Peri-implant tissue response of immediately loaded, threaded, HA-coated implants: 1-year results Kitichai Rungcharassaeng, DDS, MS,a Jaime L. Lozada, DDS,b Joseph Y. K. Kan, DDS, MS,c Jay S. Kim, PhD,d Wayne V. Campagni, DMD,e and Carlos A. Munoz, DDS, MSDf School of Dentistry, Loma Linda University, Loma Linda, Calif. Statement of problem. Although high success rates have been reported with immediately loaded implants, the peri-implant tissue response has not been well documented. Purpose. This study evaluated implant success and peri-implant tissue response of immediately loaded, threaded, hydroxyapatite (HA)-coated root-form implants supporting mandibular bar overdentures with opposing conventional maxillary complete dentures in humans. Material and methods. Five patients (3 men, 2 women; mean age 61 years) each received 4 HA-coated endosseous root-form implants in the interforaminal region in the mandible. The implants were rigidly splinted with a metal framework within 24 hours. The final EDS clip prosthesis was placed 1 to 2 weeks thereafter. The implants and peri-implant tissues were evaluated clinically and radiographically 0, 1, 3, 6, and 12 months after prosthesis placement. Data were analyzed with a repeated measures 1-way analysis of variance (P<.05). Results. All implants were stable at the end of the observation period (mean Periotest value = –5.9 ± 1.4). No peri-implant radiolucencies were noted, and no implants were lost. The mean marginal bone changes were –0.42 ± 0.34, –0.84 ± 0.55, –1.14 ± 0.80, and –1.16 ± 0.89 mm at the 1-, 3-, 6-, and 12-month follow-ups, respectively (P<.001). Significant declines in the rates of marginal bone changes at each time interval were noted (P<.001). In addition, there were significant decreases in probing depth (P<.001) and plaque index (P<.001) but no significant difference in the frequency of bleeding upon probing (P=.64). Conclusion. Within the limitations of this study, the peri-implant tissue response of immediately loaded, HA-coated implants was favorable and comparable to that of conventional, delayed-loaded implants after 1 year. (J Prosthet Dent 2002;87:173-81.) CLINICAL IMPLICATIONS The peri-implant tissue response and implant success rate in this short-term study indicate that immediately loaded, threaded, HA-coated root-form implants supporting mandibular bar overdentures may be a viable option for completely edentulous patients. However, further research and long-term clinical studies are needed to substantiate the predictability of this treatment. O sseointegrated endosseous implants have been a successful modality for treating completely and partially edentulous patients.1-4 To achieve osseointegration, certain guidelines must be strictly followed.5,6 The guidelines include an aseptic and atraumatic surgical technique, complete soft tissue coverage, and an extended healing time during which functional loading is avoided. Although aseptic and atraumatic Partial funding for this research was provided by the Loma Linda University School of Dentistry and Nobel Biocare USA, Inc. aAssistant Professor, Department of Restorative Dentistry. bProfessor and Director, Advanced Education in Implant Dentistry. cAssociate Professor, Department of Restorative Dentistry. dProfessor, Department of Biostatistics. eProfessor and Director, Advanced Education in Prosthodontics. fProfessor and Director, Biomaterial Research Center. FEBRUARY 2002 surgical techniques are still considered a prerequisite, the necessity of complete soft tissue coverage and long healing periods has been challenged.7-21 Studies have shown that nonsubmerged implants achieved similar soft and hard tissue responses and were comparably successful to submerged implants.7,8 Periods of 3 to 4 months and 4 to 6 months have been recommended as healing times for osseointegrated implants placed in the mandible and maxilla, respectively.5,6 Because long healing periods can impose esthetic and functional challenges for some patients, attempts have been made to reduce necessary healing time. Faster osseous adaptation has been demonstrated with hydroxyapatite (HA)-coated implants.9-11 A direct bone-implant interface also has been observed, even when HA-coated implants were immediately loaded.12-14 However, the routine use of THE JOURNAL OF PROSTHETIC DENTISTRY 173 THE JOURNAL OF PROSTHETIC DENTISTRY HA-coated implants has been questioned due to lack of long-term (more than 10 years) documented success rates. Johnson15 reported complications associated with HA-coated implants and suggested that HA coatings were more susceptible to bacterial infection and rapid osseous breakdown; however, this issue remains controversial. Furthermore, recommended healing times are still in the range of 3 to 6 months regardless of the type of implants used. Recently, limited animal studies have been conducted on the osteoinductive capability of bone morphogenetic proteins in conjunction with endosseous implants. The presence of these proteins seemed to induce faster bone formation around implants as observed in histologic examination.16-18 Nevertheless, no human study has been reported, and the suitable period for these implants to be loaded has not been established. Babbush et al19 described a technique of immediately loading 4 titanium plasma-sprayed (TPS) implants placed in the mandibular symphysis with an overdenture. The implants were rigidly splinted with a metal bar, and the denture was relined with soft liner within 2 to 3 days after surgery. The final clip prosthesis was placed 2 weeks later. The authors reported a cumulative failure rate of 12% after 8 years of followup. Buser et al20 reported a 3% failure rate after 33 months of follow-up with a similar technique. They splinted the implants within 24 hours and relined the prosthesis with soft tissue conditioner at 2 weeks. Schnitman et al21 reported a short-term follow-up on 7 patients who received a fixed provisional prosthesis that was immediately loaded and supported by 3-4 mandibular implants. Their 10-year follow-up22 showed a 15% failure rate in 9 patients. Tarnow et al23 reported 1- to 5-year data on 10 consecutive patients that received immediately loaded, fixed provisional prostheses. The implants were titanium, TPS, or TiO-blasted. Ten implants minimum were placed in each patient, of which a minimum of 5 implants were immediately loaded. Three percent of immediately loaded implants did not integrate. In a multicenter retrospective study on immediately loaded, implant-supported bar overdentures, Chiapasco et al24 reported an implant failure rate of 3% after a mean follow-up time of 6.4 years. There were no significant differences in the implant success rates among different implant systems (TPS, International Team for Implantology, Hand-Titanium, and New Ledermann Screw), and no correlation existed between implant length and the success rate as long as there was bicortical stabilization. Parameters that are indicative of implant success in conventional implant treatment, including marginal bone loss,25-28 level of implant stability,29-34 and periimplant parameters,35-45 have not been reported in 174 RUNGCHARASSAENG ET AL relation to immediately loaded implants. The purpose of this study was to evaluate the implant success rate and peri-implant tissue response of immediately loaded, threaded, HA-coated endosseous root-form implants supporting mandibular bar overdentures with opposing conventional maxillary complete dentures in humans after 1 year in function. MATERIAL AND METHODS The protocol of this study was approved by the Institutional Review Board of Loma Linda University (Loma Linda, Calif.). Five patients (3 men and 2 women) were included in the study. Their ages ranged from 49 to 77 years (mean=61 years). The patients were selected according to specific inclusion and exclusion criteria. The inclusion criteria were a completely edentulous maxilla and mandible, type I or II bone quality according to Lekholm and Zarb,46 and enough bone to allow for placement of 4 implants with the minimum dimension of 3.8 × 12.0 mm between the mandibular mental foramens. The exclusion criteria were insufficient bone quality or quantity that required a bone grafting procedure; aspects of the medical history that would complicate the outcome of the study—namely, alcohol abuse, drug dependency, a history of smoking, poor health, or any other medical, physical, or psychological condition that might affect the surgical procedure or the subsequent prosthodontic treatment and the required follow-up appointments; a history of head and neck radiation treatment; and a history of parafunctional habits. Procedure New maxillary and mandibular complete dentures were fabricated, inserted, and adjusted for each patient before surgical placement of the implants. A bilateral balanced occlusion was used for all prostheses. A duplication of the mandibular complete denture was made with clear autopolymerizing acrylic resin (Splint resin polymer; Great Lakes Orthodontics Ltd, Tonawanda, N.Y.) to be used as radiographic and surgical templates. Mandibular computerized tomography was performed on each patient at the Loma Linda University Medical Center. To locate the most favorable position and ideal size of the implants, the SIM/Plant program (Columbia Scientific Inc, Columbia, Md.) was used to interpret the data. Implant placement surgery was performed under local anesthesia (with intravenous sedation upon request by 2 patients). Four threaded, HA-coated implants (Steri-Oss; Nobel Biocare USA Inc, Yorba Linda, Calif.) were placed in the interforaminal region according to the manufacturer’s protocol with the use of the surgical template. Precision margin esthetics (PME) transmucosal abutments (Nobel Biocare USA Inc) of appropriate heights to create a proper plane for frameVOLUME 87 NUMBER 2 RUNGCHARASSAENG ET AL work fabrication were connected to the implants. Plastic PME copings (Nobel Biocare USA Inc) were installed on top of the abutments, and the flap was preliminarily closed with Gore-Tex suture (Nobel Biocare USA Inc). English-Donnelle-Staubli (EDS) plastic bars (Attachment International Inc, San Mateo, Calif.) of proper length were prepared and placed between the plastic PME copings. The bars and the plastic PME copings then were joined with the use of autopolymerizing acrylic resin (GC Pattern resin; GC America Inc, Chicago, Ill.). The resin pattern was left intraorally for approximately 20 minutes, removed, and transferred to the laboratory where the metal framework was fabricated in type IV gold alloy (Monogram IV; Leach & Dillon, San Diego, Calif.). Meanwhile, the PME titanium healing caps were placed on the PME abutments and final flap closure was performed, leaving the healing cap exposed. Amoxicillin 500 mg and ibuprofen 800 mg (Motrin; The Upjohn Company, Kalamazoo, Mich.) were prescribed for antibiotic coverage and pain control. The patients were instructed to use 0.12% chlorhexidine gluconate (Peridex; Procter & Gamble, Cincinnati, Ohio) twice a day for 2 weeks and to start brushing the bar regularly with an end-tufted brush (John O Butler, Chicago, Ill.) 1 week after surgery. Trial placement of the metal framework was performed within 24 hours after surgery. After satisfactory fit and stability of the framework were verified both clinically and radiographically, the bar was placed in the patient’s mouth. One to 2 weeks after the surgery, the sutures were removed. The mandibular denture was relieved so that it did not touch the bar when in position. A pick-up impression of the bar was made with the mandibular denture with vinyl polysiloxane impression material (Reprosil; Dentsply International Inc, Milford, Del.) and sent to the laboratory for relining and incorporation of the metal housing for the EDS clip (Attachment International Inc). Use of Peri-O-Floss (PHB Company and Assoc, Osseo, Wisc.) to clean underneath the bar was demonstrated for each patient, and instructions were given to floss at least once a day. After relining, the denture was placed in the mouth and adjusted, and the EDS clip was placed in the metal housing. A clinical remount was performed and the occlusion adjusted as needed to ensure the presence of bilateral balanced occlusion. Each patient was asked to return the next day for a postplacement evaluation. Follow-up examinations were made 1, 3, 6, and 12 months after denture placement. Data collection and analysis All clinical examinations and data collections were performed by 1 examiner. At each follow-up appointment, the number of implant failures, which were FEBRUARY 2002 THE JOURNAL OF PROSTHETIC DENTISTRY Fig. 1. Occlusal jig made of vinyl polysiloxane adhered to film holder to ensure reproducibility of images obtained. judged according to the success criteria proposed by Smith and Zarb47 when applicable, were recorded. Marginal bone change also was measured with the use of sequential periapical radiographs and the long cone paralleling technique.48 An occlusal jig made of vinyl polysiloxane (Exabite; GC America Inc, Alsip, Ill.) was attached to the film holder (XCP post bite blocks 540862; Dentsply, Elgin, Ill.). The jig was fabricated intraorally at the time of definitive prosthesis placement (Fig. 1). The occlusal jig was used as an aid in standardizing the angulation and position of the film in relation to the beam. The film used (Kodak Ultraspeed DF-58 or DF-55; Eastman Kodak Company, Rochester, N.Y.) depended on the anatomic limitation. Radiographs were made at 70 kVp, 10mA for 0.5 seconds, and then developed in an automatic x-ray film processor (Velopex; Velopex International Inc, Catawissa, Pa.). The marginal bone level 0, 1, 3, 6, and 12 months after loading was compared with use of the periapical radiographs. A photographic 35-mm slide of a measuring device (ruler) that was taken at 1:1 magnification was projected onto the screen and the scale measured to achieve original magnification × 10. With the projector remaining stationary, each periapical radiograph was projected onto the screen, and the marginal bone levels on the mesial and distal aspects of the implants were measured. The apical corner of the implant shoulder was used as the reference point. The distance between the reference point and the most coronal implant-bone contact point was measured and compared between different time intervals. The value was positive when the implant-bone contact point was more coronal than the reference point and was negative when the implant-bone contact point was more apical (Fig. 2). The measurements were made to the closest 1 mm and were divided by the magnification factor (×10), resulting in 0.1-mm accuracy to the true value. Measurements were made by 2 examiners 175 THE JOURNAL OF PROSTHETIC DENTISTRY RUNGCHARASSAENG ET AL Table I. Repeated measures 1-way analysis of variance (P<.001) on ranks on marginal bone change over time (n=40) Marginal bone loss (mm) Median 1 month 3 months 6 months 12 months -0.35 -0.95 -1.30 -1.30 25% 75% -0.60 -1.30 -1.80 -1.75 -0.20 -0.50 -0.50 -0.70 Mean ± SD -0.42 -0.84 -1.14 -1.16 ± ± ± ± 0.34 0.55 0.80 0.89 Vertical lines join groups that were not significantly different (Tukey test, P>.05). Fig. 2. Measurement of marginal bone change. Reference point (RP) is junction between smooth titanium surface (Ti) and rough HA-coated surface (HA). Positive value (+ve) denotes implant-bone contact more coronal to reference point; negative value (–ve) denotes implant-bone contact more apical to reference point. Fig. 3. Inverse relationship between marginal bone loss and time. (whose measurements had been calibrated), and mean values were recorded. Implant mobility was the third parameter recorded. The implant bar was removed and replaced with the PME titanium healing caps so that individual implants could be tested for mobility with the Periotest instrument (Siemens, Bensheim, Germany).32,33 Two measurements per implant were made at each appointment. When there was a discrepancy between the 2 measurements, at least a third measurement was made, and the 2 identical values were recorded. Periotest values of ≤0 indicated that osseointegration had been achieved49; values higher than 9 denoted the absence of osseointegration.33 Peri-implant parameters were recorded at each follow-up appointment. The parameters recorded at the mesiobuccal, mesiolingual, distobuccal, and distolin176 gual of each implant were: score on the modified plaque index by Mombelli et al45 (0 = no detection of plaque, 1 = plaque recognized only by running a probe across the smooth marginal surface of the implant, 2 = plaque visible with the naked eye, 3 = abundance of soft matter); probing depth (University of North Carolina color probe; Hufriedy, Chicago, Ill.) to the nearest mm; and bleeding upon probing50 (0 = no bleeding, 1 = bleeding on probing). Complications also were recorded and included soft tissue complications, significant bone loss, peri-implant radiolucency, and prosthodontic complications. Means and standard deviations were calculated for each clinical parameter at each time interval where applicable. Data were analyzed with a repeated measures 1-way analysis of variance (P<.05) (SigmaStat software; SPSS Inc, Chicago, Ill.). The interexaminer reliability of marginal bone loss measurements was analyzed with the 2-way random effects analysis of variance and expressed as the interclass correlation coefficient. RESULTS Implant failure and marginal bone change. A total of 20 implants were placed. Four implants were 3.8 × 12 mm, eight implants were 3.8 × 14 mm, seven implants were 3.8 × 16 mm, and one implant was 4.5 × 14 mm. At 12 months after immediately loading, none of the implants had lost osseointegration. This sample size yielded at least 88% power for the statistical analysis. For marginal bone change, 96% of the measurements made by the 2 examiners were within ±0.5 mm. Significant correlation between the 2 measurements (ICC=0.983, P=.00) was noted. The mean marginal bone changes were –0.42 ± 0.34, –0.84 ± 0.55, –1.14 ± 0.80, and –1.16 ± 0.89 mm at the 1-, 3-, 6-, and 12-month follow-ups, respectively (Table I). Most marginal bone change occurred during the first 6 months after loading; there was no significant change thereafter (P>.05), as shown in Figure 3. This marginal bone loss (ŷi) can be expressed in the inverse function of time (x̂i) as: ŷi = –1.2122 + 0.8139(1/x̂i) VOLUME 87 NUMBER 2 RUNGCHARASSAENG ET AL THE JOURNAL OF PROSTHETIC DENTISTRY A B C D E Fig. 4. Marginal bone level in patient 2 at 0 (A), 1 (B), 3 (C), 6 (D), and 12 months (E). In many instances, most coronal implant-bone contact (white arrow) at time of surgery was on PME abutment, which was smooth, polished surface (A). Despite significant bone loss observed at 12 months (compare distance between 2 arrows), marginal bone level did not extend apically beyond first thread (E). Black arrow indicates reference point. with a coefficient of determination (R2) of 0.9580. At 12 months postloading, marginal bone change ranged from –2.6 mm to +0.7 mm (Fig. 4). Despite significant bone loss recorded, the bone level did not extend beyond the first thread (-0.6 mm from the reference point) at any implant site. A significant decline in the rates of marginal bone change (mm/month) from 0 to 1 (–0.42 ± 0.34), 1 to 3 (-0.21 ± 0.20), 3 to 6 (–0.10 ± 0.14), and 6 to 12 (–0.003 ± 0.04) month FEBRUARY 2002 intervals also was observed (P<.001; Table II and Fig. 5). The relationship between the rate of marginal bone loss (ŷi) and time (x̂i) was expressed in the logarithmic model as ŷi = –0.4103 + 0.1695 ln(x̂i) [R2 = 0.995]. Implant mobility. All implants were stable throughout the study; the recorded Periotest values ranged from -3 to -7. There were no statistically significant differences (P=.116) between Periotest values at 1, 3, 177 THE JOURNAL OF PROSTHETIC DENTISTRY RUNGCHARASSAENG ET AL Fig. 5. Logarithmic model of relationship between rate of marginal bone loss and time. Fig. 6. Quadratic model of relationship between Periotest value and time. Table II. Repeated measures 1-way analysis of variance (P<.001) on ranks on rate of marginal bone change over time (n=40) Table III. Repeated measures 1-way analysis of variance (P<.116) on Periotest value over time (n=20) Rate of marginal bone loss (mm/mo.) Median 0-1 month 1-3 months 3-6 months 6-12 months –0.35 –0.23 –0.07 0.00 25% 75% –0.60 –0.38 –0.15 –0.02 –0.20 –0.05 0.00 0.03 Mean ± SD –0.42 –0.21 –0.10 –0.00 ± ± ± ± 0.34 0.20 0.14 0.04 Vertical lines join groups that were not significantly different (Tukey test, P>.05). 6, and 12 months (Table III and Fig. 6). The relationship between the Periotest value (ŷi) and time (x̂i) was expressed in a quadratic equation as ŷi = –5.1425 – 0.1762x̂i + 0.0097x̂i2 (R2 = 0.948). Peri-implant parameters. The mean modified plaque index at 1 month was 1.19 ± 0.75. However, it significantly decreased with time (P<.001). After 12 months, the modified plaque index was only 0.49 ± 0.90 (Table IV and Fig. 7). The logarithmic relationship between the plaque index (ŷi) and time (x̂i) was expressed as ŷi = 1.2695 – 0.2917 ln(x̂i) [R2 = 0.899]. At 1 month, probing depths >3 mm were recorded at 3 of 80 sites; however, at 3, 6, and 12 months, the probing depths at all sites were ≤3 mm. There was a significant decrease in mean probing depth from 1 to 3 months (P<.05), but it remained stable thereafter (Table V and Fig. 8). The relationship between the probing depth (ŷi) and time (x̂i) was expressed in a quadratic equation as ŷi = 2.4963 - 0.1485x̂i + 0.0087x̂i2 (R2 = 0.761). There was no correlation between modified plaque index and probing depth (P=.346). A few incidences of bleeding upon probing were recorded throughout 178 Mean ± SD 1 month 3 months 6 months 12 months –5.35 –5.50 –5.90 –5.85 ± ± ± ± 0.81 1.05 0.97 1.42 the study, but there was no significant difference (P=.64) in the frequency of bleeding upon probing at any time point (Table VI). Complications. At 1 month, the EDS bar of patient 2 was impinging on the soft tissue and therefore hindering oral hygiene care. Gingivoplasty was performed, and the problem was solved. A small hematoma (approximately 3 mm in diameter) was observed around an implant in patient 3 one day after the implant placement and was surgically removed without further complications. No other complications occurred during the observation period of this study. DISCUSSION The 100% implant success rate in this short-term prospective study is comparable to other delayed loading and immediate loading studies (85% to 97%).1-4,20-24 All implants met all the success criteria proposed by Smith and Zarb,47 where applicable. The HA coating did not appear to produce any negative effect on the overall performance of the implants. Although histomorphometric analysis to verify the level of osseointegration was not used in this study, the low Periotest values as well as the absence of periimplant radiolucencies suggested that osseointegration had been achieved and maintained. Soballe et al12,13 VOLUME 87 NUMBER 2 RUNGCHARASSAENG ET AL THE JOURNAL OF PROSTHETIC DENTISTRY Fig. 7. Logarithmic model of relationship between plaque index and time. Fig. 8. Quadratic model of relationship between probing depth and time. Table IV. Repeated measures 1-way analysis of variance (P<.001) on ranks on modified plaque index over time (n=80). Table V. Repeated measures 1-way analysis of variance (P<.001) on ranks on probing depth over time (n=80) Probing depth (mm) Modified plaque index 1 month 3 months 6 months 12 months Median 25% 75% 1.00 1.00 0.00 0.00 1.00 0.50 0.00 0.00 2.00 2.00 1.00 1.00 Mean ± SD 1.19 1.10 0.73 0.49 ± ± ± ± 0.75 0.82 1.20 0.90 Vertical lines join groups that were not significantly different (Tukey test, P<.05). 1 month 3 months 6 months 12 months Median 25% 75% 2.00 2.00 2.00 2.00 2.00 2.00 2.00 1.00 3.00 2.00 2.00 2.00 Mean ± SD 2.43 1.98 2.01 1.96 ± ± ± ± 0.57 0.64 0.63 0.72 Vertical line joins groups that were not significantly different (Tukey test, P>.05). Table VI. Chi-square test (P=.644) on frequency of bleeding upon probing over time showed that a fibrocartilaginous membrane was formed around HA-coated implants subjected to 150 mm micromovement immediately after placement and that the HA coating had the capacity to induce the replacement of the motion-induced fibrous membrane with bone. The results of this study suggest that HAcoated implants can achieve osseointegration when they are immediately loaded. The stability of the implant in bone during the healing period dictates the type of healing.6,29-31 A proposed critical amount of micromotion (≥100 mm) caused by overload can cause fibrous repair at the interface rather than osseous regeneration and osseointegration.6,29-31 In their immediate loading study, Babbush et al19 reported that, aside from infection, failure was mostly related to delayed application of the rigid splinting bar. In addition, Lum et al14 showed in their histologic evaluation that a direct bone-implant interface was achieved when an HAcoated blade-form implant was immediately loaded with rigid fixation to a firm natural tooth. Early rigid splinting of the implants seems to be crucial in an immediate loading situation, as it may help stabilize FEBRUARY 2002 No. of sites (out of 80 possible) 1 month 3 months 6 months 12 months 6 5 8 4 the implants and thus prevent detrimental micromovement. The relatively high success rate in this study might be attributed to the presence of good bone quality and quantity (type I or II, ≥3.8 × 12 mm), good primary stabilization of the implants as judged by the resistance encountered during implant placement, and the prompt placement of the rigid splinting bar. Until further information is available, it is suggested that these 3 characteristics are important aspects of success with immediate loading. The mean marginal bone change of –1.16 ± 0.89 mm measured in this study at 12 months is comparable to the values reported by others.25-27 Although there seemed to be a continuous marginal bone loss around the implants early in this study, there was no significant mar179 THE JOURNAL OF PROSTHETIC DENTISTRY ginal bone change after 6 months (P>.05). The rate of bone loss also decreased significantly as time passed (P<.001). Furthermore, the marginal bone level did not extend apically beyond the first thread (–0.6 mm from the reference point) in any of the implant sites evaluated at the end of the study. The apical corner of the implant neck was chosen as the reference point because it is the junction between the smooth titanium surface of the implant neck and the HA-coated surface of the implant body. In this study, the relation of the implant top to the original marginal bone level varied; in many instances, the most coronal implant-bone contact was on the PME abutment, which is a smooth, polished titanium surface (Fig. 4, A). Quirynen et al28 suggested that the smooth titanium surface, although not highly polished, seems to represent an unfavorable condition for close bone apposition and that a radiolucency along the smooth surface becomes visible from the moment of loading. A stress-shielding phenomenon could be the explanation.28 The results of this study indicated that the bone response around the immediately loaded, HA-coated implants was favorable and comparable to that of conventional, delayed-loaded implants.25-27 It has been suggested that the Periotest parameter of an implant provides an objective diagnosis of initial implant stability.32-34,49 In this study, Periotest values obtained from all implants at any observation period ranged from –3 to –7. These values indicated that some level of osseointegration may have been achieved in all implants.49 The fact that there was no significant difference in the Periotest values at any point in time (P=.116) suggests that osseointegration may have occurred 1 month after immediate loading, which corresponds to 6 weeks after implant placement. Thus, the question is raised whether a healing period of 6 weeks instead of 3 to 6 months could be applied to HA-coated implants placed in type I or II bone. The significance of peri-implant parameters in predicting implant success has been controversial. Although it is generally agreed that plaque accumulation could induce negative mucosal response,35-37 Smith and Zarb47 proposed that the peri-implant mucosal response should not be included in the criteria for implant success because it has not been shown to be an important factor in achieving or maintaining osseointegration.37-39 However, many researchers consider the mucosal response to be correlated to marginal bone loss and loss of osseointegration.40-42 Henry et al43 suggested that although the pathogenesis of bacterial plaque in implant dentistry is still uncertain, it should be controlled. In this study, no attempt was made to correlate peri-implant parameters to implant success. Rather, these parameters were recorded to evaluate the 180 RUNGCHARASSAENG ET AL patients’ oral hygiene status. Mombelli et al45 showed that there was no significant difference in the modified plaque index of a successful implant (1.0 ± 0.7) and failed implant (1.3 ± 1.3). The decrease in mean plaque index with time showed that, in general, the patients’ oral hygiene improved (P<.001). The very low frequency of bleeding upon probing and the mean probing depth of <3 mm indicated the presence of healthy peri-implant tissue.26,28,44,45 The decrease in probing depth (P<.001) and plaque index scores (P<.001) and the lack of significant differences in the frequency of bleeding upon probing (P=.64) during the observation periods also suggested that the periimplant mucosal condition around the immediately loaded, HA-coated implants had been stabilized. CONCLUSIONS Within the limitations of this short-term study, the bone and mucosal responses around immediately loaded, HA-coated implants were favorable and comparable to that of conventional, delayed-loaded implants. The implant success rate achieved indicates that immediately loaded, threaded, HA-coated rootform implants supporting mandibular bar overdentures may be a viable option for completely edentulous patients. We acknowledge the graduate students of the Advanced Education in Implant Dentistry Program for their participation in the treatment of the patients in this study. In addition, we thank Mr Shinichiro Maruo for his assistance in the data compilation and Dr Goichi Shiotsu for being the second examiner in measurements of marginal bone change. REFERENCES 1. Adell R, Eriksson B, Lekholm U, Branemark PI, Jemt T. Long-term followup study of osseointegrated implants in the treatment of totally edentulous jaws. Int J Oral Maxillofac Implants 1990;5:347-59. 2. Naert I, Quirynen M, van Steenberghe D, Darius P. A six-year prosthodontic study of 509 consecutively inserted implants for the treatment of partial edentulism. J Prosthet Dent 1992;67:236-45. 3. 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Periotest to monitor osseointegration and to check the occlusion in oral implantology. J Oral Implantol 1993;19:23-32. 50. van der Velden U. Probing force and the relationship of the probe tip to the periodontal tissues. J Clin Periodontol 1979;6:106-14. Reprint requests to: DR KITICHAI RUNGCHARASSAENG DEPARTMENT OF RESTORATIVE DENTISTRY LOMA LINDA UNIVERSITY SCHOOL OF DENTISTRY LOMA LINDA, CA 92350 FAX: (909)558-4803 E-MAIL: rungkit@hotmail.com Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 + 0. 10/1/121111 doi:10.1067/mpr.2002.121111 181