Finite element analysis of a four-unit all-ceramic fixed partial denture.

All-ceramic restorations are known to be prone to brittle fracture. However, a previously performed in vitro study indicates that four-unit fixed partial dentures (FPDs) with a zirconia framework are sufficiently strong to withstand occlusal forces in the posterior region. The aim of this study was to determine the stress distribution in such a four-unit FPD made of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP), under an occlusal load. A three-dimensional finite element model was constructed and a stress analysis performed with a force of 1630 N applied at the centre of the middle connector area. The location of maximum tensile stress according to finite element analysis coincided with the fracture origin of all 10 specimens fractured within the previous in vitro study. The maximum tensile stress in the area of the middle connector amounted to 633 MPa. It increased with the load being applied from the oral towards the buccal side (648 MPa) and decreased with the load being applied from the buccal towards the oral side (570 MPa). These stresses are of the same order as the flexural strength of Y-TZP, determined under standardized test conditions to be 600-1000 MPa. The model presented is intended to be used for further investigations, including thermally induced stresses during veneering.

Supra- and subgingival biofilm formation on implant abutments with different surface characteristics.

PURPOSE: The aim of the present study was to establish a noninvasive method for quantitative analysis of supra- and subgingival biofilm formation on dental implants considering different surface modifications. MATERIALS AND METHODS: Patients of both sexes were included. They had to be in generally good health, partially edentulous, and the recipient of at least 1 screw-type implant with an abutment possessing supra- and subgingival areas. Healing abutments were inserted for 14 days. The abutment surfaces were divided into quadrants that were sandblasted, ground, acid-etched, and untreated (with the latter surface as a control). Biofilm formation on the healing abutments was analyzed using scanning electron microscopy, including secondary-electron and Rutherford backscattering-detection methods. Calculation of biofilm-covered surfaces was performed depending on grey-values, considering supra- and subgingival areas. After calculating absolute and relative biofilm-covered surfaces depending on localization, the influence of surface modification on biofilm formation was analyzed. RESULTS: Fifteen healing abutments were inserted in 11 patients. In all surface properties plaque adhesion in supragingival areas was significantly higher (17.3% +/- 23.1%) than in subgingival areas (0.8% +/- 1.0%). Biofilm accumulation in supragingival areas was significantly increasing by higher surface roughness, whereas this influence was not detected in subgingival areas. CONCLUSION: The described method is valuable for investigation of supra- and subgingival biofilm adhesion on surface-modified implant abutments. There was a significant influence of surface localization (supra- and subgingival) as well as surface modification on biofilm formation.

Influence of cyclic fatigue in water on the load-bearing capacity of dental bridges made of zirconia.

The humid atmosphere and permanent occurrence of chewing forces in the oral environment lead to degradation of ceramics used for prosthetic restorations. The aim of this in vitro study was to evaluate the influence of artificial aging on the load-bearing capacity of four-unit bridges, with both undamaged and predamaged zirconia frameworks. Additionally, different parameters for chewing simulation have been investigated and a finite element analysis was made to predict the location of highest tensile stresses within the bridges. A total of 60 frameworks were milled from presintered zirconia and divided into six homogeneous groups. Prior to veneering, frameworks of two groups were "damaged" by a defined saw cut similar to an accidental flaw generated during shape cutting. After veneering, FPDs were subjected to thermal and mechanical cycling - with the exception of control groups. The load-bearing capacity of tested FPDs was significantly reduced by artificial aging. In comparison to unaged specimens, fracture resistance decreased by about 40%, whereas preliminary damage did not have a significant effect. Increasing number of cycles and increasing upper load limit failed to show any additional effect on fracture force. To predict the progression of degradation under the terms of in vitro simulation for even longer periods, further aging experiments are required.

Load-bearing capacity of all-ceramic posterior four-unit fixed partial dentures with different zirconia frameworks.

The aim of this in vitro study was to compare the load-bearing capacity of posterior four-unit fixed partial dentures (FPDs) produced with two different yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP) ceramics, one being a presintered material, the other a fully sintered, hot isostatically pressed material. Additionally, as a novel approach, the influence of preliminary mechanical damage upon the fracture force of an FPD has been investigated. A total of 20 frameworks each were milled from presintered zirconia and from fully sintered zirconia. Prior to veneering, 10 frameworks of each material were 'damaged' by a defined saw cut similar to an accidental flaw generated during shape cutting. Before fracture testing, all FPDs were subjected to thermal and mechanical cycling. Additionally, scanning electron microscopy was used to investigate fracture surfaces. Statistical analysis showed that FPDs milled from fully sintered zirconia had a significantly higher fracture resistance compared with specimens made from presintered material, whereas preliminary damage did not have a significant effect. After aging, FPDs made from both materials were capable of withstanding occlusal forces reported in the literature. Therefore, both types of Y-TZP may be suitable for posterior four-unit all-ceramic FPDs, although further prolonged aging experiments and prospective clinical trials are required to prove their fitness for clinical use.

Acupuncture in the treatment of painful dysfunction of the temporomandibular joint -- a review of the literature.

OBJECTIVE: The aim of the present study was to analyze the results of randomized clinical trials on the efficacy of acupuncture in the treatment of painful dysfunction of the temporomandibular joint. MATERIALS AND METHODS: A literature search of 3 electronic databases was performed, and only randomized studies comparing acupuncture-treated patients with either untreated or conservatively treated control groups were included. For this purpose, results were compared in narrative and tabular form. RESULTS: To date, only 8 publications representing 6 randomized clinical trials have looked into the efficacy of acupuncture in the treatment of craniomandibular dysfunction. With the exception of one, all studies were published in Sweden, between 1985 and 1992. A more recent US study was the only one to apply sham acupuncture to test the efficacy of acupuncture. All studies share methodological shortcomings, including a lack of detailed descriptions of the randomization procedures, point selection, possible dropouts and undesirable events as well as attempts to identify a possible placebo effect of the acupuncture. Only 1 study investigated long-term results. Although based on the improvement of subjective and objective criteria, all studies consider acupuncture as an effective treatment for painful dysfunction of the temporomandibular joint, the good results achieved must be interpreted with caution because of the methodological shortcomings identified. CONCLUSION: Acupuncture appears to be a suitable complementary treatment method in the management of craniomandibular dysfunction. However, its significance has to be further evaluated in future studies.

In vitro fracture resistance of four-unit fiber-reinforced composite fixed partial dentures.

OBJECTIVES: The aim of this in vitro study was to investigate the influence of glass fiber-reinforcement on the fracture resistance of four-unit composite fixed partial dentures (FPDs) in the posterior region. METHODS: A total of 70 FPDs were fabricated of the composites Sinfony, Vita Zeta and Targis. With each material, 10 FPDs were made without glass fiber-reinforcement and 10 were reinforced with the new glass fiber system EverStick. In addition, 10 FPDs were fabricated of the material combination Targis/Vectris. After thermocycling, all FPDs were loaded until failure in a universal testing machine. The FPDs were then cut and cross-sectional areas were examined by scanning electron microscopy (SEM). RESULTS: The load to fracture of the fiber-reinforced FPDs lay between 615 and 1191 N, which was significantly greater than the values found with unreinforced FPDs (between 178 and 307 N). The highest values were found with the combinations Targis/Vectris (1191 N) and Sinfony/EverStick (1137 N). SEM showed that the FPDs with EverStick reinforcement not only exhibited fracture lines in the fiber-composite interface, but also more often in the area of the fiber-reinforcement than was the case with the FPDs with Vectris reinforcement. The load to fracture was not significantly dependent on fiber quantity or course of fracture. SIGNIFICANCE: It may be concluded that the fracture resistance of four-unit composite FPDs can be significantly raised by glass fiber frameworks (p<0.05). The reinforcement effect of EverStick depended significantly on the composite used (p<0.05).

Condylar motion after open and closed treatment of mandibular condylar fractures.

PURPOSE: A comparative study was performed to evaluate the function of the temporomandibular system after open and closed treatment of condylar fractures. MATERIALS AND METHODS: A total of 37 temporomandibular joints were examined that had undergone either open treatment (n = 24) or closed treatment with maxillomandibular fixation (n = 13) for condylar fracture. The joints were investigated clinically and on the basis of radiographs. In addition, the movements of the condyles of the temporomandibular system were recorded in 3 dimensions with a computed electronic jaw tracking system (stereognathograph). RESULTS: The clinical investigation revealed no severe functional abnormality in either of the 2 groups. The mean of the recorded condyle paths was, however, consistently lower in the temporomandibular joints with closed treatment than in those with open treatment, although the difference was only significant for movements without tooth contact (Mann-Whitney U test, P < .05). CONCLUSIONS: In summary, open as well as closed treatment gave clinically acceptable functional results. However, condylar mobility was markedly greater after open treatment than after closed treatment.

The functional relationship between the craniomandibular system, cervical spine, and the sacroiliac joint: a preliminary investigation.

The hypothesis of a functional coupling between the muscles of the craniomandibular system and the muscles of other body areas is still controversial. The purpose of this pilot study was to examine whether there is a relationship between the craniomandibular system, the craniocervical system and the sacropelvic region. To test this hypothesis, the prevalence and localization of dysfunction of the cervical spine and the sacroiliac joint were examined in a prospective, experimental trial. Twenty healthy students underwent an artificial occlusal interference, which caused an occlusal interference. The upper cervical spine (CO-C3) and the sacroiliac joint were examined before, during and after this experimental test. The primary outcome with these experimental conditions was the occurrence of hypomobile functional abnormalities. In the presence of occlusal interference, functional abnormalities were detected in both regions examined and these changes were statistically significant. The clinical implications of these findings may be that a complementary examination of these areas in CMD patients could be useful.

Asymptomatic cervical spine dysfunction (CSD) in patients with internal derangement of the temporomandibular joint.

Patients with temporomandibular disorders (TMDs) frequently show symptoms related to the cervical spine. It is however unknown whether patients with TMD who have no symptoms in the neck region often have signs of cervical spine dysfunction (CSD) and whether there is a predominant localization of these asymptomatic CSDs. In a prospective and controlled examiner-blinded clinical trial, the prevalence and localization of asymptomatic CSD in patients with TMD was examined. Thirty patients with internal derangement of the temporomandibular joint but without any neck problems were compared with 30 age and gender matched healthy controls. Significantly more asymptomatic dysfunctions of the vertebral joints and increased muscle tenderness were found in the patient group. The difference between patents and nonpatients for vertebral joint dysfunction and muscle tenderness was greatest in the upper cervical spine. These findings support the thesis that a complementary examination of this area should be performed, even when TMD patents do not report any neck problems.

Early begin of splint therapy improves treatment outcome in patients with temporomandibular joint disk displacement without reduction.

The objective of this study was to determine the effect of treatment beginning at the long-term outcome after splint therapy, in patients with anterior disk displacements without reduction. Therefore, 19 patients with acute complaints (group I), 19 with subacute complaints (group II), and 17 with chronic complaints (group III) were treated with occlusal splints. The patients were evaluated regarding treatment outcome with extensive clinical examination and postal questionnaires. The percentages of pain-free patients after therapy were 84% in group I, 63% in group II, and 64% in group III. There was a statistically significantly greater increase of maximum jaw opening after therapy in group I than in the control groups (P<0.05). The improvements in mouth opening came to 19.1 mm in group I, 10.7 mm in group II, and 8.4 mm in group III. The present study indicates that an early start of treatment seems to have a positive influence on treatment outcome of patients with anterior disk displacement without reduction.

Medical and physical therapy of temporomandibular joint disk displacement without reduction.

The objective of this study was to determine the influence of medical and physical therapy on long-term treatment outcome in 72 patients with anterior disk displacement without reduction. Patients were treated solely with occlusal splints (group I), with splints and supplementary medical therapy (group II), with splints and physical therapy (group III) or with splints, medical, and physical therapy (group IV). After therapy, the maintenance of improvement was objectively and subjectively assessed with an extensive clinical examination and a postal questionnaire. The percentage of pain free patients after therapy was 76% in group I, 88% in group II, 43% in group III, and 65% in group IV. There was a statistically significant higher increase of maximum jaw opening after therapy in group II than in the control groups (p<0.05). The improvement in mouth opening came to 9.7 mm in group I, 14.5 mm in group II, 7.3 mm in group III, and 11.2 mm in group IV. Medical therapy seems to have a positive influence on the treatment outcome of patients with anterior disk displacement without reduction.