Forces and moments generated during extrusion of a maxillary central incisor with clear aligners: an in vitro study

OBJECTIVE

To assess the possibility of extrusion of a maxillary central incisor with the use of buccal and lingual pressure columns in the absence of attachments, and to evaluate the forces and moments experienced by the teeth using both thermoformed and 3D-printed clear aligners.

MATERIALS AND METHODS

A three-axis force and moment sensor (Aidin Robotics, Anyang, South Korea) was used to measure the forces and moments during extrusion of an upper left central incisor (UL1) and any forces experienced by the upper right central incisor (UR1) using thermoformed aligners and 3D-printed aligners. For the thermoformed aligners, the materials used were ATMOS® (American Orthodontics, Sheboygan, WI) and Zendura FLX® (Bay Materials LLC, Fremont, CA). 3D-printed aligners were fabricated using TC-85 clear photocurable resin (Graphy Inc., Seoul, South Korea). For each material type, three conditions were tested: Group 1: No attachment or pressure columns (control); Group 2: Attachment only; and Group 3: Pressure columns only. Each group was planned for 0.5 mm of extrusion on the UL1.

RESULTS

All force readings collected demonstrated statistically significant differences when compared by materials and when compared by groups, with a P value of < 0.001. In the absence of attachment or pressure columns (Group 1), ATMOS® and TC-85 groups exerted extrusive force on the UL1. However, significantly lower forces and moments were exerted by the TC-85 group in comparison to the ATMOS® and Zendura FLX® groups. In the presence of attachment (Group 2), all three ATMOS®, Zendura FLX® and TC-85 groups exerted extrusive force on the UL1, with the TA group showing different directions of faciolingual force, mesiodistal force and faciolingual inclination on the UR1 when compared to the other two thermoformed groups. Whereas in the presence of pressure columns (Group 3), only the TC-85 3D-printed aligner group exerted extrusive force. Thermoformed aligners generated significantly higher mean forces and moments than 3D-printed aligners. Significant levels of unintended forces and moments were present in all groups.

CONCLUSIONS

Force levels generated during extrusion with clear aligners are significantly lower with those 3D-printed using TC-85 than with those thermoformed using ATMOS® or Zendura FLX®. Attachments consistently generated extrusive forces, and may be an effective adjunct in achieving extrusion of incisors. Extrusion may be achieved without the use of attachments by utilizing pressure columns in 3D-printed aligners using TC-85. While different strategies can generate extrusive forces, there are significant unintended forces and moments.

Predictability of orthodontic tooth movement with aligners: effect of treatment design

BACKGROUNDS

The present study was designed to define: (1) which are the less predictable OTM with Invisalign aligners when the treatment plan is designed by expert operators, (2) if the presence and shape of attachments influence the predictability of OTM and (3) if patients' demographics influence OTM predictability. The sample comprises 79 prospectively recruited patients (mean age 30.8 years; SD 12.0; 23 M, 56 F), treated by expert operators with an average of 27 aligners (SD 15) in the maxillary arch and 25 aligners (SD 11) in the mandibular arch. Post-treatment digital models and final virtual treatment plan models were exported from ClinCheck® software as STL files and subsequently imported into Geomagic Qualify ®software, to compare final teeth positions. The differences were calculated and tested for statistical significance for each tooth in the mesial-distal, vestibular-lingual and occlusal-gingival directions, as well as for angulation, inclination and rotation. In addition, the statistical significance of categorical variables was tested.

RESULTS

The lack of correction was significant for all movements and in all group of teeth (P < 0.01) except for the rotation of maxillary first molar. The prescribed OTM, the group of teeth and movement, the frequency of aligner change and the use of attachment influence the outcome. The greatest discrepancies in predicted and achieved tooth position were found for angular movements and rotation of teeth characterized by round-shaped crowns, for a ratio of approximately 0.4° per 1° prescribed. Optimized attachments for upper canines and lower premolar rotation seem not working properly. Second molar movements are mostly unexpressed. Furthermore, changing the aligner every 14 days will reduce the lack of correction of the 12% with respect to 7 days aligner change.

CONCLUSIONS

Predictability of orthodontic movement with aligners still has limitations related to the biomechanics of the system: the shape of some attachments and the characteristics of aligner material need to be redefined. However, the results of this study allow to properly design the virtual treatment plan, revealing how much overcorrection is needed and which attachments are most effective.

IPR treatment and attachments design in clear aligner therapy and risk of open gingival embrasures in adults

BACKGROUND

The incidence of open gingival embrasures (OGE) in patients after fixed appliance treatment is relatively high, while there are no detailed reports on patients after clear aligner therapy. Also, no clinical studies with large sample size have investigated whether interproximal enamel reduction (IPR) can actually avoid OGE. The purpose of this study was to determine the prevalence of OGE in adults after clear aligner therapy and to investigate the risk of OGE associated with IPR treatment and attachment design, focusing on the amount and distribution in mandibular anterior teeth.

METHODS

Pre-treatment and post-treatment intraoral frontal photographs of 225 non-extraction patients were evaluated retrospectively for the occurrence and severity of OGE. The amount of IPR and the number of attachments in the anterior teeth from subjects after screening were recorded according to the first version of clear aligner software (Clincheck, San Jose, USA) and clinical medical documents. Logistic regression analysis was performed to identify the factors contributing to OGE.

RESULTS

The incidence of OGE in non-extraction patients after clear therapy between maxillary and mandibular central incisors was 25.7% and 40.3%, respectively. IPR was not associated with the occurrence of OGE but was associated with severity (P < 0.05). The number of attachments in the anterior teeth or central incisors was significantly related to the incidence of OGE (P < 0.05) but was not associated with severity.

CONCLUSION

A high rate of OGE occurs after clear aligner therapy. Clinicians should be aware of the application of IPR and the design of attachments during clear aligner therapy.

Light-curing process for clear aligners' attachment reproduction: comparison between two nanocomposites cured by the auxiliary of a new tool

BACKGROUND

Attachments' configuration play an important role during Clear Aligner Treatment (CAT) for aligner retention and control of movements planned. The aims were to compare the macroscopic morphology of attachments reproduced with flowable (FNC) and conventional (CNC) composites and the effects on them of two light-guide tips with different dimensions.

METHODS

4 resin casts derived from the initial scan of the same patient were obtained. 10 vestibular attachments were replaced on both upper and lower arches of each model with CNC (Models A, B) and FNC (Models C, D). Each composite was cured by means of the same LED lamp with both regular light-guide (Models A, B) and push and light tool® (Models C, D). The 80 attachments were qualitative analyzed by means of a digital stereo microscope. Surface roughness and waviness measurements were assessed by contact probe surface profiler (TalySurf CLI 2000; Taylor Hobson, Leicester, United Kingdom). Statistical analysis was performed with independent samples t-tests. Significance was established at the P < 0.05 level.

RESULTS

Model A showed lower values of surface roughness (Ra - 1.41 µm, Rt - 3.46 µm) and waviness (Wa - 2.36 µm, Wt - 10.95 µm) when compared with Model C. Significant reduction of waviness (Wa - 3.85 µm, Wt - 4.90 µm) was observed on Model B when compared with Model D. Significant increase of roughness and waviness parameters (Ra 3.88 µm, Rt 21.07, Wa 2.89 µm, Wt 14.74 µm) was found when CNC sample (Model A) was cured with regular light-guide tip. Higher values (Ra 2.33 µm, Rt 24.07 µm, Wa 1.67 µm, Wt 20.79 µm) were observed after regular light-guide tips curing on FNC sample (Model C).

CONCLUSIONS

CNC resins determine more regular surfaces of attachments profiles. The additional use of a smaller light- guide of the LED push and light tool® allows to improve the macroscopic morphology of the attachments and to maximize light irradiance delivering by enhancing the polymerization process and the integrity of the features during the treatment.

Fully digital workflow for reinforced mandibular implant overdenture - A novel method

Mandibular overdenture is suspected to fracture, especially in the midline and anterior region due to low surface area of coverage and minimum acrylic thickness in addition to attachments pickup holes that weakens the denture. Dentures used to be conventionally reinforced with metal meshwork which cannot be done in a digital workflow. This in vitro report introduces a novel approach of digital overdenture reinforcement using computer-aided design, computer-aided manufacturing, and rapid prototyping technologies. This novel approach provided digital reinforced, stable, and well-adapted overdenture with accurate and easy attachment pickup. Digital reinforced denture has fewer clinical steps with fewer laboratory complications. The newly developed overdenture fabrication techniques have the ability to change the conventional clinical and laboratory workflow from analog to digital. Which grantee standardization of the outcome on both research and clinical work.

Zygomatic implant-supported prosthetic rehabilitation of a patient with Brown et al. Class II c maxillary defect: A clinical report

The genesis of acquired maxillary defects poses a significant challenge when it comes to rehabilitating a patient prosthetically. These defects lead to functional and esthetic impairment, affecting the quality of life of an individual. This clinical report describes a satisfactory zygomatic implant-supported overdenture rehabilitation of a patient who underwent subtotal bilateral maxillectomy after an industrial accident. The result shows zygomatic implant-supported overdenture as a viable, predictable, and economical treatment option for a patient with an extensive maxillary defect.

Revision of the morphology of longissimus capitis, longissimus atlantis, longissimus cervicis, and the cranial part of longissimus thoracis in the domestic goat (Capra hircus): a cadaveric study

Veterinary anatomical texts have generally described the longissimus muscle only in terms of its attachment in the ox as the basic species and have not thoroughly addressed its morphology in small ruminants. Hence, the present study was designed to present the anatomical features of longissimus capitis, longissimus atlantis, longissimus cervicis, and the cranial part of longissimus thoracis of domestic goats by comparing them with the existing descriptions of these muscles in the ox. Bilateral dissections of the neck and the cranial thoracic regions of 10 domestic adult goats of both sexes were carried out. The longissimus capitis and longissimus atlantis consisted of about 5 muscle slips originating from the articular processes of C3-C7 (including their bony ridges) or T1 and the transverse process of T2. In 7 (37%) of the 19 muscles dissected, the last slips in the longissimus capitis and longissimus atlantis or in one of them showed no attachment to the vertebrae. Rather, the thoracolumbar fascia in the cranial part of the thoracic region, the cranial edge or the deep face of longissimus thoracis, and the deep face of longissimus cervicis served as the origins of the muscles. The attachment sites of the longissimus cervicis and the cranial part of the longissimus thoracis in the goat demonstrated no remarkable differences with those of the ox. Whether the attachment sites of these variants should be considered as normal or anomalous needs to be evaluated with a larger number of animals of different breeds.

Comparative evaluation of frictional resistance of extracoronal attachments of different designs and lengths in fixed partial denture: A finite element analysis

Aim:

The purpose of the study was to evaluate the frictional resistance and the vertical force required to achieve the frictional resistance for different length and designs of extracoronal attachments used in fixed partial denture (FPD).

Setting and Design:

Finite element analysis.

Materials and Methods:

Four different designs and five different lengths (3 mm, 3.5 mm, 4 mm, 4.5 mm, and 5 mm) of extracoronal attachments for FPD were selected from different manufacturers. Three-dimensional models of all the samples were simulated using Catia V5 software. The properties were incorporated to the software to simulate the clinical conditions. The frictional resistance and the vertical force required to achieve frictional resistance were analyzed using ANSYS workbench 15.0 finite element software.

Statistical Analysis Used:

ANOVA and Tukey's post hoc test.

Results:

The mean microhardness of the Variolink N resin cements were significantly higher than Panavia SA ones (P < 0.001). Variolink N cements exhibited lower sorption/solubility than Panavia SA resin cements (P < 0.05). The ceramic shade had a significant influence on the microhardness of both cements (P < 0.001) but had no significant effect on the sorption/solubility of resin cements (P > 0.05).

Conclusion:

Interposition of monolithic zirconia decreases the microhardness of resin cement especially Panavia SA. The microhardness decreased in Variolink N with the increase in the chroma saturation of ceramics. However, in Panavia SA, it was altered by the shades. For both cements, there were no statistical differences between the sorption/solubility. There was a reverse correlation between microhardness and water sorption/solubility of both cements.

Art boxes supporting parents and infants to share creative interactions at home: an art-based response to improve well-being during COVID-19 restrictions

OBJECTIVES

This article seeks to demonstrate the impact of distributing boxes of art resources and guided activities for vulnerable parents and infants to do together at home.

STUDY DESIGN

Designed in conjunction with the local arts centre and the psychology team at the University of Dundee, the art boxes were a response to planned face-to-face art interventions with families being cancelled due to COVID-19 restrictions. The aim of the art boxes is to encourage parents to make art together with their infants, fostering connection through playful, creative shared experiences. This research is currently being expanded to reach out to new families through referrals from health visitors, family nurses, and charity partners.

METHODS

Data is being collected on how the art boxes are experienced by families using a mixed-methods approach. Families complete feedback cards (online, or using the stamped addressed card included in the box) rating their experience on quantitative scales and providing open comments. Visual data are gathered through parents sharing images with us on social media. An initial sample of 10 participants has been interviewed using semistructured interviews, allowing more in-depth qualitative understanding of their experiences. These preliminary findings are discussed here.

RESULTS

The thematic analysis of initial interviews provided a rich picture of the disconnection families experienced during lockdown, why art boxes may be beneficial to parental well-being, and the mechanisms by which the boxes may help to develop connections for the parent and infant together.

CONCLUSIONS

Preliminary findings show parents reporting feeling more confident and undertaking new activities which they plan to continue. This was of particular importance during lockdown where parents report opportunities for different experiences being more limited. Parent's describe positive playful interactions and reported improvements to their own well-being from doing creative activities together with their child. Analysis of these initial interviews gives a framework of barriers and supports to connection which highlights how art boxes can facilitate connectedness between dyads with the potential to strengthen attachments.

Effect of different attachment geometries on the mechanical load exerted by PET‑G aligners during derotation of mandibular canines : An in vitro study

AIM

Derotation of rounded teeth has proved difficult for aligners to achieve. In this study, we investigated the effect of aligner attachment geometry on the three-dimensional (3D) force and moment (F/M) values exerted during derotation of a mandibular canine.

MATERIALS AND METHODS

The experiment setup comprised an acrylic mandibular arch model with a separated right canine (tooth 43) mounted on a hexapod via a 3D F/M sensor. Polyethylene terephthalate glycol (PET‑G) aligners with thicknesses of 0.5, 0.625, and 0.75 mm were tested in combination with quarter-sphere, vertical-ellipsoid, and pyramidal attachments bonded to tooth 43. The experimentally measured movement consisted of mesio- and distorotation of tooth 43 in 1° steps up to ±15° in each direction.

RESULTS

Compared with no attachment, vertical-ellipsoid and quarter-sphere attachments increased the rotational moment by a median factor of 1.5-12.3. Moment increases for pyramidal attachments were significantly smaller (Mann-Whitney U‑test, p < 0.05). Quarter-sphere attachments inhibited the intrusive forces up to 6.07° distorotation, whereas the intrusion prevention range for most aligner attachment combinations was significantly smaller (2.95° for vertical-ellipsoid and 2.88° for pyramidal attachments; Mann-Whitney U‑test, p < 0.05). None of the attachment geometries could completely prevent intrusive forces during mesiorotation.

CONCLUSION

The quarter-sphere geometry had the best overall mechanical properties because it induced relatively high rotational moment increases and counteracted unwanted intrusive forces most effectively of all three geometries. The determined maximum attachment dislodgement and intrusion prevention angles of approximately 6° provide a guide to determining setup increments for mandibular canine derotation.

Effect of Cyclic Dislodging on the Retention of Two Attachment Systems for Implant-supported Overdentures: An In Vitro Study

PURPOSE

The aim of this study was to compare and evaluate the retention of two new attachment systems used for implant-supported overdentures subjected to insertion-removal cycles.

MATERIALS AND METHODS

Twenty custom-manufactured polyvinyl chloride models mimicking implant-retained over-dentureresin blocks were fabricated and divided into two groups (n = 10): group 1 ('Kerator' attachment) and group 2 ('EMI' attachment). Each model received two parallel implants (JD evolution®) 20 mm apart and was subjected to cyclic retention forces of 10, 100, 1000, 5000, 10000 and 14600 cycles using a universal testing machine in a 0.9% sodium chloride water solution at 22° C. Data were analyzed using one-way analysis of variance; the level of significance was set at a < 0.05.

RESULTS

The 'Kerator' and 'EMI' attachment systems reported a significant decrease in retention (64 and 56.6% respectively) after 14600 insertion-removal cycles (p < 0.001). The 'EMI' attachment showed significant higher loss of retention than the 'Kerator' attachment all along the 14600 cycles (p < 0.05) except for cycles 100 and 5000 (p > 0.05).

CONCLUSION

Within the limitations of this in vitro study, both attachments reported satisfactory retentive values during the 14600 cycles, the 'Kerator' attachment showed better retention than the new 'EMI' attachment. The initial retentive force of both attachments has gradually decreased.

CLINICAL SIGNIFICANCE

Both attachment systems evaluated in this study can be used in clinical practice for implant-supported overdentures.

Retentive characteristics of individual and prefabricated polyvinylsiloxane overdenture attachments: alternative treatment options for geriatric patients

OBJECTIVES

Stud attachments are often too adhesive and too susceptible to damage for use in geriatric patients, especially when implants are angulated. This study aimed to evaluate alternative anchoring systems comprising individual and prefabricated polyvinylsiloxane (PVS) attachments.

MATERIALS AND METHODS

A total of 182 specimens with individual PVS (IPVS) attachments (Shore hardness [SH] 25, SH50, SH65], prefabricated PVS (PPVS) attachments (SM green, yellow, and red), and Locator attachments (LR blue) were fabricated (n = 7 per group). Retention force was measured using the following parameters: insertion/removal (100, 200, 500, 1000, and 5000 cycles), thermal undulation (10,000 cycles at 5-55 °C; one implant per specimen), implant angulation (0°, 5°, and 10° convergence and divergence; two implants per specimen), and artificial saliva.

RESULTS

Insertion/removal and thermal undulation caused no changes in retention force in SM green and IPVS subgroups; conversely, LR blue, SM red, and SM yellow attachments exhibited significant decreases in retention force of up to 66% (all P ≤ 0.001). Implant angulation produced relevant changes in retention force only in LR blue attachments. Artificial saliva caused a general decrease in retention force.

CONCLUSIONS

Retention force of low-retentive PVS attachments proved to be comparatively immune to dislocation and thermal undulation, as well as to implant angulation up to 10°.

CLINICAL RELEVANCE

Low-retentive PVS attachments could be a treatment option if reduced denture retention is required and/or if angulated implants are in place. Clinical studies are necessary to evaluate the materials' durability under oral conditions.

Stress analysis of mandibular implant overdentures retained with one, two, or four ball attachments: A finite element study

BACKGROUND

The aim of this study is to compare stress patterns induced by ball attachments when used to retain mandibular overdentures supported by one, two, or four dental implants.

MATERIALS AND METHODS

In this finite element study, three 3D models were prepared to simulate mandibular implant overdentures retained by one or two or four ball attachments of 3.5 mm diameter with collar height 1.6 mm. The geometric solid models were created by commercial engineering computer-aided design package then transferred to ANSYS as set of standard ACIS text files. Vertical load of 100 N was applied on the central fossa of the right molar. Stresses were evaluated at the areas of implant and attachment components, mucosa underlying overdentures, and cortical and cancellous bone adjacent to implants.

RESULTS

The results of this study showed that the Von Mises stresses generated by the application of vertical loading varied according to the number of implants used to support the overdenture. Maximum Von Mises stress on cortical bone ranged between 1.15 and 1.77 MPa in all-studied cases. Mucosa was squeezed under the one implant model. Flexibility of the overdenture material played a significant role in distributing the load stress and deformation of all underlying structure. Caps deformation was the highest when using two implants.

CONCLUSION

With increasing the number of implants, stresses and deformations of overdenture are reduced, but implants receive greater stresses and deformations. Using two implants in the canine region showed the best results when compared with using one or four implants, except for the caps.

Seeing a Brain Through an Other: The Informant's Share in the Diagnosis of Dementia

This article takes up the neuroscientific assumption of our brains as "solitary" and contrasts this understanding with the description of actual clinical practices. Drawing on observations of clinical consultations and team meetings in a world famous US center for the diagnosis of dementia, I examine how the "informant", a member of the patient's family, participates in the diagnosis process. Based on specific situations in which the informant is judged to be a "bad" one, I inquire as to how clinicians use what they understand of the affective relationships between the patient and the bad informant in order to make a diagnosis. The diagnosis of dementia in an individual is shown to draw on relational dimensions in the patient's life, made visible and enunciable only when problematic. This inquiry therefore brings out how these neurologists, even though they are engaged in a neuroscientific paradigm that conceives the brain as a self-sufficient cognitive machinery, nevertheless do consider what links us to the brains sharing our lives, in order to make sense of our networks of neurons.

Surface wear of resin composites used for Invisalign® attachments

Orthodontic treatments with Invisalign® require the use of attachments, which are composite resin buttons attached to tooth surfaces. Attachments constitute one of the most powerful tools for improving the efficiency of orthodontic tooth movement. The main purpose of this study was to evaluate surface wear over six months in two resin composites (Filtek Z350 XT, 3MESPE and Amelogen Plus TW, Ultradent Products Inc. ) used for making Invisalign® attachments. These composites were selected for their esthetic and mechanical properties. Forty attachments were bonded to the buccal surface of maxillary teeth. Materials were randomized and assigned in a double blind manner. Impressions were taken of the attachments using a preestablished technique immediately after bonding and following 6 months of clinical use. The impressions were examined by Scanning Electron Microscopy (SEM) at 12-fold magnification to identify changes in surface texture and attachment shape. Data were analyzed using Mann-Whitney's test on the overall ranking of detected changes in those variables. Statistically significant differences (P<0. 001) were found for surface wear, with greater changes in Amelogen Plus. Attachment shape did not change significantly in either material (P>0. 05). According to the results of this study, the alteration of the attachment surface during the first six months of treatment depends on the composite used, while attachment shape does not appear to be affected, so the clinical performance of the materials evaluated could be considered acceptable.

Origin and insertion of the medial patellofemoral ligament: a systematic review of anatomy

PURPOSE

The medial patellofemoral ligament (MPFL) is the major medial soft-tissue stabiliser of the patella, originating from the medial femoral condyle and inserting onto the medial patella. The exact position reported in the literature varies. Understanding the true anatomical origin and insertion of the MPFL is critical to successful reconstruction. The purpose of this systematic review was to determine these locations.

METHODS

A systematic search of published (AMED, CINAHL, MEDLINE, EMBASE, PubMed and Cochrane Library) and unpublished literature databases was conducted from their inception to the 3 February 2016. All papers investigating the anatomy of the MPFL were eligible. Methodological quality was assessed using a modified CASP tool. A narrative analysis approach was adopted to synthesise the findings.

RESULTS

After screening and review of 2045 papers, a total of 67 studies investigating the relevant anatomy were included. From this, the origin appears to be from an area rather than (as previously reported) a single point on the medial femoral condyle. The weighted average length was 56 mm with an 'hourglass' shape, fanning out at both ligament ends.

CONCLUSION

The MPFL is an hourglass-shaped structure running from a triangular space between the adductor tubercle, medial femoral epicondyle and gastrocnemius tubercle and inserts onto the superomedial aspect of the patella. Awareness of anatomy is critical for assessment, anatomical repair and successful surgical patellar stabilisation.

LEVEL OF EVIDENCE

Systematic review of anatomical dissections and imaging studies, Level IV.

Effect of abutment angulation in the retention and durability of three overdenture attachment systems: An in vitro study

PURPOSE

This in vitro study investigated and compared the durability and retention of three types of attachments.

MATERIALS AND METHODS

Three commercially available attachments were investigated: Clix®, Dalbo-Plus® and Locator®. In total, 72 samples of these attachments were placed in the acrylic resin forms and subjected to mechanical testing (5400 cycles of insertion and removal) over the respective ball or Locator abutments immersed in artificial saliva at pH 7 and 37℃. The abutments were placed at angulations of 0°, 10° and 20°. The retention force was recorded at the beginning and after 540, 1080, 2160, 3240, 4320 and 5400 insertion-removal cycles.

RESULTS

The results revealed that there were significant differences in the average values of the insertion/removal force due to angulation (F _(2.48) = 343619, P<.05) and the type of attachment (F _(7.48) = 23.220, P<.05).

CONCLUSION

Greater angulation of the abutments was found to influence the retention capacity of the attachments, and the fatigue test simulating 5 years of denture insertion and removal did not produce wear in the metal abutments.

The influence of saliva pH value on the retention and durability of bar-clip attachments

PURPOSE

The aim of this study was to compare the durability and retention of 4 types of attachments placed over computer aided design/computer aided manufacturing (CAD/CAM) titanium bars when subjected to different pH conditions.

MATERIALS AND METHODS

Four commercially available attachments were investigated: Hader Yellow, Hader Red, Ackerman Gold and Ackerman Stainless Steel. These attachments and Ackerman CAD/CAM titanium bars were placed in 2 vessels containing different artificial saliva solutions (pH 7/pH 4) at 37℃ for one month to simulate corrosion conditions, and they were then subjected to mechanical testing (5400 cycles of insertion and removal).

RESULTS

The results revealed that there were significant differences in the average values of insertion/removal force due to the pH (F (1, 24)=9.207, P<.05) and the type of attachment (F (3, 24)=11.742, P<.05).

CONCLUSION

More acidic pH values were found to have a negative influence on the retention capacity of the attachments.

Precision attachment: retained overdenture

Precision attachments are small interlocking devices to connect prosthesis and abutments that offer a variety of solutions to the challenge of balance between functional stability and cosmetic appeal. Precision attachments have wide applications, used in fixed removable bridge, removable partial dentures, overdentures, implant retained overdentures, and maxillofacial prosthesis. Attachment retained overdentures helps in distribution of masticatory forces, minimizes trauma to abutments and soft tissues, attenuate ridge resorption, improves the esthetics and retains proprioception. The following case report discusses the use of resilient stud attachments to retain maxillary and mandibular overlay complete dentures.

Endoscopic submucosal dissection for removal of superficial gastrointestinal neoplasms: A technical review

Endoscopic submucosal dissection (ESD) is now the most common endoscopic treatment in Japan for intramucosal gastrointestinal neoplasms (non-metastatic). ESD is an invasive endoscopic surgical procedure, requiring extensive knowledge, skill, and specialized equipment. ESD starts with evaluation of the lesion, as accurate assessment of the depth and margin of the lesion is essential. The devices and strategies used in ESD vary, depending on the nature of the lesion. Prior to the procedure, the operator must be knowledgeable about the treatment strategy(ies), the device(s) to use, the electrocautery machine settings, the substances to inject, and other aspects. In addition, the operator must be able to manage complications, should they arise, including immediate recognition of the complication(s) and its treatment. Finally, in case the ESD treatment is not successful, the operator should be prepared to apply alternative treatments. Thus, adequate knowledge and training are essential to successfully perform ESD.