Location of implants in the interforaminal region of the mandible and the consequences for the design of the superstructure

The location and the number of implants to support an overdenture is of major importance for the superstructure design. Sometimes, jaw bone anatomy or posteriorly placed implants enforce the use of an angular bar to achieve a position above the alveolar ridge. Loads on such a bar may introduce a moment on the implants which can result in high bone stresses and eventually the loss of the implants.
This study on stress distribution in the bone around the implants in an edentulous mandible was performed using a three-dimensional finite element model. One model with two implants placed just anteriorly of the mental foramen and connected with an anteriorly placed bar, following the curvature of the alveolar ridge, was compared with two other designs. First with a similar model but now without a bar and secondly with a model with four implants connected with straight bars.
It is concluded that loading a bar, which is placed anteriorly of the interconnecting line between two implants, causes extremely large compressive and tensile stress concentrations in the bone around the implants. Therefore, in those cases, it is advised not to connect the implants or, in case a bar-clip attachment is preferred, to place additional implants in the frontal region.     

A review of the intraosseous course of the nerves of the mandible.

A review of the literature revealed that a common feature of all human mandibles is a large nerve (inferior alveolar nerve, IAN) between the mandibular and mental foramina. This nerve sends branches directly to the teeth or contributes a variable number of branches to a plexus of nerves which does the same. The plexus originates from a separate nerve that enters the mandibular foramen. The nerve plexus has been demonstrated by dissections and not by radiology. The buccal-lingual and superior-inferior positions of the IAN were not consistent among mandibles. The intramandibular IAN frequently ran a concave curve with a posterior segment descending as it progressed anteriorly and an anterior segment that ascended to the mental foramen. A bony canal was not always observed between the mandibular and mental foramina. The canal frequently lacked definite walls, especially near the mental foramen. Bilateral symmetry (location of the canal in each half of the mandible) was common, whereas duplications of the canal were rare. Nutrient canals and other branches of the mandibular nerve have been observed within the mandible. These may have been confused for the IAN or may contribute to the plexus of nerves.     

The significance of maintaining the stability of the natural microflora of the mouth

The mouth, like other areas of the digestive tract, possesses a natural microflora, the presence of which confers several beneficial properties to the host. However, in the absence of adequate oral hygiene, dental plaque can accumulate beyond levels compatible with oral health. This leads to shifts in the balance of the predominant bacteria away from those associated with health; such shifts can predispose a site to caries or periodontal diseases. Treatment should be designed, therefore, to control rather than to eliminate dental plaque. Possible strategies to maintain the stability and beneficial properties of the natural oral microflora include the stimulation of saliva flow for an extended period directly after a meal, the avoidance of fermentable carbohydrates during between-meal periods, and improvements to oral hygiene, for example, by using products containing antiplaque or antimicrobial agents.     

Clinical-experimental study on the temperature behaviour of the mucosa of mouth related to the season of the year

A long-term investigation of 20 juvenile patients indicated a great seasonal and interdiurnal variation of the gingival temperature, which had a trend to a high interindividual correlation. The absolute individual differences was upto 2 degrees C. The lower jaw had a higher temperature than the upper jaw. The temperature of the right and left sides of the jaw differed from each other. The calculation of a standard temperature is only useful, when it is related to the individual sublingual temperature.     

Deformation analysis of the periodontium considering the viscoelasticity of the periodontal ligament

ObjectivesThe aim of the present work was, by means of a combined experimental and numerical approach, to investigate the full-field distributions of displacement, stress and strain, and their evolution with loading in the entire fresh periodontium under an externally applied force.MethodsIn situ intrusion tests were performed to identify the nonlinear, viscoelastic behavior of the periodontal ligament (PDL) of a pig mandible; a digital image correlation method was applied to examine the full-field deformation patterns in the entire periodontium. The finite element (FE) model was created based on the actual anatomic profiles of individual constituents of the tooth structure; the nonlinear and time-dependent viscoelastic properties of the PDL were input into the FE model to fit the numerical computations with the experimental measurements.ResultsThe nonlinear, viscoelastic behavior of the PDL was identified and characterized quantitatively. The simulation results were validated by the experiments. The results showed the tilting of tooth and the movement of cervical bone toward the mid-tooth in the studied periodontium under vertical compressive loading. Major strain was concentrated in the PDL, with the maxima near to the tooth apexes, at the tooth-root bifurcation and also at the sides of the tooth roots, and maintained a slight rise during holding of the applied displacement. High stress in the tooth was located mainly at the sides of tooth roots, in the bone it was concentrated near the apexes and the root bifurcation, and these stresses decreased gradually during the holding period.SignificanceThe combined approach of experiments that apply the digital image correlation method and FE analyses that take into account the nonlinear and time-dependent viscoelasticity of the PDL enables the acquisition of a full picture of detailed, realistic stress/strain fields and deformation patterns of the entire fresh periodontium, being of essence in orthodontics and dentistry.     

Role of the psychologist in the treatment of bruxism

Although there is a controversy about the importance of psychological factors in the development, enhancement and perpetuation of bruxism and other parafunctional activities, the contribution of a psychologist in the treatment of the individual patient is recommended. This contribution consists of diagnostic examination and treatment, most often a short cognitive behavior modification therapy. Because bruxism is mostly examined and treated in relation to the complaints it might cause, especially CMD-complaints, diagnosis and treatment are mostly directed at both. For the diagnosis a questionnaire is used, including a psychological test, which is followed by one or more interviews. The treatment is directed at learning to recognize bruxism activities, to practice alternative behavior, and to learn to cope better with situations that may lead to an increase of bruxism.     

Fluctuation of the microbiota of the tongue in humans

The purpose of this study was to examine whether variations occur in the % of motile micro-organisms on the dorsum of the tongue during a 1-month time-period and further to examine 2 transport fluids: the growth medium BM and reduced transport fluid (RTF), for their ability to conserve motility of microorganisms in comparison to sterile saline. Both transport fluids showed a significant reduction in the % of motile micro-organisms within 15 min. The use of RTF resulted, during a 60-min period, in a significantly higher % of motile micro-organisms compared to sterile saline. Results showed that the % of motile micro-organisms on the dorsum of the tongue was not constant. A significant reduction in the % of motile micro-organisms was observed in the course of the month involved in this study.     

A survey on the degree of satisfaction of the readers of the Belgian Review of Dental Medicine

After a readers survey, we came to the conclusion that the readership of the 'RBMD' doesn't feel the necessity to make a lot of changes at the present formula. There is a demand to insert, beside the main topic, a complementary column with news from the universities and also a need for more clinical information.     

Evaluation of osteotomy fixation changing the number, the extension and the location of the plates

We used a two-dimensional model that simulated a fractured human mandible to study the extent of load resistance of different plates. We studied 49 bovine ribs in seven groups using varying number (1 or 2), lengths of plates (4 or 6-holes), and location (near the lower or upper border). The number and location of plates had a greater effect on resistance to load than length of plates. The best mean resistance values were achieved by a combination of two parallel plates secured near the lower and upper borders, followed by single plates secured near the upper border. The lowest values were with single plates secured close to the lower border.     

Clinical significance of the structural integrity of the superior aspect of the mandibular canal

BACKGROUND: Sparse data can be found regarding the structural integrity of the superior aspect of the mandibular canal. In many cases, the mandibular canal must be carefully evaluated prior to defining patient treatment. METHODS: In this case report, a 54-year-old patient presented with a periapical infection involving the mesial root of the mandibular right second molar (#31). Radiographic evaluation revealed that the periapical lesion extended from the apex of the tooth to the superior aspect of the mandibular canal. Upon surgical removal of the tooth, an apical communication between the extraction socket and mandibular nerve was located. A guided bone regeneration procedure was performed to protect the nerve from subsequent damage and to prepare the site for future implant placement. Implants were placed in the area approximately 5 months following the regenerative procedure. RESULTS: After implant placement, the patient experienced normal function and no mandibular symptomatology. Implants have been in function for the past 4 years. CONCLUSIONS: Many factors, both pathologic and developmental, can lead to a discontinuity of the superior aspect of the mandibular canal. Normally, a thin cortical plate of bone protects the nerve. When a lack of structural integrity of the canal roof is discovered, enucleation of a periapical infection or subsequent implant placement can lead to potential disruption of the nerve. Limited information is available regarding the integrity of this protective cover. This case report underscores the importance of proper clinical diagnosis before implant placement in the posterior mandible.     

Carcinoma of the midline dorsum of the tongue

We present a case of an 80 year old female who had previously been diagnosed with lichen planus of the tongue dorsum some 10 years previously. Due to a change in the appearance of the lesion a biopsy revealed squamous cell carcinoma of the tongue. We discuss this rare diagnosis in conjunction with the possibility of an association of squamous cell carcinoma and lichen planus.     

Evaluation of the preparation of the coronal part of the mesial canals of lower molars

Canal entrances can be flared using specific, low speed, continuously rotating Ni-Ti instruments. Two such instruments were evaluated for their capacity to flare the canal entrance while respecting the initial canal axis. Lower molars (n = 20) with two distinct mesial canals were prepared to within 2.5 mm of the pulp chamber floor using Bramante's technique. Canal entrances were flared with a QUANTEC FLARE LX or an ENDOFLARE. They both had a 0.12 taper and a #25 tip diameter. The instruments were first inserted in the canals using an axial movement and then withdrawn with a selective circumferential brushing action. Photographs taken before and after each preparation were compared. No ledging or significant modification of the working length was noted. The centre of mass was displaced on average by 0.138 mm with no brushing action and 0.274 mm with brushing action. In most cases (87.5%), the centre of mass was displaced mesially. The two instruments behaved in an identical mode, both before (p = 0.3497) and after (p = 0.9304) the brushing action. Ni-Ti flaring instruments can be used to flare the canal entrance with little displacement of the initial canal axis, even when a brushing action is used.     

Ganglioneuroma of the base of the skull

Ganglioneuromas are rare benign tumors originating from the ganglion cells of the sympathetic and parasympathetic nervous system. Ganglioneuromas in the base of skull are extremely rare. In this article, we describe a case of primary ganglioneuroma below the foramen ovale observed in a 38-year-old man. The lesion was asymptomatic. The patient underwent surgical intervention for diagnostic and therapeutic purposes. Craniomaxillofacial surgery was conducted by the oral and maxillofacial surgical team and the neurosurgical team. Combined frontotemporal-preauricular infratemporal approach was used to expose the lesion. Cerebrospinal fluid leakage and facial paralysis did not occur postoperatively. The results of histopathologic examination indicated that the excised lesion was a ganglioneuroma. Clinical follow-up was done, and no recurrence has been observed up to now.     

A clinical classification of the status of the pulp and the root canal system

Many different classification systems have been advocated for pulp diseases. However, most of them are based on histopathological findings rather than clinical findings which leads to confusion since there is little correlation between them. Most classifications mix clinical and histological terms resulting in misleading terminology and diagnoses. This in turn leads to further confusion and uncertainty in clinical practice when a rational treatment plan needs to be established in order to manage a specific pathological entity. A simple, yet practical classification of pulp diseases which uses terminology related to clinical findings is proposed. This classification will help clinicians understand the progressive nature of the pulp disease processes and direct them to the most appropriate and conservative treatment strategy for each condition. With a comprehensive knowledge of the pathophysiology of pain and inflammation in the pulp tissues, clinicians may accomplish this task with confidence.     

On the repair of the dentine barrier

The overall aim of this thesis was to study some aspects of the repair of the dentine barrier, especially in conjunction with dental pulp capping. Understanding the events leading to the healing of the dentine and pulp, and hence successfully preserving the vitality and functions of the tooth, would lead to a scientific basis for a less invasive treatment of pulp exposures than performing root canal treatments. The surfaces of the body have physiological barrier functions aimed at protecting the body from external noxious agents. In the tooth, the odontoblasts, which line the outermost part of the pulp and are responsible for the formation of dentine, play a central role in the barrier function and thus in the defence mechanisms of the tooth. The micro-organisms in the caries lesion can reach the pulp via the dentinal tubules. However, the barrier function helps to prevent microbial invasion and thereby avoid deleterious inflammation and subsequent necrosis of the pulp. Dentine repair is an important part of the barrier function. There are however doubts as to whether the repair also leads to restitution of the function and the ability to withstand bacterial influx over the longer term. Pulp capping is a treatment method used when the pulp has been exposed in order to stimulate healing of the pulp and dentine. The evidence for repair of the dentine after pulp capping in humans has been studied by means of a systematic review. The focus of the literature search was studies performed in humans where hard tissue formation had been studied with the aid of a microscope. We concluded, based on the limited evidence available, that calcium hydroxide based materials but not bonding agents promote formation of a hard tissue bridge. Scientific evidence was lacking as to whether MTA was better than calcium hydroxide based materials in this regard. A gel (Emdogain Gel) containing amelogenin, known to be involved in dentinogenesis, was evaluated with regard to formation of hard tissue in a clinical study. A greater amount of hard tissue was formed after application of the gel compared to the control. Characterization of the tissue concluded it to be dentine, based on its content of type 1 collagen and dentine sialoprotein, although it was not formed as a continuous bridge covering the pulp wound. Beneath a deep caries lesion an important part of the barrier function is the odontoblasts' response to bacteria with the formation of new dentine. A cell model with odontoblasts was used to study the effects of clinical isolates from a deep carious lesion on their viability and production of type 1 collagen, the major component of the dentine in the early stages of its formation. There were bacteria that negatively affected the viability of the odontoblast-like cells and different bacteria varied in their effects on type 1 collagen production, suggesting that some bacteria may have a direct influence on the odontoblasts' ability to form dentine. In summary; Emdogain Gel initiated dentine formation, though not in a form that could constitute a barrier and there are indications that bacteria may differentially affect the odontoblasts' ability to repair the dentine barrier.     

上颌尖牙易位至上颌前磨牙颊侧的错（牙合）矫治

目的在解除上颌尖牙易位对患者的面容和牙体健康带来的影响的同时,避免由此带来的新的牙颌畸形.方法用固定矫正器将第一前磨牙拉到尖牙的牙位上.结果面部及牙列外观协调美观,咬合无障碍,有效保证了牙列的完整性.讨论由于尖牙、前磨牙唇颊侧外形相近,使这项技术的应用有了可行性.     

Individual-based prediction of the size of the supporting zones in the permanent dentition

The aims of this individual-based study were 1. to assess the actual space requirements of the permanent canines and premolars, 2. to test the reliability of the Moyers method in predicting a space deficiency at the 75% confidence level and 3. to try to find a reliable unitary prediction value (=unitary value) as a possible substitute for the calculated Moyers values. Dental cast measurements were taken of the permanent dentition of 100 females and 100 males. The average sum of the widths of the maxillary and mandibular permanent canines and premolars was 20.8 mm (17.3 to 24.3 mm). The Moyers method could predict a maxillary space deficiency in 77.5% and a mandibular space deficiency in 65.5% of the subjects. The unitary value of 22.0 mm made it possible to predict a space deficiency in 83.5% of the subjects. The unitary value thus had a higher confidence level (83.5%) than the 75% level stated by Moyers and might thus substitute the calculated Moyers values. Furthermore, the unitary value is easy and quick to handle.

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Vorhersage der Größe der Stützzonen Im blelbenden Gebiß auf individueller BasisVergleich der Moyers-Methode mit einem prognostischen Einheitswert

Zusammenfassung Die Ziele dieser individuell bezogenen Studie waren 1. die Ermittlung des tatsächlichen Platzbedarfes der bleibenden Zähne in den Stützzonen (=Stützzonenbreiten), 2. die Überprüfung der Zuverlässigkeit der Moyers-Methode zur Vorhersage eines Platzmangels auf dem Niveau 75%iger Sicherheit und 3. der Versuch, einen einheitlichen Prognosewert (=Einheitswert) als möglichen Ersatz berechneter Moyers-Werte zu finden. Vermessen wurden 200 Gebißmodelle der permanenten Dentition von 100 weiblichen und 100 männlichen Probanden. Die durchschnittliche tatsächliche Stützzonenbreite für Ober- und Unterkiefer betrug 20,8 mm (17,3 bis 24,3 mm). Die Moyers-Methode konnte einen Platzmangel im Oberkiefer bei 77,5% und im Unterkiefer bei 65,5% der Probanden vorhersagen. Der Einheitswert von 22,0 mm ermöglichte die Vorhersage eines Platzmangels bei 83,5% der Probanden. Hiermit lag beim Einheitswert das Sicherheitsniveau der Prognose eines Platzmangels mit 83,5% oberhalb des von Moyers angegebenen Wertes von 75%, und der Wert könnte somit die berechneten Moyers-Werte ersetzen. Dazu kommt beim Einheitswert die einfache Anwendbarkeit mit geringem Zeitaufwand.

     

A direct in vivo measurement of the three-dimensional orientation of the occlusal plane and of the sagittal discrepancy of the jaws

The aim of the present investigation was to three dimensionally assess craniofacial relationships in vivo. Specifically, by using a non-invasive direct technique, the following measurements were made: 1) natural head position relative to the ground; 2) orientation of the occlusal plane relative to the subject's intrinsic facial planes; and 3) anteroposterior discrepancy of the dental bases, taking into consideration all the facial hard- and soft-tissue structures. Several dental and soft-tissue facial landmarks were directly digitized from 24 adult healthy volunteers with Angle Class I occlusions by means of an electromagnetic three-dimensional computerized digitizer. In natural head position, the three-dimensional orientation of Camper's, occlusal, and mandibular planes were measured along with the anteroposterior maxillo-mandibular discrepancies. In the frontal plane projection, all the measured planes appeared about horizontal. In the lateral plane projection, on average, Camper's plane deviated from the true horizontal by approximately 18 degrees (in a 'head flexed' direction). The occlusal plane deviated from the same horizontal by about 14 degrees, while the mandibular plane had a steeper inclination (about 30 degrees ); both planes were significantly correlated to Camper's plane. The measurements of anteroposterior jaw discrepancy revealed a wide range of sagittal relationships in the analyzed subjects. The method was found to be repeatable and fast. This direct three-dimensional in vivo assessment of the orientation of occlusal plane relative to the other facial planes could allow for a more comprehensive analysis of maxillo-mandibular sagittal discrepancies.     

Mineralization patterns in the dentine of the floor of the pulp chamber of porcine molars

The relationship between the arrangement of the matrix fibre bundles and the shape of the mineralization front (mineralization pattern) were observed in the dentine of the subpulpal wall of porcine molars. The observations were made using mainly light microscopy and scanning electron microscopy on the primary dentine excluding the secondary dentine. The results obtained shows that the dentine of the subpulpal wall consists of two parts, a surface layer and the circumpulpal dentine. The surface layer can be divided into two sublayers according to the arrangement of it's matrix fibres. The mineralization pattern was also observed to have another two sublayers which did not correspond with the two fibrous subdivisions. Adjacent to the dentine-cement junction, there is a layer, measuring about 3 microns in thickness, in which the matrix fibres run parallel to the junction. The second layer is characterized by two types of fibre bundles which run perpendicularly to the dentine-cement junction. These outer radially oriented fibres are about 1-2 microns in diameter, and the inner radially oriented fibre bundles are coarse, 10 microns in diameter. In the outermost 10 microns, mineralization begins as an aggregation of mineral granules, and forms a hypermineralized layer which overlays the junctional region between the fibres which are oriented parallel and perpendicular to the dentine-cement junction. Except for the most-superficial layer, mineralizing cones surround the radial fibre bundles at the mineralizing front. The circumpulpal dentine, which forms the floor of the pulp chamber, can also be divided into two layers by the differences in their fibrous matrix. The fibres of both of these layers lay in the plane of the predentine surface. However, in the outer layer the fibres of the matrix are randomly arranged around and between the dentinal tubules, whereas in the inner layer the fibres have a preferred orientation extending radially from a central region between the roots. In the outer layer, calcospherites, which are the units of the mineral aggregation, appear at the mineralizing front. In the inner layer, at the mineralizing front, ridges, measuring approximately 10-15 microns in width, 10 microns in height and 100 microns in length, also have a preferred orientation, 90 degrees to the fibre direction. Microradiographs show that a higher mineralized "lamellae-like' region exists in the center of each ridge-crest. X-ray diffraction indicates two preferred crystallite orientation, one is parallel to the matrix fibres and the other perpendicular to the predentine surface. The latter seems to be situated in the highly mineralized lamellae. In the circumpulpal dentine, therefore the mineralizing units have a spheritic shape in the outer layer, and a columner shape in the inner layer. As far as the author is aware the columnar mineralization unit in mammalian dentine has not been described before.     

Changing the curriculum and the role of the teacher and the students in the classroom – an analysis of the process of reforming a course in oral microbiology

In 2005, a new curriculum was introduced at the School of Dentistry at the University of Copenhagen. Amongst many changes, the pedagogical concept behind theoretical teaching was changed. The main emphasis was previously on lectures and teacher controlled teaching, but the emphasis has now shifted to a more dialogue‐based teaching style for smaller groups where the students became much more active. Thus, the learning principle was now given the pride of place. The present article focuses on the pedagogical reorganisation of the course in oral microbiology where, based on interviews with students and teachers, an evaluation is made regarding how the changes were implemented and developed. Despite the fact that the students themselves wanted to abandon the lecture‐based teaching style, there was great dissatisfaction with the new dialogue‐based teaching style as the students did not think that it was possible for them to take responsibility for their learning. They would much rather listen to teachers who know the material. Initially, the teachers were very surprised by the negative attitude of the students and had to change the teaching style to more traditional teaching in groups whilst still maintaining the dialogue principle to a certain degree. In this article, the need to enter into a teaching contract between students and teachers prior to introducing new pedagogical principles is discussed.