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PubMed1992

[Extraction of second molars as orthodontic therapy].

Extraction of second molars as an orthodontic measure is a simple procedure which can lead to good clinical results. Indications as well as timing and long term effects on buccal occlusion are discussed. It is concluded that acceptable results may only be expected when the extraction is strictly indicated and carried out in cases when the third molars have reached their full crown stage but before radiographic evidence of root formation. Upper third molars with an angulation of less than 30 degrees and lower third molars with an angulation of 30-60 degrees to the occlusal plane are likely to give a satisfactory position after eruption.

Humans↗
PubMed2001

Acute effects of ovariectomy on wound healing of alveolar bone after maxillary molar extraction in aged rats.

Acute effects of ovariectomy on the bone wound healing processes after maxillary molar extraction in aged rats were examined by means of quantitative scanning electron microscopy (SEM), backscattered electron image (BSE) analysis and energy-dispersive X-ray (EDX) microanalysis. Six-month-old female rats underwent either sham operation or bilateral ovariectomy, and 7 days postoperatively, the maxillary first molars were extracted. On post-extraction days 7, 30 and 60, the dissected maxillary bone surfaces were examined by SEM to reveal the bone formative and resorptive areas around the extracted alveolar sockets. In addition, the resin-embedded maxillae were micromilled in the transverse direction through the extracted alveolar sockets, and the newly-formed bone mass on the buccal bone surfaces and within the extracted sockets was examined by BSE analysis. Compared with sham-operated controls, the extent of newly-formed bone mass on the buccal bone surfaces in OVX rats was significantly decreased, due to increased bone resorption. On the other hand, new bone formation within the extracted sockets was similar in the experimental groups. In EDX microanalysis of these newly-formed bone matrices, both Ca and P weight % and Ca/P molar ratio were similar in the experimental groups. Our results suggest that 1) acute estrogen deficiency induced by ovariectomy stimulates sustained bone resorption, but has less effect on bone formation, and 2) bone wound healing after maxillary molar extraction within extracted alveolar sockets is not significantly delayed by ovariectomy, but bony support by newly-formed bone mass on the maxillary bone surfaces at the buccal side of the extracted sockets is significantly decreased, due to increased bone resorption.

Acute Disease↗
PubMedDate not supplied

Size relationships among permanent mandibular molars in Aboriginal Australians and Papua New Guinea Highlanders.

Size relationships among crown units of permanent mandibular molars were investigated in two Sahul-Pacific samples: Aboriginal Australians (Yuendumu) and Papua New Guinea Highlanders (Wabag). Measurements of first, second, and third molars (M1, M2, and M3), including overall mesiodistal and buccolingual diameters as well as the mesiodistal and buccolingual diameters of the trigonid and talonid, were obtained from dental casts using a sliding caliper. Molar reduction was noted in talonid dimensions within both samples, but the trigonid mesiodistal diameter was not reduced in M2 or M3 compared with M1, indicating that the later-developing crown unit (talonid) was more reduced than the early-developing unit (trigonid). M2 was most reduced in size mesiodistally of the three molars, but its buccolingual diameter was not reduced. M3 was the most reduced tooth in trigonid buccolingual diameter. The percentage sexual dimorphism values were greater for the size of the talonid than for the trigonid, indicating that male values exceeded those for females by a greater amount in the later-developing crown unit. Crown dimensions were larger generally in the Aboriginal Australians from Yuendumu than in the Papua New Guinea Highlanders from Wabag, with differences being more evident in M2 and M3 than M1, especially in talonid dimensions. The trigonid, which develops early both phylogenetically and ontogenetically, tended to be relatively stable in size, whereas the later-forming talonid displayed size reduction when comparisons were made both within and between groups.

Anthropometry↗
PubMed2002

Identifying metameric variation in extant hominoid and fossil hominid mandibular molars.

Landmark data were collected from cross sections and occlusal images of mandibular molar crowns, and Euclidean distance matrix analysis (EDMA) was used to identify metameric morphological variation between the first and second mandibular molars of living taxa: Gorilla gorilla (n = 30), Pan troglodytes (n = 34), and Homo sapiens (n = 26). Two patterns of metameric variation were identified, one unique to humans and the other shared by chimpanzees and gorillas. In order to assess the utility of this type of analysis for the interpretation of the hominid fossil record, 19 mandibular molars from Sterkfontein Member 4, South Africa, were examined. The pattern of metameric variation of the Sterkfontein molars resembled that of the African great apes, and differed from the modern human pattern. These results demonstrate that data on metameric variation may provide information regarding function or developmental processes previously indiscernible from fossil material.

Animals↗
PubMed2005

Enamel thickness of deciduous and permanent molars in modern Homo sapiens.

This study presents data on the enamel thickness of deciduous (dm2) and permanent (M1-M3) molars for a geographically diverse sample of modern humans. Measurements were recorded from sections through the mesial cusps of unworn teeth. Enamel is significantly thinner on deciduous than on permanent molars, and there is a distinct trend for enamel to increase in relative thickness from M1 to M3. The relatively thicker enamel of M2s and especially M3s can be related to the overall reduction in size of more distal molar crowns, which has been attained through a differential loss of the dentine component. Enamel tends to be thicker on the protocone than on the paracone, and thicker on the protoconid than on the metaconid, but its distribution is not wholly concordant with models that predict increased thickness as a means by which to counter heavier attritional loss on these "functional" cusps. Indeed, the thickness of enamel tends to be more variable on cusp tips and occlusal surfaces than over the lateral aspects of cusps. The proportionately thicker enamel over the lateral aspects of the protocone and protoconid more likely serves as a means to prolong functional crown life by preventing cusp fracture, rather than being an adaptation to increase the attritional longevity of wear facets. The present data suggest that the human dentition is not predisposed to develop a helicoidal wear plane through the disposition of molar enamel thickness.

Africa South of the Sahara↗
PubMed1980

Supernumerary molars in Anthropoidea, Adapidae, and Archaeolemur: implications for primate dental homologies.

The model of primate dental homologies and development recently proposed by Schwartz ('75, '78) is re-evaluated in view of documented exceptions to his account of postcanine supernumerary teeth in both anthropoids and prosimians. Schwartz concluded that catarrhines and living indriids retain only two true molars in each dental quadrant. As many as six molars on one side of the jaw can develop in rare instances in catarrhines, and supernumerary molars are also known for a wide range of other primates, including Cebidae, Adapidae, and subfossil Indriidae. Polydontia cannot be explained exclusively by atavistic development. More convincing explanations regard supernumerary teeth as the result of excessive growth of the dental lamina or localized twinning of tooth buds during early development. Conventional dental formulae of catarrhines and indriids including three permanent molars remain the most plausible.

Animals↗
PubMed1983

Fluctuating asymmetry in molar dimensions and discrete morphological traits in Pima Indians.

Asymmetry in mesiodistal and buccolingual crown diameters and in eight morphologic crown traits of permanent first and second molars was analyzed in a large Pima Indian sample. Analysis of antimeric differences indicates no consistent evidence for directional asymmetry in Pima molars for either dimensions or morphologic traits. Second molars show greater degrees of metric and morphologic asymmetry than first molars. There is no conclusive evidence for either sex differences in magnitude of asymmetry or relationships between tooth size and morphologic asymmetry. Nonparametric correlations computed between asymmetry in crown dimensions and morphological traits show no significant interaction except where morphological trait development affected crown measurements. The distributions of antimeric differences for dimensional and morphologic traits demonstrate significant leptokurtic deviations from normality. This indicates fluctuating asymmetry in Pima Indians may result from several different sources of developmental variation.

Arizona↗
PubMed1994

Reanalysis of the Lukeino molar (KNM-LU 335).

This paper details a reanalysis of KNM-LU 335, a hominoid mandibular first molar dated to about 6 Ma from the Lukeino Formation, Kenya. Researchers have argued that this molar closely resembles those of modern chimpanzees and may approximate the ancestral morphotype of humans and chimpanzees. The investigation presented here describes a morphometric study of the Lukeino molar and M1s of Homo sapiens, Pan troglodytes, and early australopithecines. Results indicate that KNM-LU 335 differs from both human and chimpanzee M1s in relative distances (measured in three dimensions) between crown fissure termini. Further, the Lukeino molar shares with early australopithecines a pronounced flaring of the buccal surface of the crown not seen for either modern sample. Results of this study do not exclude KNM-LU 335 as a potential ancestral morphotype for Pan and Homo but provide no evidence that this morphotype resembled modern chimpanzees.

Animals↗
PubMed2005

Sexual dimorphism of cusp dimensions in human maxillary molars.

Cusp dimensions of human maxillary molars were compared between males and females to determine whether the later-developed, distal cusps displayed greater sexual dimorphism than the earlier-developed, mesial cusps, and whether the later-forming second molar displayed greater sexual dimorphism than the first molar. First and second permanent molar crowns (M1 and M2) were measured indirectly, using dental casts obtained from 117 Japanese (65 males and 52 females). Measurements included maximum mesiodistal and buccolingual crown diameters and the diameters of the four main cusps: the paracone, protocone, metacone, and hypocone. Mean values of crown dimensions were larger in males than in females for both M1 and M2, but the sexual difference in protocone diameter of M1 was not significant. The protocone in M1 showed the least amount of sexual dimorphism, followed by the metacone, hypocone, and paracone, while in M2, the percentage sexual dimorphism corresponded to the order of cusp formation: paracone, protocone, metacone, and hypocone. With the exception of the paracone diameter, M2 showed greater sexual dimorphism than M1. Sexual dimorphism was not always greater in the later-developed, distal cusps of M1 or M2, but the protocone, the most important cusp in terms of occlusal function, displayed the least dimorphism in M1.

Adult↗
PubMed2007

Mineralization of the mandibular third molar: a study of American blacks and whites.

The tempo of tooth mineralization is under significant genetic control, and the orderly progression of morphological changes-in concert with the long span during growth in which teeth form-makes "dental age" a useful measure of a person's degree of biological maturity. The third molar is of particular interest because (1) it is the last and most variable tooth to form and (2) it is the only tooth to complete formation after puberty, which has made it attractive in forensic and legal circles as an estimator of adulthood. Age standards are described here for mandibular third molar formation stages in a cross-sectional sample of 4,010 persons (age range: 3-25 years), with proportionate sample sizes of American blacks and whites and males and females. Formation was scored against the 15-grade ordinal scheme of Moorrees, and descriptive statistics were computed using proportional hazards survival analysis. Blacks achieved each formation stage significantly ahead of whites, but not in a uniform manner. Instead, there was an enhanced advancement in blacks during crown formation and during late stages of root formation. In both races formation proceeded faster in males, which is unique for the third molar, as prior studies suggest. Sample variance increases with the stage of formation, such that 95% confidence limits span 8 or more years for root formation stages. Consequently, the third molar provides a rough gauge of an individual's chronological age, but the considerable variability precludes any precise estimate, particularly in late adolescence where most forensic interest has focused.

Adolescent↗
PubMed2007

Carabelli's trait and tooth size of human maxillary first molars.

Carabelli's trait is a morphological feature that can occur on the protocone of human maxillary molars. This study tests the hypothesis that Carabelli's trait is correlated statistically with the dimensions of the crown's four principal cusps or whether, as a cingular feature, the trait truly accretes onto an otherwise unaffected crown. Computer-assisted image analysis was used to measure the 6 intercusp distances and 12 angular relationships among cusp tips on the permanent first molar of 300 young adult American whites. Carabelli's complex was scored using an 8-grade ordinal scheme. Crown size was quantified in three ways, namely as 1) maximum mesiodistal and buccolingual diameters, 2) the 6 intercusp distances, and 3) the 12 angular cusp arrangements. There was no sex difference in the morphological expression of Carabelli's trait in this sample. Overall crown size and intercusp distances were significantly and progressively larger in molars with larger Carabelli's trait expressions. There are graded size responses between crown size (mesiodistal and buccolingual diameters), sizes of the four principal cusps, and morphological stage of Carabelli's complex, though the statistical relationships are appreciably stronger in males than females. Carabelli's trait occurs preferentially in larger molars. In contrast, angular (shape) relationships among cusp tips are not discernibly affected by trait size in either sex. There is the situation, then, that Carabelli's trait is developmentally correlated with crown size, but with no apparent alteration of cusp arrangements, suggesting that the increases are isometric across the occlusal table. Why the association is much weaker in females remains speculative, but these data provide yet another line of evidence that, within a population, tooth size is associated in a positive fashion with crown complexity.

Dental Enamel↗
PubMed2004

Modulation of activin/bone morphogenetic protein signaling by follistatin is required for the morphogenesis of mouse molar teeth.

Teeth form as ectodermal appendages, and their morphogenesis is regulated by conserved signaling pathways. The shape of the tooth crown results from growth and folding of inner dental epithelium, and the cusp patterning is regulated by transient signaling centers, the enamel knots. Several signal proteins in the transforming growth factor-beta (TGF beta) superfamily are required for tooth development. Follistatin is an extracellular inhibitor of TGF beta signaling. To investigate the roles of follistatin during tooth development, we analyzed in detail the expression patterns of follistatin, activin beta A, as well as Bmp2, Bmp4, and Bmp7 during tooth morphogenesis. We also examined the tooth phenotypes of follistatin knockout mice and of transgenic mice overexpressing follistatin in the epithelium under the keratin 14 (K14) promoter. The folding of the dental epithelium was aberrant in the molars of follistatin knockout mice, and the cusps were shallow with reduced cell proliferation and lack of anteroposterior polarization. The functions of both primary and secondary enamel knots were apparently disturbed. In K14-follistatin transgenic mice, the molar cusp pattern was also seriously affected (although different from the follistatin knockouts) and the occlusal surfaces of the molars were whorled. Their enamel was prematurely worn. In addition, all of the third molars were missing. Our results indicate that follistatin regulates morphogenesis and shaping of the tooth crown. We propose that finely tuned antagonistic effects between follistatin and TGF beta superfamily signals are critical for enamel knot formation and function, as well as for patterning of tooth cusps.

Activins↗
PubMed2006

The effect of fiber insertion on fracture resistance of endodontically treated molars with MOD cavity and reattached fractured lingual cusps.

In this study, the effect of flowable composite reinforced with a leno wave ultra high modulus (LWUHM) polyethylene fiber (Ribbond) on fracture resistance of endodontically treated molars with MOD cavity and lingual cuspal fracture was evaluated. Sixty sound extracted human mandibular molars were randomly assigned to six groups (n = 10). Group 1 served as control. Teeth in groups 2-6 received root canal treatment and a MOD cavity preparation. Teeth in group 2 were kept unrestored. Lingual walls of specimens in groups 3-6 were fractured at the CEJ and reattached (C&B Super-Bond). Group 3 was kept unrestored, and group 4 was restored with a composite resin (CR) (AP-X). In group 5, a flowable resin (FR, Protect Liner F) and in group 6, a Ribbond in combination with FR were inserted inside the cavity before CR restoration. After finishing and polishing, the specimens were subjected to compressive loading perpendicular to the occlusal surface at a crosshead speed of 1 mm/min. The mean load necessary to fracture were recorded in Newton and the results were statistically analyzed. MOD cavity preparation reduced fracture resistance of endodontically treated teeth (p < 0.05). Fracture resistance of rebonded fractured specimens was found to be similar to that of the nonfractured samples (p > 0.05). Use of LWUHM polyethylene fiber Ribbond increased fracture strength of endodontically treated molar teeth with MOD cavity preparation and cuspal fracture (p < 0.05). As a result, it was concluded that the insertion of Ribbond inside the cavity has a positive effect on fracture strength of endodontically treated molar teeth with MOD cavity preparation and cuspal fracture.

Dental Materials↗
PubMed1995

Maxillary molar extraction causes increased bone loss in the mandible of ovariectomized rats.

Although osteoporosis is a major public health concern, its effect on oral bone has not been determined. More important may be the effect of estrogen depletion on the response of oral bone to dental treatments such as tooth extraction or pathologic processes such as periodontal disease. Our objective was to determine if maxillary molar extraction increases mandibular bone loss in the ovariectomized compared with a sham-operated control. Fifty-three ovariectomized and 53 sham-operated 6-month-old Sprague-Dawley rats were randomly assigned to the following groups: (1) ovariectomized, adult; (2) sham-operated, adult; (3) ovariectomized, adult, extraction; (4) sham-operated, adult, extraction; (5) ovariectomized, old; (6) sham-operated, old; (7) ovariectomized, old, extraction; and (8) sham-operated, old, extraction. Fourteen days following ovariectomy, the extraction groups had their bilateral maxillary molars extracted. The adult and old rats were sacrificed 114 and 200 days postovariectomy, respectively. The right mandible was tested to failure in three point bending. The bone mineral density (BMD) of the left mandible was measured with high resolution dual energy X-ray absorptiometry. The area fraction and area moment of inertia of mandible sections were determined using image processing software. In the ovariectomized rats, maxillary molar extraction resulted in decreases (p < 0.05) in the failure load (21%), stiffness (39%), BMD (3%), and bone area fraction (8%) of the mandible. However, in the sham-operated rats, these decreases following maxillary molar extraction were less (p < 0.05) than those in the ovariectomized rats and only present in the mandibles of the aged rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1997

Effect of intermittent long-lasting electrical tooth stimulation on pulpal blood flow and immunocompetent cells: a hemodynamic and immunohistochemical study in young rat molars.

Release of sensory neuropeptides after stimulation of afferent nerve fibers has previously been shown to induce vasodilation and increased vascular permeability in the dental pulp, a condition recognized as neurogenic inflammation. In the present study a possible role for the sensory neuropeptides in transendothelial migration of immunocompetent cells was investigated. The dental pulp is an isolated tissue densely innervated with sensory fibers containing neuropeptides, and following electrical stimulation of the crown, the effect on pulpal blood flow and immunocompetent cells can be studied in a noninvasive model. A laser Doppler flowmeter was used to measure relative changes in pulpal blood flow during long-lasting intermittent stimulation of innervated and denervated rat first molars. In the innervated teeth, stimulation promptly increased pulpal blood flow by on average 45% at the start of the experiment, whereas almost no blood flow increase was recorded after 4 to 5 h stimulation. Surgical sectioning of the inferior alveolar nerve abolished blood flow increase upon stimulation. After stimulation, a quantitative analysis of CD43+, CD4+, CD11+, and I-A antigen-expressing cells was performed, and the effect of stimulation on calcitonin gene-related peptide (CGRP)-immunoreactive and substance P (SP)-immunoreactive (IR) nerve fibers was studied. Immunohistochemistry was performed by the avidin-biotin peroxidase method. Stimulation resulted in an almost complete depletion of CGRP- and SP-IR nerve fibers in the first molar pulp, whereas nerve fibers in the gingiva and neighboring teeth were unaffected. A significant increase in the number of CD43+ cells was found in the innervated tooth after stimulation compared to the stimulated denervated (P < 0.01) and unstimulated control (P < 0.05) first molars. For I-A antigen-expressing cells a significant increase (P < 0.05) was found between the innervated stimulated and unstimulated control, but not between the innervated and denervated stimulated first molars. Hence, from the present experiment it is concluded that the pulpal nerves participate in and facilitate transendothelial migration of CD43+ cells during acute neurogenic inflammation.

Afferent Pathways↗
PubMed1992

Effect of traumatic occlusion on CGRP and SP immunoreactive nerve fibre morphology in rat molar pulp and periodontium.

Traumatic occlusion provides a trauma that affects the whole tooth and its supporting tissues. To study the effect of this trauma on CGRP and SP immunoreactive nerve morphology in pulp and periodontium, traumatic occlusion was induced in 2-months-old rats. The occlusal surface of the first maxillary molar in 30 rats were unilaterally raised 1 mm with a composite material. At different observation periods up to 30 days, the rats were transcardiacally perfused, the jaws demineralized, sectioned and processed for immunohistochemistry with the avidin-biotin-peroxidase method. Changes in nerve morphology, distribution and density in first and second molars and their supporting tissues were analyzed and compared in experimental (n = 30) and control rats (n = 14). Already after 5 days with traumatic occlusion, 22% of the experimental teeth had increased density of CGRP and SP immunoreactive nerves locally in gingiva, the periodontal ligament and the pulp, while in 15%, axonal proliferation and changed nerve morphology were found in the whole pulp (severe reaction). During a 20-day period, the pulpal nerve reactions progressed and included the whole pulp in 46% of the experimental teeth. The periodontal nerve responses were still localized only to the cervical and apical regions, and they remained local in these areas throughout the experimental periods. After 20 days the number of teeth with severe nerve changes seemed to decrease. The study shows that an unilateral change in occlusion of the first molar initiate nerve responses in the total molar dentition. In this experimental model the pulpal axons containing CGRP and SP reacted more serious to occlusal trauma than the nerves in the periodontium. The results indicate that the nerve changes in some cases might be transient.

Animals↗
PubMed1991

[Tooth germ transplantation or gap closure--a comparative study in the loss of the first molar].

In our study 37 transplanted and 33 mesialized molars by orthodontics were clinically and radiologically compared. The teeth moved by orthodontics showed a better long-term prognosis. As vital teeth with functioning periodontal structures and only slightly shortened roots they were equivalent to healthy teeth. However, the disadvantage of orthodontic space closure is the requirement of a good compliance due to long treatment time. The prognosis of maintaining a transplanted tooth germ is uncertain. One third of the teeth showed an altered periodontium with resorption areas. The danger of a continuing resorption, as well as a late external resorption is still a risk after a long period of time and can eventually lead to tooth loss. As a treatment alternative, germ transplantation may serve as a replacement of a single missing 6-year-molar in adolescence. Orthodontic space closure is indicated at any age with an existing dysgnathia, the loss of several first molars, the loss of space and mesial tipping of the second molars.

Adolescent↗
PubMed1995

[The effect of molar position on the distalization behavior of indirect headgear].

The asymmetric indirect headgear is a frequently used method to achieve an unilateral distalization of a molar. Cases have been observed, however, in which the distalization does not proceed in the way or to the degree predicated by the geometry of the outer bow. Among other factors, this discrepancy can be attributed to the geometry of the inner bow. This study demonstrates quantitatively and qualitatively the influence unilateral mesial movement and/or molar rotation exerts on the force system of the indirect headgear. The study makes evident that a neutralization of the molar's sagittal asymmetrical position by means of adjusting the length of the inner bow cannot be omitted. The study recommends the use of special headgear tubes extended in an oro-vestibular direction to eliminate the asymmetrical dynamics which arise in cause of the mesial rotation of a molar.

Biomechanical Phenomena↗