Effect of printing orientation on mechanical properties of 3D-printed orthodontic aligners

PURPOSE

The purpose of this study was to assess differences in the fundamental mechanical properties of resin-made three-dimensional (3D) printed orthodontic aligners according to the printing orientation.

METHODS

Twenty resin 3D-printed dumbbell-shaped specimens and 20 orthodontic aligners were fabricated and postcured in nitrogen. Half of the specimens and aligners were built in horizontal (H), the other half in vertical (V) directions. The dumbbell-shaped specimens were loaded in a tensile testing machine, while parts of the aligners were embedded in acrylic resin, ground, polished, and then underwent instrumented indentation testing (IIT). Mechanical properties that were assessed included the yield strength (YS), breaking strength (BS), plastic strain (ε), Martens hardness (HM), indentation modulus (EIT), elastic index (ηIT), and indentation relaxation (RIT). Data were analyzed statistically with independent t‑tests or Mann-Whitney tests at α = 5%.

RESULTS

No significant differences were found between specimens or aligners printed either in a horizontal or a vertical direction (P > 0.05 in all instances). Overall, the 3D-printed aligners showed acceptable mechanical propertied in terms of YS (mean 19.2 MPa; standard deviation [SD] 1.7 MPa), BS (mean 19.6 MPa; SD 1.2 MPa), ε (mean 77%; SD 11%), HM (median 89.0 N/mm2; interquartile range [IQR] 84.5-90.0 NN/m2), EIT (median 2670.5 MPa; IQR 2645.0-2726.0 MPa), ηIT (median 27.5%; IQR 25.9-28.1%), and RIT (mean 65.1%; SD 3.5%).

CONCLUSION

Printing direction seemed to have no effect on the mechanical properties of 3D-printed resin aligners, which are promising for orthodontic use.

Color changes of nanocomposites used for clear aligner attachments: an in vitro study

PURPOSE

The purpose of this study was to compare the color changes of two different nanocomposites used for two different designs of clear aligner attachments.

METHODS

In all, 120 human premolars were embedded in 12 upper dental models with 10 premolars in each model. Models were scanned and attachments were digitally designed. Conventional attachments (CA) were prepared for the first six models and optimized multiplane attachments (OA) were prepared for the other six models with packable composite (PC) on the right quadrant and flowable composite (FC) on the left quadrant of each model. The models were subjected to 2000 thermal cycles at 5 °C/55 °C and then consecutively immersed in the five different staining solutions each for 48 h to simulate external discoloration. Color measurements were taken with a spectrophotometer. Color changes (∆E*ab) of the attachments before and after immersion were compared with the Commission Internationale de l'Éclairage L*a*b* (CIELAB) color space approach.

RESULTS

When ∆E*ab values were examined, no significant difference was observed between the groups according to the attachment type (P > 0.05). After the coloration process, the flowable composite group showed less coloration than the packable composite group for both attachment designs (P < 0.05). Color difference values after the staining procedure were significantly higher in the CA-PC and OA-PC groups compared to the CA-FC and OA-FC groups (P < 0.05).

CONCLUSION

Color change of the packable nanocomposite was more pronounced than that of the flowable nanocomposite for both attachment designs. Therefore, clear aligner attachments created using flowable nanocomposite can be recommended, especially in the anterior region where esthetics are important for the patient.

Is wear time of Hawley retainers measured with microsensors related to mandibular arch stability?

PURPOSE

The aim of this study was to show a possible correlation between the mean wear time of Hawley retainers and long-term mandibular arch stability as assessed via wear time analysis with microsensors.

METHODS

This longitudinal retrospective study comprised 47 subjects (mean age 16.30 ± 1.06 years) having been treated with a nonextraction protocol and presenting moderate crowding at pretreatment. For retention, all patients were instructed to use a mandibular Hawley retainer for 12 months, and wear time was documented every 3 months during a posttreatment period of 6 months using TheraMon software. These individuals were divided into two groups. Those who adhered to a wear time equal to or more than 12 h/day (group 1A; N = 17) and those who complied for less than 12 h/day (group 2A; N = 30) were compared with respect to changes of the mandibular arch during the first 6 months of retention. Furthermore, a subgroup of 28 patients who completed a 12-month follow-up period were again divided into two groups: the individuals in group 1B (N = 12) adhered to a wear time equal to or more than 8 h/day, while those in group 2B (N = 16) complied for less than 8 h/day. Little's Irregularity Index, intercanine and intermolar widths, arch length, overjet, and overbite were measured on mandibular models taken at pretreatment (T0) and posttreatment (T1), as well as 6 months (T2) and 12 months (T3) after debonding. Pearson correlation test, independent samples t‑test, and Mann-Whitney U test were used for statistical evaluation.

RESULTS

From T1 to T2, group 1A and group 2A showed a significant relapse in intermolar width with a difference in the median value of 0.38 mm (p = 0.019). At the complete 12-month follow-up, the increase in Little's irregularity score was significantly greater in group 2B (2.54 ± 1.29 mm) than in group 1B (1.32 ± 1.03 mm; p = 0.012). The established wear time measurements showed significant negative correlations with the Little's irregularity score and overjet changes between T1 and T3 (p < 0.05).

CONCLUSIONS

The results emphasized that the use of a retainer should not fall below a level of at least 8 h/day.

Investigation of the cleaning performance of commercial orthodontic cleaning tablets regarding biofilm removal on PMMA test specimens : An ex vivo study

PURPOSE

The purpose of this ex vivo study was to compare the cleaning performance of three commercially available orthodontic cleaners on polymethyl methacrylate (PMMA) test specimens covered with biofilm.

METHODS

Twenty subjects wore an individually manufactured vacuum-formed maxillary splint with four integrated PMMA test specimens for 7 days. The four test specimens were located on the buccal surfaces of the maxillary molars. After a 7-day wearing period, the PMMA test specimens colonized by biofilm were divided into two halves. One half was placed in 150 ml of tap water or in 150 ml of cleaning solution of the cleaners Retainer Brite® (Dentsply International Raintree Essix, Sarasota, FL, USA), Kukis® Xpress (Reckitt Benckiser, Heidelberg, Germany) or Dontodent (Propack, Heidelberg, Germany) while the other half remained uncleaned. The modified o‑phthaldialdehyde (OPA) method was used to determine the amount of protein on both halves of the test specimens. The difference was tested for significance as a measure of the cleaning effect using a paired sample t‑test.

RESULTS

The cleaning performance of the three orthodontic cleaners was higher than the cleaning performance of tap water (mean 25.9 ± 6.5%). While Retainer Brite® (mean 54.5 ± 7.1%) removed significantly more biofilm than Dontodent (mean 41.5 ± 9.2%, p < 0.001) and Kukis® Xpress (mean 39.9 ± 11.5%, p < 0.001), there was no significant difference in the cleaning performance between Kukis® Xpress and Dontodent (p = 1).

CONCLUSION

Seven-day-old biofilm is only removed partially by the investigated orthodontic cleaners, so that they are not suitable as the only measure for removing established biofilms.

Treatment of skeletal class III malocclusion using a combined clear aligner and surgery-early approach : Assessment based on the American Board of Orthodontics Objective Grading System

PURPOSE

To evaluate whether clear aligner therapy (CAT) combined with a surgery-early approach can achieve good therapeutic effects in patients with skeletal class III malocclusion.

METHODS

Thirty consecutive skeletal class III malocclusion cases treated with clear aligners combined with early surgery were selected. Treatment time, lateral cephalograms and American Board of Orthodontics Objective Grading System (ABO-OGS) scores of the treatment models were measured to evaluate the treatment efficiency, facial profile, and occlusion.

RESULTS

The results showed that early surgery was achieved after 7.71 months of presurgical orthodontics, on average. ANB decreased by 5.57° (P < 0.001), and STissue N Vert to Pog' decreased by 7.29 mm (P = 0.001), both reaching normal values. The posttreatment ABO-OGS scores were 26.600 on average, meeting its standards.

CONCLUSIONS

With the assistance of CAT, early surgery can be accomplished in patients with skeletal class III malocclusion, improving their facial profile and achieving functional occlusion.

Fixed and removable orthodontic retainers, effects on periodontal health compared: A systematic review

The aim of this systematic review is to analyze the properties of the different types of orthodontic retainers, identify their differences and define which type of device is most effective and less harmful to periodontal health.

Methods

A literature search was carried out by a reviewer by consulting PubMed, Lilacs, Embase, Medline full text, Scopus, Web of Science, Cochrane library, and Science Direct electronic databases for biomedical and health literature as well as the grey literature and setting up the search from December 2010 without any restriction about articles languages.

Results

The results showed that patients who wear retainers for a long period have significant differences in clinical parameters compared to patients without retainers. The type of retainer chosen also significantly influences the overall periodontal health of patients. Fixed retainers, both glass-fibre reinforced and steel wire retainers, proved to be the retainer type with the highest plaque and calculus accumulation values compared to removable retainers. In addition, among fixed retainers, glass-fibre reinforced retainers proved to be those that mostly promote the plaque and calculus accumulation in the application site.

Conclusion

Fixed retainers are the best devices to maintain the alignment of mandibular anterior teeth in the long term. Among these devices, stainless steel lingual retainers, plain or braided, should remain the first choice. Although they are also susceptible to periodontal complications, their effect on periodontal health can be considered statistically insignificant if compared to glass-fibre reinforced retainers which, showing worse periodontal complications, should not be used.

Frequency of Pathogenic Microorganisms in Removable Orthodontic Appliances and Oral Mucosa in Children

OBJECTIVE

The aim of this study was to evaluate the frequency of Staphylococcus aureus, Pseudomonas aeruginosa, and Candida species in removable orthodontic appliances (ROA) and the support oral mucosa in children.

STUDY DESIGN

The study participants comprised 55 patients aged 6-12 years requiring ROA. The samples of biofilm colonization from the support oral mucosa and the ROA were taken prior to the use of the ROA (T0) and 4 weeks (T1) after ROA placement. The biofilm samples were seeded on chromogenic culture plates and incubated for 24-48 h.

RESULTS

The microbial species evaluated were not present in either the support oral mucosa nor in the ROA at T0. After 4 weeks, P. aeruginosa was found in the support oral mucosa with a frequency of 60%, Candida spp. with 30.9% and S. aureus with 89.09%; in the ROA, P. aeruginosa with 67.7%, Candida spp. with 32.7%, while S. aureus with 90.9%. In the ROA were found C. glabrata in 15 cases, C. albicans in 14 cases, C. tropicalis in two cases, and C. krusei in one case. In the oral mucosa there were 10 cases of C. glabrata, 14 cases of C. albicans, one case of C. tropicalis, and 0 cases of C. krusei.

CONCLUSIONS

The frequency of S. aureus, P. aeruginosa, and Candida spp. increased after the orthodontic treatment in either the ROA and or in the support oral mucosa. There is a direct relation between the use of the ROA and the increase of periodontal-pathogenic microorganisms.

An observational study comparing fixed and removable orthodontic appliances

AIM

This study aimed to investigate salivary concentrations of Streptococcus mutans (S. mutans) and some Lactobacilli, and plaque index (PI) in patients wearing fixed versus removable orthodontic appliances.

METHODS

A sample of 90 orthodontic patients (56 males and 34 females) was included in the study: 30 subjects (aged 21.5±1.5 years) were treated with removable clear aligners (CA), while for other 30 cases (aged 23.3±1.6 years) a fixed multibrackets appliance (MB) were utilized, and 30 patients (aged 18.2 ±1.5 years) wearied a removable positioner (RP). Salivary concentrations of S. mutans and Lactobacilli and PI were evaluated prior to start of the orthodontic treatment, after 3 months and 6 months.

RESULTS

After 6 months, 40% of MB patients (12 subjects over 30) showed a concentration of S. mutans associated to high risk of developing tooth decay (CFU/ml>105 ), differently from participants wearing removable appliances (odds ratio = 5.05; 95% C.I. = 1.72-14.78; chi-square = 9.64; p = 0.0019). The same trens was observed for the concentration of Lactobacilli (odds ratio = 4.33; 95% C.I. = 1.53-12.3; chi-square = 8.229; p = 0.004). In addition, over the duration of the study, CA patients maintained PI at 0 level, while MB patients experienced a statistically significant increasing trend of PI over time, and their PI became clinically/statistically relevant after 6 months, respect to CA and RP patients.

CONCLUSIONS

Comparing all the data, while, after 6 months, only about 10% of CA patients and 13.3% of RP patients achieved a microbial colonization which may lead to high risk of caries development, about 40% of MB patients - and 20% after 3 months - showed a high level of vulnerability to developing caries, which require additional strategies for plaque control and microbial colonization to be employed.

Impact of upper airway abnormalities on the success and adherence to mandibular advancement device treatment in patients with Obstructive Sleep Apnea Syndrome

Introduction

The mandibular advancement device (MAD) is a option to treat patients with Obstructive Sleep Apnea Syndrome (OSAS).

Objective

To assess the influence of upper airway abnormalities on the success of and adherence to MAD in patients with OSAS.

Methods

Prospective study with 30 patients with mild to moderate OSAS and indications for MAD. The protocol included questionnaires addressing sleep and nasal complaints, polysomnography, and upper airway assessment. The analyzed parameters of patients who showed therapeutic success and failure and those who exhibited good and poor treatment adherence were compared.

Results

28 patients completed the protocol; 64.3% responded successfully to treatment with MAD, and 60.7% exhibited good adherence to treatment. Factors associated with greater success rates were younger age (p = 0.02), smaller cervical circumference (p = 0.05), and lower AHI at baseline (p = 0.05). There was a predominance of patients without nasal abnormalities among patients treated successfully compared to those with treatment failure (p = 0.04), which was not observed in relation to adherence. Neither pharyngeal nor facial skeletal abnormalities were significantly associated with either therapeutic success or adherence.

Conclusion

MAD treatment success was significantly lower among patients with nasal abnormalities; however, treatment adherence was not influenced by the presence of upper airway or facial skeletal abnormalities.