Original study - ZZI 02/2011

Evaluation of the influence of preoperative factors
on soft tissue consolidation around single tooth implants
in the esthetic zone – A pilot study

C. K. Müller1, S. Fröbisch1, J. Chen2, S. Schultze-Mosgau1

Aim: The study aimed at identifying patient-, defect- and treatment-related factors that influence the esthetic outcome following oral rehabilitation using single tooth implant crowns.

Materials and Methods: 34 patients, who received a total of 49 dental implants at the Department of Oral and Maxillofacial Surgery/Plastic Surgery, Jena University Hospital, were analyzed in a pilot study. Patient-, defect- and treatment-related factors were documented. Employing the "Pink Esthetic Score" (PES), the "red esthetics" were judged on standardized intraoral photos. The influence of patient-, defect- and treatment-related factors on the PES score was analyzed in a multivariate statistical approach.

Results: Defect size, SAC class and the condition of periimplant bone were found to be significant variables in the description of the PES.

Conclusion: Within the limitation of a pilot study employing a small sample size, it was confirmed that insufficient hard and soft tissue represents the greatest challenge for the implantologist. Current developments in minimally invasive implantology might have the potential to enhance the esthetic outcome in the future.

Keywords: “red esthetics“; pink esthetic score; multivariate analysis

Introduction

The morphology of periimplant and periodontal tissue differs from that of marginal epithelium and supracrestal connective tissue. The periodontal marginal epithelium is thicker, has a greater amount of hemidesmosomes and is inserted further coronally than the periimplant marginal epithelium. Compared with the periodontal connective tissue, periimplant connective tissue is characterized by relative hypocellularity and poorer perfusion. Moreover, periimplant collagen fibers have a circular course, whereas around healthy teeth they insert into root cementum. The morphological differences between periimplant and periodontal tissue result in an increased tendency to inflammation of dental implants compared with healthy teeth [3, 26]. Contouring an optimally stable soft tissue sleeve at the implant emergence site is consequently of crucial importance for both the functional and the esthetic long-term success of an implant-borne restoration [25].

It is argued that different systemic and local factors influence soft tissue consolidation in the region of the implant emergence site and thus have a direct effect on esthetics [18, 22]. Underlying diseases such as diabetes mellitus and disorders of collagen metabolism and also certain long-term medications such as glucocorticoids are systemic factors that have a negative influence on the quality of the regenerated soft tissue. Local risk factors that interfere with normal soft tissue consolidation include smoking in particular, a history of radiotherapy [19], previous jaw reconstruction with microvascular anastomosis of the flap [17] and poor oral hygiene. Furthermore, the soft tissue management technique during augmentation, implant insertion and exposure appears to be extremely important for contouring the implant emergence site, and the surgeon can influence this directly [1, 30].

The aim of this study was to identify patient-, defect- and treatment-related factors that influence the esthetic outcome following oral rehabilitation using single tooth implant crowns.

 

Material and Method

Patients

The study was approved by the ethics committee of Jena University Hospital. All patients who received dental implants for oral rehabilitation at the Department of Oral and Maxillofacial Surgery/Plastic Surgery of Jena University Hospital between April 2005 and October 2007 were documented in a pilot study.

The following were the defined inclusion criteria: 1.) upper and lower implants in positions 1 to 5, 2.) prosthetic restoration by means of a single crown and 3.) at least one healthy reference tooth (anterior region: corresponding tooth on the opposite side; premolar region: neighboring tooth) in the same jaw. Patients who had previously had jaw reconstruction by means of a microvascular flap were excluded from the study.

 

Data collection

Age, gender and defect etiology (caries/periodontal lesions vs. aplasia vs. trauma) were recorded as patient-related factors.

The following were documented to describe the pre-treatment situation: implant position (upper vs. lower; single-tooth gap vs. saddle area with several neighboring implants), the condition of the periimplant hard tissue (implantation possible in local bone vs. bone augmentation with intraoral bone grafts vs. bone augmentation with iliac crest bone grafts) and the condition of the soft tissue (transmucosal healing possible vs. crestal incision [stretching] vs. oro-vestibular transposition flap vs. palatal roll vs. partial vestibuloplasty/apically positioned flap with free mucosal graft from the hard palate). The individual items were also examined for SAC classification (simple vs. advanced vs. complicated).

The treatment-related variables evaluated were the implantation concept (immediate vs. early, delayed immediate vs. late implantation, delayed immediate vs. late implantation) and treatment concept (immediate loading vs. increasing loading vs. late loading).

 

Photo analysis

Following prosthetic restoration, standardized intraoral photos were taken. All photos were taken with a digital camera (Nikon D 80, Mikro Nikkor lens with a focal length of 105 mm, ring flash or Speedlight SB 800). To ensure comparability, the reference tooth had to be clearly visible. Each photo was stored in 10x15 format with 300 dpi and a size of 5.99 megabyte.

The photos were assessed by five dental students. After an interval of four weeks, the evaluation was performed a second time by the same students. The images were now presented in reversed order.

The Pink Esthetic Score (PES) [11] was employed to assess the periimplant soft tissue esthetics. This score includes seven variables (Fig. 1). Each variable can be given a score of 0 to 2 so that a maximum PES of 14 is assigned for an optimal esthetic outcome and a score of 0 for the worst outcome. A healthy reference tooth (the contralateral tooth in the anterior region and the neighboring tooth in the premolar region) is taken as esthetically optimal (PES 14) for the individual patient. The PES was then assigned to the implant tooth relative to the reference tooth.

 

Statistics

All calculations were performed with SPSS 15.0 for Windows (SPSS Inc., Chicago, IL, USA). The patient-related data were presented as absolute and relative frequencies. The PES was represented as mean and standard deviation. The influence of patient-related factors on the esthetic outcome was first examined by univariate analysis using the Mann-Whitney test (U-test) for two samples and the Kruskal-Wallis test for several independent samples. Finally, multivariate testing was performed using linear regression analysis. Two-sided p values < 0.05 were regarded as significant.

 

Results

Patient-, defect- and treatment-related variables

34 patients in total (23 [67.6 %] male, 11 [32.4 %] female) with an average age of 37.8 years (15–73 years) were selected for the study. These patients received 49 implants with a length of 10–15 mm and a diameter of 3.25–6.8 mm (BEGO Implant Systems, Bremen, Germany; Straumann Holding AG, Basel, Switzerland; Nobel Biocare Holding AG, Zürich, Switzerland). As regards defect etiology, periodontal/carious lesions predominated (21 defects; 42.9 %), followed by aplasia (16 defects; 32.7 %) and dental trauma (12 defects; 24.4 %).

41 implants (83.7 %) were inserted in the maxilla and eight (16.3 %) in the mandible. 25 (51.0 %) implants were inserted in single-tooth gaps, while 24 (49.0 %) were inserted to treat saddle gaps where more than one tooth was missing. In 25 (51.0 %) planned implant regions, radiographs showed adequate available vertical bone of 6–10 mm in the mandible and 10 mm in the maxilla, together with sufficient transverse bone of 4–6 mm in both jaws. In 15 (30.6 %) implant regions, pre- or intra-implant augmentation procedures were necessary in the form of unilateral sinus lift or onlay graft in two to three implant regions. The autologous bone grafts were obtained in the mouth in these cases. There were extensive bone defects in nine (18.4 %) implant regions. These had to be augmented prior to implantation by onlay or inlay of avascular bone grafts from the iliac crest. In eleven (22.4 %) implant regions, the thickness of the periimplant mucosa and the width of the fixed circular periimplant keratinized gingiva of 3–4 mm were sufficient before implantation. A single-stage procedure with transmucosal implant healing was chosen. In two (4.1 %) implant regions, a crestal incision opening/stretching with central tissue increase was used for uncovering the implant. An oro-vestibular transposition graft was performed with three (6.1 %) implants to increase the volume of the periimplant soft tissue, an oro-vestibular transposition graft with palatal de-epithelialized extension (palatal roll) was performed with 18 (36.7 %) implants (Fig. 2), and papilla regeneration with targeted interdental volume increase by means of an M-shaped incision technique with four (8.2 %) implants. To widen the vestibular, periimplant area of fixed keratinized gingiva, vestibuloplasty/apically positioned flap with a free mucosal graft from the hard palate was performed with eleven (22.4 %) implants. Review of the diagnostic data showed four (8 %) simple, 19 (39 %) advanced and 26 (53 %) complex cases when the SAC classification was used.

Three (6.1 %) implants were inserted immediately after minimally invasive tooth extraction, preserving the vestibular socket wall (immediate implantation). Three more implants (6.1 %) were placed four to 16 weeks after tooth extraction when soft tissue healing was complete but bony consolidation of the socket was incomplete (early and late delayed immediate implantation). The majority of the implants (43; 87.8 %) were inserted in sockets where bony consolidation had occurred, according to the late implantation concept. Four (8.2 %) implants were restored up to the tenth postoperative day (immediate restoration). With four (8.2 %) implants, the crowns were fitted between three and four months after implantation (“increasing loading”). The remaining 41 (83.7 %) implants were loaded four to six months after implant insertion.

Esthetic evaluation

The mean implant PES was 6.55 ± 3.76 at the first evaluation and 6.55 ± 3.74 at the second evaluation.

 

Univariate analysis

The patient-related factors of age and gender had no significant influence on the “red esthetics”. Implants placed in patients with tooth loss as a result of carious/periodontal lesions achieved a PES of 5.8 ( 3.4), implants inserted because of aplasia achieved a PES of 7.6 ( 2.6) and implants following dental trauma achieved a PES of 4.2 ( 3.7). Statistically significant differences between the groups were found using the Kruskal-Wallis test (p = 0.029). As a result of the small size of the group, however, no further multivariate analysis took place.

Implants in the maxilla had a PES of 6.0 ( 3.6) while mandibular implants demonstrated a PES of 5.8 ( 3.1). The difference was not statistically significant. Implants in single tooth gaps had a PES of 6.8 (+ 3.8) while the PES obtained for implants in saddle gaps where more than one tooth was missing was 5.2 (+ 3.1). A highly significant difference (p < 0.01) was found using a U-test (Fig. 3). Implants inserted in local bone demonstrated a PES of 7.8 (+ 3.1); a PES of 4.9 (+ 3.0) was recorded after minor augmentation measures using intraoral bone, and a PES of 2.6 (+ 1.8) was found after bone augmentation with free avascular grafts from the iliac crest. A statistically highly significant difference (p = 0.02) was found between the groups. A PES of 8.5 (+ 3.3) was achieved with transgingival healing, and crestal incision opening (stretching) resulted in a PES of 4.7 (+ 1.9). The PES was 4.8 (+ 2.7) after oro-vestibular transposition, a PES of 6.4 (+ 3.5) was obtained with exposure by means of a palatal roll, use of papilla regeneration achieved a PES of 7.8 (+ 2.1) and partial vestibuloplasty/apically positioned flap with free mucosal graft resulted in a PES of 2.6 (+ 2.2). A statistically highly significant difference (p < 0.01) was found between the groups. Furthermore, the SAC classification demonstrated a statistically significant (p < 0.01) influence on the PES.

None of the treatment-related factors had a significant influence on the PES.

Multivariate analysis

In summary, the relationships between the individual para-meters in the complex interplay were found by linear regression. It was established that the group (single tooth implant/neighboring implants), the SAC classification and the need for augmentation with extraoral bone were valid variables for describing the PES and thus the esthetic outcome.

 

H0: mean PES = b0 + b1 x aug. ex. +b2 x SAC1 +b3 x SAC2 +b3 x group = 0.5 (Table 1)

 

The corrected coefficient of determination (R-squared) for this final model was 0.632. Whether the implant was placed directly in local bone or whether small local defects were augmented with intraoral bone had no significant influence on the PES (p = 0.47). The cause of the tooth loss and also the incision chosen for uncovering the implant were not necessary for description of the PES.

Discussion

Our results show that there are highly significant statistical differences in the PES of single tooth implants compared with restorations of neighboring implants. An explanation for this might be the bone resorption described by Tarnow between neighboring implants and the resulting deficiency of hard and soft tissue [27, 28]. Resorption of the interimplant bone leads to shortening of the papilla and ultimately to impairment of red and white esthetics.

The preoperative defect size, due, for instance, to atrophy and trauma, had a crucial influence on the final esthetic result of implant-borne rehabilitation. Extensive hard and soft tissue defects required extensive reconstructive measures prior to implantation. The esthetic outcomes depending on the SAC classification are analogous. It was shown that cases classified as “simple” and “advanced” SAC treatment concepts led to more attractive outcomes, while some “complex” cases achieved a lower PES, indicating an esthetically unsatisfactory outcome.

The influence of different surgical protocols [8, 10, 13, 23, 24] and prosthetic loading concepts [4, 6, 8, 12, 13] on estheti-cally successful implant restorations is also discussed. However, objective esthetic parameters have hardly been considered hitherto, so that comparison of the results was not possible [12, 21]. Using the Pink Esthetic Score, our study showed that neither the surgical time management nor the prosthetic loading concept have a statistically significant influence on the final esthetic outcome. This is in line with the studies of Jokstad and Carr, who also found no esthetically significant difference between immediately and conventionally loaded implants [14].

Despite numerous single case reports, there are so far no evidence-based data on incision techniques, flap design and indication for soft tissue augmentation [5, 9]. The present study found highly significant associations between the exposure concept and PES on univariate analysis. On multivariate analysis, however, a significant influence could not be confirmed, possibly because of the small number of cases. Surgical procedures such as papilla reconstruction and palatal roll, which can increase the volume of the soft tissue, achieved good esthetic outcomes in our study. Lower scores were assigned for implants that were uncovered by a simple crestal incision. The causes of this were a reduced soft tissue level and incomplete papillae, especially in the case of neighboring implants in the premolar area. In eleven patients (22.4 %), exposure was by means of an apically positioned flap and free mucosal graft (FMG) from the hard palate. The aim of this technique is to create a minimum circular periimplant width of fixed keratinized gingiva of 2–3 mm [2]. Although there is insufficient evidence according to recent review articles [7], it is assumed that oral hygiene is improved by the fixed keratinized gingiva and plaque accumulation is reduced [27]. This ensures the long-term esthetic and functional result. A systematic review article by Thoma et al. found that an average widening of the zone of fixed keratinized gingiva by 4.49 mm can be achieved by vestibuloplasty/apically positioned flap in combination with a free mucosal graft from the hard palate compared with untreated controls [29]. To minimize problems of donor site morbidity, allogeneic and xenogeneic substitute materials have been introduced and tested [34]. Compared with the “gold standard” of the autologous mucosal graft, however, there was a significantly lower gain of fixed keratinized gingiva and markedly greater shrinkage on follow-up [15]. Studies by our research group have shown that this shrinkage after use of allogeneic materials can be attributed to increased and prolonged recruitment of macrophages in the early healing periods with subsequent fibrocontractile tissue remodeling [16]. From the esthetic aspect, the FMG outcomes are usually unsatisfactory as a result of color mismatch and should, in consequence, be employed only in the mandible, posterior maxillary region or in wearers of overdentures [20].

Conclusions

Within the limitations of a pilot study employing a small sample size, it was confirmed that insufficient hard and soft tissue represents the greatest challenge for the implantologist. Current developments in minimally invasive hard and soft tissue management techniques might help to enhance the esthetic outcomes for these patients in the future.

 

Conflict of interests: none stated

Correspondence address

Cornelia K. Müller

Klinik und Poliklinik für Mund-, Kiefer- und Gesichtschirurgie/Plastische Chirurgie

Universitätsklinikum Jena

Erlanger Allee 101, 07747 Jena

Tel.: +49 (0) 3641 / 9 323666

Fax: +49 (0) 3641 / 9 323630

E-Mail: cornelia.mueller1@med.uni-jena.de

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Footnote

1 Klinik und Poliklinik für Mund-, Kiefer- und Gesichtschirurgie/Plastische Chirurgie, Universitätsklinikum Jena

2 Department of Dental Implantology, The Affiliated Stomatological Hospital of Fujian Medical University, Fuzhou, China

Übersetzung: LinguaDent

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