Clinical implications of the response of enamel and dentin to masticatory loads

The success of restorative procedures is dependent on comprehension of the responses of enamel and dentin, including responses to masticatory forces. The regional variation resulting from masticatory forces is critical because clinically it relates to the thickness of enamel and dentin occlusogingivally. Three-dimensional finite element models of an intact mandibular molar were developed to analyze stresses in enamel and dentin occlusogingivally, buccolingually, and mesiodistally. There were dramatic regional variations in the magnitude and character of different stresses caused by masticatory forces, and despite being organically "bonded," enamel and dentin responded independently. This unique behavior with regional variations of these tissues could have serious clinical implications during restorative procedures.     

The effect of public or private management on patients with temporomandibular joint pain dysfunction

Australians may receive free dental treatment via the public sector if they have a health care card but otherwise must seek treatment via the private sector. These two modes of dental delivery have different objectives, facilities, and patient populations. Two groups of patients, one public and one private, who presented to the same clinicians with temporomandibular joint dysfunction were studied. There were differences in age, numbers of natural teeth and some psychological features. However, the outcome to simple non-surgical management resulted in similar levels of successful treatment.     

The dental health of Indo-Chinese and Australian-born adolescents

Since 1975, more than 100,000 Indo-Chinese refugees from Vietnam, Kampuchea, and Laos have been resettled in Australia. This dental survey was undertaken to compare the dental health of 104 Australian-born and 126 Indo-Chinese adolescents from a State high school within a high migrant area of Melbourne. The mean DMFT score for the Australian-born group was 3.37 teeth, compared with 6.05 for the Vietnamese group, and 3.10 for the Kampuchean-Laotian group. More restorations and extractions were required by the Vietnamese subjects compared with the Australian-born and Kampuchean-Laotian subjects. Almost all subjects had gingivitis, however the proportion of Indo-Chinese subjects with shallow and deep pockets was greater than that of the Australian-born subjects. The periodontal health of the Kampucheans and Laotians was the most severe of the Indo-Chinese groups. These findings indicate that the Indo-Chinese adolescent refugees represent a high risk group for dental problems within the Australian population.     

Observing the tooth. The paths of light in visual and instrumental observation

The light we observe when we look at a tooth has travelled a long way through the tooth. A large fraction has passed through the dentine. There is also a sideways displacement: the point of entrance into the tooth is about 2 mm away from the point of exit. This implies that tooth color cannot correctly be measured with an instrument employing a single circular window for both illumination and measurement. Visual caries diagnosis of smooth surfaces and with Fiber Optic Trans Illumination (FOTI) is discussed in terms of light paths through the tooth.     

Polyoma virus-induced murine odontogenic tumors.

Neonatal mouse pups were injected subcutaneously with polyoma virus to induce odontogenic tumors. This treatment resulted in a spectrum of tumors that arose in organs dependent upon epithelial-mesenchymal interactions for their organogenesis, which included the teeth, salivary glands, thymus, and lacrimal glands. In addition, several odontogenic tumors with a histologic resemblance to ameloblastoma were identified and analyzed with respect to the presence of markers specific for various stages of ameloblast differentiation. Immunodetection analyses of the odontogenic tumors identified fibronectin and laminin, typical of basement membrane organization during early tooth organogenesis. These same tumors failed to express amelogenin, a gene whose expression is limited to differentiated ameloblasts. In contrast, a 47 kDa enamelin-like polypeptide was identified with the use of an antienamelin antibody. These data were interpreted to suggest that the polyoma virus truncated the differentiation pathway for these odontogenic tissues at an early stage of their development and retained the expression of basement membrane components and the enamelin-like polypeptides, yet excluded expression of amelogenin gene products. This observation suggests that polyoma viral transformation may dysregulate odontogenic tissue interactions and produce tumors composed of cells arrested at a specific stage in their development.     

The effect of surface treatment on the Knoop hardness of Dicor.

One advantage cited for the use of Dicor over other ceramic materials is a reported Knoop hardness comparable to human enamel. However, when fabricating dental restorations, a Dicor glass-ceramic casting generally is subjected to several different surface treatments because of processing, esthetic, and functional requirements. Therefore, this study compared the Knoop hardness of Dicor specimens under three conditions: (1) cerammed, (2) cerammed and shaded, and (3) sectioned to reveal internal material. Knoop hardness differences between groups were significant (P less than or equal to .05). The cerammed surface was the hardest; it was harder than human enamel. Shaded specimens had a surface hardness comparable to dental porcelain. However, the internal glass-ceramic material, located beneath the shading porcelain and cerammed surface, had a Knoop hardness slightly higher than that of human enamel.     

Microscopic analysis of the effects of ultrasonic instrumentation on the root surface of molar furcations

Twenty molars, 10 from the maxilla and 10 from the mandible with furcation areas type II (Staffileno) were instrumented in their inter-radicular area with P10 instrument of Cavitron. It was established that the furcations of easier access instrumentation were the lingual o lower teeth and the buccal of the upper, and the most difficult accessibility were the distal of upper molars. The instrumentation can leave grooves or deformations, depending on the instrument to the area. It was concluded that ultrasonic instrument are useful removing supragingival calculus and bacterial plaque, and it must be limited to perform such procedures.     

Static frictional force and surface roughness of nickel-titanium arch wires

Surface roughness and static frictional force resistance of orthodontic arch wires were measured. Nine nickel-titanium alloy arch wires were studied. One beta-titanium alloy wire, one stainless steel alloy wire, and one cobalt-chromium alloy wire were included for comparison. Arithmetic average roughness in micrometers was measured with a profilometer. Frictional force resistance was quantified by pushing wire segments through the stainless steel self-ligating brackets of a four-tooth clinical model. The cobalt-chromium alloy and the nickel-titanium alloy wires, with the exception of Sentalloy and Orthonol, exhibited the lowest frictional resistance. The stainless steel alloy and the beta-titanium alloy wires showed the highest frictional resistance. The stainless steel alloy wire was the smoothest wire tested, whereas NiTi, Marsenol, and Orthonol were the roughest. No significant correlation was found between arithmetic average roughness and frictional force values.     

The mesh diagram for analysis of facial growth

Facial growth of twins by means of proportionate analysis of changes in the location of landmarks within a rectilinear coordinate system (mesh diagram) has been conducted, utilizing cephalometric data on 148 males and 128 females, observed annually from 8 to 16 years of age. Findings show relative consistence of the facial configuration during this 8 year time period, which includes the adolescent growth spurt. The median face in each sex shows little change in the location of soft and hard tissue landmarks, except for slight advancement of the chin as well as dorsal and caudad movement of Gonion. Nonetheless, individual variations in landmark location after 8 years of growth among the subjects studied signal the hazards of prediction within the precise framework that orthodontists seek.     

Evaluation of shear strength at the cement-endodontic post interface

The strength characteristics of the cement-implant interface were evaluated for smooth-tapered, threaded, and porous-surfaced endodontic implants with the use of different cements. Specifically, tensile and torsional shear strengths were measured for zinc phosphate, polycarboxylate, glass-ionomer, silicophosphate, and AH-26 cements. The results indicated superior shear strength characteristics for threaded endodontic implants on axial loading. However, this strength was diminished when torsional forces were applied. Porous-surfaced endodontic implants showed strong resistance to both axial and torsional loading.