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PubMed2004

The eternal tooth germ is formed at the apical end of continuously growing teeth.

Rodent incisors are known to be continuously growing teeth that are maintained by both the cell-proliferation at the apical end and the attrition of the incisal edge. This type of tooth had a special epithelial structure for the maintenance of stem cells, showing the bulbous epithelial protrusion at the apical end. The morphological transition of the epithelial-mesenchymal compartment by serial transverse sections of the apical end toward the incisal direction is likely to reflect the development of the tooth germ in the prenatal stage. Based on the present histological and previous molecular biological studies, the special structure at the apical end is obviously different from the cervical loop giving rise to Hertwig's epithelial root sheath (HERS), in human, mouse and rat molar tooth germs. Hence, we propose a new concept that the eternal tooth bud producing various dental progeny is formed at the apical end of continuously growing teeth, and a new term "apical bud" for indicating this specialized epithelial structure. Furthermore, BrdU labelling analysis suggested that the guinea-pig molars, which were continuously growing teeth, also possessed plural specific proliferative regions and "apical bud" at the apical end.

Animals↗

PubMed2004

Tooth size in patients with supernumerary teeth and a control group measured by image analysis system.

OBJECTIVE: The aim of this study was to compare tooth size measurements between patients with supernumerary teeth and a control group. METHOD: The supernumerary group consisted of 56 subjects (21 females and 35 males) and the control group of 40 subjects (20 females and 20 males). All available permanent teeth on the dental casts were imaged and measured from both buccal and occlusal views using an image analysis system. Mesio-distal, bucco-lingual or occluso-gingival dimensions, area and perimeter were measured from each view. RESULTS: Supernumerary tooth patients tended to have larger tooth size measurements for almost all variables than controls. Significant differences (p<0.05) were found for the mesio-distal dimension of the upper and lower incisors and the bucco-lingual dimensions of the lower first premolars. CONCLUSIONS: The results are compatible with supernumerary teeth being a complex dental anomaly with a multifactorial aetiology in which both genetic and environmental factors are important. There is some evidence of a local effect with greater differences in tooth dimension adjacent to the site of the supernumeraries.

Adolescent↗

PubMed2004

Single tooth immediate provisional restoration of dental implants: technique and early results.

PURPOSE: Patients desire efficient restoration of missing teeth. Immediate provisionalization of implants at the time of placement can provide the patient with a tooth-like restoration. Our hypothesis is that preoperative fabrication of the implant abutment and provisional restoration can provide successful immediate provisionalization of implants, if specific diagnostic criteria are used for patient selection. PATIENTS AND METHODS: This hypothesis is evaluated by prospectively following 74 implants thus treated for 6 months to 2 years. A technique is presented to illustrate a simple and reliable method to provisionally restore a single tooth restoration. The method involves preoperative placement of an implant analog into a model, preparation of the abutment on the model, and fabrication of a provisional crown out of occlusion. At the time of surgery, the implant is placed according to the prescription of the restorative dentist, the surgeon places the abutment and provisional crown, and the final restoration is fabricated after the implant integrates. RESULTS: Seventy of 74 (94.6%) restorations have been successful with up to 2-year follow-up, which is similar to single tooth implants treated using a 2-stage protocol. CONCLUSIONS: Single tooth immediate provisionalization implants are effective techniques when specific diagnostic criteria are used.

Alveolar Process↗

PubMed2004

Intrusion and reversal of a free-standing natural tooth bounded by two implant-supported prostheses: a clinical report.

Although intrusion of natural tooth abutments in tooth-implant connected fixed prostheses has been reported, it can also occur to a free-standing natural tooth bounded by implant prostheses. For the patient described in this article, intrusion was noted with a natural tooth bounded by 2 implant-supported prostheses 5 months after insertion of the prostheses. The intrusion was reversed completely after 5 months with appropriate management. The course of treatment and possible mechanisms of intrusion are provided.

Bicuspid↗

PubMed2003

Tooth and jaw: molecular mechanisms of patterning in the first branchial arch.

The mammalian jaw apparatus is ultimately derived from the first branchial arch derivatives, the maxillary and mandibular processes, and composed of a highly specialised group of structures. Principle amongst these are the skeletal components of the mandible and maxilla and the teeth of the mature dentition. Integral to the development of these structures are signalling interactions between the stomodeal ectoderm and underlying neural crest-derived ectomesenchymal cells that populate this region. Recent evidence suggests that in the early mouse embryo, regionally restricted expression of homeobox-containing genes, such as members of the Dlx, Lhx and Gsc classes, are responsible for generating early polarity in the first branchial arch and establishing the molecular foundations for patterning of the skeletal elements. Teeth also develop on the first branchial arch and are derived from both ectoderm and the underlying ectomesenchyme. Reciprocal signalling interactions between these cell populations also control the odontogenic developmental programme, from early patterning of the future dental axis to the initiation of tooth development at specific sites within the ectoderm. In particular, members of the Fibroblast growth factor (Fgf), Bmp, Hedgehog and Wnt families of signalling molecules induce regionally restricted expression of downstream target genes in the odontogenic ectomesenchyme. Finally, the processes of morphogenesis and cellular differentiation ultimately generate a tooth of specific class. Many of the same genetic interactions that are involved in early tooth development mediate these effects through the activity of localised signalling centres within the developing tooth germ.

Animals↗

PubMed1995

Brånemark single tooth implants: a preliminary report of 76 implants.

Seventy-six Brånemark single-tooth implants were inserted over a 6-year period. Two implants (2.63%) were removed during the follow-up period. All other implants received esthetic and functional single tooth crowns placed on a single tooth abutment or a CeraOne abutment. The most common complication observed was abutment screw loosening, which occurred with 12 crowns. However, it was possible to clearly reduce the occurrence of screw loosening by applying a defined torque. Peri-implant parameters were investigated on 56 implants that were in place for more than 1 year. Acceptable implant function was demonstrated with preestablished clinical parameters and radiographs. Despite the submucosal edge of the crown, peri-implant mucositis was not a major problem. The favorable clinical and esthetic results found in the study encourage an increased application of implants for single tooth restorations.

Adolescent↗

PubMed1995

Mechanical considerations for the implant tooth-supported fixed partial denture.

The implant tooth-supported fixed partial denture presents a biomechanical design problem, because the implant is rigidly fixed within the alveolus, and the tooth is surrounded by a periodontal ligament that allows movement. Nonrigid fixed partial denture designs are advocated by some dentists as a method of compensating for this differential movement. Rigid fixed partial denture designs, however, are advocated by many clinicians. Studies have failed to show the advantage of one design over the other. This study developed an in vitro method for testing such prosthesis designs and measured movement of a natural tooth abutment during simulated function. The movement of the natural tooth abutment was not found to change substantially with the fixed partial denture designs tested.

Alveolar Process↗

PubMed1997

Theoretical study of the effects of tooth and implant mobility differences on occlusal force transmission in tooth/implant-supported partial prostheses.

STATEMENT OF PROBLEM: Despite their mobility differences under occlusal loads, a natural tooth and an implant are often used together to support fixed prostheses. In some situations, tooth/implant-supported partial prostheses include cantilever extensions, especially in the posterior region where the bone is inadequate for placement of an additional implant. PURPOSE: In this study, engineering beam theory was used to study the effects of the mobility differences between the implant and the tooth on the force and moment distribution, due to occlusal loads in tooth/implant-supported prostheses. METHODS: The prosthesis was treated as a linear elastic beam and the supports were modeled as springs with (vertical) translational and rotational stiffness. The bending moments and forces on the supports were calculated as functions of the parameters that describe the geometry, position of the occlusal load, and stiffness ratios (namely, implant or tooth) of the springs. RESULTS: Bending moments on the supports were more sensitive to the relative rotational mobility between the supports and their individual values than to the relative translational mobility. The moment at the implant was minimized when the supports had similar mobilities. A preliminary design concept was introduced and eliminated the moment at the implant without significantly increasing the magnitude of the moment at the tooth. Cantilevering the prosthesis resulted in moderately increased bending moments and considerable tensile forces on the supports for a broad range of the parameters that describe the geometry and loading. CONCLUSIONS: From this simulation, it is suggested that cantilever extensions should be avoided or supported by a short implant, which will only restrain the vertical movement of the cantilever end.

Algorithms↗

PubMed2003

Ultrastructure of developing tooth plates in the Australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi).

While the lungfish dentition is partially understood as far as morphology and light microscopic structure is concerned, the ultrastructure is not. Each tooth plate is associated with a dental lamina that develops from the inner layer of endodermal cells that form the oral epithelium. Dentines, bone and cartilage of the jaws differentiate from mesenchyme cells aggregating beneath the oral endothelium. Enamel, in the developing and in the mature form, has similarities to that of other early vertebrates, but unusual characters appear as development proceeds. Ameloblasts are capable of secreting enamel, and, with mononuclear osteoclasts, of remodelling the bone below the tooth plate. The forms of dentine, all based largely on an extracellular matrix of collagen and mineralised with biological apatite, differ from each other and from the underlying bone in the ultrastructure of associated cells and in the mineralised extracellular matrices produced. Cell processes emerging from the odontoblasts and from the osteoblasts vary in length, degree of branching and of anastomoses between the processes, although all of the cell types have large amounts of rough endoplasmic reticulum. Mineralisation of the extracellular matrices varies among the enamel, dentines and bone in the tooth plate. In addition, the development of the hard tissues of the tooth plates indicates that many of the similarities in fine structure of the dentition in lungfish, to tissues in other fish and amphibia, apparent early in development, disappear as the dentition matures.

Animals↗

PubMed2000

Initial extractions and tooth loss during supportive care in a periodontal population seeking comprehensive care.

BACKGROUND/AIMS: This retrospective survey was aimed at determining the prevalence of tooth extractions and the dental pathologies associated with them during both the active and maintenance phase of periodontal therapy in a periodontal population seeking comprehensive dental care. METHODS: A total of 273 randomly selected subjects from the oral prophylaxis clinic of the University of Berne were included. All subjects had received comprehensive care consisting of periodontal and restorative treatment and participated in a supervised maintenance program for an average of 67+/-46 months (range 5 to 278 months). The population consisted of 39.6% current smokers and 27.8% previous smokers. 6.2% of the patients had gingivitis, 20.5% mild periodontitis, 48.4% moderate and 24.9% severe periodontitis. The average frequency of the recall visits was 4.4+/-1.5 appointments/year (range 1.7-12 appointments/year). RESULTS: Results indicated that 574 out of a total of 6503 teeth were extracted; 311 teeth were extracted during active therapy and 263 during the supportive periodontal care (SPC) phase of therapy. 46% of patients received tooth extractions as part of their active treatment and 41% during their participation in the secondary prevention program. In the subgroup whose treatment plan included extractions the average number was 2.5+/-1.6 teeth per patient. Likewise, the patients who received extractions during recall lost an average of 2.35+/-1.9 teeth per subject with an incidence of 0.4+/-0.37 teeth per patient per year. These data reinforce the concept that a minority of the population is responsible for the majority of tooth extractions, both during active therapy and SPC. Periodontal disease was the only pathology observed at 57% of the extracted teeth; while caries, endodontic pathology and technical problems in the absence of periodontitis were observed in 29% of cases. CONCLUSIONS: These observations indicate that the rendered treatment was effective in the long-term maintenance of the dentition of these subjects and suggest that advanced periodontal disease represented the major cause of tooth loss in this population.

Adolescent↗

PubMed2003

Incidence and predictors of self-reported tooth loss in a representative sample of Norwegian adults.

OBJECTIVES: The purpose of this study was to determine the self-reported 12-month incidence of tooth loss among Norwegian adults and to assess the association between tooth loss and some predictor variables. METHODS: Of a two-stage nation-wide, representative random sample (n = 3958), information was obtained from 2682 subjects aged 20-79 years and the response rate was 68%. Telephone or face-to-face interviews by interviewers employed by the Central Bureau of Statistics (CBS) of Norway. Information was collected about demographic characteristics, the number of natural teeth present, the number of teeth lost during the last 12 months, and belief in keeping natural teeth for life. The present analyses are based on 2520 persons 20-79 years of age. RESULTS: The proportion of respondents who reported losing one or more teeth was 6.45% (95% confidence limits (CL) = 5.49, 7.41). The participants who reported extractions had lost on average 1.54 (range 1-9) teeth. Multiple logistic regression analysis revealed a borderline significant effect of the level of education (OR = 0.68, 95% CL = 0.46, 1.00), i.e. the odds of losing one or more teeth during the last 12 months were lower among persons with more than 12 years of education than among persons with less education. The explained variance was 1.9%. CONCLUSION: The annual incidence rate of tooth loss among Norwegian adults was found to lie within the range reported from other industrialized countries. After controlling for socio-demographic variables and the number of teeth present, the only borderline significant predictor of the incidence of tooth loss was the level of education.

Adult↗

PubMed2002

Clinico-pathological aspects of a residual natal tooth: a case report.

A Japanese girl was referred to Osaka University Dental Hospital for examination of a tooth-like structure that had erupted following spontaneous exfoliation of a natal tooth in the lower left primary central incisor region. The structure had erupted at 6 months of age, and radiographic and clinical examination showed composition of pulp and dentin, but no enamel. On histological examination, the majority of the dentin area had a tubular dentin-like appearance, while the outer area of the root appeared to be composed of an osteodentin-like substance. Most of the dentin was covered by cementum. These findings suggest that the structure had originated from a developing remnant of the extracted natal tooth, which must have remained in the gingival tissues. We termed this calcified structure a residual natal tooth.

Anodontia↗

PubMed2003

Calcification of degenerating tissues in the periodontal ligament during tooth movement.

OBJECTIVE: Calcification of degenerating tissues in the periodontal ligament (PDL) during tooth movement was investigated longitudinally. MATERIALS AND METHODS: Upper first molars of male Wistar rats were moved lingually for 1, 7 and 21 d, following which unfixed undecalcified sections of the lingual PDL (in the pressure zone) were examined histologically, histochemically (autoradiography and electron probe microanalysis). RESULTS: On d 1 of tooth movement, degenerating tissues, together with some calcified particles, were visible in the pressure zone of the lingual PDL. On d 7, substantial calcified aggregations were seen in the degenerating tissues, predominantly situated between the bone and root. This was confirmed by the 45Ca autoradiography. On d 21 of tooth movement, large calcified aggregations were still clearly evident between the bone and root. CONCLUSIONS: This calcification of the degenerating tissues is a self-defense response of the living body to prevent direct contact between alveolar bone and the tooth root during compression of the PDL, so preventing friction between them and the development of ankylosis.

Alveolar Process↗

PubMed1997

The effect of acetaminophen on tooth movement in rabbits.

Orthodontic patients have reported the use of analgesics during therapy. However, common anti-inflammatory analgesics, such as aspirin and ibuprofen, have been shown to slow the rate of tooth movement. Acetaminophen, another common analgesic, does not possess anti-inflammatory properties. The effect of acetaminophen on tooth movement was studied using New Zealand white rabbits. Experimental animals were matched to a control animal of the same sex and weight. Under anesthesia, springs were ligated between the lower first molar and incisor, resulting in approximation of these teeth. Under blinded conditions, seven of the rabbits received 1000 mgs of acetaminophen daily. Seven control animals received water. The animals were sacrificed after 21 days. The movement of incisors and molars was measured. Results showed considerable movement within both the experimental and control groups, but no significant difference in tooth movement between them. Acetaminophen has no effect on the rate of tooth movement in rabbits undergoing orthodontic treatment.

Acetaminophen↗

PubMed2000

Impression pressures against teeth in a partially edentulous model with a mobile tooth: influence of impression tray design.

The purpose of the present study was to examine the effect of custom tray designs on local pressures against teeth during the impression procedure. In a previous study, a partially edentulous simulation model with a mobile tooth was used, and the effect of custom tray designs on the displacement of the mobile tooth was examined during the impression procedure. Based on that study's results, we have assumed that the differences in impression pressures between the labial and the lingual sides of a mobile tooth could either cause or affect displacement. The present study was undertaken to determine the local impression pressures against each side of three anterior teeth, including one mobile tooth, using the same simulation model and the same custom trays as in the previous study. It was found that the local pressures exerted against teeth during the impression procedure were affected by the custom tray designs and varied according to the coronal shape, axis inclination and location of the teeth.

Analysis of Variance↗

PubMed2001

Numerical investigation of the factors affecting interfacial stresses in an MOD restored tooth by auto-meshed finite element method.

Many researches have addressed the high correlation between the fracture of restored teeth and the prepared cavity geometry. In addition, concerns about bonding versus debonding dental materials from cavity walls and different occlusal force conditions could also alter the mechanical responses in a restored tooth. This study employed an automatic mesh procedure to investigate the mechanical interactions between different interfacial conditions and cavity parameters such as pulpal wall depth under different chewing functions. The results indicated that when occlusal force was applied directly on the tooth, it could increase unfavourable stress dramatically. When interfacial fixation was simulated as the contact condition between the tooth tissue and restorative material, it might increase the fracture potential exponentially compared with the bonded interface. For pulpal wall depth analyses, greater risks of fracture for the remaining tooth were observed in deeper cavity of mesio-occlusal-distal (MOD) restorations and the existence of a pulpal wall is essential even it is only 1 mm above the gingival wall.

Bite Force↗

PubMed1995

[Ultrasound diagnosis of fetal tooth anlagen and their histologic correlates].

AIM: The present study was to examine the radiographic and histologic correlation of the respective ultrasonographic findings. METHODS: Histologic examinations were performed in 12 fetuses who had died in utero between 16 and 34 weeks of gestation. The fetuses had been examined by intrauterine sonography for tooth germs and had been subjected to additional radiographic examinations post abortum or partum. During autopsy, the tooth germs were again examined sonographically and radiographically, and non-decalcified histological sections were obtained by means of the sawing and grinding technique. RESULTS: The results obtained by histologically examining the 12 fetal jaws in the ultrasonic plane corresponded in all cases to those examined by sonography and radiology. CONCLUSION: Sonographic proof of tooth germs might gain increasing importance in future because agenesia of tooth germs is one of the principal signs of a variety of hereditary syndromes, particularly those of ectodermal origin.

Ectodermal Dysplasia↗

PubMed2001

A mechanism of noncontinuous supraosseous tooth eruption.

Numerous theories have been propounded to explain the various aspects of tooth eruption, but no general consensus exists about some of the underlying mechanisms that govern these aspects. An important unresolved issue is the source of the motive forces that displace teeth. We proposed that supraosseous eruptive forces are generated by tooth socket distortions caused by functional jaw deformations. Previous studies used basic equations of static equilibrium to demonstrate that the concomitant stretching of the oblique periodontal ligament (PDL) fibers give rise to forces that may cause supraosseous tooth eruption. For a more rigorous and expanded analysis, we applied the finite element method (FEM). Three functional loads were considered, but the FEM calculations strongly suggested that all jaw deformations contribute to tooth extrusion. It was also demonstrated that the PDL fiber disruptions that are likely to occur with increased stretching can provide a mechanism to stabilize the erupted position.

Computer Simulation↗