Influence of Cement Type on its Quality of Removal from Zirconium Oxide Implant-Supported Restorations

PURPOSE: To assess excess cement removal after cementation of implant-supported cementretained restorations using different cements. MATERIALS AND METHODS: A dental model with soft tissue imitation, 20 individual zirconium oxide abutments, and 20 zirconium oxide crowns were fabricated. Half of the restorations were cemented using resin cement (RX) and the other half with resin-modified glass-ionomer cement (GC). After cement cleaning, each crown-abutment unit was removed from the model, photographed, and analyzed from 4 surfaces, resulting in a final sample size of 80 measurements. Radiographic examination and the computerized planimetric method in Adobe Photoshop were used to determine the amount of the cement left and to evaluate the ratio between the area of cement residue and the whole crown-abutment surface. The significance was set to .05. RESULTS: GC resulted in 7.4% more cement residue on all surfaces (P < .05) than RX. The P value on three of the surfaces (all except mesial) was < .05, meaning that the data were statistically significantly different between groups and surfaces. Absolute removal of the cement was impossible in all cases (100%), and in 95% of the cases, cement remnants could not be detected radiographically. CONCLUSION: More undetected cement remains when using resin-modified glass-ionomer cement. It was impossible to remove excess of both types of cements completely. Most of the cement remains on the distal surface. Radiographic examination could not be considered as a reliable method to identify excess cement.

Interrelationships between distinct circadian manifestations of possible bruxism, perceived stress, chronotype and social jetlag in a population of undergraduate students.

This study investigates the recently hypothesized association between distinct circadian manifestations of possible bruxism in subjects with different chronotype profiles, social jetlag and levels of perceived stress. A cross-sectional study was performed by surveying dental students' of Lithuanian University of Health Sciences. A survey instrument was designed and pilot tested for reliability and validity prior to full-scale administration. The instrument consisted of four sections: socio-demographic questions, bruxism-related items, the Perceived Stress Scale and the Munich ChronoType Questionnaire. The study included 228 students (82.5% females; mean age 22.67 ± 2.27). Awake grinding was significantly associated with later chronotype values (p = 0,039). Despite the lack of significance, binary regression models demonstrated that students with later chronotypes report higher rates of possible bruxism, especially as far as awake grinding (p = .170; OR = 1.89) and sleep grinding (p = .140; OR = 1.60) are concerned. There were no significant associations between perceived stress, social jetlag and bruxism. The scores of perceived stress did not correlate with chronotype values, although a high positive correlation was found between chronotype and social jetlag (r = 0.516, p = .000). It can be concluded that later chronotypes increase the odds for self-reported bruxism, and are significantly associated with higher rates of awake grinding and social jetlag. No interrelationships were found between perceived stress, possible bruxism and social jetlag.

Lithuanian dentists' knowledge, attitudes, and clinical practices regarding obstructive sleep apnea: A nationwide cross-sectional study.

Objective: To investigate the knowledge, attitudes toward, and aspects of clinical practice regarding obstructive sleep apnea (OSA) among Lithuanian dentists. Methods: A cross-sectional study was carried out during the period from December 2016 to March 2017. A survey instrument was designed and pilot tested prior to full-scale administration. Self-administered questionnaires, including a cover letter, were distributed to 550 dentists during continuing dental education programs. Results: A total of 353 participants (64.2%) completed and returned the questionnaire. Increased years of experience were significantly associated with lesser knowledge about OSA (p < 0.05). However, there were no significant differences between general practitioners and specialists (p = 0.243). Most respondents indicated strong positive attitudes regarding OSA. The majority did not have any clinical experience regarding the management of OSA patients. Discussion: Development of additional education and practical implementation strategies should be considered in order to overcome the examined barriers.

The relationship between pathological wear of teeth and temporomandibular joint dysfunction.

OBJECTIVE: Temporomandibular joint dysfunction (TMJD) is quite frequent pathology in population. In scientific literature pathological tooth wear (PTW) is listed among the predisposing factors of it. MATERIAL AND METHODS: During the survey 189 primary patients of dental department in polyclinic of Panevezys city were examined. According to the tooth wear degree 2 groups have been formed: control group (grade 0-1) withouth TMJ dysfunction; and experimental group (grade 2-4) with presumable TMJD. RESULTS: In experimental group tooth wear of anterior and posterior region increases with age respectively (p<0.05). It was also found that centric occlusion (CO) and relative rest heights difference increases with age in the control group (p<0.05) as well as the experimental group (p=0.001). In patients with diagnosed TMJD the difference between heights in CO and relative rest was bigger than in patients without TMJD (p=0.039). In the experimental group TMJD was diagnosed the most of patients grade-4 in 90%. The most common symptom is joint sounds was observed in 72.2%. CONCLUSIONS: 35-50 and over 50 age groups of patients had a higher first molars degree of wear than the younger ones. In patients with diagnosed TMJD the difference between heights in CO and relative rest was bigger than in patients without TMJD. TMJD symptoms and of posterior teeth pathological wear interface hypothesis confirmed. In the experimental group TMJD was diagnosed the most common in 90% of patients grade-4. The most common symptom is "Nutcracker" of experimental group patients 77.2%.

Evaluation of the relationship between the occlusion parameters and symptoms of the temporomandibular joint disorder.

BACKGROUND: The aetiology of temporomandibular joint disorders (TMD) is multifactorial, whereas occlusal disharmony is one of the predisposing factors. Researchers still discuss the relation between occlusion and TMD. OBJECTIVE: The study aims to investigate the relation between static occlusal parameters and TMD clinical symptoms using T-Scan II analysis system. MATERIAL AND METHODS: The sample consisted of 44 persons divided into the treatment group of 20 TMD patients and the control group of 24 subjects without TMD. The main task of T-Scan II computerized occlusal analysis system was to record every patient's occlusion and estimate static occlusal parameters: centre of occlusal force, asymmetry index of maximum occlusal force and occlusion time. These results were compared between groups, data related to patients' complaints and clinical symptoms. The analysis was carried out using Mann-Whitney U, Kruskal-Wallis and Chi-square tests. RESULTS: Averages of the centre of occlusal force in TMD subjects were 6.55 ± 0.99 mm, in the control group - 5.88 ± 0.69 mm; the asymmetry index of maximum occlusal force averages: 15.90 ± 2.71 and 12.93 ± 1.88; occlusion time: 0.281 ± 0.036 s and 0.236 ± 0.022 s, respectively. There were no statistically significant differences between two groups but they were found in the centre of occlusal force and the asymmetry index in the two groups (p < 0.05). CONCLUSIONS: There exists a relation between complaints of patients with TMD and static occlusion parameters. Values of the centre of the occlusal force distance and the asymmetry index of occlusal force in TMD patients with pain in the temporomandibular joint (TMJ) were significantly higher than in the control group.

The relationship between unilateral mandibular angle fracture and temporomandibular joint function.

PURPOSE. Aim of this study was to analyze relation of occlusal correction and alterations of temporomandibular joint function during treatment of unilateral mandibular fractures. MATERIALS AND METHODS. We compared 49 patients treated for unilateral mandibular fracture without occlusal correction with 21 patient treated for unilateral mandibular fracture along with early and consequent occlusal analysis and correction and with 49 control subjects. Patients' complaints, mandibular movements and occlusal parameters were evaluated during the period of healing. ZEBRIS ultrasound system (Jaw Motion Analyzer, Zebris Medical GmbH, Isny, Germany) was used for analysis of mandibular movements and T-Scan analyzer (Tekscan, Inc., Boston, MA, USA) was used for occlusal analysis. RESULTS. Findings of our study showed statistically significant (p<0.05) diminution of patients complaints, mandibular movement alterations and occlusal disturbances in patients who received occlusal correction during MF treatment if compared to patients treated without occlusal correction, except noises from the joint in the injured side and mandibular lateral track to the injured side in the final stage of investigation. Despite applied treatment recovery of the TMJ function was not complete and the investigated parameters remained worse if compared to the control group. CONCLUSIONS. Results of this study confirmed positive influence of early and subsequent occlusal analysis and correction during stages of MF treatment on diminution of functional alterations of the temporomandibular joint function. Timely occlusal correction improves and hastens process of rehabilitation therefore it is indispensable part of MF treatment.

Dynamical changes of occlusion and articulation during treatment of mandibular angle fractures.

Outcomes of mandibular fractures were stated as frequent reason of temporomandibular joint dysfunctions. The objective of this study was to evaluate dynamical changes of occlusion and articulation during treatment of mandibular angle fractures. 12 subjects with mandibular angle fractures underwent analysis of occlusion and articulation in all stages of healing. Findings of investigations were presented in Posselt's and intercondylar axis diagrams, occlusiograms and relative force vs. time graphs. Comparison of results in first day, 1, 3 and 6 months after trauma showed that despite typical process of fragments healing and good fixation but with insufficiently balanced occlusion and posttraumatic discoordination of muscle activity first signs of TMJ articular discs dysfunction were found. Our results confirm the concept that early rehabilitation of mandibular function and occlusion are essential to prevent developing functional disorders of TMJ.

A three-dimensional model of the human masticatory system, including the mandible, the dentition and the temporomandibular joints.

The objective of this study was to create a three-dimensional mathematical model of a human masticatory system, including the mandible, the dentition and the temporomandibular joints. Object of research was one 20 year old dead man. The research was approved by Committee of bioethics (Kaunas University of Medicine). Required extent of computed tomography scanning and required high amount and high resolution of images increased X-ray radiation for the object and made this research impossible to perform on alive human. Spiral computed tomography scanning was performed to achieve two-dimensional images, necessary for creating three-dimensional model. The 3D modeling was done using the "Image pro plus" and "Imageware"software. A three-dimensional physiological (normal) model of a human masticatory system, simulating the mandible, the dentition and the temporomandibular joints was generated. This model system will be used subsequently in stress analysis comparison for the physiological and pathological systems after improvement of its physical properties. We suggest that computer simulation is a promising way to study musculoskeletal biomechanics of masticatory system.

Finite element analysis of stresses in the maxillary and mandibular dental arches and TMJ articular discs during clenching into maximum intercuspation, anterior and unilateral posterior occlusion.

The objective of this study was to investigate distribution of stresses in the human TMJ discs, generated during clenching into various occlusal positions. The work presents a biomechanical finite element model of interaction of mandibular and maxillary dental arches and the TMJ discs of a particular person, based on real geometrical data obtained from spiral computed tomography two-dimensional images. 3D contour coordinates - point clouds were collected from these images and solid model was created. The system under investigation consisted of eight basic parts: two rigid structures representing the mandibular and maxillary dental arches, two mandibular condyles, two mandibular fossae of temporal bone, and solid models of two articular discs. The model of maxillary dental arch was fixed in space. The model of the mandibular dental arch was able to move in space synchronically with the mandibular condyles under action of applied forces, which were considered as prescribed and known at insertion points of masticatory muscles. The motion of the mandible was constrained by interdental contact interactions and contact interaction with articular discs, which were situated in between mandibular condyles and mandibular fossae of temporal bone. The model was implemented by using LS-DYNA finite element software. The obtained results presented a 3D view of stresses exhibited in the articular discs, as well as the real contact points of dental interactions at given masticatory geometry of a particular subject and the values of interaction forces. The expected practical value of the developed model is the facilitation of biomechanical evaluations of the influence of tolerances of teeth shapes and occlusal areas together with the supporting areas on the final stress distribution in the dental arches and articular discs.