Changes in the distribution of occlusal forces in the course of the orthodontic retention phase: A prospective cohort study

PURPOSE: Aim of the present study was to assess the relative distribution of occlusal forces after orthodontic treatment and during the first 3 months of the retention phase using a computerized occlusal analysis system (T-Scan, Tekscan Inc., Norwood, MA, USA). MATERIALS AND METHODS: A total of 52 patients were included in this prospective cohort study and underwent analysis of occlusal forces on the level of tooth, jaw-half, and -quadrant during a 3-month period. Furthermore, differences between three retention protocols (group I: removable appliances in both jaws; group II: fixed 3-3 lingual retainers in both jaws; group III: removable appliance in the maxilla and fixed 3-3 lingual retainer in mandible) were assessed with Wilcoxon signed-rank tests at 5%. RESULTS: Directly after debonding, measured forces distribution were similar to published references for untreated samples. In the following, no significant difference was found between retention protocols II and III with regard to the asymmetry of the anterior occlusal forces. Both groups maintained an asymmetric force distribution in the anterior segment during the study period. There was also no difference between groups II and III in the distribution of occlusal forces for the posterior segments. Both retention concepts kept the symmetrical distribution of occlusal forces stable over the observation period. The retention concept of group I demonstrated a symmetrical distribution of occlusal forces in the anterior segment after debonding and this remained stable during the 3‑month period. In the posterior segment, no improvement of the initially asymmetric masticatory force distribution could be observed. CONCLUSIONS: All three studied retention protocols showed stability in retaining their original symmetrical or asymmetrical occlusal force distribution posteriorly/anteriorly during the 3‑month observation period. Therefore, an even distribution of occlusal forces should be the aim of the finishing phase,as no relative benefit of any single retention scheme in terms of post-debond improvement during the retention phase was seen. // ZIEL DER STUDIE: Ziel der vorliegenden Studie war es, die relative Verteilung der okklusalen Kräfte nach der kieferorthopädischen Behandlung und während der ersten 3 Monate der Retentionsphase mithilfe eines computergestützten okklusalen Analysesystems (T-Scan, Tekscan Inc., Norwood, MA, USA) zu untersuchen. MATERIAL UND METHODEN: 52 Patienten wurden in die prospektive Kohortenstudie aufgenommen und es wurde über einen Zeitraum von 3 Monaten eine Analyse der Verteilung der okklusalen Kräfte bezogen auf die einzelnen Zähne, die Kieferhälften und die unterschiedlichen Quadranten vorgenommen. Darüber hinaus wurden die Unterschiede zwischen 3 Retentionsprotokollen (Gruppe I: herausnehmbare Apparaturen in beiden Kiefern; Gruppe II: festsitzender 3‑3-Lingualretainer in beiden Kiefern; Gruppe III: herausnehmbare Apparatur im Oberkiefer und festsitzender 3‑3-Lingualretainer im Unterkiefer) mithilfe des Wilcoxon-signed-rank-Tests bei einem Signifikanzniveau von 5 % bewertet. ERGEBNISSE: Unmittelbar nach dem Debonding waren die gemessenen Kräfteverteilungen ähnlich wie in bereits veröffentlichten Studien für unbehandelte Probanden. Im Folgenden wurde kein signifikanter Unterschied zwischen den Retentionsprotokollen II und III in Bezug auf eine Asymmetrie der anterioren okklusalen Kräfte festgestellt. Beide Gruppen behielten während des Studienzeitraums eine asymmetrische Kraftverteilung im Frontzahnbereich bei. Auch bei der Verteilung der Okklusionskräfte im Seitenzahnbereich gab es keinen Unterschied zwischen den Gruppen II und III. Beide Retentionskonzepte hielten eine symmetrische Verteilung der okklusalen Kräfte über den Beobachtungszeitraum stabil. Das Retentionskonzept der Gruppe I wies im Frontzahnbereich nach dem Debonding eine symmetrische Verteilung der Okklusionskräfte auf, die über den Dreimonatszeitraum stabil blieb. Im Seitenzahnbereich konnte keine Verbesserung der initialen asymmetrischen Kaukraftverteilung beobachtet werden. SCHLUSSFOLGERUNGEN: Alle 3 untersuchten Retentionsprotokolle zeigten eine stabile Beibehaltung ihrer ursprünglichen symmetrischen oder asymmetrischen Verteilung der okklusalen Kräfte im Seitenzahnbereich bzw. im Frontzahnbereich während des 3‑monatigen Beobachtungszeitraums. Daher sollte eine gleichmäßige Verteilung der okklusalen Kräfte das Ziel bereits der Finishing-Phase der aktiven Therapie sein. Bezüglich der einzelnen Retentionsschemata zeigte keines der untersuchten Protokolle einen relativen Vorteil in Bezug auf mögliche Verbesserung der Kräfteverteilung während der Retentionsphase

Post-treatment changes in permanent retention

OBJECTIVES While permanent retention is today the method of choice to stabilize orthodontic treatment outcomes, recent studies have increasingly reported posttreatment changes in tooth position during permanent retention. We conducted this study to analyze changes in the anterior mandible, whether the changes follow an underlying movement pattern, and, aiming for a preventive strategy, whether any risk factors could be identified comparing findings with the pretreatment situations. METHODS We included 30 patients who had worn fixed Twistflex retainers (UK 3-3) extending from canine to canine in the mandible. Casts reflecting the intraoral situations before orthodontic treatment (T0), directly after completion of active therapy (T1), and 6 months later (T2) were scanned and superimposed using Imageware Surfacer software. Posttreatment changes (T2-T1) of tooth position within the retainer block were analyzed on 3D virtual models and were compared to pretreatment (T0) and treatment-related (T1-T0) findings to identify potential risk factors. RESULTS Almost all analyzed patients revealed three-dimensional changes in tooth position within the retainer block. Comparing these movements, we repeatedly found rotated retainer blocks in labio-oral direction, while the center of rotation was located at the first incisors. This pattern was associated with intercanine expansion and excessive overjet correction during orthodontic treatment. The canines underwent the most pronounced (rotational and translational) movements. CONCLUSIONS In general permanent lingual retainers are safe but in special clinical cases retainers can induce undesired tooth movement. Risk factors seem to be intercanine expansion and excessive overjet correction during orthodontic treatment. In specific cases an additional retention device might be needed

Failure patterns of different bracket systems and their influence on treatment duration: A retrospective cohort study

OBJECTIVES To compare the failure pattern of four different bracket types and to assess its effect on treatment duration. MATERIALS AND METHODS A total of 78 white patients (28 male, 50 female) with a mean age of 12.6 years were included in this retrospective cohort study and treated for a mean period of 30.6 months. The patients were treated in a private practice with stainless steel conventionally ligated brackets, ceramic conventionally ligated brackets, stainless steel self-ligating brackets, or nickel-free self-ligating brackets. The loss of at least one bracket during the course of treatment was analyzed with Cox proportional hazards survival analyses and generalized linear regression. RESULTS The overall bracket failure rate at the tooth level was 14.1% (217 brackets), with significant differences according to tooth type (between 8.0%-23.4%) and bracket type (between 11.2%-20.0%). After taking confounders into account, patients treated with ceramic brackets lost more brackets (hazard ratio = 1.62; 95% confidence interval = 1.14-2.29; P = .007) than patients with stainless steel brackets. On average, treatment time increased by 0.6 months (95% confidence interval = 0.21-1.05; P = .004) for each additional failed bracket. CONCLUSIONS Bracket failure was more often observed with ceramic brackets and was associated with increased treatment duration

The influence of enamel sandblasting on the shear bond strength and fractography of the bracket-adhesive-enamel complex tested in vitro by the DIN 13990:2017-04 standard

OBJECTIVES This study was conducted in order to investigate whether enamel sandblasting as an adjunct or substitute to the acid-etch technique has an effect on the shear bond strength (SBS) and fractography of the bracket-adhesive-enamel complex using the DIN 13990:2017-04 standard. MATERIALS AND METHODS Upper central incisor brackets (discovery®, Dentaurum, Germany) were bonded using Transbond XT™ (3M Unitek, Germany) on bovine incisors prepared by four different methods (15 samples each): sandblasting with 27 μm AlO at 1.2 bar (s), acid etching with 37.4% phosphoric acid (a), sandblasting with 27 μm AlO at 1.2 bar followed by acid etching (s1a), and sandblasting with 50 μm AlO at 5.7 bar followed by acid etching (s2a). The SBS and adhesive remnant index (ARI) were measured, followed by one-way analysis of variance and Fisher's exact tests at 5%. RESULTS The SBS in groups s (5.6 ± 2.2 MPa), a (17.1 ± 4.3 MPa), s1a (18.3 ± 4.3 MPa), and s2a (18.5 ± 4.6 MPa) indicated that the s group was significantly inferior to all the other groups (p < 0.001). Likewise, the ARI analysis indicated a different performance of the s group (mostly ARI of 0) compared to the other groups (p < 0.001) and a tendency for different ARI between the a and s1a/s2a groups. CONCLUSIONS In vitro enamel sandblasting could not substitute acid etching and did not offer improved SBS when used before acid etching, regardless of air pressure and powder granulation. Sandblasting without acid etching produced less residual resin on the tooth after debonding. CLINICAL RELEVANCE The clinical use of adjunct enamel sandblasting prior to etching to enhance SBS has to be questioned

In vitro cyclic shear fatigue of the bracket-adhesive complex: a pilot study

OBJECTIVE: The aim of this study was to describe the effect of fatigue on the shear strength of the bracket-adhesive complex. MATERIALS AND METHODS: Brackets with laser-structured (Discovery®, Dentaurum) and foil mesh bases (Ultra-Minitrim®, Dentaurum) were bonded onto silanized stainless steel flat plates with two chemically curing adhesives (No-Mix Bonding System, Dentaurum; Concise™, 3M Unitek) and aged in distilled water at 37°C for 3 days. One group of specimens was used to determine shear-bond strength. The second group underwent shear-fatigue testing with a testing machine (Zwick 1445) according to the staircase method for 1,000 cycles, and the surviving specimens were subjected to shear-strength testing. The shear strength of the fatigued and non-fatigued specimens were then compared. RESULTS: Fatigued specimens demonstrated an 8% gain in shear strength in material group A (Discovery®/No-Mix) and a 10% loss of shear strength in material group D (Ultra-Minitrim®/Concise™) compared to the non-fatigued group. We observed no statistically significant differences in material groups B (Ultra-Minitrim®/No-Mix) and C (Discovery®/Concise™). The fatigue ratio varied between 60% and 67%. Among the non-fatigued specimens, the bracket Discovery® with laser-structured base showed circa 59% greater shear strength than the foil-mesh bracket Ultra-Minitrim®, and the adhesive Concise™ about 66% more shear strength than the No-Mix. CONCLUSION: Shear fatigue of the bracket-adhesive complex for 1,000 cycles revealed a variable, material-dependent influence on the shear strength of the bracket-adhesive complex. However, the effect of fatigue on shear strength was less significant than the effect of other factors such as bracket and adhesive type

Candidate Genes for Nonsyndromic Cleft Palate Detected by Exome Sequencing

Nonsyndromic cleft palate only (nsCPO) is a facial malformation that has a livebirth prevalence of 1 in 2,500. Research suggests that the etiology of nsCPO is multifactorial, with a clear genetic component. To date, genome-wide association studies have identified only 1 conclusive common variant for nsCPO, that is, a missense variant in the gene grainyhead-like-3 ( GRHL3). Thus, the underlying genetic causes of nsCPO remain largely unknown. The present study aimed at identifying rare variants that might contribute to nsCPO risk, via whole-exome sequencing (WES), in multiply affected Central European nsCPO pedigrees. WES was performed in 2 affected first-degree relatives from each family. Variants shared between both individuals were analyzed for their potential deleterious nature and a low frequency in the general population. Genes carrying promising variants were annotated for 1) reported associations with facial development, 2) multiple occurrence of variants, and 3) expression in mouse embryonic palatal shelves. This strategy resulted in the identification of a set of 26 candidate genes that were resequenced in 132 independent nsCPO cases and 623 independent controls of 2 different ethnicities, using molecular inversion probes. No rare loss-of-function mutation was identified in either WES or resequencing step. However, we identified 2 or more missense variants predicted to be deleterious in each of 3 genes ( ACACB, PTPRS, MIB1) in individuals from independent families. In addition, the analyses identified a novel variant in GRHL3 in 1 patient and a variant in CREBBP in 2 siblings. Both genes underlie different syndromic forms of CPO. A plausible hypothesis is that the apparently nonsyndromic clefts in these 3 patients might represent hypomorphic forms of the respective syndromes. In summary, the present study identified rare variants that might contribute to nsCPO risk and suggests candidate genes for further investigation