We do not usually reply to the inquiry “Which do you prefer, Cone-Crown telescopes or magnetic attachments for direct retainers of removable partial dentures (RPD) ” They differ so much in compensatory stabilization based on the form of support, bracing and retention that it is not usually necessary to select one of the two retainers. In general, the following Trius is useful for the restoration of partially dentate subjects for years based on many years of clinical follow-up results, that is: 1. Minimizing the denture movement especially in the distal extension saddles. 2. Realizing oral and prosthetic plaque control in designing of the RPD. Apply prophylactic measures throughout the treatment. 3. Give structural toughness to the denture frameworks and plates that can be repaired after many years of wearing. We cannot simply realize the Trius in constructing RPD based on magnetic attachments, since they do not give positive bracing in themselves with rather greater retentive forces and larger denture plates and telescope-like outer crown on the cast base compensating for the lack of bracing function from the retainers. We have utilized the Cone-Crown telescope system in constructing removable bridges and RPDs using the rigid support concept with the Trius since 1974. We can use this telescope system in any situation of reconstruction in partially dentate individuals. We report on a 20-year follow-up study of the Cone-Crown system with 10-year follow up study, which was reported in 1995, with positive and superb prognoses. The Cone-Crown telescope system showed clinical superiority in the field of RPDs in theoretical analyses and superb prosthetic outcome in the long follow-up study.

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Magnetic attachments are considered to be a type of stud attachment. Due to the phenomenon of magnetic attraction, magnetic attachments provide retention which has different characteristics than that of other mechanical attachments or retainers. Unlike the retention which results from male/female fitting in mechanical attachments, magnetic attractive (retentive) forces occur when surfaces of the keeper and magnetic assembly are in close proximity or contact. The attractive force between keeper and magnetic assembly remains virtually uniform. Magnetic attractive forces provide guidance during denture insertion, thus the denture is always guided to the same position. Also, magnetic attachments protect abutments from excessive loading. However, retentive force depends on the direction of withdrawal (magnetic flux) and gap between keeper and magnetic assembly, and decreases as both increase. Conic telescopes also possess the property of constant retention which is similar to that of magnetic attachments. Still, dislodgment in the oblique direction like with magnetic attachments is impossible because of the fit of inner and outer crowns. This limitation is applicable to all mechanical attachments. Thus magnetic attachments allow various unrestricted paths of insertion and removal energy is low. Having the unique feature of “retention without bracing, ” magnetic attachments can be indicated for teeth with damaged crowns, short roots and maxillary anterior teeth abutments susceptible to lateral forces.

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The author has endeavored to apply a Konus Kronen telescope over 25 years and uses it still now. I rather wonder why the Konus Kronen telescope, which was used by many clinicians in the past, is considerably less used at present. Troubles encountered in its early stage of introduction resemble to those commonly encountered in the use of conventional clinical techniques. With the improved manipulations and better understandings, Konus Kronen telescope is considered to be applicable for a long term with good durability. My clinical experience over 10 to 15 years can support this concept. Though many troubles have been encountered in the use of Konus Kronen telescope, the following countermeasures seem to be capable of preventing these troubles adequately: 1) arrangement of varied factors involved in the retentive force, 2) control of the retentive force, 3) reduced number of abutment teeth, 4) avoidance of adverse effects due to relatively higher occlusal force when Konus Kronen telescope is applied, and 5) establishment of good collaboration with dental technicians. Konus Kronen telescope and magnetic attachment have quite different applications and target fields mutually. Recently magnetic attachment has widely used because of its simplicity, however, the concepts of Konus Kronen telescope and magnetic attachment are very different. First, Konus Kronen telescope has better supporting effects. Konus Kronen telescope clearly can hold stable occlusion for a long term basis. Secondary, periodontium around abutment tooth will not be coverd with denture plate. As a result, Konus Kronen telescope offer better periodontal health than magnetic attachment which is usually coverd. Based on these reasons, denture with magnetic attachments has to be considered as a transitional denture. Taking the detailed difference between the two approaches into consideration, the scope of application and the priority of Konus Kronen telescope are discussed in this article.

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Ten years have passed since the first insertion of a magnetic attachment in a prosthesis clinic. Assessing the effectiveness of a retainer of partial denture requires at least 10 years of experimentation. During those 10 years no particular problem occurred and the magnetic attachment has gradually become accepted by most general clinicians. However, minor problems have occurred and appropriate treatments are required. The problems concern: 1) abutment teeth, 2) denture, 3) magnet assembly, and 4) others. Troubles such as fractures when the magnetic attachment comes off the denture or when the strength of the adhesive resin weakens have gradually disappeared as the adhesive strength of the metal and resin has increased. However, periodontal problems arise in the vicinity of abutment teeth as well as problems with the functional force. In other words, both patients and clinicians must cooperate in controlling the plaque. It is therefore necessary to take sufficient countermeasure to avoid root fractures generated by the functional force taken by the abutment tooth.

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Purpose: This study examined the influence of luting systems with phosphoric acid on bond strength to dentin which was primarily subjected to temporary cementation.
Methods: An acrylic resin plate was luted to dentin except for the control group (CON) with one of three temporary cements: HY-Bond Temporary Cement Hard (HYB), Freegenol Temporary Pack (FTP), and Neodyne T (NDT). Each substrate after removal of the temporary cement was then bonded to a silane-treated ceramic material (IPS Empress) with either a proprietary bonding system (Variolink II, V 2) or a wet-bonding system (RelyX ARC, RX). Specimens were stored in water for 24 hours, then shear bond strength was determined.
Results: Bond strength of the groups bonded with the V 2 system was categorized as: CON (11.4 MPa, a, b), HYB (12.7 MPa, a), FTP (7.6 MPa, b, c), and NDT (5.9 MPa, c), whereas that of the other groups bonded with the RX system ranked as follows: CON (21.7 MPa, d), HYB (11.3 MPa, e), FTP (6.0 MPa, f), and NDT (11.2 MPa, e), (p<0.05).
Conclusions: It is concluded that the influence of temporary cements on ceramics-dentin bonding varied considerably according to the combination.

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Purpose: To determine a desirable type of post-and-core for endodontically treated teeth without coronal extension.
Materials and Methods: A human maxillary central incisor was replicated from bovine teeth with the CELAY system (MIKRONA, Switzerland), which is a new method developed to provide experimental specimen teeth. Five types of root surfaces (I-V), four different post lengths (0, 2.5, 6, 8.5 mm), and three methods of post-and-core fabrication (cast metal post-and-core, prefabricated metal post and composite resin core, composite resin post-and-core) were examined without cyclic loading in 12 conditions and with cyclic loading in 4 conditions.
Results: Root surfaces prepared along the anatomical cervical line with a palatal slope showed higher failure load than those prepared horizontal to the tooth axis. Composite resin post-and-cores with a palatally sloping root surface were the most desirable of all three methods from a combined viewpoint of failure load and mode, though the failure load decreased remarkably with cyclic loading. In contrast, both cast post-and-cores and prefabricated metal post and composite resin cores demonstrated high failure load, but showed poor failure in teeth with unrestorable crowns.
Conclusions: Composite resin post-and-cores with a palatally sloping root surface were the most desirable of all three methods examined, although their longitudinal resistance must be improved.

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Purpose: Nocturnal bruxism has been recognized as a clinically relevant problem for decades, however, the exact cause of nocturnal bruxism (NB) is not clear. This study investigated the possible association between apnea hypopnea events and masseter contraction (MC) during sleep.
Methods: Twenty-five patients (9 women and 16 men) participated in this study. Patients who had previously received continuous positive airway pressure, surgical treatment or oral appliance for obstructive sleep apnea were excluded. Sleep study was measured using all-night polysomnography. Sleep and its stage were documented by standard electroencephalographic, electrooculographic, and electromyographic (EMG) criteria. EMG activity was recorded from mental, masseter and tibialis anterior muscles. Oxygen saturation was monitored continuously with a pulse oxymeter attached to the index finger. The following classification of MC was used in this study. Phasic MC episode showed three or more EMG bursts with the duration from 0.25 to 2.0 seconds and tonic MC showed EMG bursts lasting more than 3.0 seconds. Spearman's rank correlation test was used to measure the relationship between respiratory disorder index (apnea hypopnea index: AHI, apnea index: Al, arousal index: ArI) and masseter activity index.
Results: MC episodes were elevated especially during sleep stage 1, stage 2 and stage REM. MC episodes did not appear during an apnea episode. A strong correlation was found between the frequency of MC episodes that were associated with the termination of apnea hypopnea episodes per hour of sleep and AHI.
Conclusions: The results indicated that the termination of apnea hypopnea events is often accompanied with MC. It is suggested that MC can be linked to apnea and hypopnea episodes.

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Purpose: This study examined influences of thickness and materials of experimental palatal plates on gustatory response.
Materials and Methods: In this study, the subjects were twenty non-smoking adults (11 males and 9 females) with intact dentition. Three kinds of experimental palatal plate covering their whole hard palates were made: 1.5 R plate (a resin plate with 1.5 mm thickness), 1.5 M plate (a metal plate with 1.5 mm thickness), and 0.5 M plate (a metal plate with 0.5 mm thickness). First, responses to saltor bitter taste were investigated in the gustatory test by the whole mouth method and the chewing method, with and without each plate. Then, the masticatory performance per minute was investigated with and without each plate.
Results: 1. There was no significant difference in the gustatory tests and the masticatory performance between the 1.5 R plate and 1.5 M plate. 2. In the whole mouth method, only for bitter taste, the threshold of judgment of the 0.5 M plate was significantly different from that of the 1.5 R plate or 1.5 M plate. 3. In the chewing method, for both salt and bitter tastes, the threshold of judgment of the 0.5 M plate was significantly different from that of the 1.5 R plate or 1.5 M plate. 4. The masticatory performance of the 0.5 M plate was significantly different from that of the 1.5 R plate or 1.5 M plate.
Conclusions: It is suggested that thinner metal palatal plates are effective for gustatory response.

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Purpose: The long axis of a tooth was analytically determined from 3-dimensional and measured data of the dental surface, using a non-contact high-speed device to measure the 3-dimensional form. Its validity as the long axis of the tooth was evaluated by comparing it with that determined by the conventional method.
Methods: Five upper central incisors chosen at random from 50 that were considered to be the average form in the left-hand side were measured by using the non-contact high-speed device to measure the 3-dimensional form. Applying principal component analysis and using software to analyze the 3-dimensional form, the long axis of the tooth was obtained. Furthermore, as conventional methods to determine the tooth axis reported until now, Tamazawa's method was selected. About five natural teeth, the angle that the long axis of the tooth and tooth-axes make, and the positional relation made by the long axis of the tooth and tooth-axes in level 5 sections, with the long axis of the tooth as the starting point, were compared.
Results: In the long axis of the tooth and tooth-axis, the difference of the angle that the two axes make was very small. In five data, the position of tooth-axes was approximated to the starting point, i.e., the long axis of the tooth in each section.
Conclusions: The long axis of the tooth computed from the 3-dimensional image data of the surface of the tooth used by this research may be valid as the tooth-axis. It was quantitatively to the utmost limit obtained by applying for the principal component analysis.

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Purpose: The prosthodontic preparations for abutment teeth when making a removable partial denture, i.e., rest seat and guiding plane, are prepared in enamel of natural teeth, and the cut surface of enamel is generally left as it is in the oral cavity for a long time. However, there have been no discussion of their safety and stability. This article observed histological changes of the cut surface of enamel, which was experimentally kept in the oral cavity.
Methods: The specimens made with extracted human teeth prepared partially were mounted on the experimental palatal plates, which were kept in the oral cavity of 5 persons. At 4, 8, 12 and 24 weeks, they were observed with a light microscope, a scanning electron microscope and a transmission electron microscope, and were subjected to elementary analysis with an electronic probe x-ray micro analyzer.
Results: After 4 weeks, a very thin film formed on the cut surface of enamel, but this film was not observed in the control group. The thickness of the film gradually increased, and so after 24 weeks the specimens' surface was very smooth and uniform. From these microscopic observations, the film was concluded to be the secondary dental cuticle regenerated in the oral cavity. There were no remarkable changes in the structure and the elementary analysis of the enamel under the dental cuticle.
Conclusions: The secondary dental cuticle was regenerated on the cut surface of the enamel kept in the oral cavity, and no caries in the enamel under this film occurred for about 6 months.

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Purpose: This study investigated the adhesion of Candida to silicone soft lining materials.
Methods: Three kinds of silicone soft lining samples (GC, PF, SR) were used. Each sample was divided into two groups. The first group was an intact test piece. The second group had a rough surface, a part of which had been removed with a surgical knife. To determine the adherence of saliva to the surface, test samples were placed in filtrated saliva for 5 hours, 1 day, 3 days, and 5 days. After removal from the saliva, the samples were stained with toluidine blue. To determine the adhesion of Candida to the samples, the samples were placed in three different mediums (tryptic soy broth, filtrated saliva, and saliva diluted with saline) containing Candida for 5 hours, 1 day, 3 days, and 5 days. After removal from the medium, the samples were carefully washed in running water, then stained with toluidine blue.
Results: The samples showed that the saliva was deposited on the surface of all samples. All samples placed in each medium showed that yeast-type Candida initially adhered to the surface even if mycelial-type Candida was contained in the medium. The volume of fungus on each sample increased with time. In all samples, the volume of Candida adhering to the roughened surface was conspicuously greater than that adhering to the smooth surface.
Conclusions: The results suggest that the adherence of Candida to silicone soft lining material is not dependent on the presence of saliva. However, the presence of saliva facilitates Candida adherence to silicone soft lining material. The results also show that the yeast type is dominant at the initial stage of adherence to the material. Additionally, the adherence of Candida to the soft lining material is greatly affected by roughness.

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Purpose: Laser welding is being disseminated in the dental field because of prosthetic demand. It had been difficult to repair the metallic portions of artificial teeth with metal-base dentures, but the laser welding of similar and dissimilar metals as well as the effectiveness of filler metals.
Methods: The experiment were conducted using 7 types of metals and 4 types of filler metals. Two metal plates were butted and laser welded to make sample for tensile strength test, SEM, and EPMA. A metal bar 3 mm in diameter was made to make sample for measuring thermal expansion. Welding strength tests, SEM observation, and EPMA analysis were conducted, and thermal expansion coefficient was measured.
Results: 1. In similar-metal welding, all the metals showed sufficient welding strength and good weld condition. 2. When filler metals was used, good results were obtained in welding cobalt-chrome alloy to platinum-added alloy. 3. When no filler metal was used, good results were obtained in welding cobalt-chrome alloy to gold/silver palladium alloy and platinum-added alloy, and in welding cobaltchrome alloy containing titanium to platinum-added alloy.
Conclusions: Even when dissimilar metals were welded, it was clarified that there are some welding combinations having clinically sufficient strength and that the use of filler metals is effective in some cases.

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