Excessive occlusal wear.
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Tooth Abrasion↗
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Occlusal relations and periodontal status in human adults.
A group of 66 adults provided the population for study of relations between various clinical parameters and periodontal status. Dental and habit histories and plaque scores were acquired. Occlusal features included classification of malocclusion, analysis of centric displacement, establishment of patterns of lateral and protrusive excursions, identification of tooth contacts and presence of wear facets. Periodontal analysis included pocket depths, radiographic manifestations and extent of mobility. Class I malocclusion predominated and the majority of patients did not have coincidental centric relation and centric occlusion. Group function is the most common lateral excursive pattern in the adult. Nonfunctional contacts are common as is enamel attrition. Results indicate no significant deleterious influence on the status of the periodontium by occlusal disharmonies.
Adolescent↗
Bite force production capability and efficiency in Neandertals and modern humans.
Although there is consensus that Neandertal craniofacial morphology is unique in the genus Homo, debate continues regarding the precise anatomical basis for this uniqueness and the evolutionary mechanism that produced it. In recent years, biomechanical explanations have received the most attention. Some proponents of the "anterior dental loading hypothesis" (ADLH) maintain that Neandertal facial anatomy was an adaptive response to high-magnitude forces resulting from both masticatory and paramasticatory activity. However, while many have argued that Neandertal facial structure was well-adapted to dissipate heavy occlusal loads, few have considered, much less demonstrated, the ability of the Neandertal masticatory system to generate these presumably heavy loads. In fact, the Neandertal masticatory configuration has often been simultaneously interpreted as being disadvantageous for producing large bite forces. With rare exception, analyses that attempted to resolve this conflict were qualitative rather than quantitative. Using a three-dimensional digitizer, we recorded a sequence of points on the cranium and associated mandible of the Amud 1, La Chapelle-aux-Saints, and La Ferrassie 1 Neandertals, and a sample of early and recent modern humans (n = 29), including a subsample with heavy dental wear and documented paramasticatory behavior. From these points, we calculated measures of force-production capability (i.e., magnitudes of muscle force, bite force, and condylar reaction force), measures of force production efficiency (i.e., ratios of force magnitudes and muscle mechanical advantages), and a measure of overall size (i.e., the geometric mean of all linear craniofacial measurements taken). In contrast to the expectations set forth by the ADLH, the primary dichotomy in force-production capability was not between Neandertal and modern specimens, but rather between large (robust) and small (gracile) specimens overall. Our results further suggest that the masticatory system in the genus Homo scales such that a certain level of force-production efficiency is maintained across a considerable range of size and robusticity. Natural selection was probably not acting on Neandertal facial architecture in terms of peak bite force dissipation, but rather on large tooth size to better resist wear and abrasion from submaximal (but more frequent) biting and grinding forces. We conclude that masticatory biomechanical adaptation does not underlie variation in the facial skeleton of later Pleistocene Homo in general, and that continued exploration of alternative explanations for Neandertal facial architecture (e.g., climatic, respiratory, developmental, and/or stochastic mechanisms) seems warranted.
Animals↗
[Hydroxyapatite coating on metal plates using an aerosol jet printing system].
The purpose of the present study was to investigate the properties of the hydroxyapatite (HA) layer formed by an aerosol jet printing system, aimed at application to the field of dentistry. The HA particle was adhered to the metal substrate. The particles of HA were 1 micron or less in size and were packed closely. When the composition of the formed HA layer was compared to that of the raw material powder, oxygen was increased, but Ca was decreased. Moreover, Ca and P were almost evenly distributed in the layer, but oxygen was not. Dynamic hardness of HA coatings was 31.5 +/- 1.1. The peel strength of HA coating was the highest, at 58.7-39.6 MPa, in 10 microns layer thickness. Interface fractures were observed at 10 microns layer thickness, and cohesive fractures were observed for all other layer thicknesses. The wear amount of HA coating by tooth brush abrasion was significantly large at 100 degrees C heating (p < 0.05), compared with at 250 degrees C and 500 degrees C. At any substrate temperatures, the wear amount of stainless steel substrate tended to be smaller than that of titanium substrate.
Aerosols↗
Medial pterygoid muscle activity during chewing and clenching.
Specific activity of the human medial pterygoid muscle in relation to jaw movements and occlusion during mastication and clenching tasks is unclear. EMG activity of the medial pterygoid, masseter, anterior, and posterior temporal muscles was recorded simultaneously with three dimensional incisor point movement of the mandible. Data were sampled and analyzed by an on-line computer system. Patterns of medial pterygoid muscle activity were consistent for ipsilateral chewing and demonstrated activity of the muscle on the chewing side that peaked near the onset of intercuspation. The muscle on the contralateral side was active at the onset of intercuspation for subjects with a chopping stroke and inactive for those with a more lateral stroke guided into intercuspation on cuspal inclines. Activity in the early part of the closing phase was associated with a marked jaw movement toward the chewing side. There was generally less activity in protrusive than intercuspal clenching when occlusion was normal but more activity if marked incisal wear was present or multiple tooth contacts could be attained on protrusion. Intercuspal clenching initiated less activity when force was directed posteriorly and more activity when directed anteriorly than vertical intercuspal clenching.
Adolescent↗
The relationship between hardness and structure of Pd-Cu-Ga alloys.
Most Pd-Cu-Ga alloys on the market have a yield strength of the order of 1000 MPa, which is too high for an adequate adjustment of the margins of a crown and may promote wear of an opposing natural tooth. In the present work, the structure of a commercial Pd-10 wt% Cu-9 wt% Ga alloy has been shown by means of TEM to consist of thin (5-25 nm) laths with two ordered fct phases with the composition Pd3GaxCu1-x. The c/a ratios in these fct phases are, alternatingly, greater than 1 and less than 1. The transformation of an fcc structure by short atomic movements into the fct structures occurs rapidly below 500 degrees C, as judged by thermal expansion measurements. Such fct structures are likely to provide substantial resistance to dislocation movement and thus a high yield stress and hardness. By adding 6 wt% Ag to the Pd-Cu-Ga alloy and reducing the Ga and Cu content correspondingly, a predominantly fcc structure occurred with nearly no fct laths. At the same time, the hardness was reduced to approximately half the value for the initial Pd-Cu-Ga alloy.
Chemical Phenomena↗
[Distribution of the position of the last remaining tooth in otherwise edentulous mouth, based on mass screening].
The authors examined the frequency of the last remaining tooth's positions in both arches and they found the canine in the lower arch in 63% and the second molar in 13% of the second molar. In single remaining tooth situations the rate of wearing denture is 73%. The cariological status of these teeth is negligible in relation to the bad periodontal health conditions, which are not influenced essentially by crowns or wearing dentures.
Cuspid↗
Skeletal and dental pathology of free-ranging mountain gorillas.
The mountain gorillas of the central Virungas have been the subject of field study for the last 30 years; however, our understanding of morbidity and mortality in these apes is limited. This paper describes pathological conditions of the skeleton and dentition of these animals and evaluates lesions in relation to behavioral and environmental data. The skeletal remains of 31 mountain gorillas from the Karisoke Research Center were examined for enamel wear, carious lesions, abscesses, periodontal disease, antemortem tooth loss, trauma, inflammation, arthritis, neoplasia, and developmental anomalies. Two infants, three juveniles, 13 adult males, and 13 adult females form the sample. Enamel wear in the permanent posterior dentition is moderate. Six periapical abscesses were seen; three are associated with antemortem tooth breakage. No carious lesions were observed. Pronounced calculus buildup and alveolar resorption are the most notable pathological conditions of the dentition and affect all adult animals. The primary affliction of the skeleton is arthritis, which affects 14 animals. Vertebral degenerative disease predominates, but there is also temporomandibular joint involvement. Fractures occur at seven locations in the postcranium. In addition, there are five cranial injuries, including a fractured sagittal crest, and a penetrating wound to the vault, which is believed to result from a bite. Also thought to result from a bite is a case of cranial osteomyelitis. The only other inflammatory responses are two cases of idiopathic periostitis and one idiopathic lytic lesion. Button osteomas affect two animals and are the only neoplastic conditions observed. Two animals are afflicted by developmental abnormalities: one animal by idiopathic vertebral fusion and the other by spinal scoliosis.
Age Determination by Teeth↗
Wear resistance of four luting agents as a function of marginal gap distance, cement type, and restorative material.
This study investigated the effect of marginal gap width, luting cement, and restorative material on the wear resistance of the luting cement in areas where no occlusal contact is present. Three types of resin luting cement and one resin-modified glass-ionomer cement were used with two inlay systems, a resin composite, and an all-ceramic system. Bovine enamel represented tooth structure. Toothbrush abrasion was the wear modality. Three predetermined gap widths were selected: 240 +/- 30 microns, 150 +/- 30 microns, and 60 +/- 30 microns. All specimens were thermocycled. Regardless of the luting cement or the restorative material, there was a significant difference (P < 0.05) in wear resistance of the cement among the three gap distances at both the enamel and restoration interface. Vertical wear of the luting cement at the enamel interface increased linearly with marginal gap distance when all four cements were considered together (r2 > 0.51), regardless of type of restorative material used. The resin-modified glass-ionomer cement showed the least amount of wear for all variables considered. Significant differences in wear were found between the four luting cements at wide gap distances (240 microns) at the enamel interface, regardless of type of restorative material used. No significant differences were found between the two restorative materials at the enamel interface at the three gap distances.
Animals↗
The effect of a carbonated beverage on the wear of human enamel and dental ceramics.
PURPOSE: This study was performed to investigate the effect of a carbonated beverage on the wear of human enamel and three dental ceramics: a conventional porcelain (Vitadur Alpha), a hydrothermal low-fusing ceramic (Duceram-LFC), and a machinable ceramic (Vita Mark II). MATERIALS AND METHODS: Tooth-against-ceramic specimens (10 per group) were tested in a wear machine under a load of 40 N, at a rate of 80 cycles per minute, and for a total of 25,000 cycles. The test was performed in distilled water or with intermittent exposure to a carbonated beverage (Coca-Cola). Wear was determined by measuring the height reduction of the tooth specimens and the depth of wear track in the ceramic specimens. RESULTS: ANOVA revealed a significant difference among the groups for both enamel and ceramic wear (p < .001). When tested in water, Alpha porcelain caused significantly more enamel wear and also exhibited greater wear than Duceram-LFC and Vita Mark II. However, with exposure to the carbonated beverage, the enamel wear produced by Duceram-LFC did not differ significantly from that produced by Alpha porcelain, and Vita Mark II produced the least amount of enamel wear. Overall, exposure to the carbonated beverage significantly increased the enamel wear. The wear of Duceram-LFC and Vita Mark II increased with exposure to the carbonated beverage. CONCLUSIONS: It was concluded that exposure to the carbonated beverage accelerated the enamel wear and decreased the wear resistance of Duceram-LFC and Vita Mark II ceramics. Overall, Vita Mark II was shown to be the most resistant to wear and also significantly less abrasive than conventional Alpha porcelain.
Analysis of Variance↗
[Investigation on the positions and relevant factors of wedge-shaped defects in the elderly].
OBJECTIVE: To investigate the position and relevant factors of wedge-shaped defects in elderly. METHODS: 462 elderly were examined. RESULTS: The occurrence rate of wedge-shaped defects was 99.1%, all had at least labial or buccal defects, with premolars the most frequent. However, 15.2% of them had lingual defects, most frequently in molars. No significant association were found between wedge-shaped defect position and tooth brushing or erosion factors in the group. In tooth with defect, the occlusal surface wear was more severe, the denture abutment teeth were more in number, and the functional mobility was increased; in teeth with lingual defect, these phenomena were more obvious. CONCLUSION: The wedgeshaped defects, besides tooth brushing and erosion factors, occlusal force and its accumulation plays a role as well, lingual lesions are more related to traumatic occlusal force.
Aged↗
Aberrations of the tooth arcade and mandible in Dall's sheep from southwestern Yukon.
Nine Dall's sheep (Ovis dalli dalli) collected in the Ruby Mountains of southwestern Yukon were examined for aberrations of the tooth arcade and mandible. Missing and displaced teeth were common in older sheep (greater than or equal to 6 yr). Necrosis of the mandible was observed in five of eight rams and in one ewe. Corynebacterium pyogenes was cultured from exudates from two rams with enlarged fistulated mandibles. The sequence of events leading to lesions of the tooth arcade and to "lumpy jaw" is postulated to be associated with abnormal wearing of teeth and a disrupted alignment of the tooth arcade, impaction of vegetable matter between teeth and between the gingiva and the root of the tooth, and penetration of the traumatized gingiva membrane and alveolus by oral bacteria which induce a necrotizing infection.
Animal Feed↗
Accuracy and consistency of the visual diagnosis of exposed dentine on worn occlusal/incisal surfaces.
Most indices for the assessment of wear of various aetiologies include the distinction between 'enamel still present' and 'dentine exposed' for grading. Since the visual diagnosis of exposed dentine has not yet been validated, the present study is a first attempt to investigate its accuracy and consistency. Sixty-one examiners (23 scientists, 18 university dentists and 20 dental students) were asked to diagnose 49 tooth areas with different grades of wear and to decide whether dentine was exposed (positive test) or not (negative test). Afterwards, the teeth were histologically evaluated. In 44 areas, dentine (also in all cases with minor wear) was exposed, and in 5 areas enamel was present. Overall sensitivity was 0.65, specificity 0.88 and the proportion of correct diagnoses was 0.67. The diagnosis 'dentine is exposed' was about 5 times as likely and the diagnosis 'dentine is not exposed' half as likely to come from an area with exposed dentine than from an enamel-covered area. The closeness of the visual diagnosis to the histological findings was only fair (kappa=0.27), no significant impact of professional experience was found. For inter- and intra-examiner agreement, kappa was 0.28 and 0.55, respectively. It was concluded that the diagnosis of exposed dentine is difficult.
Dental Enamel↗
[Acid erosions of tooth surface. 1. Influence of saliva, medicaments, fruit acids and mechanical stress].
The clinical aspects, etiology, pathogenesis and classification of dental erosions are reviewed. Individual susceptibility or resistance to erosive damage has been attributed to variations in the quality and quantity of saliva. A lot of medicaments reduce the salivary secretion. Under the influence of acids, in particular of fruit acids, the peripheral tooth surface are demineralized in the absence of dental plaque. The citrus juices showed potentially the worst dental properties. Abrasive brushing techniques and functional influences wear down the already damaged layer of tooth surfaces.
Acids↗
Enamel thickness and the helicoidal wear plane in modern human mandibular molars.
Helicoid occlusion has long been recognized as a feature characterizing the human dentition and has been viewed as an important morphological marker in the transition from Australopithecus to Homo. The hallmark of helicoidal wear is a buccal wear slope in anterior mandibular molars (and a corresponding lingual slope of wear in anterior maxillary molars) reversing to a flat or lingual-oriented one in posterior mandibular molars. If localized increases in enamel thickness are taken as evidence of an adaptation to increased wear resistance, then data on enamel thickness in unworn molars can be used to assess whether the region of greatest wear changes from anterior to posterior in such a way as to provide evidence for the helicoidal wear plane being a structural feature of the orofacial skeleton. Such a hypothesis was supported in a previous study on enamel thickness in modern human maxillary molars. As maxillary and mandibular precisely interdigitate, it is reasonable to expect that a similar pattern of enamel thickness distribution should be present in mandibular molars. To test this, data on the distribution of enamel thickness across functionally relevant regions of the crown were collected on a sample of twenty-nine completely unworn mandibular molars. Results suggest that enamel thickness increases slightly posteriorly but no evidence exists for morphological changes along the mandibular molar series of modern humans to follow a trend towards providing additional tooth material in areas under greater wear in accordance with a helicoidal wear model. This suggests that the patterning of enamel thickness must be viewed in conjunction with other features, such as the biomechanical behaviour of molars during occlusion and axial molar angulation, to ascertain the precise anatomical determinants of this unique feature of the human dentition.
Biomechanical Phenomena↗
Measuring periodontal disease in ancient populations: root and wear indices in study of American Indian skulls.
As an example of the collaboration of periodontologists and physical anthropologists, the skulls of two Indian populations were studied. A root index to assay periodontal disease and a wear index to evaluate occlusal wear, were developed. The first Indian population, living 400 years ago, had more decay, loss of teeth and caries; the second population, living 4,000 years ago, exhibited more periodontal disease. Starting with a sample of eight teeth, two from each quadrant, the statistical analysis showed that a smaller number of teeth would give a reliable assessment of past oral health. Based on our findings, the canines proved to be good indicators for general wear and the incisors for periodontal disease. A six-tooth index of varying teeth studied is proposed for the root index and the wear index in future studies of oral health of ancient populations.
Adolescent↗
Composite resins in the 21st century.
Human enamel and dentin should be used as the physiologic standards with which to compare composite resins, especially in the posterior region. The intrinsic surface roughness of composite resins must be equal to or lower than the surface roughness of human enamel on enamel-to-enamel occlusal contact areas (Ra = 0.64 microns). Roughness determines the biologic strength of composite resins. The nanoindentation hardness value of the filler particles (2.91 to 8.84 GPa) must not be higher than that of the hydroxyapatite crystals of human enamel (3.39 GPa). Composite resins intended for posterior use should have a Young's modulus at least equal to, and preferably higher than, that of dentin (18.500 MPa). The compressive strength of enamel (384 MPa) and dentin (297 MPa) and the fracture strength of a natural tooth (molar = 305 MPa; premolar = 248 MPa) offer excellent mechanical standards to select the optimal strength for posterior composite resins. The in vivo occlusal contact area wear rate of composite resins must be comparable to the attritional enamel wear rate (about 39 microns/y) in molars. Differential wear between enamel and composite resin on the same tooth is a new criterion for visualizing and quantifying the wear resistance of composite resins in a biologic way. Posterior resins must have a radiographic opacity that is slightly in excess of that of human enamel (198% Al). Based on these standard criteria, it can be concluded that in the 21st century the ultrafine compact-filled composite resins may be the materials of choice for restoring posterior cavities.
Analysis of Variance↗
Periodontal condition in Turkish recruits.
The periodontal condition of 300 Turkish troops was investigated using the modified Ramfjord Periodontal Disease Index. In addition, the gingival condition, presence and quantity of plaque and calculus, location and depth of periodontal pockets, tooth mobility, presence and severity of wear facets, diastema magnitude and the DMFT Index were determined. The average PDI was 3.8. Nearly 98% of the recruits suffered from gingivitis, 68% of whom exhibited moderate to severe inflammation without involvement of deeper structures. Moderate plaque accumulation and heavy calculus deposits were observed. An average DMFT of 5.09 was found. Little correlation was found between the relatively low DMFT rate and the Plaque Index.
Adult↗