A.J.M. Plasschaert

Verification of Theoretical Modeling of Heat Transmission in Teeth by in vivo Experiments

A theoretical axisymmetric tooth model, simulating the conditions involved in the drinking of a liquid of a certain temperature, was compared with results of a similar in vivo experiment. The temperature changes as a result of one draught of a hot/cold liquid were recorded within the model as well as in the surrounding environment. The experimental data obtained were compared with the calculated results for the theoretical model as determined by the Finite Element Analysis. The temperatures recorded experimentally agreed reasonably with the calculated results. It can be concluded that the assumptions which have been made concerning the described thermal loading conditions lead to a good approximation of the physical reality.

A NEW METHOD FOR MATCHING TOOTH COLORS WITH COLOR STANDARDS

A new method for quantitative intra-oral tooth color determination is presented. Basically, the tooth color is assessed by visual comparison with opaque color standards, which are logically arranged according to three visual color dimensions. The standards were analyzed spectrophotometrically, and the C.I.E. color coordinates were computed. Illumination and observation were standardized during the matching procedure. Two distinct situations, method 1 and method 2, were investigated. The situation in method 1 is to be considered as large window illumination and small window collection of the reflected light. For method 2, the same small window was used for both illumination and observation. Using both methods, the color of a tooth could be quantified into three separate color dimensions. Using method 1, the consistency among 25 examiners was high in determining the color of ten teeth; using method 2, the inter-examiner agreement was low. For the same tooth, different color standards were selected with method 1 or method 2. The standard selected with method 2 often appeared to be in disagreement within clinical expectations. The differences in results between method 1 and method 2 are explained by the optical properties of the translucent dental enamel (e.g., volume reflection). Method 1 allows for reproducible quantification of clinical tooth discoloration according to C.I.E. color specifications and can possibly be applied in prosthetic dentistry.

Tooth discoloration induced by endodontic sealers.

Endodontic therapy often results in discoloration of the tooth crown. The main causes are blood, necrotic pulp tissue, and endodontic materials. The staining potentials of various materials were examined in vitro by means of a visual method for tooth color determination. Extracted premolars were prepared, and the following sealers were introduced into the pulp cavities: Zinc oxide eugenol cement, Grossmans cement, AH26, Diaket, N2, Rieblers paste, Tubliseal, and Endomethasone. Before the sealers were applied, the original tooth colors were assessed on the external buccal tooth surfaces. Further color determinations were carried out at regular intervals up to 6 months after introduction of the sealers. Each material induced measurable tooth discoloration within 3 weeks. Rieblers paste caused the most severe discoloration while Diaket caused a mild stain. The other materials produced intermediate discolorations between those of Riebler and Diaket.

Fatigue Behavior of Direct Post-and-core-restored Premolars

Evaluation of long-term mechanical behavior of new types of restorations in clinical trials is time-consuming. A partial alternative can be found in experimental fatigue-testing, which simulates accelerated mechanical deterioration. The aim of this study was to determine the feasibility of using fatigue-testing of a complex dental restoration and to evaluate the mechanical fatigue behavior of premolar teeth restored with a titanium alloy post and an amalgam or composite core. Eighty-seven human upper premolar teeth were decoronated, embedded, and restored with a prefabricated post of 1 mm diameter. The teeth were randomly assigned to one of two groups corresponding with a core build-up of amalgam or chemically-cured core composite, respectively. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency, 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The boundary technique was used for determination of the mean fatigue strengths of the restorations at 104, 105, and 106 cycles, simulating up to 1-3 years of clinical functioning. Mean fatigue strength was expressed in percentage of initial strength: For 10 4, 105, and 106 cycles, the results were 66%, 58%, and 52%, respectively, for the amalgam and 62%, 62%, and 53% for the composite group. It is concluded that fatigue-testing of more complex systems is possible, if a suitable testing method is selected. The restorations showed a comparable strength reduction after 106 cycles of about 50% of their initial strength. The composite core build-up showed a behavior less predictable than that of the amalgam, which might be attributed to handling parameters.

Tooth discoloration induced by dental materials

Tooth discoloration after endodontic treatment is frequently attributed to drugs and filling materials. In this in vitro study the staining potential of various dental materials was investigated by means of a visual method to determine tooth color. Extracted human premolars were prepared, and the following materials were introduced into the pulp cavities: Cavit, Durelon, Dycal, Fletchers cement, IRM, AH26-silver free, gutta-percha, Duo Percha, Fuji ionomer, and zinc phosphate cement. Before the materials were applied, the original tooth color was assessed on the external buccal tooth surfaces. Further color determinations were undertaken at regular intervals for 6 months after the materials were introduced. Durelon, Fuji ionomer, Fletchers cement, and zinc phosphate cement did not induce measurable tooth discoloration. Cavit, Dycal, gutta-percha, and IRM caused a mild stain. For the teeth filled with AH26-silver free and Duo Percha, a moderate discoloration was recorded.

Bleaching of tooth discoloration caused by endodontic sealers

This in vitro study evaluated the bleaching of teeth discolored by endodontic sealers. Extracted premolars were stained from within by Grossmans cement, zinc oxide-eugenol, Tubli-Seal, AH26, Endomethasone, N2, or rieblers paste. The color of the buccal tooth surfaces was assessed immediately before and 6 months after the introduction of the sealers. Each sealer caused measurable discoloration of tooth crowns. After the sealers were removed, the stained teeth were bleached for 2 wk using a “walking bleach” technique. Six months after bleaching, the color stability of the bleached teeth was evaluated. For all teeth, a distinct change to a lighter color was noted after bleaching. Some rediscoloration was observed in each group of teeth 6 months after bleaching.

Staining patterns in teeth discolored by endodontic sealers.

The use of endodontic materials may lead to internal discoloration of teeth. In view of prevention of and therapy for tooth discoloration, the staining patterns inside discolored teeth were investigated in vitro. Extracted premolars were discolored using the following endodontic sealers: Grossmans cement, zinc oxide-eugenol, Diaket, Tubli-Seal, AH26, Endomethasone, N2, and Rieblers paste. The sealers were introduced into the pulp cavities and the color of the external buccal tooth surfaces was determined before and 7 wk after introduction of the sealers. All materials produced measurable coronal discoloration. The discolored tooth crowns were hemisectioned and internal staining patterns were studied. For all teeth, the dentin was found to be partly to entirely stained. No discoloration could be observed in the enamed. For each material the internal staining patterns were in agreement with the discolorations observed on the external surfaces.