Scratch hardness and chipping of dental ceramics under different environments

OBJECTIVE: The goal of this program was to identify promising environments that could efficiently minimize machining-induced damage of dental materials. METHODS: Single point abrasion (SPA) scratch testing was used on five materials to determine the scratch hardness and amount of edge chipping as functions of chemical environment, including air, water, saline and glycerol solutions. Limited testing was also done under additional environments expected to promote chemomachining effects via crack growth promotion or debris removal. A conical diamond indenter and a conventional tungsten carbide machining tool were used in the scratch tests. One-way ANOVA analysis was used to determine statistical differences among the variables. RESULTS: There was a consistent trend across materials that the water and saline yielded the lowest values of scratch hardness, air the next lowest, and the tests performed in glycerol yielded the highest hardness values. The measured hardness values using the conical diamond tool in the glycerol environments were about twice the hardness values measured under water and saline solutions. Environmental effects on chipping were minimal, but a linear relationship between load and per cent chipping was determined for the WC tool within the 10-50 N test range. The choice of scratch tool strongly affected scratch hardness and chipping tendency. SIGNIFICANCE: The chemical environment had an effect on machining characteristics, but the effects were more dependent on tool interactions rather than material specific properties. As a result, it may not be possible to utilize a particular single environment to substantially improve the damage response of dental materials to machining operations. Improvements in damage resistance can be environmentally obtained, but only for shallow cuts (finishing operations).     

The nature of the remaining dentin surface following application of Carisolv solution

PURPOSE: To evaluate the effect of Carisolv solution on the topography and surface hardness of dentin. METHODS: Two separate studies were carried out. Atomic force microscopy (AFM) was employed to visualize dentin surface topography on slices of previously extracted non-carious and carious teeth following the passive application of Carisolv gel for 30- and 60-second periods. A Wallace hardness instrument was used to measure the dentin surface hardness following active caries removal with Carisolv gel and the specially designed instruments. Conventional caries removal with dental burs and non-carious dentin acted as controls for the latter study. RESULTS: AFM revealed that the passive application of Carisolv gel resulted in smoother surfaces than observed on carious and non-carious dentin. There was a statistically significant difference between the mean hardness values for non-carious and Carisolv-treated dentin (P< 0.05). There was no statistically significant difference between the non-carious and bur-treated dentin nor the Carisolv and bur-treated dentin.     

Contribution of individual drugs to gingival overgrowth in adult and juvenile renal transplant patients treated with multiple therapy

Abstract. Drug regimens for transplantation often consist of multiple therapeutic agents and may result in drug-induced gingival overgrowth (DIGO). The aim of this study was to investigate the contribution of individual drugs in renal transplant patients. 147 adults (19–84 years) and 60 juveniles (3–18 years) were scored for DIGO and other clinical variables. Duration of treatment, dosage of drugs per kg body weight and serum cyclosporin levels were recorded. 44% of adults and 27% of children had DIGO. All patients were receiving prednisolone. More adults than children were administered cyclosporin, the reverse was true of azathioprine ( P 0.01), Explanatory models were evaluated by stepwise ordinal polynomial logistic regression. Statistically significant explanation ( P 0.05) of DIGO was afforded by prednisolone, nifedipine and azathioprine concentrations in adults and by cyclosporin, nifedipine and azathioprine concentrations in juveniles. Prednisolone and azathioprine were inversely related to the degree of DIGO. Plaque and irregularity scores, lip coverage and mouthbreathing status showed significant additional explanation in adults, replacing nifedipine and azathioprine in the final model. Irregularity was additionally explanatory in children, but no other clinical variables. A larger proportion of the variance of DIGO was explained by the available variables in children than in adults (pseudo r ²=0.50 versus 0.25). The degree of DIGO in renal transplant patients is influenced by the dosage of a number of individual components of multiple drug therapy independently of the presence of local clinical factors.     

Achieving primary closure and enhancing aesthetics with periodontal microsurgery.

The continuous search for improved surgical procedures to address gingival deformities is a consequence of an increasing demand for aesthetics in the periodontal clinical practice. Innovative techniques have been reported to help clinicians achieve predictability in root coverage. Significant progress can be attributed to the inclusion of the operative microscope in periodontal therapy, particularly in regards to obtaining primary closure. This article describes a microsurgical technique used to treat gingival recessions, showing its potential for obtaining optimal aesthetic results.     

Induced mandibular condylar growth in a sheep model after functional appliance treatment

This paper reports on changes in mandibular condylar growth in sheep fitted with experimental functional appliances. The paper also addresses the similarities of mandibular condylar growth in sheep and humans. Experimental functional appliances were developed, constructed and applied to four, four-month old, male sheep. Another four sheep served as matched controls. All animals received fluorochrome bone labels during the study and their weight gain also was recorded. Fifteen weeks later, all animals were sacrificed and each temporo-mandibular joint and left metacarpus were removed. Undecalcified mid-sagittal sections of the joint and metacarpus were prepared for fluorescence microscopy. The mandibular condylar growth vector in sheep was found to be in a postero-superior direction. Condylar growth in the control sheep during the experimental period varied from 8.8 to 11.9 mm, with the mean being 10.6 mm, which is quantitatively similar to two years of condylar growth in human adolescents. In the experimental sheep, the condylar growth varied from 8.5 to 13.3 mm, with the mean being 11.4 mm. When metacarpal growth and weight gain were taken into consideration using multivariant analysis, the coefficients for growth in the postero-superior and posterior direction were found to be high, with adjusted r2 as 0.84 and 0.82 respectively. The induced condylar growth was estimated to be largest in the posterior direction (2.30 mm), which is also similar to previous reports in humans. These findings suggest the appropriateness of using sheep as a model for quantitative histological analysis when investigating the mechanisms of functional appliance treatment.     

Histologic evaluation of the effect of nicotine administration on bone regeneration. A study in dogs

The objective of this study was to investigate the histometric impact of nicotine on bone regeneration of surgically created alveolar ridge defects in dogs. Sixteen mongrel dogs were used. One defect was surgically created unilaterally in the mandible, and left to heal spontaneously. The animals were randomly assigned to one of the following groups: Group 1--control (n = 8) and Group 2--subcutaneous nicotine administration (2 mg/kg) twice a day (n = 8). After 4 months, the animals were sacrificed and the specimens routinely processed for semi-serial decalcified sections. Bone height (BH), bone width (BW), bone density (BD), and bone area (BA) of the newly-formed bone were evaluated. Intergroup analysis (Mann-Whitney rank sum test) showed that regardless of the presence of nicotine, no significant differences were observed regarding bone width (BW), bone area (BA) and bone height (BH) (p > 0.05). On the other hand, it was demonstrated that nicotine administration significantly influenced the proportion of mineralized tissue within the limits of the newly-formed bone (BD) (p < 0.001). Within the limits of the present study, it can be concluded that nicotine might affect but not prevent bone healing in defects left to heal spontaneously.     

Tooth loss in maintenance patients in a private periodontal practice

A group of 162 maintenance patients, previously studied for compliance to suggested maintenance schedules, were surveyed for tooth loss over a 5-year period. The group was divided into those who complied to suggested maintenance schedules and those whose compliance was erratic. It was found that none of the patients who had complied to suggested maintenance schedules lost any teeth. In the erratic group, where all tooth loss occurred, it was found that the more often a patient presented for maintenance, the less likely he was to lose teeth. These findings are discussed in relation to current studies on efficacy of various therapies for periodontal diseases.     

Antimicrobial properties of hydrogen peroxide and sodium bicarbonate individually and in combination against selected oral, gram-negative, facultative bacteria

The topical application of hydrogen peroxide (H2O2) and sodium bicarbonate (NaHCO3), individually and in combination, has been used empirically in the treatment of periodontal diseases. In this study, we examined both minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of these disinfectants individually and in combination against selected facultative, Gram-negative oral bacteria in a microtiter dilution assay. The bacteria studied included Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, Eikenella corrodens, and Capnocytophaga gingivalis. These bacteria exhibited MBC (one hr) values ranging from 75 mumol/L to greater than 10 mmol/L and MIC from less than 5 to 500 mumol/L for H2O2. The tested bacteria exhibited MIC values for NaHCO3 of from 23 to 182 mmol/L, and the MBC (one hr) exceeded 728 mmol/L for most of the strains examined. At sublethal (sub-MIC) concentrations, sodium bicarbonate antagonized the ability of H2O2 to inhibit bacterial growth in MIC assays, but sublethal concentrations of H2O2 had no effect on the MIC values of NaHCO3. Lethal concentrations of H2O2 and NaHCO3 exhibited synergistic antimicrobial activity in combination in one-hour bactericidal assays. Since the bactericidal properties of these antimicrobial agents are synergistic, we conclude that it may be rational to use them in combination to treat certain forms of periodontal disease. Also, lower and perhaps safer concentrations of H2O2 can be used in combination with NaHCO3 when oxidative antimicrobial chemotherapy is indicated.     

Esophageal adenocarcinoma metastatic to the maxilla

Although metastatic malignant lesions in the maxilla are exceedingly rare, case reports of such lesions do appear occasionally in the literature. This article describes the clinical and pathologic features of an esophageal adenocarcinoma metastatic to the maxilla. The initial maxillary appearance of the tumor mimicked primary dental pathosis and, in addition, was the presenting sign of malignant disease in the patient. The relevant literature is reviewed, and the processes by which metastases form are discussed.