Thermal cycling distortion of porcelain fused to metal fixed partial dentures

Statement of problem. The initial fit of porcelain fused to metal restorations deteriorates during the firing cycle of porcelain. Purpose. This study evaluated thermal cycling distortion of 3-unit porcelain fused to metal frameworks at different firing stages. Material and methods. A master model was designed to represent the 2 abutments of a 3-unit fixed partial denture replacing a missing mandibular molar. Standard techniques were used to fabricate 10 castings. Half of the copings were cast in a Ni-Cr alloy and the other half in a Pd-Cu alloy. Framework distortion was measured by means of inner fit changes, horizontal linear measurements of the framework length, and vertical fit changes of each retainer. Measurements were made (1) initially, (2) after degassing firing, and (3) after glaze firing. Differences between the firing cycles created distortion values of the retainers in 3 dimensions. Repeated measures ANOVA was used to analyze data statistically. Results. Measured differences between the 2 firing stages ranged from –47 to 81.7 μm. For both alloy groups, retainers showed increase in vertical gap that implied poorer vertical fit after porcelain application. Mean values of inner fit change recorded for porcelain application firing were higher in magnitude than the values of metal-conditioning firing. In addition, no statistically significant differences were found among alloy types. Conclusions. A 3-dimensional distortion was observed both in Pd-Cu and Ni-Cr frameworks during porcelain firing cycle. The distortion seen after porcelain application firing was significantly greater than that seen after metal-conditioning firing. This result can be attributed to these factors, contamination of porcelain to the inner surface of metal coping and reduction in resilience of metal. (J Prosthet Dent 1998;80:654-60.)     

Post-orthodontic occlusal function

The significance of orthodontic treatment in the aetiology of temporomandibular dysfunction continues to be a matter of controversy. However, the evidence of any association has been generally negative. This investigation involved the examination of a study group of 87 post-orthodontic patients, the average time out of all retention being 52 months. They were compared with an untreated control group. Signs and symptoms of temporomandibular disfunction were assessed for both groups. In only one instance, soft joint click, was there found to be a significant association between the treatment category and the occurrence of the symptom, there being a higher rate of soft clicks in the post-treatment group. While this may be ascribed to orthodontic treatment, there was also a different restorative pattern in the two groups. No other significant associations were found.     

Surgical orthodontic correction of mandibular deficiency by sagittal osteotomy: Clinical and cephalometric analysis of 1-year data

A homogeneous sample of 76 mandibular retrognathic patients (mean age, 28 years) were examined for postoperative alterations after surgical treatment by bilateral sagittal split osteotomy and mandibular advancement with wire fixation. Skeletal and dental measures were obtained from preoperative, immediate postoperative, fixation-release, and 1-year cephalograms. Spearman correlation was used as a preliminary analysis to assess the relationship between postsurgical change and age, genioplasty, amount of mandibular advancement, and preoperative mandibular plane angle. Genioplasty and amount of mandibular advancement were included as independent factors in the subsequent repeated-measures analysis of variance, since these were the only two factors that showed a consistent trend of correlations with postoperative change. Genioplasty was a significant factor in the X and Y coordinate changes in pogonion, while the amount of mandibular advancement was a significant factor in the X coordinate movements of all mandibular landmarks except gonion and condylion. The mean amount of horizontal advancement was 5.2 mm, and anterior face height increased 5.1 mm. During fixation, B point moved posteriorly (x = -1.6 mm, p less than 0.01) and inferiorly (y = 1.0 mm, p less than 0.01). After fixation release, these trends were reversed, resulting in a nonsignificant net horizontal change (x = -0.5 mm, p = 0.10) and a significant net superior movement (y = -1.3 mm, p = 0.01) by 1 year. Pogonion, menton, and mandibular incisor tip showed similar patterns.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced permeability of acid-etched or ground dental enamel

Statement of problem. Acid etching creates retentive microcraters on enamel surfaces. Designing of a partial denture often involves reshaping the supporting and retentive teeth by grinding the enamel. Unfortunately, both these procedures damage the enamel surface. In vivo such surface damage takes several months to recover.Purpose. This study evaluated the effect of 1-minute etching, prolonged etching, and grinding on the permeability of dental enamel for water-soluble molecules.Material and methods. With the electron paramagnetic resonance and a two-chamber diffusion cell, the influence of etching and grinding on the diffusion of spin label molecules through the enamel was studied quantitatively. The enamel permeability was measured in 30 sound enamel samples, of which 10 samples were exposed to 1-minute etching with 37% phosphoric acid, 10 samples were etched for 5 minutes, and 10 samples were ground with a diamond bur.Results and Conclusions. All procedures significantly increased the permeability of dental enamel. These results demonstrate that in vivo the acid-etched and ground dental enamel surfaces are less protected and consequently, unless the tooth is properly protected, are more susceptible to carious lesions. Therefore ground or accidentally etched enamel should be protected. (J Prosthet Dent 1997;77:578-82)     

Factors Affecting Self-ratings of Oral Health

Objectives: The purpose of this study is to determine the relationship of self-rated oral health to a comprehensive battery of clinical, sociodemographic, physical health, and mental health measures in a well-elderly urban population. Methods : Results are based on telephone interviews and clinical assessments of 550 subjects over 65 years of age participating in a Los Angeles-based Medicare project during 1990. Subjects were mostly female, white (89%), with above-average income. Results : Findings show that: (1) the DMF measure is not as strongly related to self-rated oral health as was a single measure of missing teeth; (2) the major predictors of self-rated oral health were "worry about teeth" and "appearance of teeth" followed by total missing teeth, race, education, and depression scores; and (3) self-rated general health is related to self-rated oral health. Conclusion : Self-rated oral health may be, for older adults, a better measure of "health" than of "morbidity."     

Melanotic neuroectodermal tumour of infancy: an immunohistochemical and ultrastructural study

Two cases of melanotic neuro-ectodermal tumour of infancy (MNTI)—a rare neoplasm arising in the first year of life—are reported, with the results of immunohistochemical and ultrastructural examination. The tumours consisted of a biphasic cell population in a fibrous stroma. The small, darkly staining cells comprising the first population stained positively for synaptophysin, showing them to be neuroblasts, and the large epithelioid cells comprising the second cell population stained positively with the antibodies HMB-45 and NKI-Beteb, showing them to be melanocytes. Ultrastructural examination of the second case confirmed the biphasic nature of the tumour cells, with secretory granules and neurofilaments in the neuroblastic population, and melanosomes in the epithelioid population. These results add to the evidence supporting the neural crest origin of MNTI and confirm its formation from two distinct cell lines. Both cases have responded to local excision, with no recurrence more than a year after initial treatment.     

The Relationship Between Dental Utilization and Preventive Participation Among a Well-elderly Sample

Previous studies have shown that dental utilization by older people is lower than for the general population. This study hypothesizes that an elder's tendency toward participating in preventive health activities may be an important factor in explaining the likelihood of accessing the dentist. Subjects included 1,911 older individuals who enrolled in the UCLA Medicare Screening and Health Promotion Trial. All were interviewed about their utilization of preventive health services and participation in preventive behaviors. A recent dental visit was positively associated with all sociodemographic variables examined except age and sex. It was also related to health status questions and utilization of the preventive health services and health behaviors studied. Logistic regression analysis showed that both summary preventive health behavior and preventive service utilization variables were important factors in explaining a recent dental visit (model chi-square/221.4, P=.001) along with income, not having a removable prosthesis, and perceiving the need for dental care. This study showed that dental utilization is related to older people's participation in other preventive activities. When in contact with older people, health care professionals should consider current oral and general preventive health status and encourage appropriate referral for preventive activities.     

Salivary clearance of sugar before and after insertion of fixed orthodontic appliances

This study was conducted for the purpose of establishing the possible influence of orthodontic therapy with fixed appliances on salivary clearance of sugar. Fifteen consecutive patients between the ages 12 and 17 years took part in the investigation. Unstimulated salivary flow rate, residual volume of saliva in the mouth after swallowing (RESID), and salivary clearance of sugar was determined on two occasions, before treatment commenced and after a minimum of 3 weeks of appliance wear. Analysis of the data showed that both RESID and salivary flow rate exhibited significantly increased levels during orthodontic therapy. The insertion of fixed appliances did not seem to have any effect on the rate of salivary clearance of sugar. It was assumed that this finding could be a consequence of the combined effects of the changes in salivary flow rate and RESID.