Investigation of stress distribution within an endodontically treated tooth restored with different restorations.

Background/purpose: Recently, metal-free restoration has become the standard in prosthetic treatment. However, it is still unclear which combination is most effective in preventing root fracture and secondary caries. The purpose of this study was to evaluate the influence of different post systems, crown materials, crown thickness and luting agents on the stress distribution around the crown margins, cervical dentin and the tip of the post.

The investigation of the stress distribution in abutment teeth for connected crowns.

Background/purpose: With the advancement of an over aging society, the average number of remaining teeth has increased. However, these remaining teeth do not always have sufficient alveolar bone support, and sometimes fabricated connected crowns are applied. This study evaluated the influence of crown material, crown thickness, and alveolar bone resorption on the stress distribution within the abutment teeth of connected crowns.

Evaluation of composite resin core with prefabricated polyetheretherketone post on fracture resistance in the case of flared root canals.

The aim of this study was to use polyetheretherketone (PEEK) for the post material and evaluate the fracture load of six restoration patterns in teeth with flared root canals; composite resin core alone (Group R); glass fiber sleeve (Group S); PEEK post (Group P); glass fiber post (Group F); PEEK post in glass fiber sleeve (Group PS); glass fiber post in glass fiber sleeve (Group FS). In this study, cylindroid specimens were prepared and underwent three-point-bending test in a steady condition and after water immersion. In the loading test, the materials in clinical conditions using bovine teeth were evaluated.

Evaluation of the occlusal contact of crowns fabricated with the bite impression method.

In prosthodontic treatment, reconstruction of a proper occlusal contact relationship is very important as well as reconstruction of a proper interproximal relationship and marginal fitness. Unfortunately, occlusal relationships are sometimes lost in the process of occlusal adjustment of crowns. The purpose of this study was to compare the occlusal contacts of single crown fabricated by two different types of impression techniques.

Influence of the flexural modulus of prefabricated and experimental posts on the fracture strength and failure mode of composite resin cores.

The purpose of this study was to evaluate the influence of flexural modulus of non-metal posts on the fracture strength and failure mode of composite resin cores. Thirty-two human premolars were divided into four groups: prefabricated glass fiber post with 1.0 mm diameter and composite resin core (Group PE1.

Photoelastic stress analysis of endodontically treated teeth restored with different post systems: normal and alveolar bone resorption cases.

The present study examined the influence of different post materials and their lengths on the mechanical stress of endodontically treated incisor roots in two alveolar bone conditions. Two-dimensional photoelastic models were fabricated to simulate the endodontically treated maxillary central incisors restored with three kinds of posts materials (low Young's modulus glass fiber post, high Young's modulus glass fiber post, and prefabricated stainless steel post) and two post lengths (8 and 4 mm). Completed models were placed in a transmission polariscope and loaded with a static force of 150 N at 45° to the tooth axis.

The main occluding area in patients with fixed partial dentures.

It has become clear that food crushing is performed in the circumscribed region between functional cusps, that is, at "the main occluding area". However, the position of the main occluding area in patients with fixed partial dentures (FPDs) has not been investigated quantitatively yet. There is a possibility that the load onto the abutment teeth of FPDs is loaded excessively depending on the position of the main occluding area at the early stage of mastication.

Relationship between upper and lower molars during mastication.

Objectives: This study investigated the relationship between upper and lower molars in the early stage of mastication.

Materials And Methods: We measured the occlusal contact areas during chewing test foods using the three-dimensional shape measurement system and the six-degree-of-freedom mandibular tracking device. The reference points corresponding to "A" and "B" occlusal contacts were selected from the surface of upper dental cast (UA, UB) and lower dental cast (LA, LB).

Effect of reinforcement with resin composite on fracture strength of structurally compromised roots.

This study was aimed at evaluating the fracture resistance of structurally compromised roots restored with four different post and core systems. Thirty-two bovine roots were uniformly shaped to simulate human mandibular premolar roots. The roots were divided into four groups based on the type of restoration: cemented cast post and core (Group MC), resin composite build-up (Group CR), resin composite and prefabricated glass fiber post build-up (Group FRC), and thick-layer dual-cured resin composite-reinforced small-diameter tapered cast post and core (Group CRM).

Photoelastic stress analysis of different post and core restoration methods.

The aim of this study was to compare three types of post and core systems by analyzing the stress magnitude within the root. To this end, two-dimensional photoelastic simulation models of endodontically treated maxillary central incisors were fabricated. Three different types of post and core systems were selected for this study: composite resin post and core, composite resin core in combination with a glass fiber post, and conventional cast metal post and core.

Investigation of distortions around the cervical area of teeth restored with two kinds of crown materials.

The purpose of this study was to identify crown materials to decrease the stress concentrated at the cervical area of endodontically treated teeth. To this end, 14 extracted human mandibular premolars were divided into two groups for this study: complete cast crowns versus polymer-based crown and bridge material crowns. Both complete cast crowns (MC) and polymer-based crown and bridge material crowns (HC) were cemented with a glycidyl methacrylate-based resin cement (RC) to composite resin cores with glass fiber posts.

Stress distribution in roots restored with different types of post systems with composite resin.

Although composite resin core is used with various types of prefabricated posts, it remains unclear which kind of material is most suitable for the post. The aim of this study was to evaluate the influence of prefabricated posts on the stress distribution within the root by finite element analysis. Posts and cores were built up with composite resin and four types of prefabricated posts: two types of glass fiber posts (GFP1, GFP2) with low and high Young's moduli, a titanium post (TIP), and a stainless steel post (SSP).

Investigation of stress distribution in roots restored with different crown materials and luting agents.

The purpose of this study was to identify crown materials and luting agents that would decrease the stress concentrated at the roots of endodontically treated teeth. To this end, natural tooth model (NT), full cast crown model (gold-silver-palladium alloy; MC), polymer-based restorative material crown model (HCC), and all-ceramic crown model (ACC) were constructed. In each model, methyl methacrylate-based resin cement (MMA) and composite cement (CC) were used as luting agents.

Comparison of the main occluding area between adults and adolescents.

It has become clear that foods crushing is performed in the circumscribed region between functional cusps, that is, at "the main occluding area". However, it is not established to evaluate this area objectively. The purpose of this study was to establish the positional evaluation of the main occluding area quantitatively and evaluate the positional change depending on the age with this method.

Accuracy of temporary laser welding of FPDs by Nd:YAG laser in the oral cavity.

The purpose of this study was to investigate the accuracy of temporary fixation with laser welding for fixed partial dentures (FPDs). Five kinds of experimental FPD with different welding/soldering gaps were fabricated (0, 20, 50 microm for welding; 300 microm for soldering). Then, FPDs were temporary-fixed by laser welding or with a self-curing resin.

Study on the fracture strength of root reconstructed with post and core: alveolar bone resorbed case.

This study evaluated the influence of alveolar bone level on the fracture resistance of root restored with post and core. Forty-eight extracted human mandibular premolars were divided into six groups. Cast posts and cores were cemented (MN8 and MP8) or resin cores were built up with fiber posts and composite resin (FN8, FP8, FN4, and FP4).

The effect of occlusal contacts on adjacent tooth.

Purpose: The purpose of this study was to clarify the influence of changes of occlusal contacts on adjacent tooth displacement during articulation.

Materials And Methods: The amount and direction of displacement of the maxillary left first molar and adjacent teeth were measured using a displacement transducer, Type M-3. Seven subjects were included in this study.

Influence of occlusal height for an implant prosthesis on the periodontal tissues of the antagonist.

The purpose of this study was to investigate a suitable occlusal height for an implant prosthesis by examining the responses of the periodontal tissues around a natural antagonist. The subjects were three Japanese females with two posterior missing teeth restored by ITI system implants (Straumann). Two kinds of experimental implant prostheses were adjusted as follows; one was adjusted in heavy clenching (HC), and the other was adjusted in light clenching (LC).

[Statistical analysis of the fabrication of fixed and removable partial dentures (in 2002)].

A statistical survey based on laboratory records was performed on the number of fixed partial dentures and removable partial dentures fabricated at the dental hospital of Tokyo Medical and Dental University from April 1 to September 30, 2002. A comparison was also performed with a previous survey that had been carried out in 1997 to detect any change and possible alternations in the near future. From the findings of this statistical survey, the conclusions were as follows: 1.

[A statistical survey of the fabrication of single restorations (in 2002)].

A statistical survey based on laboratory records was carried out to determine the state of fabrication of restorations at the dental hospital of Tokyo Medical and Dental University during the six month period from April 1 to September 30, 2002. A comparison was also done with a previous survey that had been carried out in 1986 and 1997 to detect the possible change and alternations in the near future. From the findings of this survey, the following conclusions can be drawn.

Influence of environmental factors on tooth displacement.

An analysis of static occlusion including occlusal force and occlusal contact area in intercuspal position may be helpful but a dynamic analysis of occlusion should be regarded as more important for analyzing the stomatognathic system. Anthropological research has shown that the Japanese and the Mongolian populations share morphological and genetic similarities, although their dietary lives are not the same. The purpose of this study was to evaluate the relationship between environmental factors such as dietary life and stomatognathic function with a dynamic analysis of physiological tooth displacement.