Electromyographic activity of the masseter muscle after radiofrequency therapy in an animal model

Purpose

The purpose of this study was to examine changes in the electromyographic (EMG) activity of the masseter muscle after radiofrequency therapy (RF).

Methods

Twelve rabbits were used in this study: four in each group according to the number of RF applications. Preoperative EMG in the masseter muscle was used as the control. EMG was recorded at 1, 2, 3, and 4 weeks after RF in each rabbit. The recorded data were analyzed in terms of voltage and frequency, and changes in recorded variables were compared among the groups. The relative activity in peak voltage, root mean square of the action potential, area of voltage, and area of frequency were investigated.

Results

When compared to preoperative values, the variables at 3 or 4 weeks after RF application were significantly different in the single and quadruple therapy groups (P?<?0.05). There was no significant difference in the other groups (P?>?0.05). When the samples were regrouped as two groups like small number of application group (one or two point) and large number of application group (three or four points), the area of voltage and the area of frequency were significantly different between the groups at 4 weeks (P?<?0.05).

Conclusions

Masseter muscle activity after RF was significantly decreased compared to its preoperative state. The decreased activity was related to the number of applications and time elapsed after RF.     

Comparison of stability between cylindrical and conical type mini-implants. Mechanical and histological properties

OBJECTIVE: To investigate the mechanical and histologic properties of conical compared with cylindrical shaped mini-implants in terms of the success rate. MATERIALS AND METHODS: The samples consisted of cylindrical and conical groups, and commonly had 1.6 mm diameter and 6.0 mm length (Jeil Medical Corporation, Seoul, Korea) placed in beagle dogs. The mechanical study for analyzing maximum insertion torque (MIT), maximum removal torque (MRT), and torque ratio (TR; MRT/MIT) in Sawbones (Pacific Research Laboratories Inc, Vashon, Wash), and the animal study for resonance frequency analysis (RFA) and histomorphometric analysis (bone-to-implant contact and bone area) in two beagle dogs were done. All measurements were statistically evaluated using independent t-tests to determine any difference in MIT, MRT, TR, RFA, bone-to-implant contact (BIC), and bone area (BA) between the cylindrical group and conical group. A P value less than 0.05 was considered significant. RESULTS: The conical group showed significantly higher MIT and MRT than the cylindrical group in the mechanical study. However, there was no significant difference in RFA, BIC, and BA between the two groups in the animal and histomorphometric studies. CONCLUSIONS: Although the conical shaped mini-implant could induce tight contact to the adjacent bone tissue and might produce good primary stability, the conical shape may need modification of the thread structure and insertion technique to reduce the excessive insertion torque while maintaining the high resistance to removal.     

A survey of program directors: trends, challenges, and mentoring in prosthodontics. Part 1.

PURPOSE: This study consisted of two parts. Part 1, a survey of program directors, was conducted to examine current trends in advanced education in prosthodontics in the United States. Part 2 will report on the survey results distributed to the deans of US dental schools to evaluate their observations of trends in prosthodontics. MATERIALS AND METHODS: A national e-mail survey of 45 program directors was used to collect enrollment data for years 1 to 3 of prosthodontics training for US and international dental school graduates, the total number of applicants and applications considered, and the trends over time of applicants to prosthodontic programs for US dental school graduates and for international graduates. In addition, the program directors were asked to rank 13 key factors that may have contributed to any changes in the prosthodontic applicant pool. Comments were accepted on why more or less US- or internationally trained applicants have applied. Program directors were also asked for information on student financial incentives, whether their programs were state or federally funded, and whether their sponsoring institution was a dental school. RESULTS: Of the 45 program directors, 39 responded, for an 86.7% response rate. Respondents reported that 64% of their enrollments were graduates of US dental schools. Between 2000 and 2004 the applicant pool in prosthodontics increased by 23%, with 41% of program directors reporting an increase in US-trained applicants, 46.2% reporting no change, and only 12.8% reporting a decrease. Using the Spearman correlation, there was a moderate, positive statistically significant correlation that the following factors contributed to an increase in the number of US dental graduates applying to prosthodontic programs: (1) mentoring by prosthodontists at the predoctoral level, (2) interest in prosthodontics among US dental students, and (3) society's demand for a higher level of training and credentialing, (4) data depicting current and projected income for dental specialists, and (5) number of trained prosthodontists full- or part-time faculty at the predoctoral level. Only five programs offered no financial packages to offset tuition. The remaining 34 respondents reported some financial package. Among the respondents, there were 25 state-sponsored programs, 9 sponsored by private universities, and 5 sponsored by hospitals or federal agencies. CONCLUSION: An increased applicant pool and more US-trained applicants to prosthodontics programs create a more competitive applicant pool for our specialty. Program directors reported that factors such as mentoring, society's demand for a higher level of training and credentialing, data depicting current and projected income for prosthodontists, exposure to prosthodontic faculty at the predoctoral level, the dollar value of prosthodontic training, and advances in implant, aesthetic, and reconstructive dentistry have all had some impact on increasing the applicant pool to prosthodontic training in the United States.     

The association of osteoprotegerin gene polymorphisms with periodontitis

Background:  It has been demonstrated that genetic variation accounts for approximately half of the variance in periodontitis. The reported association of polymorphisms in the osteoprotegerin (OPG) gene with osteoporosis suggests that the OPG gene may also influence the genetic risk for periodontitis.
Subjects and methods:  We investigated the distribution of OPG gene polymorphisms in 49 patients with aggressive ( n  =   14) or chronic ( n  =   35) periodontitis and 49 control subjects without periodontitis, using polymerase chain reaction (PCR)–restriction fragment length polymorphism and PCR–single strand conformation polymorphism followed by direct sequencing.
Results:  A total of seven known polymorphisms and one new mutation, G373A, were identified. The T950 and G1181 alleles were more common in patients with periodontitis ( P  =   0.028 and P  =   0.047, respectively) than in control subjects. Especially, G1181 allele was associated with patients with aggressive periodontitis.
Conclusion:  The TG haplotype of T950C and G1181C polymorphisms in the OPG gene may be useful genetic markers for the prediction of periodontitis. Further studies in a larger population are required to determine whether these alleles directly contribute to periodontitis susceptibility.     

Polymerization shrinkage-strain kinetics of temporary crown and bridge materials.

OBJECTIVE: The purpose of this study was to measure the polymerization shrinkage kinetics of four commercially available polymer-based temporary crown and bridge materials, including the effect of ambient temperature. METHODS: Three dimethacrylate-based materials and one monomethacrylate-based material were investigated. The polymerization shrinkage-strains were measured by using the Bonded-disk method with initial specimen temperature at both 23 and 37 degrees C, with values particularly noted at 5, 10, and 120 min after mixing. Five recordings were taken for each material. The progress of the setting reaction and its temperature-dependence were evaluated by the kinetic curves, and net shrinkage and total shrinkage (inclusive of expansion magnitude) of each material were compared by independent sample t-test and one-way ANOVA. RESULTS: Most shrinkage occurred in the first 10 min after mixing although there was an early expansion especially with the monomethacylate in the first 5 min. At 120 min, the net shrinkage-strain at 23 and 37 degrees C of the materials used in this test ranged from 3.54 to 4.13%. The fastest setting dimethacrylate-based material and the monomethacrylate-based material showed higher shrinkage-strain than other materials. No significant differences of net shrinkage-strain were found between 23 and 37 degrees C, but higher shrinkage rates were measured at 37 degrees C than at 23 degrees C. SIGNIFICANCE: The Bonded-disk method is a suitable method for measuring temperature-dependence of shrinkage-strain of polymer-based temporary materials. The dimethacrylate-based materials are preferable to monomethacrylates for temporary restoration as judged by the magnitude of polymerization shrinkage-strain, the majority of which is apparent within 10 min from the start of mixing and may affect the clinical outcome.     

The effectiveness of auxiliary features on a tooth preparation with inadequate resistance form

STATEMENT OF PROBLEM: No study has evaluated the efficacy of auxiliary tooth preparation elements for crowns with originally reduced resistance form. PURPOSE: This study evaluated the effects of different auxiliary preparation features on the resistance form of crowns with reduced axial wall and total occlusal convergence. MATERIAL AND METHODS: An Ivorine tooth was prepared on a milling machine with 20-degree total occlusal convergence (TOC), 2.5 mm of occlusocervical dimension, and a shoulder finish line. This design lacked geometric resistance form. The crown preparation was subsequently modified to include mesiodistal grooves, mesiodistal boxes, buccolingual grooves, occlusal inclined planes, an occlusal isthmus, and reduced TOC in the axial wall from 20 to 8 degrees TOC in the cervical 1.5 mm of the axial wall. The grooves and boxes were placed into the tooth with the same 20-degree TOC as the initial axial walls. Ten standardized metal dies were used for each preparation design. Standardized complete metal crowns were fabricated for all specimens. The metal crowns were cemented on metal dies with resin-modified glass ionomer cement. A strain gauge was placed at the mid-lingual cervical area of each crown preparation margin. The resistance of each specimen was evaluated when force was applied at a 45-degree angulation to the long axis of the die in a lingual to buccal direction. The peak loads during crown dislodgment, as well as the tensile stress at the mid-lingual cervical area, were measured using a universal testing machine (Kgs) for each specimen. The control group consisted of 10 dies, with the original crown preparation having no geometric resistance form and no auxiliary preparation features. Strain gauges provided the force (Kgs) that resulted in electric currency disrupt at the crown/die interface, thus providing data regarding the force required for slight crown micromovement (2 microm). Data between control and experimental groups were compared using the Mann-Whitney U test (alpha=.05). RESULTS: Proximal grooves, proximal boxes, buccolingual grooves, occlusal inclined planes, and occlusal isthmuses were not effective at increasing a crown's resistance to dislodgement when the tooth preparation lacked resistance. The only crown modification that offered enhanced resistance form when compared with the control group was the reduced TOC in the cervical half of the axial wall. CONCLUSION: Within the limitations of this in vitro study the crown preparation modification that significantly enhanced the resistance form of a compromised tooth preparation was reducing the TOC at the cervical aspect of the axial wall. Placing auxiliary retentive features such as grooves and boxes into a compromised tooth preparation (2.5 mm occlusocervical dimension and 20-degree TOC) was not effective when these retentive features possessed the same 20-degree TOC as the prepared axial walls.     

Intermittent force in orthodontic tooth movement

A single orthodontic activation lasting one hour can initiate tooth movement. The purpose of this study is to examine tooth movement, osteoclasts, and root resorption in rats following several one-hour activations. Rats (n = 144) were randomly assigned to intermittent (multiple activations of 1 hr/day), continuous, and sham appliances. Twelve rats were killed at 3, 5, 7, and 14 days. Tooth movement, osteoclasts, osteoclast %, and root resorption % were quantified. Continuous force moved molars mesially at days 3 and 14 (p < 0.05), but intermittent and sham did not. Intermittent and continuous force increased osteoclast numbers at days 3, 5, and 7 (p < 0.05). Continuous force increased osteoclast surface on days 3 and 14 (p < 0.05). Continuous force increased root resorption at days 5, 7, and 14 (p < 0.05). These results demonstrate that orthodontic force for one hour in 24 stimulates osteoclasts at compression sites but does not stimulate tooth movement or root resorption.     

Concurrence of replicative senescence and elevated expression of p16(INK4A) with subculture-induced but not calcium-induced differentiation in normal human oral keratinocytes

Primary normal human oral keratinocytes (NHOKs) undergo differentiation in the presence of calcium concentrations higher than 0.15 mM in vitro, which is useful in investigating the mechanisms involved in the differentiation of epithelial cells. Serial subculture of NHOKs to the postmitotic stage also induces terminal differentiation. However, the detailed mechanisms of both differentiation processes remain substantially unknown. To investigate the molecular differences in these processes, NHOKs were induced to differentiate by exposure to 1.2 mM of calcium and by serial subculture to the postmitotic stage. To study whether the cells were induced to differentiate and to undergo replicative senescence, the amount of cellular involucrin and the expression of senescence-associated beta-galactosidase (SA-beta-gal) were measured respectively. The expression of replicative senescence-associated genes and the activity of telomerase from the differentiated cells were also determined. Both calcium treatment and serial subculture to the postmitotic stage notably elevated the cellular involucrin. The percentage of SA-beta-gal-positive cells was significantly elevated by the continued subculture, but such changes were not observed in keratinocytes exposed to calcium. The concentration of cellular p16(INK4A) protein was progressively increased by the continued subculture but was not changed by calcium treatment. On the other hand, the concentrations of cellular p53 were similar in both differentiation processes. However, telomerase activity was lost in NHOKs that had undergone differentiation by both calcium treatment and serial subculture. The results indicate that calcium-induced differentiation of NHOKs has similar characteristics to their serial subculture-induced differentiation, but that the differentiation processes are not identical, because calcium-induced differentiation does not concur with either replicative senescence or the gradually increased concentration of p16(INK4A).     

Eugenol inhibits K+ currents in trigeminal ganglion neurons

Eugenol, a natural capsaicin congener, is widely used in dentistry. Eugenol inhibits voltage-activated Na(+) and Ca(2+) channels in a transient receptor potential vanilloid 1 (TRPV1)-independent manner. We hypothesized that eugenol also inhibits voltage-gated K(+) currents, and investigated this in rat trigeminal ganglion neurons and in a heterologous system using whole-cell patch clamping. Eugenol inhibited voltage-gated K(+) currents, and the inhibitory effects of eugenol were observed in both capsaicin-sensitive and capsaicin-insensitive neurons. Pre-treatment with capsazepine, a well-known antagonist of TRPV1, failed to block the inhibitory effects of eugenol on K(+) currents, suggesting no involvement of TRPV1. Eugenol inhibited human Kv1.5 currents stably expressed in Ltk(-) cells, where TRPV1 is not endogenously expressed. We conclude that eugenol inhibits voltage-gated K(+) currents in a TRPV1-independent manner. The inhibition of voltage-gated K(+) currents is likely to contribute to the irritable action of eugenol. Abbreviations: human Kv1.5 channel, hKv1.5; transient receptor potential vanilloid 1, TRPV1.