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PubMed2005

A comparison of two maxillary molar distalizing appliances with the distal jet.

AIMS: Previous studies on maxillary molar distalization have usually concentrated on only one appliance and featured small sample sizes. The purpose of this retrospective study was two-fold: (1) to determine the skeletal, dental, and soft tissue effects of 3 molar distalization appliances, 2 of which do not depend upon patient compliance (ie, distal jet and Greenfield molar distalizing appliance) and 1 that does (ie, sagittal appliance combined with cervical headgear); and (2) to determine differences in treatment effects among the 3 appliances. METHODS: Pretreatment and post-distalization cephalometric radiographs were obtained for each appliance (14 females and 11 males for the distal jet; 12 females and 13 males for the Greenfield molar distalizing appliance; and 17 females and 13 males for the sagittal appliance with headgear). RESULTS: Pretreatment to transition evaluation showed significant distal movement of the first molars for the distal jet (3.4 mm), the Greenfield molar distalizing appliance (3.9 mm), and the sagittal appliance with headgear (2.1 mm). Distal tipping of the first molar was seen in all samples, but significantly more so in the Greenfield molar distalizing appliance (6.5 degrees +/- 6.6) and the sagittal appliance with headgear (13.5 degrees +/- 8. 1) than in the distal jet (3.2 degrees +/- 2.8). CONCLUSIONS: Maxillary molar distalization was effective using the distal jet, the Greenfield molar distalizing appliance, and the sagittal appliance with headgear, but better control of molar bodily movement was reported with the distal jet.

Adolescent↗
PubMed2005

Phylogenetic and environmental components of morphological variation: skull, mandible, and molar shape in marmots (Marmota, Rodentia).

The phenotype is a product of its phylogenetic history and its recent adaptation to local environments, but the relative importance of the two factors is controversial. We assessed the effects of diet, habitat, elevation, temperature, precipitation, body size, and mtDNA genetic divergence on shape variation in skulls, mandibles, and molars, structures that differ in their genetic and functional control. We asked whether these structures have adapted to environment to the same extent and whether they retain the same amount of phylogenetic signal. We studied these traits in intra- and interspecific populations of Eurasian marmots whose last common ancestor lived 2-5 million years ago. Path Analysis revealed that body size explained 10% of variation in skulls, 7% in mandibles, and 15% in molars. Local vegetation explained 7% of variation in skulls, 11% in mandibles, and 12% in molars. Dietary category explained 25% of variation in skulls, 11% in mandibles, and 9% in molars. Cyt b mtDNA divergence (phylogeny) explained 15% of variation in skulls, 7% in mandibles, and 5% in molars. Despite the percentages of phylogenetic variance, maximum-likelihood trees based on molar and skull shape recovered most phylogenetic groupings correctly, but mandible shape did not. The good performance of molars and skulls was probably due to different factors. Skulls are genetically and functionally more complicated than teeth, and they had more mathematically independent components of variation (5-6-in skulls compared to 3-in molars). The high proportion of diet-related variance was not enough to mask the phylogenetic signal. Molars had fewer independent components, but they also have less ecophenotypic variation and evolve more slowly, giving each component a proportionally stronger phylogenetic signal. Molars require larger samples for each operational taxonomic unit than the other structures because the proportion of within-taxon to between-taxon variation was higher. Good phylogenetic signal in quantitative skeletal morphology is likely to be found only when the taxa have a common ancestry no older than hundreds of thousands or millions of years (1% to 10% mtDNA divergence)--under these conditions skulls and molars provide stronger signal than mandibles.

Animals↗
PubMed2005

Third molar as an age indicator in young individuals.

The authors developed a method of chronological age estimation in young individuals on the basis of third molar developmental stage. The new method is based on the finding that time course of third molar development depends on the number of assessed third molars. That means, in individuals with 1 to 3 third molars agenesis the development of founded third molars is delayed in comparison with individuals having all third molars present. This difference is statistically significant. Retardation of development is directly proportional to the number of congenitally missing third molars. Chronological age corresponding to individual stages of third molar development was calculated separately for individuals with all four third molars present and separately for individuals with 1 to 3 third molars agenesis. With this division it was possible to decrease the error of age estimation to 1.63 years in the group of individuals with all four third molars present and to correct the age underestimation in individuals with agenesis. The elaborated method of chronological age estimation in young individuals shows incomparably much more accuracy in contrary to methods used in adults. In addition this new method is distinguishing by maximum simplicity.

Adolescent↗
PubMed1990

Impacted lower third molars and periodontal health. An epidemiological, methodological, retrospective and prospective clinical, study.

The main objective of this series of investigations was to study periodontal health of the adjacent second molars (M2) in cases of impacted lower third molars (M3) and after impacted lower third molar surgery. An epidemiological study, comprising 693 dentate individuals, was undertaken in order to obtain the prevalence, impaction and positional relationship of third molars in a normal Swedish population. The prevalence of all third molars in individuals aged 20 years was 77.0%. One in four of the vertically positioned third molars, three in four of the mesioangular, nine in ten of the distoangular and all those horizontally placed were impacted to some extent. 68.5% of the impacted third molars were in close proximity to the root of the adjacent second molars. In order to evaluate the precision and accuracy of the radiographic assessment of intrabony defects (IBD), i.e. the distance between the cemento-enamel junction and the bottom of the pocket to firm osseous contact, on the distal surface of M2, a methodological study was performed on 25 subjects. Using conventional free hand technique, intraoral radiographs were taken in the deepest part of IBD with and without a probe as indicator. Comparing the two sets of radiographs, the deviation was 1 mm or less in 87.9% of the cases. The radiopaque marker enhanced the accuracy of assessment of IBD to 96.7%. The effects of impacted lower third molar surgery on periodontal tissues of the M2 area were investigated in a retrospective clinical study comprising 215 subjects. The results two years postoperatively showed a higher prevalence of plaque, gingivitis and periodontal pockets on the distal surface of M2 than on other surfaces of the two molars adjacent to the extraction site. IBD greater than or equal to 4 mm were registered in 32.1% of the cases. The long term effects on periodontal tissues after impacted lower third molar surgery was investigated in a comparative retrospective study, two and four years postoperatively, comprising 51 cases. The improvement concerning postoperative IBD, between the two examinations, was mainly seen in individuals less than or equal to 25 years of age. No case in this age group increased in depth, while 29.6% of postoperative IBD deteriorated in individuals greater than or equal to 26 years. A multiple regression analysis was used to identify some predictors of postoperative IBD, and the material consisted of the 215 cases from the retrospective study.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed2001

Characterization of the molar masses of hemicelluloses from wood and pulps employing size exclusion chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

The molar mass parameters for arabino-4-O-methylglucuronoxylans, arabinohexenuronoxylans, 4-O-methylglucuronoxylans, hexenuronoxylans, and galactoglucomannans extracted from wood and pulps have been determined. To characterize different types of hemicelluloses, delignified wood (spruce, pine, larch, aspen, and birch) and chemical pulps (unbleached and totally chlorine-free bleached) were extracted with dimethyl sulfoxide (DMSO) or alkaline aqueous solutions. Size exclusion chromatography (SEC) with off-line matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-MS) were employed to characterize the molar masses. The hemicellulose extracts were separated by SEC into fractions each containing components with a narrow range of molar masses and the average molar mass of each fraction subsequently determined by MALDI-MS. The molar mass parameters for the hemicelluloses were then calculated on the basis of the SEC distribution curves and MALDI-MS spectra. As expected, in most cases the hemicelluloses extracted from wood (holocellulose) exhibited higher molar masses than did the corresponding hemicelluloses from chemical pulps. The molar mass parameters for hemicelluloses isolated from pulps derived from cooking samples of the same batch of softwood chips decreased in the following order: ASAM pulp > MSSAQ pulp > kraft pulp. The lowest molar masses were demonstrated by the glucuronoxylans extracted from pulps obtained by cooking with acidic sulfite. The xylans from bleached kraft pulp were characterized by molar masses that were only slightly lower than those of the corresponding xylans from unbleached pulp. The xylans extracted into DMSO exhibited somewhat lower molar masses than did the corresponding xylans extracted into alkaline aqueous solutions. In all cases the range of molar masses demonstrated by the hemicelluloses investigated was found to be rather narrow, i.e., the polydispersity index Mw/Mn was found to be approximately 1.1-1.4.

Carbohydrate Sequence↗
PubMed2001

Effect of molar rotation on arch length.

The aim of this study was to evaluate the effect of maxillary first molar rotation on arch length in patients whose Class II, division 1 malocclusion was treated with a straight-pull headgear. The sample included 19 children who represent a subset of a population enrolled for 2 years in a prospective clinical trial of Class II treatment. The inner bow was adjusted at monthly visits and the average distalizing force was 14-16 oz per side. Measurements were made with digital calipers on casts obtained at baseline and at a time point averaging 16 months (SD 3 months) into treatment. Molar movement was related to a coordinate system referenced to the midpalatal raphae and the occlusal plane through a palatal plug that could be transferred to successive casts of the same patient. Distances from the cusp tips were measured to the reference system. The distal and lateral displacement, and the rotation of the molars over time were then computed. High correlations were observed between molar rotation and tooth displacement (that is the net differential movement between the mesiobuccal - MB - and mesiopalatal - MP - cusps): r=0.9, p=0.0001 (left side); r=0.8, p=0.0001 (right side). The average rotation of the molar was 15.4 degrees (SE+/-3.80) on the left side and 10.8 degrees (SE+/-2.20) on the right side. The average differential displacements between the MB and MP cusps were 1.04 mm (SE+/-0.29) (left) and 0.73 mm (SE+/-0.23) (right). The differences between the two sides were not statistically significant. The molar rotation did not correlate with any of the following parameters: initial tooth position; initial distance between the MB and MP cusps as a correlate of molar anatomy; transverse (mostly buccal) movement of the MB and MP cusps; distal movement of the tooth, as measured by the total displacement of the MB and MP cusps. This study qualifies the relationship between molar rotation and increase in arch length. The mean total distal movement of the molar was larger (nearly 3 mm) than the average contribution of molar rotation to space gain (about 1 mm), suggesting that the distal movement of the tooth was a combination of rotation and translation (or tipping). The contribution of the molar rotation is more significant with a smaller total displacement of the tooth.

Journal Article↗
PubMed1987

Surgical repositioning of impacted mandibular second molar teeth.

Impacted second molars refractory to orthodontic treatment are frequent problems. The family dentist and the orthodontist should be on the alert for them. A philosophy for their management and the authors' experience over the past 13 years are presented. The proper time for definitive treatment of these impactions is during early adolescence, generally in the 11- to 14-year range. Impaction of the second molar is usually a problem of arch length deficiency. There may be an associated problem with a third molar impaction. The alternatives for impacted second molar treatments are surgical repositioning with or without adjacent third molar removal, removal of the second molar allowing the third molar to erupt, and transplantation of the third molar to the second molar socket. In the authors' experience, surgical repositioning has provided the most promising results of the three choices. Technical aspects of surgical repositioning are discussed along with case selection criteria. Six cases are presented to demonstrate typical problems and their management. With proper timing and intervention, the prognosis is excellent for repositioning second molar impactions.

Adolescent↗
PubMed2002

Root and canal morphology of Thai maxillary molars.

AIM: To investigate the root and canal morphology of 268 maxillary permanent molars collected from an indigenous Thai population. METHODOLOGY: The cleaned teeth were accessed, the pulp dissolved by sodium hypochlorite under ultrasonication, and the pulp system injected with Indian ink. The teeth were rendered clear by demineralization and immersion in methyl salicylate. The following observations were made: (i) number of roots and their morphology; (ii) number of root canals per root; (iii) root-canal configuration in each root using Vertucci's classification with additional modifications; and (iv) presence and location of lateral canals and intercanal communications. RESULTS: All the maxillary first and second molars had three separate roots. Only, half (51%) of the maxillary third molars had three separate roots; the other half had fused or conical roots. The majority of the distobuccal (98.1-100%) and palatal (100%) roots had type I canals. Over half of the mesiobuccal roots of first (65%) and second (55%) molars had two canals. The most common (44.2%) canal configuration in mesiobuccal roots of first molars was type IV (two canals, two foramina). A variety of canal types were found in the mesiobuccal roots of second molars. Maxillary third molars showed the greatest diversity of canal morphology. There was an increase in the prevalence of lateral canals towards the apical part of the roots and intercanal communications were present in 16% of each of first, second and third Thai maxillary molars. CONCLUSIONS: The mesiobuccal roots of Thai maxillary molars possessed a variety of canal system types. Over 50% of the first molars had a second mesiobuccal canal. The palatal and distobuccal canals mainly had type I canals. Only, a small proportion (7.3-13.3%) of the roots exhibited lateral canals which were the most common in the apical third

Carbon↗
PubMed2003

Prevalence of third molar impaction in orthodontic patients treated nonextraction and with extraction of 4 premolars.

The purposes of this study were to confirm that premolar extraction treatment is associated with mesial movement of the molars concomitant with an increase in the eruption space for the third molars and to test the hypothesis that such treatment reduces the frequency of third molar impaction. Lateral cephalograms, panoramic or periapical radiographs, and study models made before (T1) and after (T2) treatment and a minimum of 10 years postretention (T3) of 157 patients were selected from the postretention sample at the Department of Orthodontics of the University of Washington, Seattle. Treatment for 105 patients included the extraction of 4 premolars; the other 53 were treated nonextraction. These patients represented all the extraction and nonextraction patients in the sample who had at least 1 third molar at T1 or T2 and who showed evidence of full eruption or closure of the root apex at T2 or T3. Student t tests showed higher scores for third molar impaction (P <.01), less mesial movement of the molars from T1 to T2 (P <.01), and smaller retromolar space at T2 (P <.001) in both arches of the nonex patients than in the ex patients. Similarly, molar movement was more mesial from T1 to T2 in the maxilla (P <.01) and in the mandible (P <.05), and the retromolar space was larger in both arches (P <.001) of the patients with eruption than in those with impaction of the third molars. Our results suggest that premolar extraction therapy reduces the frequency of third molar impaction because of increased eruption space concomitant with mesial movement of the molars during space closure.

Adolescent↗
PubMed2000

Periodontal treatment decisions for molars: an analysis of influencing factors and long-term outcome.

BACKGROUND: The purpose of this retrospective study was 1) to analyze factors influencing the treatment decision for periodontitis-affected molars and 2) to evaluate the long-term outcome of the decision. The treatment alternatives included in the analysis were maintenance of the tooth with only non-surgically/surgically performed scaling/root planing with or without furcation plasty, root separation/resection, and tooth extraction. METHODS: Data collected from a total of 1,313 first and second molars in 222 patients (mean age 45 years; range 14 to 73 years), referred for periodontal treatment, were analyzed with respect to treatment decisions for furcation-involved teeth. The patients had been examined with respect to oral hygiene status, gingival conditions, probing depth, furcation involvement, and radiographic bone height before and after active periodontal treatment. Frequencies, mean values and standard deviations were calculated for the various variables assessed. Multiple regression models were formulated in order to analyze the influence of various variables on treatment decisions. One-hundred and sixty (72%) of the patients agreed to participate in a follow-up examination to determine the clinical and radiographic status of the molars 8 to 12 years after the active phase of treatment for evaluation of the long-term outcome of the treatment decision. RESULTS: Twenty-eight percent of the molars were extracted and 4% were root separated/resected. Factors found to significantly influence the decision of tooth extraction were tooth mobility, tooth position, lack of occlusal antagonism, degree of furcation involvement, and remaining bone support. Of the factors analyzed with respect to root separation/resection, molar position and degree of furcation involvement showed the strongest influence on the treatment decision. The 8- to 12-year follow-up examination revealed that 96% of the molars subjected to non-resective therapy were still in function. The corresponding figure for root separated/resected molars was 89%. Loss of radiographic bone support during the 10-year follow-up period was 0.1 to 0.6 mm for the various molars with the highest value for maxillary second molars. CONCLUSIONS: A conservative approach to the treatment of molars with even deep furcation invasions may show a high long-term success rate, provided maintenance care is offered.

Adolescent↗
PubMed2006

[Effects of first premolar extractions on third molar angulations].

OBJECTIVE: To compare the inclinations of third molars of patients treated orthodontically with and without premolar extractions. METHODS: Records of 37 first premolar extraction patients and 32 nonextraction patients were examined. The pretreatment and posttreatment panoramic radiographs were analyzed. The angles were measured between the long axis of the third molar and the occlusal plane and between the long axis of the third molar and the long axis of the second molar. Changes in third molar angulations from pretreatment to posttreatment for two groups were compared by Mann-Whitney U-test. RESULTS: There were statistically significant difference between the extraction and nonextraction groups in the median angle formed by the long axis of third molar angulation relative to the occlusal plane (P<0.05) and the second molar (P<0.05) in mandible but not in maxillary. In the extraction group, at the end of the orthodontic treatment, the mandibular third molars showed more uprighting than did the maxillary third molars. CONCLUSION: Orthodontic treatment involving premolar extractions improves mandibular third molar angulations.

Bicuspid↗
PubMed1994

Quantitative study of the apical nerve fibers of adult and juvenile rat molars.

The rat molar has become an important model for studies of interactions between nerves and the pulp-dentin complex, yet there is only limited quantitative information on the number and size distribution of axons entering the roots of this tooth. This study was undertaken to provide such a detailed characterization of the apical innervation of the rat molar. An additional objective was to compare the apical nerve composition of young, recently erupted rat molars with that of mature teeth in order to determine whether there is ongoing maturation of the innervation after the teeth have attained functional occlusion. A complete census was made of the nerve fibers entering the roots of both mature and recently erupted juvenile mandibular first molars in Sprague-Dawley rats. Each of the four roots of the first molars was processed for electron microscopy of thin sections near the apex. The majority of intradental nerve fibers entered the molar via the two larger (mesial and distal) roots. Within the apical root pulp, most, but not all, axons occurred within well-defined fascicles associated with blood vessels. Molars from adult animals (age 4 months) had a mean total of 232 (S.D. = 49, N = 7 teeth) myelinated fibers and 806 (S.D. = 143) unmyelinated axons entering the four roots. Fibers exceeding the A delta size range (circumference > or = 19 microns) accounted for only 4% of the myelinated axons at the apex. Molars from juvenile animals (age 4 weeks) had fewer myelinated fibers (mean 176, S.D. 18, N = 8), but more unmyelinated axons (mean 1,174, S.D. 160) than adults. The mean ratio of unmyelinated axons to myelinated axons was 6.6:1 for juveniles compared to 3.5:1 for adults. Juvenile teeth contained no myelinated fibers that exceeded 19 microns in circumference. These results indicate that the innervation of the rat molar resembles that of teeth of non-rodent mammals in that (1) innervation density is high, (2) there is a high ratio of unmyelinated axons, and (3) most of the myelinated fibers are of thin caliber. Furthermore, it appears that after the molar erupts, maturation of the nerve fiber composition continues with processes that include both a marked decrease in the number of unmyelinated axons and an increase in the number and size heterogeneity of myelinated fibers.

Animals↗
PubMed2006

Caries pattern in primary molars in Dutch 5-year-old children.

AIM: The aim of this study was to investigate the difference in caries prevalence based on quadrant dmfs data between first and second primary molars in 5-year-old Dutch children. STUDY DESIGN: Cross-sectional observational study. METHODS AND STATISTICS: For this study 692 children, all insured by a "Health Insurance Fund", living in one of four selected cities in The Netherlands were asked to participate in the study. From the original cohort 435 children (49% girls) participated. Clinical examinations were performed and only carious lesions with involvement of the dentine were reported. Lesions on the occlusal, buccal, palatinal/lingual, mesial and distal surfaces as well as lesions in buccal and palatinal pits and fissures were reported separately. No radiographs were taken. Systematic differences in dmfs between first and second molars in the same quadrant of each primary dentition were tested with the Wilcoxon signed rank test. RESULTS: Second primary molars, even after correction for caries in pits and buccal/palatinal fissures, had a statistically significant higher total dmfs than the first primary molars. The differences were mainly found on the occlusal surfaces. On proximal surfaces, the first primary molars had significant more caries than the second primary molars. The d-component constituted the major part of the caries index. CONCLUSIONS: Second primary molars, corrected for decay in the pits and buccal/palatinal fissures of this molar, are more affected by caries than first primary molars and that the differences in caries prevalence are the largest on the occlusal surface. The specific site of the caries found suggests that developmental disturbances in second primary molars may attribute to their prevalence.

Child, Preschool↗
PubMed1982

A segmental approach to mandibular molar uprighting.

Diagnosis and treatment in molar uprighting are discussed. The over-all objective in molar uprighting is ideal positioning of the molar which will eventually become an abutment tooth for a fixed prosthesis. The ideal position will provide an optimal periodontal environment for the molar(s). The specific objectives concerning protection against inflammatory periodontal diseases and occlusal traumatism, which together determine the optimal periodontal environment, are explained. Emphasis is placed on the biomechanics of molar uprighting which will achieve the desired periodontal treatment result. The specific technique recommended for the instances in which the molar is considerably angulated involves a segmental approach which utilizes a modification of the Burstone root spring. Proper application results in the dissociation of the correction of angulation and the extrusion of the molar tooth. When extrusion of the periodontally involved molar is required, then it should follow the correction of molar angulation. Other advantages of this approach involve the precision and ease of symmetrical preactivation, favorable load/deflection considerations, the low level of patient discomfort, and the reduced tendency of normal function distorting or dislodging the spring. This technique is compared by these parameters to other popular molar-uprighting techniques. It is recognized that a multidisciplinary approach to this type of dental therapy is ideal and that since treatment planning in individual cases varies greatly, each malocclusion and associated periodontal involvement should be evaluated on an individual case basis.

Biomechanical Phenomena↗
PubMed1990

A long-term study of the relationship of third molars to changes in the mandibular dental arch.

The purpose of this study is to determine the relationship of third molars to changes in the mandibular dental arch. The sample for this study consisted of four groups and subgroups. The groups consisted of premolar extraction treated, nonextraction treated with initial generalized spacing, nonextraction treated, and serial extraction untreated subjects. The subgroups were divided into persons who had mandibular third molars that were either impacted, erupted into function, congenitally absent, or extracted at least 10 years before postretention records. The mean postretention time interval was 13 years, with a range of 10 to 28 years. The mean postretention age was 28 years 6 months, with a range of 18 years 6 months to 39 years 4 months. Two-way analysis of variance with repeated measures was used to compare the changes over time (before treatment, at end of active treatment, and after retention) of groups and third molar subgroups. With time, mandibular incisor irregularity increased while arch length and intercanine width decreased. The eruption patterns of mandibular incisors and first molars were similarly dispersed in all groups studied. The findings between the subgroups in which mandibular third molars were impacted, erupted into function, congenitally absent, or extracted 10 years before postretention records revealed no significant differences between any of the subgroups for the parameters studied. No significant differences in mandibular growth were found between the third molar subgroups; this suggests that persons with third molars erupted into satisfactory function do not have a significantly different mandibular growth pattern than those whose third molars are impacted or congenitally missing. In the majority of cases some degree of mandibular incisor crowding took place after retention, but this change was not significantly different between third molar subgroups. This finding suggests that the recommendation for mandibular third molar removal with the objective of alleviating or preventing mandibular incisor irregularity may not be justified.

Adult↗
PubMed1992

Changes in lower third molar position in the young adult.

Changes in position of unerupted lower third molars between 18 and 21 years were examined in a group of 17 men and 24 women with intact lower arches. Mesiodistal third molar angulation, molar space, molar space condition, and buccolingual third molar angulation and the changes in these dimensions were measured on 60 degree cephalograms taken at 18 and 21 years. At 18 years molar space was inadequate by an average of 5.0 mm. Average changes in dimensions were statistically nonsignificant except for an increase in molar space of 0.7 mm. Changes in third molar position ranged from 39 degrees to -46 degrees in the mesiodistal and from 24 degrees to -24 degrees in the buccolingual dimension. Only 10 third molars did not change their mesiodistal angulation. Four third molars erupted fully during the observation period.

Adolescent↗
PubMed2006

Physiological properties of molar-mechanosensitive periodontal neurons in the trigeminal ganglion of the rat.

Spike discharges from periodontal mechanosensitive neurones responding to the mechanical stimulation of molar teeth were recorded from the trigeminal ganglion of rats anaesthetized with pentobarbital sodium. Maxillary molar-sensitive units were close together in a narrow, lateral area of the maxillary division of the ganglion, whereas those of mandibular molar-sensitive units were scattered throughout the mandibular division. The majority of maxillary molar-sensitive units responded only to stimulation of the first molar. They were slowly adapting and responded most strongly to pressure applied to the lingual surface and buccal cusp of the tooth or to the buccal surface and lingual cusp. By contrast, approximately one-half of the mandibular molar-sensitive units were rapidly adapting, multitooth units that responded to tooth stimulation almost equally in all directions. The other half were slowly adapting and activated most effectively by pressure applied to the lingual surface and buccal cusp of the molar tooth. These slowly adapting units consisted of first molar-sensitive, single- and multitooth units. Differences in the response characteristics of the maxillary and mandibular molar-sensitive periodontal units may reflect differences in the sensory role of individual molars.

Animals↗
PubMed2006

Molar development in common chimpanzees (Pan troglodytes).

Numerous studies have reported on enamel and dentine development in hominoid molars, although little is known about intraspecific incremental feature variation. Furthermore, a recent histological study suggested that there is little or no time between age at chimpanzee crown completion and age at molar eruption, which is unlikely given that root growth is necessary for tooth eruption. The study presented here redefines growth standards for chimpanzee molar teeth and examines variation in incremental features. The periodicity of Retzius lines in a relatively large sample was found to be 6 or 7 days. The number of Retzius lines and cuspal enamel thickness both vary within a cusp type, among cusps, and among molars, resulting in marked variation in formation time. Daily secretion rate is consistent within analogous cuspal zones (inner, middle, and outer enamel) within and among cusp types and among molar types. Significantly increasing trends are found from inner to outer cuspal enamel (3 to 5 microns/day). Cuspal initiation and completion sequences also vary, although sequences for mandibular molar cusps are more consistent. Cusp-specific formation time ranges from approximately 2 to 3 years, increasing from M1 to M2, and often decreasing from M2 to M3. These times are intermediate between radiographic studies and a previous histological study, although both formation time within cusps and overlap between molars vary considerably. Cusp-specific (coronal) extension rates range from approximately 4 to 9 microns/day, and root extension rates in the first 5 mm of roots range from 3 to 9 microns/day. These rates are greater in M1 than in M2 or M3, and they are greater in mandibular molars than in respective maxillary molars. This significant enlargement of comparative data on nonhuman primate incremental development demonstrates that developmental variation among cusp and molar types should be considered during interpretations and comparisons of small samples of fossil hominins and hominoids.

Age Determination by Teeth↗