1919

A New Enamel Restoring Agent for Use after Bleaching
1111111111

H.KAWAMATA ,M.NISHIO ,K.FUJITA ,T.ISHIZAKI ,R.HAYMAN ,and T.IKEMI
1122SANGI Co.,Ltd.Tokyo,Japan, Nihon University School of Dentistry at Matsudo,Chiba,Japan
3. Observation of Enamel Surface and Dye Penetration

1. Aim of Study

4. Results

In-office bleaching is widely practiced and appears to have little adverse effect on the teeth. But
sensitivity and relapse of discoloration often occur, requiring regular follow-up to ensure patientwell-being. We postulated that relapsed discoloration results from changes to the enamel during
the bleaching process, and developed a new, synthetic hydroxyapatite (HAP)-containing agent
designed to restore tooth enamel. We then examined its effect on (1) the surface configuration of
bleached enamel and (2) the penetrability to stains of the bleached enamel.

4-1. SEM observation
・Sound enamel showed abrasive damage from toothbrushing etc.
・The surface of bleached enamel was rougher than that of sound enamel, but becamesmooth after treatment with PRTC-SF.
・Comparison at the border between bleached enamel and bleached enamel treated withPRTC-SF in the same specimen showed that PRTC-SF-treated enamel was smootherand higher than the original bleached enamel, with apparent particle accumulation on
the enamel surface.

PRTC-SF-treated enamel surface

2. Materials and Methods

Border area

2-1. Preparation of tooth specimens
Specimens used were sound extracted human anterior teeth, after removal of the root with a dental hand engine (EX, Royal) fitted with a diamond disk (Shofu), and surface cleaning by brushingwith a regular toothpaste. A portion of the specimens were set aside for use as standard controls,
and a further group, for use in dye penetration testing, were masked with nail enamel to leave
only a small window in one aspect of the enamel surface exposed.

Bleaching enamel surface

Sound enamel surface

Bleached enamel

Bleached enamel treated with PRTC-SF

Comparison of bleached enamel (lower half) andbleached enamel treated with PRTC-SF (upper half)

Fig.3 SEM observation of enamel surface after each treatment

2-2. Bleaching treatment
A group of specimens was bleached with Hi-Lite (Shofu) (35% hydrogen peroxide), according
to the maker's instructions.

Bleached enamel treatedwith PRTC-SF

150.0

Bleached enamel treatedwith PRTC-SF

Bleached enamel

R○0.0(nm)Surface roughness (Ra) 23.1nm

46095.41

Maximum height of profile 317.8nm

Sound enamel surface

0.00(nm)Surface roughness (Ra) 44.6nm

46095.41

Maximum height of profile 579.9nm

Bleached enamel

0.0(nm)0Surface roughness (Ra) 18.3nm

46095.41

0.00

Bleached enamel treated with PRTC-SF

Fig.2 PRTC-SF treatment

2-4. Scanning electron microscope (SEM) observation
The enamel surface of control specimens, bleached specimens and post-bleaching PRTC-SFtreated specimens was compared by observation with SEM (S-4500, Hitachi).
(Observation conditions: vacc 5kv, emission 10μA, magnification 1,500 and 10,000)

200μm

Bleached enamel(nm)4390.71

Maximum height of profile 200.7nm

Fig.4 SPM observation of enamel surface after each treatment

2-6. Dye penetration
Pre-masked specimens prepared in 2-1 were subjected to bleaching, as described in 2-2, and agroup of them were then treated with PRTC-SF, as described in 2-3. All pre-masked specimens
were then subjected to staining by immersion in a solution of 0.1% Rhodamin B at 37 ℃ for 30days. After rinsing and drying, dye penetration in the two groups of pre-masked specimens wascompared by observation using a camera (EOS, Canon) equipped with a macro photo lens (MPE 65mm F2.8 1-5×, Canon).

5. Discussion

Bleached enamel

500.0

500.0

500.0

02-5. Scanning probe microscope (SPM) observation
The enamel surface of control specimens, bleached specimens and post-bleaching PRTC-SFtreated specimens was also compared by observation with SPM (SPI4000, Seiko InstrumentsInc.), which allows repeated observation of the same site in the same specimen.
(Observation conditions: scanning area 50×50μm, dynamic force mode)

4-2. SPM observation
・Sound enamel showed abrasive damage (Ra= about 20 〜 35nm) from toothbrushingetc., but the surface of bleached enamel was rougher (Ra= about 35 〜 45nm) thanthat of sound enamel, and showed much deeper surface corrugations.
・The surface of bleached enamel treated with PRTC-SF treatment, however , resembled
that of sound enamel in both smoothness (Ra= about 20 〜 30nm) and depth of surface
corrugations.
・Comparison at the border between bleached enamel and bleached enamel treated withPRTC-SF in the same specimen showed that PRTC-SF-treated enamel was bothsmoother and higher than the original bleached enamel, with apparent particle accumulation on the enamel surface.
4-3. Dye penetration test
・Both bleached enamel and bleached enamel treated with PRTC-SF showed surface
staining, but dye penetration was much deeper in the case of bleached specimens nottreated with PRTC-SF.

2-3. Post-bleaching (PRTC-SF) treatment
A portion of the bleached specimens were then treated with a new, synthetic hydroxyapatite(HA)-containing agent, PRTC Super Fine ○R * (PRTC-SF, Sangi). The PRTC-SF paste was applied to the enamel surface for 20 seconds, using a mechanically driven hand instrument (Vivamate3, Nakanishi) with contra-angle (Adagio, W&H) and rubber cup (Prophy Cup #1800, YoungDental) attached. To more closely observe the effect of PRTC-SF treatment on the post-bleachingenamel surface, half the surface area of a small number of bleached specimens was masked withnail enamel before treatment with PRTC-SF, and the masking agent removed following PRTC-SFtreatment.
* Professional "Re-Enamel" Tooth Cleaning ○R

Fig.1 Contra-angle for use in PMTC

22200μm

Bleached enamel treated with PRTC-SF

Fig.5 Dye penetration test observation

Comparison of bleached enamel (right) andbleached enamel treated with PRTC-SF (left)

Treatment of bleached enamel with the PRTC Super Fine restored the enamel
to a smoothness similar to that of sound enamel, and appeared to raise theenamel surface to a level higher than that of bleached but untreated enamel.
We postulated that this resulted from mineral deposition on the enamel byPRTC-SF, which contains synthetic hydroxyapatite, almost the same substanceas tooth enamel.
Treatment of bleached enamel with PRTC-SF also made it much more resistant to dye penetration than bleached but untreated enamel. We postulated
that mineral deposition by PRTC-SF produced a "packing effect" on the enamel surface, compensating for any damage that may be caused to the enamel
protein by bleaching agents such as hydrogen peroxide.
We concluded, from these results, that PRTC-SF is an effective agent for use
after bleaching to restore the enamel to its original surface smoothness and toprevent relapsed discoloration by reducing its permeability to stains. We
postulated that restoring smoothness to the enamel after bleaching may also
inhibit bacterial adherence, helping to protect the teeth, after bleaching, fromtooth decay.

82nd General Session & Exhibition of the IADR
MARCH, 2004
kawamata@sangi-j.co.jp