Variation in modern human enamel formation times

Most of what we know about the timing of human enamel formation comes from radiographic studies on children of known age. Here, we present new longitudinal data derived from a histological analysis of tooth enamel. Two samples, one from southern Africa and one from northern Europe, contained all anterior and molar tooth types. Two further samples contained only one tooth type: canines from a medieval Danish sample and third molars from a modern North American sample. Data were collected on 326 molars and 352 anterior teeth. Each tooth was sectioned and prepared for polarized light microscopy. We used daily enamel cross striations to determine cuspal enamel formation time, recorded the periodicity of long-period striae in the lateral enamel, and used this value to calculate enamel formation times for each decile of crown length. We present data that reveal some of the processes whereby differences in enamel formation times arise between our samples. Mean cuspal enamel formation times were similar in southern African and northern European anterior teeth, but differed in certain molar cusps. All the southern African anterior teeth completed enamel formation earlier. The greatest difference in mean chronological age at enamel completion was 5.2 vs. 6.2 years of age in lower canines. However, enamel completion times in the molar teeth showed few differences between the samples, with mean times for the longest forming cusps all falling between 3.0 years and 3.45 years. Our data suggest fewer differences between samples and smaller ranges of variation than in many radiographic studies and present a more realistic picture of worldwide variation in enamel formation times.

Periapical health related to the quality of coronal restorations and root fillings

AIMS

To evaluate the impact of the quality of coronal restorations scored on a clinical and radiographic basis and the quality of root fillings on periapical health.

METHODOLOGY

Periapical radiographs were taken of 745 root-filled teeth, randomly selected from patients attending the Ghent University Dental School. The teeth had not received restorative treatment in the previous year. The coronal status was scored both clinically according to modified Ryge's criteria, and radiographically by evaluating the presence of signs of marginal leakage or decay. The quality of the root filling was scored according to criteria of length and homogeneity and the periapical status was categorized on the basis of presence or absence of radiographic signs of apical periodontitis. The relationship between coronal status, quality of root filling and periapical health was determined. The data were analyzed using Chi2 test, Odds ratio, Spearman's r(S) and logistic regression.

RESULTS

Thirty-three percent of the teeth had apical periodontitis as diagnosed radiographically. Teeth with good and poor coronal restorations scored clinically had apical periodontitis in 31.1 and 36.8%, respectively; this difference was not statistically significant. The quality of the coronal restorations scored radiographically had a statistically significant influence on the periapical condition (P<0.001) with apical periodontitis in 23.8 and 49.1%, respectively, for acceptable and unacceptable restorations. Marginal decay did not influence the periapical status. Teeth restored without a base under the coronal filling had apical periodontitis in 41.3%, whereas teeth with a base had significantly less (P<0.005) apical periodontitis (25.9%). Composite-restored teeth exhibited apical periodontitis in 40.5% of cases whilst amalgam-restored teeth had apical periodontitis in 28.4% of cases; this difference was statistically significant (P<0.01). Root-canal posts had no influence on periapical health. The length and homogeneity of the root-canal fillings had a significant influence (P<0.01 and P<0.001, respectively) on the presence of apical periodontitis, as well as the quality of the coronal restoration scored radiographically (P<0.001).

CONCLUSION

The importance of a good coronal restoration, as well as of a good root filling should be emphasized as the technical quality of both influencing the periapical status.

Periapical status and quality of root fillings and coronal restorations in an adult Spanish population

AIM

To investigate the quality of root fillings and coronal restorations and their association with periapical status in an adult Spanish population.

METHODOLOGY

A total of 180 subjects, aged 37.1 +/- 15.7 years, who presented as new patients at the Faculty of Dentistry, Seville, Spain, were examined. All participants underwent a full-mouth radiographic survey incorporating 14 periapical radiographs. The periapical region of all root filled teeth, excluding third molars, were examined. The technical quality of root fillings was evaluated in terms of length in relation to the root apex and lateral adaptation to the canal wall. Radiographic signs of overhang or open margins associated with coronal restorations were also evaluated. Periapical status was assessed using the Periapical Index score. Statistical analyses were conducted using the Cohen's kappa test and logistic regression.

RESULTS

The total number of root filled teeth was 93, and 60 (64.5%) had apical periodontitis (AP). Presence of AP in root filled teeth was associated with inadequate adaptation of the filling (OR = 2.29; P = 0.06), inadequate length of the root filling (OR = 2.44; P = 0.048), and with poor radiographic quality of the coronal restoration (OR = 2.38; P = 0.054). Only 34.4% of the root fillings were adequate from a technical perspective. When both root fillings and coronal restorations were adequate the incidence of AP decreased to 31.3% (OR = 5.50; P < 0.01).

CONCLUSIONS

The incidence of AP in root filled teeth was high. Many root fillings were technically unsatisfactory. Adequate root fillings and coronal restorations were associated with a lower incidence of AP; an adequate root filling had a more substantial impact on the outcome of treatment than the quality of the coronal restoration.

Accuracy of linear and angular measurements on panoramic radiographs taken at various positions in vitro

The accuracy of measurement of tooth length and angulation on dental panoramic tomograms (DPTs) is thought to be highly dependent on head positioning technique. A model representing the dentition and the functional occlusal plane was designed using an acrylic framework and stainless steel wires. The aim was to investigate whether varying the position of the model affects the linear and angular measurements on DPTs. Four different positions were investigated: initial position representing natural head posture (NHP) (T1); lateral right cant of the occlusal plane (T2); lateral left cant of the occlusal plane (T3); and tilting the occlusal plane up anteriorly (T4). On each DPT, four sets of measurements were recorded: (1) Vertical linear measurements of the stainless steel pins and ratio calculations of the 'crown' and 'root' segments (represented by the wire above and below the occlusal plane, respectively); (2) angular measurements of the pins relative to the occlusal plane; (3) angular measurements of the pins relative to a constructed reference line; and (4) angular measurements of pins relative to each other in the same segment. The results showed a significant error (P < 0.05) in all measurements when the occlusal plane was tilted up anteriorly by 8 degrees. A lateral cant of the occlusal plane by less than 10 degrees without an upward anterior rotation showed no significant effect on the measurements. This would suggest that there is some tolerance of variation in head position.

Management of tooth resorption

A correct diagnosis and an understanding of the aetiology and dynamics of the processes involved in tooth resorption is critical to effective management. Tooth resorptions can be classified as: (1) trauma induced; (2) infection induced; or (3) hyperplastic invasive. Some transient trauma induced resorptions require no treatment but must be carefully monitored to check that there are no complicating issues such as infection. In cases of trauma induced replacement resorption, a multidisciplinary approach is usually necessary to ensure an optimal long-term solution. Infection induced tooth resorptions require the removal of the invading micro-organisms by endodontic therapy including intra-canal medication which can also facilitate repair of the resorbed tooth structure. The hyperplastic invasive tooth resorptions pose considerable challenges in management due to the complexity and aggressive nature of the resorptive process. With careful case selection and complete inactivation of resorptive tissue successful management can be achieved.

Long-term dental development in children after treatment for malignant disease

A radiographic dental examination was performed in 16 children conditioned with total body irradiation (TBI) and cyclophosphamide (CY) prior to bone marrow transplantation (BMT), and in 52 children treated with multiagent chemotherapy. For each child, three age- and sex-matched healthy controls were selected. Evaluation of disturbances in dental development and tooth size was based on planimetric measurements of mandibular teeth on panoramic radiographs. Short V-shaped roots were diagnosed in 94 per cent of the children treated with TBI/CY compared with 19 per cent in the chemotherapy group (P < 0.001). Children receiving TBI/CY also exhibited a pronounced reduction in tooth size compared with the controls. Reductions varied from 19 per cent in incisors to 39 per cent in the second molars. In the chemotherapy group the corresponding values were 7 and 15 per cent respectively. When comparing crown/root ratios, the indices for incisors, canines (P < 0.05) and molars (P < 0.01) in the BMT group were significantly higher than the corresponding values in the control group. This indicates that the reduction in root size was more pronounced than the reduction in crown size. The premolars in the BMT group exhibited a similar reduction in crown and root size. All developing teeth were affected by multiagent chemotherapy and radiation therapy. The most severe disturbances were found in children treated with TBI/CY at a young age.

Histological reconstruction of dental development in four individuals from a medieval site in Picardie, France

The majority of dental development studies in modern humans are based on radiographic analysis. In comparison, very few full histological studies have been carried out. In the present study, the onset of enamel formation and crown formation time have been established by histological analysis of the complete dentition in a medieval French individual. Crown formation times were established for the dentition of three further individuals. The number of cross-striations between adjacent striae of Retzius was measured and accentuated striae were used to construct a chart of the chronology of tooth development. Results on crown formation times in individual teeth when compared with previous histologic studies are slightly greater than values in a modern African male and near to or less than values in (M1) and (I) respectively in a modern population from Spitalfields, London. Histologically derived crown initiation times are earlier than those reported for radiographic studies. Values for crown formation times derived in general from radiographic studies are less than those of our study. Attention has recently been focused on the overlap of molar development as a key character for distinguishing between humans and great apes. In this study, there is an overlap in crown formation between M1 and M2 of 0.27 years and a temporal delay of 1.7 years between M2 crown completion and the initiation of the M3.

A radiographic assessment of enamel thickness in human maxillary incisors

Crown sizes of human teeth are sexually dimorphic, with male larger than female. This holds for most human groups, though the extent of dimorphism varies among populations. It is not known whether size dimorphism is due to differences in enamel thickness, dentine differences, or some combination of the two. This study examined the pattern of variation in enamel thickness on the mesial and distal margins of the four maxillary permanent incisors. Standardized periapical radiographs of the incisors of 115 adolescent American whites were measured. Enamel was significantly thicker on the distal than the mesial margins of both the lateral and central incisors, with a mean difference of 0.1 mm. There was no sexual dimorphism in the maximum mesial or distal enamel thicknesses. In contrast, the widths of the dentine of the crowns were significantly greater in males, by an average of 6.5%. Sexual dimorphism in mesiodistal diameters of the incisors seems, then, to be due to the dentine component, which is the size attained at the end of the bell stage of tooth formation. Sex-specific correlations between enamel thickness and crown width of the dentine were low (and lower for males), indicating considerable independence between regulatory mechanisms of dentine and enamel development.

Radiographic evaluation of third molar development in Spanish children and young people

Third molar development was evaluated in 786 young people aged between 4 and 20 years, all patients at the School of Dentistry of the University of Granada. The development of third molars and of mandibular second premolars and second molars was determined according to the stages proposed by Nolla. The onset of mandibular third molar formation was observed at very variable ages in this series, ranging from 5.86 to 14.66 years. The first developmental stages of maxillary third molars are not usually visible radiographically, which can lead to an incorrect diagnosis of agenesis. We found no significant relationship between the gender or age of the patient and the presence or absence of third molars. However, the presence/absence of the third molar can be predicted in 82.82% of cases when there is some degree of calcification of mandibular second molars and second premolars.

Dental age estimation and third molars: a preliminary study

The aim of the present investigation was to reconstruct the chronological age based on the dental developmental stages of third molars evaluated on orthopantomograms. A total of 1175 orthopantomograms were assembled from patients of Caucasian origin between 16 and 22 years of age. Each third molar present was scored by two observers according to a 10-stage developmental scale. The kappa statistics measured the intra- and inter-observer reliability. The general statistical analysis was based on multiple regression analysis in order to obtain multiple regression formulas for dental age estimation based on the number of third molars present on the evaluated orthopantomogram. No regression models were statistically significant when there was only one-third molar present because of the relatively small number of orthopantomograms that fitted this criterion. A strong agreement was found between the intra- and inter-observer measurements. The statistical analysis revealed both for males and females high Pearson correlation coefficients between contralateral third molars and smaller coefficients between antimeres. The obtained multiple regression formulas are only applicable in certain specified conditions, for instance when four third molars are present the following formulas should be used in a Caucasian male "age=10.2000+0.5122UL+0.5273LL" (developmental stage of upper and lower left third molars) or in case of a female "age=13.6206+0.1933UR+0.5080LR" (developmental stage of upper and lower right third molars). This investigation revealed that the chronological age of a Caucasian individual may be estimated based on regression formulas with a S.D. of 1.52 or 1.56 years for males and females, respectively, when all four third molars are present.

Early soft tissue pathosis associated with impacted third molars without pericoronal radiolucency

OBJECTIVES

This study was performed to histologically evaluate soft tissue pathosis in pericoronal tissues of impacted third molars that did not exhibit pathologic pericoronal radiolucency.

STUDY DESIGN

One hundred impacted third molars without evidence of abnormal pericoronal radiolucency (follicular space <2.0 mm) were removed for reasons other than participation in this study, and the pericoronal tissues were submitted for histopathologic examination. Specimens were fixed and processed routinely and were stained with hematoxylin and eosin before independent evaluation by each of 2 oral pathologists. A subset of both diseased and healthy tissues underwent additional evaluation for the presence of proliferating cell nuclear antigen (PCNA) for assessment of cellular activity.

RESULTS

Of the specimens submitted, 34% showed squamous metaplasia suggestive of cystic change equivalent to that found in dentigerous cysts. Soft tissue pathosis was significantly higher in patients over 21 years of age (P =.001). Five of 8 diseased specimens demonstrated PCNA uptake, whereas none of 10 healthy specimens were PCNA positive.

CONCLUSIONS

These findings suggest that radiographic appearance may not be a reliable indicator of the absence of disease within a dental follicle. We conclude that the incidence of soft tissue pathologic conditions is higher than generally assumed from radiographic examination alone.

Enamel thickness and the topography of the enamel-dentine junction in South African Plio-Pleistocene hominids with special reference to the Carabelli trait

This study explores the internal morphology of early hominid teeth using high-resolution computed tomography. Data on Carabelli feature size, enamel thickness, and the topography of the enamel-dentine junction are considered together in order to examine the relationship among these variables in the maxillary molars of gracile and robust australopithecines from South Africa. In particular, one aim is to investigate the degree to which Carabelli feature size influences enamel thickness in the plane of the mesial cusps. The results demonstrate that maxillary molars attributed to Australopithecus africanus from Sterkfontein, Taung and Makapansgat possess larger Carabelli features and thinner enamel along the lingual wall of the protocone than do specimens attributed to Paranthropus robustus from Swartkrans and Kromdraai. Distinct differences in the position of the Carabelli feature at the level of both the enamel-dentine junction and tooth crown surface between early hominid species may help explain the observed disparity in enamel thickness at that region of the tooth crown as well as offer clues to the functional role of Carabelli's cusp. As the size and position of the Carabelli feature affects the linear thickness of enamel at this one particular region of the tooth crown, future comparative studies focusing on taxa that possess moderate to strong development of the Carabelli complex should use the linear thickness of enamel taken close to the protoconal dentine horn or at the maximum projection of the Carabelli's cusp.

A radiographic comparison of apical root resorption after orthodontic treatment with a standard edgewise and a straight-wire edgewise technique

The purpose of this study was to compare the severity of apical root resorption occurring in patients treated with a standard edgewise and a straight-wire edgewise technique, and to assess the influence of known risk factors on root resorption incident to orthodontic treatment. The sample consisted of 80 patients with Angle Class II division 1 malocclusions, treated with extraction of at least two maxillary first premolars. Variables recorded for each patient included gender, age, ANB angle, overjet, overbite, trauma, habits, invagination, agenesis, tooth shedding, treatment duration, use of Class II elastics, body-build, general factors, impacted canines, and root form deviation. Forty patients were treated with a standard edgewise and 40 with a straight-wire edgewise technique, both with 0.018-inch slot brackets. Crown and root lengths of the maxillary incisors were measured on pre- and post-treatment periapical radiographs corrected for image distortion. Percentage of root shortening and root length loss in millimetres were then calculated. There was significantly more apical root resorption (P < 0.05) of both central incisors in the standard than in the straight-wire edgewise group. No significant difference was found for the lateral incisors. Root shortening of the lateral incisors was significantly associated with age, agenesis, duration of contraction period (distalization of incisors), and invagination, while root shortening of the central incisors was related to treatment group and trauma.

Three-dimensional digital modeling and setup

Obtaining accurate images of the craniofacial region is critical when developing an orthodontic diagnosis and treatment plan. The purpose of this article is to describe a new imaging method that provides complete 3-dimensional views of the maxilla and the mandible, and the model setup with individual anatomic roots. The method uses computed tomography technology and laser scanning; it offers high-resolution images with relatively low radiation exposure. Technical aspects of the new procedure and its possible uses for orthodontic diagnosis and treatment planning are discussed.

Mixed dentition analysis in a Senegalese population: elaboration of prediction tables

Estimating the size of unerupted teeth is an essential aspect of orthodontic diagnosis and treatment planning in the mixed dentition. Three main methods have been used to estimate the mesiodistal crown widths of unerupted canines and premolars: direct measurements on radiographs; calculations from prediction equations and tables; and a combination of radiographic measurements and prediction tables. Because there are clear racial differences in tooth sizes, the objectives of this study were to produce odontometric data, correlation coefficients between the combined mesiodistal widths of the permanent mandibular incisors and the canine and premolars for each quadrant, and prediction tables with the regression equations, specifically for Senegalese children. Fifty black Senegalese students (25 women, 25 men, mean age 23.50 years) were selected from the University Cheikh Anta Diop in Dakar, Senegal. The mesiodistal crown diameters of the permanent teeth were measured with calipers. Significant sexual dimorphism was found in tooth sizes. The correlation coefficients between the total mesiodistal width of the mandibular permanent incisors and that of the maxillary and mandibular canines and premolars were found to be 0.53 and 0.70, respectively. The standard error of the estimate was better (0.66) for women in the maxilla, and the r(2) values ranged from 0.46 to 0.57 for both sexes. Prediction tables were prepared. The accuracy of the prediction tables should be tested in a larger sample including more ethnic groups.

Radiographic evaluation of the status of third molars in the Asian-Indian students

PURPOSE

The purpose of this study is to assess the prevalence and agenesis of third molars, their impaction status, and the time and sequence of their eruption in the students of Asian-Indian population.

PATIENTS AND METHODS

One hundred students with ages ranging from 17.5 to 20.0 years were randomly selected. This age group was selected because this is the age at which third molars normally begin to erupt. Students who had undergone any tooth extraction or orthodontic treatment previously were not included in the study.

RESULTS

The incidence of congenital missing third molars was 11.5%, with a higher incidence in females. Of the third molars present, 31% were in mesioangular position, 42% were in the vertical position, 27% were in the distoangular position, and none were in the horizontal position. Of the 354 teeth examined, 24% of teeth were found to be erupted and 76% were in various stages of eruption. The level of eruption of third molars was 27% at A; 39%, B; and 34%, C.

CONCLUSIONS

The present study showed that at the baseline (mean age, 19.3 years), 24% of third molars were erupted, 76% were in various stages of eruption, and 11.5% were congenitally missing in the Asian-Indian student population.

Retrospective evaluation of the influence of the interleukin-1 genotype on radiographic bone levels in treated periodontal patients over 10 years

BACKGROUND

A difference in genetic susceptibility to plaque accumulation has been advocated to explain different responses to periodontal therapy. The purpose of this study is to assess the role of the interleukin-1 (IL-1) polymorphism on the rate of bone and tooth loss in non-smoking periodontally treated patients during maintenance.

METHODS

Sixty consecutive non-smoking patients (mean age 46.8 +/- 5.0) with moderate to severe periodontitis, treated and maintained for over 10 years were selected. At baseline (T0), radiographic evaluation (cemento-enamel junction [CEJ]-root apex, CEJ-bottom of defect mesial and distal, CEJ-bone crest mesial and distal, crown-root ratio) was performed. All patients received scaling and root planing; 36 patients then underwent surgical therapy. Subsequently, all patients were enrolled in a periodontal maintenance program with recall visits every 3.4 +/- 1.0 months for at least 10 years. At the latest recall visit (T2) the same radiographic measurements evaluated at baseline were taken and a DNA sample for IL-1 genetic susceptibility testing was collected and sent for analysis.

RESULTS

Twenty-three of the 60 patients (38.3%) were IL-1 genotype positive. A total of 52 teeth (3.3%) out of 1,566 were lost due to periodontitis between T0 and T2; 28 of 957 (2.9%) in the IL-1 genotype negative group and 24 of 609 (3.9%) in IL-1 genotype positive group. The mean variation in bone defect level (DeltaBD) averaged -0.04 mm in IL-1 genotype negative patients and 0.01 mm in IL-1 genotype positive patients. The mean variation in bone crest level (DeltaBC) averaged -0.24 mm in IL-1 genotype negative patients and -0.28 mm in IL-1 genotype positive patients. However, a few patients showed significant differences in response to therapy based on initial bone levels and genotype. IL-1 negative patients who showed minimal initial bone loss responded to the therapy better than the IL-1 positive patients. IL-1 positive patients with severe initial bone loss showed a better response to the therapy than IL-1 negative patients.

CONCLUSIONS

On average, there were no significant differences related to IL-1 genotype in tooth loss after 10 years in a non-smoking, well-maintained periodontal population. On an individual patient basis, the IL-1 genotype, in combination with the initial bone level, seems useful at the beginning of therapy for predicting bone level variation.

Development of clinical and radiographic signs associated with dark discolored primary incisors following traumatic injuries: a prospective controlled study

The purpose was to evaluate late complications of asymptomatic traumatized primary incisors with dark coronal discoloration. The clinical and radiographic signs of 97 teeth of the study group were recorded along a follow-up period that ranged between 12 and 75 months (mean >36 months). Children's age at time of injury ranged between 18 and 72 months (mean 40). The control group consisted of 102 non-discolored maxillary primary central incisors in 51 children older than 54 months with no history of dental trauma. In 50 teeth (52%) the color faded or became yellowish and in 47 (48%) it remained dark. Clinical signs of infection, that were diagnosed 5-58 months after the injury, were associated significantly more with dark than yellowish hues (83 and 17%, respectively). Teeth that had changed their color to become yellow presented more PCO than teeth with black/gray/brown coronal discoloration (78 and 6%, respectively). Arrest of dentine apposition was found in 15 teeth, one had yellow coronal discoloration and the remaining 14 had a dark shade. Eleven teeth showed inflammatory root resorption all with dark discoloration. Two atypical types of root resorption were observed: a surface resorption restricted to the lateral aspects of the apical half of the root while the root length remained unchanged and in the other expansion of the follicle of the permanent successor was observed. Expansion of the dental follicle was observed in 72% of all teeth with no significant difference between the various types of coronal discoloration but only half of the cases were associated with resorption of the root of the primary incisor. The various pathologic findings observed in the study group were either absent or rarely seen in the control group. It can be concluded that more than 50% of the primary incisors that retain their dark coronal discoloration acquired after dental injuries remain clinically asymptomatic till the eruption of the permanent successor even if they present accelerated root resorption. Asymptomatic traumatized primary incisors that retain their dark coronal discoloration may develop a sinus tract and inflammatory root resorption years after the injury. There is still a dilemma: which treatment is better for dark discolored primary incisors: early endodontic treatment or follow-up with the risk of development of infection and root resorption that may require extraction?

Radiographic and histological methodologies in estimating the chronology of crown development in modern humans and great apes: a review, with some applications for studies on juvenile hominids

There has been a burgeoning of interest in the last decade on growth studies in hominids. These studies have relied heavily on dental development, and have compared juvenile hominids to modern human and ape standards, which are usually established using radiographic data. There has been considerable discussion on the most appropriate methods of deriving population standards from radiographs, but very little on the accuracy of the radiographic image itself. Previous histological and dissection studies have shown that age at onset of mineralization is overestimated, and age at crown completion is underestimated using radiographs. This study considers the process of X-ray absorbence by mineralized tissues and the formation of radiographic images of developing teeth. Following tooth initiation a critical mass of mineral is required for the tooth to register superimposed on the absorbence of alveolar crypt bone, which accounts for the late identification of tooth initiation. Determination of completion of crown growth depends upon the identification of the last formed enamel at the cervix. Recognition of this key stage is difficult as crown growth slows towards the cervix, and the last secreted enamel may take months to attain full mineralization levels due to the prolonged maturation process. Morphological and geometric factors have a significant influence on the imaging of the completed crown. The last formed enamel is located on the buccal face, where enamel thins progressively to nothing. X-ray absorption by enamel at the cervix becomes insignificant, and may be counterbalanced by increased dentine absorption. Approximal enamel in contrast is clearly visualized once maturation is complete. However, developmentally this enamel face initiates later, and is completed much earlier than buccal enamel. All of the radiographic estimates of crown completion times are based upon interpretations of approximal enamel completion. These considerations suggest that the human population standards in current usage may not represent true anatomical and chronological stages of crown development, and care should be taken in referring juvenile hominids to these radiological standards.

Position of the Mental Foramen in a Korean Population: A Clinical and Radiographic Study

PURPOSE

The purpose of this study was to improve the treatment methods for the mental foramen by comparing the directly measured values with the radiographic measured values.

MATERIALS AND METHODS

One hundred and twelve mental foramina (72 males, 40 females) that were exposed during the operation were examined. The patients' age ranged from 12 to 69 years, with a mean age of 41.8 years. All patients had fully erupted lower premolars. The horizontal and vertical locations were evaluated with both direct and radiographic measurements.

RESULTS

In 72 patients (64.3%), the mental foramen was below the second premolar. In 26.8%, it was between the first and second premolar, and in 8.9%, it was below the first premolar. By radiographic readings,most of the mental foramina were found to be below the second premolar (62.5%). The average distance between the cusp tip and the superior border of the mental foramen by direct measurement was 23.42 mm and 25.69 mm in the panoramic view. The mean distance between the superior border of the mental foramen and the bottom of the mandible was 14.33 mm by direct measurement and 16.52 mm by radiographic measurements.

CONCLUSION

It is important to know the position of the mental foramen for the placement of osseointegrated implants in the mandibular premolar region. The position of the mental foramen of Koreans is closer to the cusp tips of lower premolars than Westerners.

Using ultrasound transmission velocity to analyse the mechanical properties of teeth after in vitro, in situ, and in vivo irradiation

Ultrasound transmission velocity (UTV) in isotropic material as a measure for the modulus of elasticity was correlated to mechanical properties. Changes in micromechanical properties of radiated teeth and influence of the oral cavity were to be evaluated nondestructively. UTV was measured in extracted teeth after 36 Gy and 62 Gy of in situ (enorally, with no contact to the oral cavity) and in vitro irradiation. Relative to controls, teeth subjected to 62 Gy in vivo showed higher UTV values for dentine and enamel. Sound teeth irradiated with 60 Gy in situ also showed higher UTV values for enamel, whereas dentine values were not significantly different from those of control. The mechanical properties of teeth irradiated in vitro were affected only after high experimental doses of up to 500 Gy. The difference between in vivo and in vitro mechanical properties may be due to radioxerostomia-induced damages as well as the status of dentine vitality. This supports the concept of direct radiation-induced damage in synergy with radioxerostomia-induced caries.

Radiographic features of the jaws and teeth in thalassaemia major

OBJECTIVES

This investigation aimed to compare the radiographic changes and root and crown-body lengths of the mandibular first permanent molar in a group of thalassaemic patients with a control group, matched for age and sex.

METHODS

Panoramic radiographs of 50 thalassaemic patients and 50 controls were examined for the presence of radiological changes. Crown body and root lengths were determined using the method of Seow and Lai. The average lengths were calculated and compared between the two groups.

RESULTS

The mean crown-body and root lengths of the mandibular first molar of patients with thalassaemia major were 9.58+/-0.83 mm and 11.89+/-1.33 mm, while those for the control group were 10.45+/-0.78 mm and 12.78+/-1.67 mm, respectively. A significant difference (P<0.05) was found between the mean crown-body and root values of the two groups. A significant difference (P<0.05) was also found between thalassaemic patients and controls in the occurrence of spiky-shaped roots, root and crown lengths, taurodontism, attenuated lamina dura, enlarged bone marrow spaces, small maxillary sinuses, faint inferior alveolar canal and thin cortex of the mandible.

CONCLUSIONS

While thalassaemia major may not be associated with the occurrence of either vascular canals or prominent antegonial notch, spiky-shaped and short roots, taurodonts, attenuated lamina dura, enlarged bone marrow spaces, small maxillary sinuses, absence of inferior alveolar canal and thin cortex of the mandible were found to be reliable diagnostic criteria for thalassaemia major.

Accessing developmental information of fossil hominin teeth using new synchrotron microtomography-based visualization techniques of dental surfaces and interfaces

Quantification of dental long-period growth lines (Retzius lines in enamel and Andresen lines in dentine) and matching of stress patterns (internal accentuated lines and hypoplasias) are used in determining crown formation time and age at death in juvenile fossil hominins. They yield the chronology employed for inferences of life history. Synchrotron virtual histology has been demonstrated as a non-destructive alternative to conventional invasive approaches. Nevertheless, fossil teeth are sometimes poorly preserved or physically inaccessible, preventing observation of the external expression of incremental lines (perikymata and periradicular bands). Here we present a new approach combining synchrotron virtual histology and high quality three-dimensional rendering of dental surfaces and internal interfaces. We illustrate this approach with seventeen permanent fossil hominin teeth. The outer enamel surface and enamel-dentine junction (EDJ) were segmented by capturing the phase contrast fringes at the structural interfaces. Three-dimensional models were rendered with Phong’s algorithm, and a combination of directional colored lights to enhance surface topography and the pattern of subtle variations in tissue density. The process reveals perikymata and linear enamel hypoplasias on the entire crown surface, including unerupted teeth. Using this method, highly detailed stress patterns at the EDJ allow precise matching of teeth within an individual’s dentition when virtual histology is not sufficient. We highlight that taphonomical altered enamel can in particular cases yield artificial subdivisions of perikymata when imaged using X-ray microtomography with insufficient resolution. This may complicate assessments of developmental time, although this can be circumvented by a careful analysis of external and internal structures in parallel. We further present new crown formation times for two unerupted canines from South African Australopiths, which were found to form over a rather surprisingly long time (> 4.5 years). This approach provides tools for maximizing the recovery of developmental information in teeth, especially in the most difficult cases.

Root-crown ratios of permanent teeth in a healthy Finnish population assessed from panoramic radiographs

An unfavourable root-crown (R/C) ratio caused by short dental roots may result from a developmental deficiency, root resorption after orthodontic treatment, or dental trauma. In the assessment of root shortening, subjective grading has often been used. For objective tooth measurements, varying materials and methods may make the results impossible to compare. This study used a simple, objective method to assess the R/C ratio (relative root length) of mature permanent teeth from panoramic radiographs (PRGs), tested its reproducibility and calculated the mean values of R/C ratios and their variations in a healthy Caucasian (Finnish) population. Two thousand seven hundred and seventy-nine teeth were measured on 108 PRGs. The intra- and inter-examiner reproducibility of the assessment method was good (Pearson correlation coefficients 0.87 and 0.83, respectively; P < 0.001) and the mean R/C ratios did not differ between the repeated measurements (P > 0.05). The biological variance in all cases exceeded the error variance for each tooth. These facts suggest that the method reported in this study can be used in the assessment of the relative root length of 'normal' teeth and its alterations in teeth with developmental or acquired aberrations of dental roots. Males, overall, tended to have higher R/C ratios than females; P-values varied from non-significant to less than 0.01. With the exception of the permanent lateral incisors in males and the permanent second molars in both genders, the ratios of the antagonist teeth were significantly greater in the mandible than in the maxilla (P < 0.05 for the lateral incisors of females; P < 0.001 for all other teeth). Consequently, in quantifying root shortening in developmentally short-rooted teeth, tooth- and gender-specific reference values should be employed. The Finnish R/C data reported here for all teeth except third molars could be used for comparison with other populations, patient groups or individuals where crown-root aberrations are suspected.

Bracket positioning and resets: five steps to align crowns and roots consistently

Orthodontists strive for accurate bracket positioning because it makes achieving a superior occlusion easier. Whether one uses a direct or an indirect bonding technique, the initial appliance placement typically includes some bracket-positioning errors. The clinician either corrects these errors during treatment or tediously repeats archwire bends to compensate for the misplaced brackets. The clinician should assess bracket positioning early in treatment by clinical and radiographic evaluations and then correct all positioning errors during a single dedicated reset appointment. This article describes a 5-step protocol for assessing and correcting bracket-positioning errors.