Topographic and radiographic profile assessment of dental erosion. Part II: effect of citrus fruit juices on human dentition

This study sought to monitor changes in the topography, morphology, and radiographic profiles of human permanent teeth that had been exposed to citrus fruit juices. The effect of long-term exposure was monitored for a prolonged duration of 20 weeks according to set criteria. Topographic and morphologic changes were observed at weekly intervals following challenge by test fluids (orange, lemon, and grapefruit juices) and compared with control fluids (acetic acid and water). The qualitative changes in the specimens' topography and the morphology of citrus fruit juices and control fluids are described as a function of time, in specific details. The digitized radiographic images obtained at four-week intervals were analyzed and the changes were assessed. The results indicated that orange juice specimens demonstrated the mildest changes, while lemon juice specimens displayed the most severe damage to the coronal segments of the teeth. This damage manifested as loss of cusp height, cervical enamel, and coronal radius, as well as reduction of enamel cap height. Of the tested and control fluids, lemon juice displayed the most eros ion, followed by acetic acid, grapefruit juice, orange juice, and water, which had no effect. Continued immersion in the four acidic fluids led to varying degrees of enamel loss progression.

[In vitro evaluation of correlation between the size of apical foramen and the accuracy of root ZX]

OBJECTIVE

The study was designed to investigate the relationship between the accuracy of Root ZX and the size of apical foramen, when the apical constrictions were intact or not. Methods Lengths were taken when the needle reached the '0.5' mark and 'APEX' mark on the Root ZX. The electronic apex locator (EAL)-measured canal working length (L2) and EAL-measured canal length (L1) were then compared with the actual canal working length (L') and actual canal length (L). Besides, the areas of apical foramens CS) were measured when the apical constriction were intact or not. Then the measurement deviations and the areas of apical foramens were analyzed by linear correlation and linear regression using the software SPSS 12.0. Statistical significance was considered at P < 0.05.

RESULTS

There were no significantly correlations between the area of apical foramen and the accuracy of Root ZX if the apical constriction was intact (P > 0.05). However, the accuracy of Root ZX and the size of apical foramen had significant negative correlation when the apical constriction was destroyed (P < 0.001). Then the linear regression was completed, and the linear regression equation was deltaL2 = -0.623 + 6.5965, so the critical area of the apical foramen was 0.135 mm2 if the tolerant error was set at 0.5 mm according to the statistic control.

CONCLUSION

The size of apical foramen has little effect on the accuracy of Root ZX if the apical constriction is intact. However the measurements of Root ZX should be used carefully when the apical constriction was destroyed.

Pathological or physiological erosion--is there a relationship to age?

This conventional literature review discusses whether pathological tooth wear is age dependant. It briefly reviews the components of tooth wear and the prevalence of tooth wear in children, adolescents and adults. The emphasis on terminology relating to tooth wear varies. In some countries, the role of erosion is considered the most important, whereas others consider the process to be a combination of erosion, attrition and abrasion often with one being more dominant. The importance of tooth wear or erosion indices in the assessment and the evidence for progression within subject and within lesions is described. The data from the few studies reporting pathological levels of wear reported in children and adults are discussed, in particular its relationship with age. There is little evidence to support the concept that pathological levels of erosion or wear are age dependant. There is, however, some evidence to suggest that normal levels of erosion or wear are age dependant.

The importance of width/length ratios of maxillary anterior permanent teeth in esthetic rehabilitation

The aim of this study was to investigate the importance of the width/length (W/L) ratio of maxillary anterior permanent teeth in anterior esthetic rehabilitation. Digital photographs were taken of the anterior teeth for each participant (approximately 20 years old). A maxillary impression was taken with irreversible hydrocolloid and cast in die stone under vacuum. The widest mesiodistal width and incisogingival length of the tested teeth were measured. The data were submitted to analysis of variance, which showed significant statistical differences within each parameter (P< .05). The width and length measurements varied between maxillary anterior teeth in the following or der: central incisors > canines > lateral incisors. Maxillary central incisors displayed the largest W/L ratio (85%), maxillary lateral incisors (LI) displayed the smallest W/L ratio (79%), and canines displayed the intermediate W/L ratio (83%). These dimensions have a positive effect on the final restoration; therefore, it is suggested that the specific width, length, and W/L ratio should be used in esthetic rehabilitations of maxillary anterior teeth.

Interleukin-1 gene cluster polymorphisms and gingival recessions after orthodontic treatment

INTRODUCTION

Genetic polymorphisms in the interleukin-1 gene cluster have been associated with the severity of periodontal diseases featured by a variable degree of destruction of connective tissue and bone, such as periodontitis and periimplantitis. This study was aimed to investigate if a link exists between such interleukin-1 gene polymorphisms and the development of gingival recessions during orthodontic treatment in Italian children.

METHODS

We evaluated, in 74 young Italian patients of both sexes, the -889 C/T polymorphism of the interleukin-1alpha gene and the -511 C/T and +3954 C/T polymorphisms of interleukin-1alpha gene by polymerase chain reactions-restriction fragment length polymorphism method using NcoI, AvaI and TaqI as restriction enzymes.

RESULTS

No association of interleukin-1 genotypes investigated and gingival recession occurring during orthodontic treatment were identified.

CONCLUSION

In the population studied specific interleukin-1 genotypes (linked to a higher susceptibility to bone resorption in periodontal disease) there does not appear to be any association with the development of gingival recessions during orthodontic treatment.

Variability of the dental surface: effects on orthodontic treatment

OBJECTIVES

The Author studied the variability of the vestibular surfaces of tooth usually involved in orthodontic treatment.

MATERIALS AND METHODS

200 model casts of Italian subject with complete permanent dentition have been analyzed studying the clinical crown dimension and the angulations of tangents drawn at 3 and 4 mm.

RESULTS

The authors found differences in the vestibular surfaces curvature in the last teeth of each series, more accemptuated in the lower than in the upper arch.

CONCLUSION

The conclusions of this study are related to the use of orthodontic straight wire appliances. The use of standard values with a complete torque, independently from the individuals, is based on the hypothesis of equal positioning on the tooth surface and related to the teeth axis. A variation in the torque of the upper central incisor for different kinds of straight wire appliance related to extreme variation of vestibular curvature is hypothesised.

Using digital photography to visualize, plan, and prepare a complex porcelain veneer case

Visualization and pre-operative plan are critical to efficient and thorough case preparation. Congenitally missing teeth, coupled with improper tooth positioning, can compromise the aesthetic rehabilitation outcome. Utilizing pre-treatment digital photography as an outline for tooth reduction and laser tissue re-contouring may help to create a symmetric and pleasing smile, even under less ideal conditions.

Lateral incisor root resorption and active orthodontic treatment in the early mixed dentition

AIM

To evaluate the presence of root resorption in the lateral incisor after active orthodontic treatment in the early mixed dentition.

METHODS

Twenty-six children treated at the Children's Clinic of the Schulich School of Medicine and Dentistry at the University of Western Ontario were examined radiographically for lateral incisors root resorption before and after early active treatment to align upper incisors (2 x 4 appliance). In addition, canine inclinations to the midline and to the long axis of the lateral incisor as well as the most medial position of the canine crown were measured as potential risk factors for root resorption.

RESULTS

8% (4) of the lateral incisors exhibited root resorption and the mean crown-to-root ratio of these teeth was significantly higher than that for lateral incisors not exhibiting root resorption. Similarly, mean canine inclinations to the midline and to the long axis of the lateral incisor were also significantly higher for the root resorption group. No association could be found between the most medial position of the canine crown and root resorption in the lateral incisor.

CONCLUSION

This study showed that active orthodontic treatment in the early mixed dentition does not increase the risk for root resorption in the lateral incisors as long as the clinician takes into consideration canine inclinations and their potential effect on root resorption. Limitations inherent to radiographic assessment are acknowledged.

Applicability of the dimodent equation of sex prediction in a Lebanese population sample

BACKGROUND

Sexual dimorphism represents a group of morphologic characteristics that differentiate a male from a female. Among these dimorphic traits, tooth size has been evaluated in various populations for its interest in anthropologic and forensic applications. Recent studies have shown that dental dimorphism is population-specific and that the most dimorphic tooth is the mandibular canine. In addition to the dimension of single teeth in dimorphic dental assessment, dimorphism has been evaluated, using equation of prediction, applying various dimensions of one or more teeth or indices.

PURPOSE

The objective of this preliminary study was to evaluate the applicability of the Dimodent predictive equation in sex determination in a sample of Lebanese young individuals.

MATERIALS AND METHODS

Mesiodistal widths of the mandibular canine and lateral incisor were measured from dental casts of the permanent teeth of 60 Lebanese University dental students (30 males and 30 females), aged 18-25 years. The sex-predictive equation of Fronty was applied to calculate the percentage of accurately-diagnosed sexes.

RESULTS

Accuracy of sex prediction ranged from 63.3% for males and 90% for females. Overall, the Dimodent equation enabled a correct sex determination in 76.7% of the cases. When compared to the accuracy obtained with this equation in a French population sample, the accuracy was significantly different (Z=3.1225).

CONCLUSIONS

This research supports earlier studies that sexual dimorphism is population specific. The difficulty or lack of dimorphism seems to originate from male subjects. Further investigations should include the preparation of population-specific prediction tables and testing their accuracy in a larger sample with a strongly-established Lebanese background.

The accuracy of dental panoramic radiography as an indicator of chronological age in Iranian individuals

Growth rate is dependent on genetic and environmental factors and varies between the sexes, between individuals of the same population and between populations themselves. There is strong concern over the dental and bone testing procedures conducted to determine the age of young individuals for legal reasons. Inaccurate results would lead authorities to imprison some children in adult prisons, which are unsafe and inappropriate for minors. This study was designed to determine the relationship between dental age, the age from dental panoramic radiography, skeletal age and chronological age in patients referring to dental clinics of Yazd, Iran, for third molar surgery. The sample for the study consisted of 58 subjects between 15-25 years of age. The results indicated that estimating the age by examination of extracted lower wisdom teeth was most accurate. However, as use of this method i.e. extraction of tooth or dental surgery is not possible in normal individuals. Estimating the age from dental panoramic radiography showed high accuracy when applied to the patients.

Determining tooth size ratio in an Iranian-Azari population

AIM

The aim of this investigation was to determine the tooth size ratio in an Iranian-Azari population.

METHOD AND MATERIALS

The Bolton tooth size analysis was performed on a sample of 50 plaster models (25 male subjects, 25 female subjects) of Iranian-Azari subjects. The mesiodistal widths of all teeth were obtained and the Bolton anterior ratio and overall ratio were calculated. The mean, range, and standard deviation were calculated for the anterior and overall ratio, and a coefficient of variation was obtained for the tooth size ratio.

RESULTS

For the anterior ratio (3-3), the Iranian-Azari had a mean of 78.0 mm with a standard deviation of 3.1; the range was 73.68 to 84.6 mm. For the overall ratio (6-6), the mean was 92.0 mm with a standard deviation of 2.4; the range was 88.09 to 97.5 mm.

CONCLUSIONS

The results from the Iranian-Azari subjects in the study are similar to Bolton's original data for an American population. These values and the degree of variation were similar to the original data by Bolton, indicating the Bolton analysis for Caucasian samples can be transferred to an Iranian-Azari population. It also confirms no relevant sexual dimorphism exists, and these values are valid for both male and female subjects.

A classification system to measure the implant-abutment microgap

PURPOSE

A large microgap at the implant-abutment interface has been reported to result in adverse effects, including screw loosening, abutment rotation, and abutment fracture. However, a standardized classification of the implant-abutment interface has not been established. The purposes of this investigation were (1) to propose a classification system based on the horizontal and vertical microgap of the implant-abutment interface and (2) to compare the implant-abutment interface in 4 groups of abutments.

MATERIALS AND METHODS

Forty-eight randomly selected external hexagonal implants were paired with (1) machined titanium abutments, (2) premachined palladium abutments cast-on with palladium alloy, (3) plastic burnout abutments cast with nickel chromium alloy, and (4) plastic burnout abutments cast with cobalt chromium alloy. A comparison of the horizontal and vertical microgaps at the implant-abutment interface was completed at 8 locations on each specimen to the nearest micrometer using an optical microscope with a magnification of 150x. Group means and significant differences between groups were determined by analysis of variance and Tukey multiple-comparisons post-hoc analysis. P < .05 was the threshold for statistical significance.

RESULTS

There was no significant difference between groups with respect to vertical misfit. For horizontal misfit, machined titanium abutments presented significantly higher horizontal misfit compared to other groups (P < .001). Premachined cast-on abutments had significantly higher horizontal misfit than cast NiCr abutments (P < .001). In the proposed classification system, 23% of all sites measured at the implant-abutment interface had an ideal relationship, 34% had a horizontal discrepancy only, 4% had a vertical discrepancy only, and 39% had both vertical and horizontal discrepancies.

CONCLUSION

The proposed implant-abutment classification system demonstrated a way to characterize and compare the microgap at the implant-abutment interface.

A clinical experimental simulation of changes in intercanine width associated with the correction of crowding: a pilot study

The purpose of this article is was to introduce a mathematical model, investigating the anticipated changes in intercanine width associated with the resolution of crowding, using the leeway space. A linear regression formula was computed to predict the change per millimetre of 'intercanine tip space deficiency'. After digitizing 61 mandibular casts, 14 co-ordinates per model were used to fit an 'individualized optimal curve' consisting of either a hyperbolic cosine function or parabola anteriorly and a third degree polynomial function bilaterally. The total amount of tooth material was measured between the cusp tips of the canine teeth and subtracted from the available intercanine tip arch length to render the intercanine tip space deficiency. This value was then used to allocate patients to an experimental [31 subjects, 14 boys and 17 girls, mean age 11.7 years, standard deviation (SD) 1.4 years] or a control (30 subjects, 10 boys and 20 girls, mean age 11.6 years, SD 1.1 years) group. After digitally aligning the incisors and canines on the selected optimal curve, the new intercanine width was calculated. Significant differences (P < 0.001) in intercanine expansion were found between both groups (control group: mean -0.07 mm, SD 0.31 mm; experimental group: mean 1.13 mm, SD 0.51 mm) due to a clinically significant increase of approximately 0.6 mm in intercanine width (y) per millimetre of calculated intercanine tip space deficiency (x), leading to the following regression formula: y = 0.09 + 0.52x.

Retromolar space analysis in relation to selected linear and angular measurements for an Iraqi sample

BACKGROUND

Radiographic diagnosis of the presence, position, and degree of third molar formation is a crucial part of integral treatment planning for the development of this tooth. Shortage of eruption space between lower second molar and the ramus has long been identified as a major factor in the etiology of lower third molar impaction. The purpose of the present investigation was to evaluate the validity of some angular and linear measurements made on digital panoramic imaging to be used as a reference for early prediction of lower third molar eruption or impaction.

SUBJECTS AND METHODS

Digital panoramic imaging was done on 50 individuals with full dentition and a class I occlusal relationship. The sample was divided into full-eruption and marginal-eruption groups. Nine variables (linear measurements and angles) were measured for every individual to determine the minimal and maximal values of each variable and these variables were correlated to each other using Pearson's correlation equation.

RESULTS

Lower eruption space measurements for the marginal-eruption group were smaller by more than 3 to 4 mm than that of the full-eruption group. The beta-angle, the angle formed between the long axes of lower second and third molars, showed a marked increase in their values (9 degrees to 10 degrees) when the marginal-eruption group is compared to the full-eruption group.

CONCLUSION

Third molar angle (alpha-angle), beta-angle, and gonial angle together with lower eruption space measurements are the variables that should be taken into consideration when early prediction of lower third molar eruption is performed.

The incidence of four canals in maxillary first molars

BACKGROUND

The authors conducted an in vivo study to report the incidence of fourth root canals located and treated in maxillary first molars during a seven-month period in a postgraduate endodontic program.

METHODS

In this retrospective study, the authors determined the number of canals treated by postgraduate students in an endodontic program. The attending postgraduate endodontic faculty member supervising the case verified the number of canals in the teeth. The authors then collected the data from each resident and compiled them.

RESULTS

The residents treated a total of 121 maxillary molars, 85 (70.2 percent) of which met the criterion of having four or more canals treated. Approximately 99 percent of the fourth canals were located in the mesiobuccal root.

CONCLUSIONS

Overall, 70 percent of the maxillary first molars contained at least four canals that required instrumentation.

CLINICAL IMPLICATIONS

The results of this study demonstrate that it is imperative for any dentist performing root canal therapy on maxillary first molars to examine carefully the pulpal floor to locate all canals, especially the second mesiobuccal canal. Performing thorough examinations may increase the chance of treatment success.

Influence of sex and ethnic tooth-size differences on mixed-dentition space analysis

INTRODUCTION

Most mixed-dentition space analyses were developed by using subjects of northwestern European descent and unspecified sex. The purpose of this study was to determine the predictive accuracy of the Tanaka-Johnston analysis in white and black subjects in North Carolina.

METHODS

A total of 120 subjects (30 males and 30 females in each ethnic group) were recruited from clinics at the University of North Carolina School of Dentistry. Ethnicity was verified to 2 previous generations. All subjects were less than 21 years of age and had a full complement of permanent teeth. Digital calipers were used to measure the mesiodistal widths of all teeth on study models fabricated from alginate impressions. The predicted widths of the canines and the premolars in both arches were compared with the actual measured widths.

RESULTS

In the maxillary arch, there was a significant interaction of ethnicity and sex on the predictive accuracy of the Tanaka-Johnston analysis (P = .03, factorial ANOVA). The predictive accuracy was significantly overestimated in the white female group (P <.001, least square means). In the mandibular arch, there was no significant interaction between ethnicity and sex (P = .49).

CONCLUSIONS

The Tanaka-Johnston analysis significantly overestimated in females (P <.0001) and underestimated in blacks (P <.0001) (factorial ANOVA). Regression equations were developed to increase the predictive accuracy in both arches.

Evaluation of the inclination in posterior dentoalveolar structures after rapid maxillary expansion: a new method

OBJECTIVES

In order to compare the skeletal and dental effects of rapid maxillary expansion, orthodontists need an assessment of buccal dentoalveolar inclination. The aim of the present paper is to introduce a new technique for the evaluation of buccal inclinations in dentoalveolar structures.

METHODS

Using barium sulphate solution with a paintbrush, a thin line was drawn on and between the first molars of the maxillary stone casts. Then, radiographic images of the stone casts were obtained. Buccal tipping of molar crowns and alveolar processes were evaluated on these images by means of a computerized imaging software program.

CONCLUSIONS

This new evaluation technique is inexpensive, simple and reliable for the assessment of dentoalveolar inclination. In addition, the changes in dentoalveolar structures may also be visualized by superimposing the pre- and post-treatment images.

The association between embrasure morphology and central papilla recession: a noninvasive assessment method

BACKGROUND

The distance from bone crest to contact point is only the most frequently studied of the many factors that influence whether interdental papilla are present. The purpose of this study was to discover the association between embrasure morphology and central papilla recession.

METHODS

The central papilla was visually assessed in 310 adults using paralleling periapical radiographs of the maxillary central incisors. The following vertical distances were measured: the recession distance, i.e., papilla tip (PT) to contact point (PT-CP), bone crest (BC) to contact point (BC-CP), proximal cementoenamel junction (pCEJ) to contact point (pCEJ-CP), papilla height (PH), and bone crest to proximal cementoenamel junction (BC-pCEJ). Interdental width was measured horizontally. Subjects were divided into 4 groups according to interdental width and pCEJ-CP distance: long-narrow, short-narrow, long-wide, and short-wide.

RESULTS

Statistical analysis revealed the following for all four study groups: a positive correlation between papilla recession distance and age, a positive correlation between bone crest-contact point distance and age, and a negative correlation between age and papilla height.

CONCLUSION

Central papilla recession as a result of aging occurs most frequently in the long-wide group, that is, among people who have both a wide interdental width and a long distance between the proximal cementoenamel junction and the contact point. However, other factors also affect the likelihood of central papilla recession. Thus, there is a need for further study of the interaction among these causal factors.

Immediate and six-month space changes after premature loss of a primary maxillary first molar

BACKGROUND

Premature loss of primary maxillary first molars has been associated with a number of consequences (such as tipping of the first permanent molar). The aim of the authors' study was to investigate dental-arch space problems arising as a result of premature loss of a primary maxillary first molar.

METHODS

This study was composed of 19 children who experienced unilateral premature loss of a primary maxillary first molar. The authors used each patient's intact contralateral arch segment as a control. The authors obtained maxillary dental study casts two or three days after the tooth was extracted, as well as six months later.

RESULTS

The D + E space from the extraction side six months after removal of the tooth (mean +/- standard deviation, 15.62 +/- 1.13 millimeters) was significantly smaller than the space on the control side (16.88 +/- 1.12 mm) and the initial D + E space (16.70 +/- 0.69 mm). The authors found a significantly shorter arch length (25.47 +/- 1.58 mm) and larger intercanine width (31.29 +/- 2.49 mm) six months after the tooth was extracted compared with the initial arch length (25.66 +/- 1.64 mm) and intercanine width (30.42 +/- 2.64 mm).

CONCLUSIONS

The early space changes to the maxillary arch subsequent to premature loss of a primary maxillary first molar are primarily distal drift of the primary canines toward the extraction space and palatal migration of the maxillary incisors. Although 1 mm of space was lost, which is statistically significant, this is not likely to be of sufficient clinical significance to warrant use of a space maintainer. If palatal movement appears to be needed, the dentist should consider use of a palatal arch rather than a band-and-loop maintainer.

CLINICAL IMPLICATIONS

The effects of space maintainers need to be re-evaluated in cases of unilateral premature loss of a primary maxillary first molar.

A comparison of accuracy in bracket positioning between two techniques--localizing the centre of the clinical crown and measuring the distance from the incisal edge

The placement of orthodontic brackets is guided either by localizing the centre of the clinical crown (CC) or by measuring the distance from incisal edge (ME). The purpose of this study was to examine if there are any significant differences in the accuracy of bracket positioning between these two techniques. Typodont models were simulated with a Class I malocclusion with severe crowding. Nineteen experienced orthodontists (12 males, seven females) with a mean age of 40.6 years bonded pre-adjusted straight-wire brackets (Victory MBT) on the typodonts. Each orthodontist was asked to bond 20 brackets on one typodont using the CC method and 20 brackets on another typodont using the ME method. The teeth were removed from the typodont and photographed for imaging analysis. The errors of bracket placement in the vertical, mesiodistal, and angular/tip dimensions were measured and the data were statistically assessed. An overall test of significance, using all the data, rather than the means, demonstrated a significant vertical difference between the CC and ME methods, with the ME method more accurate vertically (mean CC = 1.19, mean ME = 1.10, P = 0.002) but no significant differences for mesiodistal (mean CC = -0.08, mean ME = -0.05, P = 0.28) or for tip (mean CC = -1.61, mean ME = -1.35, P = 0.34) errors. Analysis of the overall means and the arches independently showed that there was no significant difference in bracket accuracy between the two techniques (P > 0.05). Analysis of the teeth individually showed that the ME method was better in the vertical positioning for several upper and lower anterior teeth (P < 0.01) and poorer for the upper first premolars. The mean time taken to bond the 20 brackets showed no significant difference between two methods (CC 28.53 +/- 9.51 versus ME 28.21 +/- 10.43 minutes, P > 0.05). It is suggested that bracket bonding guided by measuring the distance from incisal edge may result in improved placement for anterior teeth. Archwire bending or bracket repositioning is still necessary to compensate for the inaccuracies with both techniques.

Early Tertiary mammals from North Africa reinforce the molecular Afrotheria clade

The phylogenetic pattern and timing of the radiation of mammals, especially the geographical origins of major crown clades, are areas of controversy among molecular biologists, morphologists and palaeontologists. Molecular phylogeneticists have identified an Afrotheria clade, which includes several taxa as different as tenrecs (Tenrecidae), golden moles (Chrysochloridae), elephant-shrews (Macroscelididae), aardvarks (Tubulidentata) and paenungulates (elephants, sea cows and hyracoids). Molecular data also suggest a Cretaceous African origin for Afrotheria within Placentalia followed by a long period of endemic evolution on the Afro-Arabian continent after the mid-Cretaceous Gondwanan breakup (approx. 105-25 Myr ago). However, there was no morphological support for such a natural grouping so far. Here, we report new dental and postcranial evidence of Eocene stem hyrax and macroscelidid from North Africa that, for the first time, provides a congruent phylogenetic view with the molecular Afrotheria clade. These new fossils imply, however, substantial changes regarding the historical biogeography of afrotheres. Their long period of isolation in Africa, as assumed by molecular inferences, is now to be reconsidered inasmuch as Eocene paenungulates and elephant-shrews are here found to be related to some Early Tertiary Euramerican 'hyopsodontid condylarths' (archaic hoofed mammals). As a result, stem members of afrotherian clades are not strictly African but also include some Early Paleogene Holarctic mammals.

The chronology of third molar mineralization in the Austrian population—a contribution to forensic age estimation

The aim of the present study was to determine the chronology of third molar mineralization and to establish Austrian reference data. Therefore, a cross-sectional study was undertaken by evaluating 610 panoramic radiographs in order to assess the mineralization status of the mandibular third molars of Austrian male and female individuals (275 males and 335 females) between the ages of 12 and 24. The evaluation was carried out using the eight grade scheme of Demirjian et al. (1973). Mean ages, standard deviations, standard errors and percentile distributions are presented for each stage of development. Significant differences between the left and right mandibular third molars were not found. Males reach the developmental stages earlier than females, statistically significant differences were noted in stages E and F. Both mandibular third molars were observed in the majority of the individuals of the Austrian sample (477 individuals, 78.2%). For medicolegal purposes the likelihood of whether an Austrian individual is older than 18 years or not was determined.

Effect of ambient light and bit depth of digital radiograph on observer performance in determination of endodontic file positioning

OBJECTIVES

To examine the effects of the luminance and bit depth of digital image on observer performance for determination of endodontic file positioning.

STUDY DESIGN

Using extracted premolar teeth, no. 08 K-file was placed into the canal and positioned so that the tip was either flush or 1 mm short of the radiologic root apex. The samples were imaged with both conventional and digital radiographs at 8 and 12 bits. Eleven observers read the images under dark and bright condition, and receiver operating characteristics analysis was performed. Additionally, the interpreting time was measured.

RESULTS

The 12-bit images showed similar observer performance compared with conventional images, and better than the 8-bit images. The interpretation time for bright condition and 8-bit images was longer than for dark condition and 12-bit images.

CONCLUSION

Twelve-bit digital images were preferred to 8-bit for accurate determination of endodontic file position.

Evaluation of the Relationship between Subjects? Perception and Professional Assessment of Esthetic Treatment Needs

PURPOSE

The purposes of the present study were to (1) evaluate the esthetic dental treatment need by means of two special questionnaires, (2) determine the reliability and the construct validity of the measurement scales derived from these questionnaires, and (3) investigate the relationship between Greek subjects' perception and a professional examiner's assessment regarding the esthetic treatment need.

MATERIALS AND METHODS

Participants in this survey consisted of 132 subjects (48 males with mean age 39.0 +/- 14.5 years old, 84 females with mean age 41.7 +/- 14.5 years old) with natural teeth and fixed restorations. Subjects were asked to complete a special self-evaluation questionnaire consisting of 12 items. During the next stage, all participants were clinically examined by an experienced examiner and the data collected were used to fill out a second special professional assessment questionnaire consisting of 20 items. The forms structure used were in accordance with well-established indices used in orthodontics for assessing esthetic treatment need.

RESULTS

The reliability of the multiple correspondence analysis (MCA) analysis-derived scales was very satisfactory (Cronbach's a coefficient: a =0.82) for the total scale of the self-evaluation measurement. For the professional assessment scale, the reliability of the total scale was almost perfect (a=0.92). The MCA revealed one reliable factorial construct for the self-evaluation measurement scale and two reliable constructs for the professional measurement scale. Pearson's correlation coefficient indicated a very low agreement between self-evaluation and professional measurement scales.

CONCLUSION

The findings of this survey suggest that there was a relative disagreement between subjects' perception and professional assessment regarding the need for esthetic dental treatment. CLINICAL SIGNIFICANCE In the present survey, the agreement between subjects' perception and clinical assessment of esthetic dental treatment need was found to be very low, which highlighted the discrepancies between patients' and dentists' perceptions of esthetic needs.

Reproducibility and accuracy of measuring unerupted teeth using limited cone beam X-ray CT

OBJECTIVE

The purpose of this investigation was to determine the reproducibility among observers and accuracy of the measurement of the tooth crown width of unerupted teeth using limited area cone beam X-ray CT.

METHODS

3DX multi-image micro-CT (3DX, Morita Co., Kyoto, Japan) images of impacted supernumerary teeth in the median maxillary region taken prior to extraction were used for the samples. The width of the tooth on the 3DX image was measured five times by five individual observers. Significant differences in values among the observers in the measurement were determined by one-way analysis of variance for examining reproducibility. The measurement results of the ten samples on 3DX images were compared with the laboratory measurements using a three-dimensional co-ordinate measuring apparatus, using the Wilcoxon signed-rank sum test.

RESULTS

There was no significant difference among the observers in the measurement (P>0.05). The measurement results shown on 3DX images were significantly larger than those of the laboratory measurements (P<0.05). The mean difference was +0.088 mm.

CONCLUSIONS

3DX has high reproducibility for measuring the tooth crown width of unerupted teeth. While 3DX measurement values were larger than the laboratory measurements, the difference is clinically insignificant.

Changes in interdental papillae heights following alignment of anterior teeth

BACKGROUND

Orthodontic alignment of overlapped incisors can reduce the apparent heights of the interdental papillae leading to unsightly dark triangles or open gingival embrasures.

AIM

To determine if certain pretreatment contact point relationships between the maxillary anterior teeth were accompanied by changes in the heights of the interdental papillae after orthodontic alignment.

METHODS

Pre- and post-treatment intra-oral 35 mm slides, lateral cephalometric radiographs and study casts of 143 patients (60 males, 83 females) between 13 and 16 years of age were used. The patients had diastamata closed, imbricated teeth aligned and palatally or labially placed teeth repositioned. A sample of 25 patients (12 males, 13 females) between 13 and 16 years of age who had well-aligned anterior teeth at the start of treatment acted as a control group. All patients were treated for approximately 18 months. The clinical crowns of the maxillary incisors and the heights of the interdental papilla between the incisors were measured on projected images of the slides. The percentage increases or reductions in the heights of the interdental papillae were compared.

RESULTS

The heights of the interdental papillae increased following palatal movement of labially placed (p < 0.05) or imbricated (p < 0.05) incisors and the intrusion of one incisor relative to an adjacent incisor (p < 0.01). The heights of the interdental papillae reduced following labial movement of an imbricated (p < 0.05) or palatally placed (p < 0.05) incisor or closure of a diastema (p < 0.01). Before treatment the midline papillae in the diastema subgroup were of similar length to the midline papillae in the control group, but after treatment they were markedly shorter. The interdental papillae associated with crowded or imbricated incisors were shorter than the interdental papillae in the control group before and after treatment.

CONCLUSIONS

Dark triangles are less likely to develop following palatal movement of labially placed or imbricated teeth and the intrusion of one tooth relative to another. On the other hand, dark triangles are more likely to develop following labial movement of imbricated or palatally placed incisors and closure of a diastema. Clinicians should be alert to the possibility of dark triangles developing in the latter group, particularly in older patients.

Orthodontic Space Opening in Patients with Congenitally Missing Lateral Incisors

OBJECTIVE

To determine the best time to begin orthodontic treatment for patients scheduled for implants to replace congenitally missing upper lateral incisors. The aim of timing is to maximize the amount of bone available for implant insertion and to improve incisors inclination.

MATERIALS AND METHODS

Seventy-three plaster casts of 14 patients with 26 missing lateral incisors were cross sectioned in the center of the planned insertion of the implant, and the implant profile was projected into the area at three different times: T1--beginning of orthodontic treatment, T2-- end of orthodontic treatment, and T3--implant insertion. Deficiency of alveolar ridge volume needed for implantation was determined by Leica Quin analySIS software.

RESULTS

An increase of ridge-volume deficiency from 0.26 mm(2) at T1 to 3.77 mm(2) at T3 was found. During orthodontic treatment the incisors protruded about 9.4 degrees (differing from the O1-NA standard of 7.5 degrees ). To ensure optimal esthetic and functional implantation results, time management concerning orthodontic treatment has to be done carefully.

CONCLUSIONS

To avoid a high degree of alveolar bone atrophy and the risk of relapse and retreatment, orthodontic treatment involving tooth movement should not be initiated before the age of 13 years. Furthermore, it is important to maintain anchorage of the upper incisors because high incisor proclination causes extra-axial stress on the implant. An interdisciplinary approach is essential to provide the best treatment outcome.

A correlation study of occlusal and pulp chamber anatomy: the maxillary first molar

The success of endodontic therapy is based on a number of criteria, particularly the conservation of tooth structure. This principle requires a systematic approach to pulp chamber access. By correlating the occlusal anatomy with the location of the root canal orifice, a dentist may find a number of guidelines for improving access design. In this in vitro study, the authors evaluated 29 human maxillary first molars. Digital radiographs and digital occlusal photographs were taken of each specimen before and after decoronation at the cementoenamel junction (CEJ). The three images were superimposed on one another and evaluated for occlusal and pulpal patterns. The thickness of the pulp chamber walls of the CEJ varied, based on the circumference of individual teeth. In addition, the canal orifices at the pulp chamber floor exhibited a consistent pattern relative to the cusp tips, which may assist in access design.

Range and mean distribution frequency of individual tooth width of the maxillary anterior dentition

Proper diagnosis of tooth size for each patient is critical in treatment planning for aesthetic restorative dentistry. The goal of this study was to determine the clinically relevant range and mean distribution frequency of individual tooth width of the maxillary anterior dentition within a given population of patients. Mean values for restoration of tooth size were not interchangeable for the different group size of patients or respective tooth groups. The results of this study suggest that there exists a range value of maxillary anterior tooth width for both males and females. Gender differences are a critical factor in restoring an aesthetically pleasing smile.

LEARNING OBJECTIVES

This article will discuss the clinical significance of tooth biometry and distribution frequency, in which size for tooth restoration may vary among patients of different age, race, or sex. Upon reading this article, the reader should: Become more familiar with the range of individual tooth width of the maxillary anterior dentition and their mean distribution frequencies. Understand that gender differences may exist affecting the width of maxillary anterior teeth.

Analysis of width/length ratios of normal clinical crowns of the maxillary anterior dentition: correlation between dental proportions and facial measurements

This study aimed to determine how facial measurements explain the variability of dental proportions. The following measurements were obtained from 90 subjects: width and length of each maxillary anterior tooth, length of the nose, length of the upper lip, facial length (including the lengths of the facial thirds), intercanthal width, interalar width, intercommisural width while smiling, and maximum central incisor exposure while smiling. The combination of all facial measurements explained the variability of maxillary anterior teeth width/length ratios by only 20% to 38% in men and 16% to 27% in women. Within the population tested, the results suggest that the use of facial measurements for the selection of artificial denture teeth is generally inaccurate.

A correlation study of occlusal and pulp chamber anatomy: the mandibular first molar

Many parameters must be addressed for endodontic therapy to succeed. Because conservation of tooth structure is vital, the pulp chamber and root canal orifices should be located by using a method that is consistent yet accurate. The correlation of occlusal anatomy with the locations of the root canal orifice may aid dentists with access design. This study sought to determine if a correlation existed between occlusal surface anatomy, pulp chamber location, and root canal orifice location. This in vitro study utilized 21 human mandibular first molars. For each specimen, amalgam restorations were placed in the respective cusp tips, with gutta-percha placed in each canal at the level of the furcation. The authors made digital radiographs and occlusal photographs of each complete specimen. The samples were sectioned horizontally at the level of the cementoenamel junction (CEJ). Using a digital software program, the radiographs were superimposed with the digital photographs and correlations of pulp chamber to locate the canal orifice and occlusal surface anatomy. The authors found that the pulp chamber of the mandibular first molar lies more lingual at the level of the CEJ. In addition, the orifices were consistent in their location relative to cusp tip anatomy, a discovery that may assist dentists with the access design.

Smile Aesthetics

The aim of this article is to outline some of the factors practitioners should take into consideration when planning optimal smile aesthetics. The components of the smile that will be discussed include the smile arc, incisor/gingival display, smile width, gingival aesthetics, tooth proportionality/symmetry, contacts/connectors/embrasures and the dental midlines.

CLINICAL RELEVANCE

A systematic evaluation of the components of the smile when planning treatment will help to improve smile aesthetics and produce greater patient and dentist satisfaction.

A multidisciplinary approach to esthetic dentistry

Today's dentist does not just repair teeth to make them better for chewing. Increasingly, his or her work involves esthetics. With patients demanding more attractive teeth, dentists now must become more familiar with the formerly independent disciplines of orthodontics, periodontics, restorative dentistry, and maxillofacial surgery. This article provides a systematic method of evaluating dentofacial esthetics in a logical, interdisciplinary manner. In today's interdisciplinary dental world, treatment planning must begin with well-defined esthetic objectives. By beginning with esthetics, and taking into consideration the impact on function, structure, and biology, the clinician will be able to use the various disciplines in dentistry to deliver the highest level of dental care to each patient.

Smile design

Many scientific and artistic principles considered collectively are useful in creating a beautiful smile. The evaluation and analysis of the face, lips, gingival tissues and teeth are all considered in this process. Recognizing the ideal as a goal provides a direction for diagnosis and treatment planning for smile rejuvenation. This article focuses on the dental and dental-facial composition involved in smile design. Basic facial esthetics are reviewed as a guideline for facial analysis.

Tooth size and arch dimension in uncrowded versus crowded Class I malocclusions

AIM

The purpose of this investigation was to examine the extent to which arch dimension or tooth size contributes to dental crowding.

METHODS AND MATERIALS

Two groups of dental casts were selected. Each group consisted of 30 pairs of dental casts including equal male and female samples. The first group had Class I malocclusions without crowding or spacing. The second group exhibited Class I malocclusions with severe dental crowding (> a 5 mm space deficiency). The following parameters were measured and used to compare the two groups: individual and collective mesiodistal tooth diameters, dental arch length, as well as buccal and lingual dental arch widths in the canine and molar regions. To compare the two groups the Student's t-test with 95% confidence interval was used.

RESULTS

Statistically significant differences in both tooth diameters and transverse arch dimensions were found between the two groups. The crowded group was found to have a significantly smaller maxillary arch width and larger tooth size when compared with the uncrowded group.

CONCLUSION

The results of this study suggest under equal conditions (a Class I skeletal relationship) tooth size has a greater role in developing dental crowding.

Population structure of the classic period Maya

This study examines the population structure of Classic period (A.D. 250-900) Maya populations through analysis of odontometric variation of 827 skeletons from 12 archaeological sites in Mexico, Guatemala, Belize, and Honduras. The hypothesis that isolation by distance characterized Classic period Maya population structure is tested using Relethford and Blangero's (Hum Biol 62 (1990) 5-25) approach to R matrix analysis for quantitative traits. These results provide important biological data for understanding ancient Maya population history, particularly the effects of the competing Tikal and Calakmul hegemonies on patterns of lowland Maya site interaction. An overall F(ST) of 0.018 is found for the Maya area, indicating little among-group variation for the Classic Maya sites tested. Principal coordinates plots derived from the R matrix analysis show little regional patterning in the data, though the geographic outliers of Kaminaljuyu and a pooled Pacific Coast sample did not cluster with the lowland Maya sites. Mantel tests comparing the biological distance matrix to a geographic distance matrix found no association between genetic and geographic distance. In the Relethford-Blangero analysis, most sites possess negative or near-zero residuals, indicating minimal extraregional gene flow. The exceptions were Barton Ramie, Kaminaljuyu, and Seibal. A scaled R matrix analysis clarifies that genetic drift is a consideration for understanding Classic Maya population structure. All results indicate that isolation by distance does not describe Classic period Maya population structure.

Comparison of proximal contacts of Class II resin composite restorations in vitro

This study investigated the tightness of the proximal contact when placing posterior resin composite restorations with circumferential and sectional matrix systems in an in vitro model using a special measuring device (Tooth Pressure Meter). A manikin model was used with an artificial first molar in which an MO-preparation was ground, simulating the clinical situation of an amalgam replacement. This preparation was duplicated, resulting in 160 identically prepared teeth. These teeth were divided into 8 groups (n=20). In 2 groups, circumferential matrix bands (flat or contoured) in a Tofflemire retainer were applied. In the remaining 6 groups, 3 different separation rings were combined with 2 types of sectional matrix bands. All the cavities were restored using Clearfil Photo Bond and Clearfil AP-X. The tightness of the proximal contact was measured using the Tooth Pressure Meter. Data were statistically analyzed using SPSS 12. ANOVA was used to find differences in proximal contact tightness between the groups. Tukey tests were used to find differences between the homogeneous subgroups. The use of sectional matrices combined with separation rings resulted in tighter proximal contacts compared to when circumferential systems were used (p<0.001). The use of these devices is therefore recommended when posterior resin composite restorations are placed.

Morphological Measurements of Anatomic Landmarks in Pulp Chambers of Human Anterior Teeth

This in vitro study measured key morphological features of pulp chambers in anterior teeth and tested the hypothesis that the distance from the lingual surface (midpoint from the cusp tip to the lingual CEJ) to the pulp chamber (the midpoint from the buccal to the lingual CEJ) was similar for different tooth types. Extracted human teeth were sorted and 100 samples of each of the following tooth types were chosen: maxillary central incisor (UCI), lateral incisor (ULI), and canine (UC), as well as mandibular central incisor (LCI), lateral incisor (LLI), and canine (LC). All teeth were digitally radiographed on a 1-mm X-ray grid. The mean values of measurement C, the distance from the lingual surface to the pulp chamber, varied significantly between tooth types (p<0.001). The mean values and SNK rankings were as follows: LC (5.9+/-0.5 mm)>UC (5.5+/-0.5)=UCI (5.4+/-0.4)>ULI (5.0+/-0.4)>LLI (4.8+/-0.5)>LCI (4.4+/-0.4).

Cuspal flexure of teeth with composite restorations subjected to occlusal loading

PURPOSE

To measure in vitro the cuspal deflection produced by polymerization shrinkage and occlusal loading in mesio-occlusal (MO) and mesio-occlusal-distal (MOD) bonded composite restorations.

MATERIALS AND METHODS

Twenty first premolars were studied, attaching a small crystal ball to each cusp vertex as a reference point for intercuspal distance measurements. MO cavities were made in ten premolars and MOD cavities in the other ten. Cavities were then restored with Syntac Single adhesive and Tetric Ceram composite in two increments. A precision micrometer was used to measure intercuspal distances in unaltered teeth (baseline distance), unaltered teeth under 150 N load, restored teeth at 5 min after restoration completion, and restored teeth under 150 N load.

RESULTS

In the two study groups, both polymerization shrinkage and application of 150 N load produced a statistically significant change in intercuspal distance compared with baseline measurement. The cuspal deflection produced by 150 N load was statistically similar between unaltered and restored teeth, although polymerization shrinkage acted as a preload in the latter case (starting point was not baseline condition). The cuspal deflection produced by polymerization shrinkage and occlusal load was significantly greater in MOD than in MO restorations.

CONCLUSION

The cuspal deflection produced by composite polymerization shrinkage and occlusal loading is significantly greater in MOD vs MO composite restorations.

Prevalence of accessory tooth cusps in a contemporary and ancestral Hungarian population

Dental morphological characteristics are useful for providing information for phylogenic and genetic studies and understanding variations within and among species. Carabelli and talon cusps are expressed in several degrees and different frequencies between humans, thus being useful in comparing and characterizing populations. The purpose of this study was to examine the incidence and degree of expression of a Carabelli tubercle and talon cusps in a contemporary Hungarian population compared with similar findings in the dentition of skulls dating from the 11th century, the so-called Arpád-era. The data were collected by examination of dental plaster casts of 600 children aged 7-18 years (304 males, 296 females) undergoing orthodontic treatment. The dentitions of 147 skulls, dating from the 11th century, from the ancient Halimba-Cseres cemetery stored at the Hungarian Natural History Museum were also examined. The incidence and degree of expression of a Carabelli cusp was investigated for the upper first permanent molars and scored according to an eight-grade classification system. The talon cusps on the upper permanent lateral incisors were also examined. A chi-square test was used for statistical analysis. The prevalence of Carabelli cusps was 65.34 per cent in the contemporary and 34 per cent in the 11th century population (P < 0.01). The contemporary group showed a prevalence of talon cusps of 2.5 per cent compared with 40.8 per cent for the skills from the Arpád-era, which was significant (P < 0.001). These findings demonstrate that the contemporary Hungarian population is a mixture of European and Mongoloid races. The data are in agreement with linguistic evidence that shows that distant Hungarian ancestors belonged to the Finno-Ugrian family of people, whose habitats extended from the Baltic to the middle Urals.

The supernumerary lateral incisors--morphology and concomitant abnormalities

AIM

To assess the morphology of supernumerary lateral incisors and describe the concomitant malocclusion.

MATERIAL AND METHODS

Intraoral examination and analysis of panoramic views as well as study casts has been proceeded in 18 patients with supernumerary laterals. The widths of the normal and supernumerary laterals were measured.

RESULTS

20 supernumerary incisors were found (in 2 patients - bilateral). In 1 patient - the width of the supernumerary tooth was the same as this of the adjacent normal teeth and in 12 patients - the widths were lower. In cases of unilateral hyperdontia, 4 of the laterals adjacent to supernumerary teeth were of the same, 9 were of lower and 1 was of higher widths than the contralateral ones. Supernumerary teeth were causing midline shift in 10 patients, significant space deficiency - in 4, ectopic eruption - in 1 and excessive overjet - in 4. In 3 patients the permanent supernumerary incisors were not yet erupted and in 1 patient the tooth was retained.

CONCLUSIONS

The supernumerary lateral incisors were smaller than the adjacent ones, whereas the normal lateral incisors adjacent to supernumerary ones were smaller than the contralateral incisors. The concomitant occlusal anomalies were: excessive overjet, crowding or ectopic eruption and midline shift.

Orthodontic implications of protein undernutrition in mandibular growth. A cephalometric study in growing rats

The present experimental work analyzes the development of different mandibular units and its likely impact on the direction of mandibular displacement during facial development, and the relation between the mesiodistal dimension of the first, second, and third molars and the length of the mandibular corpus in a model of protein undernutrition with muscular atrophy in growing rats. Sixteen Wistar rats weaned at the age of 21 days were assigned to one of the following groups: control (fed a regular hard diet ad libitum) and experimental (fed a diet lacking in protein, corn flour, ad libitum). All the animals were euthanized five weeks after the onset of the experiment. Following resection of the mandibles, the mandibles were hemisected at the symphysis and fixed in 10% formalin. Remaining soft tissue was removed. Metallic landmarks were placed in the mental and mandibular foramens of one hemimandible of each rat. The hemimandibles were radiographed. The cephalometric study was performed on paper tracings of the projected image of the radiographs. Both groups exhibited a slight increase in body weight (b.w) throughout the first ten days of the experiment. After this point, the undernourished group showed no further increase in b.w., and exhibited significantly lower b.w. than controls at the end of the experiment. The cephalometric study showed that the length of the mandible as a whole, and of the condylar and angular processes was significantly lower in the undernourished group. In addition, significant differences in the vertical relation between the angular process to the mandibular corpus, the convexity of the angular process, and the ratio between total molar width (from the first to the third molar) and the length of the mandibular corpus were observed.

Anomalies of tooth formation in hypohidrotic ectodermal dysplasia

OBJECTIVE

The X-linked hypohidrotic ectodermal dysplasia (HED) is the most common type of ectodermal dysplasia. The clinical identification of possible heterozygous females can be difficult because of the varying degrees of clinical signs caused by X-chromosome inactivation. This study is the first to elaborate on anomalies of tooth formation found in a group of hemizygous males and heterozygous females with known ED1 mutations. These tooth anomalies may be used as dental biomarkers for heterozygous females, enabling an earlier diagnosis, and therefore, better treatment and genetic counselling.

METHODS

Anomalies of tooth formation were examined using panoramic radiographs, dental casts and oral photographs in hemizygous males and heterozygous females who were identified by molecular genetic analysis. The results were compared to existing controls and normative data.

RESULTS

All affected males had multiple missing permanent teeth and tooth malformations. The heterozygous females had a significantly higher frequency of agenesis of permanent teeth compared to normative data. The heterozygous females had an increased prevalence of tooth malformations and reduced tooth size, especially in the mesiodistal dimension.

CONCLUSIONS

We conclude that observed anomalies of tooth formation may be used as dental biomarkers in the clinical identification of potentially heterozygous females.

Mesial Migration Effect on Root Morphology of Mandibular Third Molars

Objective: To test the hypothesis that there is a relationship between forward mandibular third molar migration and root curvature of the mandibular third molars.

Materials and Methods: The study is comprised of 64 patients who had a history of unilateral mandibular first molar extraction before 16 years of age with no other missing teeth or prosthetic restorations in the mandible. The extraction space was fully or partly closed. The mean remaining space was 1.1 ± 0.41 mm. The root angles for the mesial and distal roots of the mandibular third molars were measured on the panoramic radiographs by calculating the differences between the angle formed by the long axis drawn perpendicular to the occlusal plane of the crown of mandibular third molar and the central line of the lower one ninth of the root through the root apex. The differences between the extracted and nonextracted sides for mesial and distal roots were analyzed using a paired sample t-test.

Results: Both mesial and distal roots were approximately 8° more vertical on the extraction sides than on the nonextraction sides. The differences were statistically significant.

Conclusion: Mesial tooth migration of mandibular third molars reduces the amount of root curvature developing on this tooth.

Mandibular First Molar Relation to Variable Lower Face Skeletal Components

Objective: To evaluate the position of the mandibular first permanent molar in the mandible relative to several factors.

Materials and Methods: A total of 185 untreated Class I and Class II patients were randomly selected from a sample of 350 patients from a single office. The palatal and mandibular planes were related to Frankfort horizontal to create the interjaw or “B” angle. Age and the mesial contact of the mandibular first molars were used. The landmarks were projected at right angles to the Frankfort horizontal for effective mandibular dimension lengths. Actual-length dimensions were projected at right angles to the mandibular plane. Pearson product moment correlation coefficients were computed to evaluate the effect of age, cranial length, and mandibular contribution to the molar's sagittal position in the mandible. Significance was reported only when P &lt; .05 to determine a 95% confidence level.

Results: Statistically significant positive correlations indicated that the mandibular molar is located more forward with increasing age, longer mandibular body length, and increasing posterior facial height. In contrast, significant negative correlations to the interjaw, mandibular plane, ramal inclination angles, and the linear ramal contribution corresponded to a more posterior position of the molar with increasing angles.

Conclusions: The mandibular first permanent molar is located more anteriorly with an older patient, a longer mandibular body, greater posterior facial height, and an acute interjaw angle. In contrast, an increase in the forward tip of the ramus places the molar in a more posterior location.

Microevolution of African American dental morphology

The African American (AA) gene pool is primarily the result of gene flow between two biologically disparate groups: West Africans (WA) and Americans of western European descent (EA). This research utilizes characteristics of dental morphology to trace genetic relationships among WA, western Europeans (EU), AA, and European Americans. Dental morphological traits are useful for this purpose because they are heritable, do not remodel during life (although they can be lost to wear or pathology), and can be compared equally among samples from past and present populations. The results of this research provide new information about human microevolution through time and space in a biocultural setting. The mean measure of divergence is used to analyze dental morphological data from 1,265 individuals in 25 samples grouped by ancestry and time. Three hypotheses associated with admixture in AA are tested. When compared with known history, results from dental morphological data are equivocal in documenting admixture in AA. Dental morphological traits do appear to reflect admixture in AA. However, changes in trait frequencies do not closely correspond with important cultural events and trends such as the institutionalized racism of the Civil War and Jim Crow era. Results are mixed concerning whether AA with greater admixture were more likely to take part in the Great Migration to southern urban centers and to the North.

The relation between tooth shape ratio and incisor arrangement in Japanese children

To investigate whether the relationship between tooth shape ratio and incisor arrangement proposed by Peck et al. in 1972 was applicable to Japanese children, we compared two groups, one with normal permanent dentition and another with crowded permanent dentition, using chronologically constructed plaster dentition models. Tooth shape ratio was obtained by dividing the incisor mesio-distal width by the labio-lingual width and then multiplying the result by 100. The results revealed a significant difference in the coronal mesio-distal diameter of the incisors between the two groups, but the other items showed no significant differences, suggesting no clear relationship between tooth shape ratio and incisor arrangement. That was, our results suggest that there is no clear relationship between tooth shape ratio of the mandibular incisors and arrangement of the permanent incisors in Japanese children.