Excess removable partial denture dynamics during function may cause mechanical trauma on the abutments and the resorption of the residual ridges. A removable partial denture should be stabilized in the spatial position by the compensatory support due to the remaining abutments and the residual ridges. In this study, the mechanism to diminish the removable partial denture dynamics was investigated by annual review of selected dental literature.
Rigid bracing of the denture, rather than rigid retention, should be required with the stability of theremovable partial denture under the protection of abutments and residual ridges. Rigid bracing of the denturewill be obtained through connecting rigidity between abutments and retainers. Great connecting rigidity andbracing are obtained through the guiding surface/guiding plate parallelism between the abutments andretainers. The occlusal force distribution should be controlled by changing the connecting rigidity betweenabutments and removable partial denture.

View full abstract

Two keys for clinically success of the removable partial denture have been recognized. One isinhibition of inflammation of periodontal tissue (biologically based). The other is proper broad forcedistribution. The retainer is generally accepted as having rigid connection. The selection and design of claspbring achievement of the rigid connection. The clasp has the functions of support, bracing, retention andreciprocation. When these well-balanced functions are performed effectively, stabilization of the removablepartial denture is acquired.
As for the four clasps (Akers clasp, double clasp, combination clasp and RPI retainer), which are oftenapplied clinically, each of the functions was assessed from the standpoint of rigid connection and my thoughtson selecting clasps are presented.

View full abstract

A term “Denture Dynamics” was originally defined as a denture movement during function by K. H. Korber, which was expanded to express the stability of occlusal contacts built on artificial teeth of removable partial dentures (RPDs) through the function of the compensatory support, bracing and retention derived from the abutment teeth and the residual ridges during mastication affected by denture movement, especially in distal extension saddle RPDs, in this paper.
The rigid support concept of the distal extension RPDs were analyzed on the basis of EBM. For the purpose of exact and long-lasting occlusal contact with RPDs, attention should be paid to realize the followings:
1. Denture movement in distal extension RPDs should be minimized to the extent of the minimal movement of the expanded saddle for the exact reconstruction of occlusal contact with as simple outline form as possible.
2. First, choose the direct retainers with sufficient connecting rigidity for minimizing the denture movement with the healthy periodontal tissues of the abutments after extensive mouth preparations on the basis of sufficient tissue support and bracing.
3. Broken stress design of low connecting rigidity RPDs are rarely indicated with poor abutments after extensive periodontal therapy, or with weak devitalized abutments.

View full abstract

Matters to consider at the time of denture design for the elderly include physical condition and the state of oral hygiene control. With consideration of these, it is important to design dentures that canfacilitate risk control, provide a good oral environment, and are easy to maintain. Telescopic systems areknown to be methods to meet these requirements, including course scroll, riegel telescope, and resiliencetelescope, and these should be used according to actual conditions. Although a resilience telescope denturemay be effective for a few cone telescopic systems, removal partial dentures can be used together with riegeltelescope or resilience telescopic system.
Improvement of the quality of eating and conversation of the elderly is planned by using these systems.

View full abstract

In a comparatively short time, a magnetic attachment is a very popular prosthodontic procedure in Japan. So far, more than 800, 000 magnetic attachments have been used by Japanese clinicians.
The reasons for the development of magnetic attachments and their success in gaining peoples' confidence are as follows:
1.Many Japanese dentists are very eager for better and new clinical systems.
2.The Japanese Society of Magnetic Applications in Dentistry (JSMAD) and other concerned persons have contributed to the conveyance of timely information to clinicians and patients.
3.Many Japanese enterprises are fond of magnets because of Japan's wide use of magnets and because of pioneers likes Professors Honda and Mishima who helped invent advanced magnetic steels such as KS and MK steel in the early 20th century.
4. The “Magfit” and the “Hicorex” have successfully met clinical demands of Japanese dentistry such as small size, perfect corrosion resistance and satisfactory retentive force.
5.Recently, most Japanese patients strongly desire to keep their original teeth even when they are badly affected with caries and/or periodontal disease. In these cases, a magnetic attachment is one of the best choices for conserving and utilizing them appropriately.

View full abstract

A prosthodontic treatment of a 39-year-old female who had severe anterior open bite with rheumatoid arthritis was reported. Rheumatoid arthritis had been diagnosed 5 years previously, and she had been hospitalized for infection of the spine, shoulder and knee joints. In her medical history, the patient stated that her mandible had continued to gradually retrude for the past 3 years, resulting in severe anterior open bite.
Because of the progressive nature of rheumatoid arthritis, the decision was made to perform a reversible procedure to apply a prosthesis made of acrylic resin for stable occlusal contact with a posterior tooth. Afterthe eighth month, even distribution of posterior tooth contact was acquired with decreased vertical overbiteof 1 mm. After maxillary anterior prosthesis made of acrylic resin were provided with suitable verticaloverbite and anterior guidance, the metal prosthesis were provided at fourteen months after the first examination.
In this report, it was suggested that occlusal management could improve anterior open bite caused byrheumatoid arthritis of TMJ, however, lateral transcranial radiography of TMJ findings still showed deformityand flattening of the condyle and the articular eminence of bilateral TMJ after treatment.

View full abstract

In the case that there are few remaining teeth, the occlusal relationship as well as the design of a denture is important.
A mandibular simulation model with 4 remaining teeth {Nos. 18, 22, 27 and 31 (universal tooth numbering system)} was used in this study.
The retainers were Akers clasp and cone-telescopic crown.
When the occlusal contact in lateral eccentric jaw relation was changed, the stress distribution on the abutment teeth and the displacement of the denture base were examined.
The following conclusion was obtained.
It was indicated that the occlusal contact in lateral eccentric jaw relation rather than the denture design influenced the stress distribution of abutment teeth and the displacement of the denture base.
The difference between the two retainers was not clarified when bilateral balanced occlusion was given.
It was indicated that bilateral balanced occlusion was effective even in the removable partial denture with retainer.

View full abstract

The analgesic effects of amitriptyline was evaluated in 11 patients with chronic orofacial pain. The patients visited Fixed Prosthodontic Clinic, Okayama University Dental Hospital with the complaint ofchronic orofacial pain. They had been treated for more than six months with occlusal appliance or physicaltherapy before this study was started, and did not have good treatment results. Ten mg per day ofamitriptyline was started, and the amount was increased gradually depending on the patient's symptoms. Themaximum dose in this study was 70 mg in one patient and most of them were receiving under 50 mg/day. Theresults indicated that amitriptyline was effective in 9 of 11 patients. Two patients showed severe side effectsand stopped receiving it. It was concluded that amitriptyline is effective in the treatment of severe chronicorofacial pain. However, there were side effects with this medicine, so it is necessary to know the effects andside effects when administering it to orofacial pain patients.

View full abstract

The purpose of this study was to review the psychological condition of persons with craniomandibular disorders.
Brain waves (αwave) of normal type occlusion of 17 subjects and craniomandibular disorders of 24 subjects were obtained. The waves were analyzed using 1/f fluctuation of brain wave, and psychological tests of STAI and CMI were conducted for psychological assessment.
The results were as follows:
1. The psychological condition made a difference between the two types.
2. 1/f fluctuation of a brain wave is possible in clinical application

View full abstract

A computer program was written to classify partially edentulous arches using the Kennedy classification system. The program classified 65, 534 possible configurations of partially missing and presentteeth in one arch. The tabulated results show great diversity of combinations of missing teeth and thepredominance of asymmetrical cases. The impact on classification of replacement or nonreplacement ofmissing second molars in the presence of first molars was also considered.

View full abstract

This study was conducted to investigate the load pressure below the basal seat of complete dentures with resilient relining and to elucidate the buffer effect of the functional pressure. A model, simulating the alveolar mucosa and pressure-displacement was prepared to investigate the use of completedentures with two kinds of resilient relining of different HDA (type A durometer hardness). Comparisons were made with the basal seat load pressure of acrylic resin base denture without relining.
The load pressure had a noticeable buffer effect, and reduction of the basal seat was obtained in maxillarycomplete dentures at a functional pressure in resilient relining material when using a simulation model whichhad the approximate form, alveolar mucosa thickness, and pressure displacement of those of edentuloussubjects. Resilient relining material became noticeable in load pressure distribution for support functions.The effect increased when using resilient relining material with a small HDA. In addition, the need for a thickrelief chamber was suggested in the case of complete dentures with resilient relining compared with acrylicresin base dentures, as well as the need for setting the same post dam degree as that for acrylic resin basedentures.

View full abstract

Complete denture wearers in the normal face group were divided into left and right deviation groups for the frontal dentoskeletal form. The mechanisms of their jaw functions were analyzed in terms ofthe lateralized mastication index and asymmetry index of masticatory muscle EMG activity. Their relationshipwas examined, and the magnitude of bite force was divided into two levels (50% and 100% MC).
The results revealed that the asymmetry index of masticatory muscle EMG activity was strongly relatedto deviation and frequency of the lateralized masticatory index, as well as the mandible in the frontaldentoskeletal form when chewing, during masticatory movement with relatively weaker bite force.

View full abstract

The influence of mechanical stimulation on the human body is extremely important. It was hypothesized that if natural vibration of the tooth is propagated to other sites of the body, this stimulation willhave an effect on those sites as well. The purpose of this study was to investigate the propagation of naturalvibration of the tooth. The impact exerted on the tooth by repeated hard jaw tapping movement was recordedon the upper canine, and propagated vibrations were recorded at the chin, zygomatic bone, forehead, vertebraprominens and clavicula. An accelerometer was used to record the vibrations. Except for clavicula, naturalvibration of the tooth in all subjects was recorded. The amplitude and duration time of the propagatedvibration were found to be greatest at the chin, followed, in descending order, by the zygomatic bone, forehead, and vertebra prominens. The pattern of power spectrum varied between recording sites. These findingssuggested that natural vibration of the tooth may influence the functions of the cells in the head and neck, andthe influence will vary with distance from the teeth and differences in the structure between the tooth andpropagated sites.

View full abstract

In prosthodontic treatment, the vertical dimension is often changed. It was suggested that the changes affected not only the physical effects but also the mental effects. The vertical dimension waschanged, and observed the EEG topography was observed to estimate the mental stress by the high verticaldimension objectively.

View full abstract

Radiopacity of prosthetic dental materials especially used in the coronal area was determined, and the values were compared with those of enamel and dentin. Radiographs of the 2 mm thick specimens were taken together with tooth slices on aluminum step wedges. Radiographic density of the specimens were measured by means of a densitometer and expressed in terms of the equivalent thickness of aluminum. The results showed that the materials containing metal oxide and metallic compound exhibited high radiopacity values, whereas polymer-based materials with low filler content showed very low radiopacity values. A radiopacity value greater than enamel may be desirable for detection of materials or for their distinction from the tooth structure on the dental radiograph.

View full abstract

Recently, finite element analysis (FEA) has been use frequently to determine the biomechanical movement of teeth. However, the condition of the jaw bone and periodontal ligament varies in the reports, and it has not been clarified.
The purpose of this study was to clarify the differences between actual displacement of human teeth obtained by loading experiment and numerical values of the FEA model. Then the influence of the condition of the jaw bone, periodontal ligament and a fixed condition exert on the analysis value was evaluated using a mandibular premolar FEA model of the buccolingual section.
As a result, it was one of the effective means to control horizontal displacement of compact bone and to gradually increase Young's modulus of periodontal ligament from tip to cervical margin, causing displacement under pressure of the two-dimensional FEA model to approximate actual values.

View full abstract

Dentures may act as a reservoir for bacteria which cause opportunistic infection such as aspiration pneumonia, and denture cleaning could prevent such an infection. Recently, the bacteriocidal effect of electrolyzed water (EW) on bacteria has been reported.
In this study, the influence of EWs on the Candida albicans biofilm in vitro was investigated. C. albicans adhered avidly to type IV collagen. The biofilm was established on the cover slip coated with type IV collagen using Luria broth at 37°C for 5 days. The biofilms were treated with several kinds of EWs, and the efficacy of EWs was investigated.
C. albicans well adhered to collagen-coated celldesk, produced glycocalyx-like substance and formed a biofilm after five-day incubation. Scanning electron microscopy revealed degradation of biofilm treated with EW. Vital CFU in the biofilm decreased time-dependently and logarithmically. Five treatments for one minute was more effective than one treatment for five minutes. The effect of EW synthesized by a home care device was equal to or higher than that synthesized by a medical device. These results suggested that EW, even if synthesized by the home care device, is a potent denture-cleanser.

View full abstract

Recent epidemiological studies have found an association between general health status such as CHD and oral health condition, particularly in people with evidence of Chlamydia pneumoniae infection. However, there is conflicting data for the relationship between CHD and the oral condition.
The purpose of this study was to understand the relationship between oral health such as caries, periodontal disease and cardiovascular disease in relation to sex differences.
Oral and microbiological examinations were conducted on 106 patients aged 50 years and over (68 males, 38 females) with cardiovascular disease, admitted to Iwate Medical University Hospital. In this study, the subjects were divided into two groups, male and female.
The conclusions were as follows:
1. Characteristic results of microbiological examination showed no significant relationship between people with cardiovascural disease.
2. As for hard tissue, previous treatment of coronal caries was higher in females than males, and morbidity of root caries was higher in males than in females.
3. Morbidity of periodontal disease was higher in people with cardiovascural disease than in normal people, and in sex differences, oral health of males was worse than females.

View full abstract

The purpose of this study was to investigate the effect of the modification of clasp assemblies under horizontal load. The simulated mandibular model with unilateral free end was fabricated for this study. The eleven types of removable partial dentures (RPDs) using different retainers respectively were constructed. These retainers were a cone-telescopic crown, Akers clasp, double Akers clasp, RPI clasp (Kratochvil type) and seven modified clasps made from the first three clasps to which an enlarged bracing arm, a positive rest with hook and a distal rest with a guide plate were added. Horizontal loads were applied, and the stress on abutment teeth and the displacement of denture base were measured.
The results were as follows:
1. Under horizontal loads, the partial denture retained by cone-telescopic crowns had the least displacement of denture base.
2. The RPDs with Akers clasps, double Akers clasps and RPI clasps generated large displacement of the denture base.
3. The stress characteristics on abutment teeth and displacement of denture base of the RPDs with modified clasps were similar to those of cone-telescopic crowns with enlarged lingual bracing arms, especially.

View full abstract

Single neuronal activities responded to low-threshold mechanical stimulation (stimulus intensity:<0.05 N) of the tooth (PDN) were intracellularly recorded from the primary somatosensory cortex (SI) in the cat anesthetized with α-chloralose and halothane. After identification of their response characteristics, neurobiotin was injected iontophoretically and morphological features of neurons were accurately analyzed.
PDNs responded to low-threshold mechanical stimulation (<0.05 N) of the tooth and received dominantly periodontal afferent without input from other intraoral structures. Most of them received periodontal input from the ipsilateral side and showed directional selectivity to mechanical stimulation.
Most PDNs intracellulary stained were classified as pyramidal neurons according to their morphological properties (13 Pyramidal and 1 non-pyramidal PDNs). Each pyramidal PDN had different morphological features. Mainly, axons of lamina III PDNs ran through relatively superficial regions of the subcortical white matter, whereas those of lamina V ran deep into the subcortical areas. The results suggested that lamina III pyramidal PDNs send periodontal sensory information to the other cortical regions and lamina V pyramidal PDNs send them to the far regions of the CNS such as the medulla and spinal cord.

View full abstract

In this study, the relationship between the composition and the flow properties of three commercial tissue conditioners was investigated. Analysis of the composition was chiefly done by infrared spectroscopy (IR). As for the liquid, plasticizer was qualitatively determined and the content of alcohol was measured by distillation. The characteristics of polymer powders were obtained by means of gel permeation chromatography (GPC), particle size analyzer and SEM. As for the flow property, the apparent viscosity of a mixture of liquid and powder was measured by a cone and plate rotational viscometer.
As a result, the liquid was a mixture of a phthalic ester plasticizer (dibutyl phthalate) with up to 13% ethyl alcohol. The polymer powders generally consisted of polyethyl methacrylate (PEMA), but one was a blend of PEMA and polyisobutyl methacrylate (iso-PBMA).
The viscosities of mixtures were found to increase rapidly with an increase in the ethyl alcohol content, and an increase in temperature. Further, the viscosity curve of the tissue conditioner, of which the powder was a blend of PEMA and iso-PBMA, showed characteristic behavior. Thus it was suggested that the flow property of the tissue conditioner was affected by the molecular structure of the polymer powder.

View full abstract

The purpose of this study was to improve the property of photo-cured type denture relining resins. Specimens of three commercial resins were cured under 4 conditions (condition 1: photo-cure follow ing manufacturer's instructions, condition 2: condition 1 +heating at 60 for 15 minutes, condition 3: repeat condition 1 three times, condition 4: condition 3+condition 2).
1. The amount of eluted monomers under conditions 2, 3 and 4 measured by HPLC was decreased compared with that of condition 1.
2. The amount of generated radicals under condition 2, 3 and 4 measured by ESR was decreased compared with that of condition 1.
3. The curing depth, water sorption and transverse strength were increased compared with those of condition 1.
4. The adaptability, surface hardness and surface roughness were not influenced by curing conditions.
The results suggested that condition 4 is the most effective method to improve the property of photo-cured type denture relining resins, and condition 3 is a simple and effective method for clinical use.

View full abstract

The position of the jaw and teeth contacts affect the evoked potential elicitable from the sternocleidomastoid muscle (SCM), which is activated during bite force production. The purpose of this study was to determine the changes of the activity of the SCM during clenching in the retruded mandibular position (RP). Six subjects were asked to clench at maximal and submaximal voluntary bite force levels when their mandible was fixed in the habitually closed position (HP) and in the retruded contact position (RP). Simultaneously, surface electromyography (EMG) of the masseter, temporal and SCM muscles was conducted. The root mean square (RMS) of the EMG in each clench effort was analyzed, and all data was normalized to the highest RMS found in the HP for each subject. EMG activity in all muscles depended on jaw position: the incidence of RMS values in RP higher than HP averaged 10.6%. The retrusion value of the condylar point was also significant: the subjects who retruded their jaw less than 0.6 mm showed higher SCM activity levels than those whose retrusion values were higher. It was concluded that SCM-EMG activity increases due to RP clenching. This is significant because muscle hyperactivity relates to muscle fatigue and pain.

View full abstract

In a previous study, it was confirmed that the head moves rhythmically and coordinately with jaw tapping movements. However, this report only referred to the vertical movements of the upper incisal point as mandibular movement. If the head moves in order to maintain balance during jaw functional movement as reported, it is expected that the upper incisal point moves not only vertically but also anteroposteriorly. The objective of the study was to assess the anteroposterior component of the head movement in order to clarify the existence of cooperated head and mandibular movement during jaw tapping. The experimental method followed in previous studies was repeated to analyze data from five young adults with the same six-degree-of-freedom measuring device.
The upper incisal points moved rhythmically anteroposteriorly, as reported for the vertical direction. The amplitude of anteroposterior motion of the upper incisal point was about 8.6% of the mandibular range of motion. The upper incisal point moved anterosuperiorly during opening and posteroinferiorly during closing. As the mandibular range of motion became greater, the amplitude of anteroposterior motion of the upper incisal point became greater. The results suggested that the vectors of head movement translation depends on the magnitude of mandibular range of motion.

View full abstract

The purpose of this study was to analyze the effect of the retainers in lower unilateral free-end removable partial dentures (U-RPD) on vertical displacement. An available jaw tracking system (TMJAWGRAPH^®) was modified to measure the jaw movement and removable partial dentures motion at the same time. Further, pyramid-shaped markers were designed to allow 3-D measurement by a geometrical method. These markers were fixed in the U-RPD, mandible and head, and allowed simultaneous 6-degree-of-freedom recording of their movements. In two U-RPD wearers, the vertical movement of the incisor point (IC) and the most posterior point in the flange (MPFP) were investigated by changing the design of retentive elements. The shape of the traces of vertical movement in the MPFP was not as smooth when chewing peanuts as it was in gum chewing, thus the dependency of motion in U-RPDs on the type of food was confirmed. On the contralateral side, the rest of the indirect retainer was effective against upper displacement, in spite of retention. Further, the data suggested that in these cases, the rotation axis for the upper displacement of the MPFP is more posterior than the fulcrum line.

View full abstract

In some studies, the insertion of unilateral free-end removable partial dentures (RPDs) is regarded as overtreatment because mastication is not improved. However, most studies on masticatory efficiency have assessed only the degree of crushing and have disregarded the influence of RPDs on the intraoral flow of food, which is an essential factor for deglutition. In this study, two new parameters were devised to evaluate, at the same time, the degree of crushing and flow of the food, 10-mesh remaining ratio and lingual transport ratio, respectively.
It was considered that patients who remove their RPDs chew unilaterally.
Unilateral chewing was examined in seven fully dentate subjects (FDT group) first, and then in nine unilateral free-end RPD wearers (RPD group).
In the FDT group, the degree of crushing and the accumulation of food particles in the lingual zone was significantly lower in unilateral chewing than in free chewing. In the RPD group, accumulation of food particles in the lingual zone was significantly lower without denture insertion than with the RPD inserted, but the degree of crushing was not significantly different.
The results indicated that RPDs are useful for the accumulation of food particles in the lingual zone, which could facilitate deglutition.

View full abstract

In this study, a new analyzing system was developed to evaluate the facial appearance of denture wearers affected by inadequate dentures and aging. In this system, the frontal and lateral digital facial images captured using a digital camera were displayed on a computer monitor and were analyzed according to the linear and angular measurements by image analysis software.
This system required a short time to complete the analysis, and showed high reliability because the dimensional error on image distortion and difference of lens-subject distance was small. The facial images of 59 dentulous subjects (44 males and 15 females aged 23 to 29 years) were analyzed. Furthermore, this system and a polygon (a standard deviation diagram) from the data on the male dentulous subjects were applied to the analysis of the facial appearance of a denture wearer (78-year-old male).
Dentures were useful to obtain lip support, but the effect of denture wearing was different for the analytical items. It was speculated that the differences in measurements between the edentulous subject with dentures and dentulous subjects were caused by aging and/or features of each edentulous subject.
This system could be useful for routine clinical use in prosthetic dentistry.

View full abstract

The purpose of this study was to investigate the working accuracy of CAD/CAM by probing the surface of the master model abutment, and its effect on the fabricated surface of three materials (titanium, thermosetting resin, and porcelain) cut to make crown and bridge. The master model abutment was measured first, the tool path for the cutting tool to run was produced, and then numerical control fabrication was applied to each material cut to measure it by the Coordinate Measuring Machine. For detailed results, two additional steps were taken and it was concluded that one-way analysis of variance statistically contrasted each measurement to the master model measurement and scanning electron microscopy confirmed eachfabricated surface.
1. Data on one-way analysis of variance
A. Titanium: smaller in the cervical area and larger in the other parts than the master model measurement.
B. Thermosetting resin: all the measured areas were smaller than those of the model except for the height.
C. Porcelain: smaller in the cervical area and larger in the other parts than those of the model.
2. Surfaces confirmed by scanning electron microscopy
A. Titanium:
a. a tool trace on the surface
B. Thermosetting resin:
a. a tool trace on the surface
b. a wave-like difference in the marginal form level of chamfer
c. an obtuse angle and chipping in the marginal angled area
d. scratches by the diamond particles of the tool
C. Porcelain
a. a tool trace on the surface
b. a rough cutting surface
c. an obtuse angle and chipping in the marginal angled area-clearer than that of the resin
In conclusion, the results proved the efficiency working accuracy of CAD/CAM by probing the surface of three kinds of material cuts. As the detailed data of each candidate for analysis, it was obvious that the fabrication of titanium is superior to the others and that it will be a great reference for future studies and dental treatment.

View full abstract