Screw Access Channel Research Articles

Zirconia full-arch implant prostheses: Survival, complications, and prosthetic space dimensions with 115 edentulous jaws.

To assess the survival and complication rates of 115 monolithic zirconia implant-supported fixed complete dental prostheses (IFCDPs) with an up to 6-year follow-up. One hundred fifteen edentulous jaws (71 patients) underwent complete-arch implant treatment with a digital workflow and were rehabilitated with monolithic zirconia IFCDPs. The primary outcome was to assess survival and complication rates while the secondary outcome was to measure the cross-sectional dimensions (prosthetic space) of those 115 monolithic zirconia IFCDPs and to correlate potential technical complications with the prosthetic space dimensions. Out of the 115 zirconia IFCDPs, 2 fractured, yielding a 98.6% survival rate up to a 6-year follow-up. The most commom minor technical complications were loss of screw access channel filling and porcelain chipping for the modified monolithic IFCDPs. There was no significant association between the count and type of complications and jaw location (maxilla vs. mandible) or prosthesis type (FP1 vs. FP3), according to Fisher's exact test. For maxillary zirconia IFCDPs, the mean square surface for the at the posterior abutment cross-sectional area was 25.18mm2 at the lingual side of the abutment and 34.19mm2 at the buccal side, respectively. The anterior abutment cross-sectional area was 33.92mm2 at the lingual side of the abutment and 29.49mm2 at the buccal side, respectively. For mandibular zirconia IFCDPs, the mean square surface at the posterior abutment cross-sectional area was 29.89 mm2 at the lingual side of the abutment and 39.05mm2 at the buccal side, respectively. The anterior abutment cross-sectional area was 27.07mm2 at the lingual side of the abutment and 56.50mm2 at the buccal side, respectively. At the connector cross-sectional area, the mean square surface for the maxillary zirconia IFCDPs was 64.33 and 90.56mm2 for the mandibular zirconia IFCDPs. The two fractures occurred in the midline (anterior area) for both maxillary FP1 prosthesis and mandibular FP3 prosthesis. The mean surface area at the connector for the maxillary FP1 prosthesis was 28.50 and 82.11mm2 for the mandibular FP3 prosthesis, and was within the range of IFCDP connector square surface area. There was no significant association between the thickness of the zirconia prosthesis and the encountered prosthesis fractures. Monolithic zirconia IFCDPs yielded a 98.6% survival rate, after a mean observation period of 62 months with an SE of 3.1. The connector mean surface area in the two fractured IFCDPs was within the square surface range (minimum-maximum) as for the remaining 113 complication-free IFCDPs.

Screw-retrievable cement-retained implant restorations: A scoping review of fracture strength and clinical performance.

The screw-retrievable cement-retained (SRCR) design combines the benefits of both screwand cement-retained implant-supported restorations. This concept has sparked interest in implant dentistry. However, there is a lack of research on fracture behaviors and clinical performance of such restorations. The aim of the present article was to review the current literature on the fracture loads and fracture modes of SRCR implant restorations - in vitro studies, and also studies demonstrating the clinical performance of such design. A literature search was conducted from January 2000 to June 2022, using 6 databases to identify studies on fracture load and clinical performance that fulfilled the eligibility criteria. Thirty-eight studies met the inclusion criteria (22 in vitro and16 in vivo). The in vivo studies comprised case reports/series/letters (9), clinical techniques (2), retrospective/prospective studies (3), and randomized controlled trials (RCTs) (2). The reviewed articles reported the effects of the SRCR design on the fracture risk if screw access channels were filled or unfilled, with regard to their diameter, and the preparation before or after glazing. The effect of the type of material used in the construction on the fracture modes SRCR restorations was also reported. The long-term clinical data was mainly retrospective and referred to metal-ceramic constructions. Limited long-term clinical data was available for all-ceramic materials and high-performance polymers (HPPs). Screw-retrievable cement-retained implant restorations appear to have potential in the monolithic design. If the SRCR construction is metal-ceramic or made of a veneered material, special design and abutment selection should be considered. High-performance polymers may be recommended as a substitute for posterior implant restoration.

Effect of the Diameter and Preparation Method of the Occlusal Screw Access Channel on Fracture Resistance of Cement-retained Implant-supported Posterior Monolithic Zirconia Crowns

Background: The favorable fracture resistance of implant-supported crowns is important. Zirconia crowns can be an acceptable treatment in relation to metal‒ceramic crowns for achieving the best clinical success. Objective: The present study evaluated the effect of the diameter and preparation method of the occlusal screw access channel on the fracture resistance of cement-retained implant-supported posterior monolithic zirconia crowns for their retrievability. Methods: Fifty-six implant-supported posterior multi-layer monolithic zirconia crowns were designed. Twenty pieces with an initial occlusal channel were designed with 2.3 and 3.5 mm diameters (n =10 each). In addition, 30 pieces with an intact occlusal surface as the control group or the crowns in which the occlusal channel was prepared with a bur were designed in 10 and 20 samples, respectively. Six additional crowns were also designed for SEM evaluations after their preparation with a bur. Results: The maximum fracture resistance value was recorded in the control group, followed by the initial access channel group with a 2.3 mm diameter. The minimum fracture resistance value was recorded in crowns with a 3.5-mm diameter hole prepared with a bur. The mean fracture strength in the groups with a 2.3 mm diameter was higher than in groups with a 3.5 mm diameter (P<0.05). Cracks in samples prepared with a bur were seen under SEM. Conclusion: This study showed that using an initial access hole with a diameter of 2.3 mm is the best choice in hybrid implant-supported crowns. However, when it is necessary to prepare an access hole with a bur, it should be done with the smallest possible diameter.

Effects of cyclic loading on loss of abutment screw torque of angled screw channel single implant crowns on narrow diameter implants

Statement of problemScrew access channels that emerge on the facial aspect of anterior screw-retained implant crowns can compromise esthetics. Recently, angled screw channels (ASCs) have been developed that can alter screw access channel angulations to improve esthetics. While ASCs can be used on narrow-diameter implants, information is limited on the loss of abutment screw torque on narrow-diameter implants with ASCs. PurposeThe purpose of this in vitro study was to compare the loss of abutment screw torque after thermocycling and the cyclic loading of ASCs from 3 different companies connected to narrow-diameter implants. Material and methodsA total of 40 narrow-diameter implants (NobelReplace Conical Connection 3.5×11.5 mm) were mounted individually in acrylic resin blocks and divided equally into 4 groups. The first group, NB-0 (Control), consisted of screw-retained zirconia crowns fabricated on ASCs at 0-degree angulation (n=10). The other 3 groups consisted of a total of 30 screw-retained zirconia crowns fabricated on ASCs at 20-degree angulation: NB-20 (Angulated Screw Channel Solutions), ATL-20 (Atlantis Custom Base Solution with angulated screw access), and DA-20 (Dynamic TiBase). Each crown was secured on the mounted implant with its corresponding titanium base insert and screw and then tightened to the manufacturer’s recommended torque with a digital torque gauge. The initial reverse torque value (RTVI) was obtained and recorded at baseline. Subsequently, a new set of screws were tightened to recommended values, and each specimen underwent thermocycling and then cyclic loading at 0 to 100 N at 10 Hz for 1 million cycles to simulate 1year of functional loading. After cyclic loading, the final reverse torque values (RTVF) were recorded and compared with the RTVI to evaluate the percentage torque loss (PTLF). Statistical analysis was performed using the Kruskal-Wallis analysis, Rank base analysis of covariance (ANCOVA), and the Tukey HSD post hoc comparisons (α=.05). ResultsSignificant differences were found for the PTLF among all groups after cyclic loading (P<.001). The PTLF in ATL-20 (51.4%) was significantly higher than in NB-0 (22.2%) (P<.001) and NB-20 (29.2%) (P=.010). No significant difference was found in the PTLF among other groups (P>.05). ConclusionsThe abutment screw torque loss after cyclic loading of the ASCs on narrow diameter implants among the 4 groups did not perform comparably. The largest percentage torque loss was recorded for the ATL-20 group. The NB-20 group demonstrated the lowest percentage torque loss. DA-20 showed percentage torque loss less than ATL-20; however, its RTVF was the lowest.

Effect of internal connection type and screw channel angle on the screw stability of anterior implant-supported zirconia crowns.

To investigate the effect of implant-abutment connection and screw channel angle on screw stability by comparing a newly introduced and an established connection, before and after cyclic loading. Implants (N = 44) with Torcfit (TF) or Crossfit (CF) connection were divided to be restored with a straight (CFS and TFS) or an angled screw access channel (CFA and TFA) titanium-base abutment (n = 11). CFA and TFA received screw-retained crowns, whereas CFS and TFS received hybrid zirconia abutments and cement-retained crowns. The initial torque value (ITV) of each complex (ITVI ) and removal torque value (RTV) after 24 h (RTVI ) were measured. Screws were replaced with new ones, ITVs were recorded again (ITVF ), and crowns were cyclically loaded (2.4 million cycles, 98 N) to measure RTVs again (RTVF ). Percentage torque loss was calculated. Data were analyzed (α = 0.05). ITVs were similar among groups (p ≥ .089). CF led to higher RTVs (p ≤ .002), while CFS had higher RTVI than CFA (p = .023). After 24 h, CFS had lower percentage torque loss than TF, while CFA had lower percentage torque loss than TFA (p ≤ .011). After cyclic loading, CF led to lower percentage torque (p < .001). The implant-abutment connection affected the removal torque values. However, no screw loosening occurred during cyclic loading, which indicated a stable connection for all groups. Screw access channel angle did not affect screw stability after cyclic loading.

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

ObjectivesTo evaluate the fabrication trueness and internal fit of hybrid abutment crowns fabricated by using additively and subtractively manufactured restorative materials. MethodsA 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). ResultsCT 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). ConclusionsOne 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.

Evaluation of the dislodgement force of splinted restorations with engaging conical abutments over multiple nonparallel implants (in-vitro study)

BackgroundSplinted multiunit cement-retained restorations with screw access channels over engaging abutments are viable implant prosthetic options. However, information regarding the maximum degree of divergence between multiple implants is lacking. The purpose of this in vitro study was to determine the maximum degree of divergence between 2 adjacent implants with conical connections that allows insertion and removal of splinted restorations with engaging preparable abutments or titanium base abutments.MethodsTwo implants were aligned in a stone base, one straight and the other at an angle ranging from 0 to 20 degrees. The implants represented an implant system that had an internal conical connection and a hexed abutment engaging the base of the connection. Two straight preparable engaging cement retained abutments were screwed onto the implants and splinted together using acrylic resin. A total of 11 angles were tested, with 7 specimens for every angle. Evaluation of dislodging force was performed by pulling out the splinted abutments after unscrewing them. This was performed subjectively by 3 blinded investigators who applied a tactile pulling force. A scale of 0–10 was used to estimate the pulling force. Objectively the dislodging force was measured in Newtons using a universal testing machine. A statistical correlation was made between the subjective and objective dislodging force values using Spearman’s rank correlation coefficient.ResultsThe mean subjective values increased gradually from 0 to 16 degrees. A sudden rise was noticed at 18 degrees (9.71 ± 0.23) and, at 20 degrees, the investigators were not able to remove the splinted abutments from the implants. The mean objective dislodgement force values increased gradually from 0 to16 degrees and abruptly from 16 degrees (13.57 ± 0.45 N) to 18 degrees (25.40 ± 0.66 N) and 20 degrees (35.22 ± 0.64). The correlation between the subjective and the objective evaluations assessed using the Spearman’s rank correlation coefficient was 0.98 indicating a statistically significant correlation (P < .001). As the objective dislodging force increased, the subjective dislodgement difficulty increased.ConclusionsSplinting cement retained restorations with screw access channels on engaging abutments is possible when multiple implants with conical connections having an internal flare angle of 8 degrees are used, with implant divergence of up to 16 degrees.

Application of 3D printed guide for locating screw access channels in cement-retained complete arch implant-supported zirconia restorations

Removal of cement-retained complete arch implant-supported zirconia restorations can be challenging. A predictable and minimally invasive technique combining cone beam computed tomography (CBCT) and intraoral scans with a virtual implant planning software program is described to identify the location of the screw access channels during the retrieval, thus minimizing damage to the existing restoration and allowing reuse.

Evaluation of debonding force of screw-retained lithium disilicate implant-supported crowns cemented to abutments of different designs and surface treatments

Statement of problemStraight preparable abutments provide an alternative to titanium bases (Ti-bases) for single-unit screw-retained implant-supported restorations. However, the debonding force between crowns with a screw access channel cemented to preparable abutments and Ti-bases of different designs and surface treatments is unclear. PurposeThe purpose of this in vitro study was to compare the debonding force of screw-retained lithium disilicate implant-supported crowns cemented to straight preparable abutments and Ti-bases of different designs and surface treatments. Material and methodsForty laboratory implant analogs (Straumann Bone Level) were embedded into epoxy resin blocks that were randomly divided into 4 groups (n=10 each) according to the abutment type used: CEREC group, Variobase group, airborne-particle abraded Variobase group, and airborne-particle abraded straight preparable abutment group. All specimens were restored with lithium disilicate crowns and cemented with resin cement to the corresponding abutments. They were thermocycled (from 5 to 55 °C for 2000 cycles) followed by cyclic loading (120 000 cycles). The tensile forces required to debond the crowns from the corresponding abutments were measured (N) by using a universal testing machine. The Shapiro–Wilk test of normality was used. Comparison between the study groups was done with 1-way ANOVA (α=.05). ResultsTensile debonding force values were significantly different according to the type of abutment used (P<.05). The highest retentive force value was recorded in the straight preparable abutment group (928.1 ±222.2 N) followed by the airborne-particle abraded Variobase group (852.6 ±164.6 N), and the CEREC group (498.8 ±136.6 N); the lowest value was reported in the Variobase group (158.6 ±85.2 N). ConclusionsThe retention of screw-retained lithium disilicate implant-supported crowns cemented to airborne-particle abraded straight preparable abutments is significantly higher than to non-surface treated Ti-bases and similar to airborne-particle abraded ones. Abrading abutments with 50-mm Al2O3 significantly increased the debonding force of the lithium disilicate crowns.

A comparative analysis of dual-axis implants placed into maxillary anterior extraction sockets versus virtual planning with uniaxial implants: A simulated cone beam computed tomography study of implant length and diameter.

The biaxial nature of the anterior maxilla poses a surgical and restorative challenge in implant dentistry. The present study sought to investigate the apical socket perforation rate (ASPR) from a simulated uniaxial implant placement and to determine the effect of implant length and diameter on ASPR when a uniaxial implant was placed compared with the orientation of the pre-existing dual-axis implant. Cone beam computed tomography (CBCT) scans from the database of three private practices were searched for patients who received dual-axis implants within the esthetic zone in immediate tooth replacement therapy. A uniaxial implant was virtually placed using the pre-existing screw access channel of the dual-axis implant as a reference. The closest length and diameter were selected for the simulated implant. ASPR by the uniaxial implant was recorded. In addition, the affordable maximum length of a corresponding uniaxial implant that would avoid apical socket perforation was measured. Eighty-one patients with a total of 101 dual-axis dental implants were selected for analysis. A simulated virtual surgical planning with uniaxial implants revealed high ASPR (48.51%). When the length of the uniaxial implant was reduced to 11 and 9 mm, ASPR was decreased to 41.58% and 20.79%, respectively. Dual-axis implant design effectively evades anatomical challenges in the anterior maxilla (esthetic zone). Considering the current evidence, efforts should be made to carefully consider the angular disparity between the extraction socket-alveolus complex and the future restorative emergence so that a harmonious biologic-esthetic result may be more predictably and consistently obtained.

Fracture Load of Monolithic CAD/CAM Ceramic Crowns Placed on Different Implant Abutments.

To evaluate the fracture load of monolithic, single-tooth implant-supported crowns cemented on solid or Ti-base (Variobase C) abutments. Besides abutment types (solid and Ti-base abutments), two ceramic systems (IPS e.max CAD and Zirconia inCoris ZI) and two occlusal thicknesses (0.5 and 1.5 mm) were also investigated in this study. In total, eight groups (n = 8) with 64 maxillary second premolar crowns were fabricated. All the crowns were cemented with resin cement, and the screw accesses in Ti-base groups were sealed with composite resin. After mechanical cycling, the specimens were submitted to fracture load test with the maximum force recorded in Newtons (N). Three-way analysis of variance (ANOVA) and Tukey post hoc test were used for statistical analyses (α = .05). Both the abutment type (P = .0001) and the ceramic system (P = .0001) significantly affected the results. Screw-access channels reduced the fracture load of crowns by half compared to those cemented on solid abutments. The 1.5-mm and 0.5-mm zirconia crowns placed on solid abutments had similar highest fracture loads, while the e.max CAD groups positioned on Ti-base abutments showed significantly lower values compared with other groups. The screw access reduces the resistance of crowns supported by Ti-base abutments compared to crowns cemented on solid abutments. The inCoris ZI showed a higher fracture load than the IPS e.max CAD regardless of the abutment type and thickness.

Evaluation of microleakage and push-out bond strength of various composite resins for sealing the screw-access channel in implant-supported restorations

Statement of problemMicroleakage and loss of the composite resin sealing the screw-access channel are frequent complications of screw-retained implant-supported prostheses. How the screw-access channel should be best restored to reduce such complications is unclear. PurposeThe purpose of this in vitro study was to evaluate the microleakage and bond strength of 3 types of composite resins (flowable, packable, and bulk-fill) with or without a bonding agent treatment to seal the screw-access channel of 2 types of restorative materials (zirconia and Co-Cr alloy) with or without thermocycling. Material and methodsIn total, 240 yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) specimens (IPS e.max ZirCAD) and 240 Co-Cr alloy (Vera PDS) specimens were prepared with a Ø3×3-mm cylindrical cavity at the center to simulate the screw-access channel. Three types of composite resins (flowable, packable, and bulk-fill resin) (Filtek Z350 XT Flowable Restorative, Filtek Z350 XT Universal Restorative, and Filtek One Bulk Fill Restorative) were applied to restore the access channel of the zirconia and Co-Cr specimens with or without a bonding agent (Single Bond Universal Adhesive). Microleakage and push-out bond strength were determined and compared by dividing the specimens into experimental groups with or without thermocycling (1000 times with 30 seconds at 5 ±2 °C and 55 ±2 °C). The results were analyzed by using a 1-way ANOVA and 4-way ANOVA. Adjustment for multiple comparisons was made with the Tukey Honestly Significant Difference (HSD) test. ResultsThe specimens subjected to thermocycling showed a lower bond strength (P<.001) and higher microleakage (P<.001) than specimens stored in a constant-temperature water bath. Specimens treated with bonding agents showed a higher bond strength (P<.001) and lower microleakage (P<.001) than specimens not treated with a bonding agent. Higher bond strengths were observed in the order of bulk-fill resin, packable resin, and flowable resin (P<.001). Packable resin showed higher microleakage than flowable resin and bulk-fill resin (P<.05). No significant difference in microleakage was found between the flowable resin and bulk-fill resin (P>.05). ConclusionsHigher bond strengths were observed in the order of bulk-fill resin, packable resin, and flowable resin. Less microleakage was observed in the flowable resin and bulk-fill resin than in the packable composite resin. Bonding agent treatment was effective in increasing bond strength and decreasing microleakage. Zirconia and Co-Cr showed a bond strength similar to that of composite resins, but zirconia showed higher microleakage than Co-Cr. Restoring the screw-access channel with the bulk-fill resin should increase bond strength and reduce microleakage.

Accuracy of digitally fabricated drilling guide to form screw-access channels in cement-retained implant prostheses: A randomized clinical trial

Statement of problemAccurate intraoral preparation of screw channels in cement-retained implant prostheses could be a treatment challenge for tilted or badly positioned implants. PurposeThe purpose of this randomized clinical trial was to evaluate screw channel accuracy for retrieving cement-retained implant prostheses by using a digitally fabricated drilling guide. Material and methodsTwenty-four participants requiring removal of cement-retained implant prostheses were recruited and consecutively assigned to 1 of 2 groups. In the first group, drilling guides were fabricated by using an intraoral scan, computer-aided design (CAD), and 3D printing to facilitate screw channel preparation (guide group). In the second group, screw channel preparation was based on panoramic radiographs without a drilling guide (freehand group). Screw channel accuracy was evaluated with a 3D analysis and subsequently compared with the ideal shape of the screw channel for linear deviation at coronal and apical levels, angular deviation, surface loss deviation, and volume loss deviation. The ideal shape of the screw-access channel was based on the Ø2.2-mm cylinder image marked along the long axis of the implant. The Mann-Whitney U and Kruskal-Wallis tests were used for statistical analyses (α=.05). ResultsThe drilling guide group showed higher dimensional accuracy than the freehand group for angular deviation (9.45 degrees versus 15.69 degrees; P=.014) and surface loss deviation (7.40 mm versus 9.53 mm; P=.001), especially when the implant was tilted more than 30 degrees. The deviation values of the screw channels were not significantly different according to implant tilt in either group (P>.05). ConclusionsDigitally fabricated drilling guides for intraoral preparation of screw channels in cement-retained implant prostheses can improve accuracy and provide a less-destructive screw channel.

Is a digital surgical guide superior for implant placement in the first molars areas?

Design The study was a randomised clinical trial comparing two independent groups for implant placement. One group was a computer-aided design/computer-aided manufacturing (CAD/CAM) implant guide (digital) and the other one used the traditional implant guide (traditional impression).Aim The study aimed to compare the outcomes of two different methods of guidance for surgical implants for missing first molars. One was prepared by intraoral digital scanning. The other was the conventional impression, which includes time to make an impression and perform surgery, fit of intraoral guide and deviation in screw access channels position. The purpose of the study was not only to find the most suitable implant guide but also to allow dentists to justify their chosen method.Methods The authors of this study included 42 participants with first molars missing and distributed them into two groups, one group using a digital production guide and the other using a traditional impression. The evaluation measured the deviation length and direction of the screw access channel position relative to implant alignments. In addition, labour time for implant guides and the intraoral fit were assessed as secondary outcomes.Results The impression time and implant surgery time for patients in the digital group were shorter than for those in the traditional group. The intraoral first fit of the guide was better for patients who underwent treatment with a digital system than it was for control patients (p <0.05). The one-time satisfaction rate of the digital group was 100%, while five cases in the control group required repetition. The difference between screw access channel positions on the left and right sides for both groups showed no significant differences.Conclusions The digital surgical guide for a first molar implant reduces the clinical, operative time and screw access deviation and therefore improves efficiency. Improved clinical outcomes indicated that there is evidence to support the use of CAD/CAM guides in dental implant placement for a single missing tooth replacement.

Filling Materials Efficacy on Preventing Biofilm Formation Inside Screw Access Channels of Implant Abutments.

The choice of the material used to fill screw access channels in implant-supported prostheses depends, in most cases, on operator's preference, without considering the susceptibility of biofilm colonization. Therefore, the aim of this study was to determine and compare the total amount of biofilm formed on different materials used to fill screw access channels in implant abutments. For this propose, titanium implant analogs were attached on abutments and divided into 5 groups: positive control (no filling material); negative control (closed with resin); and filled with cotton, gutta-percha, or polytetrafluoroethylene (PTFE). The analogs with attached abutments were then immersed in a brain heart infusion medium containing Candida albicans (strain 10231 from American Type Culture Collection [ATCC]) and incubated aerobically at 37°C with gentle agitation. After 15 days, materials were removed, and total viable biofilm on each material was quantified by methyl tetrazolium reduction assay at 490 nm. All experiments were performed in triplicate. Data were processed by IBM SPSS Statistic software using 1-way analysis of variance and Bonferroni post hoc tests to analyze differences between groups, with an overall significance level of P < .001. A significant difference was observed between cotton and gutta-percha (P < .017) and between cotton and PTFE (P < .025). However, there was no statistical difference between gutta-percha and PTFE (P > .050). Thus, this in vitro experiment showed that gutta-percha and PTFE presented lower biofilm formation compared with cotton when used to fill screw access channels. These results can provide a basis for future clinical studies that can be a guide to decreasing the occurrence of gaps and bacterial growth inside the implant/abutment attachment site. In addition, controlled in vivo studies are necessary to confirm the clinical viability of findings of this study.

A novel method of 3D printing locating guide for abutment screw removal in cement-retained implant-supported prostheses

Background/purposeCement-retained restorations have the advantages of passive fit, less complexity of clinical and laboratory methods, cost, esthetics, and dimensional stability over screw-retained restorations, especially in multiple abutment implant-supported prostheses. A common and difficult technical problem with cement-retained implant prostheses is abutment screw loosening. Three-dimensional (3D) printing is a technology that has been rapidly developed and has become widely accepted in dentistry. The aim of this study was to establish a novel method of using 3D implant planning guide to locate the abutment screw in cement-retained implant prosthesis. Materials and methodsSix standard gypsum complete denture models were used to locate the abutment screw. An implant analog (4.5 mm in diameter and 12 mm in length) was placed in the drilling hole (5 mm in diameter and 14 mm in depth). After scanning with a 3D scanner, the 3D printing software was used to design the abutment screw location guide, which was printed by a resin-based 3D printer. ResultsA total of 30 abutment screws were located and removed using the guide. The locating guide's actual diameter was 2.4 mm. The drilling point was accurate and precise, and no excessive loss of the abutment was noticed. ConclusionThe guide would help the dentist in locating the abutment screw access channel, resulting in a more precise and accurate drilling point. The guide for locating the abutment screw enhances the accuracy of screw channel access and reduces damage to the crown and abutment.

Comparing digital and traditional guides in first molar implant surgery: A randomized clinical trial.

BACKGROUND: There are few studies on the differences in clinical outcomes with implant guides made by different methods in cases with a single tooth loss and adjacent tooth supportOBJECTIVE: To compare the use of digital and traditional implant guides in patients whose first molars are absent and who are undergoing implant restoration.METHODS: This study included 42 patients with first molars missing who were randomly divided into two groups: the digital group ( 21) and the control group ( 21). A CAD/CAM digital implant guide was used in the digital group, whereas a traditional impression was used in the control group. Then, the labor time, the intraoral fit of the implant guide, and the deviation of the screw access channel position were compared between the two groups.RESULTS: The impression time and implant surgery time in the digital group were less than in the traditional group. The intraoral first fit of the guide in the digital group was higher than in the control group ( 0.05). The one-time satisfaction rate of the digital group was 100%, while five cases in the control group needed to be redone. In the digital group, there was no significant difference in the deviation of the screw access channel position between implants on the left and right sides. In the control group, the deviation of the screw access channel position on the right side was significantly lower than on the left side. Overall, the deviation of the screw access channel position was significantly lower in the digital group than in the control group.CONCLUSIONS: In a first molar implant, the digital implant guide can effectively reduce the clinical operative time and the screw access deviation and improve efficiency. The clinical results with the digital guide provide a basis for its use in implant therapy for single missing teeth.

Microleakage and Bacterial Adhesion with Three Restorative Materials Used to Seal Screw-access Channels of Implant Abutments: An In vitro Study.

Background:Proper sealing of screw-access channels against microbial microleakage is advisable for the long-term success of screw-retained implant prosthesis.Objective:This study aimed to compare the bacterial adhesion and microleakage with three restorative materials, namely, composite resin, acrylic resin and bis-acryl, that are used to cover the access channels of screw-retained implant prostheses, using polytetrafluoroethylene tape as a spacer material.Materials and Methods:In this in vitro study, 18 titanium straight abutments (Hex-lock® Zimmer) were torqued into implant analogs, which were then subdivided into three groups. The samples of each group were filled with polytetrafluoroethylene tape and sealed with the three restorative materials (Group A: composite resin; Group B: acrylic resin; Group C: bis-acryl). Measurements of surface bacterial adhesion and internal microleakage were then recorded. The results were statistically analyzed using Kruskal–Wallis and Chi-square tests.Results:No significant difference was found between the investigated materials in terms of their sealing effectiveness against microbial microleakage (P = 0.06). Regarding bacterial adhesion, composite resin showed the highest number of surface adhesion, but there was no significant difference between the three materials (P = 0.081).Conclusion:The results of this study suggest that composite resin, acrylic resin and bis-acryl materials could be used alternatively in sealing the implant access channel owing to no significant differences in terms of microleakage and bacterial adhesion.

Restoration of a nonideally placed anterior implant: A clinical report

This article describes a restorative solution for implants placed at an insufficient depth and in a patient with limited interarch space, making the esthetics, emergence profile, and retention of a cemented restoration problematic. These challenges were overcome by adhesively bonding a pressed lithium disilicate veneer to a custom cast metal abutment veneered with a thin layer of feldspathic porcelain. The ceramic veneer with the attached core engaged a facially located screw-access channel, which increased retention and resistance form and facilitated seating of the veneer. Adhesive bonding via the application of a thin layer of feldspathic porcelain on the custom dental implant abutment was also used to overcome the lack of resistance form with a veneer preparation.

Challenges in Managing a Fractured Cement-retained Crown Located at the Aesthetic Zone: A Case Report

Implant prosthesis is a popular treatment modality but it is not complication free. This article discussed the management of a cemented, all-ceramic implant crown in the maxillary anterior region that had veneering ceramic fracture after three years in function. A screw-retained prosthesis was prescribed to avoid the show of the screw access channel on the incisal edge of the crown. This was achieved by changing the location of the screw hole using the angle screw channel that overcame the angulation issue.