Effect of drain application on postoperative complaints after surgical removal of impacted wisdom teeth-a randomized observer-blinded split-mouth clinical trial.

OBJECTIVES: The aim of this randomized observer-blinded split-mouth-study is to objectively assess the influence of a rubber drain on postoperative swelling using 3D face scans as measurement method and additionally evaluate pain, trismus and complications after the osteotomy of lower third molars. MATERIAL AND METHODS: Seventy-two patients with symmetrically impacted lower wisdom teeth were recruited. Before the operation, patients rated pain using the visual analogue scale, the interincisal distance was measured, and 3D face scans were taken with an optical scanner. Each patient underwent two procedures which were at least 30 days apart. On one side, a rubber drain was inserted randomly before closure, the contralateral control side was closed without drainage. On the third and tenth postoperative day, face scans to quantify the swelling, pain evaluation and trismus measurements were performed. Due to loss of follow-up, 32 patients were excluded which resulted in 40 out of 72 patients remaining in the study. RESULTS: There was no statistical difference in using a drain on swelling and trismus on the third and tenth day (p > 0.05). Pain was slightly worse on the third day on the treatment side, but the difference was not significant (p > 0.05). We observed no differences in the number of wound infections. CONCLUSIONS: The insertion of a rubber drain does not have any influence on swelling, pain or trismus and has no impact on the number of wound infections. CLINICAL RELEVANCE: The use of a rubber drain cannot be recommended as no reduction of postoperative discomfort was detected.

The Effects of Frontal Trauma on 4 Interforaminal Dental Implants: A 3-Dimensional Finite Element Analysis Comparing Splinted and Unsplinted Implant Configurations.

PURPOSE: With increased implant-prosthodontic rehabilitation for mandibular edentulism together with the increased life expectancy and activity of the elderly population, a greater number of implant patients may be at risk of facial trauma. The aim of this 3-dimensional (3D) finite element analysis (FEA) was to evaluate the biomechanical effects of the edentulous mandible (EM) with and without implants exposed to frontal facial trauma including assessment of the fracture risk of different mandibular areas. MATERIALS AND METHODS: By use of a 3D FEA, our experimental study design comprised 3 different models (model A, EM; model B, EM with 4 unsplinted interforaminal implants; and model C, EM with 4 splinted interforaminal implants) exposed to application of symphyseal frontal trauma of 2 MPa. In 3 defined regions of interest (ROIs) (ROI 1, symphyseal area; ROI 2, mental foraminal area; and ROI 3, condylar neck), the effective stress was measured at predefined sites in the superficial cortical mandibular area. The stress values of all ROIs evaluated were compared within each model (intramodel) as well as between the 3 models (intermodel). RESULTS: For all models evaluated, a frontal traumatic load generated the highest stress levels in the condylar neck. However, for both models with implants (models B and C), the stress values were reduced significantly (P < .01) in the condylar neck region (ROI 3) but increased significantly (P < .001) in the mental foraminal area (ROI 2) compared with the EM model without implants. For the symphyseal area (ROI 1) evaluated, the unsplinted 4-implant model (model B) presented significantly (P < .001) higher stress values than the splinted implant model (model C) when frontal forces were applied. CONCLUSIONS: Regardless of splinting or lack of splinting of 4 interforaminal implants, force absorption or transmission may shift the predominant risk factor from the condylar neck to the corpus or foramen mandibulae. However, splinting of 4 interforaminal implants may be beneficial in reducing the risk of bone fracture by providing protection for anterior risk situations.

Edentulous mandible with four splinted interforaminal implants exposed to three different situations of trauma: A preliminary three-dimensional finite element analysis.

BACKGROUND/AIM: An increasing number of elderly patients with implant-prosthodontic rehabilitation of the edentulous mandible frequently show increased life activity, and consequently, a greater number of aged patients is at risk for maxillofacial trauma. The aim of this 3-dimensional (3D) finite element analysis (FEA) was to evaluate the biomechanical effects of the edentulous mandible (EM) with and without four splinted interforaminal implants exposed to three different trauma applications including assessment of different mandibular fracture risk areas. MATERIALS AND METHODS: In a 3D-FEA study design, EM with and without four splinted interforaminal implants were exposed to the application of 1000 N at the symphyseal, parasymphyseal, and mandibular angle region. On four pre-defined superficial cortical mandibular areas (symphysis region, mental foramen region, angle of mandible, and mandibular neck) representing regions of interest (ROI), the von Mises stresses were measured for the three trauma applications. For all ROIs, stress values were evaluated and compared for the different force application sites as well as between EM models with and without interforaminal implants. RESULTS: For EM with and without four splinted interformaninal implants, all traumatic loads generated the highest stress levels at the mandibular neck region. However, in the EM with four splinted interforaminal implants, an anterior symphyseal force application generated significantly (P < .01) increased stress values in the parasymphyseal (mental foramen) region than in EM without implants. For force applications at the parasymphaseal region (mental foramen) and at the angle of the mandible elevated, von Mises stress values were noted directly at the application sites without difference between edentulous mandibles with and without four interforaminal implants. CONCLUSION: In an edentulous mandible model with four splinted interforaminal implants, the condylar neck and the mental foramen represent the predilectional risk areas for mandibular fracture for both anterior symphyseal and lateral parasymphyseal force application.

Predicting primary stability of orthodontic mini-implants, according to position, screw-size, and bone quality, in the maxilla of aged patients: a cadaveric study.

This study aimed to evaluate the effect of implant size and bone condition on primary stability of orthodontic mini-implants with a view to predict the primary stability before insertion. Four-hundred and forty mini-implants of two different diameters (2.0 and 2.3 mm) and lengths (7 and 12 mm) were inserted at 11 different positions in human cadaver maxillae. Before placement of mini-implants, cone beam computed tomography (CBCT) scans were performed to measure bone density and cortical thickness and, after mini-implant placement, implant stability quotient (ISQ) values were determined by resonance frequency analysis and cofactors were analyzed to determine their influence on the primary stability. Additionally, an equation was developed to predict the expected stability based on implant size and bone quality. Bone density varied between 433 (SD 122) and 587 (SD 249) Hounsfield units (HU), and cortical thickness varied between 0.49 (SD 0.42) and 0.98 (SD 0.60) mm. The lowest ISQ value, of 15.50 (SD 7.29) (bone density: 531 (SD 219) HU; cortical thickness: 0.65 (SD 0.58) mm), was found for a mini-implant of 2.0 × 7 mm and the highest ISQ value, of 46.30 (SD 8.69) (bone density: 587 (SD 249) HU; cortical thickness: 0.98 (SD 0.60) mm), was found for a mini-implant of 2.3 × 11 mm. Statistically significant influences of the cofactors on primary stability were demonstrated. To visualize the predictive power of the model, the observed values versus the predicted values of primary stability were compared and the model fit was represented by residual plots. The expected primary stability can be estimated by a linear regression model comprising the radiologically determined bone density, cortical thickness, implant length and diameter, and placement position.

Orthodontic bracket debonding: risk of enamel fracture.

OBJECTIVES: Until now, it is not clear if various procedures of bracket debonding differ with regard to their risk of enamel fracture. Therefore, the objective of the present study was to compare these procedures biomechanically for assessing the risk of complications. MATERIALS AND METHODS: An anisotropic finite element method (FEM) model of the mandibular bone including periodontal ligament, enamel, dentin, and an orthodontic bracket was created. The morphology based on the CT data of an anatomical specimen. Typical loading conditions were defined for each method of bracket debonding (compression, shearing off, twisting off). Shortly before the adhesive's break, the induced stress in enamel, periodontal ligament, and in the alveolar bone was measured. The statistical analysis of the obtained values was performed in SPSS 19.0. RESULTS: Relatively high stresses occurred in the enamel using frontal torque (max. 44.18 MPa). With shearing off, the stresses were also high (max. 41.96 MPa), and additionally high loads occurred on the alveolar bone as well (max. 11.79 MPa). Moderate maximum values in enamel and alveolar bone appeared during the compression of the bracket wings (max. 37.12 MPa) and during debonding by lateral torque (max. 35.18 MPa). CONCLUSIONS: The present simulation results indicate that the risk of enamel fracture may depend on the individual debonding procedure. Further clinical trials are necessary to confirm that. CLINICAL RELEVANCE: For patients with prior periodontal disease or loosened teeth, a debonding procedure by compression of the bracket wings is recommended, since here the load for the periodontal structures of the tooth is lowest.

Finite element analysis of mono- and bicortical mini-implant stability.

OBJECTIVES: Loosening and loss rates of monocortical mini-implants are relatively high, therefore the following null hypothesis was tested: 'The local bone stress in mono and bicortically-anchored mini-implants is identical'. MATERIAL AND METHODS: Anisotropic Finite Element Method (FEM) models of the mandibular bone, including teeth, periodontal ligaments, orthodontic braces, and mini-implants of varying length, were created. The morphology was based on the Computed Tomography data of an anatomical preparation. All mini-implants with varying insertion depths (monocortical short, monocortical long, bicortical) were typically loaded, and the induced effective stress was calculated in the cervical area of the cortical bone. The obtained values were subsequently analysed descriptively and exploratively using the SPSS 19.0 software. RESULTS: The null hypothesis was rejected, since the stress values of each anchorage type differed significantly (Kruskal-Wallis Test, P < 0.001). Therefore, the lowest effective stress values were induced in bicortical anchorage (mean = 0.65MPa, SD = 0.06MPa) and the highest were induced in monocortical (short) anchorage of the mini-implants (mean = 1.79MPa, SD = 0.29MPa). The Spearman rank correlation was 0.821 (P < 0.001). CONCLUSIONS: The deeper the mini-implant was anchored, the lower were the effective stress values in the cervical region of the cortical bone. Bicortical implant anchorage is biomechanically more favourable than monocortical anchorage; therefore, bicortical anchorage should be especially considered in challenging clinical situations requiring heavy anchorage.

Periodontal ligament strain induced by different orthodontic bracket removal techniques: nonlinear finite-element comparison study.

OBJECTIVES: The goal of this work was to biomechanically analyze several different methods of bracket debonding and compare the strain they induce in the periodontal ligament (PDL). METHODS: The CT dataset of an anatomical specimen was divided into four segmental models of the mandible. Each model covered one tooth (32, 42, 44, and 47). One of these teeth (32) was characterized by marked loss of periodontal attachment. After suitable finite-element models were generated, material properties were defined as nonlinear for PDL and anisotropic for the alveolar bone. This was followed by simulating four bracket debonding techniques: frontal and lateral torquing, bracket-wing compression, and shear stress applied with specially designed pliers. RESULTS: The greatest strain was measured at the periodontally compromised tooth site 32 in response to frontal and lateral torquing. Both techniques also resulted in great strain around the other three teeth. Strain was markedly lower with the shear technique and virtually negligible with the compression technique. All simulated tooth sites confirmed the PDL-sparing effect of bracket-wing compression. CONCLUSION: The severity of PDL strain during orthodontic bracket removal depends on the debonding method used. The technique of compressing the bracket wings appears to trigger the smallest effect on PDL. Clinical studies should be undertaken to confirm these findings.

Indirect miniscrew anchorage: biomechanical loading of the dental anchorage during mandibular molar protraction-an FEM analysis.

AIMS: While there are many studies in the literature addressing direct miniscrew anchorage, the biomechanical effects of indirect miniscrew anchorage remain unknown. The aim of the present study was to biomechanically analyze the load on the anchor teeth during mandibular molar protraction using different types of anchorage. MATERIALS AND METHODS: Four finite element method (FEM) models of the right mandible were created using the morphological CT data of a 21-year-old male. All models were morphologically identical, but they differed in anchorage type (dental anchorage, direct miniscrew anchorage, indirect miniscrew anchorage with one anchor tooth, indirect miniscrew anchorage with two anchor teeth). To analyze the load on the dental anchorage during mandibular molar protraction, we measured the induced effective strain (µstrain) at specific control points on the alveolar bone. RESULTS: With indirect miniscrew anchorage, we observed that the effective strain at an average of 7.21 µstrain (one anchor tooth) or 6.57 µstrain (two anchor teeth) was almost as high as in pure dental anchorage where no miniscrew was used (mean 8.38 µstrain). In contrast, we noted significantly lower strain values in conjunction with direct miniscrew anchorage. We observed highly significant differences between direct and indirect simulated miniscrew anchorage (p=0.008). CONCLUSION: Our FEM results reveal relatively high loads on the dental anchorage when using indirect miniscrew anchorage. This may carry an increased risk of anchorage loss during mandibular molar protraction; however, further studies are necessary to confirm this.

Fracture risk of lithium-disilicate ceramic inlays: a finite element analysis.

OBJECTIVES: In the present study, lithium-disilicate ceramic inlays should be analyzed biomechanically according to their thickness and dimension, and it should be clarified as to whether there is a significant relationship between the inlay volume and the induced tensile stress level. METHODS: Using a new parametric CAD modeling procedure, 27 lithium-disilicate ceramic inlays with various parameters of "depth", "width", "angle" and restoration volume were generated. These inlays were integrated into the CAD model of a lower molar created from the CT data of an anatomical preparation. The resulting CAD models were, finally, three-dimensionally cross-linked to FEM models. After applying a compressive force of 200 N, Principal Tensile Stresses (PTSs) could be measured in the inlay. The values were subject to statistical analysis afterwards. RESULTS: The volume of the inlay restorations varied between 35.7 mm(3) and 82.5mm(3). The maximum PTS values (n=10) only showed a slight negative correlation with the inlay volume. The correlation coefficient according to Spearman was -0.082 (p ≤ 0.001). If the highest 1000 PTS values of each inlay were considered (n=1000), the correlation coefficient was further reduced to +0.068 (p ≤ 0.001). No significant correlation between the inlay volume and the induced PTS level could be detected. SIGNIFICANCE: Under the conditions and limitations of the present FEM study, the inlay volume did not significantly influence the tensile stress level of ceramic inlays. The results may support the thesis that volume-reduced all-ceramic inlays might not have an increased fracture risk. Further studies are needed to confirm this.

Ceramic inlays: is the inlay thickness an important factor influencing the fracture risk?

OBJECTIVES: It is still unclear whether the inlay thickness is an important factor influencing the fracture risk of ceramic inlays. As high tensile stresses increase the fracture risk of ceramic inlays, the objective of the present finite element method (FEM) study was to biomechanically analyze the correlation between inlay thickness (T) and the induced first principal stress. METHODS: Fourteen ceramic inlay models with varying thickness (0.7-2.0 mm) were generated. All inlays were combined with a CAD model of a first mandibular molar (tooth 46), including the PDL and a mandibular segment which was created by means of the CT data of an anatomical specimen. Two materials were defined for the ceramic inlays (e.max(®) or empress(®)) and an occlusal force of 100 N was applied. The first principal stress was measured within each inlay and the peak values were considered and statistically analyzed. RESULTS: The stress medians ranged from 20.7 to 22.1 MPa in e.max(®) and from 27.6 to 29.2 MPa in empress(®) inlays. A relevant correlation between the first principal stress and thickness (T) could not be detected, neither for e.max(®) (Spearman: r=0.028, p=0.001), nor for empress(®) (Spearman: r=0.010, p=0.221). In contrast, a very significant difference (p<0.001) between the two inlay materials (M) was verified. CONCLUSIONS: Under the conditions of the present FEM study, the inlay thickness does not seem to be an important factor influencing the fracture risk of ceramic inlays. However, further studies are necessary to confirm this.