Stig Karlsson

Survival rate and failure characteristics for two post designs

The dental records of 638 patients treated with 788 posts and cores were studied to analyze failure rate and failure characteristics for two post designs. Frequency of the technical failures, loss of retention, root fracture, and post fracture were recorded 4 to 5 years after post cementation. There were two types of posts: custom-cast tapered posts and parallel-sided serrated posts. The cumulative failure rate was 15% for 456 tapered posts and 8% for 332 Para-Post posts. Loss of retention was the most frequent reason for failure for both types of posts, whereas root fractures had the most serious consequences, and all resulted in extraction. A significantly higher success rate was recorded for parallel-sided serrated posts, compared with custom-cast posts, regarding the total failure rate and the severity of the failure (p < 0.05).

Influence of pH and storage time on the sorption and solubility behaviour of three composite resin materials

OBJECTIVES The aim of this study was to determine whether pH and time has any influence on the sorption and solubility behaviour of composite resin materials stored in a buffer solution. METHODS Three hybrid composite restorative resin materials (Spectrum, Z-100 and ArtGlass) with different matrix structure and filler composition were studied. One hundred and twenty specimens of each material were produced according to ISO 4049. The materials were stored in McIlvains buffer solution at different pH (4, 6 and 8) at 1, 7, 60 and 180 days. pH measurements were carried out before and after completed storage. RESULTS Time had a significant influence on the sorption and solubility behaviour of the composite resin materials tested. One of the materials Z-100 showed a significant mass increase and/or decrease depending on the pH of the solution. The material Spectrum was significantly influenced by pH, resulting in different sorption depending on the pH of the solution. CONCLUSIONS Time of storage was important for the sorption and solubility behaviour of the composite resin materials tested. Comparison of solubility for one of the materials showed twice as high values in the present study as previously reported when distilled water was used as storage medium. pH in the solution seems to have an influence on the sorption and solubility behaviour of composite resin materials. The sensitivity of the sorption and solubility behaviour to time and pH of the materials tested seems to be related to the hydrophilicity of the matrix and the chemical composition of the filler.

Mandibular movements of young adults recorded by intraorally placed light-emitting diodes.

Mandibular chewing movements of 10 young adults were registered with LED. The registrations were performed manually, and the following observations were made: 1. The mean cycle duration was reduced from 1.12 seconds for cycle 1 to 0.76 second for cycle 16. 2. The duration of the opening phase appeared to be shorter than that of the closing phase. 3. The maximal vertical movement of the mandible decreased throughout the chewing period. The results obtained in this study agree with those reported by other investigators and indicate that a system using LED is suitable for analyzing the mandibular movement pattern in clinical situations.

The fit of Procera titanium crowns: An in vitro and clinical study

In contrast to conventional casting methods for the production of a metallic crown the Procera process is based on precision machine duplication of models combined with spark erosion of the metal frame. Some of the steps in the manual handling procedure are thereby excluded. The present study evaluated, by means of a replica technique, the fit or adaptation of Procera titanium crowns to the stone die and in vivo to the tooth before cementation. For any combination, the marginal adaptation was superior to and significantly better than the occlusal areas and axial surfaces, respectively. In addition, the crowns had a significantly better fit to the stone die than to the tooth. The marginal discrepancy was approximately 60 microns in vitro and 70 microns in vivo, with a range of 3-205 microns.

The fit of gold inlays and three ceramic inlay systems: A clinical and in vitro study

Four inlay systems--gold, Cerec, Mirage, and Empress inlays--were evaluated for their adaptation to stone die and clinically to the tooth by means of a replica technique. Twenty inlays of each system were placed on premolars and molars in the lower jaw. A microscope was used to measure the adaptation at the approximal margin, at the inner axial wall, and at the occlusal cavosurface area. An overall better fit was observed for the gold inlays than for the ceramic inlays. When the different measuring locations were compared, a better fit was found for the occlusal area. The greatest discrepancies were recorded for the Cerec inlays, whereas the Mirage and Empress inlays were comparable.

Contact allergy and hand eczema in Swedish dentists

Hand eczema and contact allergy in Swedish dentists were studied in a multidisciplinary project. The aims of the study were to establish diagnoses, to investigate the occurrence of contact allergy, in particular to (meth)acrylates, and to evaluate certain consequences of hand eczema. A postal questionnaire on skin symptoms, atopy and occupational experience was mailed to 3500 dentists aged <65 years, and licensed 1965–1995. The response rate was 88%. Among dentists living in 3 major cities, 14.9% (n=191) reported hand eczema during the previous year. They were invited to a clinical examination, including patch testing with a standard and a dental series. 158/191 (83%) dentists attended, and hand eczema diagnosis was confirmed in 149/158 (94%). Irritant contact dermatitis was diagnosed in 67% and allergic contact dermatitis in 28%. On patch testing, 50% presented at least 1 positive reaction. The most frequent allergens were nickel sulfate, fragrance mix, gold sodium thiosulfate and thiuram mix. 7 (5%) had positive reactions to (meth)acrylates, all to 2‐hydroxyethyl methacrylate and 6 also to ethyleneglycol dimethacrylate. 38% had consulted a physician, 4% had been on sick‐leave and 1% had changed occupational tasks due to hand eczema. No dentist with allergy to acrylates had been on sick‐leave or changed occupation. It is concluded that dentistry is a high‐risk occupation for hand eczema, and that irritant contact dermatitis is most common. The prevalence of contact allergy to acrylates was below 1% in the population of responding dentists, and in most cases did not have serious medical, social or occupational consequences.

Influence of film thickness on joint bend strength of a ceramic/resin composite joint

OBJECTIVES The purpose of this study was to evaluate the influence of different film thicknesses of resin composite luting agents on the joint bend strength of a ceramic/resin interface. METHODS Mirage FLC (Chamelon Dental Products) and Vita Cerec (Coltène AG) duo cement were used in combination with the ceramic materials, Mirage and Vita Cerec blocks. Cement layers with thicknesses of 20 microns, 50 microns, 100 microns and 200 microns were light-cured with a high-intensity curing light. Ten specimens of each ceramic/cement combination and thickness provided a total of 80 complete test specimens. Each specimen was placed in a four-point bending jig mounted in a universal tensile testing machine and underwent loading. A paired two-tailed Students 1-test was used to evaluate differences between different series of film thicknesses and resin cement combinations. RESULTS Within each ceramic/cement combination, the bond strength values were significantly lower for the 20 micron film then the thicker films. SIGNIFICANCE Taking into account the physical and clinical properties of resin-based luting agents, available knowledge indicates that a marginal gap on the order of 50-100 microns seems to optimize performance.

AXIAL WALL CONVERGENCE OF FULL VENEER CROWN PREPARATIONS: DOCUMENTED FOR DENTAL STUDENTS AND GENERAL PRACTITIONERS

The convergence angle in 478 full crown preparations was assessed. Of these preparations, 351 had been performed by general practitioners and 127 by dental students. Groups of preparations performed on incisors, premolars, and molars were compared, as were preparations performed by dentists and students. Two different convergence angles were measured for each tooth, buccolingually and mesiodistally. The results showed a mean angle of 21 degrees. The mean values for premolars and molars differed significantly. When a comparison was made of preparations performed by students, a significant difference was found between premolars and molars. The same comparison for general practitioners showed a significant difference both for incisors compared with molars and for premolars compared with molars. A wide range was found for the convergence of the axial walls, especially for the preparations performed by general practitioners.

Influence of Parkinson's disease on oral health

Thirty patients with Parkinsons disease were investigated with regard to their oral health. They had significantly more teeth and less caries than a control group of corresponding age. However, the salivary secretion rate was significantly lower with advancing parkinsonian symptoms. It is concluded that not only motor impairment but also autonomic dysfunction, as an expression of a more advanced neuron degeneration, could be of importance when the possibility of maintaining a good oral health in parkinsonian patients is considered.

Recording of mandibular movements by intraorally placed light emitting diodes

In order to evaluate an opto-electronic system for recording mandibular movement a simulator and clinical pilot study was performed. The method was based on light emitting diodes (LED) and a photodetector system. One LED was placed intraorally and one on the forehead, the latter acting as reference. When the light spot is focused on the detector surface a photo-current will occur. This current can be used to obtain two signals linearly related to the x and y coordinates of the LED. By using two detectors the three-dimensional coordinates of a movement can be calculated, consequently also the z-coordinate. In the simulator experiment the method was shown to have a satisfactory precision and good reproducibility. The results from the clinical test indicated that it is possible to measure and record mandibular movement with a minimum of external influence to the test person.