the projected points were defined as a, b, u and 1, respectively. According to the principle of the vector analysis, the vector formula ab - ul = au - bl can always stand irrespective of how the locations of the points a, b, u and 1 vary. The vectors ab, ul, au and bl represent the anteroposterior linear relationship between the upper jaw and the lower jaw, the upper incisor and the lower incisor (overjet), the upper jaw and the upper incisor, and the lower jaw and the lower incisor, respectively with reference to the FH plane. The lateral cephalometric radiographs taken from a total of 863 class I subjects, including 422 males and 441 females, were submitted for the study. The four vector values were obtained from the tracing of each radiograph and the mean values were computed according to sex and age. If a positive value was given to the vector ab, it denoted that point "a" was anterior to point "b", while a negative value denoted that "a" was posterior to "b". Both sexes of the subjects were divided according to their ages into junior primary (JP, 6-8 years), senior primary (SP, 9-11 years), junior high (JH, 12-14 years), and senior high (SH, 15-18 years) groups. No substantial or significant mean difference of each vector between the males and the females in each age group was noted. The mean values of the vector ab were 7.4, 6.8, 6.1 and 4.7 mm in JP, SP, JH and SH groups, respectively with the male and the female data pooled together. This indicates that there was a gradual catching up tendency of mandibular versus maxillary growth. The mean values of the vector ul were 1.4, 2.8, 2.9 and 2.8 mm in each successive age group, respectively showing that the overjet was rather constant with age except in the youngest group. The corresponding mean values were -0.4, -3.9, -5.2 and -6.1 mm for the vector au and -6.3, -8.0, -8.4 and -8.0 mm for the vector bl in JP, SP, JH and SH groups, respectively. The data indicate that both upper and lower incisors were relatively more upright in the youngest group when compared with the other age groups. In the remaining groups the upper incisors exhibited a tendency of gradual labial tipping with age, whereas the lower incisors kept stable in the procumbency.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

Wear in the upper and lower incisors in relation to incisal and condylar guidance.

The incisors of 85 patients were examined for tooth wear with the aim to evaluate possible association between the degree of wear and anterior guidance. Apart from clinical functional analysis electronic axiography using the system CADIAX was carried out. Anterior guidance in protrusive movement was marked on individually mounted plaster casts and scanned using a pantograph. The cephalometric analysis program CADIAS was used for the metric determination of the anterior guidance angle to the axis-orbital plane, and in order to relate the anterior guidance to the horizontal condylar inclination. The interincisal angle was included in the evaluation as a further functional angle and according to overjet and overbite there were classified typical incisor relations. Where both anterior guidance and incisor inclination and relation were in the normal range, there was an increase in incisal tooth wear in the group investigated. With reduced functional space, frequently found together with anterior deep bite, incisor wear was less extensive. While the occurrence of parafunction was shown not to be related to anterior guidance and incisor inclination and relation parafunctions were the decisive factor in the occurrence of severe incisor wear. Where anterior guidance and incisor inclination and relation are normal, the area of enamel under load is smaller and the space for bruxism larger. Parafunctional forces thus appear to result in a higher degree of wear than is found with the reduced functional space of a steep incisor position. Anterior guidance could not be evaluated as a parafunctonal inducing factor, but only as determining the wear pattern in the individual.

Adult↗

Prevalence of shovel-shaped incisors in Saudi Arabian dental patients.

The prevalence of maxillary incisor shoveling was studied radiographically in 990 Saudi patients. According to the radiomorphologic characteristics, a new classification was developed and shovel teeth were categorized. The findings of this study showed 9% shovel-shaped incisors; among those, 4% were central incisors and 5% were lateral incisors. Frequency of dens invaginatus occurrence with the shovel-shaped incisors was also investigated. Eight percent of shovel-shaped incisors showed presence of dens invaginatus. Prevalence was found to be 4% in central shovel-shaped incisors, whereas that in lateral shovel-shaped incisors was 11%.

Adolescent↗

Changes in mandibular incisor position in Class II Division 1 malocclusion treated with premolar extractions.

The aim of this study was to investigate the magnitude of mandibular incisor retraction to be expected during full fixed appliance mechanotherapy in Class II Division 1 malocclusions treated with premolar extractions when mandibular incisor retraction was not part of the treatment plan. The material consisted of pretreatment and posttreatment cephalometric films and dental casts of 70 Class II Division 1 malocclusion patients (33 males and 37 females) treated with the preadjusted edgewise appliances. The mandibular first premolars were extracted in 31 subjects, and the mandibular second premolars were extracted in 39. The pretreatment factors that suggested a basis for the extraction choice in the mandibular arch in these patients were found to include the ratio between posterior and anterior facial heights, the maxillary-mandibular plane angle, and the residual space in the mandibular arch. The mandibular incisors were retracted in only 65% of the patients. On average, the mandibular incisors were retracted by 1.02 mm relative to the nasion-pogonion line; there was no significant difference between the 2 extraction groups. Multiple regression analysis showed that the change in the mandibular incisor position is significantly correlated with the residual space in the mandibular arch, the initial distance between the mandibular incisor and the nasion-pogonion line, maxillary-mandibular angle, and the duration of crown labial torque in the mandibular incisors. In combination, these 4 factors could explain 61% of the change in the mandibular incisor position.

Adolescent↗

Ethnic differences in upper lip response to incisor retraction.

INTRODUCTION: The purpose of this retrospective longitudinal study was to investigate the response of the upper lip to incisor retraction and to ascertain the effect of ethnicity on this response. METHODS: Pretreatment and posttreatment lateral cephalograms of 88 postpubertal female patients (44 black and 44 white; mean age, 18.45 years) were evaluated. The groups were matched by age and the amount of incisor retraction at incisor superius. RESULTS: Although significant pretreatment differences existed between the groups in some cephalometric measurements, analysis of the treatment changes demonstrated significant differences only in incisor inclination. Hard and soft tissue changes of the black group were more downward, whereas changes in the white group were more backward. Multivariate regression analysis showed that the horizontal response of the upper lip to hard tissue changes at subnasale and superior labial sulcus was different in whites than in blacks. At subnasale, stepwise multivariate regression analysis showed that ethnicity contributed to the upper lip response to incisor retraction and was significantly greater in the white group. CONCLUSIONS: The hard and soft tissue treatment changes of the black group were more downward, and those of the white group were more backward. Ethnic differences exist in the soft tissue response to hard tissue changes in the upper lip, and at subnasale and the superior labial sulcus; however, these response differences at superior labial sulcus can be explained by the ethnic differences in initial lip thickness and incisor inclination; they are not due in and of themselves to ethnicity. The change at prosthion was significantly correlated with the response of the upper lip at labrale superius to incisor retraction. Ethnicity added no increase to the predictability of the response. When incisor retraction was performed, the final horizontal upper lip position could be accurately and reliably predicted.

Adolescent↗

Relations in color among maxillary incisors and canines.

OBJECTIVES: To establish the strength of color relation among the maxillary central incisor, lateral incisor and canine teeth by using digital photography. This relation might be useful for the color reconstruction of the missing part of a tooth from the color obtained from neighboring teeth. METHODS: The L*a*b* values of the maxillary incisors and canines were determined in 100 subjects. Paired t-tests, Pearson correlations and linear regression analyses were used to describe the relation of the L*a*b* values between the three teeth for each segment (cervical, middle and incisal). RESULTS: The mean L*a*b* values of the canines differed statistically significantly from the values of the central incisors (p<0.001) except for L* and a* values in the cervical segment between the lateral incisor and canine. The color differences between the incisors were statistically significant in fewer cases. The relation in color was the highest between the cervical segments of the three teeth, with respect to L* (r = 0.45-0.65; p < 0.001), b* (r = 0.49-0.55; p < 0.001), and a* (r = 0.38-0.61; p < 0.001), and no relation was found between the incisal segments of central incisor and canine. SIGNIFICANCE: There is a relation in color between the maxillary incisors and canines, which is stronger between the cervical than between the middle and incisal segments. Therefore, the color prediction is most reliable when the cervical parts of the teeth are used.

Adult↗

An evaluation of the quality of root fillings in mandibular incisors and maxillary and mandibular canines using different methodologies.

OBJECTIVES: To evaluate the quality of root fillings in mandibular incisors and maxillary and mandibular canines using different methodologies of evaluation, namely radiographs, the fluid transport test and the percentage of gutta-percha (PGP), and to determine if a correlation occurs between the results of the different methodologies used. METHODS: One group of mandibular incisors with oval canals (n=20) and one group of maxillary and mandibular canines (n=20) were instrumented and obturated by cold lateral compaction using AH 26 as the sealer. The filled roots were bucco-lingually and mesio-distally radiographed. Using a scoring system, the quality of each root filling was radiographically evaluated, the higher the score the poorer the quality. Fluid transport along the root filling was then measured using a fluid transportation device. Each root was horizontally sectioned 4 and 6mm from the apex. Images of the cross-sections were taken, using a microscope and a digital camera. Images were scanned into a PC as TIFF images. Using a KS 100 Imaging system the canal area and the gutta-percha filled areas were measured. The percentage of gutta-percha filled areas was calculated. RESULTS: Considering the radiographic scores of the two different projections together the score was significantly higher for the mandibular incisors than for the canines (P=0.039). The radiographic score was significantly higher for the mesio-distal radiograph in comparison with the bucco-lingual radiograph (P=0.0001), for the canines as well as the incisors. Using only the bucco-lingual radiograph there was no significant difference between the mandibular incisors and the canines (P=0.992). The mandibular incisors displayed significantly more fluid transport than the canines (P=0.049). A significantly greater percentage of gutta-percha filled areas was found in the cross-sections of canines as compared to the cross-sections of mandibular incisors (P=0.000001). The correlation between the radiographic score of the mesio-distal radiograph and the PGP 4 and 6mm was significant (P=0.013). There was no significant correlation between the FT and the radiograph or the FT and the PGP. CONCLUSIONS: The quality of the root fillings in oval canal-mandibular incisors may be compromised.

Bismuth↗

The incisor-lip relationship in Herbst/multibracket appliance treatment of Class II, Division 2 malocclusions.

The purpose of this investigation was to examine the effect of Herbst/multibracket appliance treatment on the upper incisor-lower lip relationship in the management of Class II, division 2 malocclusions. The study evaluated 19 successfully treated subjects using lateral head films analyzed at 3 occasions: before (T1) and after (T2) Herbst/multibracket appliance treatment and 1-year posttreatment (T3). The average treatment (T1-T2) changes showed (1) the lower lip overlap on the upper incisors was reduced from 6.0 mm to 4.2 mm (P < .001), (2) the upper incisors were proclined 15.3 degrees (P < .001) and the lower incisors were proclined 9.6 degrees (P < .001), (3) the overbite was reduced from 7.3 mm to 1.7 mm (P < .001), and (4) the sagittal jaw base relationship (Wits) improved from +3.5 to +0.5 mm (P < .001). The average posttreatment (T2-T3) changes showed (1) the upper incisor-lower lip relationship remained stable, (2) the upper (0.6 degrees; P < .001) and lower (2.3 degrees; P < .001) incisors retroclined, (3) the overbite increased (1.2 mm; P < .001), and (4) the sagittal jaw base relationship remained unchanged. In conclusion, it was found that the upper incisor-lower lip relationship was improved by Herbst/multibracket appliance treatment and remained stable during a 1-year posttreatment period in spite of minor relapses of incisor tooth positions and relationships.

Cephalometry↗

Longitudinal cephalometric changes in incisor position, overjet, and overbite between 10 and 14 years of age.

The purpose of this study was to evaluate the longitudinal growth changes in the incisor position, overjet, and overbite between 10 and 14 years of age. Serial cephalometric radiographs of 63 subjects (31 boys and 32 girls) were taken at the ages of 10, 11, 12, and 14. The effects of age and gender on the incisor positions, overjet, and overbite were investigated by means of variance analysis and least square difference (LSD) tests. The results show that the measurements of overbite, upper incisor-NA (mm), lower incisor-NB (mm), upper incisor-NA (angle), and the interincisal angle were affected by age. The results also show that the measurements of overbite, upper incisor-NA (mm), upper incisor-NA (angle) and upper incisor-SN (angle) were affected by gender.

Adolescent↗