Diego Lops Eriberto Bressan Andrea Parpaiola Sbricoli Luca Denis Cecchinato Eugenio Romeo

Soft tissues stability of cad-cam and stock abutments in anterior regions: 2-year prospective multicentric cohort study

Authors’ affiliations: Diego Lops, Eugenio Romeo, Department of Prosthodontics, Dental Clinic, School of Dentistry, University of Milan, Milan, Italy Eriberto Bressan, Sbricoli Luca, Department of Periodontology, School of Dentistry, University of Padova, Padova, Italy Andrea Parpaiola, Department of Prosthetic Dentistry, School of Dentistry, University of Padova, Padova, Italy Denis Cecchinato, FRANCI Insitute, Padova, Italy

Key words: anterior regions, cad-cam abutments, soft tissues stability, stock abutments

Corresponding author: Diego Lops Department of Prosthodontics, Dental Clinic, School of Dentistry University of Milan Via Beldiletto 1/3, 20142 Milan, Italy Tel.: +39 0250319039 Fax: +39 0250319040 e-mail: [email protected]

stock abutments), Group 2 (titanium stock TiDesignâ abutments), Group 3 (zirconia cad-cam

Abstract Aim: Aim of this study was to verify if the type of implant abutment manufacturing, stock or cadcam, could influence the maintenance of stable gingival margins around single restorations in anterior areas. Methods: After 16 weeks of healing, implants (Osseospeed, Astra Tech Dental Implant) were positioned. Depending on the different fixture inclination and the thickness of buccal peri-implant soft tissue, abutment selection resulted in four groups: Group 1 (patients with zirconia ZirDesignâ abutments), and Group 4 (titanium cad-cam abutments). The following parameters were assessed: buccal gingival margin modification (BGM). The modification of the implant gingival margin was followed at 1 and 2 years of follow-up. A computerized analysis was performed for measurements. Differences between soft tissue margin at baseline and after 2 years measured the gingival margin recession. A general linear model was used to evaluate each group in relation to gingival recession after two years. Tukey’s post hoc test was used to compare the mean REC indexes of each group of abutments. Results: Seventy-two healthy patients (39 males and 33 females; mean age of 46 years) scheduled for single gap rehabilitation in anterior areas were enrolled. A 100% of implant survival rate was observed after 24 months of function. One failure occurred due to fracture of a Zirconia cad-cam abutment. Moreover, two abutment screw unscrewing were observed. Both for zirconia and titanium stock abutments (Group 1 and 2), the mean recession of implant buccal soft tissue was of 0.3 mm (SD of 0.3 and 0.4 mm, respectively). Soft tissue mean recession of zirconia and titanium cad-cam abutments (Group 3 and 4) was of 0.1 and

0.3 mm, respectively (SD of 0.3 and 0.4 mm,

respectively). REC values of cad-cam titanium abutments (Group 4) were significantly lower than that of Group 1 ( 0.57 mm), Group 2 ( 0.61 mm), and Group 3 ( 0.40 mm), respectively (Table 4). Conclusion: In the anterior area, the use of cad-cam abutments is related to a better soft tissue stability. Such a relationship is significant if cad-cam titanium abutments are compared to both titanium and zirconia stock abutments.

Date: Accepted 24 July 2014 To cite this article: Lops D, Bressan E, Parpaiola A, Luca S, Cecchinato D, Romeo E. Soft tissues stability of cad-cam and stock abutments in anterior regions: an up-to-2 years prospective multicentric cohort study. Clin. Oral Impl. Res. 00, 2014, 1–7 doi: 10.1111/clr.12479

Eesthetic demands of patients undergoing single implant treatment in areas exposed during smiling may be difficult to satisfy. Moreover, not always the natural appearance of the peri-implant soft tissues may be achieved (Cosyn et al. 2011, 2012; Raes et al. 2013). Regarding the medium-term follow-up of the facial gingival levels, only few data are available at present time (Kan et al. 2011; Cosyn et al. 2012). Some parameters like gingival biotype and buccal implant shoulder position were found to be associated with the gingival recession (Kan et al. 2011; Cosyn et al. 2012). Conversely, a review by Cairo

© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

et al. (2008) on the peri-implant soft tissue management concluded that these parameters are not associated with the mucosal recession around anterior implants. As the peri-implant soft tissues morphology in anterior areas is not flat, the prosthetic emergence profile should reproduce the natural soft tissues scalloping. The use of a stock abutment may result in a round shape of the mucosa, with an emergence profile not showing a natural appearance. Conversely, anatomical shape of the implant abutment may help to support the surrounding soft tissues; also this aspect may influence the stability of the

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buccal peri-implant soft tissues (Parpaiola et al. 2013). Unfortunately, no data are actually available on the comparison between soft tissue stability of prostheses supported by Cad-Cam and stock abutments in anterior areas. Such a lack of information is noticeable both for zirconia and titanium abutments, for which no clinical difference was reported on medium-term prognosis (Zembic et al. 2009, 2013; Lops et al. 2013a). The same conclusions were drawn about technical and biological complication rates of zirconia and titanium abutments. Conversely, regarding the factors affecting the presence or absence of a complete interproximal papilla, both the implant to tooth distance and the distance of the bone peak to the prosthetic contact point are considered as inter-proximal recession predictors (Ryser et al. 2005; Lops et al. 2008, 2013b; Romeo et al. 2008; Kwon et al. 2009; Chow & Wang 2010; Nisapakultorn et al. 2010; Koh et al. 2011; Cosyn et al. 2011, 2012; Vela et al. 2012). For implants with a platform-switched abutment connection, a vertical distance from the inter-proximal bone peak and the contact point of ≤5 mm and a horizontal distance between the implant and the adjacent tooth of ≥1.5 mm were significantly associated with the presence of a complete interproximal papilla. The main focus of the present prospective study was to compare the buccal soft tissue stability of Cad-Cam zirconia and titanium abutments to those of stock zirconia and titanium abutments in anterior areas, over a period of 2 years.

Material and methods Patient selection

Patients in need of single gap restoration in the anterior region (form the second premolar forward) of both maxilla and mandible were consecutively treated from September 2010 to June 2011 by means of implant-supported single-tooth dentures (ST). Each patient received a single endosseus dental implant (Osseospeedâ; Dentsply Dental Implants, Astra Tech AB, M€ olndal, Sweden). Treatments were performed at the Dental Clinic of Biomedical Sciences Institute, S. Paul Hospital, University of Milan, Italy, and at the Dental Clinic, Department of Medicine, Surgery and Dentistry, University of Padova, Italy. Written informed consent was obtained from all the subjects included in the study

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for treatment of single maxillary recession. The patients were informed about the purpose of the study, the clinical procedures, and the materials to be used. In obtaining the informed consent and in conducting the study, the principles outlined in the Declaration of Helsinki on experimentation involving human subjects were adhered to as revised in 2000. Inclusion criteria were (i) single edentulism in the anterior maxilla or mandible (from first premolar forward); (ii) absence of local inflammation; (iii) absence of oral mucosal disease; (iv) adequate oral hygiene; (v) extraction at least 6 months before; and (vi) adequate bone volume at the implant site (for placement of an implant at least 3.5 mm in diameter and 8 mm in length) evaluated on intraoral periapical radiographs and clinical evaluation. Exclusion criteria were (i) patients with systemic diseases (such as heart, coagulation, and leukocyte diseases or metabolic disorders); (ii) history of radiation therapy in the head and neck region; (iii) current treatment with steroids; (iv) neurological or psychiatric handicap that could interfere with the treatment; (v) immuno-compromised status, including infection with human immunodeficiency virus; (vi) severe clenching or bruxism; (vii) smoking habit (more than 15 cigarettes per day); (viii) drug or alcohol abuse; and (ix) inadequate compliance. Surgical procedures

A two-stage surgical technique was planned for all patients. A mucoperiosteal flap was raised without vertical releasing incisions, and an implant was inserted according to the edentulous site dimension. The flaps were sutured back to allow a submerged healing. No GBR procedures were performed and no additional soft or hard tissue grafts were used. During the healing phases, the edentulous gaps were temporarily restored with removable prostheses or provisional fixed bridges, when requested by the patient. Four months later, implants were uncovered and trans-mucosal healing abutments (Healing Abutment, Astra Tech Dental Implant, M€ olndal, Sweden) were inserted. Prosthetic procedures and patients allocation

Two weeks after surgical re-entry, an implant-level impression was taken for the fabrication of a screw-retained temporary restoration. The provisional restoration was inserted 1 week after implant-level impression.

As the manufacturer final stock abutments (Dentsply Implants, Astratech Dental, TiDesignâ and ZirDesignâ abutments, Mo¨lndal, Sweden) are provided with a maximum inclination of 15°, two different type of abutments were selected for the final restorations: stock and cad-cam abutments, respectively, for fixtures inclination within 15° or exceeding 15° that of the ideal implant axis. After 8 weeks of soft tissue conditioning by means of the provisional restoration, a final impression at implant level was taken; a precise record of the soft tissue dimensions was recorded on the cast models. The pickup impression coping was modified by adding a self-polymerizing resin (Duralay, Chicago, IL, USA) to reply the emergence profile of the provisional restoration in the cast (type IV dental stone; New Fuji-Rock, GC Corp, Tokio, Japan). The peri-implant mucosa was replicated by using a soft siliconic material around the implant analog before the dental stone application: so that an eventual inaccuracy of the soft tissue reproduction steps could be minimized. The thickness of the facial peri-implant soft tissue was measured on the master cast (Fig. 1) at the level of the implant neck through a caliper (Iwanson Decimal Caliper; Asa Dental spa, Lucca, Italy). Zirconia was selected as abutment material for buccal mucosal thickness within 2 mm; instead, titanium was selected as abutment material for buccal thickness exceeding 2 mm. The selection was based on data available in the literature about the soft tissue color changes with different abutment materials (Jung et al. 2007, 2008; Bressan et al. 2011). For this reason, no randomization was possible for the abutment material selection in anterior areas. Therefore, by considering the fixture inclination and the thickness of the facial periimplant soft tissues, the patient was treated as follows:

• • • •

Group 1: patients with zirconia stock abutments. Group 2: patients with titanium stock abutments. Group 3: patients with zirconia cad-cam abutments. Group 4: patients with titanium cad-cam abutments.

The system for cad-cam abutments milling (Atlantisâ, Mo¨lndal, Sweden) uses computeraided technology to create their abutment contours. The Atlantis process scans the master cast to detect soft tissue contours, occlusal clearance, and implant location. A

© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Lops et al  Soft tissues stability of cad-cam and stock abutments

Fig. 1. Thickness of the facial peri-implant soft tissue measured on the master cast at the level of the implant neck by means a caliper.

virtual abutment is then designed and optimized based upon parametric ideal abutment shapes with design constrains (Fig. 2). After the virtual design is completed, it is milled from a zirconia or titanium blank. Four months after implant placement, the definitive cemented prostheses were positioned. For each patient, a manual torque driver was used to secure the abutment with the fixture by means of titanium screw as recommended by the manufacturer. The definitive restorations were metal-ceramic and zirconiaceramic, respectively. To avoid any influence of the prosthetic margins on the soft tissue outcomes, a juxta-gingival emergence profile was provided for all the implant-supported restorations. Zinc oxy-phosphate cement

(Temp Bondâ; Kerr Mfg. Co., Romulus, MI, USA) was used for the fixation. Parameters analyzed

The main outcome variable, buccal gingival margin modification (BGM), was assessed at baseline, after 1 and 2 years of follow-up. To evaluate the modification of the implant gingival margin, digital photographs were taken for each patient at baseline (Fig. 3), after 1 and 2 years of follow-up (Fig. 4). A computerized analysis (Image-Jâ image processing software, Bethesda, MD, USA) was performed for the photograph measurements (Kerner et al. 2007; Lops et al. 2013b). A frontal projection was used to avoid any image distortion.

(a)

(b)

(c)

Fig. 2. Virtual abutment designed with computer-aided procedure: frontal (a), occlusal (b), and lateral (c) aspect.

© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Two setting parameters were chosen to check the reproducibility of each picture (Kerner et al. 2007; Lops et al. 2013b). They were (i) Apico-coronal vertical line (a) from the most apical point of the buccal gingival margin to the most coronal portion of the crown edge. (ii) A mesio-distal horizontal line (b) at the widest part of the crowns adjacent to the treatment site. One of the teeth adjacent to the treatment site was used for a and b measurements. Furthermore, a calibrated plastic probe (TPS probe; Vivadent, Schaan, Liechtenstein) was used on the same tooth to compare the values of a and b with those measured with the computerized analysis. Only differences of ≤0.5 mm were accepted for data calculation. To measure the gingival margin modification (BGM) on the restored implant-supported crown, three lines were drawn on each photograph (Figs 3 and 4): a guide line (AL) was drawn joining the most apical point of the buccal margin of the teeth adjacent to the implant site; a second line (TL) parallel to AL was used to indicate the most apical point of the test site buccal margin; finally, a third line (TAL) measured the distance between TL and AL. The difference between TAL at baseline and after 2 years of follow-up measured gingival margin modification (BGM) of the gingival margin. A positive score of BGM was considered as a mucosal recession. Only apical shrinkage of ≥0.5 mm was considered as soft tissue recession. Measurements were made by one of the authors (LS) and rounded off to the nearest half millimeter. Intra-examiner variability was evaluated by triplicate measurements of three soft tissue margins, to detect a maximum of 5% of the coefficient of variation for soft tissue recession and linear evaluation. Any adverse event or biological or technical complication was recorded if present at any time point. Implant survival rate calculation included as survivors: (i) Implants supporting functional and asymptomatic prostheses though showing a mean bone loss rate that exceeded the maximum limits established by the present study (within 1 mm during the first year after implant placement, and 0.2 mm per year in subsequent years). (ii) Implants showing clinical and radiographic signs of peri-implantitis (subsequently treated). Clinical mobility was mandatory for implant removal. Implants showing mobility were regarded as “failures”. Prosthetic failure was defined in the presence of one of the following conditions:

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correlation coefficient was used to measure the strength of the linear relationship between the two aforementioned variables.

Results

Fig. 3. Measurement of the gingival margin modification (BGM) at baseline. The BGM index resulted from the difference between two lines: the one (marked in red) joining the most apical point of the buccal margin of the teeth adjacent (AL) to the implant site, and the one (marked in blue) parallel to AL joining the most apical point of the test site (TL) buccal margin; finally, a third line (TAL 0), marked in yellow, measured the distance between TL and AL at baseline. Apico-coronal vertical line (a) and the mesio-distal horizontal line (b) of the adjacent tooth were chosen as setting parameters to check the reproducibility of each picture.

Fig. 4. Measurement of the gingival margin modification (BGM) after 2 years of follow-up: the difference between TAL at baseline (TAL 0) and after 2 years (TAL 2) measured the recession of the gingival margin (REC).

(i) Prosthetic framework permanent warpage or breakage. (ii) Abutment or implantto-abutment connecting screw breakage. (iii) Framework-to abutment fixing screw impairment. Prosthetic complication was attributed to the following events: (i) Prosthesis detachment. (ii) Abutment-framework screw unscrewing. (iii) Porcelain veneer permanent warpage or breakage. Statistical analysis

A power calculation test was performed prior to the study to detect a mean difference of gingival recession between groups of 0.4 mm with a standard deviation of 0.6 mm, setting a power of 80% and an alpha of 0.05. The database consisted of thirty-six patients per group. However, due to ethical reasons, it was not possible to randomly assign the groups, as it was considered that in some cases a zirconia abutment was a compulsory choice for esthetic reason. Therefore the

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initial value of recession was introduced in the model to evaluate potential differences in the initial value. The normal distribution of data was firstly analyzed and confirmed with Kolmogorov– Smirnov and Shapiro Wilk normality test (P < 0.001). Subsequently, a general linear model was used to evaluate each group in relation to gingival recession after 2 years. A one-way ANOVA model was used. By means of Tukey’s post hoc test, the mean BMG indexes of each group of abutments were compared. Initial recession values for all groups of abutments were tested to evaluate an eventual influence on the 2 years soft tissue recession values. The null hypothesis of no difference between the four groups was tested with significance level P < 0.05. Furthermore, correlation analysis between the initial mucosal thickness and amount of mucosal recession was provided. The Pearson

Seventy-two patients were included in the study; implant distribution is reported in Table 1. Forty-six of them were treated at the Dental Clinic of Biomedical Sciences Institute, S. Paul Hospital, University of Milan, Italy, while 26 at the Dental Clinic, Department of Medicine, Surgery and Dentistry, University of Padova, Italy. A total of 72 implants (Osseospeed, Astra Tech Dental Implant, Astra Tech AB, M€ olndal, Sweden) were positioned. Thirty-six patients received stock abutments: 13 zirconia (ZirDesignâ) and 23 titanium (TiDesignâ) abutments were used, respectively. Thirty-five stock abutments were used for fitting with 3.5–4 mm fixture diameter. One was used for fitting with 4.5 mm fixture diameter. Moreover, 36 patients received cadcam abutments: 20 zirconia (Atlantisâ) and 16 titanium (Atlantisâ) abutments were used, respectively. Abutment distribution is reported in Tables 1 and 2. All patients, aged between 26 and 58 years old (39 males and 33 females with a mean age of 46 years), presented good general health and the absence of local inflammation and mucosal diseases at the time of surgical procedure. The minimum follow-up was of 24 months after the start of prosthetic loading. All inserted implants were restored, and a 100% implant survival rate was observed at 2-year follow-up. All the included patients were followed at each consecutive annual examination. Therefore, no implant was classified as “drop-out”, and 72 patients were consecutively followed during the 2-years period. Clinical evaluation

During 24 months of function, no soft tissue inflammation was diagnosed to the implantsupported restorations. Values recorded for the buccal gingival modification (BGM) after 1 year follow-up are reported in Table 3. Initial recession values for all groups of abutments did not influence the 2 years soft tissue recession values (significance level 0.41). Both for zirconia and titanium stock abutments (Group 1 and 2), the mean recession of implant buccal soft tissue was 0.3 mm, respectively. Furthermore, the buccal soft tissue mean recession of zirconia and

© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Lops et al  Soft tissues stability of cad-cam and stock abutments

Table 1. Stock abutment distribution related to the implant site and implant diameter ø 3.5 mm

ø 4 mm

the prosthetic reconstructions were still in function at the end of the follow-up period, thus leading to a prosthetic cumulative survival rate of 100% for the abutments of Group 1, 2, and 4 (zirconia stock abutments, titanium stock abutments, and titanium cad-cam abutments, respectively). The prosthetic survival rate was 95% for the abutments of Group 3 (zirconia cad-cam abutments). Nevertheless, the prosthetic success rate was as follows: Group 1: 92.4%. Group 2: 95.7%. Group 3: 95%. Group 4: 100%.

ø 4.5 mm

Area

Zr

Ti

Zr

Ti

Zr

Ti

Maxillary incisors/canine Maxillary premolars Mandibular incisors/canine Mandibular premolars Total

3 2 0 3 8

2 8 0 1 11

1 4 0 0 5

2 8 0 1 11

0 0 0 0 0

0 0 1 0 1

Table 2. cad-cam abutment distribution related to the implant site and implant diameter ø 3.5 mm

ø 4 mm

ø 4.5 mm

Area

Zr

Ti

Zr

Ti

Zr

Ti

Maxillary incisors/canine Maxillary premolars Mandibular incisors/canine Mandibular premolars Total

6 3 1 1 11

1 8 0 1 10

4 3 0 2 9

1 3 0 1 5

0 0 0 0 0

0 0 1 0 1

Discussion

Table 3. Buccal soft tissue recession values (REC) Mean (mm) Median (mm) SD (mm)

Abutment Group 1

Abutment Group 2

Abutment Group 3

0.3 0.5 0.3

0.3 0.0 0.4

0.1 0.1 0.3

Abutment Group 4 0.3* 0.2* 0.4

SD, Standard deviation; Group 1, Stock Zirconia; Group 2, Stock Titanium; Group 3, cad-cam Zirconia; Group 4, cad-cam Titanium. * Negative values represent a soft tissue gain in vertical direction.

titanium cad-cam abutments (Group 3 and 4) was 0.1 and 0.3 mm, respectively (Table 3). BMG values were compared by considering the same type of abutment material, to avoid comparisons between different buccal mucosa thickness. The difference ( 0.61 mm) between mean BMG index of cad-cam titanium abutments (Group 4) was significantly lower (P = 0.000) than that of stock titanium abutments (Group 2). Differently, the difference ( 0.16 mm) between mean BMG index of cad-cam titanium abutments (Group 1) was not significantly lower (P = 0.723) than that of stock titanium abutments (Group 3) (Table 4). Furthermore, the mean buccal gingival thickness was measured; it was 1.75 and 2.75 mm for zirconia and titanium cad-cam abutments, respectively. The mean values for zirconia and titanium standard abutments were 1.72 and 2.91 mm, respectively. The correlation between the initial mucosal thickness and amount of mucosal recession was not statistically significant (P = 0.4). The Pearson correlation coefficient was used to measure the strength of the linear relationship between the two aforementioned variables.

The failed abutment was removed and replaced with an identical cad-cam abutment, so that the same final restoration could be used. Moreover, in two patients, abutment’s unscrewing was detected (Table 5). The abutments were torqued down again to 25 N/cm with a torque wrench, and the definitive restorations were cemented with temporary cement. The occlusal contacts were checked once more. No frameworks fracture was observed during the 2-years follow-up period, and no chipping of the veneering ceramic was found. All

Table 4. Comparison between recession indexes (REC) of each group of abutments 95% Confidence Interval (CI)

(I) Type of abutment Group 1: Stock Titanium

Group 2: Stock Zirconia

Group 3: cad-cam Zirconia

Group 4: cad-cam Titanium

Prosthetic evaluation

One failure occurred due to fracture of a Zirconia cad-cam abutment or loosening of an abutment screw, as reported in Table 5.

The stability of peri-implant soft tissues in the buccal aspect was described in the present study. The study included only patients restored in the anterior area, the “aesthetic area”. A better soft tissue stability was observed for zirconia and titanium cad-cam abutments if compared to that for zirconia and titanium stock abutments, respectively. Instead, as the number of patients included in this sample was quite small, the results of the present study should be confirmed by a larger sample. So that, the best performance exhibited by titanium cad-cam abutments instead of zirconia cad-cam abutments remained still unclear. The behavior of the buccal gingival margin around stock and cad-cam abutments was analyzed. Measurements have shown that the variations of gingiva height around these implants over a 2-years observation period were in the range from 0 to 1 mm. Similar findings were observed by Grunder (2000) when the soft tissue stability around 10 single-tooth implants was evaluated; guided bone regeneration and connective tissue

(J) Type of abutment Custom Zirconia Custom Titanio Stock Zirconia Custom Zirconia Custom Titanio Stock Titanio Custom Titanio Stock Zirconia Stock Titanio Custom Zirconia Stock Zirconia Stock Titanio

Mean REC difference in mm (I-J) 0.20 0.61§ 0.04 0.16 0.57§ 0.04 0.40§ 0.16 0.20 0.40§ 0.57§ 0.61§

SD Error (mm)

Significance Level

0.136 0.128 0.145 0.156 0.149 0.145 0.141 0.156 0.136 0.141 0.149 0.128

0.451 0.000 0.993 0.723 0.003 0.993 0.033 0.723 0.451 0.033 0.003 0.000

Lower Limit

Upper Limit

0.16 0.26 0.35 0.26 0.16 0.43 0.02 0.59 0.57 0.78 0.97 0.95

0.57 0.95 0.43 0.59 0.97 0.35 0.78 0.26 0.16 0.02 0.16 0.26

§Significant difference (P < 0.05, Tukey’s post hoc test). Negative values represent a soft tissue gain in vertical direction.

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Table 5. Implant distribution: prosthetic complications and failures

Site

Implant Dimensions (mm)

Type of abutment

21 24 22

4 9 11 4 9 11 3.5 9 11

Zr cad-cam Ti Stock Zr Stock

Complication (years of function)

Failure (years of function)

Antagonist natural teeth

Abutment fracture (2) Abutment screw unscrewing Abutment screw unscrewing

1 – –

Vital Vital Vital

Tooth numbers: 24 = maxillary left first premolar; 22 = maxillary left second incisor; 21 = maxillary left first incisor.

grafting were included in the treatment of all cases. They reported a soft tissue recession of 0.6 mm buccally and a minimal increase of the papilla after 1 year. Also Lops et al. (2013b) reported similar results on postextractive implants. A mean soft tissue recession of 0.3 mm was calculated in the present study for stock abutments (Group 1 and 2 together). On the contrary, a slight soft tissue gain of 0.2 mm was noted for cad-cam abutments (Group 3 and 4 together). Nevertheless, the better soft tissue stability was significant only for titanium cad-cam abutments if compared to stock. From a clinical point of view, such a finding could be added to information reported in the literature on the colorimetric performances of different materials (Jung et al. 2008; Bidra & Rungruanganunt 2013; Paniz et al. 2014; Zembic et al. 2013). Although the best results for soft tissues stability were exhibited by cad-cam titanium abutments, for thin buccal soft tissues (1 mm (thick buccal wall), respectively. Regarding the type of abutment manufacturing, in a recent systematic review by Bidra & Rungruanganunt (2013), only 8 studies on cad-cam abutments were included; a mean abutment failure rate of 1.15% was reported. All failures (3) were due to abutment fracture, and no fracture was reported on titanium abutments. In addition, only one prospective study reported on the clinical performances of both cad-cam titanium and zirconia (Pozzi et al. 2012); unfortunately, only posterior regions were included in this study. This paucity of information regarding cad-cam abutments and the interest for a customized prosthetic emergence profile to reproduce and support the soft tissues of anterior areas could prompt the aim of the present trial. On the selection of the implant abutment, stock or cad-cam, the randomization was not possible to apply because of stock abutments are provided only with a maximum inclination of 15°. Moreover, also in the abutment material selection, zirconia or titanium, no randomization was applied

because of it is reported in the literature that peri-implant soft tissue thickness lower than 2 mm could not provide to mask the color of metallic part of the prosthetic component (Jung et al. 2007, 2008). So that, for an ethical point of view, it was not acceptable to randomize the selection of the abutment material, mostly in high esthetically demanding areas. The present study was designed as a cohort study, in which every patient was treated according to what was evaluated appropriate from the clinician, and therefore no randomization of the treatment was performed. This means that in the analysis, the type of abutment was not treated as a random effect but as a fixed parameter. Such a parameter was considered in relation with the initial conditions at the site, to verify if the different abutment could have a different impact on the soft tissue appearance, considering that they were selected specifically. Therefore, such study reported a descriptive analysis on the decision taken in every different situation and how this decision affected the outcome. Moreover, no data or classification of patients based on the gingival biotype was performed in the present study. In fact, it is already reported in the literature (Bressan et al. 2011, Cabello et al. 2013) that the periimplant soft tissue thickness is related to the surgical procedures during the implant placement; a fixture palatally positioned will be surrounded by a buccal soft tissue thickness more represented that a fixture buccally positioned. Besides, such a clinical reference is independent by the gingival biotype of the patient.

Conclusions In the anterior area, the use of cad-cam abutments is related to a better soft tissue stability. Such a relationship is significant if cadcam titanium abutments are compared to both titanium stock abutments.

Acknowledgements: The authors would like to thank Prof. Cristiano Tomasi for the important contribution in the statistical analysis of the present study.

References Bidra, A.S. & Rungruanganunt, P. (2013) Clinical outcomes of implant abutments in the anterior region: a systematic review. Journal of Esthetic and Restorative Dentistry 25: 159–176.

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Bressan, E., Paniz, G., Lops, D., Corazza, B., Romeo, E. & Favero, G. (2011) Influence of abutment material on the gingival color of implant-supported all-ceramic restorations: a prospective

multicenter study. Clinical Oral Implants Research 22: 631–637. Cabello, G., Rioboo, M. & Fabrega, J.G. (2013) Immediate placement and restoration of implants

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Lops et al  Soft tissues stability of cad-cam and stock abutments

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Supporting Information Additional Supporting Information may be found in the online version of this article: Appendix S1. CONSORT 2010 checklist of information to include when reporting a randomised trial.

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Clin. Oral Impl. Res. 0, 2014 / 1–7

Soft tissues stability of cad-cam and stock abutments in anterior regions: 2-year prospective multicentric cohort study.

Aim of this study was to verify if the type of implant abutment manufacturing, stock or cad-cam, could influence the maintenance of stable gingival ma...
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