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At least 775 records · Page 43Linked to original sources
PubMed2000

The long-term survival of lower second primary molars in subjects with agenesis of the premolars.

This study investigated 41 subjects, 13 male and 28 female, with agenesis of one or both lower second premolars, and with retained lower second primary molars. Intra-oral radiographs of 59 primary teeth were examined to judge the resorption of the mesial and distal roots, and were measured to record infra-occlusion of the primary teeth and tipping of the adjacent permanent teeth. The study commenced at 11-12 years of age. The mean age at the last measurement was 20 years 6 months (SD 3.62, range 13.6-31.8 years). During the observation period, only two of the 59 primary teeth were exfoliated. Five were extracted, two of which were replaced by upper third molar transplants. Beyond the age of 20 years no teeth were lost. Root resorption varied widely between individuals, but was slow. There was no typical pattern for development of infra-occlusion. Mean infra-occlusion was 0.47 mm (SD 1.13) at 11-12 years, increasing by less than 1.0 to 1.43 mm (SD 1.13) at age 17-18 years. At age 19-20 years, 55 per cent of teeth showed infra-occlusion between 0.5 and 4.5 mm, but 45 per cent showed no infra-occlusion. The space between the first molar and first premolar was a mean of 10.35 mm (SD 0.76) at age 10-12 years compared with the mean width of the second primary molar of 10.53 mm (SD 0.51). The space reduced by less than 0.5 mm to 9.95 mm (SD 1.50) at age 17-18 years. If primary molars are present at 20 years of age they appear to have a good prognosis for long-term survival.

Adolescent↗
PubMed1991

The influence of anatomical, pathophysiological and other factors on periodontal healing after impacted lower third molar surgery. A multiple regression analysis.

A multifactorial approach has been used to identify some predictors of postoperative intrabony defects (IBD) on the distal surface of the adjacent second molar (M2) after impacted lower third molar (M3) surgery. The material consisted of 215 lower third molar removals, performed on 144 persons (age range 16-53 years; mean 27.2 years). The postoperative examination took place 2 years after impaction surgery and included both clinical and radiographic variables. Statistically significant (5% significance level) predictors of IBD found in stepwise multiple regression analyses were: (1) preoperative intrabony defect M2 distal; (2) age at the time of surgery; (3) size of contact-area M3/M2; (4) root resorption M2 distal; (5) probing dept distal surface of adjacent first molar postoperatively; (6) pathological follicle M3. The regression model with IBD as regressand produced a total R2 of 0.45. When the regressand was the difference between IBD and the preoperative intrabony defect, the regression analysis explained 62% of the variance (R2 = 0.62). These regression models explained the variance in terms of the size of the remaining postoperative intrabony defect as well as in terms of periodontal healing after impacted lower third molar surgery.

Adolescent↗
PubMed1984

Further observations on lower third molar tilt.

The angulation of lower third molars on opposite sides of the jaw was compared on 50 orthopantographic radiographs of children who had mesial migration of lower first permanent molars on one side only following unilateral extraction of lower second deciduous molars. On 36 films the lower third molar was less tilted on the extraction side. Applying a paired t-test this difference is significant (p less than 0.001). The distance of mesial migration was estimated, and the findings are discussed in relation to the hypothesis that early mesial migration of posterior teeth reduces the tilt of lower third molars.

Adolescent↗
PubMed1991

Morphologic study of the maxillary molars. 1. External anatomy.

The authors studied the external anatomy, root curvature and degree of root fusion of 744 maxillary first, second and third molars. The root lengths and root curvatures were quite similar on the first and second molars with their lingual roots curving toward the buccal on 54.6% and 52.3% of them, respectively. Complete separation of all three roots was observed on 86.4% of the first molars, 75.9% of the second molars and on only 18.8% of the third molars.

Humans↗
PubMedDate not supplied

Disturbed eruption of the permanent lower second molar: treatment and results.

To facilitate treatment of impacted lower second molars, different modes of treatment were studied retrospectively and the results related to the inclination and the degree of impaction of the tooth. Seventy-seven referred patients were treated with one of three basic methods: denudation of the second molar, orthodontics, or extraction of a molar. The methods were often combined, with a total of seventeen treatment combinations applied. Of the 95 impacted teeth, 68 percent were treated successfully, 21 percent acceptably, and 11 percent unsuccessfully. Irrespective of the degree of retention, the treatment of mesioangular impaction was most successful. The partially retained molars in the distoangular and vertical positions were particularly resistant to treatment. No method was superior to the others. Denudation could suffice, but usually a molar had to be extracted because of crowding. Orthodontic treatment was sometimes necessary to obtain correct axial inclination.

Adolescent↗
PubMed1998

Anatomic characteristics of the furcation and root surfaces of molar teeth and their significance in the clinical management of marginal periodontitis.

Treatment of periodontitis which involves the furcation area of molar teeth has always been a challenge. Sixty extracted human molar teeth were used for an anatomic study to clarify the possible morphologic factors which may affect the diagnosis, prognosis, and clinical management of periodontally involved teeth. Teeth were embedded in methylmethacrylate and cut in 70 microm cross sections from the cementoenamel junction to the apex. Cervical enamel projection, root and root trunk lengths, root proximities as well as depths of root concavities coronally, apically, and at the furcation roof were measured. Cervical enamel projections were observed in 30% of the teeth examined. The shortest root trunk was found at the buccal aspect of mandibular first molars, permitting furcation involvement at early stages of periodontal disease. The most apically located furcation was found at the distal site of maxillary first molars. Furcation roofs showed severe concavities and complex cementum morphology. Teeth exhibiting cervical enamel projection were found to have deeper root concavities compared to teeth without cervical enamel projection and mesial roots of mandibular molars possessed greater furcal concavities than distal roots. The presence of root concavities complicates the diagnosis of furcation involvement and restricts access of periodontal instruments, resulting in incomplete treatment. Furcation anatomy may also influence the long-term prognosis of the teeth by favoring the retention of bacterial deposits and making oral hygiene procedures almost impossible. The present study shows that knowledge of a tooth's unique anatomic characteristics is a prerequisite for effective periodontal therapy.

Dental Enamel↗
PubMed2004

Molar size and shape variations among Asian colobines.

Despite decades of research, little is known about morphometric differences within the dentition of Asian colobines. Although some differences, such as the M3 hypoconulid, are often cited as distinct among genera, no comprehensive assessment has been made. The objectives of this study were to document size and shape differences in third molars in eight Asian colobine genera, including Kasi, Nasalis, Presbytis, Pygathrix, Rhinopithecus, Semnopithecus, Simias, and Trachypithecus, and to quantify length differences for all molars in order to understand the potential impact of an occlusal surface area that includes the hypoconulid. To achieve these objectives, the most extensive survey yet published of Asian colobine dentition was conducted. Differences within and among genera for continuous and categorical variables were analyzed using descriptive statistics, chi-square, t-tests, and post hoc comparisons. Results indicate that species of Presbytis differ from all other Asian colobines in both the size and shape of the maxillary and mandibular third molars. Specifically, M3 of Presbytis is relatively shorter in length and less likely to exhibit a hypoconulid optimally positioned for occlusion with M3. Moreover, Presbytis expresses concomitant changes in the maxillary third molar such as absence of a distal shelf and/or a distal cusp with separated crests. We conclude that shape and size changes impact the molar size sequence patterns of Presbytis, setting this genus apart from all other Asian colobine taxa. These differences may reflect variation in overall body size, dietary adaptation, and phylogeny.

Animals↗
PubMed1983

Molar size sequence in Australian Aboriginals.

Percentage frequencies for molar size sequence of first and second molars were calculated in a group of contemporary Australian Aboriginals using mesiodistal and buccolingual dimensions, as well as crown areas. Comparisons were made between sexes, arches, and dimensions within the Aboriginal group and also between Aboriginal data and those published for other populations. The frequencies of the M2 greater than M1 molar size sequence in the Aboriginals fell within the range of frequencies reported for other contemporary populations. Differences in the frequencies of the M2 greater than M1 sequence between the sexes and between arches, together with the relatively high frequency of asymmetry in molar size sequence within Aboriginals, supported the notion that local environmental conditions acting during odontogenesis, together with differential responses to other environmental influences, play an important role in determining observed patterns of molar tooth size.

Australia↗
PubMed1984

Patterns of molar wear in hunger-gatherers and agriculturalists.

Tooth wear records valuable information on diet and methods of food preparation in prehistoric populations or extinct species. In this study, samples of modern and prehistoric hunger-gatherers and agriculturalists are used to test the hypothesis that there are systematic differences in patterns of tooth wear related to major differences in subsistence and food preparation. Flatness of molar wear is compared for five groups in hunger-gatherers (N = 298) and five groups of early agriculturalists (N = 365). Hunger-gatherers are predicted to develop flatter molar wear due to the mastication of tough and fibrous foods, whereas agriculturalists should develop oblique molar wear due to an increase in the proportion of ground and prepared food in the diet. A method is presented for the quantitative measurement and analysis of flatness of molar wear. Comparisons of wear plane angle are made between teeth matched for the same stage of occlusal surface wear, thus standardizing all groups to the same rate of wear. Agriculturalists develop highly angled occlusal wear planes on the entire molar dentition. Their wear plane angles tend to exceed hunger-gatherers by about 10 degrees in advanced wear. Wear plane angles are similar within subsistence divisions despite regional differences in particular foods. This approach can be used to provide supporting evidence of change in human subsistence and to test dietary hypotheses in hominoid evolution.

Agriculture↗
PubMed1988

Contours of maxillary molars studied in Australian aboriginals.

Distances from the central pit to the perimeter of the crown of permanent upper molars were measured on standardized occlusal photographs of dental casts representing 210 male and 181 female Aboriginals from Yuendumu in the Northern Territory of Australia. In both males and females the first molar was the largest tooth but it showed least variability. Variabilities of the distances tended to be greater for radii constructed in the buccolingual direction than for the transverse mesiodistal radii. The most marked size reduction in the molar series from first to third related to the distolingual part of the crown, which was also the most variable region. Size differences between molars in the mesial contour radii were not marked. Sexual dimorphism was evident in most crown radii, being most marked for the second molar.

Australia↗
PubMed1989

Stereophotogrammetric analysis of occlusal morphology of extant hominoid molars: phenetics and function.

Because teeth are commonly preserved in the fossil record, dental remains have often been employed in estimating evolutionary relationships among fossil hominoids. This is appropriate, however, only to the extent that dental morphology is phylogenetically informative. I have used phenetic analytic techniques to assess whether hominoid molars are likely to be useful for phylogenetic inference. Thirty-four occlusal landmarks for first and second molars were chosen; seven on each maxillary and ten on each mandibular tooth. Three-dimensional locations of these points were determined from stereophotographs of dental arcades of more than 260 specimens from six taxa (gorilla, chimpanzee, human, orangutan, siamang, and gibbon). Analytic emphasis was on canonical variates analyses of landmark coordinates for mandibular and maxillary second molars, adjusted for intergroup size differences. There is little correspondence between the systematic implications of hominoid molar morphometrics and reliable estimates of evolutionary propinquity based on interhominoid biomolecular similarities. The former seem to have been determined largely by dietary constraints. Although this suggests the possibility of using the protocol employed here to infer diets of fossil hominoids, molar crown measurements seem unlikely to serve well as phylogenetic indicators in the Hominoidea.

Animals↗
PubMed1990

Expression of the entoconulid (sixth cusp) on mandibular molar teeth of an Australian aboriginal population.

The expression and genetic basis of the entoconulid (sixth cusp) on mandibular molars were examined in a geographically isolated group of aboriginals from Yuendumu in the Northern Territory of Australia. Four grades of trait expression, ranging from trace to small, medium, and large cusps, were defined on dental casts of 399 subjects. Frequencies of occurrence were among the highest reported in human populations. Approximately 80% of dm2s showed the trait, whereas frequencies in the permanent dentition ranged from around 50% on M2 to 70% on M1 and 80% on M3. The degree of expression increased distally along the molar series, with only 3% of dm2s showing large cusps compared with 25% of M3s. Fluctuating asymmetry was highest for M2 and lowest for dm2. No strong evidence for sexual dimorphism in occurrence or degree of expression was found. Based on a quasi-continuous threshold model, a genetic contribution to entoconulid variability was observed that was strongest for M1. Significant associations were noted between entoconulid expression on mandibular molars and metaconule expression on maxillary molars, indicating that similar developmental mechanisms may influence these traits. The entoconulid and the metaconule both provide additional bulk on the distal occlusal surface of molar teeth, an area subjected to early wear during mastication in aboriginals.

Female↗
PubMed1993

Brief communication: possible third molar impactions in the hominid fossil record.

Impacted third molars affect 15%-20% of modern Americans and Western Europeans. In contrast, third molar impactions have not been reported in the early hominid fossil record. It is uncertain whether the lack of reports reflects an absence of impactions or a failure to recognize them. This communication is intended to raise awareness of the possibility of impactions by describing the appearance of impacted teeth and by noting two possible instances of impaction in early hominids. Specifically, the mandibular third molars of the Sterkfontein specimen, STS52b (Australopithecus africanus), and the left maxillary third molar of the Lake Turkana specimen, KNM-WT 17400 (Australopithecus boisei), are positioned in a manner which suggests that they would not have erupted normally. Both specimens also exhibit strong crowding of the anterior dentition, providing further support for the view that these individuals lacked sufficient space for normal eruption of the third molars. Other published reports of dental crowding in the hominid fossil record are noted, and it is suggested that more attention be paid to dental impaction and dental crowding in hominid evolution.

Animals↗
PubMed1989

A method for sampling the stages of amelogenesis on mandibular rat incisors using the molars as a reference for dissection.

A method for locating specific stages of amelogenesis on continuously erupting incisors was devised for rats weighing 101 +/- 5 g (n = 32). The technique is based on reflecting reference lines from the mandibular molars as perpendiculars to the labial surface of mandibular incisors. From these reference lines additional measurements are then made along the midline of the labial surface of the incisor in an apical or incisal direction to find the site desired for sampling. Histological studies on 24 decalcified incisors split into segments by using such reference lines and reconstructed by morphometry indicated that a reference line reflected from the contact point between the 2nd and 3rd molars crossed the enamel organ and adjacent enamel at 3,181 +/- 329 microns incisal to the start of the secretory zone of amelogenesis. A reference line from the 2nd and 1st molars crossed the enamel organ and enamel at 1,238 +/- 424 microns incisal to the start of the maturation zone of amelogenesis, while a reference line from the mesial side of the 1st molar crossed the enamel organ and enamel almost exactly where the enamel becomes completely soluble following prolonged decalcification in EDTA. Although reference lines were reproducible within a group of male rats having similar body weights, the linear distance between the apical end of the incisor and the point at which they crossed the tooth increased at a rate of 1 mm per 159 g for rats between 50 and 300 g body weight. This suggests that molars do not maintain a fixed relationship to incisors over time, and extreme care must be taken to standardize an experiment to a specific body weight when using this method.

Amelogenesis↗
PubMed1993

Expression of the neural cell adhesion molecule (NCAM) during second- and third-molar development in the mouse.

Distribution of the neural cell adhesion molecule (NCAM) during the development of the mandibular second- and third-molars of the mouse was studied by indirect immunofluorescence techniques. At the initial stage, NCAM was intensely expressed by the mesenchymal cells surrounding the dental lamina, and by the cap stage NCAM expression by the mesenchymal cells became restricted to the dental follicle. After that, in addition to the follicular mesenchyme, some cells in the basal part of the dental papilla showed NCAM-immunoreactivity for a while after the hard tissue formation had started. During root formation, the follicular cells lost NCAM first from the level of the cervical root and later from the coronal part, while an additional NCAM positive area appeared deep in the dental papilla. Even after the teeth had erupted, NCAM was expressed in the tissue surrounding the apical root and in the pulp core. During the initial and bud stages, the pattern of NCAM expression in the second and third molars was different from that in the first molar, where NCAM was found only after the late bud stage; while from the cap stage onward, it changed in the same sequence as in the first molar. The different pattern of NCAM expression implies that there is a difference in developmental events between the early stages of the first and the other two molars. On the other hand, the common sequence of NCAM expression in the tooth germs later than the cap stage suggests that NCAM plays an essential role in the formation of the basic structure of the teeth and periodontal tissues.

Animals↗
PubMed1994

[Headgear-free molar distalization].

The difficulty in treating dentoalveolar class II disharmonies is briefly outlined. An innovative treatment method is presented which makes possible a distalization without the use of headgear. In the treatment method bands are cemented on the first molars, next impressions are made of the upper and lower dental arch, and then the impressions are poured with plaster. Following this the models are mounted in centric relationship in an articulator and the bite is opened 2 mm to 3 mm, so that the molars can be moved without making occlusal contact. The apparatus, an acrylic splint, is constructed in such a fashion as to cover the palatal surfaces from 2nd premolar to 2nd premolar. In addition, the premolars are also covered occlusally and buccally and the canine tips and the incisal edges are covered labially. A headgear tube is attached at the buccal surface in the premolar region of the acrylic splint. This acrylic splint, which is itself retentive, is cemented using glass ionomer cement. Combining this apparatus with a modified Nance Button makes it possible to establish an anchoring segment which is able to retain its position in the face of molar distalization. Molar distalization is then performed using a 0.032 inch stainless steel wire, which is placed between the headgear tube of the acrylic splint and the headgear tube of the band of the first molar. Highly elastic nickel-titanium open coil springs are used as the force elements.

Acrylates↗
PubMed1986

A new culture method assuring the three-dimensional development of the mouse embryonic molar tooth in vitro.

Mandibular first molars from 17-day-old mouse embryos were cultivated in vitro for 10 days using a new organ culture method. This method consisted of using a small glass dish and an agar chamber to slowly float the molars to the gas-medium interface where they were maintained by the surface tension of the medium. The molars developed three-dimensionally through the use of this method. Five cusps with refractile dental matrix were recognized from the occlusal side. It was easy to determine antero-posterior and bucco-lingual orientation of the molars. Thick sections of the bucco-lingual plane showed the normal cytodifferentiation of ameloblasts and odontoblasts. The thick enamel layer was formed to the extent of the fissure region between cusps. Furthermore, a great quantity of stippled material accumulated between the enamel and the ameloblasts. The stippled material displayed a meshlike fibrilar structure, and at the mineralization front, it seemed that the fibrils of stippled material adjacent to the enamel had been transformed into needlelike enamel crystals. In addition, bundles of the fibrils similar to enamel crystals were found in the stippled material. As the floatation method resulted in the three-dimensional development of the molars and the development of the enamel without the presence of histological disturbances, it was considered superior to other culture methods for the facilitation of orientation and the development of cusps.

Animals↗
PubMed2004

Cephalometric changes following simultaneous first and second maxillary molar distalization using a non-compliance intraoral appliance.

AIM: The aim of this prospective study was to evaluate the dentoalveolar, skeletal and soft tissue changes induced by a modified minimal-compliance intraoral appliance following the simultaneous distalization of first and second maxillary molars. SUBJECTS AND METHODS: The study sample consisted of 14 patients with a mean age of 13.4 years treated by one clinician. In all cases a bilateral Class II molar relationship was corrected to Class I in a mean treatment period of 16.5 weeks. Lateral cephalometric analysis of the sample was based on the radiographs taken before and immediately after treatment with the appliance. The mean maxillary first molar distal movement was 1.4 mm, accompanied by a mean distal tipping of 6.8 degrees. The vertical change in molar position was insignificant. The anchorage unit was unable to completely resist the reciprocal mesial force of the activated coil spring. The second premolars were moved mesially by a mean 2.6 mm and tipped by a mean 4.1 degrees without significant extrusion. The mean increase in overjet was 0.9 mm, and the mean decrease in overbite 1.0 mm. RESULTS: The results of this study have shown that the presented intraoral appliance is an effective and reliable means of distalizing first and second maxillary molars simultaneously without the need for patient compliance. Appliance effects are limited primarily to the dentoalveolar structures. Mesial movement and slight protrusion of the anchorage unit have to be taken seriously into consideration during intraoral distalization.

Activator Appliances↗