Screw vs cement-implant-retained restorations: an experimental study in the beagle. Part 2. Immunohistochemical evaluation of the peri-implant tissues

Influence of Periodontal Status and Prosthetic Treatment on Survival and Success Rates in Implant Therapy: A 5-Year Retrospective Follow-Up Study

The objective of the present study was to evaluate the 5-year outcome of dental implant therapy and assess the survival, success, and biological and technical complications. A periodontal and prosthetic-oriented evaluation was conducted on the variables that can influence the long-term predictability of implant therapy. A total of 615 patients and 1427 dental implants from a private clinic (MedArtis Dent, Cluj-Napoca, Romania) were enrolled in the study. The study was a longitudinal cohort with data collected retrospectively from physical/digital dental records in combination with a cross-sectional clinical/radiological examination. Results showed that periodontal diagnosis at baseline had a significant impact on the marginal bone loss prediction. Data showed that the cylindrical implant with an internal 45° medium taper connection experienced a higher rate of bone resorption compared to the tapered implant with the 5° internal connection. Screw-retained restorations and overdentures showed a statistical decrease in the marginal bone level height when compared to the cemented restorations. Data from our study suggest that not only is there a powerful association between recall visits and the rate of complications in dental implant treatment, but a lack of professional maintenance predicts a higher bone level loss during the 5-year interval.

Cemented versus screw-retained zirconia-based single implant restorations: 5-year results of a randomized controlled clinical trial

Objectives

To compare cemented and screw‐retained one‐piece zirconia‐based restorations in terms of clinical, radiographic, and technical outcomes 5 years after insertion.

Materials and methods

Thirty‐four patients with single‐tooth implants were randomly restored with either a cemented lithium disilicate crown on a one‐piece customized zirconia abutment (CEM, 17 patients) or a screw‐retained crown based on a directly veneered one‐piece customized zirconia abutment (SCREW, 16 patients). All patients were recalled for a baseline examination (7–10 days after crown insertion) and then annually up to 5 years. The following outcomes were assessed: marginal bone level (changes), technical, and clinical (bleeding on probing, plaque control record, probing depth, and keratinized tissue) parameters. The Mann–Whitney U‐test was used to assess differences between the two groups.

Results

At 5 years, 26 patients (13 in each group) were re‐examined. The survival rates on the implant and restorative levels were 100% and 82.4% (equally for both groups), respectively. At 5 years, the median marginal bone level was located at −0.15 mm (IQR: −0.89 mm; 0.27 mm) (CEM) and −0.26 mm (IQR: −0.38 mm; 0.01 mm) (SCREW) below the implant shoulder (intergroup p = .9598). The median changes between baseline and the 5‐year follow‐up amounted to −0.23 mm (CEM; intragroup p = .0002) and −0.15 mm (SCREW; intragroup p = .1465) (intergroup p = .1690). The overall technical complication rate at 5 years was 15.4% (CEM) and 15.4% (SCREW) (intergroup p = 1.00). Clinical parameters remained stable over time (baseline to 5 years).

Conclusions

At 5 years, screw‐retained and cemented restorations rendered largely the same clinical, technical, and radiographic outcomes. Technical complications were frequent in both groups.

Esthetic Evaluation and Acceptability of Different Hole Designs on Implant Crowns from the Perspective of Patients and Dentists in China

PURPOSE

Abutment access hole on dental implant crowns may facilitate crown retrieval and reduce cement overflow but present esthetic obstacle for patients. This study aimed to investigate the esthetic evaluation and acceptability of implant crowns with different hole designs from the perspective of patients and dentists.

MATERIALS AND METHODS

Anterior and posterior implant zirconia crowns were fabricated into three types: no hole (NH), 1 mm micro hole (MH), and 2.5 mm regular hole (RH). The NH crown was set as the control, and the anterior and posterior crowns with MH and RH were evaluated. The subjects, who were recruited randomly, were comprised of lay patients (n=60) and professional dentists (n=30). All subjects were invited to evaluate the esthetic performance of MH and RH crowns on a Visual Analog Scale (VAS), rate them from 0 to 10, state their acceptability of these crowns, and label them as acceptable and unacceptable.

RESULTS

The ANOVA analysis of the VAS esthetic evaluation showed that the size of the hole, the position of the teeth, and the professional background of the subject significantly and independently affected esthetic perception. Crowns with MH in the posterior position had higher esthetic scores and acceptability compared with crowns with RH in the anterior position, and dentists tended to show higher acceptance and better esthetic rating for crowns with holes compared with lay patients.

CONCLUSION

The hypothesis that patients and dentists hold similar esthetic evaluations or acceptability towards implant crown hole designs was rejected. Lay patients had a lower tolerance for venting holes than dentists. Crowns with 1 mm micro holes were more recommendable than crowns with regular abutment access holes from the point of view of satisfying patients' esthetic needs.

Mechanical Pull-Out Test of a New Hybrid Fixture-Abutment Connection: An In Vitro Study

Implant abutment connection was described among the main causes of peri-implant bone resorption. The aim of this in vitro study was to test the coupling capacity, the surface modification of a new hybrid connection and the influence of repeated connection activations caused during the main clinical and laboratory phases. A total of 40 implant-abutment screw retained systems with 10°-conical and internal hexagon connection were tested. The connection was screwed, fixed to the universal test machine, removed the screw and a pull-out test was performed. Test was repeated five times in succession. Also Scanning Electron Microscopy (SEM) was used to detect microscopically surface modification. Analysis of variance and Tukey tests were used for the statistical analysis. Pull-out test reveals a mean value of 131.35 ± 16.52 Newton Centimeter (N·cm). For each single activation, results from first to fifth were: 113.9 ± 13.02, 126.1 ± 12.81, 138.11 ± 15.15, 138.8 ± 11.90 and 140 ± 12.99 N·cm. A statistically significant difference between the measurements and an increase in the removal force was shown. The collected data supports the use of this new type of connection, resulting in a very strong interface between implant and abutment. Also, repeated activation of connection can promote a better coupling of the implant-abutment interface.

A 4 Year Human, Randomized, Radiographic Study of Scalloped versus Non-Scalloped Cemented Implants

Marginal bone loss (MBL) is a key factor in long-term implant success rate. Among the different factors that influence MBL, it is the different implant shoulder designs, such as scalloped or non-scalloped, which have been widely studied on screw retained but not on cemented retained implants. Thus, the aim of the present study was to evaluate the MBL around scalloped and non-scalloped cemented retained dental implants after 4 years of loading, in humans. A total of 15 patients were enrolled in the present study. A radiographic and clinical examination was performed after implant placement (T0) and after 4 years from it (T1). The results demonstrated a differential MBL (T1-T0) of 2.436 ± 1.103 mm and 1.923 ± 1.021 mm, respectively for test (scalloped) and control (non-scalloped) groups with a statistically significant difference between them. On the other hand, no statistically significant differences were found between the groups in terms of prosthetic complication and abutment decementation, whilst ceramic crowns chipping was shown in both groups. In conclusion, the use of a scalloped platform did not provide better results on the maintenance of MBL after 4 years follow-up. In this study, this probably was determined by multiple factors, among which was the subcrestal insertion of scalloped implants.

Peri-Implant Bone Resorption during Healing Abutment Placement: The Effect of a 0.20% Chlorhexidine Gel vs. Placebo-A Randomized Double Blind Controlled Human Study

Introduction

Peri-implant marginal bone loss (MBL) seems to be more pronounced in the first year of loading despite all the studies and changes implemented to reduce it. Among the different causes, the presence of a microgap makes the interface between fixture and abutment colonizable by bacteria, causing an inflammatory response and consequent bone resorption. To reduce this several local antiseptics like chlorhexidine digluconate (CHX) were used after surgical procedures.

Aim

The objective was to radiologically compare the MBL when a 0.20% CHX gel or a placebo gel was applied to the implant-abutment interface during all surgical and prosthetic phases and for a follow-up period up to 12 months.

Method

32 patients (16 for each Group A and B) were enrolled and rehabilitated with a single implant (Cortex classic, Cortex, Shalomi, Israel). During each of the clinical stages a gel containing 0.20% CHX (Plak ®Gel; Polifarma Wellness Srl, Rome, Italy) or a placebo gel (Placebo, Polifarma Wellness Srl, Rome, Italy) was used as indicated by the randomization chart. In order to compare radiographic modification intraoral radiographs was taken. Also, clinical data regarding implant or prosthetic failure and gingival index were recorded. Data were presented as means and standard deviations (SD) and used for the statistical analysis.

Results

All implants showed no bleeding on probing and a very small plaque score at the 1 year of follow-up. MBL was statistically significantly different between the groups in every stage.

Conclusion

Results obtained showed that the use of CHX gel inside the connection significantly reduces MBL during the first year. A rigid disinfection protocol with 0.20% CHX from the time of implant insertion to crown delivery is recommended to reduce host inflammatory response and consequently MBL. This trial is registered with ClinicalTrials.gov Identifier: (Registration Number: NCT03431766).

Sem and Fractography Analysis of Screw Thread Loosening in Dental Implants

Biological and technical failures of implants have already been reported. Mechanical factors are certainly of importance in implant failures, even if their exact nature has not yet been established. The abutment screw fracture or loosening represents a rare, but quite unpleasant failure. The aim of the present research is an analysis and structural examination of screw thread or abutment loosening compared with screw threads or abutment without loosening. The loosening of screw threads was compared to screw thread without loosening of three different implant systems; Branemark (Nobel Biocare, Gothenburg, Sweden), T.B.R. implant systems (Benax, Ancona, Italy) and Restore (Lifecore Biomedical, Chaska, Minnesota, USA). In this study broken screws were excluded. A total of 16 screw thread loosenings were observed (Group I) (4 Branemark, 4 T.B.R and 5 Restore), 10 screw threads without loosening were removed (Group II), and 6 screw threads as received by the manufacturer (unused) (Group III) were used as control (2 Branemark, 2 T.B.R and 2 Restore). The loosened abutment screws were retrieved and analyzed under SEM. Many alterations and deformations were present in concavities and convexities of screw threads in group I. No macroscopic alterations or deformations were observed in groups II and III. A statistical difference of the presence of microcracks were observed between screw threads with an abutment loosening and screw threads without an abutment loosening.

Bone Behavior in Relation to the Depth of the Line of Marginal Cementation of Prostheses on Morse Cone Implants: Radiographic Evaluation in a Dog Model

PURPOSE

This study was aimed at radiographically evaluating the effect of 3 different depths of the cementation line of prosthetic crowns on the bone response around Morse cone implants.

MATERIAL AND METHODS

Five dogs underwent extractions of the lower premolars; after 3 months, placement of 30 implants, 3 mm apical to the bone level, was performed. Prefabricated cylinders of alumina, used as abutments, with 3 different transmucosal extension were cemented to the implants with zinc oxide-eugenol cement, determining the depth of the cementation lines (1.5 mm apically, and 0.5 and 2.5 mm coronally, respectively, to the bone level). In the control group, implants and abutments were placed without crowns, therefore, with no cementation line.

RESULTS

The results showed no statistically significant differences between the control and test groups regarding the different depths of the cementation line both mesially (P = 0.18) and distally (P = 0.50).

CONCLUSION

Different depths of cementation did not affect the behavior of marginal bone, indicating that crowns can be cemented with zinc oxide-eugenol cement at any distance or even at the bone level without disturbing bone healing around Morse cone implants.

Does residual cement around implant-supported restorations cause peri-implant disease? A retrospective case analysis

OBJECTIVES

The purpose of this study was to determine the relationship between patients with a history of periodontitis and development of cement-related peri-implant disease.

MATERIALS AND METHODS

Seventy-seven patients with 129 implants for this retrospective analysis were selected from completed implant cases that were scheduled for regular maintenance or had experienced mechanical or biological complications between years 2006 and 2011 in private practice. Implants with extracoronal residual cement and implants without cement remnants were analyzed. The selected cases were further divided into two groups--implants in patients with history of periodontitis (1) and implants in periodontitis-free individuals (2). The selection of these groups was made on the basis of treatment history and orthopantomograph. As a control group, a set of 238 screw-retained implant restorations, delivered to 66 patients during the same period of time was examined. The incidence of peri-implant disease among implants in all groups was calculated.

RESULTS

Peri-implant disease was evident in 62 of 73 implants with cement remnants (85%). All implants in group 1 developed peri-implantitis--4 early and 35 delayed disease cases. In the periodontally healthy group, 20 of 31 implants were diagnosed with peri-implant mucositis, 3 implants had early peri-implantitis, and 11 implants with cement remnants did not develop biological complications. In the group of implants without cement remnants, peri-implant disease was diagnosed in 17 of 56 cases (30%). In contrast, only two occurrences of peri-implant disease were registered in the control group of screw-retained restorations (1.08%).

CONCLUSIONS

Implants with cement remnants in patients with history of periodontitis may be more likely to develop peri-implantitis, compared with patients without history of periodontal infection.

Histological Evaluation of Peri-Implant Soft Tissues in Immediately Loaded Implants Featuring Different Implant-Abutment Connections: A Preliminary Study

The aim of the present study is to evaluate the peri-implant soft tissues and the amount of inflammatory cells around two different implant-abutment connections (self-locking conical connection with platform switching and screwed connection with standard abutment and internal anti-rotational system). Histological analysis was made of 14 implants, 7 with self-locking Morse tapered connection (experimental group A) and 7 with screw-retained anti-rotational connection (control group B). Sixty days after non-functional immediate loading, peri-implant tissue biopsies were performed. In the samples taken from the experimental group the peri-implant connective tissue consisted of a greater density of collagen and fibroblasts compared to the connective tissue of the control group. The experimental group specimens showed less inflammatory infiltrate close to the self-locking tapered connection compared to the tissues around the screw-retained connection. The SEM observations showed less microgap in the self-locking conical connection than in the screw connections with standard abutment and internal anti-rotational system. The presence of connective tissue with few inflammatory cells and the absence of inflammatory infiltrate, in self-locking conical connection implants is due to the minimal size of the implant-abutment microgap that does not allow the passage of fluids and bacteria from the oral cavity to the implant thus preventing tissue inflammation.

In vitro influence of ultrasonic stress, removal force preload and thermocycling on the retrievability of implant-retained crowns

OBJECTIVES

The main goals of this in vitro study were to evaluate the influence of thermocycling, ultrasonic stress and the removal force preload on the retrievability of cemented implant crowns using a clinical removal device (Coronaflex) and evaluating the tensile strength using a universal testing machine (UTM).

METHODS

Thirty-six crowns were cast from a Co-Cr alloy for 36 tapered titanium abutments (5° taper, 4.3 mm diameter, 6 mm height, Camlog, Germany). The crowns were cemented with a glass-ionomer (Ketac Cem) or a polycarboxylate (Durelon) cement, followed by 3 days of storage in ionized water without thermocycling or 150 days of storage with 37,500 thermal cycles between 5°C and 55°C. Before removal, the crowns were subjected to ultrasonic stress for 0, 5 or 10 min with a contact pressure of either 50 or 500 g. The Coronaflex was used with a removal force preload of 50 or 400 cN, respectively, applied on the point of loading. Scanning electronic microscopy (SEM) was used to evaluate the impact of the removal on the abutment screws.

RESULTS

Crowns cemented with the glass-ionomer cement were significantly easier to remove with the Coronaflex or the UTM than crowns cemented with the polycarboxylate cement (P≤0.05). Ultrasonic stress showed no significant impact on the retrievability regardless of the contact pressure or duration applied (P>0.05). No significant differences could be found for both cements when removed with the Coronaflex or the UTM (P>0.05) after thermocycling was applied. A removal force preload of 400 cN resulted in significantly reduced removal attempts in comparison with 50 cN for both cements (P≤0.05).

CONCLUSIONS

Ultrasound and thermal cycling did not result in reduced cement strength, but to retrieve the crowns, the full impact of a removal instrument has to be applied. Ketac Cem can be used as a "semipermanent" solution, whereas Durelon might serve for permanent cementation. None of the abutment screws showed signs of wear caused by the removal process.

Analysis and Structural Examination of Screw Loosening in Oral Implants

Biological and technical failures of implants have already been reported. Mechanical factors are certainly of importance in implant failures, even if their exact nature has not yet been established. The abutment screw fracture or loosening represents a rare, but quite unpleasant failure. The aim of the present research is an analysis and structural examination of screw thread or abutment. In this study broken screws were excluded. A total of 58 screw thread loosening were observed, 5 Branemark, (Nobel Biocare, Gothenburg, Sweden) 4 Implant Innovation (Riverside Drive Palm Beach Gardens, FL, USA) and 7 Restore (Lifecore Biomedical, Chaska, Minnesota, USA) and 42 T.B.R. implant (Benax, Ancona, Italy). The loosened abutment screws were retrieved and analyzed under SEM. Many alterations and deformations were present in concavities and convexities of screw threads.