Schizophrenia in twins

Attempts to save natural teeth have created numerous restorative, endodontic, and periodontal techniques it has always been considered the treatment of choice to save teeth whenever possible, and extreme efforts to save teeth are often considered because of the poor treatment alternatives for replacing them. Today osseointegration provides a predictable means of replacing teeth; therefore, retaining questionable teeth may not be as necessary as in the past. This article reviews situations in which the selective extraction of compromised natural teeth or even healthy natural teeth is considered because of alternative treatment options utilizing osseointegrated implants.     

Restoration of primary anterior teeth with composite crowns

For children with extensive caries of primary teeth, or with deformed or traumatised teeth, restoration with composite using a crown form gives excellent results. Strength is gained by full crown coverage. The aesthetics are very acceptable. The technique also allows primary teeth to be modified to resemble permanent teeth when these are missing and the primary teeth are being kept until more definitive treatment is provided. Caries is usually well controlled, and space loss due to further tooth breakdown is avoided.     

A randomized prospective trial comparing 45 and 90-ml oral sodium phosphate with X-Prep in the preparation of patients for colonoscopy

Incontinentia pigmenti is an uncommon genodermatosis that occurs in female infants. The characteristic dental defects are partial anodontia and the presence of some peg-shaped teeth. This report describes a patient with incontinentia pigmenti who exhibited multiple missing teeth in both arches. The patient had malpositioned teeth and decreased occlusal vertical dimension associated with the missing teeth. Orthodontic treatment was required for prosthetic purposes. The dental anomalies of incontinentia pigmenti and the treatment procedure are presented.     

Etiology and indications for the management of impacted teeth

Impacted teeth are a medical deformity brought about by the dietary changes of modern civilization. Ample studies exist to show that the lack of a coarse, abrasive diet--an attritive diet--is the major cause of this problem in modern civilization. Our recent ancestors did not experience this problem or the problem of the underdeveloped lower jaw and resulting Class II malocclusion to the extent present in modern society. Medical and dental scientists, practitioners, and surgeons are aware of the devastation that impacted teeth can cause to the jaws and overall health of an individual and have issued numerous warnings to the profession and to the public regarding the several clear indications for the removal of impacted teeth. The issue has been clouded by the competing economic incentives present in our society, in which fee-for-service practitioners have been and are being replaced by practitioners with a disincentive to recommend surgical care for all but acutely infected or seriously symptomatic patients presenting with impacted teeth. Oral and maxillofacial surgeons practicing in the United States at this time are aware of the many clear indications for removal of impacted teeth and make every effort to communicate this information to their patients and other dental and medical practitioners. They are also aware of the contraindications to the removal of impacted teeth and advised patients appropriately when it is safe to retain and periodically observe by radiograph certain impacted teeth.     

Non-crown and bridge stabilization of severely mobile, periodontally involved teeth. A 25-year perspective

It is the author's belief, after analyzing forces and stresses on the periodontium for more than 30 years, that stabilization of severely mobile teeth can retain teeth, if in health, almost indefinitely. Because these teeth are retained using restorative materials, recurrent caries is a problem that needs to be treated. Tooth loss resulting from caries can occur. In the author's 26 years of using extracoronal adhesive resins for splinting, the technology of adhesive bonding and restorative resins have been improved. Earlier shortcomings of the physical properties of these materials never dissuaded the author from recommending splinting. When the cases were presented to the patient and the referring dentist, the types of the current materials used to splint teeth were immaterial. Realizing that improvements in adhesives and resins would be developed, the near-hopeless teeth were retained. Because the elderly population is the fastest-growing segment of the population, caries control is more of a concern than it was 50 or more years ago. Because teeth are being retained longer in this cohort, and because caries has a greater potential to exist, supportive periodontal therapy and recalls and caries examination become more important.     

Removable partial prostheses for the elderly

Elderly partially edentulous patients can have teeth replaced with removable or fixed prostheses supported by mucosa, teeth, or implants. Age per se does not influence which option is best. Instead, the relative health of the patient, dental tissues, and the patient's finances determine treatment. A three-level index of these factors, the PTF index, is proposed to assist in the decision-making for treatment. Removable partial prostheses (RPPs) can be indicated for all patients because RPPs offer esthetic, versatile, noninvasive, and reversible features. They are particularly indicated when remaining teeth are questionable. If teeth are lost, they can be more easily added to existing RPPs compared with fixed prostheses. Six changes to ideal designs are illustrated in this article for prostheses with a compromised dentition, to make continued prosthetic service simpler.     

Neurophysiological basis, aetiology and clinical aspects of hypersensitive teeth

Dentine hypersensitivity is a common cause of dental pain. The sensitivity has been shown in clinical studies to vary greatly. The response to the treatment of hypersensitive teeth varies. It has been observed that while the treatment might be effective in some teeth, it is not so in other teeth. In some hypersensitive teeth spontaneous reduction in the hypersensitivity has been observed, while in other teeth, the sensitivity has persisted even for years. It seems probable that the hydrodynamic mechanism is the one operating in dentine sensitivity and the condition of dentine, with either blocked or open dentinal tubules, is a decisive factor in the degree of dentine sensitivity. In hypersensitive dentine the dentinal tubules are open and the pulp is inflammed. In cases where treatment is effective, probably the dentinal tubules are successfully blocked and the inflammation is resolved. If the process is not successful the teeth will be resistant to treatment. The correct therapeutic approach should aim at blocking the dentinal apertures and resolving pulpal inflammation. In addition, clinicians should be aware of clinical procedures which might result into dentine hypersensitivity.     

A new correction procedure for calibrating dental caries frequency

The incisors and canines and the premolars and molars show differential resistance to cariogenic factors. The anterior teeth have a lower caries frequency than the posterior teeth. However, these tooth classes are lost differentially in postmortem stages due to their anatomical structures. This differential postmortem tooth loss distorts proportions between the anterior and posterior tooth classes. The disproportionality can affect the calculation of total caries prevalence. In this paper, we propose a new calibration procedure which removes this disproportionality and call it the proportional correction factor. For this procedure, the caries rates of anterior and posterior teeth are corrected by multiplying the anterior teeth by three-eighths and the posterior teeth by five-eighths. These fractions are derived from the human dental formula which contains three anterior and five posterior teeth by side. The correction factor is more effective if the proportion of anterior to the posterior teeth is extremely distorted. When this procedure is used with the caries correction factor, it provides a useful way to approach to an almost true caries prevalence.     

Titanium screw implants for intermaxillary fixation of partially edentulous jaw

Establishment of the best possible relationship between upper and lower teeth is very important when treating jaw fractures and orthognathic deformities in partially edentulous patients. Many surgeons use arch bars and acrylic splints for intermaxillary fixation (IMF) to obtain the best occlusal relationships after the operation. In patients with sufficient teeth, IMF is not so difficult to realize. However, in partially edentulous patients, the available teeth may not be sufficient to apply arch bars or splints. This paper describes a system for IMF of a partially edentulous jaw. Screws made of medical-grade titanium are implanted into the alveolar ridges where two or more teeth are missing. Arch bars or acrylic splints secured on these implants and available teeth can be used safely for IMF. In vitro axial pull-out tests demonstrated that these implants can withstand the traction forces generated by elastics. Five partially edentulous patients, three with mandibular fractures and two with orthognathic problems, were treated with these implants. All patients healed without any complications and with the best possible occlusal relationships.     

Can enamel microstructure be used to establish the presence of different species of Plio-Pleistocene hominids from Omo, Ethiopia?

Microstructural characteristics of enamel are minimally influenced by extrinsic / non-genomic factors and are thus potentially important in any attempt to establish the taxonomic attribution of Plio-Pleistocene hominids. The aim of this work is to assess the potential use of enamel microstructural characteristics in attributing teeth from the Omo to different Plio-Pleistocene hominid species. First, the results from this study are compared to data for extant hominoids in order to observe whether Omo teeth show similar or larger variation. This might suggest that more than one species is represented in the Omo sample. Alternatively, a similar or smaller variation would suggest that no more than one species could be reliably recognized in the sample using enamel microstructural characteristics. Secondly, since all previous studies suggest that more than one species is present in the large sample of teeth from the Omo, enamel microstructure characteristics with the largest variability are used to group teeth into morphs. These morphs are compared with previous taxonomic attributions of Omo teeth in order to determine if the morphs grouped teeth in a similar way to previous studies. The results of this study demonstrate that enamel microanatomy characteristics in Plio-Pleistocene hominid teeth from the Omo do not present a larger variation than that observed in extant hominoid species. This suggests that no more than one species can be recognized by using these characteristics. These results also indicate a large overlap in enamel microstructure characteristics between Plio-Pleistocene hominid species from Omo and place serious doubt on the theoretical potential for using enamel microstructural characteristics as a taxonomic tool. The morphs defined in this study do not correspond with any previous taxonomic attributions based on macrostructural analysis of the same teeth and cannot be referred to different species. However, macrostructural characteristics have never been assessed in the same way in extant hominoids and it remains to be seen to what extent these characters reflect interspecific, intraspecific or even intra-individual variation. For now therefore, the taxonomy of Plio-Pleistocene hominids from the Omo still remains unresolved.     

A non-destructive dental method for age estimation

Dental radiographs have rarely been used in dental age estimation methods for adults and the aim of this investigation was to derive formulae for age calculation based on measurements of teeth and their radiographs. Age-related changes were studied in 452 extracted, unsectioned incisors, canines and premolars. The length of the apical translucent zone and extent of the periodontal retraction were measured on the teeth while the pulp length and width as well as root length and width were measured on the radiographs and the ratios between the root and pulp measurements calculated. For all types of teeth significant, negative Pearson's correlation coefficients were found between age and the ratios between the pulp and the root width. In this study also, the correlation between age and the length of the apical translucent zone was weaker than expected. The periodontal retraction was significantly correlated with age in maxillary premolars alone. Multiple regression analyses showed inclusion of the ratio between the measurements of the pulp and the root on the radiographs for all teeth; the length of the apical translucency in five types; and periodontal retraction in only three types of teeth. The correlation coefficients ranged from r = 0.48 to r = 0.90 between the chronological and the calculated age using the formulae from this multiple regression study. The strongest coefficients were for premolars. These formulae may be recommended for use in odontological age estimations in forensic and archaeological cases where teeth are loose or can be extracted and where it is important that the teeth are not sectioned.     

硬质合金齿圆锯片锯齿齿形应力分析

以锯片的实际锯切工况为背景,选取现场使用中出现问题的两种齿形,利用有限元软件建模并对锯齿部位进行应力分析,找出两种齿形在锯切工况相同时锯齿应力的分布规律,分析其对于锯片使用效果的影响,为硬质合金锯片的齿形设计提供理论依据,进而可对不同用户、不同锯切工况,有针对性的进行锯片齿形设计,改善锯切效果。     

Trend of aging on the number of teeth investigated through a survey of dental health representation in a simple equation by using a kinetic method and its application

A survey of dental health was conducted on 6,933 residents (aged 61.8 +/- 11.1) in 4 villages Nara Prefectural Uchiyoshino Health Center administers. Examinees were divided into 7 ages groups. The mean value of present teeth at each age group was calculated. Age dependency of number of teeth was investigated with a kinetic model based on the following premise. 1. Changes between age groups can be treated as a time series occurrence. 2. Number of missing teeth can be estimated as 29 - that of present teeth. Results show that the rate of decrease of the number of present teeth is of a first order in itself and the number of missing teeth. It can be mathematically expressed as follows: -dX/dt = k.X.(29 - X).......eq. (1). in which X = number of present teeth, 29 - x = number of missing teeth k = rate constant, t = time. From this simple relationship the following are suggested 1. Tooth loss is caused by the interaction of present teeth and sites where teeth are lost. 2. Integration of eq. (1) yields ln?(29 - X)/X? = 29.k.t + a.......eq. (2). in which 0 < X < 29, t = time from the youngest age group (20-29), a = constant. It appears that, from eq. (2), the dental health of a community is determined by two coefficients, 29.k and a. 3. Helping a person realize his present and future dental state and to motivate action for prevention of tooth loss by showing him his rate of decrease, "tooth age" and the predicted number of teeth a certain years later calculated from eq. (1) and eq. (2), can be of great value. 4. Eq. (2) is transformed to X = 29/?exp(29.k.t + a) + 1?, which represents the reverse S-shaped curve of the age dependency of the number of teeth. 5. Applying this method to cohort analysis will enable forecast of the trend of the number of teeth.     

Fluoro-Green and Fluoro-Red: two new fluorescent retrograde tracers with a number of unique properties

A sample of 443 Pakistani infants from four different socioeconomic areas was followed longitudinally study the emergence of the primary teeth. The mean ages of emergence of the primary teeth, without regard what kind of tooth and dental ages of the primary teeth were calculated. The subjects showed no sexual dimorphism in the emergence times of the primary teeth. The children from poor areas. were ahead by statistically significant differences from upper middle class, for emergence of the primary teeth 17-20. On comparison with Swedish standards (H?gg & Taranger, 1985) Pakistani children are delayed, by a statistically significant difference, in the emergence of primary teeth 1-16, however, they were at par in the emergence of 17-20 primary teeth.     

Multiple supernumerary teeth in two brothers: a case report

Supernumerary teeth (hyperdontia) are relatively common in the general population and occur more frequently in patients with a family history of such teeth. Supernumerary teeth have been reported in many genetic syndromes, but multiple supernumerary teeth occurring as an isolated non-syndromic trait are rare. This article describes a rare non-syndromic variety of multiple impacted supernumerary teeth in two brothers.     

Assessment of lead exposure of children from K-XRF measurements of shed teeth

Lead is accumulated and immobilized for long periods of time in teeth. Thus the Pb concentration of a tooth can be used as an indicator of the cumulative Pb intake of a child. Shed and extracted teeth were collected from children in Beijing, China and some industrial regions in the Middle Urals in Russia. The Pb levels in the teeth were measured in Philadelphia, PA using an X-ray fluorescence (XRF) technique. Since Pb deposits in the tooth during the entire period that it is in the child, the measured tooth Pb level was divided by the age of the child when the tooth was shed and expressed in terms of (microgram/g-yr). 10% (n = 100) of the teeth from Beijing, China had Pb levels exceeding 5.5 and 3% above 9 micrograms/g-yr. For comparison, in the 1970s when urban environmental Pb levels were elevated, the tooth Pb levels in Philadelphia children were similar, i.e. 10% (n = 298) of the teeth had Pb levels exceeding 7.5 and 6% were above 9 micrograms/g-yr. Children in a more rural setting, Bennington, VT, had no detectable tooth Pb (n = 200). The Pb levels in the teeth from the Urals were much higher; 50% (n = 134) of the teeth had Pb levels exceeding 7.5 and 10% exceeding 17.8 micrograms/g-yr. The tooth Pb levels observed in the teeth from Beijing, and more so from the Urals, indicate that these children are residing in Pb polluted environments. Further studies are required to determine the extent of the Pb pollution and to explore the possibility that there are associated Pb-related health deficits.     

Split-mouth study of sealant retention with carbon dioxide laser versus acid etch conditioning

A survey was carried out to determine the reasons for tooth extractions of permanent teeth in Singapore. Data were obtained from 52 dentists practising general dentistry over a period of 12 months. At the end of the 12-month period, data were collected from 1276 patients, from whom a total 272 teeth were extracted. In this population group, the results showed that the percentage of teeth extracted due to periodontal reasons and caries were about the same, that is 35.8% and 35.4%, respectively. There was an increase in teeth extracted due to periodontal reasons with age. In patients above 40 yr, an average of 76% of teeth were lost due to periodontal reasons. An average of 26.7% of teeth were lost due to periodontal reasons in patients under 40 yr old. However, the trend for loss of teeth due to caries is reversed. Posterior teeth were more frequently extract compared to anterior teeth. Third molars accounted for 24.7% of all extractions carried out, whilst central incisors were 8.0% of all extractions. Molars were often lost due to caries and lower anterior teeth were most frequently lost due to periodontal reasons. The results of this study did not demonstrate one predominant reason for extraction. Both caries and periodontal reasons were equally common causes of tooth extraction.     

Efficacy, longevity, side effects, and patient perceptions of nightguard vital bleaching

Since its introduction into dentistry in 1989, nightguard vital bleaching has been proven to be a simple and safe procedure to whiten discolored teeth. Efficacy of the technique is 95% for nontetracycline-stained teeth, and with extended treatment time, tetracycline-stained teeth can be expected to lighten in 90% of cases. Satisfactory retention of the shade change can be expected in 63% of patients 3 years posttreatment and at least 35% at 7 years. Side effects are usually mild and transient, disappearing within days of treatment completion. Patients report that they are glad they went through the procedure, and 97% recommend the procedure to a friend.     

A multidisciplinary approach to restoring posterior bite collapse

Treatment planning of posterior bite collapse cases with loss of vertical dimension can be complex. In cases where a patient's vertical dimension of occlusion has been lost, there often is drifting of posterior teeth, flaring of maxillary anterior teeth, and inadequate interarch space for a restoration. These factors are further complicated by the esthetic demands of the patient and the dentist and by the use of implants to replace missing teeth. This article presents a case report of a multidisciplinary treatment plan to achieve a functional and esthetic restoration.     

驱动辊断齿失效分析及改进

从显微组织、热处理工艺等方面对二中间辊驱动辊齿部断裂原因进行了分析。分析结果表明:驱动辊淬火加热时齿部过热是造成驱动辊断齿的主要原因;轧辊存在严重的网状碳化物也是造成冲击性能偏低的原因之一;在工艺设计方面,驱动辊齿部强度有余,韧性不足,是驱动辊断齿的隐患,通过控制网状碳化物级别提高轧辊原材料质量和降低驱动辊齿部硬度强度,可以有效提高驱动辊齿部冲击性能。