Pre-restorative crown lengthening surgery: influence of restorative treatment timing on clinical outcomes-a pilot study

OBJECTIVES

Aim of this study was to assess the influence of restorative treatment timing on the periodontal, patient and operator-reported outcomes following crown lengthening surgery (CLS).

MATERIALS AND METHODS

Eighteen study participants requiring CLS were divided into two groups based on prosthetic rehabilitation timing (6 or 14 weeks postoperatively). Clinical parameters were recorded around treated and neighboring teeth before and after surgery, 6 and 14 weeks postoperatively, at prosthesis delivery, and three and six months after. Soft tissue and radiographic bone changes were evaluated. Patients assessed their perception of the procedure by means of a questionnaire. The final treatment outcome was rated by both patients and prosthodontists.

RESULTS

CLS resulted in statistically significant and stable apical displacement of the gingival margin, at both treated and adjacent sites. Plaque and bleeding scores remained low throughout. No statistically significant differences were observed between groups for any clinical or radiographic parameter examined. Healing was uneventful and treatment outcome was satisfying for both patients and prosthodontists, without statistically significant differences between groups.

CONCLUSIONS

The present study has been characterized as pilot, because it was not possible to reach the sample size indicated by the a priori power analysis. CLS is an effective pre-prosthetic procedure as long as it is performed under a certain surgical protocol which predicts for at least a 3 mm distance between bone crest and the flap margin at suturing. Within the limitations of this study, six weeks after surgery may be an adequate healing time for the onset of prosthetic restoration.

CLINICAL RELEVANCE

Crown lengthening surgery is commonly performed in daily clinical practice with the aim to restore teeth with short clinical crowns. Based on periodontal, patient and operator-reported criteria, 6 weeks after CLS may be adequate healing time before the onset of prosthetic restoration.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03947658, 13/05/2019, retrospectively registered.

Clinical evaluation of removable partial dentures with digitally fabricated metal framework after 4 years of clinical service

This case report describes the clinical outcomes of three patients who received removable partial dentures with a completely digitally designed and manufactured metal framework. The initial intraoral impressions were prepared, and the resulting standard tessellation language files were sent to a dental laboratory, where the alloy framework was designed using inLab software and printed using a 3D printer or milled directly from a Co-Cr disc. The quality of fit of the framework was evaluated intraorally to confirm the laboratory design. The acrylic teeth were set, and the definitive partial dentures were delivered after the acrylic resin bases were processed. The follow-up time was 4 years. No complications or failures related to the components of the partial dentures were observed.

Characteristics of intraoral scan bodies and their influence on impression accuracy: A systematic review

OBJECTIVE

The aim of this systematic review was to evaluate the influence of the characteristics of intraoral scan bodies (ISBs) on the accuracy of intraoral scanning.

MATERIALS AND METHODS

An electronic search was conducted through PubMed (MEDLINE), Scopus and Cochrane Library, up to March 2023. The literature search intended to retrieve all relevant clinical and in vitro studies about the effect that the various properties of ISBs may have on the accuracy (trueness and precision) of intraoral scanning. Only publications in English language were selected with animal studies, case reports, case series, technique presentation articles and expert opinions being excluded.

RESULTS

A total of 28 studies met the inclusion criteria and were included in this systematic review. They were published between 2019 and 2023 and were all in vitro studies. Among the parameters described, the scan body material, position, geometry, height, diameter, and fixation torque were evaluated. The most common materials used for ISBs were polyetheretherketone (PEEK) and titanium alloys. The diameter and position of ISBs seemed to affect the trueness of implant impressions. Subgingival implant position and decreased ISB height affected negatively the trueness of scanning. Geometrical characteristics of ISBs also affect the implant impression accuracy, especially the bevel location and the types of designing modifications.

CONCLUSIONS

The characteristics of the currently used ISBs vary widely and the available scientific evidence is not yet conclusive about the optimal design of ISB. The implant impression accuracy achieved by any of the studied parameters is encouraging. Clinical studies are however necessary for more concrete conclusions.

CLINICAL SIGNIFICANCE

ISBs play a vital role in the digital workflow and influence significantly the accuracy and fit of implant restorations. More clinical trials are needed in order to conclude to the optimal characteristics of ISBs which would further enhance the success of the restorations.

Evaluation of marginal/internal fit of fixed dental prostheses after digital, conventional, and combination impression techniques: A systematic review

Advances of digital technology are rapidly adopted in dental practice. This systematic review aimed to collect evidence on the accuracy of fit of different types of fixed dental prostheses (FDPs) fabricated through digital, conventional, or combination impression techniques. Data collection was based on the guidelines of the preferred reporting items for systematic reviews and meta-analyses (PRISMA). Two databases (PubMed, Scopus) were searched for articles in English published between 2010 and 2021 resulting in 480 articles. Of those, 35 studies fulfilled the inclusion criteria. These articles referred to three groups of materials/techniques including all-ceramic (zirconia; lithium disilicate) and porcelain-fused-to-metal (PFM) restorations. Results showed clinically acceptable marginal fit (< 120 μm) for all materials and impression techniques. Α fully digital workflow appears more promising for the construction of short-span zirconia FDPs. Nevertheless, most articles evaluated marginal/internal fit of single crowns or short-span FDPs in vitro, while clinical data are limited for long-span FDPs. The necessity for gingival retraction remains a major drawback of all impression techniques, increasing procedural time and patient discomfort. Besides, factors related to the fabrication process, including milling and 3D printing of working models significantly influence the outcome. Overall, there still some way to go before digital technology can be incorporated in complex treatment plans in prosthodontics.

Effectiveness of conservative therapeutic modalities for temporomandibular disorders-related pain: a systematic review

PURPOSE

The aim of this systematic review was to evaluate the effectiveness of conservative different therapeutic modalities for temporomandibular disorders (TMD) pain.

MATERIALS AND METHODS

An electronic systematic search was conducted in the MEDLINE (PubMed) database to identify the randomized clinical trials (RCTs) published between 2001 and 2021. The following, simple or multiple conjunctions, search keywords were selected: TMD pain, TMD management or conservative treatment or treatment strategies and TMD pain, therapeutic modalities or interventions and TMD. Studies included must have patients older than 18 years, with painful TMD, which diagnosis was performed by Research Diagnostic Criteria for TMD or Diagnostic Criteria for TMD. Outcome variables were pain relief and post treatment pain intensity reduction. Data were analysed with non-parametric tests and the level of significance was set at p<.05.

RESULTS

Out of 1599 articles obtained, 28 RCTs fulfilled all selection criteria and were included. The results of this study show that there was a significant decrease in short-term post-treatment TMD pain with the use of occlusal splint alone or in combination with other therapeutic modalities when compared with the control group. Statistically significant differences were also detected between laser and photobiomodulation group and the control, in short-term treatment TMD-related pain.

CONCLUSIONS

The primary findings of the present systematic review showed that the occlusal splint alone or combined with other therapeutic intervention presented positive effect on short-term TMD pain reduction. Secondary outcome suggests that laser and photobiomodulation therapy had, also, a significant role in short term pain relief.

Evaluation of Elastomeric Impression Materials' Hydrophilicity: An in vitro Study

Introduction

Hydrophilicity of dental impression materials is crucial for obtaining an accurate impression and necessary for the production of a well-fitting cast restoration. The most common technique for evaluation of hydrophilicity is a contact angle measurement. The aim of the present in vitro study was to compare the water contact angles of four groups of elastomeric impression materials, before and during setting.

Material and methods

Flattened specimens (n=10) of tested impression materials were prepared by the use of a Teflon mold with specific dimensions. A 5μl droplet of deionized water fell on the specimen, and photos were taken using a Nikon D3200 DSLR camera and a 105 mm macro lens (Nikorr, Nikon) in specific time points.

Results

The CAD/CAM material showed the highest contact angle measurements. The light body polyvinylsiloxane (PVS) material 1, polyether and vinylsiloxanether material showed comparable contact angle measurements especially at the initial time point. A statistically significant reduction of contact angles was reported during setup time for all PVS, PE and vinylsiloxanether materials, while the most expressed reduction of contact angle measurements, and thus the most significant increase of hydrophilicity were reported for light wash PVS material 2.

Conclusions

The CAD/CAM impression material showed the most hydrophobic behavior. PVS materials showed excellent hydrophilicity. Polyether and polyvinyloxanether impression materials presented lower contact angle measurements, and thus superior hydrophilicity, compared with other tested materials initially and during setting. All tested impression materials presented a stepwise development of hydrophilicity during the setting stage.

Fracture strength of endodontically treated premolars restored with different post systems and metal-ceramic or monolithic zirconia crowns

The purpose of this study was to investigate the fracture strength of endodontically treated human maxillary premolars (ETP) restored with posts and metal ceramic (MC) or monolithic zirconia (MZ) crowns. Sixty ETP were randomly divided into 3 groups. Teeth in control group (C) received a resin filling. ETP in the MC group were restored with prefabricated metal posts, composite cores and MC crowns while in the MZ group with glass-fiber posts, composite cores and MZ crowns. Half of the specimens were loaded at a 135° angle and half under axial loading until fracture. The fracture modes were divided in repairable and irreparable using optical microscopy. Mean fracture strength was significantly higher for MC than for MZ crowns and control group only under axial loading. The distribution of repairable and irreparable failures presented no significant differences. Crown placement significantly improved the fracture strength of ETP irrespectively of post and crown type.

Factors Affecting Decision-Making For Congenitally Missing Permanent Maxillary Lateral Incisors: A Retrospective Study

The aims of this study were as follows: 1) to retrospectively evaluate clinical situations of patients with congenitally missing permanent maxillary lateral incisors (CMPMLI) who were referred to three dental clinics specialised in prosthodontics over a 14-year period and 2) to investigate the factors affecting decision-making for patients with CMPMLI. The records of 46 patients with CMPMLI who were treated over a period of 14 years were examined to determine the mechanism of decision-making for treatment planning and factors affecting the decision. Descriptive statistics were used in the initial analysis of the entire data set. In addition, a correlation coefficient-the nonparametric Spearman's rho coefficient-was calculated to trace any possible relation between variables or rank orders. The significance level was set at 0.05 for the analysis. The results of this study revealed that decision-making for treatment of CMPMLI is directly dependent mainly on the following four factors: 1. Patient's age at treatment commencement 2. Individual characteristics of each clinical situation, which play a crucial but not an exclusive role in the treatment approach 3. Synthesis of the participating specialists in the treating team, which plays a crucial role in the decision-making 4. Use of pin-retained resin-bonded bridges (RBBs), either bilaterally attached or cantilevered, proved to be a reliable solution in terms of aesthetics, function and soft tissue response during the study period. Clinical implication: The rationale in the decision-making process for patients with congenitally missing permanent maxillary lateral incisors was investigated in this study to determine whether specific treatment options are superior to others.

Investigation of the relationship between sleep disorders and xerostomia

OBJECTIVES

To investigate the relationship between sleep disorders, morning hyposalivation, and subjective feeling of dry mouth.

MATERIALS AND METHODS

A cross-sectional, observational, clinical study was carried out in a homogenous population sample which consists of Greek male soldiers without any medical history. After the application of oral modified Schirmer test, the sample was divided into a study group (n = 63) (MST < 25 mm/3 min) and a control group (n = 110) (MST ≥ 25 mm/3 min). In order to assess daytime sleepiness, risk of obstructive sleep apnea (OSA), sleep quality, sleep bruxism (SB), and subjective feeling of dry mouth, all the participants filled in the following scales in Greek version: Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), Berlin Questionnaire (BQ), a SB questionnaire, and Xerostomia Inventory (XI) respectively. In every subgroup that came of ESS, PSQI, BQ, and SB questionnaire scoring, subjective feeling of dry mouth was evaluated, based on XI values.

RESULTS

Statistically significant difference (p < 0.001) through PSQI scores was found between the study and control group. In contrast, a statistically significant difference was not obtained for the scores of ESS (p = 0.293), BQ (p = 0.089), and SB questionnaire (p = 0.730). XI scores introduced statistically significant difference between the subgroups of PSQI (p < 0.001), BQ (p = 0.001), SB questionnaire (p = 0.004)  and statistically weak between the subgroups of ESS (p = 0.049).

CONCLUSIONS

This is the first research study so far suggesting that patients with morning hyposalivation exhibit poor sleep quality using an objective method. The present results have, also, shown that subjective feeling of dry mouth is related to excessive daytime sleepiness, poor sleep quality, high risk of obstructive sleep apnea, and sleep bruxism, but larger-scale studies are still needed.

CLINICAL RELEVANCE

These findings should keep dentists aware of a possible association between xerostomia and sleep disorders and support larger-scale studies.

Effect of a calcium chloride solution treatment on physical and mechanical properties of glass ionomer cements

This paper details a novel method to improve wear resistance of dental glass ionomer cement (GIC) restorations. The purpose of this in vitro study was to evaluate the effect of a calcium chloride (CaCl₂) solution treatment on surface hardness, surface roughness, compressive strength, water sorption and solubility of three conventional glass ionomer cements (GICs). Additionally, the changes of the Ca composition and morphology of the surface of the tested GICs were also investigated. The experimental groups of the study were: Group 1 (control) specimens after mixing were left in the mold to set without any treatment for 5 min; Group 2 specimens were left in the mold to set for 5 min and then each specimen was immersed in 10 ml of 42.7 wt% CaCl₂ solution for 60 s. Statistical analysis was performed using one-way ANOVA and Tukey post hoc tests (a = 0.05). Calcium chloride solution treatment increased surface hardness of the GICs compared to control groups (P < 0.05), while surface roughness and compressive strength did not change after the treatment (P > 0.05). Reduction in water sorption and solubility was detected but not in all CaCl₂ solution-treatment groups. No alterations were observed in surface morphology of the GICs, while surface calcium composition was increased after the treatment (P < 0.05). The use of a CaCl₂ solution immediately after initial setting of GICs may be advantageous for some properties of the materials and possibly leads to improved prognosis and wear resistance of their restorations.

Psychopathologic Profiles of TMD Patients with Different Pain Locations

PURPOSE

The aim of this study was to examine whether psychopathologic profile is related to the location of pain in temporomandibular disorder (TMD) patients with myofascial and/or temporomandibular joint pain.

MATERIALS AND METHODS

A total of 75 painful TMD patients (39 women and 36 men) participated in the study. Participants were divided into three groups (myogenous, arthrogenous, and mixed) using the Research Diagnostic Criteria for TMD (RDC/TMD) Axis I guidelines for assessment of TMD signs and symptoms. Three psychometric instruments were used to assess the psychopathologic profile of the TMD subgroups. Patients' state and trait anxiety were assessed using the State-Trait Anxiety Inventory (STAI-S, STAI-T), depression was measured with the Center for Epidemiological Studies Depression Scale (CES-D), and psychosocial functioning was evaluated using the Global Disability Scale (Glo.Di.S). The three TMD groups were compared with Kruskal-Wallis test followed by pairwise Mann-Whitney tests relative to the psychometric scores. Statistical analyses were performed with SPSS 15.0 software.

RESULTS

No significant differences were detected among the different TMD groups in the three psychometric scales; STAI-T, CES-D, Glo.Di.S (P > .05). When the psychometric scale of state anxiety (STAI-S) was considered, significant differences were revealed between the myogenous and the arthrogenous pain groups (P = .008) and also between the mixed and the arthrogenous groups (P < .001).

CONCLUSION

These findings suggest that the psychopathologic profile is not related to the location of pain in TMD patients. However, anxiety was found to be higher in TMD patients with myogenous pain alone or combined with arthrogenous pain compared to those with only arthrogenous pain.

Restoration of endodontically treated anterior teeth with cast metallic post or prefabricated fibre post placement: 2 case reports and critical literature review

With a wide variety of post systems and materials available for the restoration of lost tooth structure of endodontically treated teeth, the clinical decision of which to use constitutes a challenge to dental practitioners. Cast metal post and cores are widely used for restoring endodontically treated teeth with extensive loss of coronal tooth structure and to retain metal-ceramic crowns. When dental aesthetics is of primary concern, the selection of the underlying restorative material becomes an important factor to consider. The fibre-reinforced posts combined with all-ceramic crowns offer a highly aesthetic outcome in anterior region restorations, but long-term evaluation is necessary in order to assess their clinical performance and longevity. The purpose of this paper was to present and compare 2 restorative options with regard to materials (cast metallic post and core versus prefabricated fibre post and composite resin core) for the prosthetic rehabilitation of cases with inadequate aesthetic appearance or fractured maxillary anterior teeth. Furthermore, the article reviews the main indications, advantages, and disadvantages from the use of the 2 post types combined with the final restorations, in order to allow the dental practitioner make the selection of appropriate restorative materials.

Comparison of elastomeric impression materials' thixotropic behavior

The improved flow characteristics of new elastomeric impression materials are significant factors in the selection ofsuitableproductsfor clinical applications. The aim of this study was to assess the thixotropic behavior and compare the flow characteristics of seven different elastomeric impression materials using a shark fin test. One polyvinylsiloxane showed the highest shark fin height values, while the newly formed vinylsiloxanether material exhibited no significant differences when compared with two polyvinylsiloxanes. One of the five polyvinylosiloxanes presented significantly lower shark fin values than all other materials. It was concluded that flow characteristics for most of the tested materials are acceptable.

Survival of ceramic veneers made of different materials after a minimum follow-up period of five years: a systematic review and meta-analysis

PURPOSE

The purpose of this systematic review was to compare the survival and complication rates of ceramic veneers produced with different techniques and materials after a minimum follow-up time of 5 years.

MATERIALS AND METHODS

A literature search was conducted, using electronic databases, relevant references, citations and journal researching, for clinical studies reporting on the survival of ceramic veneers fabricated with different techniques and materials with a mean followup time of at least 5 years. The search period spanned from January 1980 up to October 2010. Event rates were calculated for the following complications associated with ceramic veneers: fracture, debonding, marginal discoloration, marginal integrity, and caries. Summary estimates, and 5-year event rates were reported. Comparison between subgroups of different materials, as well as statistical significance, was calculated using a mixed effects model.

RESULTS

Nine studies were selected for final analysis over an initial yield of 409 titles. No study directly compared the incidence of complications between ceramic veneers fabricated from different materials. Four of the included studies reported on the survival of ceramic veneers made out of feldspathic ceramics; four studies were on glass-ceramic veneers and one study included veneers fabricated from both materials. The mean observation time ranged between 5 and 10 years. Overall, the 5-year complication rates were low, with the exception of studies reporting on extended ceramic veneers. The most frequent complication reported was marginal discoloration (9% at 5 years), followed by marginal integrity (3.9-7.7% at 5 years). There was no statistically significant difference in the event rates between the subgroups of different materials (feldspathic vs. glass-ceramic).

CONCLUSION

The results of this systematic review showed that ceramic veneers fabricated from feldspathic or glass-ceramics have an adequate clinical survival for at least 5 years of clinical service, with very low complication rates.

Attitudes of dentists regarding the restoration of root canal treated teeth: a survey in Greece

OBJECTIVES

To investigate attitudes of Greek dentists regarding the restoration of root canal treated (RCT) teeth and to compare them to recommended guidelines. Additionally, to examine relationships between degree of dentists' professional experience or region of practice location and attitudes of restoring RCT teeth.

METHOD

Data were collected from 302 dentists using a structured self-administered questionnaire. For each dentist a score was assigned reflecting the level of compliance with scientific recommendations for restoration of RCT teeth.

RESULTS

89.4% of the respondents reported that not every RCT tooth requires a post while the 46.4% stated that a post reinforces it. 76.2% of the participants believed that the ferrule design provides a reinforcement to RCT teeth. Dentists with 6-20 years of experience showed a higher level of compliance with the principles in the literature than their colleagues with less or more years of practising. No significant difference was detected between dentists practising in urban and rural areas.

CONCLUSIONS

The majority of Greek dentists had knowledge in accordance with recommended guidelines, except the aspect of the reinforcement effect by the post. In contrast to the region of practice location, the degree of professional experience influenced the restoration of root-treated teeth.

Ultrasonographic thickness and electromyographic activity of masseter muscle of human females

The aims of this study were to assess the thickness of the masseter muscle by means of ultrasonography and to investigate the relationship between masseter electromyographic activity and muscle thickness bilaterally, during maximum voluntary clenches. Participants in the study consisted of 52 young female adults (mean age 23.7 +/- 2.5 years) without craniomandibular disorders and with full natural dentitions. The thickness of the masseter muscle was measured with a real-time ultrasound equipment. Electromyographic activity was recorded with bipolar surface electrodes, during maximum voluntary clenches. The error of the methods was calculated by double recordings in 15 subjects in a 4-week interval. The measurement error for the right muscle was 0.16 mm in thickness and 16.44 microV in electromyographic activity. For the left masseter the corresponding values were 0.19 mm and 18.01 microV. The relationship of masseter muscle thickness to its electromyographic activity was estimated by Pearson's correlation coefficient. The mean masseter thickness under contracted conditions was 13.9 +/- 1.5 mm for the right side and 13.9 +/- 1.4 mm for the left side. The mean maximum electromyographic activity was 379.0 +/- 56.0 microV for the right muscle and 372.3 +/- 73.2 microV for the left. Muscle thickness was strongly correlated to electromyographic maximum activity in the right masseter (r = 0.721, P < or = 0.001) and moderately correlated in the left muscle (r = 0.407, P < or = 0.01). The difference between the two sides is possibly because of the larger method error in the left side. It is apparent that ultrasonography can be used as a useful tool to assess masseter muscle functional capacity during full effort in healthy individuals.

Evaluation of the Relationship between Subjects? Perception and Professional Assessment of Esthetic Treatment Needs

PURPOSE

The purposes of the present study were to (1) evaluate the esthetic dental treatment need by means of two special questionnaires, (2) determine the reliability and the construct validity of the measurement scales derived from these questionnaires, and (3) investigate the relationship between Greek subjects' perception and a professional examiner's assessment regarding the esthetic treatment need.

MATERIALS AND METHODS

Participants in this survey consisted of 132 subjects (48 males with mean age 39.0 +/- 14.5 years old, 84 females with mean age 41.7 +/- 14.5 years old) with natural teeth and fixed restorations. Subjects were asked to complete a special self-evaluation questionnaire consisting of 12 items. During the next stage, all participants were clinically examined by an experienced examiner and the data collected were used to fill out a second special professional assessment questionnaire consisting of 20 items. The forms structure used were in accordance with well-established indices used in orthodontics for assessing esthetic treatment need.

RESULTS

The reliability of the multiple correspondence analysis (MCA) analysis-derived scales was very satisfactory (Cronbach's a coefficient: a =0.82) for the total scale of the self-evaluation measurement. For the professional assessment scale, the reliability of the total scale was almost perfect (a=0.92). The MCA revealed one reliable factorial construct for the self-evaluation measurement scale and two reliable constructs for the professional measurement scale. Pearson's correlation coefficient indicated a very low agreement between self-evaluation and professional measurement scales.

CONCLUSION

The findings of this survey suggest that there was a relative disagreement between subjects' perception and professional assessment regarding the need for esthetic dental treatment. CLINICAL SIGNIFICANCE In the present survey, the agreement between subjects' perception and clinical assessment of esthetic dental treatment need was found to be very low, which highlighted the discrepancies between patients' and dentists' perceptions of esthetic needs.

Bite force, endurance and masseter muscle fatigue in healthy edentulous subjects and those with TMD

It is well known that bite force and EMG activity are considerably reduced in edentulous patients, but the susceptibility of their jaw-closing muscles to localized fatigue is less certain. This information is even less clear for edentulous subjects who have TMD. Eleven healthy edentulous subjects and 10 edentulous subjects with TMD participated in this study. Maximum bite force was measured first, with the transducer placed on the canine-first premolar region bilaterally, and then two rapid relaxations were made from a brief voluntary clench to 50% of maximum. A sustained voluntary clench of 50% of maximum was then maintained and endurance time was noted. EMG was recorded from both masseter muscles and the median frequency of the power spectrum of the EMG from 2 s at the beginning of the sustained clench and 2 s at the end was subsequently calculated. Two more rapid relaxations from brief clenches were performed immediately after the sustained clench. The mean maximum bite force in the healthy group was 115 N (SD +/-41) and in the TMD group was 75 N (SD +/-22), this difference being significant (P = 0.0013). The mean endurance time in the healthy group was 86 s (SD +/-51) and in the TMD group was 63 s (SD +/-20). The percentage change in the median frequency in the healthy group as a result of the sustained contraction was 6% (left) and 8.6% (right) and in the TMD group was 13.9% (left) and 12.8% (right). The percentage change in the mean relaxation half time for the healthy group was 28.5% and for the TMD group was 72%, a significant difference (P = 0.0046). It was apparent that the maximum bite force was low in edentulous subjects and was further reduced in edentulous TMD subjects; endurance time was reduced in TMD subjects; fatigue resistance of the masseter muscles was reduced in TMD subjects.

Acoustic myography, electromyography and bite force in the masseter muscle

Acoustic myography (AMG) offers some advantages over electromyography (EMG) in certain circumstances, but the use of AMG on the jaw-closing muscles has not been fully tested. The purpose of this study was to examine the relationship between AMG, EMG and force in the masseter muscles of nine healthy male subjects. The AMG was recorded using a piezoelectric crystal microphone and the EMG was recorded simultaneously with surface electrodes. Force was recorded between the anterior teeth with a strain-gauge transducer. Analysis showed that Pearson's correlation coefficient was 0.913 for force/AMG and 0.973 for force/EMG in all subjects, indicating a linear relationship between force, AMG and EMG at the four different force levels tested (25-75% of maximum). It is apparent that AMG may be used as an accurate monitor of masseter muscle force production, although some care is required in the technique.

The variability of bite force measurement between sessions, in different positions within the dental arch

The effect of measuring bite force with different patterns of transducer on different occasions was studied. Maximum voluntary bite force was measured in eight volunteers. Three transducer positions, each with a different pattern of transducer, were used; between the anterior teeth, between the second premolar and the first molar on one side and between the second premolars and first molars on both sides. Visual feedback of force was provided. Two sets of five maximum clenches were recorded with a rest period in between. This sequence was repeated for each transducer and the experiment was repeated on three different days. The highest forces were measured with the bilateral posterior transducer (mean 580 N, s.d. 235) and the lowest on the anterior transducer (mean 286 N, s.d. 164). The standard deviations of the bite force mean values were used as an indication of the variability and were subjected to a non-parametric anova (Kruskal-Wallis). The forces recorded with each transducer position were significantly different between the transducers (P < 0.01) and the maximum bite force showed least variability when measured between the posterior teeth on one side only. There was little difference in bite force between the three different sessions (P > or = 0.05) when measured in the same position within the dental arch, whichever of the three positions that may be.