Endodontic and periodontal treatment of an external cervicalresorptionJose Roberto Gonzales, DDS,a and Hille Rodekirchen, DDS,b Giessen, GermanyUNIVERSITY OF GIESSEN

External root resorption can be divided into 3 categories: 1) progressive inflammatory resorption; 2) cervicalresorption; and 3) replacement resorption. Cervical resorption is a not well recognized type of progressive externalinflammatory resorption. It occurs after injury to the cervical attachment apparatus, mostly in the area of the cervicalroot surface (precementum) below the epithelial attachment. The present article describes an abnormal case of cervicalresorption in a vital lateral maxillary incisor of a 27-year-old male patient. Endodontic treatment and subsequentperiodontal plastic-esthetic surgery were performed. Reconstruction of the defect was achieved using mineral trioxideaggregate cement. After 2 years, the tooth showed no pathologic symptoms. The present case demonstrates a novelcombined endodontic and periodontal treatment of an external root resorption. (Oral Surg Oral Med Oral Pathol Oral

Radiol Endod 2007;104:e70-e77)

Invasive cervical resorption is a clinical term used todescribe a relatively uncommon, insidious, and oftenaggressive form of external root resorption.1 In general,the history is obscure.2 It is seen in most cases as a latecomplication of traumatic injuries of the teeth, but itmay also occur after orthodontic tooth movement, or-thognatic and other dentoalveolar surgery, periodontaltreatment, bleaching of teeth, and a wide variety of“traumatic” conditions. It is characterized by a progres-sive loss of cementum and dentin with replacement byfibrovascular tissue derived from the periodontal liga-ment, with deposition of cementum-like hard tissue.3

The invasive and somewhat aggressive characteristicsof the process, coupled with its histopathologic features,raise questions as to the nature of the lesion. The invadingtissue arises from the periodontal ligament but differsfrom periodontal tissues in both structure and behavior.The precursor cells of the periodontal ligament, beingectomesenchymal in origin, have the potential to differ-entiate into cells capable of laying down fibrous tissue orcalcified tissue.4,5 For invasion to occur, a defect in thecementum-cementoid layer is a likely prerequisite.6,5

The exact cellular mechanisms are not clearly under-stood. There is evidence that proinflammatory cyto-kines play an important role in the pathogenesis andprogression.7 Interleukin-1 (IL-1) and tumor necrosisfactor alpha (TNF-�) have been shown to play a role in

aSpecialist in Periodontology, Department of Periodontology.bInstructor, Department of Operative and Preventive Dentistry.Received for publication Sep 22, 2006; returned for revision Oct 11,2006; accepted for publication Jan 22, 2007.1079-2104/$ - see front matter© 2007 Mosby, Inc. All rights reserved.

doi:10.1016/j.tripleo.2007.01.023

e70

orthodontically induced tooth movement as a sterileinflammation. During orthodontic tooth movement,these cytokines have been detected in periodontal tis-sues and crevicular fluid.8

Although there have been reports of multiple teethshowing invasive cervical resorption,9 in many casesonly a single tooth is involved. Clinically and radio-graphically, it is seen as a single resorption lacuna inthe cervical area of the tooth. The damaged area of theroot surface where the resorption starts may be verysmall and is rapidly colonized by hard tissue–resorbingcells. Usually, the cervical resorption will be transient,which means that the cemental repair will occur within2-3 weeks without treatment.2 However, a resorbingactivity for a longer period may be provided by bacte-rial products via the tubules of the cervical dentin,apparently coming from the gingival sulcus and thesurface of the tooth rather than from the root canal. Theresorbing cells will penetrate into the tooth throughthe small denuded area and cause a spreading of theresorption inside the dentin of the root. The resorptiveprocess will not then directly penetrate straight to thepulp, because of the protective qualities of the preden-tin,10,11 but rather spread around the root canal in anirregular fashion. It is because of this pattern of spread-ing inside the root that this cervical resorption is alsoreferred to as external-internal12 or invasive resorp-tion.13 With time, the resorptive process usually willpenetrate to the root canal. If a supragingival area of thecrown is reached, the well vascularized granulationtissue of the resorption lacunae may be visible throughthe enamel. A pink discoloration of the crown indicatesthe resorptive process.1 The patient will present with a

so-called pink spot or pink tooth.

OOOOEVolume 104, Number 1 Gonzales and Rodekirchen e71

After a physical injury to the root surface has oc-curred or natural cementum defects exist, the microor-ganisms of the plaque can tip the balance from a po-tentially reversible physiologic resorptive process to aprogressive pathologic one. Thus, it is necessary toeliminate the subgingival bacterial biofilm before anyother treatment of root resorption. If a perforation to theroot canal has occurred, endodontic treatment is neces-sary and should be performed before the periodontaltreatment. Thereafter, the resorption lacunae must beexposed surgically, the granulation tissue removed, andthe resorptive defect restored. This usually has beenperformed by shaping the defect as a cavity with nec-essary retentive areas and restoring it with a cavityvarnish and amalgam or an acid-etch resin technique inareas where esthetics is important. Other techniqueshave not been reported so far.

Mineral trioxide aggregate cement (MTA) (ProRoot;Dentsply, Constance, Germany) was developed forroot-end cavities to seal off the pathways of communi-cation between the root canal system and the externalsurface of the tooth.14 Long-term endodontic perfora-tions with periodontal inflammation and complete end-odontic obturations of avulsed teeth also have beensuccessfully treated with MTA.15,16 Nevertheless, onlya few clinicians have used MTA in the treatment ofexternal root resorptions.17

In the present article we demonstrate a novel end-odontic treatment and subsequent periodontal plastic-esthetic surgery of an unusual external cervical resorp-tion in a vital permanent maxillary lateral incisor.

CASE REPORTClinical examination and diagnosis

A 27-year-old male patient was referred to the Departmentof Conservative and Preventive Dentistry of the Dental Clinicat the University of Giessen and Marburg due to a pinkcoronal discoloration at the labial surface in the cervicalregion of the right lateral upper incisor. The patient did notcomplain of pain. A pinhead-size pink-colored lesion withcavitation of the enamel at the labial cervical region of tooth#7 was detected (Fig. 1). Inspection with a dental probecaused bleeding (Fig. 2). The tooth had no restorations andwas caries free. The tooth showed reaction to pulp-sensibilitytesting using dry ice. There was no pain on percussion andpalpation, but there was light pain on palpation of the mar-ginal gingiva in the labial region of the tooth. The gingivaltissue in this region was resilient.

Periodontal examination was performed assessing the follow-ing clinical parameters (6�/tooth) with a periodontal probe(PCP-UNC 15): probing pocket depth (PPD), gingival recession(GR), clinical attachment level (CAL), and bleeding on probing(BOP). The periodontal status of the patient demonstrated PPDbetween 1-4 mm and no gingival recessions. Only 2 sites withPPD of 4 mm (teeth 14 and 30) showed BOP. Tooth 17 showed

PPD of 1-2 mm and no loss of clinical attachment. When the

dimensions of the cervical resorption were carefully soundedwith a periodontal probe, a depth of 3 mm was measured in themiddle of the tooth (Fig. 3).

Radiographic examination with a gutta-percha point(Dentsply Maillefer, Ballaigues, Switzerland) positioned inthe labial defect showed a lesion extending from the cervicalregion to the coronal third of the root (Fig. 4).

Clinical symptoms and radiographic examination sug-gested a diagnosis of cervical external resorption. There wereno clinical signs of periodontal disease at this tooth.

Endodontic treatmentConservative root canal treatment was performed at the De-

partment of Conservative and Preventive Dentistry of the Dental

Fig. 1. Pinhead-size pink-colored lesion in maxillary rightlateral incisor with cavitation of the enamel.

Fig. 2. Bleeding after inspection with a dental probe.

Clinic. After the application of local anesthesia (1.8 mL Ultra-

OOOOEe72 Gonzales and Rodekirchen July 2007

cain D-S Forte; Aventis Pharma, Bad Soden, Germany), tooth #7was isolated with rubber dam, and access to the root canal wasgained. After vital extirpation of the pulp and irrigation withNaCl (0.9%), the granulation tissue was removed from thecoronal third of the root canal using a dental excavator(EXC18H; Hu-Friedy, Leimen, Germany). At the labial site, anaccess of the root canal with the periodontal ligament wasvisible using an operative microscope (OPMI S 151; CarlZeiss, Oberkochen, Germany). The resorption was sealedwith light-curing glass-ionomer cement (Ionoseal; Voco,Cuxhaven, Germany). Ionoseal was applied with a dentalprobe (EXS9; Hu-Friedy) and then light cured (Elipar FreeLight 2; 3M Espe, Seefeld, Germany) for 20 seconds. Aftercopious irrigation with H2O2 (3%) and NaOCl (5%), theaccess to the canal was widened using Gates Glidden II andIII drills (Komet, Lemgo, Germany) and the working lengthof the canal was determined radiographically (Fig. 5). There-after, the canal was shaped to size 25 using K-files (Antaeos,Munich, Germany), a Ca(OH)2 dressing (Calxyl; OCO Products,Dirnstein, Germany) was placed in position, and the accesscavity was filled with Cavit (3M Espe). Five days later, the canalwas shaped mechanically with Pro File (Dentsply/De Trey,Constance, Germany) to size 35. Before root canal filling, theposition of a Verifier (Dentsply/De Trey) was controlled by adental radiograph (Fig. 6). Subsequently the canal was filledusing the plastic Thermafil obturation technique (Thermafil;Dentsply/De Trey). AH Plus (Dentsply Maillefer) was used assealer. The radiographic control showed an obturation of thecanal to the desired length (Fig. 7). A small amount of sealer

Fig. 3. Measurements of the dimension of the cervical re-sorption with a periodontal probe.

gained access to the apical region. The root filling was covered

with glass-ionomer cement (Ketac-fil; 3M Espe), and the accessopening was filled with composite material (Herculite XRV,Kerr Manufacturing Company, Romulus, MI).

Periodontal treatmentAfter endodontic treatment, the patient was referred to the

Department of Periodontology. The periodontal treatmentwas carried out in 2 phases. In the first phase of treatment,modified plaque (PLI) and papillary bleeding (PBI) indexeswere recorded18,19 and oral hygiene instruction and suprag-ingival debridement of all teeth were performed. The patientdemonstrated a high level of motivation from the beginningof the treatment; therefore the oral hygiene indexes weremaintained at low levels (Fig. 8). Subgingival scaling wasperformed manually at sites with 4 mm PPD and BOP. At theend of this antiinfectious phase, the response to the treatmentwas reevaluated. The response was good, with an improve-ment in the oral hygiene (PLI from 36.6% to 24%, PBI 0%)and overall periodontal health (PPD and CAL �3 mm).

The second corrective phase of the therapy consisted of a

Fig. 4. Radiographic assessment of the defect with a gutta-percha point.

plastic-esthetic periodontal microsurgical procedure. The aim

OOOOEVolume 104, Number 1 Gonzales and Rodekirchen e73

was to repair the defect caused by the residual resorptioncavity without compromising esthetics. The width of theattached gingiva was analysed histochemically with Schiller’siodine solution. The microsurgical procedure was carried outusing magnifying lenses (Prismen-Lens F; Carl Zeiss Surgi-cal). Under local anesthesia (1.8 mL Ultracain D-S Forte), anaccess full thickness flap was raised from the buccal side.Since the main concern was the esthetic contour of the gin-giva, only a sulcular incision was made and extended to theadjacent incisors to maintain an even gingival contour afterthe healing process. Because the flap was only raised from thebuccal side and the interproximal bone level was intact, twosimple angular incisions were performed in the middle of theadjacent papillae, which were left intact from the palatal side.The granulation tissue was removed and the resorptive defectexamined (Fig. 9). No soft dentin was present, but there wasa communication with the canal and the root filling materialwas visible. The surface periphery of the resorptive cavityextended into the mesial and distal embrasures and wasbordered by enamel and cementum. The cementoenameljunction (CEJ) was completely involved. The CEJ was min-imally shaped and immediately restored with Charisma Pho-tocuring Universal-Microglass-Composite (Heraeus Kulzer,Wehrheim, Germany). Thereafter, the remained defect wasrestored with MTA (Dentsply). The periosteum was then cut

Fig. 5. Radiographic assessment of the working length with aK-file of ISO #20 in the canal.

so that the flap could be repositioned without tension and

sutured interproximally with 6-0 nonabsorbable sutures (Pro-lene; Ethicon, Norderstedt, Germany) (Fig. 10). At sutureremoval 1 week later, healing had been uneventful and thedesired gingival contour achieved (Fig. 11). Further postsur-gical controls were performed after 14 and 21 days. Figures12 and 13 show the clinical situation after 2 months. Peri-odontal examination demonstrated healthy gingival condi-tions without PPD and CAL more than 3 mm without BOP.The patient was completely satisfied with the appearance,despite a slight “gleam” of the restoration.

At the reevaluation after 2 years, the patient reported that thetooth had remained free of any symptoms. Clinical examinationshowed normal conditions (Fig. 14) with respect to percussion,palpation, and PPD. Radiographic examination showed no signsof pathology (Fig. 15). Small rests of sealer that gained access tothe apical region during root canal filling were resorbed.

DISCUSSIONIn the present case report, a novel treatment of an

external root resorption characterized by its cervicallocation and invasive nature is demonstrated. The clin-ically obvious pinkish color in the tooth crown of #7was the result of the highly vascular resorptive tissuethat became visible through the thin residual enamel.

Fig. 6. Radiographic assessment with Verifier of ISO #30 inthe canal after shaping of the canal.

As stated in the introduction, this pathology might be of

OOOOEe74 Gonzales and Rodekirchen July 2007

developmental origin in a small zone near the cervicalarea or the result of physical or chemical trauma.Among the potential predisposing factors, orthodontic

Fig. 7. Dental film after obturation of the canal with plasticThermafil obturation technique.

0102030405060708090100

1 2 3 4

PLIPBI

Time

%

Fig. 8. Oral hygiene indexes at different times (PLI, plaqueindex; PBI, papillary bleeding index).

treatment seems to be a very common factor.1 Cervical

resorption caused by orthodontic tooth movement isrelated to tissue pressure.2 The present patient could notremember any trauma affecting his tooth, but he had ahistory of extensive orthodontic treatment in his teen-age years which may have caused a cementum-cemen-toid deficiency that allowed direct contact betweendentin and the potentially resorptive cells of the peri-odontium.6 A basic question to be answered is whetherthis resorptive process was purely inflammatory in na-ture, activated by subgingival microorganisms, or al-ternatively a type of benign proliferative fibrovascularor fibro-osseus disorder in which the microorganismshave no pathogenic role but may become secondaryinvaders.

There is one body of opinion that considers subgin-gival microorganisms to be the activating factor.2,20-22

Fig. 9. Intrasurgical view after removing the granuation tis-sue.

Fig. 10. Clinical situation after flap reposition and interdentalsuture.

Inflammatory mediators attract resorbing cells to the

OOOOEVolume 104, Number 1 Gonzales and Rodekirchen e75

root surface.23 Some of the limited published his-topathologic material showing inflammatory cellularinfiltrates may provide support to this hypothesis.3,23

However, a contrary argument is that the presence of

Fig. 11. Clinical aspect after suture removal one week aftersurgery.

Fig. 12. Clinical aspect after 2 months.

Fig. 13. Patient’s smile after 2 months.

inflammatory cells is not necessarily indicative of a

microbiologic etiology, because there are cases in theliterature that show no inflammation.6,24 Those cases,coupled with the clinical manifestations, indicate that

Fig. 14. Clinical situation after 2 years.

Fig. 15. Radiographic follow-up after 2 years.

invasive cervical resorption is an aseptic resorptive

OOOOEe76 Gonzales and Rodekirchen July 2007

process which may on occasions become secondarilyinvaded with microorganisms.

Additionally, it has been reported that the cellularmechanisms of dental root resorptions are modulatedby proinflammatory cytokines such as IL-1 and TNF-�.7

The exact mechanisms are not clearly understood, al-though the systemic application of soluble cytokinereceptors led to a reduction or almost complete inhibi-tion of experimentally induced root resorption.25 Thisshowed that odontoclasts are cytokine sensitive and thattheir differentiation or activation is controlled by thesefactors. In the pathogenesis of periodontitis, the role ofthese proinflammatory mediators is well known.26

These include the induction of adhesion molecules andother mediators that facilitate and amplify the inflam-matory response, the stimulation of matrix metallopro-teinase, and bone resorption. The activity of these cy-tokines coincides with the critical events that occurduring periodontal disease, namely, loss of attachmentand bone resorption.

Only a few studies and case reports of treatment ofexternal resorptions in patients with periodontitis exist.In one study, it was found that the spread of rootresorption was associated with the extent of periodontalinflammation and that the capacity for repair was di-minished with greater severity of periodontitis.27 Inanother study, it was concluded that the severity ofperiodontitis plays a major role in the presence andextent of transient external root resorptions, with mostof the teeth showing resorptions on the apical third.28

These findings are consistent with the proposed theoryof pathogenesis that involves predisposing root condi-tions and perpetuating bacterial factors.2 The presentpatient, however, showed no clinical signs of periodon-tal disease.

In the present case, endodontic treatment was per-formed, although the patient did not complain aboutpain and the tooth showed reaction to pulp-sensibilitytesting using dry ice. Clinically and radiographically,however, it was detected that the extension of theresorptive defect had reached the pulp. This was con-firmed after gaining access to the root canal using anoperative microscope. After vital extirpation of the pulpand removal of granulation tissue, an access of the rootcanal with the periodontal ligament was detected. Thepulp was probably not yet infected through bacteriafrom the gingival sulcus.

Endodontic treatment was performed before the sur-gical exposure of the resorption lacuna. This has theadvantage that resorption lacunae with minute externalentrance openings may be cleaned and obturated fromthe root canal. Extrusion of irrigation fluids in theperiodontal ligament are then avoided by sealing the re-

sorption from inside the canal before beginning the

endodontic treatment. In the present case, the resorptionwas sealed with light-curing glass-ionomer cement,which was used because of its manageability, consis-tency, and color. Furthermore, this material shows anadequate density.

Owing to the esthetic relevance of the affected area,a microsurgical plastic-esthetic procedure was per-formed. A periodontal access flap was elevated onlyfrom the buccal side of the gingiva, minimally extendedjust to gain access to the root resorption. Lateral verti-cal relaxing incisions were avoided. Microsurgical ac-cess flap has been shown to positively affect the per-centage of primary closure and the amount of tissuepreservation.29 For the correction of the defect, MTAwas used. This material was developed for endodontics,because it appeared to be better than other materials forprocedures including bone.16 The material is supposedto promote the overgrowth of cementum, and it mayfacilitate the regeneration of the periodontal ligament.14

Therefore, since its development, MTA has beenmostly used as root-end filling material in endodonticsurgery for pulpotomies and apexifications. However,there are only a few case reports of the use of MTA forexternal root resportion alone or in combination withperiodontitis. Bargholz used it for repairing root perfo-rations.16 White and Bryant treated a maxillary centralincisor that presented with a sinus tract and an amalgamrestoration.17 A 2-wall osseous lesion was also associ-ated with the distal surface of tooth #8. A full-thicknessmucoperiosteal flap was reflected, the amalgam wasremoved, the defect was restored with MTA, and theosseous defect was grafted with decalcified freeze-driedbone allograft and a calcium sulfate barrier. After 15months, an 8-mm gain in clinical attachment and anincrease in radiodensity were noted, with no clinicalsigns of inflammation present.

In the present case, the use of MTA showed similargood results after periodontal surgery. No clinical signsof inflammation were found after 2 years.

The present case demonstrates a successful novelcombined endodontic and periodontal treatment for ex-ternal root resorptions. After the therapy, the patientwas satisfied with the esthetic result and the appearanceof his smile. Patient compliance and participation in thesupportive treatment will maintain the results and pro-vide an overall good prognosis.

REFERENCES1. Heithersay GS. Invasive cervical resorption: an analysis of po-

tential predisposing factors. Quintessence Int 1999;30:83-95.2. Tronstad L. Root resorption—etiology, terminology and clinical

manifestations. Endod Dent Traumatol 1988;4:241-52.3. Makkes PC, Thoden VV. Cervical external root resorption. J

Dent 1975;3:217-22.

OOOOEVolume 104, Number 1 Gonzales and Rodekirchen e77

4. Lindskog S, Blomlof L. Quality of periodontal healing. IV:Enzyme histochemical evidence for an osteoblast origin of re-parative cementum. Swed Dent J 1994;18:181-9.

5. Hammarstrom L, Lindskog S. Factors regulating and modifyingdental root resorption. Proc Finn Dent Soc 1992;88 Suppl 1:115-23.

6. Southam JC. Clinical and histological aspects of peripheral cer-vical resorption. J Periodontol 1967;38:534-8.

7. Zhang D, Goetz W, Braumann B, Bourauel C, Jaeger A. Effectof soluble receptors to interleukin-1 and tumor necrosis factoralpha on experimentally induced root resorption in rats. J Peri-odontal Res 2003;38:324-32.

8. Alhashimi N, Frithiof L, Brudvik P, Bakhiet M. Orthodontic move-ment induces high numbers of cells expressing IFN-gamma atmRNA and protein levels. J Interferon Cytokine Res 2000;20:7-12.

9. Coyle M, Toner M, Barry H. Multiple teeth showing invasivecervical resorption—an entity with little known histologic fea-tures. J Oral Pathol Med 2006;35:55-7.

10. Wedenberg C, Yumita S. Evidence for an inhibitor of osteoclastattachment in dentinal matrix. Endod Dent Traumatol 1990;6:255-9.

11. Wedenberg C. Evidence for a dentin-derived inhibitor of mac-rophage spreading. Scand J Dent Res 1987;95:381-8.

12. Frank AL. External-internal progressive resorption and its non-surgical correction. J Endod 1981;7:473-6.

13. Frank AL, Bakland LK. Nonendodontic therapy for supraosseousextracanal invasive resorption. J Endod 1987;13:348-55.

14. Abedi HR, Ingle JI. Mineral trioxide aggregate: a review of anew cement. J Calif Dent Assoc 1995;23:36-9.

15. Karp J, Bryk J, Menke E, McTigue D. The complete endodonticobturation of an avulsed immature permanent incisor with mineraltrioxide aggregate: a case report. Pediatr Dent 2006;28:273-8.

16. Bargholz C. Perforation repair with mineral trioxide aggregate: amodified matrix concept. Int Endod J 2005;38:59-69.

17. White C Jr, Bryant N. Combined therapy of mineral trioxideaggregate and guided tissue regeneration in the treatment ofexternal root resorption and an associated osseous defect. JPeriodontol 2002;73:1517-21.

18. O’Leary TJ, Drake RB, Naylor JE. The plaque control record. JPeriodontol 1972;43:38-42.

19. Saxer UP, Mühlemann HR. Motivation und Aufklärung. Schweiz

Monatszeitschr Zahnheilkunde 1975;85:905-19.

20. Gold SI, Hasselgren G. Peripheral inflammatory root resorption.A review of the literature with case reports. J Clin Periodontol1992;19:523-34.

21. Trope M. Root resorption of dental and traumatic origin: classi-fication based on etiology. Pract Periodontics Aesthet Dent 1998;10:515-22.

22. Fuss Z, Tsesis I, Lin S. Root resorption—diagnosis, classifica-tion and treatment choices based on stimulation factors. DentTraumatol 2003;19:175-82.

23. Trope M, Chivian N, Sigurdsson A, editors. Pathways of thepulp. St Louis: Mosby; 2002. p. 626-28.

24. Heithersay GS. Clinical, radiologic, and histopathologic featuresof invasive cervical resorption. Quintessence Int 1999;30:27-37.

25. Alhashimi N, Frithiof L, Brudvik P, Bakhiet M. Orthodontictooth movement and de novo synthesis of proinflammatory cy-tokines. Am J Orthod Dentofacial Orthop 2001;119:307-12.

26. Page RC. The etiology and pathogenesis of periodontitis. Com-pend Contin Educ Dent 2002;23:11-4.

27. Crespo Abelleira AC, Rodriguez Cobos MA, Fuentes B, I,Castano Oreja MT, Jorge Barreiro FJ, Rodriguez Pato RB. Mor-phological study of root surfaces in teeth with adult periodontitis.J Periodontol 1999;70:1283-91.

28. Rodriguez-Pato RB. Root resorption in chronic periodontitis: amorphometrical study. J Periodontol 2004;75:1027-32.

29. Wachtel H, Schenk G, Bohm S, Weng D, Zuhr O, Hurzeler MB.Microsurgical access flap and enamel matrix derivative for thetreatment of periodontal intrabony defects: a controlled clinicalstudy. J Clin Periodontol 2003;30:496-504.

Reprint requests:

Dr. J.R. GonzalesSpecialist in PeriodontologyDepartment of PeriodontologyFaculty of DentistryUniversity of GiessenSchlangenzahl 1435392 GiessenGermany

jose.gonzales@dentist.med.uni-giessen.de