Three dimensionally printed template with an interproximal isolation design guide consecutive closure of multiple diastema with injectable resin composite.

OBJECTIVE: This article describes a novel 3D-printed template armed with interproximal matrices to isolate interproximal contact areas and guide injectable resin composite for consecutive closure of multiple diastema. CLINICAL CONSIDERATIONS: Among several treatment options proposed for diastema closure, direct resin composite is noninvasive and easy to repair. The "composite injection technique" has been introduced to improve time efficiency and reduce technique sensitivity for clinicians. However, in the case of multiple diastema, the overflow of excess resin materials onto the adjacent teeth during injection poses challenges for recontouring the interproximal anatomy. A 3D-printed template with special-designed gaps at interproximal areas was designed and fabricated based on a virtual diagnostic wax-up. Flowable resin composite was then consecutively injected through the template to close diastemata at multiple adjacent teeth. CONCLUSION: This technique using a 3D-printed template with interproximal isolation design contributed to an efficient and accurate operation for multiple anterior diastema closure. CLINICAL SIGNIFICANCE: Efficient and accurate freehand buildups of composite restoration for multiple diastema are challenging in operative dentistry. The described noninvasive full digital workflow provides a predictable method to accurately recontour the multiple target restorations and reduce the chair-side time and technical sensitivity.

Digital intraoperative evaluation of restorative space and nontemplate-guided tooth preparation when replacing failed anterior restorations: A dental technique.

Assessing the correlation between the current restorative space and the target restorative space is important in determining whether additional tooth preparation is required when replacing failed prostheses. However, existing techniques are not always accurate or efficient. This article describes a digital workflow for the accurate chairside evaluation of the current restorative space and nontemplate-guided tooth preparation. Reference data was obtained from an initial scan of the existing restoration with an intraoral scanner. After removing the existing restoration, a second scan of the tooth was made and compared with the reference data to evaluate the current restorative space. Subsequently, the abutment tooth was prepared and rescanned, with the restorative space being re-evaluated until it met the requirements. This workflow enables the immediate and accurate evaluation of the restorative space, facilitating accurate chairside tooth preparation without the need for silicone indices or other templates, thereby saving time and cost.

A digital workflow for tooth-supported complete overdentures with a composite resin injection technique to manage the treatment of a child with ectodermal dysplasia.

This clinical report describes a digital workflow for the rehabilitation of an 8-year-old patient diagnosed with ectodermal dysplasia. Based on the patient's digital primary casts, small custom trays and an arch tracer were designed and 3-dimensionally printed. The mandibular custom tray and retention plate with a tracing screw were assembled with tracing plate, forming an individual assembled mini-arch tracer system to record the jaw relationship together with a conventional facebow and a digital articulator. In addition, composite resin injection guides were designed and fabricated to form the predesigned targeted shape of the abutment teeth and provide a buffer. By following this workflow, complete overdentures with good fit, occlusion, and acceptable esthetics were delivered.

A polyetheretherketone framework removable partial denture for a 6-year-old child with nonsyndromic oligodontia made using glass-ceramic hemispheres to enhance retention: A clinical report.

A 6-year-old child with nonsyndromic oligodontia in the mixed dentition received a removable dental prosthesis with a polyetheretherketone framework and artificial gingiva, restoring esthetics and function. Computer-aided design and computer-aided manufacturing hemispherical glass-ceramic attachments were added to the teeth under the guidance of acid-etching and bonding guides to obtain an undercut area. The bonding and cementation of the attachments and the prosthesis delivery were completed in a single visit. This method offers a suitable prosthodontic treatment option for treating children with oligodontia in the mixed dentition.

Accuracy of the novel digital non-cross-arch surgical guides with integration of tooth undercut retention and screw-bone support for implant placement in mandibular free-end.

BACKGROUND: Large cross-arch free-end surgical guides can obscure the visual field, compromising surgical accuracy due to insufficient stability at the free-end. This in vitro study aims to evaluate the accuracy of novel digital non-cross-arch surgical guides designed for implant placement at the mandibular free-end, incorporating tooth undercut retention and screw-bone support. MATERIALS AND METHODS: A mandibular dental model lacking left molars was utilized to fabricate unilateral (cross-arch) tooth-supported surgical guides (GT I, n = 20). Subsequently, two additional types of surgical guides were fabricated: GT II (covering two teeth, n = 20) and GT III (covering three teeth, n = 20). These novel surgical guides were designed to utilize the undercut of the supporting teeth for retention and enhance stability with screw-bone support at the guide's free-end. Furthermore, 60 identical guiding blocks were assembled on the three types of surgical guides to facilitate the implants' insertion. On a phantom head, 120 implant replicas were placed at the Federal Dentaire Internationale (FDI) teeth positions #36 and #37 on the dental model, employing a combination of surgical guides and guiding blocks. To assess accuracy, planned and placed implant positions were compared using intraoral optical scanning. Discrepancies in angulation and linear deviations, including the coronal/apical 3D deviations, lateral deviation as well as depth deviation, were measured. Statistical analysis was performed using two-way ANOVA and Bonferroni test (α = 0.05). RESULTS: GT I exhibited significantly largest discrepancies, including angular and linear deviations at the crest and apex at every implant site. Especially in depth, at implant site #36, the mean deviation value of GT I (0.27 ± 0.13 mm) was twice as large as GT III (0.13 ± 0.07 mm), and almost twice as large as GT II (0.14 ± 0.08 mm). However, at implant site #37, this deviation increased to almost a five-fold relationship between GT I (0.63 ± 0.12 mm) and II (0.14 ± 0.09 mm), as well as between GT I and III (0.13 ± 0.09 mm). No significant discrepancies existed between the novel surgical guides at either implant site #36 or #37. CONCLUSION: This study provides a practical protocol for enhancing accuracy of implant placement and reducing the size of free-end surgical guides used at mandibular molar sites.

Mechanical stability of angulated zirconia abutments supporting maxillary anterior single crowns on narrow-diameter implants.

OBJECTIVES: To investigate the fracture strength of angulated hybrid abutments supporting anterior single crowns on narrow-diameter implants (NDIs). MATERIAL AND METHODS: Zirconia abutment with angulations of labial inclination 0° (TZ0Z), 15° (TZ15Z), 30° (TZ30Z) and palatal inclination 15° (TZ - 15Z) was designed on 3.3-mm titanium-zirconium (Ti-Zr) NDIs. Titanium abutment connected with Ti-Zr implant (TZ0T) and 0° zirconia abutment connected with pure titanium (Ti) implant (T0Z) were control groups. Thirty-six un-restored abutments and 36 abutments restored with highly translucent zirconia (HTZ) crowns were tested. Failure loads were compared among 6 groups, and bending moments were calculated for comparison between un-restored and restored abutments. RESULTS: Failure loads of un-restored abutments were affected by the abutment angle. Sixty-seven percent samples in TZ30Z and 83% samples in TZ - 15Z group fractured at the thinnest part of the zirconia abutment and exhibited lower failure load (p < .05). Failure loads of restored abutments were close to or exceeded the maximum bite force of anterior teeth, and no differences were found among six groups (p > .05). Except TZ15Z and TZ0T group, the bending moment increased with the crown construction, especially for TZ30Z and TZ - 15Z groups (p < .001). CONCLUSIONS: The fracture strength of hybrid abutments restored with HTZ crown on Ti-Zr NDIs exceeded the bite forces of anterior teeth for all the groups and were not affected by the abutment angle. CLINICAL RELEVANCE: In terms of fracture strength, Ti-Zr NDIs combined with angulated hybrid abutments and HTZ crowns can be used in the anterior region.

Guided removal of a fractured fiber post and immediate restoration with a digitally prefabricated titanium post-and-core and zirconia crown: A clinical report.

A completely digital workflow is described for the immediate restoration of a fractured fiber post with a digitally prefabricated definitive restoration using 3-dimensionally printed guides. The geometric morphology and axis of the root canal were digitally determined by using cone beam computed tomography to localize the 3-dimensional position of the fractured fiber post. A virtual drill modeled on the shape of the fractured post was fabricated and customized for removal of the post by using a guide to facilitate the intraoral transfer of the drilling procedure. A titanium post-and-core and crown had been virtually predesigned and fabricated before the procedure, and 2 digital guides were designed for their placement. All guides were 3-dimensionally printed. By following this workflow, the removal of the fractured fiber post and immediate definitive restoration were completed in 1 visit, facilitating a more efficient, predictable, and straightforward treatment.

A digital workflow for complete arch rehabilitation with zirconia crowns on restored posterior teeth and a polyetheretherketone framework denture.

A clinical and laboratory workflow for the digital design and fabrication of zirconia crowns and polyetheretherketone removable partial dentures for complete arch rehabilitation is described. The definitive crowns and polyetheretherketone framework can be delivered simultaneously because of the digital design and milling fabrication with retentive areas, guide planes, and rest seats in high-translucency zirconia crowns. The workflow helps simplify clinical and laboratory procedures and reduces patient visits and chairside time.

A digital chairside repair protocol for removable partial dentures with polyetheretherketone frameworks.

Polyetheretherketone (PEEK) has become popular for removable partial denture (RPD) frameworks but reports on their clinical follow-up and repair are lacking. Two defective PEEK-framework RPDs were repaired with computer-aided design and manufacturing technology, saving costs and time and simplifying the treatment process.

Evaluating the microbial aerosol generated by dental instruments: addressing new challenges for oral healthcare in the hospital infection.

BACKGROUND: Using a rotary instrument or ultrasonic instrument for tooth preparation is a basic operation in the dental clinic that can produce a significant number of droplets and aerosols. The dental droplet and aerosol can lead to the transfer of harmful germs. The goal of this study was to analyze the properties of microbiological aerosol created by droplets and aerosol generated by three common tooth-preparation instruments. METHODS: Streptococcus mutans UA159 was used as the biological tracer to visualize the droplets and aerosols. The passive sampling method was used to map the three-dimensional spatial distribution and the six-stage Andersen microbial sampler (AMS) was used as the active sampling method to catch aerosol particles at a specific time. RESULTS: The aerosol concentration is related to instruments, three-dimensional spatial distribution, and dissipation time. Most aerosols were generated by air turbines. More microorganisms are concentrated at the 1.5 m plane. The majority of the post dental procedure contamination was detected within the 0-10-min period and it decreased rapidly within 30 min. CONCLUSION: This study is conducive to the proposal and improvement of relevant infection control measures in dental procedures and provides a basis for the assessment of measures, reducing the risk of nosocomial infection.

Technique to restore the midline space of central incisors using a two-in-one template: A clinical report.

Using composite resin restoration of full-coverage crowns to obtain a completely symmetrical esthetic restoration of individual central incisors remains difficult. Freehand direct composite resin restoration is challenging even for highly skilled dentists. This clinical report describes a digital protocol for achieving symmetrical restoration of two central incisors using a custom-designed, two-in-one template.

Digital workflow of labial guides for alveolar ridge reduction during implant-supported full-arch rehabilitation.

This article presents a technique for fabricating two-piece labial guides using resin and cobalt-chromium for guided alveoloplasty, implant placement, and immediate full-arch implant-supported fixed complete denture placement. This technique reduces tissue damage and overcomes the negative effect of the anatomical position of the palatal neuropore and mobility of the tissue flap on the positioning and stability of the guide. The use of labial retention metal guides with improved mechanical properties of cobalt-chromium and fixation plugs allows the unilateral placement of the guide. Thus, minimally invasive implant surgery can be performed owing to the absence of large palatal flap elevation and obstruction. Such a design provides better stability of the guides and clear visual access during surgery.

Improvement in Osseointegration of Titanium Dental Implants After Exposure to Ultraviolet-C Light for Varied Durations: An Experimental Study in Beagle Dogs.

PURPOSE: Ultraviolet-mediated photofunctionalization is a valid technology for enhancing the osseointegration of titanium implants. However, there is no consensus on the effective exposure time to ultraviolet light. The objective of this study was to evaluate the effect of different exposure times of ultraviolet-C (UVC) light on aged titanium implants and explore the optimal treatment duration of UVC photofunctionalization for osseointegration in an animal model. METHODS: Eight male beagle dogs (n = 48) were divided into a control group (n = 12) and 3 experimental groups (n = 12/12/12) which received 4-week-old implants without UVC treatment (C) or treated with UVC for 1/6 hour, 1/2 hour, and 1 hour (UVC-1/6 hour, UVC-1/2 hour, UVC-1 hour) immediately before placement. All the implants were placed 12 weeks after mandibular premolars extraction. Four dogs were euthanized after 4 and 12 weeks of healing, respectively. The marginal bone level and implant stability quotient were measured at implant placement and after sacrifice. Subsequently, micro-CT and histomorphometric analyses were performed following block harvesting. RESULTS: No significant difference in marginal bone loss between the UVC-untreated and UVC-treated groups was found at 4 or 12 weeks. At 4 weeks, significantly higher BV/TV and bone-implant contact were observed in the UVC groups than in the C group, irrespective of the UVC-photofunctionalization duration (BV/TV: UVC-1/6 hour 0.48 ± 0.11, UVC-1/2 hour 0.50 ± 0.06, and UVC-1 hour 0.47 ± 0.08, C 0.34 ± 0.04; bone-implant contact : UVC-1/6 hour 84.30 ± 5.02%, UVC-1/2 hour 85.82 ± 5.05%, and UVC-1 hour 84.98 ± 3.86%, C 71.69 ± 3.52%. P < .05), whereas, no significant difference was observed among the UVC groups. At 12 weeks, there were no significant differences between the C group and UVC groups. After 4 and 12 weeks of healing, no significant difference in implant stability quotient values was observed between the C group and UVC groups. CONCLUSIONS: UVC photofunctionalization improved the early osseointegration of aged titanium implants. However, the effect was not dependent on the UVC-light duration within the range from 1/6 hour to 1 hour.

A digital workflow for accurately and rapidly creating an immediate provisional restoration with natural emergence profile using extracted tooth.

To describe a digital workflow for creating a provisional restoration by using an extracted tooth rapidly, finally fixing the provisional restoration in the targeted position precisely and preserving the natural emergence profile from the time of provisional restoration to final restoration. CLINICAL CONSIDERATIONS: The use of extracted tooth as an immediate provisional restoration is an effective method for preserving the shape of the emergence profile. However, the existing methods for creating a provisional restoration by using natural tooth are time-consuming and there is no reliable method to precisely attach tooth to temporary abutment. This case demonstrates a new method for using patient's natural tooth as an immediate provisional restoration under a sequence of guides, which significantly reduces the chair-side time and inconvenience for clinicians and patients. Immediate provisional restoration contributes to preserving the soft tissue architecture after post-extraction implant placement, especially when using the patient's tooth as a provisional restoration. Digital technology can help to improve the chair-side clinical efficiency of dentist. CLINICAL SIGNIFICANCE: Maintaining the natural soft tissue architecture is a huge challenge in dental implantology. Use of the extracted tooth as a provisional restoration is likely to achieve an optimal outcome. And digital technology is helpful to the efficiency and accuracy of treatment.

A digital workflow with the virtual enamel evaluation and stereolithographic template for accurate tooth preparation to conservatively manage a case of complex exogenous dental erosion.

OBJECTIVE: This article describes a digital workflow using virtual enamel evaluation and a stereolithographic template for accurate tooth preparation for a complex exogenous dental erosion. CLINICAL CONSIDERATIONS: A 22-year-old man with different degrees of defects on the labial surface in esthetic area was diagnosed as exogenous dental erosion. The residual undamaged enamel area and depth of defect were measured and analyzed accurately by creating a digital virtual patient based on the pretreatment data. According to the different conditions of residual enamel and tooth defect, the treatment plans of porcelain veneer, crown and composite resin were chosen for corresponding involved teeth. Based on the virtual wax-up and the suggested material thickness, a template for tooth preparation was designed and three-dimensional printed. This template together with a special bur indicating the reduction depth accurately guided the teeth preparation and achieved a long-term effect. CONCLUSIONS: The virtual enamel evaluation contributes to obtaining the appropriate corresponding treatment plan objectively. The stereolithographic template effectively meets the accuracy of tooth preparation, preserving the tooth hard tissue to the greatest extent. CLINICAL SIGNIFICANCE: The digital workflow described here may provide a quantifiable evaluation method and an accurate tooth preparation method for exogenous dental erosion.

Accuracy of three digital waxing-guided trial restoration protocols for controlling the depths of tooth preparation for ceramic veneers.

STATEMENT OF PROBLEM: The accuracy of digital waxing-guided trial restoration protocols that have been implemented with ceramic veneers has not been reported. PURPOSE: The purpose of this in vitro study was to evaluate the accuracy of 3 digital trial restorations fabricated from digital waxing for ceramic veneers. MATERIAL AND METHODS: A uniform 0.3-mm digital waxing added to the facial surface of 30 maxillary central typodont incisors was created in a software program. The trial restorations were fabricated on typodont teeth with autopolymerizing acrylic resin by using a silicone index based on 3-dimensionally printed casts designed from the digital waxing. The 30 maxillary central incisors were divided into 3 groups: the depth cutter (0.5 mm, Komet) (DC) group, the round bur (1.5 mm, Diatech) (RB) group, and the specially designed calibrated depth bur (laser mark of 0.5 mm, Gaofeng) (CD) group. The 3 groups were randomly prepared with a random number table by 2 experienced prosthodontists aiming to produce an even facial clearance of 0.5 mm. The dimensional differences in the standard tessellation language (STL) files between the surfaces of the original teeth, digital waxing, trial restorations, and prepared teeth in the software program were measured and analyzed at the same 9 points on the labial surface. One-way ANOVA with a post hoc test was used to identify significant discrepancies between trial restorations and waxing and differences in the reduction depth of typodont teeth (RDT) and the reduction depth (RD) among the 3 techniques (α=.05). The mean relative differences (MRDs) were calculated to determine the accuracy (%). RESULTS: The thickness of the trial restorations was significantly greater than that of the digital waxings, with a discrepancy of 0.20 ±0.14 mm, especially at the cervical site. With the use of a trial restoration, the RDTs of the middle (-0.01 ±0.11 mm) and cervical locations (0.09 ±0.20 mm) showed significantly smaller preparation depths than did the other locations. Significant differences in RD were found among the 3 guided techniques (P<.05). Group DC presented the most accurate result of 0.51 ±0.08 mm with an MRD of 2%, whereas the results of 0.57 ±0.10 mm with an MRD of 14% and 0.60 ±0.11 mm with an MRD of 20% were obtained from group RB and group DC, respectively. CONCLUSIONS: The trial restoration was significantly thicker than its corresponding waxing. The DC technique presented the most accurate reduction result among the 3 protocols examined.

A digital workflow for the fabrication of an immediate implant-supported interim restoration.

Immediate interim restorations in the esthetic region are usually fabricated in situ by using the pick-up technique, which is time-consuming and has a potential for cross-infection. This article describes a rapid and precise workflow for the fabrication of an immediate implant-supported interim restoration. A cast with gingival contours and an extended tube to accommodate the implant analogs is generated preoperatively based on the virtual implant planning and a predesigned restoration. After guided osteotomy and implant insertion, the actual three-dimensional (3D) implant position is transferred precisely from the mouth to the printed cast by using the surgical guide. This technique can achieve the rapid and precise fabrication of the interim restoration with guidance immediately after the surgery, decreasing the risk of cross-infection and reducing clinical steps and time.

Effect of sealing gel on the microleakage resistance and mechanical behavior during dynamic loading of 3 implant systems.

STATEMENT OF PROBLEM: Sealing products have been produced to reduce microleakage at the implant abutment interface. However, little is known about their effectiveness and any alterations in mechanical behavior of implant systems with their application. PURPOSE: The purpose of this in vitro study was to evaluate the effect of a silicone sealing gel on implant abutment interface microleakage, abutment screw torque loss, and thread wear of implant systems in a simulated oral environment. MATERIAL AND METHODS: Five specimens each of 3 implants systems (Nobel, Straumann, and WEGO) that included sealed and unsealed groups were analyzed (N=30). Before assembling the components, toluidine blue solution was injected to the implant intaglio cavity to evaluate implant abutment interface microleakage. After tightening to the recommended torque, 20 to 200 N of 30-degree off-axis dynamic force was applied at 2 Hz for 48 hours. The toluidine blue solution was extracted to test optical density values at 1, 3, 9, 24, 33, and 48 hours. Detorque values were measured before and after cycling loading, and torque loss rates were calculated. The abutment screw morphologies were observed by using scanning electron microscopy. The coefficient of friction tendency of applying sealing gel was explored with a ball-on-flat configuration. One-way ANOVA and Student t test were used for statistical analysis (α=.05). RESULTS: The optical density value increased with the loading time, especially for Straumann group. The sealing gel decreased the implant abutment interface microleakage of Straumann assemblies after cyclic loading of 9 hours (P=.044), whereas no statistical difference was found for Nobel (P=.140) or WEGO groups (P=.402) at 6 time points. Torque loss occurred during tightening and further increased after dynamic cyclic load in each group. Among the 3 implant systems, Straumann implants reported the best antiloosening property (P<.001). The application of sealing gel reduced the initial (P=.048) and final (P=.032) torque loss rate in all the 3 systems. Scanning electron microscopy observations revealed the bottom thread tended to have more abrasion than the first thread. After applying sealing gel, less thread abrasion was found in Nobel and WEGO assemblies, whereas the protective effect was not evident for the Straumann group. The coefficient of friction of sealed group (0.17 ±0.026) was significantly (P=.012) lower than that of unsealed group (0.24 ±0.044). CONCLUSIONS: The silicone sealing gel improved the immediate fastening and long-term antiloosening performances of 3 implant systems, decreased the implant abutment interface microleakage of Straumann system, and reduced abutment screw thread abrasion of the Nobel and WEGO systems.

A digital workflow for layering composite resin restorations by using 3-dimensionally printed templates to replicate the contralateral tooth accurately and rapidly.

This article described a digital workflow for layering composite resin restorations by using a digital software program and 3-dimensionally printed templates. To mimic the appearance of the natural tooth, the computer-aided design was used to copy the shape of the contralateral tooth. Three-dimensionally printed templates to replicate the contralateral tooth accurately and rapidly can help dentists build different layers of dentin and enamel composite resin, achieving layered esthetic outcomes. This workflow provides an efficient and accurate procedure, reduces chairside time, and simplifies the application of the technically sensitive composite resin layering technique.

Optimization of the dimension of computer numerical control-milled polyetheretherketone clasps: An in vitro evaluation of accuracy.

STATEMENT OF PROBLEM: The accuracy and optimal dimensions of computer numerical control (CNC)-milled polyetheretherketone (PEEK) removable partial denture (RPD) clasps are unclear. PURPOSE: The purpose of this in vitro study was to investigate the trueness and precision of CNC-milled PEEK clasps with different thicknesses and lengths. MATERIAL AND METHODS: Ladder-shaped specimens of 2 thicknesses with 5 lengths of clasps were designed and milled with PEEK and commercially pure titanium (CP Ti) (n=6). All milled specimens were scanned and superimposed onto the design data. Three-dimensional and 2-dimensional deviation analyses were carried out to evaluate the trueness of milled PEEK clasps. The scanning data of each group were superimposed pairwise, and the 3-dimensional deviations were analyzed to evaluate the precision. Nonparametric tests, ANOVA, the Pearson correlation, and univariate linear regression were used for statistical analysis (α=.05). RESULTS: The deviation of trueness of the PEEK clasps (0.047 to 0.164 mm) was higher than that of the CP Ti clasps (0.037 to 0.060 mm) (P<.001). Increasing the length of the clasps increased the deviations (P<.001). Deviation in the 2 thicknesses was not significantly different (P=.210). The correlation coefficients of 1.0-mm-thick and 1.5-mm-thick PEEK and CP Ti clasps were 0.843, 0.794, 0.638, and 0.405. The positive correlation coefficients of PEEK were higher than those of CP Ti and those of 1.0-mm-thick clasps was higher than those of 1.5-mm-thick clasps. The deviations were evenly distributed in the 9-mm length of the clasp for CP Ti and in the 6-mm length of the clasp for PEEK. Beyond these lengths, deviations increased with increased length. The increasing amplitude of CP Ti was smaller than that of the PEEK group, and that of the 1.5-mm-thick clasp was smaller than that of the1.0-mm-thick clasp. The measured range of precision of PEEK clasps was 0.079 to 0.152 mm, while that of CP Ti clasps was 0.036 to 0.096 mm. CP Ti clasps tended to have better precision than PEEK clasps, except for the 1.0-mm-thick clasps with a length greater than 9 mm and the 1.5-mm-thick clasp with a 12-mm length. The correlation of the clasp length with precision showed that the lengths of 1.0-mm-thick clasps strongly influenced precision (PEEK, P=.020; CP Ti, P<.001); this correlation decreased sharply when the thickness of clasps was 1.5 mm (PEEK, P=.199; CP Ti, P=.107). CONCLUSIONS: Greater elasticity increased the deviations of milled clasps. The increased thickness helped the clasp remain stable during the milling process. The 1.5-mm-thick PEEK clasps in the 3-mm and 6-mm lengths were the optimal design tested.