[Effects of load and loading time on fracture toughness with indentation method].

For clinical application of ceramics such as porcelains that are frequently used as crown restoration materials, it is important to quantitatively evaluate and determine brittleness. This quality is expressed as a fracture toughness value, KIC, but no distinct method for its determination has yet been established. In order to standardize conditions for the determination of KIC by the indentation method, effects of indentation load and loading time on KIC of calcium phosphate crystalline ceramics (CP) were studied at various Vickers indentation loads and various loading times in CP plate-like segments. Furthermore, plate-like segments of each of CP, apatite (AP), mica-beta-spodumene (MIS) and mica (MIC) groups were subjected to experiment at various indentation loads at a fixed loading time to study the effects of indentation load on KIC in four kinds of Castable Ceramics. The results are summarized as follows: 1) The Vickers hardness degree of CP was decreased with an increase in indentation load and loading time, reaching the maximum value (499Hv) at 1kgf of indentation load and 5s of loading time. 2) The value of half of the crack length of CP was increased with an increase in indentation load and loading time, reaching a maximum (530 microns) at 20kgf of indentation load and 30s of loading time. 3) KIC of CP reached the maximum value (2.78MNm-3/2) at 5kgf of indentation load and 5s of loading time, and the minimum (1.52MNm-3/2) at 20kgf of indentation load and 30s of loading time. 4) Optimal experimental conditions for KIC of CP determined by indentation method were 5kgf or 10kgf of indentation load and 15s of loading time. 5) KIC values (MNm-3/2) determined at 5kgf of indentation load and 15s of loading time for CP, AP, MIS and MI were 2.27, 0.95, 1.82 and 1.81, respectively. 6) The course of cracks due to indentation force showed a linear pattern of intra-granular fracture. 7) The cracks were revealed to show median cracks by fractography.

[Fracture toughness of porcelain using indentation method].

Material resistance to brittle fracture was quantitatively evaluated in the commercial porcelains, CERA 8 (CE 8), VITA DUR (VITD), VITA VMK 68 (VIT), CERAMCO II (CE II), UNIBOND (UNB), NORITAKE SUPER PORCELAIN AAA (AAA), PENCRAFT (FEN), COSMOTECH (COM) and OPTEC HSP OPT) from values of fracture toughness (KIC) obtained in the crack on a mode I, determined upon insertion of Vickers indenter. The results are summarized as follows: 1) Mean maximum and minimum values of Vickers hardness degree of 9 kinds of commercial porcelains at 5kgf of load for 15s were 1348 (SD 98.1) for OPT abd 666 (SD 74.6) for CE 8, respectively. 2) The value of half of the diagonal of indentation (a) ranged from 42 (SD 1.5) to 58 (SD 3.3) microns, and that of half of the crack length (c) ranged from 101 (SD 4.0) to 175 (SD 17.2) microns. 3) The ratio of (c) to (a) (c/a ratio) was within the range of 2.3 to 3.3, and median cracks were present. 4) KIC in the commercial porcelains determined by the indentation method was within the range of 2.04 to 4.69MNm-3/2, showing a maximum for OPT and minimum for VITD. 5) KIC of OPT was significantly greater than that of any other material. 6) The porcelains were divided by fractography of the direction of crack course into 2 groups: a group of intra-granular fracture showing linear cracks (AAA, COM and OPT) and a group of Inter-granular fracture showing a range of non-linear cracks (CE 8, VITD, VIT, CE II, UNB ND PEN).

[Effects of additive oxide, repeating load on the fracture toughness of calcium phosphate crystalline ceramics (CPCC)].

This experimental study was performed to obtain fundamental data for the development of highly reinforced calcium phosphate crystalline ceramics (CPCC) by evaluation of fracture toughness by adding a single metal oxide such as B2O3, Na2O, Li2O, SiO2, MgO and Al2O3, which are thought to solidify and reinforce ceramics. In experiment I, values of fracture toughness for CPCC to which each oxide was added were determined by indentation method, and in experiment II dynamic test method by repeated loading was studied. The results are summarized as follows: 1) One half (a) of the diagonal of indentation was increased with an increase in indentation load, and the test fragment of CPCC with 4.7 mol% Na2O added at 10kgf of indentation load showed the maximum diagonal of indentation (145 microns), while the test fragment of CPCC containing 3.0mol% Al2O3 showed the minimum value (29 microns) at 1kgf. 2) One half (c) of the crack length was increased with an increase in indentation load, and the test fragment of CPCC containing 4.7mol% Li2O showed the maximum crack length (411 microns) at 10kgf, while the test fragment of CPCC with 4.7mol% B2O3 showed the minimum value (55 microns) at 1kgf. 3) The maximum value (2.98MNm-3/2) of fracture toughness (KIC) was observed in CPCC containing 4.7mol% B2O3 at 10kgf, while the minimum (1.02MNm-3/2) was observed in CPCC with 4.7mol% Li2O added, at 5kgf. 4) (a) was increased with an increase in the number of repetitions of loading, showing the maximum value (111 microns) for a test fragment at 10kgf with 100 repetitions and the minimum (31 microns) for a test fragment at 1kgf with just 1 repetition. 5) (c) was increased with an increase in the number of repetitions of loading, showing the maximum value (337 microns) for a test fragment at 10kgf with 100 repetitions and the minimum (64 microns) for a test fragment at 1kgf with 1 repetition. 6) KIC reached a maximum value (2.35MNm-3/2) at 5kgf and 1 of the repetition, and a minimum (1.54MNm-3/2) at 3kgf and 10 repetitions of loading.

[Craniomandibular disorders management (1) Treatment planning].

Various treatment modalities have been reported in the management of the craniomandibular disorders in the half century after Costen reported his hypothesis on the temporomandibular disorders. Recent advances in the basic sciences such as anatomy, histology, pathology, physiology and clinical trials have brought us to this new era. We have been trying to establish our diagnosis and treatment modalities in the management of the craniomandibular disorders over the past fifteen years. In this series of articles we will describe our present concept. We will first discuss diagnosis and treatment planning. After the diagnosis and initial treatment planning craniomandibular management is usually divided into two phases. Phase I is the treatment of the stomatognathic system especially the temporomandibular joint. Behavioral modification and physical therapy and splint therapy are the most common forms of treatment. Sometimes, surgical treatment is required. Phase II is the compensatory phase of the occlusion consisting of occlusal equilibration, occlusal restorations, orthodontic treatment and gnathic surgery if needed. Another phase we like to add is maintenance. In this phase, home therapy, corrective follow-up and long term observation should be emphasized. The motivation of the patient throughout the management of the craniomandibular disorder (phase I, phase II and the maintenance phase) is essential to reach to a successful result.

[The effect of the local anesthesia to the posterior ramus of the mandible in patients with temporomandibular joint problems].

Some clinicians in North America use anesthetic injections to differentiate the symptoms such as pain and stiffness in the facial area and neck in patients with TMJ problems. However, the effects and area which is influenced have not been studied. The purpose of this study was to study procedures and changes following administration of local anesthesia to the posterior ramus of the mandible. Twenty four patients with TMJ problems were used in this study. 0.5ml of 2% Lidocaine (epirenamine included) was injected into the most painful site upon palpation. The pain upon palpation test (following Krogh-Poulsen's method) was compared before and after 50 minutes. Results of this experiment were: 1) decrease of pain upon palpation was found not only in the site. In many cases subjective pain in the head and neck area was also reduced. 2) A significant reduction was found in the pain upon palpation test in the neck area. A highly significant reduction was seen in the Sterunoclydmastoid muscle only in the injected side. In the masticatory muscles. Also, reduction of pain upon palpation was seen in both lateral, medial pterygoid and digastric muscles in the injected side. 3) Contra side lateral pterygoid muscle and trapezius muscle also registered decreased pain upon palpation. 4) The mean values for the injected site were 5.7mm (S.D. 5.9) below the earlobe and the mean depth from the skin surface to the bony surface were 16.6 mm (S.D. 2.7mm). 5) The peak of the subjective effect were seen in one group in 20 minute later injection (early type) and in the 2nd group the peak were seen after 40 minutes (slowly type). 6) We did not experienced any paralysis of the facial nerve in this study.

[Distortion of working models using different silicone impression techniques].

The influences of differing strains levels of impression materials in compression and impression techniques on the distortion of working models were examined. The working models, which differed in the size of cervical spillway (2mm and 9mm) and the impression techniques applied (the two-phase technique and the wash technique), were produced by using putty-type impression materials with three different strain levels (Reprosil, Express and Exaflex) following the metal master model of mandibular denture in an abutment form. Distortion of the working models was then measured by a three-dimensional measuring system. The results were as follows. 1) The models produced through the impression technique using hard impression materials with low strain levels displayed decreases both in the degree of inclination to the X axis of the abutment tooth variations distance between the left and right abutment teeth. This procedure was found to yield a model which was proximate to the master model. 2) The impression technique incorporating a small cervical spillway resulted in decreases in variations in the distance between the right and left abutment teeth and the diameter of the molar part of the abutment tooth, and the horizontal distortion of the alveolar ridge; the model thus produced was found to be proximate to the master model. 3) Application of the two-phase technique reduced variations in height of the abutment tooth, and the use of the wash technique led to decreased variations in the distance between the right and left abutment teeth and diameter of the molar cervix of the abutment tooth. 4) Differences in strain levels of putty-type impression materials, the size of cervical spillway and the impression technique used did not influence deviation of the model toward the Y axis (vertical direction). 5) The models with least distortion of the abutment tooth were obtained by the two-phase technique using hard impression materials with lower strain levels or by the wash technique using soft materials with higher strain levels.

[Effects of cross-linking agent on the bond strength of 4-META/MMA-TBB resin].

A cross-linking agent was added to increase the bonding strength of Superbond C & B by improving its cohesiveness. PMMA powder, which was copolymerized with 0.5% (w/w) neopentylglycol dimethacrylate as a cross-linking agent, was used for the preparation of Superbond C & B. The bonding of Superbond C & B to which the cross-linking agent had been added was then examined by the pull-out test using an alloy with different levels of surface roughness prepared by two surface-processing methods (polishing with #600 waterproof abrasive paper or 50 microns sandblast processing). The results were as follows: 1. Superbond C & B had a bonding strength of 205 kgf/cm2 after polish processing of the alloy with #600 waterproof abrasive paper and 199 kgf/cm2 after 50 microns sandblast processing. The t-test showed no significant difference between the two types of processing. 2. Superbond C & B to which the cross-linking agent had been added showed a bonding strength of 285 kgf/cm2 in the material processed with #600 waterproof abrasive paper and 347 kgf/cm2 in that processed with 50 microns sandblast processing. 3. Among various combinations of bonding agents and surface processing methods, the combination of Superbond C & B with the cross-linking agent and 50 microns sandblast processing showed the highest values under all conditions.

[Studies on thermal stimulation accompanying visible-light irradiation].

Visible-light-cured composite resin is one of the most frequently used materials in clinical practice. The use of this material inevitably involves dental pulp stimulation, i.e., thermal stimulation due to visible-light irradiation, during the restoration procedure. To determine the variations of temperature involved in visible-light irradiation, the author examines differences in temperature generated by various types of visible-light curing units. Changes in the temperature under varying conditions of irradiation were also examined. The results were as follows: 1) Among the visible-light curing units used in the present study, the highest temperature was obtained from Translux CL (a rise of 17 degrees C) whereas Hiliomat showed the lowest value (a rise of 7 degrees C). 2) The temperature increased with prolongation of irradiation time, reaching a maximum level (a rise of 15 degrees C) at 60s. 3) The temperature increased with shortening of irradiation distance, reaching a maximum level (a rise of 20 degrees C) at 3mm.

[Stress analysis at the metal-enamel junction of the anterior adhesive bridge on non-prepared teeth with three dimensional photoelastic experiment].

To study the dynamic action at the metal-enamel junction of an adhesive bridge, the author calculated the values of principal stress and maximum shearing stress, and determine the stress distribution at the junction of the adhesive bridge, for which an unprepared central incisor and a canine were used as abutments for a defect of the maxillary lateral incisor, using a three-dimensional photoelastic experiment. Two models were produced for the experiment on the basis of assumed intercuspal position: Model 1 with a loading point set around the incisal edge and model 2 with a loading point at the lingual cingulum. The results were as follows. (1) In both Models, tensile stress was distributed as the principal stress at the metal-enamel junction, except for the loading point, in the adhesive bridge of the non-prepared type. (2) The maximum principal stress was observed in compressive stress at the loading point in the central incisor of Model 2, being 720 kgf/cm2. Model 2 tended to show a higher concentration of stress at the loading point than Model 1. (3) Values of compressive stress at the loading point of the central incisor and canine were compared in Models 1 and 2. The central incisor showed higher stress values than the canine in both models; the canine had 50-60% of the stress values in the central incisor. (4) Investigation of distribution of the maximum shearing stress revealed a value of 360 kgf/cm2 on the surface directly under the loading point of the central incisor and 240 kgf/cm2 at the loading point of the canine in Model 2, and 215 kgf/cm2 at the loading point of the central incisor and 120 kgf/cm2 at the loading point of the canine in model 1. These values were all above the shearing stress of adhesive resin cement.

[Photoelastic stress analysis at the metal-enamel junction of the anterior adhesive bridge on non-prepared teeth in eccentric jaw position].

To study the stress involved at the metal-enamel junction of an adhesive bridge during the eccentric movement of the mandible, the author calculated the values of principal stress and maximum shearing stress, and determined the stress distribution at the adhesive surface which exists between retainer and enamel, for which an unprepared canine and a centaral incisor, using a three-dimensional photoelastic experiment. Based on the assumed eccentric movement of the mandible, three models with loading at different parts of the adhesive bridge were used for the experiment: Model 1 with loading only on the central incisor, Model 2 with loading on the pontic of the lateral incisor and Model 3 with loading only on the canine. The results were as follows. (1) Models 1 and 3 showed stress concentration directly under the loading point, where the compressive stress was 610 kgf/cm2 in Model 1 and 610 kgf/cm2 in Model 3. (2) Model 1 showed distribution of stress of 30-80 kgf/cm2 at the metal-enamel junction of the canine, while in Model 3 the stress of 80-150 kgf/cm2 was distributed at the metal-enamel junction of the central incisor. Loading only on the canine produced higher levels and broader distribution of stress than loading only on the central incisor. (3) Model 2 showed distribution of stress of about 60 kgf/cm2 at the metal-enamel junction of the central incisor and canine. Extremely intense stress, 250 kgf/cm2, was noted in the canine slice contiguous to the pontic. Stress as high as 70 kgf/cm2 was also observed in the central incisor slice contiguous to the pontic. (4) The maximum shearing stress values were 305 kgf/cm2 in Model 1 and 325 kgf/cm2 in Model 3 at the sites directly under the loading point, showing similarly high levels. (5) A comparative investigation of the maximum shearing stress appearing at the metal-enamel junction among the models showed that the distributed maximum shearing stress in Model 3 was about twice that in Model 1. (6) Model 2 had the maximum shearing stress, which was located toward the pontic in the canine, with an intensity closed to the shearing strength of currently available adhesive resin cement, suggesting a high risk of desquamation at this site.

[Temporary restoration using light-cured resin].

In spite of various problems involved in chemically cured resin (self-curing resin), e.g., irritability, and heat and shrinkage at polymerization, it has traditionally been the material of choice in the production of temporary restorations. However, light-cured resin, which does not have the disadvantages of chemically cured resin, has recently been developed and applied to clinical treatment. The present study was conducted to examine the clinical application of light-cured resin to temporary crowns. Two types of light-cured resin and one type of chemically cured resin were examined for their mechanical properties. The properties involved in handling and setting, and the methods of producing crowns were also studied. The results were as follows: 1) In the tensile strength test, there was no significant difference between the two types of light-cured resin, i.e., Triad and Unifast LC. The tensile strength of Unifast, a chemically cured resin, was slightly greater than the others, the difference being significant. 2) The Vickers hardness test showed no significant differences between the three types of resin. 3) The mechanical properties of Triad were not influenced by differences in the curing unit (the unit for general oral use or exclusive use) used for polymerization. 4) The test of setting properties revealed that Unifast LC needed longer than Unifast from the 2nd through the 4th clinical stage. In particular, Unifast LC required about 2.5 times the duration needed by Unifast at the 2nd stage in the tray method. 5) The heat generation test showed that the exothermic temperature in Unifast was significantly higher than in the two types of light-cured resin. 6) Heat generation associated with light curing was noted during the use of a light-curing unit for oral use.

[Bonding strength of adhesive resin and calcium phosphate crystalline ceramics (CPCC)].

The bond strengths of two adhesives, Panavia EX (PE) and Superbond C & B (SB), and calcium phosphate crystalline ceramics (CPCC) were examined. Two square pieces of CPCC were joined to each other using PE, and another two pieces were joined using SB at adhesion loads of 0.2kgf and 15.0kgf. The adhered specimens were left at 37 degrees C and 60 degrees C in thermostatically controlled purified water baths for 24 hours. The bond strength was determined by means of an apparatus to measure compressive shear and bond strength. Stress distribution on the interfaces with compressive shear where the adhesive was applied was also studied by a two-dimensional photoelastic experiment. The results were as follows. 1) The test pieces joined with PE at 0.2kgf and left at 37 degrees C provided the maximum bond strength, 69 +/- 16.8kgf/cm2, while those joined at 15.0kgf and left at 60 degrees C provided the minimum bond strength, 10 +/- 5.6kgf/cm2. 2) The test pieces joined with SB at 15.0kgf and left at 60 degrees C and those joined at 0.2kgf and left at 37 degrees C provided the maximum and minimum bond strengths: 179 +/- 36.8kgf/cm2 and 70 +/- 10kgf/cm2, respectively. 3) When the adhesion load was increased from 0.2kgf to 15.0kgf, the coat thickness for PE and SB were decreased from 45 microns (SD = 11.7) to 20 microns (SD = 2.8) and from 68 microns (SD = 24.5) to 18 microns (SD = 2.9), respectively. 4) The bond strengths of PE and SB for CPCC were decreased and increased, respectively, by an increase in adhesion load, i.e., a decrease in the thickness of the coat, and an increase in the temperature of maintenance after adhesion. 6) The photoelastic experiment revealed no differences in stress distribution or shear stress between the combinations of PE and SB adhesives and adherends of SUS304 and CPCC. 7) Shear stress was distributed to the area ranging from the site of load to the base of load on the interfaces with compressive shear where adhesive was applied.

[Studies on bond strength and hardness of base materials].

Since base materials are used in the construction of abutment teeth and the cavity walls of the teeth with healthy pulp, they need considerable bonding and mechanical strength depending on the site of application. In the present study we examined bonding strength, Martens-Mayer hardness and Vickers hardness of base materials in comparison with natural dentin in order to reevaluate them in terms of prosthetic materials and to provide assessment criteria for their application to prosthetic treatment. The results were as follows: 1) The bonding test showed the lowest value (4.6kgf/cm2) in calcium hydroxide FR (HFR) and the highest (47.9kgf/cm2) in HY-Bond polycarboxylate cement (CHC), a type of polycarboxylate cement. 2) In the test of bonding strength with various types of cement, calcium hydroxide preparations and zinc phosphate cement showed low values (4.6-23.5kgf/cm2) while polycarboxylate cement and glass-ionomer cement showed relatively high values (17.8-40.5kgf/cm2). 3) The Martens-Mayer hardness test showed the highest value (10.82 x 10(4] in dentin cement (GDE) and the lowest (1.09 x 10(4] in propack (EPR). 4) The Vickers hardness test showed the highest value (82) in neo-protect cement (ZPR) and the lowest (1) in propack (EPR). 5) In both Martens-Mayer and Vickers hardness tests with various types of cement, zinc phosphate cement and glass- ionomer cement showed high values, while low values were obtained in calcium hydroxide preparations and zinc-oxide eugenol cement. 6) Zinc phosphate cement and glass-ionomer cement showed no statistically significant differences from natural dentin in either Martens-Mayer hardness or Vickers hardness.