A prospective study on single tooth reconstructions using parallel walled implants with internal connection (NobelParallel CC) and abutments with angulated screw channels (ASC)

The mechanical complications and behavior of angulated dental implant abutment systems versus conventional abutments, a narrative review

Background

Angulated screw channel (ASC) abutment allows off-axis dental implants to be used in dental restorations without the need for cementation. As this is a relatively new system, research on its clinical performance is limited.

Objectives

To summarize the available in-vitro and in-vivo studies on the mechanical and technical issues associated with the ASC system and compare its clinical performance with that of conventional implant-supported abutments.

Methods

A comprehensive literature search in PubMed, Web of Science, and ScienceDirect databases was performed, focusing on articles about angulated (angled) screw channel (ASC) systems published in English between January 2015 and November 2023. Only in-vitro and in-vivo studies were included.

Results

After analyzing the recorded articles, 26 studies (11 in vivo and 15 in vitro) were included in the final discussion and review.

Conclusion

Although the ASC system is still relatively new, and is presently outperformed by conventional abutment systems in terms of technical and mechanical properties, in short- and medium-term in-vivo studies, it was shown reliable for retaining single or multiple-unit implant restorations in both posterior and anterior zones. Still, further long-term clinical research is needed to fully elucidate the risk factors associated with ASC failures.

Comparison of Aesthetic, Mechanical Outcome, and Bone Loss in Angulated Screw Channels (ASCs) and Cement-Retained Implant-Supported Prosthesis: A Case-Control Study

Angulated-screw channels (ASCs) allow the clinician to employ screw-retained restorations in almost all cases, as the access hole can be moved away from the vestibular portion of the crown, where it would jeopardize the final esthetic result. The objective of this study was to compare screw-retained restorations employing ASCs with restorations cemented on angled abutments. In this study, 30 subjects, equally divided into two groups: group 1 (cemented restorations on angulated abutments) and group 2 (screw-retained restorations adopting ASCs), were treated and retrospectively compared after 2 years using the pink esthetic score (PES) and the white esthetic score (WES). All restorations were in use at the last follow-up, with a survival rate of 100%. Three mechanical complications were observed (2 chippings and 1 crown came loose), with a success rate of 93% in group 1 and 87% in group 2 (p > 0.05). No statistically significant differences were reported regarding the esthetic outcome; the marginal bone loss (MBL) showed better results for the screw-retained restorations, both at the distal aspect (group 1 = 0.98 mm ± 0.16; group 2 = 0.45 mm ± 0.06; p = 0.006) and at the mesial aspect (group 1 = 1.04 ± 0.27; group 2 = 0.45 ± 0.005; p < 0.001). From an esthetical perspective, screw-retained restorations with ASCs and cemented restorations on angulated abutments are both effective means of restoring implants; both have excellent esthetic outcomes, but screw-retained restorations have reduced bone loss when compared to cemented ones but are more prone to mechanical complications. Still, our results must be cautiously observed given the reduced dimension of our sample. Larger studies are needed to confirm our findings.

Clinical effect of Nobel Biocare angulated screw channel crown compared with cement crown in the aesthetic area: A retrospective cohort study with a mean 32 months follow-up (range 12 to 70 months)

OBJECTIVE

The objective of this study is to compare the clinical efficacy of angulated screw channel abutment applied in the anterior area with regular cemented crowns.

MATERIALS AND METHODS

Forty-eight patients were included and divided into two groups: the angulated screw channel group (ASC) and regular cemented group (RC) in this retrospective cohort study. The evaluation criteria included implant/restoration survival rate, keratinized mucosa width (KMW), bleeding on probing rate (BOP%), probing depth (PD), pink aesthetic score (PES), mechanical/biological complications, emergence angle (EA), the site of implant axis penetrate (SA), marginal bone loss (MBL), and buccal bone thickness (BBT) at 0 mm, 1 mm, 3 mm, 5 mm below the implant shoulder were evaluated in immediate postoperative (T0) and follow-up period (T1).

RESULTS

This retrospective cohort study included a total of 48 patients, with a mean 32 months follow-up period range from 12 months to 70 months. The study did not find any cases of implant failure or restoration failure. EA was significantly wider in the RC group than ASC group (RC: 33.53° ± 8.36° vs ASC: 27.43° ± 8.08°, p = 0.016*). While the BOP% was statistically significant higher in the RC group than ASC group (RC: 28.35% ± 22.92% vs ASC: 13.18% ± 20.00%, p = 0.027*). No significant differences were observed in the other measurements of comparison.

CONCLUSION

Within the limitations of the study, angulated screw channel (Nobel Biocare) crowns might allow the implant axis aim at incisal edge to reduce the emergence angle in the anterior area and benefit the soft-tissue during the 12-70 months follow-up period.

Frequency of screw-retained angulated screw channel single crown following immediate implant placement and provisionalization in the esthetic zone: A cone beam computed tomography study

OBJECTIVE

The purpose of this cone beam computed tomography (CBCT) study was to determine the frequency percentage of screw-retained crown using angulated screw channel (ASC) abutment for single immediate implant placement and provisionalization (IIPP) in the esthetic zone.

METHODS

The CBCT images of 200 patients without disease and without metal restorations in maxillary anterior teeth were evaluated. The mid-sagittal-sectional CBCT images of maxillary anterior teeth (#6-#11) were created in an implant planning software, screen-captured, and transferred to a presentation program. Template of tapered implants with diameter of 3.5 mm (for central and lateral incisors) and 4.3 mm (for central incisors and canines) and lengths of 13, 15, and 18 mm were applied to the sagittal images to identify the IIPP cases. To qualify for IIPP, the implant must engage >35% bone with at least 1 mm of surrounding bone and no perforations. The IIPP cases were further divided into straight screw channel (IIPPSSC) abutment or 25-degree angulated screw channel abutment (IIPPASC), based upon its restorability. The frequency percentages of possible IIPP, IIPPSSC, and IIPPASC were reported and compared among all maxillary anterior teeth.

RESULTS

A total of 1200 maxillary anterior teeth sagittal images from 200 patients (88 male and 112 female) with a mean age of 51.3 years (range 20-83 years) were evaluated in this study. The overall frequency percentages of IIPP, IIPPSSC, and IIPPASC possibility were 84% (74%-92%), 14% (10%-24%), and 75% (66%-87%), respectively.

CONCLUSION

Within the limitations of this CBCT study, 90% of single IIPP in the esthetic zone can be restored with screw-retained crown when utilizing ASC. In addition, the possibility of using a screw-retained restoration following IIPP increases about five times with ASC abutment compared to the SSC abutment.

Application of orthodontics combined with porcelain laminate veneers in the aesthetic restoration and flora regulation of anterior teeth

To evaluate the effectiveness of orthodontics in combination with porcelain laminate veneers (PLV) in the aesthetic restoration and flora regulation of anterior teeth. A retrospective analysis of 336 patients who underwent aesthetic restoration of anterior teeth in our hospital from April 2019 to September 2022 was performed and divided into a control group (n = 168) and an observation group (n = 168) according to the restorative modality. The restorative modality in the control group was conventional restorative remediation, while the restorative modality in the observation group was orthodontic combined with PLV treatment. To evaluate the excellent rate of aesthetic restoration of anterior teeth in the 2 groups, and compare the color, shape, degree of translucency, edge aesthetic score, complications and satisfaction rate of restoration of anterior teeth in the 2 groups before and after restoration. The observation group had a significantly higher rate of excellent aesthetic restorations (95.23%) compared to the control group (80.95%) (P < .001). The scores of anterior tooth color, morphology, degree of translucency and marginal aesthetics were improved in both groups after restoration compared to before restoration, and the scores were significantly higher in the observation group (P < .05). After restoration, the subgingival Digestive streptococcus, Campylobacter and Propionibacterium increased in both groups, but the number of bacterial strains was significantly less in the observation group (P < .05). Compared with the total complication rate in the control group (16.66%), the total complication rate in the observation group (2.38%) was significantly lower (P < .001). Compared with the control group (85.71%), the observation group had a significantly higher restoration satisfaction rate of 97.61%, with a statistically significant difference (P < .001). The application of orthodontics combined with PLV in the aesthetic restoration of anterior teeth has a significant clinical effect, which is conducive to improving the aesthetic restoration and satisfaction rate of anterior teeth, reducing the subgingival microbial imbalance and decreasing the incidence of complications.

A method of removing the stripped abutment screw from the angled screw channel: Technical details and a clinical report

An angled screw channel (ASC) avoids a facial screw hole by correcting the pathway of the screwdriver. However, the structure of the specially designed screw is prone to mechanical complications, including screw-head stripping. Removing an angled screw is challenging because regular screw-removal tools cannot access the ASC. A safe and convenient method for the retrieval of the stripped screw is reported.

Retention of zirconia crowns to titanium bases with straight versus angled screw access channels: an invitro study

BACKGROUND

The aim of this study was to assess the impact of abutments with angled screw access channel on the retention of zirconia crowns.

METHODS

Seven implant replicas were inserted in epoxy resin blocks. Fourteen zirconia crowns for central incisor tooth were digitally fabricated and cemented to titanium bases (Ti-bases) with resin cement. Titanium bases were categorized into 2 groups (n = 7). Control group (Group STA) included straight screw access channel abutments. Study group (Group ASC) included angled screw access channel abutments. Following aging (5 °C-55 °C, 60 s; 250,000 cycles, 100 N, 1.67 Hz), the pull-off forces (N) were recorded by using retention test (1 mm/min). Types of failure were defined as (Type 1; Adhesive failure when luting agent predominantly remained on the Ti-base surface (> 90%); Type 2; Cohesive failure when luting agent remained on both Ti-base and crown surfaces; and Type 3; Adhesive failure when luting agent predominantly remained on the crown (> 90%). Statistical analysis was conducted by using (IBM SPSS version 28). Normality was checked by using Shapiro Wilk test and Q-Q plots. Independent t-test was then used to analogize the groups.

RESULTS

Mean ± standard deviation of retention force records ranged from 1731.57 (63.68) N (group STA) to 1032.29 (89.82) N (group ASC), and there was a statistically significant variation between the 2 groups (P < .05). Failure modes were Type 2 for group STA and Type 3 for group ASC.

CONCLUSIONS

The retention of zirconia crowns to abutments with a straight screw access channel is significantly higher than abutments with angled screw access channel.

Comparative evaluation of biological, mechanical, and patient-reported outcomes of angulated screw channel abutments versus multi-unit abutment-retained single-unit implant restorations in the anterior esthetic zone: An-in vivo study

Aims

The study aimed to evaluate biological, mechanical, and patient reported parameters associated with ASC abutments and MU abutments for the fabrication of screw retained implant crowns in the anterior esthetic zone.

Setting and Design

For the study, 20 patients were selected and implants were placed within the constraints of prosthetic envelope. Later, the screw retained crown was fabricated.

Materials and Methods

Biological parameters (including implant survival rate, marginal bone levels using cone beam computed tomography, and soft tissue assessment using periodontal indices) were measured at the time of crown placement and 1 year follow up. Mechanical parameter (screw loosening) was calculated using removal torque loss (RTL) values obtained at the time of crown placement and 1 year follow up. Patient reported parameters were evaluated using a questionnaire at 1 year follow up.

Statistical Analysis Used

All data were tabulated, statistically analyzed, and compared using SPSS version 23 IBM Corporation, Armonk, NY, USA.

Results

Implant survival was found 100% in both the groups. The marginal bone level reduced considerably in both the groups from baseline to 1 year follow up. The MU abutment group had slightly less marginal bone loss than the ASC abutment group. Additionally, there was no statistically significant difference between the two groups' periodontal indices at baseline and 1-year follow-up values. At baseline, the RTL value was substantially lower (P <0.003) in the ASC abutment group than in the MU abutment group, however at the 1-year follow-up, there was no statistically significant difference in RTL or screw loosening between the two groups. Patient-reported data showed no statistically significant difference.

Conclusion

Within the constraints of this study, it was suggested that both ASC and MU abutments provide equally promising results in terms of biological, mechanical, and patient-reported parameters in the anterior esthetic region for single screw-retained crowns.

Clinician preferences for single-unit implant restoration designs and materials: A survey of the membership of the Pacific Coast Society for Prosthodontics

STATEMENT OF PROBLEM

Clinical research has difficulty keeping pace with the rapid evolution of materials, protocols, and designs of single-unit implant restorations. The clinical design preferences of prosthodontics for different clinical scenarios are lacking.

PURPOSE

The purpose of this cross-sectional survey was to determine the current prevalence of usage of various treatment options and materials for single-unit implant-supported restorations.

MATERIAL AND METHODS

From August to September of 2022, a survey invitation was sent to members of the Pacific Coast Society for Prosthodontics (PCSP). The survey was hosted online and asked 37 questions related to the materials, protocols, and design preferences for single-unit implant-supported restorations in various clinical scenarios. The prompts included the suggestion that answers should be based on preferences for the "ideal" treatment of a hypothetical patient seeking implant treatment for the replacement of a single missing tooth.

RESULTS

Of 133 questionnaires sent via email, 35 were returned. The results are presented with histograms that use color coding as an experience proxy metric. A total of 87% of respondents was in private practice, and 60% reported having restored more than 1000 single-unit implant restorations. For the replacement of a single maxillary central incisor under ideal conditions and angulation through the palatal surface, respondents preferred bone level implants (93%) and screw-retained restorations (80%), with 50% of those being zirconia with a titanium abutment and 21% being cast metal-ceramic. For an identical scenario, except that the angulation would be through the facial surface, respondents preferred the angled screw system (55%) and cemented (41%) restorations. For the replacement of a single missing mandibular molar under ideal conditions, respondents preferred bone level implants (79%) and screw-retained restorations (79%), with 70% of those being zirconia with a titanium abutment and 17% being cast metal-ceramic.

CONCLUSIONS

While a wide range of protocols, designs, and materials exist for the replacement of a single missing tooth, these results provide a snapshot of current single-unit implant prosthodontic preferences in the Western United States and Canada.

Clinical and Laboratory Outcomes of Angled Screw Channel Implant Prostheses: A Systematic Review

The purpose of this systematic review was to evaluate the clinical and laboratory outcomes of angled screw channel (ASC) restorations and to summarize the influencing factors. An electronic search of the English language literature was performed in four databases and enriched by manual searches. Retrieved studies were screened against the predefined exclusion and inclusion criteria. Eight clinical and seven laboratory studies were eligible for the analysis. The risk of bias for included observational studies was performed using the Newcastle–Ottawa quality assessment scale. Laboratory studies quality assessment method was adapted from previous published systematic reviews. Two clinical studies focused on technical outcomes and the rest reported the biological outcomes of the ASC restorations. Out of the seven laboratory studies, two studies investigated the fracture resistance of ASC restorations, four studies evaluated the reverse torque value of the nonaxially tightened screws, and one study evaluated both variables. The present review revealed that while the performance of ASC restorations is promising in short-term clinical studies, the evidence of their long-term reliability is still lacking. The laboratory studies indicated comparable fracture resistance results of the ASC restorations with the straight screw channel restorations. In addition, factors, such as initial torque value, configuration of the screw driver, screw design, abutment system, and the angulation of screw channel, were shown to influence the screw resistance to loosening.

3D-based buccal augmentation for ideal prosthetic implant alignment—an optimized method and report on 7 cases with pronounced buccal concavities

Objectives

Screw-retained restoration of implants is advantageous for biological and esthetic reasons. Due to buccal concavities, however, this preferred type of restoration can only be used in about half of the anterior indications. Based on case series, an optimized method for the treatment of such indications is to be described; the clinical reliability is to be ascertained by means of measurements (before and after augmentation) and assigned to the current literature.

Material and methods

A case series of seven cases with buccal concavities of the anterior alveolar ridge were treated with optimized method, which is presented step-by-step until the prosthetic restoration. The depths of the bone concavities were measured and related to the bone gain after augmentation procedure respectively after implantation.

Results

Linear measurements of the buccal concavities showed an average undercut of 4 mm [SD ± 1.13]. After healing period of six months, the buccal concavities could be compensated bony to such an extent that implants could be inserted in correct position and angulation. On average, there was a horizontal bone gain of 3.7 mm [SD ± 0.59]. Even after implantation and another six months of healing, stable bone dimensions could be assumed with an average of 4.3 [SD ± 0.83] mm of bone gain compared to baseline. In six of the seven cases, the favorite screw-retained, one-piece full-ceramic restoration could be fixed on the implants. Due to the implant axis, one case had to be treated with a cemented two-part full-ceramic system.

Conclusions

With the described optimized method the most favorable screw-retained restoration can also be used in situations with unfavorable concavities of buccal bone. Especially for this indication, a special form of the horizontal deficit, the customized bone regeneration with titanium meshes is highly reliable in terms of healing and extent of augmentation. However, long-term results and a study/control group are required to evaluate the effectiveness of the presented protocol.

Clinical relevance.

Since these situations require an augmentation that is up to 5 mm thick and a procedure that is as minimally invasive as possible appears to be necessary in the visible area, an optimized method is described in this publication.

Clinical and radiological outcomes of novel digital workflow and dynamic navigation for single-implant immediate loading in aesthetic zone: 1-year prospective case series

Objectives

To evaluate clinical, radiological performance of novel digital workflow integrating dynamic navigation to streamline in one‐visit single‐implant immediate loading in aesthetic zone.

Material and methods

Consecutive patients requiring one single‐implant in aesthetic zone of both jaws were treated between May and September 2017. Primary outcomes were implant and prosthetic success rates, surgical and prosthetic complications, marginal bone loss (MBL), final pink aesthetic score (PES‐f), and implant stability quotient (ISQ‐f). Secondary outcomes were ISQ‐0 and PES‐0 at implant positioning and PES‐p at definitive prosthesis placement. Potential effect of jaw (maxilla vs mandible), biotype (thin vs thick), type of incision (flap vs flapless), and implant site (healed vs. post‐extractive) on the primary outcomes (MBL, PES‐f, and ISQ‐f) was evaluated through a multivariable analysis.

Results

Fifty‐two implants were placed (follow‐up 18.6, 15–20 months). One post‐extractive implant failed. No other surgical, biological complications occurred, accounting for 98.10% cumulative success rate (CSR). No definitive prostheses failed. Mean MBL was −0.63 ± 0.25 mm (−1.69 to −0.06). PES‐f was 12.34 ± 1.41 (9–14). ISQ‐f was 78.1 ± 3.2 (70–84). Age had significantly negative effect on MBL and PES‐f (p = .0058 and p = .0052). No other variables significantly affected primary outcomes.

Conclusions

Within study limitations, investigated digital workflow integrating dynamic navigation was reliable for single‐implant immediate loading in aesthetic zone in one visit. No statistically significant difference was found for MBL, PES‐f, and ISQ‐f, considering type of incision (flap vs. flapless), implant site (healed vs post‐extractive), jaw (maxilla vs. mandible), and biotype (thick vs. thin). Live‐tracked dynamic navigation may have contributed to improve operator clinical performance regardless of implant site characteristics. Further investigations are needed to confirm positive outcomes.

The effect of implant-abutment connections on peri-implant bone levels around single implants in the aesthetic zone: A systematic review and a meta-analysis

Objective

To systematically review literature about the effect of different implant‐abutment interface designs on peri‐implant bone level changes, implant loss and mid‐buccal mucosa changes around single implants in the anterior maxilla. Reviewing three connection configurations: Platform switched conical (PS‐conical); Platform switched parallel (PS‐parallel); Platform matched parallel (PM‐parallel).

Methods

A detailed search was carried out in Pubmed, EMBASE, Cochrane, Scopus, Open Gray and African journals Online (until December 1, 2020) and was restricted to clinical prospective studies of at least 1 year and with at least 10 human participants. A meta regression analysis was carried out primarily on the pooled peri‐implant bone level changes followed by implant loss and mid‐buccal mucosa level change. Risk of bias was assessed with RoB 2.0 and ROBINS‐I. The manuscript complied with the PRISMA guidelines and was registered in the PROSPERO database (ID: 225092).

Results

A total of 5513 hits gave 44 eligible articles for the analyses. Bone level change did not differ significantly between the two platform switched connections; their bone loss scores were significantly lower than PM‐connection. The PS‐conical connections have significantly lower implant losses than the PM connection. Mid‐buccal mucosa level change was comparable between the three connection configurations. Moderate to high risk of bias was detected in the included studies.

Conclusions

The performance of PS‐conical and PS‐parallel connection configurations both favored bone loss scores compared to the PM‐parallel connection configuration. All three demonstrated mid‐buccal mucosa changes that were small and did not differ significantly amongst the groups.

Clinical, radiographic, and immunological evaluation of angulated screw-retained and cemented single-implant crowns in the esthetic region: A 1-year randomized controlled clinical trial

BACKGROUND

Screw-retained implant crowns are considered more biologically compatible than cemented crowns due to the absence of excess cement. However, traditional screw-retained implant crowns are not viable when the access hole of the screw channel would need to be located in an esthetic area, which would compromise the esthetic outcome of the treatment.

PURPOSE

To evaluate the clinical, radiographic, and immunological outcomes of angulated screw-retained and cemented single-implant crowns in the esthetic region.

MATERIALS AND METHODS

The study was a single-center, open-label, randomized controlled clinical trial. Eligible patients were randomly placed in two groups: angulated screw-retained group (AG) and cemented group (CG). Implant survival rate, bleeding on probing rate (BOP%), probing depth (PD), modified plaque index (mPI), marginal bone loss (MBL), concentrations of pro-inflammatory cytokines (TNF-α, IL-6) in peri-implant crevicular fluid (PICF), mechanical complications, and pink esthetic score/white esthetic score (PES/WES) were evaluated.

RESULTS

Fifty-six patients (AG: 29, CG: 27) attended the 1-year examination. The drop-out rate was 6.67%. No implant failure was found in both groups during the observation period. BOP% was significantly lower in the AG than that in the CG (mean, 21.84% ± 19.97% vs. 37.04% ± 26.28%, p = 0.018). The concentration of TNF-α in PICF was significantly higher in the AG than that in the CG (median, 13.54 vs. 4.62, p = 0.019). No significant difference of PD, mPI, MBL, IL-6, or mechanical complication rates was found between the two groups. Mean scores for PES/WES were 21.71 and 21.64 in the AG and CG, respectively.

CONCLUSION

Based on the present results, both treatment options showed acceptable clinical outcomes in the short term. Angulated screw-retained crowns might benefit the peri-implant soft tissue. However, studies with long-term follow-up are needed to confirm whether the higher concentration of TNF-α will compromise the long-term outcomes of treatment.

Clinical performance of posterior monolithic zirconia implant-supported fixed dental prostheses with angulated screw channels: A 3-year prospective cohort study

STATEMENT OF PROBLEM

The choice of retention type of an implant-supported fixed dental prosthesis (FDP) becomes critical when the dental implant is not placed in a prosthetically ideal location. In recent years, computer-aided design and computer-aided manufacturing (CAD-CAM) technology has enabled the correction of the location of screw access hole depending on the clinical needs of the patient. However, how FPDs with angulated screw channels (ASCs) perform clinically is unclear.

PURPOSE

The purpose of this prospective clinical study was to evaluate the mechanical complications and crestal bone loss (CBL) when posterior monolithic zirconia implant-supported FDPs with an ASC are used.

MATERIAL AND METHODS

Participants (N=37) with a missing single posterior tooth or multiple teeth, sufficient bone height, and an implant site without infection were included. Each participant received parallel-walled implants (Nobel Parallel CC) of 7-, 8.5-, or 10-mm length by using a 1-stage approach. After 4 months of healing, a conventional impression was made, and a digital workflow was followed. Monolithic zirconia restorations (Katana ML) were milled, stained, and mechanically attached to a titanium base (NobelProcera ASC abutment). CBL was measured from radiographs at 6, 12, 24, and 36 months after the placement of the prosthesis. Implant and prosthetic characteristics including implant diameter, implant length, screw channel angle (angle≤15 degrees versus angle>16 degrees), prosthetic type (single crown versus multiple-unit FDP), and antagonist dentition (natural versus prosthesis) were also recorded. A generalized linear mixed model with a log link was estimated to assess the independent predictors of CBL among the angles of ASC-retained definitive restorations and the clinically relevant variables (α=.05).

RESULTS

Thirty-seven participants received 51 implants, and the median follow-up period was 30 months (interquartile range: 22-36). Two single-crown implants failed within the first 12 months of delivery. The implant and restoration survival rate was 96% at 36 months. Screw loosening was recorded in 2 study participants. After a follow-up of 36 months, the mean ±standard deviation CBL value was 0.15 ±0.14 mm with an increase over time (P<.001). The effect of the angle of ASC, implant diameter, implant length, prosthetic type, and antagonist on the CBL was not statistically significant (P>.05).

CONCLUSIONS

CBL was not associated with the angle of ASC, implant diameter, implant length, prosthetic type, or antagonist when posterior monolithic zirconia implant-supported FDPs with ASCs were used. Screw loosening in 2 situations was the only mechanical complication during the first 3 years of service.

Effect of cyclic loading on reverse torque values of angled screw channel systems

STATEMENT OF PROBLEM

The angled screw channel concept has become popular. However, research is lacking as to how reverse torque values of nonaxially tightened implant crowns compare with axially tightened cement-retained crowns restored on angle-correcting abutments when subjected to long-term cyclic loading.

PURPOSE

The purpose of this in vitro study was to evaluate the ability of different 25-degree angled screw channel hexalobular systems to apply the target torque value on their screws, the effect of cyclic loading on their reverse torque values, and their survival compared with crowns cemented on conventional 0-degree screw channel abutments.

MATERIAL AND METHODS

A total of 28 implants were divided into 4 groups. Twenty-one angled screw channel crowns were fabricated at a 25-degree angle correction by using angled titanium (Ti) bases by 3 manufacturers DY (Dynamic Tibase), DE (AngleBase), and ASC (Angulated Screw Channel) (n=7). The fourth group, UB (Universal Base, Control), had cement-retained crowns with 25-degree custom-milled, angled zirconia abutments that were cemented onto their respective Ti bases (n=7). All implants were embedded in epoxy resin blocks and tightened to manufacturer recommended values: 35 Ncm for ASC, UB, and DE and 25 Ncm for DY. Initial torque values (ITV1) were recorded. After 24 hours, the reverse torque values (24hr-RTV1) were recorded. A new set of screws was then used for each group, and the initial torque values (ITV2) were recorded. Specimens were loaded at 2 Hz for 5 million cycles under a 200-N load, and reverse torque values (RTV2) were recorded. ANOVA (α=.05) was used to compare differences in the means of deviation of initial torque values and means of reverse torque values followed by a Tukey-Kramer post hoc analysis (α=.05). Preload efficiency was calculated for each system (RTV2/ITV2), and a survival analysis was performed by using the Lifetest procedure.

RESULTS

A significant difference in the means of deviation of initial torque values of the groups with 25-degree torque application (DY, DE, and ASC) was found when compared with UB at 0 degrees. ASC and DE had lower initial torque values than UB (P<.001 and P=.003 for ASC ITV1 and ITV2, P<.001 and P=.006 for DE ITV1 and ITV2). A significant difference was found in mean reverse torque values both for after 24 hours and after cyclic loading among all groups (P<.001). A significant difference was found between mean reverse torque values before and after cyclic loading for each group (P<.001). Preload efficiency was 43.8% for DY, 46.8% for DE, 54.2% for ASC, and 48.5% for UB. No significant difference was found in the time-to-failure survival among groups (P>.05).

CONCLUSIONS

The hexalobular system of DY delivered comparable initial torque values to its target value at 25 degrees, similar to how UB (control group) delivered at 0 degrees. ASC and DE scored lower initial torque values than their target value compared with UB. The DY abutment, which had a lower manufacturer recommended torque value, had lower reverse torque values compared with those of other groups. Time-to-failure survival of all groups was similar. Fractures at the zirconia to titanium base connection were seen with ASC crowns.

A 5 to 7-year case series on single angulated implants installed following papilla-sparing flap elevation

BACKGROUND

Bony concavities at the buccal aspect may cause a distortion between the implant axis and ideal prosthetic axis. Angulated implants can overcome this problem, yet long-term data are lacking. In addition, papilla-sparing incisions have been proposed to reduce tissue loss, yet aesthetic outcomes have not been published.

PURPOSE

To evaluate the 5 to 7-year outcome of single angulated implants installed following papilla-sparing flap elevation.

MATERIALS AND METHODS

Patients who had been consecutively treated with a single angulated implant (Co-axis®, Southern Implants, Irene, South Africa) in the anterior maxilla were re-examined after 5 to 7 years. Available data at 1 year (T1) were compared to those obtained at 5 to 7 years (T2).

RESULTS

Twenty out of 22 treated patients (11 females, 9 males, mean age of 52) with 22 implants attended the 5 to 7-year reassessment. All implants survived and stable clinical conditions could be reached with mean marginal bone loss of 1.28 mm at T2. Papilla-sparing flap elevation resulted in Pink Esthetic Score of 9.83 at T1 and 8.23 at T2 (p = 0.072). Mucosal Scarring Index was 4.61 at T1 and 3.50 at T2 (p = 0.165). The overall appearance of scarring significantly improved over time (p = 0.032), yet 59% of the cases still demonstrated scarring at T2.c CONCLUSIONS: Within the limitations of the study, angulated implants (Co-axis®, Southern Implants) reached stable clinical conditions. Papilla-sparing incisions may not be recommended in aesthetically demanding patients due to high risk of scarring.

A clinical and radiographic study of implants placed in autogenous bone grafts covered by either a platelet-rich fibrin membrane or deproteinised bovine bone mineral and a collagen membrane: a pilot randomised controlled clinical trial with a 2-year follow-up

Purpose

To compare the survival and clinical performance of implants placed in sites previously augmented with autogenous bone grafts covered by either a platelet-rich fibrin (PRF) membrane (PRF group) or a standard procedure (gold standard) involving coverage of the autogenous bone graft with deproteinised bovine bone mineral and a resorbable collagen membrane (control group).

Methods

A total of 27 partially edentulous patients (test n = 14, control n = 13) with indication for staged lateral bone block augmentation and dental implant placement were included. Twenty-four months after crown placement (range: 14–32 months), patients were recalled for a final clinical and radiographic follow-up. Outcome measures were implant survival, implant crown survival, clinical parameters of the implant, peri-implant marginal bone level, marginal bone level of adjacent tooth surfaces, biological and technical complications and patient-related outcome measures.

Results

Two implants were lost in the control group (85% survival rate); none were lost in the PRF group (100% survival rate). None of the 26 initially placed implant crowns were lost, but one implant and therefore one implant crown were lost after 20 months. Consequently, the definitive implant crown survival was 92% (95% confidence interval (CI): 73–110%) in the control group and 100% in the PRF group. No statistical difference in implant survival rate (p = 0.13) or implant crown survival was seen between the groups (p = 0.28). The mean marginal bone level at the follow-up was 0.26 mm (95% CI: 0.01–0.50 mm) in the PRF group and 0.68 mm (95% CI: 0.41–0.96 mm) in the control group. The difference between the groups was − 0.43 mm (95% CI: − 0.80 to − 0.05 mm, p = 0.03), which was statistically significant (p = 0.03). Both groups demonstrated similar healthy peri-implant soft tissue values at the final follow-up.

Conclusion

Although the current study is based on a small sample of participants, the findings suggest that the methodology of the PRF and the control group approach can both be used for bone augmentation with a similar outcome. A significant, but clinically irrelevant, higher peri-implant marginal bone level was registered in the PRF group than in the control group. Patients in both groups were highly satisfied with the treatment.

Trial registration

ClinicalTrials.gov Identifier: NCT04350749. Registered 17 April 2020. Retrospectively registered.

A multicenter cohort study on the association of the one-abutment one-time concept with marginal bone loss around bone level implants

OBJECTIVES

To investigate the association of the one-abutment one-time concept with marginal bone loss (MBL) around bone-level implants in relation to other factors.

MATERIALS AND METHODS

Records from patients treated by four experienced implant surgeons between January 2016 and July 2019 were scrutinized. Subjects treated with two bone-level implant types with varying machined collar (subgroups: 0.5 and 0.8 mm) were considered, receiving a healing abutment (HA cohort) or a permanent abutment at the time of surgery (OT cohort). The primary outcome was MBL registered at 3 months and the longest follow-up. A clustered two-part regression model for semicontinuous data was used.

RESULTS

Data pertaining to 160 patients (92 females, mean age 54) and 344 implants (125 in HA cohort, 219 in OT cohort) were available for evaluation. Mean MBL amounted to 0.52 mm (SD 0.68) after a mean follow-up of 20 (SD 9.2) months, with 33.8% of the implants showing complete bone preservation and 5.0% demonstrating >2mm MBL. OT was not related to the presence of MBL using MBL as dependent binary variable (0: no MBL; 1: MBL irrespective of its magnitude). However, OT significantly reduced the magnitude of MBL with 0.300mm when compared to HA (p = .023) in the cases where MBL was detected. Subgroup (p = .212), smoking (p = .789), history of periodontitis (p = .839), type of edentulism (p = .054), implant surgeon (p = .079), patient compliance (p = .617), and follow-up (p = .443) failed to show a significant association with MBL in the regression model. Ninety-eight % of the implants survived.

CONCLUSION

Within the limitations of a cohort study, the one-abutment one-time concept was associated with a decrease in MBL at implant sites with bone loss. Therefore, the placement of a permanent abutment at the time of surgery seems relevant to limit marginal bone-level alterations.

Influence of Screw Channel Angulation on the Fracture Resistance of Zirconia Abutments: An In Vitro Study

PURPOSE

The aim of this study was to investigate the effect of implant screw channel angulation on the fracture resistance of zirconia abutments without artificial aging.

MATERIALS AND METHODS

Ten implant replicas were embedded in a jig of autopolymerizing acrylic resin. Using a surveyor and a metallic platform, the implant replicas were mounted centrally and with an angulation of 30°. A maxillary left central incisor crown was fabricated from pattern resin and scanned. The digital design of a monolithic zirconia implant abutment-crown was completed using a 3D imaging software. For all specimens of this group (ASC₂₅ ), the screw channel was positioned at 25° to the lingual. Following fabrication, the samples were attached onto the embedded implant replicas and manually torqued to 35 Ncm as recommended by the manufacturer. The monolithic zirconia implant abutment-crowns were mounted in a metallic platform, positioned perpendicular to the indenter, and subjected to loading until failure. Crosshead speed was set at 0.5 mm/min for the universal testing machine. Data from a similar in vitro study where straight zirconia custom abutments (ASC₀ ) were subjected to static load until failure was used as a control group. An unpaired Student's t-test was used to determine if fracture resistance based on load at failure and maximum load in each group were significantly different from each other (ASC₂₅ vs ASC₀ ). Statistical significance level was inferred at p ≤ 0.05 RESULTS: Group ASC₂₅ fractured at a mean (SD) load of 215.49 (47.10) N and a mean (SD) maximum load of 420.50 (17.18) N. Group ASC₀ fractured at a mean (SD) load of 534.04 (133.77) N and a mean (SD) maximum load of 762.69 (109.59) N. The difference was statistically significant for both mean load and mean maximum load at failure (p ≤ 0.05). The survival rate of 0° zirconia abutments was significantly higher than that of 25° ASC zirconia abutments.

CONCLUSIONS

Within the limitations of this in vitro study the mean fracture load was significantly higher in the group with a straight channel angulation.

Full-zirconia single-tooth molar implant-supported restorations with angulated screw channel abutments: A 1-year prospective case series study

Background

Implant‐supported restorations in the posterior region are subjected to various complications that could be prevented by changing either the design or the material.

Purpose

The aim of this prospective case series study was to evaluate full‐zirconia implant‐supported restorations with angulated screw channel abutments in the molar region of the maxilla and mandible and their effect on hard and soft peri‐implant tissues, during a 1‐year follow‐up period.

Materials and Methods

Thirty consecutive patients with a single missing molar, sufficient bone height, and implant site free of infection were included. Each patient was to receive a parallel‐walled implant with conical connection according to a two‐staged surgical protocol. After 3 months, a full‐contour screw‐retained zirconia restoration with angulated screw channel abutment was provided. Clinical and radiographic examinations were performed 1 and 12 months after placement of the restoration. Patients' satisfaction was scored prior to treatment and after 12 months with the restoration in function. Primary outcome measure was success of the restoration.

Results

All patients could be evaluated after 12 months. Success of the restorations was 100%. From loading to the 12‐month follow‐up, the mean marginal bone loss was 0.16 mm (SD: 0.26). Mean scores for plaque, calculus, peri‐implant mucosa, bleeding, and pocket probing depth were low, depicting healthy peri‐implant conditions. Patients' satisfaction was high and had improved after treatment.

Conclusion

Full‐contour zirconia implant‐supported restorations with angulated screw channel abutments in the molar region have an excellent clinical performance after 1 year of function.