2.1

Study design, patient selection and description of the study population

The null hypothesis reflects that no difference will be determined between the restorations of Class I/II (including cuspal coverage) after an observation period of 10 years using two different composite materials ( Table 1 ).

The primary outcome of this study is the clinical service of restorations of Class I/II defects (occurrence of failure: yes/no). The following is recorded: restoration failure; if dentin or base was exposed; if contact point was missing (present periodontal inflammation); color and/or translucency beyond the normal range of tooth colors; marginal staining penetration in the direction of the pulp; marginal gap exhibiting the enamel–dentin junction; fractured, loose filling that is missing partly or completely and presence of caries (associated with the filling). This outcome is being assessed every year until 10 years after baseline (time of filling placement).

The study population was recruited from patients of the Bernhard Gottlieb University Clinic of Dentistry during one year. Each patient, who has been in need of a direct posterior restoration, was offered participation in the study. As a benefit for the patients, the composite fillings were free of charge. The patients committed to attending the annual recall by participating in the study.

To maintain a high recall rate, the patients were offered one free composite restoration in posterior teeth (in case of replacement) for every successfully attended recall. The patients can quit the study at every time without giving any reason.

Prior to the restorative treatment, each patient provided written, informed consent to participate in the study.

The patients had to meet the following inclusion criteria:

• (1)

  At least one permanent (pre-) molar in the posterior teeth with a natural antagonist (even third molar).

• (2)

  Patient’s age was over 18 years at the time of filling placement.

• (3)

  Need for restoration with single (Class I) cavity and/or multi-surface (Class II) cavities.

The exclusion criteria were as follows:

• (1)

  Teeth where sufficient isolation was not applicable.

• (2)

  Unfinished endodontic procedure/necessity of endodontic treatment.

• (3)

  Patients suffering from severe systemic disease or allergies to components of the composites and/or adhesives.

Root canal treated teeth were not considered as an exclusion criterion.

The study design of this randomized-controlled clinical trial (RCT) was created according to the American Dental Association (ADA) guidelines for posterior restorations and recommendations of the CONSORT statement . The trial is prospective, longitudinal, and single-blinded.

Patients were randomized to one of the two treatment groups (Ceram X or Tetric Ceram). All of the restorations within one patient were performed using the same filling material. After inclusion in the trial, a randomization number was assigned to each patient. Randomized filling materials were kept in numbered sealed envelopes in accordance to allocation concealment. Corresponding envelopes (due to the assigned randomization number) were opened directly before preparation of the cavity for each patient. The envelopes were provided by the Institute of Medical Statistics of the Medical University of Vienna. As a randomization method, permuted-block randomization was performed using random blocks (with block size 2, 4, 6 or 8). A block size of, e.g., 4 means, that within the next four patients, two patients were randomized to Ceram X and two were randomized to Tetric Ceram.

2.2

Clinical procedure

Dental students placed 1805 restorations in 726 premolars and 1079 molars in 456 patients during one year. University dentists, experienced in the field of adhesive dentistry, supervised the students during filling placement.

Cavity preparation was performed using rounded, cylindrical 100-μm grit diamond burs (Komet, Lemgo, Germany) under profuse water-cooling and was limited to the removal of caries to protect a maximum of tooth tissue. Caries and decayed tooth tissue was removed with rose-head burs (Komet, Lemgo, Germany). Lastly, all of the cavities were finished with 30-μm grit diamond burs (Komet, Lemgo, Germany). The preparation was performed according to common practices for placing direct adhesive restorations in posterior teeth. Deep cavities, where direct/indirect pulp capping was necessary, were treated with calcium hydroxide (Dycal, Dentsply DeTrey, Germany). Proximal contacts were achieved using a metallic matrix (Automatrix, Dentsply Caulk, Milford, DE, USA) and wooden wedges (KerrHawe, Bioggio, Switzerland). Isolation from the blood, saliva and sulcular fluid was achieved using a suction device and cotton rolls. Operative procedures and restoration placement were performed under local anesthesia if necessary (Ultracain ^® , Sanovi-Aventis, Vienna, Austria), but no rubber-dam was used. Etching with 36% phosphoric acid (Conditioner 36, Dentsply DeTrey, Konstanz, Germany) and adhesive procedures were performed according to manufacturers’ instructions. OptiBond Solo Plus was used for restorations with Tetric Ceram, and Prime&Bond NT was applied in the case of Ceram X mono. Using the incremental technique, the cavities were filled with composite in layers of approximately 2-mm thickness, adapted with a plugger and each layer light cured for at least 20 s. Light-curing units had a power output of ≥500 mW/cm ² . Contacts in occlusion and articulation were controlled with articulating paper and adjusted where necessary. Occlusal and proximal finishing was achieved with yellow and gray polishing cups (KerrHawe, Bioggio, Switzerland), flexible discs and finishing strips (Sof-Lex, 3M, St. Paul, MN, USA). A fluoride application (Elmex Fluid, GABA, Lörrach, Germany) completed the filling therapy.

2.3

The evaluation of the restoration

The evaluation of the restorations was assessed according to modified United States Public Health Service (USPHS) criteria ( Table 2 ). Due to the large number of 456 patients, the initial evaluation at baseline was performed immediately after clinical procedure. The first recall was performed after one year. University dentists, specially trained in the field of adhesive dentistry, evaluated the fillings.

2.4

Recall process

Every patient receives a written invitation two months before the annual recall appointment. If a response fails within four weeks, the patient is called by phone to arrange a new appointment. In cases where the patient does not wish to join the recall, she/he is questioned regarding the fillings directly on the phone. If a patient neither responds nor is available for a telephone call, a questionnaire will be sent asking the patient about the survival time of the fillings and the reasons for not joining the recall. Overall, four attempts (letter → call (2 times) → letter) will be performed to reach a patient until she/he is considered to be drop-out. Fig. 1 explains the recall procedure of this study as a flow chart.

Recall flow chart of the study.

2.5

Flow diagram of study participants

See Fig. 2 .

Flow of participants through each stage of the study, modified based on CONSORT .

2.6

Statistical analysis

To investigate the influence of several factors (material, age, sex, number of treated teeth at baseline, tooth position, root canal treatment at baseline, extension of the filling: mesio-distal, buccal/oral, cuspal coverage) on the occurrence of a failure ( failure per filling ) at the first recall (binary outcome yes vs. no), univariate generalized mixed models (with random factor patient) using GEEs (Generalized Estimating Equations) were performed for each potential influence factor. This model takes into account a potential correlation between the outcome of teeth within one patient (e.g., due to an insufficient oral hygiene of one patient). Furthermore, a multiple model was performed with all factors being significant in the univariate analyses. A failure (per filling) occurred if the filling had to be renewed or repaired, if a root canal treatment was necessary or the tooth (with the filling) was extracted as long as one year after baseline.

Secondly, statistical analyses were repeated without patients observed by phone calls or questionnaires to account for potential bias.

As a third type of analysis we investigated the influence of several factors determined at baseline (material, age, sex, number of root canal treatments, number of upper/lower (pre-) molar fillings and number of Class I/II fillings) on the occurrence of at least one failure ( per patient ). Therefore, first, univariate logistic regression models were performed for each of the potential influence factors. Furthermore, a multiple logistic regression model was performed with all factors being significant in the univariate analyses.

Baseline values (“age”, “number of treated teeth”, “material” and “sex”) were compared between the patients attending and patients not attending the first recall using univariate tests ( t -test or Chi-squared test). The significance level for all of the statistical analyses were set to α = 0.05.

To take into account the small number of patients to whom the modified USPHS criteria ( Table 2 ) could not be applied properly for the reasons listed below, statistical analyses using a best/worst-case scenario were performed.

• •

  The tooth with the restoration was extracted, and the patient could not provide an explanatory reason.

• •

  The patient received a partial denture that interferes with the filling placed in the present study (inclusion criterion was a natural antagonist for the opponent of the restoration).

• •

  Replacement of the restoration (alio loco) without stating the reason.

• •

  The patient had a partial/complete denture in the opposite jaw (instead of a natural antagonist), but the filling was rated very good/acceptable, and there was no interference.

• •

  The natural antagonist was missing at the first recall.

In the best-case analysis, restorations (placed in the present study) were excluded, which were unavailable for evaluation at the first recall, as mentioned above, meaning that these fillings were considered to have the same clinical behavior in regard to failures as the other observed fillings. In the worst-case analysis, all of these fillings, which were formerly excluded, were now rated as failure. For both the same statistical methods were applied.

The characteristics of the restorations were reported using descriptive statistics. The statistical analyses were performed with SAS software (version 9.1, SAS Institute Inc., Cary, NC, USA).

The ethics committee of the Medical University of Vienna approved this clinical trial (EC-No.: 277/2005).

2.1

Study design, patient selection and description of the study population

The null hypothesis reflects that no difference will be determined between the restorations of Class I/II (including cuspal coverage) after an observation period of 10 years using two different composite materials ( Table 1 ).

The primary outcome of this study is the clinical service of restorations of Class I/II defects (occurrence of failure: yes/no). The following is recorded: restoration failure; if dentin or base was exposed; if contact point was missing (present periodontal inflammation); color and/or translucency beyond the normal range of tooth colors; marginal staining penetration in the direction of the pulp; marginal gap exhibiting the enamel–dentin junction; fractured, loose filling that is missing partly or completely and presence of caries (associated with the filling). This outcome is being assessed every year until 10 years after baseline (time of filling placement).

The study population was recruited from patients of the Bernhard Gottlieb University Clinic of Dentistry during one year. Each patient, who has been in need of a direct posterior restoration, was offered participation in the study. As a benefit for the patients, the composite fillings were free of charge. The patients committed to attending the annual recall by participating in the study.

To maintain a high recall rate, the patients were offered one free composite restoration in posterior teeth (in case of replacement) for every successfully attended recall. The patients can quit the study at every time without giving any reason.

Prior to the restorative treatment, each patient provided written, informed consent to participate in the study.

The patients had to meet the following inclusion criteria:

• (1)

  At least one permanent (pre-) molar in the posterior teeth with a natural antagonist (even third molar).

• (2)

  Patient’s age was over 18 years at the time of filling placement.

• (3)

  Need for restoration with single (Class I) cavity and/or multi-surface (Class II) cavities.

The exclusion criteria were as follows:

• (1)

  Teeth where sufficient isolation was not applicable.

• (2)

  Unfinished endodontic procedure/necessity of endodontic treatment.

• (3)

  Patients suffering from severe systemic disease or allergies to components of the composites and/or adhesives.

Root canal treated teeth were not considered as an exclusion criterion.

The study design of this randomized-controlled clinical trial (RCT) was created according to the American Dental Association (ADA) guidelines for posterior restorations and recommendations of the CONSORT statement . The trial is prospective, longitudinal, and single-blinded.

Patients were randomized to one of the two treatment groups (Ceram X or Tetric Ceram). All of the restorations within one patient were performed using the same filling material. After inclusion in the trial, a randomization number was assigned to each patient. Randomized filling materials were kept in numbered sealed envelopes in accordance to allocation concealment. Corresponding envelopes (due to the assigned randomization number) were opened directly before preparation of the cavity for each patient. The envelopes were provided by the Institute of Medical Statistics of the Medical University of Vienna. As a randomization method, permuted-block randomization was performed using random blocks (with block size 2, 4, 6 or 8). A block size of, e.g., 4 means, that within the next four patients, two patients were randomized to Ceram X and two were randomized to Tetric Ceram.

2.2

Clinical procedure

Dental students placed 1805 restorations in 726 premolars and 1079 molars in 456 patients during one year. University dentists, experienced in the field of adhesive dentistry, supervised the students during filling placement.

Cavity preparation was performed using rounded, cylindrical 100-μm grit diamond burs (Komet, Lemgo, Germany) under profuse water-cooling and was limited to the removal of caries to protect a maximum of tooth tissue. Caries and decayed tooth tissue was removed with rose-head burs (Komet, Lemgo, Germany). Lastly, all of the cavities were finished with 30-μm grit diamond burs (Komet, Lemgo, Germany). The preparation was performed according to common practices for placing direct adhesive restorations in posterior teeth. Deep cavities, where direct/indirect pulp capping was necessary, were treated with calcium hydroxide (Dycal, Dentsply DeTrey, Germany). Proximal contacts were achieved using a metallic matrix (Automatrix, Dentsply Caulk, Milford, DE, USA) and wooden wedges (KerrHawe, Bioggio, Switzerland). Isolation from the blood, saliva and sulcular fluid was achieved using a suction device and cotton rolls. Operative procedures and restoration placement were performed under local anesthesia if necessary (Ultracain ^® , Sanovi-Aventis, Vienna, Austria), but no rubber-dam was used. Etching with 36% phosphoric acid (Conditioner 36, Dentsply DeTrey, Konstanz, Germany) and adhesive procedures were performed according to manufacturers’ instructions. OptiBond Solo Plus was used for restorations with Tetric Ceram, and Prime&Bond NT was applied in the case of Ceram X mono. Using the incremental technique, the cavities were filled with composite in layers of approximately 2-mm thickness, adapted with a plugger and each layer light cured for at least 20 s. Light-curing units had a power output of ≥500 mW/cm ² . Contacts in occlusion and articulation were controlled with articulating paper and adjusted where necessary. Occlusal and proximal finishing was achieved with yellow and gray polishing cups (KerrHawe, Bioggio, Switzerland), flexible discs and finishing strips (Sof-Lex, 3M, St. Paul, MN, USA). A fluoride application (Elmex Fluid, GABA, Lörrach, Germany) completed the filling therapy.

2.3

The evaluation of the restoration

The evaluation of the restorations was assessed according to modified United States Public Health Service (USPHS) criteria ( Table 2 ). Due to the large number of 456 patients, the initial evaluation at baseline was performed immediately after clinical procedure. The first recall was performed after one year. University dentists, specially trained in the field of adhesive dentistry, evaluated the fillings.

Table 2

Modified USPHS criteria for the direct clinical evaluation .

No.	Criterion	Score	Description	Methods of evaluation
1	Substance loss of the filling	A	Excellent/acceptable	Visual and probe
		C	Dentin or base exposed	Visual and probe
2	Contact point	A	– Normal contact point – No contact point and no signs of periodontal irritations	Floss
		C	– No contact point and signs of periodontal irritations – Patient wants replacement of the filling	Floss
3	Color match	A	Excellent/acceptable	Visual
		C	Color and/or translucency are beyond the normal range of tooth colors	Visual
4	Marginal staining	A	Excellent/acceptable	Visual
		C	Marginal staining penetrates in direction of the pulp	Visual
5	Marginal adaptation/integrity of the filling	A	Excellent/acceptable	Visual and probe
		C	Marginal gap until the enamel–dentin junction	Visual and probe
		D	Filling is fractured, loose, missing partly or completely	Visual and probe
6	Secondary caries	A	No evidence of caries along the margin of the restoration.	Visual and probe and X-ray
		B	Caries is associated with the filling	Visual and probe and X-ray
7	Pain (associated with the filling)	0–10	Registration of pain	Visual analogue scale
8	Occlusion	A′	Excellent/acceptable	Visual (articulating paper)
		B′	Occlusal height to high: correction performed
9	Testing of sensitivity	A′	Vital/non vital (root canal treatment at baseline)	Thermal testing (CO 2 ice)
		D′	Non vital/hypersensitivity (vital at baseline)
10	Percussion sensitivity	A′	Negative	Mirror handle
		D′	Positive
11	Radiographic examination a	A′	No pathology	X-ray
		D′	Diagnosis: marginal gap/secondary caries, apical pathology
12	Replacement is required	A′	Not required
		D′	Renewal necessary (if pain is the reason: mention if postoperative (hyper-) sensitivity persists for more than 4–8 weeks
13	Repair is necessary	A′	Not required
		C′	Repair is necessary (stating the reason(s) and a detailed description)
14	Need for tooth extraction	A′	No
		D′	Yes (reason: e.g., pulpitis, trauma, periodontal pathology or other reasons)

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