Investigation of Treatments to Improve Hardness Recovery of Softened Enamel

Objectives: This in-vitro study investigated the ability of four treatments to increase the hardening of tooth enamel initially softened by hydrochloric (HCl) acid. The treatments consisted of products that contain calcium, phosphate, and/or fluoride, and were compared with hardening by saliva alone.  

Methods: Extracted human molars were embedded in acrylic resin and polished. Vickers surface hardness (VH) was measured at each stage in the experiment. After VH_baseline, the teeth were bathed in a 10mM HCl solution for 10 minutes to mimic regurgitated stomach acid, and VH_softening was recorded. The acid-challenged teeth underwent treatment with the following products: 0.05% sodium fluoride mouthrinse (ACT), 0.4% stannous fluoride gel (Gel-Kam), casein phosphopeptide amorphous calcium phosphate (CPP-ACP) (MI-paste), fluoridated CPP-ACP paste (MI-Plus). Deionized water was used as control. Following treatment, teeth were bathed in human saliva (IRB #10-01122-XM) for one hour, and VH_hardening was recorded. Statistical analysis was performed with ANOVA followed by Student-Newman-Keuls post-hoc tests (p=0.05).

Results: VH (mean±standard deviation) are presented in the table. Same superscript letter denotes hardness values that were not significantly different among experimental stages within the same group. VH significantly decreased after HCl-challenge in all groups. After remineralization, VH increased significantly in MI-paste and MI-Plus groups, but not in the Control, ACT, and Gel-Kam. Only MI-Plus recovered the baseline VH-value.

 

	VHbaseline	VHsoftening	VHhardening
Control	376±18 a	338±20 b	344±29 b
ACT	360±32 a	321±32 b	342±33 a,b
Gel-Kam	361±18 a	325±32 b	343±25 a,b
MI-paste	362±15 a	325±7 b	345±20 c
MI-Plus	358±19 a	327±14 b	352±29 a

Conclusions: Hardness recovery of enamel softened by HCl was minimal with saliva alone. The treatment that incorporated fluoride and calcium phosphate was the most effective for enamel hardness recovery.

Acknowledgement : Supported, in part, by the UT College of Dentistry Alumni Student Research Training Program.