CASE STUDY BY

Center for Dental Research Biomaterials Research Facility Loma Linda University School of Dentistry In-Situ Clinical Evaluation of the Plaque Retention of Four Prosthetic Materials

I. Purpose

This study evaluated the clinical performance and biocompatibility of an experimental metal ceramic gold alloy for use in Fixed Prosthodontics.

II. Study Design and Methods

This study involved ten subjects in an unsupervised, parallel, two-week study duration and four prosthetic materials. Subjects wore a maxillary retainer with posterior buccal wings, which housed four materials (3 mm in diameter): a metal ceramic alloy (Goldtech), porcelain, amalgam and Captek gold alloy. The individuals wore the appliance for two weeks and plaque accumulation was measured at 24 hours, one and two weeks. This study was conducted at Loma Linda University School of Dentistry and was sponsored by the Argen Corporation. Ten adults, between the ages of 18 and 65, identified from our dental school were invited to participate in this study.

Informed Consent

The purpose and nature of the study was explained to the subjects and they were then invited to participate. Subjects were required to read, understand and sign a consent form before being enrolled in the study.

Clinical Procedures

Subjects with a full complement of maxillary teeth were selected for the study. An alginate impression was made of the maxillary and mandibular arches and an orthodontic retainer was made for the maxillary arch. The retainer was modified so that the clasps that engage in the undercuts of the molars had two orthodontic wire loops soldered from second molar to second premolar. Attached to the wires were two chip housings facing towards the cheeks, 3.0 mm in diameter and 1.2 mm in depth. Two of the materials were placed on the right side and two on the left side. The materials were secured to the housing with composite resin and light cured. Evaluations were made at 24 hours, one and two weeks.

Data Collection and Subjects Records

At 24 hours the retainers were retrieved and using a disclosing solution, the chips were stained and the amount of plaque measured and calculated in percentage.

A red dye used as a disclosing solution in periodontal therapy, was used to stain the restorative materials. The materials were then washed with a constant stream of water from a wash bottle for 10 seconds. A gentle stream of air was applied for 10 seconds to remove any surface gloss. Plaque accumulation was then ranked according to the following procedure:

0 = No visible plaque on 100 % of the surface

1 = 25% of plaque visible on the surface

2 = 50% of plaque visible on the surface

3 = 75% of plaque visible on the surface

4 = 100% of plaque visible on the surface

Each specimen was photographed with a camera at a 2:1 magnification.

The specimens were then cleaned with a toothbrush and the retainers reinserted in the subjects mouth. At one week the retainers were again removed and new measurements made. The retainers were then evaluated at two weeks. The specimens were not cleaned at the one-week appointment.

The subjects were instructed not to brush the retainers or the test specimens for the duration of the study. However they could remove the retainers from the mouth and brush their teeth in their usual manner.

Clinical Record Forms (CRF) were prepared for data collection for each participant. The CRF system developed at Loma Linda University School of Dentistry has been used in a number of previous similar clinical trials and was found to be satisfactory.

Amalgam-Captek-Goldtech-Porcelain

 

Fabrication of Specimens

Rectangular specimens, 2 x 3 mm in diameter and 1.2 mm in height were fabricated out of the following materials:

1) Goldtech Metal ceramic alloy. The alloy was cast and then polished using tripoli and rouge until a smooth mirror-like surface was obtained.

2) Porcelain. Porcelain specimens were fabricated using Classic (Ivoclar) and glazed until a smooth shiny surface appeared.

3) Amalgam. Tytin amalgam specimens were fabricated and polished using conventional polishing procedures.

4) Captek gold specimens were fabricated and polished with tripoli and rouge until a mirror-like surface was obtained.

5) The specimens were then attached to the wire loops and firmly secured with composite resin.

III. Results

Complications

No complications were noted on any of the subjects.

Testing with Specimens Facing the Buccal

All ten subjects completed the study. However, 4 of the subjects experienced too much rubbing of test area with their cheeks. This was noted because the amalgam specimens, which are well known to collect plaque, appeared clean when examined.

Because of this problem, the design was changed so that the specimens were facing forward instead of sideways and all ten subjects underwent two more weeks of testing.

Testing with Specimens Facing the Mesial

All ten subjects finished the two week test. Measurements were made at baseline, 24 hours, one and two weeks. Results of the test are listed in Table 1 and Figure 1. These results reflect a more realistic picture of the amount of plaque that materials will collect over a two-week period in the oral cavity without any oral hygiene procedures.

IV. Discussion

Several studies have shown a direct correlation between caries formation and periodontal disease to a high count of plaque in the oral cavity. When the plaque is carefully removed, periodontal disease and caries formation decreases significantly. This phenomena highlights the importance of producing restorative materials that are able to inhibit plaque formation, especially in areas where dental hygiene is difficult to achieve.

Dental plaque is an aggregate of microorganisms embedded in an organic intercellular matrix. The plaque attaches to the tooth via a film of pellicle derived from saliva. This pellicle attaches to the tooth by simple electrostatic attraction between the calcium ions in the saliva and the phosphate groups in the enamel. The plaque that accumulates in restorative materials is of different composition than that of enamel and therefore might have a higher pathogenicity.

This study evaluated the plaque accumulation of four restorative materials: amalgam, porcelain and two metal ceramic alloys: Captek and Goldtech.

Amalgam had the highest retention of plaque, because it has a low surface energy and a larger surface area compounded by the fact that it has a highly porous surface. The combination of these three factors lends the material to accumulate more plaque in clinical studies. Close view of the surface of the plaque on the amalgam shows closely packed plaque.

Porcelain, on the other hand has a very high surface energy. This free surface energy prevents the accumulation of plaque in larger quantities and when looked under the microscope, the plaque is loosely packed. The fact that plaque accumulated in highly glazed porcelain, dispells the myth that plaque does not accumulate in porcelain.

Solid metals have by nature a high surface energy. The surface energy increases as the melting point of the alloy increases. The amount of plaque accumulated also depends on the surface morphology. The rougher the surface the higher the plaque accumulation, regardless of the material.

Both Captek and Goldtech had plaque accumulation after two weeks. Captek had a higher accumulation of plaque at the end of the two weeks. We can speculate that the surface energy of Goldtech was higher than that of Captek, and therefore the wettability of the alloy was lower, allowing less plaque to accumulate. For both alloys, the plaque accumulation was loose in some areas and packed in others.

The position of the specimens in the mouth played an important role in the plaque accumulation of the specimens. It was noted that individuals with stronger muscles or tight buccal vestible had less plaque at the end of the study. This finding helps explain why the set of specimens from the first group facing the buccal cheek had less plaque, while the specimens from the second group had less plaque.

Clinically, one would not go for 2 weeks without brushing or flossing, as was done in this study. However, this points us to believe that over a long time and proper oral hygiene, Goldtech will accumulate less plaque than Captek.

V. Conclusions

1) Plaque accumulation varies depending on the type of restorative material.

2) Amalgam had the highest accumulation of plaque and porcelain the lowest.

3) Plaque accumulates over time on all materials.

4) Goldtech accumulates less plaque than Captek.