The sensitivity of bone conduction for dental implants.

Dental implants are connected to the alveolar bone by osseointegration. Dental implants could be used as a potential bone conduction (BC) hearing assistive device in the mouth. However, the BC threshold of dental implants has not been reported. The present study aimed to examine the pure tone auditory thresholds of normal human subjects to BC stimulation of the implants. Dental implants showed a significantly lower BC threshold than natural teeth and mastoids. Mandibular dental implants had BC sensitivity similar to that of maxillary dental implants. The BC threshold of anterior dental implants was significantly lower than that of posterior dental implants. Dental implants exhibited excellent BC properties.

Response of the somatosensory cortex following thermal stimuli to dental implants.

In the current study, we investigated the cortical response of the somatosensory cortex following thermal stimuli to dental implants. Five implants were inserted at the site of the left upper canine with immediate implant placement protocols in five cats. Intrinsic signal optical imaging was applied to measure the cortical responses evoked by thermal sensing via dental implants. The cortical response evoked by 60 g of tactile stimulus to implants was also examined. The response strength and activated location were compared between implants and natural teeth. Thermal stimuli via the implant could evoke reliable cortical responses in the tooth-related region. However, the response amplitude evoked by the cold stimuli applied to the implants was significantly lower than that evoked by the cold stimuli applied to the natural teeth, indicating that the implants were less sensitive to thermal change than the natural tooth. The response evoked by tactile stimuli to implants was significantly stronger than that evoked by cold stimuli. Thermal and tactile stimuli activated the same location of the tooth-related somatosensory cortex in both the implants and natural teeth. Therefore, the thermal change in implants could be detected at the cortical response level. Multimodal sensory integration of thermal and tactile functions existed for implants.

The role of gingival mechanoreceptors in the tactile function of dental implants.

Dental implants seem to restore some degree of tactile function. The aim of this study was to investigate the role of gingival mechanoreceptors in dental-implant osseoperception at the cortical-response level. The gingiva of the upper-left canine implant was stripped off under local anesthesia in five cats. We used intrinsic-signal optical imaging (ISOI) to measure the population-response characteristics of the feline oral-related cortex when separately applying punctate mechanical stimuli to the left canine implant and right intact natural canine. These response characteristics were compared under local anesthesia after removal of the gingiva. Under local anesthesia, the signal strength of the implant was significantly weaker than that of the tooth under weak but not under strong stimulus. After the gingiva was stripped off, the signal strength of the implant was significantly weaker than that of the tooth at all strengths of stimulus. Based on the evoked cortical responses, the gingiva was involved in the maximal tactile function of the implant.

Tactile sensation of natural teeth and dental implants in the somatosensory cortex.

PURPOSE: This study aimed to investigate the cortical response characteristics evoked by natural teeth and implants. METHODS: Five cats were subjected to intrinsic signal optical imaging to measure the cortical responses evoked by natural teeth and implants. The difference in tactile sensation between the implant and natural tooth was compared in detail at the cortical response level. RESULTS: Some similarities were observed between the implants and natural teeth. The stimulating-response curves of the implants and natural teeth were generally S-curves, and both implants and natural teeth preferred labial-lingual direction stimulation. The implants and natural teeth differed in terms of their tactile sensitivity: implants were weaker than natural teeth in terms of both static and dynamic sensitivity. However, after saturation, there was no significant difference in tactile strength between implants and natural teeth. CONCLUSION: Both natural teeth and implants are able to distinguish the tactile strength and stimulation direction. Although implants are less sensitive than the natural tooth, the maximal tactile function and directional preference of implants are similar to those of natural teeth.

Investigating the role of gingiva in the tactile function of teeth at the cortical level.

The role of the gingiva in the tactile perception of teeth is unclear, and the physiological basis of tooth tactile function needs to be examined at the cortical response level. In the presented study, gingiva from the upper left canine was removed under local anesthesia from five cats. Intrinsic signal optical imaging was used to measure population response characteristics of the cat oral-related cortex when punctate mechanical stimuli were separately applied to the left gingiva-stripped canine and right intact canine. Then, their response characteristics were compared. There were no significant differences in the cortical response strength between the anesthetized and unanesthetized canines. Signal strength of the gingiva-stripped tooth was significantly weaker than that of the intact tooth at low stimulus strength. However, no significant differences between the gingiva-stripped tooth and intact tooth were found after saturation. Based on the evoked cortical responses, the gingiva is involved in low-intensity tactile perception of teeth, which could explain the reason why chronic gingivitis results in the paresthesia of natural teeth.

Response characteristics of the cat somatosensory cortex following the mechanical stimulation to endodontically treated teeth with overextension.

The overextension of filling materials may take place accidentally during an endodontic root canal treatment. Previous studies to understand the correlation between overfilling and paresthesia of teeth were inconsistent. In this study, an intrinsic signal optical imaging technique was employed as the objective tool to compare the response characteristics of the cat somatosensory cortex following mechanical stimulation applied to endodontically treated teeth with overextension (ETTWO) and natural teeth. Based on the evoked cortical response, the signal strength of the ETTWO was found to be significantly higher than that of the natural teeth. However, the tactile threshold of the ETTWO was significantly lower than that of the natural teeth. It was concluded that the tactile function of ETTWO is more sensitive than that of natural teeth, and that the overextension of filling materials can cause hyperesthesia of teeth after root canal treatment.

Response characteristics of the cat somatosensory cortex following the mechanical stimulation to non-vital and vital canine.

Patients sometimes complain that non-vital teeth after root canal treatment (RCT) are paresthesia compared with vital teeth, and previous psychological studies on the tactile sensibility of non-vital teeth remained controversial. In the present study, intrinsic signal optical imaging, which served as an objective tool, was employed to compare the cortex response characteristics following forces applied to the cat non-vital and vital canines. Based on the evoked cortical responses, the response threshold, signal strength, spatial pattern, temporal dynamics and the preference of force direction, they were not significantly different between vital and non-vital canines. It seemed that the tactile sensibility of vital and non-vital teeth was comparable at the cortical response level, and pulpal receptors were not concerned in tactile function.

Population response characteristics of intrinsic signals in the cat somatosensory cortex following canine mechanical stimulation.

Intrinsic signal optical imaging has been widely used to measure functional maps in various sensory cortices due to better spatial resolution and sensitivity for detecting cortical neuroplasticity. However, application of this technique in dentistry has not been reported. In this study, intrinsic signal optical imaging was used to investigate mechanically driven responses in the cat somatosensory cortex, when punctate mechanical stimuli were applied to maxillary canines. The global signal and its spatial organization pattern were obtained. Global signal strength gradually increased with stimulus strength. There was no significant difference in response strength between contralateral and ipsilateral mechanical stimulation. A slightly greater response was recorded in the sigmoidal gyrus than in the coronal gyrus. The cat somatosensory cortex activated by sensory inputs from mechanical stimulation of canines lacks both topographical and functional organization. It is not organized into columns that represent sensory input from each tooth or direction of stimulation. These results demonstrate that intrinsic signal optical imaging is a valid tool for investigating neural responses and neuroplasticity in the somatosensory cortex that represents teeth.

Mandibular condylar morphology for bruxers with different grinding patterns.

OBJECTIVES: The purpose of this study was to investigate the mandibular condylar morphology for bruxers with different grinding patterns. METHOD: Condylar sectional morphology and condylar position of 30 subjects were determined by two viewers using cone beam computed tomography (CBCT) image data sets. The grinding patterns during sleep bruxism (SB) were determined objectively using a Brux-checker device.Chi-square tests were used for statistical analysis for the condylar morphology type between different tooth grinding patterns. Spearman's rank correlation coefficient was used for correlation analysis between condylar position and the canine guidance area during SB. RESULTS: Theincidence of condylarmorphologicaldivergence from idealwas35%.There isa significant difference in distribution of condylar morphology type between the group grinding (GG) and GG combined with mediotrusive side grinding (MG) (p < 0.05). There was no significant correlation between condylar position and canine guidance area during bruxism. DISCUSSION: MG during SB is associated with condylar morphology that is considered not to be ideal.

The study of grinding patterns and factors influencing the grinding areas during sleep bruxism.

OBJECTIVE: The purpose of this study is to investigate the grinding patterns and discuss the factors influencing the position relationship between intercuspal position (ICP) and grinding area during sleep bruxism. METHODS: Lateral condylar inclination, inclination of lateral incisal path and freedom in long centric of thirty subjects were measured. The grinding patterns during sleep bruxism were recorded with a bruxism recording device, BruxChecker. The position relationship between ICP and the grinding area was examined. Spearman's rank correlation coefficient was used for correlation analysis between grinding area and free factors (grinding patterns, freedom in long centric and discrepancy between lateral condylar inclination and inclination of lateral incisal path). RESULTS: All 12 subjects with 0mm-freedom in long centric exhibited that ICP of both sides located within the grinding areas. 4 subjects showed that ICP of both sides located outside the grinding areas. There is a significant correlation between 0mm-freedom in long centric and ICP within the grinding areas (p <0.01). CONCLUSIONS: Freedom in long centric has a significant effect on position relationship between intercuspal position and the grinding area.

A follow-up study of up to 5 years of metal-ceramic crowns in maxillary central incisors for different gingival biotypes.

The objective of this prospective clinical study was to evaluate the outcomes of metal-ceramic crown restorations in maxillary central incisors for different gingival biotypes in a Chinese population. One hundred single metal-ceramic crowns were fabricated for 100 patients (50 for thin gingival type and 50 for thick gingival type) from April 2007 to October 2007 and evaluated according to the World Dental Federation criteria at baseline and annually at all follow-up examinations for 5 years. Gingival recession was recorded at the same time, as well. The failure-free rate over the 5-year clinical trial for thin gingival type (78.0%) was significantly lower than that for thick gingival type (94.0%; P = .02). Seven crowns were ranked as failures because of esthetic problems in patients with a thin gingival type. The restored teeth with a thin gingival type exhibited more gingival recession (1.09 ± 0.22 mm) than the control teeth (0.31 ± 0.16 mm; P = .01). Gingival biotype had a significant effect on the outcomes of metal-ceramic crown restorations in maxillary central incisors.

[Self-cleaning and antimicrobial properties of methacrylic acid coupled TiO(2)/PMMA denture base resin].

PURPOSE: To study the influence of TiO2 and methacrylic acid on self-cleaning and antimicrobial properties of denture base resin. METHODS: TiO2 (2%, 4%, 6%) and methacrylic acid were respectively added into two makers' denture base resins. The self-cleaning property was assayed with measuring the decomposition of methylthioninium chloride. The antimicrobial property was tested with the pellicle-sticking method. The data were analysed by SPSS 12.0 software package for two-way ANOVA. RESULTS: The self-cleaning and antimicrobial properties of samples were improved as TiO2 increased. Methacrylic acid had no significant influence on self-cleaning and antimicrobial properties of the samples. The decomposition ratio and antimicrobial ratio of MTi4% (Rijin) were 53.96% and 71.42%, respectively. CONCLUSION: Methacrylic acid coupled TiO2/PMMA denture base resin enjoys good self-cleaning and antimicrobial properties.

The effect of finish line curvature on marginal fit of all-ceramic CAD/CAM crowns and metal-ceramic crowns.

OBJECTIVES: To investigate the effect of abutment finish line curvature on the fit of all-ceramic CAD/CAM crowns and metal-ceramic crowns. METHOD AND MATERIALS: Three types of finish line curvature abutments (1-, 3-, and 5-mm curvature) were prepared on typodont maxillary central incisors. For each type of abutment, 5 all-ceramic crowns (Cercon system, DeguDent) and 5 metal-ceramic crowns were fabricated. The marginal gaps of copings and veneered crowns were measured on a profile projector. The data were calculated and analyzed with 2-way ANOVA and Tukey HSD test (alpha = .05). RESULTS: The mean labial, lingual, mesial, and distal marginal gaps (SD) of all-ceramic crowns were similar: respectively, 54 (10), 51 (11), 47 (13), and 49 (9) microm for 1-mm curvature; 49 (12), 53 (11), 54 (10), and 55 (12) microm for 3-mm curvature; and 57 (12), 54 (11), 53 (10), and 52 (9) microm for 5-mm curvature. The mean labial, lingual, mesial, and distal marginal gaps (SD) of metal-ceramic crowns were 36 (7), 41 (9), 26 (8), and 28 (10) microm, respectively, for 1-mm curvature. The mean labial and lingual marginal gaps (SD) of metal-ceramic crowns for 3-mm curvature were 45 (8) and 48 (9) microm, respectively-significantly larger than mesial (P = .01 and .007) and distal (P = .03 and .02) gaps. The mean labial and lingual marginal gaps (SD) of metal-ceramic crowns for 5-mm curvature were 76 (10) and 74 (15) microm, respectively-significantly larger than mesial (P = .001 and .001) and distal (P = .001 and .001) gaps. CONCLUSIONS: The abutment finish line curvature had no significant effect on the marginal fit of all-ceramic crowns, but had a significant effect on the marginal fit of metal-ceramic crowns.

Fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy for different abutment finish line curvature.

OBJECTIVES: The purpose of this study was to evaluate the fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy and investigate the effect of abutment finish line curvature on the fit of crowns. METHODS: Three types of finish line curvature abutments were prepared (1, 3 and 5mm-curvature). For each type of abutment, five metal ceramic crowns of the facial veneered type were fabricated, which were cast in Au-1.6 wt% Ti alloy. Used as controls, another fifteen specimens were made from a commercially available gold alloy. The fit was measured in the as-cast and after porcelain application. RESULTS: In the as-cast specimens, the greater the finish line curvature was, the larger the gaps exhibited at the mesial and distal margins of copings, compared with labial and lingual margins. The distal margin of copings for 5mm-curvature abutments showed the largest gap (35 (7) microm). After porcelain application, the greater was the finish line curvature, the larger the labial marginal gap became (mean 44, 34, 25 microm, respectively, for 5, 3, 1mm-curvature). However, there was no significant difference on marginal gaps between specimens of Au-1.6 wt% Ti alloy and control gold alloy. SIGNIFICANCE: This study indicated that the metal ceramic crowns cast in Au-1.6 wt% Ti alloy had equivalent accuracy to those that cast in control gold alloy, and the abutment finish line curvature had a significant effect on the marginal fit of metal ceramic crowns.