Congruence between the meshes of a combined healing abutment-scan body system acquired with four different intraoral scanners and the corresponding library file: an in vitro analysis

Influence of different scan body design features and intraoral scanners on the congruence between scan body meshes and library files: An in vitro study

STATEMENT OF PROBLEM

Implant scan bodies (ISBs) present with a variety of features, including diverse design geometries and manufacturing materials. How these features influence the congruence between the clinically obtained mesh file and the software-based library file of the scan body during the alignment stage within the computer-aided design (CAD) software program is unclear. It is also uncertain how these features influence the scanning accuracy of different scanners.

PURPOSE

The purpose of this in vitro study was to investigate how various scan body shapes manufactured from different materials influence the scanning accuracy of 6 intraoral scanners (IOSs) and 1 desktop scanner.

MATERIAL AND METHODS

A 3-dimensionally (3D) printed cast fitted with 4 different implant analogs and their corresponding scan bodies (Straumann Cares RN Mono; Straumann, MIS V3 SP; MIS, Paltop SP; Paltop and TV70; TRI) was scanned using 6 intraoral scanners (Primescan; Dentsply Sirona, TRIOS 3; 3Shape A/S, TRIOS 5; 3Shape A/S, Medit i-700; Medit, Fussen S6000; Fussen, and Runyes 3DS; Runyes) and 1 desktop scanner (7series; Dental Wings). A metrology mesh comparison software program was used for analysis. Inferences were drawn using a univariate repeated measures 2-way ANOVA. Post hoc analysis was conducted with pairwise Bonferroni tests (α=.05).

RESULTS

A significant 2-way interaction was found between scanner model and scan body model, (F [5.518, 49.659]=36.251, P<.001). The mean absolute deviation for the different scanners ranged between 21 µm and 35 µm across all scan bodies, but the model of the scan body influenced the deviation of the scanner. The mean absolute deviation for the different scan bodies ranged from 19 µm to 46 µm across all scanners, but the model of the scanner influenced the deviation of the scan body.

CONCLUSIONS

Regarding implant scan body features, a design with a less complex shape and fewer sharp line angles and a design with a cylindrical shape exhibited statistically significantly higher congruence between the clinical mesh and the software library files. Regarding intraoral scanners, Primescan had a statistically significantly lower mean absolute deviation compared with that of the other scanners across all scan bodies tested.

Positional accuracy of a single implant analog in additively manufactured casts in biobased model resin

OBJECTIVES

To evaluate the positional accuracy of implant analogs in biobased model resin by comparing them to that of implant analogs in model resin casts and conventional analogs in dental stone casts.

METHODS

Polyvinylsiloxane impressions of a partially edentulous mandibular model with a single implant were made and poured in type IV dental stone. The same model was also digitized with an intraoral scanner and additively manufactured implant casts were fabricated in biobased model resin (FotoDent biobased model) and model resin (FotoDent model 2 beige-opaque) (n = 8). All casts and the model were digitized with a laboratory scanner, and the scan files were imported into a 3-dimensional analysis software (Geomagic Control X). The linear deviations of 2 standardized points on the scan body used during digitization were automatically calculated on x-, y-, and z-axes. Average deviations were used to define precision, and 1-way analysis of variance and Tukey HSD tests were used for statistical analyses (α = 0.05).

RESULTS

Biobased model resin led to higher deviations than dental stone (all axes, P ≤ 0.031) and model resin (y-axis, P = 0.015). Biobased model resin resulted in the lowest precision of implant analog position (P ≤ 0.049). The difference in the positional accuracy of implant analogs of model resin and stone casts was nonsignificant (P ≥ 0.196).

CONCLUSIONS

Implant analogs in biobased model resin casts mostly had lower positional accuracy, whereas those in model resin and stone casts had similar positional accuracy. Regardless of the material, analogs deviated more towards mesial, while buccal deviations in additively manufactured casts and lingual deviations in stone casts were more prominent.

Influence of Repeated Cut-off and Rescanning on the Trueness of the Intraoral Digital Scans

OBJECTIVES

To evaluate the effects of repeated cut-off and rescan procedures on the trueness of three intraoral scanners (IOS).

METHODS

A tooth model (#16) with a standard class II cavity was prepared, and the complete-arch was scanned using a laboratory scanner (D2000, 3Shape A/S) to obtain a reference scan. Then the typodont was scanned with three IOSs (3Shape TRIOS 3, CEREC Omnicam, and Medit i500) under two rescanning strategies (full-cut and partial-cut), with varying numbers of repeated cut-off and rescanning procedures (0, 1, 3, 5, 7, or 10). The trueness discrepancy between the reference and experimental digital scan was estimated using root mean square (RMS) calculations. Three regions of interest were selected to represent the rescanning, identification, and non-rescan area. And the discrepancies were analyzed using a linear mixed model (α=.05).

RESULTS

Cut-off and rescanning procedures significantly decreased the trueness of digital scans in all test conditions compared to the reference. However, no progressive increase in discrepancy was observed under any rescan conditions. Significant influences on trueness were found based on the IOS used, with the 3Shape system exhibiting lower RMS values. The partial-cut strategy showed lower RMS values compared to the full-cut strategy, albeit without statistical significance.

CONCLUSIONS

While repeated cut-off and rescanning procedures led to a decline in the quality of digital impressions, they did not result in discrepancy accumulation with repeated rescanning.

CLINICAL SIGNIFICANCE

To ensure high scanning accuracy in dental practice, it is advisable to minimize the rescanning area when correcting imperfections in digital scans. Additionally, selecting an appropriate scanner can help mitigate the negative effects of the rescanning technique.

Scan accuracy and time efficiency of different implant-supported fixed partial denture situations depending on the intraoral scanner and scanned area: An in vitro study

STATEMENT OF PROBLEM

The type of intraoral scanner (IOS), region of the implant, and extent of the scanned area have been reported to affect scan accuracy. However, knowledge of the accuracy of IOSs is scarce when digitizing different partially edentulous situations either with complete or partial arch scans.

PURPOSE

The purpose of this in vitro study was to investigate the scan accuracy and time efficiency of complete and partial arch scans of different partially edentulous situations with 2 implants and 2 different IOSs.

MATERIAL AND METHODS

Three maxillary models with implant spaces at the lateral incisor sites (anterior 4-unit), right first premolar and right first molar sites (posterior 3-unit), or right canine and right first molar sites (posterior 4-unit) were fabricated. After placing implants (Straumann S RN) and scan bodies (CARES Mono Scanbody), models were digitized by using an optical scanner (ATOS Capsule 200MV120) to generate reference standard tessellation language (STL) files. Complete or partial arch scans (test scans) of each model were then performed by using 2 IOSs (Primescan [PS] and TRIOS 3 [T3]) (n=14). The duration of the scans and the time needed to postprocess the STL file until the design could be started were also recorded. A metrology-grade analysis software program (GOM Inspect 2018) was used to superimpose test scan STLs over the reference STL to calculate 3D distance, interimplant distance, and angular (mesiodistal and buccopalatal) deviations. Nonparametric 2-way analysis of variance followed by Mann-Whitney tests with Holm correction were used for trueness, precision, and time efficiency analyses (α=.05).

RESULTS

The interaction between IOSs and scanned area only affected the precision of the scans when angular deviation data were considered (P≤.002). Trueness of the scans was affected by IOSs when 3D distance, interimplant distance, and mesiodistal angular deviations were considered. The scanned area affected only 3D distance deviations (P≤.006). IOSs and scanned area significantly affected the precision of scans when 3D distance, interimplant distance, and mesiodistal angular deviations were considered, while only IOSs significantly affected buccopalatal angular deviations (P≤.040). Scans from PS had higher accuracy when 3D distance deviations were considered for the anterior 4-unit and posterior 3-unit models (P≤.030), when interimplant distance deviations were considered for complete arch scans of the posterior 3-unit model (P≤.048), and when mesiodistal angular deviations were considered in the posterior 3-unit model (P≤.050). Partial arch scans had higher accuracy when 3D distance deviations of the posterior 3-unit model were considered (P≤.002). PS had higher time efficiency regardless of the model and scanned area (P≤.010), while partial arch scans had higher time efficiency when scanning the posterior 3-unit and posterior 4-unit models with PS and the posterior 3-unit model with T3 (P≤.050).

CONCLUSIONS

Partial arch scans with PS had similar or better accuracy and time efficiency than other tested scanned area-scanner pairs in tested partial edentulism situations.

Fabrication trueness and internal fit of different lithium disilicate ceramics according to post-milling firing and material type

OBJECTIVES

To evaluate whether post-milling firing and material type affect the fabrication trueness and internal fit of lithium disilicate crowns.

METHODS

A prefabricated cobalt chromium abutment was digitized to design a mandibular right first molar crown. This design file was used to fabricate crowns from different lithium disilicate ceramics (nano-lithium disilicate (AM), fully crystallized lithium disilicate (IN), advanced lithium disilicate (TS), and lithium disilicate (EX)) (n = 10). Crowns, the abutment, and the crowns when seated on the abutment were digitized by using an intraoral scanner. Fabrication trueness was assessed by using the root mean square method, while the internal fit was evaluated according to the triple scan method. These processes were repeated after the post-milling firing of AM, TS, and EX. Paired samples t-tests were used to analyze the effect of post-milling firing within AM, TS, and EX, while all materials were compared with 1-way analysis of variance and Tukey HSD tests (α = 0.05).

RESULTS

Post-milling firing reduced the surface deviations and internal gap of AM and EX (P ≤ 0.014). AM mostly had higher deviations and internal gaps than other materials (P ≤ 0.030).

CONCLUSIONS

Post-milling firing increased the trueness and internal fit of tested nano-lithium disilicate and lithium disilicate ceramics. Nano-lithium disilicate mostly had lower trueness and higher internal gap; however, the maximum meaningful differences among tested materials were small. Therefore, the adjustment duration and clinical fit of tested crowns may be similar.

CLINICAL SIGNIFICANCE

Tested lithium disilicate ceramics may be suitable alternatives to one another in terms of fabrication trueness and internal fit, considering the small differences in measured deviations and internal gaps.

Single posterior implant-supported restorations fabricated using a scannable healing abutment versus a conventional scan body: A randomized controlled trial

STATEMENT OF PROBLEM

The use of a scannable healing abutment is a convenient option for fabricating implant-supported restorations (ISRs) with a digital workflow; however, clinical studies evaluating prosthetic efficacy are lacking.

PURPOSE

The purpose of this randomized controlled trial was to investigate the prosthetic efficacy of definitive posterior single ISRs fabricated after scanning using a scannable healing abutment-scan peg (SHA-SP) in comparison with a conventional scan body (CSB). The time for data acquisition, quality of proximal and occlusal contacts, and relative occlusal force of ISRs were measured.

MATERIAL AND METHODS

Twenty-four participants eligible for single ISRs to replace the mandibular first molar with adjacent and antagonist teeth present were randomly allocated to either a study group (n=12) receiving ISRs after intraoral scanning using an SHA-SP or a control group (n=12) receiving ISRs after intraoral scanning using CSB. During the surgical procedure, a prefabricated contoured scannable healing abutment was screwed to the implant in the SHA-SP group, while a custom-made healing abutment was used in the CSB group. After a healing period of 3 months, an intraoral scan was made, and the duration of data acquisition was recorded. The ISRs were milled from zirconia and evaluated for the quality of proximal and occlusal contacts using dental floss and shim stock, respectively. The relative occlusal forces of the ISRs and their contralateral natural teeth were measured using a digital occlusal analyzer. Statistical analysis was done using an independent sample t test for quantitative variables and a Pearson chi-squared test for qualitative variables between the tested groups (α=.05).

RESULTS

The direct digital workflow using SHA-SP was statistically less time consuming than the CSB (P<.001). The 2 groups were statistically similar regarding the quality of the proximal contacts (P=.281) or occlusal contacts (P=.307) and the relative occlusal forces of ISRs (P=.315). The relative occlusal forces of the ISRs in both groups were significantly lower than those of their contralateral natural teeth (P<.001).

CONCLUSIONS

Direct digital workflow using SHA-SP was more rapid, saving clinical chairside time, and produced proximal and occlusal contacts of comparable quality with those obtained with CSB. The relative occlusal forces of ISRs in both workflows were lower than their contralateral natural teeth.

Influence of implant scan body design (height, diameter, geometry, material, and retention system) on intraoral scanning accuracy: A systematic review

PURPOSE

To evaluate the influence of implant scan body (ISB) design (height, diameter, geometry, material, and retention system) on the accuracy of digital implant scans.

MATERIAL AND METHODS

A literature search was completed in five databases: PubMed/Medline, Scopus, Embase, World of Science, and Cochrane. A manual search was also conducted. Studies reporting the evaluation of ISB design on the accuracy of digital scans obtained by using IOSs were included. Two investigators evaluated the studies independently by applying the Joanna Briggs Institute critical appraisal. A third examiner was consulted to resolve any lack of consensus. Articles were classified based on the ISB features of height, geometry, material, and retention system.

RESULTS

Twenty articles were included. Among the reviewed studies, 11 investigations analyzed the influence of different ISB geometries, 1 study assessed the impact of ISB diameter, 4 studies investigated the effect of ISB splinting, 2 articles evaluated ISB height, and 2 studies focused on the effect of ISB material on scan accuracy. In addition, 8 studies involved ISBs fabricated with different materials (1- and 2-piece polyetheretherketone and 1-piece titanium ISBs), and all of the reviewed articles tested screw-retained ISBs, except for 3 in vitro studies.

CONCLUSIONS

The findings did not enable concrete conclusions regarding the optimal ISB design, whether there is a relationship between IOS technology and a specific ISB design, or the clinical condition that maximizes intraoral scanning accuracy. Research efforts are needed to identify the optimal ISB design and its possible relationship with the IOS selected for acquiring intraoral digital implant scans.

Trueness and precision of combined healing abutment scan body system scans at different sites of maxilla after multiple repositioning of the scan body

OBJECTIVES

To evaluate the accuracy of the scans of the combined healing abutment-scan body (CHA-SB) system located at different sites of the maxilla when SBs are replaced in between each scan.

METHODS

Three SBs were seated into HAs located at the central incisor, first premolar, and first molar sites of a maxillary model inside a phantom head, and the model was scanned extraorally (CEREC Primescan SW 5.2). This procedure was repeated with new SBs until a total of 10 scans were performed. Standard tessellation language files of CHA-SBs at each implant location were isolated, transferred into analysis software (Geomagic Control X), and superimposed over the proprietary library files to analyze surface (root mean square), linear, and angular deviations. Trueness and precision were evaluated with one-way analysis of variance and Tukey tests. The correlation between surface and angular deviations was analyzed with Pearson's correlation (α=0.05).

RESULTS

Molar implant scans had the highest surface and angular deviations (P≤.006), while central incisor implant scans had higher precision (surface deviations) than premolar implant scans (P=.041). Premolar implant scans had higher accuracy than central incisor implant scans on the y-axis (P≤.029). Central incisor implant scans had the highest accuracy on the z-axis (P≤.018). A strong positive correlation was observed between surface and angular deviations (r = 0.864, P<.001).

CONCLUSION

Central incisor implant scans mostly had high accuracy and molar implant scans mostly had lower trueness. SBs were mostly positioned apically; however, the effect of SB replacement can be considered small as measured deviations were similar to those in previous studies and the precision of scans was high.

CLINICAL SIGNIFICANCE

Repositioning of scan bodies into healing abutments would be expected to result in similar single crown positioning regardless of the location of the implant, considering high scan precision with the healing abutment-scan body system. The duration of the chairside adjustments of crowns in the posterior maxilla may be longer than those in the anterior region.

Effect of scanning strategies on the accuracy of digital intraoral scanners: a meta-analysis of in vitro studies

PURPOSE

This study aimed to investigate whether the accuracy of intraoral scanners is influenced by different scanning strategies in an in vitro setting, through a systematic review and meta-analysis.

MATERIALS AND METHODS

This review was conducted in accordance with the PRISMA 2020 standard. The following PICOS approach was used: population, tooth impressions; intervention, the use of intraoral scanners with scanning strategies different from the manufacturer's instructions; control, the use of intraoral scanners following the manufacturers' requirements; outcome, accuracy of intraoral scanners; type of studies, in vitro. A comprehensive literature search was conducted across various databases including Embase, SciELO, PubMed, Scopus, and Web of Science. The inclusion criteria were based on in vitro studies that reported the accuracy of digital impressions using intraoral scanners. Analysis was performed using Review Manager software (version 5.3.5; Cochrane Collaboration, Copenhagen, Denmark). Global comparisons were made using a standardized mean difference based on random-effect models, with a significance level of α = 0.05.

RESULTS

The meta-analysis included 15 articles. Digital impression accuracy significantly improved under dry conditions (P < 0.001). Moreover, trueness and precision were enhanced when artificial landmarks were used (P ≤ 0.02) and when an S-shaped pattern was followed (P ≤ 0.01). However, the type of light used did not have a significant impact on the accuracy of the digital intraoral scanners (P ≥ 0.16).

CONCLUSION

The accuracy of digital intraoral scanners can be enhanced by employing scanning processes using artificial landmarks and digital impressions under dry conditions.

Comparison of intraoral and laboratory scanners to an industrial-grade scanner while analyzing the fabrication trueness of polymer and titanium complete-arch implant-supported frameworks

OBJECTIVES

To compare the scans of different intraoral scanners (IOSs) and laboratory scanners (LBSs) to those of an industrial-grade optical scanner by measuring deviations of complete-arch implant-supported frameworks from their virtual design file.

MATERIAL AND METHODS

Ten polyetheretherketone (PEEK) and 10 titanium (Ti) complete-arch implant-supported frameworks were milled from a master standard tessellation language (STL) file. An industrial-grade blue light scanner (AT), 2 LBSs (MT and E4), and 3 IOSs (PS, T3, and T4) were used to generate STL files of these frameworks. All STLs were imported into an analysis software (Geomagic Control X) and overall root mean square (RMS) values were calculated. Marginal surfaces of all STL files were then virtually isolated (Medit Link v 2.4.4) and marginal RMS values were calculated. Deviations in scans of tested scanners were compared with those in scans of AT by using a linear mixed effects model (α = 0.05).

RESULTS

When the scans of PEEK frameworks were considered, PS and T3 had similar overall RMS to those of AT (p ≥ .076). However, E4 and T4 had higher and MT had lower overall RMS than AT (p ≤ .002) with a maximum estimated mean difference of 13.41 µm. When the scans of Ti frameworks were considered, AT had significantly lower overall RMS than tested scanners (p ≤ .010) with a maximum estimated mean difference of 31.35 µm. Scans of tested scanners led to significantly higher marginal RMS than scans of AT (p ≤ .006) with a maximum estimated mean difference of 53.90 µm for PEEK and 40.50 µm for Ti frameworks.

CONCLUSION

Only the PEEK framework scans of PS and T3 led to similar overall deviations to those of AT. However, scans of all tested scanners resulted in higher marginal deviations than those of AT scans.

CLINICAL SIGNIFICANCE

Scans performed by using PS and T3 may be alternatives to those of tested reference industrial scanner AT, for the overall fabrication trueness analysis of complete-arch implant-supported PEEK frameworks.

Positional transfer accuracy of titanium base implant abutment provided by two different scan body designs: an invitro study

BACKGROUND

The variabilities in design and material of scan bodies have a major role in the positional transfer accuracy of implants. The purpose of this invitro study was to compare the 3D transfer accuracy (trueness and precision) of titanium base (TB) abutment position provided by 2 different scan bodies: one-piece scan body (SB) in comparison to two-piece healing abutment and scan peg (HA-SP).

METHODS

A maxillary model with a dummy implant in the 2nd premolar (Proactive Tapered Implant; Neoss) was 3D printed and TB (Ti Neolink Mono; Neoss) was tightened on the implant and scanned by using a laboratory scanner (inEos X5; Dentsply Sirona) (reference scan). An SB (Elos Medtech) and an HA-SP (Neoss) were subsequently connected to the implant and were scanned 10 times each by using the same scanner (test scans). All the scans were exported as STL files and imported into CAD software where the TBs were formed. Test scans were superimposed on reference scans for transfer accuracy analysis using 3D metrology software (GOM Inspect; GOM GmbH) in terms of angular deviation in vertical and horizontal directions, linear deviation in each XYZ axis of TBs and total linear deviation in all axes. Statistical analysis was done using independent sample t test. When Levene's test for equality of variances was significant, Welch's t-test was used. (P value < 0.05) RESULTS: Significant differences were found amongst the tested groups in both angular and linear deviation in terms of trueness with less deviation values for the SB group (P < 0.001). For the precision, significant differences were found amongst the tested groups in angular deviation in vertical direction with less deviation value for the SB group compared to HA-SP group (P < 0.001). However, no significant difference was found between the tested groups regarding the angular deviation in horizontal direction (P = 1.000). Moreover, significant differences were found amongst the tested groups in linear deviations with less linear deviations in XYZ axes for SB compared to HA-SP group (P = 0.020, < 0.001, = 0.010 respectively).

CONCLUSIONS

SB showed less angular and linear deviation values in the 3D positional transfer of TB than HA-SP indicating higher degree of accuracy of SB.

Fabrication trueness and internal fit of hybrid abutment crowns fabricated by using additively and subtractively manufactured resins

OBJECTIVES

To evaluate the fabrication trueness and internal fit of hybrid abutment crowns fabricated by using additively and subtractively manufactured restorative materials.

METHODS

A maxillary first premolar crown with a screw access channel was designed onto a digitized master titanium base abutment. This file was used to fabricate 40 crowns additively (Crowntec (CT) and VarseoSmile Crown Plus (VS)) or subtractively (Brilliant Crios (BC) and Vita Enamic (EN)) (n = 10). Crowns were digitized with an intraoral scanner and root mean square method was used to evaluate fabrication trueness. Master abutment and the crowns when seated on the abutment were also digitized with the same intraoral scanner and triple scan method was used to evaluate internal fit. Data were analyzed either with 1-way ANOVA (surface deviations) or Kruskal-Wallis (internal fit) tests (α= 0.05).

RESULTS

CT had the highest overall, external, and marginal surface deviations (P≤.030), whereas BC had the lowest external (P≤.001) and VS and EN had the lowest marginal surface deviations (P≤.007). BC had the highest intaglio surface deviations (P<.001). BC and EN had higher average gap values CT and VS (P≤.006); however, the differences within additively and subtractively manufactured materials were nonsignificant (P≥.858).

CONCLUSIONS

One of the tested additively manufactured resins (CT) resulted in mostly lower trueness than that of other materials. However, deviations at the intaglio and marginal surfaces were generally small and the maximum mean difference among test groups when average gap was considered was 17.4 µm. Therefore, clinical fit of hybrid abutment crowns fabricated with tested materials may be similar.

Effect of number of supports and build angle on the fabrication and internal fit accuracy of additively manufactured definitive resin-ceramic hybrid crowns

OBJECTIVES

To evaluate the effect of number of supports and build angle on the fabrication and internal fit accuracy (trueness and precision) of additively manufactured resin-ceramic hybrid crowns.

METHODS

A mandibular first molar crown was designed and nested on the build platform of a printer either with a 30° angle between the occlusal surface and the build platform (BLS (less support) and BMS (more support)) or its occlusal surface parallel to the build platform (VLS (less support) and VMS (more support)) to fabricate additively manufactured resin-ceramic hybrid crowns (n=14). After fabrication, supports were removed by a blinded operator and all crowns were digitized with an intraoral scanner. Fabrication accuracy (overall, external, intaglio occlusal, occlusal, and marginal) was evaluated by using root mean square (RMS) method, while internal fit was evaluated with triple scan method. RMS, average gap, and precision of these data were analyzed (α= .05).

RESULTS

VLS had higher overall deviations than BLS and VMS (P≤.039). VMS had higher occlusal deviations than BLS (P=.033). While BMS and BLS had higher marginal deviations than VLS (P≤.006), BMS also had higher values than VMS (P=.012). BLS led to higher precision than VMS (intaglio occlusal and occlusal surfaces) and VLS (occlusal surface) (P≤.008). VLS led to higher precision than BMS (marginal surface) (P=.027). Average gap values were similar (P=.723); however, BLS resulted in higher precision than VLS (P=.018).

CONCLUSIONS

Considering their high marginal and occlusal surface trueness, and similar internal occlusal deviations and average gaps (trueness), clinical fit of resin-ceramic hybrid crowns fabricated with tested parameters may be similar. Reduced number of supports and angled orientation may lead to higher precision of fit.

CLINICAL SIGNIFICANCE

Tested resin-ceramic hybrid-printer pair may be used to fabricate crowns with reduced number of supports to maintain occlusal surface integrity without compromising the fabrication accuracy and fit.

Effect of material type, torque value, and sterilization on linear displacements of a scan body: An in vitro study

BACKGROUND

There is limited knowledge on the effect of scan body (SB) material type, torque value, and sterilization on linear displacements of implant SBs.

PURPOSE

To evaluate the effect of material type, torque value, and sterilization on linear displacements of SBs during screw tightening by using digital image correlation (DIC) analysis.

MATERIALS AND METHODS

One polyetheretherketone (PEEK, Zfx Intraoral Scan Body) and one titanium SB (Ti, MPS Zimmer Scanbody R1410) were tightened with 5 Ncm torque on two implants (Zimmer TSV ⌀4.7 mm) by using a digital torque limiting device. SBs' initial spatial positions relative to the implants were recorded by using 3D DIC technique. Measurements were repeated after initially increasing torque value to 10 Ncm and then to 15 Ncm, and these steps were repeated for a total of 10 PEEK and 10 Ti SBs on both implants (n = 20). All SBs were then sterilized 25 times by using an autoclave (STATIM 5000 S G4) according to manufacturer's recommendations and all measurements were repeated. Linear displacements on three axes were calculated for each SB with increasing torque values (from 5 to 10 Ncm and from 10 to 15 Ncm) before and after sterilization. SB displacements within each torque value-sterilization pair were compared by using Mann-Whitney U test, whereas Wilcoxon signed-rank test was used to compare SB displacements within each material-torque value pair between conditions and within each material-sterilization pair between torque values (α = 0.05).

RESULTS

On x-axis, PEEK SBs had higher displacements than Ti SBs (p < 0.001), whereas sterilization (p ≤ 0.028) and 15 Ncm torque application (p ≤ 0.006) led to higher displacements of PEEK SBs. On y-axis, PEEK SBs had higher displacements than Ti SBs with 15 Ncm torque application (p ≤ 0.033). A total of 15 Ncm torque-applied PEEK SBs and 10 Ncm torque-applied Ti SBs had higher displacements after sterilization (p ≤ 0.028). Application of 15 Ncm torque led to higher displacements regardless of the material (p ≤ 0.002). On z-axis, PEEK SBs had higher displacements (p ≤ 0.015), except for 10 Ncm torque-applied sterilized SBs (p = 0.102). With 10 Ncm torque application, sterilization decreased the displacement values of PEEK SBs (p = 0.044). Greater displacements were observed with 10 Ncm torque-applied Ti SBs before sterilization and 15 Ncm torque-applied PEEK SBs after sterilization (p ≤ 0.033).

CONCLUSIONS

Axial displacement of SBs was affected by material type, torque value, and sterilization. Ti SBs mostly had lower displacements than PEEK SBs. Application of 15 Ncm torque to tested PEEK SBs should be refrained from and a calibrated tightening tool may enable the application of 10 Ncm or lower torque values for lower displacements. Sterilization generally increased PEEK SB displacements.

Error analysis of stages involved in CBCT-guided implant placement with surgical guides when different printing technologies are used

STATEMENT OF PROBLEM

Digital light processing (DLP), continuous liquid interface printing (CLIP), and stereolithography (SLA) technologies enable 3-dimensional (3D) printing of surgical guides. However, how their accuracy compares and how accuracy may affect subsequent steps in guided surgery is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the fabrication and seating accuracy of surgical guides printed by using DLP, SLA, and CLIP technologies and evaluate the positional deviation of the osteotomy site and placed implant compared with the digital implant plan.

MATERIAL AND METHODS

Twenty-one polyurethane models were divided into 3 groups and used to plan implants and design surgical guides. The guides were fabricated by using DLP, SLA, or CLIP 3D printers (n=7) and scanned, and the scan file was compared with the digital design file to analyze the fabrication accuracy at the intaglio and overall external surfaces using root mean square (RMS) values. The triple scan protocol was used to evaluate the seating accuracy of the guides on their respective models. Osteotomies were prepared on models by using the guides followed by a microcomputed tomography image of each osteotomy. The implants were placed through the guides, the scan bodies were tightened to implants, and the models were scanned to obtain the images of placed implant position. Osteotomy and placed implant images were used to calculate the entry point, apex, and long axis deviations from the planned implant position with a software program. A 2-way repeated-measures ANOVA of the RMS data was used to analyze printing and seating trueness, and homogeneity of variance analyses were used at each surface for precision. A 3-way repeated-measures ANOVA was used to analyze distance deviations over the stages (osteotomy and final implant) and locations studied, and a 2-way repeated-measures ANOVA was used for angular deviations. Homogeneity of variance analyses were performed for precision (α=.05).

RESULTS

The 3D printer type significantly affected the trueness of the guide at the intaglio surface (P<.001). SLA guides had the lowest mean RMS (59.04 μm) for intaglio surface, while CLIP had the highest mean RMS (117.14 μm). Guides from all 3D printers had low variability among measured deviations and therefore were similarly precise. The seating accuracy of SLA and DLP guides was not significantly different, but both had lower mean RMS values than CLIP (P=.003 for SLA, P=.014 for DLP). There were no significant interactions between the stage of surgery, the printer type, or the location of implant deviation (P=.734). Only the location of deviation (cervical versus apical) had a significant effect on distance deviations (P<.001). The printer type, stage of surgery, and their interaction did not significantly affect angular deviations (P=.41).

CONCLUSIONS

The 3D printing technology affected printing trueness. The intaglio surface trueness was higher with SLA and overall trueness was higher with the CLIP printer. The precision of all guides was similarly high. Guides from SLA and DLP printers had more accurate seating than those from CLIP. Higher deviations were observed at the apex; however, osteotomy and final implant position did not significantly differ from the digitally planned position.

In vitro scan accuracy and time efficiency in various implant-supported fixed partial denture situations

OBJECTIVES

To compare the accuracy and time efficiency of different digital workflows in 3 implant-supported fixed partial denture situations.

METHODS

Three partially edentulous maxillary models with 2 implants (Model 1: implants at lateral incisor sites; Model 2: implants at right canine and first molar sites; Model 3: implants at right first premolar and first molar sites) were digitized (ATOS Capsule 200MV120, n=1) for reference scans. Test scans were performed for direct (Primescan (DDW-P) and Trios 3 (DDW-T)) and indirect (IDW) digital workflows (n=14). For IDW, stone casts (type IV) were obtained from vinylsiloxanether impressions and digitized (S600 Arti). The scan/impression and post processing times were recorded. Reference and test scans were superimposed (GOM Inspect) to calculate 3D point, inter-implant distance, and angular deviations. Kruskal-Wallis and Mann-Whitney tests were used for trueness and precision analyses (α=.05).

RESULTS

Tested workflows affected trueness (P≤.030) and precision (P<.001) of scans (3D point, inter-implant distance, and angular deviations) within models. DDW-P had the highest accuracy (3D point deviations) for models 1 and 3 (P≤.046). IDW had the lowest accuracy for model 2 (P<.01). DDW-P had the highest accuracy (inter-implant distance deviations) for model 3 (P≤.048). Direct digital workflow mostly led to lower angular deviations (P≤.040), and higher precision for models 2 (mesiodistal direction) and 3 (P<.001). The time for direct digital workflow was shorter (P<.001), DDW-P being more efficient than DDW-T (P=.008).

CONCLUSION

Direct digital workflow was more accurate and efficient than indirect digital workflow in tested partial edentulism situations with 2 implants.

CLINICAL SIGNIFICANCE

Tested intraoral scanners can be recommended for accurate and efficient impressions of anterior and posterior 3- or 4-unit implant-supported fixed partial dentures.

Trueness and precision of combined healing abutment-scan body system depending on the scan pattern and implant location: an in-vitro study

OBJECTIVE

To test the effect of scan pattern and the location of the implant on the trueness and precision of implant scans when the combined healing abutment-scan body (CHA-SB) system is used.

MATERIAL AND METHODS

A partially edentulous maxillary model with CHA-SBs secured on implants at 3 different sites in the left quadrant (central incisor, first premolar, and first molar) was fabricated. The model was scanned with an industrial light scanner to generate a master reference model (MRM) file. An intraoral scanner (TRIOS 3) was used to perform the test scans (n=8) with 4 different scan patterns (SP1, SP2, SP3, and SP4) with an intraoral scanner. The test scans were superimposed over the MRM file with a metrology software to calculate the distance deviations of the CHA-SB system. Data were analyzed with a 2-way analysis of variance and Tukey's honestly significant difference tests for accuracy (α=.05).

RESULTS

Trueness (P=.001) and precision (P=.018) were significantly affected by the interaction between the scan pattern and implant location. The implant located at the central incisor site (56.7 ±35.9, 36.2 ±18.6) had higher trueness than that of located at the premolar site (94.1 ±20.4, 100.3 ±20) when SP2 (P=.037) and SP4 (P=.002) were used. The implant at the molar site (71.9 ±25.7, 147.2 ±49.7) had trueness either similar to (when SP2 was used, P≥.276) or lower than (when SP4 was used, P≤.024) those of others. Scans of the central incisor and premolar implants had the lowest trueness when scanned with SP1 (P≤.009), while the scans of molar implant showed higher trueness when performed by using SP2 and SP3 when compared with SP4 (P≤.005). When SP4 was used, the implant at the molar site had lower precision (43 ±18.9) than the implants located at the central incisor (14.1 ±11) and premolar sites (15.4 ±11.3) (P=.002). Scan patterns affected the scan precision of central incisor implant (P=.009), as SP4 (14.1 ±11) led to a higher precision than SP1 (47.7 ±27) (P=.006).

CONCLUSIONS

The scan accuracy of combined healing abutment-scan body system was affected by scan pattern and implant location. SP1, which involved palatal and rotational scans resulted in the lowest trueness for central incisor and premolar implants, while the scans of the central incisor implant showed the highest trueness among different sites when SP4 was used. However, the scan pattern and implant site had a minor effect on precision. Scan precision at different implant sites only differed when SP4 was used, which resulted in the lowest precision for molar implant.