CASE REPORT

Enamel pretreatment with sodium hypochlorite to enhance bondingin hypocalcified amelogenesis imperfecta: case report and SEM analysisRonald D. Venezie, DDS, MS George Vadiakas, DDS, MSJohn R. Christensen, DDS, MS J. Timothy Wright, DDS, MS

Abstract

Bonding composite resin to enamel of teeth affected by amelogenesis imperfecta (AI) is often problematic, especially in caseswith poorly mineralized, friable enamel. Difficulty in bonding hypomineralized enamel can significantly limit the restorativeand orthodontic treatment options for AI patients. In this report, we document a novel approach to bonding AI enamel bypretreating the tooth surface with 5% sodium hypochlorite (NaOCI), resulting in improved bonding of an orthodontic bracketto a previously impacted maxillary canine. (Pediatr Dent 16:433-36, 1994)

Introduction

Hypocalcified AI (HCAI) types are thought to resultprimarily from defects in nucleation and early enamelmineralization. However, later stages of enamel min-eralization also may be abnormal.1 The inheritance pat-tern for HCAI is reported as being autosomal domi-nant or recessive. The typical clinical features of affectedenamel include a yellow to brown color and normalenamel thickness. Affected enamel may be variablylocated on the tooth. Cervical enamel frequently is lessaffected than more coronally located enamel,a, 3 Ultra-structurally, HCAI enamel has been shown to be moreporous and have a lower mineral content per volumethan normal enamel.2 Differences in enamel proteincontent and composition have been demonstrated andcould be diagnostic for the different AI types.~-7 Certaintypes of AI can have an enamel protein content muchgreater than normal enamel. For example, HCAI enamelmay have 3 to 4% protein by weight compared with0.5% for normal enamel. There may be an associationbetween higher protein content and more severely af-fected enamel.

It is believed that bonding composite resin by theacid etch technique to enamel affected by AI is moredifficult than bonding to normal enamel (reviewed bySeowS). Sodium hypochlorite (NaOCI) is known to an excellent protein denaturant that should be capableof removing excess enamel protein. 9 Thus, we predictedthat pretreating AI enamel with sodium hypochloritewould make the enamel crystals more accessible to theetching solution, resulting in a clinically more favor-able etched surface.

The purposes of this report were to: present a novelmethod for enhancing the bonding of an orthodonticbracket to a tooth affected with HCAI by pretreatingthe tooth for 1 min with 5% NaOC1, and examine theeffect of 5% NaOC1 on the surface topography of HCAIenamel by scanning electron microscopy.

Case report

An l 1-year-old white female was referred to theDepartment of Pediatric Dentistry of the UNC Schoolof Dentistry for treatment of "hypoplastic" teeth. Uponfurther evaluation, the patient was diagnosed as hav-ing hypocalcified amelogenesis imperfecta.

After completing interim restorative care, limitedorthodontic treatment of the maxillary arch was under-taken due to an impacted maxillary left canine. Afterobtaining initial orthodontic alignment of the arch, thepatient had a mucoperiosteal flap procedure to exposethe tooth. In addition, the maxillary left second premolarwas extracted. An orthodontic button was bonded(TransbondTM, Unitek/3M, Monrovia, CA) near theincisal tip of the canine. The flap was sutured into aposition apical to the exposed canine. A gold chainsoldered to the orthodontic button was left exposed toenable delivery of extrusive force through an auxiliarywire (0.016x0.022-in. stainless steel) soldered to the basearch wire (0.018x0.025-in. stainless steel). The auxiliarywire rested in the mandibular vestibule in its passivestate. The tooth was extruded over the next 6 months.After the facial surface of the canine was sufficientlyexposed, the button and residual adhesive were re-moved, and a prophylaxis was performed using a rub-ber cup and a slurry of pumice in order to place apreangulated, pretorqued orthodontic bracket.

Several attempts made by two operators (RDV andJRC) to bond the bracket to the facial surface of thecanine using composite resin (Transbond) and the acidetch technique failed despite rigorous efforts to main-tain a dry field with cotton roll isolation. Several at-tempts to bond the bracket using glass ionomer cement(Ketac-Cem®, Espe-Premier, Norristown, PA) also wereunsuccessful, so the patient returned the followingmonth for rebonding. Neither dentin bonding agent(Gluma®, Miles Dental Products, South Bend, IN) pluscomposite resin nor glass ionomer cement yielded a

Pediatric Dentistry: November/December 1994 - Volume 16, Number 6 433

Fig 1. Mandibular left canine visiblyaffected by amelogenesis imper-fecta and depicted in scanningelectron micrographs (Figs 2-5).

bond that would re-main intact for longerthan 15 min after archwire placement.

In laboratory stud-ies of Al-affectedenamel, NaOCl hasbeen used to removeprotein and to permitbetter analysis ofenamel crystallitestructure.2 We hy-pothesized that usingNaOCl to remove ex-cess protein from theenamel would lead toa stronger bond. Thecanine was cleanedwith pumice, rinsedwith water spray, andcarefully isolated with

cotton rolls. A solution of 5% NaOCl was applied liber-ally with a brush for 1 min, and the tooth was rinsedwith water spray. After air drying, 37% phosphoricacid solution was applied to the tooth surface for 1 min.The tooth was rinsed and air dried again, and a thinlayer of enamel bonding agent was applied to the etchedenamel surface. The bracket, loaded with compositeresin (Transbond), was positioned on the tooth, andexcess resin was removed. The resin was light cured for2 min. The resulting bond was immediately subjectedto normal orthodontic forces and was successful for theremainder of the orthodontic treatment.

Scanning electron microscopy procedureThe improved bonding after NaOCl pretreatment of

HCAI enamel led us to investigate possible reasons forthis success. There was no apparent differ-ence in surface texture discernible to thenaked eye due to NaOCl pretreatment plusacid etching compared with acid etchingalone. However, it seemed likely thatNaOCl followed by acid etching producedan ultrastructural topography more con-ducive to bonding.

The mandibular canines remainedunrestored during the course of orthodon-tic treatment, so the more severely affectedmandibular left canine was selected forSEM analysis (Fig I). The labial surfacewas cleaned with a rubber cup and slurryof pumice, rinsed with water, and air dried.A baseline silicone impression (Silene®,Harry J. Bosworth, Skokie, IL) of theunetched tooth was obtained using themanufacturer's protocol and cotton rollisolation. Upon removing the polymerized

impression, cotton roll isolation was maintained to pre-vent any salivary contamination of the tooth surface.The tooth was acid-etched for 1 min, rinsed, and dried.A second impression was made as described above.The silicone impressions were poured in epoxy resin,and casts were analyzed by SEM using standard tech-niques.10 Analysis of these casts yielded control data onthe topographic changes due to acid etch alone.

Several months passed to allow the etched tooth toremineralize before initial prophylaxis and baselineimpression procedures were repeated exactly as abovefor the unetched tooth. The tooth surface was treatedwith 5% NaOCl applied with a brush for 1 min, rinsed,and dried. A second impression was obtained. Finally,the tooth was acid etched, rinsed and dried as describedabove, and a third impression was obtained. The castsof these impressions were processed and analyzed inthe same manner as the control casts from the firstappointment. Representative photomicrographs aredepicted in Figs 2-5.

ResultsThe photomicrographs obtained from replicas of the

unetched tooth at two different appointments (Figs 2A,B) confirmed that the period of remineralization wassufficient to ensure that the etched tooth regained arelatively normal SEM appearance. Thus, it seemedreasonable to compare photomicrographs of casts ob-tained during either appointment.

Acid etching alone created a sparse etch pattern sepa-rated by large areas exhibiting no etched appearance(Fig 3). These nonetched areas appeared to be coatedwith an amorphous surface layer. It is possible that thisamorphous coating was protein adsorbed from saliva.It should be noted that the cervical enamel, which isless severely affected by Al, appears to exhibit a morenormal acid etch pattern.

Fig 2. Mandibular left canine replicas of: A) unetched tooth, initial appointment,and B) unetched tooth, second appointment. Less affected enamel is locatedcervically (arrowheads). Scale bars represent 500 urn.

434 Pediatric Dentistry: November/December 1994 - Volume 16, Number 6

Fig 3. Mandibular left canine replicaafter acid etch alone. Note well-etched enamel (arrowheads) andamorphous, poorly etched areas(arrows). Scale bar represents 50 \im.

Fig 4. Mandibular left canine replicaafter 5% NaOCI alone. Note theglobular surface pattern (arrowheads).Scale bar represents 50 urn.

Fig 5. Mandibular left canine replicaafter 5% NaOCI plus acid etch. Notethe raised islands of well-etchedenamel (arrowheads). Scale barrepresents 50 urn.

NaOCI pretreatment appeared to remove the amor-phous surface material revealing a globular pattern(Fig 4). These globular structures could representblunted prism ends, ectopic surface mineralizations, orsurface deposits of calculus. Given the morphologicvariability of these surface features, they likely repre-sent several diverse structures.

Acid etching that followed NaOCI pretreatment pro-duced islands of well-etched enamel apparently sur-rounded by shallow, depressed areas with featurelessto slightly etched bases (Fig 5). There appeared to bepreferential etching of the periphery of enamel prisms.

Low-magnification photomicrographs suggestedthat NaOCI pretreatment resulted in more etched sur-face area interspersed with smaller nonetched areas(data not shown). However, we undertook no morpho-metric analysis. Therefore, we cannot conclude defini-tively that NaOCI pretreatment increased etched sur-face area.

DiscussionNaOCI is an effective protein denaturant that does

not appear to alter the structure or mineral content ofnormal or HCAI enamel crystallites.2 SEM data suggestthat NaOCI enhanced bonding in this case by remov-ing excess protein, which interfered with establishing aclinically successful acid etch pattern. The excess pro-tein may have been at least partially of salivary origin,since bond failures occurred only after the tooth hadbeen exposed to the oral environment. Imbibition stud-ies show that HCAI enamel can be more porous, andultrastructural analyses show it has rougher crystal-lites than normal enamel.2 Furthermore, HCAI enamelcan have a markedly elevated protein content due toprotein retention during development. In this case these

factors apparently interfered with the development ofa typical etch pattern using 37% phosphoric acid. NaOCIlikely produced a more favorable acid etch by exposingthe enamel mineral previously encased in acid-insolubleproteins.

One must exercise caution in interpreting the photo-micrographs depicted in this report based on a singlepatient. In addition, no morphometric analysis of thephotomicrographs was undertaken. Yet, the NaOCIpretreatment technique produced clinical success inbonding an orthodontic bracket to a tooth affected byHCAI.

We attempted several other methods of bonding anorthodontic bracket to the tooth in question and allresulted in failure. Still, other treatment options ex-isted in the event of failure of NaOCI pretreatment inestablishing a clinically successful bond. An orthodon-tic band could have been cemented to the tooth. Alter-natively, a full coverage restoration (resin crown orprefabricated stainless steel crown) could have beenplaced, relying partly on macromechanical retentionrather than solely on bonding to enamel and/or den-tin. It is true that this tooth, severely affected by Al, willrequire a full coverage restoration at a later date. How-ever, only the facial surface of the tooth was readilyaccessible. Thus, either of the above options wouldhave required a second surgical procedure to permitaccess to the entire lingual surface.

This technique of enamel pretreatment with 5%NaOCI has been attempted in bonding orthodonticbrackets for two other Al patients with apparent clini-cal success. One could speculate also about broaderapplicability for this pretreatment technique. The suc-cess of bonding sealants and composite resin restora-tions to Al-affected enamel could be enhanced. Yet we

Pediatric Dentistry: November/December 1994 - Volume 16, Number 6 435

have reason to believe that the technique would be

ineffective-- or possibly detrimental -- in certain situ-

ations. For example, some AI enamel has a normalprotein content, 6 and NaOC1 pretreatment would prob-

ably have no effect on its surface topography. On theother hand, hypomaturation AI (HMAI) enamel exhib-

its a very high protein content with small, disorganizedenamel crystals? It is possible that NaOC1 pretreatment

of HMAI enamel could result in excessive destruction

of enamel due to removal of large quantities of protein.Moreover, the enamel mineral content may be so low in

these teeth as to make bonding unsuitable. In otherwords, enamel that is severely deficient in mineral con-

tent (e.g., less than 70% mineral per volume) wouldprobably be a poor risk for any composite bonding

technique due to the inherent weakness of the enamel.As a rule of thumb, we propose that enamel that can be

penetrated easily with an explorer would not be a goodcandidate for NaOC1 pretreatment and bonding.

Even normal enamel may fracture during orthodon-

tic appliance removal. For patients affected with AI,this risk may be dramatically increased. A clinicianshould inform AI patients and/or parents in very clear

terms of potential difficulties involved in orthodontictreatment, including the possibility of fracture or loss

of affected enamel. These discussions should be welldocumented during the informed consent process.

Dr. Venezie is a fellow, department of pediatric dentistry, Universityof North Carolina at Chapel Hill; Dr. Vadiakas is in private practice inpediatric dentistry in Athens, Greece; Dr. Christensen, a dual-trainedpediatric dentist and orthodontist, maintains a private practice and isclinical assistant professor, departments of pediatric dentistry andorthodontics, UNC; Dr. Wright is associate professor, department ofpediatric dentistry.

This research was supported in part by NIH Grants DE00165 andDE10025 and by Grant MCJ-379494 from the Maternal and ChildHealth Bureau. This work was presented, in part, at the 46th AnnualSession of the American Academy of Pediatric Dentistry in KansasCity, Missouri, where Dr. Venezie received an Honorable MentionAward in the Table Clinic Competition.

1. Witkop CJ Jr, Sauk JJ Jr: Heritable defects of enamel. In: OralFacial Genetics. Stewart R, Prescott G, Eds. St Louis: CV MosbyCo, 1976, pp 151-226.

2. Wright JT, Duggal MS, Robinson C, Kirkham J, Shore R: Themineral composition and enamel ultrastructure of hypocalcifiedamelogenesis imperfecta. J Craniofac Genet Dev Biol 13:117-26, 1993.

3. Darling AI: Some observations on amelogenesis imperfectaand calcification of the dental enamel. Proc R Soc Med 49:759-65, 1956.

4. Wright JT, Butler WT: Alteration of enamel proteins inhypomaturation amelogenesis imperfecta. J Dent Res 68:1328-30, 1989.

5. Wright JT, Robinson C, Kirkham J: Enamel protein in smoothhypoplastic amelogenesis imperfecta. Pediatr Dent 14:331-37,1992.

6. Wright JT, Robinson C, Kirkham J: Enamel protein in the differ-ent types of amelogenesis imperfecta. In: The Chemistry andBiology of Mineralized Tissue, Slavkin H, Price P, Eds. NewYork: Elsevier, 1992, pp 441-50.

7. Wright JT, Aldred MJ, Crawford PJ, Kirkham J, Robinson C:Enamel ultrastructure and protein content in X-linkedamelogenesis imperfecta. Oral Surg Oral Med Oral Pathol76:192-200, 1993.

8. Seow K: Clinical diagnosis and management strategies ofamelogenesis imperfecta variants. Pediatr Dent 15:384-93,1993.

9. Wright JT, Lord V, Robinson C, Shore R: Enamel ultrastructurein pigmented hypomaturation amelogenesis imperfecta. J OralPathol Med 21:390-94, 1992.

10. Vossen ME, Letzel H, Stadhouders AM, Mertel R, HendricksFH: A rapid scanning electron microscopic replication tech-nique for clinical studies of dental restorations. Dent Mater1:158-63, 1985.

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