Cylindrical Dental Implants With Hydroxyapatite- and Titanium Plasma Spray–coated Surfaces: 5-year Results

Over the past 3 decades, dental implant use has rapidly expanded in daily clinical practice as a viable alternative to conventional fixed and removable prostheses. As a consequence of this growth, many modifications have been made to implant designs and surfaces. Cylindrical implant designs have been used for many years with excellent results1,2 to rehabilitate patients experiencing dental losses. However, today many manufacturers are replacing cylinders with threaded implant designs3–5 that can provide improved primary stability for immediate loading. Implant surface technology has also evolved from machined titanium and surfaces coated with titanium plasma spray (TPS) and hydroxyapatite (HA) to newer, textured titanium surfaces that provide increased surface topography without the addition of a coating.6–8 

Titanium plasma spray coating, introduced on dental implants in the mid-1970s, is fabricated by applying molten particles of commercially pure titanium powder to the implant surface by a plasma spraying technique.9,10 Some researchers11 have reported TPS-coated implants capable of developing a higher percentage of bone-to-implant contact (BIC) on their surfaces and through their apical vents than implants with machined surfaces, whereas others12 have reported a tendency for fibrous tissue to interpose between the TPS surface and bone. Some resorption of TPS coating is also reported in the literature,13,14 but the causes may be related to the quality of the coatings studied (eg, low-density coatings, poor bonding of the coating to the metal substrate, deficient microhardness of the coating, the presence of microcracks in the coating). Nonetheless, with excellent survival rates reported for TPS-coated implants exceeding 95% after 5 years15 to 11 years16 of clinical functioning, long-term predictability for TPS-coated implants can be comparable with or superior to other implant surfaces.

Coating dental implants with HA through a plasma spraying process was initially developed in the early 1980s,17 and HA-coated implants were first made commercially available in 1985.18 Researchers have reported that HA-coated implants exhibit a more rapid development and greater percentage of initial BIC than do noncoated titanium implants.19–22 These findings are underscored by numerous other studies that have documented HA-coated implant surfaces to be effective in achieving and maintaining a high rate of osseointegration.23–36 Despite their widely documented clinical effectiveness, controversy37 that arose during the early 1990s concerning the long-term stability of the coatings still persists. At that time, several published case reports37 suggested that HA coatings were inherently unstable, susceptible to bacterial infection, and possibly predisposed to rapid bone loss or saucerization.38–41 Although such arguments have not been clinically substantiated by long-term studies,38,39 the use of TPS- and HA-coated surfaces has nonetheless received constant study and debate for several decades.42 

To help answer some of these clinical questions, 5-year clinical follow-up data were collected on patients treated with TPS- and HA-coated cylindrical implants in the Implantology Unit of the Dental Faculty, Department of Stomatology, University of Granada, Spain. This article reports on the cumulative findings of the study.

A total of 21 patients (11 women, 10 men) aged 20 to 75 years (mean = 40.3 years) who had been treated with a total of 127 implants after providing informed consent were reappointed in the Implantology Unit for their fifth annual postoperative follow-up:

• 75 (39 maxillary, 36 mandibular) TPS-coated implants had been placed in 12 patients.

• 52 (30 maxillary, 22 mandibular) HA-coated implants had been placed in 9 patients.

• Each patient was treated only with TPS- or HA-coated implants; no individual had both types of implants.

The aims of this study were the following:

• Clinically evaluate TPS-coated (IMZ, Nobel Biocare, Yorba Linda, Calif) and HA-coated (Integral, Zimmer Dental Inc, Carlsbad, Calif) cylindrical implants after 5 years of function according to criteria proposed by McKinney et al.43 

• Determine any clinical differences between the 2 surfaces.

• Determine any clinical differences between implants in maxillary and mandibular jaw locations.

Instruments used for clinical evaluation included an intrabuccal probe, periodontal probe, pincers, mirror, and a dental radiograph developer. Materials for digital radiographic (Odontorama PC, Trophy Radiologie S.A., Marne la Valee, France) evaluations included panoramic (Figure 1) (Kodak 15 × 30 cm) and periapical (Figure 2) (Agfa 3.2 × 4.1 cm) radiographic film.

The following indices were used to assess study variables (Table 1).

The presence of inflammation on the free gingival margin and in the inserted gum was quantified by using a modification of the gingival index of Loe and Silness.44 This index was scored as 0, 1, 2, or 3 depending on the hemorrhaging response to a gentle application of a round periodontal probe to a depth of 1 to 2 mm.

The depth of the gingival sulcus was registered with a normalized periodontal probe of 0.7 mm thick while applying a pressure of 17 to 30 g.

The combined index of plaque and calculus was used to evaluate qualitatively the magnitude of the buccal deposit on the implant and adjacent tooth. The Ramfjord index,45 which is scored 0 to 3, was used to record the highest reading for soft and hard deposits during the evaluation period.

The mobility index of the endosseous implants developed by Wasserman et al46 was used, which is a modification of the Miller Index47 of horizontal tooth mobility. Quantification of the numerical index was assigned according to the subjective perception of the examiner considering the degree of mobility.

It is difficult to classify radiographs on a numerical basis because of the many possible variants caused by minor differences in cone angulation; therefore, an approximate appraisal scale was used with set locations on the implant itself and adjacent anatomical landmarks (eg, the cervical area of the implant, the root portion of the implant, the periodontal ligament of the closest natural abutment).

A questionnaire was used to assess the subjective perception of each patient on the function of the implant and the prosthesis. The questions concerned pain, mobility, functional limitations, and the presence of any other clinical problems. The patient was asked to evaluate the implant as either positive (no complications) or negative (complications present).

For this study, implant success was defined as a fully functioning implant with fewer than 2 unfavorable evaluations based on the foregoing study parameters.

In addition to these parameters, other data considered important were also recorded:

• Personal information (age, gender).

• History of major systemic disease.

• Habits (smoking or not smoking).

• Type of implant treatment.

• Presence of signs and symptoms (pain; infection; fistula; paresthesia; invasion of the mandibular canal, maxillary sinus, or nasal fossae; lesion of neighboring teeth; problems of occlusion; and problems of articulation).

A statistical analysis of the data was performed in 2 phases. In the first phase, a descriptive analysis of each of the variables, each variable's frequency distribution, and basic summary parameters (mean, standard deviation) was performed. In the second phase, crosses of the different variables were made by using Rao-Scott χ² statistics for tables in which the different implants were listed for each patient. With this methodology, for the excess of significance that could be found in a normal test, the relationship between the implants of the same patient was not attended.

Analyses of the data from the different indices indicated a generally good result in all cases. Most of the implants presented slight hyperemia or light bleeding (values 1 and 2 of the gingival-hemorrhage index) and 50% manifested anomalies in the periodontal-probe index in 1 of the 4 locations: mesial, distal, buccal, or lingual. Three implants were noteworthy in presenting more than 4 mm of bone resorption, whereas for the radiographic index 78% registered normal values and 71.7% showed an absence of mobility (Table 2). Tables 3 and 4 summarize the results according to the variables, signs, and symptoms evaluated in all 21 study patients. Only 1 patient with 9 implants had serious prior systemic illness. Most of the patients had more than 2 implants (most frequently 4 or 6). Complete dentures were the most commonly used prostheses in both the upper and lower arches. The general condition of the patients was very satisfactory, with no case of infection, invasion of the mandibular canal, or lesion of neighboring teeth. In 3 patients, pain was felt at some time during the 5 years of follow-up, and 3 patients presented a fistula during the first phase of implant treatment caused by irritation from loose abutments rather than infection.

The comparative study of the different parameters measured according to the type of implant used (TPS or HA coated) revealed no significant differences for any of the variables (Table 5). Similarly, when comparing the variables as a function of the 21 patients of the sample, no differences were found even in patients with an abnormal gingival-hemorrhage index. The same was true of the mobility index (mobility being infrequent among the patients), but those who had abnormal values registered them in all the implants (results not shown in the tables). Of the 52 HA-coated implants (Figure 3), a total of 3 (5.7%) failed, for a cumulative survival rate of 94.3%. In the 75 TPS-coated implants (Figure 4), 10 (13.3%) were lost, for a cumulative survival rate of 86.7%.

As the most noteworthy parameter in the statistical analysis, of the 127 implants studied without comparing surfaces, a higher probability of slight bleeding was found in the patients with systemic disease (Table 6). Systemic illness also resulted in a higher probability of presenting an abnormal periodontal probing index (PPI) in all its locations (Table 7). In comparing the PPI values of the various types of restorations, it was found that patients with single-tooth restorations, complete dentures, or fixed prostheses with transitional implants registered statistically significant abnormal values in the PPI (mesial and distal) with respect to those who had other types of prostheses (Table 8; Figure 5).

Comparing the data for each of the parameters evaluated regarding the treated dental arch, it was found that the implants placed in the maxillary jaw had greater probabilities of presenting abnormal PPI values for the 4 locations, and that difference was statistically significant at P < .05 (Table 9; Figure 6).

The present study sought to analyze the clinical condition and survival rates of TPS- and HA-coated cylindrical implants after 5 years of clinical functioning. Cumulative implant failures were 5 TPS-coated implants (13.3%) and 2 HA-coated implants (5.7%). These results are similar to those reported by Roynesdal et al,48 who compared 3 different types of endosseous implant surfaces (HA coated, TPS coated, machined titanium) and found that TPS-coated implants exhibited greater loss in marginal peri-implant bone.

Cumulative success rates of the remaining 114 implants were 86.7% for TPS-coated implants (n = 65) and 94.2% for HA-coated implants (n = 49). These implants were considered satisfactory because no case exhibited 2 or more unfavorable evaluations based on the established study parameters. These results coincide with those reported by other clinicians, such as Lozada et al,49 Block and Kent,50 or Golec and Krauser,51 who presented success rates of 95% for individual implants after 5 years and 90% for fixed reconstructions in the anterior segment of the mandible after 10 years. Success rates in other locations fluctuate but appear to be at least 85% success at 5 years, as reflected by the results in the current study.

Although the present study and a literature search revealed no significant differences between the 2 coatings, a comparison of the 2 surfaces by Jones et al52 found a higher failure rate for the TPS surface (8.0%) after 5 years of follow-up, whereas a comparative study by Wheeler53 found 92.7% success for TPS-coated implants and 77.8% for HA-coated implants after 8 years. Despite the disparity in opinions on the use of TPS- and HA-coated implants, some clinicians43,54 advocate the use of both implant surfaces in situations of diminished bone density with bad vascularization, in patients of advanced age when the bone height is less than 12 mm, or when the implants must be placed in a posterior maxillary position. That is, it would be considered appropriate to place the implants with these types of coatings in situations where there is poor bone quality or in cases where primary stability may be compromised.55 

In the analysis of factors that could influence the evaluation of these implants, this study found that the occurrence of a major systemic disease, as well as the type of restorative prosthesis, resulted in a statistically significant correlation in the periodontal assessment of the implants. This does not signify that the rest of the parameters studied do not decisively influence the clinical course of the osseointegration, but rather that because of the limitations of the sample size the results should be interpreted with caution. In addition, the implants studied cannot be considered as independent samples; they clearly depend on the characteristics of the patient.

With reference to the location of the implants, it is important to bear in mind that 58 implants were placed in the mandible and 69 were placed in the maxilla. In a period of 5 years, no significant differences were found in the 2 arches, except periodontal probing, which presented abnormal values in the maxilla as compared with the mandible. Only 1 HA-coated implant was considered a failure in the upper arch, and 2 were considered failures in the mandible. On the other hand, among the TPS-coated implants, 6 received a negative evaluation in the maxilla and 4 received a negative evaluation in the mandible. These results were similar to those reported in other studies,43,56,57 though it should be specified that this difference in success between the mandible and maxilla should be regarded in general terms because more factors have an influence, such as whether the patient is completely edentulous or undergoing the replacement of a single tooth, the type of implant used, and bone quality.42,43,58,59 

Finally, it should be taken into account that during functional loading of the osseointegrated implant, whether HA or TPS coated, diverse factors are involved and thus collaboration is necessary among the surgeon, prosthodontist, and periodontist to optimize the bone-integration process, avoid occlusal trauma, and maintain peri-implant soft tissues in the best health conditions. Without the joint intervention and coordination of these professionals, it would be difficult to achieve optimal treatment.

Long-term success rates were outstanding for HA-coated implants (94.3%) and acceptable for TPS-coated implants (86.7%) after 5 years of function. No significant differences were found between the 2 surfaces within the parameters studied.

The authors thank Dr. Manuel Rodríguez Pérez for publication assistance and have no financial interest in any of the products mentioned in this report.