Tooth Enamel and its Dynamic Protein Matrix

Tooth enamel is the outer covering of tooth crowns, the hardest material in the mammalian body, yet fracture resistant. The extremely high content of 95 wt% calcium phosphate in healthy adult teeth is achieved through mineralization of a proteinaceous matrix that changes in abundance and composition. Enamel-specific proteins and proteases are known to be critical for proper enamel formation. Recent proteomics analyses revealed many other proteins with their roles in enamel formation yet to be unraveled. Although the exact protein composition of healthy tooth enamel is still unknown, it is apparent that compromised enamel deviates in amount and composition of its organic material. Why these differences affect both the mineralization process before tooth eruption and the properties of erupted teeth will become apparent as proteomics protocols are adjusted to the variability between species, tooth size, sample size and ephemeral organic content of forming teeth. This review summarizes the current knowledge and published proteomics data of healthy and diseased tooth enamel, including advancements in forensic applications and disease models in animals. A summary and discussion of the status quo highlights how recent proteomics findings advance our understating of the complexity and temporal changes of extracellular matrix composition during tooth enamel formation.

Apical periodontitis healing and postoperative pain following endodontic treatment with a reciprocating single-file, single-cone approach: A randomized controlled pragmatic clinical trial

This trial assessed post-operative pain and healing of apical periodontitis following endodontic therapy with a reciprocating system compared to a crown-down technique with hand files and lateral compaction filling. One-hundred and twenty nonvital anterior teeth with apical periodontitis were randomly treated using either a reciprocating single file followed by matching-taper single-cone filling or a hand file and lateral compaction filling. Postoperative pain was assessed during the 7 days after the treatment, using a visual analogue scale and a verbal rating scale. Apical healing was assessed using the periapical index score after a 12-month follow-up. The hypothesis tested was that both protocols were equivalent and present similar effectiveness in healing periapical lesions. Data were analyzed through two one-sided tests, t-tests, as well as Mann-Whitney and Chi-squared tests (α = 0.05). Logistic regression was used to investigate the association of clinical and demographic factors with the success of treatment. Regardless of the assessment time, no difference in incidence (38%-43% at first 24h), intensity of postoperative pain, and incidence of flare-up (≈ 3%) was observed between the two endodontic protocols. Both protocols resulted in a similar healing rate of apical periodontitis. After 12 months, the success rate ranged from 73% to 78% and the difference between the treatments fell within the pre-established equivalence margin (-0.1; -0.41 to 0.2). Endodontic treatment combining a reciprocating single file with matching-taper single cone showed similar clinical effectiveness to the treatment using hand-file instrumentation and the lateral compaction filling.

Condition of mineralized tooth tissue in a population of 15-year-old adolescents living in a region of Ukraine with slightly exceeded fluorine concentration in the water

INTRODUCTION

Fluorine is a common element in nature; however, the difference between a beneficial dose and a toxic dose for the organisms is small. The main source of fluoride for humans is water in addition to food.

OBJECTIVE

The aim of this study was to estimate the degree of severity of pathological changes, namely, caries or fluorosis, in the mineralized tooth tissue of 15-year-old adolescents with respect to their hygienic and nutritional habits, and the content of fluorine in drinking water, soil and plant products.

MATERIAL AND METHODS

100 adolescents aged 15 from schools in Sosniłka, L'viv region, were examined. The condition of mineralized tooth tissue was evaluated by the caries severity, expressed by the mean number D3MFT, caries frequency and value of the SIC index. Fluorine in plant material and soil were determined according to the PN-G-04543:1982 standard, and water according to the PN-EN ISO 10304 - 1: 2009+ AC: 2012 standard.

RESULTS

Severity of caries disease expressed by the D3MFT number in the examined group of 15-year-olds was 3.39; in the group of girls - 3.08, and in the group of boys - 3.76. In the examined group, the average number of teeth with fluorosis was 7.59. Value of the SIC index among the examined population of students (n-31) was 6.26: 5.89 (n-18) for girls and 7.31 (n-13) for boys. Fluorine concentration in the water was 0.78 - 1.25(mg·dm-3). In the soil, it also did not vary across the sampled areas and amounted, on average, to 176 mg·dm-3. The biggest fluorine content noted in the dry mass of beetroots was 3.50 (mg F· kg), and the lowest - 3.34 (mg F· kg).

CONCLUSIONS

Close to optimal fluorine content lowers caries severity and frequency of fluorosis. Optimal fluorine content in drinking water and food does not require additional diet supplementation.

Building a Pediatric Oral Health Training Curriculum for Community Health Workers

OBJECTIVES

Community health workers (CHWs) are a promising approach to oral health promotion in high-risk populations. This article describes the process of creating a pediatric oral health CHW training curriculum.

DESIGN

Existing curricula were identified through outreach efforts to experts in the oral health and CHW fields, as well as PubMed and Google searches. After coding basic information, curricula were mapped to define oral health domains. Then group discussion was employed to determine final curriculum contents.

SETTING

United States.

INCLUSION CRITERIA

Curricula were included if they addressed oral health, were in English or Spanish, involved US populations, did not target dental clinicians, and whether sufficient data could be obtained.

MAIN OUTCOME MEASURES

Curricula were evaluated for delivery format, number of hours, target audience, inclusion of CHWs, completeness, and oral health content.

RESULTS

Eighteen unique curricula were identified; 14 (78%) were CHW specific. Pathologic factors, caries formation, toothbrushing basics, flossing, nutrition, sugar-sweetened beverages, oral health recommendations, baby bottle tooth decay, fluoride treatments, and fluoride were covered to some extent in 75% of curricula. More than half did not mention types of teeth, oral health during pregnancy, antifluoride, cultural humility, and special needs populations. After comparing CHW curricula with non-CHW curricula, the original 26 oral health domains were condensed into 10 CHW training domains.

CONCLUSION

Using existing evidence and expert insight, an oral health CHW training curriculum outline was created that emphasizes behaviors, social support, and navigation assistance to promote preventive oral health behaviors in families of young children. This has implications beyond oral health. CHW programs are expanding to address the social determinants of health. The process of creating this curriculum and its basic elements can be applied to other disease areas. Clearly defined trainings that are made publicly available, such as this one, support efforts to standardize the CHW field in preparation for CHW certification and reimbursement in the future.

Investigations on the adhesion of new composites for restoring cervical lesions using energy dispersive X-ray analysis and scanning electron microscopy

Restoration of noncarious cervical lesions with resin composites is one of the treatment options, but the retention of the restorations located at the crown-root junction is still a cause of clinical concern. The aim of this study was to evaluate the adhesive properties of three experimental resin composites and two commercial materials used to restore cavities prepared on extracted teeth as well as to determine the relative elemental composition of these materials. We tested the null hypothesis, which considered that the adhesive behaviours of different resin composites did not differ. The microleakage test using tracers showed that all tested materials exhibited some degree of dentinal microleakage, although they all had good dentinal adhesion. The results failed to reject the null hypothesis. The scanning electron microscopy revealed completely adapted adhesive interfaces underneath the restorations along with well-developed hybrid layers depending on the adhesive system. Energy dispersive X-ray analysis analyses showed that the restorative materials have similar chemical compositions, with some differences between the samples from the same material. The results support the implementation of experimental resins in clinical settings.

Ion Channels Involved in Tooth Pain

The tooth has an unusual sensory system that converts external stimuli predominantly into pain, yet its sensory afferents in teeth demonstrate cytochemical properties of non-nociceptive neurons. This review summarizes the recent knowledge underlying this paradoxical nociception, with a focus on the ion channels involved in tooth pain. The expression of temperature-sensitive ion channels has been extensively investigated because thermal stimulation often evokes tooth pain. However, temperature-sensitive ion channels cannot explain the sudden intense tooth pain evoked by innocuous temperatures or light air puffs, leading to the hydrodynamic theory emphasizing the microfluidic movement within the dentinal tubules for detection by mechanosensitive ion channels. Several mechanosensitive ion channels expressed in dental sensory systems have been suggested as key players in the hydrodynamic theory, and TRPM7, which is abundant in the odontoblasts, and recently discovered PIEZO receptors are promising candidates. Several ligand-gated ion channels and voltage-gated ion channels expressed in dental primary afferent neurons have been discussed in relation to their potential contribution to tooth pain. In addition, in recent years, there has been growing interest in the potential sensory role of odontoblasts; thus, the expression of ion channels in odontoblasts and their potential relation to tooth pain is also reviewed.

Developmental dental anomalies and their potential role in establishing identity in post-mortem cases: a review

Teeth may provide useful forensic evidence owing to features like uniqueness, stability and comparability. Moreover, the human dentition is heterodont, i.e. all the teeth have different morphology - incisors, canines, premolars and molars. There are sometimes deviations from normal morphology, such as the presence of extra teeth, variation in their shape and size eg the presence of an extra cusp, fractured crown/root, Carabelli's cusp, peg laterals, transpositions, fusion, etc. These differences can help forensic personnel identify bodies, especially where other methods of identification like facial features, fingerprints or DNA typing cannot yield satisfactory results as in cases of badly decomposed bodies, burnt remains, mass disasters, etc. Identification from dentition is based on the direct comparison of post-mortem dental profiles with ante-mortem dental records of the deceased. This article aims to review these developmental and morphological dental traits and their role in post-mortem identification.

The evaluation of teeth loosening of the upper jaw in adaptive period of orthodontic treatment by braces

OBJECTIVE

Introduction: Tooth loosening is divided into physiological and pathological one, but there is tooth loosening that occurs during orthodontic treatment (OT) and depends on the tissues of parodontium and strength of orthodontic apparatus. The aim of the research is to evaluate teeth loosening of the upper jaw during adaptive period in patients with permanent bite who were treated by braces.

PATIENTS AND METHODS

Materials and methods: Periostometry (device «Periotest») of teeth to 30 patients who are from 14 to 27 years old with the pathology of the first type based Angle's classification. The evaluation of teeth loosening was done before OT, in 1 month, in 3 months and in 6 months.

RESULTS

Results: The average index of teeth loosening before OT in patients included 3,08±1,29, so it corresponded to norm indices. In 1 month after braces fixation indices of tooth loosening were increased. Middle index of teeth loosening on the third month of OT was 5,84±0,77 relative units, that in 1,9 times more than periostometric indices before OT.

CONCLUSION

Conclusions: Changes of teeth loosening during OT by braces during the first month after fixation. It should be noted that during the first month of OT data of periostometry determine the enlargement of teeth loosening of all teeth in 1,38, in 3 months there is decrease of teeth loosening for all types of teeth. On the 6th month of OT indices of teeth loosening continue decreasing but with lesser intensity and not achieve such level which was to the beginning of OT.

A novel G to A transition at initiation codon and exon-intron boundary of PAX9 identified in association with familial isolated oligodontia

Several studies on experimental animals indicate that the process of organogenesis crucially depends upon the spatiotemporal dose of certain critical bio-molecules. Tooth development is also not an exception. While most of the knowledge regarding the molecular mechanism of tooth development comes from the studies on mouse model, pathogenic variations identified in human tooth agenesis also provide valuable information on mammalian tooth development. Until now five major candidate genes have been identified for tooth agenesis in human. Among them, PAX9 plays the crucial role in tooth development and in non-syndromic congenital tooth agenesis. In this study, microsatellite and SNP based genotyping identifies a disease specific haplotype block, which includes PAX9 gene, segregates with autosomal dominant tooth agenesis phenotype. Direct sequencing of PAX9 identifies a novel heterozygous G to A transition at the third base (c.3G>A) of initiation codon leading to ATG to ATA shift in all affected individuals which is absent in all unaffected relatives and 200 control chromosomes. Further, in vitro functional analysis creating PAX9 minigene construct did apparently show no effect on the splice-site migration. It is therefore proposed that haploinsufficiency of PAX9 is the causal factor for tooth agenesis in this family.

Dental Emergencies: Management Strategies That Improve Outcomes

Acute dental emergencies are a common chief complaint presenting to emergency departments, and they are increasing substantially in frequency. The diagnosis and management of dental emergencies is a core competency of the emergency clinician, and proper therapeutic strategies can significantly improve cosmetic and functional outcomes for patients. This issue provides a systematic review of the literature on common acute traumatic and atraumatic dental emergencies with a focus on the historical and physical examination findings that must be understood to identify life-threatening infections, relieve pain, salvage natural teeth, and communicate with specialists in the further management of patients after emergency treatment.

Amplified Brain Processing of Dentoalveolar Pressure Stimulus in Persistent Dentoalveolar Pain Disorder Patients

AIMS

(1) To determine the brain regions activated by dentoalveolar pressure stimulation in persistent dentoalveolar pain disorder (PDAP) patients, and (2) to compare these activation patterns to those seen in pain-free control subjects.

METHODS

A total of 13 PDAP patients and 13 matched controls completed the study. Clinical pain characteristics and psychosocial data were collected. Dentoalveolar mechanical pain thresholds were determined with a custom-made device over the painful area for patients and were used as the stimulation level during functional magnetic resonance imaging (fMRI) data acquisition. Control subjects received two stimulation levels over matched locations during fMRI scanning: one determined (as above) that evoked equally subjective pain ratings matching those of patients (subjective-pain match) and another nonpainful stimulation level matching the average stimulus intensity provided to patients (stimulus-intensity match). Clinical and psychosocial data were analyzed using independent samples t tests, Mann-Whitney U test, and Spearman rank-order correlation coefficient. fMRI data were analyzed using validated neuroimaging software and tested using a general linear model.

RESULTS

PDAP patients had greater anxiety (P<.0001) and depression scores (P=.001), more jaw function impairment (P<.0001), and greater social impact (P<.0001) than controls. No significant differences were found for brain activation spatial extent (PDAP X Controls subjective pain: P=.48; PDAP X Controls stimulus intensity: P=.12). Brain activations were significantly increased for PDAP patients compared to control subjects when matched to stimulus intensity in several regions related to the sensory-discriminative and cognitive components of pain perception, including the primary and secondary somatosensory cortices, inferior parietal lobule, insula, premotor cortex, prefrontal cortex, and thalamus. When matched to subjective pain ratings, increased brain activations were still present for PDAP patients compared to controls, although to a lesser extent.

CONCLUSION

The present results suggest that dentoalveolar pressure is processed differently in the brain of PDAP patients, and the increased activation in several brain areas is consistent with amplified pain processing.

Posterior Teeth Occlusion Associated with Cognitive Function in Nursing Home Older Residents: A Cross-Sectional Observational Study

Early detection and subsequent reduction of modifiable risk factors for cognitive decline is important for extending healthy life expectancy in the currently aging society. Although a recent increase in studies on the state or number of the teeth and cognitive function, few studies have focused on the association between posterior teeth occlusion necessary to maintain chewing function and cognitive function among older adults. This study examined the association between posterior teeth occlusion and cognitive function in nursing home older residents. In this cross-sectional study, 279 residents aged ≥60 years from eight nursing homes in Aso City, Japan participated in cognitive function and dental status assessments and completed a comprehensive questionnaire survey in 2014. Cognitive function was measured using a Mini-Mental State Examination (MMSE). Posterior teeth occlusion was assessed using a total number of functional tooth units (total-FTUs), depending on the number and location of the remaining natural and artificial teeth on implant-supported, fixed, and removable prostheses. Linear regression models were used to assess univariate and multivariate associations between total-FTUs and MMSE scores. Models were sequentially adjusted for demographic characteristics, number of natural teeth, socioeconomic status, health behaviors, comorbidities, physical function, and nutritional status. Among the 200 residents included in our analysis, mean MMSE scores and total-FTUs were 11.0 ± 8.6 and 9.3 ± 4.6, respectively. Higher total-FTUs were significantly associated with higher MMSE scores after adjustment for demographics and teeth number (B = 0.48, 95% confidence interval [CI] = 0.22–0.74). The association remained significant even after adjustment for all covariates (B = 0.25, 95% CI = 0.01–0.49). The current findings demonstrated that loss of posterior teeth occlusion was independently associated with cognitive decline in nursing home older residents in Japan. Maintenance and restoration of posterior teeth occlusion may be a preventive factor against cognitive decline in aged populations.

Dental Implants - Perceiving Patients' Satisfaction in Relation to Clinical and Electromyography Study on Implant Patients

The aim of this study is to evaluate the satisfaction of patients with posterior implants in relation to the clinical success criteria and surface electromyography (sEMG) findings of the masseter and temporalis muscles. Total 42 subjects were investigated. Twenty one subjects with posterior dental implants were interviewed using a questionnaire and the clinical success criteria were determined based on The International Congress of Oral Implantologists. The myofunction of the masticatory muscles were assessed using sEMG (21 subjects) and compared to the control group of subjects without implants (21 subjects). Out of 21 subjects, all were satisfied with the aesthetics of their implant. Twenty of them (95.2%) were satisfied with its function and stability. As for clinical criteria, 100% (50) of the implants were successful with no pain, mobility or exudates. sEMG findings showed that patients have significantly lower (p<0.01) basal or resting median power frequency but with muscle burst. During chewing, control subjects showed faster chewing action. There was no difference in reaction and recovery time of clenching for both groups. In conclusion, the satisfaction of implant patients was high, and which was in relation to the successful clinical success criteria and sEMG findings.

[The treatment effects and mechanisms of pyrroloquinoline quinone on defective teeth and mandible in Bmi-1 knockout mice]

OBJECTIVE

To investigate the treatment effects and mechanisms of pyrroloquinoline quinine(PQQ) on defective teeth and mandible in Bmi-1 knockout mice.

METHODS

Male and female Bmi1(+/-) mice were paired with each other from the same nest. At the age of 7 weeks, the mice were divided into three groups, the wild type mice received normal diet(10 mice, WT group), Bmi1(-/-) mice received normal diet (10 mice, BKO group), and the Bmi1(-/-) mice received normal diet and PQQ diet(10 mice, BKO+PQQ group). X-ray and micro- CT were used to detect mandible and dental size and bone mineral density. HE staining, histochemical and immunohistochemical methods were respectively used to detect alveolar bone thickness of cortical bone, predentin thickness of mandibular first molar, mandibular osteoblast number and osteoclast number. Flow cytometry was used to detect reactive oxygen species(ROS) levels of various organs(femur, thymus and liver). The data were statistically analyzed with one-way ANOVA and t test.

RESULTS

Compared with BKO mice, BKO+PQQ mice partially rescued total body phenotype, increased body weight and prolonged survival time. X- ray and micro- CT showed the size of the mandible and teeth and bone mineral density of PQQ+BKO mice increased compared with BKO mice. In PQQ+BKO mice, mandibular alveolar bone cortical thickness [(68.65 ± 0.25) µm] was significantly different from that in BKO mice [(42.45 ± 0.35) µm] (P<0.01). There was significant difference in predentin thickness of mandibular first molar between PQQ+BKO mice [(4.25 ± 0.15) µm] and BKO mice [(31.55 ± 0.35) µm] (P<0.001). The number of osteoblasts in the mandible of BKO+PQQ mice [(38.45 ± 0.25) cell/mm³] was significantly higher than that in the BKO mice [(18.15 ± 0.55) cell/mm³] (P<0.01). However, the number of osteoclasts in the BKO+PQQ mice [(9.45 ± 0.25) cell/mm³] was significantly lower than that in the BKO group [(14.25 ± 0.35) cell/mm³] (P<0.01). Compared with the BKO group, ROS levels of the femur, thymus and liver in the BKO+PQQ mice were significantly decreased (P<0.01).

CONCLUSIONS

The results indicate that PQQ may have treatment effects on defective teeth and mandible through promoting osteoblast bone formation and reducing osteoclast bone resorption, scavenging ROS and reducing DNA damage.

Fluorescence properties of human teeth and dental calculus for clinical applications

Fluorescent emission of human teeth and dental calculus is important for the esthetic rehabilitation of teeth, diagnosis of dental caries, and detection of dental calculus. The purposes of this review were to summarize the fluorescence and phosphorescence of human teeth by ambient ultraviolet (UV) light, to investigate the clinically relevant fluorescence measurement methods in dentistry, and to review the fluorescence of teeth and dental calculus by specific wavelength light. Dentine was three times more phosphorescent than enamel. When exposed to light sources containing UV components, the fluorescence of human teeth gives them the quality of vitality, and fluorescent emission with a peak of 440 nm is observed. Esthetic restorative materials should have fluorescence properties similar to those of natural teeth. Based on the fluorescence of teeth and restorative materials as determined with a spectrophotometer, a fluorescence parameter was defined. As to the fluorescence spectra by a specific wavelength, varied wavelengths were investigated for clinical applications, and several methods for the diagnosis of dental caries and the detection of dental calculus were developed. Since fluorescent properties of dental hard tissues have been used and would be expanded in diverse fields of clinical practice, these properties should be investigated further, embracing newly developed optical techniques.

Tensile mechanical properties of swine cortical mandibular bone

Temporary orthodontic mini implants serve as anchorage devices in orthodontic treatments. Often, they are inserted in the jaw bones, between the roots of the teeth. The stability of the mini implants within the bone is one of the major factors affecting their success and, consequently, that of the orthodontic treatment. Bone mechanical properties are important for implant stability. The aim of this study was to determine the tensile properties of the alveolar and basal mandible bones in a swine model. The diametral compression test was employed to study the properties in two orthogonal directions: mesio-distal and occluso-gingival. Small cylindrical cortical bone specimens (2.6 mm diameter, 1.5 mm thickness) were obtained from 7 mandibles using a trephine drill. The sites included different locations (anterior and posterior) and aspects (buccal and lingual) for a total of 16 specimens from each mandible. The load-displacement curves were continuously monitored while loading half of the specimens in the oclluso-gingival direction and half in the mesio-distal direction. The stiffness was calculated from the linear portion of the curve. The mesio-distal direction was 31% stiffer than the occluso-gingival direction. The basal bone was 40% stiffer than the alveolar bone. The posterior zone was 46% stiffer than the anterior zone. The lingual aspect was stiffer than the buccal aspect. Although bone specimens do not behave as brittle materials, the diametral compression test can be adequately used for determining tensile behavior when only small bone specimens can be obtained. In conclusion, to obtain maximal orthodontic mini implant stability, the force components on the implants should be oriented mostly in the mesio-distal direction.

On the initial propagation of dental caries

A multi-dimensional model for dental caries is applied to study the shape of caries lesions in a realistic tooth geometry and to examine the rate of progress of caries. An upgraded model, taking into account the outer prismless enamel layer, is derived and solved. The model demonstrates the importance of this layer in delaying the onset of caries. The conclusions are discussed in light of experimental results.

[Dynamics of dental status of pregnant women in conjunction with their vegetative and psycho-emotional performance]

The aim of this study was to investigate the dynamics of the dental status in relation to the vegetative and psycho-emotional changes in women in the 1st, 2nd, and 3rd trimester of pregnancy. Dental and clinical neurological examination was conducted to study psycho-emotional and vegetative status of 51 pregnant women aged 19-36 years, who were registered in the antenatal clinic of Poltava. The analysis of the relationship between dental indicators, vegetative and psycho-emotional status of women in the 1st, 2nd, and 3rd trimester of pregnancy are presented. Analysis of the results showed that in women in the 3rd trimester the index values of DMF and PMA grow. Despite the evidence that oral health worsens in the 3rd trimester good oral health is maintained. The vegetative function of the body and a high level of adaptive-compensatory capacity of the organism are maintained. The revealed changes of dental health, features of autonomic regulation and psycho-emotional status of pregnant women should be considered when planning dental preventive measures.

Isolation of dentin tissue by usinga new liner biodentine at management of simulated experimental caries

The aim of our study was the use of different types of isolation systems in the treatment of experimentally simulated dental caries that will allow to present additional comparative characteristic for morphological responses of the pulp.For realization of this purpose, 3 systems have been selected: UltraBlend (Ultradent), Biodentine (Septodont) and adhesive system Prime&Bond NT (Dentsply). The study was conducted at the laboratory of Alexander Natishvili Institute of Morphology. For this experiment, 12 male, 6 months of age rabbits were selected. There were created 3 experimental groups, each of which included 4 rabbits. Restoration of the teeth in experimental rabbits with Biodentine revealed sufficient physical properties enabling the operator most comfortably conduct his/her clinical activities: kneading, bringing into caries cavity, condensing and filling dental defect. Isolation of dentin by Biodentine doesn't contradict and/or reduce application of adhesive systems, which is also important for teeth restorations. Biodentine has optimal working time (final curing 10-12 minutes) enabling the operator to conduct maximal formation of material at the bottom of caries cavity.

Electrophysiological evidence on epileptiform activity enhanced by electrical stimulation of teeth in rats

The aim of this study was to evaluate the possible effects of electrical stimulation (ES) of tooth on penicillin-induced epileptiform activity in rats. Experiment was realized on 24 adult male Sprague Dawley rats. Rats were assigned three groups [stimulation group (SG), penicillin group (PG), and penicillin+stimulation group (PSG)]. In SG, ES was only applied. Ten pulses of electrical current were delivered to the teeth for a duration of 2 milliseconds at 1-second intervals from a stimulator. Currents were applied in the range of 40-240 μA with 40 μA steps. Electrocorticography (ECoG) recordings were taken before and after ES. In PG, ECoG recordings were taken before and during the injection of penicillin. In PSG, after epileptiform activity was induced, ES was applied and ECoG recordings were taken as in SG. All the data were analyzed with Student's t test. Applied currents did not cause any epileptiform activity in SG. When the PSG was compared with the PG it was seen that the spike frequency of epileptiform activity increased in a statistically significant way after application of 240 μA (P < 0·05). On the other hand current application caused an increase in the spike amplitude of the PSG compared with the amplitude of the PG, but it was not statistically significant. We concluded that ES of tooth with high current can trigger epileptiform activity in rats. For this reason, further research is required to evaluate the effects of ES of tooth for pulp testing on epileptic human subjects and antiepileptic drug users.

Teeth number anomalies in permanent dentition among non-syndromic dental patients

The aim of this study was to establish teeth number anomalies in relation to gender, tooth type, location, distribution pattern and the association between frequently missing teeth among a group of dental patients in Turkey. A total of 378 non-syndromic patients (240 females and 138 males) with an age range of 7-45 (x +/- SD = 22.07 +/- 3.6) having evidence of absent or excess teeth were evaluated in the study. Pearson Chi-square, Fisher's exact, McNemar and Kappa coefficients were used for statistical analysis. 237 patients had a total of 546 congenitally missing teeth and 141 had 185 excess teeth. Congenitally missing teeth were more commonly seen rather than the presence of supernumerary teeth. Difference was determined in the frequent locations of congenital missing and supernumerary teeth. The most frequent missing tooth type was found to be the mandibular second premolar (26.6%), while the majority of supernumerary teeth were located in the anterior region of the maxillary arch (37.9%). Both teeth number anomalies were more commonly seen among females. In hypodontia cases the occurrence of symmetrical agenesis of laterals and second premolars in maxilla; centrals and second premolars in mandible was notable. Agenesis of mandibular centrals was found to be associated with maxillary lateral agenesis in males. Also higher prevalence of molar teeth agenesis was determined in the occurrence of at least 4 teeth agenesis. These findings will serve as information about the contemporary demographic pattern of teeth number anomalies among non-syndromic Turkish dental patients and can provide evidence that agenesis of some teeth symmetrically or together are the products of the same genetic mechanisms.

Masticatory tensile developed in upper anterior teeth with chronic apical periodontitis. A finite-element analysis study

Commonly is accepted that a non-vital tooth has a higher risk of root fracture but there is a relatively little knowledge about the specific biomechanical behavior of non-vital frontal teeth with chronic apical periodontitis. The aim of our study was to evaluate the deformation and tensile generated in these teeth while vertically loading them because it is crucial to assess the moment when the absorbed occlusal forces exceed the elasticity of root dentine. Using the method of finite-element analysis, we highlighted the distribution patterns of the compressive and tension tensile, as well as their concentration areas. The vertical forces of 100 N generate deformations of no clinical risk in teeth with chronic apical periodontitis. The tensile developed in these teeth are higher than those in the vital teeth are but do not exceed the value of the elastic modulus of the radicular dentin. By increasing the force to 300 N occur elastic deformations, which cannot be neglected anymore. Even so, the 300 N forces do not generate deformations of the alveolar bone. The highest tensile at loading with 300 N was generated in vertical direction but in the cervical area of the tooth also developed tensile in lingual and mesiodistal direction that must be taken into consideration because they are near the risk limit of the elasticity modulus. The crack lines or fractures can appear both in case of excessive or even usual but accumulative occlusal forces that gradually alter the mechanical resistance of the tooth.

Dentinogenesis imperfecta - hardness and Young's modulus of teeth

Dentinogenesis imperfecta type II (DI-II) is the most common dental genetic disease with reported incidence 1 in 8000. Elasticity and hardness of the enamel of teeth are important values which are connected with their resistance to attrition. It is hypothesized that values of physical properties for healthy teeth and teeth with DI-II are different. The aim of the study was to investigate some physical properties of teeth extracted from patients with DI-II in comparison with normal teeth. The material of the study was six teeth: three lower molars, with clinical signs of DI-II, which were extracted due to complications of pulp inflammation and three other lower molars which were extracted for orthodontic reasons - well formed, without any signs of pathology. The surfaces of DI-II and normal teeth were tested on the CSM Instruments Scratch Tester machine (producer CSEM Switzerland) by Oliver and Pharr method. The indenter used was Vicker's VG-73 diamond indenter. Additionally, the Scanning Electron Microscopy (SEM) analysis of the surface of the teeth with DI-II was made. Vickers hardness of the teeth with dental pathology (DI-II) was seven times smaller, and Young's modulus six times smaller than those of healthy teeth. The parameters of hardness and elasticity of enamel of teeth with clinical diagnosis of DI-II were very much smaller than in normal teeth and because of that can be responsible for attrition.

[Functional condition of temporal and masticatory muscles in patients with malocclusion complicated by crowding of frontal teeth]

To study functional condition of temporal and masticatory muscles in patients with malocclusion, complicated by crowding of frontal teeth, 54 patients were subjected to electromyography. It was found that the degree of functional imbalance of masticatory and temporal muscles depends on the type of crowding of frontal teeth. Investigating phases of physiological rest in patients with crowding of maxilla frontal teeth high indices of oscillation amplitude of temporal muscles biopotentials (P < 0,05) were detected. The study has established that in state of compression in patients with crowding of frontal teeth of maxilla and mandibula temporal muscles are more active, what is connected with insufficient activity of masticatory muscles (P < 0,05).

Fracture behavior of human molars

Despite the durability of human teeth, which are able to withstand repeated loading while maintaining form and function, they are still susceptible to fracture. We focus here on longitudinal fracture in molar teeth-channel-like cracks that run along the enamel sidewall of the tooth between the gum line (cemento-enamel junction-CEJ) and the occlusal surface. Such fractures can often be painful and necessitate costly restorative work. The following study describes fracture experiments made on molar teeth of humans in which the molars are placed under axial compressive load using a hard indenting plate in order to induce longitudinal cracks in the enamel. Observed damage modes include fractures originating in the occlusal region ('radial-median cracks') and fractures emanating from the margin of the enamel in the region of the CEJ ('margin cracks'), as well as 'spalling' of enamel (the linking of longitudinal cracks). The loading conditions that govern fracture behavior in enamel are reported and observations made of the evolution of fracture as the load is increased. Relatively low loads were required to induce observable crack initiation-approximately 100 N for radial-median cracks and 200 N for margin cracks-both of which are less than the reported maximum biting force on a single molar tooth of several hundred Newtons. Unstable crack growth was observed to take place soon after and occurred at loads lower than those calculated by the current fracture models. Multiple cracks were observed on a single cusp, their interactions influencing crack growth behavior. The majority of the teeth tested in this study were noted to exhibit margin cracks prior to compression testing, which were apparently formed during the functional lifetime of the tooth. Such teeth were still able to withstand additional loading prior to catastrophic fracture, highlighting the remarkable damage containment capabilities of the natural tooth structure.

Constructs and scaffolds employed to regenerate dental tissue

Dental tissue injury and regeneration affects the daily lives of almost everyone. Tissue engineering is emerging as a promising therapy to regenerate missing teeth and dental tissues. The aim of regenerative dental therapies is to restore patients to full oral health. This means restoring normal function to missing or damaged tissue. Regeneration approaches use a combination of scaffolds, stem cells, growth factors, tissue engineering, organ tissue culture, transplantation, and tissue grafting. There are 8 key elements to create and use tissue constructs for tissue regeneration. These will be described in detail in this article.

[Periodontal tissue spectral assessment]

The periodontal condition was investigated by means of tooth natural frequency assessment. The correlation between tooth natural frequency and mobility was found out. The comparative estimation of percussion and spectral methods for natural frequency assessment revealed the percussion method to be more complicates because the initial acoustic signal is disturbed by external noises and hammer sound. The spectral method allows receiving reliable and reproducible results when using modified two-parametrical periodontometer.

[Orthodontic treatment in adults with compromised periodontium: biomechanical principles and clinical applications]

In recent years, there has been a dramatic increase in the number of adults receiving comprehensive orthodontic treatment. In clinical practice, management of adults may be somewhat different than for most adolescents. Adults are more likely than adolescents to have dentitions that have undergone some degree of mutilation over time, which may necessitate alterations in the treatment strategy. Excessive wear, missing and compromised teeth are some of the differences observed. For adult patients who have experienced bone and attachment loss as a consequence of periodontal disease, a new set of biomechanical requirements exists for producing the tooth movements desired during the orthodontic therapy. Proper planning and appliance design for adults presenting with multiple missing teeth may require some degree of creativity to adapt to unique malocclusions and deliver the proper biomechanical force system. In this article, current clinical application of biomechanical principles will be presented with emphasis on clinical orthodontic management of severely mutilated dentitions.

Functional tooth regeneration using a bioengineered tooth unit as a mature organ replacement regenerative therapy

Donor organ transplantation is currently an essential therapeutic approach to the replacement of a dysfunctional organ as a result of disease, injury or aging in vivo. Recent progress in the area of regenerative therapy has the potential to lead to bioengineered mature organ replacement in the future. In this proof of concept study, we here report a further development in this regard in which a bioengineered tooth unit comprising mature tooth, periodontal ligament and alveolar bone, was successfully transplanted into a properly-sized bony hole in the alveolar bone through bone integration by recipient bone remodeling in a murine transplantation model system. The bioengineered tooth unit restored enough the alveolar bone in a vertical direction into an extensive bone defect of murine lower jaw. Engrafted bioengineered tooth displayed physiological tooth functions such as mastication, periodontal ligament function for bone remodeling and responsiveness to noxious stimulations. This study thus represents a substantial advance and demonstrates the real potential for bioengineered mature organ replacement as a next generation regenerative therapy.

Stomatognathic adaptive motor syndrome is the correct diagnosis for temporomandibular disorders

Temporomandibular disorder is a generic and inadequate conception to be used as a diagnosis. It fails to express the etiology or the pathophysiology and it is mainly associated with the anatomical site. Moreover, the clinical condition presents a mandibular motor problem and not a joint problem. The hypothesis presents the new diagnosis stomatognathic motor adaptive syndrome, which comprehend a motor response and the adaptive processes it induces. Inadequate occlusal contacts cause the mandible to shift in order to reach an ideal intercuspal position. The condylar displacements are proportional to such movements. Temporomandibular joint (TMJ) receptors respond to the capsular mechanical stress and the information reaches the trigeminal sensory nuclei. The mandibular modified position seems to be relevant information and may interfere with catecholaminergic neurotransmission in basal ganglia. The main motor responses comprise increased jaw muscle tone, decreased velocity of movements and incoordination. The overload of muscle function will produce adaptive responses on many stomatognathic structures. The muscle adaptive responses are hypertonia, pain, fatigue and weakness. Temporomandibular joint presents tissue modification, disc alteration and cracking noise. Periodontium show increased periodontal membrane, bone height loss and gingival recession. Teeth manifest increased wear facets, abfraction and non-accidental fractures. The periodontal and teeth adaptive processes are usually identified as occlusal trauma. The altered stomatognathic functions will show loss of velocity during mastication and speech. Fatigue, weakness in jaw muscle and difficulties to chew hard food are related to hypertonia. Incoordination between stomatognathic muscles groups is found, causing involuntary tongue/cheek biting and lateral jaw movements on speech. Otologic complaints, as aural fullness and tinnitus, are related to the tensor tympani muscle, innervated by the trigeminal nerve.

Effect of wear on stress distributions and potential fracture in teeth

Finite element analysis is conducted on a tooth model with different degrees of wear. The model is taken as a hemispherical shell (enamel) on a compliant interior (dentin). Occlusal loading is simulated by contact with a flat or curved, hard or soft, indenter. Stress redistributions indicate that development of a wear facet may enhance some near-contact fracture modes (cone-ring cracks, radial-median cracks, edge-chipping), but have little effect on far-field modes (margin cracks). Contacts on worn surfaces with small, hard food objects are likely to be most deleterious, generating local stress concentrations and thereby accelerating the wear process. More typical contacts with larger-scale soft foods are unlikely to have such adverse effects. Implications concerning dietary habits of animals is an adjunct consideration in this work.

Diffuse noxious inhibitory controls triggered by heterotopic CO2 laser conditioning stimulation decreased the SEP amplitudes induced by electrical tooth stimulation with different intensity at an equally inhibitory rate

The purpose of this study was to investigate (1) whether selective Adelta-fiber stimulation with CO(2) laser produces a diffuse noxious inhibitory controls (DNIC) effect in the trigeminal nerve territory; and (2) whether the DNIC effect differs depending on test stimulus intensities under constant conditioning stimuli. To examine whether the CO(2) laser radiation on the dorsum of the hand selectively stimulates Adelta-fibers, laser evoked potentials (LEP) were recorded. The mean peak latency of LEP was 381.4 ms. The findings revealed that the CO(2) laser selectively stimulated Adelta-fibers. Electrical tooth stimuli with 3 levels of intensities (1.2, 1.4, 1.6 times the pain threshold) were applied to subjects as test stimulation in randomized order, with a CO(2) laser stimulus of 18 mJ/mm(2) applied to the dorsum of the hand for 4 min as the noxious conditioning stimulus. Somatosensory evoked potentials (SEP) induced by electrical tooth stimulation were recorded and tooth pain intensity was evaluated using a visual analogue scale (VAS). The amplitudes of the SEP late component and VAS values were significantly decreased only during the conditioning stimuli without aftereffect. The inhibitory rates of the amplitudes ranged from 31.3% to 34.6% and the VAS values from 29.0% to 31.2%. There were no significant differences in their inhibitory rates between the 3 test stimulus intensities. The result indicated that selective Adelta-fiber stimulation with the CO(2) laser produces a DNIC effect in the trigeminal nerve territory and suggested that the DNIC effect does not depend on the intensity of the test stimuli.

Finite element simulation of the human mandible: the role of (natural) teeth

INTRODUCTION

Individual bone quality depends on genetic, biological, and mechanical influencing factors, where the latter is accessible via Finite Element Simulation. This work is part of an interdisciplinary research project with the purpose of stepwise refinement towards anatomical reality. This approach opened the door for many interrelated applications such as atrophy of the jaw bone, periodontology, implantology, or TMJ disorders. This lecture is dedicated to the influence of dental anatomy on mandibular biomechanics.

MATERIALS AND METHODS

In general, biomechanical simulation requires reconstruction of the individual anatomy, implementation of the inhomogeneous and anisotropic material law of bone, and realization of the load case due to tooth, muscle and joint forces. The simulation chain ranges from image processing of CT data up to specifically adapted post-processing of the simulation results. In spite of ongoing research, there is still a fundamental difference of dental implants compared to natural teeth: the periodontal ligament (PDL) present at the interface between teeth and mandibular corpus. Due to its thickness of about 0.2 mm, the PDL was introduced to the simulation model by a special semiautomatic procedure.

RESULTS

Simulations "with and without PDL" proved remarkable force absorption due to the PDL, as well as qualitative changes of the stress/strain profiles of the alveolar ridge. Concerning the simulation without PDL, the observed high compressive strains at the adjacent bone were in agreement with regions of frequent implant failure.

CONCLUSION

The PDL is essential for the structural behavior of the human mandible. Based on the mechanical adaptation of bone, the comparison of the simulation with and without PDL provided special insight to the changes due to dental implants, in particular implant loss and bone resorption. Finally, the simulation will serve as a virtual platform for further evaluation (a) of implant design (b) of implant placement.

Dental compression syndrome and TMD: examining the relationship

Fifty years ago, McCollum and Stuart described a subtle pathology of function in the human masticatory system that was difficult to understand. That subtle pathology is the damage that results from compression of teeth. It is subtle because often the patient is unaware. It is pathologic because it applies untoward stress to the dentition, alveolar bone, and the TMJ. It is difficult to understand for many reasons: multiple etiology, few patient complaints, poor understanding of the deformations caused by DCS, the role of equilibration during treatment is unclear, and the dissimilar ways it takes its toll. For proper management of DCS, the general dentist should monitor for signs of compression and wear, educate the patient about the problem, and provide treatment. While every patient with a flattened dentition should not have their teeth dramatically altered or reconstructed, the dental profession should form a consensus that the natural, sharp morphology of teeth is superior to a flattened dentition, and should be preserved throughout one's lifetime.

Detection of interproximal demineralized lesions on human teeth in vitro using frequency-domain infrared photothermal radiometry and modulated luminescence

Frequency-domain photothermal radiometry (FD-PTR or PTR) is used to detect mechanical holes and demineralized enamel in the interproximal contact area of extracted human teeth. Thirty-four teeth are used in a series of experiments. Preliminary tests to detect mechanical holes created by dental burs and 37% phosphoric acid etching for 20 s on the interproximal contact points show distinct differences in the signal. Interproximal contact areas are demineralized by using a partially saturated acidic buffer system. Each sample pair is examined with PTR before and after micromachining or treating at sequential treatment periods spanning 6 h to 30 days. Dental bitewing radiographs showed no sign of demineralized lesion even for samples treated for 30 days. Microcomputer tomography (micro-CT), transverse microradiography (TMR), and scanning electron microscopy (SEM) analyses are performed. Although micro-CT and TMR measured mineral losses and lesion depths, only SEM surface images showed visible signs of treatment because of the minimal extent of the demineralization. However, the PTR amplitude increased by more than 300% after 80 h of treatment. Therefore, PTR is shown to have sufficient contrast for the detection of very early interproximal demineralized lesions. The technique further exhibits excellent signal reproducibility and consistent signal changes in the presence of interproximal demineralized lesions, attributes that could lead to PTR as a reliable probe to detect early interproximal demineralization lesions. Modulated luminescence is also measured simultaneously, but it shows a lower ability than PTR to detect these interproximal demineralized lesions.

Unilateral posterior crossbite and mastication

OBJECTIVE

This study was designed to characterize masticatory-cycle morphology, and distance of the contact glide in the closing masticatory stroke, in adult subjects with uncorrected unilateral posterior crossbite (UPXB), comparing the results obtained with those obtained in a parallel group of normal subjects.

STUDY DESIGN

Mandibular movements (masticatory movements and laterality movements with dental contact) were registered using a gnathograph (MK-6I Diagnostic System) during unilateral chewing of a piece of gum. Traces were recorded on the crossbite and non-crossbite sides in the crossbite group, and likewise on both sides in the non-crossbite group.

RESULTS

Mean contact glide distance on the crossbite side in the UPXB group was significantly lower than in the control group (p<0.001), and mean contact glide distance on the non-crossbite side in the UPXB group was significantly lower than in the control group (p=0.042). Cycle morphology was abnormal during chewing on the crossbite side, with the frequency distribution of cycle types differing significantly from that for the noncrossbite side and that for the control group (p<0.001).

CONCLUSIONS

Patients with crossbite showed alterations in both contact glide distances and masticatory cycle morphology. These alterations are probably adaptive responses allowing maintenance of adequate masticatory function despite the crossbite.

Treating Class II Patients with Removable Plates and Functional Orthopedic Appliances

OBJECTIVE

To determine the influence of physiological growth pattern and anterior tooth inclination on the outcome in Class II patients treated with removable orthodontic plates and functional orthodontic appliances.

PATIENTS AND METHODS

After recruiting 50 patients with an upper anterior proclination of 1-SN >or= 107 degrees for this retrospective study, another 50 patients with a retroclination of 1-SN <or= 95 degrees were also included. All patients initially presented a skeletal Class II relationship with a distoclusion of at least one premolar width in the region of the first molars. All patients were evaluated separately by gender and additionally subdivided into three subgroups with a horizontal, neutral, or vertical craniofacial configuration. Treatment with removable orthodontic plates (pretreatment) and functional orthodontic appliances was initiated in mixed dentition. Pre- and post-treatment lateral cephalograms were evaluated for each patient.

RESULTS

Dento-alveolar analysis showed that the inclination of the upper incisors changed in the direction of the clinical standard value independent of the craniofacial configuration, although full correction using removable orthodontic plates and functional orthodontic appliances was not always achieved. Similarly good treatment outcomes were achieved with regard to overjet and overbite. The lower incisors of all patients were in proclination after treatment. The ANB angle was reduced in both groups. Nevertheless, on average a skeletal Class II persisted in the Class II, Division 2 patients, while Class II, Division 1 patients with horizontal craniofacial configurations attained skeletal Class I.

CONCLUSIONS

Treatment of Class II patients with removable appliances resulted in differences depending on anterior tooth inclination (Class II, Division 1 and II, Division 2) and craniofacial configuration. These differences must be taken into account during treatment planning. Complete treatment success with regard to sagittal jaw balance is very difficult to achieve with removable orthodontic plates (pre-treatment) and functional orthodontic appliances alone in Class II, Division 1 cases with a vertical craniofacial configuration and generally in Class II, Division 2 cases. A particularly favorable constellation for removable treatment is a Class II, Division 1 situation with a horizontal craniofacial configuration and retroclined or orthognathic mandibular anteriors.

Influence of cavity preparation design on fracture resistance of posterior Leucite-reinforced ceramic restorations

STATEMENT OF PROBLEM

Controversy exists concerning the preferred cavity design for posterior ceramic restorations to improve their resistance to fracture under occlusal load.

PURPOSE

The aim of this study was to assess the resistance to fracture of leucite-reinforced ceramic restorations placed on molars with different cavity preparation designs.

MATERIAL AND METHODS

Ninety noncarious molars were selected, stored in 0.2% thymol solution, and divided into 9 groups (n = 10): IT, intact teeth; CsI, conservative inlay; ExI, extensive inlay; CsO/mb, conservative onlay with mesio-buccal cusp coverage; ExO/mb, entensive onlay with mesio-buccal cusp coverage; CsO/b, conservative onlay with buccal cusp coverage; ExO/b, entensive onlay with buccal cusp coverage; CsO/t, conservative onlay with total cusp coverage; ExO/t, extensive onlay with total cusp coverage. Teeth were restored with a Leucite-reinforced ceramic (Cergogold). The fracture resistance (N) was assessed under compressive load in a universal testing machine. The data were analyzed with 1-way and 2-way analyses of variance, followed by the Tukey HSD test (alpha = .05). Fracture modes were recorded, based on the degree of tooth structure and restoration damage.

RESULTS

One-way analysis showed that intact teeth had the highest fracture resistance values. Two-way analyses showed no significant differences for the isthmus extention factor, but showed a significant difference for the preparation design type of fracture (P = .03), and also for the interaction between both factors (P = .013). The fracture mode observed in all groups tended to involve only restorations.

CONCLUSION

Within the limitations of this study, it was observed that cuspal coverage does not increase fracture resistance of the posterior tooth-restoration complex restored with leucite-reinforced ceramics.

[Study of wear of restorative materials and teeth-antagonists in vitro]

Since clinical evaluation of wear turns out to be particularly time consuming, a standardized method was developed to model oral mastication. So-called artificial mouth was used to assess the extent of wear caused from different restorative materials in contact with bovine enamel. Ball heads manufactured from modern veneering ceramics, gold alloy, amalgam and resin composite materials were loaded with a contact load of 50 N for 200,000 chewing cycles. Additional thermo-cycling (5 degrees /55 degrees C) for 2,500 cycles was conducted in the artificial mouth. The worn surfaces, both on the material specimens and on the antagonist bovine enamel surfaces were volumetrically scanned under a laser microscope. Negligible wear rates were observed for the veneering ceramics and for the gold alloy. Most veneering ceramics as well as the resin composite materials caused low wear on the antagonist enamel surfaces. In contrast, the antagonist enamel was significantly damaged in contact with amalgam or some of the ceramic materials. However, modern veneering ceramics as well as gold alloys might be recommended in occlusally loaded contact with the antagonist enamel, whereas resin composite materials might be indicated for non load-bearing areas. Ceramics are contraindicated in case of bruxism.

Influence of prefabricated post material on restored teeth: fracture strength and stress distribution

AIMS

This work studied how prefabricated intraradicular post material affects the mechanical performance of restored teeth. The effect of using two different materials (glass fiber and stainless steel) with significantly different elastic moduli was studied.

METHODS

A combined theoretical and experimental method was used: first, an experimental fracture strength test was performed on 60 extracted human maxillary central incisors. The teeth were decoronated, treated endodontically and restored, 30 with glass fiber posts and 30 with stainless steel posts. The data were recorded and the results compared using an ANOVA test. Then, the finite element technique was used to develop a model of the restored tooth. For both post systems, the model allowed for the study of stress distribution patterns on the restored tooth under external loads.

RESULTS

For teeth restored with stainless steel posts, a significantly lower failure load was found, as compared with those teeth restored with glass fiber posts (520 N versus 803 N). The estimated distributions confirmed a worse mechanical performance on teeth restored using stainless steel posts, with a high stress concentration due to the significant difference between the elastic moduli of the steel and the surrounding materials.

CONCLUSION

Within the limitations of this study, post systems, where the elastic modulus of the post is similar to that of dentin and core, have a better biomechanical performance.

[Neurophysiological background of pain in the orofacial area: review of the literature]

The article presents an overview on the peripheral and central neural mechanisms underlying pain in the orofacial area. First a definition of pain and a description of general aspects of orofacial pain are presented. Characteristics of acute and chronic pain are also described. The study highlights the sense organs, the molecular mechanisms and categories of primary afferents involved in peripheral events of orofacial pain. After describing the brain-stem nuclei participating in trigeminal pain and their functional role, primary afferents involved in nociceptive sensation from the tooth pulp, explanations of dentinal sensitivity and differences between the brain-stem endings of primary afferents among different species are discussed in details. The role of higher brain centres, with a special emphasis on the thalamus and somatosensory cortex in the development of orofacial pain sensation is considered. The last section provides a review about how the activities of nociceptive neurons are controlled by higher brain centres and neurochemicals involved in pain transmission.

Bone loss and teeth

Loss of teeth results in irreversible alveolar bone resorption, and untreated dental disease causes alveolar bone lysis that ultimately leads to loss of teeth. In addition to anchoring the teeth in the alveolar ridge, the maxillary and mandibular bone allows dental restoration procedures, such as construction of root-supported implants, fixed dentures, or removable dentures. However, the functional and cosmetic results depend on the quantity and quality of the maxillary or mandibular bone, which can be affected by many normal and abnormal processes. The alveoli are particularly fragile and labile. Changes in alveolar bone vary considerably across individuals and depend directly on local factors. Many studies have investigated associations between alveolar bone status and bone mass at other skeletal sites. These studies focused chiefly on the course of parodontal disease, alveolar ridge resorption after tooth extraction, and density differences across various mandibular sites. They produced conflicting results, probably because of differences in measurement methods. Measurement sites and methods should be standardized to ensure that reliable and comparable data are obtained. To date, there are few reliable methods for obtaining quantitative measurements of bone mineral content in maxillary and mandibular bone.

Morphometric evaluation of the human tractus solitarius

We measured the cross-sectional area (CSA) of the human tractus solitarius (HTS) with the help of an image-analyzer system on a cross section of the upper part of the medulla oblongata in 44 Japanese cadavers (22 males and 22 females) and examined the relationship between age, sex and whether the subjects were dentulous or edentulous. The results showed no significant differences between the left and right sides of the HTS in either male or female subjects. However, the size of HTS decreased slightly with age in males but not at all in females, whereas tooth loss had a definite incidence on the size of HTS in females but not in male, as the CSA was smaller in edentulous females but not in edentulous males. This would tend to indicate that a decreases in taste function is connected with the aging process in male, and with tooth loss in females.

Morphometric difference in the human maxillary nerve fibers between dentulous and edentulous jaw subjects

This study was conducted to quantify the change in the number and size of myelinated nerve fibers of the maxillary nerve with tooth loss in humans. We carried out a morphometric analysis to compare the number and size of myelinated nerve fibers in the human maxillary nerve between four dentulous and four edentulous jaw cases. Our results indicated that the number of axons decreased by approximately 13,000 with tooth loss. The average size of axons remained unchanged, but there was a change in the fiber size distribution, namely the loss of a large number of small-sized axons was accompanied by the total disappearance of small number of large-sized axons.

Efficiency considerations for the purely tapered interference fit (TIF) abutments used in dental implants

A tapered interference fit provides a mechanically reliable retention mechanism for the implant-abutment interface in a dental implant. Understanding the mechanical properties of the tapered interface with or without a screw at the bottom has been the subject of a considerable amount of studies involving experiments and finite element (FE) analysis. In this paper, approximate closed-form formulas are developed to analyze the mechanics of a tapered interference fit. In particular, the insertion force, the efficiency, defined as the ratio of the pull-out force to insertion force, and the critical insertion depth, which causes the onset of plastic deformation, are analyzed. It is shown that the insertion force is a function of the taper angle, the contact length, the inner and outer radii of the implant, the static and the kinetic coefficients of friction, and the elastic modulii of the implant/abutment materials. The efficiency of the tapered interference fit, which is defined as the ratio of the pull-out force to insertion force, is found to be greater than one, for taper angles that are less than 6 deg when the friction coefficient is 0.3. A safe range of insertion forces has been shown to exist. The lower end of this range depends on the maximum pull-out force that may occur due to occlusion in the multiple tooth restorations and the efficiency of the system; and the upper end of this range depends on the plastic deformation of the abutment and the implant due to interference fit. It has been shown that using a small taper angle and a long contact length widens the safe range of insertion forces.

Influence of drinking method on tooth-surface pH in relation to dental erosion

The aim of this investigation was to study the intraoral pH response on tooth surfaces in relation to dental erosion during and after drinking a sugar-free cola-type soft drink. Six different methods of drinking were tested in a randomized order: holding; short-sipping; long-sipping; gulping; nipping; and sucking. Two methods of pH measurement were used in two series of individuals. In the first series, pH was measured by using the microtouch method in 12 healthy adults at three dental erosion-prone sites: 11 palatally; 11 buccally; and at the mesiobuccal cusp tip of 16. In the second series, pH was measured by using the telemetric method in 6 healthy individuals, producing continuous recordings of pH by means of a glass electrode in a specified approximal area. The two series showed similar results, although the telemetric method generally recorded larger pH falls. Holding the drink in the mouth before swallowing led to the most pronounced pH drop, followed by the long-sipping method. Gulping resulted in only a small decrease of pH. No differences among the three intraoral sites were found when analyzed by using the microtouch method. The conclusion from this study is that the drinking method strongly affects tooth-surface pH and thereby the risk for dental erosion. It therefore seems appropriate to include advice on the method of drinking in dietary counseling related to dental erosion.