Influence of Individual Bracket Base Design on the Shear Bond Strength of In-Office 3D Printed Brackets-An In Vitro Study.

(1) Background: Novel high-performance polymers for medical 3D printing enable in-office manufacturing of fully customized brackets. Previous studies have investigated clinically relevant parameters such as manufacturing precision, torque transmission, and fracture stability. The aim of this study is to evaluate different design options of the bracket base concerning the adhesive bond between the bracket and tooth, measured as the shear bond strength (SBS) and maximum force (Fmax) according to DIN 13990. (2) Methods: Three different designs for printed bracket bases were compared with a conventional metal bracket (C). The following configurations were chosen for the base design: Matching of the base to the anatomy of the tooth surface, size of the cross-sectional area corresponding to the control group (C), and a micro- (A) and macro- (B) retentive design of the base surface. In addition, a group with a micro-retentive base (D) matched to the tooth surface and an increased size was studied. The groups were analyzed for SBS, Fmax, and adhesive remnant index (ARI). The Kruskal-Wallis test with a post hoc test (Dunn-Bonferroni) and Mann-Whitney U test were used for statistical analysis (significance level: p < 0.05). (3) Results: The values for SBS and Fmax were highest in C (SBS: 12.0 ± 3.8 MPa; Fmax: 115.7 ± 36.6 N). For the printed brackets, there were significant differences between A and B (A: SBS 8.8 ± 2.3 MPa, Fmax 84.7 ± 21.8 N; B: SBS 12.0 ± 2.1 MPa, Fmax 106.5 ± 20.7 N). Fmax was significantly different for A and D (D: Fmax 118.5 ± 22.8 N). The ARI score was highest for A and lowest for C. (4) Conclusions: This study shows that conventional brackets form a more stable bond with the tooth than the 3D-printed brackets. However, for successful clinical use, the shear bond strength of the printed brackets can be increased with a macro-retentive design and/or enlargement of the base.

Sliding behaviour and surface quality after static air polishing of conventional and modern bracket materials : In vitro analysis.

OBJECTIVES: As part of orthodontic treatment, air polishing is routinely used for professional tooth cleaning. Thus, we investigated the effects of static powder polishing on sliding behaviour and surface quality of three different bracket materials (polymer, ceramic, metal), including a 3D-printed bracket. METHODS: Two bracket types of each material group were polished with an air-polishing device using sodium bicarbonate. Exposure times were set at 10, 20, and 60 s; the application distance was 5 mm. The force loss due to sliding resistance was tested with an orthodontic measurement and simulation system (OMSS) using a 0.016 inchâ€¯× 0.022 inch stainless steel archwire. Untreated brackets served as control. Polishing effects and slot precision were evaluated using an optical digital and scanning electron microscope. RESULTS: Sliding behaviour and slot precision differed significantly between and within the groups. Prior to polishing, polymer brackets showed the least force loss, ceramic brackets the highest. With progressive polishing time, the resistance increased significantly with titanium brackets (26 to 37%) and decreased significantly with steel brackets (36 to 25%). Polymer brackets showed the smallest changes in force loss with respect to polishing duration. Slot precision showed the largest differences between material groups and was primarily manufacturer-dependent with hardly any changes due to the polishing time. CONCLUSION: Powder polishing can positively or negatively affect the sliding properties of the bracket-archwire complex but is more dependent on the bracket-archwire material combination (i.e., manufacture-dependent slot precision). For titanium brackets, resistance only increased after 60 s of polishing. For ceramic brackets, effective reduction was observed after 10 s of polishing. Polymer brackets, including the 3D-printed brackets, showed better sliding properties than ceramic or metal brackets even after polishing for 60 s. Removal of plaque and dental calculus should lead to a noticeable improvement of the sliding properties and outweighs structural defects that may develop.

Comparative in vitro analysis of the sliding resistance of a modern 3D-printed polymer bracket in combination with different archwire types.

OBJECTIVES: To analyse the sliding resistance of a modern 3D-printed polymer bracket combined with different archwire types and to compare the results with conventionally used polymeric, ceramic and metal brackets. It was of further interest which bracket-archwire combination could be best qualified for clinical use. MATERIALS AND METHODS: The sliding behaviour was tested using an orthodontic measurement and simulation system (OMSS) for the use of two bracket types of the polymer, ceramic and metal group in combination with a 0.016 inch × 0.022 inch and 0.017 inch × 0.025 inch archwire of nickel-titanium (NiTi), titanium-molybdenum alloy (TMA) and stainless steel. Six bracket types were combined with six different archwire types and compared to each other. RESULTS: The sliding resistance showed significant differences between various the bracket-archwire complexes. The combination of 3D-printed polymer brackets with both steel archwire cross-sections showed the least values of sliding resistance (average 23-29%), while the combination of ceramic brackets with TMA archwires presented the highest (average 47%). CONCLUSIONS: The present study could show that modern 3D-printed bracket materials can have similar or even better mechanical properties than conventional ones regarding sliding resistance. Although the combination of bracket and archwire material is decisive for low sliding resistance values, the selection of the bracket material seems to have a greater influence than the selection of the archwire material or its cross section. CLINICAL RELEVANCE: It might be possible in future to combine aesthetic and biomechanical requirements for aesthetic brackets by using 3D-printing technology.

Influence of attachment bonding protocol on precision of the attachment in aligner treatments.

AIM: Precise bonding of attachments in aligner treatment is crucial to achieve the intended tooth movement. Thus, we evaluated five different bonding protocols for attachments used in aligner treatments with the goal of identifying the most precise protocol. METHODS: One ellipsoid and one rectangular attachment were exemplarily chosen and examined. All attachments were bonded using the same template aligner, which was produced by thermoforming. The bonding process was repeated 30 times with each protocol for statistical analysis. The protocols differed in the type of composite used (high viscous, low viscous), the additional application of a perforation in the attachment reservoir, and the use of a two-phase procedure with high viscous composite. All bonded attachments were laser scanned and compared to the attachments of a master model using a surface/surface matching algorithm to determine the precision, i.e., highest aberrations (maximum vertical distance) between the attachment of the master and results obtained from the various bonding protocols. Furthermore, the excessive amounts of composite bonded around the attachments were measured and compared. RESULTS: The two-phase procedure had a median aberration of 0.13 mm and a median amount of excessive composite of 7.40 mm2 (ellipsoid attachment). With the low viscous composite without a perforation in the template reservoir, similar results were achieved (median 0.13 mm) regarding the maximum vertical distance, but had an excess area of 33.50 mm2. CONCLUSION: In this in vitro study, the bonding protocol influenced the precision of bonded attachments. The bonding protocol with high viscous composite without a perforation in the attachment reservoir was the most inaccurate. The use of a low viscous composite or attachments made by a two-phase procedure with high viscous composite revealed more precise results.

Dimensional changes of the alveolar ridge contour of the premolar extraction site in adolescents.

PURPOSE: Premolar extraction in orthodontic therapy is common in adolescent patients. Knowledge of the tissue reaction in an extraction site is mainly based on studies with animal and adults. Thus, we aim to describe the time-dependent dimensional changes of the alveolar ridge contour of the premolar extraction site in adolescents. METHODS: Clinical data were obtained from a randomized controlled clinical trial (Universal Trial Number U1111-1132-6655), comparing treatment modalities with orthodontic space closure was initiated after 2-4 weeks (group A) and ≥ 12 weeks after tooth extraction (group B). Dental casts taken before the tooth extraction (T1) and before initiation of the space closure (T2) were digitalized with a 3D scanner and superimposed to analyze the dimensional changes of the alveolar ridge in early and later stage of wound healing. Linear mixed models were used for statistical analysis. RESULTS: Plaster models of 25 patients (mean age 15.2 years, 11 male and 14 female) with 66 extraction sites were enrolled. The average atrophic changes from tooth extraction to the early stage of wound healing (group A, n = 41) were in total 27.5% ± 11.8; labially 31.3% ± 15.1 and orally 23.6% ± 13.4. In group B (n = 25) the average atrophic changes were in total 38.6% ± 12.1; labially 46.2% ± 16.7; orally 31.3% ± 18.9. The atrophic changes between the groups in total (p = 0.031) and at the labial side (p = 0.012) were significant. The jaw affiliation was a significant parameter for all examined areas in regard to all cases (labial p = 0.019; oral p = 0.020; total p = 0.001). Atrophic changes between genders were not statistically different. CONCLUSIONS: Alveolar atrophy increased over time after extraction primarily in the lower jaw at the labial side. The main atrophy occurred in the first healing phase of the extraction socket. Thus, timely coordination is important to preserve sufficient bone levels. The atrophic changes of the alveolar ridge in adolescents parallel those reported for adults.

Incidence and severity of gingival invaginations associated with early versus late initiation of orthodontic space closure after tooth extraction : A multicenter pilot and randomized controlled trial.

OBJECTIVE: Gingival invaginations are a common side effect of orthodontic extraction-space closure. The timing of initiating the closure of an extraction space varies greatly in clinical practice. In this multicenter pilot and randomized controlled trial, we prospectively investigated whether initiating space closure in the early stage of wound healing would benefit the incidence and severity of invaginations developing in the extraction sites. METHODS: A total of 368 patients were screened for indications to extract at least one mandibular premolar. Those recruited were randomly assigned to one of two treatment arms: initiation of space closure either 2-4 weeks (arm A) or ≥12 weeks (arm B) after tooth extraction. Clinical data regarding treatment process and periodontal tissue response were recorded during and after space closure and analyzed by a specialized biometrics unit. The study was performed under continuous surveillance by an independent study control center. RESULTS: A total of 74 extraction sites were analyzed. Regarding the incidence of gingival invaginations, there were no significant intergroup differences [p = 0.13; group A comprising 37/44 (84.1%) and group B 29/30 (96.7%) invaginated sites]. The same was true based on either maxillary (p = 0.52) or mandibular (p = 0.21) sites only, and the severity of the invaginations did not differ between the treatment arms. CONCLUSIONS: As to the incidence and severity of gingival invaginations, we did not notice any statistically significant differences between the two timeframes. Our data do, however, provide a basis to identify additional confounders and to improve the accuracy of case-load estimations for future trials.

Influence of time after extraction on the development of gingival invagination: study protocol for a multicenter pilot randomized controlled clinical trial.

BACKGROUND: Gingival invaginations are a common side effect of orthodontic therapy involving tooth extraction and subsequent space closure. Consequences of gingival invaginations are a jeopardized stability of the space closure and hampered oral hygiene. In a retrospective study, the factor time until initiation of orthodontic space closure after tooth extraction has been identified as a potential risk factor for the development of gingival invaginations. The aim of this pilot study is to proof this hypothesis and to enable a caseload calculation for further clinical trials. The referring question is: is it possible to reduce the number of developing gingival invaginations by initiation of orthodontic space closure after tooth extraction at an early point of time? DESIGN: The intended pilot study is designed as a multicenter randomized controlled clinical trial, comparing the impact of two different time intervals from tooth extraction to initiation of orthodontic space closure on the development of gingival invaginations.Forty participants, men and women in the age range of 11 to 30 years with orthodontically related indication for tooth extraction in the lower jaw, will be randomized 1:1 in one of two treatment groups. In group A the orthodontic tooth movement into the extraction area will be initiated in a time interval 2 to 4 weeks after tooth extraction. In group B the tooth movement will be initiated in a time interval >12 weeks after extraction. A possible effect of these treatment modalities on the development of gingival invaginations will be documented at the moment of space closure or 10 months +/- 14 days after initiation of space closure respectively, by clinical documentation of the primary (reduced number of gingival invagination) and the secondary endpoint (reduction of the severity of gingival invaginations). TRIAL REGISTRATION: Universal Trial Number U1111-1132-6655; German Clinical Trials Register DRKS00004248.